Thermodynamics Research Center / ThermoML | Journal of Chemical and Engineering Data

ABSTRACT

The (p, rho, T, x) behavior of three (methane + propane) mixtures was measured with a two-sinker magnetic suspension densimeter over the temperature range of (248.15 to 373.15) K with pressures up to the dew-point pressure or 6 MPa, whichever was lower. The compositions of the gravimetrically prepared mixtures were (0.74977, 0.50688, and 0.26579) mole fraction methane. A detailed uncertainty analysis is presented. The relative combined expanded uncertainty (k = 2) in density considering all effects, including the uncertainty in composition, was 0.05 % or lower for most points, except it was larger at densities less than 5 kg*m 3. Comparisons to the GERG-2008 equation of state for natural-gas mixtures showed significant deviations in density (as large as -1.3 %) that increased with decreasing temperature, with increasing pressure, and with increasing propane fraction in the mixture. The experimental values were also used to calculate interaction virial coefficients B12(T) for this system. The B12(T) agreed well with literature values. They were constant (within experimental uncertainty) with composition, as expected from theory. In contrast, the B12(T) calculated with the GERG-2008 equation of state varied with composition.