Influence of a Hydrophobizer on the Properties of Experimental Bentonite-Containing Bipolar Membranes

Abstract

Experimental samples of bipolar ion-exchange membranes were obtained by applying liquid sulfocation exchanger LF-4SK containing bentonite clays treated with stearic acid to an anion-exchange membrane-substrate with quaternary ammonium groups MA-41. The effect of the amount of added bentonite (1, 2, 3 wt%) on the characteristics of membranes was studied. Silicon and hydroxyl of the included bentonite accelerate the dissociation of water molecules, which leads to increasing the concentration of hydrogen and hydroxyl ions during bipolar electrodialysis. Surface modification of bentonite particles with stearic acid improves the dispersion of the clay in the polymer solution. The physico-mechanical characteristics of experimental ion-exchange membranes containing bentonite treated with stearic acid are compared with a membrane containing natural untreated bentonite. The total exchange capacity, density, moisture capacity, as well as tensile strength and relative elongation were determined. The injection of a hydrophobizer into the membrane leads to a decrease in moisture content, an increase in the total exchange capacity and density of the cation-exchange layer compared to a membrane containing bentonite in its original form. The conversion of sodium sulfate (concentration 0.5 mol/dm3) was carried out with experimental bipolar ion-exchange membranes. The use of a bipolar membrane containing bentonite treated with stearic acid (3%) in the cation-exchange layer leads to an increase in the productivity of the process and a decrease in energy costs compared to a commercially available heterogeneous ion-exchange membrane with similar functional groups and not containing catalytic additives. A scheme for obtaining experimental bipolar membranes is proposed, which consists of the following stages: preparation of bentonite; treatment of bentonitewith stearic acid; preparation of anion-exchange membrane-substrate MA-41; coating the membrane-substrate with of a cation-exchange layer.