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

Abstract

The specific volume and the viscosity of enthanol-water mixtures at 25° (298.15K) and 50℃ (323.15k) have been measured under pressures up to 3200 and 800 bar (10^5 Pa), respectively. The measurements were performed by a modified Adams piezometer and a falling-cylinder viscometer. The maximum uncertainties are estimated to be 0.05% for the specific volume and 2% for the viscosity. The specific volume of the pure components and their mixtures is found to decrease monotonously with increasing pressure. The results obtained are compared with several sets of literature values. The numerical data at each temperature and composition are correlated satisfactorily as a function of pressure by both polynomial and the Tait equations. It is also found that a definite minimum appears on the isothermal compressibility versus composition isobars, arising from the complex interactions between hydrogen-bonded water and alcohol molecules. The viscosity of pure ethanol and mixtures is found to increase almost linearly with increasing pressure, whereas that of water is nearly independent of pressure in these experimental conditions. The viscosity isotherms can be formulated by a quadratic equation of pressure within the experimental error. As for the composition dependence of the viscosity, a distinct maximum appears near 0.3 mole fraction of ethanol on all isobars at both experimental temperatures.