Performance and recovering of a Zn-doped manganese oxide as a regenerable sorbent for hot coal gas desulfurization

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 degreesC using a simulated RKW coal gas, while regeneration of the sulfided sorbent has been conducted at 800 degreesC 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.