Parametric study of membrane reactors for hydrogen production via high-temperature water gas shift reaction

This study presents numerical studies of hydrogen production performance via water gas shift reaction in membrane reactor. The pre-exponential factor in describing the hydrogen permeation flux is used as the main parameter to account for the membrane permeance variation. The operating pressure, temperature and H₂O/CO molar ratio are chosen in the 1–20 atm, 400–600 °C and 1–3 ranges, respectively. Based on the numerical simulation results three distinct CO conversion regimes exist based on the pre-exponential factor value. For low pre-exponential factors corresponding to low membrane permeance, the CO conversion approaches to that obtained from a conventional reactor without hydrogen removal. For high pre-exponential factor, high CO conversion and H₂ recovery with constant values can be obtained. For intermediate pre-exponential factor range both CO conversion and H₂ recovery vary linearly with the pre-exponential factor. In the high membrane permeation case CO conversion and H₂ recovery approach limiting values as the operating pressure increases. Increasing the H₂O/CO molar ratio results in an increase in CO conversion but decrease in H₂ recovery due to hydrogen permeation driving force reduction. As the feed rate increases in the reaction side both the CO conversion and hydrogen recovery decrease because of decreased reactant residence time. The sweep gas flow rate has a significant effect on hydrogen recovery. Low sweep gas flow rate results in low CO conversion H₂ recovery while limiting CO conversion and hydrogen recovery can be reached for the high membrane permeance and high sweep gas flow rate cases.