Recovery of high purity elemental sulfur from coal syngas by liquid redox catalytic process using tannin extracts

Abstract

Liquid redox sulfur recovery (LRSR) processes using tannin extracts and vanadium pentoxide as dual redox catalysts are widely employed for removal of hydrogen sulfide and recovery of elemental sulfur from coal syngas in China. Difficulties in melting sulfur pastes, poor quality of sulfur and the running stability are the major concern of the process. In this study, tannin extracts obtained from valonia and black wattle and an industrial benchmark tannin extract designated as the LRSR's catalyst were investigated for their composition and the kinetics of sulfide oxidation. Industry samples of sulfur pastes from the LRSR processes were analyzed. The results demonstrate that the accumulation of impurities of tannin extracts along with byproducts of sulfide oxidation in scrubbing liquid prevents sulfur froth separation and affects the purity of sulfur. The pretreatment of sulfur pastes with nitric acid reduces the accumulation of the impurities and improves the purity of sulfur from 60% to 99%, leading to cleaner production of sulfur by the LRSR process.