High capacity potassium-promoted hydrotalcite for CO_2 capture in H_2 production

摘要

This paper presents an experimental study for a newly modified K_2CO_3-promoted hydro-talcite material as a novel high capacity sorbent for in-situ CO_2 capture. The sorbent is employed in the sorption enhanced steam reforming process for an efficient H_2 production at low temperature (400-500 ℃). A new set of adsorption data is reported for CO_2 adsorption over K-hydrotalcite at 400 ℃. The equilibrium sorption data obtained from a column apparatus can be adequately described by a Freundlich isotherm. The sorbent shows fast adsorption rates and attains a relatively high sorption capacity of 0.95 mol/kg on the fresh sorbent. CO_2 desorption experiments are conducted to examine the effect of humidity content in the gas purge and the regeneration time on CO_2 desorption rates. A large portion of CO_2 is easily recovered in the first few minutes of a desorption cycle due to a fast desorption step, which is associated with a physi/chemisorption step on the monolayer surface of the fresh sorbent. The complete recovery of CO_2 was then achieved in a slower desorption step associated with a reversible chemisorption in a multi-layer surface of the sorbent. The sorbent shows a loss of 8% of its fresh capacity due to an irreversible chemisorption, however, it preserves a stable working capacity of about 0.89 mol/kg, suggesting a reversible chemisorption process. The sorbent also presents a good cyclic thermal stability in the temperature range of 400-500 ℃.