Use of PC-SAFT for Global Phase Diagrams in Binary Mixtures Relevant to Natural Gases. 3. Alkane + Non-Hydrocarbons

Abstract

This work continues the systematic study of global phase diagrams in binary systems relevant for the description of natural gases using the perturbed-chain statistical associating fluid theory (PC-SAFT) equation of state (EOS). Reservoirs frequently contain non-hydrocarbon compounds such as CO2, N2, or H2S that have strong effects upon the thermodynamic properties of natural gases. Thus, we study the behavior of their binary mixtures with n-alkanes over wide pressure and temperature ranges to get a deeper insight into the intermolecular pair interactions reflected in the phase behavior of the mixtures. These systems show complex patterns within the van Konynenburg classification, and the theoretical model accurately reproduces them. In the case of H2S containing mixtures (H2S is a compound that has autoassociation hydrogen-bonding ability), we analyze several association models to obtain the most reliable approach by comparing the predicted association degree of H2S to available experimental data. A conclusion from this series of papers is that PC-SAFT is a reliable and accurate model to predict the behavior of the different types of binary mixtures involved in complex multicomponent natural gases, with the ability to describe the different patterns of fluid-phase behavior presented by the studied systems over wide pressure and temperature ranges.

Modeling the phase equilibria of hydrogen sulfide and carbon dioxide in mixture with hydrocarbons and water using the PCP-SAFT equation of state

“…Thi et al [34] compared PC-SAFT and VR-SAFT for phase equilibria of H 2 + n-alkane and CO 2 + n-alkane binary mixtures. The phase behavior of CO 2 , N 2 and H 2 S binary mixtures with n-alkanes (C1-C5) were studied by Aparicio-Martinez and Hall [35] using the PC-SAFT equation of state. The SAFT-VR equation with a dipolar term proposed by Zhao and McCabe [16] was applied to H 2 S + n-alkane binary mixtures at high pressure [36].…”

Modeling the Phase Behavior of H2S + n-Alkane Binary Mixtures Using the SAFT-VR+D Approach

“…The four site model was proposed by Forester et al and has an additional partial charge, located on the bisector H−S−H angle, which is similar to the TIP4P-like geometry proposed for water . Both the three-site and the four-site models have been used to model hydrogen sulfide in molecular simulations, – as well as in other versions of SAFT that do not explicitly include the dipole moment. – In this work, we consider the four-site potential model as it most physically mimics the H 2 S molecule. Within the SAFT-VR+D approach, H 2 S is therefore described as an associating dipolar square-well segment of diameter σ 11 , that interacts via an embedded dipole moment μ 11 , a square-well dispersion potential of a depth ε 11 and range λ 11 , and four off-center short-range attractive sites to describe the self-association.…”

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.…”