Equation of state and thermodynamic properties of pure toluene and dilute aqueous toluene solutions in the critical and supercritical regions

In this paper, we report new PVTx measurements for water + toluene binary mixtures at 11 near-critical and supercritical isotherms T = 623, 627, 629, 631, 633, 643, 645, 647, 649, 651, and 673 K and pressures up to 39 MPa at a fixed concentration of x = 0.0287 mole fraction of toluene. Using these PVTx data together with data obtained earlier by other authors, we developed a crossover Helmholtz free-energy model (CREOS) for pure toluene and dilute aqueous toluene solutions in a wide range of the parameters of state around the vapor-liquid critical points. In the temperature range 593 K less than or equal to T less than or equal to 680 K and density range 100 kg(.)m(-3) less than or equal to p less than or equal to 500 kg(.)m(-3), the CREOS reproduces the PVT data for pure toluene with an average absolute deviation (AAD) of about 0.5%, the C-P data with an AAD of about 1%, and the sound velocity data with an AAD of about 2.6%. In water + toluene mixtures, the CREOS yields an adequate description of all available experimental data in the region bounded by 0.35rho(c)(x) less than or equal to rho less than or equal to 1.65rho(c)(x) and 0.98T(c)(x) less than or equal to T less than or equal to 1.15T(c)(x) at x less than or equal to 0.04 mole fraction of toluene. The possibility of extrapolating the CREOS model to lower temperatures, 0.93T(c) less than or equal to T less than or equal toT(c) and higher densities and concentrations, up to rho = 2rho(c) and x = 0.12, is also discussed.