Use of PC-SAFT for Global Phase Diagrams in Binary Mixtures Relevant to Natural Gases. 2.n-Alkane + Other Hydrocarbons

Abstract

In this work, we extend the previously reported study of global phase diagrams in binary mixtures relevant for the description of natural gases using the perturbed-chain statistical associating fluid theory (PC-SAFT) model to systems containing n-alkanes + other nonlinear hydrocarbons. These mixtures have branched, cyclic, and aromatic compounds and provide a deeper insight into the effect upon their thermodynamic behavior by introducing additional structural complexity into the mixtures. The studied systems show different patterns of phase equilibria according to the van Konynenburg classification. The PC-SAFT model usually describes properly the previously reported n-alkane + n-alkane binary mixtures, including their varied and complex phase behavior. The results reported in this work contribute to a better understanding of the binary mixtures fluid-phase behavior and show the ability of the PC-SAFT model to describe the thermodynamic properties of these systems and to model complex intermolecular effects, and they can be useful for the modeling and understanding of natural gas properties in industrial applications.

Group-Contribution Method for the Molecular Parameters of the PC-SAFT Equation of State Taking into Account the Proximity Effect. Application to Nonassociated Compounds

“…The molecular parameters for other heavy n -alkanes were determined by Voutsas et al, Agarwal et al, and Tihic et al Also, we have found parameters for heavy n -alkanes (from eicosane up to hexatriacontane) from von Solms et al; however, they have not been fitted to experimental data, but have been extrapolated from the parameters of Gross and Sadowski . For branched alkanes, in addition to those of Gross and Sadowski, molecular parameters were obtained by Aparicio-Martinez and Hall and Tihic et al and the molecular parameters of ethers and esters were optimized by Tihic et al, extending the original matrix. Table SI-1 (see the Supporting Information) summarizes these molecular parameters from the authors cited.…”

“…Molecular coefficients, π, versus molecular mass obtained from literature parameters ,– (points) and obtained by the group-contribution method (lines).…”

“…The molecular parameters of 2,2-dimethylpropane and 2,2-dimethylbutane have been optimized by Gross and Sadowski . For other compounds of the same series, Aparicio-Martinez and Hall have optimized the molecular parameters of 2,2-dimethylpentane and Tihic et al have optimized those from 2,2-dimethylhexane to 2,2-dimethyloctane. The molecular parameter sets that best fit to a common trend are those of Gross and Sadowski and Tihic et al; on the other hand, these parameter sets were fitted from both vapor pressures and saturated liquid densities, whereas the Aparicio-Martinez and Hall set was optimized only from experimental vapor pressures.…”

Modeling of Gas Solubility in Hydrocarbons Using the Perturbed-Chain Statistical Associating Fluid Theory Equation of State

“…The perturbed-chain statistical associating fluid theory (PC-SAFT) EoS has been the subject of many investigations due to its sound theoretical basis and strong predictive power. − It finds applications in rather diverse areas, such as petroleum, biofuels, polymers, electrolytes, , and ionic liquids. ,, One key advantage that greatly benefits the parametrization of the PC-SAFT EoS is its well-behaved parameters, paving the way for the development of GC methods and BIP correlations. Such a phenomenon has been found in many studies. − GC methods have been devised to parametrize the EoS, leading to the so-called GC-PC-SAFT and critical-point-based PC-SAFT. − Ghosh et al evaluated the correlative and predictive capability of the PC-SAFT EoS on gas solubility in hydrocarbons. It was found that a single BIP, independent of both temperature and the carbon number of the solvent, is enough for accurate modeling of the gas solubility.…”

“…Nonetheless, other studies ,,, show that the modeling accuracy is improved systematically via introduction of the temperature and carbon-number dependence of the BIP. GC-PC-SAFT has been extended to model gas solubility. − ,,− However, the BIP used remains independent of temperature, although the carbon-number dependence is added. Ma et al , employed the simplified PC-SAFT (sPC-SAFT) EoS and came up with a four-parameter correlation, expressing the BIP as a function of temperature and the molecular weight of n -alkanes.…”