Measurement of the density of carbon dioxide/toluene homogeneous mixtures and correlation with equations of state

Abstract

Equations of state (EoS) can be used to estimate a wide variety of physical properties. However, there has been limited verification of the applicability of parameter sets derived from specific physical properties to correlate and estimate various other physical properties. The densities of homogeneous phase fluid mixtures of the carbon dioxide (CO2)/toluene (Tol) binary system were measured and correlated to three equations of state. The density measurements were performed using a high-pressure vibration-type density meter equipped with a circulation pump and variable-volume viewing cell, which guaranteed the homogeneity of the mixtures. The densities were measured at temperatures ranging from 313 to 353 K, pressures up to 20 MPa, and CO2 concentrations from 0 to 80 mol%. The experimental data obtained were correlated to the Tait density equation and three EoS, namely Peng–Robinson (PR), Sanchez–Lacombe (SL), and Perturbed Chain statistical associating fluid theory (PC-SAFT) EoS. Among them, SL and PC-SAFT EoS agree better with the experimental data compared to the PR EoS, presumably due to differences in the pure component parameters used in each EoS. Using parameter sets determined from the density measurements, the vapor liquid equilibrium (VLE) of the CO2/Tol mixtures was estimated. While we were unsuccessful in estimating VLE using the PR EoS, SL and PC-SAFT EoS were successfully used for the estimations. We also attempted to determine the densities from VLE correlations. It was found that SL and PC-SAFT EoS could be used to estimate the density well, whereas the PR was not predictive. From the results of the study, it is clear that for estimating density using EoS, the basic data used for determining the pure component parameters are important.