Palladium-alloy membrane reactors for fuel reforming and hydrogen production: Hydrogen Production Modeling

Endeavors have recently been concentrated on minimizing the dependency on fossil fuels in order to mitigate the ever-increasing problem of greenhouse gas (GHG) emissions. Hydrogen energy is regarded as an alternative to fossil fuels due to its cleaner emission attributes. Reforming of hydrocarbon fuels is amongst the most popular and widely used methods for hydrogen production. Hydrogen produced from reforming processes requires additional processes to separate from the reformed gases. In some cases, further purification of hydrogen has to be carried out to use the hydrogen in power generation applications. Metallic membranes, especially palladium (Pd)-based ones, have demonstrated sustainable hydrogen separation potential with around 99.99% hydrogen purity. Comprehensive and critical research investigations must be performed to optimize membrane-assisted reforming as well as to maximize the production of hydrogen. The computational fluid dynamic (CFD) can be an excellent tool to analyze and visualize the flow/ reaction/permeation mechanisms at a lower cost in contrast with the experiments. In order to provide the necessary background knowledge on membrane reactor modeling, this study reviews, summarizes and analyses the kinetics of different fuel reforming processes, equations to determine hydrogen permeation, and lastly, various geometry and operating condition adopted in the literature associated with membrane-reactor modeling works. It is indicated that hydrogen permeation through Pd-membranes depends highly on the difference in hydrogen pressure. It is found that hydrogen permeation can be improved by employing different pressure configuration, introducing sweep flow on the permeate side of the membrane, reducing retentate side flow rate, and increasing the temperature.