Membrane reactor: an integrated "membrane + reaction" system

Membrane reactor (MR) technology combines two distinct sciences such as membranes and catalysis to constitute an integrated "membrane + reaction" system. In many scientific studies published in the specialized literature, often there has been a difficult evaluation on which of them has more relevance in MR development. However, it is reasonable to affirm that catalyst performance is certainly an important aspect in the design of improved MRs, particularly in the field of hydrogen production units, for example, fulfilling the requirements for the integration of fuel processors with proton exchange membrane (PEM) fuel cells. One of the most important issues affecting the MR concerns the poisoning/contaminant effects due to the inhibition caused by some reaction products or various impurities contained in the feeds, constituting an important obstacle for their performance. Particular attention should also be given to the feedstock used for hydrogen production through reforming reactions, because they could affect the composition of the reaction products and the presence of contaminants in such streams. Reforming of natural gas is the dominant process for hydrogen generation at the industrial scale (Iulianelli et al., 2012; Moriarty and Honnery, 2007) and it is essentially used for stationary applications. Nevertheless, having in mind to solve the issues related to the formation of greenhouse gases (GHGs) and to limit the exploitation of fossil fuels, it is expected that alcohols such as ethanol, methanol, glycerol, or other bio-fuels as acetic acid, biogas, etc. could have a major impact in future applications. Furthermore, the adoption of new technologies for producing hydrogen as the MRs, alternative to the conventional reactors (CRs) could constitute an important goal in the viewpoint of intensification of the whole process (Brunetti et al., 2014). Therefore, the scope of this chapter is to provide an overview on the recent advances on MRs used to perform several reaction processes and particularly, for hydrogen generation by exploiting renewable sources.