Theoretical Examination of the Global Fluid Phase Behavior and Critical Phenomena in Carbon Dioxide +n-Alkane Binary Mixtures

Abstract

The phase behavior of carbon dioxide + n-alkane binary mixtures is studied using the statistical associating fluid theory for potentials of variable attractive range. Extensive experimental data is available in the literature concerning the homologous series of carbon dioxide + n-alkane systems; these provide an excellent example of the continuity of fluid phase behavior in binary mixtures. Continuous transitions in the types of phase behavior are observed as the molecular weight of the n-alkane is increased. In our work, the carbon dioxide and n-alkane molecules are treated as attractive spherical segments tangentially bonded together. The attractive interactions are included as square-well potentials of depth and range λ. The pure component parameters of carbon dioxide are obtained by fitting to experimental vapor pressure and saturated liquid density data from the triple to the critical point, and the optimized molecular parameters of n-alkanes are taken from a set of transferable parameters previously presented Jackson, Phys. Chem. Chem. Phys. 1999, 1, 2057]. The optimized conformal molecular parameters (segment size and dispersive energy) are rescaled in order to give the best description of the experimental critical points. The critical lines and critical end-points, which determine the types of phase behavior, are predicted by the SAFT-VR approach in very good agreement with experimental data. This is particularly gratifying as the unlike dispersion interaction and range of the potential between carbon dioxide and alkane segments are obtained from a single mixture (CO 2 + n-tridecane) and then transferred to the other systems.

An accurate density functional theory for the vapor-liquid interface of associating chain molecules based on the statistical associating fluid theory for potentials of variable range

“…In this paper we follow a standard perturbative DFT approach 13 to develop a free energy functional for inhomogeneous associating chainlike fluids based on the SAFT-VR free energy for chains formed from spherical segments with attractive interactions of variable range. 47,48 We opt for the SAFT-VR description of the reference bulk fluid as it has already been shown to provide an excellent quantitative description of the vapor-liquid and liquid-liquid fluid phase equilibria of a wide variety of systems including alkanes and perfluoroalkanes, 47,49-52 replacement refrigerants, 53 water, 54 hydrogen chloride, 55 hydrogen fluoride, 56,57 carbon dioxide, 58,59 xenon, [60][61][62][63][64] boron trifluoride, 65 aqueous electrolytes, 54,66 and polyethylene polymers. [67][68][69] An adequate treatment of the correlations in the attractive term is crucial for an accurate description of both the bulk fluid phase equilibria and the interfacial properties ͑cf.…”

Experimental and Molecular Modeling Study of the Three-Phase Behavior of (n-Decane + Carbon Dioxide + Water) at Reservoir Conditions

“…We compare our experimental findings with the predictions of SAFT-VR. 37,38 We use this method as it has already been shown in a number of studies [67][68][69][72][73][74] to provide an accurate description of the phase behaviour of mixtures consisting of alkanes, CO 2 and water, for wide ranges of thermodynamic conditions. Finally, where possible, further comparisons with data for the binary subsystems are also presented.…”

Classical density functional theory for the prediction of the surface tension and interfacial properties of fluids mixtures of chain molecules based on the statistical associating fluid theory for potentials of variable range

“…, hydrogen fluoride 105,106 , carbon dioxide 107,108 , xenon [109][110][111][112][113] , boron trifluoride…”