Preparation and characterization of cation-exchange media based on flexible polyurethane foams

摘要

Continuous electrodeionization (CEDI) is used to deionize a solution to a level attained by mixed bed ion exchange without chemical regeneration. However, handling of ion-exchange beads is laborious for a large-scale CEDI system. In this study, a new type of ion-exchange polyurethane foam containing sulfonic acid groups was synthesized by bulk condensation polymerization for use as a cation-exchange medium. Polyurethanes are synthesized by the reaction between a diisocyanate and a polyol. Toluene diisocyanate 2,4-80%, 2,6-20% (http://www..tciamerica.com/) was reacted with poly(propylene glycol) to synthesize a polyurethane prepolymer and then N,N-bis(2-hydroxylethyl)-2-aminoethanesulfonic acid (BES) was added to give a foam containing sulfonic acid groups. The functional polyurethane prepolymers were characterized by proton nuclear magnetic resonance spectroscopy (H-1 NMR), Fourier transform infrared spectroscopy (FT-IR), elemental analysis (EA), and get permeation chromatography (GPC). The ion-exchange capacity was measured as 2.5 meq/g, and the equiconductance point of the polyurethane foams were 14, 19, 29, and 33 mu/cm for BES molar ratios of 0.5, 0.7, 1.0, and 1.5, respectively. The porous plug model shows that the current flows dominantly through the solution phase of the polyurethane foam, which indicates the polyurethane foam is a suitable medium for use in a CEDI operation. (C) 2002 Wilev Periodicals, Inc. [References: 14]