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Novel design criteria for direct coal liquefaction reactors 1985

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NOVEL DESIGN CRITERIA FOR DIRECT COAL LIQUEFACTION REACTORS By JOHN MICHAEL SHAW B.A.Sc, The Un i v e r s i t y of B r i t i s h Columbia, 1981 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY i n THE FACULTY OF GRADUATE STUDIES Department of M e t a l l u r g i c a l Engineering We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA January, 1985 © John Michael Shaw, 1985 In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y available for reference and study. I further agree that permission for extensive copying of t h i s thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. I t i s understood that copying or publication of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. Department of The University of B r i t i s h Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 Date 01/OH/85 DE-6 (3/81) i i ABSTRACT A semi-batch Direct Coal Liquefaction f a c i l i t y was designed and constructed i n order to examine the impact of process variables on coal l i q u e f a c t i o n k i n e t i c s . A s e r i e s of parametric in v e s t i g a t i o n s involving bituminous, sub-bituminous coals and l i g n i t e were performed. The process variables included solvent composition, c a t a l y s t to coal r a t i o , the i n t e n s i t y of t u r b u l e n c e , the i n i t i a l d i s s o l v e d hydrogen concentration, and the s l u r r y residence time d i s t r i b u t i o n . The r e s u l t s of these in v e s t i g a t i o n s showed that process variables have a s i g n i f i c a n t impact on the rates of l i q u e f a c t i o n reactions, and that reaction rates for coal and l i g n i t e are affected i n a s i m i l a r manner. The o v e r a l l rate and maximum extent of l i q u i d and gas production was found to depend on the i n i t i a l rate of molecular hydrogen transfer to the coal p a r t i c l e s , and on the r a t i o of the i n t e n s i t y of turbulence to the l e v e l of c a t a l y s i s . This l a t t e r f i n d i n g led to the discovery of a p e r s i s t e n t dispersed l i q u i d phase within the coal l i q u e f a c t i o n environment. A reaction model, coupling these findings with a simple k i n e t i c scheme, was found to correlate the l i q u e f a c t i o n behaviour of bituminous and sub-bituminous coals and l i g n i t e , i n diverse reaction environments. The experimental r e s u l t s and the reaction model were used to develop novel design c r i t e r i a for Direct Coal Liquefaction Reactors. Two design i i i optima were i d e n t i f i e d . One optimum i s c l o s e l y approximated by an e x i s t i n g process. An a l t e r n a t i v e and p o t e n t i a l l y preferable optimum i s proposed. i v TABLE OF CONTENTS Abstract i i Table of Contents '. i v L i s t of Tables x L i s t of Figures x i i Acknowledgements x v i i Nomenclature x v i i i Quotation x x i i i 1. Introduction 1.1 General Introduction 1 1.2 Direct Coal Liquefaction - An Overview 5 1.2.0 Introduction 5 1.2.1 Coal Slurry Preparation 7 1.2.2 Coal Liquefaction 7 1.2.3 Product Separation 8 1.2.4 Solvent Treatment 9 1.2.5 Ca t a l y s i s 10 2. L i t e r a t u r e Review 11 2.1 Dir e c t Coal Liquefaction (DCL) Reactor Designs 11 2.1.0 Introduction 11 2.1.1 Liquefaction Reactor Design 22 2.1.1.0 Introduction 22 2.1.1.1 Pre-heaters 24 2.1.1.2 Contactor Design 28 2.1.1.3 Reactor Design Rationale 43 2.2 Li q u e f a c t i o n Reactions and K i n e t i c s 43 V 2.2.0 Introduction 43 2.2.1 Coal Swelling and Solvent Absorption 44 2.2.2 Primary D i s s o l u t i o n 46 2.2.3 Secondary D i s s o l u t i o n 47 2.2.4 Hydrogenation 49 2.2.4.1 Hydrogenation Reactions 49 2.2.4.2 Heterogeneous Reactions 50 2.2.4.3 Homogeneous Reactions 51 2.2.5 Hetero-Atom Removal 53 2.2.5.1 Reactions 53 2.2.5.2 C a t a l y t i c E f f e c t s 54 2.2.6 Retrogressive Reactions 57 2.3 Catalysts and Catalysis 60 2.3.1 C a t a l y t i c and S o l v o l y t i c DCL Processes 60 2.3.2 The Role of Catal y s i s 60 2.3.3 Catalysts 61 2.3.4 C a t a l y t i c A c t i v i t y of Metal Sulphides 64 2.4 Solvents 66 2.4.1 Chemical Composition 66 2.4.2 Physical Properties 67 2.4.2.0 Introduction 67 2.4.2.1 Gas S o l u b i l i t i e s i n Coal Liquids and Related Pure Aromatic Solvents at High Pressure 68 2.4.2.2 Solvent Density 81 2.4.2.3 Solvent V i s c o s i t y 82 2.5 Process and Ki n e t i c Models 85 2.5.0 Introduction 87 2.5.1 K i n e t i c Models 88 2.5.2 Process Models 93 v i 2.6 Coal Liquefaction Product Analysis 94 2.7 Summary 97 3. Objectives 100 4. Experimental 102 4.0 Introduction 102 4.1 Coal L i q u e f a c t i o n Experiments 104 4.1.1 Apparatus Design and Desc r i p t i o n 104 4.1.2 Operating Procedure 108 4.1.3 Materials I l l 4.1.3.1 Catalysts I l l 4.1.3.2 Coal s / L i g n i t e 112 4.1.3.3 L i q u e f a c t i o n Solvents 116 4.1.3.4 Analysis Solvent 116 4.1.3.5 Gases 116 4.1.4 Experiment Design 117 4.1.5 Result Analysis 121 4.1.5.0 Introduction 121 4.1.5.1 Gas Analysis 123 4.2 Fundamental Investigations 131 5. Experimental Results and Preliminary Discussion 134 5.0 Introduction 134 5.1 Data P r e c i s i o n 134 v i i 5.2 Gas Phase Phenomena 139 5.3 Reactor and Pre-heater Simulations 145 5.4 The Role of Cobalt Molybdate Catalysts i n DCL Reaction Environments 158 5.5 The Int e n s i t y of Turbulence 163 5.6 Observations of a Dispersed Phase i n a Model Solvent 171 5.7 Residual Solids Analysis 175 5.8 Summary 178 6. A Novel Reaction Model for Di r e c t Coal L i q u e f a c t i o n K i n e t i c s 179 6.0 Introduction 179 6.1 An Outline of the Proposed Reaction Model 180 6.2 Mathematical Formulation of the Model 183 6.2.0 Introduction 183 6.2.1 Preliminary Reactions 184 6.2.2 Second Stage Reactions 189 6.2.3 Residence Time D i s t r i b u t i o n s 194 6.2.4 Summary 194 v l i i 6.3 V e r i f i c a t i o n of the Model 195 6.3.0 Introduction 195 6.3.1 Experimental 198 6.3.2 Results and Discussion 200 6.4 Summary 219 7. Dir e c t Coal L i q u e f a c t i o n Reactor Design 221 7.0 Introduction 221 7.1 Pre-heater Design 221 7.2 Reactor Design 223 7.3 Catalysts 224 7.4 A Re-Evaluation of E x i s t i n g DCL Reactor Designs 225 7.5 An Optimum D i r e c t Coal Li q u e f a c t i o n Reactor Design 226 7.6 Summary 229 8. Summary 230 8.1 Conclusions 230 8.2 Suggestions f o r Further Study 231 References 233 i x Appendices 244 Appendix A: Hydrodynamic Calculations 245 Appendix B: C o r r e l a t i o n Derivations 249 Appendix C: Liquefaction T r i a l Data 251 Appendix D: The Impact of Maceral V a r i a t i o n s on the Liquefaction Behaviour of Byron Creek Coal 259 LIST OF TABLES x Table 2.1: Dir e c t Coal L i q u e f a c t i o n Process and Product Data 12 Table 2.2: W i l s o n v i l l e Pre-heater Design Data 26 Table 2.3: H-Coal Product Slate Comparsion 31 Table 2.4: Hydrodynamic C a l c u l a t i o n Summary 33 Table 2.5: CCLP Process Yi e l d s 42 Table 2.6: Catalysts 63 Table 2.7: Apparent S o l u b i l i t y Data 80 Table 2.8: Coal Solvent Densities 84 Table 2.9: Coal L i q u e f a c t i o n Reaction Models 89 Table 2.10: Product Analysis by S o l u b i l i t y 96 Table 4.1: Variables Investigated 103 Table 4.2: Catalyst P a r t i c l e Size D i s t r i b u t i o n 113 Table 4.3: Proximate and Ultimate Analyses of the Test Coals 114 Table 4.4: Apparent Gas S o l u b i l i t i e s i n Benzene 127 x i Table 5.1: Result Repeatability 136 Table 5.2: Water Gas S h i f t Reaction Data 142 Table 5.3: Coal Conversion S t a t i s t i c s for Reactor and Pre-heater Simulations 149 Table 6.1: Data Sets Selected for Model V e r i f i c a t i o n 199 Table 6.2: Optimum Parameters 213 x i i LIST OF FIGURES Figure 1.1: A Dir e c t Coal L i q u e f a c t i o n Process Schematic 6 Figure 2.1: H-Coal Process Schematic 14 Figure 2.2: SRC I Process Schematic 15 Figure 2.3: SRC II Process Schematic 16 Figure 2.4: EDS Process Schematic 17 Figure 2.5: Saarbergwerke Process Schematic 18 Figure 2.6: Ruhrkohle Process Schematic 19 Figure 2.7: CCLP Process Schematic 20 Figure 2.8: Dow Procss Schematic 21 Figure 2.9: Flow Models 23 Figure 2.10: Fow Regimes for Two-Phase Flow 25 Figure 2.11: The H-Coal Contactor 30 Figure 2.12: Catalyst Residence Time D i s t r i b u t i o n i n a H-Coal Reactor 34 Figure 2.13: Product F l e x i b i l i t y of the EDS Process 41 Figure 2.14: Coal L i q u e f a c t i o n Phenomena 45 x i i i Figure 2.15: The Hydro de NOS A c t i v i t y of Various F u n c t i o n a l i t i e s 55 Figure 2.16: Hydro de NOS Reaction Paths 55 Figure 2.17: Representative Retrogressive Reactions 58 Figure 2.18: Hydro de NOS Mechanism 65 Figure 2.19: Hydrogen S o l u b i l i t y i n Pure Organic Solvents 71 Figure 2.20: Argon S o l u b i l i t y i n Pure Organic Solvents 72 Figure 2.21: Ethane S o l u b i l i t y i n Pure Organic Solvents 72 Figure 2.22: Nitrogen S o l u b i l i t y i n Pure Organic Solvents 73 Figure 2.23: Carbon Dioxide S o l u b i l i t y i n Pure Organic Solvents 73 Figure 2.24: Two Liquefaction Reaction Sequences 75 Figure 2.25: Hydrogen and Methane S o l u b i l i t i e s In Coal Liquids 78 Figure 2.26: The Densities of Pure Organic Solvents 83 Figure 2.27: The v i s c o s i t i e s of Pure Organic Solvents 85 Figure 4.1: Experimental Apparatus Schematic 105 Figure 4.2: P a r t i c l e Size D i s t r i b u t i o n s for the Test Coals 115 x i v Figure 4.3: Continuous Flow Reactor Simulation Model 120 Figure 5.1: The Impact of Temperature Variations on Coal Conversion 137 Figure 5.2: The Impact of Residence Time Variations on Coal Conversion 138 Figure 5.3: Carbon Monoxide and Carbon Dioxide Production Contours 141 Figure 5.4: The Hydrocracking of Ethane 144 Figure 5.5: Relative Extents of CO and CH^ Production During the I n i t i a l Stages of Liquefaction Reactions 146 Figure 5.6: Hydrogen Consumption During the I n i t i a l Stages of L i q u e f a c t i o n Reactions 147 Figure 5.7: Apparent S o l u b i l i t i e s of Hydrogen i n Product Liquids 154 Figure 5.8: The Influence of C a t a l y s i s on Coal and L i g n i t e Conversion 161 Figure 5.9: The Influence of S t i r r i n g Rate on Coal and L i g n i t e Conversion 165 Figure 5.10: The Influence of S t i r r i n g Rate on Residue P a r t i c l e Size D i s t r i b u t i o n 168 XV Figure 5.11: Phase D i s t r i b u t i o n s i n a Model Two Phase Liqu e f a c t i o n Solvent at Room Temperature 173 Figure 5.12: Phase D i s t r i b u t i o n s In a Model Two Phase Liqu e f a c t i o n Solvent at Elevated Temperatures .... 174 Figure 5.13: Sulphur Concentration P r o f i l e s i n Spent Catalyst P a r t i c l e s 177 Figure 6.1: An Outline of the Model 181 Figure 6.2: The Temperature Dependence of DCL Rate Constants 192 Figure 6.3: The Modified Arrhenius Dependence of DCL Rate Constants 193 Figure 6.4: Result Summary for a V e r i f i c a t i o n T r i a l with Fies Mine Coal 201 Figure 6.5: Result Summary for a V e r i f i c a t i o n T r i a l with Hat Creek A Coal 202 Figure 6.6: Result Summary for a V e r i f i c a t i o n T r i a l with Hat Creek B Coal 203 Figure 6.7: Result Summary for a V e r i f i c a t i o n T r i a l with Middle Kittanning Coal 204 Figure 6.8: A Comparison of Predicted and Observed Results f o r Forestburg Coal Liquefied i n Solvent 2 (I) 205 xv i Figure 6.9: A Comparison of Predicted and Observed Results for Forestburg Coal L i q u e f i e d i n Solvent 2 (II) 206 Figure 6.10: A Comparison of Predicted and Observed Results for Forestburg Coal L i q u e f i e d i n Solvent 1 (I) 207 Figure 6.11: A Comparison of Predicted and Observed Results f o r Forestburg Coal L i q u e f i e d i n Solvent 1 (II) 208 Figure 6.12: A Comparison of Predicted and Observed Results f or Byron Creek Coal L i q u e f i e d i n Solvent 2 (I) 209 Figure 6.13: A Comparison of Predicted and Observed Results f or Byron Creek Coal L i q u e f i e d i n Solvent 2 (II) 210 Figure 6.14: Result Summary for a V e r i f i c a t i o n T r i a l with Saskatchewan L i g n i t e 211 Figure 7.1: A Novel Direct Coal L i q u e f a c t i o n Reactor Design 228 XV i i ACKNOWLEDGEMENTS Many people have contributed to the success of t h i s p r o j e c t . S p e c i a l thanks are due Professor E. Peters f o r h i s guidance and encouragement throughout my tenure at the Metallurgy Department, Mr. G. Mojaphoko and Mr. G. Roemer, both undergraduate Metallurgy students, f o r volunteering many summer days and evenings i n search of anwswers which frequently did not e x i s t , and Mr. Peter Kemp who always found time to analyze a few more coal samples. I am also indebted to Professor R. Butters, and Mr. H. Tump. Their assistance with experimental d i f f i c u l t i e s was always timely and constructive. The f i n a n c i a l assistance, provided by B.C. Research and the Natural Sciences and Engineering Research Council i s g r a t e f u l l y acknowledged. x v i i i NOMENCLATURE A, A constants A 1, A f Ar A T Q , Axlt A r 2 b, b C ±, C± CAT CCLP CSTR DCL d° surface area of coal per unit volume, m ^ mass f r a c t i o n of ash i n co a l , residue. argon, Archimedes number argon mole f r a c t i o n i n i n i t i a l gas, f i n a l high pressure sample, low pressure gas sample. constants mole f r a c t i o n , average mole f r a c t i o n c a t a l y s t Chevron Coal L i q u e f a c t i o n Process continuous s t i r r e d tank reactor no / oo C a dt = 1 o 9 2 -1 dispersion c o e f f i c i e n t , m s , impellor diameter, m, molecular d i f f u s i o n 2 -1 c o e f f i c i e n t , m s Direct Coal L i q u e f a c t i o n i n i t i a l mean diameter of coal p a r t i c l e s , m frequency f o r a normalized p r o b a b i l i t y d i s t r i b u t i o n . x i x EXXON Donor Solvent s t i r r i n g rate Hz a function defined by equation 4.5 -2 g r a v i t a t i o n a l a c c e l e r a t i o n m s hydrogen concentration moles»Kg ^ . solvent mole f r a c t i o n of hydrogen in I n i t i a l gas, f i n a l high pressure gas samples, low pressure gas samples. hydrogen concentration and equilibrium hydrogen concentration i n a l i q u e f a c t i o n solvent at zero time, under reaction conditions, moles»Kg ^ , ' ^ solvent f r a c t i o n of hydrogen consumed. a function defined by Equation 6.11 a function defined by Equation 6.3 a function defined by Equation 6.10 constants o v e r a l l mass transfer c o e f f i c i e n t , moles*s ^ reactor length, m molar mass, g moisture and ash free c o a l , g mean residence time the number of i d e a l s t i r r e d tanks, i n s e r i e s , which best simulate an experimental reactor XX pressure, MPa, c r i t i c a l pressure, MPa, r e l a t i v e pressure i n i t i a l and f i n a l pressure, MPa plug flow reactor „ 3 -1 gas flow rate, m s un i v e r s a l gas constant residence time d i s t r i b u t i o n s o l u b i l i t y moles»Kg * , "Atm * J ° solvent the apparent s o l u b i l i t y of a gas component i n a solvent, the s o l u b i l i t y of a gas in a single component of a complex solvent, moles»Kg ^»Atm ^ s o l u b i l i t y i n a complex solvent, s l u r r y i n j e c t i o n run moles *Kg ^ »Atm ^ Sherwood number average Sherwood number of dispersed phase droplets average i n i t i a l Sherwood number f o r coal p a r t i c l e s average i n i t i a l Sherwood number for dispersed phase droplets evolving from coal p a r t i c l e s Synthetic Natural gas Solvent Refined Coal xxi temperature, °K, c r i t i c a l temperature, °K, r e l a t i v e temperature normal b o i l i n g temperature, °K, average b o i l i n g temperature for complex mixtures, °K t o t a l coal conversion normalized time at which s l u r r y i n j e c t i o n i s commenced tanks In s e r i e s tonnes per day time, mean residence time, s maximum and minimum residence times, s s u p e r f i c i a l v e l o c i t y , m s ^ volume, m̂ gas volume i n the reactor, apparent gas volume of the s l u r r y phase, t o t a l reactor volume mole f r a c t i o n constants for the coal l i q u e f a c t i o n reaction model Chapter 6 c o m p r e s s i b i l i t y f a c t o r normalized time = t / t normalized mean residence time per pass, per reactor. f i r s t order rate constant s * v i s c o s i t y , poise kinematic v i s c o s i t y -3 density, reference density Kg m the square root of the variance of a p r o b a b i l i t y d i s t r i b u t i o n , i n t e r f a c i a l -2 tension, Kg*s accentric factor x x i i i "There i s , as every schoolboy knows i n t h i s s c i e n t i f i c age, a very close chemical r e l a t i o n between c o a l and diamonds .... Both these commodities represent wealth; but coal i s a much less portable form of property. There i S • • • 3. deplorable lack of concentration i n coal .... At the same time, there i s a f a s c i n a t i o n i n c o a l , the supreme commodity of the age i n which we are couped l i k e bewildered t r a v e l l e r s i n a ga r i s h , u n r e s t f u l h o t e l . " Joseph C o n r a d ^ 1 Chapter 1 1. INTRODUCTION 1.1 General Introduction Coal i s the only foreseeable energy resource which can be developed, on a global scale, to supplement or supplant mineral o i l and nat u r a l gas consumption as the reserves of these l a t t e r two energy resources d e c l i n e . Known and projected coal reserves contain between 1.5 and 7 times the energy remaining i n mineral o i l and natural gas f 92 1 r e s e r v e s . However, extensive use of raw coal presents a number of environmental and l o g i s t i c a l problems. Foremost among these are: (1) sulphur, nitrogen and f l y a s h emissions associated with coal combustion. (2) the u n s u i t a b i l i t y of s o l i d f u e l s f o r transportation a p p l i c a t i o n s . (3) superfluous shipping costs r e l a t e d to ash, moisture and i n e r t content. C l e a r l y , coal must be converted into conventional f u e l analogs i f the "hydrocarbon economy" i s to survive beyond the 2000-2010 f r o n t i e r p r o j e c t e d s o l e l y on the b a s i s o f m i n e r a l o i l and n a t u r a l gas [921 consumption 1 . The need to produce conventional f u e l s from coal w i l l become i n c r e a s i n g l y compelling as mineral o i l and natural gas reserves dwindle. 2 Dire c t Coal Liquefaction (DCL) i s one technological a l t e r n a t i v e for the production of low sulphur and low ash gaseous, l i q u i d and s o l i d f u e l s from c o a l . Consequently, academic and i n d u s t r i a l i n t e r e s t i n t h i s research area has i n t e n s i f i e d as the r e a l cost of conventional clean energy resources has escalated. A potpourri of DCL process designs, u t i l i z i n g d i f f e r e n t coal types and placing varying emphasis on o i l , SNG, clean coal and chemical feedstock production, have been proposed. Many of these designs are derivatives or hybrids of the o r i g i n a l process developed by Bergius et a l during the 1920's, while others are adaptations of heavy o i l processing technology. DCL processes, employing these design concepts, are cu r r e n t l y undergoing laboratory examination; some are or have been demonstrated at p i l o t s c ale, but none of the processes have been commercialized. Liquefaction reactor c a p i t a l cost i s the major technological impediment to the commercialization of DCL processes, as l i q u e f a c t i o n reactions must be conducted under extreme conditions: temperatures greater than 680 K, pressures greater than 10 MPa; i n a corrosive environment. Even under these conditions, l i q u e f a c t i o n reactions are c l a s s i f i e d as "slow". So, I t i s not s u r p r i s i n g that l i q u e f a c t i o n reactors account f o r as much as 50% of the c a p i t a l cost of DCL r 2 gg ] p r o c e s s e s ' . D e s p i t e t h i s i n c e n t i v e , i t i s p r e c i s e l y i n th i s one respect that DCL processes are most s i m i l a r . In a l l cases, l i q u e f a c t i o n reactors are sub-divided Into two multiphase components: a pre-heater, 3 operated i n slug flow, with a mean residence time of approximately 6 minutes, followed by an a x i a l l y mixed contactor where the coal mean residence time i s t y p i c a l l y greater than 15 minutes. The choice of hydrodynamically s i m i l a r reactor designs, for a l l processes, can only be r a t i o n a l i z e d on the b a s i s of a l i m i t e d c o n c e p t u a l grasp of c o a l - l i q u e f a c t i o n reaction k i n e t i c s coupled with a t r a d i t i o n a l evaluation of process economics. Experimental evidence does not suggest that t h i s design i s optimal. Process and reactor design development i n p a r t i c u l a r has been hampered by the wax and wane of research fashion. Interest i n DCL i s only aroused during periods of perceived c r i s i s ( i . e . ) p r i o r to and during World War I I , following the alleged o i l c r i s i s of 1973. Dominant themes i n the l i t e r a t u r e r e f l e c t t h i s sense of urgency. Both previous and current research emphasizes three Issues: (1) can coals within a p a r t i c u l a r country or region be l i q u e f i e d and i f so, what Is the product y i e l d and d i s t r i b u t i o n i n e x i s t i n g processes (2) what c a t a l y s t s or solvents optimize the production of p a r t i c u l a r products (3) what materials or mechanical problems must be resolved i n order to scale-up e x i s t i n g processes at the expense of others, such as: (1) what i s the mechanism for coal l i q u e f a c t i o n ; do a l l coals l i q u e f y i n the same manner; i f not, what raw coal parameters account f o r the d i f f e r e n c e 4 (2) where do the most c r i t i c a l reactions occur and are they c o n t r o l l e d by mass transfer or k i n e t i c s 3) how does reactor hydrodynamics ( a x i a l mixing, the i n t e n s i t y of turbulence a f f e c t coal l i q u e f a c t i o n k i n e t i c s ) which are r a r e l y addressed. These l a t t e r issues must be addressed, comprehensively, i f s u b s t a n t i a l improvements i n the cost effectiveness of DCL processes are to be r e a l i z e d . Currently, f o r example, i t Is d i f f i c u l t to p r e d i c t l i q u e f a c t i o n r e s u l t s f or a si n g l e coal i n s i m i l a r reactors of varying s i z e , and even more d i f f i c u l t to c o r r e l a t e l i q u e f a c t i o n data f o r a s i n g l e coal i n reactors with d i f f e r e n t hydrodynamics. Present p r e d i c t i v e models f a i l , i n part, because they do not Include the influence of phy s i c a l phenomena (the i n t e n s i t y of turbulence, the extent of a x i a l mixing, solvent properties, gas- l i q u i d - s o l i d mass transfer) on coal l i q u e f a c t i o n k i n e t i c s . Optimal l i q u e f a c t i o n reactor designs cannot be based on such poor p r e d i c t i v e models. This t h e s i s , comprising a t h e o r e t i c a l and experimental study, endeavours to i d e n t i f y process v a r i a b l e s and physical phenomena that a f f e c t the p r o d u c t i v i t y of DCL reactors for bituminus, sub-bituminus coal and l i g n i t e l i q u e f a c t i o n . Mathematical models of l i k e l y r e a c t i o n networks incorporating the e f f e c t s of process v a r i a b l e s and p h y s i c a l phenomena w i l l then be compared with experimental r e s u l t s obtained i n this and other 5 s t u d i e s . A model which can account for the l i q u e f i c t i o n behaviour of a broad range of coals and l i g n i t e i s sought. Such a model would improve our l i m i t e d understanding of coal l i q u e f a c t i o n k i n e t i c s and y i e l d more appropriate design c r i t e r i a for DCL reactors. These new design c r i t e r i a may lead to novel DCL reactor designs which l i q u e f y coal more completely or have improved spacetime y i e l d s . Such reactors may reduce or eliminate the cost d i s i n c e n t i v e for commercialization of DCL processes and f a c i l i t a t e the t r a n s i t i o n from mineral to "synthetic" f u e l s . 1.2 D i r e c t Coal L i q u e f a c t i o n - An Overview 1.2.0 Introduction Before delving into d e t a i l e d descriptions of many aspects of DCL reactor design, which comprise the following chapter, a b r i e f i n t r o d u c t i o n to DCL technology and terminology i s warranted. Those already f a m i l i a r with these topics may omit t h i s s e c t i o n . The most e f f e c t i v e way to introduce the technology and terminology associated with D i r e c t Coal L i q u e f a c t i o n i s to examine a t y p i c a l process flow sheet. Figure 1.1, referenced throughout t h i s preliminary discussion, i s not based on any p a r t i c u l a r process and indicates only the most general features of DCL processing technology. For more complete descriptions of the various l i q u e f a c t i o n processes, coal l i q u e f a c t i o n reaction k i n e t i c s e t c . , the reader i s referred to the appropriate sections of Chapter 2. 6 Gaseous Products ond By-Products: C02,H2S,NH5,CH4, Cool Gas Seporotion Solvent H„ 6 <7 Hydrogen Compressor Contactor Slurry Pre-Heoter Compressor C2H6etc Gos/Slurry Seporotion 1 * 5 * Solid Residue Process Heat Hydrogen Solvent Hydrogenation Hydrogen 4 Residue Treatment Product Oil Recycle Solvent Figure 1.1: A Dire c t Coal Liquefaction Process Schematic 7 1.2.1 Coal Slurry Preparation Slurry preparation i s the f i r s t stage i n a DCL process. Dried and pulverized coal or l i g n i t e i s combined with a solvent to form a 20-40 wt% co a l - i n - s o l v e n t s l u r r y . The solvent i s t y p i c a l l y a high b o i l i n g f r a c t i o n of the o i l produced from the coal i t s e l f and i s c a l l e d a recycle solvent. The solvent serves a number of r o l e s throughout the various stages of DCL processes but acts p r i m a r i l y as a v e h i c l e or c a r r i e r medium. The chemical and p h y s i c a l properties of solvents vary from process to process. In some processes, c a t a l y s t s are also added to the coal at th i s point. 1.2.2 Coal Liquefaction Coal s l u r r y i s compressed to between 10 and 30 MPa and combined with a gaseous hydrogen recycle stream. This multiphase mixture i s then fed to the l i q u e f a c t i o n reactor network. Coal o i l , synthetic natural gas and b y - p r o d u c t g a s e s : CO, CO^, H^S, NH^, are generated by thermal decompostion of the coal or l i g n i t e and a subsequent seri e s of homogeneous and heterogeneous reactions which occur i n the pre-heater and contactor. The p r e c i s e reaction paths vary from process to process. In some processes, gaseous or dissolved hydrogen reacts with coal fragments a r i s i n g from thermal decomposition. These reactions are believed to occur p r i n c i p a l l y on c a t a l y s t surfaces. In other processes, coal fragment- solvent i n t e r a c t i o n s predominate. Solvent properties, whether or not a 8 c a t a l y s t i s present and the precise operating conditions determine which path dominates. In general, l i q u e f a c t i o n reactions are i n i t i a t e d i n the pre-heater segment of the reactor and completed In the contactor. Coal l i q u e f a c t i o n reactions are exothermic, on balance, and a number of process v a r i a b l e s such as s l u r r y density, hydrogen r e c y c l e r a t i o , and pre-heater e x i t temperature, can be manipulated i n order to co n t r o l the reaction temperature. Consequently, the co n f i g u r a t i o n and operating conditions of pre-heaters and contactors vary somewhat from process to process. Pre-heater e x i t temperatures are t y p i c a l l y l e s s than 420°C and contactor operating temperatures are normally greater than 440°C. A x i a l mixing patterns and the scale of turbulence are determined l a r g e l y by the r e l a t i v e flow rates of hydrogen and s l u r r y . Hydrogen re c y c l e r a t i o s vary from 2 to 4. 1.2.3 Product Separation Product separation techniques vary g r e a t l y among e x i s t i n g DCL processes, and are not discussed, i n d e t a i l , i n t h i s t h e s i s . Much of the equipment i s not r a d i c a l l y d i f f e r e n t from separators encountered at conventional crude o i l processing plants, although more s p e c i a l i z e d techniques, such as anti- s o l v e n t de-ashing are employed f or ash and residua separation from the product l i q u i d . Hydrogen i s separated from the product and by-product gases, and recycled. Solvent i s separated from the product o i l and may contain r e s i d u a l c a t a l y s t . S o l i d residua and ash 9 report to a g a s i f i e r or furnace, and are used to produce hydrogen and/or process heat. 1.2.4 Solvent Treatment The p h y s i c a l and chemical properties of the solvent have an important influence on coal l i q u e f a c t i o n k i n e t i c s . Consequently, some processes hydrogenate the recycle solvent i n a c a t a l y t i c reactor p r i o r to r e c y c l e . Hydrogenation a f f e c t s both the chemical and physical properties of a solvent. The mean molar mass of the solvent i s reduced, the molar mass d i s t r i b u t i o n i s broadened, and the concentration of hydrogen donor molecules, ( i . e . ) molecules containing l a b i l e hydrogen atoms which can react with and s t a b i l i z e coal fragments, increases as a r e s u l t of hydrogenation. P h y s i c a l properties, such as v i s c o s i t y , density, the range of coal l i q u i d s soluble i n the solvent, and hydrogen s o l u b i l i t y are s i m i l a r l y a f f e c t e d . Processes which use hydrogenated solvents are re f e r r e d to as s o l v o l y t i c processes as they r e l y p r i m a r i l y on coal fragment-solvent i n t e r a c t i o n s to complete l i q u e f a c t i o n r e a c t i o n s . Processes which do not hydrogenate rec y c l e solvents r e l y p r i m a r i l y on hydrogen-catalyst-coal fragment i n t e r a c t i o n s and are c a l l e d c a t a l y t i c l i q u e f a c t i o n processes. However both modes of rea c t i o n occur i n both process types to varying degrees. 10 1.2.5 C a t a l y s t s M e t a l l i c sulphides have been i d e n t i f i e d as the most a c t i v e c a t a l y s t s for d i r e c t coal l i q u e f a c t i o n r e a c t i o n s . Since these compounds occur n a t u r a l l y and are frequently among coal constituents, c a t a l y s t s are u b i q u i t o u s a c t o r s i n DCL p r o c e s s e s . P y r i t e (FeS2) and t r a c e m e t a l l i c sulphates, which become m e t a l l i c sulphides i n s i t u , are the p r i n c i p l e n a t u r a l l y occurring c a t a l y s t s . Some processes enhance t h i s " n a t u r a l " c a t a l y t i c e f f e c t by adding powdered m e t a l l i c oxides (which s u l p h i d i z e i n s i t u ) , or aqueous m e t a l l i c s a l t solutions (which produce c o l l o i d a l m e t a l l i c sulphides In s i t u ) to the unreacted coal s l u r r y . Catalysts employed i n t h i s way are e i t h e r inexpensive or used sp a r i n g l y . These added c a t a l y s t s are r a r e l y recovered and r e c y c l e d . Other processes catalyse the solvent treatment or contactor stages s e l e c t i v e l y . These processes trap supported m e t a l l i c sulphide p e l l e t s ( t y p i c a l l y cobalt, molybdenum, or n i c k e l sulphides dispersed i n an a-alumina matrix) i n a s p e c i f i c process u n i t , and r e l y on n a t u r a l l y occurring c a t a l y t i c e f f e c t s throughout the remainder of the process. 11 Chapter 2 2. L i t e r a t u r e Review 2.1 D i r e c t Coal L i q u e f a c t i o n (DCL) Reactor Designs 2.1.0 Introduction I n d u s t r i a l DCL process research has undergone a renaissance during the past decade. Older processes, based on the pioneering DCL research of F. Bergius et a l , have been reviewed or revamped y i e l d i n g the Saarberg Werke and Ruhrkohle p r o c e s s e s ^ ' ^ ; heavy o i l processing technology has been applied to DCL ( i . e . ) the H-Coal process; and a number of new ideas r e l a t e d to c a t a l y s t s , c a t a l y s t use, and a s h / o i l separation have been tested. Process routes such as S y n t h o i l , CCL, CSF were developed during t h i s period and subsequently abandoned due to mechanical, scale-up and/or p r o d u c t i v i t y problems ̂  ' ̂ ^ . Other processes, l i s t e d on Table 2.1, have met with experimental success and are a c t i v e l y researched. Hybrid processes, incorporating design features from the processes c i t e d above, T 7 8 321 have also been considered ' ' • Preliminary work i s being conducted on the SRC-1/2 and the Lummus Clean Fuels from Coal Process (LCFFC) f o r example. The hydrogen consumption and gas y i e l d s for these processes are projected to be lower than the current processes and hetero-atom removal i s expected to be improved. F u l l y integrated operating data i s not yet TABLE 2.1 Direct Coal Liquefaction Process and Product Data PROCESS NAME OPERATINC C0NDIT1 ONS NET wt X YIELD (MAP BASIS) Temperature °C Pressure MPa MRT1 min wtX COAL in slurry Solvent Catalyst Gas Recycle Kg/Kg Coal SNG Hydrogen Consumed LIQUIDS Solids Pre-Heater Exit Reactor Percent Hetero-Atom Content S N 0 H-COAL 440-470 10-17 5-15 l heavy d l s t . Co-Mo/ rr-A^Oj 12. 6.6 58.4 .26 .90 <16.6 SRC I 415 440 12 40 25 heavy d i s t . mineral matter 0.1 8.2 3. 27.4 .6 1.3 4.1 52.4 SRC II 440 12 40 heavy d l s t . mineral matter > 0.1 18. 5. 48.5 .3 .8 4. 23. EDS 40-90 middle d i s t . 7-20 45. .1 SAARBERG WERKE AG heavy d is t . M0y 15. 5.5 54. 24.5 RUHRKOHLE 420 460-480 30 50 40 middle + heavy d i s t . M0X < 0.2 21.5 5.8 52. 21.2 CCLP 2 8. 7. 60. .013 .23 12. DOW 420 460 14 35 40 middle + heavy d i s t . co l lo ida l MoS2 22.1 5.2 46.7 .51 .49 2.8 for a single pass estimated 13 a v a i l a b l e and the processes cannot be evaluated o b j e c t i v e l y at t h i s time. Current DCL processes are categorized a r b i t r a r i l y i n the l i t e r a t u r e as " c a t a l y t i c " or " s o l v o l y t i c " processes. While these l a b e l s can be mis- leading, r e f e r to sections 1.2 and 2.3, the processes do present d i s t i n c t design a l t e r n a t i v e s . Flow sheets, f o r the processes c i t e d on Table 2.1, can be found on Figures 2.1-2.8. Many of the diff e r e n c e s between the processes occur outside the l i q u e f a c t i o n - r e a c t o r envelope, i n the a n c i l l a r y equipment ( i . e . ) hydrogen and process heat generation, de-ashing techniques, solvent hydrogenation; these differences are discussed at l e n g t h e l s e w h e r e ^ ' ̂  ' ^ . Within the l i q u e f a c t i o n - r e a c t o r envelope the processes share a number of design c r i t e r i a : (1) A pre-heater precedes the contactor(s) i n a l l cases, (2) A large quantity of hydrogen i s r e c i r c u l a t e d and has the following r o l e s : I) c o n t r o l l i n g reaction temperature i i ) promoting mixing i i i ) providing a hydrogenation medium, (3) The solvent i s a h i g h - b o i l i n g f r a c t i o n of the product o i l i ) permitting l i q u i d q u a l i t y improvement by recy c l e i i ) providing a s u i t a b l e coal d i s s o l u t i o n medium, (4) The contactors are a x i a l l y mixed with respect to the s l u r r y phase (5) Catalyst species are dispersed and move f r e e l y within the contactor(s), (6) Process operating conditions (temperature, pressure, nominal mean Hydrogen Cool V Hydrogen Recycle Reoctor Hydrocarbon Gases Recycle Gos Purification Light Distillate, T Water Hot Oil Recycle Pre heater Atmospheric Distillation HydrocJone Heavy Distillate Vacuum Distillation Bottoms Slurry Figure 2 .1 : H-Coal Process Schematic 4̂ Row Cool 1 Cool Preparation Slurry + Pumping Recycle Solvent Product Solidification 600° F 25PSIA Hydrogen ioo°f 1800 PSIA Preheater 800°f i700psia 100 °F 1600 PSIA 100 °F 65 PSIA Solvent Seporotion 600°f 30 PSIA Solids Separation 1000° F Hydrogenation Reactor Dissolver 550°f 1600 PSIA Desulfurizotion 5 5 0 » f 150 PSIA Gas Seporotion 550°f 1600 . i PSIA Pressure Letdown Product Ash Unreacted Carbon Excess Gas Sulfur Figure 2 .2 : SRC I Process Schematic OQ e Ct> CO n *0 H O n CD en CO CO o D* CD 3 tu rt o 91 Hydrogen Cool 1 X Slurry Preparation Liquefaction Figure 2.4: EDS Process Schematic Hydrogen _ } 7 V Distillote Product Separation Bottoms Gos Nophtho 7 C Solvent Hydrogenation Figure 2.5: Saarbergwerke Process Schematic Reoctors J J Vacuum Flash Gas Naphtha Middle Distillate Residue Heavy Oil Separators Distillate Oil Water Vacuum Residue Figure 2.6: Ruhrkohle Process Schematic I H, Coal J First Stoge Recycle H. Second Stoge Separation Gases Recycle Oil Primary Solids Separation Secondary Solids Seporotion Oil Residue Figure 2.7: CCLP Process Schematic o Catalyst Coal C Coal/Slurry Preparation Recycle Oil Recycle L Z Recycle Gas Clean-up S NH, 1 Gas-Liquid Separation I Feed Preheat Make-up r r r r 1 ! Vent Gas Light Oil Sour Woler Hydroclone ^ Deospholted Oil I Deospholter S NH3 H20 H20 Gosifier ^ Residue T T ASH V3L Fuel Gas T LPG Naphtha Dist. Fuel T Heavy Fuel Product Separations Figure 2.8: Dow Process Schematic ^ 22 residence time, etc.) are comparable, yet l i q u e f a c t i o n y i e l d s and product d i s t r i b u t i o n s vary widely among the d i f f e r e n t processes ( r e f e r to Table 2.1). V a r i a t i o n s i n product y i e l d and d i s t r i b u t i o n can only be rel a t e d to d e t a i l s such as the extent of a x i a l mixing, the i n t e n s i t y of turbulence, solvent composition or the precise c a t a l y s t composition. Perhaps operating conditions also play an important r o l e i n conjunction with the other process v a r i a b l e s . General aspects of DCL reactor design and the influence of design on product y i e l d and d i s t r i b u t i o n are analysed i n th i s s e c t i o n . Product y i e l d and d i s t r i b u t i o n v a r i a t i o n s a t t r i b u t e d to solvent composition, c a t a l y s t s e t c . are discussed separately. 2.1.1 L i q u e f a c t i o n Reactor Design 2.1.1.0 Introduction The d e s c r i p t i o n and ana l y s i s of reactor hydrodynamics i n v a r i a b l y involves process flow models. The following discussion i s not an exception. Five flow models, the plug flow model, the dispersed flow model, the r e c i r c u l a t i o n model, the continuously s t i r r e d tank reactor (CSTR) model and the tank i n s e r i e s (TIS) model are used to describe f l u i d flow patterns f o r various DCL reactors and pre-heaters. P i c t o r a l d e s c r i p t i o n s of these models can be found on Figure 2.9. The equations, d e f i n i n g the associated flow p a t t e r n s , are discussed elsewhere, i n d e t a i l ^ * ^ , and are simply introduced i n the text as they are required. 23 Plug Flow Model • Dispersion Model j 13 - e q , n 2 2 Recirculation Model pt> rs ~ ec*tn 2 3 Continuous Stirred Tank Model R eqtn 2-4 Tank in Series Model eqtn 2-5 Figure 2.9: Flow Models 24 2.1.1.1 Pre-heaters Pre-heaters are among the common features of a l l DCL reactor designs ( r e f e r to Figures 2.1-2.8). This piece of equipment i s intended to heat the c o a l - o i l - g a s mixture to r e a c t i o n conditions, i n i t i a t e the coal conversion process without causing the c o a l , or recycle o i l to coke. The pre-heater comprises a gas f i r e d b o i l e r , t y p i c a l l y , where the c o a l - o i l - g a s r e a c t i o n mixture flows through c o i l e d b o i l e r tubes and i s heated from ~ 20 °C to at l e a s t 350°C. The nominal mean-residence time (mrt) of the s l u r r y i n the pre-heater r a r e l y exceeds 8 minutes; le s s than 3 minutes of t h i s time i s spent at a k i n e t i c a l l y a c t i v e temperature ( i . e . ) T s l u r r y > 250°C. Pre-heater heating e f f i c i e n c y and s u s c e p t i b i l i t y to coking depends on the phase d i s t r i b u t i o n within the b o i l e r tubes and b o i l e r tube o r i e n t a t i o n . Possible flow regimes are i l l u s t r a t e d on Figure 2.10. Precise design data could only be obtained for the pre-heater at the 6 TPD SRC p i l o t plant, W i l s o n v i l l e , Alabama (Table 2.2). From o v e r a l l operating data, pre-heaters f 191 f o r the o t h e r processes appear to operate under comparable conditions . Flow pattern mapping of three phase flow systems has been performed, e x c l u s i v e l y , with air-water-inert s o l i d combinations at atmospheric c o n d i t i o n s . This work suggests that l i q u i d phase d i s p e r s i o n c o e f f i c i e n t s are unaffected by s u p e r f i c i a l l i q u i d v e l o c i t y and s o l i d s concentration, and that s o l i d and l i q u i d phase dispersion c o e f f i c i e n t s are equal regardless of Figure 2.10: Flow Regimes For Two Phase Flow 26 TABLE 2.2 W i l s o n v l l l e Pre-Heater Design Data Design S p e c i f i c a t i o n Value Pre-heater length 77.m Pre-heater diameter 3.25 cm S u p e r f i c i a l s l u r r y v e l o c i t y 20.cm s ^ S u p e r f i c i a l gas v e l o c i t y 100.cm s " 1 Pressure 12.MPa 27 r 121 flo w r e g i m e 1 1 . I f these r e s u l t s can be extended to oil-coal-hydrogen systems at high temperatures and pressures, one need only consider analogous two-phase flow systems. One flow pattern mapping study, performed with methane-oil flow at 7.7 MPa, and 38°C, i n a v e r t i c a l , 2.5 cm diameter column, suggests that the W i l s o n v i l l e pre-heater operates i n the "slug flow" r 131 regime . Results obtained from studies performed with air-water systems, i n the same diameter tubes at atmospheric conditions, concur - f o r h o r i z o n t a l , i n c l i n e d and v e r t i c a l t u b e s ^ 3 ' ̂  ' ̂ ""̂  . I t i s therefore probable i f not conclusive that pre-heaters operate i n the slug flow regime. The s l u r r y phase residence time d i s t r i b u t i o n , ( r t d ) , can be predicted r 121 from the di s p e r s i o n c o e f f i c i e n t 1 1 , D = v800 [log ( g ^ 3 Q v ~ 5 / 3 ) - 4.331] 3* 2 (2.1) and the dispersed flow model 9 1 —(1—0) C 9 = 2(*D/UL) ' 6 X p 4(D/UL) ( 2 ' 2 ) The W i l s o n v i l l e p r e - h e a t e r s l u r r y phase r t d f i t s a narrow Normal d i s t r i b u t i o n ( o = 0.04). Thus slug flow imparts strong l o c a l mixing but very l i t t l e s l u r r y phase dispersion. A l l of the s l u r r y passes through the pre-heater network within the i n t e r v a l 8 ±0.65 minutes, i f solvent evaporation and coal v o l a t i l i z a t i o n i s ignored. 28 Coal conversion reactions and the extent of r e a c t i o n occurring i n the pre-heater depends on the gas volume f l u x , the s l u r r y f l u x , the coal concentration i n the s l u r r y , pre-heater e x i t temperature and solvent c o m p o s i t i o n , i n a complex m a n n e r ' ^ ^ . S h o r t - r e s i d e n c e - t i m e , batch- autoclave experiments, performed with bituminous coals ( I l l i n o i s #6, Kentucky #14), i n d i c a t e that coal conversion, to pyridine soluble products, e x h i b i t s a weak dependence on s l u r r y Reynolds number but i s independent of hydrogen pressure and hydrogen : s l u r r y mass r a t i o R e s u l t s , from short residence time experiments conducted i n flow apparatus, note the influence of solvent q u a l i t y on the extent of coal conversion to pyridine soluble f 181 m a t e r i a l , and the hydrogenation p o t e n t i a l of the i n i t i a l products . The d i f f e r e n c e i n the hydrogen dependence between batch and flow apparatus may be a t t r i b u t e d to di f f e r e n c e s i n solvent composition, and the r o l e hydrogen p l a y s i n e s t a b l i s h i n g the s c a l e of t u r b u l e n c e and heat t r a n s f e r c h a r a c t e r i s t i c s i n flow apparatus. The presence of hydrogen should have l i t t l e impact on s l u r r y hydrodynamics i n a vigorously s t i r r e d autoclave. However, the precise r o l e of solvents and hydrogen, i n pre-heaters, i s not resolved i n the l i t e r a t u r e . 2.1.1.2 Contactor Design 2.1.1.2.0 Introduction The contactor segment of the l i q u e f a c t i o n reactor i s intended to complete the l i q u e f a c t i o n reactions and generate s u f f i c i e n t recycle solvent 29 to permit continuous o p e r a t i o n of the l i q u e f a c t i o n reactor . Contactor designs, f o r the processes c i t e d on Table 2.1, are p r o p r i e t a r y . Precise design and operating data for these processes i s scant, but s u f f i c i e n t data do e x i s t to permit a hydrodynamic c h a r a c t e r i z a t i o n of each process and to contrast the d i f f e r e n t processes. 2.1.1.2.1 Single Stage Contactors 2.1.1.2.1.1 The H-Coal Reactor The m a j o r d e s i g n f e a t u r e s a n d d i m e n s i o n s o f the H - C o a l [90 911 contactor 1 ' are i l l u s t r a t e d on Figure 2.11. The unique features of the contactor include an annular ebullated c a t a l y s t bed and forced i n t e r n a l r e c i r c u l a t i o n of processed o i l . The broad spectrum of operating data, Table 2.1, a c t u a l l y r e f l e c t two d i s t i n c t modes of operation, synthetic crude o i l and low sulphur f u e l o i l production, r e a l i z e d at or near the extrema of the processing conditions. Low sulphur f u e l o i l i s obtained at the lower temperature and short contact time extremum, while synthetic crude o i l production requires more severe processing conditions. A product s l a t e comparison f or these two modes of operation can be found on Table 2.3. C o - p r o c e s s i n g of heavy m i n e r a l o i l s and c o a l i s under i n v e s t i g a t i o n r e g i o n a l l y [20]. For th i s s p e c i f i c case, a "recycle solvent" i s not necessary. 30 [90] Figure 2.11: The H-Coal Contactor 31 TABLE 2.3 H-Coal Product Slate Comparison Coal I l l i n o i s Bituminous Desired Product Synthetic Low-Sulphur Crude Fuel O i l Normalized Product D i s t r i b u t i o n (wt%) C^-C^ Hydrocarbons 10.7 5.4 C, - 205°C D i s t i l l a t e 4 17.2 12.1 205°C-343°C D i s t i l l a t e 28.2 19.3 343°C-524°C D i s t i l l a t e 18.6 17.3 524°C + Residual O i l 10.0 29.5 Unreacted Ash-Free Coal 5.2 6.8 H 20, NH3, H 2S, CO, C0 2 15.0 12.8 T o t a l (100.0 + H 2 Reacted) 104.9 103.2 Conversion, % 94.8 93.2 32 r 90 9 1 1 H - C o a l C o n t a c t o r 1 ' ' hy d r o d y n a m i c s a r e c o n s t r a i n e d by the necessity to keep the c a t a l y s t bed f l u i d i z e d and are independent of the mode of operation - Table 2.4 comprises a summary of hydrodynamic c a l c u l a t i o n s found i n Appendix A . l . The s l u r r y s u p e r f i c i a l v e l o c i t y , i n the absence of re c y c l e , i s l e s s than one-tenth the minimum s u p e r f i c i a l f l u i d i z a t i o n v e l o c i t y . The minimum recycle r a t i o s required to achieve f l u i d i z a t i o n are 12:1 and 36:1 for f u e l o i l and synthetic crude o i l production r e s p e c t i v e l y . In both cases, the residence time d i s t r i b u t i o n , described by equation 2.3 - (N0 + 0 ) - (N0 ) m N _ 1 E 9 = N e * (mN-1)! <2'3> m=i ensures a minimum s l u r r y - c a t a l y s t contact time (approximately 0.5 min) p r i o r to recycle but i s otherwise i n d i s t i n g u i s h a b l e from the CSTR residence time d i s t r i b u t i o n , equation 2.4 E e = e ~ 9 (2.4) f 211 One can i n f e r , from the H-Coal pr o c e s s development u n i t c a t a l y s t r t d L J * ( F i g u r e 2.12) , t h a t the c o n t a c t o r i s operated a t or near the minimum f l u i d i z a t i o n condition c i t e d above. The c a t a l y s t r t d shows evidence of low frequency gross r e c i r c u l a t i o n which i s t y p i c a l hydrodynamic behaviour f o r asymmetrically f l u i d i z e d beds operating near the minimum f l u i d i z a t i o n , , [221 v e l o c i t y * B i c k e l and Thomas f i t t e d t h e i r data to the CSTR r t d model. The f i t i s poor and perhaps i n v a l i d because of the i n j e c t i o n and sampling procedures used i n th e i r study: the tracer was in j e c t e d as a plane d i s t r i b u t i o n rather than as a f l u x , and c a t a l y s t was removed from the contactor batch-wise - a continuous o u t l e t stream was not sampled [23]. In a d d i t i o n , s i g n i f i c a n t c a t a l y s t losses occurred during the course of the tracer study. 33 TABLE 2.4 Hydrodynamic C a l c u l a t i o n Summary f o r the H-Coal Reactor (f o r d e t a i l s r e f e r to Appendix A.l) S u p e r f i c i a l L i q u i d V e l o c i t i e s Value Minimum f l u i d i z a t i o n v e l o c i t y S l u r r y v e l o c i t y : syn-crude mode b o i l e r f u e l mode 2.3 - 3.5 cm s ^ 0.06 - 0.10 cm s - 1 0.19 - 0.30 cm s " 1 34 1.2 A A A O 0.8 z LLI O LU rr o.6 A A Legend A EXPERIMENTAL RTD CSTR RTD A A 0.4 A A A 0.2 0.5 1 1.5 NORMALIZED TIME Figure 2 .12: Catalyst Residence Time D i s t r i b u t i o n i n a H-Coal Contactor 35 The advantages of the H-Coal contactor design occur p r i n c i p a l l y i n the syncrude mode. R e l a t i v e l y short times, 15 min, produce high y i e l d s of hydrogenated l i q u i d s that are e a s i l y upgraded. Over 34% of the l i q u i d product can be used as a petrochemical feedstock - a percentage 1.5 times [241 g r e a t e r than the n e a r e s t r i v a l , SRCII L . The d i s a d v a n t a g e s of the process include the high costs associated with s l u r r y r e c i r c u l a t i o n and c a t a l y s t use ( e l u t r i a t i o n losses caused by p a r t i c l e abrasion, c a t a l y s t d e a c t i v a t i o n and replacement), and poor s l u r r y d i s t r i b u t o r design. Improved d i s t r i b u t o r design could reduce or eliminate c a t a l y s t bed r e c i r c u l a t i o n , thus minimizing p a r t i c l e abrasion and s h o r t c i r c u i t i n g . 2.1.1.2.1.2 The Solvent Refined Coal Contactor (SRC I & II) The SRC I and SRC II processes share a common contactor design. The contactor i s an open v e r t i c a l tube with gas i n j e c t i o n ports mounted on the r 251 s i d e s ; i t i s operated at constant temperature . The di f f e r e n c e s between the two processes p a r a l l e l the d i f f e r e n c e s between the two operating modes of the H-Coal Process. The SRC I process Is intended to produce a synthetic refined coal (SRC) - low i n ash and sulphur. This product o b j e c t i v e requires a minimum extent of r e a c t i o n . Consequently, ash bearing process streams are not returned to the contactor. D i s t i l l a t e o i l s are the primary products of the SRC I I process; high ash process streams containing unreacted c o a l , d i s t i l l a t e bottoms etc., are recycled to the contactor to enhance c a t a l y t i c e f f e c t s and improve o v e r a l l y i e l d s . Operating data f o r both processes can be found on Table 2.1. 36 The SRC contactor i s susceptible to hydrodynamic dif f e r e n c e s a r i s i n g from changes i n s c a l e . The 5.45 tonne per day W i l s o n v i l l e plant operating data suggests that a l l the gas enters with the s l u r r y at the base of the c o n t a c t o r ^ ^ . C a l c u l a t i o n s , employing equation 2.1 and the tank-in-series flow model ( T I S ) ^ 1 6 ^ , equation 2.5, N(N9)^"^ -NG E 6 ( N - l ) ! 6 ( 2 * 5 ) predict a s l u r r y r t d equivalent to the TIS model with the number of tanks i n s e r i e s , N, a p p r o x i m a t e l y equal to 1.24. Lee et a l ^ ^ f i t t e d a flow and k i n e t i c model to t y p i c a l W i l s o n v i l l e product y i e l d s and d i s t r i b u t i o n s . Their d i s p e r s i o n analysis r e s u l t s correspond to a tank i n serie s residence time d i s t r i b u t i o n with N=1.35. Gas j e t s are positioned at i n t e r v a l s along r 251 the s i d e s of the l a r g e r (45.5 tonne per day) Fort Lewis contactor and one cannot assign a sing l e dispersion c o e f f i c i e n t to the e n t i r e contactor. Experimental s l u r r y phase r t d data was obtained, f o r t h i s contactor, by i n j e c t i n g a radio a c t i v e tracer at the mid point of the contactor and measuring the tracer concentration as a function of time at the summit and b a s e ^ 2 ^ . These r e s u l t s i n d i c a t e a maximum mixing v e l o c i t y of 0.95 cm.s * and 0.67 cm.s ^ i n the top and bottom p o r t i o n s of the c o n t a c t o r . The d i f f e r e n c e i n mixing v e l o c i t y can be a t t r i b u t e d to differences i n gas f l u x , the e f f e c t of s l u r r y f l u x on counter current bulk d i f f u s i o n (the mean s l u r r y v e l o c i t y i s i n the range 0.16 - 0.48 cm.s ^"), or both. In eit h e r case, the contactor e x h i b i t s extensive a x i a l mixing and i s l i k e l y to have a residence time d i s t r i b u t i o n which corresponds to a recycle flow model or a TIS model with N<2, depending. on the influence of macro-mixing and micro-mixing e f f e c t s . 37 The SCR I and SRC II processes have commercial prospects only on a re g i o n a l b a s i s . The mean residence times are long and the product s l a t e i s r e s t r i c t e d . Bituminous coals with c a t a l y t i c a l l y a c t i v e mineral matter appear to be the only suitable feed m a t e r i a l s . 2.1.1.2.1.3 The Dow Contactor Few construction or operation d e t a i l s are a v a i l a b l e f o r the Dow r 271 Contactor . The contactor i s described as "a back-mixed, pressure vessel of open tube design"; the hydrodynamics should be comparable to the SRC contactor. The coal i s hydrogenated i n the presence of an ( o i l i n water) emulsion c a t a l y s t . The emulsion i s used to carry and dispense an inorganic molybdate s a l t which p r e c i p i t a t e s as c o l l o i d a l M0S2 i n s i t u . Molybdenum l e v e l s i n the s l u r r y are i n the range of 100 ppm.. Processing conditions are summarized on Table 2.1. The Dow contactor produces a broad range of products w e l l suited to the process requirements of a large chemical plant: petrochemical feed stocks, clean fuels f o r e l e c t r i c i t y generation, process steam e t c . . 2.1.1.2.2 Multi-stage Contactors 2.1.1.2.2.1 The Ruhrkohle Contactor Two contactor designs have been tested for the Ruhrkohle process: 38 the 0.5 tonne per day experimental plant at Bergbau-Forschung contains a [21 v e r t i c a l up-flow tubular contactor 1 , the 200 tonne per day p i l o t plant at [281 B o t t r o p employs t h r e e up-flow t u b u l a r c o n t a c t o r s i n s e r i e s 1 . The Bergbau-Forschung contactor operates at constant temperature and contains magnetically driven impellers to promote l o c a l mixing. In the absence of forced a g i t a t i o n , the s l u r r y and dispersed metal oxide c a t a l y s t r t d would resemble the TIS flow model r t d with N=1.3 (see Appendix A.3). With a g i t a t i o n , l o c a l r e c i r c u l a t i o n patterns are established about each impeller, s l u r r y d i s p e r s i o n i s reduced, and the apparent number of stages i n s e r i e s , [29 1 N, i n c r e a s e s 1 . More e x p l i c i t process data i s required to evaluate the s l u r r y r t d i n the B-F plant contactor. Each stage of the 3 stage p i l o t plant contactor operates on the same p r i n c i p l e as a bubble column and i s a x i a l l y mixed. The stages operate at constant but d i f f e r e n t temperatures and t h e o v e r a l l r e s i d e n c e time d i s t r i b u t i o n approximates 4 + tanks i n s e r i e s . The Ruhrkohle process i s at an advanced stage of development, and high y i e l d s of l i g h t and middle d i s t i l l a t e o i l s are obtained ( r e f e r to Table 2.1). Possible d e b i l i t i e s of t h i s process include a long mean residence time, and high gas and residue y i e l d s . However, the process can be used to upgrade heavy mineral o i l s , at 5 times the production rate of o i l from c o a l , with minor modifications. 39 2.1.1.2.2.2 The Saarbergwerke Contactor The Saarbergwerke contactor d i f f e r s s i g n i f i c a n t l y from the other multistage contactors (Figure 2.5). A portion of the s l u r r y feed by-passes the pre-heater and the f i r s t stage of the contactor to enter at the base of the second stage. There are 4 stages i n t o t a l , each an up-flow tubular f2] r e a c t o r 1 . Optimum ranges f o r pressure, temperature s l u r r y mean-residence- time, and gas flow rates have not been published. The absence of hydrodynamic data precludes an evaluation of a x i a l mixing e f f e c t s , and there i s i n s u f f i c i e n t data to review the contactor c r i t i c a l l y . 2.1.1.2.2.3 The EDS Contactor The EDS contactor has a staged c o n f i g u r a t i o n ^ " ^ , which i s not shown on the s i m p l i f i e d flow sheet, Figure 2.4. The contactor comprises a m u l t i - stage d i s s o l v e r , the number of stages i s not s p e c i f i e d , and a fixed-bed, c a t a l y t i c hydrogenation unit - operated as a CSTR. A vacuum d i s t i l l a t i o n u n i t s e p a r a t e s the d i s s o l v e r from the hy d r o g e n a t i o n u n i t . L i g h t h y d r o c a r b o n s ( T , < 2 0 4 ° C ) and c o a l r e s i d u e s (unreacted c o a l , ash and D l i q u e f a c t i o n products with a b o i l i n g temperature greater than 500°C) by-pass the hydrogenation unit permitting smooth operation of the fixed-catalyst-bed and minimizing synthetic natural gas formation. *The EDS p r o c e s s o u t l i n e d here Is not the o r i g i n a l one, proposed by EXXON during 1966, but a process variant developed l a t e r where a large f r a c t i o n of the vacuum bottoms i s recycled to the d i s s o l v e r . 40 The contactor can operate i n two processing modes: "high naphtha" and "mixed mode". Approximately the same l i q u i d y i e l d i s r e a l i z e d i n both modes, Figure 2.13, but under high naphtha conditions the l i q u i d products a r e p r i m a r i l y to T^<204°C l i q u i d s . The i n t e r p l a y between d i s s o l v e r and hydrogenation unit operating conditions required to achieve the processing modes i s not s p e c i f i e d but (1) hydrogen consumption i s s u b s t a n t i a l l y greater i n the "high naphtha" mode (a more hydrogenated l i q u i d i s produced, 3 to 4 times as much SNG i s produced), (2) the s l u r r y mean residence time i s longer, (3) hydrogenation conditions are more severe. Advantages of the EDS process include product s l a t e and coal feed f l e x i b i l i t y ^ ^ , and high y i e l d s of l i g h t o i l s . The disadvantages include a complex reactor network, and long residence time - e s p e c i a l l y when the hydrogenation u n i t residence time i s included. 2.1.1.2.2.4 The Chevron Coal L i q u e f a c t i o n Process (CCLP) Contactor [311 CCLP i s a r e c e n t p r o c e s s 1 . The c o n t a c t o r has two stages: the f i r s t an uncatalyzed d i s s o l v e r , the second a c a t a l y t i c hydrogen u n i t ; the processing conditions f o r both stages can be optimized separately. No operating data has been published. The high l i q u i d y i e l d s , suggested by the data on Table 2.5, can be misleading. The data was obtained from a 23 kg per day laboratory scale 50 40- 0 s Q - J UJ >- 30- O 20 a o Q. 10 Legend EZ3 DISTILLATE H NAPHTHA EH GAS L_ Figure 2.13: Product F l e x i b i l i t y of the EDS Process TABLE 2.5 CCLP Process Y i e l d s Feed Coal I l l i n o i s No.6 I l l i n o i s No.2 Dietz No.l A u s t r a l i a n Brown Coal (Burning Star) (Sunspot) (Decker) (Morwell) Products (wt%) 7.4 6.8 10.7 10.2 > C 4 l i q u i d 73.7 79.6 65.2 66.1 * Undissolved coal 9.8 4.2 11.8 4.5 H 20, CO, C0 2 15.3 17.8 20.0 28.0 H 2S, NH3 Hydrogen Consumption 5.9 8.1 7.4 8.7 O i l Y i e l d 4.6 5.2 4.2 4.4 (BBL tonne _ 1MAF Coal) * Ethyl-acetate insoluble material 43 integrated p i l o t plant: hydrogen and process heat were not generated from the coal and " l i q u i d s " with T b>500°C are included i n the d i s t i l l a t e product. R e a l i s t i c estimates of the l i q u i d y i e l d s would be lower by perhaps 15%. The process does not present a d i s t i n c t advantage over the processes c i t e d above. 2.1.1.3 Reactor Design Rationale The l i q u e f a c t i o n reactor designs c i t e d above r e f l e c t the extreme operating conditions required for Direct Coal L i q u e f a c t i o n and the desire to employ e x i s t i n g heavy o i l processing f a c i l i t i e s as DCL p l a n t s . Heavy o i l s are and have been upgraded i n very s i m i l a r r e a c t o r s . In addition, a p p l i c a t i o n s of simple 1st or 2nd order k i n e t i c models to the complex coal l i q u e f a c t i o n r e a c t i o n network has led to the conclusion that l i t t l e b e n e f i t accrues beyond segmenting a reactor into the equivalent of 4 tanks In s e r i e s ^ ^ ' (i.e.") the marginal cost of a d d i t i o n a l reactor segmentation i s not recouped by increases i n the y i e l d of o i l e t c . from the c o a l . 2.2 L i q u e f a c t i o n Reactions and K i n e t i c s 2.2.0" Introduction Coal undergoes a complex sequence of physical and chemical processes as i t i s l i q u e f i e d and hydrogenated. To date, research has focussed on an 44 a n a l y s i s of the d i s s o l u t i o n and k i n e t i c behaviour of bituminous c o a l s . The events, l i s t e d on Figure 2.14, r e f l e c t the current understanding of the o v e r a l l l i q u e f a c t i o n sequence for bituminous coals (sub-bituminous coals T 3 3 3A1 appear to e x p e r i e n c e a comparable sequence ' . While the l i q u e f a c t i o n "events", c i t e d on Figure 2.14, are not disputed, there i s l i t t l e agreement In the l i t e r a t u r e on the reaction mechanisms* rea c t i o n paths, or on the c o r r e c t t h e o r e t i c a l approach to adopt i n evaluating the r e a c t i o n k i n e t i c s connecting them. Many of the d i s p a r i t i e s can be a t t r i b u t e d to hydrodynamic e f f e c t s and other incompatable differences i n r e a c t i n g environments, or product a n a l y s i s which act as hidden v a r i a b l e s . Other d i s p a r i t i e s , i n h i b i t i n g the c o r r e l a t i o n of data obtained under comparable conditions, are caused by the presence of multiple regression minima. Often two or more sets of k i n e t i c parameters "optimize" the f i t of a reaction model to r 351 e x p e r i m e n t a l data . A l t e r n a t i v e l y , several d i f f e r e n t models may f i t the r 3 51 data e q u a l l y w e l l . C u r r e n t k i n e t i c s t u d i e s are of l i m i t e d use f o r design purposes. One must r e l y on an understanding of the fundamental l i q u e f a c t i o n phenomena, "events" and the factors which influence them. 2.2.1 Coal Swelling and Solvent Absorption Four to ten f o l d transient increases i n s l u r r y v i s c o s i t y have been * T36 37 381 r e p o r t e d f o r a v a r i e t y of 30-40% c o a l — o i l s l u r r i e s 1 ' ' J on i n i t i a l *Kentucky 9 and I l l i n o i s 6, both bituminous coals, and a Japanese coal Shin- Yubari. 45 1. SOLVENT ABSORPTION 2. PRIMARY DISSOLUTION 3. SECONDARY DISSOLUTION 4. HYDROGENATION 5. HETERO-ATOM REMOVAL 6. RETROGRESSIVE REACTIONS Figure 2.14: Coal Liquefaction Phenomena 46 heating through the 280-380°C temperature range and at elevated pressures (approximately 15 MPa). This e f f e c t has been a t t r i b u t e d to the formation of r 331 v i s c o u s l i q u i d p roducts d e r i v e d from thermal decomposition of coals r I However, c o a l p a r t i c l e s w e l l i n g was observed by Droege et a l and the increases i n apparent v i s c o s i t y are consistent with values predicted by s l u r r y transport c o r r e l a t i o n s for 50 to 100% increases In coal p a r t i c l e r 391 [40 41 421 s i z e . The swelling can r e s u l t from solvent-coal i n t e r a c t i o n s ' ' 1 r 43 ] and/or thermal decomposition of the coal . Both causes of swelling can account for the predicted increases i n p a r t i c l e s i z e and o i l absorption i n d i v i d u a l l y . 2.2.2 Primary D i s s o l u t i o n As more r e a c t i v e macerals, v o l a t i l e matter, continue to i n t e r a c t with the solvent and d i s s o l v e or evolve, l e s s r e a c t i v e maceral and mineral matter fragments become detached from the o r i g i n a l coal p a r t i c l e s , p a r t i c l e s i z e i s reduced and the v i s c o s i t y t r a n s i e n t s u b s i d e s . The destruction of coal p a r t i c l e s , i n this manner, supports the widely held view that i n i t i a l p a r t i c l e s i z e has l i t t l e influence on the rate of coal l i q u e f a c t i o n , and h i g h l i g h t s the importance of coal-solvent Interactions during the i n i t i a l stages of r e a c t i o n . In poor hydrogen-donor solvents or donor depleted T h e r e i s no e x p e r i m e n t a l evidence r e l a t e d to the method of p a r t i c l e d e s t r u c t i o n . Hydrodynamic e f f e c t s ( i . e . ) the i n t e n s i t y of turbulence may determine the extent of p a r t i c l e d e s t r u c t i o n or the p a r t i c l e s may "explode" due to gas evolution e t c . . 47 solvents, f o r example, high-molecular-weight, viscous, l i q u i d products can be formed by condensation reactions between solvent molecules and coal r 33 521 d e r i v e d r a d i c a l s or by i n t e r or i n t r a - r a d i c a l r e a c t i o n s ' . These "condensed" products can p r e c i p i t a t e during the i n i t i a l stages of r e a c t i o n [441 ( a t low temperatures or i n poor p h y s i c a l solvents) to form SRCL 1 . The condensed products formed by such reactions, including SRC, can be r e - f451 hydrogenated during subsequent stages of rea c t i o n but reduce space-time y i e l d s of lower-molecular-welght, l i q u i d products ( o i l s , naphthas). Primary d i s s o l u t i o n reactions are completed within the f i r s t 2 to 10 minutes of high T37 181 temperature contact time ' ; the c o n t r o l l i n g variables appear to include the contact temperature, coal type, and the solvent composition. These reactions are highly exothermic and generally occur before the s l u r r y enters the contactor. 2.2.3 Secondary D i s s o l u t i o n The cleavage of les s reactive bonds and k i n e t i c a l l y slower r e a c t i o n s , occurring within the dispersed coal fragments or SRC p a r t i c l e s ( p r e c i p i t a t e d during primary d i s s o l u t i o n ) , leads to secondary coal d i s s o l u t i o n . Abundant p h y s i c a l and chemical evidence supports the existence of t h i s phenomenon: [46 471 I Coal i s not s t r u c t u r a l l y homogeneous ' . Constituent macerals [42 1 e x h i b i t a broad range of r e a c t i v i t i e s under DCL c o n d i t i o n s . Coals with comparable elemental compositions can have r a d i c a l l y d i f f e r e n t maceral d i s t r i b u t i o n s and hence d i f f e r e n t average r e a c t i v i t i e s and hydrogenation p o t e n t i a l s . 48 i i Dissolution-reaction-order has been observed to f l u c t u a t e as d i s s o l u t i o n p r o g r e s s e s ' ^ . i i i The apparent a c t i v a t i o n energy of the d i s s o l u t i o n r e a c t i o n increases r 491 with the extent of d i s s o l u t i o n 1 '. m i v The d i s s o l u t i o n p o t e n t i a l for a coal i s temperature dependent, p a r t i c u l a r l y under s o l v o l y t i c l i q u e f a c t i o n c o n d i t i o n s . Two t e m p e r a t u r e ranges (350-400°C, 4 0 0 + o C ) w i t h c h a r a c t e r i s t i c a l l y d i f f e r e n t d i s s o l u t i o n k i n e t i c s have been i d e n t i f i e d ^ 3 " ' ' " ' ^ . At lower temperatures d i s s o l u t i o n i s dominated by e t h e r bond rupture ; at higher temperatures, d i s s o l u t i o n has been shown to include methyl [50,51] group cleavage 1 v Reaction models, not Incorporating secondary d i s s o l u t i o n e f f e c t s , frequently e x h i b i t poor or skewed f i t s to experimental d i s s o l u t i o n , ^ [33-35] data 1 1 . I t i s d i f f i c u l t to estimate the coal f r a c t i o n involved i n secondary d i s s o l u t i o n . By analyzing experimental r e s u l t s , f i t with r e a c t i o n models not i n c l u d i n g t h i s e f f e c t , between 5 and 20 percent of the r e a c t i v e coal appears to d i s s o l v e i n t h i s way. However, the percentage i s highly v a r i a b l e even f o r the same c o a l ; s o l v e n t e f f e c t s , l i m i t s on e x p e r i m e n t a l r e p r o d u c a b i l i t y , and differences i n r e s u l t analysis ( i . e . coal d i s s o l u t i o n can Be defined on the basis of pyridine, THF or Benzene s o l u b i l i t y ) impair Some low rank bituminous c o a l s do not appear to possess reactive ether linkages[51]. an accurate assessment. Secondary most part i n DCL contactors as they completion. 49 d i s s o l u t i o n reactions occur for the can require 2 or more hours to reach 2.2.4 Hydrogenation 2.2.4.1 Hydrogenation Reactions [ 53 1 C u r r a n e t a l p r o p o s e d a f r e e r a d i c a l mechanism f o r the t r a n s f e r of hydrogen from solvents to coal and coal derived l i q u i d s . T h i s work has been extended by other r e s e a r c h e r s ^ ^ and provides a h e l p f u l framework for examining coal hydrogenation reactions. Coal and coal derived l i q u i d s are hydrogenated by reactions with: 1) hydrogen donor molecules present i n the solvent, ( t e t r a l i n , A^U A . .[44,33-35,57] dihydropyrene, etc.) . r 541 2) dissolved molecular hydrogen 3) solvent or coal derived products hydrogenated i n s i t u ^ " * ^ . The reactions are i n i t i a t e d and propagated by free r a d i c a l s which occur both "heterogeneously and homogeneously. The r e l a t i v e importance of the three r e a c t i o n paths and the dominance of heterogeneous or homogeneous r e a c t i o n i s determined by the s p e c i f i c coal-solvent-catalyst-gas system, 5 0 reactor hydrodynamics, and operating conditions. The most r e a c t i v e path dominates. As hydrogenation progresses a sequence of r e a c t i o n paths exert d i f f e r e n t k i n e t i c s and dependencies on extensive and i n t e n s i v e system properties. 2.2.4.2 Heterogeneous Reactions Two types of heterogeneous reactions occur within DCL r e a c t o r s . The f i r s t occurs at the onset of coal d i s s o l u t i o n within coal p a r t i c l e s or on the surface of coal fragments. Coal derived free r a d i c a l s are s t a b i l i z e d by reactions 1-3 above or by condensation r e a c t i o n s . The second type of heterogeneous r e a c t i o n occurs on c a t a l y s t , ash, autoclave s u r f a c e s ^ ^ ' ^ ^ . Di s s o l v e d , low-molecular-weight, coal-derived molecules r 591 ( p h e n o l s , c a t e c h o l s , p l a n a r benzoid molecules ) are adsorbed on f 58 591 Co-Mo-alumina c a t a l y s t and metal/metal oxide/metal s u l f i d e surfaces ' . Adsorbed molecules can undergo three d i s t i n c t r e a c t i o n sequences depending on l o c a l hydrodynamic phenomena: (1) dehydrogenation followed by rapid rehydrogenation (2) dehydrogenation followed by polymerization ("3) hydrogenation and/or hydrogenolysis Reaction sequence (1) i s best exemplified by catechol adsorbed on high- T591 speed s t i r r e r s u r f a c e s . The catechol forms a surface s t a b i l i z e d free 51 r a d i c a l by donating a hydride to a coal derived r a d i c a l or molecule. The surface r a d i c a l i s rehydrogenated r a p i d l y i n the hydrogen saturated environment. Adsorbed organic molecules reacting i n t h i s way act as c a t a l y s t s . Reaction sequence (2) leads to the formation of coke or coke precursors. The dehydrogenation step i s the same as for sequence (1) . However, i n the absence of a rehydrogenating medium or i n a poorly hydrogenating medium, adsorbed r a d i c a l s undergo condensation/polymerization reactions . Coke i s i n v a r i a b l y associated with q u a r t z - c a l c i t e deposits i n SRC r e a c t o r s and forms on Co-Mo-alumina c a t a l y s t p a r t i c l e s i n the [211 H-Coal r e a c t o r 1 . Reaction mode (3) includes several classes of hydro- genolysis and hydrogenation reactions. These reactions are discussed i n sections 2.2.5 and 2.3. 2.2.4.3 Homogeneous Reactions Coal free r a d i c a l s , s t a b i l i z e d on i n i t i a l d i s s o l u t i o n , may possess [35 l a d d i t i o n a l r e a c t i v e bonds . Further, homogeneous, thermal cleavage, followed by hydrogenation, reduces the average molecular weight and r a i s e s the hydrogen to carbon atomic r a t i o of the l i q u i d products. However, re t r o g r e s s i v e reactions also occur. These reactions reduce space-time yield's of low molecular weight products and/or reduce the l i q u e f a c t i o n p o t e n t i a l of a c o a l . I d e a l l y , such reactions could be eliminated i f r a d i c a l s were hydrogenated as r a p i d l y as they were formed. P e t r a k i s et a l ^ " ^ o b t a i n e d r e s i d u a l f r e e r a d i c a l concentrations f o r a v a r i e t y of bituminous and sub-bituminous coals and l i g n i t e i n a broad range of solvents under DCL conditions. They concluded that r e s i d u a l free r a d i c a l concentrations could only be minimized, and that the rate of hydrogenation i s con t r o l l e d by the rate of hydrogen transfer to r a d i c a l s . T h i s c o n c l u s i o n i s supported by Guin et a i l ^ » ^ J who found that coal l i q u i d hydrogenation could be c o n t r o l l e d by molecular hydrogen trans f e r to the solvent, or the extent of solvent hydrogenation. Other researchers have concluded that the rate of coal d i s s o l u t i o n , ( i . e . ) r a d i c a l formation, r 531 l i m i t s the rate of hydrogenation 1 1 . These two c o n t r a d i c t o r y c o n c l u s i o n s r e f l e c t d i f f e r e n c e s i n experimental conditions and i l l u s t r a t e the temperature, pressure, c a t a l y t i c s e n s i t i v i t y of many coal-solvent-catalyst-gas DCL systems. Free r a d i c a l generation has a high a c t i v a t i o n energy. The rate of r a d i c a l r 681 f o r m a t i o n i n c r e a s e s r a p i d l y i n the temperature range 350-450°C . At low temperatures within t h i s range, r a d i c a l generation occurs slowly and good donor solvents hydrogenate r a d i c a l s as they form. Such systems are not s e n s i t i v e to (1) the presence or pressure of a hydrogen or i n e r t gas cover^"*^, (2) the solvent to coal r a t i o At higher temperatures, the rate of r a d i c a l generation can exceed the rate at which solvent alone can donate hydrogen. Under these conditions, l i q u e f a c t i o n y i e l d s are s e n s i t i v e to solvent composition, the rate of solvent rehydrogenation and hydrogen p r e s s u r e ' ̂ 3 ' ^ . Other hydrogenation r e a c t i o n paths become i m p o r t a n t ^ ^ , and retrogressive reactions become more s i g n i f i c a n t ^ ^ . 5 3 r 6 2 1 These e f f e c t s are accentuated i n poor donor solvents , or i n solvents, such as t e t r a l i n , which are subject to thermal degradation and hydro- c r a c k i n g at e l e v a t e d temperatures and p r e s s u r e s . C a t a l y s i s and ret r o g r e s s i v e reactions are discussed separately. 2.2.5 Hetero-Atom Removal 2.2.5.1 Reactions The removal of hetero-atoms, oxygen, nitrogen, and sulphur, from coal l i q u i d s i s an important aspect of d i r e c t coal l i q u e f a c t i o n . Hydro-de NOS reactions consume large quantities of hydrogen and are considered to be the rate l i m i t i n g reactions for the production of clean f u e l s from c o a l ^ ^ . The reactions occur primarily on c a t a l y t i c a l l y a c t i v e 6 u r f a c e s ^ ^ , ^ > ^ ' ; homogeneous hydro-de NOS r e a c t i o n s and thermal decomposition of N-, 0-, S- compounds are not important r e a c t i o n paths Only marginal hetero-atom removal i s r e a l i z e d i n the absence of mineral matter or o t h e r c a t a l y s t s ' . The Dow emulsion phase hydrogenation f 271 c a t a l y s t does not appear to be e f f e c t i v e i n hydro-de NOS r e a c t i o n s 1 J . The c a t a l y t i c nature of the reactions r e s t r i c t s the molecular s i z e ^ ^ and r 5 8 1 geometry 1 J from which hetero-atoms can be abstracted. R o l l m a n ^ ^ analyzed the r e a c t i v i t y of several classes of N-, 0-, S- compounds, with structures resembling those found i n coal l i q u i d s , and 54 established a hydro-de NOS hierarchy, Figure 2.15. He also established r e a c t i o n paths f o r the hydro-de NOS reactions of h e t e r o - c y c l i c compounds under DCL conditions, Figure 2.16, which are i n general agreement with work f 72 1 T8n r e p o r t e d by Weisser and Landa 1 1 , and B a d i l l a - O h l b a u m et a l 1 J . The hydrogen consumption of hydro-de NOS reactions f o r h e t e r o - c y c l i c compounds i s temperature s e n s i t i v e . At 344°C, the reactions are s e l e c t i v e : 0 and N removal i s preceded by hydrogen s a t u r a t i o n and rupture of the h e t e r o - c y c l i c r i n g , and sa t u r a t i o n of the adjacent r i n g as shown on Figure 2.16; S removal only necessitates hydrogen saturation and rupture of the hetero- c y c l i c r i n g . At higher temperatures, 400°C, the s e l e c t i v i t y i s reduced and S N 0 removal from h e t e r o - c y c l i c compounds can produce aromatic or saturated s t r u c t u r e s . S p e c i f i c hydrogen consumption i s les s f o r S removal than N or 0 removal, e s p e c i a l l y at lower temperatures, but hydrogen consumption i s minimized at higher temperatures. 2.2.5.2 C a t a l y t i c E f f e c t s Hydro-de NOS c a t a l y s t s promote hydrogenolysis (cleavage) and hydro- genation reactions for compounds found i n coal l i q u i d s . Both c a t a l y t i c reactions are subject to s y n e r g i s t i c e f f e c t s i n the presence of a l t e r n a t e adsorbed species, H 2S, H 20, NH 3 > CO: i . Hydro-deoxidation of phenol, f o r example, occurs by hydrogenolysis i n the absence of other adsorbed species, while r i n g hydrogenation preceeds hydrogenolysis i n the presence of adsorbed H S, H.O e t c ^ ^ . 55 •*-» » - o - " > CXJ * CO - . . [71] Figure 2.15: The Hydro de NOS A c t i v i t y of Various F u n c t i o n a l i t i e s © ~ ° " © * 2 Q * S20<6H2} rt <- T^400°C T<400 eC • Figure 2.16: Hydro de NOS Reaction Paths 56 i i . The r a t e of h y d r o - d e n i t r i f i c a t i o n and h y d r o d e o x i d a t i o n i s s y n e r g i s t i c a l l y enhanced i n the presence of R^S and sulphided Mo-Co- alumina c a t a l y s t f 7 ^ . i i i . The rate of hetero-atom removal from coal l i q u i d s i s reduced with r 731 increasing pressure under DCL c o n d i t i o n s 1 . The adsorption of NH^, R^S e t c . on c a t a l y s t s u r f a c e s Increases with pressure and i n h i b i t s hydro-de NOS r e a c t i o n s 1 7 4 ' 6 6 , 6 7 ^ , i v . D i r e c t hydro-deoxidation (hydrogenolysis) of phenols i s i n h i b i t e d s y n e r g i s t i c a l l y i f both sulphided Mo-Co alumina and h e t e r o - c y c l i c n i t r o g e n compounds are present. This e f f e c t i s mitigated i f R^O i s als o present 1 . These e f f e c t s are l e s s important a t temperatures greater than 400°C ̂ 7^^. Reverse r e a c t i o n s , R^S + L i q u i d product ->• Sulphided Li q u i d product, have been shown to occur under DCL c o n d i t i o n s ^ . These reactions may or may not be surface catalyzed. S t u d i e s , performed with commercial hydro-de NOS c a t a l y s t s of the M0 x and MS x type, where M i s Co and/or Mo, have shown that c a t a l y s t r e a c t i v i t y i s a l t e r e d by c a t a l y s t c o m p o s i t i o n ^ 7 ^ , the presence and structure of the s u p p d r t ^ 7 ^ ' 7 ^ , and whether the c a t a l y s t i s present i n the oxide of sulphide f o r m ^ 7 ^ ' 7 4 ^ . R e a c t i v i t y v a r i a t i o n s among c a t a l y s t s a r e r e f l e c t e d by di f f e r e n c e s i n the rate of hydro-de NOS reactions for the various 57 s t r u c t u r e s , or by differences i n the extent of product h y d r o g e n a t i o n . r 741 S u l p h i d e d c a t a l y s t s are more susceptible to R^S, CO, NH^ adsorption 1 J and are, therefore, more l i k e l y to promote hydrogenation reactions. 2.2.6 Retrogressive Reactions Retrogressive reactions include a l l reactions which increase the average molar mass of the l i q u i d products or reduce the s o l u b i l i t y of the l i q u i d products i n the solvent. Both bituminous and sub-bituminous coals and coal l i q u i d s are subject to retrogressive reactions, although sub-bituminous c o a l s / c o a l l i q u i d s are more adversely a f f e c t e d under equivalent DCL r 521 c o n d i t i o n s 1 . These reactions occur throughout the l i q u e f a c t i o n c i r c u i t : r i 8 i r 21I In p r e - h e a t e r s 1 , and contactors . Experimental studies have shown the p o t e n t i a l for retrogressive "ageing" reactions i n solvent storage tanks, t r a n s f e r l i n e s and i n the s o l v e n t recycle l o o p ^ 7 ^ » ^ ® ] . The e f f e c t s and extent of retrogressive reactions can only be minimized by maintaining a hydrogenating reaction environment i n the l i q u e f a c t i o n reactor and by minimizing the hetero-atom content of product l i q u i d s . Some retrogressive r e a c t i o n s , occurring i n pre-heaters (solvent T33 521 r521 adduction by coal r a d i c a l s 1 ' 1 coal r a d i c a l i n t e r a c t i o n s Jand contactors (reforming and heterogeneous coke formation), were mentioned previously. Other reactions which compete with hydrogenation and hydrogenolysis reactions are those d e p i c t e d on F i g u r e 2 . 1 7 ^ ^ . Water can prevent methyl bridge 0 II 3 . < Q H „ - o ^ g > ^ . [60] Figure 2.17: Representative Retrogressive Reactions 5 9 cleavage and phenolic functional groups are prone to condensation reactions. Coal l i q u i d ageing i s most pronounced i n the presence of oxygen, where the oxidative coupling of p h e n o l s ^ ^ , and the production of carbonyl groups (which form hydrogen bonds with phenols e t c ^ * ^ ) i s r e a l i z e d . In the absence of oxygen, auto-oxidation/polymerization reactions, i n i t i a t e d and r 781 propogated by r e s i d u a l f r e e r a d i c a l s are thought to occur 1 . Alkylated h e t e r o c y c l i c nitrogen compounds, present i n coal o i l , are also thought to r 971 cause product degradation . Ageing rates increase with t e m p e r a t u r e ' ^ ' ^ ' and oxygen p a r t i a l p r e s s u r e ^ * * ' . However, ageing reactions progress slowly. At temperatures le s s than 60°C, several hours to several days are required to produce noticeable changes i n product q u a l i t y . At higher temperatures extensive degradation and coke formation can occur at f 7 9 1 * short contact times by p y r o l y s i s reactions The y i e l d of coke from c o a l - l i q u i d s , under p y r o l y s i s conditions, increases with the age of the coal l i q u i d s [80]. 60 2.3 C a t a l y s t s and C a t a l y s i s 2.3.1 C a t a l y t i c and S o l v o l y t i c DCL Processes The d i s t i n c t i o n , made i n the l i t e r a t u r e , between s o l v o l y t i c and c a t a l y t i c DCL processes i s misleading. Mineral matter constituents, present i n most coals, promote hydrogenation, hydrogenolysis and hydro-de NOS reactions i n much the same way as commercial c a t a l y s t s . Direct coal l i q u e f a c t i o n processes should be treated as a continuum. The c a t a l y t i c e f f e c t s occurring i n the s o l v o l y t i c processes are simply not emphasized. 2.3.2 The Role of C a t a l y s i s C a t a l y t i c requirements for DCL processes are complex. In order to minimize hydrogen consumption, a c a t a l y s t must promote: i . hydrogenation reactions for solvent range compounds (naphthalene, pyrene, e t c ) , I i . hydrogenolysis reactions for multi c y c l i c compounds while avoiding excessive hydro-cracking of low-molecular-weight l i q u i d s and the attendant production of SNG, i i i . e f f i c i e n t hydro-de NOS reactions for compounds containing hetero- atoms, s e l e c t i v e l y . However, these c a t a l y t i c requirements are mutually exclusive. 61 A c a t a l y s t , promoting the hydrogenolysis reactions desirable for i i and i i i , would cause dehydrogenated donor-solvent molecules to undergo hydro-cracking r a t h e r than r e h y d r o g e n a t i o n r e a c t i o n s - r e d u c i n g s o l v e n t q u a l i t y . Conversely, a c a t a l y s t which promotes hydrogenation reactions causes the hydrogen consumption for i i and i i i to increase sharply. The c o n f l i c t i n g nature of the desired c a t a l y t i c r e a c t i v i t i e s l i m i t s the choice of c a t a l y s t s f o r the current generation of DCL processes and has led i n part to the d i f f e r e n t DCL reactor design philosophies. In the EDS process, for example, o n l y the middle d i s t i l l a t e p r o d u c t i s hydrogenated/hydro-cracked c a t a l y t i c a l l y , while i n the H-Coal process the mutli-pass ebullated bed reactor permits l i g h t e r components, present i n the gas phase, to bypass the ca t a l y s t . 2.3.3 C a t a l y s t s C a t a l y s t s , active within DCL reactors, include a broad range of m e t a l l i c sulphides, mixed m e t a l l i c sulphides and coal mineral matter constituents (Table 2.6). Catechols have also demonstrated c a t a l y t i c a c t i v i t y under s p e c i a l circumstances ( r e f e r to section 2.2.4.2). M e t a l l i c sulphides e x h i b i t greater c a t a l y t i c a c t i v i t y f o r hydro-de NOS, hydrogenation and hydrogenolysis reactions than the p r i n c i p l e c a t a l y t i c a l l y a c t i v e mineral m a t t e r c omponents: p y r r h o t i t e , p y r i t e , " a s h " ^ ^ ' ^ ' . However, the r e a c t i v i t y of a l l the c a t a l y s t s depends on c a t a l y s t p a r t i c l e s i z e , composition, and i f a support i s present, the composition and structure of 62 the support ̂ ' ^ ' 7 0 ^ . Metal sulphide c a t a l y s t s are subject to d e - a c t i v a t i o n through the d e p o s i t i o n of ash and coke, and the adsorption of H^S, NH^ etc . as discussed i n sections 2.2.5 and 2.1.1.2.1.1. Some of the more important e f f e c t s , r e l a t e d to the c a t a l y s t s c i t e d on Table 2.6 are summarized below: i . Micron and sub-micron metal sulphide p a r t i c l e s (Mo, Co, N i , W, Fe, Va), introduced i n t o the DCL reactor as sulphates present i n the coal or as d i s s o l v e d - s a l t emulsion c a t a l y s t s which are sulphided i n s i t u ^ 2 7 » ° 6 ] ̂  p e r f o r m w e n a s hydrogenation/hydrogenolysis c a t a l y s t s but have l i t t l e impact on hydro-de NOS re a c t i o n s . Larger metal sulphide p a r t i c l e s (Co, Mo, supported Co-Mo, Fe) promote hydro-de NOS reactions but have a lower s p e c i f i c c a t a l y t i c r e a c t i v i t y with respect to hydrogenation and hydrogenolysis reactions than f i n e p a r t W 2 7 ' 6 6 ' 6 9 } . i i . Alumina supported Co-Mo c a t a l y s t s promote hydro-de NOS reactions f o r asphaltenes s e l e c t i v e l y ; promotion by FeS i s non s e l e c t i v e ^ ^ . i i i . FeS acts p r i n c i p a l l y as a hydrogenolysis c a t a l y s t . The rate of low- molecular-weight l i q u i d formation increases i n the presence of FeS but ,[67,69] hydrogen consumption remains unchanged own 1 [69] i v . P y r r h o t i t e has been sh to promote both hydrogenation[66.67] dehydrogenation reactions 63 TABLE 2.6 Catalysts C a t a l y t i c Action Catalysts Hydrogenation/Hydrogenolysis FeS Sn (sulphides) Co-Mo/o-Al 20 3 Ni-Mo/o-Al 20 3 P y r i t e SRC Residue Hydro-de-NOS A c t i v i t y Co-Mo/a-Al 20 3 Ni-Mo/a-Al 20 3 FeS SRC Residue Dehydrogenation Pyrrhotite * Trace amounts of Ni and Mo are frequently encountered i n l a t t i c e p o s i t i o n s , and p y r i t e (FeS 2) decomposes under DCL conditions to produce p y r r h o t i t e (FeS) and H^S. 2.3.4 Catalytic Activity of Metal Sulphides 64 The c a t a l y t i c a c t i v i t y of metal sulphide c a t a l y s t s , a c t i v e i n DCL processes, has been associated with the l a t t i c e defects of non-stoichiometric s u l p h i d e s (Fe,S„ , C o Q S Q ) ' . An alternate and more complex a c t i v i t y model has been p r o p o s e d , by W e i - g o l d ' , to e x p l a i n the b i - f u c t i o n a l i t y of s u l p h i d e d Co-Mo-A^O^ c a t a l y s t s , which promote both h y d r o g e n a t i o n and hydrogenolysis reactions. The postulated active s i t e s include a molybdenum and a cobalt atom. The reaction mechanism for hydro-de NOS reactions, Figure 2.18, requires competitive co-ordination of the substrate on one of the metal atoms, rearrangement of the substrate from a a to a n "bonded" state, and the presence of a c o - o r d i n a t i v e l y unsaturated metal atom to accept the hydroxyl or thio group. I f competitive ligands (^0, rL^S, NH^) saturate the metal atoms, hydrogenolysis reactions w i l l not occur; the n bonded substrate molecule undergoes hydrogenation instead, as t h i s only requires hydride transfer from the c a t a l y s t to the substrate. This mechanism i s supported expe r imen t a l l y : (1) Meta-substituted NOS-compounds e x h i b i t very slow rates for hydro-de NOS r e a c t i o n s * . Such molecules would have the g r e a t e s t s t e r i c interference for the o+n t r a n s i t i o n . (2) Increasing the l i g a n d / c a t a l y s t r a t i o , where ligands include NOS compounds, can reduce the rate of hydro-de NOS reactions r 581 s i g n i f i c a n t l y 1 1 . High s u b s t r a t e concentrations should i n h i b i t the a-*-n t r a n s i t i o n . 65 OH Co \ c / Mo . [70] Figure 2.18: Hydro de NOS Mechanism 66 f 821 A t h i r d a c t i v i t y model,- proposed by Sapre and Gates , concurs mechanis- t i c a l l y with the Weigold model but l i m i t s the r e a c t i v e s i t e to a s i n g l e exposed metal atom. 2.4 Solvents 2.4.1 Chemical Composition Coal l i q u e f a c t i o n solvents envisioned f o r use i n i n d u s t r i a l DCL 12 27 30 311 p r o c e s s e s are high or middle b o i l i n g f r a c t i o n s ' ' ' of the coal l i q u i d s produced i n DCL reac t o r s . These solvents contain complex mixtures T85—881 of a r o m a t i c and hydroaromatic compounds , which vary with coal and process type. Some laboratory experimental programs have endeavoured to duplicate envisioned i n d u s t r i a l conditions with complex coal-derived r 3 3 34 611 s o l v e n t s ' ' . Others have used model compounds to s i m u l a t e the functions of the d i f f e r e n t classes of compounds present i n i n d u s t r i a l [ 4 4 , 4 5 , 4 9 , 5 7 , 6 1 1 _ . . , . , . . . r solvents . This work has led to the development of solvent q u a l i t y i n d i c e s f o r complex s o l v e n t s ^ ^ , and has i d e n t i f i e d d esirable solvent properties. Solvents should i . be good p h y s i c a l solvents f o r the l i q u e f a c t i o n products - phenolic and p o l y c y c l i c compounds are s u i t a b l e , ( i . e . ) phenol, fluoranthene r 441 and carbazole pyrene; t e t r a l i n i s a poor p h y s i c a l solvent r 331 i i . c o n t a i n l a b i l e hydrogen i n the form of hydro-aroma t i c s , and ar o m a t i c s which a r e r e a d i l y hydrogenated to produce hydro- 67 r44 57]* aromatics 1 ' - hydro-aromatics include compounds such as t e t r a l i n , the aromatics Include pyrene l i k e compounds which can act as hydrogen r 44l f331 donors or " s h u t t l e r s ; solvents such as "anthracene o i l " are poor hydrogen donors i i i . be stable under the conditions of use - t e t r a l i n , f o r example, decomposes at elevated temperatures 1 ' . 2.4.2 P h y s i c a l Properties 2.4.2.0 Introduc t i o n S o l v e n t p r o p e r t i e s r a r e l y c o n s i d e r e d w i t h r e s p e c t to c o a l l i q u e f a c t i o n reactor design and of p o t e n t i a l importance are: (1) Solvent density (2) The s o l u b i l i t y of hydrogen and other gases i n a solvent (3) Solvent v i s c o s i t y as functions of chemical composition and temperature. Without knowing solvent density i t i s d i f f i c u l t to determine s l u r r y mean residence time i n continuous contactors or pre-heaters. The equilibrium concentration of hydrogen Influences reaction k i n e t i c s i n batch reactors and the p o t e n t i a l f o r g a s - l i q u i d mass transfer i n continuous flow apparatus. S i m i l a r l y , the s o l u b i l i t y o f g a s e s s u c h as B^S, CO^, NH^ e t c . i m p a c t on c a t a l y s t e f f i c i e n c y and the r e a c t i o n paths they promote. S o l v e n t v i s c o s i t y *This phenomenon i s temperature s e n s i t i v e i n some cases [85]. 68 influences the scale of turbulence i n a reactor and may a f f e c t p a r t i c l e break-up and the degree of a x i a l mixing. Without considering these p h y s i c a l properties e f f e c t s a r i s i n g from changes i n solvent composition may be a t t r i b u t e d to an improper source. 2.4.2.1 Gas S o l u b i l i t i e s i n Coal Liquids and Related Pure Aromatic Solvents at High Pressure 2.4.2.1.0 Introduction The s o l u b i l i t i e s of hydrogen, low molar mass hydrocarbon gases, and by-product gases such as carbon dioxide, carbon monoxide, nitrogen, argon, hydrogen sulphide, and ammonia, i n aromatic solvents, e x h i b i t complex and disparate dependencies on the chemical composition and mean molar mass of solvents, and on temperature. A v a i l a b l e high pressure data f o r hydrogen, argon, ethane, nitrogen, carbon dioxide, carbon monoxide s o l u b i l i t i e s , i n pure organic solvents, comprise Figures 2.19 - 2.24 r e s p e c t i v e l y . These data emphasise, wherever p o s s i b l e , s o l u b i l i t i e s i n compounds commonly associated with coal l i q u e f a c t i o n solvents. S o l u b i l i t i e s i n a l i p h a t i c hydrocarbon compounds are included for comparison. The s o l u b i l i t i e s of these gases cover a broad range at a given temperature, depending on solvent composition, and e x h i b i t three d i s t i n c t types of temperature dependence. Hydrogen, nitrogen, carbon monoxide 69 s o l u b i l i t i e s increase with temperature; methane and argon s o l u b i l i t i e s remain constant or decline with temperature; carbon dioxide and ethane s o l u b i l i t i e s decline r a p i d l y with temperature. Ammonia, hydrogen sulphide and propane s o l u b i l i t i e s i n aromatic compounds are also expected to d e c l i n e with temperature. C l e a r l y , the s o l u b i l i t y behaviour of these gases does not correspond to the anticipated behaviour suggested by " i d e a l " s o l u b i l i t y t h e o r y ^ ^ * ^ , which s t a t e s t h a t gas s o l u b i l i t i e s d e c l i n e as temperature increases and are i n v e r s e l y proportional to solvent molar mass. Gas s o l u b i l i t y behaviour i n DCL systems must be analysed without the aid of t h i s frequently h e l p f u l t h e o r e t i c a l framework. In order to f a c i l i t a t e data presentation and comparison, a l l s o l u b i l i t i e s are expressed as pseudo Henry's Law constants. Deviation from Henry's Law behaviour for methane, hydrogen, carbon monoxide, and carbon dioxide s o l u b i l i t y , i n organic solvents i s l e s s than 10% f o r the pressure r <jg 99 1071 ranges c o n s i d e r e d (25-100 ATM) 1 ' ' J . This d e v i a t i o n i s ignored i n a l l cases as the probable error associated with s o l u b i l i t y measurments i s 5-10%. 2.4.2.1.1 The E f f e c t of Temperature on Gas S o l u b i l i t y The e f f e c t of temperature on gas s o l u b i l i t y can be examined i n absolute as well as r e l a t i v e terms. Pure solvents of the same c l a s s e x h i b i t the same s o l u b i l i t i e s at the same r e l a t i v e temperature, whereas gas s o l u b i l i t i e s decline at constant absolute temperature f o r solvents of the 70 same c l a s s as solvent molar mass increases. Figure 2.19 i l l u s t r a t e s t h i s phenomenon for hydrogen s o l u b i l i t i e s , where aromatic solvents are divided into three c l a s s e s : s i n g l e r i n g aromatic compounds; double r i n g aromatic compounds; and aromatic compounds comprising three or more r i n g s , or aromatic compounds containing oxygen, sulphur or nitrogen atoms. A s i m i l a r tendency i s noted, with respect to r e l a t i v e and absolute temperature, for hydrogen s o l u b i l i t y i n s t r a i g h t chain a l i p h a t i c hydrocarbons. Hydrogen s o l u b i l i t y i n n-hexane and n-hexadecane d i f f e r s by l e s s than 50% at the same r e l a t i v e temperature, whereas the d i f f e r e n c e exceeds 200% at the same absolute temperature. Figures 2.19 - 2.23, which include data for hydrogen, argon, ethane, nitrogen and carbon dioxide, suggest that the temperature dependence of gas s o l u b i l i t i e s i s consistent f o r both a l i p h a t i c and aromatic solvents. So, despite the s c a r c i t y of s o l u b i l i t y data for methane, carbon dioxide, carbon monoxide, propane, ammonia and hydrogen sulphide, the general temperature dependence of s o l u b i l i t y for these gases can be i n f e r r e d from a v a i l a b l e data i n v o l v i n g only one solvent c l a s s . The influence of temperature, on gas s o l u b i l i t y , i s appreciable - except for methane and argon s o l u b i l i t i e s . Hydrogen and nitrogen s o l u b i l i t i e s i n Benzene, for example, double between 20°C and 100°C. Carbon dioxide and ethane s o l u b i l i t i e s , i n the same solvent, drop by a factor of 5 and 2 r e s p e c t i v e l y over the same temperature i n t e r v a l . 71 100 % ® x 0 0 g! A 10- E X • • ^ 6 Jb ffi® A ffi o A ^ 1H 1 1 1 1 1 r— 0.3 0.4 0.5 0.6 0.7 0.8 0.9 RELATIVE TEMPERATURE Legend a BENZENE X N-HEXANE • N-HEXADECANE B 1-METHYL-NAPHTHALENE S TETRALM • PHENANTHRENE • TOLUENE e M-CRESOL O M-XYLENE • DIPHENYL-METHANE O QUINOLINE m THIO-NAPHTHALENE V 1.4 METHYL-BENZENE a N-BUTANE B N-PROPANE Figure 2.19: Hydrogen S o l u b i l i t y i n Pure Organic Solvents 72 0.3S 0.40 0.45 0.50 0.55 0.60 RELATIVE TEMPERATURE 0.65 0.70 Legend L BENZENE >• TOLUENE D XYLENE E BENZALDEHYDE I! N-PENTANE » N-OCTANE Figure 2.20: Argon S o l u b i l i t y i n Pure Organic Solvents Figure 2.21: Ethane S o l u b i l i t y i n Pure Organic Solvents 1000 - B - E " T T" 0.4 — i i 0.5 0.6 0.7 o.e RELATIVE TEMPERATURE — i — 0.9 Legend & BENZENE X N-HEXANE B N-HEXADECANE Nitrogen S o l u b i l i t y i n Pure Organic Solvents 1000 Legend } BENZENE 100H— 0.3 0.4 ~ ~ l — 0.6 - I— o.e 0.7 0.8 RELATIVE T E M P ERATURE o.e Carbon Dioxide S o l u b i l i t y i n Pure Organic Solvents 74 2.4.2.1.2 The E f f e c t of Solvent Composition on Gas S o l u b i l i t y S o l v e n t c o m p o s i t i o n a f f e c t s the molar mass, the e l e m e n t a l composition, and the molecular structure of a solvent, thus determining i t s c l a s s and the r e l a t i v e temperature. Gas s o l u b i l i t i e s i n solvents of d i f f e r e n t classes can be r a d i c a l l y d i f f e r e n t at the same r e l a t i v e or absolute temperature even i f solvent molar mass and molecular structure are s i m i l a r . Hydrogen s o l u b i l i t y i n m-xylene (C_H i n, mm = 106) i s 53% greater at the same r e l a t i v e temperature and 122% greater at the same absolute t e m p e r a t u r e than hydrogen s o l u b i l i t y i n m-cr e s o l ( C _ H O 0 , mm = 1 0 8 ) . S i m i l a r differences are encountered f o r hydrogen s o l u b i l i t y i n d i e t h y l benzene (^^Q^14' ^ ~ v s hydrogen s o l u b i l i t y i n thio-naphthalene (CgHgS mm = 134) - 65% and 140% r e s p e c t i v e l y . Comparable di f f e r e n c e s are noted f o r other gas s o l u b i l i t i e s . Figure 2.24 i l l u s t r a t e s the e f f e c t of 2 t y p i c a l l i q u e f a c t i o n r e a c t i o n sequences on hydrogen s o l u b i l i t y . The molecular structure and composition of the compounds remains s i m i l a r but the molar mass i s reduced. The s o l u b i l i t y r a t i o s c i t e d on Figure 2 .25 vary somewhat depending on the temperature range considered but the magnitude of the change i n s o l u b i l i t y r e a l i z e d by cleaving the aromatic structure i s enormous. 5 to 10 f o l d increases i n hydrogen s o l u b i l i t y r e s u l t at constant temperature, simply by reducing the molar mass by 50%. The increase i n s o l u b i l i t y would be much l e s s ( i . e . ) 1 . 5 - 2 f o l d i f hetero-atoms remain within the molecular s t r u c t u r e . <3«r 132 134 I 92 78 Motor 188 142 132 134 ' 92 78 Moss Solubility1 Rotio Absolute I 148 197 331 5 52 862 Relotive I 108 116 153 153 152 en®— 0 • 0 168 92 78 4 1-3 1. S o l u b i l i t y r a t i o s are reported at the same absolute and r e l a t i v e temperatures with respect to the i n i t i a l species i n each sequence. Figure 2.24: Two Liquefaction Reaction Sequences 76 The s o l u b i l i t y r e s u l t s f o r hydrogen can be used to i n t e r p r e t the s o l u b i l i t y behaviour of other gases. Carbon monoxlde'^^ and nitrogen s o l u b i l i t i e s behave i n a manner s i m i l a r to hydrogen s o l u b i l i t y . S o l u b i l i t y increases r e s u l t i n g from reductions i n molar mass or hetero-atom content are reinforced by a corresponding increase i n r e l a t i v e temperature. The s o l u b i l i t i e s of other gases argon, methane, carbon dioxide, ethane, propane et c . do not behave i n a s i m i l a r manner. Increases i n s o l u b i l i t y caused by reductions i n molar mass, or hetero-atom content are not reinfo r c e d by a corresponding increase i n r e l a t i v e temperature. On the contrary, the s o l u b i l i t i e s of these gases remain constant or decline as temperature increases. Therefore, the s o l u b i l i t i e s of these gases w i l l only tend to increase when the solvent changes from a c l a s s with a low s o l u b i l i t y to another of much higher s o l u b i l i t y . Gas s o l u b i l i t y w i l l decline i f the solvent remains within the same c l a s s a f t e r the molar mass or hetero-atom content has been reduced. 2.4.2.1.3 Gas S o l u b i l i t i e s i n Mixed Solvents 2.4.2.1.3.0 Introduction Mixed solvents such as coal l i q u i d s comprise innumerable compounds with broad ranges of molar mass, molecular structure and chemical composition. Fortunately, gas s o l u b i l i t y trends i n mixed solvents p a r a l l e l trends encountered with pure s o l v e n t s . i n general, 77 n x. S , s n S. (2.6) mix . - i i = l where Sffl^x = s o l u b i l i t y i n a mixed solvent x^ = the mole f r a c t i o n of component i i n the solvent = the s o l u b i l i t y i n pure i n = the number of components i n the mixed solvent Despite the l i m i t a t i o n s and r e s t r i c t i o n s i m p l i c i t i n an equation as simple as equation 2.6 i t was used to derive a semi-empirical equation f o r c o r r e l a t i n g gas s o l u b i l i t y data i n complex solvents. The d e t a i l s r e l a t e d to the d e r i v a t i o n of equation 2.7 can be found i n Appendix B l . Smix * 1 e x P {1.495 L n } <2'7> B jU where: A and b are constants 1.495 Tg^Q approximates the c r i t i c a l tempertature of the mixture T i s the absolute temperature (K) 2.4.2.1.3.1 Gas S o l u b i l i t i e s i n Coal L i q u i d s Very l i t t l e data on gas s o l u b i l i t i e s In coal l i q u i d s has been published. However, a v a i l a b l e data f o r hydrogen and methane s o l u b i l i t y i n coal l i q u i d s and narrow b o i l i n g f r a c t i o n s Comprise Figure 2.25. Hydrogen 78 100 E •*-> < b CO LU o 5 METHANE 10 HYDROGEN Legend A CCLP 1 TB50=483K X CCLP 2 TB50=559K • SRCII 5 TB50=524K B SRCII 9 TB50=587K H SRCII 12 TB50=636K 0.4 0.5 0.6 0.7 0.8 RELATIVE TEMPERATURE 0.9 Figure 2.25: Hydrogen and Methane S o l u b i l i t i e s i n Coal Liquids 79 s o l u b i l i t i e s i n a l l of the l i q u i d s are accurately co r r e l a t e d by equation 2.7. Methane s o l u b i l i t i e s form s t r a t i f i e d curves according to the mean molar mass of the solvent. The e f f e c t of trace components on gas s o l u b i l i t y i s a further consideration. Gas s o l u b i l i t i e s i n compounds such as hexane, pentane, butane, propane can be as great as 200 times gas s o l u b i l i t i e s i n aromatic solvents at the same temperature. A 5 mole % (1 wt%) a d d i t i o n of some combination of these compounds to a phenanthrene l i k e solvent would y i e l d a 25-50% increase i n hydrogen s o l u b i l i t y according to equation 2.6. There i s i n s u f f i c i e n t data to quantify the e f f e c t of such additions on the s o l u b i l i t i e s of other gases. 2.4.2.1.4 Apparent S o l u b i l i t y A l l of the s o l u b i l i t y data presented so far was obtained from apparatus with a gas phase comprising gaseous solvent and a s i n g l e pure s o l u t e . In g e n e r a l the gas phase was 9 8 + mole % solute, and l e s s than 2 mole % vapourlzed solvent. S o l u b i l i t y data obtained i n conjunction with l i q u e f a c t i o n experiments and of greater relevance to process design and development i s not r e a l i z e d In t h i s manner. S o l u b i l i t y determinations involve complex gas phases with widely varying composition. S o l u b i l i t i e s obtained from complex gas phases must be distinguished from s o l u b i l i t y data obtained with a r e l a t i v e l y pure gas phase. These s o l u b i l i t i e s are r e f e r r e d to as "apparent s o l u b i l i t i e s " . 80 TABLE 2.7 Apparent S o l u b i l i t y Data Compound Pair Solvent Gas Consumption mole f r a c t i o n S o l u b i l i t y -1 -1 3 moles.Kg solvent ATM xlO H 2 + CO A mixture of s t r a i g h t chain alcohols C12 " C16 <? 315°K and 60 ATM H 2 CO .69 .31 .515 .485 .43 .57 H 2 CO 2.37 4.32 2.35 4.55 2.54 4.63 H 2 + CH 4 Tetrahydro- naphthalene @ 462.4°K & 50 ATM H 2 CH 4 .8892 .1033 1.000 0.00 H 2 CH 4 4.36 12.23 4.40 81 Apparent s o l u b i l i t y data for two binary gas phases i s presented on Table 2.7. The v a r i a t i o n of s o l u b i l i t y f o r each gas component with composition i s small, less than 7%, and r e f l e c t s the v a r i a t i o n of a c t i v i t y c o e f f i c i e n t with pressure more so than i n t e r a c t i o n s between gas phase co n s t i t u e n t s . A c t i v i t y c o e f f i c i e n t s f o r gas s o l u b i l i t i e s do not stray appreciably from unity as noted i n se c t i o n 2.4.2.1 and t h i s e f f e c t was neglected as secondary. Apparent s o l u b i l i t y data i s scant but f l u c t u a t i o n s i n a c t i v i t y c o e f f i c i e n t s with gas phase composition appear to be equally secondary. Despite the probable s i m i l a r i t y between apparent and pure gas phase s o l u b i l i t i e s , i t i s important to note that they are q u a l i t a t i v e l y d i f f e r e n t . 2.4.2.2 Solvent Density R e i d et a l ' ^ ^ reviewed a number of c o r r e l a t i o n s for estimating p u r e - l i q u i d d e n s i t i e s . They found that the Gunn-Yamada c o r r e l a t i o n , equation 2.8, V ( 0 ) R P " p ^o ( 1 - oo t) (2*8) r where; T - 0.29607-0.09045 T - 0.04842 T 2 r r .33593-.33953 T + 1.5191 T 2 - 2.02512 T 3 r r r V° - / + 1.11422 T 4 0.2< T < 0.8 r 1 r r 1.0 + 1.3 ( 1 - T r ) 1 / 2 log (1-T r) - .50879 (1-T r) 0.91534 (1-T ) 2 0.8< T < 1.0 v r r 82 provided the most accurate and consistent r e s u l t s f o r the temperature range 0.2 < T r < 0.99. D e n s i t y v a l u e s predicted by equation 2.8 are t y p i c a l l y w ithin 3% of experimental values. Figure 2.26 i l l u s t r a t e s the change i n density between room temperature and c o a l - l i q u e f a c t i o n conditions f o r t e t r a l i n , naphthalene and other pure compounds associated with model solvent studies and DCL experiments. Densities for these compounds drop -3 -3 from 1 g cm at room temperature to between 0.5 and 0.65 g cm at 700K. There are no general methods for t r e a t i n g d e n s i t i e s of complex mixtures and l i t t l e data appears i n the open l i t e r a t u r e . However, one would not expect such large reductions i n solvent density with temperature, e s p e c i a l l y i n continuous process equipment - l i g h t e r , more v o l a t i l e solvent components tend to be stripped from the solvent by the r e c i r c u l a t i n g hydrogen stream. The d e n s i t i e s of DCL recycle solvents, at elevated temperatures, are l e s s than t h e i r respective room temperature d e n s i t i e s , Table 2.8, but greater -3 than 0.7 g cm at 700K. 2.4.2.3 Solvent V i s c o s i t y V i s c o s i t i e s of pure solvents are r e a d i l y estimated as a function of t e m p e r a t u r e ^ ' ^ . At temperatures removed from the c r i t i c a l point, ( i . e . ) T 00.74, r ' log (u) - A { j - - B} (2.9) 83 Figure 2.26: The Densities of Pure Organic Solvents TABLE 2.8 Coal Solvent Den s i t i e s Coal L i q u i d P h y s i c a l P r o p e r t i e s 1 1 Mean Molar Mass g T B50 (K) density g cm 3 at 15°C CLPP-A5 154.34 483. 0.9320 CLPP-A5 182.30 558. 0.9844 SRC II #5 182. 524. 0.9826 SRC II #9 212. 587. 1.0306 SRC II #12 252 636. 1.091 85 v i s c o s i t y data f o r most compounds c o r r e l a t e well with equation 2.9. As the c r i t i c a l point i s approached, v i s c o s i t y drops r a p i d l y with temperature and a more complex equation Is required: (.015174 - .02135 T + .0075 T 2 + u> (0.42552 r r v - .07674 T + .0340 T 2)} (2.10) r r ' Equation 2.10 i s appropriate f o r the r e l a t i v e temperature range 0.74 < < .98. These c o r r e l a t i o n s estimate v i s c o s i t i e s within 15% of experimental values. Kinematic v i s c o s i t i e s for a va r i e t y of aromatic and hydro-aromatic compounds and several coal derived l i q u i d s are shown on Figure 2.27. Under DCL conditions the kinematic v i s c o s i t i e s of pure 2 r i n g solvents are i n the range of 0.15 cSt. The kinematic v i s c o s i t y of anthracene, a 3 r i n g aromatic, i s approximately 0.25 cSt, and the v i s c o s i t i e s of h i g h e r - b o i l i n g , coal-derived l i q u i d s are l i k e l y to be greater s t i l l . At room temperature v i s c o s i t i e s can be 1 to 2 orders of magnitude greater. The very high v i s c o s i t i e s exhibited by some of the coal l i q u i d s at room temperature Is not unusual. Many pure compounds undergo large Increases i n v i s c o s i t y near the fre e z i n g point. M 1 / 2 P 2 / 3  c 2.5 Process and K i n e t i c Models 86 1000: CO U CO O O CO > o 1X1 z 100: Legend A BENZENE X NAPHTHALENE • TETRALIN B 1 METHYL-NAPHTHALENE 2 PJ.pi1E.N.Y.L..EJ.H.E.'? * DJPHENYL * ^ T I !9.^ENE ffi CLPP 400-450 O CLPP 500-600 + SRC #5 200 300 400 500 600 TEMPERATURE (k) 700 800 Figure 2.27: The V i s c o s i t i e s of Pure Organic Solvents 87 2.5.0 Introduction Many k i n e t i c models, with varying degrees of complexity and s o p h i s t i c a t i o n , have been proposed to describe coal l i q u e f a c t i o n k i n e t i c s (Table 2.9). Some of the models simply endeavour to p r e d i c t o v e r a l l c oal conversion to gases + l i q u i d s , while others endeavour to pr e d i c t y i e l d s of i n d i v i d u a l l i q u i d and gaseous f r a c t i o n s - f r a c t i o n s based on s o l u b i l i t y : asphaltenes, pre-asphaltenes, o i l s ; or chromatographic f r a c t i o n s : m u l t i - f u n c t i o n a l s , hydroxyls, ethers, aromatics, nitrogens. The number of f i t t e d parameters vary with the complexity of the p r e d i c t i o n s . Simple models comprise as few as 2 parameters; more complex models employ more than 30 paramaters. A l l models have had some success i n describing c o a l l i q u e f a c t i o n behaviour, but r e s t r i c t i o n s must be imposed on: (1) reactor operating conditions (temperature, pressure) (2) coal or c o a l type (3) reactor design A general model which can treat a v a r i e t y of coals under a broad range of conditions, has not yet been devised. Despite these l i m i t a t i o n s such models have been incorporated into process models i n order to evaluate process design a l t e r n a t i v e s and economics. 88 2.5.1 K i n e t i c Models The k i n e t i c models c i t e d on Table 2.9 h i g h l i g h t the lack of consensus i n the l i t e r a t u r e with respect to the s p e c i f i c mechanism(s) f o r coal l i q u e f a c t i o n . The only common feature of a l l the models i s that coal decomposes/reacts i r r e v e r s i b l y . I t has not been resolved whether or not coal behaves as a s i n g l e monolythic species or i f d i f f e r e n t c o a l components react according to d i f f e r e n t r e a c t i o n networks. Neither i s there a consensus on the products produced d i r e c t l y from c o a l , or the order of these i n i t i a l r e a c t i o n ( s ) . Equally unresolved i s the necessity or d e s i r a b i l i t y of incorporating secondary reactions ( i . e . ) asphaltenes •*• o i l s e t c . . Should such reactions be included i n a model, are they r e v e r s i b l e or i r r e v e r s i b l e , and what reaction order should be assigned to them? Yet, each of these models has been f i t t e d to experimental data, s u c c e s s f u l l y , and i s therefore v e r i f i e d i n a narrow sense. The extreme s p e c i f i c i t y of the models i s best i l l u s t r a t e d by a few examples: f 351 (1) Mohan and S i l l a 1 1 proposed two models to describe the l i q u e f a c t i o n k i n e t i c s of I l l i n o i s #6 c o a l . One based on product separation by high pressure l i q u i d chromatography; the other based on product separation by s o l u b i l i t y . Both models have two complete sets of parameters. One to describe l i q u e f a c t i o n behaviour at high temperatures, the other only v a l i d at low temperatures. The TABLE 2.9 Coal L i q u e f a c t i o n R e a c t i o n Models Models K i n e t i c Scheme Number of Parameters Assumptions Coal S o l v e n t Comments S t a p l e M o d e l s ' 3 5 ' H i l l e t at C — » A + 0 2 - f i r s t order k i n e t i c s - a s i n g l e thermal decomposition "Utah- t e t r a l l n Curran et a l \ *A + 0 4 - c o a l l e beat c h a r a c t e r i s e d as com p r i s i n g two d i f f e r e n t r e a c t i v e P i t t s b u r g t e t r a l l n s p e c i e s Llebenberg et a l 4 - c o a l produces A & 0 "bituminous** t e t r a l l n by separate r e a c t i o n sequences - Yoshlda et a l C — - A — • 0 6 - c o a l produces A & 0 by separate r e a c t i o n sequences Japanese anthracene o i l red mud and sulphur added as c a t a l y s t s Complex Models Mohan et a l ' 3 5 ' H S 1 / AR E ^ A 18 - gas g e n e r a t i o n ignored - c o a l deompoaes I r r e v e r s i b l y Into l a r g e fragments I l l i n o i s #6 t e t r a l l n - the authors propose two models ( l ) b a a e d on chromatographic s e p a r a t i o n o f l i q u i d s (2)based on s o l u b i l i t y s e p a r a t i o n . 10 - l a r g e fragments r e a c t r e v e r s l b l y to form l i g h t e r components - Model (2) f l t a the data b e t t e r - a batch r e a c t o r was used f o r the experiments 0 0 VO Gertenbach et a l [111] Cronauer et a l [3*1 1112] Shah et a l Shalabl et al r e a c t i o n s o c c u r r i n g In the pre-heater are not Included the r e v e r s i b l e r e a c t i o n C P l a not t m e l y r e v e r s i b l e . P can form coke which cannot be de s t l n g u l a h e d from c o a l a l l r e a c t i o n s are f i r s t o r d er and I r r e v e r s i b l e no d i s t i n c t i o n made f o r r e a c t i o n s In the pre- heater a l l r e a c t i o n s i n v o l v i n g c o a l are f l r a t order h y d r o c r a c k l n g r e a c t i o n s are Oth or 1st order i r r e v e r s i b l e f i r s t order r e a c t i o n k i n e t i c s Kentucky #9 B e l l Ayre sub- fa 1 turn 1 nous Big Horn sub- butunlnous Kentucky 250*C Vacuum cut of SRCII l i q u i d s - hydrogenated anthracene o i l hydrogenated phenanthrene o i l process d e r i v e d l i q u i d t e t r a l i n e f f o r t s were made to f i t the model t o the d a t a of other r e s e a r c h e r s . The f i t was poor even w i t h t h e i r own d a t a - the model p r e d i c t s a s i g n i f i c a n t i n c r e a s e i n o i l y i e l d In pl u g flow r e a c t o r s . - c o m p l e t e l y d l f f r e n t s e t of parameters f i t t e d the r e s u l t s f o r the two s o l v e n t s a s l u g flow p r e - heater f o l l o w e d by a CSTR were employed a s l u g flow pre- he a t e r f o l l o w e d by a CSTR were employed a p r o p r i e t a r y c a t a l y s e was used D i s p e r s i o n Number was a parameter and v a r i e d w i t h s l u r r y s h o r t heat-up time batch experiments were performed. Slogh e t « l | U 3 1 1 G V > * - j ) -MO IOM ASH SRC 34 - 2 stage k i n e t i c s : Ponstan #5 Vacuum tower - a s l u g f l o w pre- i 1: Instantaneous break- up of c o a l to f i x e d f r a c t i o n s of v a r i o u s bottoms from SRCII p l a n t heater and a CSTR were employed - T h i s model has been components used to s i m u l a t e 11: slow c o n v e r s i o n of the SRCII p r o c e s s . SRC and HO to l i g h t e r 2 SRC * componenta - I r r e v e r s i b l e f i r s t o r d er k i n e t i c s HO • - pre-heater has no impact on k i n e t i c s Legend for Kinet ic Schemes on Table 2.9 A asphaltenes LO l ight o i l AR aromatlcs M mult i - funct lonals B by product gases MO middle o i l C coal N nitrogens E ethers 0 o i l G gases P pre-asphaltenes H HydroxyIs SRC solvent refined coal HO heavy o i l W water 10M Inert organic matter 92 solvent, the coal and a l l other process v a r i a b l e s are unchanged. r 341 (2) The model proposed by Cronauer et a l requires two unrelated sets of parameters to describe the l i q u e f a c t i o n behaviour of a singl e coal i n two d i f f e r e n t solvents. A l l other process v a r i a b l e s are held constant. (3) The model proposed by Gertenbach et a l ^ * ^ c o r r e l a t e s data obtained by other researchers poorly and has even greater d i f f i c u l t y c o r r e l a t i n g t h e i r own data under a v a r i e t y of operating conditions. Further examples of s p e c i f i c i t y can be c i t e d but this approach does not resolve the main issu e , which i s , why are these models so s p e c i f i c ? The d i v e r s i t y of model f u n c t i o n a l forms and parameters can be at t r i b u t e d In part to data p r e c i s i o n . L i q u e f a c t i o n r e s u l t r e p e a t a b i l i t y , a parameter frequently quoted i n the l i t e r a t u r e , i s often ± 3 wt% f o r any l i q u i d or gaseous f r a c t i o n produced, when normalized with respect to the i n i t i a l coal mass. Thus a f r a c t i o n comprising 20 wt% of the i n i t i a l coal mass has a mean erro r of ± 15%. Data, t h i s imprecise, may be f i t t e d , e m p i r i c a l l y , by any curve which follows the general trend of the r e s u l t s . Differences In product a n a l y s i s also contribute to the d i v e r s i t y of models and parameters. Refer to s e c t i o n 2.6 f o r d e t a i l s . Data processing introduces two a d d i t i o n a l c o n t r i b u t i n g f a c t o r s : 93 (1) the existence of multiple regression minima may y i e l d more than one set of equally good parameters from the same data base when models are f i t t e d to experimental data. This problem becomes more severe as the number of f i t t i n g parameters increases. (2) differences i n the f i t t i n g function can y i e l d r a d i c a l l y d i f f e r e n t "optimum" parameters ( i . e . ) minimizing the absolute value of the err o r instead of the absolute value of the % error produces a skewed parameter set which f i t s observed data with l a r g e r values much better than observed data with smaller values. Differences i n observed k i n e t i c s may also be attributed to incompatible d i f f e r e n c e s i n experimental conditions ( i . e . ) dominant r e a c t i o n path(s) vary with experimental conditions (Section 2.2). However, e f f e c t s such as these cannot account wholely f o r the extreme s p e c i f i c i t y of the k i n e t i c models. Unfortunately, none of the models s a t i s f a c t o r i l y accounts f o r the observed k i n e t i c phenomena described i n s e c t i o n 2.2. In p a r t i c u l a r , the r o l e of primary and secondary coal d i s s o l u t i o n and the influence of operating conditions on k i n e t i c s Is ignored i n a l l cases. 2.5.2' Process Models Sing h et a l ^ * ^ employed t h e i r k i n e t i c model as part of process models intended to simulate various aspects of the SRCII process. They s i m u l a t e d : the SRCII Recycle System^ 1 1 4', the r e a c t i v i t y of l i q u e f a c t i o n 94 produc ts ̂  , the steady state and dynamic thermal behaviour of the SRCII fc _ [116,117] . , fc [118] c o n t a c t o r , and flows and co m p o s i t i o n s of process stream 1 . Their models ignore the changing influence of reactor hydrodynamics on l i q u e f a c t i o n k i n e t i c s as the processing conditions are a l t e r e d . Lee et a l ^ * * ' also modeled the SRC reactor but applied the di s p e r s i o n model to the contactor to allow f o r v a r i a t i o n s i n s l u r r y residence time d i s t r i b u t i o n with changing gas flow r a t e s . Their model predicts a 3% r e d u c t i o n i n t o t a l c o n v e r s i o n , f o r the same mean r e s i d e n c e time as * decreases from 0.97 to 0.1 . Contactor simulations performed by Gertenbach et a l ^ * * * ' , based s o l e l y on k i n e t i c s , suggest o n l y modest d i f f e r e n c e s between t o t a l conversions for a CSTR and a PFR at high temperatures (450°C) but a much larger d i f f e r e n c e at 400°C - approximately 1% and 10% r e s p e c t i v e l y . The r e s u l t s of these l a t t e r two studies are d i s t o r t e d because the k i n e t i c models were f i t t e d to data obtained from reactors which included plug flow pre-heaters. Generalization of t h e i r data, i n th i s way, may not be v a l i d . 2.6 Coal L i q u e f a c t i o n Product Analysis Apart from SNG y i e l d s which are i n v a r i a b l y analyzed by ga s - s o l i d chromatography, comparison of experimental l i q u e f a c t i o n r e s u l t s i s often complicated by incompatible differences i n product a n a l y s i s . L i q u i d / s o l i d r 351 p r o d u c t s are c a t e g o r i z e d , v a r i o u s l y , on the basis of f u n c t i o n a l i t y or *N D = 0.1 implies the reactor i s equivalent to a CSTR N D = 0.97 implies the reactor i s almost equivalent to a CSTR 95 s o l u b i l i t y . When categorized by f u n c t i o n a l i t y , 6 compound groups are normally i d e n t i f i e d by high pressure l i q u i d chromatography (HPLC): saturates, aromatics, ethers, nitrogens, hydroxyls, m u l t i f u n c t i o n a l s . S o l u b i l i t i e s subdivide l i q u i d / s o l i d products into the c l a s s i c f r a c t i o n s : o i l s , a s p h a l t e n e s p r e - a s p h a l t e n e s - see T a b l e 2.10. These two c l a s s i f i c a t i o n techniques are not r e a d i l y i n t e r - r e l a t e d . In a d d i t i o n , non-standard t o t a l l i q u i d y i e l d d e f i n i t i o n s are frequently encountered i n the l i t e r a t u r e . These d e f i n i t i o n s are based on quinoline s o l u b i l i t y ^ * ' , f 6 61 F831 c r e s o l s o l u b i l i t y , t e t r a l i n s o l u b i l i t y , e t c . . 96 Table 2.10 Product Analysis by S o l u b i l i t y Product Category D e f i n i t i o n s O i l s . [34,45,47]* n-pentane soluble l i q u i d s n-hexane soluble l i q u i d s t ^ » ^ ' Asphaltenes v i i-T [34,35,45,67,69] benzene soluble l i q u i d s 1 ' ' 1 [47 I 1 toluene soluble l i q u i d s 2 Pre-asphaltenes tetrahydrofuran (THF) soluble l i q u i d s ^ 3 5 » 4 5 ' AAA i 1.1 14 ^ [34,67-69] pyridine soluble l i q u i d s Notes to Table 2.10: Less Hazardous a l t e r n a t i v e according to NI0SH/0SHA Standards [84], These materials a l l attack the eyes, skin r e s p i r a t o r y system, and the c e n t r a l nervous system: pentane<toluene<THF. ^ THF s o l u b l e m a t e r i a l P y r i d i n e s o l u b l e m a t e r i a l . Raw coal i s soluble i n Pyridine but not i n THF [45,69]. 97 2.7 Summary Even a cursory review of the l i t e r a t u r e r e l a t e d to D i r e c t Coal L i q u e f a c t i o n reactor design leaves one i n a mild state of confusion. I n d u s t r i a l l i q u e f a c t i o n reactor designs comprise a very narrow range of a l t e r n a t i v e s . Such designs, employing back-mixed reactors with large gas rec y c l e r a t i o s , are normally associated with g a s - l i q u i d mass-transfer l i m i t e d r e a c t i o n - k i n e t i c s . Mathematical models, f o r DCL k i n e t i c s , suggest that the same designs are optimal or near optimal but base t h i s conclusion on s i m p l i s t i c approximations of coal l i q u e f a c t i o n k i n e t i c s . The r o l e of c a t a l y s i s , g a s - l i q u i d mass transfer and other physical phenomena i s a l l but ignored i n these models. Since data f o r these models was generally obtained from reactors which are hydrodynamically s i m i l a r to i n d u s t r i a l designs, these e f f e c t s , though i m p l i c i t l y included i n the models, can be treated as constants i f only a l i m i t e d range of reactor designs i s considered. However, these models also f a i l to include the pre-heater as an i n t e g r a l component of the o v e r a l l reactor design, and do not p r e d i c t l i q u e f a c t i o n r e s u l t s except under v e r y narrowly d e f i n e d r e a c t i o n c o n d i t i o n s . The models also f a i l to account for the apparent necessity to r e c y c l e large quantities of hydrogen i n i n d u s t r i a l r eactors. Observed k i n e t i c phenomena tend to c o n f l i c t , In whole or i n part, with both the k i n e t i c models and the choice of i n d u s t r i a l l i q u e f a c t i o n reactor designs. These observations h i g h l i g h t the importance of physical phenomena such as: (1) the i n t e n s i t y of turbulence - r e l a t i v e flow rates of gas and s l u r r y , i n pre-heaters, influences l i q u e f a c t i o n r e a c t i o n k i n e t i c s (2) the extent of a x i a l mixing - the k i n e t i c s of hetero-atom removal reactions are slow. The presence of hetero-atoms reduces the s a l e a b i l i t y of l i q u i d products. Consequently, these reactions l i m i t the p r o d u c t i v i t y of DCL reactors. (3) coal l i q u i d - solvent i n t e r a c t i o n s - poor phys i c a l solvents tend to y i e l d lower rates and extents of conversion. on coal l i q u e f a c t i o n k i n e t i c s . These observations also suggest that pre- heaters are important components of DCL reaction networks. Such a l e v e l of c o n f l i c t , between observed k i n e t i c phenomena, k i n e t i c models, and I n d u s t r i a l l i q u e f a c t i o n reactor designs, provides a poor basis for reactor design and scale-up of DCL processes. U n t i l the r o l e of physical phenomena i s resolved, l i t t l e progress can be made towards quantifying coal l i q u e f a c t i o n k i n e t i c s or designing e f f i c i e n t DCL reactors. I t may happen that the current designs are near optimal or that even r a d i c a l changes i n reactor design have l i t t l e e f f e c t on the f i n a l d i s t r i b u t i o n or y i e l d of l i q u e f a c t i o n products. In t h i s event, a c l e a r u n d e r s t a n d i n g of the p h y s i c a l phenomena, r e l a t e d to d i r e c t c o a l l i q u e f a c t i o n w i l l provide a coherent framework f o r optimizing current 99 l i q u e f a c t i o n reactor designs. Conversely, a d e t a i l e d a n a l y s i s of phy s i c a l phenomena may lead to s i g n i f i c a n t l y improved design p r i n c i p l e s f o r d i r e c t c o a l l i q u e f a c t i o n r e a c t o r s . 1 0 0 Chapter 3 3. Objectives Coal l i q u e f a c t i o n r e a c t i o n k i n e t i c s and the r e l a t i o n s h i p between r e a c t i o n k i n e t i c s and process v a r i a b l e s are so poorly understood that research i n a number of diverse areas i s warranted. This t h e s i s , comprising a t h e o r e t i c a l and experimental study i s l i m i t e d to the following o b j e c t i v e s : (1) I d e n t i f i c a t i o n of Consequential Process V a r i a b l e s . The impact of gas-phase moisture content and s y n e r g i s t i c e f f e c t s associated with the extent of a x i a l mixing, the i n t e n s i t y of turbulence, c a t a l y s i s , solvent composition and coal p a r t i c l e s i z e d i s t r i b u t i o n are inv e s t i g a t e d . A semi-batch, backmixed autoclave and a u x i l i a r y equipment are employed for this component of the s tudy. (2) Development of a Quantitative K i n e t i c Model for Coal L i q u e f a c t i o n . A quantitative k i n e t i c model, based on l i k e l y r e a c t i o n paths and observed dependencies on process v a r i a b l e s , i s used to c o r r e l a t e coal l i q u e f a c t i o n r e s u l t s obtained from this work and from the l i t e r a t u r e . The r o l e of chemical reactions and p h y s i c a l phenomena occurring i n pre-heaters i s emphasized. A v a r i e t y of coal-solvent systems are considered. 101 (3) Development of Improved Des i g n C r i t e r i a f o r D i r e c t C o a l L i q u e f a c t i o n Reactors. L i q u e f a c t i o n r e s u l t s , obtained from simulated, axially-mixed pre- heaters and reactors are combined with the k i n e t i c model i n order to characterize rate c o n t r o l l i n g phenomena i n e x i s t i n g DCL processes and predict optimal reactor designs f o r bituminous and sub-bituminous coal and l i g n i t e l i q u e f a c t i o n . 102 Chapter 4 4. Experimental 4.0 In troduc t i o n The motivation and intent of t h i s study are discussed i n the previous chapters. In order to achieve the stated o b j e c t i v e s , accurate comparative data for the l i q u e f a c t i o n behaviour of bituminous and sub- bituminous coals and l i g n i t e are required, f o r a v a r i e t y of reactor configurations and sets of values f o r process v a r i a b l e s . The p r i n c i p a l independent variables include: the amount of c a t a l y s t , the r e a c t i o n temperature, s l u r r y phase residence time and residence time d i s t r i b u t i o n , the i n t e n s i t y of turbulence ( s t i r r i n g r a t e ) , solvent composition and gas phase composition. A s i n g l e reactor network was designed to accommodate an i n v e s t i g a t i o n of these v a r i a b l e s . The objective v a r i a b l e s , employed throughout the reactor and pre-heater simulations, to determine the importance of process v a r i a b l e s , were the l i q u i d and gas y i e l d s from the tes t c o a l s . A mu l t i v a r i a b l e study of t h i s type, can lead r a p i d l y to an unwieldy number of experiments, i f one were to complete the matrix of experiments suggested on Table 4.1. However, t h i s study comprises a s e r i e s of d i s c r e t e e n q u i r i e s , aimed at e l u c i d a t i n g e f f e c t s caused by i n d i v i d u a l process v a r i a b l e s i n conjunction with a sparse matrix of experiments f o r each c o a l . TABLE 4.1 Variables Investigated Variable Values Tested Gas Phase Composition 5 MPa Hj (cold) 5 MPa + varying amounts of HjO Gas Phase Pressure Let reactor Pressure Vary Maintain I n i t i a l Pressure by Adding H 2 Axial Mixing Plug Flow Simulation (mrt ± 2 min) Axial ly mixed Simulation (mrt ± mrt) Axial ly mixed Pre-heater + Plug Flow Reactor Reaction Time 2.5 min 5.0 min 15.0 min 30.0 min Catalyst Part ic le Sire cylinders 3 mm d i a . x 3 cm long ground to 4 um Temperature 425 "C 400 °C 375°C Solvent SRC o i l + 30 vtX te t ra l ln SRC o i l Amount of Catalyst 20 grams 40 grams 80 grams 0 grams 5 grams 10 grams St i r r ing Rate 8.33 Hz 16.67 Hz 25.00 Hz Coal Forestburg Sub-bituminous Byron Creek Bituminous Saskatchewan Lignite 104 In a d d i t i o n , a n t i c i p a t e d s i m i l a r i t i e s i n the dependence of l i g n i t e , sub-bituminous and bituminous coals, on process v a r i a b l e s , further reduces the t o t a l number of experiments. Most of the exploratory experiments are performed with a s i n g l e c o a l . Consequently, as few as 80 experiments are required to complete the experimental program. The remainder of t h i s chapter i s devoted to a d e t a i l e d d e s c r i p t i o n of the apparatus and experimental techniques. 4.1 Coal L i q u e f a c t i o n Experiments 4.1.1 Apparatus Design and Des c r i p t i o n D i r e c t Coal Liq u e f a c t i o n experiments were conducted i n a v e r s a t i l e semi-batch reactor. The apparatus possesses a number of des i r a b l e features. However, the extreme operating conditions of DCL processes (450°C, 20 MPa) and the need to transport dense coal s l u r r i e s constrained the s e l e c t i o n and configuration of equipment components. Commercial components were chosen and assembled to minimize p o t e n t i a l mechanical problems, and mass balance d i s t o r t i o n s , and to f a c i l i t a t e cleaning. The major design features of the apparatus are outlined on Figure 4.1. A d e t a i l e d d e s c r i p t i o n of the apparatus, keyed to Figure 4.1, follows. 1. Slurry Storage A 2JI, me c h a n i c a l l y - s t i r r e d , Parr autoclave (#488) i s used for coal s l u r r y storage. The autoclave can be pressurized to 7 MPa i n order to control the feed pressure to the s l u r r y pump. 3 T3 5 Gas Manifold Compressor JfP- Q.co Explosion Shield 7 Blow-Out Tank r i 4 Reactor m HXr-*3-o Separator 3 J 106 2. Slurry Pump The s l u r r y pump, a va r i a b l e - s t r o k e , r e c i p r o c a t i n g , M i l r o y a l pump (Model A ), pressurizes the s l u r r y and meters s l u r r y flow at an 3 -1 average r a t e between 1.75-3.5 cm s by pulsing a v a r i a b l e f l u i d volume 44 times per minute. The pump, the smallest a v a i l a b l e pump with a s u f f i c i e n t l y high e x i t pressure, cannot operate at lower flow rates or with coal p a r t i c l e s greater than 90 ĵm i n diameter because the p a r t i c l e s tend to clog a serie s of b a l l valves i n s i d e the pump. 3. Slurry R e c i r c u l a t i o n Loop In order to simulate a x i a l l y mixed reactors and pre-heaters, s l u r r y 3 -1 flow r a t e s as low as 0.30 cm s are required. Since the minimum 3 -1 pumping r a t e i s 1.75 cm s , a s l u r r y r e c i r c u l a t i o n loop was i n s t a l l e d . A cascaded-relay c o n t r o l l e d solenoid valve (Skinner V5 Series) was used, at f i r s t , to r e c i r c u l a t e a portion of the s l u r r y to the pump. This valve was subject to plugging and did not shut or open r e a d i l y . E f f o r t s were made to improve the r e l i a b i l i t y of t h i s device, by modifying the seat and plunger, but i t was f i n a l l y replaced with a manually operated valve. 4. The Reactor S l u r r y i s fed from the r e c i r c u l a t i o n loop i n through the base of a " modified, 2A PPI reactor (AOH 34220). Design features include a va r i a b l e speed, magnetically driven s t i r r e r , i n t e r n a l cooling c o i l s and a temperature c o n t r o l l e d external heating mantle. These 107 features permit rapid and c o n t r o l l e d manipulation of reactor temperature. Steady state temperatures can be c o n t r o l l e d to within ± 1°K. The reactor i s depressurized through a gas- l i q u i d separator. The design of the separator was l a t e r r e f i n e d so that entrained s l u r r y could be c o l l e c t e d and incorporated into the mass balance. 5. Gases Gases are fed from c y l i n d e r s and pressurized, i f necessary, with a PPI compressor (model #1038) to the desired operating pressure. Gas flow to the reactor can be c o n t r o l l e d i n two ways: i . the reactor can be pressurized cold and sealed, i i . the feed back pressure c o n t r o l l e r , on the compressor, can be used to maintain a f i x e d gas pressure under conditions of net gas consumption. Gases can be sampled at the reactor sample port, or at the c y l i n d e r s . 6. S l u r r y Line Flush Once the s l u r r y i s i n j e c t e d , the s l u r r y l i n e s are flushed with o i l under nitrogen pressure to recover unused s l u r r y and clean the s l u r r y l i n e s . 7. Safety i . the reactor and a l l transfer l i n e s are connected v i a 30 MPa rupture discs to a 27X blow-out tank, i i . the reactor and blow-out tank are encased i n an exhausted explosion s h i e l d f a b r i c a t e d from 1.07 m gas p i p e l i n e stock. 108 4.1.2 Operating Procedure The o p e r a t i n g procedure f o l l o w e d f o r a l l s l u r r y i n j e c t i o n experiments, i s summarized below: 1. The s t r i p chart recorders, the gas chromatograph, the pressure transducer are a l l switched on and the cold junction for the reactor temperature c o n t r o l l e r i s f i l l e d with i c e water. Ambient pressure i s recorded. 2. The reactor i s charged with 150 g of solvent and c a t a l y s t ( i f d e s i r e d ) . The mass of solvent and c a t a l y s t i s recorded. 3. The reactor i s placed under vacuum (using an a s p i r a t o r ) and flushed twice with hydrogen to remove a i r . The reactor i s then sealed and pressurized to 5.0 MPa. A gas sample i s extracted and analysed; the i n i t i a l pressure, and the reactor temperature are recorded. 4. The s t i r r e r i s set at 1000 rpm and the heater i s turned on. The temperature control point i s set 25°K above the desired operating temperature. 5. While the reactor i s heating i . a coffee break i s taken (20 minutes) i i . dried coal (~ 230 g) i s combined with solvent (575 g SRC o i l , or 403 g SRC o i l + 172.5 g THN) in a 2A beaker. The precise 109 solvent to coal r a t i o i s 2.5:1. The s l u r r y i s then agitated with a hand mixer to remove lumps. A 10 g coal sample i s retained for a n a l y s i s . The coal and solvent masses are recorded, i i i . The pre-mixed s l u r r y i s poured into the s l u r r y storage tank, which i s then sealed. The s t i r r e r i s turned on to prevent s e t t l i n g . The mass of s l u r r y charged i s recorded, i v . The f l u s h tank i s f i l l e d with solvent using a squeeze b o t t l e . The g a s / l i q u i d separator i s weighed and replaced. A c a t c h a l l b o t t l e i s weighed and placed under the s l u r r y l i n e d r a i n . A l l masses are recorded. 6. Once the reactor has reached the temperature set point: i . The s l u r r y storage tank i s flushed and pressurized with nitrogen (3 MPa). i i . The pump i s primed by flowing s l u r r y through the r e c y c l e loop and c o l l e c t i n g a small quantity of s l u r r y at the drain ( c a t c h a l l ) . I i i . The temperature set point i s reset to the operating temperature and the s t i r r i n g rate i s changed i f desired. i v . The reactor Is sub-cooled to the operating temperature by flowing cold water through the i n t e r n a l cooling c o i l s . 7. S l u r r y flow rate Is selected, and s l u r r y i n j e c t i o n i s commenced. Cooling water i s applied, as necessary, during s l u r r y i n j e c t i o n , to maintain the operating temperature. In order to assure r e l i a b l e valve operation, during a x i a l l y mixed reactor t r i a l s , s l u r r y should be injected into the reactor in at l e a s t 10 stroke bursts . 110 8. The s l u r r y i n l e t l i n e to the reactor i s sealed once s l u r r y i n j e c t i o n i s completed. While the l i q u e f a c t i o n reactions progress i . unused s l u r r y i s c o l l e c t e d by f o r c i n g i t from the storage tank through the recycle loop to the drai n , i i . the s l u r r y l i n e s are flushed with solvent, i i i . the s l u r r y storage tank i s depressurized and cleaned, i v . the t o t a l mass of s l u r r y + f l u s h solvent c o l l e c t e d at the d r a i n , and the mass of s l u r r y r e t r i e v e d from the s l u r r y storage tank i s recorded. 9. Once the t r i a l i s completed, the reactor i s cooled to 600 K, within 200s, using the i n t e r n a l cooling c o i l s , and i s at room temperature, i n about one hour. Lunch i s eaten while the reactor c o o l s . 10. The s t i r r e r i s turned o f f and a gas sample Is extracted from the reactor. The reactor i s then depressurized, r a p i d l y , through the separator. The s t i r r e r Is switched on again for 10 seconds and a second gas sample i s extracted. These samples are analysed on the gas chromatograph. 11. The l i d i s removed from the reactor, a small s t i r r e r i s placed i n s i d e and two s l u r r y samples (~ 30 g each) are extracted while the reactor contents are being a g i t a t e d . The remaining s l u r r y i s c o l l e c t e d and f i l t e r e d , and a small l i q u i d sample i s retained f o r a n a l y s i s . The mass of the s l u r r y samples i s recorded. 12. The s l u r r y samples are dissolved temperature i n a beaker equipped The r e s u l t a n t s l u r r y i s f i l t e r e d residua i s dried overnight i n a n a l y s i s . I l l In 200 g of THF for 1 hour, at room with a magnetically driven s t i r r e r , through Gooch c r u c i b l e s . The s o l i d a vacuum oven and retained f o r 13. The apparatus i s cleaned with v a r s o l and paper towels. P a r t i c u l a r a t t e n t i o n i s paid to the s l u r r y t r a n s f e r l i n e and valve at the base of the reactor. 14. The mass of the s l u r r y i n the separator i s recorded, and mass balance c a l c u l a t i o n s are completed. 15. Coal, residua, and product l i q u i d s are submitted for external a n a l y s i s as necessary. Appropriate ASTM standards are employed. 4.1.3 M a t e r i a l s 4.1.3.1 C a t a l y s t s A cobalt-molybdenum c a t a l y s t , supported on alumina, was the p r i n c i p a l c a t a l y s t employed i n coal l i q u e f a c t i o n experiments. The c a t a l y s t comprised 12 wt% MoO^and 3 wt% CoO i n an oralumina matrix. This c a t a l y s t , supplied by Alpha Products i n the form of 3 mm diameter x 3 mm long p e l l e t s , was t y p i c a l l y ground p r i o r to use. The volume mean p a r t i c l e 112 diameter of the ground c a t a l y s t i s approximately 1.41 \m (see Table 4.2). Whole c a t a l y s t p e l l e t s and an unsupported Mo0^»l/2 H^O c a t a l y s t were also employed In selected experiments. A l l c a t a l y s t s were sulphidized i n s i t u . 4 . 1 . 3 . 2 C o a l s / L i g n i t e s The l i q u e f a c t i o n c h a r a c t e r i s t i c s of Forestburg sub-bituminous c o a l , Byron Creek bituminous coal and Saskatchewan l i g n i t e were i n v e s t i g a t e d . S l u r r y handling d i f f i c u l t i e s l i m i t e d the maximum coal p a r t i c l e s i z e to 90 um. Pulverized samples of Forestburg and Byron Creek coal were obtained. A s i g n i f i c a n t f r a c t i o n of the Forestburg coal was greater than 90 \m i n diameter. This coal was wet screened through a 90 \m screen using a custom designed semi-automatic s c r e e n i n g / s e t t l i n g device. Only the -90pm f r a c t i o n was retained. V i r t u a l l y a l l of the Byron Creek coal was les s than 90 \Jm i n diameter; i t was simply dry screened using a Tyler Ro-Tap Sieve Shaker. Since pulverized Saskatchewan l i g n i t e could not be obtained, i t was ground i n a F r i t s c h automatic mortar. Only a small quantity of l i g n i t e could be prepared i n th i s way. C l e a r l y , the test "coals" resemble but are not i d e n t i c a l to the parent "coals". Proximate and ultimate analyses of the test coals are l i s t e d on Table 4.3. P a r t i c l e s i z e d i s t r i b u t i o n s f o r the coal and l i g n i t e samples are shown on Figure 4.2. 113 TABLE 4.2 Catalyst P a r t i c l e Size D i s t r i b u t i o n Mean Diameter Number of P a r t i c l e s Volume F r a c t i o n ( Mm) (%) 0.29 214 2.10 0.88 138 37.94 1.46 28 35.16 2.05 5 17.38 2.64 1 7.42 3.22 0 0. 114 TABLE 4.3 Proximate and Ultimate Analyses of the Test Coals Forestburg Coal Bryon Creek Coal Saskatchewan L i g n i t e Proximate Analysis (dry basis) Ash 16.19 16. 26 19.91 Fixed Carbon 46.52 62. 25 43.27 V o l a t i l e Matter 37.29 21. 49 36.82 Ultimate Analysis C 66.63 83. 84 69.21 H 4.87 4. 63 4.91 N 1.46 1. 23 1.24 0 26.38 9. 97 23.97 s - 0.66 0. 32 0.68 12- 115 10- >- o z UJ O UJ cc u. 4- 2- Legend FORESTBERG 220 FORESTBERQ 236 J l r-i r J J 1 Ll i 1 1 1 20 40 60 80 PARTICLE DIAMETER (microns) 100 40- 30- >-O z iu 3 20-O UJ CC u. 10- Legend SASKATCHEWAN 401 BYRON CREEK 322 Ln 20 40 60 80 PARTICLE DIAMETER (microns) 100 Figure 4.2: P a r t i c l e Size D i s t r i b u t i o n s f o r the Test Coals 116 4.1.3.3 L i q u e f a c t i o n Solvents One of the objectives of t h i s study i s the simulation of i n d u s t r i a l l i q u e f a c t i o n environments. I n d u s t r i a l processes employ heavy o i l s or hydrogenated heavy o i l s as the recycle solvent. Such solvents have been shown to be sui t a b l e v e h i c l e s f o r DCL reactions, and r e c y c l i n g heavy o i l s y i e l d s a greater f r a c t i o n of more valuable l i g h t o i l s . Consequently, two solvents were selected f o r t h i s study. Solvent 1, comprising SRC o i l obtained from the W i l s o n v i l l e p i l o t plant combined with 30 wt% tetrahydro- naphthalene t e t r a l i n , i s used to simulate a hydrogenated process solvent. Solvent 2, comprising 100 wt% SRC o i l , simulates an untreated recycle solvent. The SRC o i l was d i s t i l l e d p r i o r to use i n order to remove water. Technical grade t e t r a l i n was added to the SRC o i l to form Solvent 1. 4.1.3.4 Analysis Solvent Tetrahydrofuran s o l u b i l i t y was used to define the base l i n e f o r coal conversion. Pre-asphaltenes, asphaltenes, o i l s e t c . are a l l soluble i n THF; raw coal i s not. Raw coal i s soluble i n pyridi n e , the other solvent frequently employed f or t h i s purpose. 4.1.3.5 Gases Dr y h y d r o g e n c o m p r i s e s 90 +Z of the i n i t i a l gas phase f o r the majority of experiments. Nitrogen, used to pre-pressurize the coal s l u r r y , 117 enters the reactor with the s l u r r y and comprises approximately 5%. Argon, added to the hydrogen c y l i n d e r , acts as a t i e substance and comprises about 2%. The remaining f r a c t i o n i s vapourized solvent. Nitrogen, argon, and hydrogen are supplied by Linde and are at l e a s t 99.9% pure. , A standard gas, containing fixed percentages of methane (5.08%), carbon dioxide (5.01%), ethane (1.00%), carbon monoxide (2.00%), argon (2.01%), nitrogen (0.97%) and hydrogen (balance), was used for s o l u b i l i t y t e s t s , and to c a l i b r a t e a Beckman GC1 Gas Chromatograph. This gas was supplied by Matheson. 4.1.4 Experiment Design The experimental program was subdivided into three phases: 1. preliminary experiments, 2. i n v e s t i g a t i o n s of gas phase phenomena, 3. i n v e s t i g a t i o n s of s l u r r y phase phenomena. Preliminary experiments established operating l i m i t s for the l i q u e f a c t i o n reactor network, resolved problems r e l a t e d to r e s u l t a n a l y s i s and mass balances, and suggested apparatus modifications and procedural changes. Results from these preliminary experiments have l i t t l e meaning i n themselves and are not reported. However, modifications and adjustments suggested by these experiments are responsible f or the accuracy and r e p e a t a b i l i t y of experiments reported i n the following chapters. 118 Investigations of gas phase phenomena consider the p o t e n t i a l r o l e of the water gas s h i f t r eaction H 2 0 + CO + ^ + C 0 2 and hydrocracking reactions (e.g.) C 2 H 6 + H 2 : 2CH 4 i as representative sources and sinks f o r hydrogen. These reactions influence hydrogen consumption patterns i f long gas phase residence times are employed i n DCL reactors. Currently, the gas phase passes through i n d u s t r i a l reactors very quickly - r e l a t i v e to the s l u r r y mean residence time. Investigations of various s l u r r y phase phenomena comprise the remainder of th i s t h e s i s . Four issues, which are not resolved by the l i t e r a t u r e , are addressed: 1. The number of active phases i n DCL reactors i s unknown. V a r i a t i o n of s t i r r i n g rate and solvent composition Is used to investigate the e f f e c t of the i n t e n s i t y of turbulence and solvent composition on g a s - l i q u i d and l i q u i d - l i q u i d or l i q u i d - s o l i d mass tra n s f e r , and the d i s t r i b u t i o n of coal derived products between the phases present. 119 2. P o s s i b l e s y n e r g i s t i c a l t e r a t i o n s of coal l i q u e f a c t i o n k i n e t i c s , caused by s l u r r y phase a x i a l mixing, are in v e s t i g a t e d . A x i a l l y mixed and plug flow reactors and pre-heaters are simulated by varying the mean residence time of the s l u r r y and the rate of s l u r r y i n j e c t i o n into the reactor. A computer model has been developed to r e l a t e pumping rate to an approximate number of tanks i n s e r i e s , f o r a normalized mean residence time. The model, shown on Figure 4.3, in d i c a t e s the time of I n i t i a l s l u r r y i n j e c t i o n and the duration of i n j e c t i o n . Slurry flow rate i s simply adjusted to f i t these bounds. 3. The r o l e of c a t a l y s t s i n DCL reactors i s investigated by varying the amount and type of c a t a l y s t i n conjunction with coal and solvent composition. 4. Reaction temperature i s varied i n order to observe p o s s i b l e t r a n s i t i o n s i n DCL k i n e t i c s . 425°C i s the maximum safe operating temperature for t h i s apparatus because the reactor must be super- heated p r i o r to s l u r r y i n j e c t i o n . These i n v e s t i g a t i o n s are by t h e i r very nature d i s c r e t e , and aimed at providing bases f o r modelling the DCL rea c t i o n environment. 120 1-1 NORMALIZED TIME Figure 4.3: Continuous Flow Reactor Simulation Model 4.1.5 Result Analysis 121 4.1.5.0 Introduction Coal l i q u e f a c t i o n experiments present a number of a n a l y t i c a l problems which account, i n part, for the poor r e s u l t r e p e a t a b i l i t y frequently quoted i n the l i t e r a t u r e . The source of these problems i s the s e n s i t i v i t y of various parameters to the o v e r a l l mass balance. However, these problems can be circumvented once they are recognized. Two recurrent problems are: (1) Evaluation of the amount of hydrogen consumed and gases produced during l i q u e f a c t i o n experiments. (2) Evaluation of t o t a l coal conversion. Gas analysis i s i n v a r i a b l y performed once the reactor i s cooled ( a f t e r batch laboratory experiments). Some researchers simply extract a gas sample from the reactor while i t i s s t i l l pressurized. This procedure ignores gas s o l u b i l i t y i n the product l i q u i d s , causing hydrogen consumption to be overestimated and gas production to be underestimated. The magnitude of the systematic errors v a r i e s with the s o l u b i l i t y of the gas components and reactor geometry. As much as 50% of ethane and carbon dioxide may be dissolved i n the product o i l . Other researchers, recognizing t h i s problem, depressurlze the reactor into a large b a l l o o n . Though t h i s improves the accuracy of gas phase measurements, the improvement i s l e s s than one expects because the gas remaining i n the autoclave has much higher concentrations of the more soluble gases than the 122 gases c o l l e c t e d i n the balloon. This f a c t i s often overlooked. Further- more, a f r a c t i o n of the s l u r r y i s entrained with the gas as i t e x i t s the reactor which can cause concurrent problems with s l u r r y phase a n a l y s i s . Gas analysis problems appear to be much l e s s severe i n a continuous flow apparatus. A n a l y t i c a l problems r e l a t e d to the evaluation of t o t a l coal conversion also vary with the reactor type and the a n a l y t i c a l method employed. In flow apparatus, for example, one must assume that representa- t i v e samples of the ingoing and outgoing s l u r r y streams can be obtained, and that flow surges do not occur, or have a very high frequency with respect to the sample time. Inevitably, flows and compositions vary. Since conversion i s s e n s i t i v e to these f l u c t u a t i o n s , large errors can r e s u l t . In batch reactors, the amount of coal i n the reactor i s known by d i r e c t measurement. Following an experiment, some researchers extract the " e n t i r e " s l u r r y phase . from the reactor and base conversion on the t o t a l amount of organic residua r e t r i e v e d . However, some s l u r r y remains In the reactor or transfer apparatus, and some i s entrained with the gas. Conversion i s overestimated and errors vary widely from experiment to experiment. Other researchers extract s l u r r y samples from the reactor and base conversion on the composition of the s o l i d residua. This approach i s more p r e c i s e . An a d d i t i o n a l problem with s l u r r y phase analysis i s that few researchers sample the ingoing coal with s u f f i c i e n t frequency. Small v a r i a t i o n s i n ash or moisture content from run to run also contribute to the uncertainty of l i q u e f a c t i o n r e s u l t s . 123 The semi-batch apparatus, described previously, and the a n a l y s i s techniques adopted for th i s study endeavour to combine the p o t e n t i a l accuracy of batch apparatus with the experimental v e r s a t i l i t y of flow apparatus. A d e s c r i p t i o n of a n a l y t i c a l techniques f o l l o w s . A.1.5.1 Gas Analysis 4.1.5.1.0 Introduction Accurate estimates of the amount of gases produced and hydrogen consumed can only be obtained i f the composition and volume of the gas phase are known, and the composition and apparent volume of gas d i s s o l v e d i n the product s l u r r y are known. The gas phase volume and composition are r e a d i l y obtained i n a semi-batch reactor network by 1) e x t r a c t i n g a gas sample at pressure 2) subjecting i t to chromatographic a n a l y s i s 3) determining the density and mass of the s l u r r y phase Estimation of the dissolved gas composition and volume i s more d i f f i c u l t , as i t involves a determination of gas s o l u b i l i t y or apparent s o l u b i l i t y In the product s l u r r y . 4.1.5.1.1 S o l u b i l i t y Estimation Gas s o l u b i l i l t y estimates are obtained i n d i r e c t l y . The estimation technique r e l i e s on the accuracy of mass balances and assumes that gas 124 samples extracted from the reactor, once i t i s depressurized, are represen- t a t i v e of the dissolved gas composition. The o v e r a l l mole f r a c t i o n of a gas component, C^, i s defined as - Cil + C i 2 (VV c i = (i + v2/v1) ( 4 , 1 ) where i s the gas phase volume i s the apparent gas volume of the l i q u i d phase and a r e t n e mole f r a c t i o n s of component i In the two phases r e s p e c t i v e l y . Equation 4.1 can be incorporated into the hydrogen and argon molar balances to obtain two equations for the f r a c t i o n of hydrogen consumed during r e a c t i o n , HC. H V P T / H V 1 o o o V 1 1 Combining equations 4.2 and 4.3 y i e l d s equation 4.4 T,V P Ar l o o o T V.P.H. o 1 1 2 H l + H2 ( V 2 / V 1 > \ h A r x + A r 2 (V2/V1)J H 2 = 0 V l (4.4) 125 which must be solved i t e r a t i v e l y f o r V^. If a gas of known composition Is used f o r s o l u b i l i t y t e s t i n g , can be obtained from equation 4.1 d i r e c t l y . Once i s o b t a i n e d the f r a c t i o n of component i dissolved i n the l i q u i d phase, F^, i s C 1 2  V2 F i = C V " C V ( 4 - 5 ) i l 1 12 2 and the s o l u b i l i t y , S^, becomes o - ^ - 1 _ J L _ ( k M i M p 1/F, - 1 ZRT, s r8 1 1 where V R = reactor volume A M = s l u r r y or o i l mass Kg s -3 p g = s l u r r y or o i l density Kg/A or g cm Z = gas comp r e s s i b i l i t y f a c t o r (1-1.03) R = the universal gas constant (.08206 Jl«Atm»mol *K S. •* s o l u b i l i t y of component i moles Kg "̂•Atm ^ Apart from uncertainties associated with mass balances, the s o l u b i l i t i e s estimated by equation 4.6 are predicated on the assumption that" representative "dissolved gas" samples can be extracted from the depressurlzed reactor. This may or may not be f e a s i b l e . A mathematical model, which considers two extreme depressurization cases: 126 1) plug-flow depre8Surization gases evolving from the s l u r r y phase force gas In the gas phase out of the reactor. The two gases do not mix. 2) completely backmlxed depressurlzation gas evolving from the s l u r r y phase mixes in t i m a t e l y and completely with the gas already present i n the gas phase and e x i t s the reactor i n proportion to i t s content i n the gas phase. was formulated to address this i s s u e . The r e s u l t s obtained from t h i s mathematical treatment are summarized on Table 4.4. The possible bounds, on depressurlzation behaviour are too broad to provide a d e f i n i t i v e answer to t h i s question except i n the event of very high or very low gas s o l u b i l i t i e s . However, the r e s u l t s do not preclude the p o s s i b i l i t y of obtaining representative dissolved gas samples over a broad range of s o l u b i l i t i e s . I f one were to consider the plug-flow extreme, for example, as l i t t l e as 2% of the gas need be dissolved In order to obtain a representative sample . A number of experimental observations suggested that reactor depressurlzation approximates the plug-flow extreme, and the method was v e r i f i e d by determining the s o l u b i l i t y of a c a l i b r a n t gas i n benzene - Table 4.4. S o l u b i l i t i e s calculated as o u t l i n e d above are compared with r e s u l t s obtained using two other experimental methods, and r e s u l t s selected *The f i n a l , c o l d r e a c t o r pressure Is t y p i c a l l y 25 to 50 times atmospheric pressure. 127 TABLE 4.A Apparent Gas S o l u b i l i t i e s i n Benzene Compound S o l u b i l i t y (moles Kg" 1 * Arm - 1 ) x 1 0 3 L i t e r a t u r e Values Method I Method II Method III 1 2 3 1 2 3 1 2 3 Ar 1 0 . 5 l 1 0 ° ] 9 . 7 1 8 . 9 7 8 . 6 3 9 . 7 4 8 . 7 4 9 . 7 5 N 2 S . o t 1 0 2 ! 5 . 2 7 8 . 0 8 4 . 4 7 2 . 2 1 4 . 4 8 8 . 1 3 CH 4 - 1 8 . 7 1 5 . 3 1 7 . 3 2 3 . 0 2 1 . 5 2 2 . 0 CO - 4 . 7 7 4 . 2 8 4 . 6 5 7 . 5 1 1 0 . 5 4 . 1 4 C 2 H 6 1 9 3 [ 1 0 1 ] 5 4 . 7 4 8 . 0 5 5 . 4 1 4 0 . 1 4 7 . 1 2 9 . c o 2 - 4 7 . 2 3 7 . 3 4 3 . 9 9 8 . 4 8 7 . 6 8 7 . 6 H 2 3.2[99] 2 . 8 2 . 1 2 . 4 0 . 9 1 1 . 4 8 3 . 6 3 S 5 . 0 1 4 . 0 6 4 . 5 8 5 . 2 4 5 . 6 3 7 . 2 6 5 . 8 7 5 . 8 9 5 . 9 2 128 from the l i t e r a t u r e . Data f o r these comparisons were c o l l e c t e d by i n j e c t i n g c a l i b r a n t gas, comprising argon, nitrogen, carbon monoxide, methane, ethane, carbon dioxide and hydrogen, i n t o the reactor over a known mass of benzene. This gas was sampled and the pressure recorded. The reactor was then s t i r r e d at 1000 rpm for approximately 15 minutes. The s t i r r e r was stopped, a second gas sample extracted, and the pressure recorded. F i n a l l y , the reactor was depressurized r a p i d l y to room temperature and a low pressure gas sample was extracted. Three t r i a l s were performed. C a l c u l a t i o n Method I i s the method described above. Method II only employs high pressure gas compositions and s o l u b i l i t i e s are defined by equation 4.7 V, / C. P 1 / 1 o C a l c u l a t i o n Method I I I , based on d i f f e r e n t i a l pressure measurements, only p r e d i c t s a mean s o l u b i l i t y f o r a l l of the gases combined - equation 4.8. 5 - ( ^ - 0 C a l c u l a t i o n Methods I and II are s e n s i t i v e to a i r leaks i n t o the gas samples and t h i s accounts f o r the scatter of the r e s u l t s . Method I, selected f o r use In th i s t h e s i s , provides the greatest accuracy and 129 consistency f o r gases with low and moderate s o l u b i l i t y ( i . e . ) argon, hydrogen, carbon monoxide, nitrogen and methane. The s o l u b i l i t i e s of very soluble gases i . e . ethane, carbon dioxide are badly underestimated. S o l u b i l i t i e s of a l l gases are systematically underestimated: - argon, methane, carbon dioxide, hydrogen and nitrogen s o l u b i l i t i e s are underestimated by approximately 20% on an absolute scale with a r e l a t i v e random error of 15%. - carbon dioxide and ethane s o l u b i l i t i e s are underestimated by ~ 50% and 60% r e s p e c t i v e l y on an absolute scale with a r e l a t i v e random error of 15%. Gas production and consumption r e s u l t s are not corrected f o r these systematic errors as they have a minimal e f f e c t on the o v e r a l l mass balance. Without t h i s c o r r e c t i o n , o v e r a l l gas production i s underestimated by l e s s than 10% with a random error of approximately 3%. The precise values vary with the composition of the gas phase. 4.1.5.2 Slurry Analysis The apparatus i s a flow device with respect to the s l u r r y phase. Consequently, the precise quantity of s l u r r y entering the reactor can only be estimated. However, the bounds on t h i s estimate are very narrow. The amount of s l u r r y placed i n the storage tank, that does not report to the s l u r r y drain, overestimates the amount of s l u r r y entering the reactor: a r e s i d u a l amount of s l u r r y remains i n the storage tank (~ 15 g), about 5 g remain i n the flushed recycle loop, and 8 to 10 g lodge i n connecting tubing. The amount of s l u r r y r e t r i e v e d from the reactor, at the end of an experiment, underestimates the amount of s l u r r y entering the rea c t o r . M a t e r i a l c l i n g s to the cooling c o i l s , the reactor w a l l , and passes through the g a s / l i q u i d separator on depressurlzation. This material cannot a l l be r e t r i e v e d and the amount varies from experiment to experiment. A f t e r performing a number of pumping t e s t s , the minus 30 gram mass balance was adopted as the standard for a l l experiments ( i . e . ) s l u r r y mass entering the reactor = s l u r r y mass charged to the reactor - s l u r r y mass reporting to the drain - 30.0 grams This equation cannot have an uncertainty greater than ± 3 g out of approximately 750 g. The mass of c o a l entering the reactor i s determined within 1 g from the estimated s l u r r y mass and the composition of the s l u r r y obtained by d i r e c t measurement. Residual s o l i d analysis i s based on a s i m i l a r p r i n c i p l e . The composition of the r e s i d u a l s o l i d s i s more r e l i a b l e than the quantity or density of s l u r r y r e t r i e v e d from the r e a c t o r . Thus, the t o t a l c o al conversion, TCC, i s defined by equation 4.9 A (1 - A^) CAT (1 - A ) T C C S 1 - (1 - A,) A, - MAFCAp « - 9 > where A^ = ash content of the moisture free coal (wt f r a c t i o n ) Aj, = ash content of the moisture free r e s i d u a l s o l i d s (wt f r a c t i o n ) 131 CAT «= c a t a l y s t charged to the reactor (g) MAFC = moisture and ash free coal charged to the reactor (g) T o t a l coal conversion for d i r e c t coal l i q u e f a c t i o n experiments performed as part of this study are repeatable to within 0.3 to 0.5%. This uncertainty i s a factor of 10 smaller than the uncertainty quoted i n the l i t e r a t u r e . 4.2 Fundamental Investigations A number of fundamental i n v e s t i g a t i o n s were undertaken with respect to s l u r r y phase analyses. I am Indebted to Mr. G. Roemer and Mr. I. Mojaphoko, both undergraduate metallurgy students, who performed two projects as part of t h e i r 398 course work. The r e s u l t s of these i n v e s t i g a t i o n s are reported i n Chapter 5. Mr. Mojaphoko analysed s o l i d residua p a r t i c l e s using an ETEC scanning e l e c t r o n microscope i n an e f f o r t to i d e n t i f y r e s i d u a l c o a l , ash and c a t a l y s t p a r t i c l e s , and examine p a r t i c l e cross-sections i n search of cross penetration e f f e c t s . Some of the e f f e c t s sought included: coke dep o s i t i o n on c a t a l y s t and ash p a r t i c l e s , and c a t a l y s t penetration into " c o a l " p a r t i c l e s . Chemical interferences and the poor r e s o l u t i o n of the ORTEC analyser hampered much of t h i s work. Mr. Roemer analysed organic residua p a r t i c l e s i z e d i s t r i b u t i o n s , as a function of the Intensity of turbulence In the reactor, using a LEITZ image analyser. If these p a r t i c l e s had formed a dispersed l i q u i d phase under DCL 132 r e a c t i o n conditions, the mean p a r t i c l e s i z e would decline as the s t i r r i n g rate increased - at the same extent of conversion. I f the p a r t i c l e s were s o l i d , or "exploded" during r e a c t i o n , s t i r r i n g rate would have l i t t l e e f f e c t on the mean p a r t i c l e s i z e . He dispersed c o a l , ash, c a t a l y s t and residua p a r t i c l e s on s l i d e s with acetone, and placed them under a micro- scope which i s connected to the image analyser through a video camera. He found that by adjusting the grey l e v e l , ash p a r t i c l e s could be d i s t i n g u i s h e d from organic matter, even when p a r t i a l l y coated with coke, and that c a t a l y s t p a r t i c l e s are much smaller than ash or "organic c o a l " p a r t i c l e s . Manual image manipulation coupled with a software package thus enabled Mr. Roemer to obtain reproducible p a r t i c l e s i z e d i s t r i b u t i o n s f or organic residua and coal p a r t i c l e s . Catalyst and spent c a t a l y s t p e l l e t s were analysed with a JOEL microprobe to determine the d i s t r i b u t i o n of phases and examine the rate of c a t a l y s t s u l p h i d i z a t i o n i n the reactor. This work endeavoured to address the nature of the c a t a l y t i c a l l y a c t i v e s i t e s on various c a t a l y s t surfaces. The unusual behaviour of DCL k i n e t i c s i n solvent 1 (30 wt% THN, 70 wt% SRC o i l ) prompted an i n v e s t i g a t i o n of the number of l i q u i d phases present at room temperature and under DCL reaction conditions. Small glass c a p i l l a r i e s were manufactured from .76 cm 0D .15 cm ID glass tubing. These c a p i l l a r i e s were p a r t i a l l y f i l l e d with THN and a small quantity of SRC o i l and then s e a l e d under vacuum. C a p i l l a r i e s were p l a c e d on an 133 alumina oxide bed inside an explosion s h i e l d and heated to 700 K. A thermocouple was placed i n a c a p i l l a r y adjacent to the test c a p i l l a r i e s . A t e m p e r a t u r e time h i s t o r y o f the p h a s e s p r e s e n t was r e c o r d e d photographically. Chapter 5 134 5. Experimental Results and Preliminary Discussion 5.0 In troduc t i o n Experimental r e s u l t s , presented i n this chapter, are summarized on Figures and short Tables, which i l l u s t r a t e key findings of the various components of the experimental program outlined i n Chapters 3 and 4. Complete sets of r e s u l t s and operating conditions f o r i n d i v i d u a l t r i a l s can be found on the Tables c o l l e c t e d i n Appendix C. Tables C . l to C.3 contain product d i s t r i b u t i o n data and process v a r i a b l e s for t r i a l s with Forestburg sub-bituminous c o a l , Byron Creek bituminous coal and Saskatchewan l i g n i t e r e s p e c t i v e l y . Tables C.4 to C.6 contain estimated s o l u b i l i t y data f o r the gas phase constituents i n the product l i q u i d s . T r i a l numbers mentioned i n the text r e f e r to this set of Tables. 5.1 Data P r e c i s i o n Before discussing the experimental r e s u l t s i n d e t a i l , i t i s important to note the p r e c i s i o n of the data presented i n t h i s chapter, as a number of the e f f e c t s examined are normally obscured by the poor r e p e a t a b i l i t y associated with coal l i q u e f a c t i o n experiments. Four l i q u e f a c t i o n t r i a l s with Forestburg coal were duplicated i n t h i s work. 135 The t o t a l conversion and gas y i e l d r e s u l t s obtained from these experiments are compared on Table 5.1. Tot a l coal conversion i s repeatable to within 0.3 wt%, a p r e c i s i o n at l e a s t an order of magnitude better than the ± 3 to 5 wt% encountered i n the l i t e r a t u r e . A comparable improvement i n t o t a l gas y i e l d p r e c i s i o n i s also r e a l i z e d . Gas y i e l d i s repeatable to within 10% of the value reported, although the composition of the gas varies with the water content of the gas phase and the mean residence time, as discussed i n Section 5.2. The r e p e a t a b i l i t y of l i q u e f a c t i o n r e s u l t s a t t e s t s to the accuracy of the a n a l y t i c a l procedures adopted f o r t h i s study and the p r e c i s i o n of the c o n t r o l of operating conditions. As Figures 5.1 and 5.2 suggest, c o a l conversion i s s e n s i t i v e to changes i n the reac t i o n temperature and the mean residence time. 2°K di f f e r e n c e s i n re a c t i o n temperature between "duplicate" t r i a l s can cause 1.5 to 2 wt% f l u c t u a t i o n s i n t o t a l conversion and 0.15 to 0.2 wt% f l u c t u a t i o n s i n gas y i e l d f o r Forestburg sub-bituminous and Byron Creek bituminous c o a l . One minute d i f f e r e n c e s i n mean residence time introduce comparable r e s u l t v a r i a t i o n s , p a r t i c u l a r l y at short residence times. Uncertainties introduced by the analysis procedures compound these f l u c t u a t i o n s and together they obscure e f f e c t s r e l a t e d to solvent composition, c a t a l y s t : c o a l r a t i o , i n t e n s i t y of turbulence, and a x i a l mixing v a r i a t i o n s . The s l u r r y i n j e c t i o n apparatus and the a n a l y t i c a l procedures employed i n t h i s work permit precise c o n t r o l of reactor temperature and mean residence time and minimize the impact of "error" 136 TABLE 5.1 Result R e p e a t a b i l i t y Duplicate Set Gas Y i e l d (wt%) To t a l Coal Conversion (wt%) 205 6.26 89.64 213 6.26 89.94 208 6.34 90.10 209 7.03 89.98 221 5.39 70.36 223 5.28 69.74 224 6.98 86.16 226 6.80 86.35 137 Figure 5.1: The Impact of Temperature Variations on Coal Conversion 138 * z o CO t£ IU > z o o —I < o o -I o 100- 80- 60- 40- 20- 10 — I — 80 Legend A FORESTBURG S0L1 CAT-20. T-696. X FORESTBURG 80L2 CAT-20. T-696. • FORESTBURG 80L1 CAT-80. T-698. IS FORESTBURG SOL2 CAT-0.0 T-698. K BYR0N_C_R_E|KJB̂ 2jCAT-20̂  T-698. * BYRON CREEK SOU CAT-20. T-698. 30 40 60 60 TO REACTION TIME (min) 10-i o-| 1 1 1 1 1 1 ' 0 10 20 30 40 60 60 70 REACTION TIME (min) Figure 5.2: the Impact of Residence Time V a r i a t i o n on Coal Conversion 139 supposition on experimental r e s u l t s . Secondary e f f e c t s , causing as l i t t l e as 0.6 wt% differences i n t o t a l conversion can be observed r e l i a b l y . 5.2 Gas Phase Phenomena Current DCL reactor designs p u r i f y and recycle large q u a n t i t i e s of hydrogen. Consequently, the gas phase residence time i s short and any r e a c t i o n s o c c u r r i n g among gas phase c o n s t i t u e n t s are r e l a t i v e l y unimportant. In batch-laboratory reactors and possible design a l t e r n a t i v e s for DCL reactor networks, gas phase residence times may be much longer and reactions occurring i n the gas phase cannot be ignored. In this work, the impact of two representative gas phase r e a c t i o n s : the water gas s h i f t r e a c t i o n H-0 + CO C0„ + H„ 2 •*• 2 2 9.0 [97] and hydrocracking reactions ( i . e . ) C 2H 6 + H 2 , 2CH 4 on hydrogen a v a i l a b i l i t y and consumption are considered. 140 The role or p o t e n t i a l r o l e of the water gas s h i f t r e a c t i o n , i n d i r e c t coal l i q u e f a c t i o n r e a c t o r s , i s disputed i n the l i t e r a t u r e . T891 T1031 Batchelder and Fu and K r i z 1 have proposed the use of synthesis gas, i n which CO and R^O become a source of hydrogen, w h i l e the p r e v a i l i n g opinion i s that the water gas s h i f t r eaction does not occur to an appreciable extent and CO cannot act as a hydrogen source. Results from t h i s work suggest that the water gas s h i f t reaction i s superimposed on the i n t r i n s i c production rates of CO and C0^ from coals. However, the rate of t h i s r e action, i n the presence of a sulphidized Co-Mo c a t a l y s t at 698K, i s not s u f f i c i e n t l y rapid for i t to approach equilibrium within 30 minutes. The superposition hypothesis was tested and confirmed by p l o t t i n g the r e l a t i v e amounts of CO and C0^ produced, during reaction, against the moisture content of the coal fed to the reactor, at constant molar extents of CO + CO2 p r o d u c t i o n - Figure 5.3. The l i n e a r i t y of the iso-production contours i s supported by the zero moisture intercepts - Table 5.2. The iso-production contours and the CO + C0^ production intercepts coincide. Further evidence of superposition can be obtained from the slope of the iso-production contours, a l so l i s t e d on Table 5.2. The r a t i o dC0„ SCO / oH 20 ' 5H20 f l u c - t u a t e s w i t h the ex t e n t of CO + C0 2 p r o d u c t i o n , suggesting that the water gas s h i f t r e a c t i o n , and CO and C0„ production occur simultaneously. 141 1.10 0.75 H 1 1 1 1 ! 0 5 10 15 20 25 COAL MOISTURE CONTENT g/Kg 0.30-1 1 0.16-1 1 1 1 • 1 1 0 6 10 15 20 25 COAL MOISTURE CONTENT g/Kg Figure 5.3: Carbon Monoxide and Carbon Dioxide Production Contours 142 TABLE 5 . 2 Water Gas S h i f t Reaction Data Experiment Groups 2 0 1 , 2 1 0 2 0 4 , 2 1 3 2 0 5 , 2 0 9 Iso-production moles (CO + c o 2 ) 1 . 0 3 1 . 1 4 1 . 2 2 Zero Moisture - Intercepts (moles) - (CO + c o 2 ) 1 . 0 8 1 . 1 5 1 . 2 3 - (CO) 0 . 3 8 9 0 . 3 1 3 0 . 5 1 0 - ( c o 2 ) 0 . 6 8 7 0 . 8 4 1 0 . 7 1 5 C O : C 0 2 0 . 5 7 0 . 3 6 0 . 7 1 4 a c o 2 ( 6 H 2 0 ) aco Km2p) - 0 . 7 6 - 0 . 5 9 - 1 . 0 6 1A3 Despite the impact of the water gas s h i f t r e a c t i o n on gas composition at longer gas phase residence times, i t has only a marginal i n f l u e n c e on hydrogen a v a i l a b i l i t y . As much as 0.5 moles of CO are produced per Kg of coal which could y i e l d a maximum of 0.5 moles of hydrogen. Y et, 1 5 + moles of hydrogen can be consumed during l i q u e f a c t i o n r e a c t i o n s . Less than 3% of the r e q u i r e d can be r e a l i z e d from t h i s source without a r t i f i c i a l l y supplementing both the CO and R^O content of the r e a c t i o n mixture and s e l e c t i v e l y c a t a l y z i n g t h i s r e a c t i o n . Gas handling and processing equipment would also have to be redesigned to accommodate a much larger gas flow r a t e . Excessive hydrocracking, p a r t i c u l a r l y of low molar mass a l i p h a t i c hydrocarbons, can lead to s u b s t a n t i a l increases i n hydrogen consumption and a reduction i n gas product value. One such r e a c t i o n C 2H 6 + H 2 j 2CH 4 Is r e a d i l y observed i n s l u r r y i n j e c t i o n experiments - Figure 5.4. This r e a c t i o n does not reach equilibrium within 60 minutes at 698K but the trend i s evident. Excessive hydrocracking, associated with long gas phase mean residence times, can counteract the b e n e f i c i a l hydrogen generation e f f e c t r e s u l t i n g from the water gas s h i f t r e a c t i o n . 144 14 0 10 20 30 40 50 60 70 REACTION TIME min Figure 5.4: The Hydrocracking of Ethane 145 Cl e a r l y , synthesis gas would only be a d e s i r a b l e hydrogenation medium i f the water gas s h i f t and hydrocracking reactions could be separated. This can be done, at l e a s t i n p r i n c i p l e , because CO tends to be produced d u r i n g the I n i t i a l moments of r e a c t i o n while CH^ evolves more slowly from the reaction mixture - Figure 5.5. Synthesis gas could be recycled through the f i r s t stage of a DCL reactor having a short mean residence time for the coal s l u r r y , while gases evolved during subsequent stages would be permitted to pass r a p i d l y through the remaining stages of the reactor. The l i m i t i n g c o n s t r a i n t on the use of synthesis gas i s that i t could only be employed i f the water gas s h i f t r eaction was catalysed and ra p i d , as greater than 50% of the hydrogen consumption, 5 to 15 moles of T& per Kg of c o a l , occurs within the f i r s t 3 minutes of r e a c t i o n even i n the presence of a "donor" solvent - Figure 5.6. 5 . 3 Reactor and Pre-heater Simulations A number of experiments were performed i n an e f f o r t to simulate a x i a l mixing patterns, f o r s l u r r i e s , i n continuous flow apparatus. Pre-heaters were simulated by isothermal experiments with 5 minute c mean residence times, while 30 minute mean residence times were used to simulate various reactor and pre-heater combinations. The operating temperatures f o r the reactor and pre-heater components of a combined simulation need not be the same. Two extreme a x i a l mixing patterns were considered: 30 1A6 25- 20- 16 10 5- Legend A CH, SOL 1 698K CAT=10. X CH, 8 0 L 2 608K CAT°20. • CO SOL 1 698K CAT-10. B CO SOL 2 698K CAT-20. ^x — i r— 1 1 1 r— 10 20 30 40 60 60 REACTION TIME min 70 20 15 10- 5- Legend A CH, SOL 1 698K CAT=20. X CH, SOL 2 698K CAT=20. • CO SOL 1 698K CAT-20. B CO SOL 2 698K CAT-20. A-- B FORESTBURG COAL 0 - f 1 1 1 1 0 10 20 30 40 60 REACTION TIME min Figure 5.5: Relative Extents of CO and methane Production During the I n i t i a l Stages of Li q u e f a c t i o n Reactions 147 40 35 H 30 o o Ik i 25 CD CO 20 H 16- F0RE8TBURQ ,o Legend • SOL 1 698K CAT-10. O SOL 2 698K CAT=20. D SOL 1 698K CAT=20. 10- -T- 10 — r 20 30 40 60 REACTION TIME min 60 70 Figure 5.6: Hydrogen Consumption During the I n i t i a l Stages of Li q u e f a c t i o n 148 - plug flow ( i . e . ) a l l of the s l u r r y has a residence time within 2 minutes of the mean. - " a x i a l l y mixed" ( i . e . ) a l l of the s l u r r y has a residence time within the i n t e r v a l 0 to 2t. E x i s t i n g processes, for example, employ a pre-heater with a plug flow residence time d i s t r i b u t i o n for the coal s l u r r y , followed by an a x i a l l y mixed contactor. This design i s approximated by r e s u l t s obtained from a x i a l l y mixed reactor simulations. Several other design variants were also modelled - Table 5.3. The need to simulate a x i a l mixing patterns i n pre-heaters as well as reactors i s evident from the l i q u e f a c t i o n r e s u l t s shown on Figure 5.1. Greater than 50% of Forestburg coal and 15% of Byron Creek c o a l i s l i q u e f i e d within 2.5 minutes at 698K, and greater than 50% of the hydrogen consumption occurs simultaneously. Experiments, with shorter mean residence times could not be performed with t h i s apparatus, but pre-heaters are c l e a r l y an Integral component of l i q u e f a c t i o n reactor networks. The reactor and pre-heater simulations i l l u s t r a t e the extreme importance of a x i a l mixing i n DCL reactor networks and provide a number of clues with respect to the nature of coal l i q u e f a c t i o n k i n e t i c s . However, at f i r s t glance, the r e s u l t s appear to present a jumble of i n c o n s i s t e n c i e s , TABLE 5.3 Coal Conversion Stat i s t i cs for Reactor and Pre-heater Simulations Simulation Total Coal Conversion and Gaa Yield wtZ Forestburg Sub-bltumlnous Coal Bryon Creek Bituminous Coal Solvent 1 Solvent 2 Solvent 1 Solvent 2 Plug flow reactor + pre-heater (89.64,89.94), ( 6.26, 6.26) (90.10,89.97), ( 6.34, 7.03) 45.81,3.09 49.95,3.32 Plug flow pre-heater (648K) + reactor (698K) 84.69, 5.40 Axial ly mixed pre-heater -I- plug flow reactor 90.54, 6.37 89.91, 5.8 Plug flow reactor + pre-heater at constant pressure 91.42, 8.18 Axial ly mixed reactor 0.00, 0.00 84.35, 7.30 51.57,3.53 47.83,3.74 Plug flow pre-heater 64.13, 4.96 62.05, 4.83 Axial ly mixed pre-heater 64.70, 5.20 59.63, 5.30 150 p a r t i c u l a r l y i f one examines them from the point of view of current k i n e t i c and process models outlined i n Chapter 2. Current coal l i q u e f a c t i o n r e a c t i o n models cannot account f o r the divergent behaviour of the two solvents when l i q u e f a c t i o n r e s u l t s from simulated a x i a l l y mixed and plug flow pre-heaters are compared. Total conversion of Forestburg coal increases from 64.1 to 64.7 wt%, i n solvent 1 (70 wt% SRC o i l + 30 wt% THN), If an a x i a l l y mixed pre-heater i s substituted for a plug flow one, whereas t o t a l conversion for the same coal declines from 62.05 to 59.63 wt%, under s i m i l a r conditions, when l i q u e f i e d i n solvent 2 (100 wt% SRC o i l ) . In a d d i t i o n , current coal l i q u e f a c t i o n models could not predict the excessive "coke" formation r e s u l t i n g i n f a i l u r e of a x i a l l y mixed reactor t r i a l s f o r Forestburg coal l i q u e f a c t i o n i n solvent 1, or the enchanced conversion of Byron Creek c o a l , from 45.81 to 51.57 wt%, i n a simulated a x i a l l y mixed vs plug flow reactor. Only i f one considers the underlying p h y s i c a l phenomena, which act as "hidden" v a r i a b l e s i n these t r i a l s , can the apparent i n c o n s i s t e n c i e s become comprehensible. One f a c t o r , contributing to the apparent i n c o n s i s t e n c i e s , i s the a n a l y s i s method i t s e l f . Coal conversion to products soluble In an a r b i t r a r y solvent Is, at best, a p r i m i t i v e measure of the extent of coal r e a c t i o n . The Forestburg coal which "coked" and plugged the reactor during the a x i a l l y mixed reactor simulations, with solvent 1, obviously reacted, even though i t did not report as THF soluble or "converted" m a t e r i a l . 151 S i m i l a r though less dramatic d i f f e r e n c e s between reacted and "converted" m a t e r i a l are observed i n a number of other reactor and pre-heater simulations. C l e a r l y , coal conversion s t a t i s t i c s only include a f r a c t i o n of the coal that undergoes hydrogenation or hydrogenolysis r e a c t i o n s . Coal which undergoes polymerization reaction, "coking", or decomposes into species that are not soluble In the c a r r i e r solvent are lumped together with the t r u l y unreactive m a t e r i a l . The conversion d i f f e r e n c e s to be explained are, therefore, merely d i f f e r e n c e s a r i s i n g from the d i s t r i b u t i o n of the reactions which the coal undergoes. I t i s also c l e a r , from Table 5.3, that a portion of coal constituents undergoing one c l a s s of reactions may subsequently undergo reactions of the other c l a s s . The reduction i n coal conversion, r e a l i z e d In an a x i a l l y mixed pre-heater simulation for Forestburg coal l i q u e f a c t i o n i n solvent 2, i s "recovered" i f a plug flow reactor follows the pre-heater. Figure 5.1 i l l u s t r a t e s a reverse example of t h i s phenomenon. Forestburg and Byron Creek c o a l conversion begins to decline at long mean residence times when these coals are l i q u e f i e d i n solvent 1. The considerations outlined above focus the search f o r hidden v a r i a b l e s on system properties that are most affected by changes i n the degree of a x i a l mixing. The composition of the c a r r i e r solvent Is the most important property l i k e l y to be affected by s l u r r y phase a x i a l mixing, as i t i n turn a l t e r s the s o l u b i l i t y of hydrogen and coal derived molecular species i n the c a r r i e r solvent. These l a t t e r two v a r i a b l e s can Impact 152 d i r e c t l y on observed coal l i q u e f a c t i o n k i n e t i c s . The extremely high hydrogen consumption rate, and the s i m i l a r i t y of th i s r a t e , during the i n i t i a l coal l i q u e f a c t i o n reactions i n both solvents, suggests that molecular hydrogen mass tr a n s f e r across e i t h e r the g a s - l i q u i d or l i q u i d - d i s p e r s e d phase i n t e r f a c e , may l i m i t the i n i t i a l rate of coal l i q u e f a c t i o n reactions - Figure 5.6. In general, the g a s - l i q u i d mass transfe r resistance can be neglected i n s t i r r e d autoclaves and bubble T 951 columns . However, i n t h i s case the s l u r r y entering the reactor does not contain dissolved hydrogen. Therefore, the i n i t i a l dissolved hydrogen concentration i s between zero and the saturated concentration of the seed o i l ( i . e . ) [H^] - 0.2 [ H ^ ] , but quickly r i s e s to the saturated concentra- t i o n . I f the i n i t i a l rate of coal l i q u e f a c t i o n reactions i s so f a s t that the i n i t i a l dissolved hydrogen concentration cannot quench the coal r a d i c a l s as r a p i d l y as they are formed, one would expect that by increasing the i n i t i a l hydrogen concentration the i n i t i a l observed coal conversion would increase (I.e.) the f r a c t i o n of the coal undergoing polymerization and other undesirable reactions would decrease. Just such an e f f e c t was observed f o r Byron Creek coal l i q u e f a c t i o n i n solvent 2. Two experiments with 2.5 minute s l u r r y mean residence times were performed at 698K. The f i r s t experiment performed i n the usual way, yie l d e d a t o t a l coal conversion of 7.32 wt%, while the second experiment, employing a hydrogen s a t u r a t e d s l u r r y ( a t 290K, 4 MPa) with [H°] = 0.4 [ H ^ ] , yielded a t o t a l coal conversion of 13.93 wt%. 153 C l e a r l y , the i n i t i a l rate of coal l i q u e f a c t i o n r e a c t i o n s , at 698K, i s c o n t r o l l e d by molecular hydrogen transfer to a dispersed condensed phase. An a d d i t i o n a l experiment was performed to test whether hydrogen mass transfer l i m i t e d reaction rates beyond the f i r s t moments of r e a c t i o n but this proved not to be the case. The experiments mentioned so f a r are "batch" with respect to the gas phase, and reactor pressure declines by about 30% during r e a c t i o n . For t h i s s i n g l e experiment hydrogen was in j e c t e d continuously into the reactor to maintain the high i n i t i a l hydrogen pressure. After a 30 minute plug flow reactor + pre-heater simulation, with Forestburg coal i n solvent 2, t o t a l coal conversion was 91.42 wt% vs 90.0 wt% when the gas pressure was allowed to drop. Much of the d i f f e r e n c e In y i e l d i s i n the form of gas y i e l d - Table 5.3. The c a r r i e r solvent-dispersed condensed phase mass transfer l i m i t a t i o n on the i n i t i a l rate of coal l i q u e f a c t i o n reactions i s a l s o supported by the apparent s o l u b i l i t y data for hydrogen i n the two solvents, as the reactions progress. These data, presented on Figure 5.7, were obtained once the reactor was cooled to room temperature. Hydrogen s o l u b i l i t i e s at reaction temperature, 698K, would be greater, as shown on Figures 2.19 and 2.25. S o l u b i l i t y d ifferences would also be amplified under reaction conditions. Hydrogen s o l u b i l i t y i n solvent 1, measured at 290K, drops by about a factor of 2 during the f i r s t 5 minutes of reaction at 698K, but by increasing the extent of s l u r r y phase a x i a l mixing, the peak hydrogen demand i s reduced and the t o t a l conversion i n the pre-heater increases s l i g h t l y . Hydrogen s o l u b i l i t y i n solvent 2 drops below the 154 Legend A FORESTBURG SOL1 CAT=20. T=698. X FORESTBURG S0L2 CAT=20. T=698. • BYRON CREEK SOL1 CAT=10. T=698. BYRON CREEK S0L2 CAT=20. T=698. DETECTION LIMIT 10 20 30 40 50 REACTION TIME Figure 5.7: Apparent S o l u b i l i t i e s of Hydrogen i n Product Liquids at 290K 155 detection l i m i t within the same time i n t e r v a l , as l i q u e f a c t i o n reactions progress. So, even though the peak hydrogen demand i s reduced, i n an a x i a l l y mixed pre-heater, the l a s t coal entering the pre-heater encounters a very low dissolved hydrogen concentration and a net decrease i n c o a l conversion r e s u l t s . Apparent hydrogen s o l u b i l i t y d i f f e r e n c e s can also account, i n part, f o r the observed differences i n coal conversion obtained from a x i a l l y mixed and plug flow r e a c t o r s . Byron Creek c o a l , l i q u e f i e d i n an a x i a l l y mixed -3 r e a c t o r with solvent 1, encounters a hydrogen s o l u b i l i t y of 3 x 10 moles H • Kg * . . • Atm *, which i s at l e a s t double the hydrogen s o l u b i l i t y 2 " ( s o l v e n t ) ' J ° ] encountered during the opening moments of a plug flow reactor/pre-heater simulation. Consequently, the i n i t i a l coal conversion Increases. The apparent hydrogen s o l u b i l i t i e s , encountered by Forestberg and Byron Creek -3 c o a l d u r i n g an a x i a l l y mixed reactor simulation are 1.06 and 1.80 x 10 moles H_ • K g * , . • Atm * r e s p e c t i v e l y . These s o l u b i l i t i e s are much 2 " ( s o l v e n t ) r 3 lower than the i n i t i a l hydrogen s o l u b i l i t y encountered during plug flow reactor simulations, and the i n i t i a l coal conversion i s reduced. Hydrodynamic e f f e c t s are superimposed on the di f f e r e n c e s i n i n i t i a l conversion ( i . e . ) conversion In plug-flow reactors should be greater than conversion i n a x i a l l y mixed reactors, i f simple nth order reaction k i n e t i c s are a p p l i c a b l e . 156 The l i q u e f a c t i o n of Forestburg c o a l , during a x i a l l y mixed reactor simulations with solvent 1, presents a more complex s i t u a t i o n . The f a i l u r e of these two t r i a l s cannot be treated as a spurious r e s u l t or as a r e f l e c t i o n of mechanical problems. Both t r i a l s f a i l e d approximately 1/3 of the way through s l u r r y i n j e c t i o n . No blockages were observed anywhere i n the s l u r r y recycle loop, which was dismantled following both t r i a l s , but "coking" occurred at the s l u r r y entry port at the base of the reactor. This material was not dislodged by a d i f f e r e n t i a l pressure exceeding 15 MPa and the s l u r r y l i n e rupture d i s c f a i l e d during both t r i a l s . What experimental factors can account f o r the f a i l u r e of these two t r i a l s ? As mentioned i n Chapter 2, large changes i n hydrogen s o l u b i l i t y r e f l e c t s i g n i f i c a n t changes i n solvent composition. The solvent composition encountered by the Forestburg coal during an a x i a l l y mixed reactor simulation has a very high hydrogen s o l u b i l i t y , suggesting that i t has both a low mean molar mass and hetero-atom content. The i n i t i a l l i q u e f a c t i o n products comprise large, complex molecules with an appreciable hetero-atom content. Such species, p a r t i c u l a r l y those containing a high hetero-atom content are u n l i k e l y to be mis c i b l e with such a solvent and may form f l o e s , m i c e l l e s , or a separate l i q u i d or s o l i d phase. The close proximity of these species could e a s i l y lead to retrogressive reactions and "coke" formafion. The same phenomenon i s not observed during a x i a l l y mixed t r i a l s with Byron Creek c o a l , because I t has a much lower hetero-atom content, Table 4.3, and less c a t a l y s t was employed during t r i a l s i n v o l v i n g t h i s coal ( i . e . ) l e s s solvent hydrogenolysis and hydrogenation occurs during these t r i a l s . Some coal derived products also appear to "condense" near the end 157 of plug flow reactor simulations, with solvent 1, i f s l u r r y phase mean residence time i s s u f f i c i e n t l y long - Figure 5.1. These two e f f e c t s are probably r e l a t e d , as Cobalt-Molybdenum c a t a l y s t s catalyse hydrogenation and hydrogenolysis reactions for mid-range compounds s e l e c t i v e l y . Large molecules, which contain most of the hetero atoms present i n a s o l v e n t t * * ^ are e i t h e r introduced into or remain i n a progressively l e s s amenable solvent and a greater f r a c t i o n of these species become i n s o l u b l e . This t o p i c i s addressed again In sections 5.5 and 5.6. The reactor and pre-heater simulations have, of necessity, been r e s t r i c t e d to an evaluation of the importance of s l u r r y phase a x i a l mixing. Other v a r i a b l e s : the c a t a l y s t to coal r a t i o , the s t i r r i n g r a te, reaction temperature, e t c . , were h e l d c o n s t a n t i f not i d e n t i c a l f o r each coal/solvent system. E f f o r t s were made to employ optimal or near optimal c a t a l y s t to coal r a t i o s f o r each coal/solvent system. However, a l l of the v a r i a b l e s are interdependent to some degree and a x i a l mixing cannot be examined i n complete i s o l a t i o n . The other v a r i a b l e s , no doubt, exert an influence on these t r i a l s . Nevertheless, the simulations have provided a number of i n s i g h t s i n t o the nature of the coal l i q u e f a c t i o n reaction environment and established a framework for evaluating other experimental r e s u l t s . The major findings r e l a t e d to these t r i a l s are: 1. The i n i t i a l coal l i q u e f a c t i o n reactions can be c o n t r o l l e d by molecular hydrogen transfer to coal or coal fragments, regardless of the donor solvent content of the l i q u e f a c t i o n solvent. 158 2. The f r a c t i o n of molecular species, produced by i n i t i a l decomposition of c o a l , that reports as "converted" material depends on the s o l u b i l i t y of the coal derived species i n the l i q u e f a c t i o n solvent. 3. The optimum reactor + pre-heater configuration i s p r i m a r i l y dependent on the i n i t i a l solvent and coal composition: - A plug flow reactor + pre-heater provide optimum r e s u l t s for coal l i q u e f a c t i o n i n solvents s i m i l a r to SRC o i l , - An a x i a l l y mixed r e a c t o r and p r e - h e a t e r are best f o r c o a l l i q u e f a c t i o n i n donor r i c h solvents, provided the coal has a low hetero-atom content. Otherwise an a x i a l l y mixed pre-heater followed by a plug flow reactor i s preferred. 5.4 The Role of Cobalt Molybdate Ca t a l y s t s i n DCL Reaction Environments Catalysts are ubiquitous actors i n d i r e c t coal l i q u e f a c t i o n r e a c t i o n environments, as noted i n Chapter 2. I t i s d i f f i c u l t to perform " c a t a l y s t f r e e " or even "added c a t a l y s t f r e e " experiments, when some mineral matter constituents and ca t e c o l s , f o r example, act as c a t a l y s t s . In a d d i t i o n , one must contend, experimentally, with the "memory e f f e c t " when employing Co-Mo c a t a l y s t s . I f a batch experiment i s performed with t h i s type of c a t a l y s t , and removed, the c a t a l y t i c e f f e c t p e r s i s t s f o r 3 or 4 a d d i t i o n a l t r i a l s even i f no more c a t a l y s t Is added^*^^. This e f f e c t 159 also contributes to the background l e v e l of c a t a l y s i s . Preliminary c a t a l y s i s t r i a l s v e r i f i e d that c a t a l y s t support and the s i z e of c a t a l y s t p a r t i c l e s influences the ef f e c t i v e n e s s of a c a t a l y s t . F o r e s t b u r g c o a l conversion, i n the presence of 20 grams of whole CoO-MoO^ on a-alumina p e l l e t s , for example, i s 13.2 wt% less than i n the presence of the same mass of f i n e l y ground c a t a l y s t p e l l e t s . One gram of ground c a t a l y s t appears to be equivalent to approximately 5.7 grams of whole c a t a l y s t p e l l e t s . An unsupported MoO^ • 1/2 R^O powdered c a t a l y s t , containing the same number of moles of Mo + Co as 20 grams of supported c a t a l y s t , was also tested. Forestburg coal conversion was 5.6 wt% l e s s i n the presence of t h i s c a t a l y s t than i n the presence of ground c a t a l y s t * p e l l e t s . Ground c a t a l y s t i s twice as e f f e c t i v e as the unsupported MoO^ • 1/2 R^O, on an equi-molar b a s i s . Ground c a t a l y s t p e l l e t s were employed i n a l l other catalysed t r i a l s . Other fixed experimental conditions included a r e a c t i o n temperature of 698K, and a s t i r r i n g rate of 16.67 Hz. 5 minute and 30 minute t r i a l s were performed with Forestburg sub-bituminous c o a l s , 15 minute t r i a l s with Saskatchewan l i g n i t e , and 30 minute t r i a l s with Byron Creek bituminous c o a l . Results obtained from these experiments are shown on Figure 5.8 and noted below. * The experimental conditions were: temperature 698K, r e a c t i o n time 30 minutes, s t i r r i n g rate 16.67 Hz. Solvent 1 was employed for the f i r s t example; solvent 2 for the second one. 160 Figure 5.8 i l l u s t r a t e s the s e n s i t i v i t y of coal and l i g n i t e conversion to the presence of added c a t a l y s t s . In the absence of such c a t a l y s t s , t o t a l coal conversion i s r a d i c a l l y reduced. The d i f f e r e n c e can be as great as 20 wt%. I f excess c a t a l y s t i s present a comparable reduction i n t o t a l coal conversion may r e s u l t . Gas y i e l d s from coals and l i g n i t e s are also affected by added c a t a l y s t s , but only when the coal or l i g n i t e i s l i q u e f i e d i n a solvent that i s not donor r i c h ( i . e . ) solvent 2. In this case, gas y i e l d drops 1 to 2 wt% i n the presence of added c a t a l y s t . Excess c a t a l y s t has no further e f f e c t on gas y i e l d . I f coals are l i q u e f i e d i n a donor r i c h solvent, gas y i e l d s are lower and added c a t a l y s t does not have a noticeable e f f e c t on gas y i e l d - perhaps background c a t a l y t i c e f f e c t s are s u f f i c i e n t to minimize gas y i e l d . The s e n s i t i v i t y of t o t a l conversion, to the presence of added c a t a l y s t and p a r t i c u l a r l y to the presence of excess c a t a l y s t , appears to be greatest f o r bituminous co a l s . Sub-bituminous coals are l e s s s e n s i t i v e and l i g n i t e s l e a s t s e n s i t i v e . Solvent composition also contributes to the s e n s i t i v i t y of coal conversion to the l e v e l of c a t a l y s i s . Coal conversion Is more adversely a f f e c t e d by non-optimal l e v e l s of c a t a l y s i s when l i q u e f i e d i n solvent 1 than i n solvent 2. This e f f e c t can be a t t r i b u t e d to di f f e r e n c e s i n the mean molar mass of the two solvents (solvent 1 comprising 70 wt% SRC o i l and 30 wt% THN has a lower mean molar mass than solvent 2 which comprises 100 wt% SRC o i l ) , and to the deportment of molecular species within the two solvents ( s e c t i o n 5.6). I t i s not 161 100 Legend A FORESTBURG SOL 2 69BK F-16.7 x FORESTBURG SOL 1 608K F-16.7 D 8A8K. LIG. SOL 2 69BK F-16.7 B BYRON CREEK SOL 2 688K F-16.7 ffi BYRON CREEK 8 0 L 1 698K F-16.7 80 100 ADDED CATALYST g 120 140 ADDED CATALYST Q Figure 5 . 8 : The Influence of C a t a l y s i s on Coal and L i g n i t e Conversion 162 s u r p r i s i n g , that the impact of c a t a l y s i s , p a r t i c u l a r l y excess c a t a l y s i s , on coal conversion i s dependent on coal type and solvent composition. Bituminous coals tend to generate larger molecular fragments than sub-bituminous coals and l i g n i t e s . Larger molecules are l e s s l i k e l y to be > soluble i n solvents undergoing catalysed hydrogenation/hydrogenolysis reactions as these reactions lead to rapid reduction i n the mean molar mass of the solvent. The reduced s o l u b i l i t y of coal derived molecular species i n the c a r r i e r solvent y i e l d s lower coal conversions. This e f f e c t would be accentuated i n a solvent with a lower i n i t i a l mean molar mass. The magnitude of the reduction i n coal on l i g n i t e conversion, when non-optimum l e v e l s of c a t a l y s i s are employed, i s time dependent. The extent of Forestburg coal conversion, i n solvent 2, i s reduced by 25.85 wt% a f t e r 5 minutes, when zero grams of c a t a l y s t are added instead of 20.0 grams. This difference drops to 21.3 wt% a f t e r 30 minutes. A s i m i l a r time dependence i s noted for Forestburg coal conversion i n solvent 1 with 20.0 vs 80.0 grams of added c a t a l y s t . A f t e r 5 minutes, there i s a 15.3 wt% di f f e r e n c e i n coal conversion which reduces to 10.5 wt% a f t e r 30 minutes. So, not only i s there an optimum l e v e l of c a t a l y s i s f o r each coal/solvent system but one defined by i n i t i a l coal solvent I n t e r a c t i o n s . C l e a r l y , the optimum l e v e l of c a t a l y s i s f o r reactor networks, employing plug flow pre-heaters, i s defined by the pre-heater r e a c t i o n environment, as long as the pre-heater e x i t temperature i s greater than the temperature at which coal begins to undergo decomposition re a c t i o n s . I f 163 the pre-heater e x i t temperature i s l e s s than this temperature, the optimum l e v e l of c a t a l y s i s w i l l be defined by r e a c t i o n conditions at the reactor i n l e t . For current and envisioned i n d u s t r i a l DCL processes, optimum l e v e l s of c a t a l y s i s are controlled by the r e a c t i o n environment i n pre-heaters. These r e s u l t s also indicate that for a x i a l l y mixed reactors, or f o r reactors employing low-molar-mass solvents, only modest l e v e l s of "added c a t a l y s t " are warranted and excess c a t a l y s i s should be avoided e s p e c i a l l y f o r bituminous coals. 5.5 The I n t e n s i t y of Turbulence The i n t e n s i t y of turbulence, which f o r autoclaves i s defined by s t i r r i n g rate and impeller geometry, i s not considered to be a v a r i a b l e of consequence f o r d i r e c t coal l i q u e f a c t i o n reactions. For laboratory r e a c t o r s , employing hydrogen gas, f o r example, the l i t e r a t u r e asserts that i t i s only necessary to assure that the reactors are "well mixed" so that adequate gas-slurry mass transfer occurs. S t i r r i n g rates of 8.33 Hz are frequently employed for this purpose. The impact of s t i r r i n g on the d e s t r u c t i o n of coal p a r t i c l e s has only been treated In a q u a l i t a t i v e manner. Whitehurst et a l ^ ^ ^ reviewed some of t h e i r own work and the work of others, and showed that coal p a r t i c l e s remained i n t a c t with l i t t l e or no apparent shrinkage, up to 80 wt% conversion, i n the absence of a g i t a t i o n , but broke up r a p i d l y when reacted i n an agitated autoclave. They also showed that s t i r r i n g rate had no influence on coal conversion to p y r i d i n e soluble material, a f t e r 2 minutes of r e a c t i o n at 698K. 164 In view of these f i n d i n g s , the r e s u l t s presented on Figure 5.9 are s u r p r i s i n g . Coal conversion to tetrahydofuran soluble material and gas y i e l d are both affected by changes i n s t i r r i n g r a t e. For any given l e v e l of c a t a l y s i s , coal conversion increases to a maximum then declines as s t i r r i n g rate i s increased. T o t a l coal conversion can vary by as much as 8 wt%. There i s no general trend f o r the dependence of gas y i e l d on s t i r r i n g rate but the f l u c t u a t i o n s can exceed 1 wt%. The apparent c o n t r a d i c t i o n between these r e s u l t s and previous findings i s r e a d i l y explained. Macerals present i n raw coal are soluble i n pyridine. Therefore, one would not expect pyridine s o l u b i l i t y to r e f l e c t the degree of conversion of coal derived species. Raw coal i s not soluble i n tetrahydrofuran. Coal derived molecular species must undergo molar mass and/or hetero-atom content reduction before they are soluble i n this solvent. Thus, THF s o l u b i l i t y i s s e n s i t i v e to the degree of coal conversion. The r e s u l t s , presented on Figure 5.9, r e f l e c t t h i s s e n s i t i v i t y . These r e s u l t s also h i g h l i g h t the interdependence of s t i r r i n g rate (the i n t e n s i t y of turbulence) and the optimum l e v e l of c a t a l y s i s . An optimum l e v e l of c a t a l y s i s i s only optimal at a s i n g l e s t i r r i n g r a t e . I f one r e f e r s back to Figure 5.8, f o r example, 5 grams of c a t a l y s t at 16.67 Hz r e s u l t i n a greater t o t a l coal conversion than 10 grams of c a t a l y s t at 8.33 Hz, for Byron Creek coal l i q u e f a c t i o n In solvent 1. 165 100- 9 0 - * 8 0 - z g CO 70- Legend A FORESTBURG S0L1 CAT-20. T-698. t -30 . x FORESTBURG SOL2 CAT-20. T-698. t - 3 0 . • FORESTBURG SQL2 CAT-20. T-688. t -5 .0 E BYRON CREEK S O U CATNIP. T=698. t - 3 0 . £ BYRON CREEK SOL2 CAT-20. T-698. t - 3 0 . 15 20 25 STIRRING RATE Hz 10 T 15 20 25 STIRRING RATE Hz Figure 5.9: The Influence of S t i r r i n g Rate on Coal and L i g n i t e Conversion 166 What experimental factors can account for the interdependence of these two variables? The only hint provided by the r e s u l t s i s that the impact o f non-optimum s t i r r i n g r a t e - c a t a l y s t combinations on c o a l conversion p e r s i s t from the i n i t i a l sequence of l i q u e f a c t i o n r e a c t i o n s . Figure 5.9 i l l u s t r a t e s t h i s e f f e c t for Forestburg coal l i q u e f a c t i o n i n solvent 2, at 698K, with 20 grams of c a t a l y s t . After 5 minutes the d i f f e r e n c e i n coal conversion between 8.33 and 16.67 Hz i s 4.75 wt%; a f t e r 30 minutes the d i f f e r e n c e i s 4.46 wt%. One can only hypothesise that the i n t e n s i t y of turbulence influences the extent of coal p a r t i c l e break-up during the i n i t i a l decomposition reactions. This would a l t e r the coal-solvent i n t e r f a c i a l area and a f f e c t the i n i t i a l rates of the l i q u e f a c t i o n r e a c t i o n s . Thus, changing the amount of c a t a l y s t at a constant s t i r r i n g rate would be equivalent to changing the s t i r r i n g rate while maintaining the same amount of c a t a l y s t . At a low s t i r r i n g rate, l i t t l e p a r t i c l e d e s t r u c t i o n occurs. Excess c a t a l y s t may be present and the extent of coal conversion Is reduced as shown i n section 5.4. At very high s t i r r i n g rates, p a r t i c l e s are reduced to f i n e powders. The rates of I n i t i a l reactions are much higher, and i f the amount of c a t a l y s t i s i n s u f f i c i e n t , inadequate c a t a l y s i s also leads to a reduction i n c o a l conversion. At an intermediate s t i r r i n g rate, the i n i t i a l rate of coal d i s s o l u t i o n and the amount of c a t a l y s t are well matched and a c o a l conversion optimum i s observed. This hypothesis was tested by Mr. G. Roemer, who examined residue p a r t i c l e s i z e d i s t r i b u t i o n s , at constant conversion, as a function of 167 s t i r r i n g r a t e . P a r t i c l e size d i s t r i b u t i o n s for residue p a r t i c l e s extracted from 5 minute l i q u e f a c t i o n t r i a l s with Forestburg coal at 8.33, 16.67 and 33.3 Hz are shown on Figure 5.10 and can be compared with the i n i t i a l coal p a r t i c l e size d i s t r i b u t i o n , Figure 4.2. The t o t a l coal conversions for these t r i a l s are 57.3, 62.05, and 55.0 wt% r e s p e c t i v e l y . The r e s u l t s Indicate that the mean diameter of organic residua p a r t i c l e s decreases from 16.4 um to 6.9 um to 5.9 um as the s t i r r i n g rate increases from 8.33 to 16.67 to 33.3 Hz. The trend i n these r e s u l t s i s l i k e l y to be accurate. However, these r e s u l t s are best treated as tentative because the numerous steps i n the analysis procedure provide ample opportunity for p a r t i c l e segregation: 1. Only small samples, comprising approximately 2000 p a r t i c l e s , can be analysed. 2. Samples extracted from v i a l s must be forced through a 90 um screen to break-up agglomerates which form during the residua f i l t r a t i o n sequence 3. Only c e r t a i n p a r t i c l e size f r a c t i o n s may disperse and remain on the s l i d e f o r analysis and only a f r a c t i o n of the p a r t i c l e s appear to undergo p a r t i c l e s i z e reduction. Nevertheless, these r e s u l t s do corroborate the proposed r e l a t i o n s h i p between s t i r r i n g rate and the l e v e l of c a t a l y s i s . 168 >-o z HI o UJ DC 12-1 10- 20 40 60 80 PARTICLE DIAMETER (microns) 100 Figure 5.10: The Influence of S t i r r i n g Rate on the Residue P a r t i c l e Size D i s t r i b u t i o n 169 As a further test of the hypothesis, the mechanical d e s t r u c t i o n of coal p a r t i c l e s , at impeller surfaces was Investigated. A 2000 \m diameter coal p a r t i c l e was placed i n a glass walled autoclave with water and s t i r r e d , f o r 2 hours, at 33.3 Hz. The autoclave and Impeller geometry, for t h i s t e s t , were the same as for the l i q u e f a c t i o n t r i a l s . No change i n p a r t i c l e s i z e was detected. Since much smaller coal p a r t i c l e s were employed i n l i q u e f a c t i o n t r i a l s , mechanical break-up of i n e r t coal p a r t i c l e s should not occur i n agitated DCL r e a c t o r s . The i n t e n s i t y of turbulence can only a f f e c t the break-up of p a r t i a l l y reacted material, e i t h e r dispersed l i q u i d droplets, or p a r t i c l e s comprising a l o o s e l y bonded s o l i d skeleton. One would expect p a r t i c l e s comprising a s o l i d skeleton to break-up along predefined f a u l t l i n e s . The f i n a l p a r t i c l e size d i s t r i b u t i o n need not be s e n s i t i v e to the s t i r r i n g induced stress i n t e n s i t y beyond a threshold value, whereas the s i z e of f l u i d droplets would be s e n s i t i v e to v a r i a t i o n s i n s t i r r i n g rate as shown r 1221 by Calderbank 1 J . Compounds l i k e l y to be i n s o l u b l e i n l i q u e f a c t i o n solvents have a high molar mass and hetero-atom content. These compounds may form viscous dispersed phase droplets at r e a c t i o n temperature and s o l i d p a r t i c l e s at room temperature. The existence of such a phase would account f o r a number of observations noted, so f a r , i n t h i s chapter. Material i n such a dispersed phase would account f o r : 170 1. reacted but "unconverted" co a l , 2. the apparent r e v e r s i b i l i t y of conversion, 3. the s e n s i t i v i t y of conversion to solvent composition, 4. r e t r o g r e s s i v e reactions - compounds most l i k e l y to undergo condensation or polymerization reactions are concentrated In droplets rather than dispersed i n a hydrogenating environment. The formation of a separate l i q u i d phase, under reaction conditions, i s the preferred explanation for observed l i q u e f a c t i o n k i n e t i c s because molecular geometry does not lend i t s e l f to f l o e or m i c e l l e formation. Coal derived molecules tend to be planar sheets with d i s t r i b u t e d hetero-atom f u n c t i o n a l - i t i e s ^ " ' " ^ r a t h e r than long c h a i n s w i t h remote f u n c t i o n a l d i f f e r e n c e s . Also, i f such species were present, they would probably be too small to be a f f e c t e d by v a r i a t i o n s i n s t i r r i n g r a t e . M a t e r i a l , i n dispersed phase dr o p l e t s , may s o l i d i f y r a p i d l y , under re a c t i o n conditions, depending on the melting point of the molecules present and/or the rate of reverse r e a c t i o n s . At room temperature the "droplets" are c e r t a i n l y s o l i d . The existence of a dispersed organic phase, other than unreacted c o a l , i s not unknown i n the Direct Coal L i q u e f a c t i o n r e a c t i o n environment. Asphaltene p r e c i p i t a t i o n occurs i n pre-heaters, under c e r t a i n conditions. An "anti-solvent" i s added to product l i q u i d s i n the Lummus mod i f i c a t i o n of the SRC process to separate ash and molecular species containing the 171 r 1231 majority of the hetero-atoms from the remainder of the product l i q u i d s . The rapid decrease i n the solvency of a solvent as i t s c r i t i c a l point i s approached i s the p r i n c i p a l method of operation of the c r i t i c a l solvent deashing p r o c e s s ^ . This work d i f f e r s from previous research only i n so f a r as the r e s u l t s suggest that a dispersed organic phase may p e r s i s t throughout the reactor network. Further evidence of the existence of a p e r s i s t e n t dispersed organic phase was obtained by close examination of the components comprising solvent 1. These r e s u l t s are reported i n section 5.6. 5 . 6 Observation of a Dispersed Phase i n a Model Solvent The r e s u l t s , presented In the previous sections of t h i s chapter, provide l i t t l e more than circumstantial evidence for the existence of a dispersed organic phase, i n coal l i q u e f a c t i o n solvents, under reaction condi t i o n s . Work reported i n this section provides more d i r e c t evidence, even though reacted coal s l u r r i e s were not analysed for the presence of a second organic phase. Ash, unreacted c o a l , and c a t a l y s t p a r t i c l e s would have i n t e r f e r e d with observations i n such s l u r r i e s , and had these problems been overcome, one would s t i l l have had to contend with the f a c t that these s l u r r i e s are opaque even across thin sections. A model solvent, containing only organic m a t e r i a l , with a translucent continuous phase was required. Such a solvent was devised from components present i n solvent 1. This solvent contained approximately 95 wt% t e t r a l i n and 5 wt% SRC o i l . 172 The bl-plex structure of the model solvent, at room temperature, i s r e a d i l y observed on Figure 5.11A. The dispersed phase, shown on t h i s f i g u r e , contains s o l i d p a r t i c l e s and f l o e s , formerly SRC o i l , which were f i r s t s e t t l e d i n a centrifuge from the t e t r a l l n matrix. Gentle rocking of the sample v i a l yielded the observed suspension. Vigorous a g i t a t i o n of the same sample v i a l yielded an opaque c o l l o i d a l suspension, Figure 5.11B, which could only be r e s e t t l e d with d i f f i c u l t y . The bi-plex structure of t h i s solvent p e r s i s t s up to about 703K, as shown by the s e r i e s of photographs, Figure 5.12, which record a temperature time h i s t o r y of a sample heating t r i a l . The solvent remained a s o l i d suspension above 475K. By 575K, two separate l i q u i d phases had emerged. Ma t e r i a l transfer between these two bulk phases continued as the solvent was heated. The c l e a r , t e t r a l i n - r i c h phase grew i n s i z e and SRC o i l droplets gradually migrated to the opaque, SRC o i l - r i c h phase. At about 703K, the two phases suddenly and v i o l e n t l y recombined. When cooled to room temperature, i t i s uncertain whether the solvent formed a c o l l o i d a l suspension or remained as a single phase. These i n v e s t i g a t i o n s have demonstrated the presence of a dispersed organic phase with solvent components frequently encountered i n d i r e c t c o a l l i q u e f a c t i o n r e a c t i o n environments. Furthermore, they show that a dispersed phase may be f l u i d under reaction conditions and s o l i d at room temperature. These f i n d i n g s provide c r u c i a l experimental v e r i f i c a t i o n for the hypothesis discussed i n preceding sections and provide a sound basis f o r the coal l i q u e f a c t i o n k i n e t i c model proposed i n Chapter 6. 173 F i g u r e 5.11: Phase D i s t r i b u t i o n s i n a Model Two Phase L i q u e f a c t i o n S o l v e n t a t Room Temperature ( A a g g l o m e r a t e d SRC o i l i n t e t r a l i n , B a C o l l o i d a l S u s p e n s i o n o f SRC o i l i n T e t r a l i n ) 20 °C 200 ° C 300 ° C 1 Hr. 350 °C 420 °C 2 Hr. 12: Phase D i s t r i b u t i o n s i n a Model Two Phase L i q u e f a c t i o n S o l v e n t a t E l e v a t e d T e mperatures ( t h e t e t r a l i n r i c h phase i s on t h e l e f t , t h e SRC o i l r i c h phase on t h e r i g h t ) . 175 5.7 Residual Solids Analysis Composition analysis of r e s i d u a l s o l i d s and c a t a l y s t p a r t i c l e s was only p a r t i a l l y s u c c e s s f u l . The value of t h i s work was l i m i t e d by the r e s o l v i n g power of the JOEL MICROPROBE, and the ORTEC analyser attached to the ETEC scanning electron microscope. Mr. G. Mojaphoko performed q u a l i t a t i v e elemental analyses on residua p a r t i c l e s and cross-sections of r e s i d u a l p a r t i c l e s , with the SEM. The objectives of this work were to: 1. i d e n t i f y the various types of p a r t i c l e s present, 2. observe, i f possible, c a t a l y s t p a r t i c l e s imbedded i n organic residua p a r t i c l e s ( i . e . ) i n v e s t i g a t e the p o s s i b i l i t y that dispersed phase reactions are catalysed. He found that i n d i v i d u a l residua p a r t i c l e s could be i d e n t i f i e d by the presence of c h a r a c t e r i s t i c elements. A high s i l i c o n content was i n v a r i a b l y associated with mineral matter, cobalt with c a t a l y s t p a r t i c l e s . I t was hoped that organic residua p a r t i c l e s would also be d e t e c t i b l e In o u t l i n e ( i . e ) as blank spaces surrounded by f i n e ash or c a t a l y s t p a r t i c l e s , or i n some other form. Unfortunately, these p a r t i c l e s were i n d i s t i n g u i s h a b l e from the background and c a t a l y s t penetration into the dispersed organic phase was not observable. 176 Elemental analysis of c a t a l y s t p e l l e t s , on the MICROPROBE, was equally inconclusive. Cobalt and molybdenum i n t e r f e r r e d with the aluminum determinations and i t was not even possible to confirm the manufacturers s p e c i f i c a t i o n s for the c a t a l y s t composition. Only the d i s t r i b u t i o n of cobalt and molybdenum, i n the raw c a t a l y s t , can be discussed with any c e r t a i n t y . These elements are d i s t r i b u t e d , i n an equimolar r a t i o , through- out much of the c a t a l y s t . Fine fluorescent nodules, containing very high concentrations of molybdenum, were also observed. I t i s not c e r t a i n whether these nodules also contain cobalt or aluminum. A cr o s s - s e c t i o n of a spent c a t a l y s t p e l l e t was also analysed on the MICROPROBE to determine the extent of c a t a l y s t sulphidation a f t e r a 30 minute exposure to the coal l i q u e f a c t i o n environment. These r e s u l t s are shown on Figure 5.13. Seven mole % sulphur Is required to completely sulphidize the c a t a l y s t . The maximum sulphur concentration observed was only 1.23 mole %. However, as these sulphur concentrations are averaged over a region, one would expect that an average sulphur concentration much less than 7 mole % would r e s u l t i n complete sulphidation of pore and external surfaces. So, even though the c a t a l y s t employed throughout t h i s study was added as an oxide, i t l i k e l y behaves as a sulphide c a t a l y s t i n s i t u . 177 Figure 5.13: Sulphur Concentration P r o f i l e s i n Spent Catalyst P a r t i c l e s 178 5.8 Summary The experimental f i n d i n g s , presented i n th i s chapter, provide a novel and detailed d e s c r i p t i o n of the Dir e c t Coal L i q u e f a c t i o n r e a c t i o n environment that accounts for the i n a b i l i t y of e x i s t i n g coal l i q u e f a c t i o n k i n e t i c models to predict l i q u e f a c t i o n r e s u l t s c o n s i s t e n t l y or coherently. The r e s u l t s highlight the importance of a dispersed f l u i d phase, the in t e n - s i t y of turbulence, and mass transfer l i m i t e d reaction k i n e t i c s during the opening moments of reaction on the o v e r a l l k i n e t i c scheme f o r coal l i q u e f a c t i o n . Neither of these e f f e c t s are included i n e x i s t i n g DCL re a c t i o n models and consequently, these models are poor p r e d i c t i v e t o o l s . The r e s u l t s a l s o show t h a t o p t i m i z a t i o n of c o a l - s o l v e n t - c a t a l y s t Interactions by manipulating the i n t e n s i t y of turbulence, the l e v e l of c a t a l y s i s and solvent composition may have a greater impact on the space time y i e l d s of desi r a b l e l i q u e f a c t i o n products and the spectrum of products produced than v a r i a t i o n of the extent of a x i a l mixing per se. This l a t t e r parameter i s frequently discussed i n the l i t e r a t u r e without consideration of the many variables a f f e c t e d simultaneously. 179 Chapter 6 A Novel Reaction Model For D i r e c t Coal L i q u e f a c t i o n K i n e t i c s 6.0 Introduction The r e a c t i o n models for Dir e c t Coal L i q u e f a c t i o n , presented i n Chapter 2, treat coal l i q u e f a c t i o n as a purely k i n e t i c process, c o n t r o l l e d by i n t r i n s i c rates of product formation from s p e c i f i c c o a l s . The experimental r e s u l t s summarized i n the previous chapter demonstrate that t h i s i s an inappropriate basis f o r modelling reactions i n such a complex r e a c t i o n environment and account f o r the extreme s p e c i f i c i t y of these models. Non k i n e t i c phenomena such as p h y s i c a l coal-solvent Interactions, mass transf e r e f f e c t s , the i n t e n s i t y of turbulence, c a t a l y s i s , e t c . a l l have an influence on coal l i q u e f a c t i o n k i n e t i c s . A novel r e a c t i o n model, which q u a n t i f i e s the impact of these process v a r i a b l e s on r e a c t i o n k i n e t i c s , i s presented i n t h i s chapter. The model predicts t o t a l conversion values, and employs as few as 4 parameters depending on the complexity of the rea c t i o n environment. Results obtained from a s e r i e s of v e r i f i c a t i o n t r i a l s performed with bituminous and sub-bituminous coals and l i g n i t e , i n diverse r e a c t i o n environments are also reported. 6.1 An Outline of the Proposed Reaction Model 180 The proposed reaction model, Figure 6.1, conforms with experimental observations summarized i n Chapter 5 and i n the l i t e r a t u r e review, and i s not r a d i c a l l y d i f f e r e n t i n appearance from previous models. I f one \ compared this model with those l i s t e d on Table 2.9, f o r example, i t would be best described as a combination of the models proposed by Curran et a l , and Singh et a l . . The major differences between the model proposed here and those proposed previously are related to the factors which co n t r o l the rates of various l i q u e f a c t i o n reactions rather than di f f e r e n c e s i n the r e a c t i o n scheme per se. Three elements contribute to the formulation of the model: 1. A f r a c t i o n of the coal or l i g n i t e i s assumed to undergo "instantaneous" thermal decomposition y i e l d i n g a spectrum of l i q u e f a c t i o n products which include gases, l i q u i d s , p a r t i a l l y converted material and coke. The f r a c t i o n of the coal or l i g n i t e p a r t i c i p a t i n g i n these reactions i s assumed to depend s o l e l y on i t s composition, while the product d i s t r i b u t i o n i s assumed to depend on the rate of hydrogen transfer to the coal or l i g n i t e p a r t i c l e s , and the s o l u b i l i t y of l i q u e f a c t i o n products i n the c a r r i e r solvent. In the absence of dissolved gaseous hydrogen, f o r example, the f r a c t i o n of the coal reporting i n i t i a l l y as l i q u i d would decline, and the f r a c t i o n reporting as coke would 181 Figure 6.1: An Outline of the Model 182 increase, because polymerization and condensation reactions are more l i k e l y to occur under these conditions. The f r a c t i o n reporting i n i t i a l l y as p a r t i a l l y converted m a t e r i a l , which i s insolub l e i n the c a r r i e r solvent, contributes to the formation of a dispersed f l u i d phase, and i s p r i m a r i l y dependent on the solvency of the c a r r i e r solvent. 2. The remainder of the coal or l i g n i t e i s assumed to undergo slow thermal decomposition i n t o the various l i q u e f a c t i o n products. These reactions are assumed to occur simultaneously with those described i n 1 above. The necessity to subdivide coal into two reactive f r a c t i o n s can be addressed from e i t h e r a maceral or molecular viewpoint. A serie s of l i q u e f a c t i o n experiments performed with Byron Creek bituminous coal and v i t r i n i t e enriched Byron Creek coal f o r ESSO Canada Ltd., Appendix D, suggest that the v i t r i n i t e present i n these coals reacts 10 times f a s t e r than the i n e r t i n i t e . On a molecular l e v e l , ether bond cleavage has been shown to be more rapid than a l k y l (methyl) bond cleavage under DCL reaction conditions. The r e l a t i v e rates of these two l i q u e f a c t i o n r e a c t i o n s are r e f l e c t e d i n the r e l a t i v e rates of C0_, CO, CH. and C 0H, production. Further segmentation of coal Z h Z o constituent r e a c t i v i t i e s , which more c o r r e c t l y correspond to the broad range of e x i s t i n g r e a c t i v i t i e s , must await more precise descriptions of coal composition and structure. 183 3. M a t e r i a l reporting to the dispersed phase i n i t i a l l y i s assumed to report eventually as e i t h e r coke or converted m a t e r i a l , depending on the rate of hydrogen trans f e r to the dispersed phase d r o p l e t s , and v a r i a t i o n s i n solvent composition with time. The rate of hydrogen transfer to the dispersed phase i s proportional to the dissolved hydrogen concentration and i n v e r s e l y proportional to the mean droplet diameter, which i s determined by the scale of turbulence. Solvent composition i s a l t e r e d by adduct formation, and c a t a l y t i c hydrogenation and hydrogenolysis reactions. These three elements comprise the basis for the proposed model and demonstrate the importance of the impact of process v a r i a b l e s on l i q u e f a c t i o n k i n e t i c s . 6.2 Mathematical Formulation of the Model 6.2.0 Introduction When formulating the reaction model, i t was necessary to resort, i n part, to e m p i rical c o r r e l a t i o n s because general theories f o r p r e d i c t i n g l i q u i d - l i q u i d s o l u b i l i t y do not e x i s t and because conversion i s such a p r i m i t i v e measure of the extent of coal r e a c t i o n . "Unconverted" m a t e r i a l , f o r example, includes the p a r t i a l l y reacted material comprising the dispersed l i q u i d phase, coke, and unreacted c o a l . 184 These components are not r e a d i l y separated. So, i n a d d i t i o n to being e m p i r i c a l , the model cannot d i s t i n g u i s h material which always reports to the dispersed phase from unreacted c o a l . Only material which can e i t h e r report to the continuous phase or the dispersed phase, depending on r e a c t i o n conditions, i s a t t r i b u t e d to the dispersed phase. Thus, the model underestimates the influence of the dispersed phase on coal l i q u e f a c t i o n r e a c t i o n s . The equations employed i n the model r e f l e c t these shortcomings. Many of the equations were developed and re f i n e d by comparing model predictions with experimental conversion values during preliminary v e r i f i c a t i o n t r i a l s . Only the f i n a l equations are presented below. 6.2.1 Preliminary Reactions The thermal decomposition of the most reactive species present i n a coal or l i g n i t e i s so rapid that i t can be viewed as an instantaneous process. In the absence of dissolved gaseous hydrogen, these reactions may lead to negative conversions, i f i n s o l u b l e adducts are formed. In the presence of hydrogen, a greater f r a c t i o n of the coal reports as converted m a t e r i a l . The extent of the reduction i n unconverted material i s assumed to be proportional to the rate of hydrogen transfer to the coal p a r t i c l e s . The rate of hydrogen trans f e r per unit mass of c o a l , K', can be expressed as 185 where Sh° = the i n i t i a l average Sherwood number D = the d i f f u s i v i t y of hydrogen i n the solvent d° = the i n i t i a l average mean diameter of the coal p a r t i c l e s p , _ = the solvent density ^solvent 3 Pcoal = the bulk coal density H = the dissolved hydrogen concentration per unit mass of solvent A' = the surface area per unit volume of coal i n c l u d i n g pores I t should be noted here that A' varies appreciably with solvent composition and coal type, and can only be estimated within an order of magnitude. Thus f o r the purpose of the model, the coal f r a c t i o n r e p o r t i n g i n i t i a l l y as unreacted m a t e r i a l , J ^ , i s defined as J l " Y< 2> " Y< 4> "solvent ( 6 ' 2 ) ^ "coal where Y(2) = the f r a c t i o n of the coal reporting as unreacted material i n the absence of hydrogen Y(4) = an empirical constant which r e l a t e s hydrogen trans f e r to an extent of conversion. 186 In the absence of pertinent data t h i s equation can be s i m p l i f i e d to i n i t i a l l y i s more d i f f i c u l t to estimate, as mentioned previously, and can only be observed i f variables other than temperature and pressure are v a r i e d . I t was noted i n Chapter 5 that an optimum c a t a l y s t to s t i r r i n g rate r a t i o e x i s t s . This was a t t r i b u t e d to the existence of an optimum r a t i o of c a t a l y t i c s o l v e n t h y d r o g e n a t i o n to d i s p e r s e d phase hydrogenation. At the optimum r a t i o of these reactions the amount of material reporting to the dispersed l i q u i d phase i s minimized. The dispersed phase, as defined by the model, ceases to ex i s t at the optimum r a t i o . I f one considers possible k i n e t i c schemes for these two r e a c t i o n s , the r a t e of c a t a l y t i c s o l v e n t h y d r o g e n a t i o n , , can be expressed as J± - Y(2) - Y(4) D H (6.3) with a possible reduction i n accuracy. The coal or l i g n i t e f r a c t i o n reporting to the dispersed phase (6.4) and the rate of dispersed droplet hydrogenation, R«, can be expressed as 187 where and K 2 are constants Cat i s the t o t a l mass of a c t i v e c a t a l y s t present i n the reactor Droplet diameter i s determined by the i n t e n s i t y of turbulence. The r e l a t i o n s h i p between turbulence and drop diameter i s well defined for r1221 r1251 s t i r r e d tanks. Calderbank 1 J and Taverides et a l 1 Jfound that d m a x . ^ F - 1 ' 2 (6.6) droplet T a v e r i d e s e t a l ^ * 2 " ^ a l s o found t h a t d a t a , o b t a i n e d by a g i t a t i n g oil-water mixtures with a s i x bladed turbine impeller, c o r r e l a t e d w e l l with 0.6 -0.8 -1.2 dT* = .06 £ drop 0.6 where F = s t i r r i n g frequency D = impeller diameter a = i n t e r f a c i a l tension I f one asserts that the mean droplet diameter i s proportional to the maximum diameter the reaction rate r a t i o becomes 1 - 4 ^ t — 274" ( 6 > 8 ) R 2 D Sh F 188 This r a t i o i s r e a d i l y normalized with respect to an optimum by d i v i d i n g i t by the dif f e r e n c e that would r e s u l t i f the i n t e n s i t y of turbulence were so large that droplets evolving from coal p a r t i c l e s would not be broken up at the impeller. The f r a c t i o n of the coal or l i g n i t e reporting to the d i s p e r s e d phase, J , i s p r o p o r t i o n a l to some f u n c t i o n of the r a t i o where Y(6) = the r e s i d u a l c a t a l y t i c e f f e c t s present i n the reactor + the c a t a l y t i c e f f e c t associated with minerals present i n the coal Y(5) = the optimum rea c t i o n rate r a t i o (6.9) F o the s t i r r i n g r a t e a t which d r o p l e t s e v o l v i n g from the coal become unstable Sh the Sherwood Number associated with the droplets evolving o from the coal Experimentally, i t was found that 189 J 2 = Y3 i f F < F q = Y ( l ) 2 J 2 = Y3 /(fit + w y . t ( 5 ) \ \ Sh F / / C a t + Y ( 6 ) _ y ( 5 ) x /Cat ^ ( 6 ) - A 0 3 l f Cat + Y(6) > y ( 5 ) ( 6 > 1 Q ) \Sh F ^ Y(5) / Sh r ' * where Y3 = Y(3)•TEMP'Sh Q H Y3 = a parameter r e l a t i n g divergence from the optimum r a t i o to the f r a c t i o n of the coal reporting to the dispersed phase i n i t i a l l y One would expect Y(3) to vary p r i m a r i l y with solvent composition. Combining equations 6.2 and 6.10 y i e l d s the coal f r a c t i o n reported as unconverted material at zero time, J . J± + J 2 (6.11) 6*2.2 Second Stage Reactions Equations 6.2 and 6.10 describe the d i s p o s i t i o n of coal components at zero time. One might assume when designing the framework f o r subsequent, k i n e t i c a l l y - c o n t r o l l e d reactions that e i t h e r a constant f r a c t i o n of the coal or the i n i t i a l l y unconverted coal i s r e a c t i v e under 190 D i r e c t Coal L i q u e f a c t i o n r e a c t i o n k i n e t i c s . However, t h i s would ignore the p o s s i b i l i t y that polymerization and condensation re a c t i o n s , which r e s u l t i n coke formation, are more l i k e l y to occur as the f r a c t i o n of the c o a l reporting i n i t i a l l y as "unconverted" material increases. Such r e t r o g r e s s i v e reactions are most l i k e l y to occur i n the dispersed phase dr o p l e t s , because these droplets contain high concentrations of large r e a c t i v e molecules. One must expect the reactive f r a c t i o n , Y7, to decrease as the i n i t i a l l y unconverted f r a c t i o n Increases. This assumption led to the development of equation 6.12 Y7 = Y(7) + (6.12) where Y(7) and Y(8) are parameters which are constant for any given c o a l . A k i n e t i c expression for the second stage reactions i s defined i n a straightforward manner. The reaction rates for the dispersed phase and the slowly r e a c t i n g coal cannot be d i s t i n g u i s h e d . So, the reaction k i n e t i c s for these two types of material are combined i n a s i n g l e k i n e t i c expression. F i r s t order r e a c t i o n k i n e t i c s , a t y p i c a l assumption i n Direct Coal L i q u e f a c t i o n models, are also assumed In t h i s model. Thus - kC (6.13) 191 where C = the r e a c t i v e f r a c t i o n of a coal remaining unreacted at a given time K = the rate constant I t would be n a t u r a l , at this point, to assert that the rate constant, K, has an Arrhenius temperature dependence. This assumption i s frequently made i n published models, despite the a r b i t r a r y d e f i n i t i o n of the rate constant. One would not expect such a rate constant to e x h i b i t an Arrhenius temperature dependence, and this proved to be the case when the model was f i t t e d to data selected from the l i t e r a t u r e - Figure 6.2. However, Arrhenius behaviour can be obtained i f the rate constant i s c o r r e l a t e d by equation 6.14, as shown on Figure 6.3. - E 1 / J 1 K = [ k Q exp ( IJ:)] x (6.14) The form of equation 6.14 suggests that only the aggregate behaviour of the coal follows an Arrhenius pattern and that the observed rate constant r e f l e c t s the f a c t that coal constituents which do not react i n i t i a l l y are more r e f r a c t o r y than the coal i t s e l f . Consequently, the a c t i v a t i o n energy r i s e s and the rate of l i q u e f a c t i o n reactions slows. This equation r 491 conforms wi t h the f i n d i n g s of Szladow e t a l ' who showed that the apparent a c t i v a t i o n energy for l i q u e f a c t i o n reactions increases with the extent of conversion. The slopes of the curves on Figure 6.3 are also noteworthy. T r i a l s employing hydrogen gas have an Arrhenius slope 192 100 10- o * CO 1- o . H — 1.40 1.45 Legend A FIES MINE X MIDDLE KITTANNING • HAT CREEK A B HAT CREEK B 1.50 1/T 1.55 * 1 Q 3 1.60 •x 1.65 Figure 6.2: The Temperature Dependence of DCL Rate Constants 193 Figure 6.3: The Modified Arrhenius Dependence Of DCL Rate Constants 194 E 4 — = - 2.65 x 10 , while the t r i a l s not employing hydrogen have a slope of K. 4 -1.38 x 10 . D e s p i t e the e m p i r i c a l nature of t h i s c o r r e l a t i o n i t i s probable that the drop i n a c t i v a t i o n energy i s due to d i f f u s i o n c o n t r o l of the l i q u e f a c t i o n r e a c t i o n k i n e t i c s i n the l a t t e r case. 6.2.3 Residence Time D i s t r i b u t i o n s The f i n a l equation required i n order to complete the model i s one which couples the s l u r r y residence time d i s t r i b u t i o n with the k i n e t i c expression, equation 6.13. A r b i t r a r y s l u r r y residence time d i s t r i b u t i o n s , which match d i s t r i b u t i o n s found i n complex reactors, can be d i g i t i z e d and combined with the model. Simple d i s t r i b u t i o n s , such as the plug flow or dispersed flow d i s t r i b u t i o n s employed i n the experimental program, can be resolved a n a l y t i c a l l y to y i e l d equations 6.15 and 6.16 r e s p e c t i v e l y . % Conversion = 100 - 100 J ( e - I C t Y7 + 1.0 - Y7) (6.15) ~ K t l _ ~Kt2 % Conversion = 100 - 100 J [ Y7 (j-— f ) + 1.0 - Y7] (6.16) v t ^ t ^ / ic 6.2.4 Summary Equations 6.2, 6.10, 6.12, 6.14 comprise a novel re a c t i o n model fo r i n t e r p r e t i n g coal l i q u e f a c t i o n data. Such a r a d i c a l departure from the nature of e x i s t i n g models would not be f e a s i b l e i n the absence of the 195 l i q u e f a c t i o n data summarized i n Chapter 5. The influence of these f i n d i n g s , p a r t i c u l a r l y the r o l e of molecular hydrogen during the i n i t i a l l i q u e f a c t i o n sequence, and the presence of a dispersed l i q u i d phase, on the understanding of DCL k i n e t i c s cannot be over emphasized. 6.3 V e r i f i c a t i o n of the Model 6.3.0 Introduction The reaction model was v e r i f i e d by regressing sets of batch coal l i q u e f a c t i o n data. The objective function was equation 6.17, where t o t a l coal conversion TCC . i - TCC ,, j V 1 e x p t l predicted 1 //-,-.% E = 2 TCC * ( 6 ' 1 7 ) e x p t l values estimated by equations 6.2, 6.10, 6.12, 6.14, and 6.15 were compared with experimental values. This function was minimized using a s u i t e of non l i n e a r optimization programs, which adjusted Y(n) values subject to the constraint that each Y(n) must contribute s i g n i f i c a n t l y to the reduction i n the percent d i f f e r e n c e between the experimental and predicted conversion values. This work was hampered to varying degrees by the uncertainty of coal l i q u e f a c t i o n data, the f a i l u r e of some researchers to report 196 pertinent data, and the general lack of data with respect to the p h y s i c a l properties of coal l i q u i d s . Inaccurate data, for example, may lead to the s e l e c t i o n of a set of parameters which f i t the data but do not conform with expectation. A l t e r n a t i v e l y , a large number of parameter sets may be found to f i t the inaccurate data equally w e l l . Even when precise data are employed i n v e r i f i c a t i o n t r a i l s , more than one set of optimum parameters may be found. However, i n this case, the preferred set can be selected o b j e c t i v e l y . The parameter set with the most broadly d i s t r i b u t e d d i f f e r e n c e s i s preferred, unless there i s some reason to question the accuracy of a s i n g l e data point. This problem becomes most severe If the number of parameters i s large, i f there are few data points, or i f the data i s very imprecise. The f a i l u r e of i n v e s t i g a t o r s to report pertinent data or the absence of such data, necessitated a number of modifications i n the equations which comprise the model. Hydrogen s o l u b i l i t i e s and d i f f u s i o n c o e f f i c i e n t s i n various l i q u e f a c t i o n media, and the density of coal l i q u i d s are the p r i n c i p a l p h y s i c a l properties required for input Into the model. These data are frequently unavailable. In such cases, one must re s o r t to approximations. Hydrogen concentration i n a l i q u i d i s proportional to pressure over a narrow temperature range. D i f f u s i o n c o e f f i c i e n t s are proportional to temperature and i n v e r s e l y proportional to solvent v i s c o s i t y , or proportional to the d i f f u s i o n c o e f f i c i e n t of another species. Consequently, J was correlated v a r i o u s l y as 197 J x - Y(2) - Y(4) D H (6.3) J = Y(2) - Y(4) Temp H (6.18) J± = Y(2) - Y(4) D (6.19) depending on the a v a i l a b i l i t y of data. The hydrogen concentration i n the solvent, H, was assumed to be e i t h e r equal to or proportional to the s o l u b i l i t i e s i n t e t r a l i n were obtained from published data, Figure 2.19; hydrogen s o l u b i l i t i e s i n SRC o i l were estimated using equation 2.7. Considering the deportment of phases i n Solvent 1, the continuous phase was assumed to be comparable to t e t r a l i n . Hydrogen s o l u b i l i t i e s were obtained accordingly. V i s c o s i t y data cannot be obtained or estimated with c e r t a i n t y so i t was assumed to be constant i n equation 6.18. This i s only v a l i d for a narrow range of temperatures. One set of data obtained from the l i t e r a t u r e did not employ hydrogen. The d i f f u s i v i t y of t e t r a l i n was assumed to be proportional to that of hydrogen, equation 6.19. The c o n c e n t r a t i o n of t e t r a l i n , e xpressed as moles • Kg *, i s constant by d e f i n i t i o n . These changes i n the equations comprising the model may have a negative impact on the p r e d i c t i v e accuracy of the model but were an e s s e n t i a l element i n the v e r i f i c a t i o n process. saturated hydrogen concentration i n the various solvents. Hydrogen 198 6.3.1 Experimental V e r i f i c a t i o n t r i a l s were performed f i r s t with batch l i q u e f a c t i o n r e s u l t s obtained from t h i s work and from the l i t e r a t u r e . Results obtained from semi-batch coal l i q u e f a c t i o n experiments, which were designed to simulate a x i a l l y mixed reactors, were then subjected to q u a l i t a t i v e v e r i f i c a t i o n t r i a l s i n order to examine the impact of residence time d i s t r i b u t i o n on model p r e d i c t i o n s . L i q u e f a c t i o n data obtained from flow apparatus were excluded from these tests because coal conversion, mean residence time and residence time d i s t r i b u t i o n s f o r s l u r r i e s , and reactor temperature p r o f i l e s are too poorly defined i n these re a c t o r s . The r e a c t i o n conditions and reactor configurations associated with the data sets selected from the l i t e r a t u r e are l i s t e d on Table 6.1. These p a r t i c u l a r data sets were selected because: 1. t e t r a l l n was used as the l i q u e f a c t i o n solvent. - t e t r a l l n i s one of the few l i q u e f a c t i o n solvents for which required phy s i c a l properties are known or can be estimated. See section 2.4. 2. these data are extensive and include a broad range of temperatures. 3. the s l u r r y residence times and residence time d i s t r i b u t i o n s are well defined. 199 TABLE 6.1 Data Seta Selected for Model Ver i f i cat ion Reference Reactor Coal 1 Data Reaction Conditions Points [451 Shalabi et a l 1 ' A Slurry Injected, Fies Mine Ky. 300 ml A .E . Autoclave Seam #9 13 Solvent - te t ra l in -D - 3.2 cm (high vo lat i le Temp. - 350,375, - F = 25 s " 1 bituminous) 400°C Hydrogen Pressure - 13.2 MPa Analysis Solvent - THF McElroy et a l ^ 1 2 6 ' Shaken Micro-reactor Hat Creek A 15 Solvent - te t ra l in containing steel bal ls (sub-bituminous) Temp. - 350,375, 400, 425°C Hat Creek B (sub-bituminous) 17 Hydrogen Pressure ~ 5.5 MPa (cold) Analysis Solvent » Pyridine Szladow et a l 1 * 9 1 Shaken Micro-reactor Middle Kittanning 23 Solvent - te t ra l in (high vo la t i le Temp. » 340,355,370 bituminous) 385,400'C Hydrogen Pressure » 0.00 MPa Analysis Solvent - Pyridine 200 Four co a l s , two bituminous and two sub-bituminous coals, and three reactor types are represented. 6.3.2 Results and Discussion The o v e r a l l f i t of the model, to the experimental data, as indica t e d by Figures 6.4 to 6.14, i s quite good. The model accurately p r e d i c t s t o t a l conversion values, f o r a v a r i e t y of bituminous and sub- bituminous coals, and l i g n i t e , i n diverse reaction environments. Only at long mean residence times does the model o c c a s i o n a l l y diverge from the experimental data. This divergence a r i s e s because the model does not include equations which account for the possible reduction i n l i q u e f a c t i o n product s o l u b i l i t y i n the c a r r i e r solvent over time. Nevertheless, the r e s u l t s confirm the ge n e r a l i t y of the proposed two stage r e a c t i o n model, r 451 S h a l a b i e t a l , f o r example, f i t t e d a s i n g l e stage coal d i s s o l u t i o n model to t h e i r l i q u e f a c t i o n r e s u l t s . The model, shown on Table 2.9, co r r e l a t e s t o t a l conversion values with 7 parameters obtained by regressing product d i s t r i b u t i o n data. Even i n t h i s case, the model proposed here f i t s the data better, Figure 6.4, and employs only 4 parameters. C l e a r l y , mass transfer c o n t r o l l e d Instantaneous decomposition followed by slow k i n e t i c a l l y c o n t r o l l e d d i s s o l u t i o n of the remaining unconverted coal f r a c t i o n p r o v i d e s a g e n e r a l framework f o r a n a l y s i n g l i q u e f a c t i o n r e a c t i o n s . 201 100-1 20-1 1 1 1 ! 0 50 100 150 200 REACTION TIME min Figure 6.4: Result Summary for a V e r i f i c a t i o n T r i a l with Fies Mine Coal 202 100-r REACTION TIME min Figure 6.5: Result Summary f o r a V e r i f i c a t i o n T r i a l with Hat Creek A Coal 203 Figure 6.6: Result Summary for a V e r i f i c a t i o n T r i a l with Hat Creek B Coal 204 Figure 6.7: Result Summary f o r a V e r i f i c a t i o n T r i a l with Middle Kittanning Coal 205 100 100 80 H * z o CO tc UJ > z o o o /// 60 H 40 20 H 04 —r— 10 _.A- Legend A DATA 698 K CAT=0.0 X DATA 698 K CAT=20. • DATA 698 K CAT=40. B DATA 698 K CAT-80. P.RJEpiCTED F=16.7 CAT=0.0 CAT" 20. C^T=40. CAT=80. 20 30 40 60 REACTION TIME min — i — 60 70 Figure 6.8: A Comparison of Predicted and Observed Results f o r Forestburg Coal L i q u e f i e d i n Solvent 2 (I) 206 100 80 60 40- 20- X^-' - t ^ . — r ^ . * X * * \ \ * A Legend A DATA 698 K CAT=0.0 t=30. \ * * \ \ * X \ \ X 698 K CAT=20. t=30. \ \ \ • CAT=40. t=30. X \ 13 CAT=80. t=30. * PREDICTED CAT=0.0 CAT=20. CAT»40. CAT=80. 10 15 20 STIRRING FREQUENCY Hz 25 Figure 6.9: A Comparison of Predicted and Observed Results f or Forestburg Coal L i q u e f i e d i n Solvent 2 (II) 100 g CO oc LU > z o o _J o 207 Legend A DATA 698 K x 673 K • 648 K PREDICTED CAT=20. 10 20 30 40 50 REACTION TIME min 60 70 100 2 o 80- Z g 0C LU > z o o 40- 20 A.-*' / / / / // / 7 Legend A DATA 698 K CAT=20. X DATA 698 K CAT=80. PREDICTED 698 K CAT°0.00 698 K CAT=20.0 698 K CAT-80.0 I I 1 1 1— 10 20 30 40 50 REACTION TIME min 60 70 Figure 6.10: A Comparison of Predicted and Observed Results f o r Forestburg Coal L i q u e f i e d i n Solvent 1 (I) 208 100 90- 80- 70- 60 50 40 A 30 r 0 Legend A DATA 698 K CAT=20. t=30. X CAT=80. t=30. PREDICTED CAT=0.00 t=30_. CAT=20.0 t=30. CAT=80.0 t=30. \ \ \ \ \ \ \ \ T 5 \ 10 15 20 STIRRING FREQUENCY Hz 25 Figure 6.11: A Comparison of Predicted and Observed Results f o r Forestburg Coal L i q u e f i e d i n Solvent 1 (II) * z o CO oc UJ > o o o 209 60 ~ 40 o CO oc UJ > z o o 20 -20 T 20 30 40 50 REACTION TIME min x .A" # / It Legend A DATA 698 K CAT-0.0 X DATA 698 K CAT-20. • DATA 698 K CAT-40. B DATA 698 K CAT-80. f.R.IRicXE.P.fr.1.?:7.5?̂ T"P:9 CAT-20. . C^T-40. CAT=80. T T 10 —I 1 20 30 40 50 REACTION TIME min 60 70 Figure 6.12: A Comparison of Predicted and Observed Results f o r Byron Creek Coal L i q u e f i e d i n Solvent 2 (I) 210 60 50- 40 X X • A 30 20- 10 0 r 0 Legend A DATA 698 K CAT=0.0 t=30. X 698 K CAT=20. t=30. • CAT=40. t=30. PREDICTED t=30. CAT=0.0 CAT=20. CAT=40. I 1 1 1 5 10 15 20 STIRRING FREQUENCY Hz 25 30 Figure 6.13: A Comparison of Predicted and Observed Results f or Byron Creek Coal L i q u i f i e d i n Solvent 2 (II) 80 211 £ 60H Z O CO 0C UJ > z o o 2 o 7/ 7 40 20 10 Legend A DATA 698 K CAT=0.0 X DATA 698 K CAT-20. • DATA 698 K CAT=40. B DATA 698 K CAT-80. ?.R.E.PI9.T.E.P. f.?.1.6.•?.. P.AT"°.-.?P CAT=20.0 CATM0.O CAT=80.0 — r 20 30 40 60 REACTION TIME min 60 70 80- Figure 6.14: Result Summary f o r a V e r i f i c a t i o n T r i a l with Saskatchewan L i g n i t e 212 The optimum parameter sets for the batch v e r i f i c a t i o n t r i a l s , Table 6.2, also confirm the g e n e r a l i t y of the proposed two stage r e a c t i o n model. Despite the large d i f f e r e n c e s i n the chemical composition and structure of these coals and l i g n i t e , and the many differences i n the r e a c t i o n environments, the l i q u e f a c t i o n behaviour of these species can be characterized i n a consistent and coherent manner. The frequency factor for the rate constant, Y(9), v a r i e s from 14 -1 7.6 x 10 s f o r the more s l o w l y r e a c t i n g sub-bituminous coals and l i g n i t e , up to 4.6 x l O 1 ^ s ^ for the more quickly reacting high v o l a t i l e bituminous coals. The only exceptions are Middle Kittanning c o a l , which was reacted i n the absence of hydrogen (the rate of l i q u e f a c t i o n reactions were assumed to be c o n t r o l l e d by d i f f u s i o n i n t h i s case) and Byron Creek c o a l which i s a p a r t i a l l y oxidized bituminous coal and consequently expected to react more slowly. The frequency factors c o r r e l a t e well with, Y(8), the parameter that accounts for the tendency of the coal to undergo re t r o g r e s s i v e reactions as the f r a c t i o n of coal reporting i n i t i a l l y as unconverted material increases. One would expect coals that have a lower tendency to undergo retrogressive reactions would have a higher net rate of production f o r "converted" material and t h i s proves to be the case. Fies Mine and Hat Creek A coals are the l e a s t s e n s i t i v e to Y(8) and have the greatest frequency f a c t o r . Hat Creek B c o a l , Saskatchewan L i g n i t e , Forestburg and Byron Creek coals are progressively more s e n s i t i v e to Y(8) and have reduced frequency f a c t o r s . 2 1 3 TABLE 6.2 Optimum Parameters Coal Solvent Pararaeters Y( l ) _ x B Y(2) ?(3) Y(4) Y(5) T(6) T(7) Y(8) * ( » > _ i s Flea Mine (HVB) Tetra l ln 1.049 1002. 1 ( ~ 6 . x l 0 _ 4 ) 2 0.7316 0.000 4 . 6 0 x l 0 1 5 Hat Creek A (SB) Tetra l ln 0.918 416.6 1 -4 2 (-2.8x10 ) 0.6531 0.000 2 .50x l0 1 5 Hat Creek B (SB) Tetra l ln 1.445 690.4 1 -4 2 (~4.6xlO y 0.6029 0.0195 1 .28x l0 1 5 Middle Kittannlng (HVB) Tetra l ln 0.909 3.46xl0~ 5 153.6 3 -4 2 (-6.6x10 y 0.04687 0.7938 4.00xl0 6 Forestburg (SB) SRC o i l SRC o i l + THN 14.52 14.52 1.379 1.154 2.88xl0~ 5 3.46xl0~ 5 8.09x10 - 4 2 3.38x10 .01909 .02285 19.12 19.12 0.25254 0.25254 0.3626 0.3626 7 .617xl0 1 4 14 7.617X10-1- Byron Creek (B) SRC o i l SRC o i l + THN 11.09 1.670 1.75xl0~ 5 6.79x10"* .0230 19.12 0.05886 0.5049 14 0.228x10 Saskatchewan Lignite SRC o i l 13.56 2.03xlO~5 .02288 19.12 0.5075 0.0252 l .OOxlO 1 5 1. J l - T(2) - Y(4) D H (6.3) 2. J 2 - T(2) - Y(4) (TEMP) (H) (6.18) 3 . J l - Y(2) - Y(4) D (6.19) 214 Parameter Y(4), which r e l a t e s the i n i t i a l rate of hydrogen mass tr a n s f e r to the coal f r a c t i o n undergoing Instantaneous conversion, also y i e l d s consistent r e s u l t s , even though d i f f e r e n t equations were used to c o r r e l a t e t h i s parameter. Values obtained from the various c o r r e l a t i o n s can be approximated by an equivalent value for equation 6.18. One would expect t h i s parameter to vary with the porosity of the coal and the s o l u b i l i t y of the i n i t i a l l i q u e f a c t i o n products i n the c a r r i e r solvent. The parameter does vary, but only over a narrow range. The values range -4 -4 -1 -1 from 3 x 10 to 8 x 10 Kg • mole • °K , i f one assumes that t e t r a l i n i s the d i f f u s i n g species i n the absence of molecular hydrogen. At s u f f i c i e n t l y high hydrogen pressures, one might also expect to observe a switch from mass transfer to k i n e t i c c o n t r o l of the "instantaneous" r e a c t i o n s . Such an e f f e c t was not observed. Parameter Y(2), the amount of the organic material r e p o r t i n g as unconverted coal i n i t i a l l y , i n the absence of a hydrogenation agent,, suggests that negative conversion i s not only possible but l i k e l y under these r e a c t i o n conditions. I f the l i q u e f a c t i o n r e s u l t s f o r Middle Kittanning coal most c l o s e l y resemble t h i s s i t u a t i o n , then Y(2) may overestimate the extent of adduct formation, i n some cases. The Y(2) value reported for Byron Creek c o a l , 1.67, corresponds to a negative conversion of 67% and i s c l e a r l y too l a r g e . This i s an understandable shortcoming of an empirical model. 215 The maximum coal f r a c t i o n which i s predicted by the model to enter the dispersed phase i s also proportional to the i n i t i a l rate of hydrogen transfe r to the c o a l . As noted previously, the model only detects marginal material which can report to e i t h e r the l i q u i d or dispersed phases. The constant of t h i s p r o p o r t i o n a l i t y , Y(3), only varies from 1.75 x 10 to 3.5 x 10 ^ Kg • mole 1 °K 1 and i s one order of magnitude smaller than Y(4). Parameter Y(5) i s the optimum r a t i o of c a t a l y t i c solvent hydrogenation reactions to dispersed phase hydrogenation reactions. The optimum r a t i o of these two reactions, Y(5), appears to be f a i r l y constant over broad ranges of solvent composition. Only one sequence of experiments, performed with Byron Creek coal i n Solvent 1, contradict t h i s statement. These experimental r e s u l t s i n d i c a t e an optimum r a t i o of approximately 0.015 vs 0.02 to 0.023 for the other t r i a l s . However, Byron Creek coal l i q u e f i e d i n Solvent 1 encountered severe and progressive r e t r o g r e s s i v e reactions that are not an t i c i p a t e d by the model. A s i m i l a r though l e s s severe e f f e c t Is encountered at longer mean residence times when Forestburg coal i s l i q u e f i e d , In Solvent 1. Had l i q u e f a c t i o n r e s u l t s f o r Byron Creek c o a l i n Solvent 1 been obtained at much shorter residence times, i t i s l i k e l y that the optimum r a t i o would be c l o s e r to .02. Parameter Y(6), i s the background l e v e l of c a t a l y s i s present i n a wel l used reactor. This includes c a t a l y t i c e f f e c t s r e l a t e d to the memory 216 e f f e c t described previously, to the presence of catecols, to the mineral matter content of the coals l i q u e f i e d . For the c a t a l y s t employed i n th i s work, the memory e f f e c t predominates and i t i s not s u r p r i s i n g that Y(6) equals 19.12 grams as t h i s i s very close to 20.09, the average l e v e l of c a t a l y s t employed i n a l l runs conducted during the experimental program. Parameter Y ( l ) , the s t i r r i n g r a te, i n Hz, at which phase droplets begin to be broken up, ind i c a t e s that the reaction environment must be turbulent before the droplets are fragmented. I f one were to employ -3 e q u a t i o n 6.7 and assume that the solvent has a density of 0.8 g cm and -2 the i n t e r f a c i a l tension i s 1 dynes cm the maximum droplet diameters f o r Byron Creek c o a l , Saskatchewan L i g n i t e , and Forestburg coal are 10.6, 8.3, and 7.6 um re s p e c t i v e l y . The volumetric mean p a r t i c l e diameters of these coals are approximately 10.3, 57.5 and 40.5 um r e s p e c t i v e l y , while the mean p a r t i c l e diameters are 4.6, 3.3, 1.7 um. In the absence of a trend i n the r e s u l t s i t i s only possible to conclude that the s i z e of dispersed phase droplets must be rela t e d to the grain s i z e of the maceral components i n the pulverized c o a l . Apart from the general s i m i l a r i t y of the parameters l i s t e d on Table 6.2, and discussed above, the near i d e n t i c a l values which characterize Forestburg coal l i q u e f a c t i o n i n Solvents 1 and 2 are noteworthy. I f one takes into account anticipated d i f f e r e n c e s i n i n i t i a l 217 product s o l u b i l i t y a l l other parameters are the same. The same k i n e t i c parameters (Y(7), Y(8), Y(9), for example, apply to both solvents. These r e s u l t s suggest that as long as r e t r o g r e s s i v e reactions do not play a major r o l e i n the l i q u e f a c t i o n r e a c t i o n sequence, s h i f t s i n the rates and extents of l i q u e f a c t i o n reactions, r e s u l t i n g from r a d i c a l changes i n solvent composition can be predicted r e l i a b l y . The l i q u e f a c t i o n r e s u l t s obtained from simulated a x i a l l y mixed r e a c t o r and p r e - h e a t e r t r i a l s , T a b l e 5.3, can o n l y be modelled q u a l i t a t i v e l y because the average hydrogen concentrations i n the c a r r i e r solvents are unknown. An a d d i t i o n a l d i f f e r e n c e , with respect to modelling, i s that the dissolved molecular hydrogen concentrations are l i k e l y to be equal to the saturated value rather than proportional to i t as assumed for the batch i n j e c t i o n t r i a l s . Quantitative v e r i f i c a t i o n of the model with respect to v a r i a t i o n s i n residence time d i s t r i b u t i o n must await more precise hydrogen s o l u b i l i t y data. Following the 30 minute a x i a l l y mixed reactor simulation with Forestburg coal In Solvent 2, the apparent hydrogen s o l u b i l i l t y was -3 -1 -1 m e a s u r e d as 0.97 x 10 moles • Kg , • Atm . T h i s v a l u e i s s o l v e n t approximately one t h i r d the s o l u b i l i t y i n the s t a r t i n g solvent, and i s too low to use equation 2.7 for e x t r a p o l a t i o n . At 698°K, the saturated hydrogen concentration i s l i k e l y to be quite low and perhaps equal to or l e s s than the i n i t i a l hydrogen concentration encountered by coal p a r t i c l e s 218 during batch t r i a l s . I f one reduces the hydrogen concentration from 1.41 to 1.25 moles Kg 1 - ^ the model w i l l d u p l i c a t e the e x p e r i m e n t a l s o l v e n t r v conversion of 84.35 wt%. A s i m i l a r approach can be adopted for the a x i a l l y mixed pre-heater simulation, also performed with Forestburg coal i n Solvent 2. The hydrogen s o l u b i l i t y i n product l i q u i d s , measured at room temperature, drops below the detection l i m i t f o r both batch and a x i a l l y mixed t r i a l s with t h i s solvent, following experiments with a 5 minute mean residence time. Consequently, one would expect the mean hydrogen concentration to be quite low. I f a hydrogen s o l u b i l i t y of 0.65 moles Kg ^ s o i v e n t * Atm ^ i s employed, the model w i l l duplicate the experimental conversion value. The simulated a x i a l l y mixed pre-heater t r i a l performed with Forestburg coal i n Solvent 1, presents the same s i t u a t i o n as noted above for the a x i a l l y mixed reactor simulation. The hydrogen s o l u b i l i t y i n the -3 -1 -1 product l i q u i d s was measured at 0.5 x 10 moles • Kg , ^ • Atm solvent which i s between one h a l f and one t h i r d of the s o l u b i l i t y i n the s t a r t i n g solvent. One finds that a hydrogen concentration of 2.48 moles • Kg 1 , , vs 2.42 for batch t r i a l s , permits the model to so l v e n t duplicate the experimental conversion value. Due to the absence of accurate hydrogen s o l u b i l i t y data on hydrogen concentration data, the r e s u l t s of these v e r i f i c a t i o n t r i a l s can 219 only be treated as q u a l i t a t i v e . However, the r e s u l t s are s e l f c onsistent, and conform with experimental observations, thus, providing s u f f i c i e n t grounds to suggest that the model may be applied to a x i a l l y mixed as w e l l as batch r e a c t o r s . The only caution which must be mentioned i s that i f the solvent i s subject to rapid hydrogenation hydrogenolysis reactions which degrade the solvent, the model w i l l not predict a catastrophic reduction i n product y i e l d . 6 . 4 Summary The novel coal l i q u e f a c t i o n r e a c t i o n model presented and v e r i f i e d i n t h i s chapter has been shown to provide a general framework f o r d e s c r i b i n g the l i q u e f a c t i o n behaviour of coals and l i g n i t e . A v a r i e t y of r e a c t i o n environments were modelled s u c c e s s f u l l y and the model appears to be a p p l i c a b l e for both a x i a l l y mixed and batch reactors. However, the g e n e r a l i t y of the model i s bounded by two important l i m i t a t i o n s . Retrogressive reactions are treated as a l i q u i d - l i q u i d i n s o l u b i l i t y problem i n v o l v i n g the solvent and the i n i t i a l l i q u e f a c t i o n products a r i s i n g from instantaneous decomposition of a c o a l . The tendency f o r l a r g e r c oal derived molecules to p r e c i p i t a t e progressively with time as the solvent undergoes hydrogenolysis reactions i s not modelled, and cannot be modelled u n t i l more general theories for l i q u i d - l i q u i d s o l u b i l i t y are developed. Retrogressive reactions can play an important r o l e i n determining the l i q u e f a c t i o n r e a c t i o n sequence. Under conditions where t h i s occurs the model i s not a p p l i c a b l e . A second r e s t r i c t i o n , envisioned 220 when the model was formulated, i s that the t r a n s i t i o n zone between l a b i l e hydrogen d i f f u s i o n and molecular hydrogen mass transf e r c o n t r o l of the i n i t i a l "Instantaneous" l i q u e f a c t i o n reactions would be d i f f i c u l t to model. The model has been shown to work well I f e i t h e r of these modes of re a c t i o n dominate, but the t r a n s i t i o n zone, occurring over a range of hydrogen concentrations, not yet i d e n t i f i e d , must be found and quantified i f the model i s to be rendered as general as p o s s i b l e . 221 Chapter 7 Di r e c t Coal L i q u e f a c t i o n Reactor Design 7.0 Introduction The experimental r e s u l t s and the coal l i q u e f a c t i o n r e a c t i o n model, which comprise the two previous chapters, focus on an a n a l y s i s and d e s c r i p t i o n of d i r e c t coal l i q u e f a c t i o n environments from a microscopic perspective. The impact of these findings on the design of pre-heaters, the use of c a t a l y s t s , and the s e l e c t i o n of s l u r r y residence time d i s t r i b u t i o n s are discussed i n t h i s chapter. Current DCL reactor designs, Table 2.1 and Figures 2.1 to 2.8, are then re-examined and a novel reactor design, which optimizes the production of l i q u i d products, i s proposed. 7.1 Pre-heater Design Pre-heaters, an often overlooked component of DCL reactors, play two Important r o l e s In l i q u e f a c t i o n processes. The r e a c t i o n conditions p r e v a i l i n g i n pre-heaters determine the rate and maximum extents of subsequent l i q u e f a c t i o n r e a c t i o n s . Pre-heaters also serve t h e i r design function as a heat trans f e r device. Proposed i n d u s t r i a l pre-heater designs, Chapter 2, are t y p i c a l l y coal or natural gas f i r e d b o i l e r s with a s i n g l e heat transfer tube, In the shape of a h e l i x . These pre-heaters 222 are operated i n slug flow and act as plug flow reactors with respect to the s l u r r y phase. As shown i n Chapter 5, t h i s c o n f i guration i s optimal i f heavy o i l s or coal l i q u i d s are used as a l i q u e f a c t i o n solvent. One could only recommend, i n t h i s p a r t i c u l a r case, that the highest possible hydrogen pressure be employed, and that the s l u r r y residence time i n t h i s device be maximized. For l i g h t e r solvents, ( i . e . ) hydrogenated middle and heavy d i s t i l l a t e o i l s , or solvents with a reduced tendency to form adducts during i n i t i a l r e actions, such a design was shown to be non-optimal, and separation of the heat transfer and reaction i n i t i a t i o n functions must be considered. The heat transfer function, served by pre-heaters, i s e s s e n t i a l , even though l i q u e f a c t i o n reactions are exothermic. The cleavage of various organic bonds, followed by hydrogen saturation of the r e s u l t i n g r a d i c a l s , y i e l d s approximately 13.0 Kcal per mole of hydrogen consumed. The c l e a v a g e of a r y l or a l k y l carbon-carbon bonds, f o l l o w e d by hydrogenation y i e l d s between 12. and 13. Kcal »mole H ^ . Comparable values f o r CO, C 0 2 and H 2 0 f o r m a t i o n are ~ 10, < 20, 10-15 K c a l »mole H " 1 , r e s p e c t i v e l y . The amount of energy released v a r i e s with the o v e r a l l molecular s t r u c t u r e . I f the hydrogen consumption behaviour of Forestburg sub-bituminous c o a l , at 698°K, i s taken as representative, 9 moles of H 2 are consumed per kilogram of MAF coal within the f i r s t 2.4 minutes of reaction; 15 moles «Kg 1 r .. are consumed within 5 minutes and 20 moles 223 a f t e r 30 minutes of reaction . P i l o t plant t r i a l s suggest that up to 35 moles of H 2 per k i l o g r a m of MAF coal can be consumed - Table 2.1. The maximum temperature r i s e r e s u l t i n g from i n i t i a l r e a c t i o n s i s approximately 50°K, f o r a 40 wt% s l u r r y , and the maximum o v e r a l l temperature r i s e i s less than 180°K. Consequently, the coal s l u r r y must be pre-heated to at least 573°K before entering a reactor. Since t h i s temperature i s below the threshold f o r l i q u e f a c t i o n reactions, the two functions of the pre-heater can be separated, i n p r i n c i p l e . J u d i c i o u s s e l e c t i o n of o p e r a t i n g c o n d i t i o n s may permit a sustainable temperature r i s e i n excess of 100°K between the pre-heater e x i t and the reactor operating temperatures. As shown i n Chapters 5 and 6, the i n i t i a l extent and rate of l i q u e f a c t i o n reactions, i n l i g h t solvents are maximized i n a reactor with a broad s l u r r y residence time d i s t r i b u t i o n and a mean residence time between 5 and 10 minutes. The i n c l u s i o n of such a reactor, with a hydrogen consumption i n excess of 20 moles *Kg \ would maximize the i n i t i a l rate of hydrogen consumption and heat evolution, and minimize the heat exchange requirement. 7.2 Reactor Design The optimum l i q u e f a c t i o n reactor design for heavy solvents, Is one where the s l u r r y has a plug flow residence time d i s t r i b u t i o n . Apart from the f i r s t few minutes of reaction, a s i m i l a r design i s also preferred 224 when l i g h t c a r r i e r solvents are employed. In f a c t , the use of a x i a l l y mixed reactors with l i g h t solvents may lead to r a d i c a l reductions i n product y i e l d . Heavy solvents are less subject to such coal-solvent i n t e r a c t i o n s and the plug flow optimum i s only shallow. Two a d d i t i o n a l parameters which must be considered are: 1. the i n t e n s i t y of turbulence - a l e v e l of turbulence s u f f i c i e n t to break-up r e s i d u a l coal p a r t i c l e s and dispersed phase droplets must be maintained throughout the reactor. 2. the c a t a l y s t to turbulence r a t i o - an optimum r a t i o must be maintained. I n d u s t r i a l Designs cannot employ a g i t a t o r s , as were used i n this study. These devices are too c o s t l y f o r such a p p l i c a t i o n s . Gas bubbles and j e t s must be used to create turbulence. Currently, there are no published papers r e l a t i n g gas f l u x or mean bubble diameter to the s i z e of dispersed phase droplets i n l i q u i d - l i q u i d - g a s systems. Fundamental i n v e s t i g a t i o n s must be performed before optimum gas d i s t r i b u t o r s can be designed and DCL p i l o t plant t r i a l s can be conducted. 7.3 C a t a l y s t s The experimental program has demonstrated the importance of added c a t a l y s t s . Added c a t a l y s t must be present wherever coal i s undergoing r e a c t i o n , i f coal conversion i s to be maximized. The optimum l e v e l of 225 c a t a l y s t i s determined by the i n t e n s i t y of turbulence. I f reactions are i n i t i a t e d i n pre-heaters, flow through c a t a l y s t s are preferred. I f c a t a l y s t i s to be contained in s i d e a reactor, the pre-heater temperature should not exceed 573°K. 7.4 A Re-Evaluation of E x i s t i n g DCL Reactor Designs Despite the absence of complete sets of operating data f o r the various l i q u e f a c t i o n processes, Table 2.1, i t i s cl e a r that they a l l v i o l a t e the optimum design c r i t e r i a proposed above. The SRC I process, f o r example, operates at a low hydrogen pressure, and does not employ an added c a t a l y s t . Consequently, adduct formation and "coking" are dominant modes of re a c t i o n , and l i t t l e upgrading of l i q u i d products occurs. The c a t a l y t i c e f f e c t of mineral matter i s enhanced i n the SRC II process and a l i g h t e r c a r r i e r solvent Is employed. Higher hydrogen concentrations are encountered i n the c a r r i e r solvent, and c a t a l y t i c hydrogenation a l s o occurs. The product d i s t r i b u t i o n i s s h i f t e d from s o l i d s to l i g h t e r l i q u i d and gaseous components. The H-Coal process does not employ a flow through c a t a l y s t . The coal entering the reactor has a minimum net c o n v e r s i o n as i r r e v e r s i b l e coke formation occurs i n the pre-heater. The pre-heater i s then followed by an ebulated bed reactor, which further reduces the maximum extent of l i q u i d formation. L i t t l e data i s a v a i l a b l e f o r the EDS Process, which employs a l i g h t solvent. Added c a t a l y s t s are not employed i n the l i q u e f a c t i o n sequence, and a plug flow pre-heater Is used. The reactor, a multi-stage tank reactor, approximates a plug flow 226 residence time d i s t r i b u t i o n f o r the reacting s l u r r y . S i g n i f i c a n t improvements i n space time y i e l d would r e s u l t from the i n t r o d u c t i o n of c a t a l y s t and a d i s t r i b u t e d residence time f o r the i n i t i a l r e a c t i o n s . The l i q u i d y i e l d of the Dow process could be improved by using a higher hydrogen pressure, and by segmenting the reactor. The Saarbergewerke and Ruhrkohle Processes both employ flow through c a t a l y s t s , a high hydrogen pressure, and a multi-stage reactor design. These design features are appropriate f o r the s e l e c t i o n of heavy o i l as a c a r r i e r solvent. Improvements could only be made i n these processes i f a non optimal c a t a l y s t to turbulence r a t i o i s c u r r e n t l y used, or i f the hydrogen concentration i n the l a t t e r stages of the reactors could be reduced to minimize synthetic natural gas production. Of the p i l o t e d D i r e c t Coal L i q u e f a c t i o n Processes, only the Saarbergewerke and Ruhrkohle Porcesses are s u f f i c i e n t l y close to design optimum to permit optimization without s i g n i f i c a n t design changes. These two processes may or may not be competitive with the reactor design proposed i n the next s e c t i o n which i s centered on an a l t e r n a t i v e design optimum. 7.5 An Optimum D i r e c t Coal L i q u e f a c t i o n Reactor Design As noted i n Chapter 5, reactors employing heavy o i l s as the c a r r i e r solvent y i e l d optimum rates of l i q u i d product formation when the s l u r r y residence time d i s t r i b u t i o n approximates plug flow. The p r o d u c t i v i t y optimum f or l i g h t e r solvents occurs when a backmixed reactor with a short mean residence time precedes a plug flow reactor with a 227 a longer mean residence time. The Saarbergewerke and Ruhrkohle Processes approximate the former optimum. The design proposed here approximates the l a t t e r optimum and affords two p o t e n t i a l advantages over the German Processes. The size of heat exchangers and the hydrogen recycle load are reduced s i g n i f i c a n t l y . The proposed reactor, Figure 7.1, i s preceded by a pre-heater and/or heat exchangers which pre-heat the s l u r r y to approximately 573K. Hydrogen saturated coal s l u r r y , hydrogen gas and c a t a l y s t enter at the base of a co-current up flow tubular reactor with a mean residence time of approximately 5 minutes. This reactor i s imbedded within another tubular reactor which i s the second stage of the reactor network. The s l u r r y e x i t s at the top of the f i r s t stage and enters the second stage. The s l u r r y passes downwards within the annulus and e x i t s the second stage a f t e r an a d d i t i o n a l 10 to 20 minutes. The p a r t i a l l y consumed hydrogen stream, which contains CO, IL^O, C0 2, also e x i t s at the top of the f i r s t stage. This gas i s re-compressed and fed to the base of the second stage of the reactor. A plug flow s l u r r y residence time i s maintained i n the second stage by f o r c i n g the gas inje c t e d at the base of the second stage through a seri e s of sieves with progressively smaller hole diameters. In order to maintain a constant i n t e n s i t y of turbulence, t h i s gas flow i s augmented by gas j e t s attached to the external wall of the reactor. 228 Figure 7.1: A Novel Coal L i q u e f a c t i o n Reactor Design ) 229 Such a design maximizes the conversion, the hydrogen consumption and the temperature r i s e i n the f i r s t stage of the reactor. Thus, there would be le s s need to recycle hydrogen. The gas entering the second stage i s at the same pressure as i n the f i r s t stage but with a s u b s t a n t i a l l y reduced hydrogen f r a c t i o n . This helps to reduce excess synthetic natural gas formation. Since there i s no pressure gradient, the containment walls of the f i r s t stage can be quite t h i n ( i . e . the sieve tray supports can also be used to support the tube) and high rates of heat transfer can be r e a l i z e d . This reduces the requirement for external high pressure heat exchange equipment by over 30%. The o v e r a l l mean residence time would also be l e s s than i n the German Processes because l i q u e f a c t i o n reactions are more rapid i n l i g h t e r l i q u e f a c t i o n solvents. 7 . 6 Summary The experimental findings of t h i s thesis i n d i c a t e the existence of two reactor design optima for D i r e c t Coal L i q u e f a c t i o n Processes, which maximize the rate and extent of l i q u i d product formation. One design optimum i s approximated by the Saarbergewerke and Ruhrkohle Processes. An a l t e r n a t i v e and p o t e n t i a l l y competitive design optimum i s proposed i n section 7.5. 230 Chapter 8 8. Summary 8.1 Conclusions A se r i e s of d i r e c t coal l i q u e f a c t i o n t r i a l s performed with coals and l i g n i t e revealed that both bituminous and sub-bituminous coals and l i g n i t e undergo a comparable sequence of reactions i n DCL r e a c t i o n environments. The maximum rate and extent of conversion was found to depend on the i n i t i a l rate of hydrogen transfer to reacting coal p a r t i c l e s , and on the r a t i o of c a t a l y s t to the i n t e n s i t y of turbulence. This l a t t e r f i n d i n g l e d to the discovery of a persistent dispersed l i q u i d phase which was unknown p r i o r to this work. The find i n g that the i n i t i a l rate of hydrogen mass transfer had such a demonstrable e f f e c t on the rate and maximum extent of l i q u e f a c t i o n reactions i s inconsistent with the view, prevalent i n the l i t e r a t u r e , that the rates and maximum extents of product formation are determined i n t r i n s i c a l l y by coal composition and st r u c t u r e . These findings provided important i n s i g h t s into the nature of DCL re a c t i o n environments and permitted the development of a general, though e m p i r i c a l , coal l i q u e f a c t i o n reaction model. This model, which couples the experimental findings with a simple k i n e t i c scheme, correlated the l i q u e f a c t i o n behaviour of bituminous and sub-bituminous coals, and 231 l i g n i t e i n diverse reaction environments. Coal l i q u e f a c t i o n r e a c t i o n models, based s o l e l y on k i n e t i c s , r a r e l y c o r r e l a t e the l i q u e f a c t i o n b e h a v i o u r of more than a s i n g l e c o a l i n a p a r t i c u l a r r e a c t i o n environment. The r e s u l t s of the experimental program and the rea c t i o n model were used to formulate design c r i t e r i a f o r Dir e c t Coal L i q u e f a c t i o n r e a c t o r s . These analyses led to i d e n t i f i c a t i o n of two DCL reactor design optima. One design optimum i s approximated by two e x i s t i n g processes: the Saarbergewerke and Ruhrkohle processes. The second optimum, a novel 2 stage reactor configuration, also conforming with the experimental f i n d i n g s , i s p o t e n t i a l l y a superior a l t e r n a t i v e . 8.2 Suggestions f o r Further Study Design and development of D i r e c t Coal L i q u e f a c t i o n processes i s fa r from complete. A de t a i l e d d e s c r i p t i o n of l i q u e f a c t i o n k i n e t i c s , and a precise d e f i n i t i o n of optimum geometries f o r l i q u e f a c t i o n reactors must await future developments. This work suggests that studies r e l a t e d to the following areas are warranted: 1. The a c q u i s i t i o n and c o r r e l a t i o n of ph y s i c a l property data f o r complex organic mixtures at high temperatures. - the lack of data pertaining to the phys i c a l properties of complex organic mixtures i n h i b i t e d some aspects of t h i s work. 232 Solvent density, v i s c o s i t y , and i n t e r f a c i a l tension data, i n p a r t i c u l a r , were found to be l a c k i n g . 2. The analysis of g a s - l i q u i d - l i q u i d three phase flow. - studies r e l a t i n g to the impact of gas f l u x , and bubble size on the s i z e of dispersed l i q u i d droplets are of the greatest p o t e n t i a l importance for D i r e c t Coal Liq u e f a c t i o n Reactor Design. 3. The improvement of a n a l y s i s methods for coal and r e s i d u a l s o l i d p a r t i c l e s . - maceral d i s t r i b u t i o n s i n f i n e l y divided coal cannot be defined with c e r t a i n t y , and f i n e unreacted coal p a r t i c l e s are d i f f i c u l t to d i s t i n g u i s h from "coke". Improvements i n t h i s area would permit the development of more precise r e a c t i o n models for DCL Processes. 4. The novel two stage l i q u e f a c t i o n reactor design. - t h i s design should be subjected to further development and t e s t i n g using a continuous bench scale reactor. 233 REFERENCES 1. Conrad, J . , V i c t o r y , Penguin Books, Harmondworth, England, p. 1, (1979). 2. S t r o b e l , B., Romey, I., R o l l i n g , G.: "German Routes to Coal Hydrogenation", Advances i n Coal Technology, L o u i s v i l l e , Kentucky, U.S.A., p. 291-316, (May 1979). 3. Storch, H.H.: "Hydrogenation of Coal and Tar", Chemistry of Coal U t i l i z a t i o n , ed. H.H. Lowry, Wiley and Sons, N.Y., V o l . 2, p 1750- 1756, (1945). 4. Bergius, F.: "The Transformation of Coal Into O i l by Means of Hydrogenation", Can. Chem. and Met., V o l . 10, p. 275-279, (1926). 5. Wolk, R.H.: "Overview of L i q u e f a c t i o n Process Technology", Advances i n Coal U t i l i z a t i o n Technology, L o u i s v i l l e , Kentucky, U.S.A., p. 273-290, (May 1979). 6. Whitehurst, D.D., M i t c h e l l , T.O., Farcasiu, M.: Coal L i q u e f a c t i o n : The Chemistry and Technology of Thermal Processes, Academic Press, N.Y., p. 355, (1980). 7. I b i d , p. 346-370. 8. Neworth, M.B.: "Development of a Two-Stage Liquefaction Process", Advances i n Coal Technology, L o u i s v i l l e , Kentucky, U.S.A., 18, p. 345-358, (May 1979). 9. Berkowitz, N.: An Introduction to Coal Technology, Academic Press, New York, p. 303-314, 1979. 10. A l p e r t , S.B., Wolk, R.H., "Liquefaction Processes", Chemistry of Coal U t i l i z a t i o n , ed. M.A. E l l i o t t , Wiley-Interscience, N.Y., 2nd Sup. V o l . , p. 1919-1990, (1981). 11. Lee, M.H. Guin, J.A., Tarrer, A.R.: "A Dispersion Model for the SRC Process', Ind. Eng. Chem. Process Des. Dev., V o l . 17, No. 2, p. 127-34, (1978). 12. Abou-El-Hassan, M.E.: "Mixing and Phase D i s t r i b u t i o n s i n Two and Three Phase Bubble Column Reactors", Proc. 3rd European Conference on Mixing, BHRA F l u i d Engineering, C r a n f i e l d , Bedford, England, V o l . 1, F2, p. 303-324, ( A p r i l 1979). 234 13. T a l t e l , Y., Bornia, D., Dukler, A.E.: "Modellilng Flow Pattern T r a n s i t i o n s for Steady Upward Gas-Liquid Flow i n V e r t i c a l Tubes", AICHE Journal, V o l . 26, No. 3, p. 345-354, (May 1980). 14. Vince, M.A., Lahey, R.T.: "On the Development of an Objective Flow Regime Indicator", Int. J . Multiphase Flow, V o l . 8, No. 2, p. 93- 124, (1982). 15. Barnea, D., Shohan, 0., T a i t e l , Y., Dukler, A.E.: "Flow Pattern T r a n s i t i o n for Horizontal and Inclined Pipes: Experimental and Comparison with Theory", Int. J . Multiphase Flow, V o l . 6, p. 217- 225, (1980). 16. Levenspiel, 0.: Chemical Reaction Engineering, 2nd, Wiley, New York, p. 272-290, (1972). 17. Han, K.W., Wen, C.Y.: " I n i t i a l Stage (Short Residence Time) Coal D i s s o l u t i o n " , FUEL, Vol. 58, p. 779-82, (Nov. 1979). 18. Whitehurst, D.D. M i t c h e l l , T.O., Farcasiu, M.: Coal L i q u e f a c t i o n The Chemistry and Technology of Thermal Processes, Academic Press, N.Y., p. 366-368, (1980). 19. Han, K.W., D i x i t , V.B., Wen, C.Y.: "Analysis and Scale-Up Consideration of Bituminous Coal Liquefaction Rate Processes", Ind. Eng. Chem. Process Des. Dev., V o l . 17, No. 1, p. 16-21, (1978). 20. Moschopedis, S.E., Speight, J.R.: "The Co-Processing of Heavy O i l and Coal", Proc. 32nd Can. Chml. Eng. Con., Vancouver, B.C., Vol.1, p. 490-496, (Oct. 1982). 21. B i c k e l , T.C., Thomas, M.G.: "Catalyst Deactivation i n the H-Coal Li q u e f a c t i o n Process. 1. Catalyst Residence Time D i s t r i b u t i o n " , Ind. Eng. Chem. Process Des. Dev., V o l . 21, p. 377-381, (1982). 22. Grace, J.R.: " F l u i d i z e d Bed Hydrodynamics", Handbook of Multiphase Systems, ed. G. Hetsroni, Hemisphere, New York, p. 8.15, (1982). 23. Levenspiel, 0.: "The Chemical Reactor Omnibook, Oregon State U n i v e r s i t y Press, C o r v a l l i s , Oregon, Ch. 68, (1979). 24. Peters, B.C.: Dow Chemical Internal Report, Dow-F-R-363, F-1534-50, (1977). Chem. Abstract N 79-11166. 235 25. F r e e l , J . , Jackson, D.M., Schmid, B.K.: "SRCII Demonstration P r o j e c t " , Chem. Eng. Progress, p. 86-91, (May 1981). 26. Shah, Y.T., Carr, N.L.: "New Experimental Techniques for High Pressure High Temperature Gas-Liquid-Solid Reactors", Proc. 2nd World Congress of Chemical Engineering, Montreal, Canada, V.3, p. 138-141, (1981). 27. M o l l , N.G., Quarderer, G.J.: "The Dow Coal L i q u e f a c t i o n Process", CEP, p. 46-51, (Nov. 1979). 28. Goethel, G.F., K l e i n , W., Hosang, H.: "Coal Li q u e f a c t i o n and Heavy O i l Processing ... Veba O i l " , Proc. 32nd Can. Chml. Eng. Con., Vancouver, B.C., V o l . 2, (Oct. 1982). 29. Fajner, D., Ma g e l l i , F., P a s q u a l l i , G.: "Modelling of Non-Standard Mixers S t i r r e d with Multiple Impellers", Chem. Eng. Commun., V o l . 17, p. 285-295, (1982). 30. Taunton, J.W., Trachte, K.L., Williams, R.D.: "Coal Feed F l e x i b i l i t y i n the EDS Coal L i q u e f a c t i o n Process", FUEL, V o l . 60, p. 788-794, (Sept. 1981). 31. Rosenthal, J.W., Danlberg, A.J., Kuehler, C.W., Cash, D.R., Freedman, W.: "The Chevron Coal L i q u e f a c t i o n Process (CCLP)", FUEL, V o l . 61, p. 1045-1050, (October 1982). 32. Schindler, H.D., Sze, M.C., Long, R.H. Unger, H.: Advanced Coal L i q u e f a c t i o n Processes Emphasize Low Hydrogen Consumption", Proc. 15th I n t e r s o c i e t y Energy Conversion Engineering Conference, S e a t t l e , Washington, V o l . 2, p. 1543-1556, (August 1980). 33. Abichandani, J.S., Shah, Y.T., Cronauer, D.C., Ruberto R.G.: "Kin e t i c s of Thermal Liquefaction of Coal", FUEL, V o l . 61, p. 276- 282, (March 1982). 34. Cronauer, D.C., Shah, Y.T., Ruberto, R.G.: "Ki n e t i c s of Thermal L i q u e f a c t i o n of B e l l e Ayr Sub-bituminous Coal", Ind. Eng. Chem. Process Des. Dev., V o l . 17, No.3, p. 281-287, (1978). 35. Mohan, G., S i l l a , H.: "Kinetics of Donor Solvent Li q u e f a c t i o n of Bituminous Coals i n Nonisothermal Experiments", Ind. Eng. Chem. Process Des. Dev., V o l . 20, p. 349-358, (1981). 236 36. Droege, J.W., S t i c k f o r d , G.H., Chauhan, S.P.: "Thermophysical Properties of Pre-heater S l u r r i e s " , Proc. 16th I n t e r s o c i e t y Energy Conversion Engineering Conference, Atlanta, V o l . 2, p. 1085-1091, (August 1981) . 37. Thurgood, J.R., Hanks, R.W., Oswald, G.E., Youngblood, E.L.: The Rheological C h a r a c t e r i z a t i o n of Coal L i q u e f a c t i o n Pre-heater S l u r r i e s " , AICHE Journal, V o l . 28, No. 1, p. 111-116, (January 1982). 38. Okutani, T., Yokoyama, S., Maekawa, Y.: " V i s c o s i t y of Coal Paste Under High Hydrogen Pressure", FUEL, V o l . 59, p. 67-69, (January 1980). 39. Turian, R.M., Yuan, T.F.: "Flow of S l u r r i e s i n P i p e l i n e s " , AICHE Journal, V o l . 23, No. 3, p. 232-242, (May 1977). 40. Weinberg, V.L., Yen, T.F.: " S o l u b i l i t y Parameters i n Coal and Coal L i q u e f a c t i o n Products", FUEL, V o l . 59, p. 287-289, (May 1980). 41. Hombach, H.P.: "General Aspects of Coal S o l u b i l i t y " , FUEL, V o l . 59, p. 465-470, (July 1980). 42. Shibaoka, M., Stephens, J.F., Russel, N.J.: "Microscopic Observations of the Swelling of a High - V o l a t i l e Bituminous Coal i n Response to Organic Solvents", FUEL, V o l . 58, p. 515-522, (Ju l y 1979). 43. Habermehl, D., Orywel, F., Beyer, H.D.: " P l a s t i c Properties of Coal", Chemistry of Coal U t i l i z a t i o n , ed. M.A. E l l i o t , Wiley, N.Y., 2nd Sup. V o l . p. 354, (1981). 44. Derbyshire, F.J., Whitehurst, D.D.: "Study of Coal Conversion i n Polycondensed Aromatic Compounds", FUEL, V o l . 60, p. 655-662, (August 1981). 45. Shalabl, M.A., Baldwin, R.M., Bain, R.L., Gary, J.H., Golden, J.D.: "Non C a t a l y t i c Coal L i q u e f a c t i o n i n a Donor Solvent. Rate of Formation of O i l , Asphaltenes, and Preasphaltenes", Ind. Eng. Chem. Process Des. Dev., V o l . 18, No. 3, p. 474-479, (1979). 46. Yarzab, R.F., Given, P.H., Spackman, W., Davies, A.: "Dependence of Coal Li q u e f a c t i o n Behavior on Coal C h a r a c t e r i s t i c s . 4. Cluster Analysis for C h a r a c t e r i s t i c s of 104 Coals", FUEL, V o l . 59, p. 81-92, (Feb. 1980). 237 47. Smith, G.C., Cook, A.C.: " C o a l i f i c a t i o n Paths of E x i n i t e , V i t r i n i t e , and I n e r t i t e " , FUEL, V o l . 59, p. 641-646, (Sept. 1980). 48. Gun, S.R., Same, J.K., Chowdhury, P.B., Muklerjee, S.K., Muklerjee, D.K.: "A Mechanistic Study of Hydrogenation of Coal. 1", FUEL, V o l . 58, p. 171-175, (March 1979). 49. Szladow, A.J., Given, P.H.: "Models and A c t i v a t i o n Energies f o r Coal Liquefaction Reactions", Ind. Eng. Chem. Process Des. Dev., V o l . 20, p. 27-33, (1981). 50. Kuhlmann, E., Boerwinkle, E., Orchln, M.: " S o l u b i l i z a t i o n of I l l i n o i s Bituminous Coal: The C r i t i c a l Importance of Methylene Group Cleavage", FUEL, V o l . 60, p. 1002-1004, (Nov. 1981). 51. Carson, D.W., Ignaslak, B.S.: "Polymeric Structure of Coal. 3. Re- examination of the Role of Ether Bonds i n Reduction of Molecular Weight of a Low-rank V i t r i n i t e Treated with Hydrogen Donor", FUEL, V o l . 59, p. 757-761, (Nov. 1980). 52. Deno, N.C., Greigger, B.A., Jones, A.D., Raktisky, W.G., Whitehurst, D.D., M i t c h e l l , T.O.: " S t r u c t u r a l Changes Occurring i n Coal L i q u e f a c t i o n " , FUEL, V o l . 59, p. 701-703, (October 1980). 53. Curran, G.P., Struck, R.T., Gorin, G.: "Mechanism of the Hydrogen- Transfer Process to Coal and Coal Extract", Ind. Eng. Chem. Process Des. Dev., V o l . 6, No.2, p. 166-173, ( A p r i l 1967). 54. Vernon, L.W. "Free Radical Chemistry of Coal L i q u e f a c t i o n : Role of Molecular Hydrogen", FUEL, V o l . 59, p. 102-106, (February 1980). 55. P e t r a k i s , L., Grandy, D.W.: "Free Radicals i n Coals and Coal Conversion 2. E f f e c t of Li q u e f a c t i o n Processing Conditions on the Formation and Quenching of Coal Free Radicals", FUEL, V o l . 59, p. 227-232, (1980). 56. Franz, J.A., Camaioni, D.I.: "Fragmentations and Rearrangements of Free Radical Intermediates during Hydro-liquefaction of Coals i n Hydrogen Donor Media", FUEL, V o l . 59, p. 803-805, (Nov. 1980). 57. Derbyshire, F.J., Varghese, P., Whitehurst, D.D.: "Syn e r g i s t i c E f f e c t s between Light and Heavy Solvent Components during Coal L i q u e f a c t i o n " , FUEL, V o l . 61, p. 859-864, (1982). 58. Houalla, M., Broderick, D.H., Sapre, A.V., Nag, N.K., de Beer, V.H.J., Gates, B.C., Kwart, H.: "Hydrodesulphurlzation of Methyl Substituted Dibenzothiophenes Catalyzed by Sulphided Co-Mo/ a-Al,0o", Journal of C a t a l y s i s , V o l . 61, p. 523-527, (1980). 238 59. Y o s h i i , T., Yaginuma, R., Yoshikaura, H., Utoh, S o i i c h i : "Unusual E f f e c t s of Catechol upon the Hydro-liquefaction of Coal", FUEL, V o l . 61, p. 865-866, (September 1982). 60. Painter, P.C., Yamada, Y., Jenkins, R.G., Coleman, M.M., Walker, P.L.: "Investigation of Retrogressive Reactions leading to Carbonization of Solvent-Refined Coal", FUEL, V o l . 58, p. 293-297, ( A p r i l 1979). 61. Mochida, I., Takarabe, A., Takeshita, K.: " S o l v o l y t i c L i q u e f a c t i o n of Coals with a ser i e s of Solvents", FUEL, V o l . 58, p. 17-23, (January 1979). 62. Longanback, J.R.: "Short-Contact-Time Coal L i q u e f a c t i o n : " E f f e c t of Coal Rank and Solvent Source on Conversions and Heptane Insoluble Product Formation", ACS Symp. Ser., 169, (New Approaches Coal Chem.) p. 131-152, (1981). 63. Whitehurst, D.D., Farcasiu, M., M i t c h e l l , T.O., Dickert, J . J . , EPRI AF-480 Ann. Rep., (1977) Ch. 8, (see r e f . 64). 64. Bejamin, B.M., Hagaman, E.W. Raaen, V.F., C o l l i n s , C.J.: "Py r o l y s i s of T e t r a l i n " , FUEL, V o l . 58, p. 386-390, (May 1979). 65. Hooper, R.J. Battaerd, H.A.J., Evans, D.G.: "Thermal D i s s o c i a t i o n of T e t r a l i n between 300 and 450°C, FUEL, V o l . 58, p. 132-138, (February 1979). 66. Guin, J.A., Tarrer, A.R., Prather, J.W., Johnson, D.R., Lee, J.M.: " E f f e c t s of Coal Minerals on the Hydrogenation, Desulphurization and Solvent E x t r a c t i o n of Coal", Ind. Eng. Chem. Process Des. Dev., V o l . 17, No. 2, p. 118-126, (1978). 67. Guin, J.A., Tarrer, A.R., Lee, J.M., Van Backle, H.F., C u r t i s , C.W.: "Further Studies of C a t a l y t i c A c t i v i t y of Coal Minerals i n Coal L i q u e f a c t i o n 2 " , Ind. Eng. Chem. Process Des. Dev., V o l . 18, No. 4, p. 631-637, (1979). 68. Ross, D.S., Blessing, J.E.: "Alcohols as H-Donor Media i n Coal Conversion", FUEL, V o l . 58, p. 433-437, (June 1979). 69. Guin, J.A., Tarrer, A.R., Lee, J.M., Lo, L., C u r t i s , C.W.: " V e r i f i c a t i o n of C a t a l y t i c A c t i v i t y of Mineral Matter by Model Compound Studies", Ind. Eng. Chem. Process Des. Dev., V o l . 18, No. 3, p. 371-376, (1979). 239 70. Weigold, H.: "Behavior of Co-Mo-Al 20 3 Catalysts i n the Hydro- deoxygenation of Phenols", FUEL, V o l . 61, p. 1021-1026, (October 1982). 71. Rollmann, L.D.: " C a t a l y t i c Hydrogenation of Model Nitrogen, S u l f u r , and Oxygen Compounds", Journal of C a t a l y s i s , V o l . 46, p. 243-252, (1977). 72. Weisser, 0., Landa, S.: " S u l f i d e C a t a l y s t s , Their Properties and Ap p l i c a t i o n s " , Pergamon Press, Oxford, (1973). 73. Ouchi, K., Chicada, T., Itoh, H.: "Pressure and Temperature E f f e c t on the Mean Chemical Structure of Coal Hydrogenolysis Product", FUEL, V o l . 58, p. 37-42, (January 1979). 74. Ratnasamy, P., Ramaswamy, A.V., Sivasanker, S.: "Basic Molecules as Probes for the Study of Mo-Alumina C a t a l y s t s " , Journal of C a t a l y s i s , V o l . 61, p. 519-522, (1980). 75. Rudnick, L.R., Whitehurst, D.D.: "The E f f e c t of Solvent Composition on the Liqu e f a c t i o n Behavior of Western Sub-bituminous Coal", A.C.S. Symp. Ser., 169 (New Approaches to Coal Chem.), p. 153-171, (1981). 76. Kershaw, J.R., Gray, D.: "Ageing Studies on Coal Hydropyrolysis L i q u i d s " , FUEL, V o l . 59, p. 436-438, (June 1980). 77. Hara, T., Jones, L., L i , N.C., Tewari, K.C.: "Ageing of SRC L i q u i d s " , FUEL, V o l . 60, p. 1143-1148, (December 1981). 78. Brown, F.R., Karn, F.S.: " S t a b i l i t y Studies of Coal-Derived L i q u i d s " , FUEL, V o l . 59, p. 431-435, (June 1980). 79. Krishnamurthy, S., Shah, Y.T., S t i e g a l , G.J.: "P y r o l y s i s of Coal L i q u i d s " , FUEL, V o l . 59, p. 738-746, (November 1980). 80. Mukherjee, S.K., Mukherjee, D.K.: "Coking C h a r a c t e r i s t i c s of Heavy O i l From Coal Hydrogenation", Indian Journal of Technology, 15 (9), p. 381-388 (89:132175h), (1977). 81. Badilla-Ohlbaum, R., P r t t , K.C., Trimm, D.L.: "A Study of N i c k e l - Molybdate Coal Hydrogenation Catalysts Using Model Feed Stocks", FUEL , V o l . 58, p. 309-314, (1979). 240 82. Sapre, A.V., Gates, B.C.: "Hydrogenation of Aromatic Hydrocarbons C a t a l y z e d by S u l f i d e d C0O-M0O3/Y -AI2O3. R e a c t i v i t i e s and Reaction Networks", Ind. Eng. Chem. Process Des. Dev., V o l . 20, p. 68-73, (1980). 83. Rottendorf, H., Wilson, M.A.: " E f f e c t s of In-S i t u Mineral Matter and a Nickel-Molybdenum Catalyst on Hydrogenation of L i d d e l Coal", FUEL, V o l . 59, p. 175-180, (1980). 84. Mackison, F.W., S t r i c o f f , R.C., Partridge, L.J. J r . : NIOSH/OSHA Pocket Guide to Chemical Hazards, DHEW (NI0SH) P u b l i c a t i o n No. 78-210, (August 1980). 85. Burke, F.P., Winschel, R.A., Pochapsky, T.C.: "Composition and Perforance of D i s t i l l a t e Recycle Solvents f r o the SRC-1 Process", FUEL, V o l . 60, p. 562-572, (July 1981). 86. Whitehurst, D.D., M i t c h e l l , T.O., Farcasiu, M.: Coal L i q u e f a c t i o n : The Chemistry and Technology of Thermal Processes, Academic Press, N.Y., p. 280-284, (1980). 87. Katoh, T., Yokoyama, S., Sanada, Y.: "Analysis of a Coal-Derived L i q u i d using High-Pressure Li q u i d Chromatography and Synchronous Fluorescence Spectrometry", FUEL, Vol. 59, p. 845-850, (December 1980). 88. L i u , T.-C, Anthony, R.G.: "Reaction Model f o r the D i s s o l u t i o n of Large P a r t i c l e s of Texas L i g n i t e " , Ind. Eng. Chem. Process Des. Dev., V o l . 20, p. 609-615, (1981). 89. Batchelder, R.F., Fu, Y.C.: "Evaluation of Use of Syngas for Coal L i q u e f a c t i o n " , Ind. Eng. Chem. Process Des. Dev., V o l . 18, No. 4, p. 594-599, (1979). 90. Johnson, C.A., Chervenak, M.C., Johanson, E.S., S t o t l e r , H.H., Winter, 0., Wolk, R.H.: "Present Status of the H-Coal Process", Proc. 2nd Symp. Clean Fuels from Coal, Inst. Gas Technol., Chicago, 111, p. 525-551, (1975). 91. S t o t l e r , H.H., Schutter, R.T.: "Status and Plans of the H-Coal P i l o t P l a n t " , Coal Processing Technology, V o l . V, ed. CEP, AICHE, New York p. 73-77, (1979). 241 92. Fettweis, G.B.: World Coal Resources - Methods of Assessment and Results, E l s e v i e r Publishing, New York, , p. 318-323, (1976). 93. Struck, R.T., Clark, W.E., Dudt, P.J., Rosenhoover, W.A., Zie l k e , C.W., Gorin, E.: Ind. Eng. Chem Process Des. Dev., 8, p. 546, (1969). 94. Falkum, E., Glenn, R.A.: FUEL, 31, p. 133, (1952). 95. Vaclav, P., Kubicek, I., Kucler, J . : Chem. Prum., 31 (2), p. 61-66, (1981) , (Chem. Abs. 94-177257-F). 96. Sharma, M.M.: CES, 38 (1), p. 21-28, (1983). 97. Data Tables, Chemistry of Coal U t i l i z a t i o n : Supplemental Volume, Ed. H.H. Lowry, Wiley and Sons, N.Y., 1963. 98. L i n , H., Sebastian, H.M., Simmik, J . J . , Chao, K.: " S o l u b i l i t i e s of Hydrogen and Methane i n Coal Liquids", Ind. Eng. Chem. Process Des. Dev., 20, pp. 253-256, (1981). 99. IUPAC: S o l u b i l i t y Data Series, V o l . 5/6, Hydrogen and Deuterium, Pergamon Press, Oxford, England, (1981). 100. IUPAC: S o l u b i l i t y Data Series, V o l . 4, Argon, Pergamon Press, Oxford, England, (1980). 101. IUPAC: S o l u b i l i t y Data Series, V o l . 9, Ethane, Pergamon Press, Oxford, England, (1982). 102. IUPAC: S o l u b i l i t y Data Series, V o l . 10, Nitrogen and A i r , Pergamon Press, Oxford, England, (1982). 103. K r i z , J.F.: "Some E f f e c t s of Carbon Monoxide i n Hydro-processessing of Heavy Feedstocks", 32nd CSChE Conference, Vancouver, B.C., (1982) . 104. Oldshue, J.Y.: " F l u i d Mixing Technology and P r a c t i c e " , Chem. Eng., pp. 82-108, June 13 (1983). 105. Sekizawa, T., Kubota, H.: "Liquid Mixing i n Multistage Bubble Columns", J . Chem. Eng. Japan, V o l . 7, No. 6, pp. 441-446, (1974). 106. Ozum, B., Glbb, W.J., du P l e s s i s , M.P.: "Modeling of Liqu e f a c t i o n Reactors", Proc. 32nd Can. Che. Eng. Conference, V o l . 1, p. 514-525, (October 1982). 242 107. Timmermans, D.: Physico-Chemical Constants of Binary Systems, V o l . 1, Interscience Pub., New York, (1959). 108. Reid, R.C., Prausnitz, J.M., Sherwood, T.K.: The Properties of Gases and Li q u i d s , 3rd Ed., McGraw-Hill, New York, p. 359, (1977). 109. Ibi d , p. 68-68. 110. Ibi d , p. 435-462. 111. Gertenbach, D.D., Baldwin, R.M., Bain, R.L.: "Modelling of Bench- Scale Coal Liquefaction Systems", Ind. Eng. Chem. Process Des. Dev., V o l . 21, p. 490-500, (1982). 112. Shah, Y.T., Cronauer, D.L., M c l l v r i e d , H.G., Paraskos, J.A.: "Kinetics of C a t a l y t i c L i q u e f a c t i o n of Big Horn Coal i n a Segmented Reactor", Ind. Eng. Chem. Process Des. Dev., V o l . 17, No. 3, p.288- 301, (1978). 113. Singh, CP.P., Shah, Y.T., Carr, N.L., Prudich, M.E.: "Liquefaction of Coal by SRC-II Process ( I ) " , Can. J . Che. Eng., V o l . 60, p. 248- 260, ( A p r i l , 1982). 114. Singh, CP.P., Shah, Y.T., Carr, N.L., Prudich, M.E.: "Liquefaction of Coal by SRC-II Process ( I I ) " , Can. J . Che. Eng., V o l . 60, p. 261- 271, ( A p r i l 1982). 115. Singh, CP.P., Shah, Y.T., Carr, N.L., Prudich, M.E.: "Liq u e f a c t i o n of Coal by SRC-II Process ( I I I ) " , Can. J . Che. Eng., V o l . 60, p. 659-665, (October 1982). 116. Singh, CP.P., Shah, Y.T., Carr, N.L., Prudich, M.E.: "Liquefaction of Coal by SRC-II Process (IV)", Can. J . Che. Eng., V o l . 60, p. 831- 841, (December 1982). 117. Singh, CP.P., Shah, Y.T., Carr, N.L., Prudich, M.E.: "Liquefaction of Coal by SRC-II Process (V)", Can. J . Che. Eng., V o l . 60, p. 842- 852, (December 1982). 118. Singh, CP.P., Shah, Y.T., Carr, N.L., Prudich, M.E.: "Process Simulation of an SRC-II Plant", Ind. Eng. Chem. Des. Dev., V o l . 22, pp. 104-118, (1983). 119. Longanbach, J.R.: "The E f f e c t s of Heavy Recycle Solvents on Coal L i q u e f a c t i o n " , CEP, Vol. 80, No. 11, p. 29-32, (1984). 243 120. Tarrer, A., Guin, J . , P i t t s , W., Henley, J . , Prather, J . , S t y l e s , G.: " E f f e c t of Coal Minerals on Reaction Rates During Coal L i q u e f a c t i o n " , L i q u i d Fuels from Coal, Ed. R.T. E l l i n g t o n , Academic Press, N.Y., p. 45-61, (1977). 121. Whitehurst, D., M i t c h e l l , T., Farcasiu, M.: Coal Liq u e f a c t i o n ; The Chemistry and Technology of Thermal Processes, Academic Press, N.Y., p. 93-112, (1980). 122. Calderbank, P.H.: Mixing, ed. Uhl, V.W., Gray, J.B., V o l . I I , p.28- 33. 123. Pelso, M., Ogren, D.F.: "Anti-Solvent Deashing", CEP, V o l . 75, No. 6, p. 41-44, (1979). 124. Adams, R.M., Knebel, A.H., Rhodes, D.E.: " C r i t i c a l Solvent Deashing", CEP, V o l . 75, No.6, p. 44-48, (1979). 125. Taverides, L.L., Stamatoudis, M.: "The Analysis of Interphase Reactions and Mass Transfer i n L i q u i d - L i q u i d Dispersions", Advances i n Chemical Engineering, V o l . I I , p. 199-268, (1980). 126. McElroy, R.: A private communication. 244 APPENDICES 245 APPENDIX A: HYDRODYNAMIC CALCULATIONS APPENDIX A. 1: HYDRODYNAMIC CALCULATIONS FOR THE H-COAL REACTOR Data: (PDU Reactor) S l u r r y concentration S l u r r y density Reactor x-sectional area Coal Flow Rate (I) syncrude ( i i ) f u e l o i l C a talyst Extrudate ( i ) length ( i i ) diameter ( i i i ) density S l u r r y V i s c o s i t y (25-40) wt% , -3 1 gem 2 371.6 cm 76.9 1-hr 225. 1-hr 4.86 mm (.3-.5)mm 1.7 gem (1-2) cp -1 -3 (assumed) p D Ca l c u l a t i o n s : F -1 (1) S u p e r f i c i a l s l u r r y v e l o c i t y = — • p c s syncrude mode = (.06 - .10) cm s f u e l o i l mode = («19 - .30) cm s (2) Minimum f l u i d i z a t i o n v e l o c i t y : U -1 -1 -1 454 36.00 mf Although the reactor Is not a f l u i d i z e d bed, f l u i d i z a t i o n equations can provide an estimate f o r the v e l o c i t y required to f l u i d i z e the "ebullated c a t a l y s t bed". 246 Re . = (27.2 2 + 0.0408 A r ) 1 / 2 - 27.2 mf A P S ( P P ~ P S ) 8 V 2 8̂ d = (1.5 • A ) 1 / 3 ( D ) 2 / 3 P Re u mf s mf d p P s u m f = (2.25 - 3.5) cm s -1 APPENDIX A.2: AXIAL MIXING IN THE SRC I REACTOR Data: W i l s o n v i l l e Reactor Gas v e l o c i t y S l u r r y v e l o c i t y reactor length p, density p., v i s c o s i t y C a l c u l a t i o n s : (1) Dispersion number D = v .800 {log (g 1'' 3 -5/3) ~ 4.331} 3' v zr%\ 2 . , D ' D.2. , u L N N <2> 0 = 2 ( u l " W } ( 1 " E X P ( " " D } ) (from the disp e r s i o n model) (3) N * \ a N =1.24 Note: In order to obtain N = 2 the gas phase v e l o c i t y must be reduced by a factor of 14. 1.8 cm s 0.335 cm s 7.0 m -3 1.0 gem 1.0 cp 248 A P P E N D I X A . 3 : A X I A L M I X I N G I N T H E R U H R K O H L E R E A C T O R Data: B-F Reactor Reactor Dimensions - length 2.0 m - volume 11.0 I Reactor Temperature 2 -3 t o t a l gas flow 1600. sm day pressure 30. MPa Sl u r r y -3 - density 1.0 gem - v i s c o s i t y 1. cp Calc u l a t i o n s : (1) D = v.800 log { ( g i / J -fjj - 4.311} 1/3 , _ A., 1^3-2 v" 2 « , D , D .2. , u L x x ( 2 ) ° = 2 ( uT " ( m? ) ( 1 " E X P ( ~ " D ) } (3) N = 1 2 a N = 1.3 249 APPENDIX B: CORRELATION DERIVATIONS APPENDIX B . l : GAS SOLUBILITY CORRELATION In regions removed from the c r i t i c a l point, ( i . e . ) T^ < 0.95, the s o l u b i l i t y of a gas In a pure compound i s approximated by log S = a + b 6 T r (B.l) or b T S = A e r (B.2) Sub s t i t u t i n g equation B.2 into equation 2.6 Smix S Jl x S 1 y i e l d s S m i x = TJ (A ± e b i (B.3) which can be s i m p l i f i e d further to b T S , = A e r (B.4) mix ' 2 5 0 where A, b, T f are weighted averages o v e r a l l the components which preserve the basic l o g - l i n e a r character of the solubility-temperature r e l a t i o n s h i p . The only thermal complication i s the evaluation of T^ f o r a s p e c i f i c s o l v e n t as A and b are constants for a l l solvent components drawn from the same on s i m i l a r c l a s s e s . For pure solvents the c r i t i c a l temperature i s proportional to the b o i l i n g temperature. ( B . 5 ) c ( 0 . 6 7 ± . 0 2 Thus a pseudo c r i t i c a l temperature can be defined for complex solvents as *c - - X ' 4 9 5 T B 5 0 < B ' 6 > where T ^ ^ Q = the temperature at which 5 0 wt% of the solvent i s d i s t i l l e d at one atmosphere pressure. Since b o i l i n g range data i s frequently supplied along with other solvent properties i n the l i t e r a t u r e , T c i s r e a d i l y obtained. Gas s o l u b i l i t i e s , i n complex m i x t u r e s , should c o r r e l a t e approximately according to APPENDIX C LIQUEFACTION TRIAL DATA TABLE C . l T r i a l Summary for Forestburg Coal Run Operating Conditions Gas Production (Consumption) Mass Balance 'X Conversion g/Kg MAF Coal grams •c RPM CAT. g SOLVENT MRT min. SIM ( H 2 ) CH4 CO C 2 H 6 c o 2 MAF Coal Input Entrained Slurry Gas L i q . Total 201 475 1000 20.0 1 30.0 PF 20.2 10.5 6.6 5.1 35.2 168.31 85.0 5.74 70.9 76.7 204 475 1000 20.0 1 30.0 PF 35.8 12.6 8.0 5.5 37.7 151.6 13.4 6.38 84.2 90.5 205 475 1000 20.0 1 30.0 PF 31.6 12.0 8.3 5.1 40.9 155.8 32.2 6.62 83.0 89.6 208 475 1000 20.0 2 30.0 PF 33.4 12.0 5.0 5.9 40.5 163.6 60.3 6.30 83.8 90.1 209 475 1000 20.0 2 30.0 PF 35.4 14.1 4.7 5.2 46.5 157.5 64.1 7.03 83.0 90.0 210 475 1000 20.0 2 30.0 PF 34.3 10.4 5.0 5.7 37.0 159.8 73.8 5.81 84.1 89.9 212 475 1000 20.0 2 30.0 PF 28.9 13.6 7.5 7.3 44.8 160.2 41.7 7.31 77.1 84.4 213 475 1000 20.0 1 30.0 PF 30.8 11.1 7.5 5.7 38.4 152.7 26.3 6.26 83.6 89.9 214 375 1000 20.0 2 30.0 PF 17.7 1.7 2.9 0.8 30.1 156.5 19.2 3.55 36.1 39.6 215 375 1000 20.0 1 30.0 PF 15.9 1.8 2.8 0.5 29.5 138.6 59.8 3.46 40.8 44.2 216 375/425 1000 20.0 1 30.0 PF 28.4 8.0 7.6 3.9 34.6 133.9 75.4 5.41 79.3 84.7 217 425 1000 20.0 2 30.0 PF 38.2 13.5 5.40 7.1 48.4 163.0 91.3 7.44 82.1 89.5 218 425 1000 20.0 2 30.0 PF 39.1 16.4 8.4 13.6 43.5 148.0 40.4 8.19 83.2 91.4 219 425 1000 20.0 1 5.0 PF 24.1 5.0 5.1 3.0 36.5 121.3 39.1 4.96 59.2 64.1 220 425 1000 20.0 2 5.0 PF 30.0 6.4 5.1 3.5 33.4 167.5 76.8 4.83 57.3 62.1 221 400 1000 20.0 2 30.0 PF 30.3 5.7 3.8 3.1 36.6 173.7 133.6 4.91 65.5 70.4 222 400 1000 20.0 1 30.0 PF 27.1 5.1 6.7 2.7 35.3 128.0 37.5 4.97 68.4 73.4 223 400 1000 20.0 2 30.0 PF 28.3 5.3 5.3 2.8 39.4 161.4 18.7 5.28 64.4 69.7 224 425 1000 40.0 2 30.0 PF 39.1 13.7 4.1 7.1 45.0 157.8 23.9 6.98 79.2 86.2 225 425 1000 80.0 2 30.0 PF 39.9 14.2 1.7 7.7 45.1 154.4 29.7 6.87 77.4 84.3 226 425 1000 40.0 2 30.0 PF 37.7 13.8 2.9 6.4 44.9 161.1 28.6 6.80 79.6 86.4 227 425 1000 80.0 Pre hydrog. 30.0 PF 29.2 5.1 3.3 3.1 31.9 116.6 52.4 4.34 53.9 58.2 229 425 1000 80.0 1 30.0 PF 33.4 8.0 4.3 5.2 30.8 125.7 58.6 4.83 44.0 48.8 230 425 1000 0.0 2 30.0 PF 17.7 14.1 7.8 7.9 52.3 55.0 8.21 61.5 69.7 231 425 1000 0.0 2 30.0 PF 6.90 5.5 5.7 2.9 44.3 147.4 29.3 5.83 30.4 36.2 232 425 500 20.0 2 30.0 PF 35.1 13.6 5.3 7.6 48.4 152.3 52.9 7.48 78.1 85.6 233 425 500 20.0 1 30.0 PF 35.3 14.1 5.5 8.1 46.4 127.4 22.6 7.40 75.5 82.9 234 425 1000 20.0 2 30.0 2 26.4 5.4 6.0 2.7 38.9 160.6 20.9 5.30 54.3 59.6 235 425 1000 20.0 1 30.0 2 24.5 5.4 6.3 3.0 37.3 157.8 28.6 5.19 59.5 64.7 236 425 500 20.0 2 30.0 PF 27.3 6.3 3.9 3.5 39.3 152.7 79.5 5.29 52.0 57.3 237 425 1000 20.0 1 15.0 PF 29.4 8.9 7.1 4.5 39.0 160.8 85.0 5.94 72.0 77.9 238 425 1000 20.0 2 30.0 2 38.1 14.9 4.0 7.7 46.4 159.5 89.9 7.30 77.1 84.4 239 425 1000 80.0 1 30.0 PF 36.7 11.1 3.9 5.5 37.2 160.9 33.1 5.77 74.0 79.8 240 425 1000 20.0 High S o l . 15.0 PF 31.1 9.2 7.0 5.0 40.8 160.8 93.6 6.19 74.4 80.6 241 425 1000 20.0 2 2.44 2 17.3 4.6 6.0 2.2 33.1 161.8 63.9 4.59 45.4 50.0 242 425 1000 20.0 1 45.0 PF 36.6 14.2 5.7 6.2 40.7 158.5 20.0 6.68 81.2 87.9 243 425 1000 20.0 2 30.0 PF 37.0 14.2 5.3 6.2 44.1 162.6 62.2 6.99 80.0 87.0 244 425 1000/ 500 20.0 2 30.0 PF 34.2 7.2 4.9 7.1 47.1 165.0 62.2 6.63 78.3 84.9 245 425 1000 20.0 2 30.0 PF 36.0 12.1 5.2 9.4 70.0 157.6 78.3 9.66 71.0 80.7 246 425 2000 20.0 2 5.0 PF 160.68 55.0 254 TABLE C.2 T r i a l Summary f o r Byron Creek Coal Run Operating C o n d i t i o n s Gas P r o d u c t i o n (Consumption) Mass Balance X Conversion g/Kg MAF Coal grams •c RPM CAT. g SOLVENT MRT min. SIM (H 2> CH 4 CO C2H6 CO, MAF Co a l Input E n t r a i n e d S l u r r y Gas L l q . T o t a l 312 425 1000 20.0 1 2.44 2 12.7 S.3 1.31 2.49 8.88 166.7 33.7 1.60 15.1 16.7 313 425 1000 0.0 2 30.0 PF 7.7 12.2 2.61 5.85 29.5 170.9 19.5 5.02 30.7 35.8 314 425 1000 20.0 2 30.0 PF 24.4 15.4 2.56 7.49 7.79 171.1 40.3 3.32 46.6 50.0 315 425 1000 40.0 2 30.0 PF 25.2 13.5 2.78 6.06 7.41 156.4 24.7 2.97 44.2 47.2 316 425 1000 80.0 2 30.0 PF 25.5 15.2 1.28 12.8 7.10 166.4 21.0 3.64 34.9 38.6 317 425 1000 20.0 2 2.44 2 169.6 13.9 320 425 1000 20.0 2 2.44 2 14.5 3.9 1.58 3.16 8.67 168.6 41.7 1.73 5.59 7.3 321 425 1000 10.0 2 30.0 PF 19.6 13.0 3.66 7.26 10.5 171.4 31.6 3.44 39.0 42.5 322 425 1000 0.0 1 30.0 PF 4.4 9.7 2.75 4.10 11.2 165.4 34.2 2.78 26.3 29.1 323 425 IOOO 10.0 1 30.0 PF 15.0 10.6 3.91 5.67 10.7 169.2 12.1 3.09 42.7 45.8 324 425 1000 20.0 1 30.0 PF 17.8 10.0 2.58 5.29 8.65 161.3 7.60 2.65 29.4 32.0 325 400 1000 10.0 1 30.0 PF 12.7 2.97 1.46 1.29 7.33 167.2 22.1 1.31 18.6 19.9 326 425 1000 20.0 2 60.0 PF 29.3 21.1 2.42 11.7 12.8 174.8 41.8 4.80 48.5 53.3 327 378 1000 20.0 2 30.0 PF 11.8 1.4 0.96 0.56 6.48 163.2 14.7 0.94 8.60 9.50 328 425 2000 20.0 2 30.0 PF 25.8 13.5 3.28 10.5 12.5 160.6 11.3 3.94 41.4 45.3 329 425 500 20.0 2 30.0 PF 23.2 13.0 2.73 7.80 8.82 165.7 0.00 3.24 43.2 46.4 330 425 1000 20.0 2 15 PF 20.3 9.6 2.29 9.53 13.6 170.5 26.3 3.51 27.9 31.4 331 425 1000 5.0 1 30.0 PF 14.2 10.4 3.08 5.39 9.19 163.1 38.5 2.80 36.6 39.4 332 425 2000 10.0 1 30.0 PF 11.7 8.7 2.60 4.91 11.1 166.9 14.2 2.74 37.4 40.1 333 425 500 10.0 1 30.0 PF 14.6 10.0 2.85 6.92 12.8 162.4 18.5 3.25 34.0 37.3 334 425 iooo 10.0 1 15 PF 12.0 5.0 2.44 1.87 6.95 169.6 18.0 1.63 32.8 34.4 335 400 1000 20.0 2 30.0 PF 16.8 4.6 1.74 2.21 6.91 165.9 20.0 1.55 24.1 25.7 336 425 1000 20.0 2 38 2 25.2 16.2 3.43 8.41 9.39 162.9 23.5 3.74 44.1 47.8 337 425 1000 10.0 1 38 2 15.2 13.5 4.02 7.21 10.6 162.2 6.00 3.53 48.0 51.6 338 425 1000 10.0 1 60 PF 15.1 10.3 3.33 4.75 8.23 167.2 11.0 2.66 41.0 43.7 TABLE C.3 T r i a l Summary for Saskatchewan Lignite Run Operating Conditions Gas Production (Consumption) Mass Balance X Conversion g/Kg MAF Coal grams °C RFM CAT. SOLVENT MRT SIM (H2) CH4 CO C 2 H 6 c o 2 MAF Entrained Gas L i q . Total g min. Coal Slurry Input 401 425 1000 0.0 2 15 PF 10.3 8.88 6.04 4.72 58.8 153.4 32.7 7.85 42.9 50.8 402 425 1000 20.0 2 15 PF 29.4 8.92 4.73 5.38 55.2 154.4 0.00 7.42 60.9 68.4 403 425 1000 40.0 2 15 PF 33.2 8.93 4.39 6.23 64.8 146..7 6.72 8.43 57.2 65.6 404 425 1000 80.0 2 15 PF 34.3 9.59 3.74 6.37 51.0 150.7 17.68 7.07 58.1 65.2 256 TABLE C.4: S o l u b i l i t y Data f o r T r i a l s with Forestburg Coal T r i a l Apparent S o l u b i l i t y moles• K _ 1 g solvent . -1 • Atm x io3 Ar N2 CH 4 CO C 2 H 6 co2 H2 224 2.9 1.5 6.5 1.9 30. 29. 4.3 225 3.3 2.3 5.5 1.9 19. 15. 3.4 226 2.1 1.2 4.3 1.9 17. 13. 2.1 227 11. 6.0 22. 9.3 95. 68. 5.4 229 20. 12. 42. 13. 168. 118. 11.0 230 14. 4.6 12.0 18. 204. 139. 5.5 231 8.5 4.0 22. 5.8 108. 76. 2.3 232 4.4 2.1 9.8 3.2 47. 31. 2.7 233 14. 6.0 37. 9.6 230. 153. 8.0 235 1.9 0.9 4.3 1.2 22. 15. 0.6 237 1.6 0.8 4.2 1.0 24. 16. 2.3 238 1.3 0.6 3.1 1.1 16. 11. 1.1 239 11. 5.2 24. 9.6 100. 68. 6.2 240 8.4 4.2 20. 6.0 96. 69. 4.1 241 8.7 5.5 17. 6.1 73. 53. 4.1 242 12. 5.9 28. 11. 127. 88. 7.4 243 3.1 1.6 6.4 2.1 25. 18. 2.1 244 1.6 0.8 6.9 1.1 14. 10. 1.0 245 8.1 5.9 15. 6.7 50. 38. 4.6 257 TABLE C.5 S o l u b i l i t y Data for T r i a l s with Byron Creek Coal T r i a l Apparent S o l u b i l i t y moles • Kg" 1 ° solvent • Atm ^ x 10 3 Ar N 2 CH 4 CO C2 H6 co 2 H2 312 9.0 4.1 19. 7.6 69. 58. 2.7 313 5.0 3.8 9.1 3.4 - - 2.8 314 2.3 1.4 5.8 2.7 24. 21. 1.1 315 2.6 1.2 5.3 2.0 1-1 15. 1.4 316 15. 8.8 29. 9.8 111. 79. 6.0 320 5.8 3.1 12.0 4.6 40. 32. 2.1 321 5.1 2.6 10. 4.0 46. 34. 2.1 322 2.9 1.6 6.4 2.2 29. 21. 0.9 323 7.1 4.0 15. 3.0 46. 43. 2.4 324 5.8 2.6 10. 4.5 46. 32. 1.8 325 8.1 4.7 17. 6.1 22. 17. 3.1 326 6.6 3.3 12. 4.6 61. 43. 4.0 328 13. 7.7 23. 11. 92. 62. 6.4 329 7.8 3.9 16. 7.3 68. 45. 3.6 330 14. 7.0 29. 12. 83. 111. 5.2 331 3.7 1.7 6.6 1.9 30. 23. 1.0 332 7.4 4.4 15. 4.2 72. 50. 2.8 333 8.6 4.4 19. 4.3 85. 56. 2.9 336 3.7 2.3 7.1 2.6 26. 20. 1.8 337 8.4 5.9 . 16. 4.4 60. 48. 3.0 338 4.0 2.6 8.0 2.1 25. 21. 1.6 258 TABLE C . 6 S o l u b i l i t y Data for T r i a l s with Saskatchewan L i g n i t e T r i a l Apparent S o l u b i l i t y moles • Kg" 1 solvent • Atm 1 x 1 0 3 Ar N 2 CH 4 CO C 2 H 6 c o 2 H 2 401 2 . 2 1 . 8 3 . 6 1 . 6 1 1 . 9 . 5 1 . 3 402 3 . 7 2 . 3 7 . 0 3 . 1 3 0 . 1 4 . 2 . 5 403 6 . 0 3 . 3 1 2 . 5 . 0 4 3 . 3 2 . 2 . 7 404 3 . 1 1 . 8 5 . 9 2 . 9 1 9 . 1 5 . 2 . 7 259 APPENDIX D D i r e c t C o a l L i q u e f a c t i o n C h a r a c t e r i s t i c s o f B y r o n C r e e k C o a l and V i t r i n i t e e n r i c h e d B y r o n C r e e k C o a l . SUMMARY The l i q u e f a c t i o n c h a r a c t e r i s t i c s o f a B y r o n C r e e k C o a l sample and a v i t r i n i t e e n r i c h e d sample, c o n c e n t r a t e d f r o m t h e same c o a l , were compared un d e r s e v e r a l d i f f e r e n t e x p e r i m e n t a l c o n d i t i o n s r e l a t e d t o t h e H - c o a l l i q u e f a c t i o n p r o c e s s . The g e n e r a l c o n c l u s i o n s a r e t h a t (a) v i t - r i n i t e i s n o t more t h a n 50% l i q u i f i a b l e , w h i l e i n e r t i n i t e i s p r o b a b l y 100% l i q u i f i a b l e ; (b) v i t r i n i t e r e a c t s about 14 t i m e s more q u i c k l y t h a n i n e r t i n i t e , i n terms o f a f i r s t - o r d e r c o n s t a n t f o r t h e l i q u e f i a b l e f r a c t i o n o f each m a c e r a l . A model t h a t c o u l d a c c o u n t f o r t h e s e r e s u l t s i s one i n w h i c h v i t r i n i t e d i s s o l v e s i n c o a l s o l v e n t much f a s t e r t h e n i t can be h y d r o g e n a t e d , l e a d i n g t o p r e c i p i t a t i o n o f u n r e a c t i v e p o l y m e r s , w h i l e i n e r t i n i t e d i s s o l v e s much more s l o w l y and so can be h y d r o g e n a t e d t o p e r m a n e n t l y s o l u b l e p r o d u c t s much more r e l i a b l y . 260 EXPERIMENTAL M a t e r i a l s : Byron Creek coal (BC) and v i t r i n i t e enriched Bryron Creek coal (VBC) were obtained from the same raw coal sample. Petrographic, proximate, and ultimate analyses of these two coals were supplied by Esso Canada L t d . These analyses are summarized on Table 1. The c a t a l y s t 12% MoO^, 3% CoO supported on an alumina matrix, was manufactured by Alpha products. The l i q u e f a c t i o n solvent comprised 90 wt% SRC o i l , from Kerr Magee Corp., a product of the W i l s o n v i l l e , Alabama SRT-1 p i l o t plant, and 10 wt% reagent grade tetrahydronaphthal The standard grade hydrogen, used in these experiments, was purchased l o c a l l y , and i s at l e a s t 99.9% pure. 261 TABLE 1. COAL ANALYSES COAL VITRINITE ENRICHED 3YR0N CREEK BYRON CREEK P e t r o g r a p h i c V i t r i n i t e 61.6 2 sd = 5 43.5 2 s d = 5 A n a l y s i s I n e r t i n i t e ' 36.6 2 sd = 5 53.3 2 sd = 5 V o l % (MMF) L i p t i n i t e 1.8 2 sd = 1 3.2 2 s d = 1 As R e c e i v e d M o i s t u r e 0.5 0.41 A n a l y s i s , wt% Ash 9.21 23.99 MAF A n a l y s i s W o l a t i l e s 27.19 28.77 wt% F i x e d Carbon 72.81 71.23 Carbon 87.54 85.21 Hydrogen 4.84 4.87 N i t r o g e n 1.27 1.27 D i f f e r e n c e 6.53 8.65 262 Experiments: Two types of experiments were performed during this study: i ) batch experiments; where c o a l , solvent, c a t a l y s t and hydrogen are charged into a cold autoclave and heated to r e a c t i o n conditions i i ) i n j e c t i o n experiments; where cold coal s l u r r y i s fed r a p i d l y into a preheated autoclave previously charged with hydrogen, c a t a l y s t and a small quantity of solvent. Batch l i q u e f a c t i o n experiments were performed because they are a standard laboratory t e s t . Such experiments have a number of drawbacks Including poorly defined t o t a l r e a c t i o n time, and r e l a t i v e l y long heat-up periods, during which solvent composition can change and coal can begin to react. S l u r r y I n j e c t i o n experiments simulate i n d u s t r i a l l i q u e f a c t i o n schemes by v i r t u a l l y eliminating heat-up time and by providing more precise c o n t r o l of t o t a l reaction time. Procedure: Both batch and i n j e c t i o n experiments were performed with the same autoclave and approximately the same amount of reagents and c a t a l y s t . A t y p i c a l charge comprised: 263 450.Og SRC-Oil 50.Og t e t r a l l n 200.0g raw coal 5.0g c a t a l y s t 5.3g hydrogen 2.5:1 o i l : coal r a t i o T o t a l r e a c t i o n time was measured from the time the autoclave reached re a c t i o n temperature (685K), f o r batch experiments, and from the midpoint of the i n j e c t i o n cycle for i n j e c t i o n experiments. A l l experiments were terminated by quenching the reactor to room temperature. Gas and s l u r r y samples were obtained, once the autoclave was c o o l . Gas samples were analysed for CO, CO2, C 2 Hg» ^3 H8 u 8 * n 8 a 8 a s chromatograph. S l u r r y samples were extracted with tetrahydrofuran to determine a baseline for l i q u e f a c t i o n y i e l d . 264 RESULTS Experimental r e s u l t s are summarized on Table 2 along with associated operating data. Based on previous experience with the apparatus and analysis procedures, the t o t a l conversion s t a t i s t i c s reported on t h i s table are reproducible to within ± 0.3 wt%. The gas y i e l d s are very small, le s s than 2.2 wt%, and consequently, the probable error i s r e l a t i v e l y large - ± 20% of the value reported. L i q u i d y i e l d i s determined by d i f f e r e n c e , and the probable error v a r i e s from ± (.4-.7)wt%, depending on the gas y i e l d . A further, systematic error i s also associated with l i q u i d y i e l d , as water, a compound not r e a d i l y separated from the r e a c t i o n products, i s included as part of the l i q u i d y i e l d . MAF Coal Conversion to Gases and L i q u i d s : L i q u i d y i e l d i s t y p i c a l l y the best i n d i c a t o r of the o v e r a l l s u i t a b i l i t y of a coal for d i r e c t coal l i q u e f a c t i o n , as coal l i q u i d s are, i n general, more valuable than the f u e l gases produced by l i q u e f a c t i o n r e a c t i o n s . In the present case, gas y i e l d i s l e s s than 5% of the t o t a l y i e l d and the discussion i s greatly s i m p l i f i e d i f t o t a l conversion i s used as a basis for comparison. A f t e r 15 minutes the t o t a l conversion of v i t r i n i t e enriched Byron Creek coal (27.5 wt%) i s much greater than the conversion of Byron Creek coal (18.34 wt%), whereas a f t e r 60 minutes the r e l a t i o n s h i p i s le s s TABLE 2: EXPERIMENTAL RESULTS Experiment 301 302 303 304 305 30 7 308 309 Operating Temp. (°C) 412 412 412 4 12 412 412 412 412 Conditions reaction time (min) 15 60 60 15 60 60 15 60 ca t a l y s t (g) 5.03 0.00 5.01 5 .03 5.04 5. 04 5.00 5.00 run type batch batch batch b atch batch i n j e c tion i n j e c t i o n i n j e c t i o n coal VBC VBC VBC BC BC VB C VBC BC Gas Production CH 2.74 8.32 9.65 3 .30 9.39 8. 09 3.73 9.86 ' (consumption) per Kg MAF coal CO 0.28 - 0.949 0.681 0. 582 0.305 1.13- C 2 H 6 1.17 5.13 6.91 1 .70 3.24 4. 60 1.83 4.32 c o 2 1.23 2.90 4.13 2 .70 1.71 1. 95 1.48 2.54 H 2 (8.21) (3.68) [14.13) (5 .67) 13.06) (10. 69) (5.63) (13.46) MAF Conversion gas 0.54 1.63 2.16 0 .77 1.50 1. 52 0.73 1.79 wt % l i q u i d 26.97 34.24 37.21 17 .57 41.33 37. 66 23.04 33.75 t o t a l 27.51 35.87 39.37 18 .34 42.83 39 .18 23.77 35.53 r O 266 s i g n i f i c a n t and reversed (42.8 wt% conversion for Byron Creek c o a l , and only 39.4 wt% conversion for v i t r i n i t e enriched Byron Creek c o a l ) . These r e s u l t s show that v i t r i n i t e reacts more quickly than i n e r t i n i t e but to a l e s s e r extent. The i n j e c t i o n experiments lead to the same conclusion. A f t e r 15 minutes of reaction, there i s a small d i f f e r e n c e between the l i q u e f a c t i o n r e s u l t s obtained from batch and i n j e c t i o n experiments f o r v i t r i n i t e enriched Byron Creek c o a l . This d i f f e r e n c e i s eliminated a f t e r 60 minutes of reaction, despite the a d d i t i o n a l 3 to 5 minutes of k i n e t i c a l l y active pre-heating time for the batch experiment. The unenriched Byron Creek c o a l , comprised p r i n c i p a l l y of the more slowly rea c t i n g maceral i n e r t i n i t e , had i n s u f f i c i e n t reaction time, even a f t e r 1 hr, to a t t a i n the same t o t a l conversion l e v e l as obtained from the batch experiment. A Semi-Empirical Reaction Model: In an e f f o r t to quantify the observed r e a c t i v i t y d i f f e r e n c e between the three macerals ( v i t r i n i t e , i n e r t i n i t e , l i p t l n i t e ) present In Byron Creek c o a l , a semi-empirical k i n e t i c model, equation 1, was devised and f i t t e d to the experimental conversion data. 3 . , To t a l MAF Conversion = J ( X ^ - X ^ exp [ X i ( t ± + t )] ) (1) = p o t e n t i a l l i q u e f i a b l e - unreacted by p o t e n t i a l l y material l i q u e f i a b l e material 267 t h e mass f r a c t i o n o f a m a c e r a l w h i c h c a n be l i q u e f i e d t h e MAF mass f r a c t i o n o f a m a c e r a l i n t h e c o a l t h e pseudo f i r s t o r d e r r a t e c o n s t a n t f o r t h e l i q u e f a c t i o n r e a c t i o n o f a m a c e r a l t = t h e measured r e a c t i o n t i m e t^" = t h e r e a c t i o n t i m e e q u i v a l e n t o f t h e k i n e t i c a l l y a c t i v e h e a t -up t i m e ( b a t c h r u n s o n l y ) The a s s u m p t i o n s i m p l i c i t i n t h i s model i n c l u d e : i ) o n l y a f r a c t i o n o f each m a c e r a l i s p o t e n t i a l l y l i q u e f i a b l e . i i ) each m a c e r a l r e a c t s s e p a r a t e l y a c c o r d i n g t o a f i r s t o r d e r i r r e v e r s i b l e r e a c t i o n t o p r o d u c e gaseous and l i q u i d p r o d u c t s . i i i ) mass t r a n s f e r o r o t h e r e f f e c t s do n o t i n t e r f e r e w i t h r e a c t i o n k i n e t i c s . The f i r s t a s s u m p t i o n i s e n c o u n t e r e d f r e q u e n t l y i n t h e l i t e r a t u r e . However, t h e second two g r o s s l y o v e r s i m p l i f y t h e complex r e a c t i o n k i n e t i c s o f d i r e c t c o a l l i q u e f a c t i o n . D e s p i t e t h e s i m p l i c i t y o f t h e model, t h e mean d e v i a t i o n between t h e p r e d i c t e d and r e a l i z e d c o n v e r s i o n s i s l e s s t h a n 8%, and much o f t h i s d e v i a t i o n can be t r a c e d t o t h e u n c e r t a i n l y a s s o c i a t e d w i t h t h e p e t r o g r a p h i c a n a l y s i s . The model i s i m p e r f e c t but i t c a n s t i l l be u s e d t o a d d r e s s t h e q u e s t i o n s r a i s e d d u r i n g t h i s s t u d y . The optimum v a l u e s o f t h e model p a r a m e t e r s , T a b l e 3, a r e s e n s i t i v e t o p e t r o g r a p h i c c o m p o s i t i o n . Thus, t h e k i n e t i c d a t a p r e s e n t e d can o n l y p r o v i d e o r d e r o f magnitude e s t i m a t e s f o r m a c e r a l r e a c t i v i t i e s . The model r e s u l t s c o n f o r m t o t h e c o n c l u s i o n s o f t h e more q u a l i t a t i v e d i s c u s - ; s i o n f o u n d i n t h e p r e v i o u s s e c t i o n . V i t r i n i t e r e a c t s 14 t i m e s more where X. = l M. = l 268 TABLE 3: OPTIMIZED KINETIC MODEL PARAMETERS MACERAL VITRINITE INERTINITE L I P T I N I T E Mass F r a c t i o n w h i c h can p o t e n t i a l l y be l i q u e f i e d ( X j 0.506 1.00 0.202 Pseudo f i r s t o r d e r r a t e c o n s t a n t (X^, m i n " ) 0.0674 0.00487 0.00414 R e a c t i o n t i m e e q u i v a l e n t o f t h e hea t - u p t i m e | o r b a t c h r u n s ( t , min) 3.96 r a p i d l y than i n e r t i n i t e , according to the model, but only h a l f of the v i t r i n i t e i s p o t e n t i a l l y l i q u e f i a b l e , whereas most of the i n e r t i n i t e p o t e n t i a l l y l i q u e f i a b l e . L i p t i n i t e reacts at about the same r a t e as i n e r t i n i t e but very l i t t l e of i t appears to be l i q u e f i a b l e . 270 CONCLUSIONS: 1. The v i t r i n i t e p r e s e n t i n B y r o n C r e e k c o a l i s o n l y about 50% l i q u i f i a b l e b u t t h e r e a c t i v e f r a c t i o n r e a c t s about 14 t i m e s as f a s t as i n e r t i n i t e i n t h e same c o a l . 2. The i n e r t i n i t e i n B y r o n C r e e k c o a l a p p e a r s t o be c o m p l e t e l y l i q u i f i a b l e , b u t r e a c t s v e r y much more s l o w l y . 3. R e s u l t s f o r l i p t i n i t e w o u l d i n d i c a t e t h a t i t i s q u i t e u n r e a c t i v e . However, t h e r e i s t o p l i t t l e l i p t i n i t e i n t h e c o a l t o o b t a i n r e l i a b l e r e s u l t s .

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