Effect of Structural Reorganization of the Surface Layer in AMN-P and OPMN-P Membranes on the Transport Characteristics of the Electronanofiltration Separation of Aqueous Ammonium Chloride Solution

Abstract

The absorption spectra of infrared radiation by membranes of the AMN-P and OPMN-P brands are analyzed. In the spectra of the surface layer of the AMN-P membrane, there is a decrease in the relative intensity of the frequencies of the carbonyl group (1724, 3392 cm–1 for air dry). For the cellulose acetate AMN-P membrane, the number of hydrophilic OH groups increases, which changes its molecular structure and transport characteristics. In the infrared radiation spectra of the surface layer of the OPMN-P membrane, the 1650–1670 cm–1 band characteristic of C=O group shows changes in the frequency of the spectrum: for air-dry and water-saturated samples, it shifts from 1652 to 1666 cm–1, respectively. Interactions of carbonyl (C=O) and amide (H–N) groups form the supramolecular structure of polyamides. Changes in the infrared radiation spectrum of the water-saturated sample of the OPMN-P membrane can be explained by the fact that the C=O…–…H–N bonds of the amide fragment do not break. Therefore, membrane swelling partially affects the structural rearrangement of the polyamide at the supramolecular level. In the electron nanofiltration separation of an aqueous solution of ammonium chloride, two intervals of change in the specific output flux are noted at fixed transmembrane pressure and experiment time. The first period occurs at a current density of 12.82 to 15.38 A/m2 and is associated with the penetration of the solvent with a slight gas formation on the electrodes. The second period is observed from 15.38 to 25.64 A/m2 and is associated with membrane degradation and intense gas formation, especially chlorine. It is noted that in the intermembrane channels the migration of cations and anions is affected by the processes of throttling, heat release, when operating in the limiting mode (when current carriers – H+ and OH–) appear, which is confirmed by the data of studies of the electrochemical parameters of the membrane system.