A new setup for the measurement of vapor-liquid phase equilibria of CO 2 -rich mixtures relevant for carbon capture and storage (CCS) transport conditions is presented. An isothermal analytical method with a variable volume cell is used. The apparatus is capable of highly accurate measurements in terms of pressure, temperature and composition, also in the critical region. Vapor-liquid equilibrium (VLE) measurements for the binary system CO 2 +N 2 are reported at 223, 270, 298 and 303 K, with estimated standard uncertainties of maximum 0.006 K in the temperature, maximum 0.003 MPa in the pressure, and maximum 0.0004 in the mole fractions of the phases. These measurements are verified against existing data. Although some data exists, there is little trustworthy data around critical conditions, and our data indicate a need to revise the parameters of existing models. A fit made against our data of the vapor-liquid equilibrium prediction of GERG-2008/EOS-CG for CO 2 +N 2 is presented. At 223 and 298 K, the critical region of the isotherm are fitted using a scaling law, and high accuracy estimates for the critical composition and pressure are found.

Accurate thermophysical data for the CO 2 -rich mixtures relevant for carbon capture, transport and storage (CCS) are essential for the development of the accurate equations of state (EOS) and models needed for the design and operation of the processes within CCS. Vapor-liquid equilibrium measurements for the binary system CO 2 +O 2 are reported at 218, 233, 253, 273, 288 and 298 K, with estimated standard uncertainties of maximum 8 mK in temperature, maximum 3 kPa in pressure, and maximum 0.0031 in the mole fractions of the phases in the mixture critical regions, and 0.0005 in the mole fractions outside the critical regions. These measurements are compared with existing data. Although some data exists, there are little trustworthy literature data around critical conditions, and the measurements in the present work indicate a need to revise the parameters of existing models. The data in the present work has significantly less scatter than most of the literature data, and range from the vapor pressure of pure CO 2 to close to the mixture critical point pressure at all six temperatures. With the measurements in the present work, the data situation for the CO 2 +O 2 system is significantly improved, forming the basis to develop better equations of state for the system. A scaling law model is fitted to the critical region data of each isotherm, and high accuracy estimates for the critical composition and pressure are found. The Peng-Robinson EOS with the alpha correction by Mathias and Copeman, the mixing rules by Wong and Sandler, and the NRTL excess Gibbs energy model is fitted to the data in the present work, with a maximum absolute average deviation of 0.01 in mole fraction.

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