COx free hydrogen production through water-gas shift reaction in different hybrid multifunctional reactors

Abstract

High-purity H-2 production from the water-gas shift (WGS) reaction was assessed. Since the WGS is limited by the equilibrium, different reactor types that allow to extract one or more products from the reaction medium, namely membrane reactor (MR; for H-2 separation), sorption-enhanced reactor (SER; for CO2 capture) and sorption-enhanced membrane reactor (SEMR; for simultaneous CO2 and H-2 removal), were used and compared with fixed-bed traditional reactor (TR). Experimental results were obtained with commercial materials, namely WGS Cu-based catalyst and K-doped hydrotalcite for CO2 capture. Additionally, in the MR and SEMR, a self-supported Pd-Ag membrane for separating H-2 selectively from the reaction zone was used. Experimental tests were performed at different temperatures and pressures, and the results obtained were compared with those predicted by theoretical simulations at the thermodynamic equilibrium. Moreover, in the case of SER, different methods for the hydrotalcite regeneration and the evaluation of its working sorption capacity under cycling conditions were also assessed. Not all sorbed CO2 can be desorbed under dry conditions (pure nitrogen purging stream); however, if steam is used during the regeneration step, all sites can be effectively regenerated, allowing to have a stable working sorption capacity. Concerning the performance of the different hybrid reactors tested, i.e. MR, SER and SEMR, it was found that all are able of overcoming the TR limitations, with performances reaching conversion above the equilibrium for the feed composition. Nonetheless, only the SER and SEMR configurations allow to obtain high-purity H-2 in all reactor exiting streams under the operating conditions herein assessed.