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(608i) Heat Integrated Steam Reforming Membrane Reactor

Authors: 
Partridge, R., ExxonMobil Research and Engineering Company
Calabro, D. C., ExxonMobil Research and Engineering Company
A heat integrated steam reforming membrane reactor was investigated for development of a gasoline fuel processor for fuel cell vehicles. This reactor utilizes Le Chatelier’s Principle for driving thermodynamically equilibrium limited steam reforming reactions at higher pressures. Steam reforming at higher pressures also reduces the palladium alloy membrane area required. Coupling steam reforming with a hydrogen selective membrane provides essentially pure hydrogen for optimal fuel cell performance.

Engineering models were used extensively to help define and refine the fuel processor design. The catalytic heat exchange reactor was coupled to a separate palladium-alloy membrane and used recycle of hydrogen depleted reformate to achieve high efficiencies at moderate operating temperatures and pressures (650ºC, 20 Bar). Recycle was achieved by using a steam ejector. Catalytic combustion of the hydrogen depleted reformate with lean air fuel cell cathode exhaust (11% O2) supplied the heat required for steam reforming. Our modeling suggested that our steam reforming approach could have thermodynamic efficiencies of up to 40%.

Screening studies were undertaken to identify high activity noble metal steam reforming catalysts. A bimetallic Ru-Ir catalyst was found to have exceptionally high activity and stability. Order-of-magnitude, improvements in catalyst performance and reactor geometry were made.

In laboratory studies excellent heat transfer was observed when conducting catalytic combustion and steam reforming co-currently on opposing walls of the wash coated reactor tubes. Several membrane geometries were used. Hydrogen permeate was obtained from a variety of feeds, including isooctane, naphtha and methane, at reaction temperatures of 600-700ºC. The experimental results were in close agreement with the modeling predictions.

While considerable research and development would be required to advance this technology, these results demonstrate the potential of the heat integrated steam reforming membrane reactor system.

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