Computational fluid dynamics study of hydrogen generation by low temperature methane reforming in a membrane reactor

• Low temperature membrane reformer for H2 generation from CH4 was analyzed by CFD.
• Removal of H2 by the Pd–Ag membrane can lead to strong concentration polarization.
• CH4 conversion of 80% is achievable at 575 °C, 10 bar and GHSV = 10,000 h−1.
• H2 recovery of 2.7–2.2 is obtainable at 575 °C, 10 bar and GHSV = 10,000–90,000 h−1.
• Reformer performance can be kinetically (catalyst)- or transport (membrane)-limited.

Concentrated solar energy can be used to drive highly endothermic reactions, such as methane reforming. An attractive route is the parabolic trough technology, which is mature and relatively inexpensive but limited to temperatures below 600 °C, when methane conversions are low. However, high conversions are achievable if hydrogen is continuously removed from the reactive stream by a membrane selective to hydrogen. In this study, low temperature methane reforming in a membrane reactor is analyzed numerically by computational fluid dynamics over a wide range of operating parameters. Effects of temperature, steam-to-carbon ratio and space velocity on conversion, hydrogen recovery and carbon monoxide selectivity are specifically investigated. Our results show that concentration polarization can be significant. Below 500 °C the reactor performance is kinetically limited by the reforming reaction, while above this temperature hydrogen separation is a limiting factor. High hydrogen recovery is achievable even at high, industrially relevant space velocities. Importantly, hydrogen separation enhances water gas shift, reducing the concentration of carbon monoxide, the main source of coke formation at low temperatures.

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