Sorption characteristics and diffusion permeability of the MA-41 anion-exchange membrane in lactic acid solutions

Abstract

The study was devoted to the investigation of the regularities of ionic and molecular transport in the system "lactic acid - sodium chloride - anion exchange membrane MA-41". Kinetic curves of ion-exchange sorption of lactic acid were plotted; it was shown that the time to reach the maximum working exchange capacity of the membrane was from 35 to 80 minutes, depending on the concentration of the solution. Isotherms of exchange sorption and non-exchange absorption of lactic acid in the solution concentration range 0.03-0.15 mol/dm³ were obtained. The exchange sorption isotherm is described by the Langmuir monomolecular adsorption equation with a high correlation coefficient. The value of non-exchange absorption of lactic acid noticeably increased at a solution concentration > 0.10 mol/dm³, however, the total amount of absorbed lactic acid (as a result of exchange and non-exchange sorption) remained lower than the total exchange capacity of the MA-41 membrane. Concentration dependences of membrane diffusion permeability in solutions of lactic acid, sodium chloride and mixed solution, where lactic acid and mineral salt are in equimolar ratio, are shown. For lactic acid in the concentration range 0.03 mol/dm³ - 0.30 mol/dm³ diffusion permeability coefficient of MA-41 membrane had a higher value than for sodium chloride. The reason for the limitation of the mineral salt transport is the Donnan exception. The presence of an equivalent amount of sodium chloride in a solution of lactic acid led to a decrease in the diffusion permeability coefficients of lactic acid by 2.5 - 3.2 times due to the conjugation of flows. The obtained experimental results will allow making a reasonable choice of the working range of concentrations of the treated solutions for the implementation of ecologically promising technologies of Donnan diffusion dialysis in the purification and production of lactic acid.