Batch dynamics for the uptake of potassium from crude polyols on Amberlite 252, a strong acid ion-exchange resin, are obtained over a wide range of conditions. Experimental data have been analyzed using a homogeneous model with finite solution volume. An increase of diffusion coefficients with the resin weight used in the purification is observed. An asymptotic maximum value, approaching the value of the diffusion coefficient in bulk solution, is reached for high resin weights or low values of external concentration. The heterogeneous nature of the resin matrix and the large size of the diffusing molecule is proposed as an explanation of this behavior. The proposed purification procedure finds general applicability for other polyol types, being economically and technically feasible.