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divalent ion-exchange with resins
ReactivePolymers, 13 (1990)
321-325 Elsevier Science Publishers B.V., Amsterdam
321
ABSTRACTS of other papers presented at the symposium
F a c i l i t a t e d p r o t o n t r a n s f e r across anion exchange membranes F . G . H e l f f e r i c h , Department of Chemical Engineering, The Pennsylvania
State University, Univer-
sity Park, PA 16802, U.S.A. Ion exchange membranes normally obstruct electrolyte transport because their Donnan action largely excludes the coion and so prevents its passage. In the specific case of acid transport across anion exchange membranes, the coion is the hydrogen ion and, under normal conditions, controls the rate of transfer. However, in the case of polyvalent acids such as sulfuric, phosphoric, or carbonic, the anion may act as proton carder and thereby provide an alternative and more effective transport mechanism that relies exclusively on anions and so is not subject to Donnan exclusion. In the case of sulfuric acid, for example, one formula unit of H2SO4 can be transferred by interdiffusion of two HSO£ in one direction and one SO42- in the other. The observed much greater permeability of a strong-base anion exchange membrane to sulfuric as compared to hydrochloric acid confirms this effect. Such facilitated proton transfer, especially by carbonate/bicarbonate, may have implications for biological systems.
Unpublished
Determinants of anion selectivity in monovalent/monovalent and monovalent/divalent ion-exchange with resins S u r e s h S u b r a m o n i a n a n d D e n n i s C l i f f o r d , Environmental Engineering Program, University of Houston, Houston, Texas 77204-4791, U.S.A. Previous research has indicated that resin characteristics, viz., active site spacing and matrix hydrophobicity, are the important determinants of monovalent/divalent anion selectivity but that resin parameters have no influence on monovalent/monovalent anion selectivity. In the first part of this study the hypothesis that aqueous-phase interactions and properties of the solvated ion are the determinants of resin affinity in systems involving only monovalent ions is proposed and subjected to statistical verification. The affinity of anions is well correlated to ionic radius. Solvation parameters such as hydration number, entropy, enthalpy and free energy of hydration are also strongly correlated to resin selectivity. A simple rule for categorizing ions as structure-makers and structure-breakers is proposed and the results are consistent with conventional classifications. In the second part of this study, an attempt is made to experimentally validate the statistically established hypothesis that the proximity of ionogenic groups controls resin selectivity in systems involving monovalent and divalent ions. Experimental verification of the concept that resins with closely spaced functionalities have an inherent preference for divalent ions over monovalent ions is provided by the selectivity trends of dicarboxylate/chloride exchange on trialkylamine resins having trimethyl-, triethyl- and tributyl-amine functional groups. References: Journal of Solution Chemistry, 18 (6) (1989) 529-543; Reactive Polymers, 9 (1988) 195-209.
321-325 Elsevier Science Publishers B.V., Amsterdam
321
ABSTRACTS of other papers presented at the symposium
F a c i l i t a t e d p r o t o n t r a n s f e r across anion exchange membranes F . G . H e l f f e r i c h , Department of Chemical Engineering, The Pennsylvania
State University, Univer-
sity Park, PA 16802, U.S.A. Ion exchange membranes normally obstruct electrolyte transport because their Donnan action largely excludes the coion and so prevents its passage. In the specific case of acid transport across anion exchange membranes, the coion is the hydrogen ion and, under normal conditions, controls the rate of transfer. However, in the case of polyvalent acids such as sulfuric, phosphoric, or carbonic, the anion may act as proton carder and thereby provide an alternative and more effective transport mechanism that relies exclusively on anions and so is not subject to Donnan exclusion. In the case of sulfuric acid, for example, one formula unit of H2SO4 can be transferred by interdiffusion of two HSO£ in one direction and one SO42- in the other. The observed much greater permeability of a strong-base anion exchange membrane to sulfuric as compared to hydrochloric acid confirms this effect. Such facilitated proton transfer, especially by carbonate/bicarbonate, may have implications for biological systems.
Unpublished
Determinants of anion selectivity in monovalent/monovalent and monovalent/divalent ion-exchange with resins S u r e s h S u b r a m o n i a n a n d D e n n i s C l i f f o r d , Environmental Engineering Program, University of Houston, Houston, Texas 77204-4791, U.S.A. Previous research has indicated that resin characteristics, viz., active site spacing and matrix hydrophobicity, are the important determinants of monovalent/divalent anion selectivity but that resin parameters have no influence on monovalent/monovalent anion selectivity. In the first part of this study the hypothesis that aqueous-phase interactions and properties of the solvated ion are the determinants of resin affinity in systems involving only monovalent ions is proposed and subjected to statistical verification. The affinity of anions is well correlated to ionic radius. Solvation parameters such as hydration number, entropy, enthalpy and free energy of hydration are also strongly correlated to resin selectivity. A simple rule for categorizing ions as structure-makers and structure-breakers is proposed and the results are consistent with conventional classifications. In the second part of this study, an attempt is made to experimentally validate the statistically established hypothesis that the proximity of ionogenic groups controls resin selectivity in systems involving monovalent and divalent ions. Experimental verification of the concept that resins with closely spaced functionalities have an inherent preference for divalent ions over monovalent ions is provided by the selectivity trends of dicarboxylate/chloride exchange on trialkylamine resins having trimethyl-, triethyl- and tributyl-amine functional groups. References: Journal of Solution Chemistry, 18 (6) (1989) 529-543; Reactive Polymers, 9 (1988) 195-209.