Density measurements on binary mixtures (nitrogen + carbon dioxide and argon + carbon dioxide) at temperatures from (298.15 to 423.15) K with pressures from (11 to 31) MPa using a single-sinker densimeter

Abstract

A single-sinker densimeter was built to specifically investigate the (p,ρ,T,x) behavior of fluid mixtures relevant for carbon capture and storage (CCS). Due to the use of a magnetic-suspension coupling, the densimeter enables measurements over the temperature range from (273.15 to 423.15)K with pressures up to 35MPa. A comprehensive analysis of the experimental uncertainties was undertaken. The expanded uncertainties (k=2) are 35mK for temperature, 3.39kPa for pressure, and 0.033% for density determination. The apparatus was used for measurements on the binary systems (nitrogen+carbon dioxide) and (argon+carbon dioxide). The compositions for both systems were (0.05 and 0.01)mole fraction carbon dioxide. Density measurements were carried out at temperatures from (298.15 to 423.15)K with pressures from (11 to 31)MPa. The relative combined expanded uncertainty (k=2) in density was 0.15% for the (nitrogen+carbon dioxide) mixtures and 0.12% for the (argon+carbon dioxide) mixtures. A major contribution to this uncertainty emerged from the uncertainty in the gas mixture composition. The new experimental data were compared to the GERG-2008 equation of state (EOS) for natural-gas mixtures as implemented in the NIST REFPROP database and to the EOS-CG, another new Helmholtz energy model for CCS mixtures as implemented in the TREND software package of Ruhr-University Bochum. Relative deviations were mostly within 0.5%. The agreement of the new density values with the only available literature data closest to the composition range under study was better than 0.1%.