Performance of butyrylcellulose membranes for benzene/cyclohexane mixtures containing a low benzene concentration by pervaporation

Butyrylcellulose (BuCell) with different degrees of butyrylation was synthesized as a membrane material for the separation of benzene/cyclohexane (Bz/Chx) mixtures. A BuCell membrane with a degree of butyrylation of 2.3 showed high benzene/cyclohexane selectivity for Bz/Chx mixtures by pervaporation. Both the permeation rate and the benzene/cyclohexane selectivity of the BuCell membrane increased with increasing benzene concentration in the feed mixture. The increase in the permeation rate resulted from an increase in the swelling of the membrane, and the increase in the benzene/cyclohexane selectivity can be attributed to an increase in the diffusion selectivity. With increasing degree of butyrylation of BuCell, the permeation rate increased; on the other hand, the benzene/cyclohexane selectivity decreased slightly. This result can qualitatively be explained by the degree of swelling, the density, and the contact angle of the BuCell membranes. The permeation and separation mechanism of Bz/Chx mixtures through BuCell membranes by pervaporation is discussed on the basis of the solution-diffusion model, which is typically applied for permeation through dense, nonporous membranes.