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Mixed oxides, prepared by calcination at 950 °C for 6 h of powder mixtures of manganese and copper oxides, have been studied as regenerable sorbents for hot coal gas desulfurization. For the stabilization of copper in the oxidation states 2+ or 1+ under strong reducing conditions of coal gas, different concentrations of component oxides have been used enhancing the formation of different mixed oxides. Copper was not stabilized by manganese oxides, but its presence in the fresh sorbent was completely necessary because it increases the sorbent reactivity and keeps the H 2 S concentration in the outlet gas from a reactor below 50 ppmv. Thermogravimetric experiments and performance tests in a fixed bed reactor have allowed the optimization of the operating conditions for a sorbent MC (1:0.1) showing a good performance in multicycle tests without apparent decay.

The performance of a ZnO-doped manganese oxide MZ(1:0.1) as a regenerable sorbent for hot coal gas desulfurization in 70-cycles tests in a fixed bed reactor has been studied. Sulfidation has been carried out at 700 °C using a simulated RKW coal gas, while regeneration of the sulfided sorbent has been conducted at 800 °C using pure air. The performance was very good as deduced from low pre-breakthrough H2S concentration in the outlet gas, high sorbent efficiency, and long durability. Despite that, a slight efficiency decay was observed that will make the sorbent become inactive after a certain number of successive cycles in use. Simple methods of preparation, similar to those used in the manufacture of the original fresh sorbents, are shown to be effective in recovering the activity of this sorbent. Additionally, because manganese sulfate plays an important role in the long durability exhibited by manganese based sorbents, the evolution of this compound in the reactor bed in a typical regeneration test has been studied by FTIR spectroscopy. It is formed during the first stages of regeneration but it decomposes then, although not completely, in the last stages of the process, acting as a por-forming additive, like graphite, in every cycle.

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