Volume 15, Nº 3 (2025)

In this work, the membranes based on crystallizable poly(hexadecy-l-methyl-siloxane) (PHDMS) were obtained and their gas transport properties in relation to a number of light hydrocarbons were investigated with a focus on n-butane and methane permeability and selectivity. A first-order phase transition (crystallization of side alkyl chains) with a melting temperature (T_m) of 26°C was detected for the PHDMS-membranes. It was shown that the membrane transport properties were significantly influenced by their phase state. The gas permeability, diffusivity and solubility undergone a sudden change in the vicinity of T_m. Thus, a decrease in temperature from 30° to 20°C leads to a decrease in the hydrocarbons permeability coefficients by an order of magnitude. On one hand, the membranes n-butane/methane selectivity at a temperature T > T_m did not exceed 25, which is comparable with the results for previously studied polyalkylmethylsiloxanes with shorter alkyl chains. On the other, the n-butane/methane selectivity of semicrystalline membranes (T < T_m), despite a noticeable reduction in gas permeability, can reach selectivity values of ~150.

A kinetic experiment in the process of dry reforming of methane was performed for the first time in a reactor with a membrane catalyst for the extractor mode, in which the hypothesis of activated mass transfer based on the phenomenon of thermal slip was used for the analysis of the results. The results obtained show that in both parts of the reaction space (in the retentate and in the permeate) of the membrane reactor, intensification of the intermediate stages of dry reforming of methane is observed, compared with the contactor modes. Unlike the contactor modes, in which the methane cracking stage is shifted toward the formation of products of this reaction, in the extractor mode, the process occurs near equilibrium, and the constants of the direct and reverse reactions are close. In this mode, the reverse reaction of the water shift is strongly shifted toward the formation of water gas.

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.