FUNDAMENTAL STUDIES ON DESIGN OF SEPARATION MEMBRANES FOR ORGANIC LIQUID MIXTURES AND IMPROVEMENT OF MEMBRANE SEPARATION

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Purpose of preparing polymer membranes with high permeability and high selectivity for organic liquid mixtures, preparation conditions of the membrane for the permeation and separation of aqueous alcohol solutions in pervaporation was investigated in detail using various polymer materials.Hydrophilic polymer membranes such as poly(vinyl alcohol) and chitosan membrane predominantly permeated water from aqueous alcohol solutions. Also, hvdrophobic polymer membranes such as poly(vinyl chloride) and polystyrene membrane selectively permeated water. In order to reveal these phenomena, composition of liquid adsorbed in the membrane was analyzed. The former membranes adsorbed water and the latter one alcohol. From these results it was found that good performance for the permeation and separation could not be obtained only increase of solubility of the permeating species into the membrane and it was very important to increase diffusivity of the permeating species in the membrane.Relationship b … More etween the structural change of membrane with heat treatment and crosslink reaction and the separation characteristic was studied from the viewpoint of molecular level. It was found that slight change of the membrane structure significantly influenced the permeation and separation characteristics.In this study, we proposed a new membrane separation technique, which was named an evapomeation method, the permeation and separation characteristics for aqueous alcohol solutions through some polymer membranes by the evapomeation were compared with those by pervaporation. In general, the separation in evapomeation was superior to that in pervaporation, but the permeability in pervaporation was better than that in evapomeation.In evapomeation, it was possible to control temperature difference between the membrane neighborhood and the feed solution. When this evapomeation method with control of the temperature difference was applied to the separation of aqueous alcohol solutions through poly(dimethylsiloxane) membrane and aqueous dimethyl sulfoxide through chitosan membrane, the former merfibrane permeated alcohols and the latter one permeated water with high selectivity.Mechanisms for organic aqueous solutions through these membranes are discussed from the viewpoints of physicochemical nature of the membrane and the permeating species. Less