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ICAL CHEMISTRY OF SOLUTIONS

Activity Coefficients of the Components of the Binary Systems Consisting of Benzene, Diphenyl, and n-Alkanes I. G. Yakovleva,*, I. K. Garkushina, and A. V. Kolyadoa a Samara

State Technical University, Samara, 443001 Russia *e-mail: [email protected]

Received October 14, 2019; revised October 14, 2019; accepted November 12, 2019

Abstract—Theoretical calculations are compared to data from an experimental study of the position of eutectics in two-component systems consisting of benzene, diphenyl, and n-alkanes with 12 to 17 carbon atoms. Data on diphenyl–n-alkane (n = 12–17) and benzene–n-alkane (n = 12–17) systems are given for the composition of eutectics, their melting points, and activity coefficients of each component. The theoretical study is based on the Schröder–Le Chatelier approach and the original UNIFAC system; the experimental study is performed via DTA. Deviations of the experimental data from ones calculated for the studied systems are presented. The change in the activity coefficients of benzene and n-hexadecane is illustrated graphically according to UNIFAC and the experimental data. Keywords: differential scanning calorimetry, diphenyl, benzene, n-alkane, UNIFAC DOI: 10.1134/S0036024420090320

INTRODUCTION High-boiling heat-transfer fluids are used in the synthesis of various materials for industry. Heat-transfer fluids consisting of organic compounds are used at temperatures above 200°C (e.g., diphenyl, diphenyl oxide, naphthalene, and glycerol, which can maintain temperatures of 100 to 400°C) [1]. However, the melting points of such substances are high, as a result of which their crystallization in the heating circuit of the reaction apparatus is possible. If the process is conducted at low ambient temperatures, mixtures of two or more organic compounds are used as a heat carrier. For example, the Dinyl (Dowtherm A) heat-transfer fluid is widely used in the chemical industry. It is a eutectic mixture with a content of 26.5 wt % diphenyl and 73.5 wt % diphenyl oxide [1]. Dinyl is characterized by a melting point of 12.3°C, while the melting points for diphenyl ether and diphenyl are 26.84 and 68.93°C, respectively. Works describing such systems include [2–21], but the n-alkane–aromatic hydrocarbon with two or more rings systems have been studied relatively little.

THEORETICAL As in [22, 23], the characteristics of phase equilibria in the considered systems were predicted prior to experimental studies, using the Schröder–Le Chatelier equation:

 ln xi =

Δ m H i (T − Tm, i ) , RTm, iT

(1)

where xi is the mole fraction of a component; ΔmHi is the enthalpy of melting of the component, J/mol; Tm,i is the melting point of the pure component, K; and R is the universal gas constant, 8.314 kJ/(mol K). When calculated with the Schröder–Le Chatelier equation, the solution was considered ideal, so the activity coefficients of the components were taken as equal to 1. This equation describes the course of the liquidus of the system from the sides of both the first and se