Theoretical Foundations of Chemical Engineering

Mathematical and computer-based models of a complex chemical-engineering roasting process as an interdependent plurality of three processes—drying, calcining, and sintering of moving, tight, and multilayered mass of phosphorite pellets in conveyer roasting machine, differing in attention to the intensity of processes of internal moisture transfer within the pellet and overwetting processes of separate horizons in heated pellet layer, have been developed, making it possible to the determine engineering parameters of the roasting mode. The adequacy of the mathematical model is checked from the comparative analysis data of calculated values of the moisture content and the temperature of pellets and parameters of heat-transfer gas, as well as moisture-transfer intensity in pellets when they are dried in the moving tight layer, were compared with the data of industrial testing. Numerous calculated experiments to determine the relative extent of drying, the moisture content, the intensity of pellet drying, and the moisture content of heat-transfer gas are carried out, in which crude pellets and the engineering data of the operating mode of a roasting machine have different parameters. An informal and mathematical statement of the problem of optimizing the chemical-energy engineering process (CEEP) for roasting the moving tight multilayered mass of phosphorite pellets within the complex chemical-energy engineering system (CEES) of the conveyer roasting machine is developed as the problem of discrete dynamic programming in light of spatiotemporal multistage processes for roasting the moving multilayered pellet mass, the intensity of the internal moisture transfer processes within the pellet, processes of overwetting the separate layers of pellets, and variables of the control stream of the heat-transfer gas; this makes it possible to enhance energy efficiency by means of intensifying heat-and-mass transfer processes of multilayered drying, calcining, and sintering. The performance criterion is the minimum cost of electrical and heat energy expended on the CEEP for roasting. The results were used to calculate energy efficient pellet roasting in CEES of the conveyer roasting machine. It has been found that, under the optimum mode of multilayered pellet roasting, there is no overwetting zone, processes of heat and moisture transfer are intensified, energy consumption decreases, and the quality of the end product increases. The problem of pellet overwetting in separate layer horizons of the drying zone of the roasting machine has been studied. The actual theoretical and practical problem of energy and resource saving in roasting pelletized crude ore in the tight layer has been solved. The mathematical model of heat-mass exchange in the pellet layer and testing its adequacy have been presented. The problem of optimizing power inputs based on the intensification of roasting processes has been solved.

Vortex contact devices for gas introduction have been developed and studied. The devices make it possible to increase the gas and liquid loading on stages compared with valve and cap devices, to reduce the fluctuations of the gas–liquid medium on the liquid surface, and to increase the separation efficiency. Based on the experimental studies and numerical modeling, a scheme of liquid and gas motion at the stage was developed, and the velocity profiles during bubbling were calculated. The stage parameters were determined: hydraulic resistance, gas content, average surface diameter of bubbles, interphase surface area, efficiency, and mass transfer coefficients. The dependences for their calculation were presented. A vortex stage for the exhausting distillation column was designed, which provides a 1.5-fold reduction of metal consumption and increased efficiency at a velocity factor of up to 3 Pa^0.5 and spray rate of 78 m³/(h m²) compared with the standard cap plate.

An environmentally friendly aqueous two-phase system based on polyethylene glycol and sodium sulfate has been proposed for the extraction of caffeine and coumarin. The kinetic dependence of distribution coefficients for caffeine and coumarin in the system under investigation has been obtained. The dependences of the quantitative characteristics of caffeine and coumarin extraction on the acidity of the medium, the concentrations of the polymer and phase-forming salt, temperature, and the molecular weight of the polymer have been found. The results of this study can be used in the development of effective chemical processes that meet green chemistry requirements.

The use of dividing-wall columns for separating the C₄₊ pyrolysis fraction is considered. The influence of the phase state of the feed flow on the energy consumption in column reboilers is investigated. It is shown for the first time that the use of dividing-wall columns is more efficient when using the feed stream with a high vapor fraction of 80–100%. The largest energy-saving effect of the dividing-wall column is provided by using the feed in the vapor phase. In this case, the energy savings can reach 30%. In addition, it is shown that the use of dividing-wall columns reduces capital costs by 18–21%.

On the basis of a thermodynamic–topological analysis of phase equilibrium diagrams of reaction mixtures formed during the liquid phase epoxidation of allyl chloride with an aqueous solution of hydrogen peroxide in an organic solvent in the presence of a heterogeneous catalyst, two principal technological separation schemes are proposed. Two lower alcohols are considered as solvents: methanol and propanol-2. Both schemes are aimed at the isolation of all components in pure form and are based on the use of special separation methods: extractive rectification with dimethyl sulfoxide (separation of allyl chloride–methanol and propanol-2–water component pairs) and a combination of rectification and delamination (separation of binary allyl chloride–water and water mixtures–epichlorohydrin). The material balances of separation schemes for mixtures of a specific composition are calculated (one composition for both mixtures is considered). To determine the operation parameters of rectification columns (the number of separation stages, feed plate, and reflux ratio), a computational experiment is conducted using the Aspen Plus® software. Preference is given to parameters ensuring the production of all substances with a purity that meets GOST (State Standard) with minimum energy consumption. The separation scheme of the mixture with propanol-2 containing one column less is characterized by a lower total number of separation stages (by 32 theoretical plates) and lower (by 11%) energy consumption compared to the separation scheme of the mixture with methanol. In addition, the epoxidation reaction with an excess of propanol-2 (the alcohol concentration should be at least 68 wt %) can significantly simplify the allocation of the target product of epichlorohydrin, which is impossible for a system with methanol.

Based on thermodynamic data for related pure substances, the relations of (n_Cl/n_H)_Eq and (n_Cl/n_H)_o have been plotted in the Si–Cl–H system. The results show that the difference of (n_Si/n_Cl)_o and (n_Si/n_Cl)_Eq is the driving force for polycrystalline silicon chemical vapor deposition (CVD). SiHCl₃ is preferred for polycrystalline silicon deposition to SiCl₄. SiH₂Cl₂ would be even better, but it is not stable as a gas and hence it is less frequently used. Then, thermodynamic simulation of polycrystalline silicon CVD in the Si–H–Cl system has been investigated. The pressure has a negative effect on polycrystalline silicon yield. The optimum temperature is 1400 K, at which the kinetic rate of rate-determining step for the main reaction is large enough. The excess hydrogen is necessary for polycrystalline silicon CVD in the Si–Cl–H system. However, the silicon deposition rate increases then decreases with increasing H₂ molar fraction. The optimum H₂ molar fraction should be determined by considering thermodynamics and transport phenomena simultaneously. Finally, the optimum conditions have been obtained as 1400 K, about 0.1 MPa, and H₂ to SiHCl₃ ratio of 15, which are close to the limited reported values in the open literature. Under the optimum conditions, the silicon yield ratio is 34.82% against 20% reported in the open literature.

The solubility of ozone in solutions of oxalic acid H₂C₂O₄ and potassium nitrate at concentrations up to 1 and 2 M, respectively, is studied at 25°C. The Sechenov constants for these electrolyte solutions are found: 0.081 ± 0.010 and 0.082 ± 0.004 M^–1, respectively. The anion-specific parameter in the Weisenberger–Schumpe gas solubility model for oxalate ion is determined: \({{h}_{{{{{\text{C}}}_{2}}{\text{O}}_{4}^{{2 - }}}}}\) = 0.1266 M^–1. A set of coefficients is determined using the experimental data from various sources to calculate the density of H₂C₂O₄ solutions as a function of temperature in the range of 5–100°C at solution concentrations up to the saturated concentration at a given temperature.

This paper investigates the thermochemical characteristics of date palm fronds (DPFs) to use as feedstock for different energy conversion processes. The proximate analysis, ultimate analysis, calorific value measurements, and elemental content measurements were carried out using some quantitative and qualitative techniques. At later stage, the gasification of DPFs was carried out in an externally hot gasifier system. The effect of gasification temperature and biomass particle size on gas composition and heating value of producer gas was investigated. The results showed that the thermochemical characteristics of DPFs were comparable with other biomass materials reported in the past literature. The gasification trials of the biomass revealed that temperature has a significant effect on gas composition, especially H₂ and CO contents. The high temperature yielded high H₂ and CO concentrations in the product gas. A good quality gas composition (in terms of H₂, CO, CH₄, and CO₂ contents) was obtained from bigger particle sizes as compared to smaller sizes. The thermochemical characteristics of DPFs and gasification results showed that DPF feedstock is comparable with other conventional biomass for production of energy through appropriate thermochemical technologies.

A support vector machine model in quantitative structure–property interaction was developed for predicting retention indices of monomethylalkanes of fuel. The total number of descriptors was calculated with Dragon software, and a subset of calculated descriptors was selected from some classes of Dragon descriptors with a stepwise multiple linear regression.