An ion-exchange process with thermal regeneration. II. Properties of weakly basic resins

Abstract

Weakly basic ion-exchange resins have been synthesized by treating cross-linked chloromethylated polystyrene beads with primary and secondary amines and with polyamines. Titration curve data show that such resins may be either homo-functional and possess flat titration curves, or heterofunctional and possess sloping titration curves, depending on whether the basic sites within the resin have the same or different basicities. A comparison of the titration curves determined at c. 20º or 80º reveals that all amine resins become weaker bases when heated, but the maximum effect is shown by the resins with homo-functional structures; e.g. the plateau-shaped curves at c. 20º and 80º of a polyvinylbenzyldiethylamine resin differ by about 1.2 of a pH unit at half neutralization. The effect is fully reversible. The influence of amino group substituents, cross-linking, salt concentration, sulphate ions, and temperature on the titration curves of weakly basic amine resins has been studied. Titration curves of a variety of commercial amine resins have been determined at c. 20º and 80º and show that at least two resins with homo-functional structures are commercially available.