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. 20� or 80� 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. 20� and 80� 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. 20� and 80� and show that at least two resins with homo-functional structures are commercially available.