Autothermal Reforming of Ethanol in a Fluidized Bed Membrane Reactor for Ultra-Pure Hydrogen Production
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In recent years, many efforts have been made to develop processes and reactor technologies for the production of cheap, ultra-pure hydrogen that can be used in efficient PEM fuel cells. Nowadays, hydrogen is mainly produced by steam reforming of natural gas in multi-tubular reactors. The main drawback of natural gas reforming is that this reaction leads to a H2 rich gas mixture also containing carbon oxides and other by-products. Consequently, in order to produce pure H2, chemical processes are carried out in a number of reaction units (typically high temperature reformer, high and low temperature shift reactors) followed by separation units (mostly pressure swing adsorption units are used). An attractive way to produce hydrogen is the reforming of renewable fuels (e.g. bio-ethanol) inside membrane reactors, where hydrogen production and hydrogen separation through selective membranes are integrated in one apparatus. In this paper the production of ultra-pure hydrogen via autothermal reforming of ethanol in a fluidized bed membrane reactor has been studied. The steam reforming of ethanol is an endothermic reaction requiring a great amount of heat. The needed energy for the steam reforming is obtained by burning part of the hydrogen recovered via the hydrogen perm-selective membrane. In this configuration, the air used for the combustion is never in contact with the reacting mixture, which makes thus autothermal reforming with integrated CO2 capture feasible. Simulation results based on a phenomenological model show that it is possible to obtain overall autothermal reforming of ethanol while 100% of hydrogen can in principle be recovered at relatively high temperatures and at high reaction pressures. At the same operating conditions, ethanol is completely converted, while the methane produced by the reaction is completely reformed to CO, CO2 and H2.