UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Degradation of diethanolamine solutions by carbonyl sulphide and carbon disulphide 1991

You don't seem to have a PDF reader installed, try download the pdf

Item Metadata

Download

Media
UBC_1991_A1 D39.pdf
UBC_1991_A1 D39.pdf [ 18MB ]
UBC_1991_A1 D39.pdf
Metadata
JSON: 1.0059005.json
JSON-LD: 1.0059005+ld.json
RDF/XML (Pretty): 1.0059005.xml
RDF/JSON: 1.0059005+rdf.json
Turtle: 1.0059005+rdf-turtle.txt
N-Triples: 1.0059005+rdf-ntriples.txt
Citation
1.0059005.ris

Full Text

DEGRADATION OF DIETHANOLAMINE SOLUTIONS BY CARBONYL SULPHIDE AND CARBON DISULPHIDE b y OLUKAYODE FATAI DAWODU B.Sc. (CHEM. ENG.), UNIVERSITY OF IFE, NIGERIA, 1982 M.Sc. (CHEM. ENG.), UNIVERSITY OF IFE, NIGERIA, 1985 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in THE FACULTY OF GRADUATE STUDIES DEPARTMENT OF CHEMICAL ENGINEERING We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA SEPTEMBER 1991 (c) OLUKAYODE F. DAWODU, 1991 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of CH-£(V\t Cfti— G rv/G.HN/ggfiJNt G The University of British Columbia Vancouver, Canada Date Q C T o f e g g - m\ DE-6 (2/88) i ABSTRACT The common i n d u s t r i a l p r a c t i c e of using aqueous solutions of diethanolamine (DEA) . f o r the removal of impurities such as carbon dioxide (CC^)/ hydrogen sulphide (H2S)/ carbonyl sulphide (COS) and carbon disulphide (CS2) from n a t u r a l , r e f i n e r y and manufactured gases often e n t a i l s i r r e v e r s i b l e reactions between the solvent and the impurities. This phenomenon i s r e f e r r e d to as amine degradation and i t not only , constitutes a loss of the amine but may contribute to operational problems such as foaming, corrosion and f o u l i n g . Degradation of DEA by COS and CS2 was studied by using- a 600 mL s t a i n l e s s s t e e l reactor under the following conditions: DEA concentration 10 - 40 wt%; temperature 120 - 195 °C; COS p a r t i a l pressure 345 - 1172 kPa; CS 2 volume 2.5 - 10.5 mL (CS2/DEA mole r a t i o of 0.055 - 0.233). An a n a l y t i c a l procedure c o n s i s t i n g of gas chromatography (GC) and gas chromatography/mass spectroscopy (GC/MS) was used to i d e n t i f y over 20 compounds i n the p a r t i a l l y degraded DEA solutions. The major degradation products are monoethanolamine (MEA), bis hydroxyethyl ethylenediamine (BHEED), bis hydroxyethyl piperazine (BHEP), hydroxyethyl oxazolidone (HEOD), hydroxyethyl imidazolidone (HEI), t r i s hydroxyethyl ethylenediamine (THEED) and bis hydroxyethyl imidazolidone (BHEI); as well as a dithiocarbamate s a l t ( in the case of the CS2-DEA systems). In addition, both COS and CS2 induced degradation formed s o l i d products which were characterized on the basis of s o l u b i l i t y , melting point, elemental composition, s o l i d probe GC/MS and i n f r a r e d a n a l y s i s . The number of degradation compounds i n the COS-DEA ii and CS2-DEA systems i s large when compared with the three major degradation compounds found i n CC^-DEA systems; t h i s demonstrates that the former systems are d i s t i n c t and more complicated than the l a t t e r system. When COS or CS2 was contacted with aqueous DEA s o l u t i o n , hydrolysis occurred and H2S, CO2, COS and, possibly, CS2 together with t h e i r r e l a t e d i o n i c species were present i n the system. S o l u b i l i t y and hydrolysis experiments were therefore conducted to e s t a b l i s h the equilibrium composition of the COS-DEA system p r i o r to the commencement of degradation. A modified Kent-Eisenberg (K/E) model which was developed to c o r r e l a t e the experimental data, showed good agreement between the experimental r e s u l t s and model p r e d i c t i o n s . Since the K/E and previous models were l i m i t e d to amine-C02 and/or H2S systems, the present modified K/E model which incorporates COS, i s a s i g n i f i c a n t improvement. The rate of degradation of DEA was found to increase with temperature, DEA concentration, COS p a r t i a l pressure and CS2 volume. On the basis of the experiments conducted to evaluate the contributions of the various compounds i n the p a r t i a l l y degraded solutions, reaction schemes were developed f o r the formation of 18 degradation compounds i n the COS-DEA and CS2-DEA systems. Despite the complexity of the reactions, the o v e r a l l degradation of DEA was well represented by a f i r s t order reaction f or the present experimental conditions. A mathematical model based on the major reaction schemes was developed to estimate the concentrations of DEA and the major degradation compounds in the COS-DEA system. iii Contrary to l i t e r a t u r e information, experiments conducted with gas mixtures of CO2 and showed that H2S enhanced the rate of DEA degradation. A d i r e c t r e s u l t of the combined e f f e c t s of H2S and CO2 on alkanolamines was the production of the corresponding lower order alkanolamines from higher order ones. The r e s u l t i n g mixed amine solution increases the routes for degradation compared to single amine solutions. The study therefore provides an i n d i c a t i o n of what to expect in terms of degradation when mixtures of alkanolamines are used for gas sweetening. i v TABLE OF CONTENTS ABSTRACT i i LIST OF TABLES x i LIST OF FIGURES x i i i ACKNOWLEDGEMENT S x x i i CHAPTER 1 INTRODUCTION 1 1.1 OBJECTIVES OF THE PRESENT STUDY ' 6 2 LITERATURE REVIEW 7 2.1 PROPERTIES OF CARBONYL SULPHIDE AND CARBON DISULPHIDE 7 2.2 ABSORPTION OF ACIDIC GASES IN AQUEOUS ALKANOLAMINE SOLUTIONS 8 2.2.1 CARBON DIOXIDE AND HYDROGEN SULPHIDE 8 2.2.2 CARBONYL SULPHIDE 9 2.2.3 CARBON DISULPHIDE 15 2.3 EQUILIBRIUM REACTIONS OF ACID GASES IN AMINE SOLUTIONS 15 2.3.1 REACTIONS OF HYDROGEN SULPHIDE 15 2.3.2 REACTIONS OF CARBON DIOXIDE 16 2.3.3 REACTIONS OF CARBONYL SULPHIDE 18 2.3.4 REACTIONS OF CARBON DISULPHIDE 20 2.4 DEGRADATION OF DIETHANOLAMINE SOLUTIONS 22 2.4.1 DEGRADATION OF DIETHANOLAMINE BY CARBON DIOXIDE 22 v 2.4.2 DEGRADATION OF DIETHANOLAMINE BY CARBONYL SULPHIDE 28 2.4.3 DEGRADATION OF DIETHANOLAMINE BY CARBON DISULPHIDE 2 9 2.5 LIMITATIONS OF THE PREVIOUS COS-DEA AND CS2-DEA DEGRADATION STUDIES 30 2.6 ANALYSIS OF DEGRADED ALKANOLAMINE SOLUTIONS 32 3 EXPERIMENTAL APPARATUS AND PROCEDURE 34 3.1 REACTOR 34 3.2 MATERIALS 35 3.3 EXPERIMENTAL PROCEDURE 37 3.4 SAMPLING 39 3.5 OPERATING CONDITIONS 40 3.6 ANALYTICAL PROCEDURE 41 3.7 TECHNIQUES USED TO IDENTIFY THE DEGRADATION PRODUCTS 42 3.7.1 GAS CHROMATOGRAPHIC (GC) ANALYSIS 43 3.7.2 GAS CHROMATOGRAPHIC/MASS SPECTROMETRIC (GC/MS) ANALYSIS 43 3.7.3 GC/MS ANALYSIS OF SILYLATED DERIVATIVES 45 3.7.4 GC ANALYSIS OF DEGRADED MIXTURE SPIKED WITH SUSPECTED COMPOUNDS 46 3.8 EXPERIMENTAL DESIGN 47 4 IDENTIFICATION OF DEGRADATION PRODUCTS 50 4.1 PRELIMINARY EXPERIMENTS 50 4.1.1 EFFECTS OF ELEVATED TEMPERATURES 50 vi 4.1.2 SURFACE EFFECTS 51 4.1.3 EFFECTS OF STIRRER SPEED 53 4.1.4 REPRODUCIBILITY 53 4.2 DEGRADATION PRODUCTS RESULTING FROM COS-DEA INTERACTIONS 54 4.3 DEGRADATION PRODUCTS RESULTING FROM CS2-DEA INTERACTIONS 76 4.4 CHARACTERIZATION OF THE SOLID PRODUCTS 78 4.4.1 SOLUBILITY 79 4.4.2 MELTING POINT 79 4.4.3 ELEMENTAL ANALYSIS 80 4.4.4 MASS SPECTRAL ANALYSIS .82 4.4.5 INFRA-RED ANALYSIS 86 5 EFFECTS OF OPERATING VARIABLES 90 5.1 COS-DEA SYSTEM 90 5.1.1 EFECTS OF INITIAL DEA CONCENTRATION 90 5.1.2 EFFECTS OF TEMPERATURE 109 5.1.3 EFFECTS OF INITIAL COS PARTIAL PRESSURE 124 5.2 CS2"DEA SYSTEM 135 5.1.1 EFECTS OF INITIAL DEA CONCENTRATION 135 5.1.2 EFFECTS OF TEMPERATURE 149 5.1.3 EFFECTS OF INITIAL VOLUME OF CS 2 161 6 EXPERIMENTS DESIGNED TO ELUCIDATE REACTION MECHANISMS 172 6.1 EFFECTS OF MIXED GASES 172 6.2 EFFECTS OF OXYGEN 183 6.3 EFFECTS OF DEGRADATION COMPOUNDS 185 vii 6.3.1 EFFECT OF ETHANOL 185 6.3.2 EFFECT OF ACETALDEHYDE 186 6.3.3 EFFECT OF ACETIC ACID 189 6.3.4 EFFECT OF ACETONE 191 6.3.5 EFFECT OF BUTANONE 191 6.3.6 EFFECT OF ETHYLENE GLYCOL 192 6.3.7 EFFECTS OF THE ALKYL ALKANOLAMINES 192 6.3.8 EFFECT OF WATER : 200 6.3.9 EFFECT OF MONOETHANOLAMINE 202 6.3.10 EFFECT OF BHEED 204 7 SOLUBILITY AND HYDROLYSIS OF CARBONYL SULPHIDE .....205 7.1 THEORY 206 7.2 EXPERIMENTAL EQUIPMENT AND PROCEDURE 212 7.2.1 PROCEDURE 212 7.2.2 ACID GAS LOADINGS . . . .' 214 7.2.3 GAS ANALYSIS 215 7.2.3 SOLUBILITY DETERMINATION AT LOW TEMPERATURES 217 7.2.5 HYDROLYSIS AT ELEVATED TEMPERATURES 219 7.3 RESULTS AND DISCUSSION OF SOLUBILITY AND HYDROLYSIS RUNS 220 7.3.1 SOLUBILITY OF COS IN DEA SOLUTIONS AT LOW TEMPERATURES 221 7.3.2 HYDROLYSIS OF COS IN DEA SOLUTIONS AT ELEVATED TEMPERATURES 226 7.3.3 MODEL PREDICTIONS 235 viii 7.3.4 REPRODUCIBILITY 238 7.3.5 COS BALANCE 238 8 REACTION MECHANISMS 240 8.1 COS-DEA DEGRADATION 240 8.1.1 FORMATION OF MONOETHANOLAMINE (MEA) 240 8.1.2 FORMATION OF ACETALDEHYDE AND KETONES 243 8.1.3 FORMATION OF ACETIC ACID 244 8.1.4 FORMATION OF ETHYL AMINOETHANOL (EAE) 246 8.1.5 FORMATION OF DIETHYL DISULPHIDE 246 8.1.6 FORMATION OF SUBSTITUTED PYRIDINES 247 8.1.7 FORMATION OF ETHYLDIETHANOLAMINE (EDEA) 248 8.1.8 FORMATION OF N,N,N -TRIS HYDROXYETHYL ETHYLENEDIAMINE (THEED) 24 9 8.1.9 FORMATION OF BIS HYDROXYETHYL ETHYLENEDIAMINE (BHEED) 250 8.1.10 FORMATION OF N,N -BIS HYDROXYETHYL PIPERAZINE (BHEP) AND N-HYDROXYETHYL PIPERAZINE (HEP) ....251 8.1.11 FORMATION OF N-HYDROXYETHYL OXAZOLIDONE (HEOD) 251 8.1.12 FORMATION OF N,N -BIS HYDROXYETHYL IMIDAZOLIDONE (BHEI) 252 8.1.13 FORMATION OF N-HYDROXYETHYL IMIDAZOLIDONE (HEI) 253 8.1.14 FORMATION OF N-HYDROXYETHYL ACETAMIDE (HEA) ...254 8.1.15 FORMATION OF ETHANETHIOIC ACID-(S- (HYDROXYETHYL) AMINO) METHYL ESTER (ETAHEAME) .254 8.2 CS2-DEA DEGRADATION 255 8.3 FORMATION OF THE SOLID PRODUCT 257 ix 9 KINETIC MODEL FOR DEA DEGRADATION 258 9.1 COS INDUCED DEGRADATION OF DEA 258 9.2 CS 2 INDUCED DEGRADATION OF DEA 267 10 CONCLUSIONS AND RECOMMENDATIONS 270 10.1 CONCLUSIONS 270 10.1.1 COS INDUCED DEGRADATION 270 10.1.2 CS 2 INDUCED DEGRADATION 273 10.2 RECOMMENDATIONS 274 NOMENCLATURE 277 REFERENCES 280 APPENDICES 287 A. l ALKANOLAMINES COMMONLY USED INDUSTRIALLY 287 A. 2 SYNTHESIS OF SELECT DEGRADATION COMPOUNDS 289 B. l CALIBRATION OF THE GAS CHROMATOGRAPH 2 93 B.2 MASS SPECTRA OF MINOR DEGRADATION COMPOUNDS 308 C EXPERIMENTAL CONCENTRATIONS 317 D COMPARISON BETWEEN EXPERIMENTAL AND PREDICTED CONCENTRATIONS 338 E ERROR AND SENSITIVITY ANALYSIS 358 F PROGRAM LISTINGS 365 x LIST OF TABLES TABLE 2.1 SELECTED PHYSICAL PROPERTIES OF COS AND CS 2 8 4.1' REPRODUCIBILITY AND EFFECT OF STIRRER SPEED IN COS-DEA SYSTEMS 54 4.2 DEGRADATION COMPOUNDS DETECTED IN COS-DEA SYSTEMS AND THEIR RETENTION TIMES IN THE GC 59 4.3 ELEMENTAL COMPOSITIONS OF THE SOLIDS FORMED IN THE COS-DEA SYSTEMS 81 4.4 ELEMENTAL COMPOSITIONS OF THE SOLIDS FORMED IN THE CS2-DEA SYSTEMS 81 4.5 FUNCTIONAL GROUPS ASSIGNMENTS IN THE SOLIDS FORMED IN THE COS-DEA AND CS2-DEA SYSTEMS 8 9 6.1 CONTRIBUTIONS OF OXYGEN TO DEGRADATION IN THE COS-DEA SYSTEM 184 6.2 CONCENTRATIONS OF DEA AND THE LOW BOILING DEGRADATION COMPOUNDS IN THE REGULAR AND EDEA-SPIKED RUNS 196 6.3 CONCENTRATIONS OF DEA AND THE LOW BOILING DEGRADATION COMPOUNDS IN THE REGULAR AND EAE-SPIKED RUNS 197 7.1 FITTING CONSTANTS IN THE HENRY'S LAW EXPRESSION FOR THE COS-DEA SYSTEM (T = 20 - 50 °C) 223 7.2 HENRY'S CONSTANTS FOR THE SOLUBILITY OF COS IN WATER 223 7.3 EQUILIBRIUM DATA FOR THE HYDROLYSIS OF COS IN AQUEOUS DEA SOLUTIONS (COMPOSITIONS ARE EXPRESSED IN MILLIMOLES) ...224 xi 7.4 EQUILIBRIUM DATA FOR THE HYDROLYSIS OF COS IN AQUEOUS DEA SOLUTIONS (LIQUID PHASE CONCENTRATIONS ARE EXPRESSED IN MOLE/MOLE DEA) 225 7.5 PREDICTED AND EXPERIMENTAL ACID GAS LOADINGS 23 9 C.l - C.20 CONCENTRATIONS OF COMPOUNDS IN THE COS-DEA SYSTEMS ...317 C.21 - C.36 CONCENTRATIONS OF COMPOUNDS IN THE CS2-DEA SYSTEMS ...327 C. 37 - C.43 CONCENTRATIONS OF COMPOUNDS IN OTHER SYSTEMS 335 D. l - D.18 COMPARISON BETWEEN EXPERIMENTAL AND PREDICTED CONCENTRATIONS 338 D. 19 - D.20 RATE CONSTANTS OBTAINED FROM THE OPTIMIZATION ROUTINE 356 E. l NITROGEN BALANCE FOR THE DEGRADATION RUNS 359 E.2 MAXIMUM DEVIATIONS IN THE DEA CONCENTRATIONS REPORTED FOR THE DEGRADATION RUNS 361 E.3 DEVIATIONS BETWEEN THE EXPERIMENTAL AND FITTED VALUES OF THE PROTONATION, CARBAMATE AND THIOCARBAMATE EQUILIBRIUM CONSTANTS 362 E.4 COMPARISON OF PROTONATION (K^) AND CARBAMATE (K 2) CONSTANTS FROM THE KENT-EISENBERG AND MODIFIED KENT-EISENBERG MODELS 362 E.5 SENSITIVITY OF THE OBJECTIVE FUNCTION TO CHANGES IN THE RATE CONSTANTS FOR THE COS-DEA SYSTEMS (% CHANGE IN k i = + 20%) 363 E.6 SENSITIVITY OF THE OBJECTIVE FUNCTION TO CHANGES IN THE RATE CONSTANTS FOR THE COS-DEA SYSTEMS (% CHANGE IN k i = - 20%) 364 xn LIST OF FIGURES Figure 1.1 Typical alkanolamine sweetening unit 4 3.1 Sketch of the reactor 36 3.2 Set-up f o r the CS2-DEA degradation experiments 38 4.1 Chromatograms of p a r t i a l l y degraded DEA solutions of 4M i n i t i a l concentration (a: 180 °C, 0.34 MPa COS; b: 150 °C, 0.34 MPa COS; c: 120 °C, 0.68 MPa COS) 52 4.2 Chromatograms showing gradual formation of degradation products i n a COS-DEA system (4M DEA, 180 °C, 0.34 MPa COS) 55 4.3 Mass spectra of peak 1 i d e n t i f i e d as Acetone (a: EI spectrum; b: EI reference spectrum; c: CI spectrum) 60 4.4 Mass spectra of peak 2 i d e n t i f i e d as Butanone (a: EI spectrum; b: EI reference spectrum; c: CI spectrum) 61 4.5 Mass spectra of peak 3 i d e n t i f i e d as MEA (a: EI spectrum; b: EI reference spectrum; c: CI spectrum; d: CI spectrum of the s i l y l d e r i v a t i v e ) 62 4.6 Mass spectra of peak 4 i d e n t i f i e d as EAE (a: EI spectrum; b: EI reference spectrum; c: CI spectrum) 63 4.7 Mass spectra of peak 5 i d e n t i f i e d as DEA (a: EI spectrum; b: EI reference spectrum; c: CI spectrum; d: CI spectrum of the s i l y l d e r i v a t i v e ) 64 4.8 Mass spectra of peak 6 i d e n t i f i e d as EDEA (a: EI spectrum; b: EI reference spectrum; c: CI spectrum; d: CI spectrum of the s i l y l d e r i v a t i v e ) 65 4.9 Mass spectra of peak 7 i d e n t i f i e d as HEA (a: EI spectrum; b: EI reference spectrum; c: CI spectrum; d: CI spectrum of the s i l y l d e r i v a t i v e ) 66 4.10 Mass spectra of peak 8 i d e n t i f i e d as HEP (a: EI spectrum; b: EI reference spectrum; c: CI spectrum; d: CI spectrum of the s i l y l d e r i v a t i v e ) 67 4.11 Mass spectra of peak 9 i d e n t i f i e d as ETHEAME (a: EI spectrum; b: CI spectrum; c: CI spectrum of s i l y l derivative) 68 xiii 4.12 Mass spectra of peak 10 i d e n t i f i e d as BHEED (a: EI spectrum; b: EI reference spectrum; c: CI spectrum; d: CI spectrum of the s i l y l derivative) 69 4.13 Mass spectra of peak 11 i d e n t i f i e d as BHEP (a: EI spectrum; b: EI reference spectrum; c: CI spectrum; d: CI spectrum of the s i l y l derivative) 70 4.14 Mass spectra of•peak 12 i d e n t i f i e d as HEOD (a: EI spectrum; b: EI reference spectrum; c: CI spectrum; d: CI spectrum of the s i l y l derivative) 71 4.15 Mass spectra of peak 13 i d e n t i f i e d as HEI (a: EI spectrum; b: EI reference spectrum; c: CI spectrum; d: CI spectrum of the s i l y l derivative) 72 4.16 Mass spectra of peak 14 i d e n t i f i e d as THEED (a: EI spectrum; b: EI reference spectrum; c: CI spectrum; d: CI spectrum of the s i l y l derivative) 73 4.17 Mass spectra of peak 15 i d e n t i f i e d as BHEI (a: EI spectrum; b: EI reference spectrum; c: CI spectrum; d: CI spectrum of the s i l y l derivative) ........74 4.18 Chromatograms of p a r t i a l l y degraded DEA solutions of 3M i n i t i a l concentration degraded with 10 mL of CS2 for 48 hours (a: 180 °C; b: 165 °C; c: 150 °C) 77 4.19 EI and CI mass spectra of the s o l i d formed i n the COS-DEA system 84 4.20 EI and CI mass spectra of the s o l i d formed i n the CS2-DEA system 85 4.21 Infra-red trace of the s o l i d formed i n the COS-DEA system ...87 4.22 Infra-red trace of the s o l i d formed i n the CS2-DEA system ...88 5.1 DEA concentration as a function of i n i t i a l DEA concentration and time ( P c o s = 0.34 MPa, T = 120 °C) 92 5.2 DEA concentration as a function of i n i t i a l DEA concentration and time ( P c o s = 0.34 MPa, T = 150 °C) 93 5.3 DEA concentration as a function of i n i t i a l DEA concentration and time ( P c o s = 0.34 MPa, T = 165 °C) 94 5.4 Overall degradation rate constant as a function of i n i t i a l DEA concentration and temperature (PQQS = ° - 3 4 MPa) 95 xiv 5.5 I n i t i a l degradation rate as a function of i n i t i a l DEA concentration and temperature (P^og = 0.34 MPa) 97 5.6 Acetone concentration as a function of i n i t i a l DEA concentration and time (PQQS = ° - 3 4 MPa, T = 165 °C) 98 5.7 Butanone concentration as a function of i n i t i a l DEA concentration and time ( P c o s = 0.34 MPa, T = 165 °C) 99 5.8 MEA concentration as a function of i n i t i a l DEA concentration and time ( P c o s = 0.34 MPa, T = 165 °C) 100 5.9 BHEED concentration as a function of i n i t i a l DEA concentration and time (P C O s = ° - 3 4 M P a ' T = 1 6 5 ° c ) 1 0 2 5.10 BHEP concentration as a function of i n i t i a l DEA concentration and time ( P C O g = °- 3 4 M P a ' T = 1 6 5 °c> 1 0 3 5.11 HEOD concentration as a function of i n i t i a l DEA concentration and time ( P C O g = 0.34 MPa, T = 165 °C) ...... 104 5.12 HEI concentration as a function of i n i t i a l DEA concentration and time (PQQS = 0.34 MPa, T = 165 °C) 105 5.13 THEED concentration as a function of i n i t i a l DEA concentration and time (P^QS = ° - 3 4 MPa, T = 165 °C) 106 5.14 BHEI concentration as a function of i n i t i a l DEA concentration and time (P C O s = 0.34 MPa, T = 165 °C) 107 5.15 DEA concentration as a function temperature and time ( P c o s = 0.34 MPa, DEA Q = 4M) 110 5.16 DEA concentration as a function temperature and time ( P c o s = 0.34 MPa, DEA Q = 3M) I l l 5.17 DEA concentration as a function temperature and time ( P c o s = 0.34 MPa, DEA Q = 2M) 112 5.18 Arrhenius plots of the o v e r a l l degradation rate constant <P C 0 S = 0.34 MPa) 113 5.19 Butanone concentration as a function of temperature and time ( P c o s = 0.34 MPa, DEA 0 = 3M) 114 5.20 Acetone concentration as a function of temperature and time ( P c o s = 0.34 MPa, DEA Q = 3M) 115 5.21 MEA concentration as a function of temperature and time ( P c o s = 0.34 MPa, DEA Q = 3M) 116 xv 5.22 BHEED concentration as a function of temperature and time ( P c o s = 0.34 MPa, DEAQ = 3M) 117 5.23 BHEP concentration as a function of temperature and time ( P c o s = 0.34 MPa, DEAQ = 3M) • 118 5.24 HEOD concentration as a function of temperature and time ( P c o s = 0.34 MPa, DEAQ = 3M) 119 5.25 HEI concentration as a function of temperature and time ( P c o s = 0.34 MPa, DEAQ = 3M) 120 5.26 THEED concentration as a function of temperature and time ( P c o s = 0.34 MPa, DEAQ = 3M) 121 5.27 BHEI concentration as a function of temperature and time ( P c o s = 0.34 MPa, DEAQ = 3M) 122 5.28 DEA concentration as a function of i n i t i a l COS p a r t i a l pressure and time (DEAQ = 3M, T = 150 °C) 125 5.29 Acetone concentration as a function of i n i t i a l COS p a r t i a l pressure and time (DEA Q = 3M, T = 150 °C) 126 5.30 Butanone concentration as a function of i n i t i a l COS p a r t i a l pressure and time (DEA D = 3M, T = 150 °C) 127 5.31 MEA concentration as a function of i n i t i a l COS p a r t i a l pressure and time (DEA Q = 3M, T = 150 °C) 128 5.32 BHEED concentration as a function of i n i t i a l COS p a r t i a l pressure and time (DEA Q = 3M, T = 150 °C) 129 5.33 BHEP concentration as a function of i n i t i a l COS p a r t i a l pressure and time (DEA Q = 3M, T = 150 °C) 130 5.34 HEOD concentration as a function of i n i t i a l COS p a r t i a l pressure and time (DEA Q = 3M, T = 150 °C) 131 5.35 HEI concentration as a function of i n i t i a l COS p a r t i a l pressure and time (DEAQ = 3M, T = 150 °C) 132 5.36 THEED concentration as a function of i n i t i a l COS p a r t i a l pressure and time (DEAQ = 3M, T = 150 °C) 133 5.37 BHEI concentration as a function of i n i t i a l COS p a r t i a l pressure and time (DEA Q = 3M, T = 150 °C) 134 5.38 DEA concentration as a function of i n i t i a l DEA concentration and time (CS2 volume = 6 mL, T = 120 °C, CS2/DEA mole r a t i o s = 0.10 - 0.20) 136 xvi 5.39 DEA concentration as a function of i n i t i a l DEA concentration and time (CS2 volume = 6 mL, T = 150 °C, CS2/DEA mole r a t i o s = 0.10 - 0.20) 137 5.40 DEA concentration as a function of i n i t i a l DEA concentration and time (CS 2 volume = 6 mL, T = 165 °C, CS2/DEA mole r a t i o s = 0.10 - 0.20) 138 5.41 Overall degradation rate constant f o r CS2-DEA systems as a function of i n i t i a l DEA concentration and temperature (CS 2 volume = 6mL, CS2/DEA mole r a t i o s = 0.10 - 0.20) 139 5.42 I n i t i a l degradation rate as a function of i n i t i a l DEA concentration and temperature (CS 2 volume = 6mL, CS2/DEA mole r a t i o s = 0.10 - 0.20) 140 5.43 MEA concentration as a function of i n i t i a l DEA concentration and time (CS 2 volume = 6 mL, T = 165 °C, CS2/DEA mole r a t i o s = 0.10 - 0.20) 142 5.44 BHEED concentration as a function of i n i t i a l DEA concentration and time (CS 2 volume = 6 mL, T = 165 °C, CS2/DEA mole r a t i o s = 0.10 - 0.20) 143 5.45 BHEP concentration as a function of i n i t i a l DEA concentration and time (CS 2 volume = 6 mL, T = 165 °C, CS2/DEA mole r a t i o s = 0.10 - 0.20) 144 5.46 HEOD concentration as a function of i n i t i a l DEA concentration and time (CS 2 volume = 6 mL, T = 165 °C, CS2/DEA mole r a t i o s = 0.10 - 0.20) 145 5.47 HEI concentration as a function of i n i t i a l DEA concentration and time (CS 2 volume = 6 mL, T = 165 °C, CS2/DEA mole r a t i o s = 0.10 - 0.20) 146 5.48 THEED concentration as a function of i n i t i a l DEA concentration and time (CS 2 volume = 6 mL, T = 165 °C, CS2/DEA mole r a t i o s = 0.10 - 0.20) 147 5.49 BHEI concentration as a function of i n i t i a l DEA concentration and time (CS 2 volume = 6 mL, T = 165 °C, CS2/DEA mole r a t i o s = 0.10 - 0.20) 148 5.50 DEA concentration as a function of temperature and time (DEA Q = 4M, CS 2 volume = 6 mL, CS2/DEA mole r a t i o = 0.10) 150 5.51 DEA concentration as a function of temperature and time (DEA Q = 3M, CS 2 volume = 6 mL, CS2/DEA mole r a t i o = 0.13) 151 x v i i 5.52 DEA concentration as a function of temperature and time (DEA Q = 2M, CS 2 volume = 6 mL, CS2/DEA mole r a t i o = 0.20) 152 5.53 Arrhenius plots f o r the o v e r a l l dagradation rate constant as a function of i n i t i a l CS 2 volume 153 5.54 MEA concentration as a function of temperature and time (DEA Q = 3M, CS 2 volume = 6 mL, CS2/DEA mole r a t i o = 0.13) 154 5.55 BHEED concentration as a function of temperature and time (DEA Q = 3M, CS 2 volume = 6 mL, CS2/DEA mole r a t i o = 0.13) 155 5.56 BHEP concentration as a function of temperature and time (DEA Q = 3M, CS 2 volume = 6 mL, CS2/DEA mole r a t i o = 0.13) 156 5.57 HEI concentration as a function of temperature and time (DEA Q = 3M, CS 2 volume = 6 mL, CS2/DEA mole r a t i o = 0.13) 157 5.58 HEOD concentration as a function of temperature and time (DEA Q = 3M, CS 2 volume = 6 mL, CS2/DEA mole r a t i o = 0.13) 158 5.59 BHEI concentration as a function of temperature and time (DEA D = 3M, CS 2 volume = 6 mL, CS2/DEA mole r a t i o = 0.13) 159 5.60 THEED concentration as a function of temperature and time (DEA Q = 3M, CS 2 volume = 6 mL, CS2/DEA mole r a t i o = 0.13) 160 5.61 DEA concentration as a function of i n i t i a l CS 2 volume and time (DEA C = 3M, T = 165 °C) 163 5.62 MEA concentration as a function of i n i t i a l CS 2 volume and time (DEA Q = 3M, T = 165 °C) 164 5.63 BHEED concentration as a function of i n i t i a l CS 2 volume and time (DEA Q = 3M, T = 165 °C) 165 5.64 BHEP concentration as a function of i n i t i a l CS 2 volume and time (DEA Q = 3M, T = 165 °C) 166 5.65 HEOD concentration as a function of i n i t i a l CS 2 volume and time (DEA D = 3M, T = 165 °C) 167 5.66 HEI concentration as a function of i n i t i a l CS 2 volume and time (DEA Q = 3M, T = 165 °C) 168 5.67 BHEI concentration as a function of i n i t i a l CS 2 volume and time (DEA Q = 3M, T = 165 °C) 169 5.68 THEED concentration as a function of i n i t i a l CS 2 volume and time (DEA 0 = 3M, T = 165 °C) 170 xviii 6.1 DEA concentrations as a function of time and gas composition (DEAQ = 3M, T = 165 °C) 175 6.2 BHEP concentrations as a function of time and gas composition (DEAQ = 3M, T = 165 °C) 176 6.3 HEOD concentrations as a function of time and gas composition (DEAQ = 3M, T = 165 °C) 177 6.4 THEED concentrations as a function of time and gas composition (DEAQ = 3M, T = 165 °C) 178 6.5 MEA concentrations as a function of time and gas composition (DEAQ = 3M, T = 165 °C) 179 6.6 BHEED concentrations as a function of time and gas composition (DEAQ = 3M, T = 165 °C) 180 6.7 HEI concentrations as a function of time and gas composition (DEAQ = 3M, T = 165 °C) 181 6.8 BHEI concentrations as a function of time and gas composition (DEAQ = 3M, T = 165 °C) 182 6.9 Chromatograms of p a r t i a l l y degraded DEA solutions of 3M i n i t i a l concentrations degraded with 10.5 mL of CS2 at 180 °C (a: regular run; b: ethanol - spiked run) 187 6.10 Chromatograms of p a r t i a l l y degraded DEA solutions of 3M i n i t i a l concentrations degraded with 10.5 mL of CS 2 at 180 °C (a: regular run; b: acetaldehyde-spiked run) 188 6.11 Chromatograms of p a r t i a l l y degraded DEA solutions of 3M i n i t i a l concentration degraded with 10.5 mL of CS 2 at 180 °C (a: regular run; b: ac e t i c acid-spiked run) 190 6.12 Chromatogram of p a r t i a l l y degraded EAE solution of IM i n i t i a l concentration degraded with 10.5 mL of CS 2 at 180 °C 193 6.13 Chromatogram of p a r t i a l l y degraded EDEA solu t i o n of IM i n i t i a l concentration degraded with 10.5 mL of CS 2 at 180 °C 194 6.14 EI mass spectrum of the compound i d e n t i f i e d as Ethyl amine in the p a r t i a l l y degraded EAE s o l u t i o n 198 6.15 EI mass spectrum of the compound i d e n t i f i e d as Ethyl acetamide in the p a r t i a l l y degraded EAE solution 198 x i x 6.16 EI mass spectrum of the compound i d e n t i f i e d as Ethyl thiazolidone i n the p a r t i a l l y degraded EAE sol u t i o n 199 6.17 EI mass spectrum of the compound i d e n t i f i e d as Ethyl thiazolidone-2-thione i n the p a r t i a l l y degraded EAE sol u t i o n 199 6.18 Concentrations of DEA as a function of time i n aqueous and non-aqueous sytems i n contact with 345 kPa of COS at 150 °C 201 7.1 Gas trapping set-up 216 7.2 Chromatogram showing a t y p i c a l separation by the Chromosil 310 t e f l o n packed column 218 7.3 Henry's constant as a function of temperature f o r COS i n aqueous DEA solutions ...222 7.4 H 2S l i q u i d loading as a function of i n i t i a l COS p a r t i a l pressure and DEA concentration at 120 °C ....227 7.5 C0 2 l i q u i d loading as a function of i n i t i a l COS p a r t i a l pressure and DEA concentration at 120 °C 228 7.6 S e l e c t i v i t y as a function of temperature and DEA concentration 229 7.7 P a r t i a l pressure of H 2S as a function of l i q u i d loading and temperature f o r a 30 wt% DEA solu t i o n 231 7.8 P a r t i a l pressure of C0 2 as a function of l i q u i d loading and temperature f o r a 30 wt% DEA solu t i o n 232 7.9 Henry's constant f o r H 2S i n aqueous DEA solutions containing also C0 2 and COS 233 7.10 Henry's constant f o r C0 2 i n aqueous DEA solutions containing also H2S and COS 234 A. l Structure of amines 288 B. l C a l i b r a t i o n curve f o r acetone 295 B.2 C a l i b r a t i o n curve f o r butanone 296 B.3 C a l i b r a t i o n curve f o r MEA 297 B.4 C a l i b r a t i o n curve f o r DEA 298 B.5 C a l i b r a t i o n curve f o r BHEED 299 xx B.6 C a l i b r a t i o n curve for BHEP 300 B.7 C a l i b r a t i o n curve for HEOD 301 B.8 C a l i b r a t i o n curve f o r HEI 302 B.9 C a l i b r a t i o n curve f o r THEED 303 B.10 C a l i b r a t i o n curve f o r BHEI 304 B . l l C a l i b r a t i o n curve f o r C0 2 305 B.12 C a l i b r a t i o n curve f o r COS 306 B.13 C a l i b r a t i o n curve for H2S ; 307 B.14 Sample and l i b r a r y EI spectra of methanol 308 B.15 Sample and l i b r a r y EI spectra of ethanol 309 B.16 Sample and l i b r a r y EI spectra of acetaldehyde 310 B.17 Sample and l i b r a r y EI spectra of a c e t i c acid 311 B.18 Sample and l i b r a r y EI spectra of methyl pyridine 312 B.19 Sample and l i b r a r y EI spectra of d i e t h y l disulphide 313 B.20 Sample and l i b r a r y EI spectra of 1,2 dithiane ...314 B.21 Sample and* l i b r a r y EI spectra of ethyl methyl pyridine 315 B.22 Mass spectra of EHEP (a: EI; b: CI) 316 x x i ACKNOWLEDGEMENTS I wish to express my gratitude to the following for t h e i r various contributions towards the completion of my doctoral program: Professor Axel Meisen f o r his supervision, guidance and encouragements, p a r t i c u l a r l y during the d i f f i c u l t moments of t h i s work ; Professor Larry Weiler for h i s help with the reaction mechanisms and other chemistry-related aspects of t h i s work; My wife, Adeyinka, and my sons, Ayoyinka and O l a n i y i , for t h e i r love, understanding and s a c r i f i c e ; My parents, brothers and s i s t e r s f o r t h e i r love and moral support. In p a r t i c u l a r , I g r a t e f u l l y acknowledge the e f f o r t s of my mother and mother-in-law i n taking care of our sons while my wife and I pursued our academic goals; The Canadian Commonwealth Scholarship and Fellowship Plan for the scholarship to pursue my doctorate program, as well as the Natural Sciences and Engineering Research Council of Canada for the grant(s) to purchase equipments and supplies; F i n a l l y , I thank God f o r g i v i n g me the health and stamina to complete the program. xxii CHAPTER 1 INTRODUCTION Natural gas consists e s s e n t i a l l y of methane, with other hydrocarbons such as ethane and propane being present i n considerably lower amounts. In addition to these hydrocarbons, the other constituents are commonly referred to as contaminants and they include carbon dioxide, hydrogen sulphide and water. In natural gas reservoirs containing large amounts of carbon dioxide and hydrogen sulphide, i t i s also usual to f i n d other impurities such as carbonyl sulphide and carbon disulphide a l b e i t at quite low concentrations. Carbonyl sulphide and carbon disulphide also occur as impurities i n r e f i n e r y and synthesis gases, p a r t i c u l a r l y those derived from coal conversion and c a t a l y t i c and thermal cracking processes. Their concentrations i n these gas streams vary from a few parts per m i l l i o n (ppm) to about 1% ( 1). The removal of impurities i s necessary f o r reasons of t o x i c i t y , c o r r o s i v i t y and environmental regulations. The extent of removal depends on the end use of the clean gas, but t y p i c a l environmental requirements f o r hydrogen sulphide i s 0.00557g H2S/m3 of natural gas, while the t o t a l sulphur content could be as high as 0.2228g /m3 of natural gas (1). A v a r i e t y of p u r i f i c a t i o n or sweetening processes are being used f o r the removal of a c i d i c contaminants. These include dry bed, d i r e c t conversion, ph y s i c a l , chemical and s p e c i a l i t y solvent processes. By f a r the most widely used p u r i f i c a t i o n proceses are the chemical solvent processes u t i l i z i n g alkanolamines as the solvent. Alkanolamines are 1 2 amino der i v a t i v e s of alcohols or alcohol d e r i v a t i v e s of ammonia, and thus possess dual f u n c t i o n a l i t y . The hydroxyl group increases the molecular weight of the amine, r e s u l t i n g i n a reduced vapour pressure and increased water s o l u b i l i t y , while the needed a l k a l i n i t y i n aqueous solutions to cause the absorption of a c i d i c gases i s provided by the amino group. The amines commonly used i n industry are monoethanolamine (MEA) and diethanolamine (DEA). Other less common ones are diglycolamine (DGA), diisopropanolamine (DIPA), methyldiethanolamine (MDEA), triethanolamine (TEA) and s t e r i c a l l y hindered amines ' such as 2-amino- methyl propanol (AMP). The s t r u c t u r a l formulae of these amines are given i n Appendix A l . The popularity of alkanolamines i n gas tr e a t i n g i s a r e s u l t of t h e i r a b i l i t y to reduce the concentrations of the contaminants to l e v e l s lower than those economically achievable with other methods. There are cu r r e n t l y over 1400 alkanolamine plants i n use world wide (2). The absorption of the a c i d i c impurities i s enhanced by r e v e r s i b l e chemical reactions with the amine. Such reactions are summarized for DEA as follows: (HOC 2H 4) 2 NH + H2S = (HOC 2H 4) 2 NH 2 + HS" 1.1 (HOC 2H 4) 2 NH + C0 2 + H 20 = (HOC 2H 4) 2 NH 2 + HCO3" 1.2 The r e v e r s i b i l i t y of these reactions form the basis of the sweetening operation and affords continuous use of the amine solution over long periods of time. The use of alkanolamines f o r gas sweetening dates back to 1930 when Bottoms (3) was granted a patent covering triethanolamine. A 3 t y p i c a l alkanolamine sweetening unit i s shown i n Figure 1.1. Feed gas enters the absorber from the bottom and contacts a downward stream of an aqueous sol u t i o n of an alkanolamine at low temperature and elevated pressure. The solvent absorbs the impurities in the gas, leaving a cleaner (sweeter) gas e x i t i n g the absorber at the top. Usually, a scrubber i s i n s t a l l e d before the absorber to remove p a r t i c u l a t e matter and entrained l i q u i d s from the feed gas. Another scrubber a f t e r the absorber removes amine droplets entrained i n the sweet gas. The " r i c h " amine s o l u t i o n leaving the bottom of the absorber i s flashed to remove dissolv e d hydrocarbons and passed through a heat exchanger before entering the s t r i p p e r at elevated temperature. A counter current flow of steam s t r i p s off the absorbed gases leaving a "lean" amine solution to ex i t the s t r i p p e r . The lean amine s o l u t i o n i s passed through a series of heat exchangers to reduce i t s temperature before returning to the absorber f o r another c y c l e . Activated carbon columns are usually i n s t a l l e d upstream of the absorber to remove impurities and foam- inducing surface active materials from a s l i p stream of the lean amine sol u t i o n . The overhead products of the s t r i p p i n g column are passed through a condenser to remove water which i s returned as r e f l u x to the s t r i p p e r . The e f f l u e n t gases, depending on t h e i r composition, may undergo further treatment such as sulphur recovery i n a Claus unit. The treated gas leaving the top of the absorber i s usually passed through a g l y c o l dehydration unit to remove water and entrained alkanolamine. In some plants, a mixture of alkanolamine and g l y c o l i s used i n the absorber, to simultaneously remove impurities and water from the feed gas. SWEET GAS O - H CONDENSER F i g u r e 1 .1: T y p i c a l a l k a n o l a m i n e s w e e t e n i n g u n i t . 5 In spite of t h e i r resistance to chemical breakdown, plant and laboratory reports i n d i c a t e that, on prolonged use, alkanolamines are transformed into undesirable products from which the amine i s not e a s i l y recovered. This phenomenon, commonly ref e r r e d to as "amine degradation", not only leads to amine losses, but may also contribute to operational problems such as foaming (4,5,17), corrosion (6-8) and f o u l i n g (9). The degradation of DEA by has been studied quite extensively (9-18) and there i s evidence that the degradation proceeds p r i m a r i l y v i a amine carbamate (e.g. (HOC^H^ ̂NCOO'H"1") which may be formed by the d i r e c t reaction of carbon dioxide with amines. Since hydrogen sulphide i s incapable of forming carbamate-type compounds, i t i s generally agreed that hydrogen sulphide does not cause amine degradation. The r e s u l t s reported by Choy (12) and Kim and S a r t o r i (13) suggest that hydrogen sulphide i n the presence of carbon dioxide a c t u a l l y hinders amine degradation. By contrast, r e l a t i v e l y l i t t l e i s known about the degradation of DEA by carbonyl sulphide and carbon disulphide. Orbach and Selleck (19) and Pearce et. a l . (20) were unable to detect appreciable amounts of degradation compounds i n COS-DEA systems and they concluded that unlike MEA, DEA i s not degraded by COS. It has been estimated that 10 - 20% of the COS-MEA reaction leads to non-regenable products (20). DEA i s therefore the preferred choice for t r e a t i n g gas streams containing COS. Osenton and Knight (21) reported that CS 2 reacted with DEA to form p r i m a r i l y a dithiocarbamate s a l t from which the amine could not be e a s i l y recovered. These conclusions notwithstanding, there are three reasons (expatiated i n Chapter 2) to believe that COS and CS 2 are capable of 6 degrading DEA. F i r s t , GOS and CS 2 may be hydrolysed to H 2S and C 0 2 with the l a t t e r causing the well known C 0 2- induced degradation. Second, previously used reaction times were too short. Third, the a n a l y t i c a l techniques used in the past were inadequate. As the supply of sweet gas and l i g h t crude o i l declines, more sour deposits containing appreciable amounts of COS and CS 2 are being processed. The present study was therefore conducted to provide q u a l i t a t i v e and quantitative information on the i n t e r a c t i o n s of COS and CS 2 with DEA, p a r t i c u l a r l y i n regard to the degradation of the amine. 1.1 OBJECTIVES OF THE PRESENT STUDY The p r i n c i p a l objectives of the present study may be stated as follows: 1. To i d e n t i f y the reaction products and to propose reaction mechanisms when COS and CS 2 are separately contacted with aqueous solutions of diethanolamine. 2. To determine the e f f e c t s of temperature, pressure and solution concentration on the reactions. 3. To i d e n t i f y the reaction products and to propose reaction mechanisms when mixtures of COS, C 0 2 and H 2S are contacted with aqueous DEA solutions. 4. To develop p r e d i c t i v e k i n e t i c models for amine degradation r e s u l t i n g from COS and CS 2 exposure. CHAPTER 2 LITERATURE REVIEW This review emphasises studies concerning the COS-DEA and CS2-DEA systems. The i n t e r a c t i o n s of the other impurities such as CO2 and H2S with DEA and other amines are also included because, as w i l l be shown i n l a t e r chapters, the p a r t i a l l y degraded DEA solutions contain mixtures of amines and a c i d gases. 2.1 PROPERTIES OF CARBONYL SULPHIDE AND CARBON DISULPHIDE Carbonyl sulphide and carbon disulphide are colourless compounds which ex i s t as a gas and l i q u i d r e s p e c t i v e l y , at standard temperature and pressure. Some selected physical properties are shown in Table 2.1. A review paper by Ferm (22) and The Encyclopedia of Chemical Technology (23) provide more extensive coverage of the properties and chemistry of COS. Other properties of CS2 as well as i t s reactions are also l i s t e d i n The Encyclopedia of Chemical Technology (24). Carbon dioxide and hydrogen sulphide are more common than COS. Their properties are not discussed here, but may be found i n most chemistry texts and encyclopediae (25,26). 7 8 Table 2.1: Selected physical properties of COS and CS Properties COS cs2 Molecular Weight 60.0 76.0 * S p e c i f i c Gravity 2.485 1.263 B o i l i n g Point <°C) - 50.2 46.2 Melting Point (°C) -138.2 -111.53 C r i t i c a l Temperature (°C) 105.0 273.0 C r i t i c a l Pressure (MPa) 6.129 7.699 *COS and CS 2 values r e f e r to a i r and water, r e s p e c t i v e l y . 2.2 ABSORPTION OF ACIDIC GASES IN AQUEOUS ALKANOLAMINE SOLUTIONS 2.2.1 CARBON DIOXIDE AND HYDROGEN SULPHIDE Several studies have been conducted on the absorption or s o l u b i l i t y of C0 2 and H2S i n alkanolamine solutions. Some of those on DEA solutions are l i s t e d i n references (27-35). The studies cover a wide range of operating conditions and provide equilibrium data e s s e n t i a l f o r the modelling and simulation of a c i d gas plants. These data, together with the reactions between the a c i d gases and the alkanolamine solutions, have been used to develop thermodynamic models to predict the equilibrium compositions i n a c i d gas-alkanolamine-water systems (36-41). 9 Since the focus of the present study i s on the degradation of DEA, the equilibrium models are not reviewed. Detailed c r i t i q u e s of the e a r l i e r models have been presented by Austgen et a l . (41). However, a shortcoming of a l l the models i s that they are l i m i t e d to CO2 and/or H2S - amine systems. Consequently, there i s a need f o r models which accomodate other impurities such as COS and/or CS2- Such a model, based on the Kent and Eisenberg (39) approach, i s presented i n Chapter 7. 2.2.2 CARBONYL SULPHIDE Early attempts at removing COS from gas streams were generally based on i t s hydrolysis i n aqueous sodium hydroxide (NaOH) according ' to the o v e r a l l equation: COS + 4 NaOH —> Na 2C0 3 + Na2S + 2 H20 2.1 One such method was described by Schultze et a l . (42) but the hydrolysis was slow and required long contact times to go to completion. Johnson et a l . (43) found that the hydrolysis could be accelerated by using aqueous mixtures of MEA and NaOH. The MEA acts as a c a t a l y s t ; i t forms a thiocarbamate with the COS, which i s then hydrolysed by NaOH thereby regenerating the MEA. These methods consumed NaOH due to the d i f f i c u l t y i n regenerating i t from sodium sulphide (Na2S) and sodium carbonate (Na 2C0 3). 10 The use of alkanolamines was regarded as a better a l t e r n a t i v e since they are e f f e c t i v e i n absorbing C0 2 and H2S and the amine i s e a s i l y regenerated. Schultze and Short (44) described a method u t i l i z i n g MEA impregnated on a bed of alumina for the absorption of COS from l i q u i d propane and butane. It was reported that the system removed COS from a stream o r i g i n a l l y containing 0.002 wt% COS, but the COS was i r r e v e r s i b l y bound to the MEA. Kearns and Beamer (45) also used aqueous solutions containing 10 - 60 wt% MEA to absorb COS from a gas stream and found that the MEA was i r r e v e r s i b l y transformed to diethanolurea. As a r e s u l t of the substantial amine losses that occur from the i r r e v e r s i b l e reactions of MEA with COS, DEA i s generally a preferred choice f o r tr e a t i n g gases containing COS. Nevertheless, the choice of DEA f o r processing COS bearing streams has been c o n t r o v e r s i a l i n the past. Kerns and Beamer (45) and Reed (46) claimed that DEA i s i n e r t to COS and cannot e f f e c t i v e l y remove COS from gas streams even though they d i d not provide d e t a i l s of t h e i r experimental conditions. On the other hand, Easthagen et a l . (47) reported that 99% of carbonyl sulphide in gaseous hydrocarbons can be removed by treatment with aqueous DEA and that the spent solution i s e a s i l y regenerated by steam s t r i p p i n g . Other studies have also shown that DEA absorbs COS from gas streams (19,20). Pearce et a l . (20) passed COS into aqueous DEA solutions and analyzed them by gas chromatography. Carbonyl sulphide was detected i n the solution and t h i s was taken as an i n d i c a t i o n that DEA absorbs COS d i r e c t l y and not i t s hydrolysis products. Orbach and Selleck (19) contacted a gas stream containing 1 mole% COS i n N 2 a l t e r n a t e l y with aqueous solutions containing 20% MEA and 35 wt% DEA at room temperature. The gas and 11 solvents flowed counter-currently i n a 25 mm I.D. glass column packed to a height of 40 cm with 6 mm O.D. glass Raschig rings. The gas leaving the column was analysed with an i n f r a - r e d spetrophotometer set to a wavelength of 4.87 microns where the absorption c o e f f i c i e n t of COS i s 9.18 X 10 " 3 mm Hg" 1 cm"1. It was found that both MEA and DEA solutions absorbed COS from the gas stream but more COS was absorbed by the DEA so l u t i o n . The absorption of COS i n amine and a l k a l i solutions was reported by Sharma and Danckwerts (48). The experimental data obtained from various contacting devices such as a wetted wall column, s t i r r e d c e l l and j e t apparatus showed that most of the amines absorbed COS. At 25 °C, the second order reaction rate constants for the amine-COS reaction ( k A M . c o s ) was approximately 1% of the rate constant for the corresponding amine-CO2 reactions. The r a t i o was only 0.25% i n the case of MEA. Less common amines such as methyl aminoethanol (MAE) and ethyl aminoethanol (EAE) gave better r e s u l t s than e i t h e r MEA or DEA in the absorption of COS. The rate constants obtained for these amines were 250 and 220 L/(mole s) re s p e c t i v e l y , as opposed to 16 and 11 L/(mole s) f o r MEA and DEA, re s p e c t i v e l y . Rahman (49) has studied the absorption of a c i d gases i n anhydrous alkanolamines. CO2 ,H2S, COS and mercaptans were contacted with MEA, DEA, DGA, DIPA and MDEA in a Claisen d i s t i l l a t i o n f l a s k at i n i t i a l pressures up to 20 psig. The temperature i n the f l a s k was not co n t r o l l e d , but depended on the heats of reactions. Temperature and pressure var i a t i o n s were recorded during the experiments which lasted 1 hour. A l l alkanolamines were found to absorb COS as indicated by the 12 drop i n the t o t a l pressure within the reaction v e s s e l . Analysis of 1 T samples of the amine-COS systems by C NMR spectroscopy revealed the presence of the respective thiocarbamates. Although the study was able to e s t a b l i s h the species i n the amine solutions, the data pertained only to anhydrous systems and are therefore of l i t t l e i n d u s t r i a l relevance. The physical s o l u b i l i t y of a gas i n a solvent with which i t reacts cannot be determined d i r e c t l y . Al-Ghawas et a l (50) therefore used the ^ 0 analogy o r i g i n a l l y proposed by Clarke (51) to determine the physical s o l u b i l i t y of COS i n 0 - 30 wt% aqueous MDEA solutions at 20 to 40 °C and 1 atm pressure. The r a t i o of the Henry's constants f o r the s o l u b i l i t y of COS and N 20 < H o C 0 S / H ° N 2 0 ) i n water and 15.5 wt% ethylene g l y c o l solutions were f i r s t determined at 25°C. The difference i n the r a t i o s f o r both systems was found to be only 0.26%. It was then assumed that t h i s r a t i o was the same for a l l temperatures and amine solutions. The Henry' s constants f o r the s o l u b i l i t y of COS i n aqueous MDEA solutions were then determined from the expression: HCOS = H°COS / H°N20 X HN20 where H°^ and H^ r e f e r to the Henry' s constant for the s o l u b i l i t y of gas i i n water and aqueous MDEA solutions, r e s p e c t i v e l y . The Henry's constants were found to range from 3.941 kPa m /mol for water at 20 °C to 7.554 kPa m3/mol f o r 30.21 wt% MDEA solution at 40 °C. The temperature v a r i a t i o n of the Henry's constant was well correlated by the Arrhenius expression. Since the focus of the study was the k i n e t i c s of the COS-MDEA reaction, only physical s o l u b i l i t y and 13 d i f f u s i v i t y data were reported. No information was provided on the t o t a l s o l u b i l i t y of COS i n MDEA solutions. It was recently reported (52) that the absorption of COS int o a l k a l i n e solutions could be enhanced by using a second emulsified l i q u i d phase. A t h e o r e t i c a l enhancement factor was defined as the r a t i o of the s p e c i f i c rate of absorption i n the base, with and without the second emulsified l i q u i d phase. Enhancement factors of 2.5 and 4.0 r e s p e c t i v e l y were achieved using toluene (20% v/v) and 2-propanol (50% v/v) as the second emulsified l i q u i d phases i n sodium hydroxide so l u t i o n at 30 °C. There was no i n d i c a t i o n whether such enhancements could be achieved i n alkanolamine systems. The operational d i f f i c u l t i e s which may accompany the use of emulsions, were not discussed e i t h e r . R e i l l y et a l . (89) have also reported that the rate of absorption of COS in MDEA solutions was enhanced by he t e r o c y c l i c amine a d d i t i v e s . Enhancements factors up to 8 f o l d were obtained f o r the range of additives concentrations investigated. The additives produced l i t t l e or no enhancements i n the corresponding CO2 systems. Other alkanolamines such as DIPA (53) and DGA (54) are used f o r absorbing COS without in c u r r i n g appreciable amine loss but t h e i r i n d u s t r i a l acceptance i s s t i l l quite l i m i t e d . Singh and B u l l i n (55) studied the k i n e t i c s of the reaction between COS and aqueous DGA over a temperature range of 307 - 322 K and pressure range of 345 - 414 kPa. They used a p e r f e c t l y mixed flow reactor operated with continuous gas and l i q u i d feeds. The composition of the amine sol u t i o n leaving the absorber was determined by gas chromatography. Although the hydrolysis of COS produces equimolar amounts of CO2 and H2S, the GC analysis 14 recorded i n s i g n i f i c a n t l e v e l s of C0 2. The l a t t e r may be due to i t s consumption i n the degradation of DGA. The rates of reaction were ca l c u l a t e d by d i v i d i n g the sum of the molar flow rates of COS (and the H2S from the hydrolysis reaction) by the volume of the reactor; they were found to be much higher than those for the COS-H2O reaction (56). This l ed to the conclusion that DGA was c a t a l y s i n g the hydrolysis of COS. A s i m i l a r e f f e c t has also been reported f o r other amines (57). The COS-DGA reaction was second order; i t was f i r s t order with respect to the amine and COS concentrations. The second order reaction rate constants obeyed the Arrhenius expression. At 27 °C, the value was 0.0023 m3/(mol s) compared to 0.166 m3/(mol s) (49) and at most 0.016 mJ/(mol s) (48,57). The l a t t e r was i n f e r r e d from the rate constant reported at 25 °C f o r the r e a c t i o n of COS with MEA, a primary amine that reacts f a s t e r than DGA. The reported values d i f f e r s i g n i f i c a n t l y but i t i s d i f f i c u l t to make a d i r e c t comparison of the rate constants for acid gas-amine reactions in aqueous and non-aqueous amine systems because of the di f f e r e n c e s in d i f f u s i v i t y , i o n i c strength, nature of g a s - l i q u i d i n t e r f a c e and physical s o l u b i l i t y . The combined e f f e c t s of these factors may explain the higher values found by Rahman. It i s c l e a r from the foregoing that COS i s absorbed d i r e c t l y into amine solutions and not i t s hydrolysis products. However, -compared to CO2 and H 2S, very l i t t l e work has been reported on the t o t a l s o l u b i l i t y of COS i n amine solutions. The few studies on COS-amine systems cover narrow temperature ranges below 50 °C. It i s not s u r p r i s i n g therefore that Vapour-Liquid-Equilibrium (VLE) models to date, are l i m i t e d to aqueous amine-CO2-H2S systems. 15 2.2.3 CARBON DISULPHIDE Osenton and Knight (21) contacted CS2 vapour with aqueous alkanolamine solutions and used changes i n system pressure to e s t a b l i s h the rates of absorption of CS2 into alkanolamine solutions. The rates of absorption followed the order S u l f i n o l > 25% DEA > 20% MEA. S u l f i n o l i s a mixture of DIPA and a physical solvent. As i n the case of COS, equilibrium data for the s o l u b i l i t y of CS2 i n amine solutions are lacking. 2.3 EQUILIBRIUM REACTIONS OF ACID GASES IN AMINE SOLUTIONS When ac i d gases are absorbed into alkanolamine solutions, i o n i c species are generated and various e q u i l i b r i a , which are discussed i n the following sections, are established. 2.3.1 REACTIONS OF HYDROGEN SULHIDE Hydrogen sulphide in aqueous amine solutions d i s s o c i a t e s i n t o H + and HS": H 2S = H + + HS" 2.2 The proton i s transferred to the amine v i r t u a l l y instantaneously (2,58): RR' NR" + H + = RR' N + R"H 2.3 16 where R and R represent H and / or -C2H4OH, depending on the class of amine, while R represents -C2H4OH. The bisulphide ion can di s s o c i a t e further: HS" = H + + S"" 2.4 However, t h i s reaction occurs only i n highly basic solutions (pH > 12 ) and can usually be disregarded f o r alkanolamine solutions contacting a c i d gases (2,58). 2.3.2 REACTIONS OF CARBON DIOXIDE The e q u i l i b r i a i n C02-amine systems can be represented by the following series of equations: C0 2 + H 20 = H + + HCO3" 2.5 HCO3" = H + + CO3"" 2.6 Reaction 2.5 has been shown to be catalysed by bases (37,58,59). The protons (or hydrogen ions) react with the amines to form protonated amines according to equation 2.3. In addition, a d i r e c t reaction occurs between CO2 and primary and secondary amines to form carbamates: RR1 NH + C0 2 = RR'NCOO" H + 2.7 17 It has been postulated that t h i s equation may involve two steps; a zwitterion intermediate i s f i r s t formed which by v i r t u e of i t s i n s t a b i l i t y , i s e a s i l y deprotonated i n the presence of a base (B) to form the carbamate (60): RR1 NH + C0 2 = RR'N +HCOO" 2.8 RR*N+HCOO" + B = BH + + RR'NCOO" 2.9 Equation 2.8 i s the rate determining step since the deprotonation of the zwitterion (Eq. 2.9) i s instantaneous (59,60). Reaction 2.7 i s much f a s t e r than the hydration of CO2 (eq. 2.5) and represents the major mode of i n t e r a c t i o n between CO2 and primary or secondary amines. T e r t i a r y amines have no l a b i l e hydrogen atoms and are therefore unable to form carbamates. Absorption of CO2 i n such amines proceeds v i a Eqs. 2.5 and 2.6. They are able to absorb H2S at a f a s t e r rate and are thus used f o r the s e l e c t i v e absorption of hydrogen sulphide. Methyldiethanolamine (MDEA) i s widely used f o r t h i s purpose (61-63). 2.3.3 REACTIONS OF CARBONYL SULPHIDE Sharma (57) postulated that, because of the s t r u c t u r a l s i m i l a r i t i e s of CO2 and COS, t h e i r reactions with amines are s i m i l a r . The relevant equations f o r the COS-DEA system would therefore be: R2NCOS" + H + R2NH + C0 2 + H2S 2 .10 2.11 18 Equation 2.10 represents the thiocarbamate formation. Primary and secondary amines undergo t h i s reaction. In the case of MEA, the thiocarbamate may be further transformed into degradation products from which the amine i s not e a s i l y recovered (19,20,64). It has been estimated that 10 to 20% of the MEA reacting with COS i s l o s t i n such i r r e v e r s i b l e reactions (20). Equation 2.11 i s the COS hydrolysis reaction. It has been represented i n t h i s form since most of the COS i n solut i o n was absorbed as thiocarbamate and also to indicate that the hydrolysis of COS i s catalyzed by the DEA. Rahman (49) and Rahman et a l . (65) confirmed through NMR spectroscopy, the presence of the respective carbamates, thiocarbamates and protons i n anhydrous .alkanolamine-acid gas systems. The H2S and CO2 produced v i a Eq. 2.11 then i n i t i a t e the reactions shown i n Eqs. 2.2 - 2.4 and 2.5 - 2.7, respectively. Al-Ghawas et a l . (50) have suggested that COS may be hydrated l i k e CO2 by forming a thio-bicarbonate ion: COS + H 20 = HC02S" + H + 2.12 The existence of HCO2S" i n sol u t i o n was not proven d i r e c t l y but was inf e r r e d from spectroscopic observations. A mixture of CO2 and H2S was bubbled through an aqueous sol u t i o n of MDEA and COS was bubbled through another aqueous MDEA sol u t i o n . Both solutions, when inspected spectrophotometrically, were found to absorb at d i f f e r e n t wavelengths; the so l u t i o n exposed to COS absorbed at 518 nm, whereas the other sol u t i o n absorbed at 503 nm. It i s known that CO2 and H2S i n solu t i o n give r i s e to HCO3" and HS", re s p e c t i v e l y . If hydrolysis of COS i s the 19 predominant reaction i n the COS-MDEA solution, the solution should absorb at the same wavelength as the MDEA solu t i o n exposed to CO2 and H2S. The observed differences i n absorption wavelengths were a t t r i b u t e d to the existence of another species, i . e . HCO2S". The o v e r a l l reaction for the COS-MDEA system was postulated as: R 2NCH 3 + H20 + COS -» R 2N +HCH 3 + HC02S" 2.13 The second order rate constant k^, was given by the expression: k 2 = 4198.74 exp (-4575.80/T). The units of k2 and T are m /mol s and Kelvin (K) r e s p e c t i v e l y . It i s therefore c l e a r that an aqueous COS-amine system at equilibrium, consists of the amine, C02, H2S, unhydrolysed COS and t h e i r derived species such as protonated amine, carbamates, thiocarbamates, hydrogen ions and bicarbonate ions. The s e l e c t i v i t y of the amine f o r these gases w i l l e s t a b l i s h the equilibrium composition of the system. 2.3.4 REACTIONS OF CARBON DISULPHIDE Osenton and Knight (21) used t h i n layer chromatography to confirm that CS 2 reacts with aqueous alkanolamine solutions. In t h e i r work, 7 mL of CS2 were added to 40 mL of aqueous amine solutions and the r e s u l t i n g mixture was s t i r r e d f o r a short time. Samples of the aqueous layer of 20 the mixture were then spotted on a s i l i c a gel TLC plate and developed i n methanol. Subsequent inspection of the plate i n iodine or U.V. l i g h t showed, i n a l l cases, the presence of a new compound i n addition to the s t a r t i n g materials. This compound was reported as amine dithiocarbamate, the product of the CS 2-amine reaction: RR NH + CS 2 = RR NCSS"H+ 2.14 The amine dithiocarbamate reacts further i n the presence of excess amine to give the dithiocarbamate s a l t of the amine: RR'NH + RR'NCSS" H + = RR'NCSS" H 2N +R 2 2.15 Kothari and Sharma (66) have determined the k i n e t i c parameters of the r e a c t i o n of CS 2 with aqueous amine solutions using s t i r r e d c e l l s . The amine solutions were contacted with CS 2 i n the vapour and l i q u i d states at temperatures between 5 and 30 °C. The k i n e t i c parameters were estimated by applying the penetration theory equation to the experimental data, and were found to be independent of the state of the CS 2 and speed of a g i t a t i o n above 25 r.p.m. The rate constants obtained for the amine-CS 2 reactions obeyed the Arrhenius expression. Diethanolamine was the only alkanolamine investigated and a rate constant of 0.10 L/g-mole-s was reported for the CS2-DEA reaction at 30 °C. By comparing the second order rate constants ^AM-CS2^ with published rate constants f o r the corresponding C0 2-amine i t was found that: kAM-C02 1 kAM-CS2 = 2 X 1 C | 4 • 21 Since KAM-C02 ^ ^A!*I-COS = 1 X 1 (57), i t follows that KAM-COS 1 KAM-CS2 = 2 X 10 2. The r a t i o s of the reaction rate constants ind i c a t e that the rates of reaction follow the order: kAM-C02 > k A M _ c o s > k A M _ c s 2 - Carbon disulphide also undergoes hydrolysis i n aqueous solutions producing COS, C0 2 and H 2S (24). The o v e r a l l reactions are: CS 2 + H 20 = COS + H 2S 2.16 COS + H 20 = C0 2 + H 2S 2.17 CS 2 hydrolysis may also occur v i a the amine dithiocarbamate: RR NCSS" H + + 2H 20 = RR NH + C0 2 + 2H2S 2.18 The C0 2/H 2S r a t i o i s therefore 1/2 compared with 1/1 for COS hydrolysis. 2.4 DEGRADATION OF DIETHANOLAMINE SOLUTIONS 2.4.1 DEGRADATION OF DIETHANOLAMINE BY CARBON DIOXIDE The degradation of DEA by carbon dioxide was f i r s t reported by Polderman and Steele (10). Two compounds, b i s hydroxyethyl piperazine (BHEP) and hydroxyethyl oxazolidone (HEOD) were detected i n the degraded solution. It was suggested that these compounds were formed as follows: DEA + C0 2 = HEOD 2.19 2 HEOD = BHEP + 2CO, 2.20 22 Later, Hakka et a l . (11) i d e n t i f i e d another compound, t r i s hydroxyethyl ethylene diamine (THEED) i n a degraded DEA solution, but offered no mechanism for i t s formation. Other more de t a i l e d studies have since been published (9, 12-18). Choy (12) conducted degradation experiments using a s t a i n l e s s s t e e l reactor at temperatures between 165 and 180 °C and CO2 pressures of up to 4238 kPa. Analysis of the solutions by gas chromatography in d i c a t e d a number of products, but only BHEP was conclusively i d e n t i f i e d . It was reported that the i n i t i a l o v e r a l l DEA degradation could be represented by f i r s t order k i n e t i c s even though the rate constant was a function of the i n i t i a l DEA concentration. Kennard (16) as well as Kennard and Meisen (14) reported r e s u l t s of degradation experiments conducted i n a 600 mL s t a i n l e s s steel r eactor. Aqueous solutions containing 5 - 100 wt% of DEA were subjected to CO2 pressures up to 4.1 MPa at temperatures ranging from 90 - 205°C. A t o t a l of 12 products were i d e n t i f i e d i n the degraded solutions, the major ones being BHEP, HEOD and THEED. The following s i m p l i f i e d mechanism, supported by experimental observations, was suggested for the formation of the major degradation products: DEA + C0 2 = HEOD 2.21 DEA + DEACOO" -> THEED 2.22 THEED —» BHEP 2.23 The i n i t i a l rate of DEA degradation was found to increase with DEA concentration, temperature and C0 2 p a r t i a l pressure; these observations 23 agreed with those of Choy (12). A pseudo f i r s t order k i n e t i c model was developed to predict the rate of degradation and the formation of the major degradation compounds. The HEOD formation (Eq. 2.21) was assumed to be i r r e v e r s i b l e and the influence of C0 2 p a r t i a l pressure on the ki n e t i c s was eliminated by e s t a b l i s h i n g the pressure beyond which C0 2 loading was constant. Thus the k i n e t i c model was r e s t r i c t e d to the ranges: DEA concentration of 0 - 100 wt%; temperatures of 90 - 175 °C; C0 2 loadings > 0.2g / g DEA. C0 2 was neither consumed nor formed i n the degradation process and was therefore suggested as cat a l y s i n g the process. Kim and S a r t o r i (13) conducted degradation experiments at 100 and 120°C using 3.2M aqueous DEA solutions containing various amounts of C0 2 and/or H 2S. The solutions were put i n sealed s t a i n l e s s s t e e l ampoules which were then immersed i n a temperature c o n t r o l l e d bath. The rate of degradation increased with increasing C0 2 loadings, producing BHEP, HEOD and THEED as the major degradation compounds. A scheme suggesting successive reactions was put f o r t h to account f o r the formation of the degradation compounds: DEA + C 0 2 = HEOD 2 . 2 4 DEA + HEOD -+ THEED 2 . 2 5 THEED -> BHEP 2 . 2 6 Rate constants f o r the reaction steps were determined at 100 and 120°C. Again, the c a t a l y t i c role of C0 2 was noted while H 2S exerted e s s e n t i a l l y no e f f e c t . It should be noted that the r a t i o of C0 2 to H 2S solution 24 Loading i n the only mixed gas run reported was 36.7. The extremely low H 2S loading might explain the si m i l a r i n i t i a l rate of degradation obtained i n the corresponding run conducted with C0 2 alone. Chakma (18) and Chakma and Meisen (9) have reported degradation of DEA by C0 2 i n a heat'transfer loop. The rate of degradation increased with temperature, DEA concentration and C0 2 p a r t i a l pressure, but decreased with solution flow rate. The mechanism suggested by Kennard and Meisen (14) was used to develop a mathematical model f o r the degradation. However, unlike i n the previous case (14), C0 2 was e x p l i c i t l y included i n the rate expressions so that the model could cover a wider range of operating conditions. In essence, the formation of HEOD and THEED was governed by second order k i n e t i c s while BHEP formation was f i r s t order as shown below: 2.27 2.28 2.29 The rate constants were reported as functions of temperature. Hsu and Kim (15) used a gas chromatograph coupled to a mass spectrometer (GC/MS) to i d e n t i f y higher molecular weight triamino degradation compounds i n aqueous DEA solutions degraded by C0 2. The mixture was f i r s t d e r i v a t i z e d to make the compounds more v o l a t i l e and thus amenable to GC/MS an a l y s i s . The procedure f o r the d e r i v a t i z a t i o n k l DEA + C0 2 -» HEOD k2 DEA + C0 2 -» THEED k3 THEED -> BHEP + C0 2 25 consisted of saturating the p a r t i a l l y degraded sol u t i o n with potassium carbonate to remove water, followed by extraction with isopropyl a l c o h o l . The alcohol was then evaporated to obtain a dehydrated o i l y material. 1 mL of anhydrous py r i d i n e , 0.2 mL of hexamethyl dis i l a z a n e and 0.1 mL of t r i m e t h y l c h l o r o s i l a n e were added to the o i l and the r e s u l t i n g mixture was vigorously shaken for 30 s and kept at room temperature f o r over 5 min u n t i l d e r i v a t i z a t i o n was' complete. In addition to DEA, HEOD, BHEP and THEED three other compounds, 3-(-(bis(2- hydroxyethyl)-amino)ethyl)-2-oxazolidone (HAO), N-(2-(N,N-bis(2- hydroxyethyl)amino)ethyl)-N -(2-hydroxyethyl)piperazine (HAP) and N,N,N ,N -tetrakis(2-hydroxyethyl)diethylenetriamine (THEDT) were i d e n t i f i e d and reaction mechanisms were proposed for t h e i r formation. Chakma (18) reported that the above procedure was not always s e l e c t i v e , sometimes r e s u l t i n g i n the d e r i v a t i s a t i o n of both-the alcohol and amino groups i n alkanolamines. Instead of a mixture of chemicals, Chakma used trimethyl s i l y l imidazole (TSIM) to d e r i v a t i z e p a r t i a l l y degraded MDEA solutions. Only the hydroxyl groups were d e r i v a t i z e d and d e r i v a t i z a t i o n was complete within 30 minutes. The s e l e c t i v e d e r i v a t i z a t i o n made i t possible to i n f e r the number of hydroxyl groups i n the underivatized compounds. Smith and Younger (17), i n a more p r a c t i c a l approach, offered some help f u l hints on the design and operation of gas plants to avoid or minimise problems such as foaming, corrosion and degradation. They reported that 10 of 19 plants investigated experienced some degradation, the products being BHEP, r e s i d u a l s a l t s , thiosulphates and probably TEA. 26 These studies have provided appreciable ins i g h t into alkanolamine degradation due to carbon dioxide. The degradation i s believed to occur p r i m a r i l y v i a amine carbamates which may be formed by the d i r e c t reaction of CO2 with amines. Since H2S i s incapable of forming carbamate-type compounds, i t i s generally agreed that H2S does not cause amine degradation. Choy (12) and Kim and S a r t o r i (13) have reported findings which suggest that H2S in the presence of C0 2 a c t u a l l y hinders amine degradation. The difference i n the mechanisms suggested by Kim and Sa r t o r i (13) and Kennard and Meisen (14) i s i n the formation of THEED. In order to determine which of the mechanisms better represents THEED formation, the equilibrium between HEOD and DEA under CX^-rich and C02- l i m i t i n g conditions as represented below, i s re-examined: co 2 DEA = DEACOO" H + = HEOD + H20 2.30 N2 DEA + C0 2 = DEACOO" H + = HEOD + H20 2.31 In the C02-rich system (Eq. 2.30), the equilibrium w i l l always favour HEOD production and can be maintained by the transformation of excess DEA carbamate (DEACOO") or HEOD to other products such as THEED. However, the high CO2 loading reduces the b a s i c i t y of the so l u t i o n and the transformation of HEOD to THEED, a reaction which involves r i n g breakage, may be s l i g h t l y hindered. On the other hand, the reaction of DEA with DEACOO" to form THEED as proposed by Kennard and Meisen w i l l proceed w e l l . In support of t h i s a s s e r tion i s the fi n d i n g of Kennard and Meisen that the HEOD concentration increased only s l i g h t l y i n an aqueous 27 sol u t i o n of DEA and HEOD that was saturated with CO2 and maintained at 175 °C for 8 hr. In the nitrogen or CO2-limiting case (Eq. 2.31), the equilibrium l i e s to the l e f t i n favour of DEA and DEACOO" formation. The equilibrium i s maintained by the reac t i o n of excess DEACOO" with DEA to form THEED. Data reported by Kim and S a r t o r i showed that i n an aqueous solution containing HEOD and DEA at 120 °C, the HEOD concentration decreased by 0.4 M while the DEA and THEED concentrations increased by 0.03 M and 0.20 M, re s p e c t i v e l y . If the mechanism of Kennard and Meisen i s correct the 0.2 M THEED could be produced from 0.2 moles/L each of DEA and DEACOO", both of which account f o r the 0.4 M drop i n HEOD concentration. Using the mechanism by Kim and S a r t o r i , the concentration data implies that the 0.2M THEED was produced from 0.2 moles of HEOD and DEA. The remaining 0.2 M drop i n HEOD i s that l o s t i n the reversal to carbamate. The l a t t e r keeps the DEA concentration approximately constant since GC analysis does not d i s t i n g u i s h between free amine and amine carbamate. Thus HEOD reversal to DEACOO" and i t s reaction with DEA to form THEED would proceed at the same rates, a s i t u a t i o n that would disrupt the equilibrium i n Eq. 2.31. The mechanism of Kennard and Meisen therefore appears to be the more applicable one to the CO2 l i m i t i n g case. In summary, the mechanism postulated by Kennard and Meisen appears to represent both the CO2 l i m i t i n g and non-limiting systems whereas the mechanism by Kim and S a r t o r i i s p a r t i a l l y applicable to the l a t t e r but not the former case. Since amine degradation i n sweetening units occurs mostly at high temperatures, a condition that l i m i t s CO2 loadings, the 28 Kennard and Meisen mechanism i s therefore more appropriate for i n d u s t r i a l s i t u a t i o n s . 2.4.2 DEGRADATION OF DIETHANOLAMINE BY CARBONYL SULPHIDE Compared with CO2-induced degradation, l i t t l e work has been reported on the COS-alkanolamine degradation reactions (19,20). Orbach and Selleck (19) contacted pure COS with 20 wt% MEA and 35 wt% DEA solutions i n a bench-scale p i l o t plant simulating a t y p i c a l , continuous absorption-regeneration process. The absorber and regenerator were operated at 40 °C and 104 °C, r e s p e c t i v e l y . Periodic . analysis of the amine solutions using Kjeldahl analysis and a c i d t i t r a t i o n revealed that, while MEA was s u b s t a n t i a l l y degraded, no loss of a l k a l i n i t y occurred i n the DEA solution over 8 hours. Although the authors reported the formation of some extraneous products, they were "too small for i s o l a t i o n and c h a r a c t e r i z a t i o n " . B e l i e v i n g that these products could be formed from small quantities of MEA i n the i n i t i a l DEA s o l u t i o n , they concluded that COS does not degrade DEA. Pearce et a l . (20) contacted, i n a batch-mode, pure COS with 20 wt% DEA solutions at temperatures ranging from 40 to 120 °C. The solutions were subsequently analyzed by i n f r a r e d and mass spectroscopy. Minor quantities of ethanol and oxazolidone were detected. However, these quantities were i n s i g n i f i c a n t compared with those formed when MEA was subjected to COS under s i m i l a r operating conditions. Pearce et a l . (20) also contacted COS with DEA continuously using an approach analogous to that of Orbach and Selleck (19). The concentrations of the 29 DEA solutions at the s t a r t and end of the experiments were determined by- wet chemical a n a l y s i s and found to be e s s e n t i a l l y the same. This again led to the conclusion that COS does not degrade DEA. A further conclusion was that COS underwent s i g n i f i c a n t hydrolysis as revealed by the presence of CO2 and H2S i n the regenerator off gas and the DEA solution leaving the absorber. 2.4.3 DEGRADATION OF DIETHANOLAMINE BY CARBON DISULPHIDE The only substantive study on alkanolamine degradation by CS2 was conducted by Osenton and Knight (21). They contacted 40 mL of a 25 wt% aqueous DEA s o l u t i o n with 7 mL of CS2 for 3 hours i n a s t i r r e d vessel at 25 °C. T i t r a t i o n of the so l u t i o n f or free amine and dithiocarbamate contents revealed the complete conversion of amine to the amine s a l t of dithiocarbamic a c i d (see eq. 2.14). When the reaction mixture was b o i l e d f o r 1 hour and analyzed i n the same manner, only 20% of the DEA was recovered from the dithiocarbamate s a l t . Using MEA instead of DEA, Osenton and Knight found that about 40% of the i n i t i a l MEA was recovered upon b o i l i n g . They also detected oxazolidone-2-thione amongst the reaction products, contrary to the findings of Pearce et a l . (20) who di d not detect any degradation compounds i n MEA/CS2 systems. It should be noted that while Osenton and Knight contacted CS2 d i r e c t l y with MEA, Pearce et a l . based t h e i r conclusions on a f i e l d test of an MEA plant which processed gas containing COS and CS2. The assumption was made that the plant's MEA loss was due to the MEA-COS reaction only. Since COS and CS2 e x i s t i n p.p.m concentrations i n sour i n d u s t r i a l gases, i t i s 30 possible that, i n the f i e l d t e s t , the CS2-MEA reactions resulted i n degradation product concentration too low to be detected by the mass spectroscopic a n a l y s i s . This may be the reason f o r the contradictory findings. 2.5 LIMITATIONS OF THE PREVIOUS COS-DEA AND CS2-DEA DEGRADATION STUDIES Conclusions of some e a r l i e r studies notwithstanding, there are three basic reasons to believe that degradation may occur i n COS-DEA and CS2-DEA systems. F i r s t , recent studies on the C02-MDEA system have shown that degradation i s possible v i a amine protonation as well as carbamate formation (18). Since COS and CS 2 hydrolyze i n aqueous systems to give H 2S and C02, s i g n i f i c a n t concentrations of H + and C0 2 may r e s u l t to induce the degradation of DEA v i a protonated DEA and DEA carbamate. Second, i t has been reported that the COS-DEA and CS2-DEA reactions forming thiocarbamate and dithiocarbamate r e s p e c t i v e l y , are two and f i v e orders of magnitude slower than the C02-DEA reaction y i e l d i n g DEA carbamate (57,66). Since C0 2-induced degradation of DEA occurs p r i m a r i l y v ia DEA carbamate, i t i s l i k e l y that the COS and CS 2 induced degradation of DEA v i a the thiocarbamates and dithiocarbamates respectively, are correspondingly slower. For instance, i t was found that at 120 °C, a C0 2 p a r t i a l pressure of 4.1 MPa and an i n i t i a l DEA concentration of 30 wt%, i t took almost 20 hours to obtain a 5% reduction i n the amine concentration and only one degradation compound was formed i n appreciable q u a n t i t i e s (16). When the degradation 31 experiments were conducted f o r extended periods of up to 30 days at low temperatures (11,13,14,16) or for eight hours at elevated temperatures (14,16), s i g n i f i c a n t decreases i n amine concentrations were recorded and more degradation compounds were formed. Since Orbach and Selleck (19) and Osenton and Knight (21) conducted t h e i r DEA degradation experiments over just 8 and 4 hours, r e s p e c t i v e l y , i t i s not s u r p r i s i n g that s i g n i f i c a n t amounts of degradation compounds could not be detected. (The durations of the experimental runs performed by Pearce et a l . (20) were not c l e a r l y indicated.) Third, the a n a l y t i c a l techniques used previously may not have been s u f f i c i e n t l y s e n s i t i v e to detect the compounds a r i s i n g from the degradation reactions. The difference between Kjedahl t o t a l nitrogen and free amine determinations were often used to e s t a b l i s h the extent of amine i n a c t i v a t i o n . Polderman et a l . (4) have noted some inconsistencies i n t h i s approach. Values obtained f o r t o t a l nitrogen includes nitrogen from the amine as well as i t s nitrogenous degradation compounds. Acid t i t r a t i o n s to determine free amine concentration provide erroneous r e s u l t s since the degradation compounds are basic and some of them are t i t r a t e d as we l l . Therefore, i t may be concluded that values obtained from the di f f e r e n c e of the two analyses may not be r e l i a b l e estimates of the degree of amine i n a c t i v a t i o n . 32 2.6 ANALYSIS OF DEGRADED ALKANOLAMINE SOLUTIONS E a r l i e r attempts to analyze degraded amine solutions used methods such as potentiometric t i t r a t i o n (67), a c i d t i t r a t i o n and Kjedahl t o t a l nitrogen determination (4,68), f r a c t i o n a l d i s t i l l a t i o n and c r y s t a l l i z a t i o n (10). These methods were generally unsuccessful f o r reasons such as lack of r e p r o d u c i b i l i t y , i n a b i l i t y to separate degradation compounds, decomposition of amines and degradation compounds at elevated temperatures. D e r i v a t i z a t i o n p r i o r to gas chromatographic analysis has also been t r i e d (69,70,71). Although f a i r l y successful, gas chromatographic analysis of d e r i v a t i z e d degraded amine solutions suffers some drawbacks. These were outlined by Saha et a l . (72) and include: time consuming procedures of preparing d e r i v a t i v e s , incomplete d e r i v a t i s a t i o n , i n s t a b i l i t y of derivatives over long periods and in the presence of water, and long period of a n a l y s i s . As a r e s u l t , they developed a d i r e c t gas chromatographic technique using a column packed with Tenax GC, a porous polymer based on 2,6-diphenyl paraphenylene oxide (73). This column s u c c e s s f u l l y separated a mixture of MEA, DEA and TEA i n about 8 minutes. The use of the Tenax GC column was extended to the analysis of degraded DEA solutions (13,74) and Kennard and Meisen (74) have reported the d e t a i l e d a n a l y t i c a l conditions f o r the ana l y s i s . However, while Kennard and Meisen (74) reported good r e s o l u t i o n of peaks, Kim and S a r t o r i (13) were unable to separate some degradation compounds with the Tenax GC column alone. To overcome t h i s problem, each analysis was repeated with a 5% SE 30/Chrom-GHP column. The lack of separation could have been due to the shorter column length (2 f t ) used 33 i n the study, as opposed to the 6 f t column used by Kennard and Meisen (74). A gas chromatographic method involving a combination of columns has also been reported by Robbins and B u l l i n (75). Tenax GC and Porapak Q columns were connected i n series f o r the analysis of amine solutions containing a c i d gases, hydrocarbons and water. The Tenax column separated the amine from the other components which were further separated by the Porapak Q column and detected by a thermal conductivity detector (TCD). A switching valve i n the set up was used to bypass the Porapak column once the l i g h t e r components had eluted. This was done to protect the Porapak column from i r r e v e r s i b l e adsorption or deactivation by the amine. Good r e s o l u t i o n was obtained f o r CC^, ̂ S , Ĥ O and MDEA within 10 minutes. The concentrations of the ac i d gases obtained from the GC analysis were i n good agreement with the values obtained from wet chemical methods. This method i s able to simultaneously determine the concentrations of ac i d gases as well as the amine and i t s degradation products. However, care should be taken i n the handling of samples from degradation runs conducted at high temperatures and pressure, to prevent f l a s h i n g of the ac i d gases and hence erroneous a c i d gas loadings. Chakma (18) as well as Chakma and Meisen (76) have also used Tenax GC columns f o r the analysis of degraded DEA and MDEA solutions. CHAPTER 3 E X P E R I M E N T A L A P P A R A T U S AND P R O C E D U R E 3.1 REACTOR The degradation experiments were c a r r i e d out using a 600 mL st a i n l e s s s t e e l reactor (model 4560, Parr Instrument Co. 111., U.S.A.), shown i n Figure 3.1. Its main features and accessories are described below: 1. A pressure gauge for monitoring the pressure within the reactor. 2. A J-type thermocouple i n a 316 s t a i n l e s s s t e e l well, to monitor the temperature within the reactor. 3. A close f i t t i n g , quartz f a b r i c heating mantle i n an insulated aluminium housing, attached to a stand to enable movement up or down as desired. 4. An automatic heater/temperature c o n t r o l l e r (model 4813EB, Parr Instrument Co., 111., U.S.A.). The c o n t r o l l e r maintains the system temperature within ± 0.5°C of the set point by regulating the power supply to the mantle. An i n d i c a t o r within the c o n t r o l l e r assembly displays the system temperature i n terms of the magnitude of the deviation from the set point. The temperature l i m i t s of the reactor are room temperature and 400°C. 5. A s t a i n l e s s s t e e l s t i r r e r , driven by a variable speed motor at speeds up to 600 r.p.m. 34 35 6. Li q u i d sampling, gas i n l e t and gas outlet valves. A 1/8" sample tube connected to the gas i n l e t / l i q u i d sampling port enables the supply of gas to and the withdrawal of l i q u i d from the reactor. 7. A rupture d i s c which breaks when the pressure within the reactor exceeds the r a t i n g of the d i s c . The r a t i n g of the disc on the reactor i s 13.78 MPa (2000 psi) at 400 °C. 8. A s t a i n l e s s s t e e l cooling c o i l f o r rapid cooling of the reactor when necessary. 9. A pyrex l i n e r to reduce contact between the reactants and the inner walls of the reactor. 3.2 MATERIALS DEA (>99% purity) was purchased from A l d r i c h Chemical Co., Inc. (Milwaukee, WI). CS 2 (>99% purity) was purchased from BDH Chemicals Inc. (Vancouver, BC). COS was supplied by Matheson Inc (Edmonton, AB) with the following p u r i t y expressed i n mole percent: COS - 97.7%, C0 2 - 1.4%, CS 2 - 0.19%, H2S - 0.01%, 0 2 - 0.1%, CO &/or N 2 - 0.6%. Nitrogen (>99% purity) was purchased from Medigas Ltd. (Vancouver, BC). The compounds used for the c a l i b r a t i o n of the gas chromatograph were purchased from A l d r i c h Chemical Co., Inc. (Milwaukee, WI) with the exception of HEOD, THEED and BHEI which were unavailable and had to be synthesized i n the laboratory. Procedures for t h e i r synthesis are described i n Appendix A2. 36 Figure 3.1: Sketch of the reactor. 37 3.3 EXPERIMENTAL PROCEDURE T y p i c a l l y , 250 mL of an aqueous DEA so l u t i o n with the desired concentration was placed i n the reactor before sealing i t . The s t i r r e r was turned on at a speed of 120 r.p.m and a i r was purged from the reactor by passing nitrogen through i t f o r about 15 min. The gas i n l e t and outlet valves were closed and the heater was turned on to bring the reactor to the desired operating temperature. Once steady state had been achieved, the pressure within the reactor was recorded as the i n i t i a l pressure. This pressure i s the sum of the vapour pressure of the amine solu t i o n and the pressure due to the r e s i d u a l nitrogen i n the reactor. COS was then introduced through a s t a i n l e s s s t e e l pressure hose connected to the pressurized COS c y l i n d e r . It was necessary to warm the COS c y l i n d e r to about 45 °C to increase the pressure within the c y l i n d e r beyond the normal value of 1.1 MPa (160 p s i ) at room temperature. The regulator on the COS cylinder was set so that the difference between the f i n a l and i n i t i a l pressures i n the reactor corresponded to the desired p a r t i a l pressure of COS for the run. The COS l i n e was l e f t open and connected throughout the experiments to ensure a continuous supply of COS to the reactor. A check valve on the COS l i n e prevented backflow even when the pressure in the reactor rose beyond the d e l i v e r y pressure set with the regulator. In the case of CS2 runs, a known volume of CS2 was placed i n a 40 mL s t a i n l e s s steel c y l i n d e r which was connected to the reactor, and F i g u r e 3 . 2 : S e t - u p f o r t h e C S 2 - D E A d e g r a d a t i o n e x p e r i m e n t s . 39 forced into the reactor with nitrogen. The d e l i v e r y pressure of the nitrogen cylinder was regulated to achieve a constant t o t a l pressure i n a l l the runs. The experimental set-up i s shown i n Figure 3.2. 3.4 SAMPLING The gas sampling l i n e was a 1/8" s t a i n l e s s s t e e l tube f i t t e d with i n l e t and outlet valves. Gas from the reactor was f i r s t trapped between the i n l e t valve of the sampling l i n e and the gas outlet valve on the reactor. With the oulet valve of the sampling l i n e closed, the i n l e t valve was opened to tr a n s f e r the gas sample to the l i n e . The sample was subsequently withdrawn with a 10 mL "pressure-lok" syringe by i n s e r t i n g the syringe through a septum i n the "swagelok" f i t t i n g connected to the outlet valve of the sampling l i n e . This arrangement was s u f f i c i e n t to reduce the pressure of the sample and make i t possible to c o l l e c t the sample without d i f f i c u l t i e s . Expansion of the sample i n the syringe during sampling, further reduced the pressure. P r i o r to sampling, the sampling l i n e was purged with the sample gas. Liquid samples were c o l l e c t e d with a 2 mL s t a i n l e s s s t e e l c o i l f i t t e d with i n l e t and outlet valves. The pressure i n the reactor was s u f f i c i e n t to force l i q u i d samples into the sampling c o i l once the sampling valve on the reactor and the i n l e t valve of the sampling c o i l were opened, while the outlet valve of the c o i l was closed. About 3 mL of solution were purged to ensure that the sample i s representative of the reactor solution. With a l l valves closed, the sampling c o i l was disconnected and r a p i d l y cooled to room temperature by immersing i t i n 40 i c e - c o l d water. The sample was then transferred into a covered glass v i a l ready for a n a l y s i s . The sampling c o i l was then flushed with water and a i r d r i e d . I t was then ready for subsequent use. 3.5 OPERATING CONDITIONS The degradation experiments were conducted under the following operating conditions: 1. DEA concentration 10 - 40 wt% (appr. 1 - 4 M) This range was chosen to cover the 10 - 35 wt% range commonly used i n d u s t r i a l l y . A few runs were done at i n i t i a l DEA concentration of 60 wt% to explore the e f f e c t of high amine concentrations on the rate of degradation. 2. Temperature 120 - 195 °C I n d u s t r i a l DEA plants operate at regeneration temperatures of about 120 °C. Part of the amine solution i s exposed to temperatures as high as 140 °C, e s p e c i a l l y at the r e b o i l e r surfaces. Temperatures as high as 195 °C have been used i n t h i s study merely to increase the rate of the reactions. In a d d i t i o n , since the reaction mechanism may change with operating temperature, a s u f f i c i e n t l y wide range of temperature needs to be covered. 41 3. COS p a r t i a l pressure 0.3 - 1.17 MPa CS2 volume 2.5 - 10.5 mL (0.055 - 0.233 mole CS 2/mole DEA) It i s recognised that these ranges are much higher than those normally encountered i n d u s t r i a l l y . They have been chosen to obtain measurable quantities of degradation compounds within a reasonable time. It should be noted that the CS2/DEA mole r a t i o s are much lower than 1.195 which was used by Osenton and Knight (21). They therefore represent plant conditions more c l o s e l y . 4. Volume of DEA so l u t i o n 250 mL This volume was considered s u f f i c i e n t so that sample withdrawals (10 x 5 mL) w i l l have no s i g n i f i c a n t e f f e c t on the volume of the l i q u i d reactant.In addition, enough space i s l e f t i n the reactor f or the gas. Chakma (18) reported s i m i l a r MDEA concentrations i n two runs conducted with i n i t i a l solution volumes of 100 and 250 mL. 3.6 ANALYTICAL PROCEDURE A Hewlett-Packard Gas Chromatograph (Model 5830A) equipped with an integrator terminal, was used to separate the various constituents of the reactor samples. The concentrations of the constituent compounds were determined from previously prepared c a l i b r a t i o n curves (see 42 Appendix B). The p r i n c i p a l operating conditions used i n the present study were: Column Detector Detector Temperature Temperature Program C a r r i e r gas Inje c t i o n Temperature Sample volume Tenax (GC and TA)., 60/80 mesh packed i n a 9'x 1/8" s t a i n l e s s steel column (supplied by SUPELCO Inc., Oakville, Ont.) H 2 flame i o n i z a t i o n (FID) 300 °C Isothermal at 150 °C for 0.5 minutes, then r a i s i n g i t to 300 °C at the rate of 8 °C/min N 2 at 23 mL/min 300 °C 0.001 mL These conditions are s i m i l a r to those used by Kennard and Meisen (74) and Chakma and Meisen (76). The i d e n t i t y of the degradation compounds cannot not be confirmed by the GC analysis alone. A combination of the techniques described below was employed. Other a n a l y t i c a l techniques were used i n order to i d e n t i f y the s o l i d reaction products. 3.7 TECHNIQUES USED TO IDENTIFY THE DEGRADATION PRODUCTS In order to i d e n t i f y the products of the degradation reactions, four successive methods were used: 43 3.7.1 GAS CHROMATOGRAPHIC (GC) ANALYSIS This analysis provides the concentrations and the retention times of the compounds. The l a t t e r should remain approximately constant under the same a n a l y t i c a l conditions, assuming l i t t l e or no column de t e r i o r a t i o n . 3.7.2 GAS CHROMATOGRAPHIC/MASS SPECTROMETRY (GC/MS) ANALYSIS The GC/MS system consists of a gas chromatograph coupled to a mass spectrometer. The unit used i n t h i s study was a Hewlett-Packard, Model 5985B. In the analysis of a mixture of compounds, the gas chromatograph vaporises and fr a c t i o n a t e s an injec t e d sample of the mixture. The vapour fra c t i o n s e l u t i n g from the GC column flow i n t o the ion source of the mass spectrometer. The ion source, maintained at high temperature and vacuum pressure, produces electrons from a hot tungsten filament which bombards the incoming vapour f r a c t i o n s , thereby causing i o n i s a t i o n and fragmentation of the molecules. The r e s u l t i n g mixture of ions i s accelerated through an e l e c t r i c f i e l d into the ion c o l l e c t o r system where they are separated according to t h e i r mass to charge (m/e) r a t i o . The charge c a r r i e d by each ion produces an e l e c t r i c current that i s detected by an electrometer and then amplified and recorded. This record of the numbers of d i f f e r e n t kinds of ions i s c a l l e d the mass spectrum. The uniqueness of the molecular fragmentation a s s i s t s with the i d e n t i f i c a t i o n of compounds because no two compounds ionise and fragment 44 i n exactly the same manner. The mass spectrum i s therefore, a "finger p r i n t " of each compound. The mass spectrometer can be operated i n the Electron Impact (EI) or Chemical Ionisation (CI) modes. In the EI mode, the ion source voltage i s about 70 eV and the system pressure i s between 10 and 10 mm Hg. Each molecule flowing across the ion source i s fragmented by d i r e c t bombardment with electrons. This bombardment generates numerous ions as the voltage applied i s s u f f i c i e n t to rupture many bonds i n the molecules. In the CI mode, the molecules to be fragmented are d i l u t e d with excess reagent gas, usually methane. At the normal system pressure, methane i s bombarded with a stream of electrons which r e s u l t s i n i o n i s a t i o n and fragmentation (77): e" CH 4 -> CH 4 + + CH 3 + + CH 2 + + CH + + C + 3.1 By maintaining the ion source at a higher pressure (usually 0 . 5 - 1 mm Hg) than the rest of the system, ion-molecule reactions occur by c o l l i s i o n : CH 4 + + CH 4 -> CH 5 + + CH 3 3.2 CH 4 + CH 3 + -+ C 2 H 5 + + H 2 3.3 CH 4 + C 2 H 5 + - C 3 H 5 + + H 2 3.4 CH 5 + i s usually the most abundant of these ions. These p o s i t i v e ions are then used to ionize the molecules of a sample. Due to the high methane 45 to sample r a t i o ( t y p i c a l l y 10 ), i o n i z a t i o n of the molecule occurs via ion - molecule c o l l i s i o n s : M + CH 5 + (M+l) + + CH 4 3.5 M + C 2 H 5 + -> (M+29)+ 3.6 M + C 3 H 5 + -» (M+41)+ 3.7 Other reactions causing proton a b s t r a c t i o n ( M - l ) + and loss of water (M+l-18) + may also occur. Since these c o l l i s i o n s occur at lower energies than d i r e c t e lectron bombardment, less fragmentation of the molecules occurs. Thus the CI spectrum displays a prominent (usually the most abundant) protonated molecular ion (M+l) +, from which the molecular weight of the compound may be i n f e r r e d . 3.7.3 GC/MS ANALYSIS OF SILYLATED DERIVATIVES To gain i n s i g h t into the structure of the degradation products, the mass spectra of the compounds i n a . s i l y l a t e d sample of the degraded solution were also obtained. S i l y l a t i o n i s a form of d e r i v a t i z a t i o n whereby s i l y l groups are introduced i n t o molecules to replace active hydrogen atoms. The s i l y l groups can a l s o replace metals i n s a l t s (78). The s i l y l a t i o n was performed with trimethyl s i l y l imidazole (TSIM) following Chakma's procedure (18). 5 mL of a degraded so l u t i o n were placed i n a glass v i a l and saturated with potassium carbonate to dehydrate the sample. Isopropyl alcohol was then added to extract the degradation compounds from the mixture. The extract was transferred to another v i a l where the alcohol was removed by evaporation, leaving a 46 viscous o i l . An excess• of TSIM was added to the o i l , the mixture was thoroughly shaken and l e f t , f o r at least 1 hour at room temperature to ensure complete d e r i v a t i z a t i o n . The d e r i v a t i z e d sample was then analysed by GC/MS. A fused s i l i c a megabore column (50% phenyl methyl s i l i c o n e , 0.53 mm ID x 10 m) was used to separate the mixture because Tenax G.C. proved to be unsuitable. Since TSIM attacks p r i m a r i l y hydroxyl groups, the CI spectra could be used to determine the molecular masses of the s i l y l a t e d compounds and hence the number of hydroxyl groups per molecule. The s i l y l a t i n g trimethyl s i l i c o n ion (TMS) has a molecular mass of 73 and replaces the hydrogen in -OH groups. Thus s i l y l a t i o n of a compound increases i t s molecular mass by 72n, where n i s the number of hydroxyl groups in the compound. 3.7.4 GC ANALYSIS OF DEGRADED MIXTURES SPIKED WITH SUSPECTED COMPOUNDS GC/MS analysis provided information on the possible i d e n t i t i e s of the unknown compounds i n degraded solutions. Pure forms of the suspected compounds were purchased or synthesized and then used to spike the sample. The spiked sample of the degraded sol u t i o n was then analysed by gas chromatography. An increase i n the peak area of the corresponding peak provided strong proof that the peak represents the unknown compound. In summary, the steps followed to i d e n t i f y the degradation compounds were: 47 1. Determination of the re t e n t i o n times under standard GC operating conditions. 2. Obtaining the EI and CI mass spectra from the GC/MS analysis. The CI spectra provided the molecular weights of the unknowns, while the EI spectra were compared with l i t e r a t u r e spectra (15,16,18,79,80) . 3. Determination of the number of hyroxyl groups i n the unknown compounds by comparing the CI spectra of the s i l y l a t e d derivatives and u n s i l y l a t e d compounds. 4. Comparing the retention times of the suspected and the unknown compounds under the same GC operating conditions. 3.8 EXPERIMENTAL DESIGN Experiments were designed i n stages that r e f l e c t the stated objectives of the study: 1. I d e n t i f i c a t i o n of reaction products Two runs each were conducted f o r the COS-DEA and CS2-DEA systems at the boundary temperatures ind i c a t e d i n section 3.5, to ascertain that the reaction products at the high temperature are s i m i l a r to those produced at the low temperature. The runs w i l l also serve to v e r i f y the fact that the high temperature merely increases the rates of the reactions. However, differences observed i n the product spectra f o r the low and 48 high temperature runs f o r the CS2-DEA system necessitated another run at 165 °C. 2. E f f e c t s of operating conditions Runs were conducted as shown below, to determine the e f f e c t s of temperature, solution concentration, i n i t i a l COS p a r t i a l pressure and i n i t i a l CS 2 volume on the degradation reactions: DEA CONC. (wt%) 195 40 30 20 * 10 where * and + denote COS-DEA and CS2-DEA runs, r e s p e c t i v e l y . The runs were conducted with an i n i t i a l COS p a r t i a l pressure of 345 kPa or an i n i t i a l CS 2 volume of 6 or 10.5 mL. It should be noted that some of the runs were conducted with a glass l i n e d reactor and are only sui t a b l e f o r q u a l i t a t i v e explanations. The above runs were only able to show the e f f e c t s of temperature and DEA concentration. A separate set of runs was conducted to determine the e f f e c t s of COS p a r t i a l pressure and CS 2 volume on the reactions. The conditions used f o r these runs are: TEMPERATURE (°C) 190 180 175 170 165 160 150 135 130 127 120 49 DEA concentration COS p a r t i a l pressure CS 2 volume Temperature 30 wt% 345, 759, 1172 kPa 2.5, 6.0, 10.5 mL 150 °C for the COS runs 165 °C for the CS 2 runs 3. E f f e c t s of mixed gas phase The o r i g i n a l i n t e n t i o n was to conduct runs using a mixture of C0 2, COS and CS 2 i n the gas phase. While i t was possible to obtain a gas mixture of COS and C0 2, there was no way to include CS 2 in the mixture and maintain i t s concentration throughout the runs. Since COS and CS 2 are eventually hydrolysed to C0 2 and H2S, a better choice was to use a mixture con s i s t i n g of the two l a t t e r gases. The re s u l t s from the use-of a C0 2/H 2S gas mixture a l s o augment the scanty data reported i n the l i t e r a t u r e on the degradation e f f e c t s of such mixtures. The operating conditions and compositions of the gas mixtures used f or these runs are discussed i n Chapter 6. 4. Additional and sp e c i a l runs Some duplicate runs were conducted to ascertain r e p r o d u c i b i l i t y . It was also found necessary to conduct more runs to elucidate the reaction mechanisms and determine the equilibrium d i s t r i b u t i o n of the ac i d gases i n the reactor. These runs are discussed i n d e t a i l i n Chapters 6 and 7, r e s p e c t i v e l y . CHAPTER 4 IDENTIFICATION OF DEGRADATION PRODUCTS 4.1 PRELIMINARY EXPERIMENTS Before proceeding with the main experimental programme, i t was necessary to conduct preliminary experiments aimed at evaluating the e f f e c t s of c e r t a i n operating variables on the degradation reactions. 4.1.1 EFFECTS OF ELEVATED TEMPERATURES Elevated temperatures were used i n t h i s study to speed up the degradation reactions. The r e s u l t s obtained under such conditions w i l l only have i n d u s t r i a l relevance i f the alkanolamines are not thermally degraded and the reaction products are s i m i l a r to those obtained at the lower temperatures commonly used i n industry. Thermal degradation experiments, conducted by heating aqueous solutions of DEA under a blanket of nitrogen, revealed the following: at 150 °C no change i n so l u t i o n composition was observed over a period of 220 hours; at 165 °C no change occurred over 60 hours; at 180 °C thermal degradation was n e g l i g i b l e up to 80 hours. Since most of the high temperature degradation runs were conducted over 48 hour periods, the influence of thermal degradation on the r e s u l t s can be disregarded. Kennard (16) also found thermal degradation to be n e g l i g i b l e when aqueous DEA 50 51 solutions were maintained at 205 °C for 8 hours under a blanket of nitrogen. Typical chromatograms of aqueous DEA solutions degraded i n the presence of COS are shown i n Figs. 4.1a to 4.1c. The q u a l i t a t i v e s i m i l a r i t y of the figures i s obvious. This suggests that the basic reaction mechanism i s not affe c t e d by temperature. Since i n d u s t r i a l DEA regenerators operate at r e b o i l e r temperatures of up to 140 °C, the products obtained i n t h i s study should also be formed under i n d u s t r i a l conditions. 4.1.2 SURFACE EFFECTS Two runs were performed with and without the pyrex l i n e r i n the reactor. The r e s u l t s indicated very s i m i l a r products, suggesting that the l i n e r d i d not a f f e c t the reaction mechanism. Since the sol u t i o n was i n contact with the s t a i n l e s s s t e e l s t i r r e r i n both cases, i t i s also c l e a r that the reactions were not influenced by the difference i n the s o l i d surface areas. However, the l i n e r caused a temperature gradient within the reactor. The r e s u l t of t h i s was the tr a n s f e r of water from the amine solu t i o n into the annulus, thereby increasing the concentration of the amine. The use of the l i n e r was therefore discontinued and a new set of runs (C.l - C.43 i n appendix C) was conducted. 14 10 15 t = 30h (a) 52 14 10 12 13 15 t = 50h (b) 3 5 14 10 12 15 t = ZI5h (c) 1: Chromatograms of p a r t i a l l y degraded DEA solutions of 4M i n i t i a l concentration (a: 180 °C, 0.34 MPa COS; b: 150 C, 0.34 MPa COS; c: 120 °C, 0.68 MPa COS). 53 4.1.3 EFFECTS OF STIRRER SPEED S t i r r i n g speed influences the rate of mass transf e r between the gas and l i q u i d phases. It was reported previously (16,18) that the rate of degradation i s slow and that changes i n s t i r r e r speed do not a f f e c t degradation rates i n CC>2-amine systems. Since the present study involves COS and CS 2 which hydrolyse to produce H2S and C0 2, i t was decided to re-examine the e f f e c t of s t i r r e r speed and hence the rates of mass tr a n s f e r on degradation. The DEA concentrations i n two runs performed at s t i r r e r speeds of 120 and 180 r.p.m. are shown i n columns 2 and 3 of Table 4.1 . The deviations i n the concentrations are generally less than ±4%. This confirms that the change i n s t i r r e r speed d i d not a f f e c t the rate of degradation. The run at 180 r.p.m was terminated a f t e r 30 hours because of a leakage from the reactor. 4.1.4 REPRODUCIBILITY Columns 2 and 4 of Table 4.1 also show DEA concentrations f o r two runs performed two weeks apart but under the same operating conditions. The deviations between concentrations are generally less than 2% and therefore lend confidence to the r e p r o d u c i b i l i t y of the experimental and a n a l y t i c a l procedures. 54 Table 4.1: Re p r o d u c i b i l i t y and e f f e c t of s t i r r e r speed i n COS-DEA degradation (DEA Q = 3 M, T = 150 °C, P c o s = 345 kPa). Time DEA CONCENTRATION AT DIFFERENT STIRRER SPEEDS (h) (moles/L) 120 rpm 180 rpm 120 rpm 0 3.01 2.98 3.00 2 3.06 2.96 2.98 4 2.91 2.91 2.86 8 2.83 2.84 2.77 12 2.76 2.78 2.69 24 2.47 2.53 2.45 30 2.31 2.31 2.30 36 2.18 2.17 48 1.93 1.91 4.2 DEGRADATION PRODUCTS RESULTING FROM COS-DEA INTERACTIONS Figure 4.2 contains chromatograms showing the gradual formation of reaction products i n a t y p i c a l run conducted with a 40 wt% DEA solut i o n , at a COS p a r t i a l pressure of 0.34 MPa and a temperature of 180 °C i n the glass l i n e d reactor. The gradual formation of reaction products i s obvious. In addition, i t was noted that the samples became more pungent and viscous as the degradation -progressed. Some p a r t i c u l a t e matter was also found i n the samples. Figure 4.2: Chromatograms showing gradual formation of degradation products i n a COS-DEA system (4M DEA, 180 °C, 0.34 MPa COS). 56 By following the techniques described in section 3.7, the compounds responsible f or the peaks l a b e l l e d i n F i g . 4.1 were i d e n t i f i e d ic and are l i s t e d i n Table 4.2. The symbols M and n OH i n Table 4.2 r e f e r to the molecular weight of the d e r i v a t i z e d compound and the number of hydroxyl groups i n the compound. It should be noted that the retention times depend, to some extent, on the concentrations of the compounds and the age of the column. The corresponding mass spectra are shown i n Figures 4.3 to 4.17. For compounds whose mass spectra were not i n the computer's data base, the l i b r a r y EI spectra r e f e r to the spectra of the pure compounds purchased or synthesized in the laboratory, depending on t h e i r commercial a v a i l a b i l i t y . A consistent pattern in the fragmentation of these hydroxyl-amino compounds i s the loss of hydroxymethyl r a d i c a l s (m/e 31) from the parent compounds to produce, i n general, the most abundant ions. Ions of mass 30 for MEA, 58 f o r EAE, 74 for DEA, 72 for HEA, 102 for EDEA, 143 for BHEP and BHEI, 100 f o r HEOD, 99 f o r HEI and HEP were generated in t h i s manner. In the case of BHEED and THEED, hydroxymethyl r a d i c a l s were also l o s t , but the p r i n c i p a l fragmentation r e s u l t e d from the cleavage of the C-C bond between two nitrogen atoms gi v i n g the most abundant ions with mass 74 f o r BHEED (N,N' isomer) and 118 f o r THEED. Water molecules were also l o s t i n the fragmentation. For example, ions of mass 74 l o s t water to give ions with mass 56 i n the case of DEA. The molecular ion peaks are not prominent i n most of the EI spectra because of the ease with which the hydroxymethyl groups break from the molecules. The c h a r a c t e r i s t i c peaks i n the CI spectra of the hydroxyl amino compounds are produced by the [M+H]+, [M+C 2H 5] + and [M+H-H20]+ ions. For the s i l y l 57 d e r i v a t i v e s , the CI spectra show prominent [M+H]+, [M+C2H5]+ and [M- CH3] + ions. The [M-CH3]+ ion i s c h a r a c t e r i s t i c of the s i l y l a t i n g agent (TSIM). The previous, tentative i d e n t i f i c a t i o n (100) of peak 9 as b i s - hydroxyethyl amino ethanol (BHEAE) now appears to be i n v a l i d . The compound has a molecular mass of 149 as indicated by i t s CI spectrum (Figure 4.11). Its s i l y l d e rivative has a molecular mass of 221 which suggests that i t contains one hydroxyl group. The EI spectrum shows the ion with mass 74 as the most abundant. Loss of the c h a r a c t e r i s t i c hydroxymethyl r a d i c a l does not produce a prominent peak even though the compound appears to have an hydroxyethyl attachment (deduced from ion 74). This, i n addition to the prominent ion of mass 89 i n the CI spectrum, suggests that the compound i s not very stable and fragments on electron bombardment to give ions with mass 89 or, more l i k e l y , 74. Based on the presently available information, the most l i k e l y structure f o r t h i s compound i s : 0 C 2H 4OH CH3-C-S-CH2 N \ H The name of the compound i s ethanethioic a c i d S - [(2-hydroxyethyl) amino] methyl ester. Its abbreviation i s ETAHEAME. This compound i s not a v a i l a b l e commercially and i t was therefore not possible to compare i t s retention time under the present GC conditions with that, of peak 9. Time and resources d i d not permit i t s synthesis during the present study. 58 It also appears that triethanolamine (TEA) was formed as a degradation compound but could not be c l e a r l y separated from BHEED under the a n a l y t i c a l conditions used. This supposition arises from the fact that the GC analysis of the s i l y l d e r i v a t i v e s showed a peak before BHEED, having a molecular weight of 365. This would suggest an underivatized hydroxyl amino compound with a molecular weight of 149 and three hydroxyl groups. Triethanolamine f i t s t h i s structure. 59 Table 4.2: Degradation compounds detected i n the COS-DEA system. Peak Retention C h a r a c t e r i s t i c Molecular Weight n OH Ident i t y Time (min) EI ions M M* (M*-M)/72 1 1. 4 - 1.5 43, 58 58 ACETONE 2 2. 2 - 2.3 29, 43, 57, 72 72 BUTANONE 3 3. 1 - 3.3 30, 42, 61 61 133 1 MEA 4 5. 2 - 5.3 30, 42, 56, 58, 74 89 89 161 1 EAE 5 9. 2 -• 10.0 45, 56, 74 105 249 2 DEA 6 10. 9 -• 11.1 30, 45, 56, 58, 74, 102 88, 133 133 277 2 EDEA 7 11. 5 -• 11.6 30, 43, 60, 72, 73 85 103 175 1 HEA 8 12 . 0 -• 12.1 42, 56, 70, 88, 112 130 130 202 1 HEP 9 13. 4 • • 13.5 56, 61, 74, 89, 118 149 149 221 1 ETAHEAME 10 15. 2 -- 15.5 44, 56, 74, 88, 100, 118, 127 148 292 2 BHEED 11 16. 2 • - 16.6 42, 56, 156 70, 100, 125 88, 113, 143 , 174 174 318 2 BHEP 12 16. ,7 • - 16.9 42, 56, 74, 88, 100 131 131 203 1 HEOD 13 18. ,2 • - 18.4 42, 56, 70, 85, 99 130 130 202 1 HEI 14 19. .7 - 19.8 42, 56, 174 70, 88, 100, 130 118, 143 192 408 3 THEED 15 21. .0 - 21.3 42, 56, 70, 99, 114, 143 130, 174 174 318 2 BHEI 60 — to 1 00 120 140 30.5-: » 1 L F R I l 3 0 0 2 SPECT . 9 ~ 1 4 2 - P r o p a n o n e ( 9 C I ) ( a ) r-i..i = C3H60 ice so - o 100 5 0 - 0 - 40 [M+H] I 5 9 87 9 ? 109 123 139 151 165 —1— 60 80 100 ' I " 120 140 160 • 7 3 . 6 183 211 223 180 2 0 0 2 2 0 -i 1 1 — 2 4 0 2 6 0 ( C ) Figure 4.3: Mass spectra of peak 1 i d e n t i f i e d as Acetone (a: EI spectrum; b: EI reference spectrum; c: CI spectrum). « 1 L F R M 3002 SFECT 233 MO= 72 C4H80 . 9 7 6 6 2 - E ' j t a n o n e ( 3 C I 9 C I ) (b) Figure 4.4: Mass spectra of peak 2 i d e n t i f i e d as Butanone (a: EI spectrum; b: EI reference spectrum; c: CI spectrum). 100 - 80 - 60 - 40 - 20 - 1 0 - I 1 ..II .1 i i • 20 i ( i | 40 1 i 60 i SO T 100 120 i 140 62 [ (a) 2 9 . ^ , , ,1 1, I " 2 LFRM 3002 SPECT 125 MM" 61 C2H7M0 .3100 E t h a n o l , 2-aitiitio- (3CI9CI) 100 - 80 - 60 - 40 - 20 - 0 - , ,1 1. i i. 2Q i i 40 60 i 80 100 i ' 120 • i 140 (b) 100 - 80 - [ M + H ] + I 62 70 .8 60 - 40 - 0 Jr 84 20 30 40 50 60 70 80 •90 too (c) (d) Figure 4.5: Mass spectra of peak 3 i d e n t i f i e d as MEA (a: EI spectrum; b: EI reference spectrum; c: CI spectrum; d: CI spectrum of the s i l y l d e r i v a t i v e ) . 63 (a) (b) (c) Figure 4.6: Mass spectra of peak 4 i d e n t i f i e d as EAE (a: EI spectrum; b: EI reference spectrum; c: CI spectrum). « 1 LFRH 3002 SPECT 1457 MM« 1©S C4H111102 .9754 E t h a n o l , 2 ,2' - i m i r,ob i s- (?CI > (b) ( M + H ] + I 1 06 8 S 70 , I 1 . > 1 116 1 134 146 " 1 162 183 21 1 — ' — I — 1 1 I — I — 1 — I — • — I I — I — ' — I — • — I — • — I — ' — I — I — I — - — I — • — 1 — 60 80 100 120 140 160 180 200 (C) (d) Figure 4.7: Mass spectra of peak 5 i d e n t i f i e d as DEA (a: EI spectrum; b: EI reference spectrum; c: CI spectrum; d: CI spectrum of the s i l y l d e r i v a t i v e ) . 65 lee - 89- 66 •49 - 29 9 I 192 58 45 74 •••<•',• •• 88 —i-L* , r 1 18 133 174 297 42.3 69 89 199 129 149 169 189 299 229 (a) (b) 199 88 69- 49 26- 9 [ M + H ] + I 134 116 192 58 72 99 162 I 174 189 211 223 6 8 88 189 128 - r - * — i — • — i — • — r 149 169 189 - 1 — ' — l — • 298 58 .9 229 ( C ) i ea - r29 . 4 188 se- 57 " 77 86 9S 163 U6 131 144 9 - 1 i I I • t. —1 '—"T— 7 •""—1 * i i 199-. 69 S9 168 129 148 1 169 139 r 20 . 4 2 - •3 (K+HJ* ?~? se- 396 229 234 250 1 1 313 . i 1. 1. — i • i — 299 ' t " 229. 249 260 2 3*3 300 (d) Figure 4.8: Mass spectra of peak 6 i d e n t i f i e d as EDEA (a: EI spectrum; b: EI reference spectrum; c: CI spectrum; d: CI spectrum of the s i l y l d e r i v a t i v e ) . 66 (a) (b) (c) (d) F i g u r e 4.9: Mass s p e c t r a of peak 7 i d e n t i f i e d as HEA ( a : EI s p e c t r u m ; b : EI r e f e r e n c e s p e c t r u m ; c: CI s p e c t r u m ; d : CI s p e c t r u m of the s i l y l d e r i v a t i v e ) . (b) (c) (d) Figure 4.10: Mass spectra of peak 8 i d e n t i f i e d as HEP (a: EI spectrum; b: EI reference spectrum; c: CI spectrum; d: CI spectrum of the s i l y l d e r i v a t i v e ) . 68 100 -, 80 60 H 40 20 0 •> r40 .6 5 45 U S 131 | '-f 14? 161 •Mil, , , Uij , 1 tl 60 1 00 120 140 160 180 200 ( a ) (b) (c) Figure 4.11: Mass spectra of peak 9 i d e n t i f i e d as ETAHEAME (a: EI spectrum; b: CI spectrum; c: CI spectrum of s i l y l d e r i v a t i v e ) . (a) (b) (c) tee 80 46 • 28 146 136 1 1 •!» | . 1 146 166 263 138 186 266 — i — • — i — • — t — 229 24e 266 277 r21 .6 2?3(M+HJ+ 30S 286 Ml , I 366 321 326 (d) Figure 4.12: Mass spectra of peak 10 i d e n t i f i e d as BHEED (a: EI spectrum; b: EI reference spectrum; c: CI spectrum; d: CI spectrum of the s i l y l d e r i v a t i v e ) 70 (b) (c) tee-i se 69 11? t46 i*e 187 202 21S 229 2S6 262 27S tee se 60 I i • ! ... , 1 I ' 1 88 100 12? 140 160 180 206 * I ' 'I • I • I • I ' r 220 246 266 3 9t*+H] + 363 e J i — i • 280 306 :47 33S 3S9 I 320 3 4 0 • ' i 1 I 1 i — » 360 3S0 4 9 6 42Q 449 466 i 1 I 1 —r- 4 * 0 21 . 21 .9 (d) Figure 4.13: Mass spectra of peak 11 i d e n t i f i e d as BHEP (a: E I spectrum; b: E I reference spectrum; c: C I spectrum; d: C I spectrum of the s i l y l d e r i v a t i v e ) . 71 (b ) [M+H] + r S 6 .8 l e a - 1 ••z s e - 114 1 S 9 e - 6 1 7 6 8 1 8 9 1 9 1 j 1 2 3 1 4 1 1, ' T — • • i ~* 1 — - — I 1 i 1 i 1 0 9 - ] 6 e 8 8 t e e 1 2 0 1 4 0 1 6 9 5 6 . 8 s e - e - 1 7 2 1 8 9 1 8 ? 1 9 9 2 8 6 2 2 3 2 6 3 > " t — • 1 " i — • • ' r i — • — i • i • i 1 3 9 2 e e 2 2 0 2 4 0 2 6 0 2 8 0 (c) (d) Figure 4.14: Mass spectra of peak 12 i d e n t i f i e d as HEOD (a: EI spectrum; b: EI reference spectrum; c: CI spectrum; d: CI spectrum of the s i l y l d e r i v a t i v e ) . (a) (b) l e e - [M+H] + I 1 3 1 r 4 3 . 6 se- 6 1 7 0 3 8 1 1 3 9 9 i e6 1 1 4 5 IS? e- iee- 1 . f 1 i 1 i 6 8 1 I 1 I 8 8 1 0 0 1 2 6 1 4 0 ' 1 1 1 166 4 8 . 6 se- 1 7 1 1 8 3 • 2 0 3 2 1 1 2 3 3 2 6 1 o- 1 1 I 1 8 0 2 0 8 2 2 0 2 4 0 260 2 8 0 < c ) (d) F i g u r e 4.15: M a s s s p e c t r a o f p e a k 13 i d e n t i f i e d a s HE-I ( a : EI s p e c t r u m ; b : EI r e f e r e n c e s p e c t r u m ; c : CI s p e c t r u m ; d : CI s p e c t r u m o f t h e s i l y l d e r i v a t i v e ) . (a) lee se - 68- 48 - 2 0 - 8 1 18 74 56 45 38 f 48 88 iee I ^ 138 ' 4 3 159 169 187 68 89 109 129 11 I 1 — I — ' ' i — I — • " i ' 140 160 180 290 r 2 1 .3 (b) (c) 199 59 - 0 - 91 103 115 30 >«« > • , I,. • 160 174 188 591 215 262 —i—•—r-^-—:—•- 100 -I 50 - 60 88 100 129 149 168 189 299 220 249 269 9 J 3 * 3 4 9 9 t « + H ] + 19.1 •19.1 299 393 319 i 1 i " i 1 • • * > — — i • i • 289 399 329 340 423 43T 4 0 0 -120 4 4 9 4 6 0 4 3 Q (d) Figure 4.16: Mass spectra of peak 14 i d e n t i f i e d as THEED (a: EI spectrum; b: EI reference spectrum; c: CI spectrum; d: CI spectrum of the s i l y l d erivative) 74 (a) ( b ) lee- {M+HJ* i rSS .2 1 88- 60- 40- 1S7 20- I M .31 M 3 283 76 88 1 189 t 2 t s 236 0- i , i i - 1 I., I 1 88 168 128 146 166 186 206 220 246 ( c ) 166 50- 0 160 50- 0 69 97 117 146 160 187 202 215 229 250 262 275 I 1 I ' I i 1 i 1 i » I • "I"' i i " i i • i 1 i 1 i 1 — i • v 1 — i * i • 60 86 166 126 146 160 180 260 220 246 266 , 3i9(H+H)* 383 ?47 I 335 359 I— i ' " i •• i » ' ' ' • i • <—t, „. ., , , • , ., , 238 308 320 340 360 330 4 00 -I—' ,—'——I—•—I—'—I—•—I 20 < j j 460 430 21 .9 21 . ? (d) Figure 4.17: Mass spectra of peak 15 i d e n t i f i e d as BHEI (a: EI spectrum; b: EI reference spectrum; c: CI spectrum; d: CI spectrum of the s i l y l d e r i v a t i v e ) . 75 The degradation compounds may be conveniently grouped into two categories: low-boiling degradation compounds which elute before DEA and h i g h - b o i l i n g degradation compounds which elute a f t e r DEA. Other low- b o i l i n g degradation compounds include methanol, ethanol, acetaldehyde and/or ethylene oxide, a c e t i c acid, methyl pyridine, d i e t h y l disulphide, ethyl methyl pyridine and 1,2 dithiane. These compounds are not included i n Table 4.2, but t h e i r EI spectra are shown in Appendix B2. Methanol, ethanol, acetaldehyde being very v o l a t i l e , were not properly separated during the GC analyses and they were barely v i s i b l e i n the chromatograms. Their presence i n the degraded solutions was deduced from the GC/MS an a l y s i s . Acetic a c i d eluted from the Tenax GC column just before butanone. In most of the analyses, i t was embedded i n the butanone peak. Methyl pyridine, ethyl methyl pyridine, d i e t h y l disulphide and 1,2 dithiane peaks were v i s i b l e and well separated but were formed in very low concentrations. Q u a l i t a t i v e analysis of the gas phase showed ethanol, acetone, butanone, pentanone, hexanone and some of the low b o i l i n g degradation compounds found i n the l i q u i d phase. In addition to the water soluble degradation compounds, an in s o l u b l e , l i g h t brown s o l i d product was also formed. Tests conducted to i d e n t i f y the s o l i d are discussed below. The present r e s u l t s are at variance with some previous findings (19,20). However, i t i s important to note that the degradation reactions proceed slowly. Even under the most severe conditions used i n t h i s study (40% DEA, 190 °C), only the low b o i l i n g degradation compounds were formed i n appreciable quantities within the f i r s t 6 hours. At 120 °C, 76 only the low b o i l i n g 'degradation compounds were detected within the f i r s t 24 hours. As pointed out e a r l i e r , perhaps the i n a b i l i t y of the previous investigators to detect degradation compounds i n COS/DEA systems was due to the short experimental durations and t h e i r a n a l y t i c a l techniques. 4.3 DEGRADATION PRODUCTS RESULTING FROM CS2-DEA INTERACTIONS Figures 4.18a-c show chromatograms of runs conducted with 10.5 mL CS 2 and 250 mL of 3M aqueous DEA solutions at 180, 165 and 150 °C, r e s p e c t i v e l y . Runs conducted at temperatures between 165 and 120 °C (e.g. Figs. 4.18b and 4.18c) gave s i m i l a r products and samples of the solutions had a l i g h t e r colour, less pungent odour and greater s o l i d s content due to the formation of the dithiocarbamate s a l t , than the corresponding COS-DEA samples. It was necessary to centrifuge the samples from the CS2-DEA runs before i n j e c t i n g them into the gas chromatograph. At 180 °C, the reaction mechanism appears to be more complex because more products were formed i n s i g n i f i c a n t q u a n t i t i e s . Furthermore, the samples were deep brown and possessed a very pungent odour. The pressure i n the reactor was a l s o found to increase by about 0.45 to 0.55 MPa (70 to 80 psi) within 3 hours, compared with approximately 0.07 to 0.15 MPa f o r the corresponding COS-DEA runs. These r e s u l t s indicate that, unlike the COS-DEA system, some reaction steps in the CS 2-induced degradation of DEA are a f f e c t e d by temperature. The resemblance between Figs. 4.18a and 4.1a-c suggests 8 V (a) (b) 34 8 (c) Figure 4.18: Chromatograms of p a r t i a l l y degraded DEA solutions of 3M i n i t i a l concentration degraded with 10 mL of CS 2 for 48 hours (a: 180 °C; b: 165 °C; c: 150 °C). 78 that degradation i n the CS2-DEA system at 180 °C i s preceded by hydrolysis of CS2 to COS with the l a t t e r causing COS-induced degradation. Following the a n a l y t i c a l procedure described e a r l i e r , the peaks l a b e l l e d 1 to 8 i n F i g . 4.18 were i d e n t i f i e d as MEA, DEA, BHEED, BHEP, HEOD, HEI, THEED and BHEI, r e s p e c t i v e l y . MEA was the only low b o i l i n g compound of s i g n i f i c a n c e detected i n CS2-DEA systems at temperatures below 165°C. A s o l i d material was also produced by the CS2-DEA systems. Solids produced i n runs conducted at temperatures of 165 °C and below, had a beige colour whereas the s o l i d s recovered from runs conducted at 180 °C were yellowish brown and s i m i l a r to those of the COS runs. 4.4 CHARACTERIZATION OF THE SOLID PRODUCTS The s o l i d s recovered from a l l the COS runs and the CS2 runs conducted at 180 °C were yellowish brown i n colour. L i q u i d samples withdrawn from both sets of runs also had the same yellowish brown appearance. GC/MS analysis of the centrifuged l i q u i d samples revealed that they contain the same compounds. In view of these s i m i l a r i t i e s , both sytems are believed to be undergoing s i m i l a r reactions. As for the CS2 runs conducted at temperatures of 165 °C and below, the recovered s o l i d had a beige colour while the l i q u i d samples were colourless and did not contain any ketones. The s o l i d formed fin e powders- on grinding, unlike the s o l i d s generated from the COS runs and CS2 runs at 180 °C 79 which were s t i c k y . In order to characterize the s o l i d materials from the CS2-DEA and COS-DEA systems, the following t e s t s were conducted. 4.4.1 SOLUBILITY The s o l u b i l i t y of the so l i d s i n a v a r i e t y of solvents such as water, ethanol, methanol, toluene, d i e t h y l ether, acetone and carbon disulphide was examined. Both the COS and CS 2 generated s o l i d s were found to be insoluble i n these solvents even when the solvents were heated to b o i l i n g . However, dimethyl formamide at b o i l i n g temperature (153 °C) was able to dissolve the s o l i d s but p r e c i p i t a t i o n occurred as soon as the solutions were cooled. The insoluble nature of the s o l i d suggests that i t i s a polymeric material. 4.4.2 MELTING POINT The melting points of the so l i d s were determined with a K o f l e r Hot Stage Microscope. The set up consisted of the Kofler hot bench mounted on a Wild Heitz microscope, a thermometer to monitor the temperature of the hot bench and a regulating transformer which c o n t r o l l e d the rate of heating. Controlled i l l u m i n a t i o n of the microscope was achieved with an on-line voltage regulator. A t i n y chip of s o l i d to be analysed was placed on a s l i d e which was then centred on the hot bench. The heating rate and hence temperature of the hot bench was c o n t r o l l e d by a series resistance connecting the hot bench to the main power supply. The resistance was 80 set i n such a manner that the temperature of the hot bench rose by 4 °C/min. While the bench was heated, the state of the s o l i d was monitored by viewing the sample at a magnification of 100. At the outset, the sample appeared as a black dot i n the f i e l d of the microscope. At the melting temperature, the sample became f l u i d and the f i e l d became illuminated. The temperature indicated on the thermometer was recorded as the melting point of the sample. Four determinations were made f o r each sample and the average temperatures were recorded. The COS generated s o l i d melted i n the range 124 °C to 138 °C with most of i t melting above 135 °C. The CS 2 s o l i d generated at temperatures below 165 °C had a narrower melting range of 138 °C and 144 °C. The size of the melting ranges suggest that the CS 2 generated s o l i d i s less contaminated than the COS generated s o l i d . Since the b o i l i n g temperature of dimethyl formamide exceeds the melting points of the s o l i d s , t h e i r apparent d i s s o l u t i o n i n the b o i l i n g solvent was due to melting. Therefore the s o l i d s can be considered insoluble i n dimethyl formamide. 4.4.3 ELEMENTAL ANALYSIS The elemental composition of the s o l i d s was determined by the Canadian M i c r o a n a l y t i c a l Laboratory, New Westminster, BC, and the r e s u l t s are shown i n Tables 4.3 and 4.4. The compositions of the s o l i d s seem to depend on the conditions used f o r the degradation runs. The percentage of sulphur decreased with increasing temperature while the reverse was the case for the other 81 Table 4.3: Elemental compositions of s o l i d s formed i n the COS-DEA systems ELEMENT COMPOSITIONS (wt%) 150 °C 180 °C wt% mole% wt% mole% c 41. . 95 28. .31 44. .11 29, ,07 H 7. .08 57. .34 7. .26 57. .41 N 1. .76 1. .02 2. .94 1. .66 0 2. .87 1. .45 3. . 94 1. . 95 s 46. . 92 11. .88 40. .14 9, .92 TOTAL 100. .58 100. .00 98. .39 100, .00 Table 4.4: Elemental compositions of s o l i d s formed i n the CS2-DEA systems. ELEMENT COMPOSITIONS (wt%) 150 °C 180 °C wt% mole% wt% mole% c 38. 97 26. .88 48. 00 29.32 H 6. 95 57. .53 7. 89 57.84 N 3.09 1. .83 4. 44 2.32 O 4.92 2. .55 6. 19 2.84 S 43.35 11. .21 33. 49 7.67 TOTAL 97.28 100. .00 100. 01 100.00 82 elements. The changes were generally more pronounced f o r the s o l i d s generated i n the CS 2 runs. This trend could be due to the fact that, except f o r sulphur, a l l other elements are contained i n the amine whose i n i t i a l concentration increases with operating temperature (due to increased evaporation of water). In the same vein, increasing temperature l i m i t s the s o l u b i l i t y of COS and CS 2 and consequently the amount of sulphur a v a i l a b l e f o r reactions i n the l i q u i d phase. The r a t i o s of the elements could be ca l c u l a t e d from the elemental analysis shown i n Tables 4.3 and 4.4. For example, i n the s o l i d generated i n the COS runs at 180 °C, the C/S, C/H, C/N, S/O, N/O, C/O, H/N and H/O r a t i o s are 2.93, 0.50, 17.50, 5.09, 0.85, 14.93, 34.57 and 29.48, re s p e c t i v e l y . These r a t i o s transform approximately to an empirical formula of C 1 5 H 3 0 N O S 5 ( E- w 400). Using the same c a l c u l a t i o n s , the formula c14 H30 N O^6 ( E > w 420) can be derived f o r the so l i d s recovered from the CS 2 system at 150 °C. The higher molecular weight of the CS 2 s o l i d would imply a higher melting point as confirmed by the melting point determinations. 4.4.4 MASS SPECTRAL ANALYSIS S o l i d probe EI and CI mass spectral analyses were performed on the s o l i d products to determine t h e i r fragmentation patterns as well as t h e i r molecular weights. Both s o l i d s produced s i m i l a r traces as shown i n Figures 4.19 and 4.20. The CS 2 s o l i d trace i s f o r the s o l i d generated i n the CS 2 run at 150 °C. Although the EI spectra resemble the l i b r a r y spectrum of a c e t i c a c i d - mercapto - 1,2 ethanediyl ester (CgH 1 Q0 4S 2) 83 with a molecular weight of 210, the elemental composition of t h i s compound i s at variance with the r e s u l t s of the elemental a n a l y s i s . Hence the i d e n t i t y of the s o l i d s i s d i f f e r e n t from that suggested by the l i b r a r y of mass spectra. The fragmentation pattern i n the CI spectra show successive losses of ions of masses 28 and 32. Since the so l i d s are r i c h i n sulphur, the ion of mass 32 i s most l i k e l y due to elemental sulphur. The ion of mass 28 could e i t h e r be a carbonyl group (C=0) or an ethenyl (C 2H 4) group. However, the very low oxygen to sulphur r a t i o i n the s o l i d s , the almost equal number of losses of masses 28 and 32 and the high carbon content of the s o l i d s , point to an ethenyl group as the fragmenting group with mass 28. It i s d i f f i c u l t to i d e n t i f y a molecular ion peak from the CI traces because of the low abundances of the high molecular weight ions. The most abundant peak has a mass of 121, suggesting a molecular weight of 120. The high melting point of the s o l i d s i s inconsistent with t h i s molecular weight. Furthemore, the absence of ions of mass 149 (M+29) makes a molecular mass of 120 very u n l i k e l y . The pattern of successive losses of masses 28 and 32 i n the CI spectra suggests a f r a g i l e l i n e a r structure containing several covalent bonds with sulphur interspersed between the ethenyl groups. The ease of bond breakage i s , perhaps, the reason f o r not having a prominent molecular ion peak. The s i m i l a r i t i e s i n the mass spectrum of the s o l i d s i s another i n d i c a t i o n that the s o l i d s have s i m i l a r structures. 84 (a) 100 5 0 0 100 50 0 J 61 7 5 I 89 I 121 105 153 181 191 2 0 9 2 2 4 80 100 120 •I I ni | -1 I.I..).. —<~i—' ••• I 1 2 . 8 140 160 180 2 0 0 1—'—r 2 2 0 2 4 r , 24 251 2 6 9 2 8 6 3 0 2 3 1 2 3 3 9 3 4 6 3 5 8 1 2 . 8 3 9 0 4 0 0 4 1 9 "I I— I I— 1 2 6 0 2 8 0 3 0 0 • 1— 1 "I' • — — I ' I ' 3 2 0 3 4 0 3 6 0 i — i — ' — l — ' — l — ' — r 3 8 0 4 0 0 (b) Figure 4.19: Mass spectra of the s o l i d formed i n the COS-DEA system (a: EI spectrum; b: CI spectrum). 85 l O O - - 1 6 . 1 S e - 4 5 69 9 2 1 1 1 7 4 1 105 t 152 184 0- J . J 1 I J . i i l , ,. III, .1 .... . ,...1 1 1 ' 1"' I 1 • i • i i 1 i I l l 1 0 0 - 60 8 9 100 120 140 160 180 r 1 6 . 1 5 0 - 2 1 2 2 2 4 2 4 0 2 7 3 3 3 2 0 - I. 1 1 • | " ' • i > i i • i 1 i i • i 2 0 0 2 2 0 2 4 0 2 6 0 2 8 0 3 6 0 3 2 0 (a) 50 241 2 7 3 301 4 1 4 2 4 0 2 6 0 2 8 0 3 0 0 3 2 0 3 4 6 3 6 0 3 8 0 400 (b) Figure 4.20: Mass spectra of the s o l i d formed in the CS2-DEA system (a: EI spectrum; b: CI spectrum). 86 4.4.5 INFRA-RED ANALYSIS To gain in s i g h t into the functional groups of the s o l i d compounds, i n f r a red (IR) absorption traces were obtained using KBr p e l l e t s i n a Bomem - Michelson 100 spectrophotometer. The r e s u l t i n g traces are shown in Figures 4.21 and 4 . 22 . Again there are obvious s i m i l a r i t i e s i n the absorption wavelenghts of both s o l i d s . It should be noted that the absorbances i n the traces are of weak to medium i n t e n s i t i e s since the transmittance scale i s from 78.7% to 102.75%, a range of only 24%. Table 4.5 shows a possible assignment of functional groups to the absorption bands i n the IR traces. The dependency of the composition of the s o l i d on the operating temperature suggests that the s o l i d s are probably not pure compounds but a mixture. If t h i s i s the case, then i t i s more appropriate to consider the s o l i d s as chemically derived organic f o u l i n g deposits. It could also be that, i n spite of the s i m i l a r i t i e s i n the r e s u l t s from the other analyses, the s o l i d s are d i f f e r e n t compounds belonging to the same homologous s e r i e s . The analyses conducted have enabled the i d e n t i f i c a t i o n of the fragments or functional groups that occur i n the s o l i d products. The insolub l e nature of the s o l i d s as well as t h e i r l e v e l of p u r i t y , posed problems that prevented further analysis and conclusive i d e n t i f i c a t i o n . Figure 4 . 2 1 : Infra-red trace of the s o l i d formed in the COS-DEA system. oo Figure 4.22: Infra-red trace of the s o l i d formed in the CS 2 -DEA system. 89 Table 4.5: Functional group assignments f or the sol i d s formed i n the COS-DEA and CS2-DEA systems. LITERATURE IR (81,82) GROUP BAND (cm" h BAND SAMPLE (cm"1) IR ASSIGNMENT ~S~CH2 670 - 760 (m) 672, 698 (m) CH 2 ~ S ~CH 2 -SH 815 - 930 (w) 910 (w) -SH 2420 - 2600(w) 2500 (w) -SH CH2-NH-CH2 3100 - 3500 (m) 3422 (w-m) CH2-NH-CH2 1480 - 1580 (w) 1492 (w) 1100 - 1200 (m) 1187 (m) 1080 - 1150 (m) 1143 (m) "<CH2>1 770 - 785 (w-m) -(CH 2) 2 735 - 745 (w-m) 755 (w) "<CH2>n -<CH2>3 725 - 735 (w-m) 721 (w-m) 2 <n <4 -(CH 2) 4 720 - 725 (w-m) 721 (w-m) -CH2OH 1400 - 1460 (w) 1424 (m) -CH2OH 1260 - 1350 (w) 1264 (w) 1010 - 1090 (s) 1053 (w) 3100 - 3500 (s) 3422 (w-m) The l e t t e r s m, s, w i n parenthesis, r e f e r to absorbances of moderate, strong and weak strengths, r e s p e c t i v e l y . CHAPTER 5 EFFECTS OF OPERATING VARIABLES ON DEA DEGRADATION The e f f e c t s of i n i t i a l DEA concentration, temperature, COS p a r t i a l pressure and CS 2 volume on the degradation reactions are discussed with p a r t i c u l a r reference to DEA and the major degradation products. The observed trends are interpreted not only to highlight the e f f e c t s that changes in the operating conditions have on the rates of degradation of DEA and the formation of degradation products, but also an attempt i s made to d i s t i n g u i s h terminal reaction products from reaction intermediates. Such d i s t i n c t i o n w i l l eventually simplify the development of reaction mechanisms. 5.1 COS-DEA SYSTEM 5.1.1 EFFECTS OF INITIAL DEA CONCENTRATION The o v e r a l l degradation of DEA may be represented by: DEA -> Products 5.1 The rate of degradation may be written as: d[DEA]/dt = - k n F « [ D E A ] n 5.2 90 91 where n i s the order of reaction and k DEA is the ov e r a l l degradation rate constant. For f i r s t order reactions, Eq. 5.2 reduces to: ln [DEA]£ ln [DEA] D - k DEA t 5.3 Eq. 5.2 may also be written i n the form: log,-d [DEA]/dt) log k D E A + n log [DEA] 5.4 According to Eq. 5.3, a semilogarithmic plot of DEA versus time should be l i n e a r with a slope corresponding to the degradation rate constant. Figures 5.1 to 5.3 show the e f f e c t of i n i t i a l DEA concentration on the degradation of the amine at 127, 150 and 165 °C, re s p e c t i v e l y . The plots are l i n e a r and thus confirm that the ove r a l l degradation of DEA follows f i r s t order k i n e t i c s at those temperatures. The rate of degradation increases with amine concentration up to 4M. Between 4 and 6M i n i t i a l concentrations, the rate of degradation decreases (see F i g . 5.4). At an i n i t i a l concentration of 6M, the amine i s i n excess of water. Under such conditions, the reactions that generate the ions which induce degradation are hindered and consequently the rate of degradation f a l l s . Kennard (16) and Chakma (18) observed s i m i l a r e f f e c t s i n CC^-DEA and CC^-MDEA systems, re s p e c t i v e l y . 92 O z o w 55 o o < w 0.0 40.0 80.0 120.0 TIME (h) 160.0 200.0 Figure 5.1: DEA concentration as a function of i n i t i a l DEA concentration and time ( P C O c = 0.34 MPa, T = 127 °C). 93 i 1 1 • 1 1 r A = 4M 1 I " 1 1 1 i I i • » 0.0 12.0 24.0 36.0 48.0 60.0 TIME (h) Figure 5.2: DEA concentration as a function of i n i t i a l DEA concentration and time ( P r o q =0.34 MPa, T = 150 °C). 94 12.0 24.0 TIME 36.0 48.0 60.0 (h) Figure 5.3: DEA concentration as a function of i n i t i a l DEA concentration and time ( P c o s = 0.34 MPa, T = 165 °C). 95 o 0.01 - 0.001 0.0 1.5 3.0 4.5 6.0 INITIAL DEA CONCENTRATION (mol/L) F i g u r e 5.4: O v e r a l l d e g r a d a t i o n r a t e c o n s t a n t a s a f u n c t i o n o f i n i t i a l DEA c o n c e n t r a t i o n a n d t e m p e r a t u r e (PQQS = ° - 3 4 M P a ) . 96 The role of water ©n amine degradation i s further addressed i n chapter 6. The i n i t i a l rate of degradation (-d[DEA]/dt) may be p l o t t e d against the i n i t i a l DEA concentration on a log-log scale. In accordance with Eq. 5.4, the slopes of such plots correspond to the order of reaction. A least squares f i t of the plots i n F i g . 5.5 produced slopes of approximately 1.4. This further confirms that the rate of degradation may be represented, i n an appropriate manner, by a f i r s t order expression. The f i r s t order representation i s only apparent since the rate constant i s dependent on the i n i t i a l DEA concentration. Figure 5.6 shows that the rate of formation of acetone increases with i n i t i a l DEA concentration. At each DEA concentration and within the durations of the experiments, the acetone concentration attains a maxima followed by a decline to an equilibrium value which appears to be independent of the i n i t i a l DEA concentration. The presence of maxima suggests that acetone i s an intermediate and undergoes further reaction. The butanone concentration increases with i n i t i a l DEA concentration and time (see F i g . 5.7). For DEA concentrations between 3 and 6M, the maximum or f i n a l butanone concentration i s independent of the i n i t i a l DEA concentration. At an i n i t i a l concentration of 2M, butanone concentration i s s t i l l on the r i s e throughout the duration of the experiment. It should be noted that the reported acetone and butanone concentrations correspond to the l i q u i d phase. Analysis of some gas samples indicated the presence of these compounds i n s i g n i f i c a n t 97 Figure 5.5: I n i t i a l degradation rate as a function of i n i t i a l DEA concentration and temperature ( P C O c = 0.34 MPa). 98 0.040 0.032 h 0.024 h 0.016 H 0.008 0.000 12.0 24.0 36.0 TIME (h) 48.0 60.0 Figure 5.6: Acetone concentration as a function of i n i t i a l DEA concentration and time (P^os = MPa, T = 165 °C) 99 0.030 > 0.024 \- 0.018 h 0.012 h 0.006 h 0.000 0.0 12.0 24.0 36.0 TIME (h) 48.0 60.0 Figure 5.7: Butanone concentration as a function of i n i t i a l DEA concentration and time (PC Os = °-34 MPa, T = 165 °C), 100 1.0 0.8 B = 6M A = 4M X = 3M • = 2M 0.8 0.4 B B A A X X A B 0.2 H A x X 0.0 * - L 0.0 12.0 24.0 36.0 TIME (h) 48.0 60.0 Figure 5.8: MEA concentration as a function of i n i t i a l DEA concentration and time ( P r 0 e = 0.34 MPa, T = 165 °C). 101 quantities i n the gas*phase as well. However, i t was not possible to determine t h e i r concentrations due to a n a l y t i c a l d i f f i c u l t i e s a r i s i n g from condensation within the gas sampling l i n e and i n the syringe during and a f t e r sample withdrawals, r e s p e c t i v e l y . Hence, the t o t a l amounts of acetone and butanone produced are greater than the plots show. As shown by F i g . 5.8, the i n i t i a l rate of MEA production and maximum MEA concentration increase with i n i t i a l DEA concentration. At l a t e r stages, the trend i s reversed suggesting that the depletion of MEA i s enhanced by increased DEA concentration. This may be due to the fa c t that the equilibrium s o l u b i l i t y of the acid gases that induce degradation increase with DEA concentration. The presence of the maxima also implies that MEA i s not a terminal product, but undergoes further reactions. The concentration-time plots f o r high b o i l i n g compounds (BHEED, BHEP, HEOD, HEI, THEED, BHEI) are shown i n Figs. 5.9 to 5.14, res p e c t i v e l y . The concentrations of these compounds were found to increase with i n i t i a l DEA concentration. It has been reported (16) that HEOD i s formed from DEA carbamate (DEACOO"), the concentration of the l a t t e r being l a r g e l y d i ctated by the equilibrium s o l u b i l i t y of CO2. Therefore, the HEOD concentration should increase with DEA concentration as shown i n F i g . 5.11, since the equilibrium s o l u b i l i t y of CO2 increases with DEA concentration. The presence of HEOD i n the degraded s o l u t i o n i s an i n d i c a t i o n of COS hydrolysis. The fact that HEOD concentration increased throughout the duration of the runs suggests that the equilibrium between DEACOO" H + and HEOD takes longer to be established i n the COS-DEA system than i n the C02-DEA system. This may be due to 102 0.40 1 r 0.32 B = 6M A = 4M X = 3M • = 2M O 0.24 0.16 0.08 0.00 B x _L 0.0 12.0 24.0 36.0 TIME (h) 48.0 60.0 Figure 5.9: BHEED concentration as a function of i n i t i a l DEA concentration and time ( P r n q = 0.34 MPa, T = 165 °C). 103 12.0 24.0 36.0 TIME (h) 48.0 60.0 Figure 5.10: BHEP concentration as a function of i n i t i a l DEA concentration and time (P CQC = 0.34 MPa, T = 165 °C). 104 0.20 O o 13 « E- S5 W O 25 O CJ> Q O W H 0.16 0.12 h 0.08 h 0.04 h 0.00 0.0 12.0 24.0 36.0 TIME (h) 48.0 60.0 Figure 5.11: HEOD concentration as a function of i n i t i a l DEA concentration and time ( P r n c = 0.34 MPa, T = 165 °C). 105 0.20 24.0 36.0 TIME (h) 48.0 60.0 Figure 5.12: HEI concentration as a function of i n i t i a l DEA concentration and time ( P r n q = 0.34 MPa, T = 165 °C). 106 12.0 24.0 36.0 TIME (h) 48.0 60.0 Figure 5.13: THEED concentration as a function of i n i t i a l DEA concentration and time ( P r 0 c = 0.34 MPa, T = 165 °C). 107 0.30 O J , o « W CJ 55 O o w « CQ 0.24 h 0.18 r- 0.12 h 0.06 h 0.00 0.0 12.0 24.0 36.0 TIME (h) 48.0 60.0 Figure 5.14: BHEI concentration as a function of i n i t i a l DEA concentration and time ( P C O c = 0.34 MPa, T = 165 °C). 108 the d i f f e r e n c e s i n the rate of degradation i n both systems or due to the lower p a r t i a l pressures of COS which were t y p i c a l l y 10% of the p a r t i a l pressures of CO2 used i n the CC^-DEA systems (14). The lack of maxima i n the HEOD concentration p r o f i l e also supports the conclusion by Kennard and Meisen (14) that HEOD i s a f i n a l product and not an intermediate as suggested by Kim and S a r t o r i (13). It i s pertinent to point out that for true f i r s t order reactions, the rate constant i s independent of the i n i t i a l concentration of reactants. The dependency of k D E A on the i n i t i a l DEA concentration observed i n the present study can be explained i n terms of the a n a l y t i c a l procedure employed as well as solution, composition. At constant COS p a r t i a l pressure and temperature, the equilibrium s o l u b i l i t y of COS and the r a t i o of free amine to ionised amine are functions of the i n i t i a l amine concentration. For d i f f e r e n t i n i t i a l DEA concentrations, t h i s r a t i o i s not necessarily the same as the r a t i o of the i n i t i a l DEA concentrations. At the high temperatures used, the free amine concentration exceeds the concentration of the amine i n the protonated carbamate or thiocarbamate forms. Since degradation i s induced by i o n i c species, e s p e c i a l l y the carbamates, the DEA concentration i n Eqs. 5.1 - 5.3 should be the i o n i c concentration. However, the GC analysis provides only the t o t a l DEA concentration as i t cannot d i s t i n g u i s h between the various forms of DEA i n so l u t i o n . Thus, when the equations are written i n terms of t o t a l DEA concentration, the dependency of k D E A on the i n i t i a l DEA concentration i s i n e v i t a b l e . 109 5.1.2 EFFECTS OF TEMPERATURE Figures 5.15 to 5.17 show the DEA concentrations as a function of time f o r various temperatures and i n i t i a l DEA concentrations of 40 wt%, 30 wt% and 20 wt% (approx. 4, 3 and 2M), re s p e c t i v e l y . The rates of degradation increase with temperature. As shown by F i g . 5.18, the degradation rate constants, k D E A obey the Arrhenius expression and thus confirm the notion of f i r s t order reaction k i n e t i c s . The rate of production and f i n a l concentration of butanone increase with temperature (Fig. 5.19). The l e v e l l i n g off observed i n butanone concentrations suggest that the compound may be a terminal product or the rea c t i o n by which i t i s produced, attains equilibrium. As shown by F i g . 5.20 and 5.21 re s p e c t i v e l y , the rates of production and depletion of acetone and MEA increase with temperature. Hence t h e i r f i n a l concentrations are i n v e r s e l y r e l a t e d to temperature. At 150 °C, the plo t s do not show maxima because the rates of depletion are much lower than the rates of production. The rate of production of BHEED increases with temperature and the high temperature pl o t s i n F i g . 5.22 show maxima. BHEED may therefore be regarded as an intermediate product, r e a c t i n g further to form other compounds. The rates of such reactions appear to be very low at temperatures below 165 °C. This explains the absence of maxima at such temperatures f o r the durations of the experiments. Rates of production and f i n a l concentrations of BHEP increase with temperature as shown by F i g . 5.23. BHEP thus behaves as a terminal product as previously reported (13,14). 110 - A =165°C x =160°C • =150°C — 1 11 1 1 1 1 1 I ' • I 0.0 12.0 24.0 36.0 48.0 60.0 TIME (h) Figure 5.15: DEA concentration as a function temperature and time < pCOS = ° ' 3 4 M P a ' D E A o = 4 M ) - I l l a = 190°C A = 165°C • = 150°C 0.0 12.0 24.0 TIME 36.0 48.0 (h) 60.0 Figure 5.16: DEA concentration as a function temperature and time ( P c o s = 0.34 MPa, DEA D = 3M). 112 10 o o t-H « o o o W Q - a = 195°C o = 180°C - A =165°C • • • =150°C 0.5 -L _L 0.0 12.0 24.0 TIME 36.0 48.0 (h) 60.0 Figure 5.17: DEA concentration as a function temperature and time ( P c o s = 0.34 MPa, DEAQ = 2M). 113 Figure 5.18: Arrhenius plots of the o v e r a l l degradation rate constant ( P c o s = 0.34 MPa). 114 0.030 \ 0.024 0.018 0.012 0.006 0.000 1 1 ~1 1 1 1 a = 190°C • A = 165°C - • = 150°C A A A A - A B B _ B • B • • B • • • B e - 8 3 • A • A • h-9— 1 0.0 12.0 24.0 36.0 TIME (h) 48.0 60.0 Figure 5.19: Butanone concentration as a function temperature and time ( P c o s =0.34 MPa, DEAD = 3M). 115 0.030 0.024 a = 190°C A = 165°C • = 150°C 0.018 B 0.012 A • 0.006 A • • 0.000 0.0 12.0 —I 1 I 24.0 36.0 TIME (h) i 48.0 60.0 F i g u r e 5 . 2 0 : A c e t o n e c o n c e n t r a t i o n a s a f u n c t i o n t e m p e r a t u r e a n d t i m e ( P C 0 S = ° - 3 4 M P a ' D E A o = 3 M ) - 116 0.8 0.6 0.4 0.2 1 1 1 —1— 1 1 1 1 • a = 190°C • A = 165°C - • = 150°C - A A - • A • • - B A - B B • a - a B • A B • t a - a • A • 1 i 1 , 1 0.0 12.0 24.0 36.0 TIME (h) 48.0 60.0 Figure 5.21: MEA concentration as a function temperature and time ( pCOS = ° - 3 4 M P a ' D E A o = 3 M ) - 117 0.35 0.28 O 0.21 0.14 0.07 0.00 a = 190°C ^ = 165°C • = 150°C s o.o 12.0 24.0 38.0 TIME (h) — I i _ 48.0 60.0 F i g u r e 5 . 2 2 : B H E E D c o n c e n t r a t i o n a s a f u n c t i o n t e m p e r a t u r e a n d t i m e ( p c 0 s = ° - 3 4 m p a ' DEAQ = 3M) 0.20 ^ 0.16 B = 1 9 0 ° C A = 1 6 5 ° C • = 1 5 0 ° C 0.12 0.08 0.04 A o.oo * • 9 o.o B •4- 12.0 _ l , 1 24.0 36.0 TIME (h) _ l 48.0 60 Figure 5.23: BHEP concentration as a function temperature and time (P C Os = °-3 4 M P a ' D E A 0 = 3 M )- 119 0.20 0.16 0.12 0.08 0.04 0.00 • = 190°C A = 165°C • = 150°C 0.0 12.0 24.0 36.0 TIME (h) 48.0 60.0 F i g u r e 5 . 2 4 : HEOD c o n c e n t r a t i o n as a f u n c t i o n t e m p e r a t u r e and t i m e (P, COS = 0.34 MPa, DEA, 3M) 120 O J , o S3 W O o o t—I w w 0.15 0.12 0.09 0.06 0.03 0.00 a = 190°C A = 165°C • = 150°C • • • m _1_ 0.0 12.0 24.0 36.0 TIME (h) 48.0 60.0 Figure 5.25: HE I concentration as a function temperature and time ( P c o s = 0.34 MPa, DEAQ = 3M). 121 0.8 a = 190°C A = 165°C • = 150°C 0.8 0.4 0.2 Bl 0.0 12.0 - 4 1 1— 24.0 36.0 TIME (h) 48.0 60.0 Figure 5.26: THEED concentration as a function temperature and time ( P c o s = 0.34 MPa, DEAQ = 3M). 122 0.40 0.32 a = 190°C A = 165°C • = 150°C 0.24 0.16 0.08 0.00 0.0 12.0 A 4- A -L 24.0 36.0 TIME (h) 48.0 60.0 Figure 5.27: BHEI concentration as a function temperature and time ( P c o s = 0.34 MPa, DEAQ = 3M). 123 For the C02-DEA system, Kennard (16) found that the HEOD production attained equilibrium and that the f i n a l concentrations decrease with increasing temperature. Figure 5.24 shows that equilibrium was not attained at T < 165 °C. However, at 165 °C, the HEOD production appears to l e v e l off to a f i n a l concentration lower than that obtained at 150 °C. Such approach to equilibrium was also observed i n the runs conducted with an i n i t i a l DEA concentration of 20 wt% and at low temperatures (see Tables C.14 and C.15). The i n i t i a l rate of HEOD production, on the other hand, increased with temperature. This trend i s consistent with the mechanism that HEOD i s produced from DEA carbamate (DEACOO") which, i n turn, i s a function of the. equilibrium C0 2 s o l u b i l i t y . Although the rate of transformation of DEA carbamate to HEOD increases with temperature (see i n i t i a l rates of HEOD production), the f i n a l concentration i s dependent on the equilibrium C0 2 s o l u b i l i t y which i s i n v ersely r e l a t e d to temperature. Hence, the equilibrium HEOD concentration should decrease as temperature increases. The HEI production and f i n a l concentration increase with temperature as shown i n Fi g . 5.25. Figure 5.26 shows that the rate of production and depletion of THEED increase with temperature. Hence at high temperatures, maxima r e s u l t . It has been reported that THEED dehydrates to BHEP (13,14). The data shown by F i g . 5.26 are consistent with the conclusion that THEED i s an intermediate product. The rate of production and f i n a l concentration of BHEI increase with temperature. No maxima are indicated by F i g . 5.27. Therefore, BHEI may be considered a terminal product. At temperatures above 165 °C, the 124 BHEI concentration increases s i g n i f i c a n t l y . The rate of decline of the compound producing BHEI should be correspondingly high at such temperatures. The depletion of BHEED exhibits t h i s t r a i t . BHEED may therefore be the intermediate product from which BHEI i s formed. 5.1.3 EFFECTS OF INITIAL COS PARTIAL PRESSURE It i s shown in chapter 7 that the equilibrium s o l u b i l i t y of COS and the concentrations of the i o n i c species that induce degradation increase with i n i t i a l COS p a r t i a l pressure. Consequently, the rate of depletion of DEA increases with i n i t i a l COS p a r t i a l pressure as shown by F i g . 5.28. The e f f e c t s of i n i t i a l COS pressure on the production of acetone and butanone are shown by F i g s . 5.2 9 and 5.30, r e s p e c t i v e l y . The rates of production of both compounds increase with the i n i t i a l COS p a r t i a l pressure. The f i n a l concentration of acetone also increases with the i n i t i a l COS p a r t i a l pressure, but a drop i n f i n a l concentration was observed f o r butanone as the pressure rose to 1171 kPa. Butanone may be depleted v i a some reactions, the rates of which increase with COS p a r t i a l pressure. The rate of production of MEA and i t s f i n a l concentration increase with i n i t i a l COS p a r t i a l pressure. The increase i s less pronounced f o r pressure increase from 759 to 1171 kPa, probably because MEA i s an intermediate product and i t s rate of depletion increases with COS p a r t i a l pressure (see F i g . 5.31). 125 10 A = 1171 kPa x = 759 kPa • = 345 kPa A 1 I t I ! I I I I I I I 0.0 12.0 24.0 36.0 48.0 60.0 TIME (h) F i g u r e 5 . 2 8 : DEA c o n c e n t r a t i o n as a f u n c t i o n of i n i t i a l COS p a r t i a l p r e s s u r e and t i m e ( D E A Q = 3M, T = 150 ° C ) . 126 0 . 0 5 0 . 0 4 - A = 1171 kPa x = 759 kPa • = 345 kPa 0 . 0 3 0 . 0 2 A X 0 .01 A X • 0 . 0 0 0 . 0 1 2 . 0 2 4 . 0 3 6 . 0 TIME (h) 4 8 . 0 6 0 . 0 Figure 5.29: Acetone concentration as a function of i n i t i a l COS p a r t i a l pressure and time (DEAD = 3M, T = 150 °C). 127 0.030 \ 0.024 A = 1171 kPa x = 759 kPa • = 345 kPa 0.018 0.012 x A X X A 0.006 A X 0.000 x A 0.0 12.0 _L 24.0 36.0 TIME (h) 48.0 60.0 Figure 5.30: Butanone concentration as a function of i n i t i a l COS p a r t i a l pressure and time (DEA Q = 3M, T = 150 °C). 128 0.0 12.0 24.0 TIME 36.0 48.0 60.0 (h) Figure 5.31: MEA concentration as a function of i n i t i a l COS p a r t i a l pressure and time (DEA Q = 3M, T = 150 °C). 129 0.15 0.12 - 0.09 0.06 0.03 A = 1171 kPa x = 759 kPa • = 345 kPa 0.00 • • • 1 g 0.0 A i 12.0 A X 24.0 36.0 TIME (h) 48.0 60.0 Figure 5.32: BHEED concentration as a function of i n i t i a l COS p a r t i a l pressure and time (DEAQ = 3M, T = 150 °C). 130 0.05 24.0 36.0 TIME (h) 48.0 60.0 Figure 5.33: BHEP concentration as a function of i n i t i a l COS p a r t i a l pressure and time (DEAC = 3M, T = 150 °C). 131 0.15 'o 2 o H W O Z o o Q O W w 0.06 h 0.03 h 0.00 12.0 24.0 36.0 TIME (h) 48.0 60.0 F i g u r e 5 . 3 4 : HEOD c o n c e n t r a t i o n as a f u n c t i o n of i n i t i a l COS p a r t i a l p r e s s u r e and t i m e ( D E A Q = 3M, T = 150 ° C ) . 132 0.15 0.12 A = 1171 kPa x = 759 kPa • = 345 kPa o 55 o I—I tt W o o o t—I w a 0.09 0.06 0.03 0.00 • • • 1 • A •4- A X 0.0 12.0 24.0 TIME 36.0 48.0 60.0 (h) Figure 5 . 3 5 : HEI concentration as a function of i n i t i a l COS p a r t i a l pressure and time (DEAQ = 3 M , T = 150 °C). 133 0.30 <-> 0.24 - A = 1171 kPa x = 759 kPa • = 345 kPa 0.18 0.12 A X 0.06 x A 0.00 0.0 12.0 24.0 36.0 TIME (h) 48.0 60.0 Figure 5.36: THEED concentration as a function of i n i t i a l COS p a r t i a l pressure and time (DEAQ = 3M, T = 150 °C). 134 0.040 A = 1171 kPa x = 759 kPa A 0.032 • = 345 kPa X 0.024 0.016 0.008 0.000 • • • 1 • 0.0 12.0 24.0 36.0 TIME (h) 48.0 60.0 Figure 5.37: BHEI concentration as a function of i n i t i a l COS p a r t i a l pressure and time ( D E A D = 3M, T = 150 °C). 135 The rates of production and f i n a l concentrations of BHEED, BHEP, HEOD, HEI, THEED and BHEI increase with COS p a r t i a l pressure as shown by- Figs. 5.32 to 5.37. In summary, the rate of DEA degradation i s more sens i t i v e to changes i n temperature than v a r i a t i o n s i n DEA concentration and COS p a r t i a l pressure. For example, at an i n i t i a l concentration of 30 wt%, a change i n temperature from 127 to 165 °C resu l t e d i n a 5 f o l d increase i n the rate of degradation. On the other hand, a 2 f o l d increase i n DEA concentration (2 - 4M) caused an increase of 1.76 i n the rate of degradation while doubling the COS p a r t i a l pressure produced a 1.4 f o l d increase i n the rate of degradation. The t o t a l concentrations of the degradation products also r e f l e c t the rates of degradation. The higher the rates, the higher the t o t a l concentrations of the degradation product's. By comparing the degradation rate constant of 0.0173 h" 1 for a C02-DEA system (Table C.43) with the value of 0.0131 h" 1 for a s i m i l a r COS-DEA system (Table C.17), i t i s seen that the rate of degradation i n the former i s just 1.3 times f a s t e r than that of the l a t t e r system. 5.2 CS2-DEA SYSTEM 5.2.1 EFFECTS OF INITIAL DEA CONCENTRATION Figures 5.38 - 5.40 show the DEA concentration as a function of time and i n i t i a l DEA concentration at temperatures of 120, 150 and 165 °C, re s p e c t i v e l y . The DEA concentration curves consist of an i n i t i a l 136 10 o 55 o I — i Oi H 52 W CJ 55 O CJ < H Q x = 3M • = 2M _L 0.0 40.0 80.0 TIME 120.0 (h) 160.0 200.0 Figure 5.38: DEA concentration as a function of i n i t i a l DEA concentration and time (CS 2 volume = 6 mL, T = 120 °C, CS2/DEA mole r a t i o s = 0.1 - 0.2). 137 1 I 1 1 i I i I i I i I 0.0 15.0 30.0 45.0 60.0 75.0 TIME (h) Figure 5.39: DEA concentration as a function of i n i t i a l DEA concentration and time (CS 2 volume = 6 mL, T = 150 °C, CS2/DEA mole r a t i o s = 0.1 - 0.2). 138 Figure 5.40: DEA concentration as a function of i n i t i a l DEA concentration and time (CS 2 volume = 6 mL, T = 165 °C, CS2/DEA mole r a t i o s = 0.1 - 0.2). 139 0.1 x =150°C • = 165°C W 0.01 0.001 1 1 1 1 1 ' 1 ' 1 0.0 1.5 3.0 4.5 6.0 INITIAL DEA CONCENTRATION (mol/L) 7.5 Figure 5.41: Overall degradation rate constant as a function of i n i t i a l DEA concentration and temperature (CS2 volume = 6 mL, CS2/DEA mole r a t i o s = 0.1 - 0.2). 140 0.1 i-J o < 55 2 o.oi Q « O w Q t-1 •—i I—I 55 0.001 A = 150°C x = 165°C INITIAL DEA CONCENTRATION (mol/L) 10 Figure 5.42: I n i t i a l degradation rate as a function of i n i t i a l DEA concentration and temperature (CS 2 volume = 6 mL, CS2/DEA mole r a t i o s = 0.1 - 0.2). 141 region of sharp decline and a second region of more moderate decline. This suggests that the degradation occurs via i n i t i a l f a s t reactions, which end a f t e r a short period of time, followed by slower reactions. The plots i n the second region are l i n e a r , suggesting that f o r t h i s region, the i n i t i a l o v e r a l l degradation exhibits f i r s t order behaviour. The degradation rate constants plotted i n F i g . 5.41 show that the rate of degradation i s l a r g e l y independent of the i n i t i a l DEA concentration at T = 150 °C. However, at 165 °C, a s l i g h t concentration dependence i s observed. As the DEA concentration increases to 60 wt%, the rate of degradation declines. The explanation offered f o r a s i m i l a r observation in the COS-DEA system also applies i n t h i s case. A further check on the f i r s t order postulate i s provided by F i g . 5.42 which i s based on the ap p l i c a t i o n of Eq. 5.4 to the second region. The curves have slopes of 1.1 thereby again confirming that the ov e r a l l degradation i s consistent with the f i r s t order assumption. The i n i t i a l rate of MEA formation increases with i n i t i a l DEA concentration, but within the experimental durations, the f i n a l MEA concentrations approach the same value i r r e s p e c t i v e of the i n i t i a l DEA concentration (Fig. 5.43). The maxima i n the plots conform to previously established trends which suggest that MEA i s an intermediate product. The approach to a constant f i n a l concentration despite the d i f f e r e n t maximum concentrations, indicates that MEA depletion i s enhanced by high DEA concentration or b a s i c i t y , as observed i n the COS-DEA system. Figures 5.44 to 5.49 show that the production of the other degradation compounds increases with i n i t i a l DEA concentration up to 40 wt%. However, between 40 and 60 wt%, a decline i s observed f o r BHEED, 142 0.60 0.48 - 0.36 - 0.24 - 0.12 - 0.00 0.0 12.0 24.0 36.0 TIME (h) 48.0 60.0 Figure 5.43: MEA concentration as a function of i n i t i a l DEA concentration and time (CS2 volume = 6 mL, T = 165 °C, CS2/DEA mole ra t i o s = 0.1 - 0.2). 143 0.25 0.20 h 0.15 h 0.10 0.05 0.00 0.0 12.0 24.0 36.0 TIME (h) 48.0 60.0 Figure 5.44: BHEED concentration as a function of i n i t i a l DEA concentration and time (CS 2 volume = 6 mL, T = 165 °C, CS2/DEA mole r a t i o s = 0.1 - 0.2). 144 O J , 55 o « E-" 55 W U 55 O cu w w pq 0.075 0.060 0.045 0.030 0.015 H = 6M A = 4M x = 3M • = 2M 0.000 • - • - » 0.0 12.0 24.0 36.0 TIME (h) _L 48.0 60.0 Figure 5.45: BHEP concentration as a function of i n i t i a l DEA concentration and time (CS2 volume = 6 mL, T = 165 °C, CS2/DEA mole r a t i o s = 0.1 - 0.2). 145 0.15 0.12 0.09 0.06 0.03 0.00 • • • B = 6M A = 4M X = 3M • = 2M 0.0 X 12.0 _L 1 r 24.0 36.0 TIME (h) 48.0 60.0 Figure 5.46: HEOD concentration as a function of i n i t i a l DEA concentration and time (CS 2 volume = 6 mL, T = 165 °C, CS2/DEA mole r a t i o s = 0.1 - 0.2). 146 0.060 0.048 h 0.036 0.024 h 0.012 h 0.000 24.0 36.0 TIME (h) 48.0 60.0 Figure 5.47: HEI concentration as a function of i n i t i a l DEA concentration and time (CS2 volume = 6 mL, T = 165 °C, CS2/DEA mole r a t i o s = 0.1 - 0.2). 147 0.0 15.0 30.0 TIME (h) 45.0 Figure 5.48: THEED concentration as a function of i n i t i a l DEA concentration and time (CS 2 volume = 6 mL, T = 165 °C, CS2/DEA mole r a t i o s = 0.1 - 0.2). 148 0.05 O J , 55 O « H 55 W o 55 o o t—( w a PQ 0.01 h 0.00 0.0 15.0 30.0 TIME (h) 45.0 60.0 Figure 5.49: BHEI concentration as a function of i n i t i a l DEA concentration and time (CS2 volume = 6 mL, T = 165 °C, CS2/DEA mole r a t i o s = 0.1 - 0.2). 149 BHEP and HEOD (Figs. 5.44 - 5.46), while the concentrations of HEI, THEED and BHEI (Figs. 5.47 - 5.49) continue to r i s e . These trends suggest that the e f f e c t of the d e c l i n i n g water content i n highly- concentrated DEA solutions i s more pronounced on some degradation reactions than others. 5.2.2 EFFECTS OF TEMPERATURE The e f f e c t s of temperature on DEA degradation are shown i n Figs. 5.50 - 5.52 at i n i t i a l DEA concentrations of 40, 30 and 20 wt%, res p e c t i v e l y . The rate of degradation increases with temperature at a l l le v e l s of i n i t i a l DEA concentration. Figure 5.53 shows that the temperature dependency of the rate constants obtained from the slopes of the curves i n Figs. 5.50 - 5.52 conforms to the Arrhenius expression. This r e s u l t i s consistent with the f i r s t order reaction k i n e t i c s suggested e a r l i e r . However, f o r T = 180 °C, degradation i s much more rapid and the plot deviate s u b s t a n t i a l l y from l i n e a r i t y (see F i g . 5.52). At t h i s temperature (and higher ones), the reactions become more complex, producing f a r more degradation compounds than at lower temperatures (see chapter 4). Consequently, the o v e r a l l rate cannot be represented by a simple f i r s t order expression. Since the highest operating temperature i n DEA plants i s f a r below 180 °C, further discussions are l i m i t e d to runs conducted at T <165 °C. The rates of production and depletion of MEA increase with temperature. Thus the f i n a l concentration of MEA decreases as temperature increases (Fig. 5.54). 150 Figure 5.50: DEA concentration as a function of temperature and time (DEA 0 = 4M, CS 2 volume = 6 mL, CS2/DEA mole r a t i o = 0.1). 151 1 I ' 1 1 1 1 I i ' • I 0.0 15.0 30.0 45.0 60.0 75.0 TIME (h) Figure 5.51: DEA concentration as a function of temperature and time (DEA Q = 3M, CS 2 volume = 6 mL, CS2/DEA mole r a t i o = 0.13). 152 O.i I i I i I i ' I i I 0.0 15.0 30.0 45.0 60.0 75.0 TIME (h) Figure 5.52: DEA concentration as a function of temperature and time (DEA D = 2M, CS 2 volume = 6 mL, CS2/DEA mole r a t i o = 0.2). 153 g u r e 5.53: A r r h e n i u s p l o t s f o r t h e o v e r a l l d e g r a d a t i o n r a t e c o n s t a n t a s a f u n c t i o n o f i n i t i a l CS2 v o l u m e . 154 0.5 0.4 A = 165°C x = 150°C 0.3 A A 0.2 0.1 A x 0.0 * A X X 0.0 15.0 JL 30.0 45.0 T IME (h) _L 60.0 75.0 gure 5.54: MEA concentration as a function of temperature and time (DEAQ = 3M, CS 2 volume = 6 mL, CS2/DEA mole r a t i o = 0.13). 155 0.20 0.16 0.12 h 0.08 h 0.04 h A = 165°C x = 150°C A A X 0.00 a a x »< - i L 0.0 15.0 30.0 45.0 TIME (h) 60.0 75.0 Figure 5.55: BHEED concentration as a function of temperature and time (DEAD = 3M, CS 2 volume = 6 mL, CS2/DEA mole r a t i o = 0.13). 156 O 55 o t—I 55 w o 55 O o CU W CQ 0.05 ^ 0 0 4 0.03 0.02 0.01 A = 165°C x = 150°C 0.00 a a a »< 0.0 _L 15.0 30.0 45.0 TIME (h) 60.0 75.0 Figure 5.56: BHEP concentration as a function of temperature and time (DEA Q = 3M, CS 2 volume = 6 mL, CS2/DEA mole r a t i o = 0.13). 157 O 55 O 55 W O 55 O Q O w 0.15 0.12 0.09 0.06 0.03 A = 1 6 5 ° C x = 1 5 0 ° C x x 0.00 IHS »— 0.0 15.0 mi L 30.0 45.0 TIME (h) 60.0 75.0 Figure 5.57: HEOD concentration as a function of temperature and time (DEA D = 3M, CS 2 volume = 6 mL, CS2/DEA mole r a t i o = 0.13). 158 0.05 0.04 0.03 0.02 0.01 A = 165°C x = 150°C 0.00 a a a—a—a—L JL _L 0.0 15.0 30.0 45.0 TIME (h) 60.0 75.0 Figure 5.58: HEI concentration as a function of temperature and time (DEA D = 3M, CS 2 volume = 6 mL, CS2/DEA mole r a t i o = 0.13) 159 O J, 55 o t—c « H 55 H O 55 o o I—t w a CQ 0.040 0.032 0.024 0.016 0.008 A = 165°C x = 150°C 0.000 a a B — B - 0.0 15.0 — 1 X — i - 30.0 TIME ± 45.0 60.0 75.0 (h) Figure 5.59: BHEI concentration as a function of temperature and time (DEA Q = 3M, CS 2 volume = 6 mL, CS2/DEA mole r a t i o = 0.13). 160 0.70 0.56 A = 165°C x = 150°C 0.42 0.28 0.14 0.00 a H H M 0.0 15.0 30.0 45.0 TIME (h) 60.0 75.0 Figure 5.60: THEED concentration as a function of temperature and time (DEAQ = 3M, CS 2 volume = 6 mL, CS2/DEA mole r a t i o = 0.13). 161 The rates of formation and f i n a l concentrations of BHEED, BHEP, HEOD, HEI and BHEI increase with increasing temperature (see Figs. 5.55 to 5.59). Except f o r HEI whose concentrations approach a constant value at each temperature l e v e l , the concentrations of the other compounds increase throughout the durations of the runs. The rate of formation of THEED increases with temperature as shown by F i g . 5.60. At 165 °C, the THEED concentration tends to a maxima while at 150 °C, the concentration increased throughout the run. This trend again confirms that the rate of depletion of THEED increases with temperature. 5.2.3 EFFECTS OF INITIAL VOLUME OF CS2 The curves i n F i g . 5.61 represent runs conducted with 250 mL of 3M aqueous DEA solutions and 2.5, 6 and 10.5 mL of CS2 at 165 °C. The corresponding CS2/DEA mole r a t i o s are 0.055, 0.133 and 0.233 re s p e c t i v e l y . The rate of DEA degradation increases with the i n i t i a l CS2 volume (or CS2/DEA mole r a t i o ) i n the reactor. The l i n e a r i t y of the plots indicates that the f i r s t order reaction k i n e t i c s are not a l t e r e d even at the highest CS 2 volume investigated. The fac t that the degradation rate constant increases with CS 2 volume and not with DEA concentration shows that when the concentration of DEA exceeds that of CS2/ the rate of degradation i s influenced by the CS2 volume and not the CS2/DEA mole r a t i o . The masses of the s o l i d products recovered from the runs increased with the i n i t i a l volume of CS2• Since DEA was i n excess 162 of CS2 in a l l the runs, the increase i n the mass of s o l i d may be due to the increase i n the formation of the dithiocarbamate s a l t as described by Eqs. 2.14 and 2.15. The increased formation of the s a l t could also be responsible for the sharper drop i n DEA concentration between 0 and 2 hours, i n the run conducted with 10.5 mL of CS2 • Figure 5.62 shows that the i n i t i a l rate of MEA formation and the maximum concentration increase with CS 2 volume. The f i n a l concentrations of MEA tend to a constant value which i s independent of the i n i t i a l CS2 volume. This suggests that MEA production and depletion probably attained equilibrium at the operating conditions. The rates of production and concentrations of BHEED, BHEP, HEOD, HEI and BHEI increase with the i n i t i a l CS 2 volume as shown by Figs. 5.63 to 5.67, re s p e c t i v e l y . At each l e v e l of CS 2, the concentration of HEOD tends towards a constant f i n a l value which suggests an approach to equilibrium. THEED production rates and concentrations also increase with i n i t i a l CS2 volume. The maxima exhibited i n F i g . 5.68, p a r t i c u l a r l y at an i n i t i a l CS 2 volume of 10.5 mL, i s i n d i c a t i v e of conversion to other compounds such as BHEP. Similar to the COS-DEA systems, the degradation reactions were p a r t i c u l a r l y s e n s i t i v e to changes i n temperature. Increasing the temperature from 120 to 165 °C f o r a 20 wt% so l u t i o n , caused a 10 f o l d increase i n the degradation rate constant. Doubling the i n i t i a l DEA concentration from 20 to 40 wt% caused 1.5 and 1.1 f o l d increases i n the rate constant at 165 and 150 °C, re s p e c t i v e l y . A four f o l d increase i n the volume of CS2 r e s u l t e d i n 3.6 f o l d increase i n the rate constant. 163 Figure 5.61: DEA concentration as a function of i n i t i a l CS2 volume and time (DEA Q = 3M, T = 165 °C). 164 0.60 0.48 I- 0.36 h 0.24 r- 0.12 h 0.00 * 0.0 12.0 24.0 36.0 TIME (h) 48.0 60.0 Figure 5.62: MEA concentration as a function of i n i t i a l CS 2 volume and time (DEAQ = 3M, T = 165 °C). 165 0.20 A - 10.5 mL x - 6.0 mL • - 2.5 mL <-*> 0.16 0.12 0 .06 0.04 I* X 0.00 u- 0.0 12.0 24.0 36.0 TIME (h) 48.0 60.0 Figure 5.63: BHEED concentration as a function of i n i t i a l CS2 volume and time (DEAQ = 3M, T = 165 °C). 166 0.05 O 55 O 5a tt H 55 W O 55 O O w OQ 0.04 - 0.00 0.02 - 0.01 - 24.0 36.0 TIME (h) 48.0 60.0 Figure 5.64: BHEP concentration as a function of i n i t i a l CS2 volume and time (DEA Q = 3M, T = 165 °C). 167 0.10 0.08 - 0.06 0.04 - 0.02 0.00 0.0 12.0 24.0 36.0 48.0 TIME (h) igure 5.65: HEOD concentration as a function of i n i t i a l CS? vol ume and time (DEA Q = 3M, T = 165 UC) 168 0.10 1 r 0.08 A - 10.5 mL x - 6.0 mL • - 2.5 mL 0.06 0.04 0.02 0.00 • • ' • 0.0 12.0 24.0 36.0 TIME (h) 48.0 60.0 Figure 5.66: HEI concentration as a function of i n i t i a l CS 2 volume and time (DEA D = 3M, T = 165 °C). 169 0.15 0.12 0.06 - 0.03 - 24.0 T IME 48.0 60.0 Figure 5.67: BHEI concentration as a function of i n i t i a l CS 2 volume and time (DEAQ = 3M, T = 165 °C). 170 0.60 0.48 - 0.36 - 0.24 0.12 0.00 0.0 12.0 24.0 36.0 TIME (h) 48.0 60.0 Figure 5.68: THEED concentration as a function of i n i t i a l C S 2 volume and time (DEAQ = 3M, T = 165 ° C ) . 171 The r e s u l t s presented i n t h i s chapter indicate that the rate of degradation of DEA i n COS-DEA systems i s dependent on the i n i t i a l DEA concentration, while i n the CS2-DEA system i t appears not to be. The detection of si m i l a r products i n both systems, suggests s i m i l a r reaction mechanisms. Therefore i t i s necessary to c l a r i f y the contradictory f i n d i n g s . It should be noted that the DEA concentrations obtained from the GC analysis are the t o t a l DEA i n each system. However, degradation i s induced p r i m a r i l y by the i o n i c species such as DEACOO", DEAH+, DEACOS", HCO3" etc. In the case of the CS2-DEA systems studied, the DEA concentration was always i n excess of CS2- Therefore, a s i g n i f i c a n t portion of CS2 i s t i e d up i n the formation of the dithiocarbamate s a l t of DEA, leaving very l i t t l e f o r conversion v i a hy d r o l y s i s . By contrast, no stable s a l t i s formed i n the COS-DEA system. The COS absorbed i s subsequently hydrolysed to CO2 and H2S. The gases i n solu t i o n undergo i o n i s a t i o n reactions to generate the ions that induce degradation. Since the s o l u b i l i t y of acid gases i n amine solutions increase with b a s i c i t y , the concentration of the ions that induce degradation w i l l increase with DEA concentration. Therefore, the COS-DEA systems, by v i r t u e of containing appreciable concentrations of CO2, H 2 S ' c o s a n d t h e i r i o n i c species, have degradation rates that are dependent on the t o t a l DEA concentration while the rates of degradation i n CS2-DEA systems which have s i g n i f i c a n t l y lower concentrations of such species are independent of t o t a l DEA concentration. It i s shown i n appendix E that the errors i n the reported concentrations are ±5% f o r DEA while those f o r the degradation products, p a r t i c u l a r l y THEED, may be up to ±20%. CHAPTER 6 EXPERIMENTS DESIGNED TO ELUCIDATE REACTION MECHANISMS The COS-DEA and CS2-DEA systems produced numerous degradation products as revealed i n Chapter 4. The res u l t s presented i n Chapter 5 showed that a number of ser i e s , p a r a l l e l and consecutive reactions are occuring i n both COS-DEA and CS2-DEA systems. However, the information i s i n s u f f i c i e n t to develop reaction mechanisms. This chapter presents the r e s u l t s of experimnents conducted to highlight the roles of the p r i n c i p a l degradation compounds and the a c i d gases i n the degradation process. The information acquired i s subsequently used to develop reaction mechanisms. 6.1 EFFECT OF MIXED GASES Compounds such as BHEP, HEOD and THEED were previously i d e n t i f i e d as the major degradation products i n the CO2-DEA system (13,14,16). Their presence i n the COS-DEA and CS2-DEA systems i s an i n d i c a t i o n that COS and CS2 are hydrolysed to CO2 and H 2S. Both systems therefore contain eventually H 2S and CO2. Five runs were conducted to e s t a b l i s h the role of H2S and C0 2 i n the degradation. Solutions containing 30 wt% DEA were subjected f o r 48 hours to the following i n i t i a l gas mixtures at 165 °C and a t o t a l pressure of 2.1 MPa: (1) 15.3% H2S, balance N 2; (2) 14.7% C02, balance N 2; (3) 15.2% C02, 15.2% H2S, balance N 2; (4) 30% C02, 15% H 2S, balance N 2; (5) 15.5% C02, 29.9% H2S, balance N 2. 172 173 Figures 6.1 - 6.8 show the concentrations of DEA and the degradation products r e s u l t i n g from the experiments. Mixture 1 d i d not cause any degradation which i s consistent with the e a r l i e r findings of Choi (12) and Kim and S a r t o r i (13). Mixture 2 produced HEOD, BHEP and THEED (consistent with the r e s u l t s of Kim and Sart o r i (13) and Kennard and Meisen (14)) whereas Mixtures 3, 4 and 5 yielded. MEA, BHEED, BHEP, HEOD, HEI, THEED and BHEI as the major products. Only the mixtures containing H 2S and C0 2 (mixtures 3 - 5) yielded ketones and the s o l i d product. These compounds must therefore be at t r i b u t e d to the sulphur species. The amount of s o l i d products increased with H 2S concentration i n the mixture, but was generally small compared to the ones recovered from the COS-DEA and CS2-DEA systems. The soli d s .resembled those of the former system. Appreciable amounts of ketones, comparable with those of the COS-DEA systems, were produced i n the system containing mixture 5, while only trace amounts were formed i n mixtures 3 and 4. The formation of the ketones i s therefore enhanced by high H2S concentration. It could be that under such conditions, the equilibrium shown below i s established: C0 2 + H 2S = COS + H 20 6.1 The COS then induces degradation as previously described i n chapter 4. As shown by F i g . 6.1, the rate of DEA degradation increases s l i g h t l y with H 2S but s i g n i f i c a n t l y with C0 2. This trend can be explained i n terms of the solu t i o n composition. As the H 2S concentration i n the gas mixture increases, the concentration of H 2S in the solu t i o n 174 a l s o increases, r e s u l t i n g i n an increase i n the r a t i o of protonated DEA to DEA carbamate. The e f f e c t of t h i s i s a reduction i n the rate of CC>2 induced degradation. Consequently, the concentrations of BHEP, HEOD and THEED decrease with increasing H2S concentration as shown i n Figs. 6.2 - 6.4, r e s p e c t i v e l y . However, the H2S i n the presence of C0 2 enables the formation of MEA, causing a s l i g h t increase i n the o v e r a l l rate of degradation. The high concentration of H 2S also i n h i b i t s the degradation of MEA through protonation. As a r e s u l t , the concentration of MEA increases with H 2S concentration, as shown in F i g . 6.5. This i n turn, a f f e c t s the production of BHEED, HEI and BHEI, and t h e i r concentrations f a l l as H 2S concentration increases or C0 2 concentration decreases (Fig. 6.6 - 6.8) . It can be concluded from these r e s u l t s that a mixture of C0 2 and H 2S which has the r e l a t i v e proportions used i n t h i s study, i s capable of inducing degradation reactions leading to the formation of MEA i n aqueous DEA solutions. The MEA undergoes further reactions to produce compounds such as BHEED, HEI and BHEI while BHEP, HEOD and THEED are produced from DEA. Hydrogen sulphide therefore a f f e c t s DEA degradation even though most of the p r i n c i p a l degradation products do not contain sulphur. The increased rate of degradation with H 2S concentration contradicts the fingings of Choi (12) and Kim and S a r t o r i (13). In the l a t t e r case, the mole r a t i o of C0 2 to H2S was 1.10 to 0.03 or 36.7/1. Given such a high r a t i o , the deduction that H2S exerts e s s e n t i a l l y no e f f e c t on the degradation i s not su r p r i s i n g . 175 I i I . I i I i I 1 1 0.0 12.0 24.0 36.0 48.0 60.0 TIME (h) Figure 6.1: DEA concentrations as a function of time and gas composition (DEAQ = 3M, T = 165 °C). 176 0.05 0.04 A - 15.27. CO, } 15. 27 H,S } baL N 2 X - 30.07. CO, } 15. 07 H,S } b o l N 2 • - 15.57 CO, t 29 . 97 H,S r baL N 2 8 - 14.77. COj \ 00 . 07 H 2 S j> baL N 0.03 0.02 0.01 A B A 0.00 x • • 0.0 12.0 24.0 36.0 TIME (h) 48.0 60.0 Figure 6.2: BHEP concentrations as a function of time and gas composition (DEAQ = 3M, T = 165 °C). 0.10 0.08 A - 15.27 CO, t 15. 27 H,S r b a l N2 X - 30. OX CO, r 15. 07. H,S } b a l N2 • - 15.57 CO, } 29. 97. H,S } baL N2 B - 14.77. CO* > 00. 07 H<S t baL N 0.06 0.04 0.02 A 0.00 A -A 1- 0.0 12.0 24.0 36.0 TIME (h) 48.0 60 Figure 6.3: HEOD concentrations as a function of time and gas composition (DEA Q = 3M, T = 165 °C). 178 1.0 0.8 A - 15.27 CO, f 15.27 H,S } baL N2 X - 30. OX CO, } 15.07 H,S i baL N2 • - 15.57 CO, t 29.97 H,S } baL N2 B - 14.77. co^ } 00.07 H*S t baL N 0.6 0.4 0.2 B 0.0 4. 4 A _? 0.0 12.0 24.0 36.0 TIME (h) 48.0 60.0 Figure 6.4: THEED concentrations as a function of time and gas composition (DEAQ = 3M, T = 165 °C). 179 0.6 0.4 0.3 0.2 X A X A A X 0.1 - * 0.0 0.0 A - 15.27 CO, J 15.27 H,S } b a l N 2 X - 30.0 / . CO. } 15.07 wis f baL N 2 • - 15.57. C O 2 } 29.97. H*S • > baL N 2 12.0 24.0 TIME 36.0 48.0 60.0 (h) F i g u r e 6 . 5 : MEA c o n c e n t r a t i o n s as a f u n c t i o n of t i m e and gas c o m p o s i t i o n ( D E A Q = 3M, T = 165 ° C ) . 180 0 . 1 0 A - 15. 27 CO, ; 15 .27. H,S ; baL N 2 X - 30. 07 15 .07 H,S ; baL N2 • - 15. 57 C 0 2 ; 29 .97 H ? ; baL "I 3 0 . 0 8 o B 2 O i—i K E-55 w a Z o u w w « « 0 . 0 6 0 . 0 4 0 . 0 2 x x g 0 . 0 0 0 . 0 1 2 . 0 2 4 . 0 3 6 . 0 TIME (h) 4 8 . 0 6 0 . 0 Figure 6.6: BHEED concentrations as a function of time and gas composition (DEAQ = 3M, T = 165 °C). 181 0.05 0.04 A - 15.27. CO, ; 15. 27. H,S ; baL N2 X - 30.07. CO, ; 15. 07. H,S ; baL N2 • - 15.57 CO* ; 29 . 97 ; baL N2 0.03 0.02 0.01 0.00 J L . 0.0 12.0 24.0 36.0 TIME (h) 48.0 60.0 Figure 6.7: HEI concentrations as a function of time and gas composition (DEAQ = 3M, T = 165 °C). 182 0.10 o a 0.08 A - 15.27. CO, } 15.27 H2S ; baL N2 X - 30.07 CO, } 15.07. H,S ; baL N2 • - 15.57 CO* r 29.97. H*S ; baL N2 55 o « H 55 W CJ 55 o CJ W w PQ 0.06 0.04 0.02 h A 0.00 2 _ i _ 0.0 12.0 24.0 36.0 TIME (h) 48.0 60.0 Figure 6.8: BHEI concentrations as a function of time and gas composition (DEA Q = 3M, T = 165 °C). 183 The only mixed gas run conducted by Choi (12) was performed by f i r s t saturating the so l u t i o n with 1480 kPa of H2S at room temperature followed by contact with 4238 kPa of C0 2 at 175 °C f o r 4 hr. The procedure s i g n i f i c a n t l y hindered the s o l u b i l i t y of C0 2 i n the amine sol u t i o n . Therefore, the reduced rate of DEA degradation compared to a C0 2 run can be linked to the low concentration of C0 2 i n the amine sol u t i o n . Since most of the degradation compounds formed i n the study were not i d e n t i f i e d , a comparison of product spectra with the present study cannot be made. 6.2 EFFECT OF OXYGEN The formation of ketones was i n i t i a l l y thought to be due to oxidation by the 0.1 mole% oxygen impurity i n the COS feed. However, the r e l a t i v e l y lower s o l u b i l i t y of oxygen i n water (1) and, by inference, i n amine so l u t i o n s , coupled with the fa c t that the ketones were formed within h a l f hour of each run make t h i s u n l i k e l y . Further, the absence of well known amine oxidative degradation products ( v i z . formic a c i d propionoic a c i d and o x a l i c a c i d (84)), demonstrates that oxidative degradation was not occuring i n the COS-DEA system. In order to remove any doubts i n t h i s regard, a run was conducted following the usual procedure, except that the DEA solution used was i n i t i a l l y exposed to a i r f o r about 16 hours. In addition, the reactor was not purged p r i o r to the commencement of the run. These actions were taken to ensure that oxygen was present i n the reactor. Table 6.1 shows the concentrations of acetone, butanone and DEA i n t h i s run and i n a corresponding run 184 conducted i n a thoroughly purged environment. The s i m i l a r concentrations i n both runs provide conclusive proof that DEA oxidation by molecular oxygen was not responsible f o r the formation of the ketones. Table 6.1: Contribution of oxygen to degradation i n COS-DEA system (DEAQ = 30 wt%, T = 150 °C, P C Q S = 345 kPa). TIME CONCENTRATIONS (MOLES/L) PURGED SYSTEM UNPURGED SYSTEM HOURS ACET BUT DEA ACET BUT DEA 0 0 .000 0.000 3.01 0.000 0 .000 3.00 2 0 .006 0.000 3.06 0.005 0.000 2.98 6 0 .007 0.002 2.91 0.007 0.002 2.86 9 0 .010 0.006 2.83 0 .010 0.007 2.77 12 0 .013 0.011 2.76 0.011 0.010 2.69 24 0 .016 0.014 2.47 0.019 0.016 2.45 30 0 .019 0.016 2.31 0.020 0.015 2.30 36 0 .021 0.017 2.18 0 .021 0.015 2.17 48 0 .015 0.016 1.93 0.022 0.017 1.91 185 6.3 EFFECTS OF DEGRADATION COMPOUNDS The e f f e c t s of the various degradation products on the degradation of DEA were studied by conducting degradation runs with 30% aqueous DEA solutions spiked with the degradation compound of i n t e r e s t . In the runs described in sections 6.3.1 to 6.3.6 below, 0.25 moles of the degradation compound of i n t e r e s t was added to the aqueous DEA solution and the mixture was contacted with 10.5 mL of CS 2 at 180 °C. CS 2 was chosen as the degrading agent because the CS2-DEA system at 180 °C behaves l i k e the COS-DEA systems at a l l temperatures used i n t h i s study. Therefore, i n terms of the water soluble products, the r e s u l t s f or a run should be applicable to a l l the COS-DEA systems investigated and the CS2-DEA systems at 180 °C. The r e s u l t s from each of these runs were then compared with the r e s u l t s from the corresponding non-spiked (regular) run. Ethanol and acetaldehyde were c l a s s i f i e d as minor degradation compounds because of t h e i r low concentrations i n the degraded DEA s o l u t i o n s . Nevertheless, since they are oxygenated compounds, i t was decided to check whether t h e i r low concentrations were due to fast transformations to ketones under the reaction conditions. 6.3.1 EFFECT OF ETHANOL The degradation of the ethanol-spiked solution r e s u l t e d i n higher concentrations of acetone, butanone and a c e t i c a c i d , but lower concentrations of MEA within the f i r s t four hours (see Figs. 6.9a and 186 6.9b). However, a f t e r rrine hours the concentrations of the ketones and ac e t i c a c i d were comparable with t h e i r respective concentrations i n the regular run, but the MEA concentration remained lower. This r e s u l t suggests that ethanol enhances the production of a c e t i c a c i d and ketones, but i n h i b i t s MEA production. Considering the fact that ethanol has two carbon atoms as opposed to acetone and butanone which have three and four carbon atoms res p e c t i v e l y , i t i s u n l i k e l y that these compounds were produced d i r e c t l y from ethanol. I t i s probable that ethanol was dehydrogenated to acetaldehyde which, i n turn, produced the ketones and ace t i c a c i d . The equal concentrations recorded f o r the ketones and ac e t i c a c i d i n both runs at 9 hr suggest an approach to equilibrium. 6.2.2 EFFECT OF ACETALDEHYDE As shown by Figs. 6.10a and 6.10b, degradation of the acetaldehyde-spiked solution r e s u l t e d i n s i g n i f i c a n t increases i n the rates of production of acetone, a c e t i c a c i d and butanone within the f i r s t four hours. The increases were three f o l d i n the f i r s t two hours. The increase i n a c e t i c a c i d concentration was accompanied by an increase i n the rate of production of HEA. By the 25 t^ hour, the rates of production of these compounds had decreased such that t h e i r concentrations i n the spiked and regular runs were comparable. The concentrations of MEA were higher i n the spiked run while the DEA concentrations were lower. This run a l s o produced higher concentrations of ETAHEAME. These observations i n d i c a t e that acetaldehyde i s involved i n the production of a c e t i c acid, acetone and butanone. 187 Figure 6.9: Chromatograms of p a r t i a l l y degraded DEA solutions of 3M i n i t i a l concentrations degraded with 10.5 mL of CS 2 at 180 °C (a: regular run; b: ethanol-spiked run). 188 Figure 6.10: Chromatograms of p a r t i a l l y degraded DEA solutions of 3M i n i t i a l concentrations degraded with 10.5 mL of CS 2 at 180 °C (a: regular run; b: acetaldehyde-spiked run). 189 The comparable concentrations of these compounds at the l a t e r stages of both runs may also be due to an approach to equilibrium brought about by some l i m i t i n g reactants. There was extensive polymerisation of acetaldehyde i n the spiked run, thereby reducing the amount a v a i l a b l e f o r the reactions. This also contributed to the decline i n the production of the ketones at the l a t e r stages of the run. 6.3.3 EFFECT OF ACETIC ACID The r e s u l t s of the ac e t i c acid-spiked run indicate that the ketones were not formed v i a a c e t i c a c i d . In f a c t , t h e i r formation was e n t i r e l y suppressed. However, the rate of degradation of DEA was increased s i g n i f i c a n t l y , r e s u l t i n g i n much higher concentrations of the high b o i l i n g degradation compounds than i n the regular run. The MEA concentration was lower due to increased conversion to HEA (see Figs. 6.11a and 6.11b). The formation of MEA implies that the hydroxyethyl group was released from DEA, yet no ketones were formed. This could be due to the fac t that under the a c i d i c condition of the run, transformation of the hydroxyethyl r a d i c a l was i n h i b i t e d . It probably reacted with a c e t i c a c i d since i t i s impossible to remain as such i n the l i q u i d phase. A l o t of s o l i d product was formed i n t h i s run. Kennard (14) observed the rate of DEA degradation by CC^ to increase with so l u t i o n pH. Since the ac e t i c a c i d spiked s o l u t i o n had a lower pH than the s o l u t i o n used f o r the regular run, the increase i n the rate of DEA degradation cannot be at t r i b u t e d to the decrease i n solution pH. 190 Figure 6.11: Chromatograms of p a r t i a l l y degraded DEA solutions of 3M i n i t i a l concentration degraded with 10.5 mL of CS 2 at 180 °C (a: regular run; b: a c e t i c acid-spiked run). 191 It i s not cl e a r at t h i s stage why the a c e t i c a c i d spiked run resu l t e d i n an increased rate of DEA degradation. 6.3.4 EFFECT OF ACETONE The acetone-spiked run resu l t e d i n s l i g h t l y reduced concentrations of butanone and DEA. In spite of the acetone production expected, the acetone peak in the chromatogram decreased progressively. This suggests that the formation of acetone may involve an equilibrium r e a c t i o n , such that the presence of acetone at the i n i t i a l stages s h i f t s the equilibrium against further production of acetone. The rates of production of ac e t i c ac i d and MEA increased within the f i r s t s ix hours, but by the 2 5 t h hour, t h e i r concentrations were s i m i l a r to those obtained i n the regular run. Acetone thus seems to a f f e c t the i n i t i a l rates of formation/depletion of MEA and a c e t i c a c i d only s l i g h t l y . 6 . 3 . 5 EFFECT OF BUTANONE Higher concentrations of acetone and a c e t i c a c i d were recorded within the f i r s t four hours of the run. By the 1 2 t n hour, t h e i r rates of production had declined such that acetone concentration was lower than i n the regular run while the a c e t i c a c i d concentration was s i m i l a r to the concentration i n the regular run. Except at 2 hr when the MEA concentration was lower than i n the regular run, other samples taken up t i l l the 1 2 t h hour showed higher MEA concentration than i n the regular run. Similar DEA concentrations were recorded i n both runs. 192 6.3.6 EFFECT OF ETHYLENE GLYCOL The production of MEA suggested that protonated DEA molecules were los i n g hydroxyethyl groups. Chakma (18) who had studied the CO2-MDEA system at elevated temperatures, suggested that the hydroxyethyl group released from MDEA produced ethylene g l y c o l v i a ethylene oxide. In t h i s study however, ethylene g l y c o l was not detected. It i s known that aldehydes and ketones could be produced from the transformations of substituted d i o l s (85). In order to check whether the apparent absence of ethylene g l y c o l i n t h i s study was due to the fast transformation to acetaldehyde or ketones, an ethylene glycol-spiked run was conducted. No increases were observed i n the concentrations of the ketones. This indicated that acetaldehyde and ketones were not formed by rapid tranformations i n v o l v i n g ethylene g l y c o l . 6.3.7 EFECTS OF ETHYL DIETHANOLAMINE AND ETHYL AMINOETHANOL Methanol, ethanol, acetaldehyde, acetone, a c e t i c a c i d and butanone a l l contain a l k y l groups, whereas DEA which was the s t a r t i n g material does not. Examination of the product spectrum of the degraded solutions shows the presence of two a l k y l alkanolamines, v i z . EDEA and EAE. Therefore, i t was decided to check whether or not these compounds could produce the low b o i l i n g degradation compounds with a l k y l groups. The tests were done by degrading IM solutions of EDEA and EAE at 180 °C with 10.5 mL of CS 2. Figures 6.12 and 6.13, which are chromatograms of 193 la < Id Figure 6.12: Chromatogram of p a r t i a l l y degraded EDEA solu t i o n of IM i n i t i a l concentration degraded with 10.5 mL of CS 2 at 180 °C for 30 hours. Figure 6.13: Chromatogram of p a r t i a l l y degraded EAE sol u t i o n of IM i n i t i a l concentration degraded with 10.5 mL of CS2 at 180 °C f o r 24 hours. 195 samples withdrawn from these runs, show that EDEA and EAE are degraded by CS2 and by inference COS, to form acetone, a c e t i c a c i d and butanone among other products. The runs also showed the production of ethyl amine from EAE which i n turn was formed from EDEA. This trend i s consistent with the loss of a hydroxyethyl group from the parent compound as previously observed i n the formation of MEA from DEA. The fact that the hydroxyethyl group was released rather than the a l k y l group, coupled with the production of a c e t i c a c i d and the ketones, demonstrate that these low b o i l i n g degradation compounds were formed through complex transformations of the hydroxyethyl r a d i c a l . Two further runs were then performed using DEA solutions spiked with EDEA and EAE to check the contributions of these compounds to DEA degradation. As shown by Tables 6.2 and 6.3, spiking with EDEA and EAE caused increases i n the rates of production of acetone, butanone and also a c e t i c a c i d . Acetic a c i d was not included i n the table because the amount formed was only i n f e r r e d from the GC peak areas. Beyond 12 hours, s i m i l a r concentrations were recorded for acetone and butanone i n the spiked and regular runs. The approach to equilibrium suggests that acetone and butanone may have been produced from some equilibrium reactions. The MEA concentration was i n i t i a l l y lower i n the spiked runs, but approached the same maximum value as i n the regular run. The increased conversion of MEA to HEA i n the spiked run, due to the increased production of a c e t i c a c i d , r e s u l t e d in a lower f i n a l concentration of MEA. The concentrations of DEA are comparable at the i n i t i a l stages, but at the l a t t e r stages of the EDEA spiked run, lower DEA concentrations were recorded than i n the regular run. 196 Table 6.2: Concentratiens of DEA and the low b o i l i n g degradation compounds i n the regular and the EDEA-spiked runs* (DEA Q = 3M, EDEA0 = 0.25M, T = 180 °C, CS 2 volume = 10.5 mL). TIME REGULAR RUN SPIKED RUN HOUR ACET BUT MEA DEA ACET BUT MEA DEA 0 0 .00 0. 00 0. .00 3.10 0 .00 0.00 0.00 3.10 2 0 .01 0. 00 0. .11 3.08 0 .04 0.01 0.00 3.05 4 0 .02 0. 02 0. .23 2.85 0 .06 0.03 0.17 2.82 6 0 .06 0. 03 0. .35 2.54 0 .08 0.04 0.33 2.63 9 0 .08 0. 04 0, .48 2.15 0 .08 0.05 0.46 2.29 12 0 .07 0. 04 0, .57 1.87 0 .08 0.05 0.56 1.53 25 0 .03 0. 03 0. .46 0.88 0 .06 0.05 0.45 0.85 30 0 .04 0 . 04 0 .48 0 .76 0 .05 0 .04 0.43 0.59 48 0 .03 0. 04 0 .35 0 .45 0 .03 0.04 0.23 0.36 * The experiments reported i n Tables 6.2 and 6.3 were performed i n a glass l i n e d reactor. . The reported concentrations are higher than what would be obtained i n a reactor without the l i n e r . 197 Table 6.3: Concentrations of DEA and the low b o i l i n g degradation compounds i n the regular and the EAE-spiked runs (DEAQ = 3M, EAE Q = 0.25M, T =180 °C, CS 2 volume = 10.5 mL). TIME REGULAR RUN SPIKED RUN HOUR ACET BUT MEA DEA ACET BUT MEA DEA 0 0 .00 0 .00 0.00 3 .10 0.00 0 .00 0 .00 3.08 2 0 .01 0 .00 0.11 3 .08 0.04 0 .02 0 .06 3.00 4 0 .02 0 .02 0.23 2 .85 0.05 0 .03 0 .18 2.69 6 0 .06 0 .03 0.35 . 2 .54 0.06 0 .04 0 .33 2.49 9 0 .08 0 .04 0.48 2 . 15 0.07 0 .04 0 .46 2.24 12 0 .07 0 .04 0 .57 1 .87 0.06 0 .04 0 .56 2.00 25 0 .03 0 .03 0.46 0 .88 0.04 0 .04 0 .46 1.03 30 0 .04 0 .04 0.48 0 .76 0.04 0 .04 0 .44 0.75 48 0 .03 0 .04 0.35 0 .45 0 .02 0 .04 0 .25 0.43 The EAE run also provides an opportunity to evaluate the gas t r e a t i n g p o t e n t i a l of t h i s amine. Sharma and Danckwerts (48) had found EAE to be over 10 times more e f f e c t i v e than MEA and DEA i n absorbing COS. However, since there were no data on the resistance of EAE to degradation, no d e f i n i t e conclusions could be reached on i t s gas t r e a t i n g p o t e n t i a l . 198 Figure 6.14: EI mass spectrum of the compound i d e n t i f i e d as Ethyl amine in the p a r t i a l l y degraded EAE so l u t i o n . Figure 6.15: EI mass spectrum of the compound i d e n t i f i e d as Ethyl acetamide i n the p a r t i a l l y degraded EAE solu t i o n . 199 Figure 6.16: EI mass spectrum of the compound i d e n t i f i e d as Ethyl thiazolidone i n the p a r t i a l l y degraded EAE s o l u t i o n . Figure 6.17: EI mass spectrum of the compound i d e n t i f i e d as Ethyl thiazolidone-2-thione i n the p a r t i a l l y degraded EAE solution. 200 The present r e s u l t s show that EAE i s degraded by COS and CS2 just l i k e DEA. In a d i t i o n to acetone, butanone and a c e t i c a c i d , other degradation products t e n t a t i v e l y i d e n t i f i e d from the EI mass spectra were ethyl amine, ethyl acetamide, ethyl thiazolidone and ethyl thiazolidone-2-thione. The EI spectra of these compounds are shown i n Figs. 6.14 to 6.17. No s o l i d s were formed i n the EAE system, hence less f o u l i n g occurs. EAE degrades fa s t e r than DEA since 65% of the amine was l o s t i n 24 hours compared to a 55% DEA loss under s i m i l a r conditions. Since the major degradation compounds have r i n g structures, the amine could be recovered by the addition of a base, as i s done i n the case of HEOD (18). Therefore degraded EAE solutions may be amenable to the same chemical p u r i f i c a t i o n methods as those used f o r degraded DEA so l u t i o n s . 6.3.8 EFFECT OF WATER The r o l e played by water i n the degradation of DEA by COS and CS2 was investigated by conducting a run with a solu t i o n c o n s i s t i n g of 30% DEA and 70% MDEA at 150 °C and 345 kPa of COS for 48 hours. The temperature of 150 °C was chosen because i t has been shown that MDEA degradation at t h i s temperature i s n e g l i g i b l e within 48 hours (18). The samples from t h i s run were very viscous and d i f f i c u l t to draw int o the syringe. This affected the r e p r o d u c i b i l i t y of the GC a n a l y s i s . As shown by F i g . 6.18, degradation i n the non-aqueous system was s i g n i f i c a n t l y reduced, the concentration of the amine being f a i r l y 201 10 A = NON-AQUEOUS x = AQUEOUS $-X A A * x A X _L 0.0 12.0 24.0 TIME 36.0 48.0 60.0 (h) Figure 6.18: Concentrations of DEA as a function of time i n aqueous and non-aqueous sytems i n contact with 345 kPa of COS at 150 °C. 202 constant. Degradation compounds produced i n very low concentrations include BHEP, HEOD, HEI, THEED and ETAHEAME. THEED could have been formed by the d i r e c t reaction of DEA with DEA thiocarbamate. Dehydration of THEED to produce BHEP would provide some water for hydrolysis of COS to CO2 and hence the formation of HEOD. Since MEA was not detected, i t i s c l e a r that the presence of water i s e s s e n t i a l f or i t s formation. DEA usually contains some MEA as an impurity. This may be responsible for the small amounts of HEI formed. Degradation products such as BHEED and BHEI were also i n s i g n i f i c a n t i n the non-aqueous system and t h i s could be li n k e d to the absence of substantial amounts of MEA. A low b o i l i n g compound having the same retention time as acetone, but i d e n t i f i e d as ethane t h i o l , was also produced. In summary, water plays a s i g n i f i c a n t role not only i n terms of the rate of degradation, but also i n i n i t i a t i n g the hydrolysis reactions and consequently the formation of MEA and the other low b o i l i n g degradation compounds. 6.3.9 EFFECT OF MONOETHANOLAMINE Three runs were conducted to study the e f f e c t s of MEA on DEA degradation. In the f i r s t run, an aqueous mixture containing approximately IM MEA and 3M DEA, was heated and maintained at 165 °C under a blanket of nitrogen for 48 hours. No degradation compounds were formed i n t h i s run; t h i s provides an i n d i c a t i o n that DEA and MEA do not react d i r e c t l y and are not thermally degraded at 165 °C. 203 The second run was conducted f o r 32 hours under the same conditions as i n the f i r s t run except that 758 kPa. of carbon dioxide was used i n place of nitrogen. Degradation products such as BHEED, HEOD, BHEP, HEI, THEED and BHEI were formed. As shown in Table C.42 i n appendix C, the concentrations of DEA and MEA decreased while those of BHEI, HEI and BHEP increased with time. The HEOD concentration increased to a maximum value and then f e l l s l i g h t l y . Both THEED and BHEED concentrations a l s o passed through maxima. Since the degradation of aqueous DEA by produces mainly BHEP, HEOD and THEED, the formation of BHEI, BHEED and HEI i n aqueous MEA/DEA/C02 system can be a t t r i b u t e d to reactions i n v o l v i n g MEA, DEA and t h e i r respective carbamates. The behaviour of MEA when subjected to a gas mixture containing CO2 and H2S, as was the case i n the p a r t i a l l y degraded DEA-COS systems, was investigated i n the t h i r d run. A 2M MEA solution was contacted with a gas mixture containing 15.5% CO2, 29.9% H2S i n nitrogen, f o r 48 h at 165 °C and a p a r t i a l pressure of 1.55 MPa. Acetone and butanone were detected i n the p a r t i a l l y degraded solution. The formation of the ketones would imply the presence of ammonia, i n accord with the formation of MEA from DEA, EAE from EDEA, and ethyl amine from EAE. The non-detection of ammonia may be due to i t s high v o l a t i l i t y as well as the i n a b i l i t y of the FID to detect the gas. Ammonia was probably involved i n the formation of the pyridines. HEI was the only high b o i l i n g degradation compound formed, a l b e i t at low concentration. This may be as a r e s u l t of the p r e f e r e n t i a l protonation of MEA thereby l i m i t i n g the amount of MEA carbamate a v a i l a b l e to form appreciable 204 quantities of hydroxyethyl ethylenediamine (HEED) and oxazolidone (OZD), the other degradation products of MEA-CO2 reactions. 6.3.10 EFFECT OF BHEED The trends in BHEED and THEED concentrations suggest that they are intermediate compounds. THEED i s known to dehydrate to BHEP (13,14). T h e o r e t i c a l l y , BHEED could dehydrate in a s i m i l a r manner to produce HEP. BHEED could also react with CO2 to form BHEI. In order to determine the degradation compounds o r i g i n a t i n g from BHEED, an aqueous sol u t i o n of 0.2M BHEED was contacted with C0 2 at 180°C. Analysis of reaction samples showed the gradual formation of BHEI and by the 6 t h hour, the concentration of BHEI was 0.17M. HEP was not detected, but trace amounts of HEOD were formed. I t appears that CO2 reacted with BHEED to form BHEED carbamate, which was then dehydrated to form BHEI. Perhaps i n a CO2 l i m i t i n g environment, dehydration of BHEED would have produced HEP. BHEED carbamate i n aqueous s o l u t i o n may also e s t a b l i s h an equilibrium with MEA and DEA carbamate, the l a t t e r forming HEOD. The very low concentration of HEOD and the absence of HEP i n t h i s run suggests that BHEED, i n the presence of excess CO2, i s more l i k e l y transformed to BHEI than to HEOD or HEP. The behaviour of BHEP, HEOD and THEED i s well documented by Kennard (16) and the mechanisms for t h e i r formation are known. Therefore, no runs were conducted i n respect to these compounds. CHAPTER 7 SOLUBILITY AND HYDROLYSIS OF CARBONYL SULPHIDE When COS i s absorbed into aqueous solutions, i t hydrolyzes to CO2 and H2S according to the o v e r a l l r e a c t i o n : COS + H20 = C0 2 + H2S 7.1 Thompson et a l . (56) have obtained rate constants f o r the hydrolysis at temperatures between 15 and 47 °C. Sharma (57) has shown that the hydrolysis i s catalysed by bases. Thus an aqueous solution o r i g i n a l l y containing DEA and COS, i s eventually made up of the hydrolysis products, unreacted COS and i o n i c species derived from t h e i r i n t e r a c t i o n s with DEA and water. S o l u b i l i t y and hydrolysis proceed r e l a t i v e l y f a s t e r than amine degradation. Therefore, the extent of degradation i s l a r g e l y determined by the equilibrium composition of the sol u t i o n p r i o r to the commencement of degradation. This chapter describes experiments conducted to e s t a b l i s h the equilibrium composition of the COS-DEA system before the commencement of s i g n i f i c a n t degradation. The r e s u l t s of the experiments are analysed and an equ i l i b r i u m model i s developed to predict the equilibrium concentrations of COS, H 2S and C0 2. These r e s u l t s could be used i n the development of a k i n e t i c model f o r DEA degradation by COS, as well as i n the design and modelling of COS absorption processes u t i l i z i n g DEA. 205 206 7.1 THEORY The attainment of equilibrium i n a system c o n s i s t i n g i n i t i a l l y of gaseous COS and an aqueous DEA solution may be regarded as involving the following steps: ( i ) Physical absorption of COS into water, ( i i ) Reaction between DEA and absorbed COS to form DEA thiocarbamate, ( i i i ) Hydrolysis of absorbed COS and DEA thiocarbamate to y i e l d CO2 and H 2S, (iv) R e d i s t r i b u t i o n of COS, C0 2, H 2S and t h e i r associated compounds between the l i q u i d and gas phases. At low temperatures, steps ( i ) and ( i i ) are very much f a s t e r than ( i i i ) and i t i s therefore possible to measure absorption without s i g n i f i c a n t hydrolysis during the early stages of contact between COS and aqueous DEA solutions. By contrast, at elevated temperatures, steps ( i i i ) and (iv) are rapid and d i s t i n c t i o n between absorption and hydrolysis i s not e a s i l y achieved experimentally. 1. Absorption Regime (Steps i and i i ) The physical absorption of gas i into water may be described by Henry 1 s law, i . e . H i = p i / c i 7 - 2 where P^ and c^ denote the p a r t i a l pressure and l i q u i d phase concentration of p h y s i c a l l y absorbed species i , r e s p e c t i v e l y . When component i reacts to form i o n i c complexes, such as DEA thiocarbamate, 207 ^COS R2NCOS" H + = R2NH + COS 7 . 3 then Henry' s Law may be written as Hi* = P j / C i * 7 . 4 * where Cj_ now denotes the t o t a l ( i . e . p h y s i c a l l y absorbed and chemically bound) concentration of component i i n solution. The temperature v a r i a t i o n of the Henry's constants may be represented by the Arrhenius expression: In {HL*) = Ai + Bi/T 7 . 5 where the constants A^ and can be obtained from l e a s t square f i t s of the semilogarithmic plots of vs 1/T. 2. Hydrolysis Regime (Steps i i i and iv) The DEA thiocarbamate formation i s a rapid reaction and the o v e r a l l COS hydrolysis i s therefore governed, i n e f f e c t , by the hydroly s i s of DEA thiocarbamate: R2NCOS" H + + H 2 0 = R2NH + C 0 2 + H 2S 7 . 6 208 The newly formed CO2 and p a r t i c i p a t e i n the well known reactions for aqueous DEA solutions (36-41): K l R 2NH 2 + = H + + R2NH 7.7 K2 R2NCOO" + H20 = R2NH + HCO3" 7.8 K3 + H20 + C0 2 = H + + HCO3 7.9 K 4 • H20 = H + + OH 7.10 - K 5 + HCO3 = H + + CO3 7.11 K6 + H2S = H + + HS 7.12 K 7 + HS = H + + S 7.13 Reactions 7.3, 7.7 to 7.13 can be described by a model of the type f i r s t proposed by Kent and Eisenberg ( 3 9 ) : K-L = [H +] [R 2NH] / [ R 2 N H 2 + ] 7.14 K 2 = [R 2NH] [HCO3"] / [R 2NCOO"] 7.15 209 and K 3 = [H + ] [HC03"] / tco 2] K 4 = [H + ] [OH"] K5 = (H + ] [CO3"] / [HCO3"] K6 = [H+] [HS"] / [H2S] K 7 = [H + ] [S""] / [HS"] Kcos = [R2NH ] [COS] / [R2NCOS'] [H + HC02 = = PC02 / [co 2] HH2S = = PH2S / [H2S] 7.16 7.17 7.18 7.19 7.20 7.21 7.22 7.23 HCOS = PCOS / [ C 0 S ] 7 - 2 4 where [i] denotes the concentration of component i i n solu t i o n . As was the case f o r the Kent-Eisenberg model, Eqs. 7.14 to 7.21 assume an excess of water, unit a c t i v i t y c o e f f i c i e n t s and incorporate system non- i d e a l i t i e s i n t o the equilibrium constants governing the carbamate, thiocarbamate and amine protonation reactions. In addition to the mass action equations and Henry1 s law, the following charge and material balances apply: Charge: [R 2NH 2 + ] + [H + ] = [HCO3"] + [R2NCOO"] + 2 [CO3"] + [OH'] + [HS"] + 2[S""] + [R2NCOS"] 7.25 DEA: m = [R2NH] + [R2NCOO"] + [R2NCOS"] + [R 2NH 2 +] 7.26 H2S: m 0 ^ 2 2 = [H2S] + [HS"] + [S""] 7.27 2 1 0 C O o : m OQQ2 =. [C02] + [HC03"] + [R2NC00"] + [CO3""] 7.28 C O S ; m o Q̂g = [COS] + [R2NCOS"] 7.29 where m and a.^ represent the t o t a l DEA concentration and the DEA loading by a c i d gas i , r e s p e c t i v e l y . The above 16 equations contain 20 unknown operating variables (14 concentrations: m, [H +], [R2NH], [R 2NH +], [HCO3"], [R2NCOO"], [C02], [OH"], [C03""], [HS"], [H2S] , [S""], [R2NCOS"], [COS]; 3 p a r t i a l pressures: PQQ2' PH2S' pCOS ; ^ loadings: O^.Q2' o^s' °COS' ' T n e s Y s t e m i s therefore f u l l y s p e c i f i e d provided the equilibrium and Henry1 s constants are known and four operating variables are given. For most design c a l c u l a t i o n s the l a t t e r are the three p a r t i a l pressures (pc02' I?H2S' P^os * a n c * t^ i e t o t a-'- D E A concentration (m). Equations 7.14 to 7.29 were combined to y i e l d four independent model equations: PH2S = (HH2S 1 K 6 K 7 ) ( A [ H + ] 2 1 ( 1 + [ H + ] 1 K 7 n 7.30 7.31 211 [H+] P C O S where: A B C K' A (1 + K ? / <K7 + [H + ] )) / (1 + m / K^K' ) + B (1 + K 2K 5 / (K 2K 5 + K 2 [H + ] + m [H + ] / K' ) ) / (1 + m / K^K' ) + K 4 / ( [H + ] (1 + m / K1K' )) + (C/(m-C)) (1 + H + / K-L + ( P c o 2 / H c o 2 ) (K 3 / (K 2H +))) (m / K ) / (1 + m / K-̂ K* ) 7.32 (C / (m-O) ( K c o s H c o s H +) (1 + (H + / Kx) + PCOS K3 / < K2 HC02 H + ) ) 7 , 3 3 m °H2S " PH2S 1 HH2S m °t02 " PC02 1 HC02 7.34 7.35 M ^ O S " P C O S 1 H C O S 7.36 1 + [H+] / K x + (K 3 / K 2) ( P c o 2 / ( H c o 2 [H +])) + P C O S / * KCOS H C O S H + ) > 7.37 The variables m, PQO2' pH2S' P C O S ' QC02 a n d ^23 c o u l d b e r e a d i l y found experimentally. By contrast, <eos w a s v e r Y small under the experimental conditions and therefore d i f f i c u l t to determine accurately. 212 7.2 EXPERIMENTAL EQUIPMENT AND PROCEDURE The experiments were conducted with the 600 mL s t a i n l e s s s t e e l reactor described i n d e t a i l i n Chapter 3. 7.2.1 PROCEDURE 100 mL of the aqueous DEA so l u t i o n of the desired concentration were placed i n the reactor which was then sealed t i g h t l y . Nitrogen was passed into the reactor to purge the unit of oxygen. The l i q u i d i n l e t and gas sampling valves were closed and the reactor was heated to the desired operating temperature while s t i r r i n g i t s contents. The pressure increase was recorded as the vapour pressure ( P Q E A ) o f t n e aqueous DEA s o l u t i o n at the operating temperature. COS from a pre-weighed st e e l bomb was passed into the reactor to a t t a i n a t o t a l pressure P T such that PT " PDEA equalled the desired p a r t i a l pressure of COS. As COS was absorbed into the DEA s o l u t i o n , the t o t a l pressure dropped and more COS was added as necessary to maintain the system pressure at P T. Equilibrium COS s o l u b i l i t y was deemed to be achieved when the system pressure remained constant for times varying from 7 min at 180 °C to over 25 min at 120 °C, without the addition of COS. At t h i s point, the s t e e l bomb was disconnected from the reactor and re-weighed. Hydrolysis of the dissolved COS to H 2S and C 0 2 , and the subsequent exchange of gases between the gas and l i q u i d phases, res u l t e d i n a gradual increase of the t o t a l reactor pressure. When the pressure reached a constant value thereby i n d i c a t i n g true equilibrium, both the gas and l i q u i d 213 phases were sampled. Gas phase samples were obtained by opening and c l o s i n g the gas sampling valve thereby trapping the sample gas within a short section of tubing which had been previously purged. The tubing was f i t t e d with a septum and the sample was then drawn in t o a "pressure - lok" syringe and kept for a n a l y s i s . L i q u i d phase samples were forced by the reactor pressure into a s t a i n l e s s s t e e l sampling c o i l which was then immersed i n i c e - c o l d water to reduce the temperature and pressure quickly. Two sets of experiments were conducted under the following conditions: Low temperature s o l u b i l i t y experiments: DEA concentration: 0 - 40 wt% Temperature: 20 50 °C COS p a r t i a l pressure: 345 kPa Elevated temperature hydrolysis experiments: DEA concentration: 10 40 wt% Temperature: 120 - 180 °C COS p a r t i a l pressure: 345 - 1172 kPa A few equilibrium hydrolysis experiments were also conducted at 40 C using 30 % DEA solutions and i n i t i a l COS p a r t i a l pressures of 72 - 210 kPa. 214 7.2.2 ACID GAS LOADINGS Wet chemical methods could not be used for the analysis of the samples because of t h e i r n o n - s p e c i f i c i t y . Instead, the gas trapping set-up shown i n F i g . 7.1 was used to c o l l e c t the gases dissolved i n the l i q u i d samples. The set-up i s s i m i l a r to the " C h i t t i c k " apparatus used f o r the determination of C0 2 i n carbonate samples (90). The displacement s o l u t i o n was prepared by d i s s o l v i n g 200 g of NaCl and 2 g of NaHCC>3 i n 700 mL of d i s t i l l e d water. 2 mL of Methyl Orange i n d i c a t o r and enough concentrated HC1 were added to make the solution a c i d i c . The solution was s t i r r e d to remove a l l dissolved acid gases. This so l u t i o n was placed i n the l e v e l l i n g bulb, gas burette and connecting tubing. P r i o r to sample introduction, the l e v e l l i n g bulb was moved up along a t r i p o d stand to bring the l e v e l of the displacement so l u t i o n to the zero mark i n the gas measuring burette. The sample i n l e t valve and sampling points were opened and nitrogen was passed into the system to purge i t of oxygen and/or carbon dioxide. The pressure was allowed to b u i l d up within the system by quic k l y c l o s i n g a l l outlets before the flow of nitrogen was stopped. The sample i n l e t valve was then opened and l a t e r closed again to r a i s e the displacement solution i n the gas burette as high as po s s i b l e . The l e v e l l i n g bulb was then lowered and a period of about 15 min was allowed to elapse for the pressure and temperature to reach equilibrium. Once the temperature and pressure had s t a b i l i z e d , the l e v e l of the displacement solution i n the gas burette stayed constant unless the system was leaking. The point at which the pressure i n the system equalled atmospheric pressure was established and 215 recorded as the i n i t i a l burette reading. A f r a c t i o n of the cooled sample i n the sampling c o i l was then transferred i n t o the f l a s k . Excess d i l u t e HCl solution (2 M or 5 M) was added from the a c i d burette and l i b e r a t e d the gases dissolved i n the sample. The magnetic s t i r r e r was turned on to ensure complete mixing within the f l a s k . The a c i d gases displaced the solution i n the gas burette u n t i l the pressure within the system was equal to atmospheric pressure. Total displacement was usually achieved i n less than 30 minutes. To prevent the escape of l i b e r a t e d gases through the a c i d burette during sample introduction, the displacement solution i n the l e v e l l i n g bulb was kept at a lower l e v e l than i n the gas burette at a l l times during the displacement of the gases. Thereafter, the l e v e l l i n g bulb was moved up and down several times depending on the volume of gas displaced, to ensure uniform gas composition within the system. The point of equal pressure i n both arms of the displacement so l u t i o n was again determined and recorded as the f i n a l burette reading. "Pressure lok" gas syringes were then used to c o l l e c t gas samples from the two sampling points along the tubing. The pressure within the system was maintained at atmospheric during sampling. The ambient temperature was also monitored. 7.2.3 GAS ANALYSIS Gas samples withdrawn from the reactor and the gas trapping set-up were analyzed with a Varian (Vista 6000) gas chromatograph equipped with a CD 401 data s t a t i o n . Using helium as the c a r r i e r gas, the gas mixture 2 1 6 A flask B magnetic stir bar C magnetic stirrer D burette E sample introduction valve f;.q sampling ports G tube H gas measuring tube I leveling bulb F i g u r e 7 . 1 : G a s t r a p p i n g s e t u p ( 8 6 ) . 2 1 7 was separated i n the order N2/ C0 2, COS and H 2S by a 6' x 1/8" ID Teflon column containing Chromosil 310 packings (supplied by Supelco Inc., Oakville, Ont.). The GC was operated at 40 °C. Gases e l u t i n g from the column were sensed by a thermal condu c t i v i t y detector (TCD). Each analysis was completed within three minutes. A t y p i c a l chromatogram i s shown i n F i g . 7.2. E f f l u e n t gases from the GC were absorbed into a 30 wt% MEA solution to prevent p o l l u t i o n of the environment. Peak areas recorded for each compound were converted to volume concentrations using previously prepared c a l i b r a t i o n p l o t s (see Appendix B). The l a t t e r showed l i n e a r r e l a t i o n s h i p s between concentration and peak area f o r the range of concentrations encountered i n the study. 7.2.4 SOLUBILITY DETERMINATION AT LOW TEMPERATURES For each run, the quantity of COS fed into the reactor from the steel bomb was determined as the di f f e r e n c e between the f i n a l and i n i t i a l weights of the bomb. Using the reactor temperature, pressure and volume as well as the vapour pressure of the DEA solution < P D E A ' ' the moles of COS i n the gas phase were determined by the Peng and Robinson equation of state (87). This value was then subtracted from the moles of COS fed into the reactor to obtain the moles of COS dissolved i n the l i q u i d phase. The scale used to weigh the bomb i s accurate within 0.1 g. 2 1 8 F i g . 7 . 2 : C h r o m a t o g r a m s h o w i n g a t y p i c a l s e p a r a t i o n i n t h e C h r o m o s i l 3 1 0 t e f l o n p a c k e d c o l u m n . 219 7.2.5 HYDROLYSIS AT ELEVATED TEMPERATURES Data obtained from the analyses of the gas and l i q u i d samples were treated as follows: Gas samples 1. The previously obtained c a l i b r a t i o n curves were used to convert the GC peak areas to concentrations expressed i n vol or mole %. 2. The concentrations were normalized to obtain the mole f r a c t i o n of each gas on an acidic, gas ba s i s . 3. The p a r t i a l pressure of each gas was calculated from P i = Vi PT* where P T denotes the t o t a l p a r t i a l pressure of the a c i d gases. 4. The p a r t i a l pressures were converted to moles using the Peng- Robinson equation of state (87). Liquid samples 1. The volume of l i q u i d sample t r a n s f e r r e d to the gas trapping set- up, V s, was determined as the differe n c e between the volume of the sampling c o i l and the ad d i t i v e volumes of the residual 220 l i q u i d i n the sampling c o i l and l i n e connected to the gas trapping set-up. 2. The t o t a l volume of gas l i b e r a t e d from the l i q u i d sample, V d, was the difference between the f i n a l and i n i t i a l burette readings. 3. The t o t a l moles of acid gas l i b e r a t e d were ca l c u l a t e d using the i d e a l gas law. This was then m u l t i p l i e d by the r a t i o V^/Vg to obtain the t o t a l moles of the various gases in the l i q u i d phase of the reactor. 4. Peak areas from GC analyses were converted to vol %, which was then equated to mole % and normalized to obtain the mole f r a c t i o n of each gas. 5. The moles of the i n d i v i d u a l gases i n the l i q u i d phase of the reactor were calculated by multiplying the t o t a l moles of a c i d gas by i t s mole f r a c t i o n . 7.3 RESULTS AND DISCUSSION OF SOLUBILITY AND HYDROLYSIS RUNS In accordance with expectation, the reactor pressure was found to decline s h o r t l y a f t e r the introduction to of COS due to i t s absorption. The decline could be o f f s e t by adding more COS. At a c e r t a i n point i n time the system pressure was found to r i s e again due to hydrolysis u n t i l 221 a f i n a l constant pressure was attained. The absorption and hydrolysis regimes were c l e a r l y d i s t i n g u i s h a b l e at low temperatures, but they overlapped at elevated temperatures. 7.3.1 SOLUBILITY OF COS IN DEA SOLUTIONS AT LOW TEMPERATURES The Henry's constants f o r COS are shown i n F i g . 7.3 and the corresponding c o e f f i c i e n t s f o r Eq. 7.5 are summarized i n Table 7.1. Since the Henry's constants were c a l c u l a t e d on the premise that, at low temperatures, the hydrolysis of COS in amine solutions i s slow, the gas phase was assumed to consist only of COS, nitrogen and water vapour. To check the v a l i d i t y of t h i s assumption, the l i q u i d and gas phase compositions were determined f o r the absorption of COS i n 40 wt% DEA s o l u t i o n at 50 °C (see Run 27 i n Tables 7.3 and 7.4). The extent of hy d r o l y s i s , c a l c u l a t e d as the f r a c t i o n of the t o t a l COS that was present e i t h e r as C0 2 or H2S, was about 16%. COS constituted about 90 % of the a c i d gases i n the gas phase. Since the increase i n system pressure was used as the i n d i c a t o r of t r a n s i t i o n to hydrolysis, i t i s c e r t a i n that, at the time the system was sampled, some hydrolysis had already occurred. Therefore the extent of hydrolysis at equilibrium s o l u b i l i t y w i l l be less than 16%, j u s t i f y i n g the assumption of n e g l i g i b l e h y d r o l y s i s . The Henry' s constants obtained f o r the COS-H20 system i n the present study may be compared with e a r l i e r r e s u l t s . As seen from Table 7.2, the good agreement between the values i s an i n d i c a t i o n of the r e l i a b i l i t y of the present experimental method and data. 222 ltf O CO 10° CO PH 10" ~1 r 1 i r • 1 i - - + = 0% DEA • 0 = 1 0 % DEA - A = 2 0 % DEA 0 = 3 0 % DEA - X = 4 0 % DEA - © — • • f _U _U  L.  - —— e— o _ A ^ - M " 1 - - A -• • L-l — B Ej - 1 1 1 . X 1 X - , i 1 — X 3 . 0 3.1 3 . 2 3 . 3 10 3 /T (K" 1) 3 .4 3 . 5 F i g u r e 7.3: H e n r y ' s c o n s t a n t a s a f u n c t i o n o f t e m p e r a t u r e f o r C O S i n a q u e o u s D E A s o l u t i o n s . 223 Table 7.1: F i t t i n g constants i n the Henry's law expression f o r the COS-DEA system (T = 20 - 50 °C). DEA Cone, wt % ACOS BCOS 0 10.00 -2562.83 10 1.21 -494.73 20 0.50 -478.68 30 -0.10 -416.82 40 -0.11 -504.86 Table 7.2: Henry's constants f o r the s o l u b i l i t y of COS i n water. Henry's constants, H C Og (kPa m /mol) T Al-Ghawas Perry and This work °C et a l . (50) Green (88) 20 3.92 3.99 3.52 30 5.05 5.54 4.70 40 6.59 6.16 50 7.93 224 Table 7.3: Equilibrium data f o r the hydrolysis of COS i n aqueous DEA solutions. (The compositions are expressed i n m i l l i moles.) RUN GAS PHASE LIQUID PHASE TOTAL ERROR # C0 2 COS H2S C0 2 COS H 2S C0 2 COS H 2S % 1 31 .0 1 .6 21 .5 23.0 0.2 30. 9 54 .0 1.8 52. 4 1 .57 2 31 .7 1 . 4 21 .5 17.8 0.3 27. 6 49 .6 1.7 49. 1 0 .52 3 28 .5 1 .5 20 .4 9.8 0.4 16. 5 38 .3 1.9 36. 9 1 .93 4 31 .4 2 .7 20 .6 14.3 0.2 23. 6 45 .6 2.8 44. 2 1 .58 5 32 .0 0 .7 21 .4 12.3 BDL a 21. 3 44 .3 0.7 42. 7 1 .84 6 33 .5 1 .7 21 .4 15.9 0.1 26. 3 49 .4 1. 9 47. 6 1 .87 7 6.2 .5 4 .2 44 .4 38.1 BDL 53. 8 100 .6 4.2 98. 2 1 .25 8 65 .1 3 . 9 48 . 9 51.2 BDL 68. 0 116 .4 3.9 116. 9 0 .22 9 61 .2 8 .1 50 .5 63.2 0.3 72. 1 124 .4 8.4 122. 5 0 .77 10 64 .0 5 .8 43 .8 29.8 BDL 45. 9 93 .8 5.8 89. 7 2 .32 11 87 .5 9 .8 63 .6 34.2 BDL 59. 5 121 .7 9.8 123. 2 0 .58 12 112 .6 6 .8 80 .3 46 .7 BDL 68. 3 159 .2 6.8 148 . 6 3 .58 13 29 . 9 1 .5 24 .2 51.8 BDL 54. 1 81 .7 1.5 78. 3 2 .12 14 46 .4 2 .2 36 .4 53.1 0.3 58. 0 99 .5 2.5 94. 4 2 .68 15 33 .4 1 .2 23 .7 41.7 BDL 45. 7 75 .0 1.2 69. 5 4 .02 16 52 .2 2 .2 38 .6 46.6 0.5 55. 3 98 .8 2.7 93. 9 2 .63 17 68 .3 10 .4 51 .8 48 .7 0.3 64. 7 17 .0 10.7 116. 5 0 .21 18 51 .2 4 .3 36 . 1 18.8 0.7 32. 8 70 .1 5.0 68. 9 0 .84 19 66 .7 6 .3 50 .5 24.8 0.6 48. 4 91 .5 6.9 98. 9 3 .75 20 36 .6 3 . 1 25 .5 32.2 0.2 44. 3 68 .8 3.3 69. 8 0 .71 21 54 .8 5 .5 41 .7 • 36.1 0.4 52. 7 90 .9 5.9 94. 5 1 .90 22 71 .4 8 . 9 55 .6 37.0 0.4 59. 5 108 .4 9.2 115. 2 2 .94 23 50 .2 2 .0 35 .6 29.0 0.6 46. 3 79 .2 2.6 81. 9 1 .67 24 35 .5 3 .7 45 .9 106.2 0.9 101. 6 141 .8 4.5 147. 5 1 .94 25 26 .9 3 .1 36 .2 107.2 0.6 105. 1 134 .0 3.7 141. 3 2 .57 26 16 .1 0 .7 28 .0 96.4 0.3 89. 2 112 .5 0.7 117. 2 2 .02 27 1 . 9 62 .1 5 .2 24.0 87.0 25. 5 25 . 9 149.1 30. 7 7 .85 a BDL indicates that the COS reading was below the detectable l i m i t . Error i s calculated as the % deviation of H2S or C0 2 concentration from the mean of the C0 2 and H 2S concentrations. 225 Table 7 . 4 : Equilibrium data f o r the hydrolysis of COS (Liquid phase concentrations are expressed i n mole/mole DEA). RUN OPERATING LIQUID LOADING PARTIAL PRESSURE # CONDITIONS3 (mole/mole DEA) (kPa) C T P c o 2 COS H2S c o 2 COS H 2 ,S 1 40 150 345 0 .058 0.001 0 .078 217. 23 11. 06 150. 72 2 40 165 345 0 .045 0.001 0 .070 230. 26 10. 17 155. 81 3 40 180 345 0 .025 0.001 0 .042 214. 29 11. 65 153. 07 4 30 165 345 0 .049 0.001 0 .081 227. 59 19. 38 149. 28 5 20 165 345 0 .064 0.001 0 .110 232. 14 5. 41 155. 24 6 20 150 345 0 .082 BDL b 0 .135 234. 43 12. 19 149. 61 7 40 150 689 0 .097 BDL 0 .136 436. 48 29. 65 309. 13 8 40 135 689 0 .130 BDL 0 .172 438. 26 26. 19 328. 03 9 40 120 689 0 .160 BDL 0 .182 396. 52 52. 87 325. 87 10 30 150 689 0 .102 BDL 0 .156 446. 81 40. 55 305. 12 11 30 150 896 0 .116 0.001 0 .203 609. 45 68. 71 441. 65 12 40 150 1112 0 .118 BDL 0 .173 781. 67 47. 93 555. 52 13 40 120 345 0 .131 BDL 0 .137 194. 59 9. 76 157. 43 14 40 120 517 0 .134 BDL 0 . 147 301. 41 14. 15 235. 73 15 30 120 345 0 .142 0.001 0 . 156 217. 16 7. 72 154. 14 16 30 120 517 0 .159 BDL 0 . 188 338. 79 14. 44 249. 75 17 30 120 689 0 .166 0.002 0 .220 442. 08 67. 75 334. 33 18 20 150 517 0 .097 0.002 0 .169 358. 28 30. 38 252. 27 19 20 150 689 0 .128 0.003 0 .249 465. 39 44. 34 351. 66 20 20 120 345 0 .166 0.001 0 .229 238. 19 19. 95 165. 66 21 20 120 517 0 .186 0.002 0 .272 355. 40 36. 04 270. 11 22 20 120 689 0 .191 0.002 0 .307 462. 06 57. 75 358. 81 23 30 150 517 0 .099 0.002 0 .158 350. 85 13. 81 248. 65 24 30 40 210 0 .362 0.003 0 .346 183. 40 19. 01 235. 18 25 30 40 141 0 .365 0.002 0 .358 138. 93 16. 10 186. 08 26 30 40 72 0 .328 0.001 0 .304 83. 21 3. 52 144. 13 27 40 50 345 0 .081 0 .294 0 .086 9. 69 308. 37 26. 50 a C = DEA concentration (wt%), T = Temperature (°C), P = I n i t i a l p a r t i a l pressure of COS (kPa). b BDL indicates that the loadings f e l l below the detectable l i m i t . 226 7.3.2 HYDROLYSIS OF COS IN DEA SOLUTIONS AT ELEVATED TEMPERATURES The d i s t r i b u t i o n of the various components i n the reactor at equilibrium conditions i s shown i n Table 7.3. The data are presented i n terms of p a r t i a l pressures and solution loadings, along with the operating conditions, i n Table 7.4. By reaction stoichiometry i n Eq. 7.1, one mole of COS reacts with one mole of water to produce one mole each of C0 2 and H 2S. Therefore, the t o t a l moles of C0 2 and H 2S should be equal in each run. The deviations r e s u l t i n g from the analyses were generally below ±5 %. Due to the low concentration of COS ( p a r t i c u l a r l y i n the l i q u i d phase) i t was not always possible to detect COS with the TCD. Even when COS was detected, i t s concentration was so small that the r e l i a b i l i t y of the r e s u l t s was uncertain. The experimental r e s u l t s show that H 2S was p r e f e r e n t i a l l y dissolved r e l a t i v e to C0 2 and COS. L i q u i d loadings of carbon dioxide and hydrogen sulphide were generally two orders of magnitude (or more) higher than the COS loadings. The concentrations of hydrogen sulphide and carbon dioxide i n the l i q u i d phase also increased with increasing DEA concentration and i n i t i a l COS p a r t i a l pressure, but decreased with increasing temperature (Figs. 7.4 and 7.5). Figure 7.6 shows that the H 2S/C0 2 r a t i o i n solution, which i s a measure of the s e l e c t i v i t y f o r H 2S, decreased with increasing solution concentration, but increased with increasing temperature. This suggests that increasing the amine concentration enhances amine carbamation more than protonation, while increasing the temperature makes carbamation more d i f f i c u l t . 227 ^ 1 0 0 0 PH M + = 20% DEA o = 30% DEA A = 40% DEA 3 0 0 0 . 1 2 0 . 1 8 0 . 2 4 0 . 3 0 0 . 3 6 LIQUID LOADING (mol H 2 S/mol DEA) 0 . 4 2 Figure 7 . 4 : H2S l i q u i d loading as a function of i n i t i a l COS p a r t i a l pressure and DEA concentration at 120 °C. 228 a? Pu M, W « 00 w PH PH <J HH H PH CO O HH <5 HH HH 1000 300 0.10 0.13 0.16 0.19 0.22 LIQUID LOADING (mol C 0 2 / m o l DEA) 0.25 Figure 7.5: C0 2 l i q u i d loading as a function of i n i t i a l COS p a r t i a l pressure and DEA concentration at 120 °C. 229 CM O u I—I o & CO CM o O CO 2.5 2.0 1.5 1.0 0.5 + = 120°C o = 150°C A = 165°C • = 180°C JL A O • A _L 0.0 10.0 20.0 30.0 40.0 DEA CONCENTRATION (wt%) 50.0 Figure 7.6: S e l e c t i v i t y as a function of temperature and DEA concentration. 230 The data at 40 C show comparable concentrations of CO2 and H2S in solution, with p a r t i a l pressures of H 2S being higher than those of C0 2. This i s i n contrast with the trend at high temperatures where the p a r t i a l pressure of H2S was lower than that of C02. It appears that at such low temperatures the ac i d gas loadings were high, causing desorption of H 2S into the gas phase. Desorption of H2S i n amine systems with high H2S and C0 2 l i q u i d loadings have been reported in the l i t e r a t u r e (89). Figures 7.7 and 7.8 show t y p i c a l p l o t s of p a r t i a l pressure versus loading. The wider spread of the H 2S plots i s i n d i c a t i v e of i t s p r e f e r e n t i a l absorption. Henry's constants plotted against inverse temperature (see Figs. 7.9 and 7.10), were also found to follow the Arrhenius r e l a t i o n s h i p . The plots tend towards a convergence temperature which appears to be lower f o r H 2S than C02. This trend could be l i n k e d to the various reactions occurring in the system as well as the higher s e l e c t i v i t y of H 2S. When H 2S i s absorbed into the amine soluti o n , the absorption takes two forms: chemical and physical absorption. As the temperature increases, the solution becomes more concentrated and the p h y s i c a l l y dissolved H 2S decreases. At a temperature T c, which i s the convergence temperature, the concentration of the amine solution i s very high and physical d i s s o l u t i o n becomes n e g l i g i b l e . At t h i s temperature, the concentration of the amine solu t i o n i s almost independent of the i n i t i a l concentration, r e s u l t i n g i n equal absorption of H 2S. Since the equilibrium p a r t i a l pressure of H 2S i s dependent on the s o l u t i o n concentration, the p a r t i a l pressures at the convergence temperature are also s i m i l a r . Hence the same Henry's 231 1000 03 PH & W PH & CO C/D W PH PH I - J <! H PH £ CO CM 100 50 - 1 1 1 — « - 1 1 •'• -I 1 - • =40°C - + = 120*0 - - O=150°C - • o - • + - - o - o + • • + • I 1 1 1 0.0 0.1 0.2 0.3 0.4 LIQUID LOADING (mol H 2 S / m o l DEA) 0.5 Figure 7.7: P a r t i a l pressure of H 2S as a function of l i q u i d loading and temperature f o r a 30 wt% DEA solution. 232 1000 & w PH & CO CO w PH PH t-H <5 i — i tt CVJ O CJ 100 50 • = 40°C - + = 120°C O=150°C - o + o -L 0.0 0.1 0.2 0.3 0.4 LIQUID LOADING (mol C 0 2 / m o l DEA) 0.5 Figure 7.8: P a r t i a l pressure of C0 2 as a function of l i q u i d loading and temperature for a 30 wt% DEA s o l u t i o n . 233 2.1 2.2 2.3 2.4 2.5 2.6 1 0 3 / T ( K " 1 ) Figure 7 . 9 : Henry's constant f or H 2S i n aqueous DEA solutions containing also C 0 2 and COS. 234 Figure 7.10: Henry's constant f or C0 2 i n aqueous DEA solutions containing also H 2S and COS. 235 constants are obtained. In the case of CC>2/ the gas i s also absorbed p h y s i c a l l y and chemically, chemical absorption being v i a the carbamate re a c t i o n and the hydration of CO2. As long as some water i s s t i l l a v a i l a b l e i n the sol u t i o n , there w i l l be diff e r e n c e s i n the amount of hydrated C0 2. Hence the t o t a l CC>2 absorbed and the Henry's constants are s t i l l functions of the i n i t i a l DEA concentration. The convergence temperature corresponds to the temperature at which water i s v i r t u a l l y absent from the l i q u i d phase. The presence of a convergence temperature may be pe c u l i a r to the current experimental set-up since the vapour space .was 500 mL compared to 100 mL of l i q u i d . Although degradation reactions involving CO2 could a f f e c t i t s concentration, analysis of l i q u i d samples following the previously outlined procedures (see Chapter 3), indicated such reactions to be n e g l i g i b l e within the duration of the experiments. 7.3.3 MODEL PREDICTIONS In order to use Eqs. 7.30 to 7.33 to predict VLE, i t i s necessary to l i m i t the unknowns to four. K3 to K7, HQQ2 a n c * HH2S a r e known from the work of Kent and Eisenberg (39), and are given i n appendix E. H C Og was found i n t h i s study by performing COS s o l u b i l i t y experiments i n pure water at low temperatures and extrapolating the r e s u l t s to higher temperatures by means of Eq. 7.5. The other unknowns are K-̂ , K2 and KCOS ; t h e l a t t e r has not been reported previously f o r the present system. Although K-̂  and K2 have been reported by Kent and 236 Eisenberg (39), the •constants were derived from experimental measurements obtained from amine systems containing single a c i d gases and operating at temperatures below 140 °C. Since the present system contained C02, H 2S and COS and was operated at elevated temperatures, K^, K 2 and K C O g were a l l c a l c u l a t e d from the present experimental data. The following procedure was used: For each run, the p h y s i c a l l y dissolved C0 2, H 2S and COS were determined from Eqs. 7.22 to 7.24 and Eq. 7.30 was solved f o r the H + concentration. Once these four concentrations were known, i t was possible to solve Eqs. 7. 16 to 7.20 for [HC03~] , [OH"], [C0 3"], [HS"] and [ S " ] , res p e c t i v e l y . The concentration values were then substituted into Eqs. 7.28, 7.29 and 7.25 to obtain [R2NCOO"], [R2NCOS"] and [R 2NH 2 +]. The free amine concentration, [R2NH], was ca l c u l a t e d from Eq. 7.26. K^, K 2 and K c o s were then determined by s u b s t i t u t i n g the relevant concentrations into Eqs. 7.14, 7.15 and 7.21. and K 2 were found to be stronger functions of temperature than amine concentration and p a r t i a l pressure. The pressure and concentration dependencies were eliminated by f i n d i n g the arithmetic average of the constants obtained f o r a l l runs conducted at the same temperature. Kc0S on the other hand, exhibited wider scatter and the best f i t through the average values was, at best, a marginal function of temperature. The r e s u l t i n g temperature dependencies are: x :os exp( -6.58 exp( 6.97 exp( 15.90 3979.22 / T) 2498.39 / T) 77.31 / T) 237 As shown i n appendix E, the present K̂  values are one to two times those reported previously by Kent and Eisenberg (39) while the K 2 values are approximately twice those found by the l a t t e r authors. The deviations i n the K-̂ , K 2 and K c o s values are estimated as ±11%, ± 17% and ± 30% r e s p e c t i v e l y . To test the model, the constants c a l c u l a t e d by the above procedure were substituted into Eqs. 7.30 to 7.33 and the equations were solved by means of the non-linear equation solver NDINVT (90)) for the p a r t i a l pressures corresponding to runs 1 to 26 i n Table 7.4. As shown i n Table 7.5, the predicted loadings matched the experimental values f a i r l y w e l l. Even though more robust thermodynamic models, which consider system n o n - i d e a l i t i e s and i o n i c i n t e r a c t i o n s , have been developed, deviations greater than 20 % s t i l l occur between predictions and experimental measurements f o r mixed gas systems, p a r t i c u l a r l y at high loadings and high temperatures (40,41). Such deviations are mostly due to the lack of l i t e r a t u r e data f o r the equilibrium constant for carbamate formation at moderate to high temperatures. It has also been suggested that i n t e r a c t i o n parameters involving species derived from C0 2 and H2S, may have to be considered to obtain better predictions at high loadings (40). The fa c t that the present model gives good predictions fo r H2S and C0 2 loadings and i s also able to predict COS loadings f a i r l y well, i s a s i g n i f i c a n t improvement over the previous equilibrium models which give predictions f o r C0 2 and/or H2S loadings alone. 238 7.3.4 REPRODUCIBILITY Some experiments were repeated to estimate the errors inherent i n the experimental and a n a l y t i c a l procedures. For the s o l u b i l i t y runs at less than 50 °C, the average error i n the Henry's constants was less than ±3 % f o r the COS-DEA systems. In the case of the COS-H2O system, because of the small amount of p h y s i c a l l y absorbed COS, a ±1 % error i n the amount of COS fed into the reactor, translated to errors of ±4 % (or more) i n the Henry's constants depending on the operating temperature. For the high temperature experiments, errors i n the gas, l i q u i d and t o t a l moles measurements for H 2S were less than .±3 %, while C0 2 measurements recorded average errors of about ±5 %. As stated e a r l i e r , the COS concentrations could not be determined with s u f f i c i e n t confidence because of t h e i r values and the lack of s e n s i t i v i t y of the thermal conductivity detector. 7.3.5 COS BALANCE Material balances were performed on COS by comparing the amount introduced i n t o the reactor with the amount reported as COS, C0 2 and H 2S from the analysis of the gas and l i q u i d phases of the reactor. More than 90 % of the COS was accounted f o r i n systems with low to moderate ac i d gas loadings ( 0.6 mole/mole DEA). At higher loadings, the figure dropped to about 85 %. This i s probably due to the fact that at such loadings, small errors i n the determination of the volume of l i q u i d 239 samples transferred to the gas trapping set-up amplify the errors i n the ov e r a l l figures f o r the a c i d gases i n the system. Table 7.5: Predicted and experimental a c i d gas loadings. CARBON DIOXIDE HYDROGEN SULPHIDE CARBONYL SULPHIDE (mol C0 2/mol DEA) (mol H2S/mol DEA) (mol COS/mol DEA) RUN PRED EXP DEV(%) PRED EXP DEV(%) PRED EXP 1 0 .065 0 .058 + 12 .07 0 .087 0 .078 + 11. 54 0 .001 0, .001 2 0 .045 0 .045 0 .00 0 .068 0 .070 - 2. 86 0 .001 0, .001 3 0 .028 0 .025 + 12 .00 0 .050 0 .042 + 19. 05 0 .001 0, .001 4 0 .048 0 .049 - 2 .04 0 .080 0 .081 - 1. 23 0 .002 0. .001 5 0 .055 0 .064 -14 .06 0 .105 0 .110 - 4. 55 0 .001 0. .001 6 0 .080 0 .082 - 2 .44 0 .134 0 . 135 - 0. 74 0 .001 0, .001 7 0 .090 0 .097 - 7 .22 0 .129 0 .136 - 5. 15 0 .002 0 , .001 8 0 .127 0 .130 - 2 .31 0 .162 0 .172 - 5. 81 0 .002 0, .001 9 0 .165 0 . 160 + 3 .13 0 .187 0 .182 + 2. 75 0 .004 0, .001 10 0 .097 0 . 102 - 4 .90 0 .154 0 .156 - 1. 28 0 .002 0. .001 11 0 .110 0 .116 - 5 .17 0 .192 0 .203 - 5. 42 0 .003 0, .001 12 0 .117 0 .118 - 0 .85 0 .180 0 . 173 + 4. 05 0 .002 0 , .001 13 0 .130 0 .131 - 0 .76 0 .130 0 . 137 - 5. 11 0 .001 0 , .001 14 0 .153 0 .134 + 14 .18 0 .158 0 .147 + 7. 48 0 .001 0, .001 15 0 .143 0 .142 + 0 .70 0 .151 0 .156 + 3. 21 0 .001 0. .001 16 0 .167 0 .159 + 5 .03 0 .194 0 .188 + 3. 19 0 .001 0, .001 17 0 .181 0 .166 + 9 .04 0 .225 0 .220 + 2. 27 0 .004 0, .002 18 0 .096 0 .097 - 1 .03 0 .182 0 .169 + 7. 69 0 .002 0. .002 19 0 . 107 0 .128 -16 .41 0 .222 0 .249 -10. 84 0 .002 0, .003 20 0 .157 0 .166 - 5 .42 0 .202 0 .229 -11. 79 0 .002 0. .001 21 0 .178 0 .186 - 4 .30 0 .263 0 .272 - 3. 31 0 .002 0. .002 22 0 .195 0 .191 + 2 .09 0 .304 0 .307 - 0. 98 0 .003 0, .002 23 0 .085 0 .099 -14 . 14 0 .139 0 .158 -12. 03 0 .001 0, .002 24 0 .434 0 .362 + 19 .89 0 .286 0 .346 -17. 34 0 .003 0 , .003 25 0 .417 0 .365 + 14 .25 0 .261 0 .358 -27. 09 0 .003 0. .002 26 0 .372 0 .328 + 13 .41 0 .257 0 .304 + 15. 46 0 .002 0. .001 CHAPTER 8 REACTION MECHANISMS On the basis of observations discussed i n Chapters 6 and 7, reaction mechanisms describing the formation of the various degradation compounds can be formulated. 8.1 COS-DEA DEGRADATION 8.1.1 FORMATION OF MEA The formation of MEA and the low b o i l i n g degradation compounds appears to be i n i t i a t e d by the absorption and hydrolysis of COS described by Eqs. 8.1 and 8.2. R2NH + COS = R2NCOS" H + 8.1 R2NCOS" H + + H20 = R2NH + H2S + C0 2 8.2 The d i s s o l v e d carbon dioxide gives r i s e mainly to H + and HCO3", whereas hydrogen sulphide y i e l d s p r i m a r i l y H + and HS": C0 2 + H20 = H + + HCO3" 8.3 H 2S = H + + HS" 8.4 240 241 The DEA molecules are r e a d i l y protonated: R2NH + H + = R 2NH2 + 8 - 5 where R denotes -C2H4OH. The DEA molecules also react with C0 2 to form DEA carbamate, R2NH + C0 2 = R2NCOO H + 8.6 which establishes an equilibrium with the bicarbonate ions: R2NH + HC0 3" = R2NCOO" + H 20 8.7 Equations 8.1 to 8.5 and 8.7 can be combined to give the ov e r a l l reaction f o r the COS-DEA system: 2R2NH + COS + H 20 = R 2NH 2 + + R2NCOO" + H + + HS" 8. The protonated diethanolamine molecule loses one hydroxyethyl group to form MEA: HOC 2H 4 H H \ / co 2 / N + = HOC2H4-N + " +C 2H 4OH " 8.9 / \ . \ HOC 2H 4 H H DEAH+ MEA 242 Since MEA was formed only i n DEA systems containing both H 2S and C0 2, the transformation i n Eq. 8.9 therefore proceeds only i n alkanolamine systems containing both C0 2 and H 2S. Analogous reactions v i z : formation of EAE from EDEA and ethyl amine from EAE, suggest that the C0 2 need not be in the carbamate form. The hydroxyethyl group i s i n quotation marks because i t does not exi s t as such i n solu t i o n . It i s suggested that i t i s transformed according to the following scheme: The bisulphide ion formed i n Eq. 8.4 reacts with C0 2 to form the t h i o l of the bicarbonate ion as proposed by Al-Ghawas et a l . (50): HS" + C0 2 = HC02S" 8.10 The thiobicarbonate ion then reacts with the hydroxyethyl group to form an enol of acetaldehyde: H HC0 2S" + " +C 2H 4OH " -* CH 2 = C-OH + H 2S + C0 2 8.11 This reaction provides a means f o r the fa s t transformation of the hydroxyethyl group released i n Eq. 8.9, and i s probably the d r i v i n g force f o r the formation of MEA. The presence of H 2S and C0 2 i n Eq. 8.11 indicates that both compounds are not used up, but only catalyze the transformation of DEA to MEA. Eq. 8.11 also explains the lack of formation of MEA i n C02-DEA or H2S-DEA systems, since such systems cannot form the thiobicarbonate ion. 243 8.1.2 FORMATION OF ACETALDEHYDE AND KETONES Acetaldehyde i s formed from a fa s t transformation of i t s enol: H H CH 2 = C-OH -. CH3-C = 0 8.12 Two moles of acetaldehyde then condense i n an a l d o l reaction, followed by reaction with COS to form an acetoacetic a c i d : H OH H 2 CH3-C = 0 -» CH3-CH-CH2-C = 0 8.13 OH H 0 0 CH3-CH-CH2-C = 0 +2 COS + H 20 -> CH3-C-CH2-C-OH + 2 CO + 2 H2S 8.14 Acetoacetic a c i d The acetoacetic a c i d breaks down under heat to form acetone: 0 0 CH3 A \ C / CH3-C-CH2-C-OH -> = 0 + CO, 8.15 CH3 ACETONE The reactions described by Eqs. 8.11 to 8.15 proceed very fast under the operating conditions used i n t h i s study, hence only the end product, acetone was detected i n appreciable q u a n t i t i e s . 244 Butanone may be formed by s i m i l a r reactions, but the reaction steps are not f u l l y understood. Chakma (18) detected ethylene oxide and ethylene g l y c o l i n MDEA solutions degraded by C0 2 and a t t r i b u t e d those compounds to the hydroxyethyl group released from protonated MDEA. The lack of formation of ethylene g l y c o l i n the present study, despite the release of the hydroxyethyl group, suggests that, given the composition of the so l u t i o n i n the present study, the reaction i n Eq. .8.11 i s a more favourable route f o r the transformation of the hydroxyethyl group. 8.1.3 FORMATION OF ACETIC ACID Acetaldehyde may undergo l i q u i d phase oxidation by COS to produce a c e t i c a c i d : H OH 0 I I c o s II CH3-C = O + H20 -» CH3-C-H -. CH3-C-OH + CO + H2S 8.16 OH ACETIC ACID Due to the presence of hydrogen sulphide i n the solutions i t i s not un l i k e l y that t h i o a c e t i c a c i d was also formed. Some of the chromatograms showed peaks at the shoulders of butanone and MEA peaks. The mechanisms proposed above can be used to explain some of the trends observed i n the ethanol, acetaldehyde and a c e t i c a c i d spiked runs. Recall that ethanol spiking r e s u l t e d i n reduced MEA concentrations and increased concentrations of the ketones and a c e t i c a c i d at the 245 i n i t i a l stages of the runs. The acetaldehyde spiked run caused increased MEA concentration and s i g n i f i c a n t l y higher concentrations of the ketones and a c e t i c a c i d i n the f i r s t four hours of the run. In the ethanol spiked run, ethanol was probably dehydrogenated to acetaldehyde. The absence of suitable c a t a l y s t s would l i m i t the extent of t h i s reaction. The acetaldehyde produced from ethanol disturbs the e x i s t i n g equilibrium i n equation 8.11. This disturbance also a f f e c t s the equilibrium in equation 8.9 by s h i f t i n g i t away from MEA production. Since acetaldehyde a l s o generates a c e t i c a c i d which, in turn, converts some MEA to HEA, the equilibrium i n equation 8.9 i s again s h i f t e d , t h i s time i n favour of MEA production. The decreases observed i n MEA concentration suggest that the o v e r a l l e f f e c t of these disturbances i s a s h i f t i n equilibrium against MEA production. The same explanations apply to the observed trends i n the acetaldehyde spiked run. However, the much higher acetaldehyde concentration and, by inference, higher a c e t i c a c i d concentration, would cause a greater depletion of MEA via HEA production. Hence the equilibrium eventually s h i f t s i n favour of MEA production. The e f f e c t of the higher MEA depletion on the equilibrium i n equation 8.9 i s also the reason for the higher rate of DEA degradation observed i n the a c e t i c a c i d spiked run. This explains the contradictions between t h i s r e s u l t and an e a r l i e r work that reported decreased rate of DEA degradation with increased so l u t i o n a c i d i t y (16). The lack of formation of the ketones i n the a c e t i c a c i d spiked run may be due to a reaction between the hydroxyethyl group and a c e t i c a c i d . It could also be that a c e t i c a c i d increased the a c i d i t y of the solution such that the 246 enol of acetaldehyde could not form. The absence of acetaldehyde thus prevented the formation of the ketones. 8.1.4 FORMATION OF ETHYL AMINOETHANOL (EAE) The mechanism for the formation of EAE i s s i m i l a r to that of MEA formation from DEA. It involves the loss of a hydroxyethyl group from a protonated EDEA, the former being r a p i d l y transformed to acetaldehyde v i a the enol: C 2 H 5 C 2H 4OH C 2H 5 \ / \ N + = N-H + CH3CHO + H + 8.17 / \ / H C 2H 4OH HOC 2H 4 EAE 8.1.5 FORMATION OF DIETHYL DISULPHIDE Diethyl disulphide could form by the following reactions: C 2H 5OH + H2S C 2H 5SH + H 20 8.18 2 C 2H 5SH + COS -» C 2H 5-S-S-C 2H 5 + CO + H 2S 8.19 DIETHYL DISULPHIDE Another minor sulphur compound detected was 1,2 dit h i a n e . From the ava i l a b l e information, i t i s not c l e a r how t h i s compound was formed. 247 8.1.6 FORMATION OF SUBSTITUTED PYRIDINES There i s s u f f i c i e n t experimental evidence that protonated DEA, EDEA and EAE may lose an hydroxyethyl group to produce the respective lower order amines. Ammonia may be produced from protonated MEA i n a si m i l a r manner. The high v o l a t i l i t y and r e a c t i v i t y of ammonia makes i t s detection almost impossible under the a n a l y t i c a l conditions used i n t h i s study. Its formation can be i n f e r r e d from the presence of pyridine d e r i v a t i v e s i n the degraded s o l u t i o n . The substituted pyridines were probably formed from the reactions of ammonia with acetaldehyde. Such reactions proceed well with paraldehyde as the s t a r t i n g material, but a much lower y i e l d i s obtained with acetaldehyde (91). Methyl pyridine may have formed according to the following condensation reactions: 2 CH3-CHO H CH3-CH=CH-CHO + H 20 8.20 CH3-CH=CH-CHO + CH3-CHO - CH3-CH=CH-CH=CH-CHO + H 20 8.21 CH 2 / \ HC CH CH3-CH=CH-CH = CH-CHO + NH3 -> II II + H2° 8 - 2 2 HC C-CH3 \ / NH METHYL DIHYDROPYRIDINE Methyl dihydropyridine then reacts with COS to form methyl pyridine: 248 CH 2 CH / \ / \\ HC CH HC CH I I + COS •-. || | + CO + H 2S 8.23 HC C-CH3 HC C-CH3 \ / \ // NH N METHYL PYRIDINE Ethyl methyl pyridine may form by a re l a t e d condensation, but a precise scheme cannot be offered. 8.1.7 FORMATION OF ETHYLDIETHANOLAMINE (EDEA) In the presence of n i c k e l c a t a l y s t s and hydrogen, a l k y l amines have been formed from aqueous or a l c o h o l i c ammonia and acetaldehyde (92). Production of EDEA may proceed i n an analogous manner between DEA and acetaldehyde: C 2H 4OH OH C 2H 4OH H C 2H 4OH / I / I / CH3CHO + H-N - CH 3 -C-N - CH3-C=N+ + OH" \ I \ \ C 2H 4OH H C 2H 4OH C 2H 4OH 8.24 H C 2H 4OH C 2H 4OH I / H 2 S 1 CH3-C=N+ -t CH3CH2-N + H + + S 8.25 \ \ C 2H 4OH C 2H 4OH EDEA 249 The absence of a c a t a l y s t . i s probably responsible f o r the low concentrations of EDEA recorded i n most of the runs. It should be noted that CS2 may also serve the ro l e of an ox i d i z i n g agent where COS appears i n the above reaction mechanisms. In such cases, the byproduct w i l l be carbon monosulphide (CS) instead of carbon monoxide (CO). 8.1.8 FORMATION OF N,N,N' -TRIS HYDROXYETHYL ETHYLENEDIAMINE (THEED) The production of THEED from DEA or DEA and DEA carbamate has already been reported by Kennard and Meisen (14): HOC 2H 4 HOC 2H 4 C 2H 4OH \ 1 \ / N-H -> N-C2H4-N + H 20 8.26 / / \ HOC 2H 4 H C 2H 4OH DEA THEED or HOC 2H 4 HOC 2H 4 HOC 2H 4 C 2H 4OH \ \ \ / N-H + NCOO" H + -» N-C2H4-N / / / \ . HOC 2H 4 HOC 2H 4 H G2H4OH DEA DEA CARBAMATE + H 20 + C0 2 8.27 250 Equation 8 . 2 6 represents the thermal route f o r THEED formation and may- be discounted at the temperatures used i n t h i s study. 8 . 1 . 9 FORMATION OF BIS HYDROXYETHYL ETHYLENEDIAMINE (BHEED) BHEED was formed from the reaction between MEA and DEA carbamate or vice versa: HOC2H4 HOC 2H 4 HOC 2H 4 H \ \ \ / N-H + NCOO" H + -. N-C2H4-N / / / \ HOC 2H 4 H HOC 2H 4 H DEA MEA CARBAMATE N, N BHEED + H 2 0 + C 0 2 8 . 2 8 or HOC 2H 4 HOC 2H 4 HOC 2H 4 C 2H 4OH \ \ \ / N-H + NCOO" H + -> N-C2H4-N + H 2 0 + C 0 2 / / / \ H HOC 2H 4 H H MEA DEA CARBAMATE N,N BHEED 8 . 2 9 The thermal formation of BHEED (reaction of DEA with MEA) does not proceed r e a d i l y at the temperatures used i n t h i s study. The above equations represent the o v e r a l l reactions and may, in d e t a i l , involve addi t i o n a l i o n i c steps. 251 8.1.10 FORMATION OF N?N -BIS HYDROXYETHYL PIPERAZINE (BHEP) AND N-HYDROXYETHYL PIPERAZINE (HEP) Both THEED and BHEED may undergo dehydration, which leads to the formation of BHEP and HEP, resp e c t i v e l y : HOC 2H 4 C 2H 4OH C 2H 4 \ / / \ N-C2H4-N - HOC2H4-N N-C2H4OH + H 20 8.30 / \ \ / H C 2H 4OH ^2^4 THEED BHEP and HOC 2H 4 C 2H 4OH C 2H 4 \ / / \ N-C2H4-N -> HOC2H4-N N-H + H 20 8.31 / \ \ / H H C2H^ BHEED HEP 8.1.11 FORMATION OF N-HYDROXYETHYL OXAZOLIDONE (HEOD) Kim and S a r t o r i (13) and Kennard and Meisen (14) have shown that DEA carbamate dehydrates to HEOD and that an equilibrium e x i s t s between both compounds: 252 H0C2H^ 2̂̂ " ~ ̂*̂ 2 / \ / HOC 2H 4 C NCOO" H + 0 N-C2H4OH + H 20 8.32 HEOD 8.1.12 FORMATION OF N,N' -BIS HYDROXYETHYL IMIDAZOLIDONE (BHEI) BHEI r e s u l t s from the dehydration of BHEED carbamate: HOC 2H 4 C 2H 4OH H 2C - CH 2 \ / I i N-C2H4-N -. HOC2H4-N N-C2H4OH + H 20 8.33 / \ \ / H C-O" H + C II II O o BHEI and the reaction between MEA and DEA carbamate: HOC 2H 4 HOC 2H 4 H 2C - CH 2 \ \ | | N-H + NCOO" H + -> HOC2H4-N N-C2H4OH + 2 H 20 8.34 / / \ / H HOC 2H 4 C O BHEI The l a t t e r i s a two step reaction c o n s i s t i n g of the coupling of MEA and DEA carbamate to form an intermediate, and the c y c l i z a t i o n of the 253 intermediate product. BHEED carbamate appears to be the most likely- intermediate product and since BHEED was a stable intermediate, the formation of BHEI i s better represented by Eq. 8.33. In a l l the systems studied, the formation of BHEED preceeds that of BHEI. 8.1.13 FORMATION OF N-HYDROXYETHYL IMIDAZOLIDONE (HEI) The formation of HEI proceeds v i a the reaction between MEA and MEA carbamate: HOC 2H 4 HOC 2H 4 H 2C - CH 2 \ \ | | N-H + NCOO" H + -> HOC2H4-N N-H + 2 H 20 8.35 / / \ / H H C 0 HEI The same reaction could produce hydroxyethyl ethylenediamine (HEED), but t h i s compound was not detected probably due to i t s transformation to HEI through a reaction s i m i l a r to Eq. 8.33. Therefore, Eq. 8.35 may involve HEED as an intermediate. 254 8.1.14 FORMATION OF N-HYDROXYETHYL ACETAMIDE (HEA) Acetic ac i d reacts r e a d i l y with MEA to form HEA: C 2H 4OH 0 C 2H 4OH / I  1 I -> CH3-C-N \ \ CH3-C-OH + H-N + H 20 8.36 HEA 8.1.15 FORMATION OF ETHANETHIOIC ACID -(S-(HYDROXYETHYL) AMINO) METHYL ESTER (ETAHEAME) This compound can be synthesized by condensing monoethanolamine, t h i o a c e t i c a c i d and formaldehyde i n a Mannich reaction (93): H C 2H 4OH H C 2H 4OH \ / \ / C=0 + H-N -. C=N + H 20 8.37 / \ / H H H 0 H C 2H 4OH 0 H C 2H 4OH II \ / II I / CH3-C-SH + C=N -> CH3-C-S-C-N 8.38 / I \ H H H ETAHEAME Monoethanolamine was detected i n the degraded so l u t i o n . Thioacetic could have been formed from a c e t i c a c i d and H 2S. Formaldehyde may have been a 255 by-product of some reactions r e l a t e d to the ones described above. Thus the three reactants needed to produce t h i s compound appear to be ava i l a b l e i n the degraded solution. 8.2 CS2-DEA DEGRADATION The experimental observations suggest that the mechanism previously developed f o r the COS-DEA system also applies, to a large extent, to the CS2-DEA system. In the l a t t e r case, amine dithiocarbamate i s also formed, HOC 2H 4 HOC 2H 4 \ \ N-H + CS 2 = N-C-S" H + 8.38 / / II HOC 2H 4 HOC 2H 4 S DEA DITHIOCARBAMATE which may react with add i t i o n a l DEA to y i e l d the dithiocarbamate s a l t of DEA: HOC 2H 4 HOC 2H 4 HOC 2H 4 H C 2H 4OH \ \ \ \ / N-H + NCSS" H + N-C-S" N + 8.39 / / / 1 / \ HOC 2H 4 HOC 2H 4 HOC 2H 4 S H C 2H 4OH DEA DITHIOCARBAMATE SALT 256 At high temperatures *such as 180 °C, the dithiocarbamate s a l t i s unstable, reverting to DEA and CS 2. The l a t t e r i s then hydrolysed to COS, C0 2 and H 2S. C0 2 subsequently undergoes the t y p i c a l i o n i z a t i o n and DEA carbamate formation reactions as shown i n Equations 8.4 and 8.5. H2S i s also ionized and forms protonated DEA according to Equations 8.3 and 8.6. The subsequent reactions then proceed as already shown for the COS-DEA system, r e s u l t i n g i n the formation of degradation products. At lower temperatures (T < 165 °C), the dithiocarbamate s a l t i s s u f f i c i e n t l y stable and t i e s up a greater amount of CS 2. Less CS 2 i s l e f t f o r hydrolysis and consequently, less COS, C0 2 and H2S are formed compared to the q u a n t i t i e s at 180 °C- The much lower concentrations of the a c i d gases cause degradation to proceed with the formation of very l i t t l e ketones as observed f o r some H2S/C02-DEA systems and the CS2-DEA systems at T < 165 °C. The extremely high rate of DEA degradation at 180 °C, r e l a t i v e to 165 °C (see F i g . 5.52), can be a t t r i b u t e d to the high concentrations of H 2S and C0 2 r e s u l t i n g from the breakdown of the unstable dithiocarbamate s a l t . Under t h i s condition, the DEA i s p r e f e r e n t i a l l y transformed to MEA. The consequence of t h i s i s that the concentrations of the compounds formed d i r e c t l y from MEA (e.g. HEI, HEA) were higher at 180 °C than at 165 °C, while the concentrations of compounds r e s u l t i n g from reactions inv o l v i n g DEA (BHEED, HEOD, and THEED) were s i g n i f i c a n t l y lower at 180 °C than at 165 °C (see Tables C.26 and C.27 i n appendix C). 257 8.3 FORMATION OF THE SOLID PRODUCTS Since the s o l i d products were not conclusively i d e n t i f i e d , no mechanisms are offered f o r t h e i r formation. Some re a c t i o n mechanisms show the formation of elemental sulphur. As well, runs conducted f o r short durations (t < 12 h) only produced sulphur deposits but not the s o l i d product. Considering the elements that c o n s t i t u t e the s o l i d product, i t appears that i t s formation was the r e s u l t of reactions involving sulphur, the amine and the hydroxyethyl group. CHAPTER 9 KINETIC MODEL FOR DEA DEGRADATION 9.1 COS INDUCED DEGRADATION OF DEA The re a c t i o n mechanisms proposed i n Chapter 8 can be summarized by the following equations: DEA + COS DEACOS"H+ + H 20 H 20 + C0 2 H2S DEA + H + DEA + C0 2 DEAH+ + C0 2 DEACOO~H+ + MEA DEACOO"H+ + DEA THEED + C0 2 DEACOO~H+ MEACOO"H+ + MEA BHEED + C0 2 THIOACETIC ACID + MEA + HCHO ACETIC ACID + MEA ACETALDEHYDE + DEA = DEACOS"H+ 9.1 = DEA + H2S + C0 2 9.2 = H + + HC03" 9.3 = H + + HS" 9.4 = DEAH+ 9.5 = DEACOO~H+ 9.6 = MEA + R+ + C0 2 9.7 -> BHEED + C0 2 + H 20 9.8 THEED + C0 2 + H 20 9.9 -> BHEP + C0 2 + H 20 9.10 = HEOD + H 20 9.11 -t HEI + H 20 9.12 BHEI + H 20 9.13 -> ETAHEAME + H 20 9.14 H HEA + H 20 9.15 -» EDEA + % Oo 9.16 258 259 EDEA + H + = EAE + R+. 9.17 EAE + H + = ETHYL AMINE + R + 9.18 BHEED -> HEP + H20 9.19 3 CH3CHO + NH3 + COS METHYL PYRIDINE + H2S + 3 H20 + CO 9.20 2 CH3CHO + 2 COS + H20 -> ACETONE + 2 CO + 2 H2S + C0 2 9.21 CH3CHO + H20 + COS -t ACETIC ACID + CO + H20 9.22 C 2H 5OH + C 2H 5SH + COS -> DIETHYL DISULPHIDE + CO + H20 9.23 The number of equations demonstrates the complexity of DEA degradation by COS. In order to develop a k i n e t i c model based on the reactions, the following s i m p l i f y i n g assumptions are invoked. * The s o l u b i l i t y and hydrolysis reactions governed by Equations 9.1 to 9.6 are much f a s t e r than the degradation reactions, and equilibrium a c i d gas loadings are achieved p r i o r to the commencement of any s i g n i f i c a n t degradation. This s i m p l i f i c a t i o n has been used s u c c e s s f u l l y i n the past (13,14,18). * With the exception of Equations 9.1 to 9.6, a l l reactions are considered to be i r r e v e r s i b l e because the experimental data suggest that f o r the duration of the experiments, equilibrium was s t i l l i n favour of products formation (forward r e a c t i o n ) . * Ionic species such as DEAH+ and DEACOO"H+ may be written as: DEAH+ + HS" = DEA + H 2S 260 DEACOO~H+ = DEA + C0 2 * The reaction between MEA and DEACOO" i s equivalent to the reac t i o n between MEACOO" and DEA. * The amine solutions are s u f f i c i e n t l y d i l u t e so that the concentration of water can be neglected i n the k i n e t i c expressions. * When C0 2 or H 2S appears on both sides of an equation, i t i s considered to act as a c a t a l y s t and need not be included i n the k i n e t i c expressions. * Except f o r the runs conducted at temperatures above 180 °C, the concentrations of ETAHEAME, HEA, EDEA, HEP and the low b o i l i n g degradation compounds (except MEA) were generally low. In add i t i o n , some of the reactions do not t i e up any nitrogen atoms. Therefore, Eqs. 9. 14 - 9.23 are considered as secondary degradation reactions and are neglected i n the k i n e t i c expressions. * Reactions leading to the formation of s o l i d s are neglected because elemental analysis showed that the amount of amine responsible f o r s o l i d s formation i s small. The above assumptions lead to the following s i m p l i f i e d set of reactions: 261 k l DEA -» MEA + CH3CHO 9.24 k2 DEA + MEA -. BHEED + H 20 9.25 k3 DEA + C0 2 HEOD + H 20 9.26 k4 2 MEA + C0 2 -. HEI + H 20 9.27 k5 2DEA THEED + H 20 9.28 k6 THEED BHEP + H 20 9.2 9 k7 BHEED + C0 2 -» BHEI + H 20 9.30 The corresponding rate equations are: d[DEA]/dt = - k 1 [DEA] - k 2 [DEA] [MEA] - k 5 [DEA] - k 3 [DEA] [C02] 9.31 d[MEA]/dt = k x [DEA] -k 4 [MEA] 2 [C021 - k 2 [DEA] [MEA] 9.32 d [BHEED]/dt = k 2 [MEA] [DEA] - k ? [BHEED] [C021 9.33 d [BHEP]/dt = k 6 [THEED] 9.34 262 d[HEOD]/dt = k 3 [DEA] [C02] 9.35 d[HEI]/dt = k 4 [MEA]^ [C02] 9.36 d[THEED]/dt = k 5 [DEA] - kg [THEED] 9.37 d[BHEI]/dt = k 7 [BHEED] [C02] 9.38 where [i] denotes concentration of specie i i n units of mol/L. Equations 9.31 to 9.38 represent the s i m p l i f i e d k i n e t i c model for the DEA degradation by COS. Although the C0 2 and H 2S loadings were obtained from the COS s o l u b i l i t y and hydrolysis system described by Equations 9.1 to 9.6, these values were assumed to be e i t h e r constant or not l i m i t i n g throughout the duration of the runs. Therefore, the acid gas loadings can be lumped into the rate constants. It i s recognized that, as degradation proceeds, the concentration of DEA f a l l s thereby causing a reduction i n the C0 2 and H 2S solution loadings. However, since MEA and other degradation compounds such as BHEED, THEED and BHEP (94) are also able to absorb a c i d gases, t h e i r presence i n the degraded s o l u t i o n w i l l compensate for the reduction i n a c i d gas loadings associated with the reduction i n DEA concentration. The a c i d gas loadings should therefore remain approximately constant. Equations 9.31 - 9.38 are k i n e t i c expressions and do not s t r i c t l y follow the reaction stoichiometries. For example THEED formation has a molecularity of two with respect to DEA according to Eqs. 9.9 and 9.28, but the f i r s t order 263 k i n e t i c representation i n Eq. 9.37 has been found i n the past (16,18), to represent experimental data better. This was also the case i n the present study. In order to solve Eqs. 9.31 - 9.38, the rate constants k^ to k^ must be known. They were determined by f i r s t f i t t i n g a 5th order polynomial expression to the concentration - time measurements for DEA, MEA, BHEED, BHEP, HEOD, HEI, THEED and BHEI. In t h i s way, the concentrations f o r each compound could be found at uniform time intervals.. For each experimental run, a non-linear optimization routine, NLPQL (95) was used to search f o r the set of rate constants k^ to kj which gave the best agreement with the experimental measurements. The objective function, which was minimized i n the search, was defined as: N 8 S E (Yc i t - Ye i t ) 2 / Ymaxj^2 9.39 t=l i=l where i = 1, 2,...8 denotes the compounds (DEA, MEA, BHEED, BHEP, HEOD, HEI, THEED, BHEI, r e s p e c t i v e l y ) i n the k i n e t i c expressions and t = 1, 2,...N indicates the time at which samples were taken. Yc.^, Ye i and Ymax^ denote the calculated, experimental and maximum experimental concentrations f o r compound i , r e s p e c t i v e l y . The term Ymax^ was introduced as a weighting f a c t o r to account f o r the considerable differences between the concentrations of DEA and the degradation 264 products. A Runge-Kutta d i f f e r e n t i a l equation solver (96), was employed to solve the set of d i f f e r e n t i a l equations. As shown i n Table D.19 i n appendix D, the rate constants obtained from the above procedure were functions of temperature and pressure. Except f o r k.3 and k^, the dependency on the i n i t i a l DEA concentration d i d not follow any s p e c i f i c pattern and was therefore a t t r i b u t e d to scatter i n the experimental data and/or approximations i n the NLPQL and Runge-Kutta routines. The v a r i a t i o n with concentration was eliminated by taking the average of the constants (except k 3 and k 5) for a l l runs conducted at the same temperatures and COS p a r t i a l pressures. For a l l the runs conducted at an i n i t i a l COS p a r t i a l pressure of 345 kPa and temperatures below 165 °C, the rate constants could be represented by the Arrhenius expressions shown below: k l = 4. 353 X 10 4 exp ( -56,174/RT) 9. 40 k2 = 1. 525 X 10 7 exp ( -80,282/RT) 9. 41 k 4 = 8. 554 X 10 8 exp (-94,931/RT) 9. 42 k6 = = 5. ,398 X 10 4 exp ( -59,315/RT) 9. 43 k ? = = 1. ,412 X 10 2 exp (-31,077/RT) 9. 44 k3 -= 4. .029 X 10 3 exp ( -55,063/RT) (for DEA Q = = 4M) 9. 45 k3 = = 2, .683 X 10 3 exp ( -54, 924/RT) (for DEAQ = = 3M) 9. 46 k3 = = 1. .774 X 10 2 exp ( -47,272/RT) (for DEAQ = = 2M) 9. 47 k5 = = 9 .900 X 10 6 exp (-77,450/RT) (for DEAD = = 4M) 9. 48 k5 = = 1 . 931 X 10 7 exp ( -82,670/RT) (for DEAQ = = 3M) 9. 49 265 k 5 = 1.343 X 10 6 exp (•-75,604/RT) (for DEA = 2M) 9.50 The a c t i v a t i o n energies are i n units of J/mole while the frequency -1 -1 factors and the rate constants are in units of h or L (mol h) , depending on the order of the reaction. Values of the a c t i v a t i o n energies are t y p i c a l of l i q u i d phase reactions (97), but some of the frequency factors are unusually low. The rate constants k^, k 2, k 3 and kg for runs conducted at d i f f e r e n t pressures were found to be r e l a t e d by the expression: :P2 = k P l x ( P 2 / P i > ° - 5 9.51 The pressure v a r i a t i o n of k 4 can be represented by the expression: k p 2 = k p l X ( P 2 / P 1 ) 1 - 1 9 9.52 Rate constants kg and k 7 were roughly independent of pressure. Since DEA and MEA have the highest absorption capacities compared to the other compounds, i t i s not s u r p r i s i n g that the rate constants that control the reactions involving these two compounds are the ones aff e c t e d by changes i n pressure. By using Eqs. 9.40 - 9.52, i t was possible to obtain the rate constants governing the degradation reactions conducted under the following operating conditions: 266 DEA concentration- 20 - 40 wt% (appr. 2 - 4M) Temperature 120 - 165 °C COS p a r t i a l pressure 345 - 1172 kPa The rate constants were then substituted i n the k i n e t i c expressions and the expressions were solved with the Runge-Kutta routine (96). Tables D.l - D.18 i n appendix D, show the predicted and experimental concentrations for DEA and the major degradation compounds. The maximum deviation between the experimental and predicted DEA concentrations was approximately 22%, averaging below 8% at T < 180 °C. MEA predictions were also good, with an average deviation of about 18%, except for runs conducted at T > 165 °C where more substantial deviations were recorded. This was due to the fa c t that some reactions such as the formation of HEA which consume MEA but considered as minor reactions, become appreciable at high temperatures. At such temperatures the experimental concentrations show maxima but the model predictions did not, consequently r e s u l t i n g i n deviations that increased with time. In the case of THEED, the model predicted lower concentrations for experimental concentrations greater than 0.2M. The c o n s i s t e n t l y negative deviations suggest that a f a i r l y appreciable degree of er r o r may be associated with the experimental concentrations p a r t i c u l a r l y at high THEED concentrations, since the THEED used f o r c a l i b r a t i o n was not pure (see appendix A.2.2). The model predictions f o r BHEED, BHEP, HEOD, HEI and BHEI were i n general, f a i r l y good. However, because of the generally low concentrations of these compounds, a q u a l i t a t i v e assesment does not give a f a i r representation of the model predictions since a d i f f e r e n c e 267 of 0.01M between the experimental and predicted concentrations often r e s u l t i n deviations above 25%. In summary, the model gave s a t i s f a c t o r y predictions f o r the operating conditions i n d i c a t e d above. It should be possible to extend the range of a p p l i c a b i l i t y to COS p a r t i a l pressures lower than 345 kPa without any s i g n i f i c a n t e r r o r s . Results of s e n s i t i v i t y analyses (shown in d e t a i l i n appendix E.2) indicate that the rate constants obtained from the optimisation method are accurate within ±20%. 9.2 CS 2 INDUCED DEGRADATION OF DEA The experimental r e s u l t s suggest that the mechanism previously developed f o r the COS-DEA system should also apply, to a large extent, to the CS2-DEA system. At T < 165 °C, the dithiocarbamate s a l t formation e i t h e r reaches completion or attai n s equilibrium within two hours. During t h i s period, no degradation compounds were formed i n appreciable amounts. Subsequently, degradation products began to form. Since the products formed were the same as those found i n the COS-DEA system, the reaction mechanism and the rate expressions describing the l a t t e r (Eqs. 9.31 - 9.38) should also apply to the CS2-DEA system. In addition, the reactions occurring i n the f i r s t few hours v i z . the dithiocarbamate s a l t formation and the hydrolysis of CS 2 which produces the species that subsequently induce degradation, must be included i n the rate expressions. The r e s u l t i n g rate equations that describe the CS2-DEA system are as follows: 268 d [DEA] /dt = - k i [DEA] - k 2 [DEA] [MEA] - k 5 [DEA] - k 3 [DEA] [C02] - kg [DEA] [CS2] 9.53 d[MEA]/dt = k x [DEA] -k 4 [MEA] 2 [C02] - k 2 [DEA] [MEA] 9.54 d [BHEED] /dt = k 2 [MEA] [DEA] - k ? [BHEED] [C02] 9.55 d[BHEP]/dt = kg [THEED] 9.56 d [HEOD] /dt = k 3 [DEA] [C02] 9.57 d[HEI]/dt = k 4 [MEA] 2 [C02] 9.58 d [THEED]/dt = k 5 [DEA] - kg [THEED] 9.59 d[BHEI]/dt = k ? [BHEED] [C02] 9.60 d[CS 2]/dt = -k 9 [DEA] [CS2] - kg [CS2] 9.61 d[SALT]/dt = kg [DEA] [CS2] 9.62 The assumption of excess water s t i l l holds and the concentration of water i s excluded from Eq. 9.61. When the s a l t formation and hydrolysis reactions were discounted, i t was possible to obtain the rate constants k i - k 7 by following the optimisation procedure described e a r l i e r . The r e s u l t i n g constants are 269 given i n Table D .20 i n appendix D. However, the optimisation routine d i d not produce reasonable values of kg and kg when Eqs. 9.53 - 9.62 were solved simultaneously. This may be due to the fact that the concentrations of the dithiocarbamate s a l t were not determined during the f i r s t few hours of each run when DEA was consumed p r i m a r i l y i n the s a l t formation. It could also be that Eq. 9.61 describing the consumption of CS2 v i a hydrolysis and the s a l t formation need to be modified. There i s therefore the need to get more experimental data and a better understanding of the reactions occurring within the f i r s t few hours of each run, before a model can be developed to cover the degradation reactions as well as the dithiocarbamate s a l t formation. This aspect w i l l be addressed i n a subsequent study. CHAPTER 10 C O N C L U S I O N S AND RECOMMENDATIONS 10.1 CONCLUSIONS 10.1.1 COS INDUCED DEGRADATION 1. Carbonyl sulphide degrades DEA to form water soluble degradation products and an insoluble sulphur - r i c h s o l i d . 2. The reactions i n the COS-DEA system can be broken down into three stages. F i r s t i s the formation of the DEA thiocarbamate which enhances the absorption of COS. Second i s the hydrolysis of COS or DEA thiocarbamate and the r e d i s t r i b u t i o n of COS, C 0 2 , H 2S and t h e i r associated compounds between the gas and l i q u i d phases to e s t a b l i s h system equilibrium. The t h i r d stage involves the amine degradation reactions leading to the conversion of DEA to degradation compounds. At low temperatures, stages 1 and 2. can be c l e a r l y distinguished, whereas at high temperatures, hydrolysis i s f a s t and d i s t i n c t i o n between the two stages i s not e a s i l y observed. Reactions i n stage 3 are much slower than those i n the f i r s t two stages, such that equilibrium s o l u b i l i t y and hydrolysis i s usually achieved p r i o r to the commencement of any appreciable degradation. 270 271 3. Gas and l i q u i d phase compositions were determined f o r the COS-DEA system on attainment of equilibrium hydrolysis. The equilibrium could be represented by a modified Kent-Eisenberg model which i s able to simulate a gas mixture containing COS i n addition to CO2 and H2S. Previous equilibrium models are l i m i t e d to the absorption of CO2 and H2S mixtures. The modified model i s therefore a s i g n i f i c a n t improvement. 4. Even though COS hydrolyses to CO2, DEA degradation by COS i s d i s t i n c t because products not previously i d e n t i f i e d i n CO2-induced degradation were formed i n the COS-DEA system. 5. The major degradation compounds i n the COS-DEA system are MEA, BHEED, BHEP, HEOD, HEI, THEED and BHEI. 6. THEED, BHEP and HEOD are produced from degradation reactions i n v o l v i n g DEA and the CO2 generated from the hydrolysis of COS. 7. Protonated DEA d^N^"1") loses a hydroxyethyl group (R +) to form MEA. This reaction occurs only i n DEA solutions containing both H2S and CO2 with the l a t t e r acting as a c a t a l y s t . Similar transformations occurred i n MEA, EAE and EDEA solutions, and may therefore, be generalized f o r solutions of primary, secondary and t e r t i a r y amines. 8. The hydroxyethyl group released during the formation of MEA i n i t i a t e and undergo some complex reactions leading to the formation of low b o i l i n g degradation compounds such as acetaldehyde, ethanol, acetone, a c e t i c acid, butanone, 1,2 dithiane , d i e t h y l disulphide, substituted pyridines as well as HEA and EDEA. 272 9. MEA degrades to HEI and also reacts with a c e t i c a c i d to form HEA. 10. BHEI and BHEED are formed from reactions involving MEA, DEA and t h e i r carbamates. BHEI i s also formed from BHEED carbamate. 11. H2S alone does not degrade DEA, but i t s mixture with CO2 degrades DEA to form MEA as well as other products. For such gas mixtures, the rate of DEA degradation increases s l i g h t l y with H2S concentration but s i g n i f i c a n t l y with CO2 concentration. 12. The rate of degradation of DEA by COS increases with so l u t i o n temperature, amine concentration and COS p a r t i a l pressure. 13. The degradation of DEA by COS i s f i r s t order with respect to DEA within the following operating ranges: DEA concentration: 20 - 40 wt%; Temperature: 120 - 180 °C; COS p a r t i a l pressure: 0.34 - 1.17 MPa. The o v e r a l l degradation rate constant, k D E A , increased with amine concentration, temperature and COS p a r t i a l pressure. The temperature dependency could be represented by the Arrhenius expression. At DEA concentrations above 40 wt%, the rate of degradation decreased due to the l i m i t a t i o n of water f o r c e r t a i n i o n i c reactions that control the degradation process. 14. A k i n e t i c model based on the s i m p l i f i e d reaction mechanism was developed to predict the formation of degradation products as well as the depletion of DEA within the following operating regimes: DEA concentration: 20 - 40 wt%; Temperature: 120 - 165 °C; COS p a r t i a l pressure: 0.34 - 1.17 MPa. The f a i r l y good agreement between the experimental values and model predictions validates the reaction mechanism. 273 10.1.2 CS 2 INDUCED DEGRADATION 1. CS 2 degrades DEA to form water soluble products as well as a dithiocarbamate s a l t and a sulphur - r i c h s o l i d . 2. The CS 2 f i r s t reacts with DEA to form DEA dithiocarbamate which reacts with another molecule of DEA to form the DEA dithiocarbamate s a l t . At 180 °C, the s a l t i s unstable, reverting to DEA and CS 2, while at T < 165 °C, the s a l t remains i n the form of insoluble s o l i d p a r t i c l e s . CS 2 i s also hydrolysed to COS, C0 2 and H 2S, but the extent of the hydrolysis products i s l i m i t e d by the amount of CS 2 t i e d up i n the s a l t . When the concentrations of the hydrolysis products are low as was the case at T < 165 °C, MEA i s the only low b o i l i n g degradation compound of s i g n i f i c a n c e . When the concentrations of the hydrolysis products are high due to the i n s t a b i l i t y of the dithiocarbamate s a l t at 180 °C, MEA and other low b o i l i n g degradation compounds are formed i n appreciable q u a n t i t i e s . In summary, the degradation products of CS2-DEA systems are s i m i l a r to those of the COS-DEA systems and the same reaction mechanism applies for t h e i r formation. 3. The rate of degradation increased with amine concentration, temperature and i n i t i a l CS 2 volume (or CS2/DEA mole r a t i o ) . 4. The degradation of DEA by CS 2 i s f i r s t order with respect to DEA within the following operating ranges: DEA concentration: 20 - 40 wt%; Temperature: 120 - 165 °C; CS 2 volumes:, 2.5 - 10.5 mL (CS2/DEA mole r a t i o s of 0.055 - 0.233). The o v e r a l l degradation rate constant increased with temperature and CS 2 volume ( CS2/DEA 274 mole r a t i o ) but was l a r g e l y independent of the amine concentration. The temperature dependency of the rate constant was well represented by the Arrhenius expression. 5. The reaction rate constants were determined for the region where amine degradation was c o n t r o l l e d mainly by the hydrolysis products i . e . a f t e r the formation of the dithiocarbamate s a l t had ceased. However, there were not s u f f i c i e n t experimental data to develop a model to cover a l l the reactions occurring i n the CS2-DEA system. 6. The so l i d s formed i n the CS2-DEA system and the COS-DEA system were not conclusively i d e n t i f i e d , but analysis shows that they are insoluble, high molecular weight, high melting substances, containing ethenyl and sulphur units i n covalent bonding. The COS-DEA and CS2-DEA systems produced 7 and 8 major degradation compounds, r e s p e c t i v e l y , as well as the s o l i d products. These numbers, when compared with 3 major products f o r the CO2-DEA system, demonstrate that the former systems are d i s t i n c t and more complicated than the l a t t e r . 10.2 RECOMMENDATIONS 1. DEA plants should be operated under conditions that minimize degradation. In t h i s respect, temperature control i n the heat exchanger and r e b o i l e r i s e s s e n t i a l i n making sure that the solution temperature i s kept as low as possible and preferably around 120 °C, but c e r t a i n l y not at the expense of e f f i c i e n t 275 s t r i p p i n g . In p a r t i c u l a r , skin temperatures of heat t r a n s f e r surfaces should be monitored, as they are often much higher than the bulk f l u i d temperatures. Since MEA and diamines are known to be p a r t i c u l a r l y corrosive at high temperatures and i n the presence of CC>2, temperature control i s paramount i n minimising corrosion. DEA concentration should also be kept at the minimum value necessary to meet the desired t r e a t i n g capacity. Formation of s o l i d products may create f o u l i n g deposits i n piping, heat exchangers and r e b o i l e r s . As a r e s u l t , pressure drops w i l l r i s e and heat transfer c o e f f i c i e n t s w i l l f a l l leading to increased o v e r a l l energy costs f o r the plants. Cleaning of piping and heat exchangers i s also expensive. It i s therefore advisable to provide e f f i c i e n t f i l t r a t i o n c a p a b i l i t i e s to remove the sulphur deposits before they react with other compounds to form the s o l i d product. DEA plants t r e a t i n g gases containing COS and/or CS 2 should be operated under conditions that enhance t h e i r hydrolysis to C 0 2 and H 2S. Such action would minimise f o u l i n g since degradation by a mixture of H 2S and C 0 2 does not r e s u l t i n substantial s o l i d formation. Increased b a s i c i t y by means other than increasing the amine concentration, may achieve t h i s goal. The s o l i d products need to be subjected to further analysis such as Nuclear Magnetic Resonance Spectroscopy (NMR), X-ray d i f f r a c t i o n etc. to conclusively determine t h e i r i d e n t i t y . Studies should be conducted to evaluate the po t e n t i a l of Ethyl aminoethanol (EAE) and Methyl aminoethanol (MAE) as gas t r e a t i n g 276 solvents. Both amines have been reported to absorb COS over ten times f a s t e r than DEA. The emphasis i n the studies should be on the resistance of the amines to degradation by ac i d gases, t h e i r capacity to absorb a c i d gases, foaming and corrosion tendencies. More d e t a i l e d studies should be conducted on the degradative e f f e c t s of mixtures of CO2 and H2S on the amines used i n gas tr e a t i n g operations. Of p a r t i c u l a r i n t e r e s t i s MDEA which i s used f o r the s e l e c t i v e absorption of H2S from sour gas streams. The formation of the dithiocarbamate s a l t i n the CS2-DEA system should be investigated i n d e t a i l . The data acquired can be combined with those reported i n t h i s study to develop a k i n e t i c model that covers a l l reactions occurring i n the CS2-DEA system. There appears to be enough information from t h i s and other degradation studies to attempt to develop a p u r i f i c a t i o n scheme based on the reversal of the degradation reactions. N O M E N C L A T U R E ACET Acetone (2-Propanone). BHEED Bis(hydroxyethyl) ethylenediamine (N,N and N,N isomers). BHEI N,N -bis(hydroxyethyl) imidazolidone. BHEP N,N -bis(hydroxyethyl) piperazine. BHEU N,N -bis(hydroxyethyl) urea. BUT Butanone (Methyl ethyl ketone). C^ Concentration of gas i in solution (mol/m ). CI Chemical Ionisation mode of operation i n the GC/MS. CO2 Carbon dioxide. COS Carbonyl sulphide. CS2 Carbon disulphide. DEA Diethanolamine. DEACOO" DEA carbamate. DEACOS" DEA thiocarbamate. DEACSS" DEA dithiocarbamate.- DGA Diglycolamine. DIPA Diisopropanolamine. EAE Ethylaminoethanol. EDEA Ethyldiethanolamine. EHEP Ethyl hydroxyethyl piperazine. EI Electron Impact mode of operation i n the GC/MS. ETAHEAME Ethanethioic acid S (hydroxyethyl) amino methyl ester. FID Flame Ionisation Detector. GC Gas chromatograph. 277 278 GC/MS Gas chromatograph coupled to a mass spectrometer. Henry's constant for the physical s o l u b i l i t y of compound i (kPa m 3/mol). Hj_ Henry's constant f o r the s o l u b i l i t y of compound i in aqueous DEA so l u t i o n (kPa m /mol). H2S Hydrogen sulphide. HEA N-hydroxyethyl acetamide. HEI N-hydroxyethyl imidazolidone. HEOD N-hydroxyethyl oxazolidone. HEP N-hydroxyethyl piperazine. IR Infrared. [ i ] t L i q u i d phase concentration of specie i i n mol/L at time t. k Reaction rate constant. k D E A Overall DEA degradation rate constant ( h " 1 ) . kAM-C02 Second order reaction rate constant for amine-CO2 reaction (L/mol s ) . kAM-COS Second order reaction rate constant for amine-COS reaction (L/mol s ) . kAM-CS2 Second order reaction rate constant for amine-CS 2 reaction (L/mol s ) . k^ - kj Reaction rate constants i n the k i n e t i c expressions for COS-DEA and CS2-DEA degradation. - K7 Equilibrium constants governing the i o n i c reactions i n the COS-DEA system (mol/L). K C Q C. Equilibrium constant governing the formation of DEA thiocarbamate. 279 MDEA Methyldiethanolamine. MEA Monoethanolamine. m DEA concentration (mol/L). i?DEA Vapour pressure of aqueous DEA so l u t i o n (kPa). P^ P a r t i a l pressure of compound i (kPa). P T Total system pressure (kPa). P T Sum of the p a r t i a l pressures of a c i d gases. R C 2H 4OH. T Temperature (K or °C). t Time (h). TCD Thermal Conductivity Detector. TEA Triethanolamine. THEED N,N,N -tris(hydroxyethyl) ethylenediamine. TSIM Trimethyl s i l y l imidazole. V d Difference between the f i n a l and i n i t i a l burette readings. V^ Volume of the l i q u i d phase i n the reactor. V s Volume of the l i q u i d sample t r a n s f e r r e d to the gas trapping set-up. y^ Mole f r a c t i o n of gas i i n the gas phase. Y c ^ j . Calculated (predicted) concentration of compound i at time t . Y e ^ t Experimental concentration of compound i at time t. Ymax^ Maximum experimental concentration of compound i . a i Loading of gas i (mol of gas i / mol DEA). REFERENCES 1. Kohl, A.L and Riesenfeld, F.C., "Gas P u r i f i c a t i o n " , 4th E d i t i o n , Gulf Publishing Company, Houston, Texas, (1985). 2. A s t a r i t a , G. "Mass Transfer With Chemical Reaction", E l s e v i e r Publishing Company, New York (1967). 3. Bottoms, R.R., U.S. Patent 1,783,901 (1930). 4. Smith, R.F., Travis Chemicals, Calgary, Alberta (1978). Quoted i n reference 1. 5. Pauley, R.C. and Hashema, R. "Analysis of Foaming Mechanisms i n Amine Plants", Proc. 39th Ann. Gas Conditioning Conf., Norman, Oklahoma; 219-247, (1989). 6. Moore, K.L., "Corrosion Problems i n a Refinery Diethanolamine System", Corrosion, N.A.C.E., 16, 111 (1960). 7. H a l l , W.D., and Barron, J.G., "Solving Gas Treating Problems - A Dif f e r e n t Approach", Proc. 31st Annual Gas Conditioning Conference, Norman, OK, March 2 - 4 , 1981. 8. Chakma, A. and Meisen, A., " C o r r o s i v i t y of Diethanolamine Solutions and Their Degradation Products", Ind. Eng. Chem. Prod. Res. Dev., 25(4), 627 (1986). 9. Chakma, A and Meisen, A., "Degradation of Aqueous DEA Solutions i n a Heat Transfer Tube", Can. J . Chem. Eng., 65, 264 (1987). 10. Polderman, L.D. and Steele, A.B., "Why Diethanolamine Breaks Down in Gas Treating Service", O i l Gas J . , 54(5), 206(1956). 11. Hakka, L.D., Sing,K.P., Bata G.L., Testart A.G. and Andrejchyshyn W.M., "Some Aspects of Diethanolamine Degradation i n Gas Sweetening", Gas Processing/Canada, 61(1), 32 (1968). 12. Choy E.T., "Degradation of DEA Treating Solutions", M.A.Sc. Thesis, University of B r i t i s h Columbia, B.C., (1978). 13. Kim C.J. and Sa r t o r i G., "Kinetics and Mechanism of Diethanolamine Degradation i n Aqueous Solutions Containing Carbon Dioxide", Int. J. Chem. Ki n e t i c s , 16, 1257 (1984). 14. Kennard, M.L. and Meisen, A., "Mechanisms and Ki n e t i c s of Diethanolamine Degradation", Ind. Eng. Chem. Fund., 24(2), 129 (1985 ). 280 2 8 1 15. Hsu, C S . and Kim, C.J., "Diethanolamine (DEA) Degradation under Gas-Treating Conditions", Ind. Eng. Chem. Prod'. Res. Dev., 24, 630 (1985). 16. Kennard, M.L., "Degradation of Diethanolamine Solutions", Ph.D. Thesis, U n i v e r s i t y of B r i t i s h Columbia, B.C., (1983). 17. Smith, R.F. and Younger, A.H., "Tips on DEA Treating", Hydro. P r o c , 51(7), 98 (1972). 18. Chakma A., "Studies on DEA and MDEA Degradation", Ph.D. Thesis, University of B r i t i s h Columbia, B.C., (1987). 19. Orbach, H.K. and Selleck, F.T., "The e f f e c t of Carbonyl Sulphide on Ethanolamine Solutions", Unpublished Paper (Quoted with permission of F.T. Selleck, Fluor Corporation). 20. Pearce, R.L., Arnold, J.L. and H a l l , C.K., "Studies Show Carbonyl Sulfide Problem", Hydro. P r o c , 40(8 ), 121 (1961 ). 21. Osenton J.B. and Knight A.R., "Reaction of Carbon Disulphide with Alkanolamines Used i n the Sweetening of Natural Gas", Paper Presented at the Fourth Quarterly Meeting of the Can. Gas. Proc. Assoc., Calgary (Nov. 20, 1970). 22. Ferm, R.J., "Chemistry of Carbonyl Sulphide", Chem. Rev. 57, 621 (1957). 23. Kirk-Othmer Encyclopedia of Chemical Technology, 2nd Ed., 19, 372 (1964). 24. Kirk-Othmer Encyclopedia of Chemical Technology, 2nd Ed., 4, 370 (1964). 25. Kirk-Othmer Encyclopedia of Chemical Technology, 2nd Ed., 4, 353 (1964). 26. Kirk-Othmer Encyclopedia of Chemical Technology, 2nd Ed., 19, 375 (1964). 27. Mason, J.W. and Dodge, B.F., "Equilibrium Absorption of Carbon Dioxide by Solutions of the Ethanolamine", Trans. Am. Inst. Chem. Eng., 32, 27 (1936). 28. Lee, J.I, Otto, F.D. and Mather, A.E, " S o l u b i l i t y of Carbon Dioxide i n Aqueous Diethanolamine Solutions at High Pressures", J . Chem. Eng. Data, 17(4), 465 (1972). 29. Lee, J.I, Otto, F.D. and Mather, A.E, " S o l u b i l i t y of Hydrogen Sulphide i n Aqueous Diethanolamine Solutions at High Pressures", J. Chem. Eng. Data, 18(1), 71 (1973). 282 30. Lee, J.I, Otto, F.D. and Mather, A.E, " P a r t i a l Pressures of Hydrogen Sulphide over Aqueous Diethanolamine Solutions", J . Chem. Eng. Data, 18(4), 420 (1973). 31. Lee, J.I, Otto, F.D. and Mather, A.E, "The S o l u b i l i t y of Mixtures of Carbon Dioxide and Hydrogen Sulphide i n Aqueous Diethanolamine Solutions", Can. J. Chem. Eng., 52, 125 (1974). 32. Lawson, J.D. and Garst, A.W., "Gas Sweetening Data: Equilibrium S o l u b i l i t y of Hydrogen Sulphide and Carbon Dioxide i n Aqueous Monoethanolamine and Aqueous Diethanolamine Solutions", J . Chem. Eng. Data, 21(1), 20 (1976). 33. Kennard, M.L. and Meisen, A., " S o l u b i l i t y of Carbon Dioxide i n Aqueous Solutions of Diethanolamine at High Temperatures and Pressures", J. Chem. Eng. Data, 29(3), 309 (1983). 34. L a i , D., Otto, F.D. and Mather/ A.E, "The S o l u b i l i t y of H 2S and CO2 i n a Diethanolamine Solution at Low P a r t i a l Pressures", Can. J. Chem. Eng., 63, 681 (1985). 35. B h a i r i , A., Mains, G., and Maddox, R.N., "Experimental Equilibrium Between CO2 and Ethanolamines", Proc. of Annual Gas Proc. Assoc. Convention, 1985. 36. Atwood, K, Arnold, M.R. and Kindrick, R.C., "Equilibrium For The System, Ethanolamines-Hydrogen Sulphide-Water", Ind. Eng. Chem., 49(9), 1439 (1957). 37. Danckwerts, P.V. and McNeil, K.M., "The Absorption of Carbon Dioxide Into Aqueous Amine Solutions and The Ef f e c t s of Ca t a l y s i s " , Trans. Inst. Chem. Eng., 45, T32 (1967). 38. Klyamer, S.D., Kolesnikova, T.S. and Rodin, Yu.A., Gazov. Prom., 18(2), 44 (1973). 39. Kent, R.L. and Eisenberg, B., "Better Data For Amine Treating", Hydro. P r o c , 55(2), 87 (1976). 40. Deshmukh, R.D. and Mather, A.E., "A Mathematical Model For Equilibrium S o l u b i l i t y of Hydrogen Sulphide and Carbon Dioxide i n Aqueous Alkanolamine Solutions", Chem. Eng. S c i . , 36, 355 (1981). 41. Austgen, D.M., Rochelle, G.T., Peng, X and Chen, C.C., "Model of Vapour-Liquid Equilibrium For Aqueous Acid Gas-Alkanolamine Systems Using the Electrolyte-NRTL Equation", Ind. Eng. Chem. Res., 28, 1060 (1989). 42. Schultze, W.A., Ruoho, A.A. and Short, G.H., U.S. Patent 2,315,663 (Apr. 1943). 283 43. Johnson, A.B. and Condit, D.H., U.S. Patent 2,594,311 (Apr. 1952). 44. Schultze, W.A. and Short, G.H., U.S. Patent 2,309,871 (1943). 45. Kerns, J.W. and Beamer, M., U.S. Patent 2,331,342 (Feb. 1943). 46. Reed, R.M., U.S. Patent 2,383,416 (Aug. 1941). 47. Easthergen, J.H. and A l l e n , H.I., U.S. Patent 2,726,992 (Dec. 1955 ) . 48. Sharma, M.M. and Danckwerts, P.V., "Absorption of Carbonyl Sulphide i n Amines and A l a k l i s " , Chem. Eng. S c i . , 19, 991 (1964). 49. Rahman, M.A., "Study of Reactions of Carbon Dioxide and Sulphur Containing Compounds with Ethanolamines", Ph.D Thesis, U n i v e r s i t y of Oklahoma State University, Okla., U.S.A. (1984). 50. Al-Ghawas, H.A., Ruiz-Ibanez, G. and Sandall, O.C., "Absorption of Carbonyl Sulphide i n Aqueous Methyldiethanolamine", Chem. Eng. S c i . , 44(3), 631 (1989). 51. Clarke, J.K.A., "Kinetics of Absorption of Carbon Dioxide i n Monoethanolamine Solutions at Short Contact Times", Ind. Eng. Chem. Fund., 3 , 239 (1964); 52. Chauduhuri, S.K. and Sharma, M.M., "Absorption of Carbonyl Sulphide i n Aqueous A l k a l i n e Solutions: New Strategies", Ind. Eng. Chem. Res., 28, 870 (1989). 53. K l e i n , J.P., O i l and Gas J . , Sept. 10, 109 (1970). 54. McClure, G.P. and Morrow, D.C., "Amine Process Removes COS from Propane Economically", 77(27), 106 (1979). 55. Singh, M. and B u l l i n , J.A., "Determination of Rate Constants f o r the Reaction Between Diglycolamine and Carbonyl Sulphide", Gas Separation and P u r i f i c a t i o n 2, 131 (1988). 56. Thompson, H.W., Kearton. C F . and Lamb, S.A., "Kinetics of the Reaction between Carbonyl Sulphide and Water", J . Chem. Soc. 1033 (1935). 57. Sharma, M.M., "Kinetics of Reactions of Carbonyl Sulphide and Carbon Dioxide with Amines and Ca t a l y s i s by Bronsted Bases of the Hydrolysis of COS", Trans. Faraday Soc. 61, 681 (1965). 58. Sharma, M.M. and Danckwerts, P.V., "Fast Reactions of CO2 i n Alk a l i n e Solutions", Chem. Eng. S c i . , 18, 729 (1963). 284 59. Sharma, M.M. and -Danckwerts, P.V., "Cat a l y s i s by Bronsted bases of the Reaction between C0 2 and Water", Trans. Faraday S o c , 59, 386 (1963). 60. Caplow, M., "Kinetics of Carbamate Formation and Breakdown", J . Am. Chem. S o c , 90, 6795 (1968). 61. Fr a z i e r , H.D. and Kohl, A.L., "Selective Absorption of Hydrogen Sulphide From Gas Streams", Ind. Eng. Chem., 42(11), 2288, 1950. 62. V i d a u r r i , F.C. and Kahre, L.C., "Recover H 2S S e l e c t i v e l y from Sour Gas Streams", Hydrocarbon Processing, 56(11), 333 (1977). 63. Daviet, G.R., Sundermann, R., Donelly, S. and B u l l i n , J.A., "Simulation Values Prove Out i n DEA to MDEA Switch", O i l Gas J . , 82(32), 47 (1984). 64. B e r l i e , E.M., Estep, J.W. and Ronicker, F.J., "Preventing MEA Degradation", Chem. Eng. Prog., 61(4), 82 (1965). 65. Rahman, M.A., Maddox, R.N. and Mains, G.J., "Reactions of Carbonyl Sulphide'and Methyl Mercaptan with Ethanolamines", Ind. Eng. Chem. Res., 28, 470 (1989). 66. Khotari, P.J. and Sharma, M.M., "Kinetics of Reaction Between CS 2 and Amines", Chem. Eng. S c i . , 21, 391 (1966). 67. Henry, M.S. and Grennert, M., Petroluem Refiner, 34(6), 177 (1955). 68. Gas Conditioning Fact Book, The Dow Chemical Company, Midland, Michigan, (1962 ).. 69. Brydia, L.E. and Persinger, H.E., "Quantitative Gas Chromatographic Determination of Ethanolamines as T r i f l u o r o a c e t y l Derivatives", Anal. Chem., 39(11), 1318 (1967). 70. Piekos, R., Kobyiczyk, K. and Grzybowski, J . , "Quantitative Gas Chromatographic Determination of Ethanolamines as T r i m e t h y l s i l y l Derivatives", Anal. Chem., 47(7), 1157 (1975). 71. Choy, E.T. and Meisen, A., "Gas Chromatographic Detection of Diethanolamine and i t s Degradation Products", J Chrom., 187, 145 (1980). 72. Saha N.C., Jan, S.K. and Dua, R.K., "A Rapid and Powerful Method for the Direct Gas Chromatographic Analysis of Alkanolamines: Application to Ethanolamines", Chromatographia, 10(7), 368 (1977). 285 73. Van Wijk, R., "The Use of Poly-Para-2,6-Diphenyl-Phenylene Oxide as a Porous Polymer i n Gas Chromatography", J . Chrom. S c i . , 8, 418 (1970). 74. Kennard, M.L. and Meisen, A., "Gas Chromatographic Technique f o r Analyzing P a r t i a l l y Degraded Diethanolamine Solutions", J . Chrom., 267, 373 (1983). 75. Robbins G.D. and B u l l i n J.A., "Analysis of Amine Solutions by Gas Chromatography", Presented at AIChE National Meeting, C a l i f o r n i a , (May 20 - 23, 1984); Energy Progr., 4, 229 (1984). 76. Chakma, A. and Meisen, A, " I d e n t i f i c a t i o n of Methyl Diethanolamine Degradation Products by Gas Chromatography and Gas Chromatography- Mass Spectrometry", J . Chrom., 457, 287 (1988). 77. Pecsok, R., Shields, L.D., Cairns, T. and McWilliam, I.G., "Modern Methods of Chemical Analysis", 2nd E d i t i o n , John Wiley & Sons Inc., New York. (1976) . 78. Pierce, A.E., " S i l y l a t i o n of Organic Compounds", Pierce Chemical Co., 111. (1968). 79. EPA/NIH Mass Spectral Data Base, National Stand. Ref. Data Service, Natl. Bur. of Stand., U.S., (1983). 80. Eight Peak Index of Mass Spectra, 2nd Ed., Mass Spectrometry Data Centre, AWRE, Reading, U.K., (1974). 81. Dean, J.A., "Handbook of Organic Chemistry", Chapter 6, McGraw H i l l Book Co., New York, (1987). 82. Simmons, W.W ( e d i t o r ) , "The Sadtler Handbook of Infrared Spectra", Sadtler Research Laboratories Inc., Pennsylvania, (1978). 83. R e i l l y , J.T., Schubert, C.N., Lindner, J.R., Donohue, M.D. and K e l l y , R.M., " E f f e c t of Heterocyclic Amine Additives on the Absorption Rates of Carbonyl Sulphide and Carbon Dioxide i n Aqueous Methyldiethanolamine", Chem. Eng. Comm., 93, 181 (1990). 84. Blanc, C , G r a i l , M. and Demarais, G., "Amine Degradation Products Play no Part i n Corrosion at Gas Sweetening Plants", O i l Gas J . , Nov.15, pl28 (1982). 85. P a t a i , S ( e d i t o r ) , "The Chemistry of the Carbonyl Group", Chapter 15, p761, Interscience Publishers, New York (1966). 86. Horowitz, W., AOAC Methods, 12th E d i t i o n , George Banta Co., (1975) . 286 87. Peng, D.Y. and Robinson, D.B., "A New Two-Constant Equation of State", Ind. Eng. Chem. Fund., 15(1), 59 (1976). 88. Perry, R.H. and Green, D.W., "Chemical Engineers Handbook", 6th E d i t i o n , McGraw H i l l , New York, (1984). 89. Savage, D.W., Funk, E.W., Yu> CW. and A s t a r i t a , G., "Selective Absorption of H 2S and C0 2 i n Aqueous Solutions of Methyldiethanolamine", Ind. Eng. Chem. Fund., 25, 326 (1986). 90. Moore, C , "UBC NLE - Zeroes of Nonlinear Equations", University of B r i t i s h Columbia Computing Centre Document, Vancouver, BC. (1984). 91. Astle, M.S., " I n d u s t r i a l Organic Nitrogen Compounds", Reinhold Publishing Corporation, New York, 134 (1961). 92. Kirk-Othmer Encyclopedia of Chemical Technology, 2nd Ed., 81, 77 (1964). 93. Lysenko, N.M., "Condensation of Primary Amines with Paraformaldehyde and Thiocarboxylic Acids", Zhur. Org. Khimii, 10 (10), 2049 (1974). 94. Chakma, A. and Meisen, A. ^ ' S o l u b i l i t y of C0 2 i n Aqueous Methyldiethanolamine and N,N - Bis hydroxyethyl piperazine Solutions", Ind. Eng. Chem. Res. 26, 2461 (1987). 95. Vaessen, W., "U.B.C. NLP - Nonlinear Function Optimization", The University of B r i t i s h Columbia Computing Centre Document, Vancouver, B.C., 1983. 96. Moore, C , "U.B.C. RKC - Runge Kutta with Error Control", The University of B r i t i s h Columbia Computing Centre Document, Vancouver, B.C., 1983. 97. Levenspiel, 0., "Chemical Reaction Engineering", 2nd e d i t i o n , John Wiley & Sons Inc., New York, 1972. 98. Drechsel, E.K., "N-Vinyl-2-Oxazolidone", J. Org. Chem., 22, 849 (1957). 99. Moller, H. and Osberghaus, R., "Cosmetic Agent Containing •Moisturizing Agents for Skin" Ger. Offen 2,746,650 ( A p r i l 1979). Chem. Abst. 91:128904u. 100. Dawodu, O.F. and Meisen, A., "Amine Degradation by Carbonyl Sulphide and Carbon Disulphide", Proceedings of the 39th Annual Gas Conditioning Conference, Norman, Okla., p 9 - 71 (1989). APPENDIX A . l ALKANOLAMINES COMMONLY USED INDUSTRIALLY / MONOETHANOLAMINE (MEA) - H-N C 2H 4OH \ H / DIGLYCOLAMINE (DGA) OR H-N B / B * -HYDROXYAMINOETHYL ETHER \ C 2H 4OC 2H 4OH H / DIETHANOLAMINE (DEA) H-N C 2H 4OH \ C 2H 4OH DIISOPROPANOLAMINE (DIPA) CH3CCH2-N-CH2CCH3 I \ I OH H OH TRIETHANOLAMINE (TEA) HOC2H4-N C 2H 4OH / \ C 2H 4OH 287 METHYLDIETHANOLAMINE (MDEA) 2-AMINO-2 METHYL -1-PROPANOL (AMP) 288 C 2H 4OH / CH3-N \ C 2H 4OH H CH 3 \ | N-C-CH2OH / | H CH 3 Figure A . l : Structures of alkanolamines used i n gas t r e a t i n g operations 289 A.2 SYNTHESIS OF SELECT DEGRADATION COMPOUNDS Some of the degradation compounds, HEOD, THEED and BHEI were not ava i l a b l e commercially. They had to be synthesized f o r subsequent c a l i b r a t i o n of the GC so that t h e i r concentrations i n the degraded solutions could be qua n t i f i e d . The synthesis methods are described below: A.2.1 HEOD SYNTHESIS HEOD was synthesized according to the procedure of Dreschel (98). DEA and d i e t h y l carbonate, the l a t t e r i n 20% excess on a molar basis, were placed i n the g l a s s - l i n e d reactor. The reactor was sealed and the contents s t i r r e d f o r about an hour to thoroughly mix the immiscible l i q u i d s . Heat was then applied to bring the temperature of the autoclave to 110 °C and maintained as such for 22 hours. HEOD was expected to be produced according to the rea c t i o n : HOC 2H 4 C 2 H 5 ° H 2 C " C H 2 \ \ | | N-H + C = 0 -t O N-C2H4OH + 2 C 2H 5OH / / \ / H0C 2H 4 C 2 H 5 ° c 0 DEA DIETHYL CARBONATE HEOD The temperature was then r a i s e d and maintained at 130 °C u n t i l ethanol production ceased. The gas outlet valve on the autoclave was l e f t open 290 throughout the duration of the reaction so that the by-product ethanol, continuously flowed out into a c o l l e c t i n g beaker. GC analysis of the cooled product showed that i t contained mainly HEOD, as well as ethanol and r e s i d u a l d i e t h y l carbonate. The l a t t e r two were removed by evaporation i n a rotavapor at reduced pressure. The o i l y , coloured product was p u r i f i e d by mixing with activated carbon and then f i l t e r e d to give a product which on ana l y s i s , contained over 95% HEOD. This f i n a l product was used to generate the c a l i b r a t i o n curve f o r HEOD. A.2.2 THEED SYNTHESIS THEED was synthesized by following the procedure of Kennard (14). 105 g of DEA was reacted with 87 g of N-hydroxyethyl imine (HEM) i n the presence of 5 g of aluminium c h l o r i d e , at 120 °C for 24 hours. The reactants were placed i n the autoclave which was then sealed and pressurized to 0.7 MPa with nitrogen. THEED was expected to be produced according to the reaction: HOC 0H„ H,C HOC0H,, H -2n4 n2 \ N-H + / 2 n4 \ \ / N-C2H4OH -t N-C2H4-N / / \ HOC 2H 4 H 2C HOC 2H 4 C 2H 4OH DEA HEM THEED Despite several t r i a l s , THEED produced from the reaction was lower than the 70 - 80 % y i e l d obtained by Kennard (16) and Chakma (18). The crude product mixture was p u r i f i e d by column chromatography. The mixture was 291 f i r s t d i l u t e d with water and then passed at the rate of 0.5 mL / min, through a 15 mm ID glass column packed to a height of 40 cm with 60 200 mesh s i l i c a g e l . Water was again used as the e l u t i n g solvent. The THEED f r a c t i o n was concentrated i n a rotavapor at reduced pressure to give a f i n a l product mixture containing approximately 48% THEED, 47% DEA and 5% BHEP on a molar basis. By using the previously prepared c a l i b r a t i o n curves of DEA and BHEP, i t was poss i b l e to cal c u l a t e the concentration of THEED i n each sol u t i o n of the mixture and hence es t a b l i s h the c a l i b r a t i o n curve f o r THEED. A. 2. 3 HEI SYNTHESIS N-hydroxyethyl imidazolidone (HEI) was synthesized according to l i t e r a t u r e procedure (99). Equimolar amounts of urea and Hydroxyethyl ethylene diamine (HEED) were placed i n the reactor and maintained at 200 °C f or 4 hours. The following reaction was expected to occur: HOC 2H 4 H H 2N H 2C - CH 2 \ / \ | | N-C2H4-N + C = 0 -> H-N N-C2H4OH + 2 NH3 / \ / \ / H H H 2N C 0 HEED UREA HEI GC/MS analysis confirmed the reaction product as HEI. The product was further p u r i f i e d by act i v a t e d carbon adsorption. GC analysis of the f i n a l product indicated a p u r i t y of 97% +. 292 A.2.4 BHEI SYNTHESIS BHEI was synthesized by reacting BHEED with urea (20% excess) at 225 °C for 4 hours i n the autocalve. This technique i s an adaptation of the procedure f o r the synthesis of HEI and was expected to generate BHEI according to the reaction: HOC 2H 4 C 2H 4OH \ / N-C2H4-N / \ H H N N'BHEED At the end of the reaction, the ammonia formed was discharged through the gas outlet valve into the fume hood. Analysis of the crude mixture by gas chromatography and GC/MS revealed a BHEI content of over 80%. The mixture was further p u r i f i e d by column chromatography. A 15 mm ID glass column was packed to a height of 40 cm with 70 - 230 mesh s i l i c a g e l . The impure mixture was s l i g h t l y d i l u t e d with water, t r a n s f e r r e d to the top of the column and a f t e r adsorption, was eluted with water at a flow rate of 0.5 mL/min. The BHEI f r a c t i o n s were concentrated i n a rotavapor at reduced pressure. GC analysis showed that the f i n a l product had a p u r i t y of over 95%. + C = 0 -> HOC2H4-N N-C2H4OH + 2 NH3 H 2N H 2C - CH 2 / \ / H 2N C 0 UREA • B H E I 293 APPENDIX B B.l CALIBRATION OF THE GAS CHROMATOGRAPH B . l . l DEGRADATION RUNS Once the degradation compounds had been i d e n t i f i e d , i t was necessary to quantify them. This was done by preparing c a l i b r a t i o n curves of GC peak area versus concentration. Commercial compounds were used except i n the case of HEOD, HEI, THEED and BHEI which were not available commercially and had to be synthesized (see Appendix A.2). Typical c a l i b r a t i o n curves f o r the major compounds are shown i n Figs. B.l - B.10. C a l i b r a t i o n equations were generated for each compound from a least squares f i t of the concentration and peak areas. These equations were subsequently used to calculate the concentrations of the various compounds i n the samples of the degraded solutions once the GC peak areas were known. As the Tenax columns aged or had to be replaced, new c a l i b r a t i o n curves were prepared. The frequency of r e - c a l i b r a t i o n depended on the extent of usage of the column. On the average, new curves were prepared a f t e r every four or f i v e runs i n v o l v i n g 10 sample withdrawals each ( t h i s , i n turn, corresponds to about 120 to 150 GC i n j e c t i o n s ) . Due to the number of curves generated, the c a l i b r a t i o n usually required about 2 to 3 days. 294 B.l.2 SOLUBILITY AND HYDROLYSIS RUNS Known volumes of factory analysed standard mixtures containing H 2S and C0 2 were drawn into pressure lok syringes and d i l u t e d with appropriate amounts of nitrogen to obtain the desired concentrations of the gases. In the case of COS the pure gas was withdrawn from the gas c y l i n d e r and d i l u t e d with nitrogen. The mixtures i n the syringes were properly mixed p r i o r to t h e i r analysis with the Varian GC containing a TCD. D e t a i l s of the operating conditions have been provided i n Chapter 7. The c a l i b r a t i o n curves were generated by p l o t t i n g the peak areas •obtained from the GC analysis against the concentration (vol%) of each gas in the mixtures. Typical c a l i b r a t i o n curves are shown i n Figs. B . l l - B.13  296 0.10 o 55 O i—i « H 55 W O 55 O o w 55 o 55 0.08 H 0.06 0.04 h 0.02 h 0.00 0.0 0.8 1.6 2.4 3.2 BUTANONE PEAK AREA ( 1 0 6 ) Figure B.2: C a l i b r a t i o n curve f o r butanone. 297 Figure B . 3 : C a l i b r a t i o n curve for MEA. 298 6.0 i i | i | i | i | i 0.0 30.0 60.0 90.0 120.0 150.0 DEA PEAK AREA (106) Figure B.4: C a l i b r a t i o n curve for DEA. 299 Figure B . 5 : C a l i b r a t i o n curve f o r BHEED. 300 0.30 i . 1 1 1 1 1 1 r 0.0 3.5 7.0 10.5 14.0 17.5 BHEP PEAK AREA (10°) Figure B.6: C a l i b r a t i o n curve for BHEP. 301 Figure B . 7 : C a l i b r a t i o n curve f o r HEOD. 302 o.70 I 1 1 1 1 1 1 1 r 0.0 2.5 5.0 7.5 10.0 12.5 HEI PEAK AREA ( 1 0 6 ) F i g u r e B . 8 : C a l i b r a t i o n c u r v e f o r H E I . 303 Figure B . 9 : C a l i b r a t i o n curve for THEED. 304 Figure B.10: C a l i b r a t i o n curve f o r BHEI. 305 F i g u r e B . l l : C a l i b r a t i o n c u r v e f o r CO2. 306 Figure B.12: C a l i b r a t i o n curve for COS. 307 Figure B.13: C a l i b r a t i o n curve f o r H2S. 308 B.2 EI SPECTRA OF MINOR DEGRADATION COMPOUNDS IN THE COS-DEA SYSTEM 1 LFRN 3802 SPECT 15 . 9756 Me thano1 (8CI9CI) CH40 F i g u r e B . 1 4 : S a m p l e a n d l i b r a r y E I s p e c t r a o f m e t h a n o l . 309 * 1 L F R M 3 0 8 2 S P E C T 4 9 MW = 4 6 C 2 H 6 0 . 9 8 0 3 E t h a n o l ( 9 C I ) Figure B.15: Sample and l i b r a r y EI spectra of ethanol. 3 1 0 « 1 LFRH 3092 SPECT 37 MW= 44 C2H40 .7396 f i c e t a l d e h y d e (SCI9CI) Figure B.16: Sample and l i b r a r y EI spectra of acetaldehyde. 311 1 8 0 - 8 0 - 6 0 - 4 0 - 2 6 - 6 - i M I 1 . , . . . .] i 11 i ; 11 11 11 i i i j i i i 11 11 2 0 3 8 4 0 1 1 . . j 1 1 1 ! J i 1 1 1 5 8 c 1 1 * • i • • • 1 i • • 1 - i • • • 1 i 0 7 8 8 8 9 0 I|| 1 - | | ' « 1 L F R N 3 6 0 2 S P E C T 108 . 7 8 8 8 P i ce t i c a c i d ( 8 C I 9 C I ) ! t1l.J= 6 8 C 2 H 4 0 2 1 6 6 -i 3 6 - 6 6 - 4 6 - 2 6 - 6 - l 1 , 1 2@ 3 0 4 0 111 111 • i • | i i i i 5 0 t 0 7 0 8 0 9 6 Figure B .17 : Sample and l i b r a r y EI spec t ra of a c e t i c a c i d . 312 * 1 . 7 5 9 7 L F R H 3 0 0 2 S P E C T 7e.6 MW = P y r i d i n e , 2 - r o e t h y l - ( 9 C I ) 9 3 C 6 H 7 H 1 0 0 - 8 0 - 6 0 - 4 0 - 2 0 - 0 " ill , 1 1 1 2 0 4 0 6 6 i • I 8 6 100 • i 1 2 0 Figure B.18: Sample and l i b r a r y EI spectra of methyl pyridine. 313 1 8 8 i 8 8 - 6 8 - 4 8 - 2 8 - 1 h i 0 - 1 ... , .,1 .1... . , ! . . , i' .1 1 I • i 2 0 ' 1 1 I 1 1 1 4 8 6 0 )' 1 | ! j 8 0 100 1 128 1 i 148 r 1 8 0 . 0 ' - i , , « 1 L F R N 3 0 0 2 S P E C T 2 6 5 9 MUI= 1 2 2 C 4 H 1 8 S 2 . 9 7 8 6 D i s u l f i d e , d i e t h y l 19CI) Figur B.19: Sample and l i b r a r y EI spectra of d i e t h y l disulphide. 314 4 9 . 6 " .1.1..I, * 1 L F R N 3 6 6 2 S P E C T 2 5 5 1 MW= 1 2 6 C 4 H3S 2 . 3 5 6 2 1 , 2 - D i t h i a n e ( 9 C I ) 1 0 0 3 6 6 0 - 4 6 - 2 9 - 6 - 2 6 —i— 4 6 I I I 6 6 "i—'-—i 1—i—•—r- 8 6 1 0 6 1 2 0 — i — • — r 1 4 0 1 6 6 Figure B.20: Sample and EI spectra of 1,2 dithiane. 315 «t 1 L F R H 3 0 0 2 S P E C T 2 6 3 3 MtJ= 121 C S H 1 1 H . 9 8 0 9 P y r i d i n e , S - e t h y 1 - 2 - r a e t h y 1 - ( 9 C I ) 1 8 0 - SO - 6 8 - 4 0 - 2 8 - 1 , !,! 1 1 ' 1 2 0 4 0 6 0 • • 1 0 0 I • I 1 2 8 1 i 1 4 0 Figure B.21: Sample and l i b r a r y EI spectra of ethyl methyl pyridine. 3 1 6 108 -i se 60 48 20 70 60 - r 1 - 80 1 2 7 98 109 148 100 128 12.4 1' • ' , • , • , 148 160 180 260 (a) (b) Figure B.22: Mass spectra of EHEP (a: EI; b: CI) 3 1 7 C EXPERIMENTAL CONCENTRATIONS •C.l COS-DEA SYSTEMS Table C . l : Concentrations of compounds i n COS-DEA system. [DEA] Q = 40 wt%, T = 165 °C, P c o g = 345 kPa. TIME CONCENTRATION (mol/L) (H) DEA ACET BUT MEA BHEED BHEP HEOD HEI THEED BHEI 0 4 .20 0. .000 0. ,000 0 .000 0 .000 0 .000 0 .000 0 .000 0 .000 0. .000 2 4 .09 0. .010 0. ,004 0 .129 0 .000 0 .000 0 .000 0 .000 0 .000 0. .000 4 3 .90 0. .013 0. .010 0 .202 0 .014 0 .000 0 .010 0 .000 0 .000 0, .000 6 3 .68 0. .015 0. .013 0 .263 0 .020 0 .003 0 .015 0 .000 0 .000 0. .000 8 3 .48 0, .017 0, .013 0 .312 0 .028 0 .007 0 .027 0 .000 0 .085 0. .000 12 3 .27 0, .019 0, .016 0 .487 0 .046 0 .014 0 .043 0 .000 0 .133 0, .000 24 2 .77 0 , .015 0, .020 0 .730 0 . 156 0 .033 0 .107 0 .069 0 .461 0, .040 30 2 .37 0. .013 0, .019 0 .687 0 .211 0 .039 0 .119 0 .096 0 .587 0, .105 36 2 . 15 0 .011 0 .020 0 .655 0 .233 0 .043 0 .122 0 .108 0 .615 0 .127 48 1 .59 0 .010 0 .020 0 .578 0 .286 0 .074 0 .146 0 .131 0 .845 0 .245 k D E A = 0.0194 h" 1 Table C.2: Concentrations of compounds i n COS-DEA system. [DEA] Q = 40 wt%, T = 160 °C, P c o s = 345 kPa. TIME CONCENTRATION (mol/L) (H) DEA ACET BUT MEA BHEED BHEP HEOD HEI THEED BHEI 0 4 .12 0 .000 0. ,000 0 .000 0 .000 0 .000 0 .000 0 .000 0 .000 0 .000 2 4 .02 0 .008 0. .003 0 .083 0 .000 0 .000 0 .000 0 .000 0 .000 0 .000 4 3 .83 0 .009 0. .005 0 .136 0 .010 0 .000 0 .000 0 .000 0 .000 0 .000 6 3 .71 0 .011 0, .010 0 .200 0 .017 0 .000 0 .010. 0 .000 0 .000 0 .000 8 3 .71 0 .013 0, .014 0 .284 0 .024 0 .004 0 .025 0 .000 0 .078 0 .000 12 3 .45 0 .015 0, .016 0 .405 0 .036 0 .008 0 .036 0 .000 0 .106 0 .000 24 3 .02 0 .013 0, .018 0 .550 0 .116 0 .021 0 .088 0 .052 0 .431 0 .050 30 2 .78 0 .011 0 .019 0 .644 0 . 172 0 .029 0 .099 0 .065 0 .615 0 .079 36 2 .58 0 .011 0 .020 0 .637 0 .209 0 .036 0 .117 0 .070 0 .730 0 .121 k n c, s = 0.0127 h 318 Table C.3: Concentratirons of compounds i n COS-DEA system. [DEA] Q = 40 wt%, T = 150 °C, P c o g = 345 kPa. TIME CONCENTRATION (mol/L) (H) DEA ACET BUT MEA BHEED BHEP HEOD HEI THEED BHEI 0 4. .17 0. .000 0. .000 0 .000 0 .000 0 .000 0 .000 0 .000 0 .000 0 .000 2 4. .09 0. .007 0. .001 0 .068 0 .000 0 .000 0 .000 0 .000 0 .000 0 .000 4 3. . 95 0. .009 0. .003 0 .108 0 .007 0 .000 0 .000 0 .000 0 .000 0 .000 6 3. .85 0, .011 0. .005 0 .157 0 .014 0 .000 0 .007 0 .000 0 .000 0 .000 8 3. .74 0, .013 0, .008 0 .206 0 .021 0 .000 0 .010 0 .000 0 .000 0 .000 12 3. .79 0, .016 0, .014 0 .318 0 .029 0 .006 0 .020 0 .000 0 .000 0 .000 24 3. .42 0, .021 0. .018 0 .535 0 .043 0 .012 0 .042 0 .000 0 .122 0 .005 30 3. .08 0, .020 0, .017 0 .576 0 .053 0 .016 0 .048 0 .000 0 .145 0 .009 36 2. .92 0. .019 0, .018 0 .704 0 .073 0 .019 0 .060 0 .009 0 .211 0 .016 48 2. .69 0, .019 0, .019 0 .769 0 . 141 0 .033 0 .110 0 .012 0 .326 0 .027 54 2, .59 0 .020 0, .018 0 .773 0 .173 0 .043 0 .116 0 .020 0 .364 0 .036 k n c. a = 0.0089 h Table C.4: Concentrations of compounds i n COS-DEA system. [DEA] Q = 40 wt%, T = 127 °C, P c o s = 345 kPa. TIME CONCENTRATION (mol/L) (H) DEA ACET BUT MEA BHEED BHEP HEOD HEI THEED BHEI 0 4 .20 0 .000 0. 000 0 .000 0 .000 0 .000 0 .000 0 .000 0 .000 0 .000 12 4 .00 0 .012 0. 002 0 .098 0 .000 0 .000 0 .000 0 .000 0 .000 0 .000 20 3 .86 0 .018 0. 004 0 .218 0 .005 0 .000 0 .025 0 .000 0 .000 0 .000 44 3 .50 0 .020 0. 009 0 .390 0 .020 0 .005 0 .047 0 .000 0 .035 0 .000 68 3 .20 0 .020 0. 011 0 .570 0 .038 0 .011 0 .068 0 .011 0 .123 0 .031 92 2 .86 0 .022 0. 012 0 .649 0 .050 0 .016 0' .077 0 .013 0 .198 0 .055 116 2 .61 0 .019 0. 013 0 .679 0 .091 0 .023 0 .107 0 .015 0 .310 0 .079 140 2 .33 0 .024 0. 014 0 .635 0 .128 0 .038 0 . 127 0 .028 0 .439 0 .100 164 2 .12 0 .023 0. 013 0 .685 0 .160 0 .047 0 . 142 0 .036 0 .532 0 . 147 k n c , s = 0.0042 h 3 1 9 Table C.5: Concentrations of compounds i n COS-DEA system. [DEA] Q = 30 wt%, T = 190 °C, P c o s = 345 kPa. TIME CONCENTRATION (mol/L) (H) DEA ACET BUT MEA BHEED BHEP HEOD HEI THEED BHEI 0 3 .11 0 .000 0, .000 0. .000 0 .000 0 .000 0 .000 0. .000 0 .000 0. .000 2 2 . 90 0 .010 0, .006 0. .130 0 .000 0 .000 0 .010 0. .000 0 .000 0. .000 4 2 .66 0 .013 0. .008 0. .220 0 .000 0 .002 0 .014 0. .000 0 .000 0. ,000 6 2 .57 0 .016 0, .010 0. ,330 0 .010 0 .005 0 .024 0. .000 0 .040 0. .000 8 2 .42 0 .013 0, .011 0. .390 0 .020 0 .008 0 .031 0. .017 0 .110 0, .000 12 2 .13 0 .012 0, .013 0. .440 0 .040 0 .011 0 .042 0, .020 0 .200 0. .010 24 1 .32 0 .012 0, .017 0. .410 0 . 150 0 .044 0 .081 0, .039 0 .500 0, .116 30 1 .16 0 .013 0 .018 0, .380 0 .180 0 .072 0 .088 0, .049 0 .590 0, .187 36 1 .00 0 .010 0 .019 0, .340 0 .190 0 .098 0 .093 0, .054 0 .600 0, .242 48 0 .82 0 .008 0 .017 0, .290 0 .170 0 .134 0 .088 0, .066 0 .530 0, .305 k n c, A = 0.0291 h" 1 Table C.6: Concentrations of compounds i n COS-DEA system. [DEA] Q = 30 wt%, T = 170 °C, P C Q S = 345 kPa. TIME CONCENTRATION (mol/L) (H) DEA ACET BUT MEA BHEED BHEP HEOD HEI THEED BHEI 0 3 .04 0 .000 0. .000 0 .000 0 .000 0 .000 0 .000 0 .000 0 .000 0 .000 2 2 .86 0 .007 0. .003 0 .023 0 .000 0 .000 0 .016 0 .000 0 .000 0 .000 4 2 .85 0 .010 0. .006 0 .089 0 .000 0 .000 0 .020 0 .000 0 .000 0 .000 6 2 .60 0 .012 0. .007 0 .133 0 .000 0 .000 0 .022 0 .000 0 .000 0 .000 8 2 .56 0 .013 0. .007 0 .193 0 .000 0 .003 0 .025 0 .000 0 .000 0 .000 12 2 .49 0 .012 0. .008 0 .276 0 .008 0 .005 0 .036 0 .000 0 .000 0 .000 24 2 .05 0 .010 0, .010 0 .461 0 .038 0 .009 0 .0.64 0 .016 0 .190 0 .000 30 1 .91 0 .010 0, .012 0 .500 0 .112 0 .017 0 .107 0 .023 0 .390 0 .070 36 1 .74 0 .010 0, .014 0 .489 0 .138 0 .022 0 .117 0 .029 0 .480 0 .100 48 1 .38 0 .009 0 .014 0 .412 0 . 175 0 .038 0 .136 0 .034 0 .630 0 .190 60 1 .02 0 .007 0 .013 0 .308 0 . 157 0 .048 0 .116 0 .034 0 .610 0 .220 knc.> = 0.0168 h 320 Table C . 7 : Concentrations of compounds i n COS-DEA system. [DEA]Q = 30 wt%, T = 165 °C, P C Q S = 345 kPa. TIME CONCENTRATION (mol/L) (H) DEA ACET BUT MEA BHEED BHEP HEOD HEI THEED BHEI 0 3 . 0 0 0 . 0 0 0 0 . . 0 0 0 0 . 0 0 0 0 . 0 0 0 0 . 0 0 0 0 . 0 0 0 0 . 0 0 0 0 . 0 0 0 0 . 0 0 0 2 3 . 01 0 . 0 0 7 0. . 0 0 3 0 . 0 8 2 0 . 0 0 0 0 . 0 0 0 0 . 0 0 0 0 . 0 0 0 0 . 0 0 0 0 . 0 0 0 4 2 . 8 2 0 . 0 1 0 0, . 0 0 5 0 . 1 0 0 0 . 0 1 2 0 . 0 0 0 0 . 0 0 6 0 . 0 0 0 0 . 0 0 0 0 . 0 0 0 8 2 . 6 3 0 . 0 1 3 0, .011 0 . 2 0 5 0 . 0 1 6 0 . 0 0 0 0 . 0 1 7 0 . 0 0 0 0 . 0 0 0 0 . 0 0 0 12 2 . 5 0 0 . 0 1 6 0. . 018 0 . 3 0 0 0 . 0 2 1 0 . 0 0 3 0 . 0 2 7 ' 0 . 0 0 2 0 . 0 6 7 0 . 0 0 0 24 2 . 0 9 0 . 0 2 4 0. .021 0 . 4 5 4 0 . 0 4 7 0 . 0 1 7 0 . 0 3 3 0 . 0 0 8 0 . 0 8 7 0 . 0 1 3 30 1 . 8 9 0 . 0 2 4 0, . 0 2 0 0 . 5 5 1 0 . 0 6 6 0 . 0 2 3 0 . 0 5 1 0 . 0 1 6 0 . 1 1 7 0 . 0 1 5 36 1 . 7 3 0 . 0 2 2 0, . 0 2 0 0 . 6 2 4 0 . 0 8 8 0 . 0 2 7 0 . 0 5 8 0 . 0 2 2 0 . 1 4 9 0 . 0 2 0 48 1 . 3 6 0 . 0 1 6 0, . 021 0 . 6 2 7 0 . 1 2 7 0 . 0 4 0 0 . 0 7 0 0 . 0 3 9 0 . 2 8 7 0 . 0 4 0 knc., = 0 . 0 1 6 2 h " Table C . 8 : Concentrations of compounds i n COS-DEA system. [DEA]Q = 30 wt%, T = 160 °C, P c o s = 3 4 5 kPa. TIME CONCENTRATION (mol/L) (H) DEA ACET BUT MEA BHEED BHEP HEOD HEI THEED BHEI 0 3 . 0 5 0 . 0 0 0 0 . . 0 0 0 0 . 0 0 0 0 . 0 0 0 0 . 0 0 0 0 . 0 0 0 0 . 0 0 0 0 . 0 0 0 0 . 0 0 0 2 3 . 0 8 0 . 0 0 7 0 . . 0 0 0 0 . 0 0 5 0 . 0 0 0 0 . 0 0 0 0 . 0 0 0 0 . 0 0 0 0 . 0 0 0 0 . 0 0 0 4 2 . 9 9 0 . 0 0 8 0. . 0 0 4 0 . 0 5 0 0 . 0 0 0 0 . 0 0 0 0 . 0 1 0 0 . 0 0 0 0 . 0 0 0 0 . 0 0 0 8 2 . 8 3 0 . 0 1 0 0. . 0 0 6 0 . 1 1 0 0 . 0 0 0 0 . 0 0 0 0 . 0 1 9 0 . 0 0 0 0 . 0 0 0 0 . 0 0 0 12 2 . 7 2 0 . 0 1 4 0. . 0 0 9 0 . 1 9 2 0 . 0 0 4 0 . 0 0 2 0 . 0 2 5 0 . 0 0 0 0 . 0 0 0 0 . 0 0 0 24 2 . 3 9 0 . 0 1 6 0. .011 0 . 3 6 4 0 . 0 1 0 0 . 0 0 6 0 . 0 3 9 0 . 0 0 0 0 . 0 0 5 0 . 0 0 0 30 2 . 2 4 0 . 0 1 4 0, . 011 0 . 4 0 0 0 . 0 2 0 0 . 0 0 8 0 . 0 5 4 0 . 0 0 3 0 . 100 0 . 0 0 0 36 2 . 0 2 0 . 0 1 3 0, . 0 1 2 0 . 4 4 0 0 . 0 3 0 0 . 0 1 0 0 . 0 6 2 0 . 0 0 6 0 . 1 5 0 0 . 0 0 5 48 1 . 7 0 0 . 0 1 0 0, . 0 1 2 0 . 5 1 0 0 . 0 7 0 0 . 0 1 2 0 . 0 9 1 0 . 0 2 2 0 . 3 0 0 0 . 0 5 0 k n P , = 0 . 0 1 2 0 h " 1 321 Table C.9: Concentrations of compounds i n COS-DEA system. [DEA] Q = 30 wt%, T = 150 °C, P c o s = 345 kPa. TIME CONCENTRATION (mol/L) (H) DEA ACET BUT MEA BHEED BHEP HEOD HEI THEED BHEI 0 3. .01 0 .000 0 .000 0 .000 0 .000 0 .000 0 .000 0, ,000 0. .000 0 .000 2 3. .06 0 .006 0 .000 0 .044 0 .000 0 .000 0 .000 0. .000 0. .000 0 .000 4 2. . 91 0 .007 0 .002 0 .077 0 .000 0 .000 0 .000 0. .000 0. .000 0 .000 8 2. .83 0 .010 0 .006 0 .127 0 .009 0 .000 0 .005 0. .000 0. .000 0 .000 12 2, .76 0 .013 0 .011 0 .200 0 .012 0 .000 0 .010 0. .000 0. .000 0 .000 24 2, .47 0 .016 0 .014 0 .319 0 .019 0 .008 0 .020 0. .000 0, .000 0 .000 30 2, .31 0 .019 0 .016 0 .402 0 .022 0 .009 0 .031 0, .000 0, .030 0 .000 36 2, .18 0 .022 0 .017 0 .488 0 .035 0 .017 0 .056 0, .006 0, .080 0 .011 48 1, .93 0 .015 0 .016 0 .572 0 .073 0 .024 0 .086 0. .009 0, .142 0 .017 k ™ ™ = 0.0094 h Table C.10: Concentrations of compounds i n COS-DEA system. [DEA] Q = 30 wt%, T = 127 °C, P c o s = 345 kPa. TIME CONCENTRATION (mdl/L) (H) DEA ACET BUT MEA BHEED BHEP HEOD HEI THEED BHEI 0 3 .08 0 .000 0 .000 0 .000 0 .000 0. 000 0 .000 0. .000 0 .000 0 .000 24 2 .94 0 .010 0 .003 0 .162 0 .000 0. 000 0 .000 0. .000 0 .000 0 .000 48 2 .73 0 .019 0 .010 0 .280 0 .000 0. 000 0 .018 0. .000 0 .000 0 .000 80 2 .51 0 .019 0 .010 0 .410 0 .000 0. 000 0 .030 0. .003 0 .050 0 .000 96 2 .35 0 .020 0 .010 0 .500 0 .005 0. 003 0 .033 0. .005 0 .070 0 .000 124 2 .19 0 .022 0 .009 0 .610 0 .017 0. 011 0 .047 0. .006 0 .108 0 .012 146 1 .95 0 .016 0 .008 0 .660 0 .029 0. 012 0 .054 0 , .008 0 .152 0 .024 168 1 .88 0 .018 0 .010 0 .730 0 .057 0. 017 0 .085 0. .018 0 .222 0 .054 192 1 .88 0 .020 0 .011 0 .840 0 .082 0. 028 0 .113 0, .024 0 .281 0 .076 k n c,R = 0.0031 h 322 Table C . l l : Concentrations of compounds in COS-DEA system. [DEA] Q = 20 wt%, T = 195 °C, P C Q S = 345 kPa. TIME CONCENTRATION (mol/L) (H) DEA ACET BUT MEA BHEED BHEP HEOD HEI THEED BHEI 0 1 . 97 0 .000 0 .000 0 .000 0 . 000 0 .000 0 .000 0 .000 0 .000 0 .000 2 1 .84 0 .007 0 .005 0 .103 0 . 000 0 .000 0 .000 0 .000 0 .000 0 .000 4 1 .70 0 .008 0 .007 0 .154 0. .000 0 .000 0 .000 0 .000 0 .000 0 .000 6 1 .63 0 .009 0 .008 0 .203 0. .000 0 .000 0 .000 0 .000 0 .000 0 .000 8 1 .54 0 .008 0 .008 0 .227 0 . 015 0 .004 0 .010 0 .000 0 .000 0 .000 12 1 .40 0 .011 0 .010 0 .321 0. .024 0 .007 0 .015 0 .007 0 .076 0 .000 24 1 .00 0 .011 0 .014 0 .402 0. .059 0 .017 0 .027 0 .031 0 .149 0 .024 30 0 .79 0 .008 0 .014 0 .353 0. .110 0 .028 0 .047 0 .071 0 .227 0 .077 36 0 .68 0 .008 0 .013 0 .335 0 , .121 0 .040 0 .050 0 .088 0 .257 0 .112 kDEA = °-0293 h" 1 Table C.12: Concentrations of compounds i n COS-DEA system. [DEA] Q = 20 wt%, T = 180 °C, P c o s = 345 kPa. TIME CONCENTRATION (mol/L) (H) DEA ACET BUT MEA BHEED BHEP HEOD HEI THEED BHEI 0 1 . 98 0 .000 0 .000 0 .000 0 .000 0. .000 0 .000 0 .000 0 .000 0 .000 2 1 .85 0 .004 0 .003 0 .062 0 .000 0, .000 0 .000 0 .000 0 .000 0 .000 4 1 .78 0 .005 0 .005 0 .092 0 .000 0, .000 0 .000 0 .000 0 .000 0 .000 6 1 .73 0 .007 0 .006 0 .139 0 .000 0 . 000 0 .000 0 .000 0 .000 0 .000 8 1 .64 0 .008 0 .007 0 .179 0 .013 0. .003 0 .000 0 .000 0 .000 0 .000 12 1 .52 0 .009 0 .008 0 .235 0 .015 0, .006 0 .010 0 .000 . 0 .007 0 .000 24 1 .17 0 .011 0 .011 0 .371 0 .031 0 .011 0 .025 0 .014 0 .096 0 .014 30 1 .02 0 .009 0 .010 0 .346 0 .054 0 .015 0 .033 0 .032 0 .165 0 .019 36 0 .87 0 .009 0 .011 0 .366 0 .089 0 .019 0 .046 0 .052 0 .198 0 .048 48 0 .72 0 .008 0 .013 0 .370 0 .093 0 .030 0 .048 0 .076 0 .201 0 .064 k n i ?, = 0.0214 h 323 Table C . 1 3 : Concen t ra t i ons of compounds i n COS-DEA system. [DEA] Q = 20 wt%, T = 165 °C, P c o s = 345 kPa . TIME CONCENTRATION (mol/L) (H) DEA ACET BUT MEA BHEED BHEP HEOD HEI THEED BHEI 0 1 . 91 0 , .000 0, .000 0 .000 0 .000 0. .000 0 .000 0 .000 0 .000 0. .000 2 1 .97 0, .004 0. .002 0 .042 0 .000 0. .000 0 .000 0 .000 0 .000 0. .000 4 1 .86 0 , .005 0, .003 0 .063 0 .000 0. .000 0 .000 0 .000 0 .000 0, .000 8 1 .78 0, .007 0, .006 0 .109 0 .000 0. .000 0 .000 0 .000 0 .000 0. .000 12 1 .83 0, .008 0, .008 0 .153 0 .012 0. .000 0 .000 0 .000 0 .000 0, .000 24- 1 .52 0, .010 0, .010 0 .258 0 .016 0, .000 0 .015 0 .000 0 .000 0, .000 30 1 .41 0, .010 0, .010 0 .294 0 .018 0, .005 0 .019 0 .004 0 .072 0. .000 36 1 .33 0, .010 0, .011 0 .333 0 .027 0, .009 0 .027 0 .007 0 .088 0, .014 48 1 .15 0, .010 0 .012 0 .410 0 .052 0, .014 0 .038 0 .013 0 .127 0, .022 knr., = 0.0110 h Table C.14: Concentrations of compounds in COS-DEA system. [DEA] Q = 20 wt%, T = 150 °C, P c o s = 345 kPa. TIME CONCENTRATION (mol/L) (H) DEA ACET BUT MEA BHEED BHEP HEOD HEI THEED BHEI 0 1 . 96 0 .000 0 .000 0 .000 0 .000 0 .000 0 .000 0 .000 0 .000 0 .000 2 1 .92 0 .003 0 .000 0 .000 0 .000 0 .000 0 .000 0 .000 0 .000 0 .000 4 1 .88 0 .004 0 .001 0 .039 0 .000 0 .000 0 .000 0 .000 0 .000 0 .000 8 1 .85 0 .007 0 .003 0 .081 0 .000 0 .000 0 .005 0 .000 0 .000 0 .000 12 1 .88 0 .009 0 .006 0 .120 0 .000 0 .000 0 .010 0 .000 0 .000 0 .000 24 1 .70 0 .010 0 .010 0 .200 0 .014 0 .001 0 .012 0 .000 0 .000 0 .000 30 1 .55 0 .010 0 .009 0 .234 0 .015 0 .003 0 .017 0 .000 0 .000 0 .000 36 1 .62 0 .012 0 .011 0 .295 0 .017 0 .004 0 .019 0 .002 0 .000 0 .000 48 1 .42 0 .013 0 .012 0 .316 0 .016 0 .005 0 .019 0 .004 0 .000 0 .008 60 1 .26 0 .015 0 .013 0 .351 0 .017 0 .008 0 .020 0 .006 0 .061 0 .012 k n r . s = 0.0070 h~ 324 Table C.15: Concentrations of compounds i n COS-DEA system. [DEA] Q = 20 wt%, T = 135 °C, P c o g = 345 kPa. TIME CONCENTRATION (mol/L) (H) DEA ACET BUT MEA BHEED BHEP HEOD HEI THEED BHEI 0 1 . 99 0 .000 0 .000 0. .000 0 .000 0 .000 0 .000 0 .000 0 .000 0. .000 24 1 .82 0 .008 0 .003 0. .100 0 .000 0 .000 0 .000 0 .000 0 .000 0. .000 48 1 .74 0 .009 0 .006 0. .157 0 .000 0 .000 0 .000 0 .000 0 .000 0. .000 72 1 .56 0 .012 0 .008 0. .'215 0 .000 0 .000 0 .010 0 .000 0 .000 0. .000 96 1 .35 0 .011 0 .009 0, .251 0 .013 0 .000 0 .016 0 .000 0 .000 0. .000 120 1 .30 0 .009 0 .009 0. .317 0 .024 0 .007 0 .019 0 .000 0 .000 0, .000 144 1 .12 0 .011 0 .009 0, .315 0 .031 0 .009 0 .032 0 .000 0 .077 0, .015 168 1 .12 0 .011 0 .009 0, .386 0 .039 0 .010 0 .030 0 .000 0 .091 0, .017 192 0 . 96 0 .009 0 .008 0, .430 0 .040 0 .012 0 .035 0 .015 0 . 145 0, .025 216 0 . 90 0 .010 0 .008 0, .440 0 .035 0 .011 0 .034 0 .020 0 .123 0, .025 kni., = 0.0038 h" 1 Table C.16: Concentrations of compounds i n COS-DEA system. [DEA] Q = 20 wt%, T = 127 °C, P c o s = 345 kPa. TIME CONCENTRATION (mol/L) (H) DEA ACET BUT MEA BHEED BHEP HEOD HEI THEED BHEI 0 2. .00 0 .000 0 .000 0. .000 0 .000 0 .000 0. .000 0 .000 0 .000 0 .000 10 1. .97 0 .006 0 .000 0. .021 0 .000 0 .000 0. .013 0 .000 0 .000 0 .000 22 1. .85 0 .008 0 .003 0 . 062 0 .000 0 .000 0. .014 0 .000 0 .000 0 .000 46 1. .82 0 .010 0 .006 0. .151 0 .000 0 .000 0. .018 0 .000 0 .000 0 .000 70 1. .63 0 .009 0 .007 0. .220 0 .000 0 .000 0, .018 0 .000 0 .000 0 .000 94 1, .50 0 .010 0 .008 0, .306 0 .004 0 .000 0, .026 0 .000 0 .035 0 .000 118 1, .62 0 .011 0 .008 0, .414 0 .009 0 .000 0. .0.40 0 .000 0 .054 0 .000 142 1, .35 0 .010 0 .008 0, .422 0 .015 0 .005 0, .047 0 .000 0 .058 0 .018 166 1 .23 0 .009 0 .007 0, .451 0 .028 0 .010 0 .054 0 .010 0 .133 0 .033 k n c, x = 0.0029 h 325 Table C.17: Concentrations of compounds i n COS-DEA system. [DEA] Q = 30 wt%, T = 150 °C, P C Q S = 759 kPa. TIME CONCENTRATION (mol/L) (H) DEA ACET BUT MEA BHEED BHEP HEOD HEI THEED BHEI 0 2 .93 0. ,000 0, ,000 0. ,000 0 .000 0 .000 0 .000 0 .000 0 .000 0 .000 2 2 . 90 0. .007 0. ,001 0. ,068 0 .000 0 .000 0 .000 0 .000 0 .000 0 .000 4 2 .84 0. .011 0. .003 0. .113 0 .000 0 .000 0 .000 0 .000 0 .000 0 .000 8 2 .75 0. .015 0. .008 0. ,200 0 .000 0 .005 0 .020 0 .000 0 .000 0 .000 12 2 .60 0, .019 0. .013 0. .270 0 .010 0 .006 0 .025 0 .000 0 .000 0 .000 24 2 .29 0. .037 0, .021 0. .468 0 .041 0 .011 0 .037 0 .006 0 .069 0 .000 30 2 .12 0, .027 0, .018 0, .551 0 .055 0 .018 0 .052 0 .009 0 .089 0 .007 36 1 .86 0, .028 0, .018 0, .622 0 .070 0 .023 0 .060 0 .012 0 .103 0 .015 48 1 .55 0, .025 0, .018 0, .697 0 .096 0 .032 0 .080 0 .067 0 .197 0 .032 k D E A = 0.0131 h"-1 Table C.18: Concentrations of compounds i n COS-DEA system. [DEA] Q = 30 wt%, T = 150 °C, P c o s = 1172 kPa. TIME CONCENTRATION (mol/L) (H) DEA ACET BUT MEA BHEED BHEP HEOD HEI THEED BHEI 0 2. , 95 0 .000 0 .000 0 .000 0 .000 0. 000 0 .000 0 .000 0. .000 0 .000 2 2. . 90 0 .009 0 .000 0 .088 0 .000 0. 000 0 .000 0 .000 0, .000 0 .000 4 2 . 87 0 .015 0 .001 0 .146 0 .000 0. 000 0 .020 0 .000 0. .000 0 .000 8 2. .70 0 .022 0 .009 0 .239 0 .000 0. 007 0 .025 0 .000 0. .000 0 .000 12 2. .48 0 .026 0 .013 0 .316 0 .021 0. 010 0 .043 0 .004 0. .000 0 .000 24 2 , .00 0 .030 0 .015 0 .474 0 .047 0. 016 0 .060 0 .011 0 , .022 0 .000 30 1, .82 0 .039 0 .015 0 .570 0 .069 0. 023 0 .065 0 .031 0, .117 0 .014 36 1. .61 0 .035 0 .013 0 .646 0 .086 0. 027 0 .067 0 .056 0, .200 0 .018 48 1 .25 0 .033 0 .014 0 .661 0 .116 0. 041 0 . 107 0 .092 0 .251 0 .033 k n c, s = 0.0180 h 326 Table C.19: Concentrations of compounds i n COS-DEA system. [DEA] Q = 60 wt%, T = 165 °C, P c o s = 345 kPa. TIME CONCENTRATION (mol/L) (H) DEA ACET BUT MEA BHEED BHEP HEOD HEI THEED BHEI 0 6 .21 0 .000 0 .000 0 .000 0, .000 0. .000 0 .000 0. .000 0 . 000 0. .000 2 6 .24 0 .016 0 .005 0 .156 0. .000 0. .000 0 .025 0. .000 0. .000 0. .000 4 5 .96 0 .022 0 .012 0 .273 0. .027 0. .008 0 .032 0. .000 0. .042 0. .000 8 5 .46 0 .026 0 .016 0 .424 0 , .039 0 , .015 0 .041 0. .000 0. .168 0, .000 12 5 .00 0 .022 0 .017 0 .549 0, .105 0, .032 0 .080 0, .024 0, .305 0, .000 24 4 .05 0 .016 0 .017 0 .655 0, .224 0, .055 0 .174 0, .089 0, .799 0, .070 30 3 .53 0 .009 0 .018 0 .682 0, .321 0, .064 0 .177 0, .133 1. .190 • 0 . 141 k n ™ = 0.0194 h Table C.20: Concentrations of compounds i n COS-DEA system. [DEA] 0 = 30 wt%, T = 150 °C, P c o s = 345 kPa. (Run conducted to determine the e f f e c t of oxygen) TIME CONCENTRATION (mol/L) (H) DEA ACET BUT MEA BHEED BHEP HEOD HEI THEED BHEI 0 3 .00 0 .000 0 .000 0 .000 0. .000 0 .000 0 .000 0. .000 0 .000 0. .000 2 2 .98 0 .005 0 .000 0 .059 0. .000 0 .000 0 .000 0. .000 0 .000 0. .000 4 2 .86 0 .007 0 .002 0 .085 0. .000 0 .000 0 .000 0. .000 0 .000 0 , .000 8 2 .77 0 .010 0 .007 0 .143 0. .000 0 .006 0 .000 0, .000 0 .000 0. .000 12 2 .69 0 .011 0 .010 0 .198 0. .000 0 .007 0 .018 0, .000 0 .000 0. .000 24 2 .45 0 .017 0 .016 0 .330 0. .021 0 .010 0 .023 0, .000 0 .000 0, .000 30 2 .30 0 .020 0 .015 0 .380 0, .024 0 .013 0 .026 0, .007 0 .036 0, .000 36 2 .17 0 .021 0 .015 0 .436 0, .054 0 .020 0 .078 0, .009 0 .073 0. .012 48 1 . 91 0 .022 0 .017 0 .531 0, .073 0 .033 0 . 107 0 .012 0 .121 0. .016 k n r, A = 0.0096 h 327 C.2 CSo-DEA SYSTEMS Table C.21: Concentrations of compounds i n CS2-DEA system. [DEA] Q = 40 wt%, T = 165 °C, CS 2 volume = 6.0 mL. TIME CONCENTRATION (mol/L) (H) DEA MEA BHEED BHEP HEOD HEI THEED BHEI 0 4. .30 0 .000 0.000 0. .000 0. .000 0, .000 0 .000 0 .000 2 3. . 97 0 .023 0.000 0. .000 0. .000 0. .000 0 .000 0 .000 4 3. .75 0 .086 0.036 0. .004 0. .010 0, .000 0 .000 0 .000 8 3. .63 0 .180 0.060 0. .008 0. .020 0, .000 0 .010 0 .000 12 3. .25 0 .277 0.074 0, .015 0, .033 0, .008 0 .141 0 .000 24 2, .83 0 .298 0.128 0, .025 0, .081 0. .018 0 .420 0 .000 30 2. .54 0 .308 0.155 0 , .028 0, .094 0, .030 0 .560 0 .017 36 2. .34 0 .287 0.175 0 , .036 0, .108 0 .034 0 .640 0 .022 48 2. . 14 0 .256 0.193 0, .053 0, .130 0 .044 0 .721 0 .040 k n l 7 S = 0.0138 h" Table C.22: Concentrations of compounds i n CS2-DEA system. [DEA] Q = 40 wt%, T = 150 °C, CS 2 volume = 6.0 mL. TIME CONCENTRATION (mol/L) (H) DEA MEA BHEED BHEP HEOD HEI THEED BHEI 0 4 .16 0 .000 0 .000 0 .000 0 .000 0 .000 0 .000 0 .000 2 3 . 93 0 .012 0 .000 0 .000 0 .000 0 .000 0 .000 0 .000 4 3 .71 0 .043 0 .000 0 .000 0 .007 0 .000 0 .000 0 .000 8 3 .71 0 .126 0 .000 0 .000 0 .008 0 .000 0 .000 0 .000 12 3 .57 0 .188 0 .010 0 .008 0 .015 0 .000 0 .032 0 .000 24 3 .33 0 .253 0 .047 0 .011 0 .034 0 .010 0 .010 0 .000 36 3 .37 0 .309 0 .070 0 .016 0 .051 0 .018 0 .310 0 .000 49 2 .96 0 .326 0 .095 0 .024 0 .052 0 .028 0 .384 0 .011 60 2 .75 0 .292 0 .141 0 .030 0 .100 0 .031 0 .422 0 .016 72 2 .53 0 .295 0 .163 0 .034 0 .108 0 .032 0 .520 0 .022 k n P , = 0.0057 h 328 Table C . 2 3 : Concen t ra t ions of compounds i n CS2-DEA system. [DEA] Q = 30 wt%, T = 165 °C, C S 2 volume = 6.0 mL. TIME CONCENTRATION (mol/L) (H) DEA MEA BHEED BHEP HEOD HEI THEED BHEI 0 2 .96 0. 000 0 .000 0. .000 0 .000 0 .000 0 .000 0.000 2 2 .80 0. 030 0 .000 0. .000 0 .000 0 .000 0 .000 0.000 4 2 .70 0. 076 0 .016 0, .000 0 .005 0 .000 0 .000 0.000 8 2 .68 0. 166 0 .020 0. .004 0 .017 0 .000 0 .040 0.000 12 2 .57 0. 209 0 .031 0, .008 0 .020 0 .000 0 .080 0.000 24 2 .29 0. 282 0 .066 0, .013 0 .037 0 .010 0 .146 0.000 30 2 .12 0. 291 0 .084 0, .015 0 .045 0 .022 0 .310 0.013 36 1 . 97 0. 291 0 .124 0. .020 0 .056 0 .025 0 .360 0.018 48 1 .76 0. 243 0 .144 0, .025 0 .085 0 .029 0 .407 0.031 k n - a = 0.0101 h Table C.24: Concentrations of compounds i n CS2-DEA system. [DEA] Q = 30 wt%, T = 150 °C, CS 2 volume = 6.0 mL. TIME (H) DEA MEA BHEED CONCENTRATION (mol /L) BHEP HEOD HEI THEED BHEI 0 2 .96 0 .000 0 .000 0 .000 0 .000 0 .000 0. 000 0 .000 2 2 .72 0 .008 0 .000 0 .000 0.000 0 .000 0. 000 0 .000 4 2 .71 0 .030 0 .000 0 .000 0.000 0 .000 0. 000 0 .000 8 2 .68 0 .075 0 .000 0 .000 0.006 0 .000 0. 000 0 .000 12 2 .78 0 . 149 0 .019 0 .000 0.010 0 .000 0. 000 0 .000 24 2 .62 0 .195 0 .030 0 .007 0.021 0 .000 0. 000 0 .000 34 2 .31 0 .257 0 .042 0 .010 0.026 0 .005 . 0. 110 0 .000 48 2 .24 0 .293 0 .056 0 .014 0.037 0 .010 0. 170 0 .008 60 1 . 97 0 .283 0 .073 0 .016 0.043 0 .022 0. 254 0 .017 70 1 . 90 0 .272 0 .089 0 .021 0.047 0 .025 0. 350 0 .022 k n I , a = 0.0056 h 329 Table C.25: Concentrations of compounds i n CSo-DEA system. [DEA] n = 30 wt%, 120 °C, CS2 volume = 6.0 mL. TIME (H) DEA MEA BHEED CONCENTRATION (mol/L) BHEP HEOD HEI THEED BHEI 0 3 .00 0. ,000 0. ,000 0.000 0 .000 0. .000 0 .000 0 .000 2 2 .88 0. .000 0. .000 0.000 0 .000 0. .000 0 .000 0 .000 4 2 .76 0. .000 0. ,000 0.000 0 .005 0. .000 0 .000 0 .000 24 2 .57 0, .042 0, .000 0.000 0 .012 0. .000 0 .000 0 .000 52 2 .57 0. .088 0. .017 0.003 0 .016 0, .000 0 .008 0 .000 72 2 .56 0. .149 0. .020 0.004 0 .018 0. .000 0 .013 0 .000 96 2 .46 0. .176 0. .022 0.006 0 .020 0, .000 0 .013 0 .000 120 2 .24 0, .221 0, .025 0.005 0 .018 0, .000 0 .021 ' 0 .000 146 2 .08 0, .260 0, .034 0.007 0 .026 0, .000 0 .048 0 .000 168 2 .05 0, .289 0, .032 0.008 0 .030 0, .006 0 .056 0-.008 "DEA 0.0018 h" Table C.26: Concentrations of compounds i n CS2-DEA system. [DEA] 20 wt%, T = 180 UC, CS 2 volume 6.0 mL. TIME (H) DEA ACET BUT CONCENTRATION (mol/L) MEA BHEED BHEP HEOD HEI THEED BHEI 0 2 .11 0 .000 0. ,000 0. 000 0. .000 0. 000 0 .000 0. 000 0 .000 0 .000 2 1 .64 0 .001 0. ,000 0. 040 0. .000 0. 000 0 .000 0. 000 0 .000 0 .000 4 1 .57 0 .004 0 , .002 0 . 048 0, .000 0. 000 0 .000 0. 000 0 .000 0 .000 8 1 .43 0 .019 0, .011 0. 121 0, .012 0. 005 0 .009 0. 007 0 .000 0 .000 12 1 .32 0 .032 0. .022 0. 179 0, .018 0. 012 0 .012 0. 013 0 .000 0 .000 24 0 .70 0 .051 0, .042 0 . 215 0 .055 0. 017 0 .015 0. 024 0 .000 0 .000 30 0 .37 0 .050 0, .047 0 . 246 0 .045 0. 013 0 . 0 1 1 0. 035 0 .000 0 .000 36 0 .23 0 .044 0, .047 0. 221 0 .041 0. 012 0 .013 0. 046 0 .008 0 .010 TIME (H) CONCENTRATION EAE HEA (mol/L) EDEA 0 0. .000 0. .000 0.000 2 0. .000 0. .000 0.000 4 0. .000 0. .000 0.000 8 0, .000 0, .000 0.000 12 0, .018 0, .060 0.000 24 0. .050 0, .143 0.037 30 0 .060 0, .132 0.025 36 0 .052 0 .110 0.018 330 Table C . 2 7 : Concen t ra t i ons of compounds i n CS2-DEA system. [DEA] Q = 20 wt%, T = 165 °C, C S 2 volume = 6 . 0 mL. TIME CONCENTRATION (mol /L) (H) DEA MEA BHEED BHEP HEOD HEI THEED BHEI 0 2 .04 0 .000 0. .000 0 .000 0. .000 0. .000 0 .000 0 .000 2 1 . 99 0 .018 0, .000 0 .000 0. .000 0. .000 0 .000 0 .000 4 1 .89 0 .048 0, .023 0 .000 0, .000 0, .000 0 .000 0 .000 8 1 .74 0 .089 0, .030 0 .003 0. .014 0. .000 0 .000 0 .000 12 1 .76 0 .158 0, .034 0 .004 0, .019 0. .000 0 .000 0 .000 24 1 .53 0 .209 0, .034 0 .005 0, .020 0, .000 0 .000 0 .000 30 1 .42 0 .256 0, .067 0 .006 0, .027 0, .005 0 .150 0 .000 36 1 .37 0 .282 0, .086 0 .007 0, .038 0, .007 0 .195 0 .006 48 1 .21 0 .255 0 .100 0 .012 0, .041 0, .010 0 .222 0 .015 k D E A = 0.0091 h - 1 Table C . 2 8 : Concen t ra t i ons of compounds i n CS2-DEA system. [DEA] Q = 20 wt%, T = 150 °C, C S 2 volume = 6.0 mL. TIME CONCENTRATION (mol /L) (H) DEA MEA BHEED BHEP HEOD HEI THEED BHEI 0 2 .03 0 .000 0. ,000 0 .000 0. .000 0 .000 0.000 0.000 2 1 .89 0 .000 0. .000 0 .000 0 . 000 0 .000 0.000 0.000 4 1 . 93 0 .007 0. .000 0 .000 0. .000 0 .000 0.000 0.000 8 1 .87 0 .024 0. .000 0 .000 0 , .000 0 .000 0.000 0.000 12 1 .85 0 .052 0. .000 0 .000 0. .005 0 .000 0.000 0.000 24 1 .72 0 .095 0. .000 0 .000 0. .014 0 .000 0.000 0.000 36 1 .66 0 .133 0 , .005 0 .001 0 , .015 0 .000 0.000 0.000 48 1 .54 0 .168 0, .015 0 .011 0, .018 0 .000 0.000 0.000 60 1 .46 0 .202 0 .031 0 .013 0, .026 0 .006 0.058 0.023 72 1 .31 0 .196 0 .039 0 .014 0 .029 0 .016 0.084 0.040 kntrs = 0.0052 h 331 Table C.29: Concentrations of compounds i n CS2-DEA system. [DEA] Q = 20 wt%, T = 120 °C, CS 2 volume = 6.0 mL. TIME CONCENTRATION (mol/L) (H) DEA MEA BHEED BHEP HEOD HEI THEED BHEI 0 1 . 90 0 .000 0. .000 0 .000 0 .000 0 .000 0 .000 0 .000 2 1 .78 0 .000 0, .000 0 .000 0 .000 0 .000 0 .000 0 .000 4 1 .75 0 .000 0, .000 0 .000 0 .000 0 .000 0 .000 0 .000 24 1 .66 0 .019 0, .000 0 .000 0 .013 0 .000 0 .000 0 .000 48 1 .64 0 .052 0, .006 0 .000 0 .015 0 .000 0 .000 0 .000 72 1 .60 0 .074 0, .008 0 .004 0 .016 0 .000 0 .000 0 .000 96 1 .56 0 .101 0, .011 0 .005 0 .017 0 .000 0 .000 0 .000 120 1 .52 0 .145 0, .019 0 .005 0 .021 0 .000 0 .000 0 .000 144 1 .48 0 .191 0 .023 0 .006 0 .020 0 .000 0 .013 0 .000 168 1 .45 0 .220 0 .024 0 .007 0 .022 0 .005 0 .014 0 .000 k D E A = 0.009 h' A Table C.30: Concentrations of compounds i n CS2-DEA system. [DEA] Q = 60 wt%, T = 165 °C, CS 2 volume = 6.0 mL. TIME CONCENTRATION (mol/L) (H) DEA MEA BHEED BHEP HEOD HEI THEED BHEI 0 6. 32 0 .000 0 . 000 0 .000 0. 000 0 .000 0. .000 0.000 2 5. 76 0 .062 0. .022 0 .000 0. 012 0 .000 0. .015 0.000 4 5. 52 0.130 0. .028 0 .009 0. 013 0 .000 0. ,033 0.000 8 5. 47 0.246 0, .039 0 .011 0. 022 0 .018 0. .081 0.000 12 5. 09 0.366 0 , .052 0 .011 0. 028 0 .026 0. ,167 0.007 24 4 . 74 0 .481 0 , .080 0 .017 0. 047 0 .036 0. .381 0.013 30 4. 30 0.506 0, .130 0 .021 0. 055 0 .046 0, .640 0.020 36 3. 90 0.459 0 . 150 0 .022 0. 059 0 .047 0, .760 0.028 knc,, = 0.0106 h 332 Table C.31: Concentrations of compounds i n CS2-DEA system. [DEA] Q = 30 wt%, T = 165 °C, CS 2 volume = 2.5 mL. TIME CONCENTRATION (mol/L) (H) DEA MEA BHEED BHEP HEOD HEI THEED BHEI 0 3 .01 0 .000 0 .000 0. .000 0.000 0 .000 0. .000 0 .000 2 2 .78 0 .041 0 .017 0, .000 0.000 0 .000 0. .000 0 .000 4 2 .73 0 .055 0 .018 0, .000 0.000 0 .000 0. .000 0 .000 8 2 .62 0 .083 0 .021 0, .004 0.013 0 .000 0. .027 0 .000 12 2 .55 0 .123 0 .024 0, .006 0.016 0 .000 0. .048 0 .000 24 2 .52 0 .183 0 .029 0, .008 0.023 0 .000 0, .088 0 .000 30 2 .41 0 .220 0 .042 0 .009 0.028 0 .000 0, .180 0 .007 36 2 .33 0 .239 0 .050 0 .011 0.029 0 .015 0, .253 0 .009 48 2 .18 0 .232 0 .061 0 .014 0.035 0 .019 0 , .334 0 .013 k n r, a= 0.0048 h" Table C.32: Concentrations of compounds i n CS2-DEA system. [DEA] 0 = 30 wt%, T = 165 °C, CS 2 volume = 10.5 mL. TIME CONCENTRATION (mol/L) (H) DEA MEA BHEED BHEP HEOD HEI THEED BHEI 0 3 .07 0 .000 0 .000 0. .000 0 .000 0.000 0.000 0 .000 2 2 .53 0 .046 0 .010 0 . 000 0 .000 0.000 0.012 0 .000 4 2 .42 0 .055 0 .015 0. .000 0 .017 0.007 0.013 0 .000 8 2 .30 0 . 155 0 .028 0. .008 0 .021 0.008 0.016 0 .000 12 2 .21 0 .338 0 .045 0, .010 0 .030 0 .023 0.046 0 .000 24 1 .91 0 .420 0 .093 0, .018 0 .062 0.043 0.199 0 .034 30 1 .60 0 .411 0 .131 0, .019 0 .061 0.053 0.333 0 .056 36 1 .37 0 .379 0 .157 0, .023 0 .078 0.057 0.417 0 .075 48 1 . 14 0 .305 0 .143 0 .028 0 .068 0.056 0 .438 0 .099 k n i r, = 0.0173 h 333 Table C.33: Concentrations of compounds i n CS2-DEA system. [DEA] Q = 30 wt%, T = 190 °C, CS 2 volume = 10.5 mL. TIME CONCENTRATION (mol/L) (H) DEA ACET BUT MEA BHEED BHEP HEOD HEI THEED BHEI 0 3 .11 0. .000 0, .000 0 .000 0 .000 0, .000 0, .000 0 .000 0. .000 0. .000 2 2 .72 0, .038 0, .023 0 .060 0 .000 0, .000 0, .000 0 .000 0. .000 0. .000 4 2 .29 0, .053 0, .035 0 .200 0 .020 0. .010 0, .035 0 .000 0. .000 0. .000 6 1 .96 0, .079 0, .050 0 .350 0 .026 0, .016 0, .040 0 .000 0. .000 0. .000 12 • 1 .21 0, .081 0, .052 0 .480 0 .058 0, .029 0, .052 0 .045 0. .110 0. .074 24 0 .86 0, .057 0 , .044 0 .540 0 .096 0, .041 0, .067 0 .086 0. .170 0. .093 30 0 .58 0. .045 0, .041 0 .520 0 .110 0, .042 0. .066 0 .137 0. .190 0. .127 36 0 .42 0 .036 0 .041 0 .450 0 .110 0 .045 0 .066 0 .200 0, .160 0, .172 48 0 .25 0 .031 0 .040 0 .380 0 .100 0 .055 0 .068 0 .230 0 . 155 0, .232 The EAE, HEA and EDEA formed i n t h i s run were not q u a n t i f i e d . Table C.34: Concentrations of compounds i n CS2-DEA system. [DEA] Q = 30 wt%, T = 175 °C, CS 2 volume = 10.5 mL. TIME CONCENTRATION (mol/L) (H) DEA MEA BHEED BHEP HEOD HEI THEED BHEI 0 3. 11 0 .000 0. .000 0 .000 0 .000 0 .000 0 .000 0 .000 2 2. 55 0 .036 0. .000 0 .000 0 .015 0 .000 0 .000 0 .000 4 2. 43 0 .086 0. .017 0 .005 0 .040 0 .000 0 .000 0 .000 6 2 . 27 0 .173 0. .026 0 .008 0 .050 0 .002 0 .000 0 .000 12 1. 88 0 .321 0. .060 0 .008 0 .069 0 .007 0 .125 0 .010 24 1. 37 0 .290 0, .132 0 .027 0 .092 0 .046 0 .450 0 .122 30 1. 13 0 .280 0 , .142 0 .035 0 .090 0 .050 0 .500 0 .155 36 1. 01 0 .267 0 .153 0 .046 0 .095 0 .056 0 .540 0 .190 48 0. 78 0 .220 0 . 141 0 .067 0 .087 0 .069 0 .530 0 .272 k n j r, = 0.0272 h 334 Table C.35: Concentrations of compounds i n CS2-DEA system. [DEA] Q = 30 wt%, T = 160 °C, CS 2 volume = 10.5 mL. TIME CONCENTRATION (mol/L) (H) DEA MEA BHEED BHEP HEOD HEI THEED BHEI 0 3 .08 0 .000 0 .000 0 .000 0 .000 0 .000 0. .000 0 .000 2 2 .62 0 .010 0 .000 0 .000 0 .000 0 .000 0. .000 0 .000 4 2 .57 0 .030 0 .000 0 .000 0 .000 0 .000 0. .000 0 .000 6 2 .54 0 .080 0 .007 0 .000 0 .020 0 .000 0. .000 0 .000 8 2 .50 0 .140 0 .013 0 .001 0 .027 0 .000 0. .000 0 .000 12 2 .43 0 .240 0 .020 0 .002 0 .034 0 .000 0, .000 0 .000 24 1 .93 0 .360 0 .040 0 .003 0 .057 0 .014 0, .170 0 .025 30 1 .78 0 .350 0 .090 0 .011 0 .088 0 .030 0, .290 0 .058 36 1 .65 0 .370 0 .110 0 .013 0 .096 0 .032 0, .390 0 .083 48 1 .31 0 .280 0 .120 0 .021 0 .091 0 .041 0, .450 0-.120 60 1 .13 0 .280 0 .130 0 .029 0 .096 0 .047 0, .530 0 .160 knT., = 0.0148 h" Table C.36: Concentrations of compounds i n CS2-DEA system. [DEA] Q = 30 wt%, T = 130 °C, CS 2 volume = 10.5 mL. TIME CONCENTRATION (mol/L) (H) DEA MEA BHEED BHEP HEOD HEI THEED BHEI 0 3.08 0 .000 0 .000 0.000 0 .000 0. .000 0 .000 0 .000 2 2.76 0 .000 0 .000 0.000 0 .000 0 , .000 0 .000 0 .000 4 2 .77 0 .000 0 .000 0 .000 0 .000 0 . 000 0 .000 0 .000 24 2.51 0 .031 0 .000 0.000 0 .000 0. .000 0 .000 0 .000 48 2.44 0 .123 0 .000 0.000 0 .000 0. .000 0 .000 0 .000 72 2.24 0 .242 0 .013 0.002 0 .031 0, .000 0 .038 0 .000 98 2.08 0 .340 0 .027 0.004 0 .043 0, .009 0 .122 0 .000 120 1.93 0 .410 0 .032 0.004 0 .048 0 , .013 0 . 157 0 .024 144 1.81 0 .444 0 .045 0.005 0 .069 0, .016 0 .209 0 .031 k n c, a = 0 .0034 h" 1 335 C.3 OTHER SYSTEMS. Table C.37: Gas mixture of 15% H2S in nitrogen was contacted with 30 wt% aqueous DEA so l u t i o n f o r 48 h. No degradation occurred. Table C.38: Concentrations of compounds i n aqueous DEA solution degraded with a gas mixture containing 14.7% C0 2 i n nitrogen (DEA Q = 3.0 mol/L; T = 165 °C; pgas mixture 1.55 MPa). TIME CONCENTRATION (mol/L) (H) DEA BHEP HEOD THEED 0 3. ,00 0.000 0.000 0.000 2 2. .96 0.000 0.020 0.000 4 2. .86 0.000 0.023 0.005 8 2. .79 0.003 0.026 0.044 12 2, .76 0.005 0.027 0 .099 24 2, .64 0.008 0.035 0.197 30 2, .49 0.010 0.037 0.364 36 2 .41 0.012 0.037 0.447 48 2 .27 0.016 0.040 0.522 k n i,j = 0.0056 h Table C.39: Concentrations of compounds i n aqueous DEA so l u t i o n degraded with a gas mixture containing 15.2% C0 2 and 15.2% H 2S i n nitrogen (DEAQ = 3.0 mol/L; T = 165 °C; pgas mixture 1.55 MPa). TIME CONCENTRATION (mol/L) (H) DEA MEA BHEED BHEP HEOD HEI THEED BHEI 0 3 .00 0 .000 0 .000 0 .000 0 .000 0 .000 0 .000 0 .000 2 2 . 94 0 .047 0 .000 0 .000 0 .000 0 .000 0 .000 0 .000 4 2 .79 0 .059 0 .000 0 .000 0 .013 0 .000 0 .000 0 .000 8 2 .69 0 .089 0 .004 0 .003 0 .015 0 .000 0 .019 0 .000 12 2 .72 0 . 141 0 .008 0 .004 0 .017 0 .000 0 .041 0 .000 24 2 .53 0 .166 0 .015 0 .007 0 .029 0 .005 0 .098 0 .000 30 2 .34 0 .205 0 .032 0 .009 0 .031 0 .012 0 .183 0 .000 36 2 .23 0 .216 0 .037 0 .010 0 .033 0 .013 0 .222 0 .003 48 2 .02 0 .195 0 .049 0 .012 0 .037 0 .016 0 .319 0 .010 k n l 7 A = 0.0077 h" 336 Table C.40: Concentrations of compounds i n aqueous DEA solu t i o n degraded with a gas mixture containing 30.0% CO2 and 15.0% H 2S in nitrogen (DEA 0 = 3.0 mol/L; T = 165 °C; pgas mixture = 1 , 5 5 M P a ) • TIME CONCENTRATION (mol/L) (H) DEA MEA BHEED BHEP HEOD HEI THEED BHEI 0 3. .00 0 .000 0 .000 0 .000 0. ,000 0 .000 0. .000 0 .000 2 2, . 91 0 .066 0 .005 0 .002 0 . 023 0 .000 0. .005 0 .000 4 2. .84 0 .098 0 .006 0 .002 0. .027 0 .000 0, .020 0 .000 8 2, .65 0 .144 0 .010 0 .003 0. .031 0 .000 0, .053 0 .000 12 2, .51 0 .188 0 .026 0 .005 0. .048 0 .000 0, .133 0 .000 24 2, .17 0 .182 0 .045 0 .011 0, .063 0 .016 0, .344 0 .010 30 1. . 91 0 .175 0 .068 0 .017 0. .067 0 .021 0 .518 0 .022 36 1. .70 0 .155 0 .073 0 .020 0, .064 0 .025 0 .567 0 .038 48 1, .48 0 .130 0 .081 0 .034 0, .073 0 .029 0 .672 0 .057 k n r r a = 0.0150 h Table C.41: Concentrations of compounds i n aqueous DEA so l u t i o n degraded with a gas mixture containing 15.5% C0 2 and 29.9% H 2S in nitrogen (DEAQ = 3.0 mol/L; T = 165 °C; pgas mixture = 1 , 5 5 M P a ) • TIME CONCENTRATION (mol/L) (H) DEA ACET BUT MEA BHEED BHEP HEOD HEI THEED BHEI 0 3. ,00 0 .000 0 .000 0 .000 0 .000 0 .000 0. ,000 0 .000 0 .000 0 . ,000 2 2. , 90 0 .004 0 .001 0 .068 0 .000 0 .000 0. ,000 0 .000 0 .000 0. ,000 4 2. .74 0 .006 0 .003 0 .101 0 .000 0 .000 0. .005 0 .000 0 .000 0. ,000 8 2, .63 0 .007 0 .005 0 .157 0 .005 0 .000 0, .010 0 .000 0 .012 0. .000 12 2. .59 0 .010 0 .008 0 .225 0 .008 0 .004 0, .016 0 .000 0 .024 0. .000 24 2, .36 0 .009 0 .009 0 .299 0 .015 0 .006 0, .021 0 .000 0 .050 0, .000 30 2, .26 0 .009 0 .011 0 .386 0 .033 0 .008 0 .021 0 .003 0 .093 0, .000 36 2, .10 0 .008 0 .011 0 .412 0 .043 0 .009 0 .022 0 .004 0 .121 0, .004 48 1 .95 0 .007 0 .012 0 .425 0 .063 0 .013 0 .035 0 .005 0 .180 0, .012 k n r r, = 0.0085 h 337 Table C.42: Concentrations of compounds i n aqueous DEA solution i n i t i a l l y containing MEA. (DEA Q = 2.90 mol/L; MEAQ = 1 mol/L; T = 165 °C; P C Q 2 = 758 kPa) . TIME CONCENTRATION (mol/L) (H) DEA MEA BHEED BHEP HEOD HEI THEED BHEI 0 2. .90 0.964 0 .000 0, .000 0 .000 0 .000 0 .000 0. 000 2 2. ,67 0.890 0 .041 0, .003 0 .118 0 .000 0 .028 0. ,000 4 2. .25 0.821 0 .085 0. .006 0 . 130 0 .000 0 .177 0. ,019 6 2. .15 0.801 0 . 137 0 , .008 0 . 154 0 .000 0 .301 0'. ,035 8 1. .94 0.740 0 .155 0, .012 0 .148 0 .000 0 .335 0. ,047 11 1. .83 0.732 0 .198 0, .017 0 .161 0 .000 0 .442 0. ,081 20 1. .40 0.568 0 .211 0 .034 0 .164 0 .010 0 .512 0. ,188 26 1. .12 0.477 0 .218 0 .048 0 .120 0 .012 0 .566 0. ,258 32 0, .94 0.396 0 .204 0 .066 0 .119 0 .015 0 .661 0. ,384 kni,, = 0.0338 h Table C.43: Concentrations of compounds i n aqueous DEA solution degraded with C0 2 (DEA Q = 3.00 mol/L; T = 150 °C; PC02 = 759 kPa). TIME CONCENTRATION (mol/L) (H) DEA BHEP HEOD THEED 0 3.00 0.000 0.000 0.000 2 2.73 0.004 0.083 0.000 4 2.63 0.006 0.163 0.000 8 2.49 0.007 0 .205 0 .182 12 2.32 0.010 0.261 0.311 24 1.93 0.021 0.291 0.413 30 1.73 0.029 0.302 0.670 36 1.53 0.038 0.301 0.772 knc,„ = 0.0173 h 338 APPENDIX D D. COMPARISON BETWEEN EXPERIMENTAL AND PREDICTED CONCENTRATIONS Table D.l: [DEA] Q = 40 wt%, T = 165 °C, P c o s = 345 kPa. CONCENTRATIONS (mol/L) TIME DEA MEA BHEED BHEP (H) EXPT PRED EXPT PRED EXPT PRED EXPT PRED 0 4.25 4. .25 0. .000 0 .000 0 .000 0. 000 0.000 0 .000 6 3.68 3. .86 0. .265 0 .220 0 .016 0. 013 0.003 0 .002 12 3.29 3. ,49 0. .483 0 .383 0 .055 0. 036 0.014 0 .008 18 2.98 3. .15 0. .638 0 .514 0 .105 0. 064 0.025 0 .017 24 2.71 2. .83 0. .711 0 .621 0 .157 0 . 093 0.033 0 .028 30 2.43 2. .53 0, .706 0 .706 0 .203 0. 118 0.039 0 .042 36 2.13 2. .27 0. .649 0 .775 0 .239 0. 140 0.043 0 .057 42 1.84 2. .03 0, .584 0 .829 0 .266 0 . 157 0.052 0 .075 48 1.59 1, .81 0, .578 0 .871 0 .285 0. 170 0 .074 0 .094 TIME HEOD HEI THEED BHEI (H) EXPT PRED EXPT PRED EXPT PRED EXPT PRED 0 0 .000 0 .000 0 . .000 0 .000 0 .000 0 .000 0. 000 0 .000 6 0 .015 0 .027 0. .000 0 .005 0 .019 0 .145 0. 000 0 .003 12 0 .047 o 0 .051 0. .010 0 .007 0 .153 0 .266 0. 003 0 .007 18 0 .080 0 .073 0, .036 0 .012 0 .321 0 .372 0. 020 0 .016 24 0 . 105 0 .092 0, .066 0 .020 0 .467 0 .463 0. 049 0 .029 30 0 .119 0 .110 0, .092 0 .031 0 .566 0 .542 0. 088 0 .046 36 0 .123 0 .125 0, .112 0 .045 0 .628 0 .608 0. 136 0 .068 . 42 0 .127 0 .139 0 . 124 0 .060 0 .695 0 .665 0. 190 0 .093 48 0 . 146 0 .152 0 .130 0 .078 0 .844 0 .712 0. 244 0 .120 339 Table D.2: [DEA] Q = 40 wt%, T = 160 °C, P c o s = 345 kPa. CONCENTRATIONS (mol/L) TIME DEA MEA BHEED BHEP (H) EXPT PRED EXPT PRED EXPT PRED EXPT PRED 0 4 . 1 3 4 . 1 3 0 . 000 0 . . 0 0 0 0 . . 0 0 0 0 . 0 0 0 0 . 0 0 0 0 . 0 0 0 6 3 . 7 5 3 . 8 2 0 . 2 1 7 0 , . 1 6 7 0 . . 0 1 6 0 . 0 0 6 0 . 0 0 2 0 . 0 0 1 12 3 . 4 7 3 . 5 2 0 . 382 0 , . 3 1 0 0 . . 0 3 6 0 . 0 2 1 0 . 0 0 8 0 . 0 0 5 18 3 . 2 4 3 . 2 4 0 . 4 9 9 0 , . 4 3 1 0, . 0 7 0 0 . 0 4 0 0 . 0 1 5 0 . 0 1 0 24 3 . 0 1 2 . 9 8 0 . 5 7 7 0, . 5 3 4 0, . 1 1 8 0 . 0 6 1 0 . 0 2 2 0 . 0 1 8 30 2 . 7 8 2 . 7 3 0 . 622 0. . 6 2 2 0, . 1 7 1 0 . 0 8 1 0 . 0 2 8 0 . 0 2 7 36 2 . 5 8 2 . 5 0 0 . 642 0 , . 6 9 5 0, . 2 0 9 0 . 1 0 0 0 . 0 3 6 0 . 0 3 7 TIME HEOD HEI THEED BHEI (H) EXPT PRED EXPT PRED EXPT PRED EXPT PRED 0 0 .000 0 .000 0. ,000 0 .000 0. .000 0 .000 0. .000 0.000 6 0 .011 0 .022 0. .000 0 .001 0. .023 0 .106 0. .000 0.001 12 0 .039 0 .042 0, .005 0 .002 0. .113 0 .201 0. .004 0.003 18 0 .067 0 .061 0. .022 0 .005 0, .258 0 .287 0, .019 0.008 24 0 .087 0 .078 0, .047 0 .009 0 , .436 0 .363 0, .046 0.015 30 0 .100 0 .094 0, .069 0 .015 0, .610 0 .431 0, .082 0.026 36 0 .117 0 .108 0, .069 0 .023 0, .731 0 .491 0, .120 0.040 340 Table D.3: [DEA] Q = 40 wt%, T = 150 °C, P c o s = 345 kPa. CONCENTRATIONS (mol/L) TIME DEA MEA BHEED BHEP (H) EXPT PRED EXPT PRED EXPT PRED EXPT PRED 0 4 .15 4 .15 0, .000 0 .000 0 .000 0 .000 0 .000 0 .000 6 3 .89 3 . 95 0, .166 0 .120 0 .016 0 .003 0 .001 0 .001 12 3 .70 3 .75 0, .303 0 .228 0 .026 0 .009 0 .005 0 .002 18 3 .53 3 .55 0, .420 0 .326 0 .033 0 .019 0 .008 0 .005 24 3 .35 3 .36 0. .521 0 .415 0 .041 0 .030 0 .012 0 .008 30 3 .15 3 .18 0, .609 0 .495 0 .055 0 .042 0 .016 0 .012 36 2 . 95 3 .01 0, .683 0 .567 0 .076 0 .055 0 .020 0 .017 42 2 .76 2 .84 0, .740 0 .633 0 .104 0 .067 0 .025 0 .022 48 2 .63 2 .68 0, .772 0 .691 0 .138 0 .078 0 .032 0 .028 54 2 .62 2 .53 0, .772 0 .744 0 .174 0 .089 0 .043 0 .035 TIME HEOD HEI THEED BHEI (H) EXPT PRED EXPT PRED EXPT PRED EXPT PRED 0 0 .000 0, .000 0. .000 0 .000 0 .000 0.000 0 .000 0 .000 6 0 .008 0, .016 0 , .000 0 .000 0 .000 0.069 0 .000 0 .000 12 0 .017 0, .030 0. .000 0 .000 0 .015 0.130 0 .000 0 .001 18 0 .026 0, .044 0. .000 0 .001 0 .052 0.186 0 .002 0 .003 24 0 .036 0, .058 0. .001 0 .003 0 .102 0.239 0 .005 0 .006 30 0 .050 0, .070 0 , .002 0 .005 0 . 157 0.288 0 .010 0 .010 36 0 .067 0, .082 0. .005 0 .007 0 .214 0.333 0 .015 0 .016 42 0 .085 0 , .093 0. .009 0 .011 0 .270 0.375 0 .021 0 .024 48 0 .104 0, .104 0. .014 0 .015 0 .321 0.414 0 .028 0 .033 54 0 .119 0 .114 0. .019 0 .020 0 .366 0.450 0 .036 0 .043 3 4 1 Table D.4: [DEA] Q = 40 wt%, T = 127 °C, P c o s = 345 kPa. CONCENTRATIONS (mol/L) TIME DEA MEA BHEED BHEP (H) EXPT PRED EXPT PRED EXPT PRED EXPT PRED 0 4 . .20 4. .20 0 . 0 0 0 0 . 0 0 0 0 . 0 0 0 0 . 0 0 0 0 . 0 0 0 0, . 0 0 0 24 3 . .80 3. .90 0 . 2 2 8 0 . 1 9 2 0 . 0 0 9 0 . 0 0 4 0 . 0 0 2 0 , . 001 48 3 . . 45 3, .62 0 . 4 3 9 0 . 3 6 0 0 . 0 2 0 0 . 0 1 4 0 . 0 0 5 0, . 0 0 3 72 3 . . 13 3. . 3 5 0 . 5 8 8 0 . 5 0 9 0 . 0 3 7 0 . 0 2 6 0 . 0 1 1 0, . 0 0 7 96 2 . . 83 3. . 0 9 0 . 6 5 7 0 . 6 3 9 0 . 0 6 2 0 . 0 3 9 0 . 0 1 8 0, . 0 1 3 120 2 . . 5 5 2. . 8 5 0 . 6 6 2 0 . 7 5 3 0 . 0 9 5 0 . 0 5 0 0 . 0 2 7 0 . 0 1 9 144 2 . ,30 2. . 62 0 . 6 4 9 0 . 8 5 3 0 . 1 3 2 0 . 0 6 0 0 . 0 3 8 0 . 0 2 6 TIME HEOD HEI THEED BHEI (H) EXPT PRED EXPT PRED EXPT PRED EXPT PRED 0 0 .000 0 .000 0 .000 0 .000 0 .000 0. 000 0 .000 0. .000 24 0 .025 0 .025 0 .000 0 .000 0 .007 0. 073 0 .000 0. .004 48 0 .048 0 .049 0 .004 0 .001 0 .050 0. 139 0 .011 0. .007 72 0 .068 0 .070 0 .009 0 .003 0 .124 0. 199 0 .034 0, .013 96 0 .088 0 .090 0 .014 0 .005 0 .223 0. 252 0 .057 0, .022 120 0 .108 0 .109 0 .019 0 .009 0 .336 0. 300 0 .081 0, .035 144 0 .129 0 .126 0 .027 0 .015 0 .450 0. 343 0 . 109 0, .052 342 Table D.5: [DEA] Q = 30 wt%, T = 190 °C, P c o s = 345 kPa. CONCENTRATIONS (mol/L) TIME DEA MEA BHEED BHEP (H) EXPT PRED EXPT PRED EXPT PRED EXPT PRED 0 3, .08 3, .08 0 .000 0 .000 0 .000 0. 000 0 .000 0 .000 6 2, .56 2, .53 0 .320 0 .298 0 .008 0. 034 0 .004 0 .005 12 2, .09 2, .03 0 .444 0 .483 0 .048 0. 090 0 .012 0 .019 18 1, .68 1, .62 0 .455 0 .593 0 .100 0. 138 0 .025 0 .038 24 1, .36 1, .28 0 .416 0 .654 0 .148 0. 169 0 .045 0 .063 30 1. .14 1. .01 0 .372 0 .685 0 .180 0. 184 0 .071 0 .090 36 1. .00 0, .79 0 .343 0 .695 0 .192 0. 184 0 .099 0 .118 42 0. .91 0, .62 0 .326 0 .692 0 .188 0. 176 0 .123 0 .148 48 0. .84 0, .49 0 .299 0 .681 0 .175 0. 162 0 .134 0 .178 TIME HEOD HEI THEED BHEI (H) EXPT PRED EXPT PRED EXPT PRED EXPT PRED 0 0 .001 0 .001 0 .000 0 .000 0 .000 0 .000 0 .000 0 .000 6 0 .023 0 .030 0 .006 0 .003 0 .049 0 .148 0 .000 0 .007 12 0 .045 0 .053 0 .018 0 .019 0 .198 0 .258 0 .016 0 .024 18 0 .064 0 .072 0 .031 0 .049 0 .368 0 .338 0 .057 0 .054 24 0 .079 0 .087 0 .041 0 .088 0 .507 0 .392 0 .116 0 .095 30 0 .089 0 .098 0 .049 0 .133 0 .586 0 .427 0 .182 0 . 142 36 0 .093 0 .107 0 .053 0 .181 0 .602 0 .447 0 .246 0 .191 42 0 .092 0 .115 0 .058 0 .229 0 .570 0 .456 0 .293 0 .239 48 0 .089 0 .120 0 .064 0 .277 0 .533 0 .456 0 .307 0 .283 343 Table D.6: [DEA] Q = 30-wt%, T = 170 °C, P C Q S = 345 kPa. CONCENTRATIONS (mol/L) TIME DEA MEA BHEED BHEP (H) EXPT PRED EXPT PRED EXPT PRED EXPT PRED 0 3, .02 3 .02 0 .000 0 .000 0 .000 0, .000 0 .000 0. .000 6 2. .68 2 .76 0 .138 0 .171 0 .000 0, .011 0 .001 0, .002 12 2, .43 2 .51 0 .275 0 .313 0 .007 0, .027 0 .004 0, .005 18 2. .23 2 .27 0 .385 0 .429 0 .029 0. .048 0 .006 0. .010 24 2. .07 2 .05 0 .461 0 .523 0 .060 0. .069 0 .010 0 . 016 30 1. . 91 1 .84 0 .497 0 .599 0 .096 0. .089 0 .016 0. .024 36 1, .74 1 .65 0 .496 0 .660 0 .132 0, .106 0 .023 0. .032 42 1, .56 1 .48 0 .462 0 .708 0 .163 0, .118 0 .030 0, .041 48 1, .38 1 .33 0 .409 0 .746 0 .182 0, .128 0 .038 0, .051 54 1. .19 1 .19 0 .350 0 .775 0 .182 0. .134 0 .044 0. .062 60 1. .02 1 .06 0 .309 0 .797 0 .156 0. .136 0 .048 0. .073 TIME HEOD HEI THEED BHEI (H) EXPT PRED EXPT PRED EXPT PRED EXPT PRED 0 0 . 000 0 .000 0 .000 0 .000 0 .000 0 , .000 0 .000 0 . 000 6 0, .016 0 .016 0 .000 0 .001 0 .000 0, .076 0 .000 0. .003 12 0, .035 0 .030 0 .002 0 .003 0 .021 0, .127 0 .000 0, .006 18 0, .055 0 .043 0 .008 0 .008 0 .108 0. .172 0 .002 0. ,013 24 0, .076 0 .054 0 .016 0 .016 0 .226 0. .210 0 .021 0 . 024 30 0, .097 0 .065 0 .023 0 .026 0 .355 0, .243 0 .053 0. ,038 36 0 , .116 0 .074 0 .029 0 .039 0 .478 0, .271 0 .097 0. .056 42 0, .131 0 .082 0 .033 0 .055 0 .579 0, .294 0 .147 0. .077 48 0, .139 0 .090 0 .034 0 .072 0 .643 0, .313 0 .193 0. .099 54 0 , .135 0 .097 0 .035 0 .091 0 .656 0, .328 0 .223 0. ,123 60 0, .115 0 .103 0 .034 0 .111 0 .606 0, .340 0 .221 0. .148 Table D.7: [DEA] Q = 30 wt%, T = 165 °C, P c o s = 345 kPa. CONCENTRATIONS (mol/L) TIME DEA MEA BHEED BHEP (H) EXPT PRED EXPT PRED EXPT PRED EXPT PRED 0 3, . 04 3 . 0 4 0 . 0 0 0 0. . 0 0 0 0 . 0 0 0 0 . 0 0 0 0 . 0 0 0 0 . 0 0 0 6 2, . 7 5 2 . 8 2 0 . 1 6 9 0, . 1 4 9 0 . 0 1 2 0 . 0 0 5 0 . 0 0 0 0 . 0 0 1 12 2, . 4 9 2 . 61 0 . 2 8 3 0, . 2 7 5 0 . 0 2 2 0 . 0 1 7 0 . 0 0 4 0 . 0 0 3 18 2, . 2 7 2 . 41 0 . 3 7 6 0, . 3 8 3 0 . 0 3 2 0 . 0 3 3 0 . 0 1 0 0 . 0 0 6 24 2. . 08 2 . 21 0 . 4 6 3 0, . 4 7 5 0 . 0 4 7 0 . 0 5 1 0 . 0 1 7 0 . 0 1 0 30 1, . 90 2 . 0 3 0 . 5 4 9 0, . 5 5 2 0 . 0 6 6 0 . 0 6 7 0 . 0 2 2 0 . 0 1 5 36 1, . 7 3 1 . 8 6 0 . 6 2 2 0, . 6 1 8 0 . 0 8 8 0 . 0 8 3 0 . 0 2 8 0 . 0 2 0 42 1, . 5 5 1 . 71 0 . 6 6 1 0, . 6 7 3 0 . 1 1 0 0 . 0 9 6 0 . 0 3 3 0 . 0 2 6 48 1. . 3 6 1 . 5 6 0 . 6 2 7 0 . 7 1 8 0 . 1 2 7 0 . 1 0 7 0 . 0 4 0 0 . 0 3 3 TIME HEOD HEI THEED BHEI (H) EXPT PRED EXPT PRED EXPT PRED EXPT PRED 0 0 .000 0. .000 0. 000 0. ,000 0. .000 0 .000 0 .000 0 .000 6 0 .013 0. ,013 0. 000 0. .000 0. .011 0 .046 0 .000 0 .001 12 0 .023 0. .026 0. 001 0, .001 0. .041 0 .088 0 .002 0 .003 18 0 .030 0. .037 0. 004 0. .004 0. .071 0 .125 0 .007 0 .007 24 0 .038 0. .047 0. 009 0. .009 0 , .097 0 .158 0 .012 0 .014 30 0 .048 0, .057 0. 015 0, .015 0, .118 0 .187 0 .016 0 .024 36 0 .059 0, .066 0. 022 0, .024 0, . 145 0 .213 0 .020 0 .037 42 0 .068 0, .074 0. 031 0, .034 0, .193 0 .236 0 .027 0 .051 48 0 .070 0, .081 0. 039 0, .046 0, .288 0 .255 0 .040 0 .068 345 Table D.8: [DEA] Q = 30*wt%, T = 160 °C, P c o s = 345 kPa. CONCENTRATIONS (mol/L) TIME DEA MEA BHEED BHEP (H) EXPT PRED EXPT PRED EXPT PRED EXPT PRED 0 . 3 . 0 9 3 . 0 9 0 . 0 0 0 0 . 0 0 0 0 . 0 0 0 0 . . 0 0 0 0 . . 0 0 0 0 . . 0 0 0 6 2 .91 2 . 91 0 . 0 7 9 0 . 1 2 7 0 . 0 0 1 0 . . 0 0 3 0 . .001 0, . 0 0 0 12 2 . 7 4 2 . 7 3 0 . 1 8 6 0 . 2 4 0 0 . 0 0 2 0, . 0 1 2 0 . . 0 0 2 0, . 0 0 2 18 2 . 5 6 2 . 5 6 0 . 2 8 5 0 . 3 3 9 0 . 0 0 6 0, . 0 2 4 0, . 0 0 4 0, . 0 0 4 24 2 . 3 9 2 . 3 9 0 . 3 6 2 0 . 4 2 7 0 . 0 1 1 0, . 0 3 7 0, . 0 0 6 0, . 0 0 6 30 2 . 21 2 . 2 3 0 . 4 0 9 0 . 5 0 3 0 . 0 1 9 0, . 0 5 1 0, . 0 0 8 0, . 0 0 9 36 2 . 0 4 2 . 0 8 0 . 4 3 4 0 . 5 7 0 0 . 0 3 1 0'. . 0 6 4 0, . 0 1 0 0 . 0 1 3 42 1 . 8 7 1 . 9 4 0 . 4 5 4 0 . 6 2 9 0 . 0 4 7 0, . 0 7 6 0 . 0 1 1 0 . 0 1 7 48 1 . 7 2 1 . 8 0 0 . 4 9 8 0. . 6 8 0 0 . 0 6 8 0 . 0 8 7 0 . 0 1 2 0 . 0 2 2 TIME HEOD HEI THEED BHEI (H) EXPT PRED EXPT PRED EXPT PRED EXPT PRED 0 0 .000 0 .000 0 .000 0 .000 0 .000 0 .000 0. .000 0 .000 6 0 .014 0 .011 0 .000 0 .000 0 .000 0 .037 0 . ,000 0 .000 12 0 .024 0 .022 0 .000 0 .001 0 .000 0 .070 0. .000 0 .001 18 0 .033 0 .032 0 .000 0 .002 0 .000 0 .101 0. .000 0 .004 24 0 .041 0 .042 0 .000 0 .005 0 .019 0 .129 0. .000 0 .009 30 0 .051 0 .050 0 .002 0 .009 0 .077 0 .154 0, .000 0 .015 36 0 .063 0 .059 0 .006 0 .014 0 . 157 0 .177 0, .005 0 .024 42 0 .076 0 .066 0 .012 0 .021 0 .241 0 .197 0, .018 0 .035 48 0 .089 0 .073 0 .020 0 .028 0 .298 0 .216 0, .044 0 .047 346 Table D.9: [DEA] Q = 30 wt%, T = 150 °C, P C Q S = 345 kPa. CONCENTRATIONS (mol/L) TIME DEA MEA BHEED BHEP (H) EXPT PRED EXPT PRED EXPT PRED EXPT PRED 0 3 . 0 4 3 . 0 4 0 . 0 0 0 0 . 0 0 0 0, . 0 0 0 0 . 0 0 0 0 . 0 0 0 0 , . 0 0 0 6 2 . 8 9 2 . 9 2 0 . 1 1 1 0 . 0 8 8 0, . 0 0 5 0 . 0 0 1 0 . 0 0 0 0, . 0 0 0 12 2 . 7 5 2 . 8 0 0 . 1 8 6 0 . 1 7 1 0. . 011 0 . 0 0 5 0 . 0 0 1 0 . . 001 18 2 . 61 2 . 6 8 0 . 2 5 2 0 . 2 4 7 0. . 0 1 5 0 . 0 1 1 0 . 0 0 3 0. . 001 24 2 . 4 6 2 . 5 7 0 . 3 2 3 0 . 3 1 7 0, . 0 1 9 0 . 0 1 7 0 . 0 0 7 0, . 0 0 2 30 2 . 3 2 2 . 4 6 0 . 4 0 3 0 . 3 8 2 0. . 0 2 4 0 . 0 2 4 0 . 0 1 1 0. . 0 0 4 • 36 2 . 1 8 2 . 3 5 0 . 4 8 5 0 . 4 4 2 0, . 0 3 3 0 . 0 3 2 0 . 0 1 6 0. . 0 0 5 42 2 . 0 5 2 . 2 5 0 . 5 5 1 0 . 4 9 7 0. . 0 4 9 0 . 0 4 0 0 . 0 2 1 0, . 0 0 7 48 1 . 9 3 2 . 1 5 0 . 5 7 2 0 . 5 4 8 0, . 0 7 3 0 . 0 4 7 0 . 0 2 4 0, . 0 0 9 TIME HEOD HEI THEED BHEI (H) EXPT PRED EXPT PRED EXPT PRED EXPT PRED 0 0, .000 0 . 000 0 .000 0 .000 0 .000 0.000 0 .000 0, .000 6 0, .003 0, .008 0 .000 0 .000 0 .000 0.021 0 .001 0, .000 12 0, .005 0. .016 0 .000 0 .000 0 .000 0.041 0 .000 0. .000 18 0, .010 0 . 023 0 .000 0 .001 0 .000 0.060 0 .000 0, .001 24 0, .020 0. .030 0 .000 0 .001 0 .002 0.078 0 .000 0, .003 30 0 .035 0. .036 0 .002 0 .003 0 .033 0.094 0 .003 0, .006 36 0, .053 0. .043 0 .006 0 .004 0 .077 0.110 0 .009 0, .009 42 0, .072 0. .049 0 .009 0 .006 0 .122 0.125 0 .015 0 , .014 48 0, .086 0. .055 0 .009 0 .009 0 .142 0.139 0 .017 0 .019 347 Table D.10: [DEA] Q = 30 wt%, T = 127 °C, P c o s = 345 kPa. CONCENTRATIONS (mol/L) TIME DEA MEA BHEED BHEP (H) EXPT PRED EXPT PRED EXPT PRED EXPT PRED 0 3 .09 3, .09 0. .000 0 .000 0, .000 0.000 0. .000 0.000 24 2 .92 2, .90 0, .157 0 .144 0, .000 0.002 0, .000 0.000 48 2 .75 2, .73 0, .281 0 .272 0, .000 0.008 0. .000 0.001 72 2 .57 2, .56 0. .388 0 .388 0, .001 0.015 0, .000 0.002 96 2 .37 2, .40 0. .489 0 .493 0, .005 0.023 0. .003 0.004 120 2 .18 2, .24 0, .583 0 .587 0, .013 0.030 0. .008 0.006 144 2 .00 2, .10 0, .667 0 .672 0, .029 0.036 0, .013 0.008 168 1 .87 1. .96 0. .726 0 .748 0, .057 0.042 0. .017 0.011 TIME HEOD HEI THEED BHEI (H) EXPT PRED EXPT PRED EXPT PRED EXPT PRED 0 0 .000 0 .000 0. .000 0 .000 0 .000 0 .000 0 , .000 0.000 24 0 .002 0 .013 0. .000 0 .000 0 .000 0 .024 0. .000 0.000 48 0 .015 0 .025 0. .001 0 .001 0 .009 0 .044 0. .000 0.002 72 0 .027 0 .037 0. .003 0 .002 0 .036 0 .062 0, .000 0.005 96 0 .036 0 .047 0. .004 0 .003 0 .067 0 .079 0, .001 0.011 120 0 .042 0 .057 0, .005 0 .006 0 .102 0 .094 0, .008". 0.019 144 0 .054 0 .067 0. .008 0 .009 0 .148 0 .108 0, .024 0 .028 168 0 .085 0 .075 0. .018 0 .013 0 .221 0 . 120 0 , .054 0.040 348 Table D . l l : [DEA] Q = 20 wt%, T = 195 °C, P c o s = 345 kPa. CONCENTRATIONS (mol/L) TIME DEA MEA BHEED BHEP (H) EXPT PRED EXPT PRED EXPT PRED EXPT PRED 0 1, , 97 1. .97 0 .000 0 .000 0, .000 0 .000 0.000 0.000 6 1, .62 1. .63 0 .200 0 .241 0. .007 0 .021 0.002 0.002 12 1. .40 1. .33 0 .321 0 .387 0. .017 0 .057 0.006 0.008 18 1. .21 1, .07 0 .380 0 .478 0. .038 0 .088 0.012 0.016 24 1. .00 0, .85 0 .389 0 .530 0. .068 0 .108 0.018 0.025 30 0, .79 0, .68 0 .365 0 .557 0, .102 0 .117 0.027 0.036 36 0. .68 0, .54 0 .332 0 .566 0, .123 0 .117 0.040 0.048 TIME HEOD HEI THEED BHEI (H) EXPT PRED EXPT PRED EXPT PRED EXPT PRED 0 0 .000 0 .000 0. .000 0 .000 0.000 0.000 0 .000 0 .000 6 0 .004 0 .010 0. .003 0 .003 0.006 0.051 0 .001 0 .002 12 0 .012 0 .018 0. .003 0 .016 0.052 0.089 0 .000 0 .014 18 0 .021 0 .025 0 , .013 0 .041 0.110 0.116 0 .002 0 .035 24 0 .032 0 .031 0, .036 0 .075 0.166 0.134 0 .030 0 .063 30 0 .043 0 .035 0. .067 0 .113 0.214 0.146 0 .072 0 .096 36 0 .051 0 .038 0, .089 0 .155 0 .260 0.152 0 .113 0 .130 349 Table D.12: [DEA] Q = 20 wt%, T = 180 °C, P c o s = 345 kPa. CONCENTRATIONS (mol/L) TIME DEA MEA BHEED BHEP (H) EXPT PRED EXPT PRED EXPT PRED EXPT PRED 0 1. . 96 1. .96 0 . 0 0 0 0 . 0 0 0 0 . 0 0 0 0 . 0 0 0 0 . 0 0 0 0 . 0 0 0 6 1. .71 1. .76 0 . 1 3 8 0 . 1 5 9 0 . 0 0 7 0 . 0 0 7 0 . 0 0 1 0 . 0 0 1 12 1. .52 1. .56 0 . 2 4 4 0 . 2 8 2 0 . 0 1 0 0 . 0 2 3 0 . 0 0 5 0 . 0 0 3 18 1, . 3 4 1. . 38 0 . 3 1 6 0 . 3 7 9 0 . 0 1 6 0 . 0 4 0 ' 0 . 0 0 8 0 . 0 0 5 24 1, . 18 1. .22 0 . 3 5 5 0 . 4 5 4 0 . 0 3 3 0 . 0 5 7 0 . 0 1 2 0 . 0 0 9 30 1, .02 1. . 0 7 0 . 3 6 5 0 . 5 1 2 0 . 0 5 8 0 . 0 7 1 0 . 0 1 5 0 . 0 1 4 36 0, . 8 7 0, . 9 4 0 . 3 5 8 0 . 5 5 5 0 . 0 8 5 0 . 0 8 1 0 . 0 1 9 0 . 0 1 9 42 0, . 76 0, . 82 0 . 3 5 3 0 . 5 8 7 0 . 1 0 3 0 . 0 8 8 0 . 0 2 3 0 . 0 2 4 48 0, . 72 0, .71 0 . 3 7 0 0 . 6 1 0 0 . 0 9 3 0 . 0 9 1 0 . 0 3 0 0 . 0 3 0 TIME HEOD HEI THEED BHEI (H) EXPT PRED EXPT PRED EXPT PRED EXPT PRED 0 0 .000 0 . 000 0 .000 0 .000 0 .000 0 .000 0 .000 0 .000 6 0 .002 0, .007 0 .000 0 .001 0 .010 0 .028 0 .001 0 .001 12 0 .007 0, .013 0 .000 0 .003 0 .036 0 .052 0 .000 0 .004 18 0 .015 0, .019 0 .004 0 .010 0 .072 0 .072 0 .002 0 .011 24 0 .025 0, .024 0 .014 0 .020 0 .115 0 .088 0 .010 0 .022 30 0 .035 0, .028 0 .032 0 .034 0 .159 0 .101 0 .026 0 .036 36 0 .044 0 .032 0 .052 0 .050 0 .195 0 .112 0 .044 0 .053 42 0 .050 0 .035 0 .070 0 .069 0 .214 0 .120 0 .061 0 .871 48 0 .048 0 .038 0 .076 0 .090 0 .202 0 .126 0 .064 0 .091 350 Table D.13: [DEA] Q = 20 wt%, T = 165 °C, P c o s = 345 kPa. CONCENTRATIONS (mol/L) TIME DEA MEA BHEED BHEP (H) EXPT PRED EXPT PRED EXPT PRED EXPT PRED 0 1 . 9 3 1. . 93 0 . 0 0 0 0 . 0 0 0 0 . . 0 0 0 0 , . 0 0 0 0 . . 0 0 0 0 . 0 0 0 6 1 . 8 7 1, .81 0 . 0 8 8 0 . 1 0 0 0 . . 0 0 2 0, . 0 0 2 0 . . 0 0 0 0 . 0 0 0 12 1 . 7 7 1, . 6 9 0 . 1 5 5 0 . 1 8 5 0 . . 0 0 7 0, . 0 0 8 0. . 0 0 0 0 . 0 0 1 18 1 . 6 5 1, . 58 0 . 2 0 9 0 . 2 6 0 0. . 0 1 2 0, . 0 1 5 0. . 0 0 0 0 . 0 0 2 24 1 . 5 3 1, . 48 0 . 2 5 5 0 . 3 2 7 0, . 0 1 6 0, . 0 2 2 0. . 0 0 2 0 . 0 0 3 30 1 . 4 2 1. . 3 7 0 . 2 9 5 0 . 3 8 6 0 . , 0 2 0 0 . . 0 3 0 0 . , 0 0 5 0 . 0 0 4 36 1 . 3 2 1, .28 0 . 3 3 3 0 . 4 3 7 0 . . 0 2 5 0 . . 0 3 8 0 . . 0 0 9 0 . 0 0 6 42 1 . 2 3 1, . 1 9 0 . 3 7 1 0 . 4 8 3 0 . , 0 3 4 0. . 0 4 5 0 . , 0 1 2 0 . 0 0 8 48 1 . 1 5 1, .10 0 . 4 1 0 0 . 5 2 2 0 . . 0 5 2 0, . 051 0. . 0 1 4 0 . 0 1 0 TIME HEOD HEI THEED BHEI (H) EXPT PRED EXPT PRED EXPT PRED EXPT PRED 0 0. .000 0 .000 0.000 0 .000 0 .000 0 .000 0 .000 0 .000 6 0 . 000 0 .005 0.000 0 .000 0 .000 0 .014 0 .001 0 .000 12 0. .002 0 .010 0.000 0 .001 0 .000 0 .027 0 .000 0 .001 18 0. .007 0 .014 0.000 0 .002 0 .000 0 .039 0 .000 0 .003 24 0. .013 0 .017 0.001 0 .004 0 .016 0 .050 0 .000 0 .006 30 0. .020 0 .021 0.003 0 .007 0 .052 0 .059 0 .004 0 .010 36 0. .027 0 .024 0.007 0 .011 0 .097 0 .068 0 .012 0 .016 42 0. .033 0 .027 0.011 0 .016 0 .131 0 .075 0 .020 0 .023 48 0. .038 0 .030 0.013 0 .023 0 .126 0 .082 0 .022 0 .031 351 Table D.14: [DEA] Q = 20 wt%, T = 150 °C, P c o s =345 kPa. CONCENTRATIONS (mol/L) TIME DEA MEA BHEED BHEP (H) EXPT PRED EXPT PRED EXPT PRED EXPT PRED 0 1 . 94 1 .94 0.000 0. .000 0, .000 0. .000 0 .000 0, .000 6 1 .89 1 .87 0.057 0. .057 0, .000 0. .001 0 .000 0, .000 12 1 .83 1 .80 0.114 0 , .111 0, .002 0, .003 0 .000 0, .000 18 1 .76 1 .74 0.164 0 , .161 0 , .007 0 , .005 0 .001 0, .001 24 1 .69 1 .67 0 .208 0, .209 0, .012 0, .008 0 .002 0, .001 30 1 .62 1 .61 0.245 0. ,254 0. .016 0. .011 0 .003 0. .002 36 1 .56 1 .55 0 .276 0. .296 0, .017 0, .014 0 .004 0. .002 42 1 .50 1 .49 0.302 0. .336 0. .017 0. .018 0 .004 0, .003 48 1 .43 1 .43 0.323 0. .373 0, .016 0, .021 0 .005 0, .003 54 1 .36 1 .38 0.339 0, ,408 0, .015 0, .024 0 .006 0, .004 60 1 .26 1 .32 0.350 0. .440 0, .017 0, .028 0 .008 0, .005 TIME HEOD HEI THEED BHEI (H) EXPT PRED EXPT PRED EXPT PRED EXPT PRED 0 0 .000 0 .000 0 .000 0 .000 0 .000 0 .000 0 .000 0 .000 6 0 .000 0 .003 0 .000 0 .000 0 .000 0 .008 0 .000 0 .000 12 0 .004 0 .006 0 .000 0 .000 0 .000 0 .015 0 .000 0 .000 18 0 .008 0 .009 0 .000 0 .000 0 .000 0 .021 0 .000 0 .001 24 0 .013 0 .011 0 .000 0 .001 0 .000 0 .027 0 .000 0 .002 30 0 .017 0 .014 0 .001 0 .001 0 .000 0 .033 0 .000 0 .003 36 0 .019 0 .016 0 .001 0 .002 0 .000 0 .038 0 .001 0 .004 42 0 .019 0 .019 0 .003 0 .003 0 .000 0 .043 0 .004 0 .006 48 0 .019 0 .021 0 .004 0 .004 0 .002 0 .048 0 .007 0 .009 54 0 .019 0 .023 0 .005 0 .006 0 .021 0 .052 0 .010 0 .011 60 0 .020 0 .025 0 .006 0 .007 0 .061 0 .057 0 .012 0 .015 352 Table D.15: [DEA] Q = 20 wt%, T = 135 °C, P c o s = 345 kPa. CONCENTRATIONS (mol/L) TIME DEA MEA BHEED BHEP (H) EXPT PRED EXPT PRED EXPT PRED EXPT PRED 0 1 . 98 1 . 9 8 0 . 0 0 0 0 . . 0 0 0 0 . . 0 0 0 0 . 0 0 0 0 . 0 0 0 0 . 0 0 0 24 1 . 8 6 1 . 8 3 0 . 0 9 7 0 . . 125 0, . 0 0 0 0 . 0 0 3 0 . 0 0 0 0 . 0 0 0 48 1 . 7 0 1 . 6 9 0 . 1 6 3 0 . . 2 3 7 0, . 0 0 0 0 . 0 0 7 0 . 0 0 0 0 . 0 0 1 72 1 . 5 4 1 . 5 5 0 . 2 1 2 0 , . 3 3 5 0, . 0 0 4 0 . 0 1 3 0 . 0 0 1 0 . 0 0 2 96 1 . 4 0 1 . 4 3 0 . 2 5 4 0 , . 4 2 2 0, . 0 1 2 0 . 0 1 8 0 . 0 0 3 0 . 0 0 3 120 .1 . 2 7 1 .31 0 . 2 96 0 . . 4 9 9 0, . 0 2 2 0 . 0 2 3 0 . 0 0 6 0 . 0 0 5 144 1 . 1 6 1 . 2 0 0 . 3 4 0 0 , . 5 6 6 0, . 0 3 2 0 . 0 2 7 0 . 0 0 9 0 . 0 0 7 168 1 . 0 7 1 . 1 0 0 . 3 8 3 0, . 6 2 5 0, . 0 3 9 0 . 0 3 0 0 . 0 1 1 0 . 0 0 9 192 0 . 9 9 1 . 0 0 0 . 4 2 1 0 . 6 7 6 0 . 0 4 1 0 . 0 3 2 0 . 0 1 2 0 . 0 1 1 216 0 . 8 9 0 .91 0 . 4 4 4 0 . 7 2 0 0 . 0 3 4 0 . 0 3 3 0 . 0 1 1 0 . 0 1 3 TIME HEOD HEI THEED BHEI (H) EXPT PRED EXPT PRED EXPT PRED EXPT PRED 0 0 .000 0. .000 0 .000 0. .000 0 .000 0 .000 0 .000 0 .000 24 0 .000 0. .007 0 .001 0. .000 0 .000 0 .013 0 .001 0 .001 48 0 .002 0. ,014 0 .001 0, .001 0 .000 0 .024 0 .000 0 .002 72 0 .008 0. .020 0 .000 0, .002 0 .000 0 .034 0 .000 0 .006 96 0 .015 0. .026 0 .000 0, .004 0 .000 0 .043 0 .000 0 .011 120 0 .022 0. .031 0 .000 0, .007 0 .020 0 .050 0 .004 0 .018 144 0 .028 0. .036 0 .001 0, .011 0 .059 0 .057 0 .011 0 .027 168 0 .032 0. .040 0 .005 0, .016 0 .104 0 .063 0 .019 0 .037 192 0 .034 0, .044 0 .009 0 .022 0 .135 0 .068 0 .025 0 .048 216 0 .034 0, .048 0 .014 0 .029 0 .126 0 .072 0 .025 0 .060 353 Table D.16: [DEA] Q = 20 wt%, T = 127 °C, P c o s = 345 kPa. CONCENTRATIONS (mol/L) TIME DEA MEA BHEED BHEP (H) EXPT PRED EXPT PRED EXPT PRED EXPT PRED 0 1, .99 1 . 99 0. .000 0 .000 0 .000 0 .000 0. .000 0. .000 24 1, .89 1 .88 0, .067 0 .092 0 .000 0 .001 0, .000 0, .000 48 1. .76 1 .78 0. .149 0 .177 0 .000 0 .003 0. .000 0. .001 72 1. .62 1 .68 0. .237 0 .256 0 .001 0 .006 0. .000 0 . ,001 96 1, .50 1 .58 0, .322 0 .328 0 .004 0 .010 0. .001 0, .002 120 1, .41 1 .49 0, .395 0 .394 0 .009 0 .013 0, .003 0. .003 144 1, .32 1 .40 0. .441 0 .455 0 .017 0 .016 0, ,006 0. .003 TIME HEOD HEI THEED BHEI (H) EXPT PRED EXPT PRED EXPT PRED EXPT PRED 0 0 .000 0 .000 0.000 0 .000 0 .000 0 .000 0 .000 0 .000 24 0 .003 0 .006 0.000 0 .000 0 .000 0 .011 0 .001 0 .000 48 0 .011 0 .011 0.000 0 .000 0 .000 0 .018 0 .000 0 .001 72 0 .020 0 .016 0.000 0 .001 0 .011 0 .025 0 .000 0 .002 96 0 .029 0 .020 0.000 0 .001 0 .029 0 .031 0 .000 0 .005 120 0 .039 0 .025 0 .000 0 .003 0 .053 0 .037 0 .005 0 .008 144 0 .048 0 .029 0.003 0 .004 0 .087 0 .043 0 .016 0 .012 354 Table D.17: [DEA] Q = 30 wt%, T = 150 °C, P C Q S = 759 kPa. CONCENTRATIONS (mol/L) TIME DEA MEA BHEED BHEP (H) EXPT PRED EXPT PRED EXPT PRED EXPT PRED 0 2 . 9 5 2 . 95 0 . . 0 0 0 0 . 000 0 . 0 0 0 0 . 0 0 0 0 . 0 0 0 0 . 0 0 0 6 2 . 7 8 2 . 7 7 0 . . 1 5 7 0 . 130 0 . 0 0 0 0 . 0 0 4 0 . 0 0 3 0 . 0 0 0 12 2 . 6 3 2 . 61 0 . . 2 7 5 0 . 241 0 . 0 0 9 0 . 0 1 1 0 . 0 0 5 0 . 0 0 1 18 2 . 4 7 2 . 4 4 0 . . 3 7 5 0 . 340 0 . 0 2 4 0 . 0 2 1 0 . 0 0 8 0 . 0 0 2 24 2 . 2 9 2 . 2 9 0 . . 4 6 5 0 . 427 0 . 0 4 0 0 . 0 3 3 0 . 0 1 2 0 . 0 0 4 30 2 . 0 9 2 . 1 4 0 , . 5 5 0 0 . 504 0 . 0 5 6 0 . 0 4 5 0 . 0 1 7 0 . 0 0 5 36 1 . 8 8 2 . 0 0 0. . 6 2 4 0 . 571 0 . 0 7 0 0 . 0 5 7 0 . 0 2 3 0 . 0 0 8 42 1 . 6 9 1 . 8 6 0, . 6 7 9 0 . 6 2 9 0 . 0 8 2 0 . 0 6 9 0 . 0 2 9 0 . 0 1 0 48 1 . 5 5 1 . 7 4 0, . 6 9 7 0 . 680 0 . 0 9 6 0 . 0 7 9 0 . 0 3 2 0 . 0 1 3 TIME HEOD HEI THEED BHEI (H) EXPT PRED EXPT PRED EXPT PRED EXPT PRED 0 0. .000 0 .000 0. 000 0 .000 0 .000 0 .000 0.000 0 .000 6 0. ,011 0 .011 0. 000 0 .001 0 .000 0 .033 0.000 0 .000 12 0 . 023 0 .022 0. 002 0 .002 0 .003 0 .061 0.000 0 .001 18 0. .032 0 .032 0. 004 0 .004 0 .021 0 .086 0.000 0 .003 24 0. .041 0 .041 0. 006 0 .008 0 .048 0 .110 0.001 0 .006 30 0. .050 0 .050 0. 008 0 .013 0 .083 0 .132 0.007 0 .011 36 0, .060 0 .058 0. 013 0 .020 0 . 124 0 .151 0.015 0 .018 42 0, .070 0 .066 0. 030 0 .029 0 .169 0 .169 0.025 0 .025 48 0, .080 0 .073 0. 067 0 .040 0 .218 0 .186 0.032 0 .035 Table D.18: [DEA] Q = 30 wt%, T = 150 °C, P c o s = 1171 kPa. CONCENTRATIONS (mol/L) TIME DEA MEA BHEED BHEP (H) EXPT PRED EXPT PRED EXPT PRED EXPT PRED 0 2 . 96 2 . 96 0 .000 0 .000 0 .000 0 .000 0 .000 0 .000 6 2 .77 2 .74 0 .199 0 . 157 0 .003 0 .005 0 .004 0 .000 12 2 .51 2 .54 0 .314 0 .290 0 .014 0 .016 0 .009 0 .001 18 2 .24 2 .34 0 .396 0 .403 0 .031 0 .030 0 .013 0 .002 24 2 .00 2 . 15 0 .477 0 .499 0 .050 0 .046 0 .018 0 .004 30 1 .80 1 .98 0 .565 0 .579 0 .068 0 .063 0 .022 0 .006 36 1 .63 1 .81 0 .649 0 .645 0 .085 0 .078 0 .027 0 .009 42 1 .46 1 .66 0 .698 0 .699 0 .101 0 .091 0 .033 0 .012 48 1 .25 1 .52 0 .661 0 .742 0 .116 0 .103 0 .041 0 .015 TIME HEOD HEI THEED BHEI (H) EXPT PRED EXPT PRED EXPT PRED EXPT PRED 0 0 .000 0. .000 0 .000 0 .000 0.000 0 .000 0 .000 0 .000 6 0 .021 0. .014 0 .002 0 .000 0.000 0 .037 0 .000 0 .000 12 0 .041 0, .027 0 .001 0 .003 0 .000 0 .071 0 .000 0 .001 • 18 0 .054 0, .039 0 .003 0 .008 0 .000 0 .102 0 .000 0 .004 24 0 .061 0 , .050 0 .013 0 .016 0.033 0 .130 0 .003 0 .009 30 0 .064 0 , .060 0 .031 0 .028 0.109 0 .155 0 .010 0 .016 36 0 .067 0, .069 0 .055 0 .044 0.202 0 .178 0 .020 0 .024 42 0 .078 0, .078 0 .079 0 .063 0.269 0 .198 0 .029 0 .035 48 0 .107 0 .085 0 .092 0 .085 0.251 0 .216 0 .033 0 .047 356 Table D.19: Rate constants obtained f o r the COS-DEA systems using the optimisation routine. RUN OPERATING RATE CONSTANTS (X 10 3) # CONDITIONS* (h" 1 or L mol" 1 h" 1) C T P k •1 k •2 k3 k 4 k 5 k 6 k ? 1 40 165 345 10. 40 8. 20 1 .10 10. 90 6. 00 3. 50 30.60 2 40 160 345 9. 50 7. 00 1 .00 11. 00 5. 70 3. 30 35.10 3 40 150 345 6. 00 2. 30 0 .56 1. 00 1. 80 4. 60 10.80 4 40 127 345 2. 10 1. 20 0 .27 0. 80 0. 86 1. 25 13.20 5 30 190 345 12. 40 22. 00 1 .30 14. 40 9. 45 7. 40 54.00 6 30 170 345 8. 20 12. 00 1 .30 6. 00 5. 60 2. 30 38.00 7 30 165 345 8. 40 3. 77 0 .65 3. 80 2. 10 7. 80 14.70 8 30 160 345 5. 10 2. 20 0 .67 3. 00 1. 65 3. 00 24.20 9 30 150 345 5. 50 2. 10 0 .53 1. 60 0. 91 10. 00 16.00 10 30 127 345 1. 90 0. 42 0 .15 0. 41 0. 38 1. 10 13.60 11 20 195 345 14 . 40 15. 10 0 . 91 24. 90 5. 10 8. 20 45.80 12 20 180 345 10. 20 10. 00 0 .74 19. 10 3. 60 5. 20 29.70 13 20 165 345 6. 40 3. 90 0 .40 4. 20 1. 50 5. 20 26.30 14 20 150 345 4. 40 1. 60 0 .24 1. 80 0. 20 13. 70 20 .00 15 20 135 345 1. 60 0. 84 0 .10 0 . 57 0. 33 1. 20 5.00 16 20 127 345 1. 90 0. 52 0 .18 0. 31 0. 28 0. 95 14.00 17 30 150 759 8. 20 2. 90 0 .69 4. 00 1. 60 8. 80 10 .00 18 30 150 1171 9. 40 3. 50 0 .92 8. 30 2. 30 7. 90 14 .00 19 60 165 345 9. 00 6. 40 1 .30 16. 00 6. 90 5. 30 29.00 C, T, P r e f e r to DEA concentration (wt%), Temperature (°C) and COS p a r t i a l pressure (kPa), r e s p e c t i v e l y . 357 Table D.20: Rate constants obtained for the CS2-DEA systems using the optimisation routine. RUN OPERATING RATE CONSTANTS (X 10 J) # CONDITIONS* <h" 1 or L mol" 1 h" 1 > C T V k l k2 k3 k4 k •5 k6 k ? 1 60 165 6.0 4.34 2.81 0.33 12.74 3. 93 2.00 11.49 2 40 165 6.0 4.42 8.75 0.96 19.10 6. 01 2.85 7.58 3 30 165 6.0 5.14 8. 97 0.72 15.33 4. 42 2.87 9.37 4 20 165 6.0 6.33 10.12 0.64 5.79 2. 57 2.71 5.17 5 40. 150 6.0 2.64 4.12 0.47 10.08 2. 41 2.21 5.60 6 30 150 6.0 3.04 3.88 0.32 7.89 1. 86 2.46 8.33 7 20 150 6.0 2.45 2.78 0.25 6.74 0. 49 9.81 8.51 8 30 175 10.5 12. 90 30.62 1.85 30.95 10. 46 4.56 59.25 9 30 165 10.5 9.59 13.88 1.05 18.36 6. 03 2.82 25.84 10 30 160 10.5 8.54 14.30 1.38 14.14 5 . 21 1.77 38.43 11 30 130 10.5 1.58 0.71 0.17 1.77 0. 51 0.50 2.40 12 30 165 2.5 3.06 3.99 0.34 13.24 2. 80 2.26 9.22 C, T, V r e f e r to DEA concentration (wt%), Temperature (°C) and CS 2 volume (mL), re s p e c t i v e l y . 358 APPENDIX E ERROR AND S E N S I T I V I T Y A N A L Y S I S E . l ERROR ANALYSIS Errors i n the GC analysis could a r i s e from any of the following: a i r bubbles trapped i n the i n j e c t e d sample, inconsistency of samples in j e c t e d i n t o the GC due to the presence of s o l i d p a r t i c l e s , GC i n t e g r a t i o n e r r o r f or very large peaks, fusion of small peaks with larger adjacent ones, and inconsistent sample volume. The e f f e c t of the l a s t f a c t o r was minimized by using a syringe f i t t e d with a "Chaney adaptor" to ensure the withdrawal of a constant sample volume. In the case of the s o l u b i l i t y and hydrolysis runs, gas samples were transferred i n t o a constant volume c o i l placed between the i n j e c t i o n port and the column i n l e t . Excess volume was discharged through a purge l i n e connected to the c o i l . This arrangement ensured that the volumes of samples analysed were equal. Each analysis was repeated at least three times and the average of the r e s u l t s was recorded. In general, r e s u l t s of repeated analyses were reproducible within ±10%. The p r e c i s i o n was even better f o r c a l i b r a t i o n samples because they contained no s o l i d s . It i s d i f f i c u l t to provide precise values for the various sources of error, but a nitrogen balance gives an estimate of the o v e r a l l error involved i n the degradation experiments. For each degradation run, a nitrogen balance can be expressed as follows: N (DEA)O = N (DEA)t + N (DEGRADATION PRODUCTS)f 359 = N (DEA)t + N (MEA)t + N (BHEED)t + N (BHEP)t + N (HEOD)t + N (HEI)t + N (THEED)t + N (BHEI)t E - 1 or [DEA] Q = [DEA] t + [MEA] fc + 2 [BHEED] t + 2 [BHEP] fc + [HEOD] fc + 2 [HEI ] t + 2 [THEED] t + 2 [BHEI],. E.2 where [ i ] t denotes the concentration of compound i i n mol/L at time t . In Table E . l , N L and N R r e f e r to the L.H.S and R.H.S re s p e c t i v e l y , of Eq. E.2. The experimental data used i n the c a l c u l a t i o n s are provided i n appendix C. Table E . l : Nitrogen balance f o r the degradation runs. RUN N L NR % DEV* RUN N L NR % DEV 1 4.20 5.48 + 30 .48 22 4.16 4.48 + 7.69 2 4.12 5.67 + 37 .62 23 3.10 3.36 + 8.39 3 4.17 4 .75 + 13 .91 24 2. 96 3.23 + 9.12 4 4.20 4 .79 + 14 .05 25 3.00 2.59 -13.70 5 3.11 3.61 + 16 .08 26 2.11 0.87 -58.77 6 3.04 3.58 + 17 .76 27 2 .04 2.22 + 8.82 7 3.00 3.12 + 4 .00 28 2.03 1. 92 - 5.42 8 3.05 3.21 + 5 .25 29 1. 90 1.79 - 5.68 9 3.01 3.12 + 3 .65 30 6.32 6.43 + 1.74 10 3.08 3.43 + 10 .20 31 3.01 3.33 +10.63 11 1. 97 2.30 + 16 .75 32 3.07 3.04 - 0.98 12 1. 98 2 .07 + 4 .55 33 3.11 2.24 -27.97 13 1.91 2.05 + 7 .33 34 3.11 3.25 + 4.50 14 1.96 1.84 - 6 .12 35 3.08 3.30 + 7.14 15 1. 99 1.80 - 9 .55 36 3.08 2 . 94 - 4.55 16 2.00 2.16 + 8 .00 37 NO DEGRADATION 17 2.93 3.18 + 8 .53 38 3.00 3.38 + 12 .67 18 2.95 3.08 + 4 .41 39 3.00 3.06 + 2.00 19 6.21 8.09 + 30 .27 40 3.00 3.43 +14.33 20 3.00 3.06 + 2 .00 41 3.00 2. 96 - 1.33 21 4.30 4.63 + 7 .67 42 3.86 4.12 + 6.74 43 3.10 3.45 +11.29 % DEV = 100 X (N R - NT )/N- 360 The deviations af*e generally below 20%. Higher deviations obtained i n some runs are probably due to outdated c a l i b r a t i o n s and errors i n the THEED concentrations when produced i n large amounts. It should be r e c a l l e d that THEED was the only compound not ava i l a b l e i n the pure form. Runs 26 and 33 were CS2 runs conducted at temperatures above 180 °C. The high negative deviations i n those runs suggest that some products of the reactions were not qua n t i f i e d e i t h e r because they are very v o l a t i l e , or could not be detected by the FID. By discounting deviations above 20%, an average deviation of +5 .46% i s obtained for the degradation runs. This value w i l l be s l i g h t l y higher when the minor degradation compounds containing nitrogen are included i n the balance. Nevertheless, the o v e r a l l value i s an i n d i c a t i o n of the r e l i a b i l i t y of the experimental data. In addition to the nitrogen balance, a measure of the confidence i n the DEA concentration data can be obtained from the scatter between the experimental and f i t t e d concentrations. Using the data f o r the DEA plots i n chapter 5 , a maximum deviation of + 13% was obtained, with an average of ± 3 . 9 8 % (see Table E . 2 ) . This value i s close to the 5 . 4 6 % average deviation obtained from the t o t a l nitrogen balance. Therefore, the average deviation i n the reported concentrations i s estimated at + 5%, with a maximum of + 13% for DEA (based on Table E . 2 ) and ± 20% for the degradation products (based on the nitrogen balance). 361 Table E .2 : Maximum deviations i n the DEA concentrations reported for the degradation runs. RUN3 % DEVIATION13 RUN3 % DEVIATION13 1 - 4. 81 17 - 3 .91 2 + 1. 70 18 + 3 .45 3 - 2 . 73 19 + 2 .53 4 - 1. 00 21 - 4 .60 5 + 12. 79 22 - 5 . 96 7 + 2. 64 23 + 2 .12 9 - 1. 83 24 - 5 .26 10 + 3. 17 25 - 4 .37 11 - 3. 25 27 - 3 .81 12 + 3. 83 28 + 3 .01 13 - 5. 47 29 + 1 .59 14 - 5. 20 30 - 3 .94 15 + 4. 55 31 + 2 .45 16 - 3. 47 32 - 7 .94 3 Data used are from the corresponding table in appendix C. % DEVIATION = ( F i t t e d - Experimental)/Experimental Using a si m i l a r approach, the deviations i n Table E . 3 were generated f o r the equilibrium constants governing amine protonation (K^ ), carbamate formation (K2) and thiocarbamate formation ( K c o s ) . The maximum deviations. are ±11%, ±17% and ±30% f o r K^, K 2 and K c o s, res p e c t i v e l y . Table E .4 shows that, f o r temperatures between 120 and 180 °C, obtained from the modified Kent-Eisenberg model i s one to two times the value obtained from the Kent-Eisenberg model, while K 2 from the former i s approximately twice that of the l a t t e r . 362 Table E.3 : Deviations between the experimental and f i t t e d values of the protonation, carbamate and thiocarbamate equilibrium constants. TEMPERATURE K 1 (X 10 7) K 2 K c o s (10 6) °C EXPT FIT % DEV EXPT FIT % DEV EXPT FIT % DEV 180 3.46 3.18 - 8.09 5.10 4.27 -16.27 7.84 6.77 -13.61 165 2.16 2.39 +10.65 3.02 3.53 +16.89 6.69 6.73 + 0.60 150 1.73 1.75 + 1.16 2.60 2.89 +11.15 5.14 6.69 +30.00 120 0.91 0.88 - 2.86 2.00 1.84 - 8.00 7.47 6.60 -11.65 Table E.4 : Comparison of protonation (K-̂ ) and carbamate (K 2) constants from the Kent-Eisenberg and modified Kent-Eisenberg models. TEMPERATURE FACTOR3 °C K l K2 180 1 .07 2.20 165 1.23 2.10 150 1.42 2.00 120 1.99 1.79 a FACTOR i s the r a t i o of the predictions from the modified Kent- Eisenberg model to that from the Kent-Eisenberg model. E.2 SENSITIVITY ANALYSIS Tables E.5 and E.6 show the s e n s i t i v i t i e s of the objective function F, as defined i n chapter 9, to +20% and -20% changes 363 respectively, i n the optimal rate constants. F was most sens i t i v e to k^, often r e s u l t i n g i n changes exceeding 100%. Changes i n k 2 to ky varied F by less than 20% on the average. Despite the s e n s i t i v i t y of F to k-̂ , the changes in the model predictions as a r e s u l t of changes i n the rate constants were always below 20%, and generally below 10%. The accuracy of the reported rate constants should therefore be of the order of ± 20%. Table E.5: S e n s i t i v i t y of the objective function to changes i n the rate constants f o r the COS-DEA systems (% change i n kj_ = + 20%). RUN % CHANGE IN THE OBJECTIVE FUNCTION # k l k2 k3 k4 k5 k6 k 7 1 + 14.54 + 11.66 - 6. 38 + 9.13 -18.61 -13.60 - 0.23 2 + 11.56 + 8.50 - 2. 41 + 4.14 + 2.11 - 0.83 - 0.45 3 + 28.58 + 4.10 - 36. 85 - 1.30 -32.13 + 4.91 - 4.76 4 - 34.68 + 16.90 - 18. 51 + 2.33 + 2.46 + 1.90 - 1.27 5 - 82.27 + 23.97 - 3. 14 -33.81 + 0.50 - 6.36 + 0.64 6 - 49.67 + 14.83 + 9. 87 -10.00 + 3.00 - 4.59 + 0.78 7 -134.44 - 5.93 - 86. 52 -11.90 -24.88 + 11.31 -17.78 8 -119.26 - 4 .78 + 1. 44 - 2.61 - 6.63 - 2.53 ' + 1.69 9 - 2.62 - 1.01 + 11. 18 - 0.21 - 6.03 + 3.87 - 1.23 10 -119.14 - 10.76 -105. 44 + 0.36 + 6.38 + 1.15 + 0.60 11 -126.50 + 12.93 + 0. 76 -42.49 + 2.08 - 3.26 - 0.97 12 -109.70 + 7.99 + 4. 16 - 4.51 + 5.97 - 1.39 - 3.61 13 -155.80 + 4.47 - 1. 95 - 4.21 + 3.97 + 0.66 + 0.23 14 -216.07 + 3.64 - 15. 02 + 0.76 - 9.94 + 1.98 + 0.66 15 - 84.23 + 5.99 - 8. 33 - 1.94 + 1.99 - 0.10 - 1.66 16 - 95.33 + 0.17 + 37. 52 - 0.32 + 2.77 + 0.13 + 0.28 17 - 0.09 - 4.47 - 12. 01 - 0.28 - 6.93 + 8.31 - 4.01 18 - 42.70 - 5.09 + 3. 43 + 8.75 + 0.49 + 6.94 - 3.41 364 Table E . 6 : S e n s i t i v i t y of the objective function to changes i n the rate constants f o r the COS-DEA systems (% change i n k± = - 2 0 % ) . % CHANGE IN THE OBJECTIVE FUNCTION k l k 2 k 3 k 4 1 - 34 . 21 - 1 6 . 8 2 - 4 . 61 - 1 0 . 8 5 + 3, .81 + 5 . 2 9 0 . 9 7 2 - 32 . 0 5 - 1 1 . 1 7 - 8 . 72 - 4 . 4 7 - 1 2 , . 02 - 2 . 0 9 + 0 . 1 7 3 - 83 . 5 8 - 9 . 4 1 + 4 . 41 + 0 . 71 + 1 1 , . 0 7 -11 . 6 9 + 4 . 3 4 4 - 21 . 31 - 2 0 . 8 2 - 1 9 . 03 - 2 . 7 7 - 1 2 . .51 - 3 . 3 5 + 0 . 6 4 5 + 51 . 95 - 3 4 . 9 3 - 0 . 17 + 28 . 9 7 - 6, . 6 4 + 2 . 9 9 - 2 . 5 6 6 + 27 . 6 0 - 2 0 . 3 9 - 1 5 . 60 + 6 . 9 5 - 6, . 62 + 3 . 0 6 - 2 . 2 5 7 - 1 1 4 . 0 6 - 2 9 . 5 9 + 1 0 . 37 - 1 . 6 7 - 6. . 92 - 1 9 . 3 9 + 12 . 61 8 + 57 . 6 7 - 2 . 2 7 - 2 2 . 07 + 0 . 8 3 - 0, . 24 + 1 . 3 6 - 3 . 0 9 9 - 73 . 7 8 - 2 . 6 9 - 3 2 . 96 - 0 . 1 4 + 1. . 26 - 4 . 3 5 + 0 . 92 10 - 1 2 1 . 1 1 + 1 . 7 8 + 2 8 . 59 - 1 . 7 0 - 1 3 , . 7 4 - 2 . 3 0 - 3 . 0 6 11 + 69 . 6 4 - 2 5 . 9 1 - 2 . 81 + 29 . 4 2 - 5, . 40 + 1 .71 - 1 . 5 5 12 + 40 . 5 7 - 2 0 . 5 6 - 9 . 06 - 9 . 5 8 - 9. . 9 3 - 0 . 2 8 + 0 . 9 9 13 + 72 . 92 - 1 1 . 6 7 - 6 . 40 + 1 . 3 9 - 6. . 88 - 1 . 3 5 - 1 . 5 5 14 + 20 . 1 2 - 1 0 . 0 2 - 5 . 47 - 1 . 7 7 + 6. . 2 5 - 2 . 5 4 - 1 . 7 8 15 + 57 . 3 5 - 8 . 0 7 + 3 . 54 + 0 . 9 3 - 2 , . 6 3 - 0 . 11 + 1 . 5 0 16 - 34 . 2 2 - 2 . 2 7 - 5 5 . 13 + 0 . 0 5 - 4, . 0 7 - 0 . 3 4 - 0 . 8 2 17 - 1 4 7 . 1 2 - 7 . 5 0 - 3 0 . 83 - 6 . 91 - 2 . .51 - 9 . 3 5 + 2 . 8 0 18 - 99 . 4 5 - 8 . 0 2 - 3 9 . 22 - 2 8 . 0 4 - 8, . 50 - 7 . 7 8 + 2 . 0 2 APPENDIX F PROGRAM LISTINGS C THIS PROGRAM DETERMINES THE PROTONATION AND CARBAMATION C CONSTANTS IN THE MODIFIED K/E MODEL. THE CONSTANTS ARE LATER C EXPRESSED AS FUNCTIONS OF TEMPERATURE AND THEN USED TO OBTAIN C THE MODEL PREDICTIONS. C C IMPLICIT REAL*8(A-H,0-Z) DIMENSION DEAC50),PCO2(50),PCOS(50),PH2S(50),YCO2(50),YCOS(50), 1YH2S(50),T(50),F(4),ACCEST(4),X(4), COMMON/BLKA/CK1,CK2,CK3,CK4,CK5,CK6,CK7,CK8,CK9,CKC COMMON/BLKB/Y1,Y2,Y3,HI,H2,H3, DEAC,Pl, P2, P3 EXTERNAL FCN C C INPUT VARIABLES C DATA A1,A2,A3,A4,A5,A6,A7,A8,A9/-2.551D0,4.8255D0,-241.818D0, 1 39.5554D0,-294.74D0,-304.689D0,-657.965D0,104.518D0,22.2819D0/ DATA B1/B2/B3,B4,B5,B6/B7/B8,B9/-5.652D3/-1.885D3,298.25D3, 1 -98.7903,364.38503,387.2103,916.3103,-136.8103,-13.83103/ DATA C1,C2,C3,C4,C5,C6,C7 ̂ 8^9/0.00,0.00,-148.5306, 56.8806, 1 -184.16D6,-194.76D6,-490.63D6,73.77D6,6.91D6/ DATA D1,D2,D3,D4,D5,D6,D7,D8,D9/O.DO,O.DO,332.6D8,-146.5D8, 1 415.808,438.108,1153.108,-174.708,-15.608/ DATA El,E2,E3,E4,E5,E6,E7,E8,E9/0.D0,0.D0,-282.4D10,+136.1O10, 1 -354.3D10,-373.2D10,-1010.2O10,152.2D10,12.0D10/ DATA F1,F2,F3,F4,F5,F6,F7/F8/1.0344D0,2.922370-2,26.207099D0, 1 -10.394767DO,3.749716DO,0.19297775DO,9.0006721D-3,74.282674DO/ N=4 C C INPUT NUMBER OF RUNS C READ(5,10)NRUN 10 FORMAT(12) C C INPUT DEA CONCENTRATIONS AND TEMPERATURES C DO 20 I=1,NRUN READ(5,15)DEA(I) ,T(I) 15 FORMAT(F5.3,2X,F6.2) 20 CONTINUE C C INPUT PARTIAL PRESSURES (KPa) AND ACID GAS LOADINGS (mol/mol DEA) C FOR EACH RUN C DO 30 I=1,NRUN READ(5,25)YC02(I) ,YCOS(I),YH2S(I) ,PC02(I),PCOS(I),PH2S(I) 25 FORMAT(3(F5.3,2X),3(F6.2,2X)) 30 CONTINUE C WRITE(6,35) 35 FORMAT(//17X,'PREDICTED AND EXPERIMENTAL ACID GAS LOADINGS'//) WRITE(6,40) 40 FORMAT(13X,'CARBON DIOXIDE',10X,'HYDROGEN SULPHIDE',6X, 1'CARBONYL SULPHIDE'/) WRITE(6,45) 45 FORMAT(2X,'RUN',3X,'PRED',3X,'EXPT',3X,'DEV (%)',3X,'PRED', 13X,'EXTAL',3X,'DEV (%)',3X,*PRED',3X,'EXPT') DO 55 I=1,NRUN C C CALCULATE EQUILIBRIUM CONSTANTS FROM KENT/EISENBERG (K/E) MODEL 366 c C CK1=DEXP(A1+B1/T(I)+C1/(TCI)**2)+D1/(T(I)**3)+ E1/(T(I)**4)) 1 C CK2=DEXP(A2+B2/T(I) +C2/ (Td) **2) +D2/(T(I) **3) +E2/(T(I) **4) ) CK3=DEXP(A3+B3/T(I)+C3/(T(I)**2)+D3/(T(I)**3)+E3/(T(I)**4)) CK4=DEXP(A4+B4/T(I)+C4/(T(I)**2)+D4/(T(I)**3)+E4/(T(I)**4)) CK5=DEXP(A5+B5/T(I)+C5/(T(I)**2)+D5/(T(I)**3)+E5/(T(I)**4)) CK6=DEXP(A6+B6/T(I)+C6/T(I)**2+D6/T(I)**3+E6/T(I)**4) CK7=DEXP(A7+B7/T(I)+C7/T(I)**2+D7/T(I)**3+E7/T(I)**4) CK8=(DEXP(A8+B8/T(I)+C8/(T(I)**2)+D8/(T(I)**3) +E8/(T(I) **4) ) )/7.5025D0 CK9 =(DEXP(A9+B9/T(I)+C9/(T(I)**2)+D9/(T(I)**3)+E9/(T(I)**4)))/7.5025D0 C C SAVE CURRENT PARAMETERS (DEA CONCENTRATION, HENRY'S CONSTANTS, C LOADINGS AND PARTIAL PRESSURES AS SINGLE VARIABLES C DEAC=DEA(I) H1=CK8 H2=CK9 H3 = l.D3MDEXP(9.291OD0-2313.4324D0/T(I) ) ) Y1=YH2S(I) Y2=YC02(I) Y3=YCOS(I) IF(Y3.EQ.0.D0)Y3=0.001D0 P1=PH2S(I) P2=PC02(I) P3=PCOS(I) C C CALCULATE CONCENTRATIONS OF SPECIES IN SOLUTION. DONE ONLY WHEN C DETERMINING K l , K2 AND KC FROM EXPERIMENTAL DATA C PK=(P1*CK6/H1)*(1.D0+CK7) HP=PK/(DEAC*Y1-P1/H1) H2S=P1/H1 C02=P2/H2 COS=P3/H3 HC03=CK3*C02/HP C03=CK5*HC03/HP HS=CK6*H2S/HP SS=CK7*HS/HP DEAC00=Y2*DEAC-HC03-C03-C02 DEACOS=Y3*DEAC-COS DEAH=HCO3+DEACOO+2.D0*CO3+CK4/HP+HS+2.D0*SS+DEACOS-HP DEAF=DEAC-DEACOO-DEACOS-DEAH C C CALCULATE Kl,K2,KCOS FROM EXPERIMENTAL DATA C C CK1= DEAF* HP/DEAH C CK2=DEAF*HC03/DEACOO C CKC=DEAF*COS/(DEACOS*HP) C C KI,K2,KC AS FUNCTIONS OF TEMPERATURE C CK1=DEXP(-5.0058-4459.9476/T(.I) ) CK2=DEXP(5.0809-1716.4522/T(I) ) CKC=DEXP(19.0833-1440.0543/T(I) ) C C SET INPUT PARAMETERS AND INITIAL GUESSES FOR THE NON LINEAR C SOLVER (NDINVT) ERR=1-D-12 MAXIT=200000 367 u C SET INITIAL GUESS FOR YH2S=X(1),YC02=X(2),HPLUS=X(3),YCOS=X(4) C (OR SET INITIAL GUESSES FOR K1,K2,HP,KC) C X(l)=1.D-1 X(2)=1.D-l X(3)=1.D-1 X(4)=l.D-3 C CALL NDINVT(N,X,F,ACCEST,MAXIT,ERR,FCN,&60) C X1=X(1) X2=X(2) HP1=X(3) X3=X(4) C C CALCULATE DEVIATIONS BETWEEN EXPERIMENTAL VALUES AND MODEL C PREDICTIONS C DEV1= ( (Xl-Yl) /YI) MOO.DO DEV2=((X2-Y2)/Y2)*100.DO C C SOLUTION C WRITE(6,50)I,X2,Y2,DEV2,X1,Y1,DEV1,X3,YC0S(I) 50 FORMAT(2X,I2,2(4X,F5.3,3X,F5.3,3X,F7.2),4X,F5.3,4X,F5.3) 55 CONTINUE GO TO 70 60 WRITE(6,65) 65 FORMAT(10X,'ROUTINE FAILURE') 70 STOP END C C SUBROUTINE FCN(X,F) IMPLICIT REAL*8(A-H,O-Z) DIMENSION XU) ,F(1) COMMON/BLKA/CK1,CK2,CK3,CK4,CK5,CK6,CK7,CK8,CK9,CKC COMMON/BLKB/Y1,Y2,Y3,HI,H2,H3,DEAC,Pl,P2,P3 C C THE 4 MODEL EQUATIONS TO BE SOLVED BY NDINVT C FU) =P1- (HI / (CK6*CK7) ) * (DEAC*X(1) -Pl/Hl) * (X(3) **2) / (1 .D0+X(3) /CK7) C F(2)=P2-(H2/(CK3*CK5))*(DEAC*X(2)-P2/H2)*(X(3)**2)/(l.D0+X(3)/ 1CK5+DEAC*X(3)/(CK2*CK5*(1.D0+X(3)/CK1+(P2/(H2*X(3)))*(CK3/CK2) 1+(P3/(H3*CKC*X(3)))))) C F(3) =X(3) * U.D0+DEAC/.(CK1* (l.D0+X(3) /CK1+ (P2/(H2*X(3) ) ) * (CK3/CK2 1)+(P3/(CKC*H3*X(3))))))-(DEAC*X(1)-Pl/Hl)*(1.D0+CK7/(CK7+X(3))) 1-(DEAC*X(2) -P2/H2) *U.D0+CK2*CK5/(CK2*CK5+CK2*X(3) +DEAC*X(3) / 1U.D0+X(3)/CK1+(P2/(H2*X(3)))*(CK3/CK2)+(P3/(CKC*H3 1*X(3))))))-CK4/X(3)-((DEAC*X(4)-P3/H3) /(DEAC-(DEAC 1*X(4)-P3/H3)))*(1.D0+X(3)/CK1+(P2/H2)*(CK3/(CK2 1*X(3))))*(DEAC/(1.D0+X(3)/CK1+(CK3/(CK2*X(3)) 1*P2/H2+P3/(CKC*X(3)*H3)))) C F(4)=P3-H3*((DEAC*X(4)-P3/H3)/(DEAC-(DEAC*X(4)-P3/H3))) 1*(CKC*X<3)*(l.D0+X(3)/CK1+(P2/H2)*(CK3/(CK2*X(3))))) C RETURN END 368 c C PROGRAMME TO DETERMINE THE RATE CONSTANTS IN THE KINETIC C EXPRESSIONS FOR THE COS-DEA AND CS2-DEA SYSTEMS C IMPLICIT REAL*8(A-H,0-2) DIMENSION All(50),A12(50),A13(50),A14(50),A15(50),A21(50), 1A22(50),A23(50), A24(50),A25(50),A31(50),A32(50),A33(50),A34(50), 1A35(50),A41(50),A42(50),A43(50),A44(50),A45(50),A51(50),A52(50), 1A53(50),A54(50),A55(50),A61(50),A62(50),A63(50),A64(50),A65(50), 1A7K50) ,A72(50) ,A73(50) ,A74(50) ,A75(50) ,A81(50) ,A82<50) ,A83(50) , 1A84(50),A85(50),RKL(50),RKU(50),X<80),Y(10),NT(50),RC(10) C 1YY(50,50) COMMON/BLKA/YC(80,80),YF(80),YE(80,80),YMAX(8) COMMON/BLKB/RK(15) COMMON DX,N,NE INTEGER FLAG INTEGER FAIL C C Input maximum values of rate constants f o r each search (RC) and C time f o r each run (NT) i n hours. Values d i f f e r e n t from those C below may be input through READ statements C DATA RC/0.01D0,0.02D0,0.03D0,0.04D0,0.05D0,0.06D0, 1 0.07D0,0.08D0,0.09D0,0.10D0/ DATA NT/48,36,54,48,60,3*48,168,36,2*48,60,216,30,2*48,166,168, 1 164/ C C Input the numbers of runs (NRUN), equations (NE) C and var i a b l e s (NVAR) C R E A D ( 5 , 1 0 )N R U N , N E ,N V A R 10 F O R M A T(3(12,2X)) C C Input i n i t i a l guesses of rate constants, R K(1) R K ( 8 ) . C R E A D(5,15) ( R K(L),L=1,7) 15 F0RMAT(7(F3.1,1X)) C C Input the f i v e polynomial f i t t i n g constants f o r DEA (1) and the C degradation compounds (2-8) C DO 25 1=1,NRUN READ(5,20)All(I),A12(I),A13(I),A14(I),A15(I) 20 FORMAT(5(2X,E15.8) ) 25 CONTINUE DO 30 1=1,NRUN READ(5,20)A21(I),A22(I),A23(I),A24(I) ,A25(I) 30 CONTINUE DO 35 1=1,NRUN READ(5,20)A31(I),A32(I),A33(I),A34(I) ,A35(I) 35 CONTINUE DO 40 1=1,NRUN READ(5,20)A41(I),A42(I),A43(I),A44(I),A45(I) 40 CONTINUE DO 45 1=1,NRUN READ(5,20)A51(I),A52(I) ,A53(I) ,A54(I) ,A55(I) 45 CONTINUE DO 50 1=1,NRUN READ (5,20)A61(1),A62(I),A63(I) ,A64(I) ,A65(I) 50 CONTINUE 369 DO 55 1=1,NRUN R E A D ( 5 , 2 0 ) A 7 1 ( I ) , A 7 2 ( I ) , A 7 3 ( I ) , A 7 4 ( I ) , A 7 5 ( I ) 55 CONTINUE DO 60 1=1,NRUN R E A D ( 5 , 2 0 ) A 8 1 ( I ) , A 8 2 ( I ) , A 8 3 ( I ) , A 8 4 ( I ) , A 8 5 ( I ) 60 CONTINUE C C C a l c u l a t e e x p t a l c o n c e n t r a t i o n s a t s e l e c t e d t i m e s , u s i n g a f o u r t h C o r d e r p o l y n o m i a l f i t t i n g e q u a t i o n d e r i v e d i n a p r e v i o u s p rog ramme. C DO 65 1=1,8 Y M A X ( I ) = 0 . D 0 65 CONTINUE C DX=4 X U ) =0.D0 DO 135 L=1,NRUN C L = l N=1+NT(L)/DX DO 70 J = 1 , N JM=J-1 I F ( J . G E . 2 ) X ( J ) = X ( J M ) + D X C Y E ( 1 , J ) = A 1 1 ( L ) + A 1 2 ( L ) * X ( J ) +A13(L)*X(J>**2+A14 < L ) * X ( J ) * * 3 1 + A 1 5 ( L ) * X { J ) **4 I F ( Y E ( 1 , J ) . L T . 0 - D O ) Y E ( 1 , J ) = 0 . D O Y C ( 1 , J ) = Y E ( 1 , J ) Y M A X ( l ) = D M A X 1 ( Y M A X ( l ) , Y E ( 1 , J ) ) C YE ( 2 , J ) = A 2 1 ( L ) + A 2 2 ( L ) * X ( J ) + A 2 3 ( L ) * X ( J ) * * 2 + A 2 4 ( L ) * X ( J ) * * 3 1 + A 2 5 ( L ) * X ( J ) **4 I F ( Y E ( 2 , J ) . L T . 0 . D O ) Y E ( 2 , J ) =0.D0 Y C ( 2 , J ) = Y E ( 2 , J ) Y M A X ( 2 ) = D M A X 1 ( Y M A X ( 2 ) , Y E ( 2 , J ) ) C YE ( 3 , J ) = A 3 1 ( L ) + A 3 2 ( L ) * X ( J ) + A 3 3 ( L ) * X ( J ) * * 2 + A 3 4 ( L ) * X ( J ) * * 3 1 + A 3 5 ( L ) * X ( J ) * * 4 I F ( Y E ( 3 , J ) . L T . 0 . D 0 ) Y E ( 3 , J ) =0.D0 Y C ( 3 , J ) = Y E ( 3 , J ) YMAX(3)=DMAX1(YMAX(3) , Y E ( 3 , J ) ) C Y E ( 4 , J ) = A 4 1 ( L ) + A 4 2 ( L ) * X ( J ) + A 4 3 ( L ) * X ( J ) * * 2 + A 4 4 ( L ) * X ( J ) * * 3 1 + A 4 5 ( L ) * X ( J ) * * 4 I F ( Y E ( 4 , J ) . L T . 0 . D 0 ) Y E ( 4 , J ) =0.D0 Y C ( 4 , J ) = Y E ( 4 , J ) Y M A X ( 4 ) = D M A X 1 ( Y M A X ( 4 ) , Y E ( 4 , J ) ) C Y E ( 5 , J) = A 5 1 ( L ) + A 5 2 C L ) * X ( J ) + A 5 3 ( L ) * X ( J ) * * 2 + A 5 4 ( L ) * X ( J ) * * 3 1 + A 5 5 ( L ) * X ( J ) **4 I F ( Y E ( 5 , J ) . L T . 0 . D O ) Y E ( 5 , J ) =0.D0 Y C ( 5 , J ) = Y E ( 5 , J ) Y M A X ( 5 ) = D M A X 1 ( Y M A X ( 5 ) , Y E ( 5 , J ) ) C Y E ( 6 , J ) = A 6 1 ( L ) + A 6 2 ( L ) * X ( J ) + A 6 3 ( L ) * X ( J ) * * 2 + A 6 4 ( L ) * X ( J ) * * 3 1+A65(L> * X ( J ) **4 I F ( Y E ( 6 , J ) . L T . 0 . D 0 ) Y E ( 6 , J ) =0.D0 Y C ( 6 , J ) = Y E ( 6 , J ) Y M A X ( 6 ) = D M A X 1 ( Y M A X ( 6 ) , Y E ( 6 , J ) ) C Y E ( 7 , J ) = A 7 1 ( L ) + A 7 2 ( L ) * X ( J ) + A 7 3 ( L ) * X ( J ) * * 2 + A 7 4 ( L ) * X ( J ) * * 3 370 1 + A 7 5 ( L ) * X ( J ) * * 4 I F ( Y E ( 7 , J ) . L T . 0 . D O ) Y E ( 7 , J ) = 0 . D 0 Y C ( 7 , J ) = Y E ( 7 , J ) Y M A X ( 7 ) = D M A X 1 ( Y M A X ( 7 ) , Y E ( 7 , J ) ) C Y E ( 8 / J ) = A 8 1 ( L ) + A 8 2 ( L ) * X ( J ) + A 8 3 ( L ) * X ( J ) * * 2 + A 8 4 ( L ) * X ( J ) * * 3 1 + A 8 5 ( L ) * X ( J ) * * 4 I F (YE ( 8 , J ) . L T . 0 . D O ) YE (8 , J ) =0.D0 Y C ( 8 , J ) = Y E ( 8 , J ) Y M A X ( 8 ) = D M A X 1 ( Y M A X ( 8 ) , Y E ( 8 , J ) ) 70 CONTINUE C C I n p u t p a r a m e t e r s f o r o p t i m i z a t i o n r o u t i n e . The r o u t i n e NLPQLO i s C u s e d t o o p t i m i z e t h e v a l u e s o f t h e r a t e c o n s t a n t s by m i n i m i s i n g C t h e s q u a r e o f t h e d i f f e r e n c e s b e t w e e n e x p e r i m e n t a l and c a l c u l a t e d C c o n c e n t r a t i o n s f o r a l l compounds f o r e a c h i n t e g r a t i o n i n t e r v a l C u s e d i n R u n g e - K u t t a (RKC) C C C U p p e r and l o w e r bounds o f t h e r a t e c o n s t a n t s C DO 130 KOUNT=1,10 DO 75 J=1 ,NVAR 75 R K ( J ) = l . D - 4 DO 80 L L = 1 , NVAR R K L ( L L ) = 0 . D 0 RKU(LL)=RC(KOUNT) 80 CONTINUE C C O t h e r o p t i m i s a t i o n p a r a m e t e r s C ME=0 M=0 MMAX=0 MAXIT=15000 MXFLSE=200 LOG=20000 A C C U R = l . D - 6 SCBOU=l .D3 C C A L L N L P Q L O ( M , M E , N V A R , R K , F 2 , R K L , R K U , A C C U R , S C B O U , M X F L S E , M A X I T , 1 L O G / F A I L ) W R I T E ( 6 , 8 5 ) F A I L , F 2 85 FORMAT( '0RETURN CODE FROM N L P Q L O : * , 1 6 / 1 ' F I N A L FUNCTION V A L U E : ' , 1 P G 1 6 . 8 / ) DO 125 K K = 1 , 2 I F ( K K . E Q . 2 ) G O TO 95 K l = l K2 = 4 W R I T E ( 6 , 9 0 ) 90 F O R M A T ( / / 3 X , ' T I M E ' , 7 X , ' D E A * , 1 1 X , ' M E A * , 1 0 X , ' B H E E D ' , 9 X , ' B H E P ' ) GO TO 105 95 K l = 5 K2 = 8 W R I T E ( 6 , 1 0 0 ) 100 F O R M A T ( / / 3 X , ' T I M E ' , 7 X , ' H E O D 1 , 1 0 X , ' H E I ' , 1 0 X , ' T H E E D ' , 9 X , ' B H E I ' ) 105 W R I T E ( 6 , 1 1 0 ) 110 F O R M A T ( 4 X , ' ( H ) ' , 3 X , ' E X P T ' , 3 X , ' P R E D ' , 3 X , ' E X P T ' , 3 X , ' P R E D ' , 3 X , 1 ' E X P T ' , 3 X , ' P R E D ' , 3 X , ' E X P T ' , 3 X , ' P R E D ' ) DO 120 1 = 1 , N , 3 371 W R I T E ( 6 , U 5 ) X ( I ) , ( Y E ( J , I ) , Y C ( J , I ) , J = K 1 , K 2 ) 115 F O R M A T ( 2 X , F 5 . 1 , 8 ( 3 X , F 4 . 2 ) ) 120 CONTINUE 125 CONTINUE 130 CONTINUE 135 CONTINUE STOP END C C SUBROUTINE F U N K ( T I , Y , F ) I M P L I C I T R E A L * 8 ( A - H , 0 - Z ) DIMENSION Y d ) , F ( 1 ) COMMON/BLKA/YC1(80 ,80) , Y F ( 8 0 ) , Y E ( 8 0 , 8 0 ) , Y M A X ( 8 ) COMMON/BLKB/RK(15) COMMON/RKC$/OK LOGICAL OK I F ( . N O T . O K ) S T O P C F ( l ) = - R K ( l ) * Y ( 1 ) - R K ( 2 ) * Y ( 1 ) * Y ( 2 ) - R K ( 3 ) * Y ( 1 ) - R K ( 5 ) * Y ( 1 ) F ( 2 ) = R K ( 1 ) * Y ( 1 ) - R K ( 2 ) * Y ( 1 ) * Y ( 2 ) - R K ( 4 ) * Y ( 2 ) * * 2 F ( 3 ) = R K ( 2 ) * Y ( 1 ) * Y ( 2 ) - R K ( 7 ) * Y ( 3 ) F ( 4 ) =RK(6) *Y(7) F ( 5 ) = R K ( 3 ) * Y ( 1 ) F ( 6 ) = R K ( 4 ) * Y < 2 ) * * 2 F ( 7 ) = R K ( 5 ) * Y ( 1 ) - R K ( 6 ) * Y ( 7 ) F ( 8 ) =RK(7) *Y(3) C RETURN END C C SUBROUTINE F U N C ( M , M E , M M A X , N V A R , F 2 , G , R K ) I M P L I C I T R E A L * 8 ( A - H , 0 - Z ) DIMENSION R K ( 1 5 ) , T ( 2 0 ) , S ( 2 0 ) , P ( 2 0 ) , F ( 2 0 ) , Y ( 2 0 ) COMMON/BLKA/YC1(80 ,80) , Y F ( 8 0 ) , Y E ( 8 0 , 8 0 ) , Y M A X ( 8 ) COMMON D X , N , N E EXTERNAL FUNK C E P S = l . D - 6 T I = 0 . D 0 TF=DX*N H = ( T F - T I ) / 2 5 6 . D 0 HMIN=1.D-3*H DO 10 J=1 ,NE Y ( J ) = Y E ( J , 1 ) 10 CONTINUE TF=DX C C C a l l RKC routine C DO 20 J J =2,N C A L L D R K C ( N E , T I , T F , Y , F , H , H M I N , E P S , F U N K , T , S , P) DO 15 J=1 ,NE Y C 1 ( J , J J ) = Y ( J ) 15 CONTINUE TF=TF+DX 20 CONTINUE SUMI=0.DO DO 30 L = l , 8 SUM=O.DO DO 25 11 = 1 , N S U M = S U M + ( Y E ( L , I I ) - Y C 1 ( L , I I ) ) * * 2 CONTINUE IF(YMAX(L)-EQ.O.DO)SUM1=SUM1+SUM IF(YMAX(L) .GT.O.DO)SUM1=SUM1+SUM/YMAX(L) CONTINUE F2=SUM1 RETURN END

Cite

Citation Scheme:

    

Usage Statistics

Country Views Downloads
United States 5 0
Canada 5 0
China 4 0
Japan 2 0
Malaysia 1 0
City Views Downloads
Weston 4 0
Beijing 4 0
Unknown 2 0
Tokyo 2 0
Regina 1 0
Midland 1 0
Wilmington 1 0
Kuala Lumpur 1 0
Ashburn 1 0

{[{ mDataHeader[type] }]} {[{ month[type] }]} {[{ tData[type] }]}

Share

Share to:

Comment

Related Items