Saturated phase densities of (CO2 + H2O) at temperatures from (293 to 450) K and pressures up to 64 MPa

An apparatus consisting of an equilibrium cell connected to two vibrating tube densimeters and two syringe pumps was used to measure the saturated phase densities of (CO2 + H2O) at temperatures from (293 to 450) K and pressures up to 64 MPa, with estimated average standard uncertainties of 1.5 kg · m−3 for the CO2-rich phase and 1.0 kg · m−3 for the aqueous phase. The densimeters were housed in the same thermostat as the equilibrium cell and were calibrated in situ using pure water, CO2 and helium. Following mixing, samples of each saturated phase were displaced sequentially at constant pressure from the equilibrium cell into the vibrating tube densimeters connected to the top (CO2-rich phase) and bottom (aqueous phase) of the cell. The aqueous phase densities are predicted to within 3 kg · m−3 using empirical models for the phase compositions and partial molar volumes of each component. However, a recently developed multi-parameter equation of state (EOS) for this binary mixture, Gernert and Span [32], was found to under predict the measured aqueous phase density by up to 13 kg · m−3. The density of the CO2-rich phase was always within about 8 kg · m−3 of the density for pure CO2 at the same pressure and temperature; the differences were most positive near the critical density, and became negative at temperatures above about 373 K and pressures below about 10 MPa. For this phase, the multi-parameter EOS of Gernert and Span describes the measured densities to within 5 kg · m−3, whereas the computationally-efficient cubic EOS model of Spycher and Pruess (2010), commonly used in simulations of subsurface CO2 sequestration, deviates from the experimental data by a maximum of about 8 kg · m−3

Density and phase behavior of the CO2 + methylbenzene system in wide ranges of temperatures and pressures

Knowledge of the thermophysical properties of CO2-hydrocarbon mixtures over extended ranges of temperature and pressure is crucial in the design and operation of many carbon capture and utilization processes. In this paper, we report phase behavior, saturated-phase densities, and compressed-liquid densities of CO2 + methylbenzene at temperatures between 283 K and 473 K and at pressures up to 65 MPa over the full composition range. The saturated-phase densities were correlated by a recently developed empirical equation with an absolute average relative deviation (ΔAARD) of ∼0.5%. The compressed-fluid densities were also correlated using an empirical equation with an ΔAARD value of 0.3%. The new data have been compared with the predictions of two equations of state: the predictive Peng–Robinson (PPR-78) equation of state and the SAFT-γ Mie equation of state. In both of these models, binary parameters are estimated using functional group contributions. Both models provided satisfactory representation of the vapor–liquid equilibrium and saturated-phase-density data, but the accuracy decreased in the prediction of the compressed-liquid densities where the ΔAARD was ∼2%. The isothermal compressibility and isobaric expansivity are also reported here and were predicted better with SAFT-γ Mie than with PPR-78. Overall, the comparisons showed that SAFT-γ Mie performs somewhat better than PPR-78, but the results suggest that further refinement of the SAFT-γ Mie parameter table are required