Vol 13, No 6 (2023)

This work is aimed at obtaining a membrane material that is resistant to the formation of a precipitate on the surface upon contact with an ABE fermentation mixture and has a good separating ability during the pervaporation isolation of n-butanol from a water–alcohol mixture. In this regard, in this work, for the first time, the creation of pervaporation membranes based on polymethyltrifluoroethylacrylatesiloxane (F3-Acr), as well as a copolymer of polydecylmethylsiloxane and polymethyltrifluoroethylacrylatesiloxane (C10-F3-Acr) is proposed. In comparison with polydecylmethylsiloxane (C10), the structure and sorption properties of the developed membrane materials for n-butanol, ethanol and acetone were studied. It should be noted that the highest sorption of n-butanol is characteristic of C10-F3-Acr (0.46 g/g). Changes in surface properties were assessed by the contact angle and elemental composition of the surface before and after exposure for 1 month in a fermentation medium. The transport and separating properties of the synthesized membrane materials were studied in the vacuum pervaporation mode during the separation of a model ABE fermentation mixture. It was shown that the introduction of a fluorine-containing substituent into the side chain of polysiloxane made it possible to increase the hydrophilicity of the polymer: the water flow for F3-Acr was 0.7 × 10^–6 kg m m^–2 h^–1, which is almost 3 times higher than for C10. It is worth noting the positive effect of the combination of C10 and F3-Acr groups in polysiloxane. Thus, with an increase in the total flow by 60% compared to the C10 membrane, the values of the separation factor for n-butanol, acetone, and ethanol were 40.5, 32.7, and 4.3 and increased by 6, 15, and 12%, respectively, compared to the C10 membrane. For the C10-F3-Acr membrane, the pervaporation separation index for n-butanol, acetone, and ethanol was 136, 109, and 11. Therefore, this membrane is twice as efficient as C10. Taking into account the absence of detectable contamination of the surface of the membrane material with fermentation products, one can note the high potential of the C10-F3-Acr membrane for the task of isolating alcohols from the ABE fermentation mixture.

The external stationary flow of a viscous incompressible fluid and the convective-diffusion mass transfer of a solute in an ordered system of parallel hollow fiber membranes arranged normally to the flow direction are calculated in the ranges of Reynolds numbers \(\operatorname{Re} \) = 0.01–100 and Schmidt numbers \({\text{Sc}}\) = 1–1000. The Navier–Stokes equations and the equation of convective diffusion were solved using the methods of computational fluid dynamics with a no-slip boundary condition and with a constant solute concentration condition on the outer surface of the streamlined fiber. The calculations were performed for a row of fibers and for a multi-fiber system consisting of four and sixteen rows of fibers. The outlet concentrations and the fiber solute retention efficiencies \(\eta \) were calculated depending on the packing density of the fibers and the \(\operatorname{Re} \) and \({\text{Sc}}\) numbers. It is shown that it is possible to use the fiber solute retention efficiency \(\eta \) defined for a single row of fibers to predict the retention efficiency of an extended multi-row fibrous bed.

The influence of the content of tetrafluoroethylene (TFE) groups on the gas transport properties of vinylidene fluoride (VDF) and tetrafluoroethylene copolymers has been studied. Experimental values of the permeability coefficients P and diffusion coefficients D for gases H₂, He, N₂, O₂, CO₂, as well as lower hydrocarbons CH₄, C₂H₄ and C₂H₆ were measured and their solubility coefficients S were calculated. The values of the solubility coefficients of CO₂ and C₂H₄ were found to deviate from the linear correlation of lg S on the Lennard-Jones potential. An explanation of this effect was proposed based on facilitated transport models. It was demonstrated that an increase in the content of TFE groups leads to a significant increase in the permeability coefficients of the penetrants studied mainly due to an increase in their diffusion coefficients. So, the permeability coefficient of helium and hydrogen increases approximately in 2.5 times, for carbon dioxide in 3 times, for argon, oxygen, methane and ethylene in 3.5 times, and for nitrogen and ethane in 4.4 times, respectively. These gas separation parameters in combination with good film-forming properties and commercial availability allows us to consider the studied VDF-TFE copolymers as promising materials for the fabrication of composite gas separation membranes.

With the development of oil fields, the proportion of the highest molecular weight component, asphaltenes, increases in the composition of the extracted raw materials. The tendency of asphaltenes to aggregate causes a number of problems, which makes the problem of oil deasphalting relevant. In this work, studies were carried out on the separation of the asphaltene fraction from oil using PAN membranes. In order to reduce the pore size of membranes obtained by the phase inversion method, an additional component, acetone, was introduced into the spinning solution. The permeability of the resulting membranes for water is 37.6 ± 1.7 L/(m² h atm), and for toluene, 25.3 ± 1.8 L/(m² h atm), and the pore size is 4.6±0.5 nm. When filtering oil solutions diluted with toluene (1 g/L), the retention capacity of membranes for asphaltenes was 73 ± 4% and more than 95% if the oil content in the solution was more than 10 g/L. A study was made of the parameters of membrane clogging during the filtration of oil solutions in toluene. It is noted that when passing from toluene to oil solutions, the permeability of membranes decreases by 10 times. At the same time, the decrease in permeability is reversible, and when the oil solution was replaced with a pure solvent, the membrane restored up to 99% of its permeability.