PMRs Utilizing Non–Pressure-Driven Membrane Techniques

In the present chapter it is shown how photocatalytic membrane reactors utilizing membrane processes, which are not pressure driven, can exploit various mechanisms to obtain a substantial improvement of the process. The fundamentals of this particular type of membrane reactors are reviewed including the effects of the most important parameters and the methods and rules of coupling photocatalysis and membrane separation. The survey of the studies on photocatalytic membrane reactors (PMRs) utilizing pervaporation, dialysis, membrane contactors and membrane distillation offers the opportunity of discussing the advantages with respect to PMRs adopting pressure driven membrane processes. Indeed, the strengths of the investigated processes are the high retention of the photocatalytic powders with minor fouling problems, the simpler and cheaper apparatuses and the possibility of selectively removing or recovering the products. Finally, the reasons, which currently limit the application of these membrane reactors, are illustrated together with the very interesting future perspectives.