Zeolite Membrane Reactor for High-Temperature Water-Gas Shift Reaction: Effects of Membrane Properties and Operating Conditions

Modified MFI-type zeolite membranes were investigated as high-temperature water-gas shift (WGS) membrane reactors (MRs) in combination with a nanocrystalline Fe/Ce WGS catalyst. The effects of the MR operating conditions and the membrane separation performance on the CO conversion (χ CO ) were studied experimentally and by calculations using a simple one-dimensional plug-flow reactor (PFR) model. The experimental results showed that, at high temperatures (e.g., >500 °C), the zeolite MR with moderate H 2 selectivity (e.g., α H 2 /CO 2 ∼ 31, and α H 2 /CO ∼ 25) and permeance ( P m,H 2 ∼ 0.9 × 10 –7 mol s –1 m –2 Pa –1 ) was capable of overcoming the limit of equilibrium CO conversion and χ CO of the MR could be further enhanced by increasing the reaction pressure while keeping the permeate pressure unchanged. At high temperatures and high reaction pressures, CO is rapidly consumed by a fast reaction that minimizes the membrane permeation of unreacted CO; meanwhile, the efficiency of H 2 removal is improved as a result of the increased H 2 partial pressure difference across the membrane. The model calculations have indicated that the current membrane has the potential to achieve high CO conversion of χ CO > 99% under practically meaningful operating conditions.