The pervaporation characteristics of water-ethanol mixture through cellulose acetate symmetric and asymmetric membranes, silicone rubber membrane and silicone composite membrane have been investigated. The permeation rate and separation factor were tested at different operating conditions such as feed composition, temperature and downstream pressure.
In cellulose acetate symmetric membrane, maximum permeation rate occurred at about 60 mol % water. The rate of permeation increased with temperature, and the activation energies of permeation ranged from 4.6-7.2 kcal/mol. The separation factor for water increased with temperature.
The permeation rate of cellulose acetate asymmetric membrane was greater than that of symmetric membrane, but separation factor was smaller. The most important condition of preparing cellulose acetate asymmetric membrane was evaporation time of solvent.
Silicone rubber membrane was selective for ethanol. The permeation rate increased, but the separation factor decreased with increasing temperature and with increasing ethanol fraction in feed. The activation energies of permeation ranged from 6.3-7.4 kcal/mol.
Silicone composite membrane was prepared by coating of poly (dimethyl siloxane) on polysulfone porous support membrane. The permeation rate of composite membrane was greater than that of homogeneous silicone rubber membrane. The separation factor, however, was reduced.
As downstream pressure was increased, the permeation rate was decreased.