Theoretical Foundations of Chemical Engineering最新文献

The operation of heat- and mass-transfer equipment with a fluidized bed is described. The process of crystallization of polyethylene terephthalate granulate in a fluidized bed in the production of polyester technical yarns is considered. It is proposed to carry out pulse control of the fluidizing agent flow rate to increase heat and mass transfer and eliminate the gluing of granules.

A mathematical model of a reciprocating compressor is presented, consisting of a system of moving solid bodies, the center of mass of which is displaced, leading to vibrations of the compressor casing that is mounted on a suspension relative to a stationary base. The suspension elements possess dissipative properties and dissipate the energy transmitted to them, resulting in a loss of part of the mechanical energy generated by the electric motor. The vibrations of the reciprocating machine on the suspension are characterized by the vibration velocity, which is one of the most important environmental indicators. In this regard, assessing and, if necessary, minimizing these losses, as well as investigating the influence of the suspension parameters on the output characteristics of the compressor, becomes relevant. The proposed mathematical model is based on the methodology of the thermodynamics of open systems, the laws of mechanics describing the relative motion of the reciprocating elements, and the laws governing the motion of the center of mass of the system of moving elements, as well as the motion of the system relative to the center of mass. The mathematical model has been validated on the household refrigerator compressor KKh-0.125. The results obtained confirm the adequacy of the developed mathematical model.

The article considers the main stages of evolution of the mathematical model of the physico-chemical stages of catalytic dehydrogenation of ethylbenzene during styrene production. The new structural elements of the mathematical model describing the chemical processes of heat exchange and ethylbenzene dehydrogenation are presented. The introduction of additional mathematical dependences makes it possible to reduce the number of structural and parametric uncertainties characteristic of previously known models of dehydrogenation kinetics. A system of logically interconnected models is developed as a digital equivalent of an automated process control system. The synthesis of the digital predictive control system equivalent within the model-oriented design concept framework is described. A method for synthesizing hierarchical models of chemical–technological systems is proposed. A software emulation of the automated control system of the process under study is performed. The results of computer implementation of the digital equivalent in the form of predicted trajectories of changes in the parameters of the state of the technological process, reaction medium, and catalyst are presented.

The article is devoted to an analysis of the role of chemical technology in the development of the concept of best available techniques and the features of its practical application in the development and updating of BAT Reference Documents, as well as their use for the purposes of environmental and technological industrial regulation. The evolution of the concept of best available techniques is briefly described, and its basic principles are outlined, in the substantiation of which leading Russian scientists took part. It has been shown that the best avaiulable techniques are aimed at resource and energy efficiency enhancement and negative environmental impact reduction. An analysis of the main trends in the development of mineral fertilizer production technologies is presented. The paper presents BAT-associated emission levels, resource efficeincy parameters, and cardon intensity indicators for the best available and perspective techniques. It is emphasized that chemical technologies play a key role in reducing the negative impact on the environment in various industries; projects for cleaning exhaust gases from sulfur oxides developed for metallurgical enterprises are analyzed. The article presents the views of an international group of authors on the prospects for improving the concept of best available techniques and expanding the practice of its application in the Russian Federation and abroad.

The main problems arising in gas-condensate fields are the presence of condensate, water formation, and mechanical impurities, which leads to a significant change in the range of technological parameters of the inlet separators. An urgent task is to study the processes taking place in separation equipment in order to recommend its operating mode or modernize the separator without replacing it. Thus, the purpose of the research presented in the article is to study the hydrodynamics of separation equipment in gas condensate fields. Due to the complexity of calculating the separation of gas–liquid flow in separators, as well as determining the efficiency of separation equipment in different technological modes, the study of hydrodynamic processes taking place in separation equipment is interesting from a scientific point of view and has great practical significance in the development and design of separators. This article presents research using CFD modeling aimed at studying the efficiency of separators. As a result of modeling, the distribution of the gas–liquid flow for the tangential inlet of the separator and the tray with direct-flow centrifugal elements is obtained, the modes are studied, and the influence of the gas flow rate on the operating efficiency of the equipment is analyzed. The influence of the size of the moisture droplets contained in the gas flow on the possibility of its entrainment with the flow leaving the separator is established. The larger the droplet size, the better they are separated in direct-flow elements. At high gas flow rates through the apparatus, a large amount of water can be carried away in daily equivalent, which negatively affects pipeline fittings or gas pumping units. As a result of the study, conclusions are drawn regarding the need for more strict maintenance of the technological regime of the process.

Rubber-fabric composites belong to a class of anisotropic reinforced composite laminates intended for operation in contact with a liquid medium. Each layer of such composites performs a specific function in the operation of printing machines. The rubber layer is located on the surface of the material and is impenetrable with respect to hydrophilic liquids, but can swell to a limited extent in organic solvents. The fabric layers provide structural integrity and tension of the layered composite material; they are protected from the penetration of a liquid medium by layers of rubber in a plane perpendicular to the arrangement of the layers. In the plane parallel to the arrangement of the layers, the fabric is permeable with respect to aqueous solutions and organic solvents. This permeability is based on the capillary effect of absorption. In order to eliminate the anisotropy of the permeability of reinforced layered composite materials, it is proposed to apply additional layers on the end surface to block the access of liquid to the capillary space through the pores, gaps between the threads, and fibers of the fabric layers. The additional layers are applied by brushing or dipping into solutions of suspensions and emulsions of film-forming polymers such as polyvinyl alcohol, polytetrafluoroethylene, and acrylic polyester. Techniques for estimating the porosity experimentally and calculating the average radius of the capillaries based on a physical model of the composite porous structure are presented. The capillary pressure leading to absorption is described based on Laplace’s law. The laboratory testing bench represents an upgraded Klemm–Winkier device. The penetration of liquids into the porous structure of a rubber-fabric composite through the end surface is measured. The sizes of the pores in the structure of the composite and their number, volume, and the rate of pore filling with water through the end surface of the samples of anisotropic reinforced layered composites used in printing are calculated. A decrease in water permeability through the protective layers at the end surface is shown depending on the chemical and phase composition of the film-forming polymers. The diagrams of the permeability, absorption kinetics, and porosity parameters of the rubber-fabric composite are compared. The fractions of capillaries with different diameters and their distribution throughout the cross-sectional area are determined.

This paper presents studies of the kinetic regularities of physical absorption of gases (CO₂, H₂S, SO₂, NH₃) in a wide range of interphase distribution coefficients and phase motion velocities during the downward film flow of a liquid along the inner surface of vertical tubes, providing a “fixed surface” of interphase exchange. For gases with different solubility, some common tendencies were revealed for different gases. For the dependences of the absorption coefficient on the gas velocity, the general tendency is as follows: the absorption coefficient increases with an increase in the gas velocity to a certain value. At low gas velocities, it ceases to grow for low-solubility gases. It is of interest from both theoretical and practical viewpoints to examine the character of kinetic tendencies for the zone of the dependences of the absorption mass transfer coefficient on the gas phase velocity. Having reached a certain value at a given irrigation density, other process conditions being constant, the absorption mass transfer coefficient ceases to depend on the gas phase velocity. Based on the analysis of experiments, it can be concluded that the values of the absorption mass transfer coefficient for gases of different solubility under the same conditions depend on the equilibrium constants. Thus, for absorption of low concentrations, for which the process is not complicated by significant changes in the physical constants of the liquid during absorption, it is possible to obtain general kinetic dependences that are common to the absorption coefficients of gases of different solubility.

A new hydrophobic eutectic solvent based on triisobutylphosphine sulfide (TIBPS) and menthol is proposed, its main physicochemical properties are studied, and its extraction capacity for Fe(III), Al(III), and Li(I) ions is assessed. For the TIBPS/menthol system, a solid–liquid phase diagram is constructed and the interaction between the components in the eutectic solvent is established using IR and NMR spectroscopy. The temperature dependences of the dynamic viscosity, density, and refractive index of the proposed eutectic solvent are established. The extraction of Fe(III), Al(III), and Li(I) ions from hydrochloric acid solutions using TIBPS/menthol is studied depending on the concentration of HCl and NaCl, the volume ratio of the phases, and the initial concentration of the metal. The temperature dependences of the degree of extraction of metal ions are obtained and an assessment of the thermodynamic parameters of extraction is carried out. The indices of re-extraction of Fe(III) ions from the organic phase with distilled water are determined and the degree of its extraction with repeated use of the eutectic solvent is established. The potential of using the proposed hydrophobic eutectic solvent for the extraction of metals from aqueous solutions is shown.

The crystallization process of a practically important zeolite of clinoptilolite has been studied, which can be used as an adsorbent, catalyst. The influence of various factors on the speed and selectivity of synthesis using natural minerals obsidian and halloysite of Nakhchivan has been investigated. The starting material was a natural mineral of Nakhchivan—volcanic glass obsidian from the peak of Gapydzhik of Ordubad district and halloysite of Pirigel deposits. The influence of temperature of 100–250°C, the mass ratio of the initial components of halloysite (H) and obsidian (O) H : O equal to 1 : 1, 1 : 2, 1 : 3, 2 : 1 and 3 : 1, a concentration of a thermal solution of NaOH of 10–30%, the duration of the process is in the range of 10–50 h and the “aging” process on the crystallization of clinoptilolite were studied. It has been established that the optimal conditions for the synthesis of clinoptilolite with 100% crystallinity and phase purity is as follows: temperature 150 ± 2°C, concentration of thermal solution of NaOH of 15–20%, quantitative ratio of the initial components of halloysite (H) and obsidian (O) H : O, equal to 1 : 2, processing time—20 h. The synthesis of zeolite of clinoptilolite using natural minerals from the Nakhchivan Autonomous Republic was carried out in the presence of tetramethylammonium hydroxide (TMAOH). The effect of temperature, concentration of thermal alkali solution, ratio of initial components, process time, duration of “aging” on crystallization of clinoptilolite was studied. It has been shown that violation of optimal synthesis conditions leads to a decrease in the selectivity of the process and the formation of other zeolites (phillipsite, gismondine), aluminosilicates (anortithe, albite) or mixtures thereof, as well as quartz and cristobalite. The “aging” process was studied in the duration range from 1 to 3 days. It has been established that an increase in the duration of “aging” leads to an increase in the linear rate of crystallization of clinoptilolite zeolite.