Theoretical Foundations of Chemical Engineering最新文献

NASICON with a composition of Na₃Zr₂Si₂PO₁₂ was first synthesized by pyrolysis of a mixture of organic solutions. The ratio of initial components required for the formation of this composition was determined. The temperature conditions for processing the precursor were examined. The material was obtained with an average grain size of 0.2 μm. The composition and morphology of the compound were confirmed by X-ray diffraction analysis and scanning electron microscopy. The synthesis of NASICON takes 9 h on the average, which is the minimum time among all known methods for the preparation of this material.

This article presents the experimental results of extraction chromatography separation in a cascade of sieve tray extraction columns operating in the mode of continuous flow of the disperse mobile phase. The possibility of extraction separation of rare-earth metals in a cascade of sieve tray extraction columns operating in the liquid–liquid chromatography mode is demonstrated.

Chemical looping with oxygen uncoupling (CLOU), an environmentally friendly method for power generation, has been extensively developed in recent years. The main disadvantages of this method, associated with incomplete fuel combustion, ash withdrawal, and dust entrainment, can be solved by changing the structural and process parameters. The simplest fuel reactor for the combustion of methane gas is considered using computer simulation. The gas-phase pressure distribution and its velocity gradient in transverse and longitudinal cross-sections of the reactor are studied in the present work. Using the obtained data, the maximum power of the fuel reactor for implementing the CLOU process is calculated and the requirements for an oxygen accumulator to achieve the claimed performance are formulated.

Studies on the sorption of rare-earth metals, uranium, and thorium from nitric acid solutions on different phosphor-containing solid extragents produced by the Russian ZAO Axion-RDM are performed. It is demonstrated that effective extraction of REM on phosphor-containing solid extragents is possible from solutions with HNO₃ concentration up to 0.1 M and extraction of uranium and thorium from solutions of up to 6 M.

In the present study, an artificial neural network (ANN) model and three well-known correlations were used to predict the smoke points of 430 kerosene distillates from their specific gravities and distillation temperatures. The ANN model was developed in MATLAB software, it is a feedforward multilayer perceptron with a single hidden layer. The optimal number of neurons in the hidden layer as well as the best training algorithm and the best values of connection weights and biases were determined by trial and error using the nftool command. The early stopping technique by cross-validation was employed to avoid overfitting of the model. The developed model composed of 17 sigmoid hidden neurons and one linear output neuron was trained with the Levenberg-Marquardt backpropagation algorithm. This model allowed the prediction of smoke points with a coefficient of determination of 0.852, an average absolute deviation of 1.4 mm and an average absolute relative deviation of 6%. Statistical analysis of the results indicated that the prediction accuracy of the ANN model is higher than that of the conventional correlations. Indeed, in addition to its effectiveness, the proposed ANN method for the estimation of smoke points has the advantages of low-cost and easy implementation, as it relies on simple laboratory tests. Thus, the developed ANN model is a reliable tool that can be used in petroleum refineries for fast quality control of kerosene distillates.

The possibility of regulating the structure and morphology of precipitates forming in the CaO–P₂O₅–H₂O system in the low concentration region during neutralization of acidic solutions with lime milk is studied. The effect of the main technological parameters (temperature and pH) on the crystallization of calcium phosphates from dilute CaO–P₂O₅–H₂O solutions, other conditions being equal, is determined. The formation of dicalcium phosphate under neutralization of the model acidic solutions in the range of pH 4.5–6.5 is reported; at higher pH values, the formation of tricalcium phosphate crystalline hydrate is observed. The formation of hydroxyapatite crystals is not established. It is demonstrated by the physicochemical analysis of the forming precipitates that an increase in the neutralization temperature facilitates an increase in the tricalcium phosphate crystallization rate at lower pH values.

The article presents a compact and exhaustive interpretation of the foundations of energodynamics and shows that it significantly extends the horizons of natural science and opens new avenues to improve the scientific bases of chemical technology.

Layered magnesium aluminum hydroxide Mg₄Al₂(OH)₁₂CO₃⋅3.85H₂O with the hydrotalcite structure is obtained by the solid-phase interaction of AlCl₃⋅6H₂O and MgCl₂⋅6H₂O with (NH₄)₂CO₃ at room temperature. The change in the phase composition of the products of its heat treatment in the temperature range 180–600°C is studied. It is determined by DSC/TG that the thermal decomposition occurs in two stages: the first stage occurs in the temperature range 180–215°C; the second, in the range 400–440°C. The apparent activation energies E_a of both stages of thermal decomposition are found by the model-free Kissinger method to be 62.85 and 141.86 kJ/mol, respectively. The obtained E_a values agree well with the literature data and indicate that both stages are single-step kinetic processes.

In some cases, a reaction in the oscillatory mode has a higher selectivity for the target product. To organize production in this mode, it is necessary to determine the conditions under which fluctuations occur, as well as to consider the very nature of the fluctuations. In this work, a parametric analysis of the basic kinetic model of an oscillatory reaction without autocatalysis was made. The boundaries of the parameters at which the system oscillates were found. Phase portraits of the system and bifurcation curves were constructed. Stationary states of the system were analyzed. The type and number of stationary states were identified. It was shown that the system at certain parameters has three stationary states: two unstable nodes and a saddle. Parametric analysis of basic models will allow selecting initial approximations for calculations of more complex models of real reactions.