Modeling of CO_2-selective water gas shift membrane reactor for fuel cell

摘要

Water gas shift (WGS) reaction is critical to hydrogen purification for fuel cells. Being reversible and exothermic, the WGS reaction in the traditional fixed bed reactor is not efficient. Using a CO_2-selective membrane reactor shifts the reaction towards the product side, which enhances the conversion of CO and increases the purity of the H_2 product at a high pressure. The simultaneous reaction and transport process in the countercurrent WGS membrane reactor was simulated by using a one-dimensional non-isothermal model, and the effect of several system parameters including CO_2/H_2 selectivity, CO_2 permeability, and sweep-to-feed molar flow rate ratio were investigated. The synthesis gases from both autothermal reforming and steam reforming were used as the feed gas, while heated air was used as the sweep gas. A published WGS reaction rate expression with the commercial Cu/ZnO catalyst was incorporated into the model. The modeling results show that a CO concentration of less than 10 ppm, a H_2 recovery of greater than 97%, and a H_2 concentration of greater than 54% (on the dry basis) are achievable from autothermal reforming syngas. If steam reforming syngas is used as the feed gas, H_2 concentration can be as high as 99.64% (on the dry basis).