Theoretical Foundations of Chemical Engineering最新文献

When processing ores of rare, nonferrous, and radioactive metals, increasing attention has been given to the two-stage countercurrent leaching method. Compared with single-stage cocurrent leaching, this approach makes it possible to improve the recovery of valuable elements with the same consumption of chemical reagents or, conversely, to reduce reagent consumption while maintaining process efficiency. The two-stage countercurrent leaching method was previously widely applied at uranium mining enterprises in the United States, and recently, greater attention has been paid to its study in the domestic industry. The application of this method is complicated by labor-intensive phase separation and washing operations, such as filtration and thickening; however, with advances in equipment design and the development of effective flocculating additives, these challenges are now being successfully addressed. This paper presents the results of laboratory tests of the two-stage countercurrent leaching of vanadium and other metals from black shale ores. Using this method, the total sulfuric acid consumption was reduced from 18.0 to 12.8%, while the average vanadium recovery increased from 83.0 to 92.5%. It was established that applying a mixture of two flocculants, Praestol 2500 and Praestol 650, with a total consumption of 275 g/t solid after the first leaching stage, resulted in a specific filtration rate of 7.6 t/(m² day). At the second stage, the specific filtration rate reached 8.9 t/(m² day) using the same flocculants at a dosage of 350 g/t solid. These results made it possible to recommend high-performance vacuum filters of the disk and belt types for phase separation after the first and second stages, respectively. Based on the obtained data, a process flow diagram for black shale ore processing was developed, and the initial data for pilot plant design were established.

The solid-phase exchange method is a promising direction in the synthesis of micron- and nanoscale materials. The mechanism and energy of the reactions are determined by the exchange of parts of molecules involved in the interaction. The solid-phase synthesis of zinc ferrite in the ZnSO₄‒Fe₂(SO₄)₃–Na₂O₂ system is considered as an object of research. Thermodynamic calculations show that the temperature in the reaction system reaches 1300 K, which is sufficient for the formation of ferrite. The sodium sulfate and oxygen formed in the reaction prevent the agglomeration of ferrite particles. A mathematical model of the process is proposed, including differential equations of solid-phase chemical kinetics and energy balance under non-isothermal conditions. A software implementation of the model is developed. Numerical analysis establishes that the thermophysical parameters of the system and side reactions have a significant effect on the process of ferrite formation. Increasing sample size and decreasing heat loss contribute to the formation of zinc ferrite. Zinc ferrite powders are obtained and their magnetic characteristics are determined.

Indoor air quality is a pressing issue due to concerns about the health of citizens. One of the new methods of cleaning indoor air is to spray a special adsorbent aerosol. In this work, nanosized TiO₂ and ZnO particles are considered as such absorbents, also having photocatalytic activity. In order to increase the efficiency of neutralization of toxic gases, the work studies the influence of environmental conditions such as humidity, temperature, and atmospheric composition, as well as spray conditions and particle concentration, on this process. Environmental conditions, primarily humidity, influence the dynamics of vapor neutralization. These factors determine both the surface processes on particles and the efficiency of generating active radicals involved in oxidation reactions. In the work the results of a theoretical study of the influence of environmental conditions and particle concentration on the neutralization of toxic gases are presented. An experiment is conducted to purify air from vapors of a model substance (acetone) under various humidity conditions (from 25 to 90%). Spraying is carried out using a pulsed method based on the energy of the VEM in an experimental climatic chamber with a volume of 10 m³. The concentration of acetone vapor in the air is recorded using an IR spectrometer and the size of the aerosol particles is measured using an optical method based on the principle of small-angle scattering. The results show a high degree of adsorption (up to 85% in 1500 s), but at high humidity of about 90% the process rate is slower. Neutralization mechanisms are discussed. The importance of high aerosol dispersion for successful vapor neutralization is emphasized. The results of the work will be used to improve the method of aerosol air purification from toxic vapors and gases.

Evaporative cooling towers are the most widely used systems for cooling recycled water in industrial processes. Wet-cooled cooling towers are heavy consumers of water, so technologies and operating strategies are strongly recommended to optimize these devices. Replacing a wet-cooled cooling tower with a hybrid or dry one will reduce water consumption. The authors have developed and patented the design of a hybrid cooling tower. The design of a hybrid cooling tower consisting of several sections represented by heat-exchanger tubes of the radiator (dry block) and contact elements in the form of corrugated plates (wet block) is described. The thermal characteristics and performance of the cooling tower are influenced by the type and location of the sprinkler fillers. The purpose of the study is to evaluate and analyze the thermohydrodynamic quantities characterizing heat transfer. The calculated dependences for determining the average heat transfer coefficient are presented. Calculations are carried out to determine the heat-transfer coefficients for various pipe arrangements in the cooling tower sprinkler unit. The thermal power of a cooling tower operating in the dry mode is estimated using well-known criterion equations. Correction coefficients for calculating the Nusselt criterion are presented. Numerical modeling is used to verify the adequacy of the application of the criteria equations and the influence of the location of pipes in the radiator on the cooling characteristics. It is determined that the equations obtained by Mikheev most accurately describe the studied process of cooling the liquid in the sprinkler unit of a dry cooling tower using a correction factor that takes into account the relative position of the tubes. At the same time, the average deviation of the values of the total heat flow does not exceed 5.1%, and the maximum is no more than 10.2%.

Vortex-type devices play an important role in the enhancement of many industrial processes. The implementation of vortex-type devices can be of use in increasing the productivity of technological installations in the chemical and related industries, reducing overall dimensions, significantly enhancing the processes taking place in the devices, and increasing process efficiency and product quality. The paper considers the advantages of using vortex-type devices for particle separation, since they have a high separation capacity, as well as for implementing heat- and mass-transfer processes, for example, cooling of recycled water at thermal power plants. At the same time, each specific device requires conducting research before it is implemented into production aimed at studying the operating conditions with specific diverse media. An analysis of the available designs has shown that the problem of selecting a device for conducting a specific industrial process is complicated by the distinctive features of dispersed medium flows (liquid or solid). The paper considers the special features of the dispersed phase used in various devices, which should be taken into account when choosing the design of vortex-type devices. The proposed selection scheme for choosing vortex-type devices of various types takes into account the features of their application. The paper considers designs of separators with modified bent profile inserts, inclined plates in the intertubular space, a block-type separator in two modifications of the rear surface, as well as a multivortex separator and a vortex chamber with a spray device. The advantages, disadvantages, and rational scope of application of the developed vortex-type devices in the chemical technology production processes are analyzed. Recommendations are given on the preferred choice of structural designs of separators with a vortex flow structure.

The urgent problem of reducing the influence of the segregation effect on the homogeneity of the final product when mixing solid dispersed materials must be addressed, in particular in such industries as powder metallurgy, pharmaceuticals, and glass production. Segregation significantly affects the physical and chemical properties of multicomponent systems. The main objective of the work is to study the mechanisms of rarefied flow formation at the initial stage of mixing by a vane atomizer with elastic plates to prevent segregation. Data are obtained on the distribution of particles of individual solid dispersed components by levels (shelves) of a vertical trap under different operating modes of the rotary unit. The pilot plant is a model rotary unit with a vane atomizer; its design features are a curvilinear guide device for preliminary mixing, elastic elements in the form of narrow plates for converting components into dispersed flows, and a corrugated baffle for setting different directions of particle movement. The plates are made of polyethylene terephthalate glycol-modified plastic and are fixed on the drum-cylinder along the tangent planes. At this stage of the experimental tests, the distribution of the component particles is studied before interaction with the corrugated baffle plate, then the operating mode of the model installation is set by selecting the values of the drum rotation frequency and the parameter for adjusting the position of the curvilinear guide device, taking into account the physical properties of the mixed materials and their granulometric composition. It is found that at a drum rotation frequency of 400 min^–1, the control indicator (the maximum value of the proportion of component particles from their total number when settling on one shelf of the vertical trap) for natural sand is exceeded by 1.27 times compared to the data for soda ash.

In order to purify natural gas from hydrogen sulfide (H₂S), it is proposed to use an energy-efficient and environmentally friendly gas hydrate crystallization technology. Mathematical modeling of the effect of changing propane (C₃H₈) concentration (0–3.50 mol %) on the gas hydrate distribution coefficient of H₂S and the fraction of gas hydrate cavities filled with gases is performed. The model gas mixture of CH₄ (concentration is normalized)–C₂H₆ (2.00 mol %)–C₃H₈ (0–3.50 mol %)–n-C₄H₁₀ (1.00 mol %)–n-C₅H₁₂ (1.00 mol %)–N₂ (3.00 mol %)–CO₂ (0.60 mol %)–H₂S (2.50 mol %) at T = 278.15 K and P = 4.00 MPa is studied. It is found that with an increase in the concentration of C₃H₈ from 0 to 3.50 mol.%, an insignificant decrease in the gas hydrate distribution coefficient of H₂S from 18.71 to 17.32 is observed. H₂S molecules mainly fill small gas hydrate cavities, the filling fraction of which is 0.51. It is shown that in the case of an increase in the concentration of C₃H₈ from 0 to 3.50 mol %, the dissociation pressure of the studied gas mixture significantly decreases from 2.33 to 1.01 MPa. It is concluded that high concentrations of C₃H₈ do not lead to a significant deterioration in the concentration of H₂S in the gas hydrate phase but increase the energy efficiency of the technology due to the lower hydrate formation pressure.

An approximate solution that describes the large-scale wave and fine-structured ligament components of periodic flows with a positive definite frequency of ({{omega }} > 0) is constructed based on the fundamental system of hydrodynamic equations in the linear approximation. The solutions are obtained in the two-dimensional approximation of an incompressible uniformly stratified fluid with allowance for the uneven distribution of salinity.

The contact melting of the Cu–Ag bimetallic nanolayer is simulated using full-atom molecular dynamics. The resulting system is of the eutectic type. Fractal analysis is used to control the change of its internal state. The fractal dimension is evaluated using the box-counting method. The analysis of the evolution of the fractal dimension of the nanolayer thickness partition sections over time shows that this characteristic well reflects the evolution of the main structural motifs of the studied system.

A theoretical study of coordination and noncovalent bonds properties was performed by modeling uniaxial mechanical deformation of the crystal cell of bis(2-N,6-N-dibutylpyridin-2,6-dicarboxamide)nickel(II) dichloride. Stretching deformation of the crystal structure along its crystallographic axes was modeled using the 3-corrected Hartree–Fock method with semiempirical corrections for weak interactions (the Grimme dispersion correction D3, basis set superposition error removal by atom-pairwise geometrical counterpoise correction, gCP, and correction for short-range basis set incompleteness effects, SRB) with periodic boundary conditions. The geometry of the bis(2-N,6-N-dibutylpyridin-2,6-dicarboxamide) complex demonstrates high stability under increased deformation. Analysis of bond lengths and dihedral angles within the metal complex revealed only minor changes; in particular, the bond length change was 4.3% for N–Ni–N and 5.4% for Ni–O. Straightening of one N-butylamine chain conformation was observed under high stretching deformation of the crystal cell (7–8 Å), based on analysis of dihedral angles and distances between specific atoms of the N-butylamine chain, supporting the hypothesis of a forced and twisted conformation state of bis(2-N,6-N-dibutylpyridin-2,6-dicarboxamide). At the final deformation steps (8–10 Å), a cavity and a crack appeared due to shifts of neighboring metal complexes relative to each other, affecting the location of chloride ions. Cavities and cracks formed regardless of the axis along which the tensile deformation was modeled, indicating that the crystal exhibits brittleness rather than elasticity.