Dispersion activity coefficient models. Part 2: perturbed chain equations of state

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An equation is proposed that predicts the dispersion contribution in activity models of alkanes. Our approach requires as input the topology and the van der Waals volume of the compounds, as well as two universal energy constants. It has been derived from the perturbed chain equations of state taking as reference state the pressure at infinity, which brings the molecules into a liquid close-packed structure (LCP). At this condition the second perturbation integral vanishes. The first perturbation integral is evaluated at LCP. We explain why the power series expression for the first perturbation integral yields non-realistic results for PC-SAFT at this condition. Using the theoretical framework of PC-SAFT, we apply topology theory to get realistic values for this integral at LCP. The obtained dispersion equation in combination with a generalized expression for the combinatorial contribution gives activity coefficients of mixtures of alkanes with an average absolute deviation of 4.5%, which is at the level of UNIFAC(Do). It demonstrates that the proposed model can replace the modified combinatorial contribution in UNIFAC and COSMO-RS models, thereby eliminating systematic deviations in prediction of molecules having a small alkyl fraction. It also shows that the systematic deviations of the van Laar activity coefficient model, which is based on the van der Waals equation of state, are a result of neglecting the shape and polyatomic character of molecules.

TaalEngels
Artikelnummer112286
Aantal pagina's18
TijdschriftFluid Phase Equilibria
Volume502
DOI's
StatusGepubliceerd - 15 dec 2019

Vingerafdruk

Activity coefficients
Equations of state
equations of state
Alkanes
coefficients
deviation
perturbation
Paraffins
alkanes
Molecules
Liquids
topology
liquids
Topology
molecules
power series
trucks
infinity
predictions
energy

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    title = "Dispersion activity coefficient models. Part 2: perturbed chain equations of state",
    abstract = "An equation is proposed that predicts the dispersion contribution in activity models of alkanes. Our approach requires as input the topology and the van der Waals volume of the compounds, as well as two universal energy constants. It has been derived from the perturbed chain equations of state taking as reference state the pressure at infinity, which brings the molecules into a liquid close-packed structure (LCP). At this condition the second perturbation integral vanishes. The first perturbation integral is evaluated at LCP. We explain why the power series expression for the first perturbation integral yields non-realistic results for PC-SAFT at this condition. Using the theoretical framework of PC-SAFT, we apply topology theory to get realistic values for this integral at LCP. The obtained dispersion equation in combination with a generalized expression for the combinatorial contribution gives activity coefficients of mixtures of alkanes with an average absolute deviation of 4.5{\%}, which is at the level of UNIFAC(Do). It demonstrates that the proposed model can replace the modified combinatorial contribution in UNIFAC and COSMO-RS models, thereby eliminating systematic deviations in prediction of molecules having a small alkyl fraction. It also shows that the systematic deviations of the van Laar activity coefficient model, which is based on the van der Waals equation of state, are a result of neglecting the shape and polyatomic character of molecules.",
    keywords = "Activity model, Cubic equation of state, Dispersion, PC-SAFT, Perturbation theory, Topology theory, Zagreb index",
    author = "Krooshof, {Gerard J.P.} and Remco Tuinier and {de With}, Gijsbertus",
    year = "2019",
    month = "12",
    day = "15",
    doi = "10.1016/j.fluid.2019.112286",
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    Dispersion activity coefficient models. Part 2 : perturbed chain equations of state. / Krooshof, Gerard J.P. (Corresponding author); Tuinier, Remco; de With, Gijsbertus.

    In: Fluid Phase Equilibria, Vol. 502, 112286, 15.12.2019.

    Onderzoeksoutput: Bijdrage aan tijdschriftTijdschriftartikelAcademicpeer review

    TY - JOUR

    T1 - Dispersion activity coefficient models. Part 2

    T2 - Fluid Phase Equilibria

    AU - Krooshof,Gerard J.P.

    AU - Tuinier,Remco

    AU - de With,Gijsbertus

    PY - 2019/12/15

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    AB - An equation is proposed that predicts the dispersion contribution in activity models of alkanes. Our approach requires as input the topology and the van der Waals volume of the compounds, as well as two universal energy constants. It has been derived from the perturbed chain equations of state taking as reference state the pressure at infinity, which brings the molecules into a liquid close-packed structure (LCP). At this condition the second perturbation integral vanishes. The first perturbation integral is evaluated at LCP. We explain why the power series expression for the first perturbation integral yields non-realistic results for PC-SAFT at this condition. Using the theoretical framework of PC-SAFT, we apply topology theory to get realistic values for this integral at LCP. The obtained dispersion equation in combination with a generalized expression for the combinatorial contribution gives activity coefficients of mixtures of alkanes with an average absolute deviation of 4.5%, which is at the level of UNIFAC(Do). It demonstrates that the proposed model can replace the modified combinatorial contribution in UNIFAC and COSMO-RS models, thereby eliminating systematic deviations in prediction of molecules having a small alkyl fraction. It also shows that the systematic deviations of the van Laar activity coefficient model, which is based on the van der Waals equation of state, are a result of neglecting the shape and polyatomic character of molecules.

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    KW - Topology theory

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