Theoretical Foundations of Chemical Engineering最新文献

The paper presents the results of simulation schemes of different structures for the distillation separation of a methanol–ethanol–water mixture with agents exhibiting different selective effect: monoethanolamine, morpholine, N-methylpyrrolidone, and pyrrolidine. The working pressure of the columns in the schemes is 101.32 kPa. For pyrrolidine, the options for introducing the agent above and below the feed level of the methanol–ethanol–water mixture are considered. According to the criterion of total energy costs for separation, it is recommended to use extractive distillation with monoethanolamine.

Obtaining sorbents from waste is an important task of modern industry, the solution of which will eliminate a number of pressing problems. This paper examines the effect of changing the parameters of the process of obtaining composite sorption-active materials (CSAM) of the composition “carbon black–clay material” from technogenic waste on the parameters of the porous structure. The dependence of the changes in material characteristics on the quantitative ratio of the components and the type of clay material is shown. When the type of clay material changes, the strength of the CSAM changes, while the porous structure of the material remains virtually unchanged. It has been established that when the sintering temperature changes, the specific surface area changes while the maximum volume of the sorption space remains constant.

Synthesis of Si₃N₄–SiC–Si₂N₂O–Fe₃C–Fe powder composite has been carried out in a layer-by-layer combustion mode using ferrosilicon and shungite dust waste as raw materials. The influence of the main synthesis parameters (mixture composition, gas pressure) on the phase composition of combustion products was established. The microstructure of combustion products is represented by intergrowths of small faceted crystals and crystals in the form of thin plates of irregular shape. The process of high-temperature interaction of a ferrosilicon–shungite mixture with gaseous nitrogen was studied using differential scanning calorimetry. It has been shown that, at 600–1070°С, the shungite carbon burns out. The process of active nitriding of ferrosilicon is carried out at a temperature of over 1270°С. The mechanism of chemical transformations during the interaction of ferrosilicon with shungite additives in a nitrogen atmosphere was studied.

The work presents the results of single-stage extraction purification of straight-run kerosene, light and heavy diesel fractions, atmospheric gas oil, light vacuum gas oil, as well as visbreaking gas oil and light catalytic cracking gas oil, from sulfur- and nitrogen-containing components and polyaromatic hydrocarbons under the same conditions: a mixture of N-methylpyrrolidone–ethylene glycol of 60 : 40 wt % is used the extractant; the extractant : raw material mass ratio is 1 : 1; and the temperature is 40°C. It is established that the degree of extraction of extractable components from petroleum products of similar fractional composition increases in the following series: straight-run fractions ( < ) visbreaking gasoil ( < ) light catalytic cracking gas oil. In the production of marine fuels that meet environmental requirements, the most effective is the extraction purification of gas oils from secondary oil-refining processes, which have an increased content of heterocyclic sulfur and nitrogen compounds of an aromatic nature, and polyaromatic hydrocarbons with short alkyl substituents, stable in thermal and catalytic processes.

This paper presents the experimental studies of kinetic tendencies in the physical absorption of gases (CO₂, H₂S, SO₂, NH₃) in a wide range of phase velocities during the downward film flow of a liquid along the inner surface of a vertical tube. In each experiment, the temperature of the gas and liquid was maintained constant by passing them through the coils submerged in thermostatted vessels. The amount of absorbed gas was determined by analyzing the concentration of the component in the gas–air mixture before and after the apparatus and by control analysis of the liquid leaving the apparatus. For further reliability of gas concentrations obtained by chemical analysis of the initial and final gas–air mixture, the liquid concentration after the apparatus was also determined in a number of experiments. Empirical dependences of the mass transfer coefficient (K_OG) on the gas velocity (V_g) were obtained. The discrepancy between the experimental data on absorption in many cases does not exceed 10%. Based on the experimental data, it can be noted that the K_OG values for CO₂, H₂S, and SO₂ in the first region, where they increase with the gas velocity, coincide with K_OG for ammonia obtained at the same V_g, which is associated with the prevailing gas phase resistance to the substance transfer under these conditions. For poorly soluble gases, however, the phase resistance ratio transforms already at relatively low gas velocities. In this case, the mass transfer coefficient, which is independent of V_g, changes with the irrigation density.

Relevance: Carbon capture and storage technology involving geological storage of carbon dioxide in deep aquifers is widely used in the world as this technology is aimed at reducing the emission of greenhouse gases into the Earth’s atmosphere and minimizing the influence of these gases on global climate change. Objective: To carry out preliminary investigation of the features of water–rock–carbon-dioxide interactions in application to carbonate reservoirs, which are widespread in hydrogeological basins over the territory of the Russian Federation and are potentially suitable as carbon dioxide storage facilities. These processes are considered on the example of the ancient Siberian Platform, where industrial production of hydrocarbons is currently increasing and a series of large-scale projects in the area of petroleum and gas chemistry are underway. Methods: Mathematical physical and chemical modeling is applied to solve the problem. The calculations are implemented by the HydroGeo software package, in which the achievement of chemical equilibria for the “water–rock” system is implemented on the basis of the method of equilibrium constants. Results: The obtained results allow us to evaluate the directions of geochemical processes in the reservoirs under consideration and to provide qualitative estimation of changes in the pore space under the conditions of its saturation with carbon dioxide, with respect to different saturation degrees. It is established that solution acidification is observed as a result of its saturation with CO₂, with the transition of chemical elements to the prevailing forms of complex ions bound with hydrocarbonate and chloride ions (Mn, Na, K). At the same time, saturation with carbon dioxide does not have such a substantial effect on the forms of Ca and Fe migration. Special attention is paid to Al, which is transformed almost completely from complex forms into Al³⁺ in the presence of carbon dioxide. In the studied reference samples, rather intense transformation of the reservoir rocks with redistribution of elements between the primary and secondary mineral phases is observed (both rock dissolution and precipitation up to several hundred g/dm³) with comparatively small absolute changes in open porosity. In a number of the considered objects, the dissolution of calcite and dolomite proceeds due to a decrease in pH. The directions of the transformations, as well as the trend of changes in the filtration-capacity properties, are determined by the specific mineralogical combination of the reservoir rocks and the brine present in them, as well as by the stage of evolution of the system under consideration (the first part of the considered combinations is initially far from equilibrium and continues interacting, while the second part is close to equilibrium and is transformed into the non-equilibrium state due to saturation with carbon dioxide).

Determining pressure drops upon flowing of a two-phase steam–water mixture in natural circulation loop elements is an integrated engineering problem. The conditions to which each element is exposed exert a significant effect on the operation of the system as a whole, and a large scope of empirical data is required to determine the flow parameters. Modern numerical methods for analyzing two-phase flows have significant limitations and require setting the interphase boundary depending on the flowing mode and initial conditions. As a consequence, it can be set only approximately provided that a reliable methodology for predicting these modes is available. Nowadays, there are only a few examples of solving problems in fluid mechanics by means of numerical methods in such a formulation according to which the interaction between the liquid and gas phases is not set, but can be determined in the course of solving the problem. In this connection, the studies performed by various researchers are based on experiments and are presented in the form of engineering calculation methods within a limited range of initial conditions. The proposed approach to the solution of the circulation equation consists in searching for its analytical solution taking into account empirical data obtained in earlier studies and in assessing their effect on the calculation results as a whole. Further, this approach should be generalized to a wider class of initial conditions, as well as to loops of more complicated configurations to optimize the calculation procedure provided by the standard method and to elaborate more detailed recommendations for designing the evaporation loops of boilers with natural circulation. This novel approach is used as a base for studying the effect of evaporator heat absorption exerted on the loop operation with the same loop design. It is found that a maximum flow rate is observed in the loop. The flow rate limitations depend on the loop design, on the physical properties of the fluid, and on the phase slip.

The present study explores methodologies for investigating the structure of the vapor–liquid equilibrium diagram of multicomponent systems. This investigation serves as a foundation for the predesign of distillation process flowsheets. A thorough analysis is conducted to assess the merits and limitations of existing methodologies, highlighting the efficacy of employing diverse techniques contingent on the system’s phase behavior specificity (e.g., the presence of one (two) singular points and internal separatrix manifolds). A group of systems that demonstrate the same deviations from ideality (in the absence of saddle-type ternary azeotropes) is identified. For these systems, it is possible to analyze the diagram structure based on the minimum amount of available information (i.e., boiling points of components and azeotropes). The proposed approach does not necessitate geometric construction of the concentration simplex, its scan, or individual components of the system. The proposed technique for analyzing the diagram structure of multicomponent systems is illustrated on the example of three industrial mixtures comprising different components.

The behavior of a shaft with an axial mixer, suspended on a drive shaft along the axis of the mixer by means of a Hooke joint depends on the type of mixer, the physical properties of the fluid being mixed, and the rotation frequency of the mixer. Based on general hydrodynamic principles, equations are derived for calculating two limiting frequencies within which free precessional rotation of the shaft occurs, as well as equations for calculating the power consumed for mixing and the radius of the circle described by the center of the mixer during precessional motion. The coefficients of the proposed equations are found or refined experimentally.

A comparative study of micromixing in a microreactor with counter-current intensively swirling flows (MRISF-CC) is performed for different methods of flow feed using the iodide–iodate technique. The dependence of the micromixing quality (the so-called segregation index) on the specific energy dissipation rate is found for three methods of feeding solutions to the device. In the first and second methods, the solutions are fed to the tangential and axial nozzles of the left and right chambers of the device, respectively (corresponds to the mixing conditions in the single-stage microreactor MRISF-1). In the third case, the solutions are fed to two tangential nozzles and both flows are intensively swirled and mixed in a limited volume, while the axial and circumferential velocity components are directed towards each other. In the third case, the quality of micromixing was up to ten times higher (at a given value of the specific energy dissipation rate) than in the first two cases, and up to 2400 times higher than in a device with a magnetic stirrer. Thus, the implementation of mixing of counter swirling flows provides improvement in the quality of micromixing compared to other types of microreactors with swirling flows. The effect of reducing the exponent to ≈2.2 in the formula relating the specific energy dissipation rate to the total flow rate of solutions has been found, which can be explained by the mutual damping of the angular momentum during the interaction of two vortices. The obtained results make it possible to explain the influence of the micromixing conditions on the synthesis of nanosized particles from solutions.