Selective removal and recovery of sulfur dioxide from effluent gases

Abstract

A process for the selective removal and recovery of sulfur dioxide from effluent gases is disclosed. The sulfur dioxide is recovered in a sulfur dioxide absorption/desorption cycle which utilizes a liquid solvent to selectively absorb sulfur dioxide from the effluent gas. The liquid solvent includes an organic phosphorous compound selected from phosphate triesters, phosphonate diesters, phosphinate monoesters and mixtures thereof. Preferably, the liquid solvent includes phosphonate diesters of the formula ##STR1## wherein R.sup.1, R.sup.2 and R.sup.3 are independently aryl or C.sub.1 to C.sub.8 alkyl. The organic phosphonate diesters are substantially water immiscible, the solubility of water in the organic phosphonate diester being less than about 10 weight percent at 25.degree. C., and have a vapor pressure less than about 1 Pa at 50.degree. C. In accordance with a preferred embodiment, the liquid solvent include dibutyl butyl phosphonate. The absorbed sulfur dioxide is subsequently stripped to regenerate the organic phosphorous solvent and produce a gas enriched in sulfur dioxide content. The sulfur dioxide-enriched gas may be used as part of the feed gas to a contact sulfuric acid plant or a Claus plant for the preparation of elemental sulfur or be cooled to condense sulfur dioxide in the form of a liquid product. The present invention is particularly useful in producing a sulfur dioxide-enriched gas from gases relatively weak in sulfur dioxide content.