A method of polishing coal synthesis by electrochemical operation is being perfected. An electrochemical potential gradient is used to remove H{sub 2}S from the coal gas stream, leaving only H{sub 2} to enrich the exiting polished gases. Sulfur byproduct is swept away by an inert sweep gas and later condensed. Current experiments are based on improving selective removal from low initial H{sub 2}S contents (10 ppm). High flow rate data is also being investigated along with sealing the cell housings. Latest option for consistent removal and seals is Zircar manufactured membranes.

The cobalt cathode used in the EMS proved stable and efficient. Removal of H{sub 2}S was deterred by the possibility of hydrogen cross-over from process gases creating alternate reactions unfavorable to the removal system. Application of back pressure from the anode side of the cell would be the simplest solution to H{sub 2} cross-over. Examination of water proof of the vapor in the anode exit gases would provide proof of the aforementioned reaction hypothesis. Cobalt aluminate formation should not prove problematic, since degradation of the Co Cathode did not occur as a result. Once equilibrium is reached electrolyte addition is not necessary, therefore not a major concern.

An advanced process for the separation of hydrogen sulfide from coal gasification product streams through an electrochemical membrane is being developed using the funds from this grant. H{sub 2}S is removed from the syn-gas stream, split into hydrogen, which enriches the syn-gas, and sulfur, which can be condensed from an inert gas sweep stream. The process allows removal of H{sub 2}S without cooling the gas stream and with neglible pressure loss through the separator. The process is economically attractive by the lack of adsorbents and the lack of a Claus process for sulfur recovery.

Experimentation with a rigidized, electrolyte filled tile, left much to be desired. The instability of the tiles at molten conditions ( > 550{degree}C), provided the necessary mechanism for H{sub 2} to penetrate the membrane. Once H{sub 2} cross-over occurs the entire objective of electrochemical separation becomes nullified. The Zircar membranes used last quarter provided excellent protection against H{sub 2}, prompting a reversion back to them. If porosities are strictly adhered to and the water-gas shift is properly handled, the membranes should provide an adequate mechanism for selective H{sub 2}S removal.

Work has continued on application of this technology to polishing H{sub 2}S from simulated coal gasification process streams. Both stainless steel and MACOR housings were successfully used, with 98% (100 ppmv H{sub 2}S to 2 ppmv H{sub 2}S) removal observed at a flow rate of 230 cc/min and a process temperature of 700{degrees}C with stainless steel housings (Run 57) and greater than 80% (11 ppmv H{sub 2}S to less than 2 ppmv H{sub 2}S) at a flow rate of 100 cc/min and a temperature of 650{degrees}C with MACOR housings (Run 65). Work has continued with attempts to increase removal efficiency by increasing the density of the membrane and slowing down H{sub 2} diffusion from the cathode side to the anode side of the cell.