Hydrogen production from water gas shift reactions in association with separation using a palladium membrane tube

Hydrogen production from water gas shift reactions (WGSRs) of synthesis gas (syngas) followed by separation via a Pd membrane was studied experimentally. In the reactions, a variety of combinations of a high-temperature shift reaction (HTSR), a low-temperature shift reaction (LTSR) and a palladium (Pd) membrane tube were considered. The results indicated that the CO conversion from the LTSR was close to that of the HTSR and LTSR in series; however, the latter with the Pd membrane could provide a much low CO concentration at the permeate side. On the other hand, while the produced hydrogen diffused through the membrane, methane was also found at the both sides of the membrane due to the methanation reaction activated by the Pd membrane. In the present system, increasing the steam/CO ratio enhanced the forward reaction of the WGSRs and elongated the residence time of the reactants in the catalyst beds, resulting in the increases of CO conversion and hydrogen recovery. As a whole, the concentration of CO in the separated hydrogen was lower than 50ppm from the combination of the HTSR and the LTSR with the membrane, whereby the produced hydrogen could be applied in proton exchange membrane fuel cells.