Specific volume and viscosity of methanol-water mixtures under high pressure

Abstract

New experimental data on the specific volume and the viscosity of methanol-water mixtures are presented as functions of temperature, pressure and composition. The specific volume has been measured by means of an improved "high pressure burette" apparatus within an error of 0.05 percent, covering temperatures from 10 to 75℃ and pressures up 2000 bar. The viscosity has been obtained by a falling-cylinder viscometer with the uncertainty of less than two percent, covering the same temperature range and pressures up to 700 bar. The specific volume of this system is found to decrease monotonously with increasing pressure. The experimental results agree well with several literature values. The numerical data at each temperature and composition are correlated satisfactorily as a function of pressure by the Tait equation. The isothermal compressibilities and the excess volumes are also determined from the experimental data. It is found that a definite minimum appears on the isothermal compressibility versus composition isobars at temperatures lower than 25℃. The excess volumes are always negative and increase with increasing pressure or lowering temperature. The viscosity of pure methanol and its water mixtures is found to increase almost linearly with increasing pressure, whereas that of water decreases with pressure at 10℃ and 25℃ within the present experimental conditions. The viscosity isotherms can be represented by a quadratic equation of pressure within the experimental errors. As for the composition dependence of the viscosity, a distinct maximum appears near 0.3 mole fraction of methanol on all isobars at each temperature. The maximum shifts slightly to higher methanol fraction with increasing temperature or pressure.