NEAR-CRITICAL AND SUPERCRITICAL-FLUID DENSITIES OF CO2-SF6 MIXTURES

A recently proposed technique for the separation of the major recyclab le thermoplastics incorporates the variable density of CO2-SF6 mixture s at mild temperatures and elevated pressures. Therefore, near-critica l liquid and supercritical fluid densities of these mixtures were dete rmined at temperatures between 294 K and 338 K and pressures up to 47 MPa. Mixtures containing SF6 mole fractions from 0.230-0.849 were used . The temperature-pressure conditions required to attain a specified d ensity were determined in a high-pressure, variable-volume cell by iso thermally compressing a fluid of known composition until a glass densi ty float remained suspended in the fluid. The densities of the eight f loats used in this study ranged from 900.0 to 1449.4 kg M-3. The resul ts were correlated with the modified Lawal-Lake-Silberberg (MLLS) EOS, designed specifically for accurate near-critical liquid and supercrit ical fluid phase densities, the mean field lattice gas (MFLG) EOS and the Benedict-Webb-Rubin-Starling (BWRS) EOS. Both the MLLS and the MFL G equations had three adjustable parameters for mixture density correl ations, while the BWRS had only one. Better results for mixture densit ies were obtained with the MLLS EOS, which yielded an average absolute pressure deviation (AAPD) of 4.49% at a specified temperature, densit y and composition. The AAPDs for the MFLG and the BWRS EOS were 7.07% and 7.64%, respectively.