Densities and dew points of vapor mixtures of methane plus propane and methane plus propane plus hexane using a dual-sinker densimeter

A commercial density/sorption system has been converted to a dual-sinker de nsimeter and used to make density measurements for some light hydrocarbon m ixtures in the compressed gas region and near dewpoint conditions. Argon wa s used as a reference fluid for calibration of the measurement system. Expe rimental uncertainties in density for methane were estimated as +/-(0.029% + 0.013 kg m(-3)), including claimed uncertainties in the argon reference d ata. Measured methane densities at temperatures of (273 to 313) K and press ures to 12 MPa agreed within combined uncertainties with a methane equation of state in the literature (claimed uncertainty of 0.03%). Densities are r eported along isotherms in this same range for selected methane + propane a nd methane + propane + hexane mixtures with cricondentherms below 293 K. Es timated experimental uncertainties for these mixtures are slightly larger t han those for pure methane, because of uncertainties in compositions. Addit ional isochoric experiments were performed on some of these mixtures to inv estigate the mass adsorbed on each sinker as dew-point conditions are appro ached. Significant adsorption occurred up to 2 K above the dew point for th e binary mixtures and 5 K for the ternary mixtures. Adsorption progressivel y increased as the dew-point temperature was approached, resulting in chang es in gas-phase composition and density. These experiments allowed dew-poin t conditions and densities to be estimated.