New density data and equations of state assessment for multicomponent CO2-rich mixtures relevant to CO2 transport for CCS applications

Accurate knowledge of the thermodynamic properties of CO 2 -rich mixtures is crucial for optimizing the design and operation of the Carbon Capture, Utilization, and Storage (CCUS) chain, including the transportation step. In this work, combining measurements and modelling activities, new experimental density data are presented for five gravimetrically prepared multicomponent CO 2 -rich mixtures with CO 2 mole fractions ranging from 0.859 to 0.952 and different concentrations of impurities such as N 2 , O 2 , Ar, CH 4 , and H 2 . Density measurements were conducted using a Vibrating Tube Densimeter (VTD) at temperatures from (273 to 313) K and pressures up to 22 MPa. The VTD has been calibrated against pure CO 2 and further validated with pure propane and known binary mixtures of CO 2 + CH 4 and CO 2 + O 2 . A semi-empirical calibration model parameters has been fitted for the VTD. Measurements have been performed at vapor, liquid and supercritical phases. The combined expanded relative uncertainty in density ( k = 2) is estimated to be 0.4 % ≤ U ( ρ ) ≤ 2.5 % with values ≤ 1 % for most density data points. To evaluate the accuracy of existing thermodynamic models, the performance of several equations of state, including GERG-2008, EOS-CG-2021, PC-SAFT, and the cubic equations of state based on Peng-Robinson, is evaluated against the new experimental data. The Helmholtz-energy based GERG-2008 and EOS-CG-2021 formulations provided comparable results and outperformed other models, with Average Absolute Relative Deviations (AARD%) close to 1 % for most of the measured densities and across the different phases and are the most accurate equations of state for density computation for multi-component CO 2 -rich mixtures. PC-SAFT showed reasonable results in the liquid region with AARD% between (0.4 and 1.7) %, however becoming less accurate near saturation conditions or at supercritical temperatures. The Peng-Robinson cubic equation of state predicted densities within ±3 % of relative deviation for most data points, although larger deviations are reported when the critical region is approached.