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

Abstract

ASTER DISCLAIMERThis report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any wananty, express or implied, or assumes any legal liability orresponsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or p m e s disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, pmcess. or service by trade m e , trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United St@& Government or any agency thereof. The views and opinions of authos expressed herein do not neceSSarily state or reflect those of the United States Govemment or any agency thereof.This report has been reproduced diiectly from the best available copy.Available to DOE List of Tables EXECUTIVE SUMMARYElectrochemical cells which separate H,S and So, from hot gas streams have two important materials issues that limit their successful industrial applicatioq: (1) membranes and (2) electrodes. These were the focus of the present study.For the H,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. In-lab densification of a zirconia weave/knit mat using submicron particles of zirconia in an aqueous suspension provided the most efficient and ckonomical manufacturing technique. Electrode materials of lithiated Ni converted to NiO in-situ were successful in polishing applications; however H,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, 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 pprn to 100 pprn H,S and 100 pprn to 10 pprn H,S proved over 90% removal with applied aprent was economically feasible due to high current efficiencies (-100%) and low polarizations; therefore low power requirements for removal applications in the above ranges.Polishing of H,S from 10 ppm to e 1 ppm tested the most stringent application of the electrochemical cell due to the low concentration of H2S compared to CO,. Removals over 90% were achieved; power requirements for this level of removal are negligible.For the SO2 work, an extensive search was conducted for a suitable membrane material for use in the So, removal system. The most favorable material found was Si,N, proven to be more efficient than other possible mater...