Issues

The results of a study on the oxidation of coals with varying degrees of coalification in an oxygen atmosphere and a water-oxygen fluid (oxygen excess coefficient 1.22—1.43) are presented. The experiments were carried out in the reactor heated at a constant rate (1 °C/min) to 550 °C. The temporal dependences of the temperature and pressure of the reaction mixtures indicate that the addition of water vapor to oxygen reduces the temperature of ignition of the coals and intensifies their combustion. This effect is most pronounced for coals with a high degree of coalification. At certain values of total heat release, coal oxidation in both O₂ and H₂O/O₂ fluids proceeds via a thermal explosion mechanism. The influence of the composition of organic and mineral components of coals on their ability to ignite is discussed.

The article presents the results of an experimental study of the phase behavior of the binary mixture «freon R404A-acetone»» carried out at temperatures of 356.15 K, 372.15 K and 392.15 K. I—II type of phase behavior according to the Williams classification is established. The article presents the results of a study of the supercritical fluid extraction process as applied to the problem of extracting acetone from its aqueous solution of 3.5% and 10 % concentration. In the process carried out at a temperature of 356.15 K (83 °C), an increase in the efficiency of the extraction process was established as the pressure approaches its critical value for the designated binary system.

This article presents an environmentally friendly and cost-effective system for cleaning oil and operational contaminants from marine pipelines using supercritical carbon dioxide as a solvent. A process flow diagram for cleaning oil contaminants from pipelines with a cleaning efficiency of up to 97 % is described. Using a pi peline cleaning system using supercritical carbon dioxide as a cleaning agent simplifies the process of cleaning the internal surfaces of pipelines of various lengths, diameters, and configurations, significantly reduces repair and restoration time, reduces labor intensity, minimizes liquid oil-containing waste generated during cleaning, and reduces the material and energy costs of processing it.

N-Butyl-N-methyl-1-phenylpyrrolo[1,2-a]pyrazine-3-carboxamide (GML-3) is a compound exhibiting both anxiolytic and antidepressant activity. Like most substances being developed as active pharmaceutical ingredients (API), it is practically insoluble in water, which may negatively affect its bioavailability and complicate tablet formulation. According to the Noyes—Whitney equation, solubilization of poorly water-soluble APIs may be achieved by increasing their contact surface area with the aqueous medium or by creating a supersaturated state in solution. The API surface area can be increased by micronization using the rapid expansion of supercritical solution (RESS) method. The solubility of GML-3 in CO₂ allows its micronization via RESS and the development of tablets with micronized API. The aim of this study was to develop GML-3 tablets containing API micronized by RESS, with improved dissolution kinetics.

Extracts from the aspen bark (Populus tremula L.) were obtained using supercritical (SC) fluid extraction with carbon dioxide at 313.15 and 333.15 K and pressures ranging from 15 to 35 MPa. Chromatography-mass spectrometry was used to determine the component of the CO₂ extract of Populus tremula L., revealing a significant amount of fatty acids and their esters. Traditional liquid extraction with petroleum ether was found to be significantly less efficient than SC-CO₂ extraction in terms of the content of steroidal and triterpenoid components of the aspen bark in the final product.

The effect of SC-CO₂ and SC-CHF₃ treatment of poly(1-trimethylsilyl-1-propyne) [PTMSP] films on their mechanical properties and gas permeability was investigated. Treatment of PTMSP films in supercritical fluids (SCF) leads to a decrease in the elastic modulus (Young’s modulus, E) and an increase in the relative elongation at break (ε), which is especially pronounced when processing films under high pressure (35 MPa). It is shown that the permeability coefficients of films treated at a pressure of 150 MPa either remain at the level of the initial untreated film (time of treatment 3 hours) or decrease noticeably (time of treatment 20 hours). At the same time, treatment of the films at a higher pressure of 35 MPa leads to a noticeable increase in the permeability coefficients. Films treated with both SCFs have a noticeably lower rate of decrease in permeability coefficients over time compared to untreated PTMSP. Thus, in untreated film after 1 year of storage in air, the permeability coefficients for O₂, N₂ and CO₂ decreased by 50—60 %, while in treated films, the decrease in permeability over the same period is 10—40 %. The permeability values after 1 year for the sample with the greatest increase in permeability after treatment in SCF are close to the level of the initial permeability values of the untreated film. Thus, the work shows that by varying the type of fluid and the mode of film treatment, it is possible to carry out structural modification of PTMSP and effectively influence both the level of permeability and stabilization of transport parameters over time.

The catalytic properties of palladium and palladium-copper composite deposited on γ-Al₂O₃ from a supercritical carbon dioxide (SC-CO₂) medium have been studied in the reaction of selective hydrogenation of acetylene into ethylene. Palladium and copper complexes with hexafluoroacetylacetone were used as precursors of the active component. Acetylene hydrogenation was studied in a reaction mixture (in vol. %): 1.0 C₂H₂, 93.7 C₂H₄, 5.3 H₂, simulating a mixture used in the industrial process of acetylene removal from ethylene obtained by pyrolysis of various hydrocarbons. It is shown that the Pd/Al₂O₃ sample obtained by deposition of palladium from a SC-CO2 medium with subsequent reduction in hydrogen has an «egg-shell» type of distribution of the active component — it is concentrated in a thin (about 0.07 ± 0.01 mm) outer layer of a spherical carrier granule with a diameter of ∼1 mm. In the case of the PdCu/Al₂O₃ composite, an uneven distribution of the deposited component is also observed, but to a considerable depth along the diameter of the pellet. The Pd/Al₂O₃ sample showed high activity and moderate selectivity in the hydrogenation of acetylene to ethylene. After crushing and loading the fraction of 0.2—0.4 mm into the reactor, the same sample shows higher selectivity while maintaining high activity. The PdCu/Al₂O₃ sample showed substantially lower activity and selectivity in the target process. The results obtained demonstrate a high sensitivity of the catalytic properties to the method of deposited palladium-containing systems synthesis and a significant effect of the transfer processes in the grain and in the catalyst layer on the parameters of the acetylene hydrogenation in an acetylene-ethylene mixture.

Two series of polyimide aerogels (PI AEs) based on 4,4'-oxidianiline (ODA) and two dianhydrides were synthesized: 3,3',4,4'-benzophenone tetracarboxylic acid (BTDA) and pyromellitic acid (PMDA) by low-temperature polycondensation in dimethylformamide monomers pairs (ODA—BTDA) and (ODA—PMDA) with the addition of a crosslinking agent — 1,2,3-tris-(4-aminophenyl)benzene (TAB), chemical in situ imidization in solution, and subsequent drying of the PI gel with a supercritical (SC) fluid — SC-CO₂. PI AEs with a specific surface area up to S_s = 230 m²/g were obtained. The effect of the chemical structure of anhydride and the content of TAFB on the amount of shrinkage and S_s of synthesized PI AEs has been studied. The morphological structure of PI AEs has been studied by scanning electron microscopy. The S_s values for PI AEs obtained by drying with preliminary solvent replacement (DMFA) with acetone and without solvent replacement are compared. It has been shown that SK-drying without solvent replacement shows S_s higher values. Carrying out the SC drying stage without first replacing the solvent significantly reduces the total duration of the PI AEs production process.

The solubility isotherms of N-tert-butylacrylamide (NTBA) monomer and azobisisobutyronitrile (AIBN) initiator for radical polymerization in carbon dioxide at temperatures and pressures ranging from 0.1 to 40.0 MPa and 305.0 to 353.2 K were determined using synthetic visual methods. The maximum concentrations of NTBA and AIBN at these conditions were determined. The phase behavior patterns of low-molecular weight compounds with low melting points in CO₂ were discussed. It’s shown that AIBN solubility doesn’t limit the range of conditions for the polymerization process using NTBA.

For the first time in Russia, experience was used to evaluate the fungicidal effect of supercritical fluid carbon dioxide on 12 types of micromycetes that destroy paper. For the purpose of further use for disinfection treatment of library and museum collections, the effectiveness of various modes was assessed on paper samples with foci of biodamage caused by the micromycete Aspergillus niger: pure supercritical carbon dioxide and with the addition of ethanol as a co-solvent at a concentration of 2% and 4 %. Pure supercritical carbon dioxide results in minimal reduction of microorganisms on the surface of samples. Treatment with supercritical carbon dioxide in the presence of alcohol as a co-solvent has a pronounced fungicidal effect, which was demonstrated on all test cultures.
Processing in supercritical carbon dioxide with the addition of 4% ethanol with stirring allows for a high degree of sterilization and is a promising method for processing library collections.

The solubility of a series of copper salts (carbonate, acetate, benzoate and thiocyanate) in supercritical carbon dioxide at 308—328 K and 10—30 MPa was determined. The results were described using the Peng—Robinson equation of state and the Mukhopadhyay and Rao mixing rule. The results are necessary for developing technological approaches to the impregnation of polymeric materials and creating composite materials based on them.

The dependences of the reaction mixture density on temperature are analyzed for the following processes: 1) catalytic hydrogenation of CO₂; 2) conversion of phenol and cyclohexanol in sub- and supercritical water. The density measurements were performed using «Lazerokhim» fiber-optic densitometer. The state of the waveguide end face surface after measurements at elevated temperature was analyzed using scanning electron microscopy (SEM). It was found that for non-aqueous reaction mixtures, the laser-optical method of density monitoring is applicable in a wide range of temperatures and pressures. In the case of water and water-organic mixtures, correct determination of the densities is possible only at temperatures of 25—190°C, since an increase in temperature above 200°C leads to irreversible etching of the silicate optical waveguide end face surface by water-containing fluid.

A non-catalytic transesterification (alcoholysis) reaction of bornyl acetate in commercial fir needle oil has been carried out for the first time using supercritical lower alcohols - methanol, ethanol and isopropanol. Only the use of methanol is shown to provide high conversion and selectivity of the reaction. Thus, at 350 °C for 1 hour of reaction in autoclave-type reactor 93 % selectivity on borneol with 90 % conversion of bornyl acetate was achieved. A further increase in reaction time leads to a decrease in borneol selectivity, accompanied by an unexpected increase in camphor concentration.

Dimethyl sulfoxide (DMSO) is proposed as a solvent at the gelation stage during the synthesis of transparent aerogels based on tetramethyl orthosilicate and 3-aminopropyltrimethoxysilane (APTMS). The transparency of the aerogels varied depending on the content of the aminopropyl fragment. The textural characteristics of the aerogels were studied. It was shown that the use of DMSO instead of isopropanol, a standard solvent for the synthesis of gels, allows one to significantly increase the specific surface area of the aerogels. Using DMSO as a solvent, transparent aerogels based on APTMS and modified with fragments of perfluorononanoic acid and L-phenylalanine were obtained. The possibility of obtaining transparent aerogels containing amino complexes of transition metals, namely copper and palladium, was demonstrated.

Mathematical models of the solubility of various groups of organic substances in supercritical carbon dioxide are proposed. The developed models are based on the quantitative structure-property ratio method. The key feature of the method is to obtain the relationship between the predicted property and the structure of the substance molecule (molecular descri ptors). As part of the work, molecular descri ptors affecting solubility were selected and dependences of the solubility of organic substances in supercritical carbon dioxide were obtained using the multiple linear regression method. The models were developed using a developed software and analytical complex and an original database containing information on the solubility of substances in supercritical carbon dioxide and information on the molecular descri ptors of soluble substances. The predictive ability of the developed models was evaluated using training and test samples of experimental data on the solubility of substances in supercritical carbon dioxide at various pressure and temperature parameters. Based on the results obtained, it was concluded that the developed models are promising for predicting the solubility of substances in supercritical carbon dioxide.

This study focuses on the chemical modification of a polymer promising for gas separation membranes to enhance its CO₂ selectivity. The possibility of introducing butylimidazolium bromide (BIm⁺Br^-) into the structure of poly(1-trimethylsilyl-1-propyne) (PTMSP) via a two-step process was demonstrated: bromination of the initial polymer with N-bromosuccinimide followed by reaction with a tertiary amine—N-butylimidazole. Supercritical CO₂ and CHF₃ were used as reaction media, offering advantages over organic solvents, such as non-toxicity, non-flammability, and environmental safety. Depending on the process conditions, the proposed method allows for tuning the BIm⁺Br^- content in the polymer structure. The obtained modified polymers exhibit good film-forming properties, thermal stability, and enhanced resistance to aliphatic, alicyclic, halogenated, and aromatic hydrocarbons. It was found that increasing the BIm⁺Br^- content in the polymer improves the selectivity of CO₂/N₂ and CO₂/CH₄ separation while maintaining high gas permeability. These results open new possibilities for designing efficient membrane materials for industrial gas separation applications.

The results of an experimental study of aluminum oxidation with sub- and supercritical water in the range of 350—410 °C for 60—300 min are presented. It is shown that aluminum hydroxides and oxides with a developed surface are formed as a result of oxidation. A non-monotonic dependence of the specific surface area of the oxidation products on the process temperature is revealed, caused by the formation of various compounds and phases of aluminum oxide. Calcination of the oxidation products at 550 °C leads to the formation of γ-, χ- and α-phases of Al₂O₃ in a ratio determined by the temperature and time of oxidation in a water fluid.

A software package has been developed in the Python programming language for the conceptual design of a process flow diagram for producing chitosan aerogel particles. The software package covers the calculation of the entire production chain, including the stages of solution preparation, gelation, solvent replacement in the gel pores, and supercritical drying. The structure of the package includes a mathematical model of flow hydrodynamics in a receiving tank, a model of diffusion mass transfer in the porous structure of chitosan gel particles, a material balance calculation, an equipment parameter calculation unit, and a technical and economic assessment subsystem. Using the software package, the user can determine the optimal parameters for the process of producing chitosan aerogel particles and create a preliminary process flow diagram for the production process adapted to the specified constraints. The software package is designed to scale the technology for producing chitosan aerogel particles and calculate the cost of production at various productivity levels.