Understanding the effect of H2S on the capture of CO2 using K-doped Li4SiO4 sorbent

Li 4 SiO 4 is a well-acknowledged CO 2 sorbent in the sorption-enhanced reforming system for low-cost H 2 production with a high purity. However, the inevitable presence of H 2 S in the biomass-derived syngas etc. could possibly affect the in-situ CO 2 adsorption significantly, which is important but has never been reported. In this work, the adsorption of CO 2 using Li 4 SiO 4 was investigated under varying H 2 S concentrations and reaction temperatures, and a series of characterization techniques were utilized to understand the effect of H 2 S and its action mechanism. The results show that the presence of H 2 S causes a rapid loss-in-capacity of Li 4 SiO 4 in capturing CO 2 during the cyclic reactions, and a higher concentration greatly exacerbates the problem. Moreover, the negative impact of H 2 S is found to have a strong relationship to the reaction temperature. It is proposed that at 325~475 °C, Li 4 SiO 4 and H 2 S react to form bits of Li 2 S and some kinds of sulfates, and at 625~775 °C, a large amount of dense KLiSO 4 is generated covering the surface of the sorbent. In contrast, at a high temperature above 925 °C, sintering of Li 4 SiO 4 plays a critical role, leading to a significant change on its microstructure.