Phase equilibrium of CO2-Rich System for CCUS applications

Greenhouse gas emissions are a global concern, and carbon dioxide (CO₂) is one of the main contributors to climate change. Therefore, the development of mitigation strategies is necessary. Carbon Capture, Utilization, and Storage (CCUS) is a technological approach that aims to capture CO₂ from industrial sources, utilize it in industrial processes, or store it to reduce atmospheric emissions. The design and operation of CCUS systems depend on accurate thermodynamic data, particularly for CO₂-rich mixtures containing impurities. In this study, a CO₂-rich mixture (CO₂ 97.89%, N₂ 2.00%, Ar 0.10%, CH₄ 0.01% mol/mol) was investigated to contribute to the limited experimental vapor–liquid equilibrium (VLE) data available for such systems and to evaluate the performance of thermodynamic models and commercial software. The objective was to assess the ability of these tools to predict the phase behavior of CO₂-rich mixtures relevant to CCUS applications. VLE data were obtained using a synthetic method over the temperature range of 278–302 K in a variable-volume PVT cell equipped with a sliding piston. Phase transitions were identified using two approaches: visual observation of phase interface formation and analysis of changes in the slope of the pressure–volume (P–V) curve associated with the appearance of a new phase. The experimental results were compared with predictions from Multiflash-CPA (Infochem) and REFPROP. The results show that Multiflash-CPA provides accurate bubble-point predictions at lower temperatures, while REFPROP performs better above approximately 288 K. For dew-point calculations, both models present small deviations, with maximum errors of up to 4%. Overall, the agreement between experimental data and model predictions indicates that both Multiflash-CPA and REFPROP are applicable to the prediction of phase behavior and phase transition boundaries of CO₂-rich mixtures containing low levels of impurities in CCUS processes.