Alkali-Alumina Sorbents for High-Temperature Removal of SO_2

Abstract

The high-temperature removal of SO_2 by sorbents consisting of sodium and lithium salts supported on α-Al_2O_3 has been investigated with emphasis on the chemistry of regeneration. The sulfated sorbents were regenerated by reduction with CO at 700–800°C in a thermogravimetric analyzer and a packed-bed microreactor. Sulfur removal from the sorbent and distribution of gaseous products were measured at different alkali loadings, temperatures, and CO concentrations. The results are interpreted in terms of a network of reactions wherein alumina is important as a catalyst and as a reactant. During regeneration sulfate is converted to aluminate and sulfide, the fraction of aluminate defining the extent of regeneration. The rate and extent of sulfur removal increase with the ratio of alumina to alkali and are higher in the presence of lithium. The product gas consists of SO_2, COS, and elemental sulfur, the latter compound constituting up to 35% of the sulfur removed.

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