Pressure Dependence of the Vapor−Liquid−Liquid Phase Behavior in Ternary Mixtures Consisting of n-Alkanes, n-Perfluoroalkanes, and Carbon Dioxide

Abstract

Expansion of an organic solvent by an inert gas can be used to tune the solvent's liquid density, solubility strength, and transport properties. In particular, gas expansion can be used to induce miscibility at low temperatures for solvent combinations that are biphasic at standard pressure. Configurational-bias Monte Carlo simulations in the Gibbs ensemble were carried out to investigate the vapor-liquid-liquid equilibria and microscopic structures for two ternary systems: n-decane/n-perfluorohexane/CO2 and n-hexane/n-perfluorodecane/CO2. These simulations employed the united-atom version of the transferable potential for phase equilibria (TraPPE-UA) force field. Initial simulations for binary mixtures of n-alkanes and n-perfluoroalkanes showed that special mixing parameters are required for the unlike interactions of CHx and CFy pseudoatoms to yield satisfactory results. The calculated upper critical solution pressures for the ternary mixtures at a temperature of 298 K are in excellent agreement with the available experimental data and predictions using the SAFT-VR (statistical associating fluid theory of variable range) equation of state. The simulations yield asymmetric compositions for the coexisting liquid phases and different degrees of microheterogeneity as measured by local mole fraction enhancements.

Liquid Mixtures Involving Hydrogenated and Fluorinated Chains: (p, ρ, T, x) Surface of (Ethanol + 2,2,2-Trifluoroethanol), Experimental and Simulation

“…This reduction in the H−F atom interactions is comparable to a reduction of 10% in united atom models. Zhang and Siepmann, 12 using the united atom version of the TraPPE force field, found that a 1% increase of the unlike size parameter and an 11% reduction of the unlike well depth were necessary to obtain an adequate fit of the liquid−liquid envelope for the CH 4 /CF 4 mixture. More recently, Potoff and Bernard-Brunel 13 developed united atom force fields for alkanes and perfluoroalkanes based on Mie potentials.…”

State conditions transferability of vapor–liquid equilibria via fluctuation solution theory with correlation function integrals from molecular dynamics simulation

“…at many mole fractions to give an accurate result, and therefore be very time-consuming. Instead, we determine activity coefficients by fitting the parameters in the (appropriately differentiated) modified Margules [4] equation for G E , 12 α 21 x 1 x 2 α 12 x 1 + α 21 x 2 + ηx 1 x 2 (1.3) to the simulation results from Eq. (1.2).…”

“…Our atomic charges are the same as those of Chen et al [8] except for the carbon atoms attached to fluorines. In the united atom force fields available for fluoroalkanes [11,12], the CF 2 and CF 3 beads are electro-neutral. We retained this feature by making the corresponding groups of atoms electro-neutral in the HFF-227ea description.…”

Monte Carlo predictions for the phase behavior of H2 S+n-alkane, H2 S+CO2, CO2+CH4 and H2 S+CO2+CH4 mixtures

“…Mixtures of CO 2 and n-alkanes have been studied extensively both by experiment (71)(72)(73)(74)(75)(76)(77)(78) and more recently through Monte Carlo simulations (34,47,(79)(80)(81)(82). In Fig.…”