Investigation of Critical Properties and Surface Tensions for n-Alkanes by Perturbed-Chain Statistical Associating Fluid Theory Combined with Density-Gradient Theory and Renormalization-Group Theory

Abstract

The perturbed-chain statistical associating fluid theory (PC−SAFT) and density-gradient theory (DGT) are used to construct an equation of state (EOS) applicable for nonuniform fluids. In the bulk phases, the nonuniform EOS reduces to PC−SAFT and the phase equilibria inside the critical region are calculated by combining the renormalization-group theory (RGT). In the vapor−liquid surface, the density profile, surface thickness, and surface tension are calculated by using the nonuniform EOS with the equilibrium bulk properties as input. Investigation shows that PC−SAFT is able to provide accurate critical properties by combining the RGT and correlating the surface tensions for both the light and heavy n-alkanes satisfactorily by combining the DGT.

Application of a renormalization-group treatment to the statistical associating fluid theory for potentials of variable range (SAFT-VR)

“…In usual implementations of the RG relations in SAFT approaches 53,54,[59][60][61] , equations (26) and (27) are expressed asf…”

“…However, in these other works 48,49,[51][52][53][54][59][60][61] , the cutoff length L has a slightly different meaning: it instead separates the classic (mean-field) part of the free energy and the non-classic (critical)…”

“…Defining the volume as V n = (λ n ) 3 leads to the expression of K n used by Prausnitz et al 48,49,51,52 and later contributions 53,54,[59][60][61] , where…”

Interfacial properties of selected binary mixtures containing n-alkanes

“…In principle, the Helmholtz energy density can be described from any equation of state (EoS), with the consequence that a single EoS can be used to predict both phase equilibrium and interfacial properties. Previous works demonstrated that the combination of the SGT with cubic type EoS [6][7][8][20][21][22][23][24][25][26][27] as well as molecular based EoS [9,[28][29][30][31][32][33] models is promising for correlating and/or predicting interfacial properties in some pure hydrocarbon and hydrocarbon mixtures in a wide range of temperatures, pressures and concentrations. Both the SGT and available EoS models require at some stage experimental data for pure component parameter fitting.…”

“…SGT and SAFT are well known, and only the equations that are central to this work will be recalled in this section. In spite of this, it is noteworthy that only a few papers are devoted to use SGT approach with the SAFT EoS for the hydrocarbon mixtures [9,[30][31][32][33].…”