Enhanced CO_2 Sorption Performance of CaO/Ca_3Al_2O_6 Sorbent with Steam Addition

摘要

CO_2 enhanced sorption methane steam reforming (SESMR) for hydrogen production is a potential approach to economically provide hydrogen and to reduce CO_2 emission. The key point for this process is to develop a kind of proper CO_2 sorbents with high adsorptive capacity. CaO/Ca_3Al_2O_6 sorbents have been proved to be a promising sorbent for CO_2 sorption in our previous investigation. However, the sorbents still suffer from low CO_2 sorption capacity. There have reported that the presence of steam during carbonation would influence the CO_2 capture performance. Considering the abundant existing steam in real SESMR process, it is necessary to understand its effect on the CO_2 sorption performance of the home-made CaO/Ca_3Al_2O_6 sorbents. In this work, the effect of steam addition during carbonation were investigated over CaO/Ca_3Al_2O_6 sorbents in a thermogravimetric analyzer and a fixed bed reactor system. Various concentrations of steam up to 10 vol% were provided during carbonation process. Results showed that superior CO_2 sorption capacity could be achieved as the steam concentration increased, which was derived from the increased surface area and pore volume, the sorbent reactivity was significantly increased for all concentrations of steam injected during carbonation step. The presence of 10vol% steam increased the CO_2 capture capacity by 37%. The steam promotion mechanism in the carbonation process was ascribed to the production/transient of Ca(OH)_2 and the improvement of CO_2 molecular diffusion.