Vapor−Liquid Equilibrium of Carbon Dioxide−Perfluoroalkane Mixtures:  Experimental Data and SAFT Modeling

Abstract

Pressure-composition diagrams were measured at different temperatures ranging from 293.15 to 353.15 K for different perfluoroalkanes including linear (perfluoro-n-octane), cyclic (perfluorodecalin and perfluoromethylcyclohexane), and aromatic compounds (perfluorobenzene and perfluorotoluene), at pressures up to 100 bar. Measurements were performed using a high-pressure cell with a sapphire window that allows direct observation of the phase transition. The different molecular structures were chosen in order to check the influence of the nature of the solvent on the carbon dioxide solubility. The soft-statistical associating fluid theory (soft-SAFT) equation of state (EoS) was used to describe the phase behavior of the mixtures studied, searching for transferable parameters with predictive capability. Optimized values for the chain length, Lennard-Jones (LJ) diameter, and dispersive energy are provided for the different perfluoroalkanes and for carbon dioxide. The effect of the explicit inclusion of a quadrupole moment on carbon dioxide, perfluorobenzene, and perfluorotoluene was studied by adding a polar term to the original soft-SAFT EoS.

Modeling the vapor–liquid equilibrium and association of nitrogen dioxide/dinitrogen tetroxide and its mixtures with carbon dioxide

“…In that case, agreement is similar to the one obtained with Dias's parameter set without crossover but, as this second parameter set was not refitted, it deviates more in the liquid phase; a fact already pointed out by Llovell et al [5]. Quadrupolar interactions were explicitly considered in all cases with quadrupolar parameter Q taken from the value fitted by Dias et al [21] which compared well with experimental values of the CO 2 quadrupole. The value of the calculated critical points are presented in the Table 2; stressing the excellent agreement achieved thanks to the crossover treatment.…”

“…The third set of parameters in table 1 (dotted lines in figure 1) corresponds to optimized parameters from the original equation, without including the crossover term, as obtained by Dias et al. [21]. These parameters were optimized to best fit the phase diagram, except the critical region.…”

“…These parameters were optimized to best fit the phase diagram, except the critical region. The first set of parameters in table 1 were optimized in the present work when applying the crossover soft-SAFT equation to the same set of experimental data as in Dias et al [21] (full lines in figure 1). Thanks to the crossover treatment, the overall curve is very well reproduced, including the critical region.…”

“…The modeling of CO 2 is routinely done using cubic equation of state. However, CO 2 bears a quadrupole that, if not considered in the modeling, provides inaccurate mixture predictions that have to be corrected by the use of binary interaction parameters [21]. A recent modeling of CO 2 -perfluoroalkanes vapor -liquid equilibrium mixtures using the soft-SAFT equation of state showed that no binary interaction parameters are required when the quadrupolar moment on carbon dioxide is explicitly included and molecules do not greatly differ in size.…”

“…A recent modeling of CO 2 -perfluoroalkanes vapor -liquid equilibrium mixtures using the soft-SAFT equation of state showed that no binary interaction parameters are required when the quadrupolar moment on carbon dioxide is explicitly included and molecules do not greatly differ in size. In that case, the quadrupolar effect on the phase equilibrium is not hidden in the binary parameter value but explicitly described increasing the model extrapolation capability [21].…”