Comparing and modeling the dehydrogenation of ethanol in a plug-flow reactor and a Pd-Ag membrane reactor

In this study the performance of a membrane reactor was compared to that of a plug-flow reactor for the dehydrogenation of ethanol. The membrane consisted of a 2.2 mum Pd-Ag film (23 wt% Ag) deposited on the inside of an asymmetric a-alumina membrane tube (SCT). The membrane tube was packed with a 14.5 wt% Cu on SiO2 catalyst. The effects of the sweep gas flow rate, the ethanol feed flow rate, and the temperature on acetaldehyde yield and selectivity were investigated. A model was developed using measured kinetic data and membrane permeance data to predict the performance of the membrane reactor. The membrane reactor performed significantly better than the plug-flow reactor at all temperatures tested. The best results were obtained at 275 degreesC, where the total ethanol exit conversion increased from 45% (plug-flow reactor) to 60% at low feed flow rates and from 36% to 46% at high feed flow rates. The acetaldehyde selectivity for the membrane reactor increased from the lower 80% range to above 90% at 275 degreesC. The model underpredicted the total ethanol conversion, indicating that the measured reaction rate parameters for a differential reactor were lower than those for the membrane reactor.