The integration of membranes inside a catalytic reactor is an intensification strategy to combine separation and reaction steps in one single physical unit. In this case, a selective removal or addition of a reactant or product will occur, which can circumvent thermodynamic equilibrium and drive the system performance towards a higher product selectivity. In the case of an inorganic membrane reactor, a membrane separation is coupled with a reaction system (e.g., steam reforming, autothermal reforming, etc.), while in a membrane bioreactor a biological treatment is combined with a separation through the membranes. The objective of this article is to review the latest developments in membrane reactors in both inorganic and membrane bioreactors, followed by a report on new trends, applications, and future perspectives.

In this research the performance of a fluidized bed membrane reactor for high temperature water gas shift and its long term stability was investigated to provide a proof-of-concept of the new system at lab scale. A demonstration unit with a capacity of 1 Nm³/h of ultra-pure H₂ was designed, built and operated over 900 h of continuous work. Firstly, the performance of the membranes were investigated at different inlet gas compositions and at different temperatures and H₂ partial pressure differences. The membranes showed very high H₂ fluxes (3.89 × 10⁻⁶ mol·m⁻²·Pa⁻¹·s⁻¹ at 400 °C and 1 atm pressure difference) with a H₂/N₂ ideal perm-selectivity (up to 21,000 when integrating five membranes in the module) beyond the DOE 2015 targets. Monitoring the performance of the membranes and the reactor confirmed a very stable performance of the unit for continuous high temperature water gas shift under bubbling fluidization conditions. Several experiments were carried out at different temperatures, pressures and various inlet compositions to determine the optimum operating window for the reactor. The obtained results showed high hydrogen recovery factors, and very low CO concentrations at the permeate side (in average <10 ppm), so that the produced hydrogen can be directly fed to a low temperature PEM fuel cell.

Chemical Looping is an interesting technology that allows (partial) oxidation of a fuel without direct contact between the fuel and air. Instead, a solid material, referred to as oxygen carrier, is used to transport the oxygen from the air to the fuel by solid circulation between two reactors operated under different conditions. As such, the products of the fuel oxidation are nitrogen free. In the case of combustion (full oxidation), this means that the CO2 is not diluted with nitrogen. In the case of reforming/partial oxidation, the syngas is nitrogen free and thus easier to purify. In the presence of an H2 permselective membrane, the syngas production (through chemical looping) and pure H2 separation are combined in the same unit. This chapter introduces the chemical looping principle and describes a new reactor concept that combines the advantages of chemical looping technology and membrane reactors. This concept is referred to as Membrane-Assisted Chemical Looping Reforming (MA-CLR), which allows high hydrogen purity with integrated CO2 capture and high energy efficiency.