Vol 13, No 3 (2023)

The physicochemical properties of experimental heterogeneous MK-40 and MA-41 membranes with different ratios of ion-exchange resin and polyethylene binder in their composition are studied. It is shown that the specific electrical conductivity in 0.01–1 M NaCl solution decreases by more than 3 times for cation-exchange membranes and by 2 times for anion-exchange ones with a decrease in the content of ion-exchange resin in the membranes from 69 to 55%. It has been established that the diffusion permeability of anion-exchange membranes is more sensitive to their composition and naturally increases with an increase in the ion-exchange resin proportion in the composition. Information on the influence of the heterogeneous membrane composition on its structure, obtained by method of standard contact porosimetry, is supplemented by the calculation of transport-structural parameters of the microheterogeneous and extended three-wire models of the ion-exchange membrane.

Ion-exchange membranes with high specific selectivity towards singly charged ions are in demand in various industries. One of the ways to increase the specific selectivity can be formation of a thin layer on the membrane surface with a charge opposite to the charge of its fixed groups. The possibility of forming such a layer due to the specific interaction of calcium ions with the sulfonate groups of the membrane during treatment with a high-intensity electric current in a CaCl₂ solution is studied. The ability of heterogeneous (MK-40, Ralex CMH) and homogeneous (CMX, CJMC-5) sulfocationite membranes for specific adsorption of calcium ions on their surface is investigated. It is shown that the CMX membrane exhibits this ability to the greatest extent, which is due to the higher density of \( - {\text{SO}}_{3}^{ - }\) groups on its surface compared to other studied membranes. It is found that the formation of a thin positively charged layer on the surface of the CMX membrane increases the permselectivity coefficient of the membrane, \({{P}_{{{{{\text{N}}{{{\text{a}}}^{{\text{ + }}}}} \mathord{\left/ {\vphantom {{{\text{N}}{{{\text{a}}}^{{\text{ + }}}}} {{\text{C}}{{{\text{a}}}^{{{\text{2 + }}}}}}}} \right.} {{\text{C}}{{{\text{a}}}^{{{\text{2 + }}}}}}}}}},\) by 69%. At the same time, the presence of such a layer does not lead to an increase in undesirable water splitting, which occurs when applying widely used as modifiers polyelectrolytes with amino groups.

A series of composite ion-exchange membranes based on a heterogeneous cation-exchange MK-40 membrane and polyaniline was obtained under the conditions of electrodiffusion of a monomer and an oxidizing agent. The process of polyaniline synthesis on the membrane surface was accompanied by the registration of chronopotentiograms and the pH of the solution leaving the desalination compartment. The initial MK-40 cation-exchange membrane and the composites based on it were studied by voltammetry and chronopotentiometry in NaCl, CaCl₂, and MgCl₂ solutions in the same electrodialysis flow cell in which the composites were obtained. To calculate the transport numbers of counterions in membranes in CaCl₂ and MgCl₂ solutions by the chronopotentiometric method, the apparent fraction of the conducting membrane surface in the NaCl solution was calculated based on experimental data on the potentiometric transport numbers of counterions in the membrane. The conditions for the synthesis of polyaniline on the surface of a heterogeneous MK-40 membrane, leading to the preparation of samples with selectivity to singly charged ions, are revealed.

In this work, for the first time, we studied the permeability of individual lower hydrocarbons and in a C₁/C₄ mixture for films based on PTMSP of a new cis-enriched configurational composition (the content of cis-units in the samples was 80 and 90%). The methane permeability of freshly prepared cis-regular PTMSP films (90% of cis-units) exposed to air for a month is higher than the corresponding values of PTMSP films with 80% cis-units. The X-ray diffraction data indicate a looser packing of the cis-regular PTMSP. The introduction of the antioxidant Irganox 1076 into PTMSP films leads to a decrease in the initial level of the methane flux. At the same time, the permeability of films with the addition of Irganox 1076 over time (within 1 month) decreases much more slowly compared to films without the addition of an antioxidant. The permeability of individual lower hydrocarbons through PTMSP films without and with the addition of Irganox 1076 increases in the order С₁ < C₂ < C₃ < C₄. The value of the separation factor in the n-butane/methane mixture reaches 33, which is almost 7 times higher than the selectivity for individual components. The high level of n‑butane permeability of cis-enriched PTMSP is maintained for at least a month of films storage in air.