EXCESS MOLAR VOLUMES AND DENSITIES OF (METHANOL PLUS WATER) AT TEMPERATURES BETWEEN 323 K AND 573 K AND PRESSURES OF 7.0 MPA AND 13.5 MPA

Densities of {xCH(3)OH + (1-x)H2O} relative to water were measured in a vibrating-tube densimeter at the temperatures (323, 373, 423, 473, 5 23, and 573) K and at pressures of 7.0 MPa and 13.5 MPa. Excess molar volumes V-m(E) for {xCH(3)OH + (1-x)H2O} were calculated from the expe rimental densities for the mixtures, using accurate equations of state for water and methanol. The data were treated with a modified corresp onding-states model based on the properties of pure water. An empirica l function was used to fit small differences between the compression f actors of {xCH(3)OH + (1-x)H2O} and the compression factor of H2O at t he same reduced temperature and the same reduced pressure. The corresp onding-states treatment reproduces the measured densities to within th e experimental uncertainty of 0.4 kg.m(-3) at all of the temperatures and pressures studied, except at T = 573 K and p = 13.5 MPa. The densi ties, excess molar volumes, partial molar volumes, isothermal compress ions, and cubic expansion coefficients from the model are consistent w ith the limited literature data available. The behaviour of V-m(E) at T = 573.6 K and p = 13.7 MPa indicates either a very narrow region of (vapour + liquid) phase separation, or near-critical behaviour at x ap proximate to 0.44 with the critical pressure p(c) less than or equal t o 13.5 MPa. (C) 1997 Academic Press Limited.