Density characteristics of CO2–CH4 binary mixtures at temperatures from (300 to 308.15) K and pressures from (2 to 18) MPa

Abstract

The accurate densities of CO2–CH4 binary mixtures with CO2 mole fraction of 0.0998, 0.2017, 0.3997, 0.6015, 0.7985 and 0.8988 at temperatures from (300 to 308.15)K and pressures from (2 to 18)MPa were measured using a high-precision magnetic suspension balance. The combined standard uncertainties of temperature and pressure were estimated as 0.02K and 0.001MPa, respectively. The density measurement uncertainty of MSB was estimated as 0.029kg·m−3. Taking the effect of composition uncertainty and sorption into account, the combined standard uncertainties in the density measurement of CO2–CH4 mixtures were around 0.30% with CO2 mole fraction lower than 0.60 while they increased up to 0.96% with CO2 mole fraction higher than 0.80 at pressure of 9.0–11.0MPa. The measured densities were compared with the calculation from GERG-2008 EOS. It showed relatively good agreements between the GERG-2008 EOS and the measured densities with CO2 mole fraction lower than 0.60 at 300K as the relative deviations were generally within 2.0%. When CO2 mole fraction was higher than 0.80 at 300K, the relative deviations firstly increased to the maximum 3.73% in the vicinity of critical pressure and then decreased close to zero with the increasing pressure. The experimental data at other temperatures have the similar variation trends. Thus it’s difficult to apply GERG-2008 EOS to predict the density characteristics of CO2–CH4 binary mixtures with high CO2 mole fraction in the vicinity of the critical point accurately.