Thermophysical properties of gaseous carbon dioxide-water mixtures

Abstract

A Burnett-Isochoric apparatus was used to obtain precise, experimental, vapor-phase P-ρ-T data for pure water and for mixtures of 2%, 5%, 10%, 25%, and 50% water in carbon dioxide for temperatures from 298.15 K to 498.15 K at 25 K intervals, and pressures from 27 kPa to 10.34 MPa or the vapor pressure (or dew point) at each temperature. The experimental measurements for pure water, along with compressibility data from the literature, were used to characterize physical adsorption within the Burnett-Isochoric apparatus using the Brunauer-Emmett-Teller (B-E-T) adsorption model coupled with the sequential Burnett equations. The resulting adsorption constants were used to correct the compressibility data for the mixtures and precise values were obtained for the second virial coefficients, enthalpies, and other derived thermodynamic properties. Interaction second virial coefficients, B₁₂, and interaction third virial coefficients, C₁₁₂ and C₁₂₂, were also determined from the mixture virial coefficients and compared with values obtained values obtained using prediction methods such as that by Tsonopoulos (1974). Also, the proper temperature dependence for the binary interaction coefficient, k₁₂, (calculated from the precise B₁₂ measurements) was established. The densities are considered accurate to 4/10,000, and the mixture second virial coefficients to ±3 cm³/mol. Dew points (±1 K and ±14 kPa) were also measured for the above mixtures by noting the change in slope of the isochores. The dew point pressures were predicted using a priori methods such as that proposed by Eubank et al. (1986) for their natural gas-water mixtures, and compared with other experimental measurements and with VLE prediction methods, such as they by Heidemann and Prausnitz (1977).