Application of Sodium Chloride Solutions to Regeneration of Anion-Exchange Membranes Used for Improving Grape Juices and Wines

Abstract

Membrane technologies, in particular, electrodialysis, are increasingly being used to stabilize and condition juices and wines. This work is aimed at finding environmentally appropriate “mild” methods for regeneration of anion-exchange membranes that are used in these processes. It has been shown that the fouling of anion-exchange membranes by grape wine components leads to an increase in both their electrical resistance by 30 or more times and thickness. The behavior of the resistance and its values in grape juice and wine for the investigated membranes are similar, apparently, due to the similar chemical composition of these liquid media. Treatment with NaCl solutions leads to partial degradation of the formed colloidal particles as a result of to the salting-out effect. The higher the salt concentration in the regenerating solution, the closer the conductivity values of the regenerated membranes are to the original values. The thinner the membrane and the larger its pores, the faster and more complete the regeneration process. If the contact time of anion-exchange membranes with wine does not exceed 70 h, salt regeneration can almost completely restore their selectivity. For example, in the case of homogeneous AMX-Sb membrane, the transport numbers of the counterion Cl⁻ in the initial and regenerated samples differ by no more than 1%. In the case of heterogeneous MA-41P membrane, this difference increases to 3%.