Sorption of neutral components in ion-exchange resins. 1. Effect of cross-link density and counterion on selective sorption of water-ethanol mixtures in sulfonated PS-DVB resins

Experimental data for the distribution of water-ethanol mixtures between a solid phase and a liquid phase at 298 K are reported. The solid phases studied were gel-type sulfonated poly(styrene-co-divinylbenzene) resins of different degrees of cross-linking (4-8% DVB) and carrying different, counterions (Na+, Ca2+, and La3+). The shear moduli of the resin beads were also measured to characterize their elastic properties. All resins absorb water selectively, and the selectivity increases with increasing cross-link density. The low selectivity of the less densely cross-linked resins is shown to be mainly due to the mutual interaction of the solvents in the resin phase resulting in a pronounced maximum in the ethanol sorption isotherms. The influence of the counterion on the selectivity is more complex. At high water contents, the water selectivity of the Na+ resin is higher than that of the Ca2+ and La3+ resins, whereas the selectivities are approximately equal at low water contents. The elastic properties of the resin beads remain unchanged from pure water to water mole fractions of around 0.4, where a sharp rise in the shear modulus occurs. The data are analyzed by means of a model based on the UNIQUAC equation and the affine network theory of elasticity. The effect of cross-link density an the selectivity and solvent content of the resina can be explained satisfactorily with the model. However, the calculated and experimental sorption isotherms for the La3+ resins deviate appreciably at low external water contents. The discrepancies are discussed on the basis of the elastic properties of the resins and the specific solvation interactions.