CHARACTERISTICS OF PERMEATION AND SEPARATION OF AQUEOUS ALCOHOL-SOLUTIONS THROUGH CROSS-LINKED PULLULAN MEMBRANES

The permeation and separation characteristics of aqueous alcohol solutions through crosslinked pullulan membranes were investigated in pervapouration and evapomeation. Pullulan is highly hydrophilic polysaccharide that is easily soluble in water, so that pullulan was crosslinked with glutaraldehyde for use as a separation membrane for aqueous alcohol solutions. The crosslinked pullulan membranes preferentially permeated water from aqueous ethanol solutions above about 25 wt% of ethanol in the feed concentration in pervapouration and below 90 wt% of ethanol in evapomeation. The selectivity for water in evapomeation was higher than that in pervapouration. The permeation rate in the former, however, was lower than that in the latter. These results were attributed to the swelling of the membrane by the feed solution in the latter method. In evapomeation, the selectivity and permeation rate decreased with the increase of ethanol concentration in the feed vapour. However, such behaviour was not observed in pervapouration. The different results between the evapomeation and the pervapouration methods are discussed from the viewpoint of the structure of the membrane in both methods.