Cellulose-poly(acrylamide-acrylic acid) interpenetrating polymer network membranes for the pervaporation of water-ethanol mixtures. II. Effect of ionic group contents and cellulose matrix modification

The separation properties in the dehydration of a water-ethanol mixture and the swelling behavior of interpenetrating polymer network (IPN) pervaporation membranes based on a cellulose or cellulose-hydroxyethyl cellulose (HEC) matrix and poly(acrylamide and/or acrylic acid) were investigated depending on the ionic acrylate groups content (gamma) in synthetic polymer chains (0-100 mol %), the HEC content in the matrix (0-50 wt %), and the temperature (25-60 degreesC). The separation factor (alpha), permeation rate (P), and separation index (alphaP) significantly improved with increasing gamma values only for the separation of concentrated ethanol solutions (similar to 86 wt %). For more dilute solutions of ethanol (similar to 46 wt %), the P and aP values also increased but no considerable increase in a was observed. All types of membranes based on the cellulose matrix were characterized by a drastic decrease in the values of P at [EtOH] greater than or equal to 90 wt % and, as a result, a decrease in the separation index (kg m(-2) h(-1)) from similar to 2000 (for 86 wt % EtOH, 50 degreesC) to similar to 240 (for 95 wt % EtOH, 50 degreesC), which correlates with a decrease in the degree of membrane swelling. The modification of the cellulose matrix by introducing HEC into it makes it possible to increase considerably the membrane swelling in concentrated EtOH solutions and, hence, the alphaP value to similar to 760 (95 wt % EtOH, 50 degreesC). All types of IPN membranes exhibit a marked increase in both alpha and P when the temperature increases from 25 to 60 degreesC. (C) 2001 John Wiley & Sons, Inc.