Permeation and Separation Characteristics of a Mixture of Benzene/Cyclohexane through Cellulose Alkyl Ester Membranes during Pervaporation

Abstract

Summary: Cellulose alkyl esters such as ethyl, butyryl, pentyl, and heptyl cellulose with different numbers of carbon in the alkyl ester group were synthesized for the separation of a mixture of benzene/cyclohexane (Bz/Chx = 5/95 w/w) with a low concentration of benzene. All of cellulose alkyl ester membranes showed high benzene/cyclohexane selectivity for a Bz/Chx mixture in pervaporation. With increasing carbon number in the ester groups, the permeation rate increased but the benzene/cyclohexane selectivity decreased. The increase in the permeation rate could be attributed to an increase in the swelling of the membrane due to the feed mixture, and the decrease in the benzene/cyclohexane selectivity was dependent on both the decrease in the solubility selectivity and the diffusion selectivity. These pervaporation characteristics are discussed from the viewpoints of chemical and physical structure of the cellulose alkyl ester membranes such as the degree of swelling, the contact angle, and the density of the cellulose ester membranes, and the solution composition absorbed into their membranes.