PVTx measurements for water plus toluene mixtures in the near-critical andsupercritical regions

The PVTx relationships of dilute (1 - x) water + x toluene mixtures were me asured in the near-critical and supercritical regions, with a constant-volu me piezometer immersed in a precision thermostat. The ITS-90 temperature wa s measured with a 10 Omega platinum resistance thermometer (PRT-10) with an uncertainty of 10 mK. Pressure was measured by means of a dead-weight gaug e with an uncertainty of 1.5-2.0 kPa. Uncertainties of the density measurem ents are estimated to be 0.05-0.15%, depending on the experimental pressure and temperature. The uncertainty in composition measurement is 0.001 mole fraction. Measurements were made on near-critical and supercritical isother ms between 623 and 673 K at pressures from 11 to 46 MPa and densities betwe en 54 and 579 kg(.)m(-3) for three composition mole fractions of toluene (0 .0008, 0.0022, and 0.0085). The measured PVTx data for (1 - x) water + x to luene mixtures were compared with values calculated from a recently develop ed crossover equation of state and published measurements. The PVTx measure ments were used to derive values of the Krichevskii parameter, excess volum es, and apparent molar volumes. The method of isochoric break points was us ed to extract the phase transition temperatures and pressures for each meas ured isochore. The critical anomalies of the supercritical (1 - x) water x toluene mixtures and the behavior of the Krichevskii function near the so lvent's (water) critical point are discussed.