Calculation of Solid−Liquid−Gas Equilibrium for Binary Systems Containing CO₂

Two equations typically used for the pure-solid fugacity proved to be identical by selecting an appropriate relation for the pure-solid vapor pressure and the pure-liquid vapor pressure. On the basis of the pure-solid fugacity, a semipredictive model using solubility data (SMS) and a calculation model combining with G E models (CMG) were developed to calculate the solid−liquid−gas (SLG) coexistence lines of pure substances in the presence of CO 2 . For the SMS model, the Peng−Robinson equation of state (PR-EoS) with the van der Waals one-fluid mixing rule is used to correlate the solute solubility in CO 2 to obtain the interaction parameter k 12, which is further employed to predict the SLG coexistence lines by two methods: one adopts the fugacity coefficient of the solute in the liquid phase by an equation of state calculation (SMS-φ); the other uses the activity coefficient of the solute in the liquid phase calculated from the UNIFAC model (SMS-γ). For the CMG model, the PR-EoS with the linear combination of Vidal and Michelsen (LCVM) mixing rule, the Michelsen modified Huron-Vidal (MHV1) mixing rule, and a modified version (mLCVM) with the re-evaluated parameter λ = 0.18 are used. Results show that the SMS model can provide acceptable calculations of the SLG coexistence lines for most of the investigated systems. The predicted melting temperatures and solute compositions in liquid phase from a constant k 12 are slightly better than those from the correlated one, while the predicted solute solubility data in CO 2 from a constant k 12 are worse than those from the correlated one. The CMG model with the mLCVM mixing rule calculates well the melting temperatures and solute compositions in liquid phase at SLG equilibrium and also gives acceptable calculations of the solute solubilities in supercritical CO 2 .