A MEMBRANE PROCESS FOR HOT-GAS CLEANUP AND DECOMPOSITION OF H2S TO ELEMENTAL SULFUR

AS THE U.S. SEEKS ENERGY INDEPENDENCE, COAL CONVERSION AND UTILIZATION PROCESSES WILL PLAY AN INCREASINGLY IMPORTANT ROLE IN PROVIDING ENERGY SOURCES. FOR THESE PROCESSES TO BESUCCESSFULLY EXPLOITED, METHODS MUST BE DEVELOPED FOR REMOVING CONTAMINANTS, PARTICULARLY HYDROGEN SULFIDE (H2S), FROM THE HOT COAL GAS STREAMS. THUS, MULTICONTAMINANT-CONTROL TECHNOLOGIES ARE NEEDED THAT ALSO REDUCE H2S TO PRODUCE ELEMENTAL SULFUR. IN ADDITION, THESE TECHNOLOGIES MUST BE ABLE TO WITHSTAND THE HIGH TEMPERATURESAND PRESSURES OF THE COAL GASIFICATION PROCESS. PHASE I OF THIS PROJECT IS DEVELOPING A SYSTEM BASED ON A NOVEL CATALYTIC HYDROGEN-PERMEABLE METAL MEMBRANE. IN THIS SYSTEM, PURE HYDROGEN (H2) IS FIRST SEPARATED FROM THE COAL GAS, ALLOWING THE GASIFIER TO BE AIR-BLOWN RATHER THAN OXYGEN-BLOWN. NEXT, THE H2S IS DECOMPOSED TO SULFUR AND H2. H2 ALSO PERMEATES THE MEMBRANE, DRIVING THE DECOMPOSITION TO COMPLETION. THIS MEMBRANE-BASED SYSTEM ALSO CATALYZES THE WATER-GAS SHIFT REACTION TO MAXIMIZE THE PRODUCTION OF PURE H2. THUS, THIS TWO-STAGE SYSTEM REPLACESMANY UNIT PROCESSES CURRENTLY REQUIRED FOR H2 PRODUCTION FROM COAL, INCLUDING AN OXYGEN PLANT, A CLAUS PLANT, SHIFT REACTORS, AND GAS SCRUBBERS. IN PHASE I, THE TECHNICAL FEASIBILITY OF THE PROCESS IS BEING DEMONSTRATED BY (1) DEMONSTRATING THAT THE H2 PERMEABILITY OF THE MEMBRANE IS HIGH ENOUGH AFTER OPTIMIZATION TO BE PRACTICAL; (2) VERIFYING THAT THE MEMBRANE, WHICH IS DESIGNED TO BE RESISTANT TO H2S, IS INDEED RESISTANT AT HIGH TEMPERATURE AND PRESSURE; AND (3) VERIFYING THAT "COOKING" IS NOT A PROBLEM OR, ALTERNATIVELY, DETERMINING A SIMPLE METHOD FOR HANDLING THAT PROBLEM. SUCCESS IN PHASE I WILL LEAD TO A PHASE II EFFORT FOCUSSED ON OPTIMIZING THE PROCESS AND BUILDING A BENCH-SCALE UNIT. A SUCCESSFUL BENCH-SCALE DEMONSTRATION CAN BE EXPECTED TO CONVINCE PRIVATE INDUSTRY TO FUND THE REMAINING DEVELOPMENT NECESSARY TO COMMERCIALIZETHE SYSTEM.