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Fine Chemical Technologies

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Vol 13, No 3 (2018)
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https://doi.org/10.32362/2410-6593-2018-13-3

THEORETICAL BASES OF CHEMICAL TECHNOLOGY

5-22 160
Abstract
The paper presents an analysis of the current state of research on separation flowsheets based on the combination of distillation and phase separation processes, as well as heteroazeotropic distillation. It is shown that the works of foreign researchers devoted to the study of flowhseets with decanters are more focused on finding ways to reduce energy consumption by introducing additional separators, a combination of several methods (extractive and heteroazeotropic complex columns with external decanters. The task of synthesizing all possible separation flowsheets is not considered in these works. In this paper, a complete set of flowsheets of different structures based on the combination of distillation and phase separation processes, including the use of columns with an external decanter, is proposed for water - butyl acetate - methanol and methanol - heptane-water ternary mixtures separation. Aspen Plus and NRTL model were used for mathematical modelling of phase equilibrium (the relative error of describing liquid-vapor and liquid-liquid equilibrium is less than 5%) was chosen as a method of research. Operating parameters for distillation columns (the number of theoretical plates, feed plate, reflux ratio) and the total energy consumption were obtained for each case. The necessity of using a double feed-plate column for separating of propanol-1 - water - butanol-1 and ethyl acetate - water - butyl acetate ternary systems was explained by the presence of extractive effect. Analytical review of modern publications and results of own research allowed to formulate a number of recommendations for the synthesis of energy effective flowsheets based on a combination of distillation and phase separation processes.
23-29 174
Abstract
The heat costs in distillation columns were determined for the purpose of separating a four-component gas mixture in gas fractionators with various component selection sequences. A method for selecting the optimal scheme was developed. It is based on the concept of “internal energy saving” upon rectification. Internal energy saving means multiple steam operation on the plates of a distillation column, namely, its condensation on each plate with the release of the heat of condensation, which is used for the evaporation of the liquid entering the plate to obtain a new steam composition. It was shown that when binary and three-component mixtures are separated and products of equal purity are obtained, the heat costs are related to the internal energy saving. The calculation of the internal energy saving in a three-column system for the separation of a four-component mixture was carried out. The calculation confirms that, as the internal energy saving increases and, accordingly, the average internal energy saving in the system of columns increases, the total heat consumption is reduced. The results of calculating three separation schemes of the four-component mixture were compared using the program Aspen Plus with different methods for describing the phase equilibrium (NRTL, Peng-Robinson, Chao-Seader) was carried out. It was shown that the calculations with the use of Peng-Robinson and Chao-Seader methods match.
30-40 235
Abstract
Variants of the extractive distillation of chloroform - methanol - tetrahydrofuran equimolar mixture with industrial separating agents are considered. The basic system shows opposite deviations from the ideal behavior, because it contains binary azeotropes with minimum and maximum boiling points (3.3.1-4 system according to Serafimov’s classification). The choice of selective substances for extractive distillation was carried out taking into account the concentration dependences of the excess molar Gibbs energy of the binary constituents of the derivative system “chloroform - methanol - tetrahydrofuran - industrial test agent (ethylene glycol (EG), dimethyl sulfoxide (DMSO), N-methylpyrrolidone (N-MP))” at 101.32 kPa. Based on the results of the evaluation of the thermodynamic criterion, DMSO and N-MP are recommended. Both agents show selective effect when separating two binary constituents. EG is selective only with respect to chloroform-tetrahydrofuran mixture. Since the tested agents show different selective effects, the final agent choice determines the qualitative composition of the product flows in the column for the extractive distillation of the three-component mixture (the first column of the flowsheet) and, accordingly, the structure of the total flowsheet. The schemes consist of two two-column complexes for extractive distillation (for the basic three-component mixture and for the binary mixture). The maximum contribution to the total reboiler energy consumption of the distillation columns is made by the first extractive distillation column: 65% (EG), 53% (N-MP) and 24% (DMSO). The use of the most selective agent reduces the energy consumption of this column: the reboiler load is maximal in the case of EG, in comparison with which the load is 47% lower in the case of N-MP and 76% lower in the case of DMSO.
41-48 182
Abstract
Conditions of sharp distillation were considered for zeotropic quaternary system (two pairs of components are characterized by relative volatility close to 1) and systems with one (with minimum or maximum boiling point) and two (with minimum and maximum boiling point) binary azeotropes. Regions of compositions for which sharp distillation is effective (distillate and bottom flows don't contain common components) were determined on the basis of analyzing diagrams of unit manifolds of distribution coefficients (distribution coefficients of two components are higher than one, and those of another two components - lower than one). This kind of separation can be recommended if it doesn’t cause an increase in the number of apparatuses in the separation flowsheet. If the system contains azeotropes of saddle type that can generate separatric manifolds, the possibility and expedience of sharp separation decreases. The conclusions were confirmed by simulation of the distillation process in AspenPlus V.10.0 for real and industrially important quaternary systems: ethyl acetate - benzene - toluene - butyl acetate; acetone - methanol - ethanol - propanol-2; methyl acetate - methanol - acetic acid - acetic anhydride and cyclohexene - cyclohexane - cyclohexanone - phenol. Mathematical modeling was carried out using local compositions models Wilson and NRTL-HOC. The relative error of vapor-liquid equilibrium description is less than 4%. The vapor-liquid equilibrium was simulated, a phase diagram was constructed and analyzed, the parameters of sharp distillation column operation (the number of stages, the feed-stage and reflux ratio) were determined for all systems. The effectiveness of using sharp distillation for the system with phenol was confirmed for a wide range of compositions.

CHEMISTRY AND TECHNOLOGY OF ORGANIC SUBSTANCES

49-56 119
Abstract
A technological process of manufacturing glycidol designed for the production capacity of 10 thousand tons per year and consisting in the direct oxidation of allyl alcohol with an aqueous solution of hydrogen peroxide in the presence of nanostructured titanium silicate in methanol is proposed. Due to the exothermic process, the solvent is not only a homogenizer of the mixture of the initial reagents of the epoxy process - allyl alcohol and hydrogen peroxide ensuring their interaction on the surface of the solid catalyst: it also prevents overheating of the reaction mass. On the basis of the research trial of the process the optimal parameters of the process were determined: temperature 30-40 °C; pressure 0.25 MPa; the initial hydrogen peroxide : allyl alcohol ratio = 1:(3-4) mass., methanol concentration in the reaction mixture 12-13 mol/l. Hydrogen peroxide conversion is 98%, the yield of the glycidol - 94%, the selectivity is no less than 95%. The process includes three main stages: (1) raw materials preparation, (2) liquid-phase epoxidation of allyl alcohol, (3) distillation of the target product. The scheme involves recirculation of unreacted allyl alcohol and the solvent - methanol. The developed technological process provides the following indicators (per 1 t of commercial glycidol): consumption of allyl alcohol no more than 0.843 t; consumption of hydrogen peroxide no more than 0.50 t (calculated for 100% hydrogen peroxide); consumption of methanol is no more than 0.022 tons All the waste products correspond to the 3-rd or 4-th hazard class.

CHEMISTRY AND TECHNOLOGY OF INORGANIC MATERIALS

57-63 120
Abstract
It is proposed to consider the process of carbon materials oxidative activation from the positions of topochemical reactions involving chemisorption of the activating agent (oxidizer) on the material surface active centers followed by chemical interaction. Such an approach makes it possible to control the process of creating a carbon material with the desired characteristics of the porous space. It is assumed that the oxidizer chemisorption active centers are amorphous carbon, which is localized on the material crystallites boundaries. The change in the length of these boundaries will lead to a change in the process rate. It is shown that the number of such active centers on the carbon material surface depends on the size of the crystallites. It will have a significant impact not only on the rate of activation, but also on the possibility of the process flow on the surface or with porosity formation. Mathematical models describing the carbon sample specific surface changing in the oxidation process are proposed. They allow quantifying the proportion of carbon that is oxidized on the sample surface or with pores formation, as well as quantifying the number of pores. It is shown that the ratio of pore formation and surface oxidation processes depends on the oxidation temperature, the oxidizer nature and its flow rate. The proportion of porosity formation decreases with the increase in the oxidant flow rate and the increase in temperature. It was experimentally shown that in order to obtain a material with a more developed porous space and a high specific surface it is preferable to use carbon dioxide as an oxidizing agent.
64-71 159
Abstract
The article is dedicated to finding out the specific features of the behavior of rare-earth metals in hydrometallurgical processing of pyrochlore-monazite-goetite ores of the Chuktukonsky ore field is shown in the work. Chuktukonsky ore field is a potential source of rare earth metals. The mentioned ores are practically unenforceable. Hydrometallurgical methods for their complex processing were suggested. Agitational and autoclave nitric acid leaching depending on such technological parameters as temperature, HNO3 concentration, process duration, S:L ratio and the use of H2O2 were studied. The possibility of transferring manganese (that is present in a significant amount in the ore) into a nitric acid solution by hydrogen peroxide was considered. Based on the results of the conducted studies, the distribution of REM in the products of the hydrometallurgical conversion of pyrochlore-monazitegoetite ore was estimated. It was found out that incomplete opening of the ore material was observed during agitational leaching: average REM recovery into the solution is 60%. The study made it possible to solve the problem of purifying nitric acid solutions from phosphorus that hinders the subsequent extraction and separation of rare earth metal ions forming strong complexes with rare earths. Removal of phosphorus from the solution was achieved by conducting the process under pressure at elevated temperatures (200-230 0C). It was found that the optimal decomposition conditions ensuring the transfer of almost 99% of the REM into the nitric acid solution are: 25% solution of HNO3, ore size - 0.071 mm; 5% by volume H2O2; t(160 0С) = 1 h; t(230 0С) = 1 h, gradual temperature increase from 160 to 230 0С; S:L = 1:8. Autoclave nitric-acid leaching allows selecting rare earth metals from the main part of iron, phosphorus and niobium.

SYNTHESIS AND PROCESSING OF POLYMERS AND POLYMERIC COMPOSITES

72-78 129
Abstract
The accelerated stress cracking of monolithic polycarbonate sheets was investigated. Cracking of polycarbonate organic glasses during operation leading to a drop in impact strength and transparency is their main disadvantage. The main role in the acceleration of the process of cracking is played by the stresses that arise when they are formed and mounted. The aim of this work was to investigate the dependence of the cracking start time on the stress applied to the sheet monolithic polycarbonate. This makes it possible to predict the lifetime of polycarbonate products. The experiments were carried out in air and in contact with an adsorption-active medium (a mixture of toluene and n-propanol). The stresses applied to the samples varied in the range from 25 to 55 MPa. It is shown that the dependence of the cracking start time of a polycarbonate on the applied stress can be described by Zhurkov exponential equation. The coefficients of this equation for the processes of cracking in air and in contact with the adsorption-active liquid are calculated. It is established that the activation energy of the polycarbonate cracking process (129.5 kJ/mol) is close in magnitude to the activation energy of the thermal-oxidative destruction (about 145-155 kJ/mol). In contact with the adsorption-active mixture of toluene (25% mass.) and n-propanol, the activation energy of the cracking is reduced to 98.5 kJ/mol. At the same time, the structural coefficient in the Zhurkov equation ("activation volume") increases from 1.45 to 2.45 nm3. The analysis of the obtained results made it possible to predict the lifetime of monolithic polycarbonate sheets and products made of them at various operating stresses
79-85 132
Abstract
The article studies the structure and properties of ethylene vinyl acetate rubbers and the influence of the vinyl acetate (VA) units content in the rubber on the technological, physical-mechanical, operating and electrical properties of vulcanizates. The results of the study prove that the distinctive feature of ethylene vinyl acetate rubbers compared to other rubbers is their thermoplastic properties and low viscosity. Besides, the high resistance to ozone, heat and oil resistance and good mechanical properties of vulcanizates based on them make this type of polymer materials very promising for the creation of modern products. It is shown that the values of elasticity modulus, strength, elongation and tear resistance are increased with increasing VA units content in the rubber. Besides, swelling in hydrocarbon media decreases. Vulcanizates containing 40-45% of VA have satisfactory electrical characteristics and good moisture resistance and can be used as the base insulating rubber. Vulcanizates with a high content of vinyl acetate units (60-70%) have high oil and heat resistance. Therefore, their use in rubber compounds for cable jackets is most effective. The study of the properties of ethylene vinyl acetate rubbers and their vulcanizates allowed to develop formulations of insulating and jacket rubbers and to determine the most promising areas of their application for modern cable products of special purpose in the petrochemical, aerospace, transport and shipbuilding industries.


ISSN 2410-6593 (Print)
ISSN 2686-7575 (Online)