Relation of Wertheim association constants to concentration-based equilibrium constants for mixtures with chain-forming components

Bala, Aseel M.; Lira, Carl T.

doi:10.1016/j.fluid.2016.09.015

Cited by 12 publications

(35 citation statements)

References 56 publications

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“…Recent molecular dynamics simulation studies further show the binary interaction parameters can be related to the potentials of mean force and the radii of first neighboring shells 3 . Nevertheless, the NRTL model is known to have difficulties in correlating phase equilibrium data of association systems 4,5 . For example, it is difficult to identify a set of binary interaction parameters that can consistently represent both the vapor–liquid equilibrium (VLE) and liquid–liquid equilibrium (LLE) for systems like methanol–cyclohexane binary and 1‐butanol–water binary 6 …”

Section: Introductionmentioning

confidence: 99%

Nonrandom two‐liquid activity coefficient model with association theory

Hao

Chen

2020

AIChE Journal

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Considered one of the most versatile and widely used classical thermodynamic models to correlate phase equilibria behavior of nonideal systems, the nonrandom two‐liquid (NRTL) theory does not explicitly account for specific chemical associations such as hydrogen bonding. This deficiency has been recognized as the cause for unsatisfactory representation of association systems like methanol–alkanes binaries. This work presents a practical approach to integrate Wertheim's perturbation theory for association contribution with the classical NRTL model. Specifically, the association contribution is calculated from pre‐determined molecule‐specific association strengths while the physical interaction contribution is captured with NRTL binary interaction parameters. The resulting association NRTL model correlates fluid phase equilibria of association systems with few adjustable parameters and offers improved predictive capability for higher order systems.

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Section: Introductionmentioning

confidence: 99%

Nonrandom two‐liquid activity coefficient model with association theory

Hao

Chen

2020

AIChE Journal

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“…Δ can be considered to be a concentration-based equilibrium constant, K c , with a couple of differences. Δ includes the term g ij ( d , ρ) that is composition-dependent, but the term is sometimes assumed to be independent of composition.…”

Section: Models In Current Engineering Practice and Association Theorymentioning

confidence: 99%

Wertheim’s Association Theory for Phase Equilibrium Modeling in Chemical Engineering Practice

Lira

Elliott

Gupta

et al. 2022

Ind. Eng. Chem. Res.

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Association and complex formation are the most important contributors to nonidealities in modeling phase equilibria. Models based on Wertheim's association theory are reviewed in the context of current industrial practice, showing great promise in resolving many of the shortcomings of the currently available models. Several pitfalls of common models are highlighted, showing the advantages of association theory. Infinite dilution activity coefficients can provide valuable insights into the liquid phase nonidealities. Trends for various mixture classifications are tabulated and explained simply in terms of "differences in molecular association". The need for a systematic procedure to characterize association parameters is cited as the most important barrier to broader implementation of these models. Improper characterizations can undermine the advantages of association theory, possibly confusing whether it offers any advantage. Resolving these issues will improve traditional small molecule phase equilibrium modeling and many other applications as well.

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“…There has been recent work to include a separate, approximate form of the SAFT association free energy − as an added term in activity coefficient models with some success. The approach followed by Bala and Lira and later by Hao and Chen , was first proposed by Fu et al Unlike the model presented here, their approach is based on approximating the excess Gibbs energy with the excess Helmholtz free energy, an unnecessary approximation that leads to unclear assumptions. We will explain the approximations necessary to justify their resulting equations in a future publication in which we present a simplified activity coefficient model.…”

Section: Introductionmentioning

confidence: 99%

Activity Coefficients from an Equation of State: Novel Approach for Fast Phase Equilibrium Calculations

Chapman

Fouad

2021

Ind. Eng. Chem. Res.

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Deviation from ideal solution behavior is due to differences in intermolecular interactions, e.g., molecular size, shape, dispersion, multipolar, and hydrogen bonding interactions. Activity coefficients characterize deviations from ideal solution behavior; however, most activity coefficient models lack the physics to explicitly account for intermolecular forces such as hydrogen bonding and multipolar interactions. At the same time, molecular theories (in the form of equations of state) that explicitly account for hydrogen bonding and multipolar interactions have been developed and validated versus molecular simulation results and experiment. In this work, we present a novel approach to calculate activity coefficients using theoretically based equations of state that explicitly describe these molecular interactions. The suggested approach enables phase equilibrium calculations to be performed at a significantly faster rate in comparison to conventional fugacity coefficient approaches. This is attributed to the fact that the molar volume is treated as an input in the approach; hence, iterations over the volume at a given pressure are not required. The polar and perturbed chain form of the statistical associating fluid theory (Polar PC-SAFT) is used in this paper to develop an activity coefficient model (SAFT-AC) for mixtures where self-association, solvation, and dipolar interactions dominate. Excellent agreement with experimental data was observed for all systems. The latter validates the use of the suggested approach as a powerful means for rapid phase equilibrium calculations in process simulators and PVT modeling software, providing consistency between activity coefficient and fugacity coefficient approaches. Extensions should lead to smart simulation methods where the simulation decides when to switch between activity coefficient and fugacity coefficient approaches depending on system conditions.

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Relation of Wertheim association constants to concentration-based equilibrium constants for mixtures with chain-forming components

Cited by 12 publications

References 56 publications

Nonrandom two‐liquid activity coefficient model with association theory

Nonrandom two‐liquid activity coefficient model with association theory

Wertheim’s Association Theory for Phase Equilibrium Modeling in Chemical Engineering Practice

Activity Coefficients from an Equation of State: Novel Approach for Fast Phase Equilibrium Calculations

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