Experimental Study and Thermodynamic Modeling of Isothermal VLE Properties of the Binary CO₂ + Pyridine Mixture at High Temperatures and High Pressures

The phase equilibrium properties (isothermal VLE, PTxy behavior) of the CO₂ and pyridine binary mixture were studied. The measurements were carried out using a high-temperature and high-pressure optical cell. The measurements were performed at three selected supercritical isotherms of 313.15, 333.15, and 353.15 K and at pressures of up to 12.35 MPa. The liquid-vapor critical curve properties (P_C, T_C, x_C) of the CO₂ + pyridine system have been estimated using the measured VLE data. Based on the derived critical curve data, the value of the physically meaningful and theoretically important Krichevskii parameter of the mixture was estimated. The derived value of the Krichevskii parameter, together with reference thermodynamic property data of the pure supercritical solvent (CO₂), can be used to calculate all thermodynamic properties of the dilute mixture near the critical point of pure CO₂. The new measured VLE data were successfully calculated with the Peng-Robinson, 1978 (E-PPR78) model of the equation of state (EoS). The EoS accurately predicts the critical curve behavior of the CO₂ + pyridine mixture and determines its vapor-liquid equilibrium properties across the temperature range of (313.15 to 353.15) K.