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

Abstract

A statistical associating fluid theory for potential of variable range has been recently developed to model dipolar fluids (SAFT-VR+D) [Zhao and McCabe, J. Chem. Phys. 2006, 125, 104504]. The SAFT-VR+D equation explicitly accounts for dipolar interactions and their effect on the thermodynamics and structure of a fluid by using the generalized mean spherical approximation (GMSA) to describe a reference fluid of dipolar square-well segments. In this work, we apply the SAFT-VR+D approach to real mixtures of dipolar fluids. In particular, we examine the high-pressure phase diagram of hydrogen sulfide+n-alkane binary mixtures. Hydrogen sulfide is modeled as an associating spherical molecule with four off-center sites to mimic hydrogen bonding and an embedded dipole moment (micro) to describe the polarity of H2S. The n-alkane molecules are modeled as spherical segments tangentially bonded together to form chains of length m, as in the original SAFT-VR approach. By using simple Lorentz-Berthelot combining rules, the theoretical predictions from the SAFT-VR+D equation are found to be in excellent overall agreement with experimental data. In particular, the theory is able to accurately describe the different types of phase behavior observed for these mixtures as the molecular weight of the alkane is varied: type III phase behavior, according to the scheme of classification by Scott and Konynenburg, for the H2S+methane system, type IIA (with the presence of azeotropy) for the H2S+ethane and+propane mixtures; and type I phase behavior for mixtures of H2S and longer n-alkanes up to n-decane. The theory is also able to predict in a qualitative manner the solubility of hydrogen sulfide in heavy n-alkanes.

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

“…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]. A Group-Contribution SAFT (GC-SAFT) approach based on London's theory [37,38] has been developed for binary mixtures containing CO 2 , N 2 , H 2 S, alkanes, and aromatics.…”

On Molecular-Based Equations of State: Perturbation Theories, Simple Models, and SAFT Modeling

“…Besides the original SAFT with hard sphere monomers, SAFT-HS, two other main versions are SAFT-VR (variable range) [87,88] and PC-SAFT (perturbed chain) [49]. Furthermore, there is also a group contribution version, SAFT-γ [89], SAFT-RPM [90][91][92] dealing with electrolytes, and SAFT-VR-D [81,93] for dipolar and dipolar and associating fluids. The most recent development includes SAFT-µ [80,94] whose monomer units interact via a Mie-type potential with adjustable exponents.…”

Prediction of Interfacial Properties of Ternary, Sulfur-containing Mixtures

“…The mixtures containing CO 2 were already investigated in the literature, , and consequently, a value for k ij is known. The binary subsystem H 2 S + heptane was also studied in the literature , using SAFT approach. However, dos Ramos et al used the SAFT variable range approach.…”

“…The binary subsystem H 2 S + heptane was also studied in the literature , using SAFT approach. However, dos Ramos et al used the SAFT variable range approach. Tang and Gross applied also PC-SAFT and they obtained a value of k ij = 0.0781.…”

“…To the best of our knowledge, we could not find any ternary equilibrium data and no data related to the surface tension for these binary and ternary H 2 S or SO 2 containing mixtures. The phase behavior of the most binary subsystems (CO 2 + heptane, CO 2 + SO 2 , , CO 2 + H 2 S, ,, H 2 S + heptane , ) were already modeled using SAFT-approach. Additionally, the surface properties of the binary subsystems (CO 2 + heptane; CO 2 + SO 2 , , CO 2 + H 2 S) were studied using SAFT-approach in combination with the DGT.…”