Calculation of Azeotropic Properties for Ternary Mixtures with the PC-SAFT Equation of State

Abstract

In this study, a novel approach employing the Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT) Equation of State was introduced to investigate azeotropic behavior in ternary mixtures and explore their liquid-vapor equilibria. The temperature range spans (243.15323.5) K, covering a broad spectrum of conditions relevant to industrial and chemical processes. Our analysis focuses on six different ternary mixtures: Difluoromethane (R32) + 1,1-difluoroethane (R152a) + 2,3,3,3-tetrafluoropro-1-ene (R1234yf); Isobutane (R600a) + 1,1-difluoroethane (R152a) + 1,1,2,2-tetrafluoroethane (R134); 1,1,1,2-tetrafluoroethane (R134a) + 2,3,3,3-tetrafluoropro-1-ene (R1234yf) + isobutane (R600a); 1,1,1,2-tetrafluoroethane (R134a) + 2,3,3,3-tetrafluoropro-1-ene (R1234yf) + dimethyl ether (DME); isobutene (R600a) + 1,3,3,3-tetrafluoropropene (R12345ze(E)) + trifluoroiodomethane (R13I1); and difluoromethane (R32) + fluoroethane (R161) + 1,3,3,3-tetrafluoropropene (R1234ze(E)). Among these, only three mixtures exhibit azeotropic behavior. The PC-SAFT equation of state, incorporating an expansion form tailored for Vapor-Liquid Equilibrium (VLE) calculations within ternary mixtures, determined azeotropic composition and pressure based on the Gibbs-Konovalov theorem, which characterizes azeotropic behavior under constant temperature. Our estimations of the VLE and azeotropic composition and pressure closely align with experimental data. The maximum relative error in pressure does not exceed 4.2% for the R600a + R152a + R134 mixture and remains less than 6.56% for the liquid composition of R1234ze(E) within the (R600a + R1234ze(E) + R13I1) ternary mixture. These results underscore the reliability and accuracy of the PC-SAFT equation of state in modeling azeotropes within ternary mixtures.