Isochoric heat capacity measurements for H2O + CH3OH mixture in the near-critical and supercritical regions

The isochoric heat capacity of two (0.5004 and 0.5014 mole fraction of methanol) H2O + CH3OH mixtures has been measured in a range of temperatures from 371 to 579 K and densities between 214 and 394 kg m−3. Measurements were made with a high-temperature, high-pressure, nearly constant-volume adiabatic calorimeter. The measurements were performed in the one- and two-phase regions including the coexistence curve, and in the near-critical and supercritical regions. Temperatures at the phase transition curve TS(ρ) for each of the measured densities and the critical parameters (TC and ρC) for the 0.4996H2O + 0.5004CH3OH mixture were obtained using the method of quasi-static thermograms. The uncertainty of the heat-capacity measurements is estimated to be 2%. Uncertainties of the density, temperature and concentration measurements are estimated to be 0.15%, 15 mK and 5 × 10−5 mole fraction, respectively. The derived values of the critical parameters, together with published data, were used to calculate the value of the Krichevskii parameter. The near-critical isochoric heat capacity behavior for the 0.4996H2O + 0.5004CH3OH mixture was studied using the principle of isomorphism of the critical phenomena in binary mixtures.