The Effects of Co-Capture Impurities on the Phase Behaviour of CCUS Fluid Systems: Experimental Measurements and Thermodynamic Modelling of Vapour-Liquid Equilibria in CO2-Rich System

Abstract This study carried out bubble point experimental measurements for CO2-rich binary (CO2-CH4) system using the constant composition expansion method at low temperatures (228.15 – 273.15 K). For all the data points, the measurements' uncertainties were 0.14 K and 0.03 MPa, and a maximum composition uncertainty of 0.03%. The experimental data were used to validate the predictive accuracies of two thermodynamic models - Multi-Fluid Helmholtz Energy Approximation (MFHEA) and Peng-Robinson (PR) equations of state (EoSs). The results revealed that the presence of the impurities increased the bubble point pressures of the mixture, and MFHEA gave a better prediction of the binary system. The literature experimental (bubble and dew points) data also fit both model lines with less than 5% deviations for all the data points. The study also showed that, the lower the temperature, the more significant the effects of the co-capture impurities on the bubble points of CO2. The higher the volume fractions of the impurities, the higher their effects on the bubble points of CO2. Therefore, not considering the presence of the impurities or assuming a pure CO2 in the CCUS process would clearly lead to flow assurance issues like two phase flow when single phase is expected.