Theoretical Foundations of Chemical Engineering最新文献

The development of continious single-phase and two-phase microreactors and microextractors requires information on the hydrodynamics of the flows in such devices: velocity and vorticity distributions, mixing efficiency, and two-phase flow regimes, and their influence on the mass-transfer rate. The paper presents studies of the local hydrodynamic characteristics of flow and mass-transfer processes in T-type microchannels using optical techniques. For a single-phase microreactor, the velocity fields and concentration fields are measured. The intensification of mixing during the transition to the engulfment flow regime is shown. For two-phase microreactors with different sets of immiscible liquids, flow regimes are visualized, and a dimensionless complex for generalizing the experimental data is proposed. It is shown that neural-network algorithms trained on a large sample allow predicting flow regimes with high accuracy (up to 98%). The slug flow regime with superposition of external pressure pulsations of the dispersed phase is investigated. It is shown that the velocity field inside the plugs changes periodically, which can be used to intensify mass transfer. Using the micron-resolution laser-induced fluorescence (micro-LIF) technique, local mass transfer in a two-phase microextractor is studied.

The article presents a mathematical model of the degradation of the active surface of a platinum catalyst in a hydrogen–air (oxygen) fuel cell with a proton-conducting polymer electrolyte. The mathematical model is a system of integral–differential equations solved by the finite-difference method. The model takes into account the following phenomena: electrochemical dissolution of platinum nanoparticles, particle growth (due to deposition and migration, Ostwald ripening, and coalescence of platinum nanoparticles on the surface of a carbon carrier), diffusion of platinum ions in the ionomer, and their introduction into the membrane. The calculations are performed for two types of platinum catalysts: a commercial monoplatinum system synthesized on carbon black and a catalytic system synthesized on carbon nanotubes. As a result of modeling, data are obtained on the size distribution of the platinum particles and the values of the electrochemically active surface area depending on the time of accelerated stress testing.

In modeling liquid–vapor phase equilibrium, the actual structure of the solution is often disregarded, and a monomolecular structure of the substances is assumed. This study proposes an experimental combined method for determining the molecular weight of associated components and their degree of association. The method consists of several steps. In the first step, the molar heat of vaporization of the substance is determined experimentally based on the dependence of vapor pressure on temperature. In the second step, the specific (weight-based) heat of vaporization of the substance is measured experimentally. In the third step, the molecular weight of the substance is calculated from the ratio of the specific heat of vaporization to the molar heat of vaporization. Using the water–acetic acid system as an example, the formation of molecular complexes of acetic acid in both the vapor and liquid phases and their effect on phase equilibrium are demonstrated.

The possibility of using magnetic fluids as a cooling agent in condensers of distillation columns is considered. It is known that the energy costs for condensing vapors and cooling the product in condensers of distillation columns can constitute a significant part of the total costs. Therefore, a number of studies are devoted to the problem of their reduction. These include the use of thermal integration, new designs of heat-transfer equipment, and the development of more efficient cooling agents. The latter include specially developed magnetic fluids. Due to a number of unique thermal–physical properties, they find a wide variety of technological applications, including the intensification of heat transfer in rectification columns. The aim of this work was to evaluate the reduction of energy costs for condensation of vapors in the condenser of a distillation column by replacing traditional cooling agents (water, brines, etc.) with magnetic fluid solutions. This assessment is carried out using the example of columns for the extraction of acetone and isopropyl alcohol in the production of hydrogen peroxide. The following magnetic fluids are considered: an aqueous solution of aluminum oxide nanoparticles, an aqueous solution of copper oxide nanoparticles, and an aqueous solution of single-walled carbon nanotubes (SWCNT). The volume content of the metal oxide particles varies from 0 to 6%. The dependences of the growth of the heat-transfer coefficient on the volume content of the metal oxide nanoparticles and SWCNT particles are obtained. Comparison of the efficiency of using the three selected nanofluids shows that the greatest increase in the heat-transfer coefficient occurs when using SWCNT.

A new approach to formulating low-viscosity marine fuels is proposed, based on a comprehensive analysis of experimental data and means of mathematical modeling. The approach is based on established patterns of mixing medium and heavy distillates from oil refining that form fuels which are more than 95% aromatic and paraffinic-naphthenic hydrocarbons in a ratio of approximately 1 : 2. A combinatorial scheme of testing is used to determine the hydrocarbon composition of the components and fuels. The obtained data are used to create a mathematical model for calculating the formulas of low-viscosity marine fuels according to their components’ composition of hydrocarbons without the need for additional research on the latter in a wide range of indicators. The set of identified patterns and approaches to modeling validate the expansion of a fuel’s raw material base by replacing up to 70% of its valuable components with lower-margin petroleum products.

This paper presents an algorithm for improving the organization of chemical-technological systems (CTSs) with several levels of aggregation based on information approach. The algorithm assumes the sequential solution of optimization problems according to the top-down principle, starting from the upper to the lower macroscopic levels, and then to the optimization problem at the microlevel. When solving optimization problems at all macrolevels, the optimization criterion is macroentropy, whose maximization in accordance with the zeroth law of thermodynamics is responsible for the optimal distribution of energy between elements and subsystems. The implementation of the algorithm is illustrated using the example of a system with a double-chamber heating furnace consisting of convection and radiation chambers combined into a single thermal unit. The determination of the tendencies of optimal organization of the CTS with the furnace as a single thermal unit and the furnace as a subsystem with a discrete element structure was made on the basis of the equivalent temperature distribution diagram determining the weight coefficients of the processes comprising the macroentropy criterion.

This paper presents the results of determining the composition of vacuum gas oil, a raw material for deep oil-refining processes, using two-dimensional gas chromatography. These results are the basis for describing the formalized mechanism of hydrocarbon transformations of high-boiling oil fractions in the processes of hydrocracking and catalytic cracking. The found hydrocarbon composition is used in modeling the composition of vacuum gas oil using the structure-oriented lumping method. The increment vectors of hydrocarbons contained in vacuum gas oil are compiled. The normal boiling point of the fraction is calculated for these vectors. Using the developed algorithm, the component composition of the raw material of the second stage of hydrocracking is reconstructed, according to which its fractional composition is calculated; the calculation error does not exceed 4°C. Based on laboratory and numerical studies, the reaction schemes of the processes of hydrocracking and catalytic cracking of vacuum gas oil are compiled. The studies performed using a mathematical model of cracking show that the involvement in the processing of mixed raw materials containing 15% distillate slack and 15% extract of selective oil purification allows increasing the productivity of the catalytic cracking unit and provides a favorable fuel mode for its operation.

A theoretical analysis of the influence of the distribution of the local specific energy dissipation rate on the specific surface area of phase contact and the superficial and volumetric mass-transfer coefficients in devices with heterophase processes and a liquid continuous phase, as well as on the quality of mixing in devices with homophase reactions in the liquid phase, is performed. It is shown that the average value of the specific energy dissipation rate for the volume of the apparatus is not a complete criterion for assessing the useful effect, since it does not take into account, on the one hand, the local level of energy dissipation in the active zones, and on the other hand, the features of the flow structure and the local residence time in the active zones, depending on the geometry of the apparatus and the method of introducing energy into it. Limiting cases are discussed: a non-uniform distribution of energy in the presence of a zone of small volume with a high dissipation rate and an ideally uniform distribution of energy throughout the entire volume of the apparatus. In the first case, a significant portion of the volume is used inefficiently; in the second case, an excessive amount of energy is expended. In this regard, the concepts of dosed distributed energy input for long-term processes and maximum concentration of energy in a microvolume for fast-flowing processes are considered.

The paper presents theoretical and experimental studies of spray drying technology for the production of dry powder pharmaceuticals for inhalation use. A numerical simulation of atomizing air flows in and around a pneumatic injector nozzle is presented and is then used to determine the key parameters of the atomizing process, namely, the atomizing air velocity relative to the liquid feed velocity. The range of permissible atomizing air velocities and the influence of this parameter on the size of the resulting particles are determined. Based on the obtained modeling results, a method for producing microparticles with an average size of 2.6 µm and a distribution from 1 to 4 µm is proposed.

A hydrophobic deep eutectic solvent based on di(2,4,4-trimethylpentyl)phosphinic acid and phenol is proposed as an extractant for the separation of a number of rare-earth element ions from nitrate solutions. Experimental data on the interphase distribution of Pr, Nd, Tb, Dy, and Yb ions in the di(2,4,4-trimethylpentyl)phosphinic acid/phenol system are obtained with varying key process conditions: medium acidity, salting-out agent concentration, component ratio in the eutectic solvent, metal concentration, etc. The study establishes the mechanism of rare-earth-metal cation extraction by the proposed eutectic solvent and the composition of the extracted compounds using the tilt angle method. A study of metal ion re-extraction from the organic phase with mineral acid solutions is conducted, and the possibility of repeated use of the proposed eutectic solvent in chemical engineering processes is assessed. The obtained results indicate the potential of using the deep eutectic solvent di(2,4,4-trimethylpentyl)phosphinic acid/phenol for the extraction of rare-earth-metal cations in magnetic waste recycling processes.