Vapour-liquid equilibria and density modelling of CO₂-rich systems with PC-SAFT and SAFT-VR Mie

Carbon capture and storage (CCS) is nowadays considered as one of the most promising methods to counterbalance the CO2 emissions from the combustion of fossil fuels, natural gas processing, cement manufacturing, etc. The development and research of accurate thermodynamic models to predict thermophysical properties are required for a safe, optimum and worthwhile transport and storage of CO2-rich steams. One important aspect of these equations of state concerns the prediction of densities and understanding of phase diagrams. The prediction of the transport properties are strongly dependant of the accuracy of these equations of state (EoSs). Therefore, in the present work two molecular based EoSs are compared in order to evaluate their capability to describe the densities and phase behaviour of systems relevant to CCS.
The EoSs considered herein are the perturbed-chain SAFT (PC-SAFT) [1], and the other one is SAFT-VR Mie based on the Mie intermolecular potential [2]. The SAFT-EoSs are used to describe the phase diagrams (vapour-liquid equilibria (VLE) and vapour-liquid-liquid equilibria (VLLE)) and the densities of gas, liquid and supercritical phases. To assess and compare the adequacy of the selected models, the modelling results are compared against experimental data of several CO2-rich systems in a wide range of conditions of temperature, pressure and compositions from the literature. The studied systems of interest for CCS are CO2 mixed with O2, N2, Ar, H2S and hydrocarbons.
Both SAFT-EoSs showed low Absolute Average Deviations (below 5%) between the modelling results and the experimental data from the literature. However, significant differences are observed between PC-SAFT and SAFT-VR Mie depending on the experimental conditions.