This work reports supercritical water oxidation (SCWO) of organic pollutants in industrial wastewater in the absence and presence of catalysts. To increase the efficiency of the oxidation process, the SCWO of organic compounds in industrial wastewater was performed in the presence of various iron- and manganese-containing heterogeneous catalysts (Fe-Ac, Fe-OH, and Mn-Al). The catalytic and non-catalytic SCWO of organic compounds in wastewater from PJSC “Nizhnekamskneftekhim”, generated from the epoxidation of propylene with ethylbenzene hydroperoxide in the process of producing propylene oxide and styrene (PO/SM), was performed. The effect of operational parameters (temperature, pressure, residence time, type of catalysts, oxygen excess ratio, etc.) on the efficiency of the process of oxidation of organic compounds in the wastewater was studied. SCWO was studied in a flow reactor with induction heating under different temperatures (between 673.15 and 873.15 K) and at a pressure of 22.5 MPa. The reaction time ranged from 1.8 to 4.83 min. Compressed air was used as an oxidizing agent (oxidant) with an oxidant ratio of two to four. A pseudo-first-order model expressed the kinetics of the SCWO processes, and the rate constants were evaluated. In the present work, in order to optimize the operation parameters of the SCWO process, we used the thermodynamic properties of near- and supercritical water by taking into account the asymmetric behavior of the liquid–vapor coexistence curve.

The phase behavior of binary systems containing organic components (phenol and acetone) and potential extractants (carbon dioxide and propane–butane mixture), which were proposed to be used in the supercritical state to treat the industrial wastewater from PAO Kazanorgsintez, is analyzed. The phase behavior of the CO₂–acetone thermodynamic system in the near-critical region (313 K) is studied using a high-pressure optical cell. In this binary system, various phase states are detected, including areas of critical opalescence and complete miscibility. Supercritical fluid extraction (SFE) is investigated in treating a model aqueous solution of phenol and acetone with the concentration corresponding to industrial wastewater.

One of the promising ways to solve the environmental problems are associated with the disposal of industrial waste as well as isolating molybdenum and important organic components from the wastewater. There could be used processes with working environments in a supercritical fluid (SCF) state which studied in this article. This approach was the subject of research the results of which are presented in the work. Previously the authors of the article opted for combining a supercritical fluid extraction process with carbon dioxide as an extracting agent. Since the task was to isolate organic compounds and oxidize the remaining organic components of wastewater and simultaneously precipitate the inorganic component under supercritical conditions for an aqueous solution. Both processes turned out to be knowledge-intensive and saturated. The implementation of the oxidation process in supercritical conditions has significant advantages over traditional methods, namely, thermal neutralization and control disposal by reducing the amount of emissions into the atmosphere and soil, improving the quality of neutralization, and the possibility of recycling neutralized water. It is possible to use the heat of an exothermic reaction for internal production needs with the appropriate composition of the wastewater. The article presents the results of a study of the oxidation process of an industrial molybdenum-containing wastewater of a propylene epoxidation process carried out under supercritical fluid conditions (T = 673–873 K, P = 22.5 MPa). The experiments were carried out in a flow reactor using oxygen from air as an oxidizing agent. It was studied the influence of thermodynamic conditions on the efficiency of the process of oxidation of organic compounds of wastewater. There was isolated and characterized the elemental composition of the inorganic residue in which the concentration of molybdenum was carried out on the plant of a highfrequency induction plasma.The authors would like to thank the Russian Foundation for Basic Research (Agreement No. 18-29-06041) for the funding provided to them.

Rapeseed oil transesterification reaction with ethanol under supercritical fluid conditions was performed either in the presence of catalysts or without them. The catalysts were Al₂O₃ and AlOOH, obtained after Al₂O₃ hydrothermal processing, and CaO/Al₂O₃ and CaO/AlOOH, obtained after permeation. The obtained product was measured for dynamic viscosity and density. Based on these data, kinematic viscosity was calculated. Biodiesel fuel was separated via centrifugation to extract more viscous ethyl esters of saturated fatty acids and unreacted triglycerides in order to comply with the standards for biodiesel fuel. Analyses have found that the maximum content of obtained ethyl esters of fatty acids in a reaction product before separation is reached, in the case of using the CaO/AlOOH catalyst, is in the amount of 93.34% by mass; and none of the samples’ kinematic viscosity values comply with the standards for biodiesel fuel. Performing centrifugation allowed us to reduce viscosity and increase biodiesel fuel concentration to reach the EN14214 standard requirements. Also, a significant deterioration of the initial catalysts’ strength after the singular experiment has been observed: Al₂O₃ by 22.4%, AlOOH by 13.89%, CaO/Al₂O₃ by 25.13%, and CaO/AlOOH by 17.27%.