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Degradation of diethanolamine solutions Kennard, Malcolm L. 1983

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DEGRADATION OF DIETHANOLAMINE SOLUTIONS by  MALCOLM L. KENNARD B.Sc, University of Nottingham, England, 1974 M.A.Sc., University of B r i t i s h Columbia, 1978  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 January 1983 © Malcolm L. Kennard, 1983  In p r e s e n t i n g requirements  this thesis f o r an  of  British  it  freely available  agree t h a t for  that  Library  s h a l l make  for reference  and  study.  I  for extensive copying of  h i s or  be  her  copying or  f i n a n c i a l gain  shall  g r a n t e d by  publication  not  be  Date  DE-6  (.3/81)  of  further this  Columbia  thesis  head o f  this  my  It is thesis  a l l o w e d w i t h o u t my  of  The U n i v e r s i t y o f B r i t i s h 1956 Main Mall V a n c o u v e r , Canada V6T 1Y3  the  representatives.  permission.  Department  University  the  s c h o l a r l y p u r p o s e s may  understood  the  the  I agree that  permission by  f u l f i l m e n t of  advanced degree a t  Columbia,  department or for  in partial  written  ABSTRACT Raw natural gas contains acid gases such as H S 2  be removed before the gas can be sold.  has become widely accepted by industry.  which must  (DEA) as a solvent  The process i s simply based  of the acid gases in aqueous DEA.  reactions can occur when DEA reacts with the C0 compounds.  2  The removal of these gases i s  c a l l e d "sweetening" and the use of Diethanolamine  on the absorption and desorption  and C0  2  Side  to produce degradation  This degradation causes a loss in valuable DEA and an increase  in plant operating costs. The reaction between DEA and C0  was  2  a 600 ml s t i r r e d autoclave, to determine concentration, and reaction pressure. using gas chromatography.  studied experimentally, using  the effect of temperature,  Degraded DEA samples were analysed  A f a s t , simple, and r e l i a b l e technique  developed to analyse degraded DEA samples, which was plant use. DEA  DEA  was  i d e a l l y suited to  . Over 12 degradation compounds were detected in the degraded  solutions using gas chromatography and mass spectroscopy. Degradation mechanisms are proposed for the production of the various  compounds.  It was found that the degradation of DEA was very sensitive  to temperature,  DEA concentration, and C0  2  s o l u b i l i t y of less than 0.2 g  C0 /g DEA.  To study the effect of C0  of reaction  pressure, simple s o l u b i l i t y experiments were performed  2  2  s o l u b i l i t y , which i s a function to  cover the range of 100-200°C, 413.7-4137 kPa (60-600 psi) p a r t i a l pressure of C0  2  and DEA concentration of 10, 20, and 30 wt % DEA.  I t was  found t h a t the r e a c t i o n between DEA  and C0  was  2  extremely  complex c o n s i s t i n g of a m i x t u r e of e q u i l i b r i a , p a r a l l e l , s e r i e s , ionic reactions.  However, the o v e r a l l d e g r a d a t i o n of DEA  and  c o u l d be  simply  d e s c r i b e d by a pseudo f i r s t o r d e r r e a c t i o n . The main d e g r a d a t i o n p r o d u c t s were HEOD, THEED, and BHEP. was  concluded  t h a t C0  a c t e d as a c a t a l y s t b e i n g n e i t h e r consumed nor  2  produced  d u r i n g the d e g r a d a t i o n of DEA  produced  from DEA  and C 0 , 2  c o n v e r t e d back to DEA The  but was  t o THEED and BHEP.  HEOD was  found to be u n s t a b l e and c o u l d be  or r e a c t to form THEED and BHEP.  f o l l o w i n g simple k i n e t i c model was  d e g r a d a t i o n of DEA  It  developed  to p r e d i c t  the  and the p r o d u c t i o n of the major d e g r a d a t i o n compounds:-  DEA BHEP The model covered the ranges of DEA 175°C, and C0  2  Attempts  c o n c e n t r a t i o n 0-100  s o l u b i l i t i e s g r e a t e r than 0.2  were made t o p u r i f y degraded DEA  c l a i m e d t h a t a c t i v a t e d carbon f i l t e r s compounds.  g C0 /g 2  wt % DEA,  DEA.  solutions.  I t has been  are u s e f u l i n removing d e g r a d a t i o n  However, t e s t s w i t h a c t i v a t e d carbon proved  p a b l e of removing any of the major d e g r a d a t i o n compounds.  See Nomenclature  90-  i t t o be  inca-  TABLE OF CONTENTS ABSTRACT  ,ii  LIST OF TABLES  ix  LIST OF FIGURES  xi  ACKNOWLEDGEMENTS  xv  Chapter 1  2  3  4  5  INTRODUCTION  1  1.1  4  Objectives of the present study  LITERATURE REVIEW  5  2.1 2.2  Absorption of C0 DEA degradation  2.3  Analysis of DEA and i t s degradation products  2  in aqueous DEA  solutions  5 9 ...  13  DEVELOPMENT OF THE ANALYTICAL TECHNIQUE  17  3.1  18 19 19 21 21 23 23 28 29 29 30  Gas chromatographic technique 3.1.1 Evaluation of the Tenax G.C. column 3.1.2 Operating conditions 3.2 A n a l y t i c a l procedure and performance 3.2.1 Column performance 3.3 G.C. c a l i b r a t i o n 3.4 Maintenance of chromatographic equipment 3.5 Advantages of the a n a l y t i c a l technique 3.6 Errors 3.6.1 Accuracy 3.7 Units of DEA concentration SYNTHESIS OF SELECT DEGRADATION COMPOUNDS FOR CALIBRATION OF THE GAS CHROMATOGRAPH 4.1 Synthesis of HEOD  31 31  4.2  34  THEED synthesis  IDENTIFICATION OF DEGRADATION COMPOUNDS  38  5.1 5.2 5.3  38 39 40  I d e n t i f i c a t i o n using the gas chromatograph I d e n t i f i c a t i o n using a GC/MS Identified degradation compounds iv  6  7  EXPERIMENTAL EQUIPMENT AND PROCEDURE FOR THE CONTROLLED DEGRADATION OF DEA  45  6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8  45 47 49 49 50 50 52 52  PRELIMINARY EXPERIMENTS AND DEVELOPMENT OF THE EXPERIMENTAL PROGRAMME 7.1  high temperatures f o r the degradation 54 54 56 56 56 58 58 59 59 59 60  RESULTS AND DISCUSSION OF EXPERIMENTS DESIGNED TO STUDY THE KINETICS OF THE DEGRADATION REACTION  62  7.5  8.1  8.2 8.3 9  Use of runs 7.1.1 7.1.2 7.1.3 7.1.4  54  Temperature comparisons Comparison with i n d u s t r i a l samples Thermal degradation J u s t i f i c a t i o n f o r the use of elevated temperatures Effect of metal surfaces Effect of s t i r r e r speed and reactant volume Reproducibility 7.4.1 Samples 7.4.2 Runs Experimental programme ,  7.2 7.3 7.4  8  600 ml. autoclave Loading the autoclave Sampling Analysis of the l i q u i d samples Analysis of the gas phase Experimental procedure Maintenance and performance Sources of errors  Effect of temperature 8.1.1 Degradation products 8.1.1.1 HEOD 8.1.1.2 THEED 8.1.1.3 BHEP Effect of i n i t i a l DEA concentration E f f e c t of pressure  EXPERIMENTS DESIGNED TO ELUCIDATE THE DEGRADATION MECHANISM 9.1 9.2  Effect Effect 9.2.1 9.2.2  of pH of bicarbonate and carbonate ions C0 s o l u b i l i t y data Runs using HC0 ~ and C0 instead of C0 E f f e c t of water Thermal degradation C0 s o l u b i l i t y studies 2  3  95 95 98 98  3  2  9.3 9.4 9.5  64 72 72 72 79 79 84  2  v  103 108 115 120  10  EXPERIMENTS DESIGNED TO STUDY THE BEHAVIOUR OF THE MAJOR DEGRADATION COMPOUNDS AND IMPURITIES IN THE DEA FEED 10.1 10.2 10.3 10.4 10.5  11  Long term run BHEP runs HEOD runs THEED runs Experiments to study the e f f e c t of impurities in the DEA feed  DEVELOPMENT OF A MECHANISM FOR DEA DEGRADATION 11.1  11.3  11.5  142  Formation and reactions of the major degradation compounds 146 11.1.1 Formation of HEOD 146 11.1.2 Behaviour of HEOD under reaction conditions 147 11.1.2.1 Proof that BHEP i s not produced d i r e c t l y from HEOD .. 147 11.1.2.2 Equilibrium between HEOD and DEA carbamate 150 11.1.2.3 Proof that THEED i s not produced d i r e c t l y from HEOD 153 11.1.3 Proposed model for the production and reactions of HEOD 153 11.1.4 E f f e c t of temperature on the production of HEOD 157 11.1.5 Reaction of HEOD and DEA under N 158 11.1.6 Formation of THEED 158 11.1.7 Formation of BHEP 160 Discussion of the degradation routes 160 11.2.1 Ionic route 160 11.2.2 Molecular route 162 11.2.2.1 Molecular runs 162 11.2.3 Thermal route 163 Discussion of anomalous experimental observations 164 11.3.1 The relationship between i n i t i a l k j ) and DEA concentration 164 11.3.2 Arrhenius plot 164 11.3.3 Log [DEA] versus time plots 166 11.3.4 Explanation of the effect of pH 168 The formation of minor degradation compounds ... 169 11.4.1 MEA degradation 169 11.4.2 Reaction between MEA and DEA 172 11.4.3 Minor degradation compounds produced from DEA 174 11.4.4 The reaction between DEA and TEA 175 Summary 175 11.5.1 Conclusions of the degradation experiments 175 E A  11.4  125 128 129 137  145  2  11.2  125  vi  12  KINETIC STUDIES  180  12.1  180 181 183 184  12.2 12.3  12.4 12.5 13  14  Development of a k i n e t i c model 12.1.2 Simplified degradation mechanism Theory Calculation of the k values 12.3.1 Method (A)—The plot of [THEED] vs. t goes through a maximum 12.3.2 Method (B)—The plot of [THEED] vs. t does not go through a maximum Comparison of the experimental results with the predictions of the model Application of the model  184 185 188 188  PURIFICATION. OF DEGRADED DEA SOLUTIONS  194  13.1 13.2 13.3 13.4 13.5  194 195 198 198 199  Use of activated Use of solvents Removal of BHEP Removal of HEOD Conclusion  carbon  CONCLUSIONS AND RECOMMENDATIONS  200  14.1  202  P r a c t i c a l implications  of the present study  NOMENCLATURE  205  REFERENCES  207  Appendices A Sources of equipment and chemicals  212  B  Experimental results for the degradation of DEA by C0  214  The s o l u b i l i t y of C0 i n DEA solutions at high temperature and pressure C.l Experimental method C.2 Calculation of C0 s o l u b i l i t y C.3 Example C.4 Results  249 249 252 253 254  D  Derivation  258  E  Comparison between the experimental results and the prediction of the k i n e t i c model  2  C  2  2  of the k i n e t i c model  vii  261  F  Mass spectra of DEA and related degradation compounds F . l Mass spectra of DEA and i t s degradation compounds F.2 Mass spectra of minor degradation compounds F.3- Mass spectra of impurities i n the DEA feed F.4 Mass spectra of associated compounds F.5 Summary  viii  277 277 277 277 277 277  LIST OF TABLES Table 2.1  9.6 9.7  Equations governing C0 absorption i n aqueous DEA solution 6 A n a l y t i c a l equipment and operating conditions for G.C. analysis 20 Compounds found i n degraded DEA solutions 44 Comparison of r e p r o d u c i b i l i t y of degradation runs .... 59 Summary of experiments performed with C0 at 4137 kPa (600 psi) 60 I n i t i a l DEA concentration and i n i t i a l DEA degradation rates at 205°C 68 I n i t i a l DEA concentration and i n i t i a l DEA degradation rates at 175°C 68 I n i t i a l DEA concentration and i n i t i a l DEA degradation rates at 150°C 70 Comparison of C0 s o l u b i l i t i e s in DEA solutions 99 Summary of HC0 and C 0 — runs 103 Comparison of k^p. values for runs conducted with KHC0 and C0 , 108 Summary of the molecular runs 109 Comparison of k £A ^ ° l l > i o n i c , and standard runs 114 Summary of thermal runs 115 Comparison of k ^ ^ for thermal and standard runs 115  9.8  Overall k ^  3.1 5.1 7.1 7.2 8.1 8.2 8.3 9.1 9.2 9.3  2  2  2  _  3  3  9.4 9.5  9.9 9.10 10.1 10.2 10.3 11.1 13.1  3  2  o r m  e c u  a r  n  E A  as a function of C0  2  solubility for  degradation runs of 30 wt % DEA at 195°C C0 s o l u b i l i t y as a function of temperature i n a 30 wt % DEA solution under a t o t a l pressure of 4137 kPa (600 p s i ) C0 s o l u b i l i t y as a function of DEA concentration f o r solutions at 205°C under a t o t a l pressure of 4137 kPa (600 psi) Summary of runs to study the behaviour of the major degradation compounds for reactions under CO, and N  120  2  122  2  2  122 128 142  Experimental conditions of runs performed to determine the e f f e c t s of DEA feed impurities 142 P r i n c i p a l DEA degradation routes under various conditions 176 E f f e c t of various solvents on degraded DEA solutions .. 198  ix  B.l 4B. 73 C. l C.2 C.3 C.4 E.l 4E. 15 F. l  Run 1 4 Run 73 Vapour pressure of DEA solutions as a function of temperature S o l u b i l i t y of C0 i n 30 wt % DEA S o l u b i l i t y of C0 i n 20 wt % DEA S o l u b i l i t y of C0 i n 10 wt % DEA Comparisons between experimental and predicted concentrations 4Comparisons between experimental and predicted concentrations Molecular formula and major peaks of mass spectra of compounds studied 2 2  2  x  215 248 250 255 256 257 262  276 293  LIST OF FIGURES Figure 1.1 Flow sheet of the basic amine process 2 2.1 Shuttle mechanism for C0 absorption into aqueous amine solutions 8 3.1 Typical chromatogram for MEA, DEA, and TEA 22 3.2 Typical chromatogram of a degraded DEA solution 22 3.3 Calibration plot for DEA 24 3.4 Calibration plot for HEOD 25 3.5 Calibration plot for BHEP 26 3.6 Calibration plot for THEED 27 4.1 Chromatogram of substituted ethylenediamines ... 36 5.1 Chromatogram showing peak of unknown compound 41 5.2 Mass spectrum of HEOD 42 5.3 Mass spectrum of unknown compound 42 5.4 Typical chromatogram of a degraded DEA solution 43 6.1 Sketch of 600 ml. autoclave 46 6.2 Sketch of the autoclave loading system 48 7.1 Chromatogram of a 30 wt % DEA solution degraded at 205°C under 4137 kPa C0 (time—1 hr.) 55 7.2 Chromatogram of a 30 wt % DEA solution degraded at 120°C under 4137 kPa C0 (time—150 hr.) 55 7.3 Chromatogram of a degraded DEA solution from a gas sweetening unit operated at Aquitaine Canada Ltd 57 7.4 Chromatogram of a degraded DEA solution from a gas sweetening unit operated by Hudson's Bay O i l and Gas Co. Ltd 57 8.1 Typical chromatograms of a 30 wt % DEA solution degraded at 205°C under 4137 kPa 63 8.2 DEA concentration as a function of time and temperature (4137 kPa C0 , 205-162°C) ' 65 8.3 DEA concentration as a function of time and temperature (4137 kPa C0 , 150-90°C) 66 8.4 I n i t i a l degradation rate as a function of i n i t i a l DEA concentration and temperature 69 8.5 Arrhenius plot for a 30 wt % DEA solution degraded with C0 at 4137 kPa 71 8.6 HEOD concentration as a function of time and temperature (30 wt % DEA, 4137 kPa C0 , 205-162°C) ... 73 8.7 HEOD concentration as a function of time and temperature (30 wt % DEA, 4137 kPa C0 , 150-90°C) 74 8.8 THEED concentration as a function of time and temperature (30 wt % DEA, 4137 kPa C0 , 205-162°C) ... 75 2  2  2  2  2  2  2  2  2  xi  )  8.9  THEED concentration as a function of time and temperature (30 wt % DEA, 4137 kPa C0 , 150-90°C) 76 BHEP concentration as a function of time and temperature (30 wt % DEA, 4137 kPa C0 , 206-162°C) ... 77 BHEP concentration as a function of time and temperature (30 wt % DEA, 4137 kPa C0 , 150- 90°C) ... 78 DEA concentration as a function of time and i n i t i a l DEA concentration (4137 kPa C0 , 205°C) 80 DEA concentration as a function of time and i n i t i a l DEA concentration (4137 kPa C0 , 175°C) 81 DEA concentration as a function of time and i n i t i a l DEA concentration (4137 kPa C0 , 150°C) 82 knj? function of i n i t i a l DEA concentration and 2  8.10  2  8.11  2  8.12  2  8.13  2  8.14  2  8.15  a  s  a  A  temperature (4137 kPa C0 ) 83 Arrhenius plot for varying DEA solution strengths degraded with C0 at 4137 kPa 85 8.17 HEOD concentration as a function of time and i n i t i a l DEA concentration (4137 kPa C0 , 205°C) 86 8.18 THEED concentration as a function of time and i n i t i a l DEA concentration (4137 kPa C0 , 205°C) 87 8.19 BHEP concentration as a function of time and i n i t i a l DEA concentration (4137 kPa C0 , 205°C) 88 8.20 DEA concentration as a function of time and C0 pressure (30 wt % DEA, 195°C) 90 8.21 k^,,. as a function of reaction pressure (30 wt % DEA, DtA 195°C) 91 8.22 HEOD concentration as a function of time and C0 pressure (30 wt % DEA, 195°C) 92 8.23 THEED concentration as a function of time and C0 pressure (30 wt % DEA, 195°C) 93 8.24 BHEP concentration as a function of time and C0 pressure (30 wt % DEA, 195°C) 94 9.1 DEA concentration as a function of time and solution pH (30 wt % DEA, 4137 kPa C0 , 205°C) 96 9.2 S o l u b i l i t y of C0 i n 30 wt % DEA 100 9.3 S o l u b i l i t y of C0 i n 20 wt % DEA 101 9.4 S o l u b i l i t y of C0 i n 10 wt % DEA 102 9.5 DEA concentration as a function of time and temperature (using KHC0 , 30 wt % DEA, 4137 kPa N ) .. 104 9.6 HEOD concentration as a function of time and temperature (using KHC0 , 30 wt % DEA, 4137 kPa N ) .. 105 9.7 THEED concentration as a function of time and temperature (using KHC0 , 30 wt % DEA, 4137 kPa N ) .. 106 9.8 BHEP concentration as a function of time and temperature (using KHC0 , 30 wt % DEA, 4137 kPa N ) .. 107 9.9 DEA concentration as a function of time and i n i t i a l DEA concentration (no water present, 4137 kPa C0 , 205°C) 110 9.10 HEOD concentration as a function of time and i n i t i a l DEA concentration (no water present, 4137 kPa C0 , 205°C) I l l 2  8.16  2  2  2  2  2  2  2  2  2  2  2  2  3  2  3  2  3  2  3  2  2  2  xii  9.11  THEED concentration as a function of time and i n i t i a l DEA concentration (no water present, 4137 kPa C0 , 205°C) 112 BHEP concentration as a function of time and i n i t i a l DEA concentration (no water present, 4137 kPa C0 , 205°C) 113 DEA concentration as a function of time and temperature (no C0 present, 30 wt % DEA, 4137 kPa N ) 116 THEED concentration as a function of time and temperature (no C0 present, 30 wt % DEA, 4137 kPa N ) 118 BHEP concentration as a function of time and temperature (no C0 present, 30 wt % DEA, 4137 kPa N ) 119 k „ . as a function of CO, concentration (30 wt % DEA DEA, 195°C) 121 DEA concentration as a function of time and C0 pressure (30 wt % DEA, 205°C) 124 Typical plots of concentration as a function of time for DEA and i t s degradation products 126 Concentration of DEA, HEOD, THEED, and BHEP as a function of time (30 wt % DEA, 4137 kPa C0 , 205°C) .. 127 DEA concentration as a function of time and degradation products (30 wt % DEA, 4137 kPa C0 , 205°C) 130 Concentration of DEA, HEOD, THEED, and BHEP as a function of time (reactants—DEA and HEOD, 4137 kPa C0 , 205°C) 132 DEA concentration as a function of time ( r e a c t a n t s — degraded DEA solution, 4137 kPa C0 or N , 175°C) 133 HEOD concentration as a function of time ( r e a c t a n t s — degraded DEA solution, 4137 kPa C0 or N , 175°C) 134 THEED concentration as a function of time ( r e a c t a n t s — degraded DEA solution, 4137 kPa C0 or N , 175°C) 135 BHEP concentration as a function of time ( r e a c t a n t s — degraded DEA solution, 4137 kPa C0 or N , 175°C) 136 Concentration of DEA, THEED, and BHEP as a function of time (reactants—DEA and THEED, 4137 kPa N , 205°C) 138 Concentration of DEA, HEOD, THEED, and BHEP as a function of time (reactants—DEA and THEED, 4137 kPa C0 , 205°C) 140 logfTHEED] as a function of time (reactants—DEA and THEED, 4137 kPa C0 or N , 205°C) 141 Typical chromatogram of a degraded solution of DEA and MEA 144 Qualitative plots of concentration versus time, showing the possible relationships between HEOD and BHEP 148 Sketch of the concentration of HEOD and BHEP as a function of time for run 65 148 Sketch of the concentration of HEOD and BHEP as a function of time for runs 8 and 10 151 Sketch of the concentration of HEOD and THEED as a function of time for runs ,1 to 12 154 Schematic diagram of degradation of DEA 157 2  9.12  2  9.13  2  9.14 9.15 9.16  2  2  2  2  2  2  9.17 10.1 10.2  2  2  10.3  2  10.4 10.5 10.6 10.7 10.8 10.9  2  2  2  2  2  2  2  2  2  2  10.10  2  10.11  2  10.12 11.1 11.2 11.3 11.4 11.5  2  xiii  11.6  Sketch of k ^ ^ as a function of i n t i a l DEA  12.4  concentration Sketch of the Arrhenius plots f o r ionic, molecular, and standard runs Schematic diagram showing the possible routes for the degradation of DEA Typical plot of [THEED] versus time Comparison between the experimental and theoretical values of DEA, HEOD, THEED, and BHEP concentrations as a function of time (run 6) Comparison between the experimental and theoretical values of DEA, HEOD, THEED, and BHEP concentrations as a function of time (run 23) Arrhenius plots for k i at various i n i t i a l DEA concentrations (DEA HEOD) Arrhenius plots for k 2 at various i n i t i a l DEA  189  12.5  concentrations (DEA -^-*THEED) Arrhenius plot for k at various i n i t i a l DEA  190  12.6  concentrations (THEED -^-BHEP) Sketch of Arrhenius plots for k i and k2 at various i n i t i a l DEA concentrations Typical chromatograms of p a r t i a l l y degraded DEA solutions taken upstream and downstream of an activated carbon f i l t e r located in a large gas plant Typical chromatograms of p a r t i a l l y degraded DEA solutions under laboratory conditions; before and after contact with activated carbon DEA solution vapour pressure as a function of temperature and DEA concentration Mass spectrum of DEA Mass spectrum of BHEP Mass spectrum of HEOD Mass spectrum of THEED Mass spectrum of BHEED Mass spectrum of HEED Mass spectrum of HEI Mass spectrum of HEM Mass spectrum of HEP Mass spectrum of OZD Mass spectrum of TEHEED Mass spectrum of MEA Mass spectrum of TEA Mass spectrum of BHG Mass spectrum of DEEA Mass spectrum of MDEA  191  11.7 11.8 12.1 12.2  12.3  12.7 13.1  13.2 C.l F.l F.2 F.3 F.4 F.5 F.6 F.7 F.8 F.9 F.10 F.ll F.12 F.13 F.14 F.15 F.16  165 167 179 184 186  187  3  xiv  193  196 197 251 278 279 280 281 282 283 284 285 286 287 288 289 289 290 291 292  ACKNOWLEDGEMENTS The author wishes to thank the following:- Dr. Axel Meisen f o r h i s supervision and guidance throughout the course of this work; - Nina Thurston for her excellent typing; - P a t r i c i a Parsons who drew the figures. The f i n a n c i a l assistance provided by the Canadian Gas Processors Association for this work i s gratefully  xv  acknowledged.  CHAPTER 1  INTRODUCTION Raw natural gas leaving the geological formation frequently  contains  undesirable compounds such as hydrogen sulphide, carbon dioxide, and water.  The acid gases and the water must be removed before the natural  gas can be sold in order to minimize pipe line corrosion, pumping costs, health hazards, and p o l l u t i o n when the gas is f i n a l l y burnt or converted. P u r i f i c a t i o n , or 'sweetening', of large volumes of 'sour' natural gas requires a process which is e f f i c i e n t  and inexpensive.  for a p u r i f i c a t i o n process to be e f f i c i e n t , simple, and r e l a t i v e l y trouble free.  Further, in order  i t must be regenerative,  The use of aqueous diethanolamine  (DEA) has emerged as the best approach to the sweetening of sour natural gas. The process is based on the reaction of a weak base (DEA) with a weak acid (H S or C0 ) to give a water soluble s a l t . 2  may be summarized as (H0-C HJ 2  2  (H0-C H ) 2  4  2  The reactions  2  follows:-  NH + H S c=± (H0-C H ) 2  2  NH + C0 + H 0 ^ 2  2  1|  2  NH  (H0"C H ) 2  HS"  + 2  4  2  NH  [1.1] + 2  These reactions are reversible and the e q u i l i b r i a  HC0 ~ 3  [1.2]  may be shifted by  regulating the temperature. The basic i n d u s t r i a l process  (see F i g . 1.1)  consists  essentially  of contacting the sour natural gas with a counter current stream of an aqueous DEA solution (usually about 15-30 wt % DEA) at 30-50°C and at  2  ACID GAS  SWEET  SOUR GAS >  Figure  1.1  Flow sheet of the b a s i c amine p r o c e s s  )  STEAM  3 pressures ranging from atmospheric to well over 6895 kPa (1000 p s i ) . The acid gases are absorbed by the DEA and the 'rich' DEA i s then pumped to an amine stripper.  In the stripper the pressure i s reduced and the  temperature raised to 100-120°C, which i s s u f f i c i e n t to remove a l l but trace quantities of the acid gases.  The 'lean' DEA  i s then recycled  back to the absorber. DEA's popularity i s based on several factors:-  low energy require-  ments compared with most other solvents, high a f f i n i t y for acid gases, and resistance to degradation. ible transformation of DEA  Degradation i s defined as the i r r e v e r s -  into undesirable compounds.  Plant experience  has shown, however, that degradation does occur and with, at times, surp r i s i n g speed.  Incidents have been reported in which gas plants have  lost their entire DEA  inventory within a matter of days.  Degradation i s undesirable for three main reasons. represents a loss of valuable DEA; accumulate  First, i t  second, the degradation products  leading to equipment fouling;  t h i r d , i t i s suspected that  some degradation products are highly corrosive.  Plant operators have  t r i e d to solve the problem by changing operating conditions and/or i n s t a l l i n g activated carbon filters.''" the degradation compounds.  The f i l t e r s are believed to absorb  In some cases these measures are successful,  but in others they are inadequate for reasons which are not c l e a r l y understood.  Furthermore,  satisfactory procedures for one gas plant are often  i n e f f e c t i v e for others.  There can therefore be no doubt that the  Canadian gas processing industry incurs multimillion dollar costs every year due to DEA degradation.  losses and increased maintenance r e s u l t i n g from DEA Consequently, there i s a strong incentive to learn  how to prevent (or at least minimize) DEA degradation.  1.1  Objectives of the present study Although DEA samples from i n d u s t r i a l sweetening  units are routinely .  analysed to monitor the purity of the solution and to detect degradation compounds, very l i t t l e has been published in the open l i t e r a t u r e on DEA degradation.  Furthermore  the available studies are purely qualitative  and no attempt has been made to explain quantitatively the degradation behavior. Thus the main objectives of this study are:a)  To develop a simple a n a l y t i c a l technique for analysing degraded DEA solutions.  Preferably, the technique should be suited for plant use.  b)  To isolate and identify the primary degradation compounds.  c)  To determine  the degradation rates as a function of  temperature,  pressure, and i n i t i a l DEA concentration. d)  To elucidate a reaction mechanism for the production of the various degradation compounds.  e)  To develop a k i n e t i c model which can predict the degradation of DEA and the production of degradation compounds under typical i n d u s t r i a l conditions.  f)  To propose ways of reducing DEA degradation in i n d u s t r i a l  sweetening  units. g)  To investigate ways of purifying degraded DEA  solutions and to study  the effectiveness of activated carbon. Since DEA degradation r e s u l t s primarily from reaction with the present study emphasizes degradation due to C0 other compounds such as 0 , CS 2  2  and  COS.  2  C0 , 2  rather than H S 2  and  CHAPTER 2 LITERATURE REVIEW The DEA sweetening process has been widely accepted for removing 2-7 C0  2  and H S from natural gas.  There have been several studies mainly 8—11  2  directed at improving plant performance  and removing degradation  112 8 products. ' ' In addition there are several handbooks available which review natural gas processing and present general a n a l y t i c a l methods f o r 13-17 routine analysis of gas treating solutions. However, there are surprisingly few references dealing s p e c i f i c a l l y with DEA degradation and the analysis of the degradation products.  In  fact most of the experimental studies have been limited to the absorption of C0 into DEA which takes place i n a matter of seconds whereas degrada• j of * months. *u tion takes place over a period 2  1  2.1  Absorption of C0  8  -  2  9  i n aqueous DEA solutions  2  The mechanism of C0  2  absorption, unlike that of H S, i s not simple 2  and involves the establishment of several equilibrium reactions. the l i t e r a t u r e on C0 not f u l l y  2  Although  absorption i s extensive, the absorption i s s t i l l  understood.  When a C0 molecule dissolves i n water, due to i t s acidic chemical 2  c h a r a c t e r i s t i c s i t f i r s t hydrates Eq. 2.1. i n Table 2.1).  The H C0 2  t  o  form carbonic acid, H C0 (see 2  3  3  molecule, i n turn, s l i g h t l y dissociates  to form hydrogen (H ) and bicarbonate (HC0 +  3  ) ions.  The bicarbonate ion  6 Table 2.1 Equations governing C0 absorption i n aqueous DEA solution (R denotes C Hit0H) 2  2  Acid-base  C0  + H0 ^  2  H C0  2  H C0  2  reaction  [2.1]  3  ^  HC0 ~ + H  +  [2.2]  HC0 ~ ^  C0 ~~ + H  +  [2.3]  2  3  3  3  3  R NH + H 0 ^ZT R N H 2  2  R NH + H  2  ^ ± R NH  +  2  C0  2  + 0H~  + 2  [2.4] [2.5]  + 2  + OH" ^ ± HC0 ~  2  [2.6]  3  R NH 2  + HC0 ~ ^  + 2  3  2R NH 2  + 2  [R NH ] 2  2  3  [R NH ] [ C 0 ~ ]  [2.8]  +  3  2  [2.7]  +  2  + C0 " ^  +  2  [R NH ] [HC0 ~] 2  2  2  3  [C0 ~~] + C0 + H 0 3  2  2[R NH ] [HC0 ~] +  2  2  Carbamate  R NH + C0 2  3  [2.9]  formation  R NH COO~  [2.10]  +  2  2  2  R NH C00~ + H 0  R NC00" + H*0  [2.11]  R NH C00~ + 0H~ ^  R NC00~ + H 0  [2.12]  +  2  2  2  +  2  R NH C00~ + R NH R NC00~ + H 2  +  2  +  2  R NC00~ + R NH  +  2  2  2  + H0 ^ 2  2  R NH 2  + 2  2  + HC0 ~ 3  [2.13] [2.14]  7 and the DEA m o l e c u l e may (see Eq. 2.7).  then r e a c t t h e r e b y f o r m i n g the DEA b i c a r b o n a t e  The s o l u b i l i t y of C0  presence of DEA.  3  i n water i s thus enhanced by the  T h i s i s due t o DEA b e i n g a l k a l i n e and f o r m i n g h y d r o x y l  i o n s (OH ) w i t h w a t e r . t o form HC0  2  The OH  (see Eq. 2.6).  can then a l s o r e a c t d i r e c t l y w i t h C0 The o v e r a l l r a t e of C0  2  2  a b s o r p t i o n by  these a c i d - b a s e r e a c t i o n s i s q u i t e s l o w , e s p e c i a l l y when compared to the a b s o r p t i o n of H S.  The d i f f e r e n c e between these r a t e s of a b s o r p t i o n  2  has l e d t o the development of amine p r o c e s s e s t h a t are a b l e to s e l e c t i v e l y 30,31,32 absorb  H S. 2  A second s e t of C0 the l a b i l e hydrogen the C0  2  absorption r e a c t i o n s also occurs i n v o l v i n g  atom p r e s e n t i n the DEA m o l e c u l e .  I n t h i s case  molecule r e a c t s d i r e c t l y a c c o r d i n g t o Eq. 2.10 w i t h the DEA  2  mole-  c u l e t o form a z w i t t e r o n complex, i . e . , a d i p o l e molecule which i s e x t r e m e l y 23  unstable.  The z w i t t e r o n i s then r a p i d l y d e p r o t o n a t e d by w a t e r ,  or another amine m o l e c u l e mate, R NC00 . 2  (see Eqns. 2.11  The r a t e of C0  2  t o 2.13), t o form the DEA  OH carba-  a b s o r p t i o n v i a the carbamate r e a c t i o n s  i s much f a s t e r than the C0 a c i d - b a s e r e a c t i o n , but s t i l l somewhat s l o w e r than the H S a b s o r p t i o n r e a c t i o n . 21 . . A s t a r i t a e t a l . proposed t h a t the enhancement of C0 solubility 2  2  2  i n water by DEA  i s due t o a r a t h e r complex "mass t r a n s f e r w i t h c h e m i c a l  r e a c t i o n " mechanism.  I n the r e g i o n near the g a s - l i q u i d i n t e r f a c e ,  C0  2  was p o s t u l a t e d t o d i s s o l v e i n the water and undergo the f a s t carbamate reactions. steep C0  2  The r e a c t i o n s were b e l i e v e d t o be f a s t enough t o cause a c o n c e n t r a t i o n p r o f i l e near the g a s - l i q u i d i n t e r f a c e and t h e r e -  by i n c r e a s i n g the mass t r a n s f e r r a t e .  The carbamate i o n d i f f u s e s  the b u l k of the l i q u i d where i t r e v e r t s t o b i c a r b o n a t e and f r e e amine (see Eq. 2.14).  into  liberates  The amine i s then a b l e t o d i f f u s e back t o  8 the interface region where i t can react with additional C0  2  in an increased  3  s o l u b i l i t y of C0 by converting 2  This results  C0 to HC0 2  The q u a l i -  tative behaviour i s shown i n F i g . 2.1. Gas phase  CO,  CO,  Fast reaction with amine to carbamate  Slower reaction C0 and hydroxyl ion  Gas-1iquid Interface  Amine diffusion  2  Carbamate diffusion  Slow reversion of carbamate to amine and bicarbonate  Bulk of l i q u i d phase F i g . 2.1  HCO,  Shuttle mechanism f o r C0 absorption solutions 2  into aqueous amine  33 Jorgensen DEA.  has proposed an additional reaction between C0 and 2  In t h i s case the C0 reacts with an alcohol group i n the DEA mole2  cule to form an a l k y l carbonate. RNH-C H 0 + H,0  [2.15]  RNH-C.H^O  [2.16]  RNH-C-HijOH + OH  + CO.  2  4  RNH-C,H„-0-C  \  However, this reaction occurs only i n strongly alkaline solutions (pH 26 > 13) and at low temperatures.  I t i s therefore u n l i k e l y to be of  importance i n natural gas treating units.  Several authors have also +  proposed the existence of the R NCOO 2  R NH 2  2  24 25 29 complex.  in aqueous solutions this complex can be considered  '  '  However,  to be almost com-  p l e t e l y dissassociated. Thus the gas treating solution can be considered  to be a complex  mixture of ionized species i n e q u i l i b r i a consisting mainly of H , OH , +  HC0 ~, R NC00~' R NH , as well as the molecules C0 and R NH. +  3  2.2  2  2  2  2  2  DEA degradation Besides the establishment  of the ionic e q u i l i b r i a within the gas  treating solution, there are certain side reactions by which DEA and  DEA  +*  carbamate (R NC00  H )  2  i s not e a s i l y recovered  undergo further change.  DEA, i n general,  from these compounds and these side reactions  are termed the "degradation reactions." DEA  degradation i s a complex phenomenon.  Smith and Younger  as well as Nonhebel^ have reported that degradation apparently on temperature, pressure,  depends  gas composition, amine concentration, pH, and  the presence of metal ions.  However, the quantitative relationships  between these variables and degradation have not been reported. therefore, impossible  '^ '^  It i s ,  to predict DEA degradation rates or, a l t e r n a t i v e l y ,  to estimate improvements from changes i n operating variables. tion i s further complicated  The s i t u a -  by the fact that the degradation products  are large organic molecules which are d i f f i c u l t to detect and i d e n t i f y . * — + DEA carbamate i s written i n the ionic form, R NC00 H , since in aqueous solutions i t can only exist as ions. Carbamic acid, R NCOOH, i s extremely unstable and reverts to DEA and C0 ; R NC00H has never been i s o l a t e d . 2  2  2  2  10 Polderman and Steele  34  were the f i r s t to publish a comprehensive  investigation on DEA degradation i n 1956. .  Their work consisted essen-  t i a l l y of placing a 25 wt % DEA solution into a pressure vessel, saturating  i t with C0 at 25°C, sealing the vessel and r a i s i n g the temperature 2  to between 100-175°C.  The pressure inside the vessel ranged from 1257.3-  4137kPa (180-600 p s i ) .  After eight hours the vessel was cooled to room  temperature and the contents analysed by f r a c t i o n a l d i s t i l l a t i o n and crystallization.  The DEA loss ranged from 0% at 100°C and 1257.3 kPa  (180 psi) to 97% at 175°C and 4137 kPa (600 p s i ) .  They  discovered  N,N-bis(2-hydroxyethy1)piperazine, or BHEP, i n the degraded solutions and  suggested the following reaction for i t s formation. 0  H0-C,Hu  II  \  N-H + C0 —*• H0-C H 2  H0-C H 2  /  2  2  2  u  DEA  4  /  - N I CH  C  \  0  I CH  2  [2.17]  + H0 2  2  HEOD  0  II 2  /  HO-C.Hi, - N  I  CH  HEOD  2  C  v  \  0 — • H0-C,H„ - N  I  CH  2  /  \  CH, - CH.  CH  BHEP  2  - CH  \  /  N-C,H„-0H  2  + 2C0  2  [2.18]  HEOD or 3-(2-hydroxyethyl)-2-oxazolidone was regarded as an intermediate and somewhat unstable compound.  The authors also noted the presence  of other degradation products but did not characterize them owing to the lack of suitable a n a l y t i c a l techniques. Equations 2.17  and 2.18  indicate that C0  i . e . , i t i s neither consumed nor formed.  2  acts l i k e a catalyst,  If the reaction scheme i s  correct, then DEA degradation i s governed by a f i r s t order k i n e t i c equation provided C0  2  i s present in excess.  Since DEA and C0  2  are primarily  present as ions in aqueous solutions, i t i s unlikely that the above reactions are r e a l i s t i c . 35 Using more sophisticated a n a l y t i c a l techniques, Hakka et a l . were also able to detect  N,N,N'-tris(2-hydroxyethyl)ethylenediamine,  or THEED in degraded DEA  solutions.  However, they did not propose a  reaction mechanism for i t s formation.  According to Hakka et a l . , THEED  occurred frequently in gas treating solutions and was one of the major degradation compounds. 2 3 36 These authors and others ' '  found that both BHEP and THEED have  acid gas removal properties v i r t u a l l y  i d e n t i c a l to those of DEA.  How-  ever, under gas treating conditions, only one of the nitrogen atoms in the BHEP or THEED molecule i s l i k e l y to combine with the acid gas.  Hence,  on a weight basis, the capacity of the treating solution f a l l s with increasing DEA  degradation. 12  Smith and Younger  41  and others  have discussed DEA  and mentioned several other degradation compounds.  degradation  One of these com-  pounds was found to have the same retention time as triethanolamine, or TEA,  i n the gas chromatographic  analysis.  In many cases the DEA treating solution contains small amounts  of monoethanolamine, or MEA.  This compound can also d e g r a d e  3 8 , 3 9  '^  0  forming oxazolidone (OZD), l-(2-hydroxyethyl)imidazolidone (HEI), N,N'-bis(hydroxyethyl) urea (BHEU),  and N-(hydroxyethyl)ethylenediamine  (HEED). 36 In a recent study by Blanc et a l . C0  2  and i n another experiment  with HEOD.  in a sealed autoclave at temperatures  the authors reacted DEA with Both experiments were conducted  of 90-130°C.  They proposed various  reaction mechanisms for the production of HEOD, THEED, and BHEP and other degradation compounds.  However, they provided no quantitative data in  support of these mechanisms. 41 42 Choy  '  performed  a se_ries of controlled experiments  and found  that DEA degradation appears to be f i r s t order between 165-185°C and at C0  2  pressures ranging from 1207-4137 kPa (175-600 p s i ) .  Degradation  rates were, however, affected by i n i t i a l DEA concentration, which cannot be explained in terms of a simple f i r s t order mechanism.  Furthermore,  several degradation compounds were detected, and although their chemical structure was not determined,  their concentration changes with time sug-  gested a series of simultaneous and consecutive degradation reactions. 43-45 Recent work by Kennard and Meisen  have confirmed that DEA degradation  is not a simple f i r s t order reaction. There i s another type of degradation compound which are called heat stable s a l t s .  These salts occur when a stronger acid than H S  or C0 reacts with the amine forming an unregenerable 2  2  s a l t , i . e . , DEA  i s not e a s i l y recovered by the action of increasing the temperature the bond i s too stable.  since  These stronger acids were described i n the 46 47 36 early work by Henry and Grennert. ' Blanc et a l . later i d e n t i f i e d them as formic, acetic, propionic, and oxalic acids. The production of  these acids has been attributed to the presence of oxygen although the mechanism for production i s not c l e a r l y understood.  Since the present  study i s concerned with the reaction between DEA and C0 , heat stable 2  salts w i l l not be considered further. 7 34 Degradation compounds of high molecular weight have been proposed ' but not i d e n t i f i e d .  These compounds may be linear polycarbamides  con-  taining polyalkylene amine structures. Other studies have been mainly concerned with the effect of degradation products on corrosion. ^ '  '  '  DEA  i t s e l f i s not considered  corrosive, but degraded DEA solutions can attack mild s t e e l .  It has  36 been suggested,  however, that since the pH of 30 wt % to DEA  the range of 11.5-10 at temperatures mild steel becomes impossible.  i s in  of 20-100°C then the corrosion of  Further, i t has been shown that the 2  major degradation compounds BHEP and THEED are r e l a t i v e l y noncorrosive. ' 3 34 35 36 '  '  '  The corrosion may,  therefore, be caused by other trace  impurities such as cyanides, chlorides, or the organic acids. 2.3  Analysis of DEA and i t s degradation products A quantitative study on DEA degradation i s dependent on a r e l i a b l e  a n a l y t i c a l procedure for measuring the degradation compounds.  The anal-  y s i s of DEA and i t s degradation compounds has proven to be rather d i f f i cult because the degradation products tend to: a)  have f a i r l y low vapour pressures;  b)  decompose at elevated temperatures;  c)  be highly polar;  d)  occur i n low concentrations.  and  There i s another problem which arises from the fact that degraded tions are a complex mixture of ionized species i n equilibrium.  soluThe  14 process of analysis may  have the effect of s h i f t i n g the equilibrium and  i t therefore becomes impossible to isolate and measure each component in the form in which i t exists in the degraded solution.  For example,  i t i s impossible to isolate the carbamate R NCOOH since i t readily decom2  poses to C0  and  2  DEA. 46 44  Henry  and Grennert  '  were amongst the f i r s t researchers interested  in the detection and measurement of DEA  salts in refinery samples.  investigated four types of acidic materials:  They  a) organic acids, b) chlor-  ides, c) cyanides and thiocyanates, and d) sulphites, sulphates, and thiosulphates. analysis.  They used mainly potentiometric t i t r a t i o n for the  DEA  They also discussed conventional wet chemical methods such  as t i t r a t i o n and kjeldahl total nitrogen determination, as well as other methods for the determination of total sulphur, sulphide,  mercaptide,  sulphate, thiocyanate, cyanide, chloride, carbonate, a l k a l i n i t y , and sodium.  This study was however limited because i t f a i l e d to detect  organic degradation compounds. lished by Dow  The "Gas Conditioning Fact Book," pub-  Chemical Company^ provides a description of conventional  wet chemical methods for testing DEA  samples.  However, these methods  are again unsuitable for i d e n t i f y i n g DEA degradation compounds. A comprehensive study on the analysis of DEA gas treating solutions 37 was produced by Gough.  Here an attempt was made to describe anal-  y t i c a l schemes that would lead to a useful interpretation of q u a l i t y . Two  schemes were described:  a) a comprehensive scheme for component  analysis, used when detailed information on composition  i s required;  b) a simple scheme for quality evaluation, useful on a routine basis and providing information required for routine plant operation. Unfortunately this study was  also not suitable for observing and  identifying  15 the individual degradation compounds. 48 Brydia and Persmger analysing ethanolamines.  described a chromatographic technique for Because direct chromatographic procedures  were not e n t i r e l y successful (excessive peak t a i l i n g due to strong hydrogen bonding), d e r i v a t i z a t i o n p r i o r to chromatographic separation was investigated.  T r i f l u o r o a c e t y l anhydride was used to convert non v o l a t i l e  amines into v o l a t i l e amine t r i f l u o r o a c e t y l derivatives.  The authors  experienced problems with r e p r o d u c i b i l i t y , precision, and the presence  49 of water.  Piekos et a l .  . . eliminated these shortcomings by converting  the alkanolamines to t r i m e t h y l s i l y l derivatives.  N,0-bis(trimethylsilyl)  acetamide was used which reacts with both the amino and hydroxyl groups of the alkanolamines.  The process i s called s i l y l a t i o n and produces  f a i r l y stable compounds which are more easily separated and i d e n t i f i e d by gas chromatography.  The addition of a t r i m e t h y l s i l y l group also  decreases the p o l a r i t y of the alkanolamine and reduces hydrogen bonding. S i l y l a t e d compounds are more v o l a t i l e and more stable due to the reduction of reactive s i t e s .  Successful separation of MEA,  DEA, and TEA derivatives  was conducted and the presence of up to 5% of.water could be tolerated, provided there was a large excess of s i l y l a t i n g agent. A recent paper by Saha et al.^° investigated problems a r i s i n g from converting the amines to stable derivatives prior to analysis by gas chromatography.  For example, derivative preparation i s time consuming,  the derivative reactions may be incomplete and the derivatives may not be stable for long periods.  Consequently the use of organic polymer  beads as the column packing for G.C. analysis of alkanolamines was tigated.  The authors found that Tenax  inves-  G.C.,"^ which i s a porous poly-  mer based on 2,6-diphenyl-paraphenylene oxide, was able to separate  alkanolamines with excellent r e s u l t s . an aqueous mixture of MEA, a 1/8"  O.D,  DEA,  The authors were able to separate  and TEA i n less than eight minutes using  4' long stainless steel column.  No sample preparation  was  required and the column was unaffected by the presence of water. Probably the only study dealing s p e c i f i c a l l y with the analysis of 52 DEA  and i t s degradation products was  that performed by Choy and Meisen.  Their technique consisted of f i r s t drying the degraded DEA  sample by  a i r s t r i p p i n g , d i s s o l v i n g i t in dimethyl formamide and s i l y l a t i n g i t with N,0-bis(trimethylsilyl)acetamide. then separated with 8% 0V17 tion.  using a 1/8"  O.D,  The s i l y l a t e d compounds were  6' long stainless steel column packed  on 80/100 mesh chromosorb followed by flame i o n i z a t i o n detec-  Although the method was  r e l i a b l e and accurate,  suming and unsuitable for plant use.  i t was  time con-  In p a r t i c u l a r , the s i l y l a t i o n  stage required considerable care p a r t i c u l a r l y with regard to the removal of water. Other methods for the analysis of amines and amine related compounds 53 54 have been reported.  These studies include paper chromatography,  s a l t i n g out chromatography,and  thin layer chromatography ."^  ' All  these methods suffered from excessive t a i l i n g and lack of r e p r o d u c i b i l i t y . Also none of these methods have been applied to DEA  degradation compounds.  CHAPTER 3  DEVELOPMENT OF THE ANALYTICAL TECHNIQUE . Before a study of DEA degradation could be undertaken a r e l i a b l e , quantitative method of analysis of DEA and i t s degradation products had to be developed.  The method should be rapid, highly sensitive, and  require minimal sample size and preparation.  Furthermore  i t i s desirable  for the method to be applicable f o r i n d u s t r i a l as well as laboratory use. Many methods have been investigated for the analysis of DEA and i t s degradation products such as wet chemistry, i n f r a red and u l t r a v i o l e t spectroscopy, paper and thin layer chromatography.  However,  they a l l tend to have drawbacks such as being generally inaccurate, nons p e c i f i c , unreliable, and expensive.  In addition, these methods tend  41 to be slow and inconvenient.  Choy  stated that gas chromatography  was probably the most promising a n a l y t i c a l technique.  As mentioned  before, one of the problems of analysing DEA and i t s products i s their low vapour pressure. temperatures.  This requires the use of high i n j e c t i o n and column  However poor thermal s t a b i l i t y of DEA leads to problems  with the r e p r o d u c i b i l i t y of measurements.  Also, the polar hydroxyl  and amino groups have a strong a f f i n i t y f o r most column packings.  This  results i n long elution times, large peak broadening, and peak assymetry. The presence of water i n the sample also creates problems since only a few column packings can tolerate aqueous samples.  18 3.1  Gas chromatographic  technique  52 Choy's method  using derivative gas chromatography although r e l i a b l e ,  was f e l t to be too time consuming and unsuitable for plant use.  This was  due to the complicated sample preparation since the s i l y l a t i o n reactions were extremely sensitive to water.  Furthermore, there i s the problem  of incomplete s i l y l a t i o n of a l l compounds.  S i l y l a t i o n of the hydrogen 54  bound to the nitrogen atom of alkanolamines i s known to be d i f f i c u l t . An attempt was therefore made to find a simpler and more direct technique for analysing DEA and i t s degradation compounds.  A thorough  review of the l i t e r a t u r e yielded an a r t i c l e by Saha et a l . ^ who Tenax G.C.  to separate alkanolamines.  Tenax G.C.  i s a porous  used  polymer  based on 2,6-diphenyl-paraphenylene oxide which has a weakly interacting surface and can be used at temperatures up to 450°C.  According to the  manufacturers, columns may be operated for several weeks at temperatures up to 400°C without s i g n i f i c a n t baseline d r i f t and decomposition of the packing.  Since the organic polymer beads are solids, mass transfer  is rapid and fast elution and sharp peaks are obtainable. Using a temperature programmable gas chromatograph (Hewlett Packard Model 5830A), a 1/8" O.D, Tenax G.C.  6' long stainless steel column packed with  (purchased from A l l t e c h  and found to be successful.  Associates, I l l i n o i s ) was  tested  Two other packings, which could tolerate  aqueous samples, were also tested;  these being 4% Carbowax 20m on 60/80  58 mesh Carbopack B  (purchased from Supelco Inc., Penna.) and 28% Pennwalt 59  223 + 4% kOH on 80/100 mesh Gas-chrom R Lab. Inc., Penna.).  (purchased from Applied Science  Both columns were found to be unsuitable due to  either low s e n s i t i v i t y on excessive peak t a i l i n g .  19 3.1.1  Evaluation of the Tenax G.C.  column.  I n i t i a l tests were  performed with solutions made by mixing d i s t i l l e d water with reagent grade MEA,  DEA,  and TEA.  Using a flame ionization detector, nitrogen  as the c a r r i e r gas and temperature was obtained.  programming, excellent separation  From the l i t e r a t u r e review i t was apparent that the main  degradation compounds are HEOD, THEED, and BHEP. BHEP could be obtained commercially.  Unfortunately only  Therefore standards for HEOD and  THEED were prepared in the laboratory and their synthesis i s described in chapter 4. column.  A l l three compounds were easily separated with the Tenax  A paper by Alltech Associates I n c . ^ indicated that stainless  steel causes ethanolamine  to undergo c a t a l y t i c degradation.  However,  no evidence of degradation within the column was observed for any of the compounds tested. at high temperatures  Although the inlet port and column were operated (up to 300°C), there was no observable thermal decom-  position of the tested compounds.  This was confirmed by the sharp, sym-  metric, and highly reproducible peaks. 3 ."1.2  Operating conditions.  After several i n i t i a l t r i a l s , optimum  conditions were found for the separation of DEA and i t s degradation products.  Table 3.1 summarizes the f a c i l i t i e s and operating conditions  used for the separation. Temperature programming was used in order to achieve a good separation of a l l degradation compounds, since these compounds varied considerably in molecular weight and p o l a r i t y . was adopted  The maximum temperature  to ensure that a l l compounds were v o l a t i l i z e d .  even at this temperature  of 300°C However,  i t i s possible that some of the very heavy  tion compounds, such as the polylinear carbamides did not elute.  degrada-  Usually  a luL sample in conjunction with an attentuation value of 13-14, was  found  Table 3.1  A n a l y t i c a l equipment and operating conditions for G.C. analysis  Gas Chromatograph Manufacturer  Hewlett Packard  Model  5830A  Detector  H  2  flame ionization  Chromatographic Column Material  Stainless steel  Dimensions  1/8" O.D, 6' long  Packing  Tenax G.C., 60/80 mesh  Operating Conditions Carrier gas  N  Injection port temp.  300°C  Detector port temp.  300°C  Column temp.  Isothermal at 150°C for 0.5 min.,  2  at 25 ml/min  then temperature raised at 8°C/ min to 300°C Syringe Manufacturer  Hamilton Co.  Model  701, lOpL, with fixed needle and Chaney adapter  Injected sample size  luL  21 to be suitable for the detection and separation of a l l compounds. ever, i n some cases the sample size was trace quantities of degradation 3.2  How-  increased to 2uL or more to detect-  compounds.  A n a l y t i c a l procedure and performance Typically l.OpL samples of the degraded DEA  solution were injected  d i r e c t l y into the column with a precision syringe f i t t e d with a Chaney adapter.  The adapter was used to ensure that a constant volume of sample  was  injected into the column.  was  used at the injection port.  To improve the accuracy, a needle guide This guide not only protects the f r a g i l e  syringe needle, but serves as a spacer for needle penetration and the septum l i f e by using a single hole for repeated  injections.  lengthens Needle  guides were found to be indispensible for high precision work. The analysis was  usually performed for a period of 30 minutes in  order to ensure the elution of heavy compounds.  After each run the  column had to be cooled from 300°C to 150°C which took about 5 minutes. Therefore, a complete analysis required a total of about 35 minutes. DEA  and known degradation products could be detected accurately  down to concentrations of about 0.5 wt %. lent ( t y p i c a l l y within ± 5.0% with a new  The r e p r o d u c i b i l i t y was excelcolumn) and peak t a i l i n g  baseline d r i f t did not represent special d i f f i c u l t i e s . and 3.2  Figures  show examples of the separation achieved with the Tenax  and 3.1 G.C.  column. 3.2.1  Column performance.  The column i t s e l f required no special  care and was conditioned simply by passing nitrogen through i t at i t s maximum operating temperature (300°C) for 8-10 a f a i r l y long l i f e ; nearly a year.  hours.  for example, one column was  The column has  i n continual use for  However, when a column f a i l s , i t f a i l s r a p i d l y and  22  TEA MEA  DEA  Figure 3.1  Figure 3.2  Typical chromatogram for MEA, DEA, and TEA  Typical chromatogram of a degraded DEA solution  23 becomes incapable of separating the heavy compounds.  It i s l i k e l y that  the column becomes clogged with the polylinear carbamide compounds, which • probably never leave the column.  Thus the more degraded the sample  the shorter the column l i f e . In some cases a 9' column was  used instead of the standard 6' column.  This improved the separation of degraded compounds, especially ation of BHEP and HEOD.  the separ-  Also i t allowed a direct comparison to be made 36  between the results of this study and those of Blanc et a l . a 9' Tenax G.C.  column.  who  used  However, the longer column increased the elution  times, and most analyses were therefore performed using the 6' column. 3.3 G.C. c a l i b r a t i o n Calibration plots of concentration versus peak area were produced simply by i n j e c t i n g known concentrations of the various degradation compounds into the chromatograph and noting the peak area which was matically calculated by the chromatograph's computer.  auto-  At least f i v e  injections were made for each concentration and the peak area averaged. Figures 3.3 to 3.6  show the c a l i b r a t i o n for DEA,  HEOD, BHEP, and THEED.  This form of c a l i b r a t i o n did not use an internal standard and is termed 'direct c a l i b r a t i o n ' . 3.4  Maintenance of chromatographic equipment Generally very l i t t l e maintenance i s required.  chromatograph and syringes must be kept clean.  Basically  the  In some cases deposits  tend to b u i l d up in the i n j e c t i o n port and have to be removed.  Further-  more, deposits accumulate on the detector jets and can result i n excessive spiking (or noise) on the chromatogram.  The cleaning of the flame ioniza-  tion detector i s d i f f i c u l t and the removal of the probes i s not recommended unless absolutely necessary.  An easier method i s to inject, 10-30uL  F i g u r e 3.4  C a l i b r a t i o n p l o t f o r HEOD  BHEP P E A K A R E A Figure 3.5  Calibration plot for BHEP  Figure 3.6  Calibration plot for THEED  28 of Freon 113 flame ionization detector cleaner (purchased from Supelco, Inc.) with equipment operating under normal conditions.  Freon elutes  from the column and produces hydrogen fluoride as the cleaning agent when burnt i n the hydrogen flame. Since the column does eventually wear out i t i s considered good practice to check the c a l i b r a t i o n at least once a month with standard samples.  If there i s considerable disagreement  between the c a l i b r a t i o n  curve and the analysis of the standard samples, then the column should be replaced. Septa should be replaced at least every 50 injections since they tend to accumulate deposits and eventually begin to leak. No other routine maintenance i s required except keeping the machine clean and free of dust. boards may  The g r i l l  to the fan which cools the c i r c u i t  get clogged with dust and r e s t r i c t the flow of cooling a i r  causing overheating of the c i r c u i t boards. periodically.  Thus the g r i l l must be  checked  The printer i s generally trouble free requiring only  cleaning of the slide rod for the printer head and keeping i t free of o i l and grease. 3.5  Advantages of the a n a l y t i c a l technique The advantages of the present a n a l y t i c a l technique can be summarized  as follows. 1.  No sample preparation required.  2.  Water has no effect on the column.  3.  Very simple.  4.  Long column l i f e .  5.  Small sample required.  6.  Reliable and reproducible.  7.  Speed, i . e . , analysis i s completed in less than 35 minutes.  8.  S u i t a b i l i t y for plant use.  3.6  Errors The major source of error arises  during sample i n j e c t i o n .  Since  d i r e c t c a l i b r a t i o n was used to determine the concentration, then each sample i n j e c t i o n had to be as i d e n t i c a l as possible. ing  For example, increas  the injection time usually resulted in s l i g h t l y larger peak areas,  since a small volume of l i q u i d , otherwise held in the needle, i s p a r t i a l l y vapourized and enters the column.  Another problem with direct c a l i b r a t i o n  is the s e n s i t i v i t y of the detector i s assumed to remain constant from day to day.  This assumption i s only v a l i d provided the detector i s  kept clean.  Another source of error i s changes in the flow of c a r r i e r  gas.  As the column becomes clogged, the flow tends to f a l l unless  adjusted.  Therefore, i t i s best to check the flow of c a r r i e r gas d a i l y .  The only other noticeable error i s concerned with the calculation of  the peak areas which the chromatograph performs automatically.  long as the peaks are sharp and symmetrical l i n e d r i f t , there i s usually no problem. or bunch, the automatic  As  and there i s l i t t l e base If the peaks tend to t a i l  integrator may make small errors in deciding  where to begin and end integration.  In general, this form of error  is minor compared to that produced by sample i n j e c t i o n . 3.6.1  Accuracy.  The accuracy of the technique can be simply c a l -  culated using the r e l a t i v e standard deviation o . D  30 where  N = number of measurements x = measured value x = arithmetic mean a = standard deviation  For example, f o r the analysis of a sample of DEA the following six concentrations were recorded for a sample of aqueous DEA of known concentra-  -3 tion 3.5 x 10  moles/cc.:-  3.54 x 10~ , 3.45 x 10" , 3.52 3  3  3.43 x i o "  x  10~ , 3.51 3  x  10~ , 3.55 x 1 0 , 3  _ 3  3  x = 3.5 x 10~  3  o = 2.19 x 10~  o  5  R  = 6.3 x i o "  3  Similarly the following f i v e concentrations were recorded for a sample -3 of aqueous DEA of known concentration 0.95 x 10 9.25 x i o " , 9.75 x i o " , 1.01 4  4  x = 9.652 x 10~ o = 1.745 x 10~  5  x  10~ , 9.81 3  x  moles/cc.:-  10~ , 9.35 4  x  10  _ 4  4  o  R  = 1.81 x 10~  2  There i s of course one f i n a l source of error and that occurs when reading the c a l i b r a t i o n curves.  Therefore considering a l l the error  sources and the r e l a t i v e standard deviation, the accuracy of the a n a l y t i c a l technique has been found to be ± 5%. 3.7  Units of DEA concentration DEA concentration i s , throughout  of wt % or moles/cc.  this study, expressed i n units  I t should be noted that since the molecular weight  of DEA i s 105, the concentration expressed as moles/cc can roughly be _2  converted to wt % by multiplying by 10 ; e.g., 1.5 * 10 roughly equivalent to 15 wt %.  moles/cc i s  CHAPTER 4 SYNTHESIS OF SELECT DEGRADATION COMPOUNDS FOR CALIBRATION OF THE GAS CHROMATOGRAPH  In order to study DEA degradation quantitatively i t i s necessary to measure the concentration of DEA and i t s major degradation products in solution.  In order to calibrate the chromatograph, standards of  the various degradation compounds had to be obtained.  From previous  studies the major degradation compounds were thought to be HEOD, THEED, and BHEP.  Unfortunately, only BHEP was available commercially.  HEOD  could only be obtained from ICN Pharmaceuticals, Inc. but i t s purity was found to be too low for c a l i b r a t i o n .  It i s l i k e l y that HEOD reverts  slowly to DEA and this i s discussed further in chapter 11. unavailable from any commercial source.  THEED was  It was, therefore, decided  to synthesize both HEOD and THEED i n the laboratory. 4.1  Synthesis of HEOD A thorough search of the l i t e r a t u r e , back to 1920, revealed only  the following methods for synthesizing 2-oxazolidones: a)  From alkanolamines and phosgene.^  The alkanolamine  i s reacted  with phosgene in chloroform i n the presence of lead carbonate which neutralizes the hydrochloric acid produced  31  i n the reaction.  0  II RNH - C.Hi, - OH + COCL,  • R-N  0 + 2HCL  I  CH  CH  2  b)  [4.1]  I  2  From alkanolamines and d i a l k y l carbonate.  62 63 ' 0  II  R'O  C \  RNH - C H 2  4  - OH +  NaOH C = 0  /  \  • R-N -2R'0H * | CH  / R'O  0 | CH  2  [4.2]  2  NaOH acts as a basic catalyst. 64 c)  From 8 halogenalkyl carbamate.  The carbamate i s boiled i n an  aqueous KOH solution. 0  II  0  C  II  RNH - C - 0 - C-H^-CL  KOH •  /  \  R-N  0 + KCL + H,0  I  I  CH  CH  2  d)  [4.3]  2  From ethylene oxide (EO) and a hydroxyl alkyl  isocyanateThe  oxide i s heated with the isocyanate i n the presence of potassium  iodide  or lithium chloride, which act as c a t a l y s t s .  0  / CH  2  C  \  /  - CH  2  + R-N=C=0  • R-N  0  I  CH  2  e)  \ [4.4]  I  CH  2  From ethylene oxide (EO) and 2-oxazolidone  (OZD).^^  Equal amounts  of ethylene oxide and oxazolidone are heated i n the presence of a trace amount of water.  33  0 0  / \  CH  2  - CH  2  C  /  + H-N  1  CH  0  \  /  0 —«- H0-C H^ - N 2  1  CH  2  CH  2  C  \ I  2  0  [A.5]  I  CH  2  With the exception of (e) the methods were non-specific for the production of HEOD.  Furthermore  complete details of the reaction condi-  tions were not stated. Methods (b) and (e) were attempted with p a r t i a l success. method (b) the following synthesis was performed.  Using  Equal amounts of  ethyl carbonate and diethanolamine were mixed and 15g charged to a 25ml. pressure reactor together with about 5g of IN sodium hydroxide.  The  reactor was sealed and pressured to about 689.5 kPa (100 psi) with n i t r o gen.  The reactor was then placed in a water bath and heated to about  50°C for one hour. ing.  The results of this experiment were rather disappoint-  HEOD was produced only in low amounts since there were many side  reactions taking place.  It was f e l t that p u r i f i c a t i o n would prove  diffi-  cult as well as time consuming and therefore method (e) was t r i e d . Equal amounts of ethylene oxide and oxazolidone were mixed and 15g charged to the 25 ml. pressure reactor before adding about l g of water.  The reactor was sealed and pressurized to about 689.5 kPa (100  psi) with nitrogen.  The reactor was placed i n a water bath and heated  to 70°C for about eight hours.  HEOD conversions of about 70% were achieved  with MEA and DEA being the main impurities. tion proved once again to be very d i f f i c u l t . such as d i s t i l l a t i o n ; and pyridine;  However, further p u r i f i c a Several methods were t r i e d  solvent extraction with chloroform, a c e t o n i t r i l e  and gel chromatography.  None of these approaches were  34 very successful.  Since HEOD was required i n a purity of at least 95%,  for c a l i b r a t i o n of the chromatograph, i t was decided to e n l i s t the help of a small firm s p e c i a l i z i n g i n custom synthesis of rare chemicals (Synthecan Lab., Inc., Vancouver).  A pure 50g sample was purchased and  used for the c a l i b r a t i o n . 4.2  THEED synthesis Information  with regards  to synthesis of THEED proved very  diffi-  cult to find and a thorough l i t e r a t u r e survey revealed only one relevant reference.^  Three different methods were t r i e d for the synthesis of  THEED and are summarized below. a)  From ethylenediamine  (ED) and chloroethanol.  The reaction was  expected to produce the following compounds:H N-C H^-NH 2  2  2  + HOC H^CL  •  2  H0C H -NH-C Hu-NH 2  u  2  (HEED)  2  + (HOC Hu) -N-C Hu-NH 2  2  2  (BHEED)  2  + (HOC Hu) -N-C Hu-NH-C HuOH 2  2  2  + (HOC H ) -N-C Hu2  4  2  2  N-(C HuOH) 2  + HCL  the mixture to about 100°C.  2  (TEHEED) [4.6]  The reaction was i n i t i a l l y performed by mixing chloroethanol, i n the molar r a t i o  (THEED)  2  ethylenediamine  with  of 1:3, i n a glass beaker and heating  Unfortunately  the reaction was found to  be highly exothermic and a very viscous yellow substance was produced. Analysis showed that no THEED was produced.  A similar experiment con-  ducted at 50°C resulted i n no reaction taking place. A more controlled experiment was performed where 15 cc. of the reaction mixture was placed i n the 25 ml. pressure reactor and the reactor pressurized to about 689.5 kPa (100 psi) with nitrogen.  The reactor  35 was then heated to 90°C in a water bath for about 1 hr.  The reaction  produced numerous compounds one of which may have been THEED.  Purifica-  tion would have been too d i f f i c u l t and therefore other methods were t r i e d . b)  From ethylenediamine  and ethylene oxide.  less exothermic and easier to control.  This reaction was f a r  The expected products were similar  to those stated in Eq. 4.6. 15g of a mixture containing 3 moles of ethylene oxide to one mole of ethylenediamine  were charged to the 25 ml. pressure reactor.  About  68 lg of water was added as a catalyst.  The reactor was sealed and pres-  sured to 689.5 kPa (100 psi) with nitrogen and heated to about 50°C in a water bath for one hour. Fig.  4.1).  Five d i s t i n c t compounds were produced (see  Two of the peaks corresponded to the two isomers of BHEED,  namely (H0C U ) -N-C H^-NH., and (HOC Hu)-NH-C H -NH-(C H OH). 2  k  2  2  2  2  l4  2  1<  The  substituted ethylene diamines were produced in the following amounts: HEED 17.7%, BHEED 32.4%, THEED 35.8%, and TEHEED 14.1%.  Since a l l these  compounds had similar c h a r a c t e r i s t i c s i t was f e l t once again that p u r i f i cation would present problems especially since THEED was present in only 36% purity. c)  Thus a t h i r d method was t r i e d .  From diethanolamine and N-(2-hydroxyethyl)ethylenimine (HEM).  The  following reaction was expected to occur:CH, (H0C H.J NH + H0-C H«, • =N 2  2  2  |  • (HOC H« ),-N-C Hi,-NH-C Hi OH 2  t  a  2  t  [4.7]  CH  2  Approximately 200 cc. of an equimolar solution of DEA and HEM was charged to a 600 ml. s t i r r e d autoclave (details of the autoclave are given i n chapter 6).  The 600 ml. autoclave was used so the reaction  could be followed more closely by removing samples while the reaction  36  Figure 4.1  Chromatogram of substituted ethylenediamines  was s t i l l being carried out. to the reaction mixture.  About 5g of aluminium chloride were added  The autoclave was sealed and pressurized to  689.5 kPa (100 psi) with nitrogen and heated to 120°C for about eight hours. DEA.  THEED was produced at about 78% purity, the major impurity being However, even this concentration was not s u f f i c i e n t l y high f o r  c a l i b r a t i n g the gas chromatograph.  After trying several methods of  p u r i f i c a t i o n i t was found that gel chromatography was most suitable and i t was possible to produce THEED of 95% purity.  A 2 cm. diameter, 40  cm. long glass column was used f o r the gel chromatography. was packed with 60-200 mesh s i l i c a g e l .  Since THEED and DEA are both  soluble in water, water was used as the solvent. hydroxide was found to aid separation.  The column  A trace of ammonium  lOcc. samples of impure THEED  were charged to the column and an elution rate of about l c c . per 10 minutes was established.  Fractions were collected and analysed for THEED content.  When s u f f i c i e n t THEED had been collected the samples were concentrated by b o i l i n g off the water thereby leaving a viscous colourless l i q u i d of THEED.  CHAPTER 5 IDENTIFICATION OF DEGRADATION COMPOUNDS 5.1  I d e n t i f i c a t i o n using the gas chromatograph Before proceeding to the study of degradation reactions the compounds  responsible for the peaks on chromatograms had to be i d e n t i f i e d .  For  a typical run ( i . e . , run number 3, where 30 wt % DEA was degraded f o r eight hours under A137 kPa (600 psi) C0  2  at 205°C) over 20 peaks were  observed.  To identify these peaks where possible the following method  was used.  I f a compound was suspected of being produced  (based on i n f o r -  mation from the l i t e r a t u r e or otherwise), then i t was either purchased or synthesized in the laboratory (see chapter A).  A known concentration  of the compound was injected into the chromatograph and i t s retention time noted.  This retention time could then be compared with the elution  times of the degraded  sample of DEA.  If a degradation compound produced  a peak with the same retention time as that of the standard compound i t could be inferred that the degradation compound and standard compound were the same.  However, this method does not give a completely r e l i a b l e  i d e n t i f i c a t i o n of a compound since there can be more than one compound with the same retention time.  For example, a peak occurred after about  12 minutes which i s also the retention time for TEA.  It i s u n l i k e l y ,  however, that TEA i s a degradation product and i t i s probable that the peak i s caused by another compound.  TEA does exist as an impurity of  38  39 1-2 wt % i n the DEA solution.  However, the peak area i s usually much  greater than that produced by TEA i n the concentration range of 1-2 wt %. Thus further information i s required for the positive i d e n t i f i c a t i o n of a degradation compound.  It was found that using a gas chromatograph  and a mass spectrometer (GC/MS) was best suited for this task. 5.2  I d e n t i f i c a t i o n using a GC/MS The mass spectrometer simply vapourizes a compound and produces  ions from the neutral molecules by bombarding the vapour with electrons. The ions are formed into a beam and accelerated through the f i e l d of a powerful electromagnet.  The ions are forced into a c i r c u l a r path and  become separated according to their mass to charge r a t i o .  The different  ions are detected by an electrometer which measures the charge collected on current carried by the ions.  Recording the changes in charge a spectro-  graph i s produced of ion current versus mass number.  Thus each peak  on the spectrograph corresponds to a d i f f e r e n t ion.  Since the molecule  fragments i n the same manner under similar conditions, the mass spectrograph provides a c h a r a c t e r i s t i c "thumbprint" f o r each compound.  The  use of a gas chromatograph with the mass spectrometer makes the GC/MS a very useful t o o l . Samples of the degraded DEA solution were injected into the GC which separated the compounds.  Then each compound flowed into the MS  and produced a mass spectrograph corresponding to each peak on the chromatograph. A Hewlett Packard GC/MS (Model 5985B) was used to produce mass spectrographs of a l l suspected compounds.  Only the mass spectrographs  of MEA, DEA, and TEA could be found i n the available r e g i s t r i e s of mass spectral data.  Therefore, standard mass spectrographs were made from  AO  pure samples of DEA degradation compounds.  These standard mass spectro-  graphs are given i n Appendix F. Samples of degraded DEA solutions could then be analysed using the GC/MS.  The resulting  spectrographs were compared with the standard  spectrographs enabling a positive For  i d e n t i f i c a t i o n of a degradation compound.  example i t was suspected the compound producing the peak marked  by the arrow i n Figure 5.1 was HEOD. The mass spectrographs for HEOD and the unknown compound are shown in Figs. 5.2 and 5.3.  As can be seen they are very similar.  The most  notable s i m i l a r i t y being the two peaks of masses 100 and 101, which are characteristic 5. 3  Identified  of HEOD.  Therefore HEOD could be p o s i t i v e l y  identified.  degradation compounds  Using the methods previously described i t was possible to identify 14 compounds i n degraded DEA solutions (e.g., F i g . 5.4 shows a typical chromatograph of a degraded DEA solution).  Many other compounds were  detected, but since their concentrations were extremely low their  identi-  f i c a t i o n was considered not worth pursuing. Table 5.1 i s a summary of the compounds detected with their retention times using the Tenax G.C. column and conditions described i n chapter 3.  Mass spectrographs for these compounds are found i n Appendix F.  Possible mechanisms for their production w i l l be discussed i n chapter 11.  Figure 5.1  Chromatogram showing peak of unknown compound  ice  i  ioo  so  41  131 1S4  4 0  I, 1 l.il  r  ieo  '  1  120  F i g u r e 5.2  Mass spectrum of HEOD  Figure 5.3  Mass spectrum of unknown compound  —1 140  • 1  DEA  Figure 5.4  Typic al chromatogram of a degraded DEA solution  Table 5.1  Compounds found i n degraded DEA solutions  Compound  Retention time min.*  MEA  1.4-1.5  HEM  3.1-3.5  HEED  6.8-7.2  DEA  7.4-8.0  HEP  9.8-10.2  OZD  10.4-10.6  TEA  12.0-12.5  BHEED  12.8-13.2  BHEP  13.0-13.6  HEOD  13.4-14.0  HE I  15.5-16.0  THEED  17.2-17.4  BHEI  18.2-18.5  TEHEED  20.4-20.6  *This w i l l vary s l i g h t l y according to the concentration of the compound present i n the sample and the age of the column.  CHAPTER 6 EXPERIMENTAL EQUIPMENT AND PROCEDURE FOR THE CONTROLLED DEGRADATION OF DEA  6.1  600 ml.autoclave Since DEA degradation i s rather complex, the experiments  be performed  under c a r e f u l l y controlled conditions.  i t was necessary to keep the temperature  had to  In p a r t i c u l a r ,  and pressure constant f o r the  f u l l duration of a run. The main component of the experimental equipment was a 600 ml. stainless steel autoclave supplied by the Parr Instrument (Model 4560).  The autoclave could be operated from room  up to 400°C at pressures ranging from atmospheric psi).  Company, 111. temperature  to 13.79 MPa (2000  The p r i n c i p l e features of the reactor (see F i g . 6.1) are summar-  ized below. 1.  Variable speed s t i r r e r , 0-600 r.p.m., driven by a drive assembly that could be e a s i l y disconnected and swung aside to allow f u l l access to the autoclave head f i t t i n g s .  2.  Valves f o r adding gas, removing gas, and withdrawing  l i q u i d samples  during runs. 3.  A 0-2000 p s i  4.  A safety rupture disc.  5.  A close f i t t i n g , quartz f a b r i c heating mantle i n an insulated aluminium housing.  pressure gauge, accurate to within ± 5 p s i .  The heater could be e a s i l y lowered from the autoclave 45  Figure 6-1  Sketch of 600 ml. autoclave  47 without disturbing the s t i r r e r or affecting any of the head  connec-  tions . 6.  A J-type thermocouple i n a stainless steel well placed within the autoclave for measuring the reaction temperature.  7.  An automatic temperature c o n t r o l l e r (Parr, Model 4831EB) whose output is monitored by a d i g i t a l thermometer (Doric, Series 400A, Model 410A) and recorded on a s t r i p chart recorder (Corning, Model 840). The controller was capable of holding the temperature to within ± 0.5°C of the desired value for an i n d e f i n i t e period (experiments l a s t i n g up to 30 days were performed).  8.  An internal cooling c o i l , which was useful for c o n t r o l l i n g exothermic reactions and for rapid cooling at the end of a run.  9.  The autoclave could be f i t t e d with a pyrex l i n e r so that experiments could be performed without the reactants coming into contact with the  6.2  metal surface of the autoclave.  Loading the autoclave It was desirable to inject the aqueous DEA solution into the auto-  clave, which had been raised to the desired operating temperature.  This  measure minimized the problem of accounting for the time required to heat the autoclave and feed at the beginning of a run.  A modified 500  ml. pressure sampling cylinder was used for the i n j e c t i o n (see F i g . 6,2). The cylinder was f i r s t .purged with C0 run  being conducted.  2  or N  2  depending on the type of  The purging was necessary to remove any oxygen  which could react with DEA forming heat stable s a l t s .  The cylinder  was then f i l l e d with about 250 ml. of aqueous DEA solution and pressurized with C0  2  or N  2  to the operating pressure.  The contents of the cylinder  were then discharged into the autoclave which was at operating  f - K H — /  A  DO—-  DEA C O 2 cylinder  Autoclave 500ml. cylinder  Figure 6.2  Sketch of the autoclave loading system  .0-  00  49 temperature.  A short amount of time (5-10 min.) was then required for  the temperature 6.3  and pressure to l e v e l o f f .  Sampling Sampling was done at the operating temperature  and pressure by  means of a 5 ml. c o i l e d sample tube f i t t e d with an i n l e t and outlet valve. The sample tube could be easily f i t t e d and removed from the l i q u i d sample port of the autoclave during a run. The following method was used for obtaining a sample from the reaction mixture.  The sample tube was f i r s t connected to the autoclave  sample port.  The autoclave sample valve was opened with the sample  tube i n l e t and outlet valves closed.  The sample tube i n l e t valve was  then opened and a l i q u i d sample was forced into the tube under the reactor pressure.  The outlet valve was then opened s l i g h t l y  l i t t l e sample.  to bleed off a  A l l the valves were then shut and the sample tube removed  and placed in water for rapid cooling.  The sample was then removed  from the tube and stored in a glass sample bottle under a blanket of nitrogen for later use. 6.4  Analysis of the l i q u i d samples The samples for the runs were stored in 7 ml. glass bottles with  screw tops.  1 p i . samples were then injected into the gas chromatograph  under the conditions described in chapter 3.  When the 30 minute anal-  y s i s was complete the peak areas and retention times of the major peaks of the chromatogram were recorded.  Using the c a l i b r a t i o n curves (see  Figs. 3.3-3.6) the concentrations of DEA and i t s major degradation products could be determined.  Using these data, curves of concentration  versus time could be plotted and studied.  50 6.5  Analysis of the gas phase The degradation of DEA by C0  2  did not result in the production  of measurable amounts of gaseous degradation products.  Aqueous samples  of degraded DEA, which had been removed from the autoclave at various times during a run, were analysed for carbon, hydrogen, oxygen, and nitroge The concentration of each element i n the l i q u i d phase did not change during the runs.  This indicates that no gaseous products were formed  in the DEA degradation. sidered 6.6  Therefore, analysis of the gas phase was con-  unnecessary.  Experimental  procedure  A typical controlled degradation run involves reacting an aqueous DEA solution with C 0 at a desired temperature 2  length of time. the run.  and pressure for a specific  Samples were removed at regular intervals  throughout  The subsequent procedure was followed.  1.  The autoclave was f i r s t sealed empty.  2.  The autoclave and modified sampling cylinder were then purged with C0  .  2  3.  The autoclave was heated to the desired operating  temperature.  4.  About 250 ml. of fresh aqueous DEA solution of known concentration was charged to the modified sampling cylinder.  5.  The aqueous DEA was injected under pressure into the autoclave. The s t i r r e r speed was set at about 150 r.p.m. and several minutes were allowed for the temperature  and pressure to settle down.  I n i t i a l l y the C0 was absorbed by the DEA and the autoclave pressure 2  had to be checked regularly over the f i r s t half hour of the run. C0  2  was added when necessary to keep the operating pressure constant.  Also, since the absorption of C0  2  i s an exothermic reaction, water  was passed through the cooling c o i l to maintain the operating temperature.  After about 30 min. the temperature  became steady and required no further attention.  and pressure (Usually much  less than half an hour was required, depending on operating temperature, pressure, and DEA concentration.) 6.  Samples were removed at regular intervals during the run using the sampling tube.  After the sample had been transferred to  the sampling bottle the sampling tube was thoroughly cleaned with d i s t i l l e d water and dried with a i r . 7.  When the run was completed,  the heating jacket of the autoclave  was switched off and removed.  Water was then passed  through  the cooling c o i l and the autoclave and contents rapidly cooled to room 8.  temperature.  When the autoclave was at room temperature  the pressure was reduced  to atmospheric and the autoclave opened.  Once the contents  had been removed the autoclave was thoroughly cleaned with d i s t i l l e d water. Most runs were conducted with 250 ml. of solution i n the 600 ml. autoclave.  This volume of solution was considered s u f f i c i e n t so that  the removal of several samples did not have a s i g n i f i c a n t effect on the reactant volume.  Also the reactant volume was not too large to l i m i t  the a v a i l a b i l i t y of C0 ^. 2  a l l the runs.  It was hoped that C0 would be i n excess for 2  A pressure of 600 p s i , used i n most runs, was chosen 34 41  partly to compare the results of this work with other studies partly because i t i s close to pressures used i n d u s t r i a l l y . of the experiment  '  and  The duration  depended simply on how long i t took for s i g n i f i c a n t  degradation to take place.  52 6.7  Maintenance and performance The main problem with the autoclave was gas leakage around the  s t i r r e r shaft.  There i s a short hose nipple, which can be used to monitor  the packing gland to detect any leakage as the packing elements and s t i r r e r shaft become worn. ally.  Repacking, therefore, had to be carried out periodic-  The frequency with which the gland was repacked depended on oper-  ating temperature and pressure, nature of the reactants, and the state of repair of the other various elements of the s t i r r e r assembly.  How-  ever, as a r u l e , the packing elements were usually replaced after 200 to 300 hours of service.  On several occasions the s t i r r e r shaft, i n  the v i c i n i t y of the packing, became worn and had to be replaced. than' leakage, the autoclave was r e l a t i v e l y trouble free. only other problem was cleaning. water was s u f f i c i e n t .  Other  Perhaps the  Usually flushing the equipment with  However, a slow build-up of a thick viscous residue  occurred and, p e r i o d i c a l l y , the whole equipment had to be dismantled and thoroughly cleaned using water. 6 .8  Sources of errors It i s possible that a sample may have a composition s l i g h t l y d i f f e r -  ent from the composition of the solution in the autoclave.  When a sample  is removed from the autoclave i t undergoes temperature and pressure changes which may cause the e q u i l i b r i a set up in the bulk l i q u i d to change. errors could also occur in recording .the time of sample removal.  Slight However  this error becomes i n s i g n i f i c a n t for runs of over eight hours. The temperature controller operates using a simple on/off control. This caused the temperature to o s c i l l a t e between ± 1°C at 205°C.  Again  this error i s minimal and, due to the regular o s c i l l a t i o n , i s averaged out.  53 Other small errors occur in the reading of the pressure gauge and loss of C0  2  through sampling and minor leaks.  CHAPTER 7  PRELIMINARY EXPERIMENTS AND DEVELOPMENT OF THE EXPERIMENTAL PROGRAMME 7.1  Use of high temperatures for the degradation runs Since the degradation reaction under plant operating conditions  is extremely slow i t was decided to conduct the majority of experiments in the temperature range of 175°-205°C. to achieve s i g n i f i c a n t degradation weeks.  In this range i t i s possible  in a matter of hours rather than  However, i t had to be established that the degradation products  produced at elevated temperatures were similar to those produced under plant conditions. ing  This was done by f i r s t comparing the results of degrad-  30 wt % DEA with 4137 kPa (600 psi) C0  2  at 205°C and 120°C (see runs  3 and 11, d e t a i l s of which can be found in Appendix B).  Secondly, degraded  samples of DEA produced in the laboratory were compared with samples obtained from i n d u s t r i a l DEA gas treating units. 7.1.1  Temperature comparisons.  Figure 7.1 shows the chromatogram  -3 of a degraded solution of DEA whose i n i t i a l concentration was 3 moles/cc (~30 wt %) and had been degraded with C0  2  x  10  at 205°C for one hour.  Figure 7.2 shows the chromatogram of a similar sample which was contacted with C0  2  at 120°C for 150 hr.  _3 In both cases the DEA had degraded from 3 * 10 2.1 x 10  _3  moles/cc to about  moles/cc, and three main degradation products were formed 54  HEOD  Figure 7.2  Chromatogram of a 30 wt % DEA solution degraded at 120°C under 4137 kPa C0 (time—150 hr.) 2  56 although i n d i f f e r e n t amounts. BHEP, and THEED.  These compounds were i d e n t i f i e d as HEOD,  The reason for the difference i n concentration of  these compounds w i l l be discussed i n chapter 11. 7.1.2  Comparison with i n d u s t r i a l samples.  Figures 7.3 and 7.4  show chromatograms of DEA treating solutions supplied by Aquitaine Canada Ltd. and Hudson's Bay O i l and Gas Company Ltd. and THEED are evident.  Peaks of HEOD, BHEP,  A fourth peak i s present i n the i n d u s t r i a l samples  which i s probably TEA, since i n d u s t r i a l DEA solutions contain s i g n i f i c a n t quantities of TEA compared with reagent grade DEA. From Figs. 7.1-7.4 i t i s seen that there are strong s i m i l a r i t i e s between the composition of DEA solutions degraded under laboratory conditions at high and low temperatures and those degraded under i n d u s t r i a l conditions.  It may, therefore, be concluded that DEA undergoes essen-  t i a l l y the same kind of reaction in each case. 7.1.3  Thermal degradation.  It i s known that DEA can undergo thermal  decomposition at i t s b o i l i n g p o i n t . T h e r e f o r e , i t had to be determined whether thermal degradation was s i g n i f i c a n t at 205°C.  A simple test  was conducted i n which a 30 wt % solution of DEA was heated to 205°C for 8 hr. under 4137 kPa (600 psi) of nitrogen (run 53).  No s i g n i f i c a n t  change i n the DEA concentration or the formation of degradation compounds were noted.  However, i n a similar test which lasted 200 hours (run  54), measurable quantities of BHEP and THEED were produced. the runs conducted at elevated temperatures  Since a l l  lasted only eight hours,  thermal degradation was not considered to be s i g n i f i c a n t . 7.1.4  J u s t i f i c a t i o n for the use of elevated temperatures.  Experi-  ments conducted at temperatures well above the operating temperature of an i n d u s t r i a l gas treating unit i s j u s t i f i e d for the following reasons.  Figure 7.3  Chromatogram of a degraded DEA solution from a gas sweetening unit operated by Aquitaine Canada Ltd.  Figure 7.A  Chromatogram of a degraded DEA solution from a gas sweetening unit operated by Hudson's Bay O i l and Gas Co. Ltd.  58 1.  Elevated temperatures accelerate the DEA degradation and make i t possible to complete tests i n hours rather than weeks.  2.  Degradation products formed at elevated temperatures are quite similar to those produced under plant conditions.  3.  Temperatures experienced by DEA in operating plants may, points, be much higher than expected.  at certain  For example, the surface  temperature of the heating tubes in the stripper reboiler can be considerably higher than the bulk DEA 4.  temperature.  Thermal degradation of DEA i s not a problem at temperatures up to 205°C.  7.2  Effect of metal surfaces It has been reported that the presence of metal ions may  degradation.^'^  affect  Therefore, to determine the influence of the stainless  steel surface of the autoclave, several runs were conducted using a pyrex l i n e r in the autoclave.  The results of these runs were compared with  those from i d e n t i c a l runs where the l i n e r was absent.  No s i g n i f i c a n t  change was noted and therefore subsequent runs did not use the pyrex liner. 7.3  Effect of s t i r r e r speed and reactant volume Various s t i r r e r speeds i n the range of 10-150 r.p.m. and reactant  volumes i n the range of 50-450 ml were used. was to determine i f the mass transfer of C0 the  2  The purpose of these runs from the atmosphere above  solution to the DEA was affected by s t i r r e r speed and/or volume of  available C0 . 2  ,No s i g n i f i c a n t effects were noted.  This was probably  due to the fact that the degradation reaction i s extremely slow i n comparison to C0  2  dissolving into the DEA solution (see chapter 2).  DEA solution i s saturated with C0  2  Hence the  before any s i g n i f i c a n t degradation  59 takes place and changes such as s t i r r e r speed, have l i t t l e 7.4  effect.  Reproducibility 7.4.1  Samples.  Degraded samples of DEA were, i n general, very  stable at room temperature.  Analysis of samples over a two year period  were found to be v i r t u a l l y i d e n t i c a l .  This not only demonstrated the  s t a b i l i t y of the samples but also the r e l i a b i l i t y of the a n a l y t i c a l procedure . 7.4.2  Runs.  Several runs were repeated over a two year period  and were found to agree well within ± 5%.  For  example, Table 7.1 shows  the concentration of DEA versus time for three different runs where a -3 3 * 10  moles/cc DEA solution was degraded at 175°C under 4137 kPa  psi) C0 .  Run C was conducted two years after runs A and B.  2  Table 7.1  Comparison  Sample Hours  of r e p r o d u c i b i l i t y of degradation runs  Concentration of DEA moles/cc Run A Run B Run C  0  3.00 x 1 0 ~  1  2.67  2.85  2.76  2  2.36  2.39  2.43  3  1.988  2.13  2.19  4  1.84  1.87  1.9  5  1.58  1.63  1.7  6  1.44  1.45  1.45  7  1.24  1.23  1.3  8  1.08  1.17  1.12  3  3.085 x  io"  3  3.1 x 10  -3  (600  60  7.5  Experimental programme Having established a simple experimental procedure to observe the  degradation of DEA under controlled conditions, i t was attempted to devise an experimental programme which could produce s u f f i c i e n t information to develop a k i n e t i c model for the reactions.  Experiments were there-  fore conducted to observe the effect of temperature, t o t a l pressure and i n i t i a l DEA concentration.  Table 7 . 2  Table 7.2 summarizes the runs carried out.  Summary of experiments performed with C 0 at kPa (600 psi) 2  4137  I n i t i a l DEA Concentration wt %  Temperature °C 250  220  205  100  *  80  x  60  195  185  175  162  150  140  *  X  120  90  x  X  40  145  X  x  30  x  x  x  20  X  15  X  10  x  x X  X  x  x  x  X  X  X  5  x  x  x  x  X  X X  x  A subsequent series of experiments degraded 30 wt % DEA at 195°C under the following pressures of C0 :- 6895(1000), 5516(800), 2  4137(600),  3448(500), 2758(400), 2067(300), 1517(220) kPa (psi). The r e s u l t s of a l l these sets of experiments are tabulated i n Appendix B. It was l a t e r discovered that these experiments were not s u f f i c i e n t to explain f u l l y the degradation mechanism although they could be used  as the basis for developing a k i n e t i c model of the reactions.  Therefore,  further runs were performed to study the degradation mechanism and are described in chapters 9 and 10.  For this reason the chapter on experi-  mental results and discussion has been s p l i t into three chapters.  Chap-  ter 8 discusses experiments designed to study the k i n e t i c s , chapter 9 discusses experiments designed to study the degradation mechanism, and chapter 10 discusses experiments designed to study the behaviour of the major degradation compounds and feed impurities.  CHAPTER 8  RESULTS AND DISCUSSION OF EXPERIMENTS DESIGNED TO STUDY THE  The in  KINETICS OF THE DEGRADATION REACTION  r e s u l t s of the d e g r a d a t i o n runs are t a b u l a t e d i n Appendix B  the form of c o n c e n t r a t i o n of DEA and i t s main d e g r a d a t i o n  v e r s u s time.  F i g u r e 8.1 shows t y p i c a l chromatograms  products  of a DEA s o l u t i o n  degraded under l a b c o n d i t i o n s (run 3) c o r r e s p o n d i n g t o samples at  2 hour i n t e r v a l s .  Three major d e g r a d a t i o n peaks produced  HEOD, and THEED are e v i d e n t . solution.  taken by BHEP,  The MEA peak i s an impurity i n the i n t i a l  The HEOD and THEED peaks i n c r e a s e s h a r p l y at f i r s t  e i t h e r remain constant  i n s i z e or decrease.  T h i s suggests  HEOD and THEED are i n t e r m e d i a t e d e g r a d a t i o n compounds.  and then  that both  The DEA peak  decreases p r o g r e s s i v e l y whereas the BHEP peak grows. I t was observed c o l o u r changing gressed.  t h a t the DEA s o l u t i o n slowly darkened with the  from a l i g h t y e l l o w to a dark brown as d e g r a d a t i o n  pro-  A l s o there was a change i n odour with the s o l u t i o n becoming  more pungent. Although many other d e g r a d a t i o n compounds were d e t e c t e d e s p e c i a l l y at  h i g h temperatures,  in  full,  i t i s b e l i e v e d t h a t i t was o n l y necessary  data on DEA, BHEP, HEOD, and THEED.  to record,  T h i s c o n c l u s i o n was reached  because the o t h e r minor d e g r a d a t i o n compounds e x i s t e d g e n e r a l l y i n very low c o n c e n t r a t i o n s and, p r o b a b l y ,  had l i t t l e  62  e f f e c t on the k i n e t i c  model.  63  DEA  Time: Figure 8.1  A hr  . Time:  6 hr  Typical chromatograms of a 30 wt % DEA solution degraded at 205°C under 4137 kPa C0 2  64 8.1  Effect of  temperature  Figures 8.2 and 8.3 show the change of DEA concentration with time when a solution consisting i n i t i a l l y of about 30 wt % DEA to C0  i s subjected  at a pressure of 4137 kPa (600 psi) and temperatures  2  90-250°C (runs 1-12).  ranging from  The results have been plotted on semi-logarithmic 34 41  scales.  The reason for this i s that e a r l i e r work  '  suggested  the  i n i t i a l degradation of DEA to be governed by a f i r s t order reaction. Hence, when C0  2  i s in excess, DEA was thought  to degrade according to  the following equations :DEA  D E  ^  dl^Al . _  products k n E A  [  D  E  A  [8.1] l  t  [ 8  .  2 ]  where [DEA] = concentration of DEA at time t t J  t = time k„. DEA  = overall reaction rate constant  The integrated form of Eqn. 8.2 i s : k  log  [DEA]  = log [DEA]  t  If the degradation of DEA  Q  DEA  t  -  [8.3]  i s f i r s t order then a semi-logarithmic  plot of [DEA] versus t should be a straight Examination of Figs. 8.2 and 8.3  line.  indicates that the data f a l l on  straight lines especially at low temperatures.  However, at high tempera-  tures, the degradation rate slows perceptibly after about 5 hours. an extended  In  run (run 32, F i g . 10.2) where 30 wt % DEA was degraded under  4137 kPa (600 psi) C0  2  at 205°C for 50 hours, the DEA concentration  approached a nearly constant value of about 2 wt %. the reaction i s more complicated than i n i t i a l l y  This suggests that  suspected.  It i s possible  DEA CONCENTRATION (xlO moles/cc) 3  J  L  DEA CONCENTRATION (xlO moles/cc) 3  99  that C0  2  may  cease to be in excess as the run proceeds, or the  tion products themselves may reactions are r e v e r s i b l e .  degrada-  i n h i b i t the degradation or the degradation These p o s s i b i l i t i e s w i l l be discussed later  in chapter 11. Since i t was not clear whether the i n t i a l degradation was governed by a f i r s t order reaction, further confirmation was  sought.  Using  69 Levenspiel's technique  , the reaction order was obtained from studying  i n i t i a l degradation rates.  Assuming C0  2  i s in excess the general degrada  tion reaction i s of the form:k  DEA  a [DEA] Hence or  log{-  d  ^  E A ]  }  products . . ^ = log{k  [8.4]  * ) + a log {[DEA]}  [ D E A ]  D E A  . [8.6]  [ 8  5 ]  Therefore, i f the log of i n i t i a l degradation rate i s plotted against log  of the i n i t i a l concentration, then a straight l i n e should be  with a slope equivalent to the reaction order.  The i n i t i a l  produced  degradation  rates were calculated from runs of varying i n i t i a l DEA concentration (runs 13-29) at 205, 175, and 150°C. 8.1 to 8.3.  Figure 8.4  The results are tabulated in Tables  shows the corresponding p l o t s .  Table 8.1  Run No.  I n i t i a l DEA concentration and i n i t i a l degradation rates at 205°C  Initial concentration moles/cc  Initial degradation rate moles/cc.hr.  13  10  14  8  2  15  6  1.4  16  4  1.18  3  3  0.85  17  2  0.5  19  1  0.26  Table  8.2  Run No.  x  io"  3  2.2  io  x  I n i t i a l DEA concentration and i n i t i a l degradation rates at 175°C  Init i a l concentration moles/cc 10~  10  22  6  6  6  3  3.8  23  2  2.2  24  1.5  1.65  25  1  0.91  3  -  3  DEA  Initial degradation rate moles/cc.hr.  21  x  DEA  11  x  10"  4  69  Figure 8.4  I n i t i a l degradation rate as a function of i n i t i a l DEA concentration and temperature  70 Table 8.3  I n i t i a l DEA concentration and i n i t i a l DEA degradation rates at 150°C  Run No.  Using  io  - 3  26  6  8  3  7.1  27  2  3.8  28  1.5  2.6  29  1  2.0  the method  of  log(-  iLLEIi^!)  to  range  from  tion  Initial degradation rate moles/cc.hr.  Initial concentration moles/cc  reaction  of  x  t o 0.996.  is first  x  least squares lines were f i t t e d  versus log [DEA].  1.025  12.9  The  Thus  10"  to  slopes of the lines  i t c a n be a s s u m e d  5  the  plots  were  the i n i t i a l  found degrada-  order.  A further check i s provided by an Arrhenius plot based on  the r e l a -  tionship:-  k log k where  D E A  D £ A  = A exp. {-E/RT}  = log A -  2  - ^ •i  [8.7] [8.8]  A = frequency factor E = activation energy R = universal gas constant T = absolute  temperature  If the data, when plotted as log k ^  E A  vs. 1/T, f a l l on a straight line  then the f i r s t order hypothesis i s confirmed. plot where k ^  E A  Figure 8.5 i s an Arrhenius  i s calculated from the i n i t i a l slopes of the curves in  Figs. 8.1 and 8.2.  As can be seen, the plot i s linear at temperatures  71  ranging from 90-170°C.  However, at higher temperatures,  there i s a  departure from the straight line behaviour, once again indicating that more complex reactions are taking place. order behaviour  It i s l i k e l y that the f i r s t  i s only apparent, i . e . , there may be several consecutive  reactions taking place which are affected d i f f e r e n t l y by temperature. What can be concluded, however, i s that the reaction i s highly sensitive to temperature.  The i n i t i a l degradation rate increases by nearly a  factor of 3000 as the temperature i s raised from 90 to 205°C. 8.1.1  Degradation products.  Figures 8.6 to 8.11 show plots of  HEOD, THEED, and BHEP concentration versus time.  Solid lines are drawn  through the experimental data points to indicate any observable trends. 8.1.1.1  HEOD.  It can be seen from Figs. 8.6 and 8.7 that there  is a rapid production of HEOD which levels o f f .  The i n i t i a l rate i n -  creases with temperature although the overall amount of HEOD produced decreases.  HEOD does not appear, therefore, to act as an intermediate 34  of  the type suggested by the mechanism of Polderman and Steele.  It  may be possible f o r HEOD to be a f i n a l product of DEA degradation, which is thermally unstable.  This point w i l l be discussed further i n chapter  11. 8.1.1.2  THEED.  Figs. 8.8 and 8.9 show that the THEED concentra-  tion increases with time at a s l i g h t l y lower rate than the HEOD concent r a t i o n , reaching a maximum value before decreasing again.  The time  required to reach the maximum concentration decreases with increasing temperature. HEOD.  THEED appears to behave more l i k e an intermediate than  F i g u r e 8.6  HEOD c o n c e n t r a t i o n ns a f u n c t i o n of time and (30 wt % DF.A, 4137 kPa C 0 , 205-162°C) 2  temperature  Figure 8 . 7  HEOD concentration as a function of time and temperature (30 wt % DEA, 4137 kPn C 0 , 150-90°C) 2  TIME (hr) Figure  8.8  THEED c o n c e n t r . i t i o n (30 wt  % DEA,  4137  as a f u n c t i o n kPA  C0 , 2  of  time  205-l62°C)  and  temperature  as  TIME (hr) F i g u r e 8.10  BHEP c o n c e n t r a t i o n as a f u n c t i o n of time and temperature (30 wt % DEA, 4137 kPn CO,, 206-162°C) —i  i  0  20  40  60  1  1  1  80  100  120  \  140  TIME (hr) F i g u r e 8.11  BHEP c o n c e n t r a t i o n as n f u n c t i o n of time and temperature (30 wt % DEA, 4137 kl'n CO, , 150- 90°C)  160  79 8.1.1.3  BHEP.  Figures 8.10 and 8.11 show that the concentration  of BHEP r i s e s steadily with time. ing  rapidly with temperature.  The overall production of BHEP increas-  At temperatures greater than about 185°C,  the production of BHEP ( i . e . , the slope of the BHEP concentration versus time curve) starts to f a l l s l i g h t l y after several hours and this implies that the concentration of a certain intermediate i s f a l l i n g .  HEOD cannot  be this intermediate since i t s concentration remains r e l a t i v e l y  constant  after an i n i t i a l period and this would result in the production of BHEP becoming constant.  THEED i s more l i k e l y to be the intermediate  sible for the formation of BHEP.  respon-  THEED's concentration f a l l s after  reaching a maximum and this would cause the production of BHEP to f a l l as observed  in Figs. 8.10 and 8.11.  This w i l l be discussed further  in chapter 11. 8.2  Effect of i n i t i a l DEA concentration The results of degradation experiments conducted by using different  i n i t i a l DEA concentration were rather confusing.  Figures 8.12 to 8.14  show the change i n DEA concentration with time for varying solution strengths at temperatures of 205°C, 175°C, and 150°C. tend to deviate from the straight l i n e behaviour at high  Again, the plots temperatures.  If i t i s assumed that the i n i t i a l degradation rate i s f i r s t order, then k  DEA  should be independent of the i n i t i a l DEA concentration.  How-  ever this i s c l e a r l y not the case as shown by F i g . 8.15, which i s a plot of k p £  A  versus i n i t i a l DEA concentration.  It appears there are three  regimes:1.  0-10 wt % where the degradation rate constant of DEA i s constant at a low value.  2.  10-30 wt % where the rate constant rapidly increases with increasing  TIME (hr) Figure 8.12  DEA concentration ns a function of time and concentration (4137 kPn C0 , 205°C)  initial  DEA  2  00  o  TIME (hr) F i g u r e 8.13  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 time and (4137 kPa CO,, 175°C)  initial  DEA  concentration t—*  10  20  30  40  50  TIME (hr) Figure  8.14  DEA  concentration  (4137 kPa CO,,  ,is a  150"C)  function  of  time  and  initial  DEA  concentrati  INITIAL DEA CONCENTRATION (wt %) Figure 8.15 k ^ ^  as a function of i n i t i a l DEA  and temperature (4137 kPa  C0 ) 2  concentration  84  i n i t i a l DEA concentration. 3.  30-100 wt % where the rate constant  i s high and r e l a t i v e l y  constant,  decreasing s l i g h t l y as the i n i t i a l DEA concentration nears 100 wt %. Figure 8.16 shows the Arrhenius plot for various i n i t i a l DEA concentrations.  Again the three regions can c l e a r l y be seen.  At this stage i t was not possible to explain this behaviour.  Thus  more experiments had to be conducted and these are reported in chapters 9 and 10. Figures 8.17 to 8.19 show typical plots of HEOD, THEED, and BHEP concentrations versus time as a function of i n i t i a l DEA concentration at  205°C.  off,  As before the HEOD concentration r i s e s rapidly and then levels  whereas THEED tends to a maximum concentration before f a l l i n g again  (especially at high i n i t i a l DEA concentrations). to be produced from THEED rather than HEOD.  BHEP once again appears  It i s interesting to note  that the production of BHEP and HEOD are both lower at an i n i t i a l DEA concentration of 100 wt % than at 80 wt %.  This i s reflected in the  values being lower at 100 wt % than 80 wt %.  I n i t i a l l y , at 100 wt % DEA, the only water present  E  A  degradation.  i s in the form of  As the degradation reaction proceeds  water i s produced as a degradation product 8.3  D  This behaviour indicates  that water may play a s i g n i f i c a n t role i n the overall  a trace impurity in the DEA feed.  k  (see chapter 2, Eq. 2.17).  Effect of pressure Typical plots of changes i n DEA concentration versus time as a  function of overall pressure are shown i n Figure 8.20. were conducted at 195°C.  These experiments  At this temperature the water i n the 30 wt %  DEA solution exerts a considerable pressure of about 1202 kPa (174.3 psi).  Therefore, i t must be noted that the p a r t i a l pressure of C0  2  85  i  I  i  2.1  2  I  .  2  2  . Figure 8.16  r  1  I  .  3  2  I  .  4  2  1  .  5  L_  1000/T (°k"')  Arrhenius plot for varying DEA degraded with C0 at 4137 kPa 2  solution strengths  2  .  6  Figure 8.18  THEED c o n c e n t r a t i o n a s . (4137 kPa C0 , 205°C) 2  a  f u n c t i o n of  time  and  initial  DEA  concentration  1.  1  0  1  2  3  4  5  6  7  TIME (hr) F i g u r e 8.19  BHEP c o n c e n t r a t i o n ns ;i f u n c t i o n of time and i n i t i a l DEA c o n c e n t r a t i o n (4137 kPa C 0 , 205°C) 2  00 00  is considerably less than the t o t a l pressure.  From F i g . 8.20 i t can be  seen that degradation increases with increasing pressure up to about 4137 kPa (600 psi) t o t a l pressure; is noted.  above that pressure l i t t l e change  Figure 8.21 shows the i n i t i a l k ^ ^ values as a function of  t o t a l pressure when a solution containing i n i t i a l l y graded at 195°C.  Both Figs. 8.20 and 8.21 imply that C0  at pressures below 4137 kPa (600 p s i ) . determine the s o l u b i l i t y of C0 sures.  30 wt % DEA i s de-  2  2  i s limiting  Therefore, i t was necessary to  i n DEA solutions at these overall pres-  Using these concentrations i t could then be determined whether  or not i n d u s t r i a l units were operating under C0  2  l i m i t i n g conditions and  how to relate the results of this study to i n d u s t r i a l units. nately, high temperature data on C0  2  not available in the open l i t e r a t u r e .  Unfortu-  s o l u b i l i t y in DEA solutions were Hence s o l u b i l i t y experiments  were performed to obtain these data and are discussed in chapter 9 and Appendix C. Figures 8.22 to 8.24 show plots of HEOD, THEED, and BHEP concentration versus time as a function of overall reaction pressure at 195°C.  Figure  8.20  DEA (30  c o n c e n t r a t i o n as a wt % DEA, 195°C)  f u n c t i o n of  time  and  pressure  (PSI) 0 0 T  4  I  0  0 6  1  0  0  8  1  0  0  REACTION PRESSURE (kPa) Figure  8.21  kp,-. as a function of reaction pressure DEA (30 wt % DEA, 195°C)  1 0 0 0  1—  Figure  8.22  HEOD c o n c e n t r a t i o n  as  (30 wt % DEA, 195°C)  a  f u n c t i o n of  time  and  pressure  IO  TIME (hr) Figure 8.23  THEED c o n c e n t r a t i o n as a f u n c t i o n of time and (30 wt % DEA, 1.95°C)  pressure  BHEP C O N C E N T R A T I O N (xlO ' ' m o l e s / c c )  TO C i-l  ro  03 o rq  -o  rr o o  3  o  >  n  3 rr  "1 Cu  n  3 n  o  3  3  ro  CJ 3 C  •a cn  •J:  C  -1  CHAPTER 9 EXPERIMENTS DESIGNED TO ELUCIDATE THE DEGRADATION MECHANISM Before a k i n e t i c model could be devised insight into the degradation mechanism.  i t was  necessary to gain  The experiments described  in  chapters 7 and 8 gave some idea of the mechanism but they also generated many questions which needed to be answered such as, "why DEA  concentration  log  [DEA]  Therefore,  a f f e c t the reaction rate?" and  "why  does the  initial  do the plots of  vs. time deviate from the linear behaviour at high temperatures?" the following studies were conducted in order to explain  the  questions posed by chapters 7 and 8 and to develop a comprehensive model of the degradation of 9.1  DEA.  Effect of pH Since the DEA  solutions are complex mixtures of ionized species,  i t i s highly l i k e l y that changes in pH w i l l affect the equilibrium in turn, the o v e r a l l degradation r e a c t i o n . ^ ' ^ .  DEA  make the solution alkaline whereas the dissolved C0 the solution a c i d i c .  DEA  i t s e l f tends to tends to render  Runs were carried out where the DEA  more a l k a l i n e or a c i d i c by adding NaOH or HCL 43).  2  and,  feed was made  respectively (runs Al to  The e f f e c t of these changes i n pH can be seen in F i g . 9.1 where concentration  i s plotted as a function of time for d i f f e r e n t i n i t i a l  solution pH measured at room temperature and at atmospheric  pressure.  It must be r e a l i z e d that the pH of the reaction mixture under operating  95  TIME Figure  9.1  DEA  c o n c e n t r n t i o n as a  (hr)  function  of  (30 wt % DEA, A137 kPa C0 , 205°C) 2  time  and  solution  pH  conditions w i l l be d i f f e r e n t to that at room temperature.  However,  i t was not possible to measure the solution pH under operating conditions with the equipment a v a i l a b l e .  An aqueous solution containing 30 wt  % DEA has a pH of about 11.2 at room temperature.  Therefore, the run  at a pH of 11.2 i n F i g . 9.1 (run 3) can be considered the reference experiment . As seen from F i g . 9.1, lowering the pH reduces the degradation rate.  By changing the i n i t i a l solution pH from 12.24 to 9 the degrada-  tion rate i s reduced by a factor of over 5.  The effect of pH can be  linked with the s o l u b i l i t y of C0 i n the DEA solution. 2  The s o l u b i l i t y  of C0 being increased by the action of hydroxyl ions:2  C0  2  + 0H~ ^  At low pH the s o l u b i l i t y of C0  2  HC0 ~  [9.1]  3  i s greatly reduced and hence the degrada-  tion rate i s lower. Further studies revealed that, when NaOH i s added to HEOD i n solution most of the HEOD i s converted HEOD ring i s unstable.  to DEA.  This indicates that the  It appears that the electron deficient carbonyl  atom of the r i n g i s attacked by OH , r e s u l t i n g i n r i n g opening.^ 0  II  0  CjHit-OH HEOD  DEA  At present, i t i s not possible to explain why a reduction i n HEOD concentration increases DEA degradation. further i n chapter 11.  This w i l l be investigated  98 9.2  Effect of bicarbonate and carbonate DEA  ions  treating solutions with dissolved C0 contain various ionic 2  and molecular compounds such as: R NH, R NH , R NC00~, HC0 ~' C0 +  2  and C0 .  2  2  2  3  3  ,  Since the pH has such a strong effect on degradation, i t i s  2  l i k e l y that degradation involves some ionic compounds.  Therefore, tests  were conducted where DEA was reacted with potassium carbonate  (K C0 ) 2  3  and potassium bicarbonate (KHC0 ) under 4137 kPa (600 psi) of nitrogen. 3  Thus i n i t i a l l y the reaction mixture contained C0 C0 . 2  or HC0  3  3  and no free  Under these highly alkaline conditions i t i s v i r t u a l l y impossible  for HC0  3  or C0  to d i r e c t l y revert to free C0 .  3  2  For these runs the molar concentrations of C0  3  and HC0  3  were  made equivalent to that of C0 dissolved in DEA under normal reaction 2  conditions.  This was to ensure that any changes noted in the degradation  reaction were not due to differences in the amount of C0 mixture either as free C0 or HC0 2  3  or C0  3  .  2  in the reaction  Unfortunately the open  l i t e r a t u r e did not provide data on C0 s o l u b i l i t y in DEA under the reaction 2  conditions of this study.  Therefore, a series of s o l u b i l i t y experiments  had to be performed to produce the necessary data. 9.2.1  CO; s o l u b i l i t y data.  A simple method for determining the  s o l u b i l i t y of C0 in DEA solutions under high temperature and pressure 2  was developed.  Details of the method used are given in Appendix C.  S o l u b i l i t i e s were determined  for the following conditions:-  DEA concentration - 30, 20, and 10 wt % Temperature  - 205 to 100°C  Overall pressure  - 413.7 to 4137 kPa (60 to 600 psi)  It must be noted that the o v e r a l l pressure i n the autoclave was made up from C0 and water vapour from the aqueous DEA solution (and 2  99 to a small extent from DEA i t s e l f ) .  For example at 205°C the vapour  pressure of a 30 wt % DEA solution i s 1503 kPa (218 p s i ) . to 9.4 summarize the r e s u l t s of the s o l u b i l i t y  Figures 9.2  experiments.  It i s realized that the method used f o r determining the C0 i t y was very simple and probably not very accurate.  solubil-  2  However the purpose  of these experiments was only to obtain approximate s o l u b i l i t i e s to within ± 10%.  To check the accuracy of the method, the s o l u b i l i t y results were  compared to those in the l i t e r a t u r e where the data overlapped.  The  comparisons are shown in Table 9.1. Table 9.1 DEA Cone wt %  C0  Temp °C  Comparison of C0  partial pressure psi kPa 2  C0  s o l u b i l i t i e s in DEA solutions  2  concentration g C0 /g DEA This study Literature 2  2  % Difference  Reference  20  100  100.0  689.5  0.272  0.27  0.74  71  20  120  100.0  689.5  0.238  0.212  12.26  71  20  140  100.0  689.5  0.204  0.186  7.53  71  20  100  316.0 2178.8  0.366  0.348  5.17  71  20  120  316.0 2178.8  0.331  0.294  12.58  71  20  140  316.0 2178.8  0.29  0.25  16.00  71  25  107  591.6  0.22*  0.218  0.92  72  25  107  317.0 2185.7  0.31*  0.287  8.01  72  25  121  335.8  0.165*  0.143  15.38  72  25  121  230.0 1585.9  0.275*  0.248  10.90  72  25  121  402.0 2771.2  0.33*  0.3  10.00  72  85.8  48.7  Av = 9.04 *Extrapolated r e s u l t s from Figs. 9.2 and 9.3  PARTIAL PRESSURE C 0 (PSI) 2  PARTIAL PRESSURE C 0 10  20  40  n  0.6  50  i  60  i  80  i  (PSI)  2  100  i  0.5  (kPa)  F i g u r e 9.3  S o l u b i l i t y of C0  2  i n 20 wt % DEA  200  300  400  1  1  1  500  r  PARTIAL PRESSURE C 0  2  (PSI)  (kPa) Figure 9.4  S o l u b i l i t y of C0  2  in 10 wt % DEA  o  ho  103 9.2.2  Runs using HC0 ~ and C 0 " 3  3  instead of C0  The runs  2  performed  are summarized i n Table 9.2.  Table 9. 2  Run No.  Summary o f HCO," and C 0 ~ 3  DEA Cone wt %  44  Temp °C  runs  Nitrogen Pressure psi kPa  Ion*  Run time hr.  30  205  600  4137  co "  45  30  205  600  4137  HC0  46  30  175  600  4137  HC0 ~  24  47  30  150  600  4137  HC0 ~  50  3  3  3  3  8 30  *The amount of the s a l t used was c a l c u l a t e d by the f o l l o w i n g method: For example using run 41 the s o l u b i l i t y of C0 under operating cond i t i o n s £ 0.17 g C0 /g DEA Wt. of DEA s o l u t i o n = 300 g MW of C0 = 44 Cone, of DEA = 30 wt % MW of KHC0 = 100 Weight of DEA = 90 g Required C0 = 90 x 0.17 = 15.3 g Required KHC0 = 15.3 * 100/44 = 34.8 g 2  2  2  3  2  3  Run 44 using K C0 2  r e s u l t e d i n no degradation.  3  Therefore C0  can be considered to play no part i n the degradation of DEA.  3  Since  the solution was highly a l k a l i n e due to the presence of both DEA and HC0 , 3  it  was  assumed  that C0  2  was only present i n the carbonate  form.  Figure 9.5 shows DEA concentration as a function of time f o r runs 45 to 47 i n which KHC0  3  was used.  The p l o t s are l i n e a r up to about  -3 0.9 x 10  moles/cc  DEA.  Figures 9.6 to 9.8 show the corresponding  p l o t s f o r the degradation products. to that observed  by using pure C0  2  The degradation appears  similar  but the rates are very much lower.  For example, the degradation products formed at 205°C (run 45) are produced i n s i m i l a r amounts to an equivalent run using C0 8.2) instead of KHCO, . 3  2  (run 3, F i g .  Table 9.3 shows the k^,,. values f o r the KHCO, DEA 3  10  20  30  TIME (hr) Figure  9 . 5 DEA  concentration  as  a f u n c t i o n of  ( u s i n g KHCO,, 30 wt % DEA,  4 137 kPa  time  N) 2  and  temperature  TIME (hr) Figure  9.6  HEOD c o n c e n t r n t i o n as a f u n c t i o n o f t i m e ( u s i n g KHCO, , 30 wt 7. DEA, 4137 kPa N )  and  temperature  2  i—• o  F i g u r e 9.7  THEED c o n c e n t r a t i o n as a f u n c t i o n of time and ( u s i n g KHCO,, 30 wt % DEA, 4137 kPa N ) 2  temperature  LOl  108 runs and equivalent CO, runs. n  Also, the k__. values for runs where DEA  2  10 wt % DEA i s degraded under C0 are l i s t e d . 2  The close s i m i l a r i t y  between the k^_, values for the ionic runs and the CO, runs at 10 wt DEA 2  % DEA i s noteworthy. Table 9.3  Comparison of k^^. values for runs conducted with KHC0 and C0 3  2  ^EA 30 wt % standard (C0 Runs)  ( h r _ 1 )  Temp °C  30 wt % ionic (KHC0 Runs) 3  2  10 wt % standard (C0 Runs) 2  205  0.104  0.29  0.101  175  0.026  0.121  0.0242  150  0.0053  0.031  0.0055  The major difference between the ionic runs and the standard C0 runs i s the production of HEOD. KHC0 . 3  2  Very l i t t l e HEOD i s produced using  The lower production of HEOD could be linked with the fact that  the solution i s more basic than under standard conditions (KHC0  3  more basic than DEA).  being  As mentioned previously, increasing the a l k a l i n i t y  causes HEOD to break down and to i n h i b i t the production of HEOD. From these results i t can be concluded that DEA degradation can be caused by HC0  3  .  However, other reactions must also take place since  the degradation increases when pure C0 i s used. 2  9.3  E f f e c t of water To investigate degradation by other than ionic routes, degradation  experiments were conducted with C0 i n the absence of water. 2  achieved by d i l u t i n g DEA with methyldiethanolamine,  MDEA.  This was MDEA i s similar  to DEA but r e l a t i v e l y inert to C0 and does not react with DEA under 2  109 operating conditions (see run 53).  Since water was absent from the  reaction mixture, ions could not be formed and hence degradation could only be caused by C0  reacting d i r e c t l y with DEA.  2  present, these runs are called "molecular runs".  Since no ions are It must be remembered  that the reactions producing HEOD, THEED, and BHEP a l l are accompanied by the production of water.  However water i s never in excess as in  the standard runs performed with aqueous DEA formed are summarized in Table  Table 9.4  Run No  solutions.  9.A.  Summary of the molecular runs  DEA cone wt %  Temp °C  Pressure of C0 psi kPa  48  66.7  205  600  4137  49  40  205  600  4137  50  30  205  600  4137  51  30  175  600  4137  52  30  150  600  4137  Figures 9.9 to 9.12  The runs per-  2  show the results of the runs at 205 C. =  Once  again the three major degradation products are formed in r e l a t i v e l y the same amounts as in the standard runs;  however, the rate i s slower and k^  decreases s l i g h t l y with i n i t i a l DEA concentration. Thus i t appears that DEA can degrade by two p a r a l l e l reaction paths, one involving pure C0 of k p  E A  2  and the other HC0  3  .  Table 9.5 gives the values  for the molecular runs and compares them with those for the ionic  runs and standard runs.  F i g u r e 9.10  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 time and (no water p r e s e n t , 4137 kPn C 0 , 205°C) 2  i n i t i a l DEA  concentration  INIT. DEA CONC.  TIME (hr) Figure 9.11  THEED concentration as a function of time and i n i t i a l DEA concentration (no water present, 4137 kPa C0 , 205°C) 2  Figure  9.12  BHEP c o n c e n t r a t i o n (no w a t e r p r e s e n t ,  as a f u n c t i o n o f t i m e and 4 137 kPa C 0 , 2 0 5 ° C ) 2  initial  DEA  concentration  114 Table 9.5 DEA cone wt %  Comparison of k ^ ^ f o r molecular, ionic, and standard runs Temp °C  Molecular  205  0.195  -  0.195  -  66.7  205  0.175  -  0.3  -  40  205  0.168  -  0.32  -  30  205  0.14  0.104  0.29  0.244  30  175  0.075  0.025  0.121  0.10  30  150  0.0203  0.0053  0.031  0.0253  100  ^EA ^ ^ Ionic Standard h r  Molecular + Ionic  Assuming there are two p a r a l l e l reactions degrading DEA then basic kinetic theory indicates that the overall degradation rate i s the sum of the rates for the two p a r a l l e l reactions, i . e . , (k _.) „ = (k „.). . + (k__ ) . , DEA overall DEA ionic DEA molecular n  n  [9.3]  A  Referring to Table 9.5, i t can be seen that the sum of the k values for the two degradation routes i s close to the k values for the standard run.  In a l l cases the sum the rate constants i s lower than the standard  value and this i s probably due to the fact that the molecular runs exclude water.  In a normal run water i s always present and i t seems l i k e l y  that water may help the molecular route hence increasing k p £ molecular runs.  A  for the  Table 9.5 also shows that the k ^ . f o r the molecular DEA  runs decreases s l i g h t l y with decreasing concentration. i s that another degradation product i s water.  A possible reason  At high concentrations  of DEA, more water i s produced which can a i d the overall degradation. The implications of the p o s s i b i l i t y of two degradation routes w i l l be discussed further i n chapter 11 and an attempt w i l l be made to explain why the i n i t i a l DEA concentration affects the overall rate constant k^^ (see F i g . 8.15).  A  115 9.A  Thermal degradation One of the reasons f o r the d i f f i c u l t y i n purifying degraded DEA  solutions i s the fact that DEA breaks down at i t s b o i l i n g point.  A  simple test where DEA was boiled at atmospheric pressure under nitrogen for about 30 minutes resulted in 20% degradation producing THEED and BHEP.  It was, therefore, decided to investigate the thermal degradation  of 30 wt % DEA under operating conditions.  Two runs were carried out  under conditions summarized in Table 9.6.  Table 9..6  Run No  I n i t i a l DEA Cone wt %  Summary of thermal runs  Pressure (Nitrogen) psi kPa  Temp °C  Duration of run hr.  5A  30  600  A137  205  200  55  30  600  A137  250  25  Figure 9.13 shows plots of DEA concentration as a function of time. They are both linear on semi-logarithmic scales indicating a f i r s t order reaction with the reaction rate being about one hundredth of that under standard conditions at 205°C (see Table 9.7). Table 9.7  DEA cone wt %  Comparison of kp^^for thermal and standard runs (hr" ) 1  Temp °C  ^EA Thermal  Standard  30  205  0.00365  0.29  • 30  250  0.033  0.69  911  117 BHEP and THEED were the major degradation products. and 9.15 show plots of concentration versus time.  Figures 9.14  The plots tend to  indicate that a series reaction i s taking place, i . e . , DEA  • THEED — • BHEP  [9.4]  The second reaction i s more temperature  sensitive than the f i r s t .  Although the thermal degradation of DEA appears f i r s t order, i t does not agree with the stochiometric equations, where two molecules of DEA are required to produce one molecule of THEED or BHEP. reaction i s not as simple as i t appears.  Therefore the  It i s possible that an i n t e r -  mediate i s slowly produced from DEA v i a a f i r s t order reaction, which is rapidly consumed to produce THEED. DEA  • Intermediate  2 Intermediate THEED  For example:[9.5]  • THEED + H 0 2  • BHEP + H 0  [9.6] [9.7]  2  What the results show i s that BHEP can be produced from THEED which 34 does not agree with the mechanism proposed by Polderman and Steele. Hence, thermal degradation represents a t h i r d route f o r the degradation of DEA although i t s contribution i s i n s i g n i f i c a n t at low temperatures. The major degradation products BHEP and THEED are produced  i n similar  amounts i n the thermal runs under nitrogen to the standard runs under C0  2  although at a vastly decreased rate.  that C0  I t i s possible, therefore,  i s just acting as a c a t a l y s t .  In a t y p i c a l run and even f o r  runs of over 200 hr (e.g., run 10) C0  i s neither produced nor consumed  2  2  which tends to confirm the p o s s i b i l i t y that C0  2  i s acting as a c a t a l y s t .  TIME (hr) Figure  9.15  BHEP c o n c e n t r a t i o n a s a f u n c t i o n o f t i m e a n d (no C 0 p r e s e n t , 30 wt % DEA, 4137 k P a N ) 2  2  temperature  120 9.5  C0  2  s o l u b i l i t y studies  It was assumed that C0  would be i n excess for a l l the experiments  2  and therefore could be neglected referring pressure  i n devising a kinetic model.  However,  to F i g . 8.21, chapter 8, i t was noted that the t o t a l reaction affected the degradation rate up to about 4137 kPa (600 p s i ) .  Using F i g . 9.2 i t was possible to plot k ^  E A  as a function of C0  2  concen-  tration i n DEA (see Table 9.8 and F i g . 9.16).  Table 9.8  Overall k  D £ A  as a function of C0  2  s o l u b i l i t y for  degradation runs of 30 wt % DEA at 195°C Total Pressure psi kPa  P a r t i a l Pressure of C0 psi kPa  Solubility g C0 /g DEA  2  k  DEA  2  hr"  1  1000  6895  825.7  5693.2  0.312  0.23  800  5516  625.7  4314.2  0.259  0.23  600  4137  425.7  2935.2  0.196  0.23  500  3448  325.7  2245.7  0.165  0.185  400  2758  225.7  1556.2  0.127  0.154  300  2069  125.7  866.7  0.08  0.098  220  1517  45.7  315.1  0.043  0.061  From F i g . 9.16 i t appears that i f the C0 approximately 0.2 g C0 /g DEA, then C0 2  2  2  concentration f a l l s below  becomes l i m i t i n g and must be  included i n the degradation model. It was found that at high temperatures the concentration of C0 i s very close to 0.2 g C0 /g DEA i n a 30 wt % DEA solution under 600 2  psi  C0 . 2  At 195°C the C0  (see Table 9.9).  2  concentration f a l l s below the 0.2 level  2  SOLUBILITY O F C O 2 IN D E A (g C 0 / g DEA) 2  Figure.9.16  k  D  E  (30  A  as a f u n c t i o n wt % DEA,  o f C0  195°C)  2  concentration  122 Table 9.9  C0 s o l u b i l i t y as a function of temperature i n a 30 wt % DEA solution under a t o t a l pressure of 4137 kPa (600 p s i ) 2  Temperature °C  P a r t i a l Pressure of C0 psi kPa  S o l u b i l i t y of C0 g C0 /g DEA  2  2  2  205  381.4  2629.8  0.168  195  425.7  2935.2  0.194  185  461.4  3181.4  0.221  175  494.1  3406.8  0.245  150  544.3  3752.9  0.32  120  575.4  3967.4  0.38  Also increasing the concentration of DEA tends to reduce the r a t i o of C0  2  to DEA as shown in Table 9.10.  Table 9.10  C0 s o l u b i l i t y as a function of DEA concentration for solutions at 205°C under a t o t a l pressure of 4137 kPa (600 psi) 2  Concentration of DEA wt %  P a r t i a l pressure of C0 psi kPa  2  S o l u b i l i t y of C0 g C0 /g DEA  30  381.4  2629.8  0.168  20  370.0  2551.2  0.196  10  358.0  2468.4  0.28  Therefore, i t can be concluded  2  2  that for runs at high DEA concentra-  tion and high temperatures, the concentration of C0 i f not below the value of 0.2 g C0 /g DEA. 2  2  w i l l be very close to  Thus a possible explanation  for the deviation from the straight l i n e behaviour observed in certain DEA concentration versus time plots could be due to changes in the C0 concentration i n the reaction mixture.  Although i t appears that no  2  C0  i s consumed during a reaction ( i . e . , there i s no change in pressure  2  during a run) i t i s possible that C0 reacts slower with DEA 9.1)  or the C0  2  2  i s being converted to a form which  ( i . e . , see the ionic runs discussed in section  becomes t i e d up i n some manner with the degradation com-  pounds (see the BHEP runs discussed i n section 10.2). Referring to F i g . 8.20, increased beyond 4137 kPa  i t can be seen that, as the pressure i s  (600 psi) the deviation of the plot from the  linear form decreases, although the i n i t i a l k ^ .  remains the same.  This  indicates, for example, that for the 6895 kPa (1000 psi) run (run 33) the concentration remains above 0.2 g C0 /g DEA for the entire run. 2  A run (run 55) was performed where 30 wt % DEA was degraded at 205°C under twice the usual C0 Figure 9.17  2  pressure, i . e . , 8275 kPa (1200 p s i ) .  shows a comparison of the results of the run at 8275 kPa  (1200 psi) (run 56) with a standard run at 4137 kPa (600 psi) (run 3). The plot of log [DEA] versus time i s completely linear at 8275 kPa psi)  whereas the standard run starts to deviate after only 2 hours of  reaction time. C0  2  (1200  This c l e a r l y demonstrates that, at high  l i m i t a t i o n affects the rate of degradation.  discussed i n chapter 11.  temperatures,  This w i l l be further  Figure 9.17  DEA concentration as a function of time and C 0 pressure 2  (30  wt  % DEA, 205°C)  CHAPTER 10 EXPERIMENTS DESIGNED TO STUDY THE BEHAVIOUR OF THE MAJOR DEGRADATION COMPOUNDS AND IMPURITIES IN THE DEA FEED In general, the degradation of DEA and production of i t s degradation compounds can be summarized by the qualitative plots shown in F i g . 10.1. The plots suggest that BHEP i s produced i n a series reaction from DEA via THEED.  This hypothesis needed to be confirmed and, also the role  of HEOD needed to be understood.  Furthermore,  i t was necessary to deter-  mine whether any equilibrium reactions played a role in DEA degradation. To answer these questions, the following tests were performed  (see Table  10.1). 10.1  Long term run Figure 10.2 shows a plot of concentration versus time for DEA,  HEOD, THEED, and BHEP. to zero.  As can be seen, DEA, HEOD, and THEED a l l tend  BHEP appears to be the main degradation compound.  However,  under these extreme conditions many other compounds are produced and BHEP accounts f o r only about 50% of the DEA l o s t .  It i s possible that  under these conditions high molecular weight polymers are produced which may not be detected by gas chromatography.  The conclusion from this  run i s simple, overall there i s no equilibrium between DEA and i t s degradation products.  '  125  126  TIME Figure 10.1  Typical plots of concentration as a function of time for DEA and i t s degradation products  TIME (hr) Figure 10.2  Concentration of DEA, HEOD, THEED, and BHEP as a function of time (30 wt % DEA, 4137 kPa C 0 , 205°C) 2  No  ^  128 Table 10.1 Summary of runs to study the behaviour of the major degradation compounds  lun lo. 33 57  Feed Concentration moles/cc THEED HEOD  DEA  3*10~  _  59 60  3*10"  61  3*10~  62 63 64 65 66 67 68 69  —  _ 4  _  3  -  3  3*10~  _  1.0*10"  -4 3..3 xlO  2.7*10~  3  •3  •3 1.5*10" -3 1.5x10" —  -3 1.2x10* -3 1.2x10"  C0  205  N  205  C0  205  C0  150  C0  -  205  N  2  1  -  205  N  8  it  2  0.28*10~  175  C0  8  tt  0.28xl0"  175  N  8  it  -  205  co  1  -  205  N  1  11  2  205  N  8  ft  2  205  co  8  It  4.7xl0~  3  _  2 .6*10~  -  2 .6xl0~  3  -  2 .6xl0~  3  3  long term run  205  -4 5x10 -4 5*10 3.55xl0  4  50  Comments  C0  4.7xl0  4.24*10~ -4 -4 9.7x10 4x10 -4 -4 9.7x10 4x10 2 .6xl0~  Run Time Gas hr.  205  —  -  3  BHEP  -  _  -3 3*10 3*10"  58  -  -  3  Temp °C  -4  _A  4  4  4  -  2  8  2  2  2  2  2  2  2  2  2  BHEP studies  8  11  8  ti  50  11  60  11  HEOD studies  THEED studies  A l l the runs were performed at 4137 kPa (600 p s i )  10.2  BHEP runs The s t a b i l i t y  of BHEP was f i r s t tested in run 57 and i t was found  that BHEP did not undergo any form of degradation.  In run 58 BHEP was  mixed with DEA and pressured to 4137 kPa (600 psi) of nitrogen to see whether BHEP would react with DEA. to take place.  Again, no reaction was observed  Thus i t can be concluded that BHEP i s a f i n a l  degrada-  tion product and that, o v e r a l l , DEA i s slowly converted to BHEP by a slow complex series of degradation reactions. Run 59 was carried out to determine whether the presence of BHEP and other degradation products had any effect on the overall degradatio  129 The feed was made up from a mixture of degraded DEA solution and fresh DEA to give an overall DEA concentration of about 30 wt %.  A similar  run was performed where 30 wt % DEA was degraded i n the presence of only BHEP (run 60). . Figure 10.3 compares the degradation of DEA for runs 59 and 60 with a standard run (run 3).  As can be seen, the DEA degrada-  tion appears to be inhibited by the presence of degradation products, especially BHEP.  A possible explanation f o r this behaviour i s that  degradation products (and/or BHEP) are tying up some of the available C0  2  dissolved in the reaction mixture.  This may then cause the r a t i o  of available C0 to DEA to f a l l below 0.2 g C0 /g DEA and therefore reduce 2  2  the rate of degradation.  Run 60 was extended to 50 hours after which  the reaction mixture was v i r t u a l l y i d e n t i c a l to that of the standard long term run (run 33). In a similar experiment to run 60 where the reaction was performed at 150°C instead of 205°C (see run 61) no i n h i b i t i n g effect due to BHEP was observed.  Thus i t appears as i f the presence of BHEP or degradation  products tends to slow down the rate of degradation only i n situations where the concentration of C0 i s very close to or below the l i m i t i n g 2  value of 0.2 g C0 /g DEA. 2  Also run 60 shows that the addition of BHEP  to the reaction mixture has no effect on the overall production of BHEP from DEA.  Therefore, i t can be concluded that BHEP i s not i n equilibrium  with DEA or other degradation products. 10.3  HEOD runs An aqueous solution of HEOD was heated to 205°C for one hour under  nitrogen (run 62).  DEA, THEED, and a trace of BHEP were produced.  This  indicated that there must be some form of equilibrium between HEOD and DEA.  It i s unlikely that there i s any equilibrium between HEOD and  u  TIME F i g u r e 10.3  (hr)  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 time and d e g r a d a t i o n (30 wt % DEA, 4137 kPa C 0 , 205°C) 2  products  131 THEED since THEED i s unable to form HEOD (see run 66 or 67).  However,  i t was not possible at this stage to confirm whether THEED and BHEP were being produced from HEOD or DEA. Figure 10.4 shows the concentration versus time curves for the degradation of a mixture of HEOD and DEA under nitrogen  (run 63).  As  can be seen, the HEOD i s mainly converted to THEED and a trace of BHEP; the DEA loss i s f a i r l y The  small.  feed used i n runs 64 and 65 were produced by degrading a 30  wt % DEA solution at 175°C under 4137 kPa (600 psi) of C0 for 6 hr. 2  The product was removed from the autoclave  and heated to drive o f f any  dissolved C0 . 2  Run  64 i s an extended standard  run (see run 6) and, in run 65 the  mixture i s degraded under nitrogen instead of C0 . 2  10.8  compare the results of the two runs.  Figures 10.5 to  For run 64 i t appears that  HEOD i s playing v i r t u a l l y no part i n the degradation of DEA and i t s concentration remains nearly unchanged. whereas the BHEP concentration is carried out under nitrogen  THEED increases then f a l l s  increases steadily.  slightly  When the same reaction  (run 65) some major differences are noted.  The rate of DEA degradation i s less than that of the run under C0 , but 2  i t i s s t i l l quite s i g n i f i c a n t .  Since i t was established e a r l i e r (section  9.4) that DEA does not degrade noticeably at 175°C under nitrogen, i t i s clear that the C0 and/or HC0 2  3  of HEOD to DEA or the formation 10.6  are provided either by the breakdown  of THEED.  I t can be seen from F i g .  that HEOD does not break down completely but i t s concentration levels  off after sharply f a l l i n g .  This indicates some form of equilibrium  has been established between HEOD and i t s breakdown products or DEA.  TIME (hr) 10.4  C o n c e n t r a t i o n of DEA, HEOD, THEED, and BHEP as a f u n c t i o n of time ( r e a c t a n t s — D E A and HEOD, 4 1 3 7 kPa N » 205°C) 2  TIME Figure 10.5  (hr)  DEA concentration as a function of time (reactants—degraded DEA solution, 4137 kPa C0  2  or N , 2  175°C)  LO  'A—  u  o E o  z o I—  <  2.0  »—  z  RUN  LU  u  Z  o  A— 1.0  n  64 (COjl  O — 6 5 IN J  u a  O 8  TIME (hr) Figure  10.6  HEOD c o n c e n t r a t i o n a s a f u n c t i o n o f t i m e ( r e a c t a n t s — d e g r a d e d DEA s o l u t i o n , A 137 kPa C 0  2  or N , 2  175°C)  CO  u  oUJ  I 0  I 1  I 2  I 3  I 4  I 5  I 6  _ l 7  L_l 8  TIME (hr) OJ  Figure  10.8  BHEP c o n c e n t r a t i o n a s a f u n c t i o n o f t i m e ( r e a c t a n t s — d e g r a d e d DEA s o l u t i o n , 4137 k P a  °^  C0  2  or N , 2  175°C)  137 What appears to be taking place i s that HEOD reacts to form either DEA or THEED and HC0  3  .  The bicarbonate  ion then reacts with DEA to produce  either more HEOD or other degradation products.  In the case of run 65  i t seems that DEA just degrades to THEED and BHEP once s u f f i c i e n t HC0  3  has been produced from the breakdown of HEOD.  In the case of run 64  i t appears that HEOD need not undergo any breakdown since the solution has s u f f i c i e n t HC0  3  or C0 provided by the C0 atmosphere. 2  2  In summary the following points can be made:1.  DEA can degrade to HEOD i n the presence of C0 .  2.  HEOD can break down to DEA.  3.  HEOD does not break down i n the presence of DEA and C0 •  4.  HEOD p a r t i a l l y breaks down i n the presence of DEA and N .  2  2  2  Points 1 to 4 imply that HEOD may be involved i n a reversible reaction with DEA.  However, i t i s not a straightforward equilibrium and i t i s  possible that HEOD i s i n equilibrium with a degradation product of DEA which i s i n turn i n equilibrium with DEA.  This intermediate  product,  i f i t exists, i s not detected by gas chromatography or i s not produced in s u f f i c i e n t quantities to measure. 10.4  THEED runs An aqueous solution of THEED was heated to 205°C under 4137 kPa  C0  2  f o r one hour (run 66).  The only product produced was BHEP.  A  similar run under 4137 kPa (600 psi) nitrogen (run 67) also produced BHEP but i n a much smaller quantity.  I t , therefore, appears that BHEP  can be d i r e c t l y produced from THEED with C0 acting l i k e a c a t a l y s t . 2  Runs 68 and 69 were conducted to determine the e f f e c t of DEA on the reaction of THEED. time for run 68.  Figure 10.9 shows the plots of concentration versus The concentration of DEA remains unchanged for the  C O N C E N T R A T I O N (xlO  3  moles/cc)  139 8 hour run. 10.9  This indicates that DEA and THEED do not react.  Figure  also shows that, as the THEED concentration decreases the BHEP con-  centration increases proportionately.  This indicates a stochiometric  relationship between the two compounds. Figure 10.10 shows the effect of C0 of THEED to BHEP (run 69). of C0 . 2  2  which speeds up the conversion  DEA degrades s l i g h t l y due to the presence  It i s interesting to note that the degradation of the 12 wt  % DEA i n this run i s much slower than i t would have been i f the THEED were not present.  It appears that THEED, l i k e BHEP, i s able to reduce  the a v a i l a b i l i t y of C0  2  and.HC0  3  for DEA attack.  Figure 10.11 shows plots of the THEED concentration versus time for  the two runs.  The curves are i n i t i a l l y  order reaction of THEED forming BHEP.  linear and indicate a f i r s t  The asymptotic  behaviour exhibited  by the THEED concentration i n run 69 i s probably due to the fact that additional THEED i s formed from the DEA degradation. CO, causes the k to increase about f i v e - f o l d . THEED 1  the values of k obtained from F i g . 10.11. THEED  The e f f e c t of Table 10.2 shows  It i s interesting to  note that the value of k under 4137 kPa (600 psi) CO. at 205°C i s THEED 2  very close to that obtained from the k i n e t i c model of the degradation of DEA which w i l l be developed i n chapter 12.  1  I  1  1  1 COMPOUND  0  1  2  3  4  5  6  7  TIME (hr) Figure  10.10  C o n c e n t r a t i o n o f DF,A, HEOD, THEED, and BHEP a s a f u n c t i o n o f t i m e ( r e a c t a n t s — D E A and THEED, 4137 kPa CO,, 205°C)  Figure 10.11  log[THEED] ns a f u n c t i o n of time ( r e a c t a n t s —DEA and TI IKED, 41.37 kPa C 0  2  o r N , 205°C) 2  142 Table 10.2  THEED  k  for reactions under C0  THEED _i hr  k  10.5  Run No.  Gas  Pressure kPa psi  68  C0  600  4137  0.25  69  N  600  4137  0.057  Experiments  2  2  1  and N  2  THEED  k  hr"  m  °  d  2  e  l  1  0.26  -  1  to study the e f f e c t of impurities in the DEA feed  The main impurities in the DEA feed are MEA and TEA.  Four runs  were carried out to determine whether these impurities degrade and whether they react with DEA to form any other degradation compounds.  Table  10.3 summarizes the conditions of the runs performed. Table 10.3  Experimental conditions of runs performed to determine the effects of DEA feed impurities  Concentration Wt % MEA TEA DEA  Run No. 70  30  71  -  72  10  73  -  Temperature °C  C0 Pressure p s i kPa 2  -  -  205  600  4137  30  -  205  600  4137  -  20  205  600  4137  10  20  205  600  4137  The degradation of MEA produced mainly HEI with small amounts of 0ZD and HEED.  I t was also noticed that samples of degraded MEA solu-  tions which had been stored at room temperature of ammonia.  TEA was unaffected by C0  2  f o r several months, smelt  and no degradation compounds  were detected. When DEA was degraded  i n the presence of MEA (run 72) several  143 new peaks were detected on the chromatogram.  Figure 10.12  is a typical  chromatogram from run 72, with a l l the major peaks l a b e l l e d . The major degradation compounds produced as a result of the reaction between DEA and MEA  under 4137 kPa  (600 psi) C0  2  were found to be  HEP,  BHEED, and BHEI. Run  73, where DEA was degraded in the presence of TEA, produced  l i t t l e change from that using pure DEA. with a retention time of 20.6 minutes.  However a small peak was This was  detected  i d e n t i f i e d to be TEHEED.  The mechanism for the production of these new degradation compounds w i l l be discussed in chapter  11.  144  DEA BHEI MEA  BHEP THEED BHEED  1  HEOD 1  HEI HEP  WVrr F i g u r e 10.12  T y p i c a l chromatogram o f a degraded s o l u t i o n of DEA and MEA  CHAPTER 11  DEVELOPMENT OF A MECHANISM FOR DEA DEGRADATION In this chapter, the results of the experiments w i l l be discussed and an attempt w i l l be made to explain the observed phenomena.  The  overall purpose of this chapter i s to develop a model for the degradation of DEA by C0 . 2  Reaction mechanisms are proposed which may  production of the compounds detected in the degraded DEA  explain the  solutions.  Certain  reaction steps are, however, not f u l l y confirmed since, in some cases, there was no way of testing their v a l i d i t y within the scope of this work. Thus certain aspects of the mechanisms remain proposals for explaining experimental observations. The chapter i s s p l i t up into five sections.  The f i r s t  section  deals with the formation and reactions of HEOD, THEED, and BHEP.  In  the second, the concept of three degradation routes ( i . e . , ionic, molecular, and thermal) i s developed.  The t h i r d section contains an explanation  of observations which are at variance with the concepts proposed f i r s t two sections.  in the  The fourth section provides an explanation of the  production of minor degradation compounds.  In the f i f t h section the  conclusions of this chapter are summarized and an o v e r a l l model of DEA degradation i s presented.  145  146 11.1  Formation and reactions of the major degradation compounds 11.1.1  Formation of HEOD.  Referring to chapter 2 the following  set of e q u i l i b r i a were established between C0 and DEA. 2  Aqueous  conditions:  R NH + C0 2  Non-aqueous  +H  2  or high DEA  R NH COO  2  -t-  R NC00  +  2  conditions  2 R NH + C0 2  R NH COO"  2  concentrations:  + R NH  2  [11.1]  R NCOO H NR +  2  2  2  2  [11.2]  Also DEA i s able to react with the bicarbonate ion i n the following manner:R NH + H  ~ R NH +  +  2  R NH + HC0 " 2  R NC00  +  3  2  2  [11.3]  2  H R NH HC0 '  +  2  2  3  + H" + H 0  2  [11.4]  2  In each case the amine carbamate ion i s formed, R NC00 2  either with H  or H 0 3  or R NH 2  linked  By internal dehydration of the carba-  2  mate, HEOD can be produced:0  II  0  C  R-N-C-0 .  I \":  C2H4-  H< +  CH  0H T  0 + H0  -» R-N  [11.5]  2  CH,  2  DEA carbamate  HEOD  or, at high DEA concentrations:0  0  " ! -  R-N-C7O  I \"  ... H,  C NR,  C H -0-j21_ _ / 2  II  +/  4  H  R-N  0 + R NH + H 0 2  I  CH„  CH, HEOD  DEA  2  [11.6]  147 11.1.2  Behaviour of HEOD under reaction conditions  11.1.2.1  Proof that BHEP i s not produced d i r e c t l y from HEOD. 34  Polderman and Steele  proposed that two molecules of HEOD react to form  BHEP. 0 C R-N j CH  x  2  \  *  - *  ch  0 CH - CH \ + f | CH 0 N-R \ / 2  CH  X  2  • R-N  2  \  2  c  N-R + 2C0  [11.7]  2  \ > CH - CH'2  2 HEOD  /  2  BHEP  This reaction seems unlikely since four bonds must be broken. the results of the experimental  runs do not support this route.  Also  From  the stochiometric equation of this route:2 HEOD  BHEP  [11.8]  the rate of production of BHEP then becomes d [  ^ dt  H E P ]  = k[HEOD]  2  [11.9]  Figure 11.1 shows the graphical relationship for plots of concentration versus time for HEOD and BHEP based on Eq. 11.9.  For example,  Eq. 11.9 states that i f the concentration of HEOD i s constant then the concentration of BHEP should increase l i n e a r l y . In none of the experiments was this form of relationship observed. For example i n run 65 (see F i g . 11.2) the concentration of HEOD f a l l s sharply, whereas the concentration of BHEP r i s e s with increasing slope ( i . e . , the rate of production of BHEP increases). Other examples can be found with the experiments conducted at 140°C  HEOD  BHEP  . A  u z O u  I  • TIME  Figure 11.1  Qualitative plots of concentration versus time, showing the possible relationships between HEOD and BHEP  148  149  TIME  Figure 11.2  Sketch of the concentration of HEOD and BHEP as a function of time for run 65  150 and 150°C (see runs 10 and 8).  Here the concentration of HEOD reaches  a maximum then f a l l s , whereas the BHEP concentration r i s e s with increasing rate (see F i g . 11.3). S i m i l a r l y , the runs using KHC0  3  instead of C0  2  ( i . e . , the ionic  runs section 9.2) provide convincing proof that BHEP i s not produced from HEOD.  Again, i n these runs the concentration of HEOD r i s e s to  a maximum and then f a l l s , whereas the concentration of BHEP increases with increasing rate.  Also in these runs the production of HEOD i s  much lower when using KHC0  3  is unaffected.  instead of C0 , but the production of BHEP 2  What appears l i k e l y i s that BHEP i s being produced from  THEED rather than HEOD. F i n a l l y when the long term run (see section 10.1, F i g . 10.2) i s studied, i t can be seen that the concentration of BHEP levels o f f .  The  only possible ways for BHEP to level o f f are either that BHEP comes to equilibrium with an intermediate  (which has been shown not to take place,  see section 10.2), or that the concentration of the intermediate to zero.  falls  The concentration of HEOD after a run time of 50 hr. i s about -A  1.15  x  10  moles/cc and therefore unlikely to be the intermediate whereas  the concentration of THEED has dropped v i r t u a l l y to zero. 11.1.2.2  Equilibrium between HEOD and DEA carbamate.  Blanc  36 et a l .  suggested  that HEOD i s attacked by water which breaks the ring  to form carbamic acid.  The acid then reacts with a molecule of DEA  to form THEED. 0  II  C  / R-N  I  CH  I  2  \ 0 + H.O  - CH HEOD  2  • R.NCOOH Carbamic acid  [11.10]  TIME Figure 11.3  Sketch of the concentration of HEOD and BHEP as a function of time f o r runs 8 and 10  152 0 i i II i 1  ill  H /  .,  R -NrC-0;-H + jlO^-CjHu " N  • R N-C H -NR  2  Carbamic acid  2  2  DEA  4  2  + H 0 + C0 2  2  [11.11]  THEED  The problem with this proposal i s that the carbamic acid i s highly unstable and exists i n aqueous solutions only as the carbamate ion R NCOO . 2  Since HEOD i s formed from the carbamate ion, i t seems unlikely that the next stage of degradation i s for HEOD to revert back again to the carbamate ion.  This can be seen in Equation 11.12 below.  DEA + C0  - + • R NC00 H  2  - + DFA • R NGOO H THEED  • HEOD  2  2  [11.12]  What actually appears to be happening i s that HEOD i s in equilibrium with the carbamate ion and i s not an intermediate i n the production of THEED or BHEP.  See Equation 11.13 below:  DEA + CO,  • R NC00~H 2  • THEED  +  U  [11.13]  HEOD When there i s a limited amount of water ( i . e . , at high DEA concentrations) , i t may be possible for HEOD to become an intermediate according to the following equation. 2 DEA + C0  • R NC00 H NR _  2  THEED  2  +  2  *  2  • HEOD + H 0 + DEA 2  [11.14]  R NCOOH + DEA « 2  In the absence of water the carbamate can link with a molecule of DEA.  Carbamic acid may then be formed from HEOD and react with DEA  to form THEED.  However, i n the normal s i t u a t i o n ( i . e . , DEA concentration  < 40 wt % ) , HEOD i s unlikely to be an important intermediate i n the formation of either THEED or BHEP.  153 11.1.2.3  Proof that THEED i s not produced d i r e c t l y from HEOD.  Referring to run 65 where HEOD and DEA are reacted i n the absence of C0 , 2  i t i s observed that the concentration of HEOD f a l l s sharply then  levels off (Fig. 10.6).  If HEOD were just an intermediate  tration would tend to f a l l to zero.  If i t i s assumed that THEED i s produced  from HEOD, then the k i n e t i c relationship follows k  k  2 HEOD d  [  T  ^  E  D  THEED ]  i t s concen-  from the reaction:-  fe  • products  = k [HE0D]  J  a  [11.15]  - k^ [THEED]  [11.16]  The product k [HEOD] becomes constant when the concentration of HEOD becomes constant. When k^[THEED] equals k [HE0D] , the concentration 2  2  a  of THEED must level o f f since —-—3 dt  - becomes zero.  This i s clearly-not  the case as can be seen from F i g . 11.4, which shows the general of THEED and HEOD concentrations  plot  versus time for the temperature experi-  ments (runs 1 to 12). 11.1.3  Proposed model for the production  and reactions of HEOD.  It has been shown that BHEP and THEED are not d i r e c t l y produced from HEOD.  However, run 62 indicated that HEOD can react to form DEA, BHEP,  and THEED.  These observations  may be explained by r e f e r r i n g to the  following model in which HEOD i s in equilibrium with the DEA carbamate ion and this i s , i n turn, i n equilibrium with DEA:DEA + C0 ^ 2  R NC00 H _  +  2  • THEED  • products  [11.17]  HEOD According  to this scheme, heating HEOD causes i t to f i r s t break down  to the carbamate which, i n turn, either reverts to DEA or reacts with i t s e l f or DEA to produce THEED.  THEED can then i n turn produce BHEP.  Using this scheme i s i t possible to explain the behaviour of HEOD  154  TIME Figure 11.4  Sketch of the concentration of HEOD and THEED as a function of time for runs 1 to 12  155 under various operating conditions?  An equilibrium i s f i r s t established  (very quickly) between DEA, C0 , and R NC00 H .  Next, a second e q u i l i -  +  2  2  brium i s established between R NC00 H  +  2  At the same time R NC00 H  i s slowly removed by further degradation.  +  2  Therefore,  and HEOD at a much slower rate.  the concentration  of HEOD should i n i t i a l l y r i s e rapidly u n t i l  an equilibrium l e v e l i s established with R NCOO  and then start to f a l l  2  as the l e v e l of R NCOO  falls.  2  mentally.  In some cases this was observed experi-  However, at high temperatures the concentration  of HEOD was  observed to r i s e rapidly and then level off or i n some cases f a l l very slowly. Thus the above scheme i s too s i m p l i s t i c and needs refinement. consider  First  the equilibrium reactions between DEA, C0 , and water. A l l 2  of the e q u i l i b r i a are established rapidly in comparison with the degradation reactions:C0  2  + H  0 ^  2  H  R NH + H 0 ^ 2  + HC0 ~  +  R NH  2  2  R NH + H ^ ± R N H +  2  C0  2  2  + 0H~ ^  + 2  + 0H~  [11.19] [11.20]  + 2  HC0 ~  [11.21]  3  R NH + HC0 ~ ^ 2  [11.18]  3  R NC00~ + H 0  3  2  [11.22]  2  R NH + C0 ^ZT R NH C00~  [11.23]  +  2  2  R NH C00~ +  2  2  • R NC00~ + H  [11.24]  +  2  Since the deprotonation of the zwitteron  (Eqn. 11.24) i s p r a c t i c a l l y  instantaneous^ the formation of the carbamate from C0 and DEA can be 2  considered  irreversible  (Eqns. 11.23 and 11.24).  The bicarbonate and  the protonated DEA are able to form the amine bicarbonate which can e s t a b l i a further equilibrium reaction with the carbamate.(Eq. 11.26).  156 R NH 2  + HC0  + 2  [R NH ] +  2  2  ^  _ 3  [HCO3-]  [R NH ] +  2  [11.25]  [HCO3-]  2  Z=± R NC00 + H _  2  +  + H0  [11.26]  2  The last reaction (Eqn. 11.26) i s considered to be much slower than the other reactions.  This i s based on the fact that in the ionic  reactions (sect. 9.2), DEA degrades at a slower rate than normal. is discussed in sect. 11.2.1.)  (This  A l l these equations (Eqns. 11.18-11.26)  can be simplified to the following relationship. R NH+CO +H 0 ^ £ 2  2  2  R NCOO + H _  +  2  + H0  —  S  2  R NH 2  + 2  + HC0  [11.27]  _ 3  It needs to be remembered that the s o l u b i l i t y of C0  2  for most high  temperature runs l i e s between 0.2-0.3 g C0 /g DEA or about 0.45-0.7 moles 2  C0 /moles DEA.  Therefore, DEA w i l l i n i t i a l l y be in excess for the high  2  temperature runs.  The reaction mixture w i l l consist e s s e n t i a l l y of  DEA either in the free or protonated form and C0  i s tied up either as  2  the bicarbonate or carbamate ion. Degradation appears to begin with the carbamate ion dehydrating to form HEOD and slowly an equilibrium i s set up between HEOD and R NC00 . 2  If no additional degradation were to take place, then the HEOD concentration would level o f f . THEED.  However, R NC00 2  further reacts slowly to form  Since the concentration of R NC00~ f a l l s i t would be expected 2  that HEOD would also decrease.  This does not occur and thus some mechan-  ism must be keeping the concentration of R NCOO  constant.  2  is assumed that a l l the C0 extra R NCOO 2  DEA.  2  i s tied up either as HC0  3  Since i t .  or R NC00 , the 2  i s not being produced from the reaction between C0  2  and  The formation of THEED, however, produces bicarbonate ions.  These  ions w i l l then upset the right hand side of the e q u i l i b r i a , Eqn. 11.27, causing more R NC00 2  excess DEA.  to be produced from the HC0  reacting with the  3  This process restores the l e v e l of R NC00~ to i t s o r i g i n a l 2  157 value and keeps the HEOD concentration constant.  What actually happens  is that the excess DEA i s slowly converted to THEED v i a the formation of  R NC00  from R N H  2  2  + 2  and HC0  (Eqn. 11.26).  _ 3  is available, the concentration of R NC00  starts to f a l l and so w i l l  2  HEOD.  When no more free DEA  Figure 11.5 summarizes the proposed mechanism. HEOD + 2 H 0 2  C0.-K)H or H,0 R.NH+H or H 0 1 _ i HC0 + R NH _  +  2  R NH+C0 +H 0 — • R NCOO~+H +H 0  .  +  2  2  2  2  products  *  2  +  3  2  2  THEED + HCO  excess R NH  +H  2  Figure 11.5 Schematic diagram of degradation of DEA. It must be remembered that the chromatographic analysis i s unable to d i f f e r e n t i a t e between R NH, R NH , and. R NCOO~. +  2  2  2  2  This causes d i f f i -  c u l t i e s i n confirming the above mechanism and therefore i t must remain for  the present only a theory based on inference. 11.1.4  out  Effect of temperature on the production of HEOD.  in section 8.1.1.1, the maximum concentration of HEOD f a l l s with  increasing reaction temperature. this. of  As pointed  There are possibly two reasons for  The f i r s t i s simply that the s o l u b i l i t y and hence concentration  C0 i n the reaction mixture f a l l s with increasing temperature. 2  fore the levels of R NCOO 2  and hence HEOD also f a l l .  There-  The second reason  i s more subtle and may be due to the fact that the reaction forming THEED i s more temperature sensitive than the reaction forming HEOD. at high temperatures the formation of THEED from R NC00 2  favoured.  Thus  i s increasingly  This was confirmed by the k i n e t i c model developed i n chapter  12 (see Figs. 12.4 and 12.7).  158 11.1.5  Reaction of HEOD and DEA under N .  Using the proposed model  2  i t i s possible to explain the r e s u l t s of run 65 (see Figs. 10.5 to 10.8). . I n i t i a l l y the concentration of HEOD w i l l f a l l rapidly as the carbamate i s formed.  However, as the equilibrium i s established the concentra-  t i o n of HEOD levels o f f .  At the same time e q u i l i b r i a are established  between R NC00~, R NH , and HC0 ~ (see Eqn. 11.26).  Then R NC00~ slowly  +  2  2  2  3  reacts to form THEED and HC0  3  .  Thus a cycle i s set up where the DEA  feed i s able to combine with the HC0  produced by the formation of THEED,  3  to form more R NC00 . 2  2  Therefore DEA i s slowly consumed forming THEED  with the concentrations of HEOD, R NC00 , and HC0 2  3  a l l remaining r e l a t i v e l y  constant. 11.1.6  Formation of THEED.  It seems unlikely that THEED i s produced 36  from HEOD as proposed by Blanc et a l . the  carbamate  What i s suggested here i s that  ion reacts either with i t s e l f or a molecule of DEA to form  THEED i n the following manner. R R  R  iQ  \  N C-0 . . .H +H0;-CHi,-N 7  R  2  R  ^ C - 0 ...H  +  N-CjHu-N  /  \  0  + H +HC0, +  -  +  C-0 ...H 0  DEA carbamate  DEA carbamate  /  THEED carbamate  [11.28]  R .-CjHu-N R DEA carbamate  ion.  +  2  \  H  R  DEA  In reaction 11.28 a carbamate carbamate  + H +HC0,  N-C H^-N H  [11.29]  THEED ion i s formed similar to the DEA  This THEED carbamate  ion may then revert to THEED or  159 4  react further to form BHEP (discussed i n section 11.1.7). In the absence of water or at high DEA concentrations i t appears that HEOD may act as an intermediate i n the formation of THEED as proposed 36 by Blanc et a l .  (see Eqns. 11.10 and 11.11).  THEED can also be produced d i r e c t l y from DEA by the dehydration of two molecules of DEA.  This reaction can be considered the 'thermal  degradation' of DEA (see section 9.4). R  R  \  , N  r  ,  H + HO  r  / '  / •  \  R  /  N - C-H^-N  /  H  DEA  R  \  C-Hu-N  '  R  + H,0  [11.30]  \  R  H  DEA  THEED  A third possible route, which can also be considered a thermal degradation route (see section 4.2) i s where DEA loses a molecule of water to form an imine (HEM).  The imine can then react with another 2  molecule of DEA producing THEED. R-N  H CH  2  - CH  2  •}• OH  2  [11.31]  2  HEM CH — _  R  2  X  ^  /  N - CjH^-N  / R  DEA  R  \  •  \ CH,  R  /  + H f N  \ HEM  + H0  CH  DEA  R-N  CH,  [11.32]  \  H  R THEED  160 11.1.7  Formation of BHEP.  After studying the various plots  of concentration versus time, i t became evident that BHEP was not produced 34 from HEOD as suggested by Polderman and Steele  .  What i s proposed here  is that THEED dehydrates to form BHEP. R C H, R 2  N  -  /  R-N  C HK-N 2  H  \ C H  CjH^OH  2  THEED  N - R  + H0  [11.33]  2  4  BHEP  It was observed from the experiments (see sect. 10.4) that the rate of this reaction was increased considerably by the presence of C0 and HC0  .  3  It seems l i k e l y that C0  2  increases the rate of conversion  of THEED to BHEP in a similar manner to the degradation via the formation of a carbamate. the degradation  2  Thus C0 and HC0 2  3  of DEA, i . e . , not only catalyse  of DEA to HEOD and THEED, but also the degradation of  THEED to BHEP. R  R N-CjH^-N  HOfC.H,,  X  C H, 2  N-R +H +HC0, [11.34]  R-N c-o"  II  C H  .H  2  4  0 BHEP  THEED carbamate 11.2  Discussion of the degradation 11.2.1  tion products that HC0  3  Ionic route.  routes  The runs using KHC0  3  yielded similar degrada-  to those formed i n the normal C0 run.  aids  2  This indicates  the degradation of DEA i n a similar way to C0 .  How-  2  ever, the rate of degradation due to HC0  i s considerably  only small amounts of HEOD are produced.  The reason f o r the lower  3  rate of reaction i s the fact that the amine salt  lower and  ( i . e . , R NH 2  2  HC0  3  )  161 must break down to form the amine carbamate. IH  H-0!  /"  0  \  II -  RN  C = 0  2  • R N-C-0 2  ... H  + H0  [11.35]  2  H ••• • 0 Under normal conditions the  carbamate  can be produced quickly  by free C0 reacting with DEA. 2  The proposed ionic route may be summarized by the following equations. R NH + H 0 ^ 2  R NH  2  2  0H~ + C0 ^ 2  + 2  3  R NCOO~H ^  +  2  [11.38]  +  2  3  2  2  [11.39]  2  R NC00~H +R NH +  2  R N-C Hu-NRH 2  [R NH ] [HC0 ]~ ;z± R NCOO~H +H 0 HEOD + H 0  +  2  2  [11.37]  3  + HC0 ~  2  [11.36]  HC0 ~  2  R NH  + H0~  + 2  • R N-C H^-NRH + HC0 ~ + H 3  [11.40]  • R-N-(C Hu) -N-R + H 0  [11.41]  2  2  2  2  +  2  The low concentration of HEOD produced in the runs using KHC0  3  can be explained simply by the fact that the presence of KHC0  3  tends  to increase the solution a l k a l i n i t y as opposed to C0 which decreases 2  the solution a l k a l i n i t y . unstable  Under alkaline conditions HEOD becomes more  (see sect. 9.1).  Therefore HEOD w i l l exist at lower concentra-  tions in alkaline solutions, i . e . , there i s a s h i f t in the equilibrium from HEOD towards the carbamate. Referring to Table 9.3 i n section 9.2, i t was noticed that the i n i t i a l rate constants  ( k ^ ^ ) for the ionic runs were v i r t u a l l y  identical  to those where solutions of 10 wt % DEA and lower were degraded with C0 . 2  From this i t can be concluded  that, at low concentrations of DEA  the favoured degradation route i s the ionic route. that the proportion of R N H 2  + 2  It must be remembered  to the t o t a l DEA concentration i s at i t s  maximum at low DEA concentrations.  162 11.2.2  Molecular route.  Before discussing this route a d i s t i n c -  tion must be made between the so c a l l e d "molecular runs" and the "molecular route."  The molecular runs involved degrading DEA with C0  of water.  The rate of degradation was  reacts d i r e c t l y with C0  to form the carbamate ion. the carbamate i s produced 11.2.2.1  in the absence  slower than normal due to the  fact that water was unable to aid the degradation. denotes the route where DEA  2  The "molecular route" 2  in aqueous solutions  This i s comparable to the ionic route where from the ions R NH 2  Molecular runs.  + 2  and HC0  3  .  It was observed that DEA  in the absence of water to produce HEOD, THEED, and BHEP.  could degrade The  proposed  route i s as follows:R NH + C0 2  ^  2  R NH C00 +  R NH + R NH C00~  • R NC00~H NR  +  2  2  2  HEOD + H 0  2  2  2  R N-C H„-NRH 2  [11.44]  2  [11.45]  2  R NCOOH + R NH 2  2  • R NCOOH  2  2  2  HEOD + R NH + H 0  +  2  [11.43]  +  2  R NC00~H NR  [11.42]  _  2  • R N-C Hi*-NRH + H 0 + C0 2  2  2  [11.46]  2  • R-N-(C H J -N-R + H 0  The overall reaction  2  rate  2  [11.47]  2  i s much  lower than that observed under normal  conditions because more steps are involved and reaction 11.45 requires water to attack the HEOD ring structure.  Water i s present in the DEA  feed only as a trace impurity, but, with the water produced 11.44, there i s s u f f i c i e n t water to begin the degradation.  in reaction As the degrada-  tion proceeds, more water i s formed. The following equations summarize the molecular route under normal reaction conditions where water i s present in excess.  163 RjNH + C0 ^=T  R NH COO~ 2  R NH COO~ + H 0 ^  R NCOO~H + H 0  +  2  [11.48]  +  2  [11.49]  +  2  2  2  R N C O O ~ H ^ HEOD + H 0 +  2  2  R NCOO"H + R NH  • R N-C H -NRH + HC0 ~ + H  +  2  2  2  11.2.3  2  4  [11.50]  +  3  y R-N-(C Hu) -N-R + H 0  R N-C H„-NRH 2  2  2  2  [11.51]  2  Thermal route.  The t h i r d route for the degradation of  DEA consists of DEA reacting with i t s e l f to produce THEED.  This implies  that the reaction should be second order with respect to DEA.  However,  the experimental results indicate that a f i r s t order reaction (see sect. 9.4) i s taking place.  Thus DEA may f i r s t be degrading to an intermediate,  which then reacts with DEA to give THEED. be HEM as mentioned i n sect. 11.1.6.  A possible intermediate could  The proposed thermal degradation  route becomes:k R NH  CH, a  2  + H0  • R-N_  [11.52]  2  . CH  2  CH  2  kb  R NH + R-N. CH  R N-C H -NRH 2  2  U  R N-C H -NRH 2  2  2  [11.53]  4  2  • R-N- (C Hi,) -N-R + H 0 2  2  [11.54]  2  The rate of DEA degradation becomes:- l51Al = d  The chromatographic degradation mixture.  + k [HEM])[DEA]  [11.55]  b  analysis did not p o s i t i v e l y detect HEM i n the  If HEM was being produced  i t may be assumed that  i t s concentration i s very small and r e l a t i v e l y constant.  Thus the forma-  tion of HEM becomes rate c o n t r o l l i n g and the degradation of DEA becomes a pseudo f i r s t order reaction, i . e . ,  164  _ d[D|Ai 11.3  =  k t [ D E A ]  [ n > 5 6 ]  Discussion of anomalous experimental observations 11.3.1  Figure 11.6  The relationship between i n i t i a l k p i s a t y p i c a l sketch of i n i t i a l k ^ ^  E A  and DEA concentration.  versus DEA concentration.  Three d i s t i n c t regions are observed: Region I (0-10 wt %  DEA)  In this region the main degradation route appears to be the ionic route (see sections 9.2  and 11.2.1).  Region II (10-30 wt % DEA) As the concentration increases, the proportion of DEA as R N H 2  + 2  falls  existing  and the degradation route becomes a combination of the  ionic and molecular routes with the molecular route gaining dominance. The overall k „ . therefore becomes the sum of the k values for the two DEA p a r a l l e l degradation reactions. k „. = ( k „ ) . . + (k „.) . . DEA DEA ionic DEA molecular n  4  n  [11.57]  Since the thermal route i s so much slower than either the ionic or the molecular route i t s contribution to degradation should be n e g l i g i b l e . Region III (30-100 wt %  DEA)  As the concentration of DEA continues to r i s e the concentration of water f a l l s .  Thus the reaction becomes limited by water and the  rate decreases u n t i l , at 100%, the degradation becomes that proposed for  the molecular runs, i . e . , Eqns. 11.42 11.3.2  8.5,  Arrhenius plot.  to 11.47.  Referring to the Arrhenius plot i n F i g .  i t was observed that, at high temperatures,  the data tended to deviate  from the linear form and the measured rate constants (k__.) became much DEA smaller than the predicted ones. One reason for this deviation could  165  166 be simply that, at high temperatures,  the C0 s o l u b i l i t y decreases and 2  the C0 concentration becomes l i m i t i n g .  Another possible reason i s  2  that the ionic route becomes increasingly important with r i s i n g temperature.  This can be seen i n the following sketch. (Fig. 11.7) of the Arr-  henius plots comparing ionic and molecular runs with standard runs. What seems to be occurring i s the amount of R NCOO 2  the molecular route f a l l s with increasing temperature.  produced by This could be  due to the zwitteron being converted back to DEA before i t is. deprotonated to form the carbamate.  Therefore the overall production of R NCOO 2  f a l l s with increasing temperature  and i n h i b i t s the overall degradation.  In summary the formation of the carbamate ion becomes:R NH + C0  2  R NH + C0  2  2  2  >• R NCOO~H  R NH COO~  *• R NCOO~H  +  3  11.3.3  at high temps.  +  2  R NH + HC0 ~ ^ 2  at low temps, (molecular route)  +  2  2  R NCOO~H + H 0 +  2  2  (molecular route)  at a l l temps, (ionic route)  Log [DEA] versus time p l o t s .  At high temperatures i t  was observed that the semi-logarithmic plots of DEA versus time were linear only for a few hours and then began to deviate.  This indicates  that the i n i t i a l pseudo f i r s t order degradation reaction of DEA became inhibited as the reaction progressed.  This i n h i b i t i o n could be the  result of the following. 1.  At high temperatures  the concentration of C0 i s very close to the 2  c r i t i c a l value of 0.2 g C0 /g DEA.  Any reduction i n this l e v e l  2  w i l l cause the degradation rate to f a l l . 2.  It has been shown that the presence of degradation compounds (especia l l y BHEP) i n h i b i t s degradation at high temperatures by tying up some of the available C0 . 2  3.  As the degradation proceeds, the C0 i s converted to HC0 2  3  v i a the  167  log  k  D E A  l/T F i g u r e 11.7  Sketch of the A r r h e n i u s p l o t s f o r and s t a n d a r d runs  ionic,  molecular,  f o r m a t i o n o f the d e g r a d a t i o n p r o d u c t s and R NC00 . 2  p r o d u c t i o n o f a d d i t i o n a l R NC00  must proceed  2  which i s slower than t h e o v e r a l l r a t e . rate w i l l 4.  through  Therefore the the i o n i c  Thus t h e o v e r a l l  route  degradation-  tend t o f a l l .  As the r e a c t i o n proceeds the m i x t u r e becomes more a c i d i c due t o C0  2  and t h e r e d u c t i o n o f DEA.(Although BHEP and THEED a r e a l k a l i n e , two moles of DEA a r e r e q u i r e d t o produce each mole of THEED and BHEP; hence the number o f moles of a l k a l i n e s p e c i e s f a l l s . ) '  Experiments  have shown t h a t r e d u c i n g the pH reduces  rate.  11.3.4  the d e g r a d a t i o n  E x p l a n a t i o n of the e f f e c t of pH.  The e x p e r i m e n t a l  results  show t h a t i n c r e a s i n g the pH i n c r e a s e s the r a t e of d e g r a d a t i o n and reduces the p r o d u c t i o n of HEOD. 1.  T h i s can be e x p l a i n e d as f o l l o w s . •  I n c r e a s i n g the a l k a l i n i t y z w i t t e r o n formed by C0 tend t o s t a b i l i z e  2  tends t o a i d the d e p r o t o n a t i o n of the  r e a c t i n g w i t h DEA, whereas a c i d c o n d i t i o n s  the z w i t t e r o n .  R NH + C0 Z=T R NH COO" + 0 H +  2  2  R NH + C 0 2  R NH COO" + H +  2  Therefore  _  2  • R NCOO~ + H 0 2  [11.58]  2  • R NH COOH  +  [11.59]  +  2  2  i n c r e a s i n g the pH tends t o i n c r e a s e the l e v e l of carbamate  and hence d e g r a d a t i o n . 2.  I n c r e a s i n g the a l k a l i n i t y bicarbonate formation.  i n c r e a s e s t h e s o l u b i l i t y o f C 0 v i a the 2  T h i s i n c r e a s e i n C0 a v a i l a b i l i t y  under c o n d i t i o n s where C 0 3.  2  2  i slimiting,  will,  increase the degradation.  HEOD i s a t t a c k e d by h y d r o x y l i o n s , r e a c t i n g t o form the carbamate. Thus an i n c r e a s e i n pH reduces c o n c e n t r a t i o n o f HEOD.  t h e s t a b i l i t y of HEOD and hence the  169  11.4  The formation of minor degradation compounds Besides the production of the major degradation compounds HEOD,  BHEP, and THEED, many other compounds have been detected by the chromatographic analysis and mass spectrometry. are produced  These ''minor" degradation compounds  i n low amounts and may be ignored when developing the kinetic  model of the degradation.  These compounds may result from the reaction  of DEA with impurities in the feed and various thermal routes. 11.4.1  MEA degradation.  Probably the major impurity i n the DEA  feed i s MEA which undergoes degradation when subjected to C0 temperature  and pressure.  2  under high  The degradation has been f a i r l y well documented. 38  According to Polderman et a l .  MEA f i r s t degrades to OZD, probably v i a  the formation of MEA carbamate (RNHCOO ). 0  II  / RNH, + CO,  C  \  • H-N  0 + H,0  I  [11.60]  I  CH  CH  2  2  MEA  OZD  OZD then reacts with another MEA molecule to form HEI. 0  0  II  H-N CH  X  C  II \  0 + RNH  2  CH  2  OZD  • H-N CH  2  MEA  C  /  \  N-R + H 0  [11.61] .  2  CH  2  2  HEI 40  This route was l a t e r shown by Yazvikova et a l . two stages.  to consist of  The OZD reacts with MEA to form the urea, BHEU.  then undergoes dehydration to form HEI.  BHEU  170 0  II  c  H  H-N  -* R  CH  2  OZD  R \  H -N-C-N  /  /  [11.62]  \ H BHEU  MEA 0  I  c 2  I  HOJC.H  CH,  CH, BHEU  The  [11.63]  N-R + H 0  -»- H-N  HEI  lone pair of electrons from the nitrogen atom of the basic  MEA molecule attack the electron deficient carboxyl atom in the OZD ring and open i t up to produce BHEU.  If the ring i s opened by OH  a carba-  mate i s formed and i t i s possible that an equilibrium i s set up between OZD and MEA carbamate.  This equilibrium i s equivalent  in this work between HEOD and DEA carbamate.  to that proposed  BHEU may also be formed  by MEA reacting d i r e c t l y with the MEA carbamate in the following manner. R  n N-CTO  /  ... H  '  "  R  H  / '  //  '  H  H  MEA carbamate  MEA  N-R  \s / /  / H  R  0  N-C-N  + H0  \  \  2  [11.64]  *  H BHEU  The BHEU can then undergo dehydration to form HEI as i n Eqn. 11.63. The next stage of the degradation i s the hydrolysis of HEI to form HEED i n the presence of OH  ions.  0  I c  /  \ N-R  H-N  OH-  H 0  +  CH  2  y  \  ^N-C H -N ^  •  2  CH  2  R  H  4  H  2  + HC0  N  [11.65]  3  H  HEI  HEED  The f i n a l stage i s the dehydration of HEED to form piperazine or P. H  C,Hu  H  \  /  / N-C,Hu-N  ^ <L \ H  ^  H-N  •  \  \  C Hu+OH  /  N-H + H , 0  [11.66]  CjHu  2  HEED  P  HEED can also be formed d i r e c t l y  by MEA reacting with MEA carbamate.  (This i s similar to DEA reacting with DEA carbamate to form THEED.) R  \  ' ~  ~  ll .  +  1  '  N-C-0 . . . H  / H  ! H  '  HO7C.Hu  /"  /  \  \  R-N MEA carbamate  \  /  • R  \H N-H MEA  H  \  HO-C.H4-N  1  R  H  •  /  H  -  +  + HCO, + H  \  /  H  N-C,Hu-N  /  / N-C.H4-N  H  + H.O HEED  [11.67]  [11.68]  \  F i n a l l yH HEED may of MEA. H be formed by H the thermal degradation H MEA  MEA  HEED  The chromatographic  analysis of a degraded MEA solution only i n d i -  cated the formation of OZD, HEI, HEED, and P. reveal BHEU.  However, i t f a i l e d to  I t was also not possible to analyse for urea and other  substituted ureas.  Either the ureas broke down i n the chromatographic  172 column or they had no e f f e c t on the flame ionization detector. 11.4.2  Reaction between MEA and DEA.  It i s possible for MEA  carbamate to react with DEA to form N,N-bis-(hydroxyethyl) ethylenediamine or BHEED. R.  i  l  0  i  Nfc-0 !  N  /  ... H  +  +  f  HO  C.Hi, -  N  /  H  \  •  \  H  R  /  R  MEA carbamate  'N-C,HI»-N'  H  DEA  /  H  \ R  BHEED +  HCO3-  + H  [11.69]  +  BHEED can then dehydrate to form N-(hydroxyethyl) piperazine or HEP. R  H  \  C,Hu  / N-C Hu-N ?  x' H  /  \  • R-N  ,  ^-  \  \  CjHufOH  /  N-H + H,0  [11.70]  C Hu 2  BHEED  HEP Another degradation route could proceed v i a the formation of a  substituted urea.  MEA carbamate may react with DEA to  form  NNN'-tris(hydroxyethyl) urea or THEU. R  „  \  R  R  s,-r-- --. /  \  +  N-C7O  ...H  H-f-N  H  >-  R  MEA carbamate  DEA  _  S  R  / + H,0  N - C - N  H  [11.71]  R THEU  The urea can then dehydrate to form NN-bis(hydroxyethyl) imidazolidone or BHEI.  173 0  II  R  _  \  R  C  8 /  N-C-N  H  —  /  • R-N C Hi,fOH  \  CH  2  N-R + H.O CH  2  THEU  [11.72]  2  BHEI  Hydroxyl ions can then catalyse the hydrolysis of BHEI to form NN-bis(hydroxyethyl) ethylenediamine or BHEED. 0 ll  C /  R \  R-N  OH" ^  N-R + H.O  I  \  CH  2  / N-C.H^-N  I  CH  R  H  2  /  + HC0  \  BHEI  [11.73]  3  H  BHEED  The compounds THEU, BHEI, BHEED, and HEP may  a l l be produced by  reactions similar to Eqns. 11.67 to 11-73, which are i n i t i a t e d by TEA carbamate reacting with MEA.  The only difference being the direct forma-  tion of BHEED from DEA carbamate and MEA where another isomer of BHEED is R  formed.  \  .7, >% -  N-C-0  /'  •  ... H  ,  H  /  HO-C.H^-N  '  R •  \  R  H DEA carbamate  \ /  N-C.H^-N  R  MEA  /  H + HCO,  \ H  + H  [11.74]  BHEED  There i s one further route leading to the formation of BHEED, i . e . , the d i r e c t reaction between DEA and R  R  R  ----- /  \  /  •  MEA  / N-C.H^-N  \  / H  DEA  R  \  N-C.H^fOH + H-J-N H  MEA.  + H.O  \  H  H BHEED  [11.75]  174  BHEI, BHEED, and HEP were a l l detected i n small amounts in degraded solutions of DEA.  The formation of THEU i s only suspected since this  compound could not be detected with the present a n a l y t i c a l 11.4.3  technique.  Minor degradation compounds produced from DEA.  Since  40 . BHEU can be formed from MEA and C0 ,  i t seems l i k e l y that  2  N,N,N,N'-tetra(hydroxyethyl) urea or TEHEU may be formed from DEA and C0 .  The proposed  2  R  route i s : -  Q \  R  II,--  /  N-C-0  R  + - - - . /  '  ... H  + H-N  R  •  \ R  DEA carbamate  Q \  R  II  /  /  N-C-N  \  R  + H,0  [11.76]  R  DEA  TEHEU  TEHEU i s unlikely to undergo further degradation since i t has no l a b i l e hydrogen ( i . e . , free hydrogen) attached to the nitrogen atom. Again the production of this compound i s only proposed  since i t could  not be detected. One other degradation route between two molecules of DEA was pro36  posed by Blanc et a l .  They suggested  that two molecules of DEA react  forming N,N'-bis(hydroxyethyl amino ethyl) ether or BHEAE with the loss of water. R  R  /  N-C,H -0H + H - 0 - C.HH-N  — •  u  '  \  H  R  R  N-C-H^-O-C.H^-N  / H  \  H  H + H0 2  DEA  DEA  [11.77]  BHEAE  No standards for this compound could be obtained and therefore i t could not be determined whether i t was produced during the degradation of DEA.  11.4.4  The reaction between DEA and TEA.  undergo any measurable degradation.  TEA i t s e l f does not  However, i t i s able to react with  DEA to form NNNN-tetra(hydroxyethyl)ethylenediamine  or TEHEED.  Two  routes are possible, one involving DEA carbamate the other pure DEA. R  r„ \  R  i ll  'N-C-0  R  i  ... H  + HO - C.Hu-N i  ' l  •  N-C H -N 2  \  2  /  R  R  DEA carbamate  \  R + HC0  4  3  \  2  R  R  TEA  + H  3  [11.78]  TEHEED  or  \  R  /  /* NfH + HO 7 C H^-N  R  \  R  •  \  / R  DEA  TEA  /* 1-C H N r  R  + HO  \  [11.79]  R  TEHEED  TEHEED was the heaviest compound detected in the analysis of degraded DEA solutions. 11.5  Summary The following section summarizes the p r i n c i p l e conclusions of this  chapter. 11.5.1  Conclusions of the degradation experiments.  Table 11.1  gives the main degradation routes f o r the range of operating conditions studied.  176 Table 11.1 P r i n c i p a l DEA degradation routes under various conditions  Temp °C  DEA Concentration Wt %  90-175  0-10  600  4137  Ionic  —  90-175  10-30  600  4137  Ionic+Molecular  -  90-175  30-100  600  4137  Mainly molecular  175-250  0-10  600  4137  Ionic+Thermal  175-250  10-30  600  4137  Ionic+Molecular+ Thermal  co  175-250  30-100  600  4137  Ionic+Molecular+ Thermal  C0 +H 0  Total pressure psi kPa  Limiting compounds  l Route  H0 2  -  2  2  2  2  3  The routes are:a)  Ionic:-  R NH +HC0 ~  b)  Molecular:-  c)  Thermal:-  +  2  2  3  R NH+C0 2  R NH 2  2  • R NC00~H  +  • products  • R NC00~H  +  • products  2  2  • products  2  At high temperatures  the thermal route w i l l start to contribute to  the degradation, although only to a small extent. 3  At high temperatures  and DEA concentrations (> 30 wt % ) , the ionic  route contributes more to the degradation than at lower  temperatures  where the molecular route i s responsible f o r most of the degradation. This i s probably due to the reduction i n the formation of the carbamate v i a the molecular route, because the zwitteron reverts back to DEA faster than i t i s deprotonated  to form the carbamate.  177 11.5.2  Summary of the degradation reactions  11.5.2.1 1)  2)  Reactions involving DEA.  2 DEA  • THEED + H 0  THEED  • BHEP + H 0  DEA  2  2  • HEM + H 0 2  HEM + DEA  3)  THEED  • BHEP + H 0  2 DEA  • BHEAE + H 0  11.5.2.2 1)  • THEED 2  2  Reactions involving DEA and C0 . 2  DEA + C0 — • DEA carbamate 2  DEA carbamate  • HEOD + H 0 2  DEA carbamate + DEA 2 DEA carbamate THEED  2  3  • THEED carbamate + H C0 2  2  DEA + C0  2  • BHEP + H C0 2  DEA + C0  2  3  • DEA carbamate  DEA carbamate + DEA 3)  + H C0  • BHEP + H 0  THEED carbamate 2)  • THEED  »• TEHEU + H 0 2  • DEA carbamate  DEA carbamate —»• HEOD + H 0 2  HEOD + DEA 11.5.2.3 1)  2 MEA HEED  11.5.2.4 1)  • TEHEU  Reactions involving MEA. • HEED + H 0 2  •P + H 0 2  Reactions involving MEA and CQ .  MEA + C0  2  2  • MEA carbamate  MEA carbamate —>• OZD + H 0 2  MEA carbamate + MEA — » • HEED + H C0 2  HEED — • P + H 0 2  3  3  178 11.5.2.5 1)  Reactions involving MEA and DEA.  MEA + DEA BHEED  11.5.2.6 1)  • BHEED + H 0 2  • HEP + H 0 2  Reactions involving MEA, DEA, and C0 . 2  MEA + C0  • MEA carbamate  2  MEA carbamate + DEA — • BHEED + H C0 2  BHEED or  • HEP + H 0 2  DEA + C0 — • DEA carbamate 2  DEA carbamate + MEA BHEED' 2)  MEA + C0  DEA + C0  2  • TEHEU + H 0 2  • BHEI + H 0 2  2  BHEED  • BHEED + H C0 2  3  • HEP + H 0 2  Reactions involving DEA and TEA.  DEA + TEA  11.5.2.8  »- TEHEED + H 0 2  Reactions involving DEA, TEA, and C0 . 2  DEA + C0  2  • DEA carbamate  DEA carbamate + TEA Note:  • TEHEU + H 0  • DEA carbamate  2  BHE1 + 2 H 0  1)  3  • MEA carbamate  2  TEHEU  1)  2  2  DEA carbamate + MEA  11.5.2.7  • BHEED' + H C0  • HEP + H 0  MEA carbamate + DEA or  3  • TEHEED + H C0 2  3  Wherever the carbamate i s used the ion i s being referred to. Also H C0 2  11.5.3  3  exists under operating conditions as HC0  The degradation mechanism.  3  and H . +  Figure 11.8 shows the major  reactions responsible f o r the degradation of DEA with C0 . 2  CO, + H,0 ^ 2 HCO, + H  I  CO, + OH R-N (HEOD)  0  CH,  CH.  R,NH + H,0 Z=Z  R,NCOO + H (DEA)  —  HCO,"  + H,0 R,NH,  I  — IR,NH, ] {HCO,"|  R,NH,  +  or H,0~ or R,NH,  H  + 0H~  +  +  HCO,"  ©  R,NH  I  ©  R,NH  R.N - C - R.N  or  I  R.NCOO"  0 (TEHEU) R,NH  R,N - C,H - NRH H  + H + HCO,  (THEED) CH,  major degradation route  R-N  RjNH •  minor degradation route  CH, (HEM)  R-N  / \  \ C H» 2  R.NH  — —  —»  HRN-C H,,-0-C H»-NRH 2  2  (BHEP)  /  N-R  + H,0  © © ©  Molecular route Ionic route Thermal route  (BHEAE)  Figure 11.8 Schematic diagram showing the possible routes for the degradation of DEA  CHAPTER 12  KINETIC STUDIES 12.1  Development of a k i n e t i c model The purpose of the model i s to predict, quantitatively, the  tion of DEA and the production o f " i t s degradation compounds.  degrada-  At times  a model can be based on the stochiometric equations of the reaction. Unfortunately in the case of DEA the degradation reaction i s extremely complex involving several e q u i l i b r i a , p a r a l l e l and series reactions. Therefore i t i s necessary to simplify the scheme as presented in chapter 11, F i g . 11.8. From the experiments  i t was established that the i n i t i a l  degradation  of DEA was pseudo f i r s t order with the Arrhenius relationship being obeyed up to about 175°C. linear form.  Above 175°C the Arrhenius plot deviated from the  A simple kinetic model based on i n i t i a l k „ , values DEA  could  r  not predict t h i s . that temperatures  Since, under i n d u s t r i a l conditions i t i s unlikely ever exceed  able up to about 175°C.  150°C, a k i n e t i c model need only be a p p l i c -  Above t h i s , the predictions of the model may  severely disagree with measurements. The model may  also be simplified by removing the effect of  This can be done by assuming that the C0 not l i m i t i n g . 0.2 g C0 /g DEA, 2  This occurs when the C0  2  2  concentration i s constant or  2  concentration i s greater than  i . e . , at low temperatures 180  C0 .  and high t o t a l reaction  181 pressure.  Thus the ranges of conditions covered by the following model Temp:  90-175°C  DEA  cone:  C0  loading:  2  0-100 wt % > 0.2 g C0 /g DEA 2  Under these conditions the Arrhenius plots can be considered linear and the effect of C0  2  ignored.  F i n a l l y the model has to deal with the effect of i n i t i a l DEA concentration on k ^ ^ .  Based on the assumption that DEA degradation was  governed by a pseudo f i r s t order reaction, experiments showed that k ^ ^ was not independent of the i n i t i a l DEA concentration (see F i g . 8.15). The figure shows three d i s t i n c t regions 0-10, 10-30, and 30-100 wt % DEA.  The simplest way for the model to deal with this effect i s to  produce a series of Arrhenius plots similar to F i g . 8.16, which cover the DEA concentration range for each reaction of the k i n e t i c model.  The  plots could be used to obtain the k value of each reaction at any given set of operating conditions. 12.1.2 between C0  2  Simplified degradation mechanism.  The equilibrium reactions  and DEA and the formation of R NC00  a matter of seconds.  2  Therefore,  i s established within  these i n i t i a l fast reactions may be  ignored, when compared to the slow degradation reactions, since they are not rate c o n t r o l l i n g . For simplicity the model w i l l consider R NC00 2  as DEA.  Also,  since the ionic and molecular routes both r e s u l t i n i d e n t i c a l degradation products they w i l l be considered as one route.  The thermal route can  be ignored since i t i s much slower than the normal degradation. the model can be simplified into the following set of equations.  Thus  182 k DEA ^ ! HEOD k'  [12.1]  k" [12.2]  DEA — » • THEED k' ' ' THEED  [12.3]  • BHEP  These equations s t i l l present a problem.  It has been shown that  the i n i t i a l DEA degradation i s governed by a pseudo f i r s t order reaction. Therefore the rate of DEA degradation should be represented by an equation of the form:_ djDEAl dt  =  k  [  D  £  A  ]  Unfortunately the Eqns. 12.1 to 12.3 do not show t h i s , instead they  suggest  an equation of the form:-  d  i D dt  E A ]  = (k+k")[DEA] - k'[HEOD]  [12.5]  To deal with this i t was decided to make the production of HEOD an i r r e v e r s i b l e reaction.  This could be j u s t i f i e d since, at low temper-  atures the equilibrium between R NCOO 2  and HEOD i s established slowly  and the plots of concentration of HEOD versus time do not l e v e l o f f . Furthermore, the concentration of HEOD when compared to that of DEA i s very much smaller and s l i g h t errors i n the prediction of the concentration of HEOD should not affect the overall model.  Thus, the degradation  mechanism can be simplified as follows:HEOD  [12.6]  DEA \ THEED  • BHEP  183 It must be r e a l i z e d that this i s not a stochiometric r e l a t i o n s h i p but a k i n e t i c r e l a t i o n s h i p , which can be reduced to a model f o r p r e d i c t ing the degradation of DEA. 12.2  Theory Using Eqn. 12.6 i t i s possible to write equations for the rate  of change of the various compounds, i . e . : -  1151*1 ^ O D l dt d [ T t  .  ? dt  = - ki[DEA] - k [DEA]  k  l  [  D  E  A  ]  2  [12.9]  3  k [THEED]  =  .8]  [ 1 2  = k [ DEA ] - k [THEED]  E E D ]  d[BHEP] dt  [12.7]  2  [12.10]  3  As shown i n Appendix D, these equations can be solved to give:[DEA] [HEOD]  t  [THEED]  [BHEP]  t  _ -  t  =[DEA]o  r n T ? A l  DEA] 0  k  2  k 3  = [DEA]  = [DEA] o _ ^ (  + k 2  , (1 "  K1+K2  (e  _  ( k l + k 2  k  e  -  (  k  i  - e  _ ( k l + k 2 ) t  3  [12.11]  ( k l + k z ) t  (1 -  rr-^-  )  k 3  e~  Q  +  K  2  )  _ k 3 t  T  :  [12.12]  )  )  _-(k +ki)t ) e 2  k 3  [12.13]  _  ki+k ( k l + k 2  2  ) *  _-k t ) 3  N  [12.14] Since i n many cases the p l o t s of THEED concentration versus time go through a maximum (Fig. 12.1), r e l a t i o n s h i p s can be derived f o r r e l a t i n g ki,k  2  and k  3  using t max and [THEED]max.  Again d e t a i l s are given i n  Appendix D. -i [12.15J  £n(k /k +kx) t max = —. j\——,—7— ks-(k +ki) 3  M  2  9  lt  2  i [THEED]max [DEA]  , i i i k -(ki+k2) _ k k +kis ~ k +ki k 3  2  (  2  v  2  3  f  l  2  1  6  1  184  imox  TIME  •  Figure 12.1 T y p i c a l p l o t of [THEED] versus time In  addition, k  12.3  Calculation  DEA  =  k  l  +  k  [12.17]  2  of the k values  Using the experimental data of DEA, HEOD, THEED, and BHEP concent r a t i o n s versus time and equations 12.7 to 12.17, the following  methods  were used to c a l c u l a t e k i , k 2 , and k 3 . 12.3.1 1.  Method ( A ) — T h e  From the l i n e a r p l o t s of log[DEA] versus time, an i n i t i a l k ^ ^ was calculated  2.  p l o t of [THEED] vs. t goes through a maximum.  from the slope of the p l o t .  Using the r e s u l t s of HEOD concentration versus time and Eqn. 12.12, i t was possible  to c a l c u l a t e a value of k j .  could be c a l c u l a t e d averaged.  Several values of k i  f o r d i f f e r e n t times and concentrations and then  A l t e r n a t i v e l y a p l o t of [HEOD] vs. J ^ - k  (1 - e "  ( k l + k 2 ) t  )  185 could be made;  the slope of this line i s k i .  3.  Using Eqn. 12.17, k i and k j ^ ; k  could be calculated.  4.  Using the determined values of t max and [THEED]max, and Eqns. 12.15  2  and 12.16, i t was possible to calculate k 3 .  T r i a l and error were  used to solve each equation and the value of k  3  was optimized between  both equations. 5.  Using the values of k i , k , and k 2  3  with Eqns. 12.11 to 12.14 theor-  e t i c a l values of DEA, HEOD, THEED, and BHEP concentrations could be calculated. Figure 12.2 shows a typical plot of the model predictions (dashed lines) compared with the experimental results (points) using method (A) (see run 6) . 12.3.2 a maximum. 4.  k  3  Method (B)--The plot of [THEED] vs. t does not go through Steps (l)-(3) are identical to those for method (A).  may be calculated using the d i f f e r e n t i a l Eqn. 12.10.  of BHEP production can be determined time at various times.  from the slope of [BHEP] versus  By p l o t t i n g (d[BHEP]/dt)  t  against [THEED]  straight line should be obtained whose slope w i l l give k . 3  k  3  The rate  a  Alternatively  may be calculated d i r e c t l y from Eqn. 12.10 at various times and the  results averaged. on the value of k  This method of calculating k 3  3  may be used as a check  calculated by method (A).  Figures 12.3 shows a t y p i c a l plot of the model predictions compared with the experimental results for run 23.  3.0  EXPERIMENTAL COMPOUND O —DEA  2.5  A — HEOD • —THEED • — BHEP THEORETICAL  2.0  1.5  5"  1.0  A  0.5  •  —••—9' 6  • 8  10  12  14  TIME (hr) Figure 12.2  Comparison between the experimental and theoretical values of DEA, HEOD, THEED, and BHEP concentrations as a function of time (run 6)  OO a  2  3  4  5  6  7  TIME (hr) Figure 12.3  C o m p a r i s o n b e t w e e n t h e e x p e r i m e n t a l and t h e o r e t i c a l v a l u e s o f DEA, THEED, and BHEI' c o n c e n t r a t i o n s a s a f u n c t i o n o f time ( r u n 23)  HEOD,  188 12.4  Comparison of the experimental results with the predictions of the model Tables of experimental results versus predicted results are presented  in Appendix E.  The model gave a very good prediction of the concentra-  tions of DEA, THEED, and BHEP for various reaction times (see Figs. 12.2 and 12.3).  In the case of HEOD, the model tended to over-predict the  concentration after a certain reaction time.  This was to be expected  since the model did not account for the reversible reaction between HEOD and DEA (or more correctly R NC00 ). _  2  12.5  Application of the model Figures 12.4 to 12.6 show Arrhenius plots for k i , k , and ka.2  values of the k's were determined (A) or (B).  from the experimental data using method  The plots for k i and k  regimes observed  The  2  both conform to the three concentration  in the Arrhenius plot for k ^ ^ (see F i g . 8.16).  In  general the lower curve covers concentrations ranging from 0 to 10 wt % DEA and the upper curve covers concentrations between 30 to 100 wt % DEA.  For concentrations i n the range of 10 to 30 wt % DEA there can  be considered a series of curves between the two extremes.  (See F i g .  12.7, which shows an example of finding the k value at 140°C for a 17 wt % DEA solution.) The Arrhenius plot for k  3  (Fig. 12.6) i s unaffected by DEA concen-  tration and tends to confirm the fact that BHEP i s produced from THEED. Also this plot i s a straight l i n e even at high temperatures.  It i s  interesting to note that i f this plot i s extrapolated to 205°C the k value obtained agrees very closely with the value of 0.25 hr  1  calculated  from the results of run 69 (section 10.4) where THEED was degraded under C0  2  to BHEP.  189  191  192 To predict the degradation of a given DEA solution under a specified set of conditions, example.  the method i s i l l u s t r a t e d by means of a numerical  Let 17 wt % DEA be absorbing C0  2  at 14 0C at a t o t a l pressure  of 4137 kPa (600 p s i ) . 1.  F i r s t determine  to 12.6.  the values of k i , k , and k  For k i and k  2  2  3  from the Figs. 12.4  estimate the value of the 17 wt % Arrhenius  plot which l i e s between the 10 wt % and 30 wt % to curves and read o f f the corresponding k value f o r the given temperature, Fig. 2.  i . e . , 140°C (see  12.7). Using these values of k i , k , and k 2  3  and Eqns. 12.11 to 12.14 the  concentrations of DEA, HEOD, THEED, and BHEP can be calculated f o r any desired  time.  Figure 12.7  Sketch of Arrhenius plots for k i and k i n i t i a l DEA concentrations  2  at various  CHAPTER 13 PURIFICATION OF DEGRADED DEA SOLUTIONS It i s not possible to p u r i f y DEA by standard means such as d i s t i l l a t i o n since DEA and i t s degradation products have similar vapour pressures.  Also at atmospheric pressure, DEA degrades near i t s b o i l i n g  point.  In addition some of the degradation compounds d i s t i l l over a  range of b o i l i n g temperatures, which rules out the p o s s i b i l i t y of vacuum distillation. 13.1  Use of activated carbon Activated carbon f i l t e r s have been used in several natural gas  treating units to purify degraded DEA solutions.  Usually a 5-10% s l i p -  stream of the DEA solvent i s passed continually through an activated carbon f i l t e r .  Although i t has been claimed by some that the f i l t e r s  are very s u c c e s s f u l , ^ ' ^ their general effectiveness has yet to be proven. It appears that the activated carbon absorbs surface active compounds, which may be the cause of foaming, and may remove some dissolved heavy hydrocarbons and possibly some of the heat stable s a l t s .  There i s however  l i t t l e evidence to date that the f i l t e r s are able to remove any of the degradation compounds. In order to determine whether activated carbon can remove degradation compounds, samples from i n d u s t r i a l f i l t e r units were tested and a series of experiments were conducted i n the laboratory. 194  195 Figure 13.1 shows two t y p i c a l chromatograms obtained from samples taken upstream and downstream of an activated carbon f i l t e r gas plant.  in a large  The s i m i l a r i t y between the chromatograms c l e a r l y indicates  that the f i l t e r was i n e f f e c t i v e for removing degradation compounds. Samples of DEA solutions degraded in the laboratory were contacted with activated carbon for periods ranging from a few hours to a few weeks at room temperature as well as at 50°C.  In none of these experiments  was the activated carbon found to change s i g n i f i c a n t l y the concentration of  the degradation compounds.  An example of the results can be seen  in F i g . 13.2. Although none of the major degradation compounds were removed, the  degraded DEA solutions did change from a dark brown colour to a light  yellow.  It therefore seems that activated carbon i s unable to remove  HEOD, THEED, or BHEP from degraded DEA solutions. 13.2  Use of solvents Several experiments were conducted to find a solvent in which DEA  was soluble and i t s major degradation compounds were not or vice versa. If a successful solvent i s found then a possible p u r i f i c a t i o n method could be developed.  Unfortunately the tests were generally unsuccess-  f u l . E i t h e r DEA and i t s degradation compounds were a l l soluble or a l l were insoluble.  The results are tabulated in Table 13.1.  a)  Sample taken upstream of f i l t e r  Figure 13.1  Typical chromatograms of p a r t i a l l y degraded DEA solutions taken upstream and downstream of an activated carbon f i l t e r located i n a large gas plant  197  BHEP  a)  Sample before contact with activated carbon  dBHEP  rSample after contact with activated carbon 1  b)  Figure 13.2  Typical chromatograms of p a r t i a l l y degraded DEA solutions under laboratory conditions; before and after contact with activated carbon  198 Table 13.1  Effect of various  Solvent  solvents on degraded DEA solutions Comments  Acetonitrile CH CN  DEA and degradation compounds insoluble. soluble.  Furan  DEA and degradation compounds p a r t i a l l y  3  Water soluble.  C4H4O  Pyridine  DEA and degradation compounds soluble.  C5H5N  Chloroform CHCL  DEA, HEOD, THEED soluble, BHEP p a r t i a l l y Water soluble.  Ethyl alcohol  DEA and degradation compounds p a r t i a l l y  soluble.  DEA and degradation compounds p a r t i a l l y  soluble.  3  soluble.  C2H5OH  N-propyl alcohol C3H7OH  13.3  Removal of BHEP When most of the water i s stripped off from a degraded DEA solution  with a high BHEP  concentration  -4 ( i . e . , ^ > 5 10 moles/cc),BHEP starts  to c r y s t a l l i z e out at room temperature.  It i s useful to keep a small  amount of water in the solution since i t prevents DEA from s o l i d i f y i n g (the melting point of DEA i s 27-30°C). be removed by vacuum f i l t r a t i o n .  The crystals of BHEP can then  The c r y s t a l s usually have some viscous  DEA adhering to them which can be washed off with propyl 13.4  alcohol.  Removal of HEOD HEOD i s e a s i l y attacked by OH  ions to give R NC00 . 2  Therefore,  a simple way to recover DEA from HEOD would be to add NaOH to the degraded DEA solution and apply heat to drive off C0  2  from the carbamate.  However a further problem may r e s u l t from the fact that addition of NaOH increases  the C0  2  s o l u b i l i t y , which may i n turn increase the degradation  199 (see pH experiments, section 9.1). 13.5 Conclusion In conclusion, the present p u r i f i c a t i o n experiments met with success.  little  It i s recommended that natural gas processing plants try to  operate under conditions which minimize degradation, to purify heavily degraded solutions.  rather than try  CHAPTER 14 CONCLUSIONS AND RECOMMENDATIONS  The overall reaction between C0  2  and DEA consists of two stages.  The f i r s t stage i s the rapid establishment of a complex equilibrium between DEA, C0 , HC0 , 0H~, R NH , and R NC00~.  The second  +  2  3  2  2  2  stage, called the degradation reaction, i s very much slower and DEA i s converted i r r e v e r s i b l y to degradation compounds. The degradation reaction between DEA and C0  2  i s complex and cannot  be described by a simple stochiometric equation. The major degradation compounds are HEOD, THEED, and BHEP. Minor degradation compounds which were detected, are HEED, HEP, OZD, BHEED, HEI, BHEI, and TEHEED.  Some of these compounds  were produced by the reaction of DEA with impurities in the feed such as MEA and TEA. The degradation reaction proceeds v i a the formation of the DEA carbamate ion  (R NCOO ).  a)  'The molecular route', where C0  2  The carbamate can be produced by two routes:2  reacts d i r e c t l y with DEA  to form the carbamate. b)  'The ionic route' where C0 , i n the form of HC0 2  DEA i n the form of R N H 2  + 2  3  to give a s a l t .  , reacts with  The salt can then  degrade to give the carbamate. DEA can also degrade without the presence of C0 and BHEP.  2  forming THEED  This reaction i s very much slower than the normal 200  201 degradation reaction involving C0 .  It appears that C0  2  as a c a t a l y s t , with C0 7.  2  2  acts  being neither produced nor consumed.  The carbamate i s able to either form HEOD and set up an equilibrium or react with i t s e l f or a molecule of DEA to form THEED.  8.  F i n a l l y THEED can degrade to form BHEP. to be catalysed by  9.  This reaction also appears  C0 . 2  The overall i n i t i a l rate of DEA degradation i s governed by a pseudo f i r s t order reaction.  10.  The rate of DEA degradation i s strongly affected by The Arrhenius plot confirms t h i s .  temperature.  However at temperatures  greater  than 175°C, the plot deviates from the straight line behaviour. This was explained by a)  C0  becoming l i m i t i n g and b) the molecular route becoming  2  modified at high 11.  temperatures.  The rate constant (^£ ) A  DEA  concentration.  a)  0-10  b)  10-30  i s also strongly affected by  Three regions can be defined:  wt % DEA, where the main degradation route i s ionic. % DEA,  where the It . sharply increases as the degradation DEA  is a combination of molecular and c)  initial  30-100 wt % DEA,  ionic.  where the main degradation route i s molecular.  The rate slowly f a l l s as water becomes l i m i t i n g . 12.  The degradation rate i s unaffected by C0  2  pressure provided the C0  concentration in the reaction mixture i s greater than about 0.2 g C0 /g 2  13.  DEA.  The degradation rate increases with increasing pH. probably due to a) increased C0  2  This i s  s o l u b i l i t y and b) an increase i n  the concentration of the carbamate.  2  202 14.  The degradation rate i s inhibited by the presence of degradation products, especially BHEP, at high temperatures.  This i s probably  due to C0 being tied up with the degradation products, which 2  reduces the concentration of available C0 for DEA degradation tc less 2  than 0.2 g C0 /g DEA. 2  15.  Using a simplified degradation model HEOD  DEA  THEED  • BHEP  i t was possible to develop equations for predicting the degradation of DEA and production of degradation compounds.  The model covered  the ranges of 90-175°C, 0-100 wt % DEA for C0 concentrations greater 2  than 0.2 g C0 /g DEA. 2  16.  Activated carbon was found to be incapable of removing any of the major degradation compounds.  17.  BHEP can be p a r t i a l l y removed by drying degraded DEA solutions and allowing BHEP to c r y s t a l l i z e out.  18.  DEA can be recovered from HEOD by adding NaOH to the degraded DEA solution and applying heat.  14.1  P r a c t i c a l implications of the present study a)  The effect of temperature.  The design and operation of DEA  units must avoid the creation of elevated temperatures plant.  throughout the  The heat transfer surfaces of the stripper reboiler  (especially  when gas f i r e d ) are p a r t i c u l a r l y prone to the formation of localized hot spots.  To prevent such hot spots i n operating plants, the DEA  c i r c u l a t i o n through the stripper reboiler should be kept high and the steam or gas temperatures kept low.  I f , for some reason, the DEA c i r c u -  l a t i o n should decrease, immediate action must be taken to reduce the steam pressure or fuel gas flow. degradation may take place.  There are two other s i t e s where major  The f i r s t i s within the heat exchanger  that heats the r i c h amine stream with the lean amine stream.  In some 13  cases the temperature  of the r i c h amine stream may be as high as 125°C.  The second s i t e i s at the base of the absorber. of the raw natural gas i s high the temperature  If the C0  2  content  of the r i c h amine at the  base of the absorber may r i s e to 110-120°C. In many DEA units only the bulk solution temperatures It must be remembered that the skin temperatures  are measured  of heat transfer surface  can be very much higher, p a r t i c u l a r l y during process upsets. on bulk temperatures b)  Reliance  i s therefore inadequate.  Effect of pressure.  The p a r t i a l pressures of C0  2  kept as low as possible i n order to minimize DEA degradation. i t i s not usual to exercise control over the C0  2  should be Although  content of the raw gas  entering a plant, i t may be possible to d i l u t e the raw gas with some p u r i f i e d natural gas thus d i l u t i n g the overall C0  2  content.  This d i l u t  would not only reduce the degradation rate, i t would also reduce the heat of absorption when C0  2  keep the overall temperature c)  i s absorbed  into DEA.  This would help to  i n the absorber low.  E f f e c t of DEA concentration.  Ideally the plants should t r y  to operate with low DEA solution strengths ( i f possible well below 20 wt % ) .  However, l i m i t a t i o n s are imposed by the desired plant capacity.  Future design of gas treating plants should consider larger equipment f o r operation with d i l u t e solutions of DEA and d i l u t e raw gas feed.  204 Again a d i l u t e solution of DEA would reduce l o c a l increases in temperature, due to the C0  2  absorption.  However, studies would have to be made to  determine the cost effectiveness of these measures. d)  E f f e c t of activated carbon f i l t e r s .  Although the activated  carbon appears unable to remove the major degradation products,  i t is  not  recommended to remove the f i l t e r s from existing plants.  The f i l t e r s  may  serve other useful functions such as removing surfactants which can  cause foaming, heat stable s a l t s which may cause corrosion and they can act  as a means for removing fine p a r t i c u l a t e s . e)  P u r i f i c a t i o n of degraded DEA solutions.  of DEA solutions i s very d i f f i c u l t provide equipment  Since p u r i f i c a t i o n  i t i s recommended that rather than  to purify the solutions the plant should be b u i l t and  operated in such a way so as to minimize degradation. f)  A n a l y t i c a l technique.  The chromatographic a n a l y t i c a l technique  developed in this study i s ideally suited for plant use.  The method  is simple and r e l a t i v e l y fast with no sample preparation required. this method, i t i s possible to monitor DEA streams regularly.  Using  If degrada-  tion occurs, i t i s easy to detect and appropriate action can quickly be taken to minimize the DEA 14.2  losses.  Experimental recommendations a)  Measurement of pH.  DEA degradation appears to be affected by  solution pH measured at room temperature.  It would, therefore, be useful  to measure pH at the high temperature and pressure of a t y p i c a l degradation experiment. b)  Measurement of DEA carbamate concentration.  The proposed degra-  dation of DEA appears to proceed v i a the production of DEA carbamate.  To  further c l a r i f y the degradation mechanism i t would be useful to determine  204a the concentration of the DEA carbamate. tographic a n a l y t i c a l  However, using the existing  chroma-  technique i t i s impossible to detect the carbamate  since i t i s unstable and reverts back to DEA.  S i l y l a t i o n may  stabilize  the carbamate s u f f i c i e n t l y to allow i t s concentration to be determined using chromatography.  205 NOMENCLATURE Symbol  Explanation and t y p i c a l units  A  Frequency factor i n the Arrhenius Eq. 8.7 (hr  BHEAE  Bis (hydroxyethylaminoethyl) ether  BHEED  N,N-Bis(hydroxyethyl) ethylenediamine  BHEI  N,N-Bis(hydroxyethyl) imidazolidone  BHEP  N,N-Bis(hydroxyethyl) piperazine  BHEU  N ,N-Bis(hydroxyethyl) urea  BHG  N,N-Bis(hydroxyethyl) glycine  DEA  Diethanolamine  DEEA  Diethyl ethanolamine  E  Activation energy in the Arrhenius Eq. 8.7 (Cal/g mol)  ED  Ethylenediamine  EO  Ethylene oxide  GC/MS  Gas chromatograph with mass spectrometer  HEED  N-(hydroxyethyl) ethylenediamine  HEI  N-(hydroxyethyl) imidazolidone  HEM  N-(hydroxyethyl) ethylenimine  HEOD  3-(hydroxyethyl)-2-oxazolidone  HEP  N-(hydroxyethyl) piperazine  k  Reaction rate constant Overall reaction rate constant f o r the degradation of DEA,  k  DEA  (hr" ) 1  ki,k ,k 2  3  Rate constants used i n the k i n e t i c model of the degradation of DEA, Eqns. 12.7-12.17, ( h r ) _ 1  MDEA  Me thy1d ie thano1amine  MEA  Monoethanolamine  206 OZD  Oxazolidone  P  Piperazine  R-  -C H OH  T  Absolute temperature (°K)  t  Time (hr)  TEA  Triethanolamine  TEHEED  N,N,N,N-Tetra(hydroxyethyl)  ethylenediamine  TEHEU  N,N,N,N-Tetra(hydroxyethyl)  urea  THEED  N,N,N-Tris(hydroxyethyl) ethylenediamine  THEU  N,N,N-Tris(hydroxyethyl) urea  2  4  [  ]  Denotes concentration (g mol/cc)  [  ]  Denotes concentration at time t (g mol/cc)  207  REFERENCES 1.  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E., "The Mass Spectra of Organic Molecules," Elsevier Publishing Co., (1968).  212 APPENDIX A Sources of Equipment and Chemicals a)  Equipment  Item  Supplier  Model  Chromatograph Gas Chromatograph Syringe Septa Column  Hewlett Packard, Alvondale, PA. Hamilton Co., Reno, Nev. Supelco Inc., Bellefonte, Penn. Supelco Inc., Bellefonte, Penn."  5830 701 Microsep F-174 Tenax G.C.  Mass spectrometer  Hewlett Packard, Vancouver  5985 B  Reactor Temperature controller D i g i t a l thermometer  Parr Instrument Co., 111. Parr Instrument Co., 111. Doric Instruments, Que.  Chart recorder  Corning  4560 4831 EB Series 400A, No. 410A 840  Autoclave  b)  Chemicals  Chemical Acentonitrile BHG BHEED BHEI BHEP  co  2  Chloroethanol Chloroform DEA DEE A ED EO Ethyl alcohol Ethyl carbonate Furan HCL HEED HEI HEOD HEM HEP MEA  Supplier Mallinckrodt Ltd., Paris, Kentucky BDH Biochemicals Ltd., Poole, England ICN Pharmaceuticals Inc., Plainview, N.Y. Frinton Laboratories, Vineland, N.J. A l d r i c h Chemical Co. , Milwaukee, Wis. Union Carbide, Vancouver, B.C. A l d r i c h Chemical Co., Milwaukee, Wis. Caledon Laboratories Ltd., Georgetown, Ont. Matheson Coleman and B e l l , Norwood, Ohio A l d r i c h Chemical Co., Milwaukee, Wis. A l d r i c h Chemical Co., Milwaukee, Wis. Matheson of Canada Ltd., Whitby, Ont. Mallinckrodt Chemical Works, St. Louis, Mo. Eastman Kodak Company, Rochester, N.Y. Aldrich Chemical Co., Milwaukee, Wis. A l l i e d Chemicals Canada Ltd., St. C l a i r e , Quebec A l d r i c h Chemical Co., Milwaukee, Wis. Frinton Laboratories, Vineland, N.S. Synthecon Laboratories, Vancouver, B.C. A l d r i c h Chemical Co., Milwaukee, Wis. A l d r i c h Chemical Co., Mulwaukee, Wis. Malinckrodt, St. Louis, Mo.  Appendix A (cont.) Chemical MDEA NaOH OZD Potassium bicarbonate Potassium carbonate Pyridine N-propyl alcohol S i l i c a gel TEA TEHEED  Supplier A l d r i c h Chemical Co., Milwaukee, Wis. Fisher S c i e n t i f i c Co., Fairlawn, N.J. Mallinckrodt Chemical Works, St. Louis, Mo. Mallinckrodt Chemical Works, St. Louis, Mo. Mallinckrodt Inc., Paris, Kentucky Anachemia Chemicals Ltd., Toronto A l d r i c h Chemical Co., Milwaukee, Wis. ICN,K and K Laboratories Inc., Cleveland, Ohio  214 APPENDIX B Experimental results for the degradation of DEA by CO, Although certain other degradation compounds were detected in degraded solutions of DEA, only data on DEA, BHEP, HEOD, and THEED are recorded here.  This was because the other minor degradation compounds and certain  feed impurities, such as MEA, existed in very low concentrations and, therefore, they could be ignored when developing the k i n e t i c model.  TABLE B.1 RUN 1 : 30 WT% DEA, 250C, 4137 kPa (600 p s i ) C02 SAMPLE hr 0.00 0.50 1 .00 1 .67 2.50 3.50 5.00 6.50 7.83  DEA 3.00 2.32 1.81 1 .37 1 .04 0.72 0.62 0.48 0.38  kDEA = 0.691  CONC. MOLES/CC X10-3 BHEP HEOD  _  _  0.01 6 0.091 0.131 0.323 0.391 0.553 0.663 0.695  THEED  0.063 0.073 0.088 0.075 0.085 0.085 0.086 0.091  0. 180 0.200 0.250 0.220 0. 120 0.020 - .  -  hr-1  TABLE B.2 RUN 2 : 30 WT% DEA, 225C, 4137 kPa (600 p s i ) C02 SAMPLE hr 0.00 0.58 1 .00 1 .67 2.67 3.58 5.00 6.00 8.75  DEA 3.00 2.38 2.24 1 .76 1 .44 1 .05 0.82 0.68 0.57  kDEA = 0 . 3 9 9 h r - 1  CONC. MOLES/CC X10-3 BHEP HEOD  THEED  _  -  0.019 0.080 0.195 0.311 0.412 0.459 0.541  0. 125 0. 140 0. 135 0. 125 0.135 0.125 0. 120 0.118  0.210 0.460 0.600 0.710 0.700 0.441 0.335 0.171  TABLE B.3 RUN 3 : 30 WT% DEA, 205C, 4137 k P a (600 p s i ) C02 SAMPLE hr 0.00 1 .00 2.00 3.00 4.00 5.00 6.00 7.00 8.00  CONC. MOLES/CC X10-3 BHEP HEOD  DEA 3.02 2.24 1 .63 1 .26 0.95 0.78 0.71 0.65 0.57  _  THEED  _  0.010 0.051 0.111 0. 170 0.245 0.332 0.396 0.423  0.170 0.200 0.195 0.203 0.203 0.208 0.208 0.208  0.360 0.640 0.840 0.820 0.700 0.650 0.576 0.500  kDEA = 0.291 h r - 1  TABLE B.4 RUN 4 : 30 WT% SAMPLE hr 0.00 1 .00 2.00 3.00 4.00 5.00 6.00 8.00 8.00  DEA, 195C, 4137 k P a (600 p s i ) C02  DEA 3.14 2.30 1 .89 1 .47 1.21 0.91 0.82 0.74 0.63  kDEA = 0.23 h r - 1  CONC. MOLES/CC X10-3 BHEP HEOD  THEED mm-  -  0.025 0.071 0.104 0. 156 0.215 0.256 0.292  0. 188 0.233 0.250 0.228 0.220 0.243 0.220 0.215  0.280 0.610 0.870 0.870 0.790 0.760 0.720 0.680  W  a  PJ >  > S *0 IT"  o o o o o o o o o o o o o o o o o o o o o o o o  C  -3 >  dd tr 1  z PJ  a  PJ >  w  PJ  CO 00 V j O M J 1 ,(» W W O O  O O  O O  O O  O O  O O  -  O O  O  O O  O O  tr  to ro ro w  uiff»(»-'ro*>uia)owmo focno>-**»*»ao*»oo>^j*»  a  PJ >  O  I  PJ >  o o o o o o o o o r o w r j o o o o o o 00 N) O VD VD m m w-  I I I  i^.OO>OOK)K)COCOai  o o w z a: o PJ • TJ  PJ  cncncn*»*»*>>t»<&>cofo-> *»cn*»oococr\t\>-'cr\cncn o o o c n o o c n o o o o  cn ac 0 PJ  o a  0  »  0 1 1 CO  o o - * o o o o o o o o  -3  U) O U ) CD 03 v l O M t k N) - • o v o c n - ' a ^ c n o c n c n c o c o  PJ PJ  o o o o o o o o o o o  X  O  O  3: 0 f  o o o o o o o o o o o  cn  CO  0 0  tr  COVO-«tO*»-J-«0 iO 00 0 0 — ' O O O O O O O O O O O  1  —  -» —  —  t o t o CO  f  a  PJ >  O  O  O  O  _ » _ . _ . —  \D — KD 0  0  0  O  > 0 0  w z X n PJ •  O  0 0 0 00 c o — CO tO - J 0 c n cn  3  O tr  1  CO  PJ  0 Cu CT> O O  T>  CO  O O to  31 PJ  to o O O O  tr  0  0  0  0  0  0  0  co c o c o c o c o c o to -> - ' O O O O O - J 0 0 U l - O - O - U l O  O  O  O  O  O  O  O  O  vovovDvoco-ocnco o c n c o t o t o o - J o t o o o o o o c n o  X  PJ  in \ O  0  O a X —* O 1 1 co  X  PJ PJ  0  TABLE B.7 RUN 7 : 30 WT% DEA, 162C, 4137 kPa ( 6 0 0 p s i ) C02 SAMPLE hr 0.00 1 .00 2.00 3.00 4.00 5.00 6.00 7.00 8.00  DEA 3.000 2.803 2.620 2.450 2.280 2. 137 2.000 1.870 1 .744  CONC. MOLES/CC X I 0 - 3 BHEP HEOD  _  _  0.0101  0.0150 0.0201 0.0254 0.0350 0.0420  THEED  0.105 0.200 0.275 0.320 0.364 0.412 0.420 0.425  0.090 0.200 0.290 0.388 0.460 0.561 0.653 0.731  kDEA = 0.0678 h r - 1  TABLE  B.8  RUN 8 : 30 WT% DEA, SAMPLE hr  DEA  0.00 5.00 10.00 15.00 20.00 25.00 30.00 40.00 50.00 60.00 71 .40 81.10 95.00  3.000 2.600 2.200 1 .860 1 .560 1.310 1.110 0.840 0.710 0.580 0.570 0.455 0.420  kDEA = 0.0316 h r - 1  150C, 4137 k P a ( 6 0 0 p s i ) C02 CONC. MOLES/CC X10-3 BHEP HEOD _  0.0098 0.0210 0.0380 0.0425 0.0550 0.0640 0.0860 0.1060 0.1300 0.1500 0.1860 0.2100  THEED _  0.250 0.350 0.470 0.510 0.550 0.570 0.570 0.542 0.540 0.541 0.540 0.500  0.075 0.150 0.400 0.652 0.751 0.900 1 .075 1 .225 1 .200 1 .060 0.910 0.810  TABLE B.9 RUN 9 : 30WT% DEA, 145C, 4137 k P a ( 6 0 0 p s i ) C02 SAMPLE hr  DEA  0.00 3.25 13.75 19.75 28.50 39.50 48.50 60.00 69.00  3.200 3.000 2.430 2. 160 1 .740 1 .430 1 .360 1 .050 0.920  CONC. MOLES/CC X10-3 BHEP HEOD —  0.0173 0.0210 0.0620 0.0740 0.1040 0.1240  THEED  _  0.215 0.488 0.580 0.600 0.621 0.600 0.605 0.580  -  0.250 0.403 0.551 0.790  0.881  0.925 0.944  kDEA = 0.0195 h r - 1  TABLE B.10 RUN 10 : 30WT% DEA , 140C, 4137kPa ( 6 0 0 p s i ) C02 SAMPLE hr 0.00 10.00 20.00 30.00 40.00 50.00 60.00 80.00 100.00 130.00 154.80 178.00 201.00 kDEA =  DEA 3.000 2.850 2.540 2.260 2.000 1 .754 1 .605 1 .270 1 .010 0.830 0.670 0.560 0.530 0.0115 h r - 1  CONC. MOLES/CC X10-3 BHEP HEOD  —  -  0.0120 0.0210 0.0330 0.0415 0.0510 0.0700 0.1050 0.1550 0.1700 0.2060 0.2560  _  0.250 0.450 0.575 0.660 0.710 0.710 0.660 0.700 0.700 0.610 0.580 0.575  THEED _  0. 120 0.320 0.504 0.581 0.700 0.751 0.863 0.950 0.910 0.892 0.810 0.754  TABLE B.11 RUN 11 : 30WT% DEA, SAMPLE hr 0.00 20.00 40.00 60.00 80.00 100.00 120.00 140.00 160.00 180.00 200.00  DEA  120C, 4137 kPa (600 p s i )  CONC. MOLES/CC X10-3 BHEP HEOD _  3. 150 3.000 2.900 2.800 2.650 2.500 2.340 2.244 2.131 2.000 1 .905  -• -  0.0060 0.0084 0.0100 0.0180 0.0250 0.0310  C02  THEED  _  0. 150 0.300 0.380 0.525 0.600 0.705 0.751 0.760 0.770 0.780  -  0.056 0.089 0.100 0. 140 0.225 0.240 0.313 0.345 0.375  kDEA = 0.0026 hr-1  TABLE B.12 RUN 12 : 30WT% DEA, 90C, 4137 kPa (600 p s i ) SAMPLE hr 0.00 100.00 160.00 300.00 441.00 511.00 631.00 700.00  DEA  CONC. MOLES/CC X10-3 BHEP HEOD  3.530 3.500 3.420 3.455 3.403 3.361 3.310 3.280  kDEA = 0.000142 hr-1  —  — 0.050 0.090 0.155 0.191 0.216 0.250 0.290  C02  THEED _  --  -  0.014 0.048 0.060  TABLE B.13 RUN 13 : 100WT% DEA, 205C, 4137 kPa (600 p s i ) SAMPLE hr  DEA  0.00 1 .08 2.67 3.92 4.92 6.00 7.00 7.93  10.00 8.00 6.41 4.60 3.71 2.84 2.56 2.12  CONC. MOLES/CC X10-3 BHEP HEOD —  0.069 0. 172 0.282 0.370 0.524 0.643 0.754  _  0.255 0.275 0.263 0.250 0.245 0.247 0.225  C02  THEED —  3.200 3.860 4.070 3.645 3.540 2.650 1 .958  kDEA = 0.195 hr-1  TABLE B.14 RUN 14 : 80WT% DEA SAMPLE hr 0.00 0.78 2.00 3.00 4.00 5.00 6.00 6.95 8.58  DEA 7.80 5.98 4.62 3.31 2.20 1 .93 1 .48 1 .34 1 .09  kDEA = 0.277 hr-1  , 205C, 4137 kPa (600 p s i ) CONC. MOLES/CC X10-3 BHEP HEOD  -  0.0224 0.0960 0.2220 0.3260 0.4980 0.6560 0.8200 0.8700  — 0. 190 0.265 0.275 0.248 0.263 0.240 0.250 0.235  C02  THEED  -  1 .525 2.535 3.070 3.000 2.725 2.340 1 .980 1 .258  TABLE B.15 RUN 15 : 60WT% DEA, 205C, 4137 kPa (600 p s i ) C02 SAMPLE hr 0.00 1.00 1 .87 3.00 4.00 5.05 6.08 6.92 8.00  DEA 6.18 4.18 3.42 2.68 1 .80 1 .36 1.15 1 .06 0.95  CONC. MOLES/CC X10-3 BHEP HEOD  — 0.0425 0.0800 0.1710 0.2560 0.3580 0.4490 0.5620 0.6370  _  0.195 0.225 0.240 0.225 0.222 0.205 0.210 0.200  THEED  _ 1 .500 1 .950 2.030 1 .834 1 .560 1 . 168 1 . 169 0.954  kDEA = 0.314 hr-1  TABLE B.16 RUN 16 : 40WT% DEA, 205C, 4137 kPa (600 p s i ) C02 SAMPLE hr 0.00 1 .00 2.08 4.00 5.00 6.08 7.17 8.08  DEA 4.000 2.800 2.000 1.410 1 . 180 1 .000 0.921 0.804  kDEA = 0.320 hr-1  CONC. MOLES/CC XI0-3 BHEP HEOD —  0.0100 0.0720 0.2090 0.2900 0.3850 0.4860 0.5400  _  0. 170 0.210 0.228 0.225 0.225 0.220 0.220  THEED  _ 0.720 1 .230 1 .268 1 .093 0.946 0.760 0.718  TABLE B.17 RUN 17 : 20WT% DEA, 205C, 4137 kPa (600 p s i ) C02 SAMPLE hr 0.00 1 .00 2.00 3.00 4.00 5.00 6.00 7.00 8.00  DEA 2.050 1 .680 1 .280 1 .050 0.858 0.770 0.658 0.588 0.538  kDEA = 0.241  CONC. MOLES/CC X10-3 BHEP HEOD  _ 0.0050 0.0363 0.0621 0.1140 0.1500 0.1780 0.2150 0.2400  THEED  _  0.153 0. 176 0. 186 0. 1 93 0. 175 0. 175 0. 176 0.181  -  0.060 0.252 0.326 0.350 0.291 0.278 0.265  hr-1  TABLE B.18 RUN 18 : 15WT% DEA, 205C, 4137 kPa (600 p s i ) C02 SAMPLE hr 0.00 0.50 1 .00 2.00 3.00 4.00 5.50 6.25 7.56  DEA 1 .500 1 .333 1.212 1.161 0.984 0.810 0.735 0.650 0.615  kDEA = 0.131  hr-1  CONC. MOLES/CC XI0-3 BHEP HEOD  —  -  0.0025 0.0108 0.0280 0.0480 0.0845 0.1130 0.1280  THEED  _  0.045 0.065 0. 105 0.125 0.151 0. 152 0. 150 0.113  -  0.018 0.043 0. 186 0.242 0.272 0.261 0.229  TABLE B.19 RUN 19 : 10WT% DEA, 205C, 4137 kPa (600 p s i ) C02 SAMPLE hr  DEA  0.00 1 .00 2.00 3.00 4.00 5.00 6.00 7.00 8.00  0.935 0.820 0.735 0.643 0.575 0.540 0.448 0.387 0.358  CONC. MOLES/CC X10-3 BHEP HEOD  —  -  0.0080 0.0145 0.0250 0.0495 0.0650 0.0793 0.0838  THEED  _  0.073 0.125 0.140 0. 153 0. 169 0. 163 0. 130 0.115  -  0.009 0.021 0.031 0.040 0.046 0.046  kDEA = 0.104 h r - 1  TABLE B.20 RUN 2 0 : 5 WT% DEA, 205C, 4137 kPa (600 p s i ) C02 SAMPLE hr 0.00 0.66 1 .75 2.75 4.08 5.08 6.08 7.08 8.00  DEA 0.520 0.470 0.440 0.406 0.371 0.334 0.311 , 0.300 0.260  kDEA = 0.098 h r - 1  CONC. MOLES/CC X10-3 BHEP HEOD  0.0025 0.0049 0.0105 0.0190 0.0228 0.0300  —  0.020 0.035 0.048 0.050 0.061 0.074 0.063 0.055  THEED _  0.015 0.028 0.044 0.068 0.063 0.062  TABLE B:21 RUN 21 : 100WT% DEA, SAMPLE hr 0.0 1.0 3.0 4.0 5.0 6.5 8.0  DEA 10.00 9.0 7.10 6.90 6.30 5.50 4.80  175C, 4137 kPa (600 p s i ) C02  CONC. MOLES/CC X10-3 BHEP HEOD THEED —  0.020 0.092 0.130 0. 174 0.272 0.334  _  0.315 0.445 0.435 0.415 0.416 0.403  _  0.810 2.545 2.960 3.410 3.050 2.550  kDEA = 0.092 hr-1  TABLE B.22 RUN 22 : 60WT% DEA, SAMPLE hr 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0  DEA 6.00 5.35 4.81 4.25 3.74 3.38 3.21 2.65 2.25  kDEA = 0.118 hr-1  175C, 4137. kPa (600 p s i ) C02 CONC. MOLES/CC X10-3 BHEP HEOD THEED  0.035 0.065 0.092 0.115 0.180 0.206 0.250  —  0. 190 0.360 0.450 0.450 0.450 0.420 0.431 0.398  _  0.300 0.940 1 .400 1 .660 1 .840 1 .914 1 .980 2.046  CSl CN  CM  O  .—  x E-«  •rH Ul  O  ro Cu M  U CJ \ LO  *—  ro  i— K  a  o  in r-  ' - T - C N C N C N C N C N C N  w  X  O O O O O O O O  «  •W  a X  z n o u  W PQ  <*o *t  <o  o  o  o  o  o  «-  o  o  o  o  o  o  CM ro i n r - cn o  CM  Z  CO  u U  K  O  t o o t o c o c o « - o — CMinr-cn^rovor^O O O O " — >—  P  O  u  1o  X  \  o o o o o o o  I  i  i  cN«-toinm**inroto ocotoincocN — o c n  Q  u J  o X  in  U in  u X z PQ o u  u  < w  rC  CM  to ro o co cn co CN CM i n o o o o o o  o  OH  •u  < a  i  1  —  o o o o o  o  —  CN r CO CN CO — in » j f n m c M r - - o o o  Q  O CM  ro  O O O O O O  to  Q  CM •  1  o*—  ro  o  dp  O «—«—«—•— CN CN  1  CO  to  OH  w  w  ro  o o  o o o o o o o o or--«-inintor^cn  X  *•  U X  EH  ro I  o to  o o o o CM in o in o CM r- CM in  Q U  CJ  o o o o o o o o  OD  a  o  r  EE  O  CM O  o o o o o o o m i n m CM » f o o> ^-CMro^inininvo  Q  in  CM  w OH »H  2 rC < to  o  o  o  o  o  o  o  o  o  — cNro**mvor-co  PQ  o  CO  a  w CM  J a , iH  o  z  <  o r-cNm*invocoo  m < D E-  2 xs, to  o o o o o o o o  TABLE B.25 RUN 25 : 10WT% DEA, 175C, 4137 k P a ( 6 0 0 p s i ) C02 SAMPLE hr  DEA  0.0 2.0 4.0 6.0 8.0 10.0 15.0 20.0  1 .010 0.940 0.900 0.855 0.810 0.770 0.680 0.610  CONC. MOLES/CC X 1 0 - 3 BHEP HEOD  —  0.0080  0.0175 0.0400 0.0460  — 0.020 0.040 0.060 0.080 0.090 0. 100 0. 106  THEED _  0.048  0.068 0.060 0.100 0. 142  kDEA = 0.0242 h r - 1  TABLE B.26 RUN 26 : 60WT% DEA, 150C, 4137 kPa (600 p s i ) C02 SAMPLE hr  DEA  0.0 2.0 4.0 6.0 8.0 10.0 15.0 24.0  6.00 5.66 5.30 5.00 4.71 4.46 3.83 2.95  kDEA = 0.0297 h r - 1  CONC. MOLES/CC X 1 0 - 3 BHEP HEOD _  0.009  0.011 0.021 0.043 0.110  _  0.110 0.230 0.382 0.460 0.541 0.625 0.550  THEED  _ 0.210 0.400 0.650 0.850 1 .000 1 .380 1 .520  TABLE B.27 RUN 27 : 20WT% DEA, 150C, 4137 kPa (600 p s i ) C02 SAMPLE hr  DEA  0.0 5.0 10.0 15.0 20.0 30.0 40.0 60.0 71.5 80.0 97.5  2.16 1 .92 1 .72 1 .54 1 .39 1.12 0.89 0.65 0.61 0.55 0.53  CONC. MOLES/CC X10-3 BHEP HEOD  —  -  0.020 0.033 0.045 0.077 0.089 0.097 0. 100  — 0.100 0.210 0.330 0.390 0.440 0.470 0.520 0.425 0.440 0.410  THEED _  0.120 0.210 0.300 0.380 0.481 0.561 0.632 0.551 0.540 0.410  kDEA = 0.022 h r - 1  TABLE B.28 RUN 28 : 15WT% DEA, 150C, 4137 kPa (600 p s i ) C02 SAMPLE hr  DEA  0.0 5.0 10.0 15.0 20.0 30.0 40.0 50.0  1 .51 1 .45 1 .35 1 .29 1.21 1 .09 0.98 0.92  kDEA = 0.0104 h r - 1  CONC. MOLES/CC X10- 3 BHEP HEOD —  0.0040 0.0060 0.0150 0.0220 0.0311  _  0.040 0.082 0.120 0.151 0.215 0.221 0.225  THEED _  0.024 0.063 0.100 0. 132 0.181 0.238 0.275  TABLE B.29 RUN 29 : 10WT% DEA, 150C, 4137 kPa (600 p s i ) C02 SAMPLE hr  DEA  0.0 5.0 10.0 15.0 20.0 30.0 40.0 50.0  1 .000 0.978 0.946 0.921 0.896 0.848 0.803 0.715  CONC. MOLES/CC X10-3 BHEP HEOD  — -  0.004 0.008 0.012  — -  0.027 0.046 0.058 0.086 0.110 0. 125  THEED  -  -  0.055 0.085 0.092  kDEA = 0.0055 h r - 1  TABLE B.30 RUN 30 : 5WT% DEA, 150C, 4137 kPa (600 p s i ) C02 SAMPLE hr  DEA  0.0 5.0 10.0 15.0 20.0 30.0 40.0  0.520 0.500 0.488 0.482 0.471 0.440 0.413  kDEA = 0.00518 h r - 1  CONC. MOLES/CC X10-3 HEOD BHEP  0.0041 0.0053  -  -  0.0142 0.0200 0.0294 0.0421 0.0541  THEED  --  0.021 0.035 0.039  TABLE B.31 RUN 31 : 100WT% DEA, SAMPLE hr 0.00 19.67 43.70 67.70 91 .70 120.70 163.70 187.70 211.41 236.44  DEA 10.0 9.54 8.77 7.98 6.95 5.01 3.71 3.21 2.78 2.41  120C, 4137 kPa (600 p s i ) CONC. MOLES/CC X10-3 BHEP HEOD  0.0180 0.0425 0.0738 0.0975 0.1340 0.1610 0.1800  -  0.580 0.992 1 .063 1 .094 1.171 1 .170 1 . 164 1.171 1 .175  C02  THEED  1 . 160 2.610 3.050 3.351 3.548 3.544 3.320 3.030  kDEA = 0.003 hr-1  TABLE B.32 RUN 32 : 20WT% DEA, SAMPLE hr 0.0 20.0 40.0 60.0 80.0 100.0 140.0 160.0 180.0 200.0  DEA 2. 150 2.070 2.040 1 .930 1 .850 1 .710 1 .650 1 .538 1 .551 1.510  kDEA = 0.0022 h r - 1  120C, 4137 kPa (600 p s i ) CONC. MOLES/CC X10-3 BHEP HEOD  —  --  -  0.0018 0.0033 0.0043 0.0056 0.0066  — 0.060 0.150 0.210 0.275 0.330 0.430 0.450 0.470 0.460  C02  THEED  —  -  0.050 0.066 0. 104 0.121 0. 154 0. 170 0. 180 0.210  TABLE B.33 RUN 33 : 30WT% DEA, 205C, 4137 kPa ( 6 0 0 p s i ) C02 SAMPLE hr  DEA  0.0 1.0 2.0 3.0 4.0 5.0 6.0 8.0 10.0 13.0 24.0 27.0 31.0 51 .0  3.050 2.290 1.810 1 .370 0.940 0.760 0.710 0.600 0.490 0.410 0.203 0.200 0.1 36 0.075  CONC. MOLES/CC X10-3 BHEP HEOD  — 0.0375 0.0510 0.1060 0.1560 0.2320 0.2950 0.3710 0.4252 0.5250 0.6151 0.6500 0.7000 0.7150  _  0.150 0.210 0.210 0.190 0.200 0.200 0. 175 0. 150 0.150 0.100 0.121 0.125 0.115  THEED _  0.221 0.354 0.460 0.461 0.440 0.460 0.450 0.400 0.321 0. 1 54 0.110 0.091 0.008  kDEA = 0.3 h r - 1  TABLE B.34 RUN 34 : 30WT% DEA, 195C, 6895 k P a ( 1 0 0 0 p s i ) C02 SAMPLE hr 0.00 1 .00 4.00 5.25 5.93 6.83 8.00  DEA 3.02 2.38 1 .28 0.95 0.77 0.62 0.56  kDEA = 0.23 h r - 1  CONC. MOLES/CC X10-3 BHEP HEOD _  0.021 0.131 0.179 0.221 0.249 0.272  _  0.400 0.395 0.394 0.375 0.355 0.375  THEED _  0.205 0.850 0.780 0.780 0.750 0.654  TABLE B.35 RUN 35 : 30WT% DEA, SAMPLE hr 0.00 0.67 1 .67 2.67 3.67 4.67 5.67 7.17 8.00  DEA 3.00 2.71 2.05 1.71 1 .26 0.98 0.89 0.64 0.51  195C, 5156 kPa (800 p s i ) C02 CONC. MOLES/CC X10-3 HEOD BHEP  -  0.0275 0.0353 0.0800 0.1110 0.1710 0.2060 0.2660 0.2752  -  0.225 0.375 0.388 0.390 0.384 0.384 0.375 0.355  THEED  -  0. 150 0.450 0.668 0.881 0.849 0.765 0.651 0.575  kDEA = 0.23 h r - 1  TABLE B.36 RUN 36 : 30WT% DEA, SAMPLE hr 0.00 1 .00 1 .83 3.08 4.00 5.08 7.25 7.92  DEA 3.040 2.380 1 .950 1 .480 1 .205 0.907 0.689 0.638  kDEA = 0.23 h r - 1  195C, 4137 kPa (600 p s i ) C02 CONC. MOLES/CC X10-3 HEOD BHEP  0.015 0.031 0.080 0.126 0. 155 0.254 0.267  -  0.202 0.247 0.250 0.228 0.258 0.258 0.260  THEED  0.210 0.531 0.850 0.891 0.785 0.714 0.681  TABLE B.37 RUN 37 : 30WT% DEA, 195C, 3448 kPa ( 5 0 0 p s i ) C02 SAMPLE hr 0.0 1.0 2.0 4.0 5.0 6.0 7.0 8.8  DEA 3.000 2.438 2. 188 1 .630 1 .275 1 .000 0.935 0.775  CONC. MOLES/CC X10-3 HEOD BHEP  -  0.0055 0.0288 0.0865 0.1220 0.1560 0.2030 0.2420  -  0.128 0.198 0.190 0.208 0.200 0.215 0.202  THEED  -  0.076 0.250 0.560 0.609 0.660 0.786 0.761  kDEA = 0.185 hr-1  TABLE B.38 RUN 38 : 30WT% DEA, SAMPLE hr 0.00 0.92 2.00 3.00 4.08 5.08 6.00 7.08 8.17  DEA 3.030 2.610 2.380 1 .940 1 .780 1 .450 1 .220 1 .050 0.985  kDEA = 0.154 hr-1  195C, 2758 kPa (400 p s i ) C02 CONC. MOLES/CC X10-3 HEOD BHEP  0.0135 0.0475 0.0640 0.0840 0.1150 0.1560 0.1700  -  0.075 0.115 0.145 0. 138 0.165 0.155 0.145 0.148  THEED  -  0.074 0. 100 0.380 0.620 0.714 0.721 0.691 0.720  TABLE B.39 RUN 39 : 30WT% DEA, 195C, 2069 k P a ( 3 0 0 p s i ) C02 SAMPLE hr 0.00 1 .08 2.00 3.58 4.17 5.33 6. 17 8.00  DEA 3.13 2.75 2.48 2.24 1.91 1 .88 1 .69 1.41  CONC. MOLES/CC X10-3 BHEP HEOD  _ 0.0090 0.0323 0.0404 0.0617 0.0910 0.1060  _  0.045 0.081 0.088 0.082 0.099 0.088 0.098  THEED _  0.051 0.247 0.384 0.545 0.650 0.785  kDEA = 0.098 h r - 1  TABLE B.40 RUN 40 : 30WT% DEA, 195C, 1517 kPa (220 p s i ) C02 SAMPLE hr 0.00 1 .00 2.09 3.00 4.25 6.23 8.00  DEA 3.10 2.94 2.73 2.55 2.45 2.25 1 .96  kDEA = 0.061 h r - 1  CONC. MOLES/CC X10-3 BHEP HEOD _  0.0030 0.0080 0.0138 0.0275 0.0374 0.0428  THEED  _  0.020 0.041 0.053 0.054 0.053 0.025  0.021 0.043 0. 145 0.265 0.451 0.498  TABLE B.41 RUN 41 : 30WT% D E A , 2 0 5 C , 41*37 k P a pH a d j u s t e d t o 1 2 . 3 SAMPLE hr 0.00 0.75 1 .83 2.83 3.83 4.83 5.50 7.00 8.00 kDEA = 0 . 3 6 6  DEA 3.000 2.210 1 .500 1 .060 0.815 0.630 0.540 0.478 0.428  CONC. MOLES/CC X 1 0 - 3 BHEP HEOD  — 0.0425 0.1080 0.1610 0.2150 0.2640 0.3480 0.4020 0.4280  0.0 1.0 2.0 3.0 4.0 5.0 6.0 8.4 kDEA = 0 . 1 5 7  C02  THEED  — 0.180 0 . 164 0.171 0 . 158 0 . 138 0 . 125 0.078 0.071  0.248 0.650 0.750 0.630 0.710 0.680 0.650 0.640  hr-1  TABLE B . 4 2 RUN 42 : 30WT% D E A , 2 0 5 C , 4 1 3 7 pH a d j u s t e d t o 1 0 . 0 SAMPLE hr  (600 p s i )  DEA 2.93 2.53 2.35 1 .78 1 .50 1.41 1.19 1 .02 hr-1  kPa  (600 p s i )  CONC. MOLES/CC X 1 0 - 3 BHEP HEOD  -  0.2411 0.3980  THEED  _  _ 0.0485 0.1040 0.1450 0.2020  C02  0 . 150 0 . 195 0.263 0.258 0.242 0.245 0 . 175  0 . 135 0.293 0.504 0.485  0.381 0.364 0.228  TABLE B.43. RUN 43 : 30WT% DEA, 205C, 4137 kPa (600 p s i ) C02 pH a d j u s t e d t o 9.0 SAMPLE hr 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0  CONC. MOLES/CC X10-3 BHEP HEOD  DEA 3.02 2.78 2.70 2.68 2.21 2.16 2.04 1 .92  _  -  0.0125 0.0425 0.0925 0. 1300 0.1950 0.2150  _ 0. 160 0.204 0.284 0.280 0.284 0.288 0.304  THEED  _ 0.094 0.193 0.261 0.340 0.300 0.280 0.225  kDEA = 0.0675 hr-1  TABLE  B.44  RUN 44 : 30 WT%DEA, 205C, 4137 kPa (600 p s i ) N2 0.14 g/cc K2C03 No degradation  took p l a c e .  TABLE B.4 5 RUN 45 : 30WT% DEA, 205C, 4137 kPa (600 p s i ) N2 0.1227 g/cc of KHC03 SAMPLE hr  DEA  0.0 2.0 4.0 6.0 8.0 10.0 12.0 24.0 28.0 31.0  3.10 2.50 2.02 1.61 1 .35 1 .05 0.86 0.55 0.47 0.44  kDEA = 0.109 hr-1  CONC. MOLES/CC X10-3 BHEP HEOD  -  -  0.0413 0.0750 0.1350 0.1560 0.2010 0.3860 0.4240 0.4322  0.062 0.075 0.075 0.065 0.045 0.025  -  THEED  — 0.550 0.806 0.910 0.922 0.910 0.840 0.571 0.502 0.446  237  TABLE B.46 RUN 46 : 30WT% DEA, 175C, 4137 kPa (600 p s i ) N2 0. 1 334 g/cc of KHC03 SAMPLE hr 0.0  1.0  2.0 3.4 7.0 13.0 24.0  CONC. MOLES/CC X10- 3 BHEP HEOD  DEA 3. 12 3.00 2.88 2.76 2.48  2.18  1  .46  0.0035 0.0075 0.0148 0.0650  — 0.018 0.031 0.036 0.040 0.037 0.036  THEED _  0.012 0.048 0.156 0.350 0.550 0.810  kDEA = 0. 0245 hr-1  'ABLE B.47 RUN 47 : 30WT% DEA, 150C, 4137 kPa (600 p s i ) N2 0.218 g/cc of KHC03 SAMPLE hr  DEA  0.0 6.0 24.0 32.8 47.0  3.10 2.98 2.80 2.61 2.38  CONC. MOLES/CC XI 0- 3 BHEP HEOD -  0.0028  0.0073  — 0.0123 0.0231 0.0250 0.0250  THEED _  0.030 0.246 0.261 0.440  kDEA = 0.0054 hr-1  TABLE B.48 RUN 48 : 66.7WT% DEA i n MDEA, 205C, 4137 kPa (600 p s i ) C02 SAMPLE hr 0.00 1 .00 2.00 4.33 5.00 7.37 8.75  DEA  CONC. MOLES/CC X10-3 BHEP HEOD  6.67 5.80 5.20 3.10 2.79 1 .86 1 .42  kDEA = 0.1733 hr-1  0.010 0.028 0.114 0.143 0.268 0.296  — 0. 130 0.175 0.218 0.230 0.213 0.210  THEED  — 0.410 1 .000 2.060 2.180 2.100 1.910  238  TABLE B.49 RUN 49 : 40WT% DEA i n MDEA, 205C, 4137 kPa (600 p s i ) C02 SAMPLE hr 0.0 1.0 3.0 4.0 5. 1 6. 1 8.0  DEA 3.92 3.26 2.34 2.03 1 .58 1.41 1 .00  CONC. MOLES/CC X10-3 BHEP HEOD  -  0.0175 0.0398 0.0605 0.0825 0.1390  _  0.100 0. 175 0.201 0.214 0.216 0.210  THEED _  0.302 0.880 1.210 1.418 1 .510 1 .290  kDEA = 0.169 h r - 1  TABLE B.50 RUN 50 : 30WT% DEA i n MDEA, 205C, 4137 kPa (600 p s i ) SAMPLE hr 0.00 1 .00 2.00 3.00 4. 10 5.00 6.16 7.16 7.84  DEA 3.10 2.80 2.34 2.20 1.71 1 .62 1 .28 1 .09 1 .03  kDEA = 0.145 h r - 1  CONC. MOLES/CC X10-3 BHEP HEOD —  0.0125 0.0215 0.0363 0.0563 0.0704  —  0.070 0. 125 0.141 0. 178 0.188 0.202 0.208 0.200  THEED _  0.036 0.151 0.212 0.460 0.571 0.684 0.775 0.860  C02  239  TABLE B.51 RUN 51 : 30 WT% DEA i n MDEA, 175C, 4137 kPa (600 p s i ) C02 SAMPLE hr 0.0 2.0 4.0 6.0 8.0  DEA  CONC. MOLES/CC X10-3 BHEP HEOD —  3.000 2.580 2.214 1.911 1.614  0.0263 0.0514  THEED  _  0.091 0.201 0.271 0.304  _  0. 100 0.210 0.490 0.580  kDEA = 0.076 hr-1  TABLE B.52 RUN 52 : 30WT% DEA i n MDEA, 150C, 4137 kPa (600 p s i ) C02 SAMPLE hr  DEA  0.0 5.0 27.3 51.5  '3.09 2.82 1 .96 1 .32  CONC. MOLES/CC X10-3 BHEP HEOD  THEED  _  0.0213  0.040 0. 125 0.238  -  0. 1 46 0.520  kDEA = 0.0204 hr-1  TABLE B.53 RUN 53 : 30WT% DEA i n MDEA, 205C, 4137 kPa (600 p s i ) N2 No d e g r a d a t i o n of 8 h r .  took p l a c e over a p e r i o d  TABLE B.54 RUN 54 : 30WT% DEA, 205C, 4137 k P a ( 6 0 0 p s i ) N2 SAMPLE hr 0.00 7.50 24.00 31 .50 48.00 74.50 96.00 105.55 130.05 155.00 168.50 179.00 199.04  DEA  CONC. MOLES/CC X I 0 - 3 BHEP HEOD  2.96 2.83 2.77 2.66 2.52 2.23 2.14 1 .95 1 .85 1 .66 1 .60 1 .56 1 .50  -  0.008 0.018 0.033 0.053 0.090 0.140 0. 167 0.220 0.247 0.283 0.305 0.345  —  -  THEED _  0.040 0.120 0.210 0.288 0.420 0.500 0.530 0.520 0.500 0.481 0.440 0.400  kDEA = 0.00365 h r - 1  TABLE B.55 RUN 55 : 30WT% DEA, 250C, 4137 k P a ( 6 0 0 p s i ) N2 SAMPLE hr  DEA  0.00 2.00 5.50 7.83 25.33  3.00 2.74 2.55 2.31 1 .31  kDEA = 0.058 h r - 1  CONC. MOLES/CC X10-3 BHEP HEOD  — 0.030 0.075 0. 122 0.492  —  —  THEED  — 0.020 0.113 0. 154 0.221  241  TABLE B.56 RUN 56 : 30WT% DEA, 205C, 8382 kPa (1200 p s i ) C02 SAMPLE hr  DEA  0.00 1 .00 3.17 4.00 5.25 6.00 7.00 8.50  3.00 2.16 1 .08 0.79 0.53 0.41 0.31 0.23  CONC. MOLES/CC X10-3 BHEP HEOD  — 0.0198 0.1600 0.2060 0.3252 0.3440 0.4080 0.4963  _  0.201 0.280 0.261 0.275 0.280 0.228 0.223  THEED _  0.530 0.604 0.531 0.441 0.380 0.330 0.275  kDEA = 0.328 hr-1  TABLE B.57 RUN  56 : 5X10-4 MOLES/CC BHEP, 205C, 4137 kPa (600 p s i ) C02 No d e g r a d a t i o n o b s e r v e d  over a p e r i o d  of 8 hr .  TABLE B.58 RUN 58 : 30WT% DEA + 5X10-4 MOLES/CC BHEP, 205C, 4137 kPa (600 p s i ) N2 No d e g r a d a t i o n o b s e r v e d  over a p e r i o d  of 8 h r .  242  TABLE B.59 RUN 59 : 30WT% DEA + DEGRADATION PRODUCTS, 205C, 4137 kPa (600 p s i ) C02 SAMPLE hr 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0  DEA 3.08 2.34 1 .88 1 .55 1 .38 1.12 0.95 0.86 0.75  CONC. MOLES/CC XI0-3 BHEP HEOD 0.355 0.386 0.518 0.535 0.645 0.754 0.780 0.801 0.836  0.275 0.283 0.315 0.301 0.273 0.272 0.253 0.263 0.235  THEED 0.330 0.810 1 . 160 1.131 0.861 0.856 0.801 0.850 0.605  kDEA = 0.26 hr-1  TABLE B.60 RUN 60 : 30WT% DEA + 5X10-4 MOLES/CC BHEP , 205C, (600 p s i ) C02 SAMPLE hr  DEA  0.0 0-.7 2.5 3.2 4.0 6.0 9.0 22.5 26.0 29.6 49.0  3.050 2.520 1 .762 1 .580 1 .350 1 .000 0.790 0.363 0.265 0.205 0.141  kDEA = 0.219 hr-1  CONC. MOLES/CC XI0-3 BHEP HEOD 0.466 0.481 0.576 0.607 0.654 0.721 0.794 0.953 1 .048 1 .054 1.171  -  0.238 0.252 0.253 0.233 0.225 0.21 1 0. 134 0.143 0.108 0.084  THEED  — 0.131 0.531 0.551 0.652 0.509 0.400 0.202 0.051 0.010 —  243  TABLE B.61 RUN 61 : 30WT% D E A + 5 X 1 0 - 4 M O L E S / C C (600 p s i ) C02 SAMPLE hr  DEA  0.0 10.0 25.0 40.0 60.0  3.000 2.230 1 .301 0.881 0.572  kDEA = 0 . 0 3 0 1  BHEP,  CONC. MOLES/CC X 1 0 - 3 BHEP HEOD 0.466 0.501 0.523 0.556 0.584  150C, 4137 kPa  THEED  _ 0.368 0.541 0.560 0.534  0.171 0.754 1 .042 1 .021  hr-1  TABLE B . 6 2 RUN 62 : 3 X 1 0 - 3 M O L E S / C C HEOD,  205C,  4137 k P a  (600 p s i )  A f t e r 1 hr the a n a l y s i s showed the p r e s e n c e HEOD,DEA,THEED, and a t r a c e of BHEP.  TABLE B . 6 3 RUN 63 : 10WT% D E A + 0 . 4 2 5 X 1 0 - 3 M O L E S / C C H E O D , ( 6 0 0 p s i ) N2 SAMPLE hr 0.0 2.0 5.0 8.0  DEA 1 .040 1 .000 0.938 0.825  CONC. MOLES/CC X 1 0 - 3 BHEP HEOD  0.0113 0.0235 0.0275  0.425 0 . 178 0.083 0.040  THEED  0.091 0 . 187 0.238  205C,  N2  of  4137 k P a  244  TABLE B.64 RUN 64 : 15WT% DEA + DEGRADATION (600 p s i ) C 0 2 , SAMPLE hr 0.00 1 .00 2.23 3.00 5.00 6.23 7.00 8.00  DEA 1.42 1 .44 1.31  1.19  1.10 1 .04 1 .00 0.97  CONC. MOLES/CC X10-3 BHEP HEOD 0.0275 0.0463 0.0701 0.0825 0.. 1 1 60 0.1400 0.1580 0. 1740  TABLE B.65 RUN 65 : 15WT% DEA + DEGRADATION (600 p s i ) N2 SAMPLE hr 0.00 1 .00 1 .57 3.00 4.00 5.00 6.12 7.00 8.42  DEA 1 .52 1 .50 1 .46 1 .43 1 .32 1 .29 1 .24 1 .20 1.18  PRODUCTS,  THEED  0.398 0.413 0.435 0.434 0.450 0.442 0.444 0.448  0.970 1.011 1.118 1 . 150 1.181 1.171 1 .063 0.984  PRODUCTS,  175C, 4137 kPa  CONC. MOLES/CC X10-3 BHEP HEOD 0.0275 0.0428 0.0450 0.0664 0.0780 0.0963 0.1130 0.131 1 0.1580  175C, 4137 kPa  0.398 0.285 0.253 0.235 0.201 0.193 0.180 0.188 0.191  THEED 0.970 1 .041 1.101 1 . 160 1 .202 1 .225 1 .250 1 .244 1 .252  245  TABLE B.66 RUN 66 : 2.6X10-3 MOLES/CC  THEED, 205C, 4137 kPa (600 p s i ) C02  A f t e r 1 hr the only product (-0.6X10.3 m o l e s / c c ) .  TABLE B.67 RUN 67 : 2.6X10-3 MOLES/CC  produced  was BHEP  THEED, 205C, 4137 kPa (600 p s i ) N2  A f t e r 1 h r a t r a c e amount o f BHEP was (-0.12X10-3 m o l e s / c c ) .  TABLE B.68 RUN 68 : 12WT% DEA + 2.6X10-3 MOLES/CC (600 p s i ) N2 SAMPLE hr 0.00 1 .00 2.67 4.00 5.75 8.33  DEA 1 .210 1 .200 1 .204 1.212 1 .208 1.211  THEED, 205C, 4137 kPa  CONC. MOLES/CC X10-3 BHEP HEOD  -  0.210 0.440 0.565 0.670 0.861  -  produced  THEED 2.580 2.450 2. 160 2.080 1 .860 1 .630  246  TABLE B.69 RUN 65 : 12WT% DEA + 2.6X10-3 MOLES/CC THEED, 205C, 4137 kPa (600 p s i ) C02 SAMPLE hr 0.00 1 .00 2.00 3.75 6.33 7.67  DEA 1 . 180 1.151 1.111 1 .068 0.971 0.875  CONC. MOLES/CC X10-3 BHEP HEOD  0.371 0.673 1.018 1 .260 1 .450  _  0.285 0.330 0.233 0. 185 0.203  THEED 2.580 2.021 1 .560 1 .061 0.860 0.731  TABLE B.70 RUN 70 : 30WT% MEA, 205C, 4137 kPa (600 p s i ) C02 SAMPLE hr 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0  MEA 5.490 4.689 4.115 3.689 3.230 2.670 2.246 2.082 1 .705  CONC. MOLES/CC X10-3 HEI* HEED*  -80.6 441 .6 556. 1 698.8 850.4 1028.0 1283.0 1233.0  * C o n c . a s peak a r e a T r a c e amounts o f o z d d e t e c t e d  _  1 .3 10.5 12.5 37.7 40.5 44.8 83.8 110.4  247  TABLE B.71 RUN 71 : 30WT% TEA, 205C, 4137 kPa (600 p s i ) C02 No d e g r a d a t i o n of 8 h r .  observed  over  a period  TABLE B.72 RUN 72 : 10WT% MEA + 25WT% DEA, 205C, 4137 kPa(600 p s i ) C02 SAMPLE hr  MEA  0.0 0.5 1.0 2.3 3.0 4.0 5.0 6.0 7.0 23.5  1 .639 1 .540 1.210 0.967 0.803 0.672 0.541 0.451 0.410 0.230  hr 0.0 0.5 1.0 2.3 3.0 4.0 5.0 6.0 7.0 23.5  DEA  HEP*  -3.3 37.2 40.0 51.5 63.0 64.9 89.0  *Conc. a s peak  area  CONC . MOLES/CC X10-3 BHEP HEOD  2.540 2.520 2.050 1 .700 1 .480 1 .200 1 .060 0.841 . 0.800 0.530  BHEEP*  -  104.7 355.0 497.3 656.2 617.1 580.9 502.3 487.3 282.7  0.015  —  0.043 0.1 36 0.202 0.281 0.318 0.374 0.389  0.063 0.101 0.124 0. 145 0. 125 0. 125 0. 120 0. 120 0.095  HEI*  BHEI *  —  _  -49.0  -21.0  72.7 91.0 127.0 120.0 129.0 193.6  141.0 182.0 108.0 137.0 164.4 192.0  THEED _  -  0.108 0.203 0.400 0.400 0.401 0.379 0.362 0. 188  248  TABLE B.73 RUN 73 : 1 0WT% TEA + 20WT% DEA, 205C, 4137 kPa(600 p s i ) C02 SAMPLE hr 0.0 2.0 4.0 6.0 8.0  TEA 0.671 0.670 0.662 0.654 0.649  DEA 2.00 1 .08 0.84 0.47 0.41  * C o n c . a s peak a r e a  CONC. MOLES/CC X10 -3 BHEP HEOD THEED  — --  0.113 0.250 0.282  TEHEED*  _  0.133 0. 135 0. 134 0.131  0.230 0.510 0.433 0.301  10.0 21 . 1 35.0 51 .4  249 APPENDIX C The s o l u b i l i t y of C0  2  in DEA solutions at high temperature  and pressure  Some knowledge of the s o l u b i l i t y of C0 under operating conditions was 2  required i n order to carry out the ionic experiments  in section 9.2.  Unfortunately the open l i t e r a t u r e did not provide the required information. Therefore, a series of simple s o l u b i l i t y experiments were performed to provide the necessary data. C.1  Experimental method E s s e n t i a l l y the method consisted of:  1.  F i l l i n g a 2 L high pressure bomb to 5156 kPa (800psi) with C0 and 2  then weighing the bomb and C0 . 2  The scales were accurate for changes  of down to 0.2 g. 2.  The 600 ml autoclave (see sect. 6.1) was charged with 450 ml of a  specified aqueous DEA solution and sealed. to the required temperature  The autoclave was then heated  with the s t i r r e r in operation at about 150  r.p.m. 3.  The bomb was then connected to the autoclave and C0 was fed into 2  the autoclave to the required pressure.  After equilibrium had been  reached the bomb was disconnected. 4.  The bomb was then reweighed and the weight of C0 fed to the auto2  clave noted. 5.  The above procedure was repeated many times to cover the following  range of conditions: a)  DEA concentration:-  b)  Temperature:-  c)  Overall pressure:  30, 20, and 10 wt %  205-100°C 413.7-4137 kPa (60-600 psi)  It should be noted that o v e r a l l pressure i n the autoclave was made up  250 from the p a r t i a l pressure of C0  2  and the vapour pressure of the water  vapour from the aqueous DEA solution and to a very small extent from the DEA i t s e l f .  For example at 205°C the vapour pressure of pure water  i s 1700 kPa (246.6 psi) and the vapour pressure of DEA i s 8.6 kPa (1.25 psi).  Therefore to determine  the p a r t i a l pressure of C0  i n the auto-  2  clave a knowledge of the vapour pressure of the aqueous DEA solution was required.  To determine  experiments were performed. to the autoclave.  A specified concentration of DEA was charged  The autoclave was heated to a specified  and the pressure noted. noted again.  the vapour pressure the following simple  The temperature  temperature  was then raised and the pressure  This was repeated up to 205°C.  Table C . l gives the results  which are plotted i n Figure C . l .  Table C . l Vapour pressure of DEA solutions as a function of temperature  0  DEA cone 10 kPa  Vapour pressure p s i wt % 30 20 psi kPa psi  Temp. °C  psi  kPa  psi  100  14.69  101 .3  14.69  101. 3  14.69  101 .3  14.69  101 .3  120  29.40  202 .7  28.69  197. 8  27.0  186 .2  24.43  168 .4  140  54.96  379 .0  52.57  362. 5  49.1  338 .5  43.57  300 .4  160  92.50  637 .8  88.14  607. 7  82.29  567 .4  71.93  496 .0  180  148.96  1027 .1  142.86  985.  133.29  919 .0  121.43  837 .3  200  227.50  1568 .6  221.29  1525. 8  214.29  1477 .5  196.14  1352 .4  210  285.9  1971 .3  273.43  1885. 3  259.71  1790 .7  243.29  1677 .5  kPa  251  TEMPERATURE (°C) Figure C . l  DEA solution vapour pressure as a function of temperature and DEA concentration  252 C.2  Calculation of CO,  solubility  From the knowledge of the total weight of C0  2  used, total pressure  in reactor, vapour pressure of aqueous DEA solution, temperature and concentration of DEA, the s o l u b i l i t y of C0  2  was calculated as g of  C0 /g of DEA using the following method. 2  The main problem was to determine the mass of C0 phase.  in the vapour  2  It was f i r s t assumed the mixture of C0 , water vapour, and DEA 2  vapour was ideal and the p a r t i a l pressure of each component was proportional to i t s molar concentration. pressure of C0  2  Therefore to determine the p a r t i a l  in the vapour phase the vapour pressure of the aqueous  DEA solution was simply subtracted from the total pressure, i . e . , PP  r - r ,  C0  = P 2  total  -V.P.  DEA solution  1  fC.ll J  Knowing the p a r t i a l pressure of C0 , the volume of the vapour phase  (i.e.,  2  600-450 ml = 150 ml) and the temperature; the number of moles of C0 could be calculated using an equation of state.  Since for the range  of conditions studied the compressibility factor for C0 0.99-0.92 i t could be assumed C0  2  2  2  lay in the range  existed as an ideal gas.  j^  ie  y  ^  a n  e r  Waals equation of state was used to calculate the number of moles. (P +  (V-nb) = nRT  [C.2]  Although there are more accurate equations of state available, the Van der Waals r e l a t i o n yet  i s s t i l l useful for providing an approximate  simple, a n a l y t i c a l representation of the behaviour of a gas. Once the number of moles of C0  mined the mass of C0  2  2  in the vapour phase had been deter-  in the DEA solution could simply be obtained by  subtracting the vapour phase mass of C0 to the autoclave, i . e . ,  2  from the t o t a l mass of C0  2  fed  253 Mass of C0 dissolved i n DEA solution = t o t a l mass of C0 fed to autoclave 2  2  - mass of C0 From the mass of C0 •of C0 C.3  2  2  i n vapour phase  [C.3]  dissolved i n the aqueous DEA solution the s o l u b i l i t y  as g C0 /g DEA could be e a s i l y calculated.  2  2  Example The following shows how the s o l u b i l i t y of C0  2  i n a 30 wt % DEA  solution at 205°C under a total pressure of 4137 kPa (600 psi) was c a l culated . Total weight of C0  2  fed to autoclave = 31.5 g  Volume of Reactor = 625 cc Volume of Solution = 410 cc Volume of C0  2  = 215 cc  Density of 30 wt % DEA = 1.088 Wt of DEA in solution = 133.9 g a)  At 205°C the vapour pressure of 30 wt % DEA = 1510 kPa (219 psi) the p a r t i a l pressure of C0  in the vapour phase  2  = 4137 - 1510 = 2627 kPa (381 psi) b)  2627 kPa (381 psi) of C0  2  at 205°C i n a volume of 215 cc corresponds  to a mass of n moles using Eqn. C.2. P = 2627 kPa (381 p s i ) = 25.94 atm V  = 0.215 L  T = 205°C  = 478°K  R  = 0.082055 L atm/°K mole  For C0 :2  a  = 3.59 L  b  = 0.0427 L/mole  2  atm/mole  2  254 Eqn.  C.2 becomes (25.94 + "p I'^y)  (0.215 - n(0.0427))  = n x 0.082055 * 478 n = 0.151 moles = 6.47 g c)  The mass of C0 31.5  d)  2  dissolved i n the DEA solution i s : - 6.47 = 25.03 g  Therefore the s o l u b i l i t y of C0 i s : 2  = 0.187 g C0 /g DEA 2  It i s r e a l i z e d that the c a l c u l a t i o n of the mass of C0 phase may be somewhat inaccurate. mass of C0 solved C0  2  2  i n the vapour  However, when i t i s noted that the  in the vapour phase i s usually less than 30% of the C0  2  dis-  in the l i q u i d phase then errors of about ± 24% i n the vapour phase  mass w i l l only cause an error of about ± 10% in the calculation of  solubility. C.4  2  An accuracy of ± 10% i s considered  suitable f o r these studies.  Results The following tables give the s o l u b i l i t y of C0  2  in DEA solutions  at varying temperature and t o t a l pressure as a function of C0 pressure i n the vapour phase. ize these tabulated r e s u l t s .  2  partial  Figures 9.2 to 9.4 i n section 9.2 summar-  TABLE C.2 SOLUBILITY OF C02 IN 30WT% DEA TEMP.  TOTAL PRESSURE  C  psi  200  550.0 405.0 275.0 470.0 350.0 236.0 400.0 295.0 196.0 520.0 338.0 245.0 160.0 452.0 290.0 195.0 132.0 600.0 360.0 250.0 1 52.0 1 05.0 508.0 291 .0 220.0 118.0 83.0 445.0 240.0 177.0 90.0 65.0 555.0 410.0 200.0 140.0 68.0 45.5 510.0 390.0 170.0 119.0 53.0 32.6 475.0 355.0 150.0 89.0 40.0 24.0  n  190 n  ??  180 it it  170 n  it it  160 it it  n  150 n n  n n  1 40 « it  n it  130 n n n n  120 n  it  n •t  n  110 •t it it it  n  100 It  It It It It  kPa 3793.3 2792.5 1896.1 3240.7 2413.3 1627.2 2758.0 2034.0 1351.4 3585.4 2330.5 1689.3 1 103.2 3136.5 2000.0 1334.5 910.1 4137.0 2482.2 1723.8 1048.0 723.9 3502.7 2006.4 1516.9 813.6 572.3 3068.3 1654.8 1220.4 620.6 448.2 3826.7 2826.9 1379.0 965.3 468.9 313.7 3516.5 2689.1 1 172.2 820.5 365.4 224.8 3275.1 2447.7 1034.3 613.7 275.8 165.5  PARTIAL PRESSURE OF C02 psi kPa 400.7 208.7 78.7 375.3 194.3 80.3 350.6 173.6 74.6 427. 1 310.1 1 52. 1 67. 1 379.7 250.7 122.7 59.7 543.4 301 .4 193.4 95.4 48.4 464.6 247.6 176.6 74.6 39.6 412.7 207.7 145.0 57.0 32.7 530.7 385.7 175.7 115.7 43.7 21.2 491 .4 371 .4 151 .4 100.4 34.4 14.0 461 .6 341 .6 136.6 75.6 26.6 10.6  2762.9 1439.0 542.6 2587.7 1340.0 553.7 2417.4 1197.0 514.4 2945.0 2138.2 1048.7 462.7 2618.0 1728.6 846.0 411.6 3746.7 2078.2 1333.5 657.8 333.7 3203.4 1707.2 1217.7 514.4 273.0 2845.6 1432.1 999.8 393.0 225.5 3659.2 2659.4 1210.1 797.8 301 .3 146.7 3388.2 2560.8 1043.9 692.3 237.2 96.5 3182.7 2355.3 941 .9 521 .3 183.4 73.1  SOLUBILITY OF C02 gC02/gDEA 0. 183 0.114 0.089 0.190 0.120 0.081 0.192 0. 123 0.090 0.236 0.202 0. 128 0.090 0.240 0.200 0. 132 0.094 0.312 0.240 0. 195 0. 1 37 0. 1 04 0.328 0.248 0.209 0.141 0. 106 0.330 0.249 0.210 0. 144 0.111  0.376 0.330 0.248 0.212 0. 147 0.111 0.381 0.344 0.256 0.215 0.149 0.108 0.392 0.355 0.264 0.217 0.149 0.108  TABLE C.3 SOLUBILITY OF C02 IN 20WT% DEA TEMP.  TOTAL PRESSURE  C  psi  200  560.0 405.0 307.0 503.0 342.0 246.0 436.0 286.0 214.0 552.0 378.0 238.0 180.0 489.0 314.0 190.0 140.0 600.0 426.0 256.0 150.0 108.0 525.0 364.0 217.0 115.0 82.0 469.0 301 .0 186.0 86.0 61.0 516.0 410.0 266.0 156.0 68.5 47.0 470.0 367.0 220.0 137.0 54.5 35.0 414.0 327.0 199.0 ,113.8 42.0 27.0  n  n  190 fi n  180 n  fi  170 n n  fi  160 fi fi  150 fi  ti  140 n  fi  130 n  fi fi n  120 n  n  110 ft  n  100 fl fl f» fl n  kPA 3861.2 2792.5 2116.8 3468.2 2358.1 1696.2 3006.2 1972.0 1475.5 3806.0 | 2606.3 1641.0 1241.1 3371.7 2165.0 1310.1 965.3 4137.0 2937.3 1765.1 1034.3 744.7 3619.9 2509.8 1496.2 792.9 565.4 3233.8 2075.4 1282.5 593.0 420.6 3557.8 2827.0 1834. 1 1075.6 472.3 324.1 3240.7 2530.5 1516.9 944.6 375.8 241 .3 2854.5 2254.7 1372.1 784.6 289.6 186.2  256  PARTIAL PRESSURE OF C02 psi kPa 353.3 198.3 100.3 338.2 183.2 87.2 305.0 1 55. 1 83. 1 450.5 276.5 136.5 78.5 410.0 235.0 111.0 61 .0 538.5 364.5 194.5 88.5 46.5 477.7 316.7 169.7 67.7 34.7 433.7 265.7 150.7 50.7 25.7 490.0 384.0 240.0 130.0 42.5 21.0 450.5 347.5 200.5 117.5 35.0 15.5 400.2 313.2 185.2 100.0 28.2 13.2  2436.0 1367.3 691 .6 2331.9 1263.2 601 .2 2103.0 1069.4 573.0 3106.2 1906.5 941 .2 541 .3 2827.0 1620.3 765.3 420.6 3713.0 2513.2 1341 .1 610.2 320.6 3293.7 2182.7 1156.3 466.8 239.3 2990.4 2521.5 1039.1 349.6 177.7 3378.6 2647.7 1654.2 896.4 293.0 144.8 3106.2 2396.0 1382.5 810.2 241 .3 106.9 2759.4 2159.5 1276.9 689.5 194.4 91 .0  SOLUBILITY OF CO 2 gC02/gDEA 0. 198 0. 152 0.112 0.200 0. 154 0.115 0.205 0.159 0. 123 0.255 0.211 0. 162 0. 129 0.270 0.226 0. 168 0. 142 0.315 0.280 0.236 0.183 0. 144 0.330 0.290 0.240 0. 177 0. 146 0.339 0.295 0.248 0. 183 0. 148 0.381 0.351 0.306 0.257 0.185 0. 150 0.391 0.357 0.315 0.270 0.190 0.153 0.404 0.365 0.318 0.275 0.197 0.156  TABLE C.4 S O L U B I L I T Y OF C02 I N 10WT% TEMP.  . TOTAL PRESSURE  C  psi  kPa  200  555.0 418.0 275.0 495.0 363.0 238.0 431 .0 310.0 198.0 555.0 380.0 262.0 163.0 482.0 332.0 218.0 130.0 600.0 416.0 281 .0  3826.7 2882.1 1896.0 3413.0 2502.9 1641.0 2971.7 2137.5 1365.2 3826.7 2620.1 1806.5 1123.9 3323.4 2289.1 1503.1 896.4 4137.0 2868.3 1937.5 1248.0 710.2 3675.0 2482.2 1599.6 1013.6 551 .6 3295.8 2151.2 1330.7 850.8 427.5 3902.6 2999.3 1834.1 1123.9 675.7 324.1 3516.5 2702.9 1558.3 937.7 558.5 262.0 3192.4 2434.0 1324.0 827.4 448.2 200.0  n n  190 it n  180 ti n  170 fi  160 n  ti n  1 50 ti n  « fi  140 fi  w n  II  130 n n n n  120 n n  fi n  110 n  It fi fi it  100 fl fl fl fl fl  181.0  103.0 533.0 360.0 232.0 147.0 80.0 478.0 312.0 193.0 123.4 62.0 566.0 435.0 266.0 163.0 98.0 47.0 510.0 392.0 226.0 136.0 81.0 38.0 463.0 353.0 192.0 120.0 65.0 29.0  257  DEA PARTIAL PRESSURE OF C02 psi kPa 337.9 200.9 70.9 321 .3 189.2 64.2 290.5 169.5 57.5 444.9 269.9 151.9 52.9 396.2 246.2 132.2 44.2 533.5 349.5 214.5 114.5 36.5 481 .9 295.9 180.9 95.9 28.9 439.6 273.6 154.6 85.0 23.6 538.3 407.3 238.3 135.3 70.3 19.3 489.6 371 .6 205.6 1 15.6 60.6 17.6 448.7 338.7 177.7 105.7 50.7 15.3  2329.8 1385.2 488.9 2214.7 1303.2 442.7 2003.0 1168.7 369.5 3067.6 1861.0 1047.4 364.7 2731.8 1697.5 91 1 .5 304.8 3678.5 2409.8 1479.0 789.5 251 .7 3322.7 2040.2 1247.3 661 .2 199.3 3031.0 1886.5 1066.0 586. 1 162.7 3711.6 2808.3 1645.1 932.9 484.7 133.1 3375.8 2562.2 1417.6 797.1 417.8 121.4 3093.8 2334.4 1255.2 728.8 349.6 105.5  SOLUBILITY OF CO 2 gC02/gDEA 0.279 0.246 0. 185 0.290 0.249 0.189 0.295 0.257 0.191 0.338 0.300 0.262 0. 193 0.352 0.316 0.270 0.196 0.423 0.376 0.334 0.279 0.200 0.464 0.396 0.349 0.287 0.200 0.482 0.408 0.355 0.292 0.205 0.558 0.510 0.430 0.370 0.300 0.200 0.580 0.530 0.435 0.376 0.303 0.207 0.598 0.540 0.450 0.382 0.305 0.208  258 APPENDIX D Derivation of the k i n e t i c model Using the s i m p l i f i e d degradation route developed in section 12.1, i.e.,  .  HEOD  THEED  BHEP  the following equations were derived for the rate of change of the various compounds. d  ° "  l  • -MDEA] - k [DEA]  ]  dIDEA] , . where  k  [D.l]  2  = k  D £ A  W  D  x  + k  =  k  l  l  E  A  ]  [ B  2 ]  [D.3]  2  D  _  E  A  [D.4]  l  dt d [ T  d [  " dt  £ E D ]  = k [DEA] - k [THEED] 2  ^ dt  H E P ]  [D.5]  3  = k [THEED]  [D.6]  3  Integrating Eqn. D.l y i e l d s [DEA]^ = [DEA]o "  [D.7]  ( k l + k 2 ) t  e  Equation D.4 was then integrated: d  [HEOD]  i dt§ ° 5 l E  = ki[DEA] t  t  = k [DEA] [-  t  = [DEA] o  [HEOD]  1  0  e  = k [DEA] 1u  0  e  ~  ( k l + k 2 ) t  -(ki+k )t t 2  (1 - "  ( k l + k 2 ) t  e  ]  )  [D.8]  Equation D.5 was integrated as follows: iLZHEEDl dt  +  ic_ [THEED] 3  t  - k [DEA] 2  0  e "  0  ^ ^  This i s a f i r s t - o r d e r linear d i f f e r e n t i a l equation which can be multiplied k, t by the integrating factor e . J  [THEED]^ e  = k [DEA]  k 3 t  2  = [THEED]  ™  k  = [DEA]  t  J* < 3 - ( k i + k ) ) t k  0  e  2  t  f l c T T O )  ^ . ( j ^ )  0  d  (e  e  - "  _ ( k l + k 2 ) t  (  k 3 t  e  - ^ ) )  k  )  t  ]  t  [D.9]  Equation D.6 was then solved. d[BHEP] _ k [THEED] rTUFFHi ^ - 3  -k i, r n r M , -<k +k )t - e -k t) . [DEA] „ ^ T k j ^ y (e 2  t  a  2  [BHEP] = [DEA] o . , [~ jr-^ "( i+ 2)t t " k -(ki+k ) (ki+k ) k  1 k  k  e  3  -  2  rr.FAl  k  2  i i  /,  2 3  3  .i \  ~ 3t , k  , (ki+k ) e  k  - k e  2  k -(k k )  [ D t A i o  3  3  1 +  -k t t o s  3  -(ki+k )t t 1  J2  3  k (k k )  1  2  3  1 +  J  z  0  This s i m p l i f i e s to: [BHEP] = [DEA] o r^t ki+k  U " „ <l\^ , ~^ ^)t k -(ki+k ) +  k  e  2  3  i+ 2 k  3  " 3t k  e  k -(k!+k )  2  2  [D.10]  In many cases the plots of [THEED] versus time pass through a maximum.  The location of this maxima can be found by d i f f e r e n t i a t i n g Eqn.  D.9 and setting d[THEED]/dt = 0.  The time at which the maximum concen-  tration of THEED occurs i s thus: d[THEED] dt  [DEA]Q =  k  ,  2  k -(k k ) 3  1 +  (  2  "  ( k  . l  + k  - ( k i + k ) t max e ~ k t max 2  e  3  2)  - ( k i + k ) t max ^ . 2  e  +  k  3 *  - k t max. 3  .  )=0  , k (ki+k ) 3  2  The maximum concentration of THEED can be found by combining Eqns. D.9 and D . l l :  260 [THEED]  max  _ [DEA]p k  _ r  2  k -(ki+k ) 3  (k +ki) k -(k 4-ki) 2  3  2  m  , k , k +k/_ 3  2  _ _kj k -(k +k!) ' 3  2  2  This simplifies to: [THEED] max  [DEA]o  k k +ki 2  2  ,k +ki k 2  K  ;  3  k 3  ~  ( k l + k 2 ) r [ D > 1 2 ]  , k ^ "Sti+kA J 3  261 APPENDIX E Comparison between the experimental results and the prediction of the k i n e t i c model The following tables compare the experimentally measured values of DEA, BHEP, HEOD, and THEED concentrations with the values predicted by the k i n e t i c model developed i n chapter 12.  For a l l the tables the concentra-  tion i n moles/cc and a l l k values are given in hr ^. total operating pressure i s 4137 kPa (600 p s i ) .  For each case the  TABLE E.1 COMPARISON BETWEEN EXPERIMENTAL AND PREDICTED CONCS. FOR 60WT% DEA DEGRADED AT 175C DEA  BHEP  SAMPLE hr  EXP  CALC  0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0  6.000 5.350 4.810 4.250 3.741 3.380 3.210 2.650 2.251  6.000 5.330 4.741 4.211 3.740 3.330 2.960 2.630 2.334  SAMPLE hr  EXP  0.0 1 .0 2.0 3.0 4.0 5.0 6.0 7.0 8.0  0. 190 0.360 0.451 0.450 0.440 0.420 0.431 0.398  kDEA k1 k2 k3  = = = =  EXP  CALC  —  —  -  0.0350 0.0651 0.0920 0.1150 0.1800 0.2060 0.2511  THEED  HEOD  -  0.118 0.0363 0.0817 0.0360  0.0080 0.0321 0.0678 0.1161 0.1718 0.2360 0.3060 0.3820  CALC  — 0.205 0.380 0.550 0.670 0.822 0.935 0.950 1.010  EXP  — 0.300 0.940 1.400 1 .661 1 .840 1.914 1 .980 2. 150  CALC  -  0.454 0.842 1.171 1 .453 1 .682 1 .870 2.030 2. 150  TABLE E.2 COMPARISON BETWEEN EXPERIMENTAL AND FOR 60WT% DEA DEGRADED AT 150C SAMPLE hr 0.0 2.0 4.0 6.0 8.0 10.0 15.0 24.0  0.0 2.0 4.0 6.0 8.0 10.0 15.0 24.0  6.000 5.650 5.330 5.022 4.730 4.460 3.240 2.940  EXP  CALC  _  _  0.0090 0.0110 0.0210 0.0430 0.1100  HEOD EXP  CALC  EXP  -  -  —  0.110 0.230 0.383 0.460 0.541 0.625 0.550  = = = =  BHEP CALC  6.000 5.660 5.300 5.000 4.710 4.460 3.830 2.950  SAMPLE hr  kDEA ki k2 k3  DEA EXP  0.0297 0.0109 0.0188 0.0040  PREDICTED CONCS.  0. 1 27 0.247 0.359 0.466 0.566 0.792 1.120  0.210 0.400 0.650 0.850 1 .000 1 .380 1 .520  0.0076 0.0101 0.0200 0.0430 0.1010  THEED CALC _  0.218 0.422 0.612 0.790 0.956 1 .320 1 .840  TABLE E.3 COMPARISON BETWEEN EXPERIMENTAL AND FOR 30WT% DEA DEGRADED AT 175C SAMPLE hr 0.0 1.0 2.0 3.0 4.0 5.0 6.0 8.0 10.0 12.0 14.0  SAMPLE hr  CALC  3.040 2.670 2.360 2.000 1 .840 1 .580 1 .440 1.110 0.860 0.651 0.520  3.040 2.660 2.360 2.051 1 .849 1.610 1 .450 1 . 1 30 0.895 0.702 0.550  EXP  —  0.0 1.0 2.0 3.0 4.0 6.0 8.0 10.0 12.0 14.0  kDEA k1 k2 k3  DEA EXP  0. 1 50 0.250 0.360 0.410 0.425 0.485 0.541 0.550 0.540  = = = =  0.1210 0.0474 0.0736 0.0350  BHEP EXP  0.0150  0.0139 0.0350 0.0500 0.0611 0.1030 0.1700 0.2370 0.3120 0.3810  0.0280 0.0580 0.0620 0.0980 0.2060 0.2200 0.2840  EXP  THEED CALC _  _  0. 1 34 0.253 0.358 0.451 0.534 0.729 0.825 0.850 0.870  CALC  _  HEOD CALC  PREDICTED CONCS.  0. 130 0.280 0.450 0.660 0.760 0.910 1 .050 0.990 0.960  0.200 0.380 0.525 0.650 0.750 0.970 1 .044 1 .066 1 .025  TABLE E.4 COMPARISON BETWEEN EXPERIMENTAL AND FOR 30WT% DEA DEGRADED AT 162C SAMPLE hr 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0  SAMPLE hr 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0  kDEA k1 k2 k3  DEA EXP  CALC  3.000 2.803 2.620 2.450 2.280 2. 137 2.000 1 .870 1.744  3.000 2.800 2.610 2.410 2.240 2. 1 20 1 .975 1 .880 1 .720  BHEP EXP  -  0.0101 0.0150 0.0201 0.0254 0.0350 0.0420  HEOD  CALC  0.0073 0.0126 0.0194 0.0270 0.0354 0.0460  THEED  EXP  CALC  EXP  CALC  -  -  —  _  0.105 0.200 0.275 0.320 0.364 0.412 0.420 0.450  = = = =  PREDICTED CONCS  0.0678 0.0260 0.0418 0.0140  0.075 0. 146 0.212 0.273 0.330 0.385 0.435 0.482  0.090 0.200 0.290 0.388 0.460 0.561 0.653 0.731  0. 120 0.230 0.330 0.426 0.513 0.591 0.663 0.730  TABLE E.5 COMPARISON BETWEEN EXPERIMENTAL AND FOR 30WT% DEA DEGRADED AT 150C SAMPLE hr 0.0 5.0 10.0 15.0 20.0 25.0 30.0 40.0 50.0 60.0  EXP  —  0.0 5.0 10.0 15.0 20.0 25.0 30.0 40.0 50.0 60.0  0.250 0.350 0.470 0.510 0.550 0.570 0.570 0.542 0.540  = = = =  0.0316 0.0142 0.0168 0.0040  BHEP CALC  3.000 2.600 2.200 1 .860 1 .560 1.310 1.110 0.840 0.710 0.580  SAMPLE hr  kDEA k1 k2 k3  DEA EXP  PREDICTED CONCS.  3.000 2.600 2.200 1 .881 1 .610 1 .380 1.180 0.868 0.637 0.480  EXP  CALC  _  0.0098 0.0210 0.0380 0.0425 0.0550 0.0640 0.0860 0.1060 0.1300  HEOD  0.0024 0.0100 0.0190 0.0322 0.0480 0.0652 0.0980 0.1090 0.1490  THEED CALC  EXP  CALC  _  _  _  0. 197 0.366 0.501 0.640 0.740 0.830 0.980 1 .050 1 .070  0.075 0. 150 0.400 0.652 0.751 0.900 1 .075 1 .225 1 .200  0.231 0.424 0.560 0.719 0.830 0.920 1 .059 1 . 132 1 .189  TABLE E.6 COMPARISON BETWEEN EXPERIMENTAL AND PREDICTED CONCS. FOR 30WT% DEA DEGRADED AT 140C SAMPLE hr 0.0 10.0 20.0 30.0 40.0 50.0 60.0 80.0 100.0  0.0 10.0 20.0 30.0 40.0 50.0 60.0 80.0 100.0  3.000 2.850 2.500 2.200 2.000 1 .745 1 .560 1 .240 0.980  EXP  CALC  _  -  0.0120 0.0210 0.0330 0.0415 0.0510 0.0700 0.1050  HEOD  -  0.0042 0.0110 0.0180 0.0370 0.0480 0.0650 0.0890  THEED  EXP  CALC  EXP  CALC  —  _  _  _  0.250 0.450 0.575 0.660 0.710 0.710 0.660 0.700  = = = =  BHEP CALC  3.000 2.850 2.540 2.260 2.000 1 .754 1 .605 1 .270 1.010  SAMPLE hr  kDEA k1 k2 k3  DEA EXP  0.01150 0.00563 0.00587 0.00140  0.171 0.322 0.460 0.576 0.700 0.780 0.940 1 .060  0. 120 0.320 0.504 0.581 0.700 0.751 0.863 0.950  0. 1 76 0.330 0.466 0.584 0.700 0.775 0.921 1 .031  TABLE E.7 COMPARISON BETWEEN EXPERIMENTAL AND PREDICTED CONCS. FOR 30WT% DEA DEGRADED AT 120C SAMPLE hr 0.0 20.0 40.0 60.0 80.0 100.0 120.0 140.0 160.0 180.0 200.0  0.0 20.0 40.0 60.0 80.0 100.0 1 20.0 140.0 160.0 180.0 200.0  3. 150 2.990 2.840 2.702 2.560 2.430 2.306 2.200 2.080 1 .970 1 .870  EXP  CALC  —  _  0.0060  0.0033  0.0084 0.0100 0.0180 0.0250 0.0310  0.0041 0.0063 0.0088 0.0121 0.0151  HEOD  THEED  EXP  CALC  EXP  CALC  —  —  —  —  0. 150 0.300 0.380 0.525 0.600 0.705 0.751 0.760 0.770 0.780  = = = =  BHEP CALC  3. 150 3.000 2.900 2.800 2.650 2.500 2.340 2.244 2.131 2.000 1 .905  SAMPLE hr  kDEA k1 k2 k3  DEA EXP  0.00260 0.00182 0.00078 0.00030  0. 120 0.218 0.318 0.414 0.505 0.590 0.673 0.750 0.824 0.894  -  0.056 0.089 0. 100 0. 140 0.225 0.240 0.313 0.345 0.375  -  0.093 0. 125 0. 175 0.213 0.250 0.280 0.313 0.343 0.371  TABLE E.8 COMPARISON BETWEEN EXPERIMENTAL AND PREDICTED CONCS. FOR 30WT% DEA DEGRADED AT 90C SAMPLE hr 0.0 100.0 160.0 300.0 441 .0 511.0 631 .0 700.0  kDEA k1 k2 k3  CALC  3.580 3.520 3.420 3.455 3.403 3.361 3.310 3.280  SAMPLE hr 0.0 1 00.0 160.0 300.0 441 .0 511.0 631 .0 700.0  DEA EXP  3.580 3.533 3.487 3.441 3.378 3.346 3.300 3.264  BHEP EXP  CALC  _  _  -  -—  -  CALC  —  _  0.050 0.090 0. 155 0.191 0.216 0.250 0.290  = 0.000142 = 0.000140 = 0.000002 = -  0.046 0.092 0. 137 0. 199 0.230 0.282 0.310  -— —  -  HEOD EXP  —  EXP  0.018 0.024 0.048 0.060  THEED CALC  — — 0.0181 0.0302 0.0348 0.0427 0.0507  TABLE E.9 COMPARISON BETWEEN EXPERIMENTAL AND FOR 20WT% DEA DEGRADED AT 175C SAMPLE hr 0.0 1 .0 2.0 3.0 4.0 5.0 6.0 7.0 8.0  EXP  -  0.0 1 .0 2.0 3.0 4.0 5.0 6.0 7.0 8.0  0. 100 0. 170 0.210 0.250 0.250 0.260 0.270 0.290  = = = =  0.1010 0.0318 0.0692 0.0390  BHEP CALC  2.020 1.810 1 .660 1 .550 1 .350 1 .240 1 . 150 1 .030 0.910  SAMPLE hr  kDEA k1 k2 k3  DEA EXP  PREDICTED CONCS.  EXP _  2.020 1.810 1 .640 1 .480 1 .340 1.210 1 .090 0.986 0.890  0.036 0.054 0.074 0.096 0. 105  CALC  EXP  _  _  0.024  HEOD  0.061 0.115 0.165 0.210 0.250 0.286 0.319 0.339  CALC  0. 150 0.250 0.320 0.440 0.500 0.540 0.590 0.615  0.025 0.038 0.046 0.050 0.082 0.112  THEED CALC „  0.129 0.241 0.336 0.419 0.489 0.548 0.598 0.638  TABLE E.10 COMPARISON BETWEEN EXPERIMENTAL AND PREDICTED CONCS FOR 20WT% DEA DEGRADED AT 150C SAMPLE hr 0.0 5.0 10.0 15.0 20.0 30.0 40.0 60.0  SAMPLE hr 0.0 5.0 10.0 15.0 20.0 30.0 40.0 60.0  DEA EXP  BHEP CALC  2. 160 1 .920 1 .720 1 .540 1 .390 1 . 120 0.890 0.650  2. 160 1 .940 1 .730 1 .553 1 .390 1 . 120 0.896 0.580  EXP  CALC  _  _  0.020  -0.016  0.033 0.045 0.077  0.033 0.055 0.096  HEOD EXP  CALC  —  _  0. 100 0.210 0.330 0.390 0.440 0.470 0.520  kDEA = 0 .022 k1 0 .011 k2 0 .011 k3 0 .004  0.112 0.213 0.304 0.384 0.522 0.570 0.791  EXP  THEED CALC _  0. 120 0.210 0.300 0.380 0.481 0.561 0.632  0.110 0.219 0.294 0.368 0.488 0.577 0.686  TABLE E.11 COMPARISON BETWEEN EXPERIMENTAL AND FOR 20WT% DEA DEGRADED AT 120C SAMPLE hr 0.0 20.0 40.0 60.0 80.0 100.0 1 40.0 160.0 180.0 200.0  BHEP CALC 2.1 50 2.057 1 .970 1 .880 1 .800 1 .725 1 .580 1.513 1 .450 1 .390  EXP  -  0.060 0.150 0.210 0.275 0.330 0.430 0.450 0.470 0.460  = = = <=  0.0022 0.0016 0.0006 0.0003  -  -  0.0018 0.0033 0.0043 0.0056 0.0066  DEA EXP  CALC  _  -  0.0020 0.0033 0.0045 0.0053 0.0063  THEED CALC  EXP  _  0.0 20.0 40.0 60.0 80.0 100.0 140.0 160.0 180.0 200.0  kDEA k1 k2 k3  DEA EXP 2.150 2.070 2.040 1.930 1 .850 1.710 1 .650 1 .538 1 .551 1.510  SAMPLE hr  PREDICTED CONCS.  CALC _  0.067 0. 132 0. 195 0.252 0.309 0.415 0.460 0.510 0.557  0.050 0.066 0. 104 0.121 0. 154 0. 170 ,0.180 0.210  0.025 0.049 0.072 0.088 0.114 0. 152 0. 170 0.181 0.202  TABLE E.12 COMPARISON BETWEEN EXPERIMENTAL AND PREDICTED CONCS. FOR 15WT% DEA DEGRADED AT 175C SAMPLE hr 0.0 1.0 2.0 3.0 4.0 5.0 6.0 8.0 10.0  CALC  1 .500 1 .420 1 .370 1.310 1 .240 1 . 180 1 . 120 1 .080 1.010  SAMPLE hr  EXP  -  0.0 1 .0 2.0 3.0 4.0 5.0 6.0 8.0 10.0  kDEA k1 k2 k3  DEA EXP  0.026 0.050 0.076 0.093 0.118 0.131 0. 160 0.171  = = = =  0.0490 0.0173 0.0317 0.0400  1 .500 1 .436 1 .369 1 .294 1 .241 1 . 176 1 . 125 1 .020 0.930  BHEP EXP _  _ 0.025 0.050 0.073 0.940 0.118 0. 135 0. 172 0.205  —  -  -  0.0060 0.0130 0.0200 0.0280 0.0490 0.0580  HEOD CALC  CALC  EXP  0.050 0. 100 0. 120 0. 170 0. 172 0.225 0.250  -  0.0040 0.0120 0.0208 0.0320 0.0487 0.0618  THEED CALC  -  0.067 0. 100 0. 122 0. 146 0. 1 67 0.204 0.234  TABLE E.13 COMPARISON BETWEEN EXPERIMENTAL AND FOR 15WT% DEA DEGRADED AT 150C SAMPLE hr 0.0 5.0 10.0 15.0 20.0 30.0 40.0 50.0  SAMPLE hr 0.0 5.0 10.0 15.0 20.0 30.0 40.0 50.0  DEA EXP  CALC  1.510 1 .450 1.350 1 .290 1 .210 1 .090 0.980 0.920  1.510 1 .420 1 .346 1 .274 1.212 1 .085 0.974 0.874  PREDICTED CONCS.  BHEP EXP  CALC _  0.0040 0.0060 0.0150 0.0220 0.0340  HEOD  -  0.0016 0.0038 0.0060 0.0130 0.0218 0.0324  THEED  EXP  CALC  EXP  CALC  -  —  _  _  0.040 0.082 0. 120 0.151 0.215 0.221 0.225  kDEA = 0.0108 k1 = 0.0057 k2 =0.0051 k3 = 0.0043  0.042 0.081 0.118 0. 154 0.219 0.278 0.330  0.024 0.063 0. 1 00 0. 132 0.181 0.238 0.275  0.055 0.071 0. 100 0. 132 0. 183 0.227 0.263  TABLE E.14 COMPARISON BETWEEN EXPERIMENTAL AND FOR 10WT% DEA DEGRADED AT 175C SAMPLE hr 0.0 2.0 4.0 6.0 8.0 10.0 15.0 20.0  CALC  1 .010 0.940 0.900 0.855 0.810 0.770 0.680 0.610  SAMPLE hr  EXP  —  0.0 2.0 4.0 6.0 8.0 10.0 15.0 20.0  kDEA k1 k2 k3  DEA EXP  0.020 0.040 0.060 0.080 0.090 0.100 0.106  = = = =  0.0242 0.0106 0.0136 0.0340  1.010 0.953 0.900 0.865 0.824 0.780 0.696 0.610  BHEP EXP  0.0080 0.0175 0.0400 0.0460  HEOD CALC  EXP  _  0.020 0.040 0.059 0.077 0.094 0. 133 0. 168  PREDICTED CONCS.  -  -  0.048 0.068 0.060 0. 100 0. 142  CALC  — — — 0.0141 0.0196 0.0400 0.0648  THEED CALC  — —  0.070 0.090 0.101 0.131 0.151  TABLE E.15 COMPARISON BETWEEN EXPERIMENTAL AND PREDICTED CONCS FOR 10WT% DEA DEGRADED AT 150C SAMPLE hr 0.0 5.0 10.0 15.0 20.0 30.0 40.0 50.0  CALC  1 .000 0.978 0.946 0.921 0.896 0.848 0.803 0.715  SAMPLE hr 0.0 5.0 10.0 15.0 20.0 30.0 40.0 50.0  kDEA k1 k2 k3  DEA EXP  EXP  -  0.027 0.046 0.058 0.086 0.110 0. 125  = = = =  0.0055 0.0030 0.0025 0.0040  1 .000 0.974 0.940 0.920 0.894 0.850 0.804 0.760  BHEP EXP  0.0040 0.0080 0.0120  HEOD CALC  EXP  -  — —  0.029 0.043 0.057 0.083 0.108 0.131  0.0550 0.0851 0.0920  CALC  — _ _  0.0018 0.0040 0.0071 0.0106  THEED CALC  _  — 0.0456 0.0600 0.0827 0.0987  277 APPENDIX F Mass s p e c t r a of DEA and r e l a t e d d e g r a d a t i o n  compounds  The f o l l o w i n g i s b a s i c a l l y a l i b r a r y of mass s p e c t r a f o r DEA and i t s degradation  compounds.  Out o f the 16 compounds a n a l y s e d  f o r MEA, DEA, and TEA c o u l d be found i n e x i s t i n g mass s p e c t r a F.1  Mass s p e c t r a of DEA and i t s d e g r a d a t i o n  only  spectra  libraries.  compounds  F i g u r e s F . l t o F.4 show the mass s p e c t r a of DEA, BHEP, HEOD, and THEED. F.2  Mass s p e c t r a of minor d e g r a d a t i o n  compounds  F i g u r e s F.5 t o F . l l show the mass s p e c t r a of BHEED, HEED, H E I , HEM, HEP, OZD, and TEHEED. F. 3  Mass s p e c t r a of i m p u r i t i e s i n the DEA feed F i g u r e s F.12 and F.13 show the mass s p e c t r a of MEA and TEA.  F.4  Mass s p e c t r a of a s s o c i a t e d compounds F i g u r e s F.14 t o F.16 show the mass s p e c t r a of BHG, DEEA, and MDEA. BHG o r b i s - ( h y d r o x y e t h y l ) g l y c i n e has been c o n s i d e r e d  t o be a d e g r a -  2 d a t i o n compound by some a u t h o r s .  However, no t r a c e of BHG was found  i n t h e degraded DEA s o l u t i o n s and no mechanism seems f e a s i b l e p r o d u c t i o n under p r e s e n t  experimental  DEEA o r d i e t h y l e t h a n o l a m i n e substituted with a hydroxyethyl  for i t s  conditions.  i s a t e r t i a r y amine w i t h one hydrogen  group and the o t h e r two hydrogens s u b s t i -  t u t e d w i t h e t h y l groups. F.5  Summary Table F . l gives the molecular  producing  f o r m u l a and the mass of t h e i o n s  t h e major peaks i n t h e mass s p e c t r a of each compound  analysed.  100 1  -? i 4  80 -  60 56 40 -  .20 -  1  rt -• > .1i  40  S6 Ii Hi i 1 1 60  1  |  Figure F . l  , .!• i :0  •  112 I  122  . , . . . , | . | . „ , , . . . . ! • ,..,.|  1 00  1 20  143 '  i 1 40  157 160  174 1*0  207 i  1  i 1 •' 200  Mass spectrum of DEA ho 00  ioe 42  so  60 14;  100  40  1 13  20  125 156  40  Figure F.2  llll Hi 1 00  Mass spectrum of BHEP  120  140  100 T 1 00  so H  6L1  40  42  £0H 64  40  60  Figure F.3  131  74 •I  154 • I ft 0  1 00  —i  120  '  r"—•  1  1  r  140  Mass spectrum of HEOD  CO  o  llQO  11S  30  143  60 1 00  sc.  40 20 0 1100  130 ll li,,,, ,11111 11 11, I i u II 1 OO  J  40  60  , i-  Jill .|HJ-M-i-  I • I-J 1.1,1. 120  140  30 H 60 40 H 1 74  156 •t"  160 Figure F.4  18 ISO  199 —, V M 11  207 —,  £17 •  £4: 240  Mass spectrum of THEED OO  100  l  74  80 H  60 i 56 40  A  20 H  44 97  40  -,  T  60 Figure F.5  r-  I  so  117 11.  I  1 OO  •. 11 i 120  129 1  149  157  ' 'I  140  Mass spectrum of BHEED ho  CO  Figure F.6  Mass spectrum of HEED  ho CO CO  Figure F.7  Mass spectrum of HEI oo  Figure F.8  Mass spectrum of HEM K5 CO  100  ~t  l Q'3  so  40  20  112  H  130 40  50  I  Figure F.9  60  70  • •nlllll.l  80  90  I  " i ' " ' i '" 'i • " M  1  1 00  1 10  120  1 30  Mass spectrum of HEP CO ON  40  50  Figure F.10  to  '  70  SO  90  100  1 10  Mass spectrum of OZD ho CO  F i g u r e F . l l Mass spectrum of TEHEED ho Co 00  1  100-1 1 80 -  30  6040 20 -  61  42  0 -  1  1  1  1  I 1 • ., . . h I 40  1  20 Figure F.12  69 i . ' i  ,  J 1  77  1"'  1  60  86  94  105  1  100  80  Mass spectrum of MEA  100 - j  806040 20 0 -  1  •  i  • . • 40  I  1  Figure F.13  1  i  •'  80  1 I  1 1  •  i  '  i  1  1 20  i  160  1  i  i  -  200  i  '  i  240  i  '  r—• 280  r  Mass spectrum of TEA t-o  CO VD  Figure F.14  Mass spectrum of BHG  100 ~\  I  50 -n  40  20 42 102  i — 20  F i g u r e F.15  "t 40  Mass spectrum of DEEA  -i——t-^ 1 00  1 1  Figure F.16  Mass spectrum of MDEA r-o SO  Table F . l  Molecular formula and major peaks of mass spectra of compounds studied  Compound  M.W.  \ / H  N,N-bis-(hydroxyethyl) ethylenediamine  Parent ion  C2H4-OH  H0-C H„ 2  BHEED  Major Peaks  / N-CzH^-N  148  74, 56, 44  174  156,143,125,113, 100,98,70,56,42  0 II N-CH -C-0H  163  118,74,56,45  N-H  105  74,56,45  \ H  BHEP N-C^-OH  HO-C2H4-N  N,N-bis-(hydroxyethyl) piperazine  H0-C H 2  u  BHG  2  N,N-bis-(hydroxyethyl) glycine H0-C Ht, 2  HO-C^ DEA Diethanolamine H0-C Hi, 2  ro  Table F . l (cont.)  Compound  -  C H 2  DEEA  b  \  M.W.  H4-OH  Diethylethanolamine C H 2  Major Peaks  Parent ion  117  86,58,42  /  104  74,56,44  -  130  100,99,70,56,42  /  87  56,42  /  5  H  \  HEED N-(hydroxyethyl) ethylenediamine  N- C ^ - N  / H  /  \  H  *  0 HEI N-(hydroxyethyl) itnidazolidone  /  ''\  HO-C H -N 2  4  N-H  1  CH  1  CH  2  2  CH, HEM  /  /  HO-CH.,-N 2  N-(hydroxyethyl) ethylenimine  \\  CH  2  ho  Table F . l (cont.)  Compound  M.W.  Major Peaks  Parent ion  131  101,100,56,42  /  130  112,99,88,70,56, 42  /  119  88,44  61  61,30  0  II  C HEOD  /  H0-C?H.,-N  \  I  3-(hydroxyethyl)-2-oxazolidone  CH  0  I  CH  2  2  CH ?  HEP H0-C H^-N  N-H  2  \  N-(hydroxyethyl) piperazine  / C HL, 2  H0-C Hi, 2  MDEA N-CH  3  Methyldiethanolamine HO-C2H1,  MEA N-C H -0H 2  Monoethanolamine  4  Table F . l (cont.)  Compound  M.W.  Major Peaks  Parent ion  0  a 1 c  OZD  /  Oxazolidone  \  H-N  0  1  CH  87  87,59,42  /  149  118,56,31  -  236  118,100,88,75, 56,45  -  192  143,118,100,88, 70,56,42  -  1  CH  2  2  HO-C2H4  TEA  \ N-C?Hi»-0H  Triethanolamine  / H0-C Hi, 2  HO-C H 2  CH>,-OH  u  2  TEHEED  \  N,N,N,N-tetra-(hydroxyethyl) ethylenediamine  / N-C H -N 2  4  /  \  4  C2H4-OH  1|  C H -OH  HO-C H 2  HO-C H 2  THEED  \  /. N-C2H4-N  N,N,N-tris-(hydroxyethyl) ethylenediamine  / HO-C2H4  Note:  2  \  4  H  The underlined major peaks represent the ion with the r e l a t i v e abundance of 100%.  Publications: 1.  Kennard, M.L. and Meisen, A., "Aerosol C o l l e c t i o n i n Granular Beds" The 2nd World F i l t r a t i o n Congress, 1979, London, pages 229-238.  2.  Kennard, M.L. and Meisen, A., "Degradation of Diethanolamine S o l u t i o n s " , paper presented at the Annual Meeting of the Canadian Gas Processors Association, 1979, Calgary.  3.  Kennard, M.L. and Meisen, A., "Control DEA Degradation", Hydrocarbon Processing, A p r i l 1980, pages 103-106.  4.  Meisen, A. and Kennard, M.L., " P r a c t i c a l Aspects of DEA Degradation Studies", paper presented at the 3rd Quarterly Meeting of the Canadian Gas Processors A s s o c i a t i o n , Calgary, 1981.  5.  Meisen, A. and Kennard, M.L., "DEA Degradation Mechanism", Hydrocarbon Processing, Oct. 1982, pages 105-108.  

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