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

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.