Absorption and desorption of SO2in aqueous solutions ofdiamine-based molten salts

Abstract

SO2 absorption and desorption behaviors were investigated in aqueous solutions of diamine-derived molten salts with a tertiary amine group on the cation and a chloride anion, including butyl-(2-dimethylaminoethyl)-dimethylammonium chloride ([BTMEDA]Cl, pKb = 8.2), 1-butyl-1,4-dimethylpiperazinium chloride ([BDMP]Cl, pKb = 9.8), and 1-butyl-4-aza-1-azoniabicyclo[2,2,2]octane chloride ([BDABCO]Cl, pKb = 11.1). The SO2 absorption and desorption performance of the molten salt were greatly affected by the basicity of the molten salt. Spectroscopic, X-ray crystallographic, and computational results for the interactions of SO2 with molten salts suggest that two types of SO2-containg species could be generated depending on the basicity of the unquaternized amino group: a dicationic species comprising two different anions, HSO3− and Cl−, and a monocationic species bearing Cl− interacting with neutral H2SO3.