Experimental study and thermodynamic modelling of isothermal VLE properties of binary C₃H₈ + pyridine mixture at high temperatures and high pressures

Isothermal vapor–liquid equilibrium (VLE) data ( PTxy ) for the binary supercritical propane (C₃H₈) + pyridine system were measured at three isotherms, T = (403.15, 423.15, and 443.15) K, and pressures ranging from ( 0.89 to 7.05) MPa, using a high-temperature, high-pressure optical cell apparatus. From the measured VLE data, the vapor–liquid critical point parameters ( P C , T C , x C ) of the mixture were determined. The initial slope of the critical lines, together with the slope of the vapor pressure curve of pure C₃H₈ at the critical point, was employed to evaluate the Krichevskii parameter ∂ P ∂ x T C V C ∞ , a theoretically significant parameter with rigorous microscopic foundations. The predictive performance of three theoretically based models with universal, system-independent binary parameters, namely PC-SAFT (with two alternative sets of pyridine molecular parameters) and CP-PC-SAFT, was assessed against the new VLE data, as well as available critical, liquid–liquid equilibrium (LLE), and excess enthalpy data for n -alkane + pyridine mixtures. The results demonstrate that CP-PC-SAFT provides superior overall reliability compared with both PC-SAFT approaches.