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Hydrogen production in palladium and palladium-copper membrane reactors at 1173K in the presence of hydrogen sulfide

Dissertation
Author: Osemwengie Uyi Iyoha
Abstract:
The efficacy of producing high-purity H2 from coal-derived syngas via the high-temperature water-gas shift reaction (WGSR) in catalyst-free Pd and 80wt%Pd-Cu membrane reactors (MRs) was evaluated in the absence and presence of H2 S. The impetus for this study stems from the fact that successfully integrating water-gas shift MRs to the coal gasifier process has the potential of increasing the efficiency of the coal-to-H2 process, thereby significantly reducing the cost of H2 production from coal. To this end, the effect of the WGSR environment on 80wt%Pd-Cu MRs was studied over a wide range of temperatures. Results indicate minimal impact of the WGSR environment on the 80wt%Pd-Cu membrane at 1173K. Subsequently, using pure reactant gases (CO and steam), the rapid rate of H 2 extraction from the reaction zone, coupled with the moderate catalytic activity of the Pd-based walls was shown to enhance the CO conversion beyond the equilibrium value of 54% at 1173K, in the absence of additional heterogeneous catalysts in both Pd and 80wt%Pd-Cu MRs. The effect of H2 S contamination in the coal-derived syngas on Pd and 80wt%Pd-Cu membranes at 1173K was also studied. Results indicate that the sulfidization of Pd-based membranes is strongly dependent on the H2 S-to-H2 ratio and not merely the inlet H2 S concentration. The Pd and 80wt%Pd-Cu MRs were shown to maintain their structural integrity at 1173K in the presence of H2 S-to-H2 ratios below 0.0011 (∼1,000 ppm H2 S-in-H2 ). A COMSOL Multiphysics model developed to analyze and predict performance of the water-gas shift MRs in the presence of H2 S indicated that the MRs could be operated with low H2 S concentrations. Finally, the feasibility of high-purity H2 generation from coal-derived syngas was investigated using simulated syngas feed containing 53%CO, 35%H 2 and 12%CO2 . The effect of H2 S contamination on MR performance was investigated by introducing varying concentrations of H2 S to the syngas mixture. When the H2 S-to-H2 ratio in the MR was maintained below 0.0011 (∼1,000 ppm H2 S-in-H 2 ), the MR was observed to maintain its structural integrity and H 2 selectivity, however, a precipitous reduction in CO conversion was observed. Increasing H2 S concentrations such that the H2 S-in-H 2 ratio increased above about 0.0014 resulted in MR failure within minutes.

TABLE OF CONTENTS

1.0 CHAPTER ONE: INTRODUCTION.....................................................................1 1.1 WATER-GAS SHIFT REACTION....................................................................3 1.2 MEMBRANE REACTORS................................................................................4 1.2.1 Pd-based Membranes..................................................................................4 1.2.2 Water-gas Shift Membrane Reactors..........................................................6 1.3 ADVANTAGES OF MEMBRANE REACTOR INTEGRATION TO THE COAL GASIFICATION PROCESS..............................................................................8 1.4 PROJECT OBJECTIVES...................................................................................9 2.0 CHAPTER TWO: THE EFFECTS OF H 2 O, CO AND CO 2 ON THE H 2

PERMEANCE AND SURFACE CHARACTERISTICS OF 1 MM THICK PD 80WT% CU MEMBRANES.................................................................................................................12 2.1 INTRODUCTION............................................................................................13 2.2 EXPERIMENTAL............................................................................................16 2.2.1 Permeance Apparatus................................................................................16 2.2.2 SEM Analysis...........................................................................................19 2.2.3 Determination of Permeance.....................................................................19 2.3 RESULTS AND DISCUSSION.......................................................................20 2.3.1 Determination of Hydrogen Permeance....................................................20

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2.3.2 Effect of H 2 O on H 2 -Permeance and Surface Morphology......................22 2.3.2.1 Effect of H 2 O on H 2 -Permeance...........................................................22 2.3.2.2 Effect of H 2 O on the Pd 80wt% Cu Surface Morphology..........................25 2.3.3 Effect of CO on H 2 -Permeance and Surface Morphology........................28 2.3.3.1 Effect of CO on H 2 -Permeance.............................................................28 2.3.3.2 Effect of CO on Pd 80wt% Cu Surface Morphology.................................30 2.3.4 Effect of CO 2 on H 2 -Permeance and Surface Morphology.......................35 2.3.4.1 Effect of CO 2 on H 2 -Permeance:...................................................................35 2.3.4.2 Effect of CO 2 on Pd 80wt% Cu Surface Morphology........................................39 2.4 CONCLUSIONS...............................................................................................41 3.0 CHAPTER THREE: WALL-CATALYZED WATER-GAS SHIFT REACTION IN MULTI-TUBULAR, Pd AND 80WT%Pd-20WT%Cu MEMBRANE REACTORS AT 1173K.........................................................................................................................43 3.1 INTRODUCTION............................................................................................44 3.2 EXPERIMENTAL............................................................................................50 3.2.1 Experimental Apparatus............................................................................50 3.2.2 Non-membrane Reactors for Control Experiments..................................53 3.2.3 Membrane Reactors..................................................................................54 3.2.4 SEM-EDS Analysis..................................................................................56 3.3 RESULTS AND DISCUSSION.......................................................................57 3.3.1 Control Experiments.................................................................................57 3.3.2 Membrane Reactor Studies.......................................................................57

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3.3.3 SEM-EDS Analyses of Pd-based Membrane Reactors............................61 3.4 CONCLUSIONS...............................................................................................67 4.0 CHAPTER FOUR: THE INFLUENCE OF H 2 S-TO-H 2 PARTIAL PRESSURE RATIO ON THE SULFIDIZATION OF Pd AND 80WT%Pd-Cu MEMBRANES.......69 4.1 INTRODUCTION............................................................................................70 4.2 EXPERIMENTAL............................................................................................81 4.2.1 Effect of H 2 S-to-H 2 Ratio on Sulfidization of Pd and Pd-Cu Membranes 81 4.2.2 SEM-EDS Analysis..................................................................................83 4.3 RESULTS AND DISCUSSION.......................................................................84 4.3.1 Interaction of Pd and Cu With H 2 S...........................................................84 4.3.2 Equilibrium H 2 -to-H 2 S Ratio for Sulfidization of Pd and Cu...................86 4.3.3 Correlation of Literature Results..............................................................90 4.3.4 Current Experimental Results.................................................................101 4.4 CONCLUSION...............................................................................................113 5.0 CHAPTER FIVE: COMSOL MULTIPHYSICS MODELING OF A Pd MEMBRANE REACTOR FOR THE WATER-GAS SHIFT REACTION IN THE PRESENCE OF H 2 S.......................................................................................................115 5.1 INTRODUCTION..........................................................................................116 5.2 MEMBRANE REACTOR AND COMSOL MODEL...................................120 5.2.1 COMSOL Membrane Reactor Model Development..............................121 5.2.1.1 Model Assumptions............................................................................122 5.2.1.2 Governing Equations..........................................................................123

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5.3 SIMULATION RESULTS.............................................................................128 5.3.1 Model Validation Results.......................................................................128 5.3.1.1 WGSR in Pd Membrane Reactor Using CO and Steam.....................128 5.3.1.2 WGSR in Pd Membrane Reactor Using Syngas and Steam...............132 5.3.2 Effect of Increased Catalytic Activity and H 2 Permeance on Membrane Reactor Performance...............................................................................................135 5.3.3 Predicting the Sulfidization of Pd MR for WGSR Using Syngas Containing H 2 S.......................................................................................................137 5.3.3.1 Effect of CO Conversion and H 2 Recovery in Pd MR on H 2 S-to-H 2

Ratio .............................................................................................................138 5.3.3.2 Effect of Deactivation of Catalytic Pd walls on CO Conversion and H 2 S-to-H 2 Ratio..................................................................................................141 5.4 CONCLUSION...............................................................................................143 6.0 CHAPTER SIX: H 2 PRODUCTION FROM SIMULATED COAL SYNGAS CONTAINING H 2 S IN MULTI-TUBULAR, Pd AND 80WT%Pd-20WT%Cu MEMBRANE REACTORS AT 1173K.........................................................................146 6.1 INTRODUCTION..........................................................................................147 6.2 EXPERIMENTAL..........................................................................................151 6.2.1 WGS reaction in Multi-tube Pd and Pd-Cu Membrane Reactors...........151 6.2.2 SEM-EDS Analysis................................................................................155 6.3 RESULTS AND DISCUSSION.....................................................................155 6.3.1 H 2 Permeance..........................................................................................155 6.3.2 Four-tube Pd and Pd-Cu MR Testing Using Simulated, H 2 S-free, Syngas Feed .................................................................................................................157

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6.3.3.1 WGSMR in Pd MR Using Simulated, H 2 S-free, Syngas Feed...........158 6.3.3.2 WGSMR in Pd 80wt% Cu MRs Using Simulated, H 2 S-free, Syngas Feed... .............................................................................................................161 6.3.3.3 SEM-EDS Analysis of Pd MR............................................................164 6.3.3.4 SEM-EDS Analysis of Pd 80wt% Cu MR...............................................165 6.3.3 Four-tube Pd and Pd 80wt% Cu MR Using Simulated Syngas Feed Containing H 2 S.......................................................................................................167 6.3.3.1 WGSR in Pd MR Using Simulated Syngas Feed Containing H 2 S.....167 6.3.3.2 WGS in Pd 80wt% Cu MR Using Simulated Syngas Feed Containing H 2 S. .............................................................................................................170 6.3.3.3 SEM-EDS Analyses of Pd MRs After H 2 S-containing Syngas Exposure .............................................................................................................174 6.3.3.4 SEM-EDS Analyses of Pd 80wt% Cu MRs After H 2 S-containing Syngas Exposure .............................................................................................................179 6.4 CONCLUSION...............................................................................................183 7.0 CHAPTER SEVEN: SUMMARY & RECOMMENDATIONS........................186 7.1 INTRODUCTION..........................................................................................186 7.2 SUMMARY OF MEMBRANE REACTOR PROJECT................................186 7.3 RECOMMENDATIONS................................................................................189 Appendix A .................................................................................................................... 191

Appendix B .................................................................................................................... 205

BIBLIOGRAPHY........................................................................................................... 207

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LIST OF TABLES

Table 1. H 2 -permeance values obtained for the Pd 80wt% Cu membrane in the presence of the 90%H 2 -He and 50%H 2 -H 2 O feed streams..............................................................24 Table 2: Summary of membrane-assisted WGSRs, also known as water-gas shift membrane reactors, WGSMR.......................................................................................46 Table 3. Summary of published literature results involving the effect of H 2 S exposure to Pd-based membranes....................................................................................................75 Table 4. Comparison of predicted minimum H 2 S-in-H 2 required for stable Pd 4 S formation at various experimental temperatures with published experimental results.................91 Table 5. Summary of current investigation comparing experimental results to predicted outcome of the respective 125 µm Pd and Pd 80wt% Cu membranes exposed to various H 2 S-to-H 2 ratios at 1173K for 30 minutes..................................................................112 Table 6. Stoichiometric coefficient for components in WGSR......................................125 Table 7: Parameters used in the simulation....................................................................127 Table 8: Inlet mass fraction composition used in the simulations..................................127 Table 9: Retentate pressures used in the simulations......................................................128

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LIST OF FIGURES

Figure 1. Principle of WGSMR. H 2 is continuously extracted from the tube-side reaction zone into the permeate-side, shifting the equilibrium to higher product CO 2 and H 2

formation.........................................................................................................................7 Figure 2. Schematic of Hydrogen Membrane Test unit (HMT unit)................................18 Figure 3. H 2 -permeance of a 1 mm Pd and a 1 mm Pd 80wt% Cu membrane obtained in the presence of a 90%H 2 -He feed.......................................................................................22 Figure 4. H 2 flux versus the difference between the square roots of H 2 partial pressures on the retentate- and permeate-sides as a function of temperature for a 90%H 2 -He (solid lines) and 50%H 2 -H 2 O (dashed lines) feed...................................................................23 Figure 5. Effect of 50%H 2 O concentration on the H 2 -permeance of 1 mm Pd 80wt% Cu at 0.62 and 1.55 MPa total unit pressure. k* is equal to the permeance (mol H 2 /(m 2 ·s·Pa 0.5 )) for the 50%H 2 -H 2 O feed mixture divided by permeance of the 90%H 2 - He feed mixture.............................................................................................................25 Figure 6. SEM micrographs of a (a) fresh Pd 80wt% Cu membrane polished with 1200 grit silicon carbide paper, (b) Pd 80wt% Cu membrane after H 2 exposure at 623–1173K and pressure of 0.62-2.17 MPa, (c & d) Pd 80wt% Cu membrane after exposure to 50%H 2 - H 2 O feed stream at 908K and total unit pressure of 1.55 MPa for 24hrs, (e & f) Pd 80wt% Cu membrane after exposure to 50%H 2 -H 2 O feed stream at 1173K and total unit pressure of 1.55 MPa for 24hrs..............................................................................28 Figure 7. Effect of 50%CO concentration on the H 2 permeance of 1 mm Pd 80wt% Cu at 0.62 and 1.55 MPa. k* is equal to the permeance (mol H 2 /(m 2 ·s·Pa 0.5 )) for the mixed feed stream (H 2 -CO) divided by permeance of the neat 90%H 2 -He feed mixture.......29 Figure 8. Raw H 2 permeance data for the Pd 80wt% Cu membrane at 908K with a 90%H 2 - He retentate feed (diamonds) and a 50%H 2 -CO retentate feed (open circles) stream at pressures of 0.62 and 1.55 MPa....................................................................................30 Figure 9. Photograph of the Pd 80wt% Cu membrane after exposure to CO. Conditions: 623 – 1173K, 0.62 and 1.55 MPa. Testing concluded after re-exposure of membrane to 50%H 2 -CO feed at 908K and 0.62 MPa.......................................................................31

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Figure 10. SEM micrographs of the feed-side surface of Pd 80wt% Cu membrane after exposure to 50%H 2 -CO feed at 908K showing deposited carbon on the surface. The membrane was exposed to feed stream for 24 hrs. The surface was also exposed to small amounts (<5% each) of CO 2 , H 2 O and CH 4 reaction products...........................33 Figure 11. SEM micrographs of the feed-side surface of the Pd 80wt% Cu membrane after exposure to 50%H 2 -CO feed at 1038K and 1.11 MPa. The membrane was exposed to the feed stream for 24hrs. CO 2 , CH 4 and steam were also present as a result of side reactions........................................................................................................................34 Figure 12. SEM micrographs of the feed-side surface of the Pd 80wt% Cu membrane after exposure to 50%H 2 -CO feed at 1173K and 1.11 MPa. The membrane was exposed to feed stream for 24hrs....................................................................................................35 Figure 13. Effect of 50%CO 2 concentration on the H 2 permeance of 1 mm Pd 80wt% Cu at 1.11 and 2.17 MPa. k* is equal to the permeance (mol H 2 /(m 2 ·s·Pa 0.5 )) for the mixed feed stream (H 2 - CO 2 ) divided by permeance of the neat 90%H 2 -He feed. Driving force for flux was based on the average H 2 retentate composition...............................37 Figure 14. Comparison of equilibrium rWGSR conversion versus observed experimental conversions at total reactor pressures of 1.11 and 2.17 MPa for various temperatures, for an equimolar CO 2 :H 2 inlet feed mixture.................................................................38 Figure 15. SEM micrographs of the feed-side surface of the Pd 80wt% Cu membrane after exposure to 50%H 2 -CO 2 stream at 908K. The membrane was exposed to 50%H 2 -CO 2

at 1.11 MPa for 6 hrs and then 2.17 MPa for another 6 hrs..........................................39 Figure 16. SEM micrographs of the feed-side surface of the Pd 80wt% Cu membrane after exposure to 50%H 2 -CO 2 stream at 1038K. The membrane was exposed to H 2 -CO 2 at 1.11 MPa for 6 hrs and then 2.17 MPa for another 6 hrs..............................................40 Figure 17. SEM micrographs of the feed-side surface of the Pd 80wt% Cu membrane after exposure to 50%H 2 -CO 2 stream at 1173K. The membrane was exposed to H 2 -CO 2 at 1.11 MPa for 12 hrs and then 2.17 MPa for another 8 hrs............................................40 Figure 18. Detail of the NETL four-tube Pd-based membrane reactor...........................56 Figure 19. CO conversion at 1173K for Steam-to-CO ratio of 1.5 in quartz-lined stainless-steel, stainless-steel, Pd and Pd 80wt% Cu reactors as a function of residence time. Equilibrium conversion at these conditions is ~54%...........................................59 Figure 20. CO conversion at 1173K and 2 s residence time for various steam-to-CO ratios in Pd and Pd 80wt% Cu four-tube reactors........................................................................59 Figure 21. High purity H 2 recovery as a function of residence time for Pd

and Pd 80wt% Cu four-tube reactors at 1173K and H 2 O:CO ratio of 1.5..................................................61

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Figure 22. SEM image of the inner (retentate) surface of the as-received Pd tube showing grooves on the membrane surface.................................................................................63 Figure 23. SEM image of the inner (retentate) surface of the as-received Pd 80wt% Cu tube showing surface contamination (black patches) and dimples on membrane surface...64 Figure 24. EDS spectrum of fresh Pd 80wt% Cu surface showing metal shaving on membrane surface (Fe) in addition to Al and Si contamination in membrane sample.64 Figure 25. SEM images of the outer (permeate) surface of Pd

MR after 10 days of WGSR at 1173K........................................................................................................................65 Figure 26. SEM image of inner (retentate) surface of Pd

MR after 10 days of WGSR at 1173K depicting holes on membrane surface...............................................................65 Figure 27. SEM image of inner (retentate) surface of Pd 80wt% Cu

MR after 10 days of WGSR testing at 1173K................................................................................................66 Figure 28. EDS spectrum of grain boundary location of Pd 80wt% Cu sample above revealing Al contamination within the grain boundary................................................66 Figure 29. Schematic of mini tubular membrane assembly used for H 2 S-H 2 experiments. .......................................................................................................................................83 Figure 30. Ratio of H 2 S-to-H 2 for Pd 4 S (Taylor 1985) formation as a function of T (K) for pure Pd (solid line) and Pd 80 Cu (dashed line – generated by assuming a Pd = X Pd

(0.7)). Activity of Pd in Pd 80 Cu alloy at 883K (triangle) and 1000K (circle) obtained from experimental values from Myles et al. (Myles et al. 1968)..................................87 Figure 31. (a) Ratio of H 2 S-to-H 2 for Cu 2 S formation for pure Cu (solid line- thermodynamic values from Barin (Barin 1993)) and Pd 80 Cu (dashed line – generated by assuming a Cu = X Cu (0.3)). Experimental values for the activity of Cu in Pd-Cu alloy of 0.05 and 0.1 at 883K (diamond) and 1000K (circle), respectively, were obtained from Myles et al. (Myles et al. 1968)............................................................................88 Figure 32. Comparison of H 2 S-to-H 2 equilibrium ratio predicted from data from Taylor et al. (solid line) to literature results involving pure Pd membranes exposed to various H 2 S-to-H 2 pressure ratios at various temperatures indicating sulfidization (hollow shapes). Squares indicate results form current experimental results discussed in the subsequent section involving Pd membranes at 1173K, showing conditions of sulfidization (hollow square) and condition of no sulfidization (filled square)..........100 Figure 33. SEM image of inner surface of Pd membrane exposed to 0.005 H 2 S-to-H 2 ratio (5,000 ppm H 2 S-in-H 2 ) for 30 mins at 1173K............................................................101 Figure 34. EDS spectrum of rectangular region pf Pd membrane above exposed to 0.005 H 2 S-to-H 2 ratio (5,000 ppm H 2 S-in-H 2 ) for 30 mins at 1173K indicating Pd sulfide formation.....................................................................................................................102

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Figure 35. SEM image of inner surface of Pd 80wt% Cu membrane exposed to 0.005 H 2 S-to- H 2 ratio (5,000 ppm H 2 S-in-H 2 )for 30 mins at 1173K................................................103 Figure 36. EDS spectrum of position 1 on surface of the Pd 80wt% Cu membrane exposed to 0.005 H 2 S-to-H 2 ratio (5,000 ppm H 2 S-in-H 2 ) for 30 minutes as 1173K indicating negligible sulfide formation on this region of the sample..........................................103 Figure 37. EDS spectrum of position 2 on the Pd 80wt% Cu membrane exposed to 0.005 H 2 S-to-H 2 ratio (5,000 ppm H 2 S-in-H 2 ) for 30 minutes as 1173K indicating sulfide growth on the sample..................................................................................................104 Figure 38. SEM image of inner surface of Pd membrane exposed to 0.002 H 2 S-to-H 2 ratio (2,000 ppm H 2 S-in-H 2 ) for 30 mins at 1173K............................................................105 Figure 39. EDS spectrum of surface of Pd membrane exposed to 0.002 H 2 S-to-H 2 ratio (2,000 ppm H 2 S-in-H 2 ) for 30mins at 1173K depicting sulfide formation.................105 Figure 40. High magnification SEM image of inner surface of Pd membrane exposed to 0.002 H 2 S-to-H 2 ratio (2,000 ppm H 2 S-in-H 2 ) for 30 minutes at 1173K showing regions of sulfidized and unsulfidized Pd...................................................................106 Figure 41. EDS spectrum of surface of Pd membrane (labeled 1) exposed to 0.002 H 2 S- to-H 2 ratio (2,000 ppm H 2 S-in-H 2 ) for 30mins at 1173K depicting negligible sulfide region..........................................................................................................................106 Figure 42. EDS spectrum of surface of Pd membrane (labeled 2) exposed to 0.002 H 2 S- to-H 2 ratio (2,000 ppm H 2 S-in-H 2 ) for 30mins at 1173K depicting sulfidized Pd.....107 Figure 43. SEM image of inner surface of the Pd 80wt% Cu membrane exposed to 0.002 H 2 S-to-H 2 ratio (2,000 ppm H 2 S-in-H 2 ) for 30 mins at 1173K showing islands of Pd- Cu (grayish regions) and Cu-S (dark regions)............................................................108 Figure 44. EDS spectrum of position 1 on surface of the Pd 80wt% Cu membrane exposed to 0.002 H 2 S-to-H 2 ratio (2,000 ppm H 2 S-in-H 2 ) for 30 mins at 1173K indicating negligible sulfide formation on this region of the sample..........................................108 Figure 45.EDS spectrum of position 2 on surface of the Pd 80wt% Cu membrane exposed to 0.002 H 2 S-to-H 2 ratio (2,000 ppm H 2 S-in-H 2 ) for 30 mins at 1173K showing copper sulfide formation.........................................................................................................109 Figure 46. SEM image of inner surface of Pd membrane exposed to 0.0011 H 2 S-to-H 2

ratio (1,100 ppm H 2 S-in-H 2 ) for 30 mins at 1173K showing a smooth membrane surface.........................................................................................................................110 Figure 47. EDS spectrum of surface of the Pd membrane exposed to 0.0011 H 2 S-to-H 2

ratio (1,100 ppm H 2 S-in-H 2 ) for 30 mins at 1173K showing no detectable sulfide formation.....................................................................................................................110

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Figure 48.SEM image of inner surface of the Pd 80wt% Cu membrane exposed to 0.0011 H 2 S-to-H 2 ratio (1,100 ppm H 2 S-in-H 2 ) for 30 mins at 1173K showing a smooth membrane surface.......................................................................................................111 Figure 49. EDS spectrum of surface of the Pd 80wt% Cu u membrane exposed to 0.0011 H 2 S-to-H 2 ratio (1,100 ppm H 2 S-in-H 2 ) for 30 mins at 1173K showing no detectable sulfide formation.........................................................................................................111 Figure 50. Geometry of membrane reactor depicting modeled domain.........................122 Figure 51. Comparison of experimental (Chapter 3) and current simulation results for CO conversion in the Pd MR at 1173K as a function of residence time (Case 1). Equilibrium CO conversion at these conditions ≈ 54%..............................................130 Figure 52. CO, H 2 O, CO 2 and H 2 axial concentration profiles in the Pd MR for residence times (based on inlet gas flow rate) of 0.82 (a), 1.81 (b), 3.01 (c) and 4.96s (d) corresponding to CO conversions of 53.7, 75.3, 84.9 and 93.2%, respectively (Case 1). The experimental measurements of the effluent concentrations of the various components at the exit of the reactor are also plotted for comparison.......................131 Figure 53. Normalized gas superficial velocity profile as a function of reactor length for residence times (based on inlet gas flow rate) of 0.82, 1.81, 3.01 and 4.96s (Case 1). .....................................................................................................................................131 Figure 54. Comparison of experimental and current simulation results for CO conversion in the Pd MR at 1173K for 0.7, 1.2 and 2s residence time (based on inlet gas flow rate) using simulated syngas feed (29.5%CO, 19.5%H 2 , 6.7%CO 2 and 44.3%H 2 O). Membrane apparent permeance value = 4.4*10 -5 mols/(m 2 ·s·Pa 0.5 ) (Case 2). Equilibrium CO conversion at these conditions ≈ 32%..............................................133 Figure 55. CO, H 2 O, CO 2 and H 2 concentration profiles in the Pd MR for residence times (based on inlet gas flow rate) of 0.7 (a), 1.2 (b), and 2s (c) corresponding to CO conversions of 56.1, 82.3 and 99.1%, respectively (Case 2). The experimental measurements of the effluent concentrations of the various components at the exit of the reactor are also plotted for comparison.................................................................134 Figure 56. Normalized superficial velocity as a function of MR length for residence times (based on inlet gas flow rate) of 0.7, 1.2 and 2.0s corresponding to CO conversions of 56.1, 82.3 and 99.1%, respectively (Case 2)...............................................................135 Figure 57. Effect of increasing apparent H 2 permeance on CO conversion via the WGSR in Pd MR at 1173K using a correction factor of 50. Equilibrium CO conversion at these conditions ≈ 54%...............................................................................................136 Figure 58. Effect of increasing membrane catalytic activity on CO conversion via the WGSR in Pd MR at 1173K, maintaining the membrane apparent H 2 permeance of 1.5*10 -5 mols/(m 2 ·s·Pa 0.5 ) constant. Equilibrium CO conversion at these conditions ≈ 54%.............................................................................................................................137

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Figure 59. H 2 S concentration profile in Pd MR as a function of reactor length for residence times of 0.7, 1.2 and 2.0s, corresponding to CO conversions of 56.1, 82.3 and 99.1% using syngas containing 10 ppm H 2 S.......................................................140 Figure 60. H 2 S-to-H 2 ratio in Pd MR as a function of reactor length for residence times of 0.7, 1.2 and 2.0s, corresponding to CO conversions of 56.1, 82.3 and 99.1% using syngas containing 10 ppm H 2 S. Dashed line represents H 2 S-to-H 2 ratio for sulfidization of Pd at 1173K............................................................................................................140 Figure 61. Effect of H 2 S catalytic poisoning of Pd MR on CO conversion (a), H 2 S concentration profile (b), H 2 concentration profile (c) and H 2 S-to-H 2 ratio (d) for syngas containing 10 ppm H 2 S at 1173K and 0.7s residence time. Correction factor reduced from 50 to 25 and then to 10 to simulate 50% and 80% reduction in catalytic activity of Pd, respectively. Dashed line (d) represents H 2 S-to-H 2 ratio for sulfidization of Pd at 1173K............................................................................................................143 Figure 62. Detail of the NETL four-tube Pd-based membrane reactor.........................154 Figure 63. H 2 permeance of Pd (a) and Pd 80wt% Cu (b) MRs in 90%H 2 -He and 90%H 2 - 1,000 ppm H 2 S-He atmospheres at 1173K.................................................................157 Figure 64. Real-time concentration (CO, CO 2 and H 2 ) trend in the four-tube Pd MR at 1173K for 0.7s, 1.2s and 2s residence times using simulated syngas feed (53%CO, 35%H 2 and 12%CO 2 ) and steam-to-CO ratio of 1.5. MR exposed to syngas environment for ~60 hours..........................................................................................160 Figure 65. Real-time CO conversion and H 2 recovery trend in the four-tube Pd MR at 1173K for residence times of 0.7s, 1.2s and 2s using simulated syngas (53%CO, 35%H 2 and 12%CO 2 ) feed and steam-to-CO ratio of 1.5. Equilibrium CO conversion at this condition ≈ 32%. MR exposed to syngas environment for ~60 hours, and developed pinholes after about 3 days at 1173K........................................................161 Figure 66. Real-time concentration (CO, CO 2 and H 2 ) trend in the four-tube Pd 80wt% Cu MR at 1173K for 0.96, 2 and 2.8s residence times using simulated syngas feed (53%CO, 35%H 2 and 12%CO 2 ) and steam-to-CO ratio of 1.5. MR operated for about 6 days without failure.....................................................................................................163 Figure 67. Real-time CO conversion and H 2 recovery trend in the four-tube Pd 80wt% Cu MR at 1173K for residence times of 0.96, 2 and 2.8s using simulated syngas (53%CO, 35%H 2 and 12%CO 2 ) feed and steam-to-CO ratio of 1.5. Equilibrium CO conversion at this condition ≈ 32%. The Pd 80wt% Cu MR was successfully operated for about 6 days without failure.............................................................................................................164 Figure 68. SEM (a) and EDS (b) images of inner (retentate) surface of Pd

MR after 3 days of WGSR with H 2 S-free syngas feed at 1173K depicting large grains and moderate pitting on membrane surface.......................................................................165

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Figure 69. SEM (a) and EDS (b) images of inner (retentate) surface of Pd 80wt% Cu

MR after 6 days of WGSR with H 2 S-free syngas feed at 1173K depicting relatively smooth membrane surface.......................................................................................................166 Figure 70. Real-time CO conversion and H 2 recovery trend in the four-tube Pd MR at 1173K for residence times of 0.4s before and after reaction testing with 30 ppm H 2 S- syngas. Membrane failed within minutes of exposure to 50 ppm H 2 S that began at 68hrs............................................................................................................................169 Figure 71. Real-time concentration (CO, CO 2 and H 2 ) trend for the four-tube Pd MR at 1173K and 0.4s residence time before and after reaction testing with 30 ppm H 2 S- syngas. Membrane failed within minutes of exposure to 50 ppm H 2 S that began at 68hrs............................................................................................................................170 Figure 72. Real-time CO conversion trend and H 2 recovery in the four-tube Pd 80wt% Cu MR at 1173K and residence time of 2s before and after 40 and 60 ppm H 2 S-syngas reaction testing. Membrane failed after exposure to 90 ppm H 2 S..............................173 Figure 73. Real-time concentration (CO, CO 2 and H 2 ) trend for the four-tube Pd 80wt% Cu MR at 1173K and 2s residence time before and after 40 and 60 ppm H 2 S-syngas reaction testing. Membrane failed after exposure to 90 ppm H 2 S..............................174 Figure 74. SEM-EDS images of ruptured Pd MR tube depicting the outer (permeate) surface (a), the inner (retentate) surface (b) of the Pd

MR after 3 days of WGSR with H 2 S-containing syngas feed at 1173K and 0.5s residence time. EDS analysis (c) of the inner surface of the ruptured region shown in (b) revealed negligible sulfide presence. .....................................................................................................................................176 Figure 75. SEM-EDS images of fracture faces of ruptured Pd MR tube (a) after 3 days of WGSR with H 2 S-containing syngas feed at 1173K and 0.5s residence time. EDS analysis of the magnified grain boundary region (b) detected sulfur within of the grain boundary groove (c), while no sulfur was detected in areas removed from the grain boundary (d)................................................................................................................177 Figure 76. SEM (a) and EDS (b) inner (retentate) surface image of inlet region of Pd

MR after 3 days of WGSR with H 2 S-containing syngas feed at 1173K depicting relatively smooth surface and negligible sulfide presence, respectively....................................178 Figure 77. SEM (a) and EDS (b) inner (retentate) surface analysis of outlet region of Pd MR after 3 days of WGSR with H 2 S-containing syngas feed at 1173K depicting pitted surface and negligible sulfide presence, respectively.................................................178 Figure 78. SEM (a) and EDS (b) inner (retentate) surface image of inlet region of Pd 80wt% Cu

MR after 6 days of WGSR with H 2 S-containing syngas feed at 1173K depicting relatively smooth surface and negligible sulfide presence, respectively....181 Figure 79. SEM-EDS images of inner (retentate) surface analysis of the ruptured Pd 80wt% Cu

MR where failure occurred after exposure to 90 ppm H 2 S-containing syngas

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feed, after 6 days of testing at 1173K depicting cracked surface (a). A magnified section of surface (b) revealed a highly modified surface. EDS analysis of the surface did not detect any sulfur presence (c).........................................................................182 Figure 80. SEM-EDS images of fracture faces (a) of ruptured Pd 80wt% Cu

MR where failure occurred after exposure to 90 ppm H 2 S-containing syngas feed, after 6 days of testing at 1173K. EDS analysis (b) detected no sulfur presence................................182 Figure 81. SEM (a) and EDS (b) inner (retentate) surface analysis of outlet region of the ruptured Pd 80wt% Cu MR after 7 days of WGSR with H 2 S-containing syngas feed at 1173K depicting severely pitted surface and negligible sulfide presence, respectively. .....................................................................................................................................183

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ACKNOWLEDGEMENTS

I would like to express my sincere gratitude to my advisor, Dr. Robert Enick, for his wit and candor in guiding me through my Ph.D. work. I am forever indebted to you. I would also like to acknowledge my committee members, Drs. G. Meier, I. Wender, G. Veser and A. Cugini for their insightful discussions. My colleagues at the National Energy Technology Laboratory, Bryan Morreale, Bret Howard, Richard Killmeyer and Mike Ciocco. I sincerely appreciate your time and helpful discussions over the years. I wish to express my gratitude to the National Energy Technology Lab for funding this project. I am very grateful for the opportunity to have worked in this field. I would also like to acknowledge the technical prowess and support of the engineering technicians and computer personnel of Parsons Project Services, Paul Dieter, Bill Brown, Ron Hirsh, Jack Thoms and Russell Miller who operate and maintain the Hydrogen Membrane Test Units. Thanks for all your support. Finally, this work is dedicated to my family for their love, prayers and encouragement that motivated me and kept me focused throughout my academic career. To my mother, Efe Iyoha, for her endless love and words of wisdom. To my father and role model, Wilson Iyoha, for his mentorship and support. For teaching me that with hard work, everything is possible. My siblings, Egaugie, Ifueko, Otabor and Amenze, you were my inspiration.

Full document contains 234 pages
Abstract: The efficacy of producing high-purity H2 from coal-derived syngas via the high-temperature water-gas shift reaction (WGSR) in catalyst-free Pd and 80wt%Pd-Cu membrane reactors (MRs) was evaluated in the absence and presence of H2 S. The impetus for this study stems from the fact that successfully integrating water-gas shift MRs to the coal gasifier process has the potential of increasing the efficiency of the coal-to-H2 process, thereby significantly reducing the cost of H2 production from coal. To this end, the effect of the WGSR environment on 80wt%Pd-Cu MRs was studied over a wide range of temperatures. Results indicate minimal impact of the WGSR environment on the 80wt%Pd-Cu membrane at 1173K. Subsequently, using pure reactant gases (CO and steam), the rapid rate of H 2 extraction from the reaction zone, coupled with the moderate catalytic activity of the Pd-based walls was shown to enhance the CO conversion beyond the equilibrium value of 54% at 1173K, in the absence of additional heterogeneous catalysts in both Pd and 80wt%Pd-Cu MRs. The effect of H2 S contamination in the coal-derived syngas on Pd and 80wt%Pd-Cu membranes at 1173K was also studied. Results indicate that the sulfidization of Pd-based membranes is strongly dependent on the H2 S-to-H2 ratio and not merely the inlet H2 S concentration. The Pd and 80wt%Pd-Cu MRs were shown to maintain their structural integrity at 1173K in the presence of H2 S-to-H2 ratios below 0.0011 (∼1,000 ppm H2 S-in-H2 ). A COMSOL Multiphysics model developed to analyze and predict performance of the water-gas shift MRs in the presence of H2 S indicated that the MRs could be operated with low H2 S concentrations. Finally, the feasibility of high-purity H2 generation from coal-derived syngas was investigated using simulated syngas feed containing 53%CO, 35%H 2 and 12%CO2 . The effect of H2 S contamination on MR performance was investigated by introducing varying concentrations of H2 S to the syngas mixture. When the H2 S-to-H2 ratio in the MR was maintained below 0.0011 (∼1,000 ppm H2 S-in-H 2 ), the MR was observed to maintain its structural integrity and H 2 selectivity, however, a precipitous reduction in CO conversion was observed. Increasing H2 S concentrations such that the H2 S-in-H 2 ratio increased above about 0.0014 resulted in MR failure within minutes.