COCURRENT MEMBRANE REACTORS VS PFRS FOR SHIFTING DEHYDROGENATION EQUILIBRIUM

Membrane reactor performance in reversible reactions like dehydrogenat ion is often compared to plug-flow reactor performance. Analysis of co current membrane-reactor design equations shows that as the Damkohler- Peclet product varies from 0 to infinity, the membrane reactor approac hes a fully diluted or undiluted plug-flow reactor. If its yield is ma ximized by varying this parameter, the optimum cocurrent membrane reac tor is often one of these limiting cases, and a membrane reactor offer s no advantage over a plug-flow reactor. When the optimum membrane rea ctor does not correspond to one of these limiting cases, there still m ay be a plug-flow reactor system that offers equal or higher yields. A nalysis of plug-flow-reactor performance indicates that there is an op timum degree of dilution; while the optimized membrane reactor yield m ay be greater than either an undiluted or a fully diluted plug-flow re actor; it may not be greater than an optimally diluted plug-flow react or. When using porous membranes the membrane reactor yield is at most 7% greater than the yield using a plug-flow reactor. The porous membra nes enhance the yields in a regime where the reactor would not be like ly to operate. Much larger yield advantages are possible, but only whe n the membrane is highly permselective, as with dense membranes. Highl y permselective membranes also enhance the yields in a regime where th e membrane reactor process is likely to be operated.