Vol 13, No 2 (2023)

The article presents the results of a computational and analytical study of hybrid RO–MD (Reverse Osmosis–Membrane Distillation) technologies for desalination of the Caspian Sea, providing for the production of an additional amount of desalinated water by the MD method from RO concentrates heated to 50–80°C due to waste heat of fuel combustion products in steam boilers. Two options for solving the problem of the formation of CaCO₃ and CaSO₄ precipitates on membranes were studied: with preliminary nanofiltration (NF) or Na-cationation (Na) of sea water, as an alternative to the use of antiscalants (AS) and acid. The negative environmental effect of most plants (eutrophication of water bodies) and their low efficiency at high concentrations of desalinated water are taken into account. The Langelier index (СаСО₃) and the degree of concentrate saturation (СаSO₄) were used as criteria for precipitation of deposits on the membranes. The NF and RO processes were studied using the ROSA computer program, and the MD and Na processes were studied by computer simulation of the corresponding calculation models. It was found that at a 70% permeate yield at the NF and RO stages, the possibility of calcium precipitation on the RO and MD membranes is prevented, but their precipitation on the NF membranes is predicted, which makes the use of AS forced. At the same time, additional permeate production at the MD stage from RO concentrates reaches 40% of the amount of permeate from RO stadium, and the electricity consumption in general according to the scheme is 1.88 kWh/m³. Reducing the calcium hardness of sea water to 50 µg-eq/dm³ by the Na-cationization method makes it possible to refuse both the use of AS and acidification with sulfuric acid with additional production of MD permeate – 27% relative to RO permeate. Electricity consumption rises to 2.5 kWh/m³. To use the known advantages of NF without the use of AS, a hybrid Na–NF–RO–MD scheme is proposed. It has been established that at 80% yields of NF and RO permeates, to prevent the formation of CaSO₄ precipitates at all stages of treatment, it is sufficient to reduce the hardness of sea water from 16 to 5.5 m-eq/dm³, and by acidifying the softened water to exclude the formation of CaCO₃ precipitates.

New results of one-sided surface modification of polymeric films and composite membranes of polyvinyltrimethylsilane (PVTMS) using low-temperature plasma are presented. The treatment was carried out by direct current discharge at the cathode and anode, air was used as the working gas, the exposure time was from 10 to 60 s, and the working pressure in the chamber was 15–20 Pa. The structure of the surface layers was analyzed by XPS, AFM and SEM, and the contact properties of the surface were also studied. The effective permeability coefficients for O₂, N₂, CH₄, CO₂, He, and H₂, as well as for gas diffusion, for cathode-treated PVTMS films are experimentally obtained, and the effective gas solubility coefficients are calculated. The permeability coefficients of the studied gases for composite membranes with a selective PVTMS layer modified at the cathode and anode were determined. It has been noted that the choice of electrode significantly affects not only the chemical structure of the surface and near-surface layers of PVTMS, but also the gas transport parameters of the modified samples. At the same time, during the treatment of PVTMS films at the cathode for 30 s, it was possible to achieve an increase in the O₂/N₂ selectivity by more than two times relative to the initial value. It has been established that the results of modification of composite membranes differ from those obtained for homogeneous films and it was possible to achieve O₂/N₂ selectivity in 2.5 times higher than the initial value. The potential of using surface modification of polymer films and membranes by low-temperature plasma to improve their gas separation properties is shown.

The paper considers some aspects of obtaining metal nanowires by matrix synthesis based on track membranes. In the first part of the paper, the main ideas of the method are considered and a review of the literature on the synthesis of nanowires of various types of single component (from one metal) and multicomponent—from two or more metals is given. In the second part of the review, variants of obtaining homogeneous structures of so-called alloyed nanowires and heterogeneous structures of so-called layered nanowires are considered. Several specific features of the electrodeposition method during the process in a limited volume of membrane pores are considered. In the second part of the work, the experimental results obtained by the authors in the study of electrodeposition of nanowires made of an iron–nickel alloy are considered. The so-called abnormal electrodeposition of iron was detected. The dependence of the integral element composition of the obtained nanowires on the pore diameter and on the growth voltage is discussed. Data on the nature of the distribution of elements along the length of nanowires are obtained. The unevenness of the composition is determined by the conditions of production (in particular, the different diffusion mobility of ions in narrow pore channels) and also depends on the voltage and diameter of the pore channels. Based on the X-ray diffraction data, the type of lattice (hcc) is determined and the nature of the change in the lattice parameter is shown, presumably associated with the difference in the ionic radii of metals.