Modeling and design of membrane reactors

Membrane reactors are attracting increasing interest because of the opportunity they represent in increasing the efficiency of small-scale systems. Their use in gas phase reactions has been proposed for a variety of applications, where they may act either as selective extractors or as distributors. In particular, membrane reactors are generally employed for the selective permeation of hydrogen. For instance, they have been proposed for hydrogen production through reactions, such as steam reforming of hydrocarbons, water gas shift, propane and ethane dehydrogenation, and ammonia decomposition. Such applications require the use of Pd-based membranes, through which hydrogen permeates selectively, enhancing conversion and allowing the production of pure hydrogen. Perovskite-based membranes, which present a high selectivity towards oxygen permeation, are instead used as distributors for reactions, such as the partial oxidation of methane or ammonia, autothermal reforming, and oxidative dehy-drogenation of alkanes. In this case, the use of the membranes allows the achievement of uniform species concentrations along reactors, leading to a higher product selectivity; however, they may also be used as extractors to enhance conversion. Processes that take advantage of oxygen extraction include the coupling of oxygen-consuming reactions with water splitting, thermal decomposition of CO2, and NOx decomposition. In other applications, the reaction is localized on the membrane, which acts as the catalyst and separator at the same time. The modeling of membrane reactors is essential to exploit all the benefits that can be derived from their optimal design, but it represents an ongoing challenge because of the complexity of describing systems in which the transport of mass, momentum, and energy are strongly coupled. With reference to mass transport, the effects of convection, dispersion, reaction, and permeation should, in principle, be simultaneously accounted for. Gas composition may affect membrane permeance and the coupling of the rates of permeation and reaction can result in multiple steady states. The reaction and permeation may cause a change in density that affects momentum transport. Furthermore, temperature gradients may be formed as a consequence of the heat of reaction, energy transport associated with the permeation, and the potential presence of a heating system. The purpose of this Special Issue is to publish research papers on advances in membrane reactor modeling and design, as well as review papers. Potential topics include the modeling of: Membrane reactors for enhanced conversion/product selectivity Membrane reactors for controlled feed distribution Membrane reactors for coupled reactor systems Catalytic membrane reactors