Separation of liquid benzene/cyclohexane mixtures by perstraction and pervaporation

The separation of liquid mixtures of benzene and cyclohexane by perstraction and pervaporation was studied and the effectiveness of these two membrane separation processes was compared. The membranes used for this purpose were made from a polymer alloy composed of cellulose acetate and a phosphoryl ester derivative of poly (dimethylphenylene oxide). This alloy has a glass transition temperature of over 200°C and is more permeable to benzene than to cyclohexane. Both the permeability of the alloy membranes and their selectivity for benzene relative to cyclohexane could be significantly enhanced by suitable annealing and conditioning procedures. The permeability of the membranes increased and their selectivity decreased as the benzene concentration in the “feed” mixtures was increased. The same effects were observed by raising the temperature. The permeation rates of the benzene/cyclohexane mixtures were found to be higher in pervaporation than in perstraction, particularly at lower benzene concentrations in the feed mixtures, while the membrane selectivity was the same in the two processes. This comparative study is the first of its kind and provides information on the relative advantages and disadvantages of perstraction and pervaporation.