Correct evaluation of the effective concentration polarization influence in membrane-assisted devices. Case study: H-2 production by Water Gas Shift in Pd-membrane reactors

摘要

In this paper, a non-conventional approach is introduced to correctly measure the overall effective influence of concentration polarization in membrane-assisted devices. The basis of this study starts from considering that the Concentration Polarization Coefficient (CPC) tends to become high in those device zones where permeation driving force is relatively small (i.e., small flux). Therefore, these zones have to provide a small contribution to the overall polarization level, as membrane is not influential to the process. However, if calculating the average CPC along the device using the standard method, an unrealistic overestimation of the overall polarization level results, which is not representative of the real behavior of device. To avoid such an issue, a novel coefficient, here-named Effective Average CPC (EAC), is introduced and used. This coefficient, representing a more useful method to determine the real polarization extent in a membrane-assisted device, is then investigated as a function of key-engineering working parameters, like temperature, total feed and permeate pressure and Gas Hourly Space Velocity (GHSV), determining the conditions allowing the overall polarization level to be minimized. (C) 2015 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.