Virial Coefficients of Methane, Ethane, and Their Mixtures at Low Temperatures

Abstract

A Burnett apparatus designed specifically for the measurement of virial coefficients was constructed and used to establish the second and some third virial coefficients of methane, ethane, and five equally spaced compositions at 273.15°, 240.00°, and 215.00°K. Second and third virial coefficients for methane were also determined at 200°, 191.06°, and 131.93°K. By using a gas-lubricated dead-weight gage located in a vacuum of approximately 25 μ Hg, absolute pressures could be read directly. The gage located in an ambient vacuum also allowed the determination of accurate compressibility factors from 40 atm down to the neighborhood of one atmosphere pressure. A recently developed method for the determination of virial coefficients directly from Burnett pressure measurements was applied. The range of the experimental apparatus enabled the determination of several negative values of the third virial coefficients at low reduced temperatures along with positive values at the higher temperatures. The experimental second and third virial coefficients of this and past studies were used to determine the Kihara, Lennard-Jones, and square well potential parameters. The accuracy of the representation of the virial data by the parameters over a wide range of temperatures is given.