Vol 57, No 1 (2023)

The practical implementation of new highly efficient methods of liquid–liquid chromatography requires preliminary mathematical modeling for the conditions of the separation process being developed, including its equipment design. In this work, two approaches to the mathematical description of the processes of liquid–liquid chromatography are theoretically analyzed, one of which is based on solving the material-balance equations of a model of a cascade of equilibrium steps, and the other of which uses the Gaussian distribution to describe the outlet concentration profiles of the components of the mixture being separated. It is shown that, if the number of equilibrium steps (characterizing the efficiency of the chromatographic system) is N ≥ 50, then the separation processes can be mathematically modeled using the simpler dependences obtained from the Gaussian distribution. For the conditions when the efficiency of the chromatographic system is N < 50, dependences are obtained using the model of equilibrium steps for mathematical modeling of the processes of separation by various methods of liquid–liquid chromatography.

The application of heat pumps in extractive distillation is studied on the example of the acetone–methanol mixture. The dependence of the efficiency on the feed mixture composition is investigated. It is found that the most effective in the whole range of feed compositions is the scheme with a heat pump in which the compressed overhead vapor of the regeneration column heats its own reboiler. A criterion for estimating the energy savings is suggested, based on which a number of efficiency conditions of heat-pump application both in extractive distillation and in distillation in general are formulated. Proceeding from the obtained results, a preliminary discrimination algorithm for versions of the distillation schemes with heat pumps is offered.

The results of comparative analysis for the key factors of the mechanism of oil-recovery enhancement with the use of gases in a supercritical fluid state as applied to carbon dioxide and propane (propane/butane mixtures) are presented. The above-mentioned factors as a subject of consideration incorporate the dissolving ability of compressed gases with respect to oil and its components, the phase behavior of binary systems containing the mentioned displacing agents and oil hydrocarbons, the critical parameters for the binary systems of fluid-phase behavior types I–II, the compressibility of carbon dioxide and propane under oil-displacement process conditions in tertiary oil production, the viscosity of the media participating in the discussed process and, finally, the swelling of oil as a result of its saturation with a gas. The results of experimental implementation under supercritical fluid conditions are given for an extraction oil-recovery process with carbon dioxide as an extragent in one case and propane in the other case. It is established that propane and propane/butane mixtures are three or more times superior to CO2 in dissolving ability with respect to oil components under displacement-process conditions; that they more often form systems of fluid-phase behavior types I–II with the oil components, which is preferable for the process of its recovery; that the compressor power spent on the compression of carbon dioxide and methane is threefold or more higher than for propane; and, finally, that propane has a much lower viscosity under oil-displacement conditions. In sum, propane and propane/butane mixtures are preferable for use in the oil-displacement process within the framework of tertiary oil production.

Hydrogels are promising for use in tissue engineering as matrices for cell incubation and with subsequent use of such biomaterial systems as bioinks suitable for 3D bioprinting. The heat and mass transfer in hydrogel materials based on agarose and gelatin with model microorganisms incubated in the bulk of the gel are studied by the optical methods of spectroscopy and microscopy. The propagation of the fronts of the nutrient medium in pure gelatin hydrogels and mixed hydrogels based on agarose with the addition of gelatin are compared to determine the diffusion properties of the mixed hydrogels that can ensure the delivery of nutrient components to microorganisms. New data are obtained on the degree of heterogeneity in the growth of microorganisms during their bulk incubation under various temperature conditions of incubation, which is necessary to control the properties of bioink in bioprinting. An analytical description of the curve of cell growth in the gel is proposed, and on its basis an expression for determining the cell growth rate is obtained. A numerical model is developed to describe the absorption of nutrients by cells during their growth.

A dual-cascade system for the purification of regenerated uranium hexafluoride from 232, 234, 236U is proposed. In the first cascade, regenerated uranium is enriched to a 235U concentration of no less than 20% with a decrease in the mass 236U/235U ratio. Its additional feed flow is waste uranium hexafluoride, whose contaminated flow is removed as an additional product. The second additional feed flow is natural uranium hexafluoride. The main product flow from the first cascade is sent as a feed flow to the second cascade. Its waste purified from 232, 234U is diluted with low-enriched or natural uranium hexafluoride to the 235U concentration less than 5%. A numerical experiment is also performed. It is shown that the product formed after diluting the waste of the second cascade satisfies the ASTM C996-20 specification requirements for enriched commercial uranium hexafluoride in terms of  232, 234, 236U.

Hydroxides of alkali and alkaline earth metals are most widely used as catalysts for transesterification of triglycerides of fatty acids in biodiesel production. After biodiesel purification, the determination of catalyst residue is performed to prevent their excess accumulation. Catalysts can promote the degradation of biodiesel. In this research, a simple, fast, and environmentally friendly strategy for the sensitive determination of transesterification catalysts (sodium, potassium, calcium, and magnesium) in biodiesel samples by flame atomization atomic absorption spectrometry is developed. The developed procedure is based on ultrasound assistant dispersive liquid–liquid microextraction of the catalysts in a hydrophilic deep eutectic solvent prepared by mixing quaternary ammonium salt and carboxylic acid. The effect of the nature of the deep eutectic solvent on the mass transfer of catalysts is investigated; in addition, the microextraction procedure conditions are optimized to obtain high sensitivity. The limits of detection established for the proposed procedure are 0.03 mg kg–1 for all analytes. No hazardous and volatile organic solvents are required for sample pretreatment. Sample preparation time is less 15 min.

The vapor–liquid equilibrium of the tetrahydrofuran–acetonitrile system, the equimolar tetrahydrofuran–acetonitrile–chloroform mixture is experimentally studied. The effect of various amounts of dimethyl sulfoxide on the relative volatilities of the components at 101.32 kPa is investigated. The extractive distillation flowsheets of the tetrahydrofuran–acetonitrile–chloroform mixture with dimethyl sulfoxide are calculated.