Effect of hydrotrope on the electrochemical behavior of Dowex-50 membrane in aqueous solution of uni–univalent electrolyte

Membrane potential and membrane conductance measurements have been carried out using Dowex-50Kynar membrane, sodium chloride and urea as a hydrotrope, mixture of varying composition to examine the hydrotrope effect on electrochemical character of the membrane. A significant change on membrane electrochemical character is observed in the presence of hydrotrope due to changed co-ion exclusion. The Donnan equilibrium has been incorporated to estimate the activity coefficient of counter ion, ypm, and solute, y±m in the membrane phase along with the parameter, so called Ф expressing non-ideality. Solute rejection performance of the membrane is examined when electrolyte concentration remains constant and hydrotrope concentration varies and vice-versa. In both cases, membrane specific conductance depends on NaCl and hydrotrope concentrations differently. Friction caused through the membrane by the variation in concentration of hydrotrope is greater than friction caused by the variation in concentration of NaCl. Zeta potential is sensitive to the variation of hydrotrope concentration but insensitive to the variation of electrolyte concentration. The membrane system shows the behavior of NF membrane because Pe ≪ 1 is estimated in both cases.

Membrane heterogeneity disappears gradually with increase of water activity in the membrane phase. Water activity also facilitates mass transfer along with the ionization of ionogenic groups of the membrane. Hydrotrope reduces mass transfer and solute rejection performance of the membrane. Membrane morphology slightly affected by hydrotrope (urea) and NaCl.Figure optionsDownload as PowerPoint slideHighlights
► Hydrotrope (urea) affects electrochemical behavior of the membrane.
► Permselectivity decreases on increasing hydrotrope and electrolyte concentrations.
► Membrane fouling resistant ability increases in the presence of hydrotrope.
► Water activity affects the ionization of ionogenic groups of the membrane.
► Ions and water transport are endowed with entropy production per unit volume.