A 3-PHASE TERNARY MODEL FOR CO2-SOLID-LIQUID EQUILIBRIUM AT MODERATE PRESSURES

In this work, we present a simple, totally predictive, three-phase mod eling for systems containing CO2-solid-liquid for evaluation of cosolv ents in the supercritical-fluid extraction (SCFE) of volatile matter o f Brazilian mineral coals. The liquid phase is modeled by the traditio nal regular solution theory while the gas phase is represented by the Peng-Robinson/Stryjek-Vera equation of state and the heavy component i s taken as a pure solid. In the liquid phase, supercritical CO2 is con sidered a hypothetical liquid, its standard fugacity being given by a specific correlation. The results of the solid-liquid-gas equilibrium calculations are in good agreement with experimental data of the mixtu re CO2-naphthalene-toluene 1 at moderate pressures although no adjusta ble parameters were used. When a liquid phase is present, the results of the simulations involving the mixtures CO2-naphthalene-toluene and CO2-naphthalene-n-pentane indicate higher concentrations of naphthalen e in the gas phase when the cosolvent is n-pentane. These results show that both the solid-cosolvent interactions and the volatility of the cosolvent should be taken into account.