Electrochemical membrane separation of H 2 S from reducing gas streams

An improved electrochemical membrane was tested with simulated coal gas having concentrations from 25 to 4,500 ppm H 2 S. The process produces elemental hydrogen that enriches the process gas stream at the cathode and elemental sulfur vapor that emerges from the anode. Removal efficiencies average up to 90% at any inlet level; current efficiencies are near 100% at the high inlet concentrations, decreasing significantly at lower H 2 S levels as the competing reduction of H 2 O becomes more favored. Molten carbonate fuel cell (MCFC) materials can be used exclusively at the MCFC operating temperature of 650°C, with the low concentrations of H 2 S, including the NiO cathode. At concentrations higher than about 60 ppm the operating temperature must be lowered approximately 50°C to avoid melting of the sulfided nickel cathode.