PHASE EQUILIBRIUM STATES IN A TWO-COMPONENT DIPHENYL-n-NONADECANE SYSTEM

Abstract

The melting curves of the diphenyl-n-nonadecane system were calculated using the Schroeder equation and using the UNIFAC and UNIFAC Dortmund methods. The calculation results showed that the diphenyl-n-nonadecane system is eutectic. The compositions experimentally studied by the method of differential thermal analysis and calculated by the indicated methods are not eutectic. Individual substances and 9 compositions within the studied system were experimentally studied using a differential scanning calorimeter. Based on the data obtained, a phase diagram was constructed, including one single-phase field above the liquidus curve and 4 two-phase fields – α-n-C19H40+(Ph)2, β-n-C19H40+(Ph)2, L+n-C19H40, L+(Ph)2. The predominant branch of the liquidus curve belongs to the more refractory component, diphenyl. In the solidus at a temperature of 18.7 °C, a polymorphic transformation α-n-C19H40 ⇆ β-n-C19H40 is noted, which coincides with the literature temperature data. The heating DTA curve of the eutectic alloy showed two endoeffects corresponding to the polymorphic transition of n-nonadecane and the melting of the eutectic. The calculation of the eutectic coordinates by the UNIFAC Dortmund method showed the smallest deviation in the composition of the eutectic alloy from the experimental data. For an alloy of eutectic composition, the specific enthalpy of melting, the molar values of the entropy and enthalpy of melting, the volumetric specific enthalpy of melting, and the density for standard conditions are determined. This two-component system was studied by low-temperature differential thermal analysis. The eutectic melt can be used in industry as a heat carrier. Also, the eutectic composition of the diphenyl-n-nonadecane system under study can be used as a working fluid of a heat accumulator. For citation: Kazakova A.I., Yakovlev I.G., Garkushin I.K. Phase equilibrium states in a two-component diphenyl-n-nonadecane system. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2023. V. 66. N 6. P. 46-53. DOI: 10.6060/ivkkt.20236606.6733.