PVT measurements for pure methanol in the near-critical and supercritical regions

PVT properties of pure methanol were measured in the near-critical and supercritical regions. Measurements were made with a constant-volume piezometer immersed in a precision air thermostat. The maximum uncertainty of the density measurements was estimated to be 0.15%. The uncertainties of the temperature and pressure measurements were, respectively, 15 mK and 0.05%. Measurements were performed at seven near-critical isochores between 113 and 370 kg m−3 and at pressures from 1.4 to 40 MPa. The range of temperature was 423–653 K. Using the two-phase PVT data, the values of vapor–pressure and saturated liquid and vapor density were determined by means the analytical extrapolating technique in the temperature range from 423 to 512.7 K. The measured one-phase PVT data and saturated property data ( T S , P S , ρ ′ S , ρ ″ S ) for pure methanol were compared with the values calculated from fundamental IUPAC and crossover equations of state and with precise experimental PVT data reported by other authors. From the saturated liquid and vapor density and vapor–pressure data in the critical region the values of the critical parameters (TC = 512.75 ± 0.1 K, PC = 8.120 ± 0.02 MPa, and ρC = 271.6 ± 3 kg m−3) were extracted. For three isochores (113.5, 252.4, and 368.2 kg m−3) the measurements were performed in both cooling and heating regimes to estimate the effect of thermal decomposition (chemical reaction) on the PVT properties of methanol.