High temperature membrane separation techniques have been applied to gas mixtures involved in coal utilization. For coal gasification, H{sub 2}S has been 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. For coal combustion, SO{sub 2} has been separated from the flue gas, with concentrated SO{sub 3} produced as a by-product. Both processes appear economically viable but each requires fundamental improvements: both the H{sub 2}S and SO{sub 2} cells require more efficient membranes and the H{sub 2}S cell needs a more efficient anode. Membranes will be fabricated by either hotpressing, impregnation of sintered bodies, or tape casting. Research conducted during the present quarter is highlighted, with an emphasis on progress toward these goals. Membranes tested for SO{sub x} removal and H{sub 2}S were Si{sub 3}N{sub 4} and zirconia, respectively.

Membrane testing in the full-cell environment has been successful in H{sub 2}S removal applications, but largely ineffective for obtaining high current efficiencies due to hydrogen leakage through the membrane. A preprocessed zirconia membrane successful in past experiments was utilized in continued efforts to truncate hydrogen cross-over. An alternative material forming a stabilized conductive cathode under 100 ppmv H{sub 2}S conditions is possible with Co. Development of a Co cathode identical in porosity and pore size to aforementioned nickel cathodes was successfully fabricated and utilized experimentally this quarter.

Successful removal of SO{sub x} from flue gas depends on the development of a membrane able to achieve a current density of 50 ma/cm{sup 2} at a total voltage of approximately 1V. Flooding of electrode has been identified as a problem, leading to increasing polarization over time. The resulting reduction of surface area also tends to limit the mass transfer flux, reducing the efficiency of the cell. To reduce flooding, new materials and techniques of manufacture will be investigated, in the attempt to produce a ceramic membrane of approximately 50% theoretical density. This membrane must have proper pore size distribution to ensure sufficient capillary force to prevent impregnated electrolyte from flooding electrodes, and subsequently drying the ceramic membrane. Various methods of matrix production were studied this quarter: tape casting, pressing and sintering, and slip casting. Each will be discussed in turn. Electrolyte introduction to the cell is a continuing problem. The development of a method is still being investigated. Ideally, the electrolyte would be introduced as powder with binder in a green body. This binder would bum away at temperatures of approximately 300{degrees}C, leaving pure electrolyte to melt and complete the ionic path necessary for the electrochemical cell. The electrolyte …