Thermodynamic modeling of VLE and VLLE for the ternary system of 2,3,3,3-tetrafluoroprop-1-ene(R1234yf) + propane (R290) + 1,1,1,2-tetrafluoroethane(R134a) at 253.15 K-313.15 K

The excess Gibbs free energy-equation of state (GEEoS) models is presented based on the Peng-Robinson (PR) EoS combined with the Wong-Sandler (WS) mixing rule and the modified UNIFAC group contribution method (PR-WS-MUNIFAC). The average absolute deviation (AAD) of vapor phase mass fraction and the absolute average relative deviation (AARD) of pressure are 0.0047 and 0.53%, respectively, for R152a + R1234yf; 0.0064、0.0050 and 1.59%, respectively, for R32 + R125 + R134a. The VLE properties of the ternary mixture R1234yf + R290 + R134a as a drop-in replacement for R134a were predicted over the temperature range of (253.15-313.15 K) at 10 K intervals. The vapor-liquid-liquid equilibrium (VLLE) was qualitatively analyzed in theory, and the relevant phase equilibrium diagrams were constructed. The R290 + R134a system has clear characteristics of VLLE near the azeotropic point; the pressure of the upper critical end point (UCEP) is approximately 1.627 MPa. Liquid phase separation also exists in the ternary system of R1234yf + R290 + R134a.