Isochoric p-rho-T measurements on {(x)CO2+(1-x)C2H6,x approximate to 0.25,0.49, 0.74} from (220 to 400) K at pressures to 35 MPa

The p-rho -T relationships were measured for binary hydrocarbon mixtures co ntaining carbon dioxide (CO2) and ethane (C2H6). Temperatures ranged from ( 220 to 400) K with pressures up to 35 MPa. Measurements of p-rho -T were co nducted on compressed gaseous and liquid samples with the mole fraction com positions {(x)CO2 + (1 - x)C2H6} for x = 0.251 68, 0.492 33, and 0.739 79. These mixtures were prepared gravimetrically to match, within 0.000 12 mole fraction, the compositions (0.251 66, 0.492 45, 0.739 78) of three mixture s which had been used by three laboratories for measurements of key thermop hysical. properties, including the density. For the p-rho -T apparatus used in this study, the uncertainty of the temperature is 0.03 K, and for press ure, it is 0.01% at p>3 MPa and 0.05% at p<3 MPa. The principal source of u ncertainty in density is the cell volume (<similar to>28.5 cm(3)) whose sta ndard uncertainty is 0.003 cm(3). When all components of experimental uncer tainty are considered, the expanded relative uncertainty (with a coverage f actor k = 2 and thus a two-standard-deviation estimate) of the density meas urements is estimated to be 0.05%.