Theoretical Foundations of Chemical Engineering最新文献

This work involves the intensification of vacuum sublimation drying of alginate–chitosan biopolymer matrices at each stage of the process: from preliminary freezing to the drying itself. The main part of the article presents and describes the designs of installations for carrying out the process of freezing with ultrasound exposure and drying with infrared and ultrasound exposure. A series of experiments have been conducted to study the kinetics of freezing and drying under various conditions. It is found that the use of ultrasound at the freezing stage allows the formation of materials with wide directional channels in the volume of the polymer framework, which subsequently leads to the active mass transfer of moisture at the drying stage.

A mathematical description is developed for predicting the physicomechanical properties of sulfur vulcanizates of diene rubbers obtained in the presence of complex vulcanization activators. The concentrations of the components of the complex vulcanization activator, as well as the technological modes of its production, are selected as input parameters. Based on a sample of over 800 experiments, dependences are established for the changes in the modulus and conditional strength on stretching, as well as the relative elongation at breaking, in relation to the ratio of the activator components, temperature, and duration of its synthesis. Statistical data processing is conducted, including Shapiro–Wilk statistical tests. Using neural network technology, a mathematical model is synthesized to describe the influence of the composition of the vulcanization activator and the conditions of its synthesis on the physicomechanical properties of the vulcanizates. The neural network is trained using a dataset containing 784 experiments, and the quality of the approximation is assessed on a control sample of 76 experiments. The obtained values of the relative error in determining the conditional strength and relative elongation by the computational method are approximately 6%. A graphical representation of the results of the simulation is provided.

Based on theoretical research and laboratory tests, an original design of a jet-type bioreactor designed for growing methane-oxidizing bacteria was developed. A series of tests were conducted that demonstrate the unit efficiency, providing required cultivation productivity with the specified energy consumption for producing biomass. The main operating parameters of the fermentation unit (pH, temperature, pressure, the composition of the gas nutrients, and the flow rate inside the apparatus) were given, and problems associated with the limits on their permissible values (particularly the pressure effect and the composition of oxygen-containing gas on the cultivation behavior) were discussed. The effectiveness of using special structural elements in bioreactors was confirmed, which were designed to create a hydrodynamic regime that provide the necessary conditions for culture growth.

This paper examines the process of isomerization of hydrocarbon fluid in a chemical reactor with a catalyst layer, designed for the synthesis of promising products and materials. The main flow parameters necessary for the correct description of hydroisomerization in a chemical reactor are identified. A new mathematical model has been constructed, including the Navier–Stokes equations regularized on the basis of the quasi-hydrodynamic approach, averaged over a representative elementary volume, and a system of convection–diffusion equations for calculating the concentration of raw materials and reaction products. For the proposed model, a computational algorithm was developed and its computer implementation is carried out. The originality of the developed modeling methodology lies in the combination of the quasi-hydrodynamic approach with methods for calculating hydrocarbon flows in porous media. Within the framework of this methodology, trial calculations of a specific applied problem are carried out, demonstrating the correctness of the developed numerical approach.

A mathematical model of heat and mass transfer in the “reservoir–horizontal well” system is proposed. An inverse coefficient problem is set to assess the filtration properties of an oil reservoir. Temperature change curves obtained using multisensor technology are used as initial information. A computational algorithm for solving the inverse coefficient problem based on regularization methods is proposed. It allows one to build an inflow profile along the borehole of a horizontal well and evaluate the filtration properties of the reservoir under various fluid flow regimes in the borehole.

The temperature regimes of reactors for the catalytic isoprene polymerization process in bulk are considered, specifically periodic reactors with a stationary thin layer of the reaction mixture and a cascade of apparatuses consisting of forepolymerizers and reactors with a stationary layer. The optimal temperature regimes are determined based on minimizing the processing time while maintaining constraints on the maximum polymerization temperature and the allowable temperature gradient across the height of the layer. Using computational experimentation, the optimal temperature regimes for bulk polymerization of isoprene up to a final conversion of 90% are determined for two different process equipment configurations. The optimal temperature regime for reactors with a stationary layer involves a single-step increase in the temperature of the coolant in the jacket. The optimal polymerization regime in the cascade of reactors involves a two-stage process: in the first stage, the reaction occurs in a stirred reactor until a conversion of 15%, and in the second stage, the process takes place in reactors with a stationary layer at a constant coolant temperature in the jacket.

The authors study physicochemical characteristics of the kinetics of agglomerated charge dissociation at different temperatures conditions with impurities added during the melting process. The level of oxygen in the gas, the size of the ore, and the added impurities, are the main factors that determine the rate of sulfate dissociation and allow the viscosity and melting point of the agglomeration melt to be changed. The study is based on high-temperature derivatography, with which different ranges of temperature are considered and the rates of dissociation of minerals are determined. The experimental technique developed for studying the kinetics of sulfate dissociation can be used to study the thermophysical patterns of chemical and metallurgical calcination in a large group of iron-containing ore materials.

The sol-gel synthesis of zircon, zirconium oxide, and composite powder precursors based on them has been performed in two ways: reverse precipitation and the microreactor method in a two-stage apparatus with intensively swirled reagent flows. A comparison of the synthesis results at all stages is carried out—(1 ‒ x)(H₂SiO₃‒ZrO(OH)₂)‒xZrO(OH)₂ precursor powders, after calcination at 850°С, as well as after sintering powders in the temperature range of 1000‒1300°С. The thermal behavior of the initial nanosized compositions is studied using differential scanning calorimetry and thermogravimetry and dilatometry methods. The temperature coefficients of linear expansion of ceramic samples are estimated. Microhardness values for the (1 – x)ZrSiO₄–xZrO₂ ceramic composites are given with different backgrounds.

This paper presents a mathematical model of the granulation process in a fluidized bed of diammonium sulfate solutions. Expressions are derived for calculating granule growth, the density function of granule distribution at the apparatus outlet, and the distribution variance as a function of external recycle characteristics and process parameters. The adequacy of the proposed mathematical description to the actual process is demonstrated.

Mathematical modeling is used to show that a rise in temperature intensifies both convective and diffusion transport. An intensification of convective transport is observed along with an increase in the consumption of carbon dioxide. The effect of convective transport in the free volume of a dryer and the boundary layer of its plate is especially noticeable at the first stage of supercritical drying. Raising the pressure has no appreciable effect on the rate of supercritical drying.