Testing of hydrotalcite-based sorbents for CO2 and H2S capture for use in sorption enhanced water gas shift

The feasibility of the sorption enhanced water gas shift (SEWGS) process under sour conditions is shown. The sour-SEWGS process constitutes a second generation pre-combustion carbon capture technology for the application in an IGCC. As a first critical step, the suitability of a K2CO3 promoted hydrotalcite-based CO2 sorbent is demonstrated by means of adsorption and regeneration experiments in the presence of 2000 ppm H2S. In multiple cycle experiments at 400 °C and 5 bar, the sorbent displays reversible co-adsorption of CO2 and H2S. The CO2 sorption capacity is not significantly affected compared to sulphur-free conditions. A mechanistic model assuming two different sites for H2S interaction explains qualitatively the interactions of CO2 and H2S with the sorbent. On the type A sites, CO2 and H2S display competitive sorption where CO2 is favoured. The type B sites only allow H2S uptake and may involve the formation of metal sulphides. This material behaviour means that the sour-SEWGS process likely eliminates CO2 and H2S simultaneously from the syngas and that an almost CO2 and H2S-free H2 stream and a CO2 + H2S stream can be produced.