Ultrasonic velocity in binary mixtures under high pressures and their thermodynamic properties II : binary mixtures for benzene-toluene and benzene-o-xylene

Abstract

The ultrasonic velocities in the binary mixtures of benzene-toluene and benzene-o-xylene were measured at 20, 30 and 40℃ under pressures up to 2000 bar (10^5Pn), by a pulse technique of fixed-path type at a frequency of 1 MHz with an estimated error of less than 0.3 percent. At atmospheric pressure, the isotherms for the ultrasonic velocity in benzene-o-xylene mixture changed smoothly with the composition, while, that in benzene-toluene mixture showed some irregularity in the benzene-rich region. As to pressure effects, the ultrasonic velocity in the pure components and their mixtures of a certain composition increased parabolically with increasing pressure. The densities have been calculated from the experimental results by using the pressure dependency of ultrasonic velocity under the experimental condition. The densities thus obtained for pure liquids coincided with the experimental values reported in the literature within 0.3 percent in the range of pressures from 1 to 2000 bar. Then, from the measured values of ultrasonic velocity and the calculated densities, some thermodynamic properties, i.e. the isothermal and adiabatic compressibilities and the expansion coefficient were also derived with a good accuracy. For benzene-toluene mixtures, the composition dependencies of these values showed unusual behaviors at the benzene-rich region.