Effect of Pressure on High-Temperature Water Gas Shift Reaction in Microporous Zeolite Membrane Reactor

A water gas shift (WGS) membrane reactor (MR) has been constructed using a MFI-type zeolite disk membrane packed with a cerium-doped ferrite catalyst. The WGS reaction was performed at high temperatures of 400-550 degrees C, and the effect of reaction pressure on the MR performance was investigated in a range from 2 to 6 atm with the permeate side swept by nitrogen at atmospheric pressure. Increasing temperature and pressure enhance both the reaction rate and the rate of H-2 membrane permeation that in turn significantly enhances the CO conversion. The equilibrium limit of CO conversion can be surpassed in the MR at high pressure and/or high temperature. It has been demonstrated in this study that membranes with moderate H-2 selectivity can be effective for enhancing CO conversion at high operation temperature and pressure with the cost of low H-2 concentration in the permeate stream. The timely removal of H-2 from the catalyst bed dramatically reduced the undesirable methane production because H-2 is a reactant for methanation reactions in the WGS system. Both the zeolite membrane and the Fe/Ce catalyst also exhibited good resistances to high concentration of H2S in WGS reactions.