ABSTRACT:For the purpose of separating aqueous alcohol by the use of pervaporation technique, a composite membrane of chitosan (CT) dip-coated cellulose acetate (CA) hollow-fiber membranes, CT-d-CA, was investigated. The effects of air-gap distance in the spinning of CA hollow-fiber membranes, chitosan concentration, and sorts of aqueous alcohol solutions on the pervaporation performances were studied. Compared with unmodified CA hollow-fiber membrane, the CT-d-CA composite hollow-fiber membrane effectively increases the permselectivity of water. The thickness of coating layer increases with an increase in chitosan concentration. As the concentration of chitosan solution increased, the permeation rate decreased and the concentration of water in the permeate increased. In addition, the effects of feed composition and feed solution temperature on the pervaporation performances were also investigated. The permeation rate and water content in permeate at 25°C for a 90 wt % aqueous isopropanol solution through the CT-d-CA composite hollow-fiber membrane with a 5-cm air-gap distance spun, 2 wt % chitosan dip-coated system were 169.5 g/m 2 h and 98.9 wt %, respectively.

ABSTRACT:A series of novel solvent-soluble polyimides based on the diamine of 3,3-bis[4-(4-aminophenoxy)phenyl] phthalide (BAPP) were prepared. The effects of the dianhydride structures on the pervaporation performance of aqueous alcohol mixtures through these polyimide membranes were studied. The BAPP-based polyimide membranes exhibited water permselectivity during all process runs. The permeation rate increased with the addition of bulky groups to the polyimide backbone. The effects of the feed solution concentration, feed solution temperature, and carbon atom number of the feed alcohol on the pervaporation performance were also investigated systematically. Optimum pervaporation results, a separation factor of 22 and a permeation rate of 270 g/m 2 h, were obtained for a 90 wt % feed aqueous ethanol solution through a 3,3Ј,4,4Ј-biphenyl tetracarboxylic dianhydride polyimide membrane at 25°C.