Vapor−Liquid Equilibria and Critical Behavior of Heavy n-Alkanes Using Transferable Parameters from the Soft-SAFT Equation of State

Abstract

A new set of molecular transferable parameters for the n-alkane series is proposed. n-Alkanes are modeled as homonuclear chainlike molecules formed by tangentially bonded Lennard-Jones segments of equal diameter and the same dispersive energy. Phase equilibria calculations of heavy pure members of the series, up to n-octatetracontane (n-C 48 H 98 ), and of ethane/n-decane and ethane/n-eicosane mixtures are performed with the soft-SAFT (statistical associating fluid theory) equation of state. This SAFT-type equation explicitly accounts for repulsive and dispersive forces in the reference term through a Lennard-Jones interaction potential, and it has been proven to accurately describe the phase behavior of light n-alkanes. Using the new set of parameters, the soft-SAFT equation is able to accurately predict the phase behavior of pure heavy n-alkanes. The dependence of the critical properties of pure n-alkanes with the carbon number is also predicted to be in quantitative agreement with experimental data, validating, at the same time, some recent simulation results of heavy members of the series. For the mixtures, the use of simple Lorentz-Berthelot combining rules provides quantitative agreement with experimental data over a broad range of temperatures and pressures. The physical meaning and transferability of these parameters are also discussed.

On the behaviour of solutions of xenon in liquid cycloalkanes: Solubility of xenon in cyclopentane

“…The inter-and intra-molecular interactions between the segments are taken into account through the Lennard-Jones potential. These models had been used previously in the literature to accurately represent a great variety of molecules, including xenon [3,6,7,[46][47][48] and nalkanes [12,[49][50][51][52][53]. They have also been used to predict the phase behaviour of pure and binary systems, including cyclic molecules [3,28] and hypothetical cycloalkane molecules [5].…”

A density functional theory for vapor-liquid interfaces using the PCP-SAFT equation of state

“…A successful theoretical framework for nonspherical and associating fluids, the statistical associating fluid theory ͑SAFT͒ equation of state, has been developed by Chapman et al 7,8 based on Wertheim's thermodynamic perturbation theory of first order ͑TPT1͒. [9][10][11][12] Several modifications were suggested over the years, [13][14][15][16][17] with widespread applications. 18 The TPT1 of Wertheim is formulated in density functional form and has been applied to inhomogeneous associating fluids in several studies.…”

Phase Equilibria Calculations of Polyethylene Solutions from SAFT-Type Equations of State

“…First, polyethylene molecular parameters were obtained by extrapolation of the correlation of parameters with molecular weight from the n-alkane series: 29 where m is the length of the chain of segments, σ is the size of each segment (LJ diameter), is the energy of the segments, and M n is the number molecular weight (in g/mol). Units of σ and /k B are in Å and K, respectively.…”

“…14,20 Having the model thus defined, molecular parameters are needed to define the uniqueness of each fluid in terms of the SAFT EoS description. The soft-SAFT model, which is described in detail in the literature, 14,29 has three parameters for nonassociating fluids: the size of LJ singular segments, σ, the energy of the segments, i.e., the well-depth of the LJ potential, , and the number of segments, m. For associating fluids, two more parameters are required: the association energy, HB , and the volume of association, k HB . In most applications of soft-SAFT to experimental systems these parameters were estimated by fitting the pure component vapor pressure and saturated liquid densities simultaneously.…”