Evapomeation characteristics of cross-linked quaternized chitosan membranes for the separation of an ethanol/water azeotrope

Abstract

The permeation and separation characteristics during evapomeation of an ethanol/water azeotrope (96.5 wt.-% ethanol) through quaternized chitosan (q-Chito) membranes and cross-linked q-Chito membranes, which were cross-linked with diethylene glycol diglycidyl ether (DEDGE), were studied. Both the q-Chito and the cross-linked q-Chito membranes showed high water-permselectivity for an ethanol/water azeotrope. The permeation rates for both membranes decreased and the water-permselectivities increased, with an increasing degree of quaternization of the chitosan and cross-linker concentration. The mechanism of separation for the ethanol/water azeotrope through the q-Chito and cross-linked q-Chito membranes was analyzed by the solution-diffusion model. Increasing permeation temperature increased the permeation rate and decreased the water-permselectivity for both membranes. However, the permeation rates of a cross-linked q-Chito membrane at 60–80°C were almost the same as those of the q-Chito membrane, and the separation factors for water-permselectivity (α =4 100–4 200) in the former were greater by two orders of magnitude as compared to the latter (α = 47–58). The above results were discussed from the viewpoints of the physical and chemical structure of the q-Chito and cross-linked q-Chito membranes. Effects of the degree of quaternization on the separation factor (□), the sorption selectivity (○), and the diffusion selectivity (•) for an ethanol/water azeotrope using the q-Chito membranes.