Diffusion of acetic, malonic and citric acids through commercial anion-exchange membranes and modified anion-exchange membrane Ralex AMH

This work is devoted to the investigation of the neutral salts diffusion, sodium acetate, sodium malonate, and sodium citrate through heterogeneous anion-exchange Ralex AMH, MA-41, and MA-40 membranes, through the homogeneous Lancytom AHT membrane, and the two-layer Ralex AMH/MF-4SK membrane from 0.1–0.5 mol-eq/L solutions into deionized water. Diffusion, as one of the ion transport mechanisms during the synthesis of organic acids from their salts using electromembrane methods, affects the main electrochemical characteristics of these processes. It is shown that the differential diffusion permeability coefficients (K) of salts through the homogeneous membrane are several times lower than those through heterogeneous membranes. In the series “sodium acetate – sodium malonate – sodium citrate,” the slope of the K coefficient dependence on the salt concentration changes from positive to negative. Calculating the ionic composition of the solution formed after the experiment using pH and specific conductivity shows that, in addition to neutral salts, it contains hydrolysis products—acetic acid, hydromalonates, and hydro- and dihydrogen citrates. These hydrolysis products increase the solution’s specific conductivity and may be the cause of the negative slope in the K coefficient dependence on the sodium citrate concentration across membranes. The effect of hydrolysis of neutral salts of polybasic acids must be taken into account when measuring the K coefficient using the salt diffusion method through a membrane into deionized water.

anion-exchange membrane, bilayer membrane, sodium acetate, sodium malonate, sodium citrate, diffusion transport