PVTx and Isochoric Heat Capacity Measurements for Aqueous Methanol Solutions

Isochoric heat capacity and PVTx properties of an aqueous methanol solution (0.50 mass fraction or 0.36 mole fraction of methanol) were measured in the liquid phase with a twin-cell adiabatic calorimeter. Temperatures ranged from 333 to 422 K, and pressures ranged to 20 MPa. The calorimetric cell (70 cm3 capacity) was surrounded by adiabatic thermal shielding (high vacuum) and a steel-sheathed electric heater wound tightly on its surface. By combining the various sources of experimental uncertainty using a root-sum-of-squares formula, the relative uncertainty of CV is estimated to be 2%. The uncertainties of the density, temperature (absolute), and pressure measurements are, respectively, about 0.1%, 40 mK, and ±7 kPa. The measured densities were used to calculate excess molar volumes that were compared with values calculated with a reliable model by Simonson et al. Good agreement within ±0.008 cm3 ·mol−1 (or ±0.03% of the density) was found between measured values of excess molar volume and those calculated from the model. Values of saturated liquid densities were determined by extrapolating experimental P-T data to the saturation curve.