Vapor permeation of aqueous ethanol mixtures through agarose membranes

Vapor permeation membranes were obtained from a “green” polymer, agarose. Agarose and crosslinked agarose membranes preferentially transported water vapor from aqueous ethanol mixtures by vapor permeation. Diffusion experiments revealed that the permselectivity toward water vapor was expressed by both solubility selectivity and diffusivity selectivity. Differential calorimetric melting endotherms of the membranes were studied to clarify the state of water in the membrane. The results revealed that there were a couple of states of water in the membrane, such as bound and free (bulk) water. The present study suggests that the existence of bound water in a membrane is requisite to selectively transport water vapor from aqueous ethanol mixture by vapor permeation. In addition, preliminary study revealed that the membranes were applicable to forward osmosis.