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 on the
selectivity and solvent content of the resins 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.
ABSTRACT:The effect of the solvent composition on the elasticity of strong and weak cation-and anion-exchange resin beads was studied. Poly(styrene-co-divinylbenzene) resins containing sulfonic acid or quaternary ammonium groups and an acrylic acid resin crosslinked with divinylbenzene were immersed in water, NaCl solutions, or aqueous alcohol solutions and the shear modulus was measured with a uniaxial compression method. The elastic data were compared with the swelling properties. In pure water the shear moduli increased when the crosslink density, counterion valence, counterion size, and functional group size increased. Two additional phenomena in the elastic behavior were observed when the swelling degree of the resins was changed by the addition of alcohol or salt. A decrease of the modulus was observed when moving from the fully swollen state to a less swollen state, and a steep upturn of the modulus took place at a characteristic swelling region. The depth of the minimum and the location of the transition from the rubbery to the glassy state depended on the characteristics of the resins. The finite expansibility of the polymer chains and the glass transition explained these findings.
Partition of d-xylose between ion-exchange resins and different water−ethanol mixtures at 298
K was studied. Gel-type sulfonated poly(styrene-co-divinylbenzene) resins cross-linked with 4
or 8 wt % divinylbenzene and carrying Na+, Ca2+, or La3+ as the counterion were used as the
absorbent phases. Sorption of d-xylose increases with decreasing water mole fraction in the
solvent mixture, irrespective of the resin. The increasing sorption is explained by the selective
water uptake of the resin and the far better solubility of d-xylose in water than in ethanol. At
high water contents, sorption of d-xylose increases with decreasing cross-link density, while
the enhanced water selectivity of the densely cross-linked resin improves sorption at low water
contents. The experimental data were compared with the literature data for d-glucose.
Complexation of both sugars with the metal ions studied is shown to be negligible, and the
sugars are absorbed more effectively by the resin loaded with the less solvated univalent
counterion. The sorption model based on the UNIQUAC equation and the affine network theory
of elasticity explains satisfactorily sorption of individual components from the ternary water−ethanol−sugar solutions.
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