A REGENERABLE COPPER-BASED SORBENT FOR H2S REMOVAL FROM COAL GASES

Much of the sulfur sorbent research and development work has focused c onsiderably on zinc-based sorbents. Because of concern over the gradua l loss of reactivity and physical deterioration in long-term cyclic op eration at elevated temperature, extensive research is still being con ducted to improve the performance of zinc-based sorbents; justifiably, however, investigation of nonzinc-based materials has also been pursu ed as a logical approach to develop more effective alternatives. This paper reports on research conducted for the development of copper-base d sorbents for hot coal gas desulfurization applications in the temper ature range of 550-650 degrees C. A thermodynamic analysis is given to rationalize the selection of chromia (Cr2O3), and its potential super iority to alumina (Al2O3), for the stabilization of copper oxide (Cu2O ) against complete reduction to elemental copper (Cu) upon exposure to a fuel gas in the indicated temperature range. The results of packed- bed experiments carried out for the determination of optimum operating conditions as well as the evaluation of the long-term durability and regenerability of a selected copper chromite sorbent are presented and discussed. The regenerable copper chromite sorbent developed, designa ted as CuCr-29, is capable of achieving less than 5 ppmv H2S concentra tion in the cleaned fuel gas. The optimum desulfurization temperature in terms of sorbent efficiency (terminal H2S levels in the cleaned fue l gas) and utilization (sulfur capacity at breakthrough or effective c apacity) for this sorbent is determined to be about 600 degrees C. Sor bent regeneration with a dilute O-2-N-2 gas mixture at 750 degrees C e nsured complete conversion of the copper sulfide to oxide without sulf ate formation or reactivity deterioration in subsequent cycles.