Selection of CO2 chemisorbent for fuel-cell grade H2 production by sorption-enhanced water gas shift reaction

New experimental data are reported to demonstrate that high purity H2 can be directly produced by sorption-enhanced water gas shift (WGS) reaction using synthesis gas (CO + H2O) as sorber-reactor feed gas. An admixture of a commercial WGS catalyst and a proprietary CO2 chemisorbent (K2CO3 promoted hydrotalcite or Na2O promoted alumina) was used in the sorber-reactor for removal of CO2, the WGS reaction by-product, from the reaction zone. The promoted alumina was found to be a superior CO2 chemisorbent for this application because (a) it could directly produce a fuel-cell grade H2 product (<10–20 ppm CO) at reaction temperatures of 200 and 400 °C, and (b) it produced ∼45.6% more high purity H2 product per unit amount of sorbent than the promoted hydrotalcite at 400 °C. Furthermore, the specific fuel-cell grade H2 productivity by the promoted alumina at a reaction temperature of 200 °C was ∼3.6 times larger than that at 400 °C. These striking differences in the performance of the two CO2 chemisorbents were caused by the differences in their CO2 sorption equilibria and kinetics.