Topological transformations of phase diagrams of quaternary systems through the boundary tangential azeotrope stage
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Full Articles Topological transformations of phase diagrams of quaternary systems through the boundary tangential azeotrope stage A. V. Frolkova, A. K. Frolkova, and T. E. Ososkova MIREA — Russian Technological University, M. V. Lomonosov Institute of Fine Chemical Technologies, 86 prosp. Vernadskogo, 119451 Moscow, Russian Federation. Fax: +7 (495) 244 9287. E-mail: [email protected] The specific features of quaternary system phase diagram transformations induced by formation of boundary tangential azeotrope were investigated. The characteristics of bifurcation states corresponding to the transition from one structure of the diagram to another were determined. The principal possible transformations of diagrams with varying pressure were illustrated by the systems acetone—chloroform—ethanol—water and chloroform—ethanol—cyclohexane—water. The obtained results expand the understanding of thermodynamics of heterogeneous equilibria of multicomponent systems and make it possible to solve the practical problem of maintaining favorable phase equilibrium conditions for rectification in certain pressure ranges. Key words: vapor—liquid equilibrium, quaternary systems, singular point, boundary tangential azeotrope.
Information on liquid—vapor, liquid—liquid phase equilibria form the basis for the development of new and the improvement of existing technologies for the separation of multicomponent liquid mixtures characterized by complex intermolecular interactions. These interactions manifest themselves by the presence of various azeotropes within the system, which impose restrictions on the possibility of complete separation of mixtures or isolation of target products with the required purity. The study of the specific features of formation and evolution of the structure of vapor—liquid equilibrium (VLE) diagrams plays an important role in the development of energy-efficient, environmentally friendly separation technologies. A methodological approach toward
these technological problems involves the thermodynamictopological analysis of phase diagram structures.1—7 The structure of the VLE diagram is determined by the presence of singular points, i.e., points that signifies identical compositions of vapor and liquid, with temperature or pressure having extreme values characteristic of pure components and azeotropes. In accordance with boiling points, singular points correspond to stable (unstable) node and saddle type points. If in a certain range of external parameters (temperature or pressure) the number of azeotropes and their type remains unchanged, the structure is considered coarse. The transition from one coarse structure to another occurs at a single value of the parameter through the bifurcation state8 (fine structure),
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2059—2066, November, 2020. 1066-5285/20/6911-2059 © 2020 Springer Science+Business Media LLC
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Russ. Chem. Bull., Int. Ed., Vol. 69, No. 11, November, 2020
when the concentration of one or more components b
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