High-temperature sulfidation-regeneration of CO-Al_2O_3 sorbents

Abstract

Thermogravimetric analysis (TGA) and flow-reactor experiments were used to study sulfidation-regeneration of highly porous CuO-Al_2O_3 sorbents. In TGA studies, sulfidation of reduced sorbents produced a high-temperature form of digenite (Cu_(9+x)S_5) as the major crystalline product. When a platinum pan was used in the TGA, significant sulfur chemisorption on alumina occurred. Sulfur chemisorption on alumina was eliminated by use of a quartz sample pan. Reaction of the mixed-oxide sorbents with a mixture of H_2S, H_2, H_2O, and N_2 in a packed-bed microreactor, at temperatures between 550 and 800 °C, yielded prebreakthrough outlet-H_2S levels considerably lower than those predicted by the sulfidation equilibrium of metallic copper. Independent reduction experiments confirmed that alumina stabilizes CuO against complete reduction to Cu. With this mechanism at work, low prebreakthrough H_2S levels are attributed to sulfidation reactions of copper at oxidation states of +1 or +2. The sulfided sorbents were completely regenerable in air/N_2 mixtures with no deterioration of subsequent sulfidation performance.

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