Kinetics of Mn-based sorbents for hot coal gas desulfurization. Quarterly progress report, March 15, 1995--July 15, 1995

Hot gas desulfurization may be accomplished by using solid sorbents such as oxides of those metals that form stable sulfides. The effectiveness of a desulfurizing agent in treating such gases is related to the predicted equilibrium partial pressure of hydrogen sulfide which will be present in a phase combination of the reduced form of sulfide and oxide phases. The focus of much current work being performed by the Department of Energy on sorbent development is in the use of zinc ferrite, zinc titanate, and Z-Sorb. The latter sorbent is a commercial product consisting of ZnO, a promoter, and a proprietary supporting matrix designed to provide stability and prolong sorbent life. Although these Zn-based sorbents have been the subject of extensive pilot-scale and process development work, all sorbents produced to date still experience structural and reactive degradation over multi-cycle use at relatively moderate temperatures. An effective alternative to zinc-based sorbents could be manganese sorbents which withstand high temperature operation and also maintain structural and reactive integrity over many cycles, as investigations by Ben-Slimane and Hepworth have indicated. Thermodynamic limits may prevent MnO from achieving the low sulfur specifications of the product gas for use in a molten carbonate fuel cell, but under the correct conditions the guideline for IGCC systems can easily be achieved. Furthermore, manganese sorbents could possibly be used in conjunction with a polishing sorbent (such as zinc oxide) possessing more favorable thermodynamic properties to reach levels acceptable for fuel cell applications (< 10 ppmv). Such an arrangement may not require that the zinc sulfide be regenerated since the sulfur concentration of the cleaned gas is low enough that the zinc oxide may be discarded when exhausted