Determination of the compressibility factorZ(p, T) of three methane-ethane mixtures using the dielectric constant method

Abstract

The compressibility behavior of three mixtures of the CH₄ C₂ H₆, system has been investigated experimentally by means of the dielectric constant method. Precise ( ± 1 ppm) measurements of the dielectric constant (ε) as a function of the pressure (P) along one isotherm (T) are combined with the first three dielectric virial coefficients (A,B, andC) in order to obtain accurate values of the molar density (p). The compressibility factorZ=P/( _p RT) was obtained from the measured values ofp,P, andT. The coefficientA, is determined from the measurements of ε as a function ofP, while the higher-order coefficients (B, andC,) are obtained by an expansion technique. We report the measured values ofZ at 295.15 K up to 12 MPa for three mixtures of CH₄-C₂-H₆ containing, respectively. 9.54, 35.3, and 75.4% (molar) of ethane. Their exact composition was determined by weighing during the mixing process. The first three dielectric virial coefficients and the mixed second dielectric virial coefficient for the CH₄,-C₂, H₆ system agree with the calculated or the literature values within the limits of uncertainties. For the mixture containing 90.46% CH₄+C₂H₆, deviations in compressibility are of the order of 0.4% from GERG.