Dense sodium alginate (SA) membranes crosslinked with glutaraldehyde (GA) have been prepared by the solution method, wherein a nonsolvent of SA (acetone) was used in a reaction solution instead of an aqueous salt solution. Through infrared radation, X-ray diffractometry, and the swelling measurement, the crosslinking reaction between the hydroxyl groups of SA and the aldehyde groups of GA was characterized. To investigate the selective sorption behavior of the crosslinked SA membranes, swelling measurements of the membranes in ethanol-water mixtures of 70-90 wt % ethanol contents were conducted by equipment that was able to measure precisely the concentration and amount of the liquid absorbed in the membranes. It was observed that the crosslinking could reduce both the solubility of water in the resulting membrane and the permselectivity of the membrane toward water at the expense of membrane stability against water. The pervaporation separation of a ethanol-water mixture was conducted with the membranes prepared at different GA contents in the reaction solution. When the membrane was prepared at a higher GA content, both flux and separation factor to water were found to be reduced, thus resulting from the more crosslinking structure in it. The pervaporation separations of ethanol-water mixtures were also performed at different feed compositions and temperatures ranging from 40 to 80ЊC. A decline in the pervaporative performance was observed due to the relaxation of polymeric chains taking place during pervaporation, depending on operating temperature and feed composition. The relaxational phenomena were also elucidated through an analysis on experimental data of the membrane performance measured by repeating the operation in the given temperature range.

Dense sodium alginate (SA) membranes crosslinked with glutaraldehyde were prepared by a new solution technique, which had different extents of crosslinking gradient structures. The SA membranes having a crosslinking gradient structure were fabricated by exposing one side of the membrane to the reaction solution while blocking the other side by a polyester film to prevent the reaction solution from contacting it. The extent of the crosslinking gradient was controlled by the exposing time. When the swelling measurements were performed with uniformly crosslinked membranes in aqueous solutions of 70-90 wt % ethanol contents, it was observed that the crosslinking could reduce both the solubility of water in the membrane and the permselectivity of the membrane toward water. The pervaporation separation of the ethanol-water mixture of 90 wt % ethanol content was carried out with membranes with different extents of crosslinking gradients. As the crosslinking gradient was developed more across the membrane, the resulting flux as well as the separation factor to water was found to decrease while the membrane became stable against water. The pervaporation performances of the membranes with different membrane loadings in a membrane cell were also discussed using the schematic concentration and activity profiles of the permeant developed in them. The pervaporation separations of the ethanol/water mixtures through the membrane with an optimal crosslinking gradient were performed at different feed compositions and temperatures ranging from 40 to 80ЊC. The change in the membrane performance due to the relaxation process during pervaporation was observed with the operating temperature and feed composition. The relaxational phenomena were also elucidated through an analysis of the experimental data of the membrane performance measured by repeating the operation in a given temperature range.