Influence of the support layer on the flux limitation in pervaporation

For the implementation of membranes in industry, economically feasible fluxes are a prerequisite. An analysis of the literature on pervaporation and vapour permeation (VP) fluxes through ceramic membranes by a simple modelling approach revealed that support resistances might strongly determine the magnitude of the permeation fluxes. Major focus in literature has been on dehydration of organics compared to the separation of organic mixtures. The fluxes reported for dehydration, up to 30 kg m(-2)h(-1), are significantly higher, which already resulted in implementation of zeolite membranes in an industrial process. For the separation of organic mixtures, fluxes of that magnitude have not been reported so far. The pressure drop over the support layer was calculated from the data reported to determine the contribution of the support layer(s) to the overall mass-transfer resistance. Especially for dehydration cases, but also for some organics separations the selective layer has already such a good performance that the support is controlling the flux magnitude. In these cases further improvement of the support properties is recommended to promote industrial applications and process intensification. The transport through the support is mainly by Knudsen diffusion due to its general orientation at the low-pressure side. The important parameters that are amenable for further optimisation are membrane thickness, porosity, tortuosity, and pore diameter. Further improvement of membrane performance can be obtained by operation at higher temperatures, since this increases the driving force for permeation over the membrane. (C) 2003 Elsevier B.V. All rights reserved.