Composite Membranes with a Polyvinyltrimethylsilane Skin Layer for Separation of Water–Alcohol Mixtures

Abstract

The paper presents the characteristics of a laboratory-made water-selective composite membrane with a selective layer of hydrophobic polyvinyltrimethylsilane (PVTMS) for use in the processes of vapor-phase membrane recovery of alcohols from dilute aqueous alcohol mixtures of biogenic origin. The support is a polyacrylonitrile ultrafiltration membrane, and the PVTMS skin layer of the resulting composite membrane has a thickness of 3 to 4 microns. The vapor transport and separation characteristics of the membrane for water–ethanol and water–butanol mixtures in the temperature range of 60–80°C have been studied. It has been shown that the membrane selectivity varies in the range of 23–39 for the water/ethanol pair or 100–140 for the water/butanol pair. A specific feature of the hydrophobic water-selective membrane as applied to the vapor-phase process is the stability of its characteristics due to the absence of swelling, in contrast to hydrophilic water-selective membranes whose characteristics substantially depend on the activity of water vapor. The process of vapor-phase membrane recovery of ethanol and butanol from dilute aqueous alcohol mixtures of biogenic origin with their initial concentrations of 10 and 1 wt %, respectively, has been mathematically modeled on the basis of the experimental data. The calculation results show that the composite membrane obtained makes it possible to concentrate ethanol and butanol to 95 and 98 wt % with degrees of recovery of more than 0.8 and more than 0.9, respectively.