Experimental study and modeling of the isothermal VLE properties of ethylbenzene in supercritical solvents (CO2 and C3H8)

Abstract

The isothermal VLE properties (PTxy) of two binary mixtures of ethylbenzene+CO2 and ethylbenzene+C3H8 at temperatures of (313.15, 333.15, 353.15) K, (393.15, 413.15, 433.15) K and at pressures up to 13 MPa and 6.4 MPa, respectively, were measured in the present work using a high-temperature and high-pressure optical cell VLE apparatus based on the static-analytic method. The combined expanded absolute uncertainty of the temperature, and the relative uncertainty of pressure, and concentration measurements at 0.95 confidence level with a coverage factor of k = 2 is estimated to be 0.15 K, 0.002 (or within 0.002–0.02 MPa, depending on temperature and pressure ranges), and 0.03, respectively, and 0.035 (or within 0.0001–0.028 mol fraction depending on temperature and pressure ranges), respectively. The critical parameters (TC, PC, xC) of the both mixtures were determined based on the measured isothermal phase equilibrium VLE data. Using the derived and reported critical property data (initial slopes of the critical curves at the solvent critical point, CO2 and C3H8) for ethylbenzene+CO2 and ethylbenzene+C3H8 mixtures, the values of the physical meaning (theoretically important) Krichevskii parameter have been calculated. The effect of the critical solvent (CO2 and C3H8) on the value of the Krichevskii parameter is studied. Pure- and mixture- like thermodynamic behavior (Fisher’s renormalization of the critical behavior of dilute mixtures) and structural properties (cluster sizes) of the infinite dilute mixture near the critical point of pure solvents (CO2 and C3H8) have been studied based on the Krichevskii parameter and initial slopes of the critical curves. Accuracies of the Perturbed-Chain Statistical Association Fluid Theory (PC-SAFT) and its Critical Point-based revision (CP-PC-SAFT) models in estimating the measured VLE data with the zero value of the binary adjustable parameter k12 were compared with E-PPR78 (Enhanced Predictive Peng–Robinson, 1978) approach.