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The isothermal vapor−liquid equilibrium (VLE, pressure, temperature, and composition of coexisting vapor and liquid phases, PTxy) was directly determined using a high-pressure optical cell for binary propane + phenol and ternary tetracosane + propane/n-butane systems. Measurements were carried out at three selected isotherms of 383.15, 403.15, and 423.15 K at pressures from 0.94 to 14.5 MPa for propane + phenol and 403.15, 423.15, and 443.15 K at pressures up to 7.5 MPa for tetracosane + propane/n-butane systems. The critical property data (T C and P C ) for both mixtures have been derived from the measured VLE data. Based on the initial slopes of the critical lines (shape of the critical lines), the qualitative behavior (pure-and mixture-like behavior) of the isochoric heat capacity (C Vx , weak singular property), isobaric heat capacity (C Px ), and isothermal compressibility (K Tx , strong singular property) of the propane + phenol binary mixture near the critical point has been studied. It is demonstrated that the simplest version of critical point-based perturbed-chain statistical association fluid theory neglecting the complex molecular background of phenol yields reasonably accurate predictions of its pure compound properties. With the value of k 12 obtained by fitting the present data of propane + phenol, this model yields reliable predictions for VLE in the systems of other n-alkanes, benzene, carbon monoxide, and nitrogen.

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A high-temperature and high-pressure optical cell VLE apparatus has been applied to measure phase equilibrium properties of n-tetradecane in the supercritical binary solvent (0.367propane + 0.633 n-butane mass fraction) at temperatures of 413.15 K, 433.15 K, and 453.15 K between of pressures (0.9 and 6.6) MPa. The combined expanded uncertainty of the temperature, pressure, and concentration measurements at 0.95 confidence level with a coverage factor of k = 2 is estimated to be 0.15 K, 0.0022, and 0.035, respectively. The critical parameters (TC, PC, ) were determined based on the measured isothermal phase equilibrium data of the ternary system n-tetradecane + propane/n-butane. It is shown that the critical temperature and pressure of the n-tetradecane + propane/n-butane system increases with concentration of n-tetradecane increases.

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