Pervaporation of volatile organics from water: II. Influence of permeate pressure on partial fluxes

Hydrophobic pervaporation is being developed within the area of separation of volatile organic compounds from dilute aqueous solutions. Optimisation of the pervaporation process for these types of applications is often very complex due to the many different organic compounds which are to be separated simultaneously. The permeate pressure is one of the key process parameters that has a considerable impact on both selectivities and partial fluxes. In this study, a model for predicting the permeate pressure dependence of the partial fluxes of the organic compounds to be separated was developed. The model includes both the effect of external mass transfer and the effect of altered permeabilities due to membrane plasticisation for the various permeants. Both these effects were proved to effect the partial fluxes to a significant extent. The model was shown to be applicable to organic permeants within the groups of alcohols, esters and aldehydes. Adequate information about the membrane separation factor and the overall separation factor together with the total flux at one specific permeate pressure is all that is needed for the application of this model.