Journal of Chemical and Engineering Data, Vol.59, No.12, 4151-4164, 2014
Vapor-Phase (p, rho, T, x) Behavior and Virial Coefficients for the (Methane plus Propane) System
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 B-12(T) for this system. The B-12(T) agreed well with literature values. They were constant (within experimental uncertainty) with composition, as expected from theory. In contrast, the B-12(T) calculated with the GERG-2008 equation of state varied with composition.