Relationship between permselectivity and permeability in pervaporation of water/alcohol mixture

Abstract

The evaporation mechanism of a water/alcohol mixture with a polymeric membrane was investigated. Flory-Huggins thermodynamics was adopted to introduce the selective dissolution factor, R. It was shown that the value of R of a water permselective membrane increases as permeability decreases, and that it has no upper limit. For an ethanol permselective membrane, R has a maximum value at a certain value of the swelling ratio. Making some assumptions for R, a semi-quantitative relationship between permselectivity and permeability, J, was derived for a water permselective membrane and examined experimentally. When the swelling ratio is changed, it can be said that selectivity is proportional to J 1−( 1 s ) depending on s, the molecular volume ratio of water to alcohol.