High-temperature membranes for H{sub 2}S and SO{sub 2} separations. Final report

Electrochemical cells which separate H{sub 2}S and S0{sub 2} from hot gas streams have two important materials issues that limit their successful industrial application: (1) membranes and (2) electrodes. These were the focus of the present study. For the H{sub 2}S work, experimental analysis incorporated several membrane and electrode materials; densified zirconia provided the best matrices for entrainment of electrolytic species, ionic mobility, and a process-gas barricade hindering the capabilities of gas cross-over, alternate reactions. Electrode materials of lithiated Ni converted to NiO in-situ were successful in polishing applications; however H{sub 2}S levels >100 ppM converted the NiO cathode to a molten nickel sulfide necessitating the use of Co. Lithiated NiO for the anode material remained morphologically stable and conductive in all experimentation. High temperature electrochemical removal of H{sub 2}S from coal gasification streams has been shown on the bench scale level at the Georgia Institute of Technology utilizing the aforementioned materials. Experimental removals from 1000 ppM to 100 ppM H{sub 2}S and 100 ppM to 10 ppM H{sub 2}S proved over 90% removal with applied current was economically feasible due to high current efficiencies ({approximately}100%) and low polarizations. For the S0{sub 2}work, an extensive search was conducted for a suitable membrane material for use in the S0{sub 2} removal system. The most favorable material found was Si{sub 3}N{sub 4}, proven to be more efficient than other possible materials. New lithiated NiO electrodes were also developed and characterized, proving more stable than previously used pervoskite electrodes. The combination of these new components led to 90% removal at near 100% current efficiency over a wide range of current densities