Hydrogen purification for fuel cells by carbon dioxide removal membrane followed by water gas shift reaction

In this study, a process combining carbon dioxide removal by using a polymeric membrane with a subsequent water gas shift (WGS) reaction was developed to purify hydrogen for fuel cells. The polymeric CO2-removal membranes were synthesized by incorporating amino acid salts and polyamine into crosslinked poly(vinyl alcohol). The membranes showed high CO2 permeability and CO2/H-2 selectivity in temperatures ranging from 110 to 170 degrees C. A rectangular membrane permeation cell with well-defined countercurrent gas flows was used to study the CO2 removal. A feed gas consisting of 1% CO, 17% CO2, 45% H-2, and 37% N-2 was used to simulate the synthesis gas from autothermal reforming of gasoline with air. With this permeation cell running at 120 degrees C, the CO2 concentration in the gas mixture was reduced from 17% to as low as 10 ppm, resulting in more than 99.5% of CO2 removed. Then, with another feed gas consisting of 1.19% CO, 0.10% CO2, 53.87% H-2, and 44.84% N-2 used to simulate the synthesis gas after the CO2-removal step, a reactor packed with a commercial low-temperature WGS catalyst was operated at 140-150 degrees C to convert CO to H-2. With such a low CO2 concentration in the feed gas, the reversible WGS reaction was shifted forward so that the CO concentration was decreased from 1.19% to less than 10 ppm (on dry basis), which met the requirement of proton-exchange membrane fuel cells. The WGS reactor had a gas hourly space velocity of 7650 h(-1) at 150 degrees C, and the H-2 concentration in the exit was more than 54 mol% (on dry basis).