Heterosegmental Modeling of Long-Chain Molecules and Related Mixtures using PC-SAFT: 1. Polar Compounds

Abstract

A broad range of fatty acids as well as fatty-acid-based, long-chain compounds are synthesized on the basis of triglycerides, which are mainly found in natural fats and oils. These long-chain compounds comprise, for instance, fatty-acid methyl and ethyl esters and fatty aldehydes. Saturated representatives of these individual families are composed of an identical head domain which is connected to an n‑alkylic residue that only varies in chain length within a homologous series. In this work, this fact was taken into account for modeling of thermodynamic properties using a heterosegmental approach of the Perturbed Chain Statistical Associating Fluid Theory. For this purpose, the n-alkylic residue within a homologous series was modeled using the pure-component parameters of n-alkanes, whereas the parameters for each identical head domain were universally determined. With this heterosegmental approach, polar interactions among the identical head domains were explicitly taken into account. Due to its group-contribution-like character, the heterosegmental approach enables the prediction of thermodynamic properties of other compounds within a homologous series. Applying the new approach, vapor pressures and liquid densities of the pure long-chain compounds could be represented in very good agreement with the available experimental data. Furthermore, the interactions between the n-alkylic residue and water can be described using independent solubility data of the binary n-alkane + water mixtures. Excess enthalpies and excess volumes of the binary long-chain compound + n-alkane mixtures as well as mutual solubilities in the binary methyl alkanoate + water mixtures were predicted to be in remarkable agreement with the available experimental data for a broad range of chain lengths.

Application of PC-SAFT and DGT for the Prediction of Self-Assembly

“…While the transfer contribution of the original model increases continuously with temperature, the transfer contribution computed with PC-SAFT exhibits a minimum which is connected to the solubility minimum of n -octane in water at T = 318 K . The reason for this minimum in the solubility is still controversially discussed in the literature. ,, This minimum can also be found in the solubility of other compounds than n -alkanes in water. , Moreover, all of these minima can be correctly modeled using PC-SAFT. − The data depicted in Figure clearly show that the description of the hydrophobic effect including the minima in μ g ,Tr 0 / k B T is now possible, because experimental data related to the LLE rather than related to the VLE of n -alkane + water mixtures were used for estimating the binary interaction parameters of PC-SAFT …”

Measurement and Prediction of Excess Properties of Binary Mixtures Methyl Decanoate + an Even-Numbered n-Alkane (C6–C16) at 298.15 K

“…With the new experimental data of this work in hand, both excess properties were predicted using a heterosegmental approach of PC-SAFT proposed by Haarmann et al and the group-contribution EOS SAFT-γ Mie. , In Figure , the full predictions of the molar excess volumes v E of the six binary mixtures methyl decanoate + n -alkane ( n -hexane (C 6 ), n -octane (C 8 ), n -decane (C 10 ), n -dodecane (C 12 ), n -tetradecane (C 14 ), and n -hexadecane (C 16 )) are shown for both the heterosegmental approach of PC-SAFT and SAFT-γ Mie. The respective % ARDs are given in Table .…”

“…Thus, the predictive thermodynamic modeling of both excess properties is preferable. To the best of our knowledge, the excess properties of the binary mixtures methyl alkanoate + n -alkane have so far only been modeled in a predictive manner by Haarmann et al Applying a heterosegmental approach of the Perturbed Chain Statistical Associating Fluid Theory (PC-SAFT), the molar excess volumes v E and the molar excess enthalpies h E of various binary mixtures methyl alkanoate + n -alkane were predicted in very good agreement with the experimental data . In particular, Haarmann et al predicted the molar excess volumes v E and the molar excess enthalpies h E of the binary mixtures methyl decanoate + n -alkane comprising odd-numbered n -alkanes.…”

“…An additional dipole moment μ ik can be taken into account for dipolar interactions . While each n -alkane was modeled as a nonpolar chain of identical segments (homosegmental), methyl decanoate was described as comprising two different types of segments (heterosegmental) forming a nonpolar tail domain and a polar head domain as illustrated in Figure a . While the tail domain represents the n -nonylic residue, the head domain comprises the polar functional methyl-ester head moiety (−COOCH 3 ).…”

“…While the tail domain represents the n -nonylic residue, the head domain comprises the polar functional methyl-ester head moiety (−COOCH 3 ). Due to the similarity of the n -nonylic residue to n -nonane, the tail domain of methyl decanoate was described using the PC-SAFT pure component parameters of n -nonane according to the heterosegmental approach of PC-SAFT proposed by Haarmann et al Applying this approach, the following contributions were considered for the dimensionless residual Helmholtz energy ã res where the hard-chain contribution ã hc represents the hard-chain reference fluid in PC-SAFT, which is perturbed due to dispersive ( ã disp ) and dipolar ( ã dipol ) perturbations. In Table , the PC-SAFT parameters used in this work are given for methyl decanoate and the considered n -alkanes.…”