Sorption of carboxylate ions by strongly basic anion exchangers

Abstract

Equilibrium data are reported for the exchange between chloride and a series of carboxylate ions on certain strong-base anion exchange resins. The carboxylates ranged from butyrate to decanoate and, within this range, sorption of the anions was entirely accounted for by ion-exchange, i.e. no significant electrolyte sorption or uptake of free acid occurred. Polystyrene resins showed a regular increase in affinity for carboxylate as the chain length of the latter increased and a value for the standard free energy change for the transfer of a methylene group from aqueous solution to the resin phase has been estimated as –2200 J mol^–1. This value is comparable to that for certain adsorption processes and it is concluded that hydrophobic interaction between the resin matrix and the hydrocarbon chains of the carboxylates is responsible for the increasing affinity. With an acrylic resin, however, no such interaction occurs and there is strong evidence of association of carboxylate ions within the resin, rather like the formation of micelles in bulk solution.