Hydrogen Purification for Fuel Cells by Carbon Dioxide Removal Membrane Followed by Water Gas Shift Reaction

Abstract

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/H2 selectivity in temperatures ranging from 110 to 170°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% H2, and 37% N2 was used to simulate the synthesis gas from autothermal reforming of gasoline with air. With this permeation cell running at 120°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% H2, and 44.84% N2 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°C to convert CO to H2. 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°C, and the H2 concentration in the exit was more than 54 mol% (on dry basis).