A regenerable copper-based sorbent for H2S removal from coal gases

Much of the sulfur sorbent research and development work has focused considerably on zinc-based sorbents. Because of concern over the gradual loss of reactivity and physical deterioration in long-term cyclic operation at elevated temperature, extensive research is still being conducted to improve the performance of zinc-based sorbents; justifiably, however, investigation of nonzinc-based materials has also been pursued as a logical approach to develop more effective alternatives. This paper reports on research conducted for the development of copper-based sorbents for hot coal gas desulfurization applications in the temperature range of 550-650 degrees C. A thermodynamic analysis is given to rationalize the selection of chromia (Cr2O3), and its potential superiority 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, designated as CuCr-29, is capable of achieving less than 5 ppmv H2S concentration in the cleaned fuel gas. The optimum desulfurization temperature in terms of sorbent efficiency (terminal H2S levels in the cleaned fuel gas) and utilization (sulfur capacity at breakthrough or effective capacity) for this sorbent is determined to be about 600 degrees C. Sorbent regeneration with a dilute O-2-N-2 gas mixture at 750 degrees C ensured complete conversion of the copper sulfide to oxide without sulfate formation or reactivity deterioration in subsequent cycles.