Kinetics of Coal Fly Ash Chlorination by Phosgene Douglas John Adelman Iowa State University
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Iowa State University Capstones, Theses and Retrospective Theses and Dissertations Dissertations 1984 Kinetics of coal fly ash chlorination by phosgene Douglas John Adelman Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/rtd Part of the Chemical Engineering Commons Recommended Citation Adelman, Douglas John, "Kinetics of coal fly ash chlorination by phosgene " (1984). Retrospective Theses and Dissertations. 8971. https://lib.dr.iastate.edu/rtd/8971 This Dissertation is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. It has been accepted for inclusion in Retrospective Theses and Dissertations by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. INFORMATION TO USERS This reproduction was made from a copy of a document sent to us for microfilming. 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Zeeb Road Ann Arbor, Ml 48106 8423616 Adelman, Douglas John KINETICS OF COAL FLY ASH CHLORINATION BY PHOSGENE Iowa State University PH.D. University Microfilms Intcrnstioriâ! 300 N.Zeeb Road, Ann Arbor, Ml 48106 PLEASE NOTE: In all cases this material has been filmed in the best possible way from the available copy. Problems encountered vwth this document have been identified here with a check mark V . 1. Glossy photographs or pages ^ 2. Colored illustrations, paper or print 3. Photographs with dark background 4. Illustrations are poor copy 5. Pages with black marks, not original copy 6. Print shows through as there is text on both sides of page 7. Indistinct, broken or small print on several pages / 8. Print exceeds margin requirements 9. Tightly bound copy with print lost in spine 10. Computer printout pages with indistinct print 11. Page(s) lacking v/hen material received, and not available from school or author. 12. Page(s) seem to be missing in numbering only as text follows. 13. Two pages numbered . Text follows. 14. Curling and wrinkled pages 15. Other University Microfilms International Kinetics of coal fly ash chlorination by phosgene by Douglas John Âdelman A Dissertation Submitted to the Graduate Faculty in Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY Major: Chemical Engineering Approved: Signature was redacted for privacy. In Charge of Major Work Signature was redacted for privacy. For the Magor Department Signature was redacted for privacy. For tlfe ^ast/ate College Iowa State University Ames, Iowa 1984 ii 'lABLE OF CONTENTS Page SYMBOLS viii INTRODUCTION 1 LITERATURE REVIEW 3 Chlorination Studies 3 Carbon and chlorine sources 4 Phosgene concentration, temperature, and total pressure 9 Fly ash form 9 Additives 9 Silicon tetrachloride recycle 10 Gas-Solid Reaction Kinetics 11 REACTION MODEL 15 Implications of Fly Ash Physical and Chemical Properties 15 Assumptions 22 Phosgene and Fly Ash Mass Balances 23 Effective Diffusion Coefficient Determination 27 Chemisorption Considerations 29 EXPERIMENTAL WORK 33 Data Sets Collected and Their Purpose 33 Equipment 34 Electrobalance flow system 35 Electrobalance closed system 41 Diffusion cell system 42 Gas chromatograph 45 Other systems 45 ill Experimental Procedures and Data Analysis 46 Initial reaction rates 46 Kinetic parameter determination 47 Effective diffusion coefficient 52 B.E.T. surface area 53 Chemisorption 56 RESULTS AND DISCUSSION 58 Fly Ash Characteristics 58 Phosgene Rate Dependence 60 Stoichiometric Coefficient 61 Phosgene Dissociation 63 Activation Energy and Frequency Factor 70 Powder and pellet initial rate data 70 Pellet integral data 7 1 Kinetic Parameter Comparison 73 Fly Ash Reaction Model 74 Tortuosity and Reaction Modulus Results 76 B.E.T. Surface Areas 78 Chemisorption Results 83 X-ray Diffraction Results 85 Knudsen-Cell Mass Spectrometer Results 87 FLY ASH CHLORINATION REACTOR DESIGN 89 Assumptions 89 iv Reactor Design Model 94 Fly ash reaction 95 Phosgene reaction and dissociation 96 Phosgene input requirements 99 Bed and pellet porosities 101 Heat flux 102 Reactor pressure 103 Design program summary 105 Reactor Design Results 107 Preliminary reactor design 107 Alternate reactor design 114 CONCLUSIONS 116 Fly Ash-Phosgene Kinetic Study 116 Reactor Design 117 RECOMMENDAnONS 118 BIBLIOGRAPHY 120 ACKNOWLEDGMENTS 126 APPENDIX A: SOFTWARE 127 B.E.T. Surface Area 127 Experimental Reactor Design 129 Fly Ash Reaction Model 131 Chlorlnation Reactor Design 13 2 APPENDIX B: REACTION MODULUS DETERMINATION 139 V LIST OF FIGURES Page Figure 1. Scanning electron microscope pictures of fly ash powder chlorinated by phosgene at 625 °C to conversions of: A - 0..0, B - 0.05, C - 0.20 and D - 0.30. Magnification = lOOOX (1 cm = 10 microns) 17 Figure 2. Scanning electron microscope pictures of fly ash powder chlorinated by phosgene at 625 °C to conversions of: A - 0.0, B - 0.05, C - 0.20, and D - 0.30. Magnification = 5000X (1 cm = 2 microns) 19 Figure 3. Gravimetric system used in gas-solid reaction experiments. 36 Figure 4. Alternate flow reactor, closed tube, and pellet and powder sample supports 38 Figure 5. Steady-state diffusion cell and gas-sampling loop system 43 Figure 6. Full-scale top and sectioned views of diffusion cell 44 Figure 7. Fly ash powder conversion rates as a function of phosgene partial pressure 61 Figure 8. Metal oxide conversions versus fly ash conversion for fly ash pellets reacted with phosgene 62 Figure 9. Arrhenius plot resulting from integral fly ash reaction data uncorrected for phosgene dissociation 65 Figure 10. Arrhenius plot resulting from fly ash powder initial conversion rate data 69 Figure 11. Arrhenius plot resulting from fly ash pellet initial conversion rate data 71 Figure 12. Fly ash conversion versus time data plotted according to the shrinking-core model 7 2 vi Figure 13. Arrhenius plot resulting from extended fly ash chlorination data corrected for phosgene dissociation 74 Figure 14. Arrhenius plot of powder and pellet initial conversion rate data and pellet extended conversion data 7 5 Figure 15. Comparison of reaction model predictions to experimental fly ash conversion-time data at the specified conditions 76 Figure 16. Comparison of reaction model predictions to experimental fly ash conversion-time data at the specified conditions 77 Figure 17. Nitrogen adsorption isotherm data plotted according to the B.E.T. equation 79 Figure 18. Comparison of measured to predicted fly ash pellet surface areas 80 Figure 19. Specific weight of phosgene chemisorbed as a function of fly ash conversion 84 Figure 20. Comparison of x-ray diffraction spectra as a function of fly ash conversion 86 Figure 21. Reactor pressure as a function of the bed height 109 Figure 22. Fraction of phosgene dissociated as a function of bed height 110 Figure 23. Phosgene conversion (dissociation and reaction) and fly ash conversion versus bed height 111 Figure 24. Reactor heat flux as a function of bed height 112 vil LIST OF TABLES Page Table 1. As received and leached compositions of Texas lignite fly ash 59 Table 2. Leached Texas lignite fly ash physical properties 60 Table 3. Equilibrium phosgene partial pressures calculated at the temperatures indicated and a total phosgene partial pressure of 0.96 atm 66 Table 4. Inlet and outlet phosgene partial pressures as a function of temperature and total reaction gas flow rate. Helium was used as the diluent 67 Table 5. Specific surface area as a function of conversion predicted by assuming fly ash reacts as shrinking, hard spheres 8 2 Table 6. Results of fly ash reactor design calculations 108 Table 7. Estimated initial values for the effective molecular, Knudsen, and overall diffusion coefficients as a function of temperature 142 Table 8. Initial rate constant and reaction modulus values calculated for the reaction of 0.1 cm thick fly ash pellets 142 viii SYMBOLS fly ash Inert phase specific surface area, m 2-1g o 2 area per nitrogen moleculc, 16.2 Â Initial fly ash specific surface area, m 2g -1 area of sample, cm 2 stoichiometric coefficient, g^^y (Gcocig)"^ derivative of alumina versus fly ash conversion expression B.E.T.