Thermodynamic behaviour of homonuclear and heteronuclear Lennard-Jones chains with association sites from simulation and theory

VEGA, FELIPE J. BLAS and LOURDES F.

doi:10.1080/002689797170707

Cited by 66 publications

(11 citation statements)

References 44 publications

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“…26 Whereas the computation of interfacial properties of polymer models has been the subject of a number of recent papers, 6,[27][28][29][30] results for the well-known fully flexible LJ model, in which LJ segments ͑monomers͒ are tangentially bonded to form molecular chains, are scarce. The bulk thermodynamic properties of this model have been studied extensively by simulation, including not only the vapor-liquid phase behavior [31][32][33][34] but also the solid-fluid equilibria. [35][36][37] A knowledge of the interfacial properties of this model is much more limited, however.…”

Section: Introductionmentioning

confidence: 99%

Vapor-liquid interfacial properties of fully flexible Lennard-Jones chains

Blas

MacDowell²,

Miguel³

et al. 2008

The Journal of Chemical Physics

115

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We consider the computation of the interfacial properties of molecular chains from direct simulation of the vapor-liquid interface. The molecules are modeled as fully flexible chains formed from tangentially bonded monomers with truncated Lennard-Jones interactions. Four different model systems comprising of 4, 8, 12, and 16 monomers per molecule are considered. The simulations are performed in the canonical ensemble, and the vapor-liquid interfacial tension is evaluated using the test area and the wandering interface methods. In addition to the surface tension, we also obtain density profiles, coexistence densities, critical temperature and density, and interfacial thickness as functions of temperature, paying particular attention to the effect of the chain length on these properties. According to our results, the main effect of increasing the chain length (at fixed temperature) is to sharpen the vapor-liquid interface and to increase the width of the biphasic coexistence region. As a result, the interfacial thickness decreases and the surface tension increases as the molecular chains get longer. The interfacial thickness and surface tension appear to exhibit an asymptotic limiting behavior for long chains. A similar behavior is also observed for the coexistence densities and critical properties. Our simulation results indicate that the asymptotic regime is reached for Lennard-Jones chains formed from eight monomer segments. We also include a preliminary study on the effect of the cutoff distance on the interfacial properties. Our results indicate that all of the properties exhibit a dependence with the distance at which the interactions are truncated, though the relative effect varies from one property to the other. The interfacial thickness and, more particularly, the interfacial tension are found to be strongly dependent on the particular choice of cutoff, whereas the density profiles and coexistence densities are, in general, less sensitive to the truncation.

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Section: Introductionmentioning

confidence: 99%

Vapor-liquid interfacial properties of fully flexible Lennard-Jones chains

Blas

MacDowell²,

Miguel³

et al. 2008

The Journal of Chemical Physics

115

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“…75 An accurate representation of derivative properties is a stringent test even with a more sophisticated thermodynamic treatment such as SAFT. One of the first detailed studies of the performance of SAFT-type methods in the description of such properties was carried out by Colina et al 79 These authors examined the Joule-Thomson inversion curve obtained with the LJ-based soft-SAFT EoS 64,80 and found that although good agreement could be achieved, the description was very sensitive to the values of the molecular parameters. In a subsequent study different versions of the SAFT EoS were compared, and deviations of up to 20% from the experimental values of the derivative properties were found.…”

Section: Introductionmentioning

confidence: 99%

Group contribution methodology based on the statistical associating fluid theory for heteronuclear molecules formed from Mie segments

Papaioannou

Lafitte

Avendaño

et al. 2014

The Journal of Chemical Physics

237

429

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A group contribution method for associating chain molecules based on the statistical associating fluid theory (SAFT-) The Journal of Chemical Physics 127, 234903 (2007) (2013)] is formulated within the framework of a group contribution approach (SAFT-γ Mie). Molecules are represented as comprising distinct functional (chemical) groups based on a fused heteronuclear molecular model, where the interactions between segments are described with the Mie (generalized Lennard-Jonesium) potential of variable attractive and repulsive range. A key feature of the new theory is the accurate description of the monomeric group-group interactions by application of a high-temperature perturbation expansion up to third order. The capabilities of the SAFT-γ Mie approach are exemplified by studying the thermodynamic properties of two chemical families, the n-alkanes and the n-alkyl esters, by developing parameters for the methyl, methylene, and carboxylate functional groups (CH 3 , CH 2 , and COO). The approach is shown to describe accurately the fluid-phase behavior of the compounds considered with absolute average deviations of 1.20% and 0.42% for the vapor pressure and saturated liquid density, respectively, which represents a clear improvement over other existing SAFT-based group contribution approaches. The use of Mie potentials to describe the group-group interaction is shown to allow accurate simultaneous descriptions of the fluid-phase behavior and second-order thermodynamic derivative properties of the pure fluids based on a single set of group parameters. Furthermore, the application of the perturbation expansion to third order for the description of the reference monomeric fluid improves the predictions of the theory for the fluid-phase behavior of pure components in the near-critical region. The predictive capabilities of the approach stem from its formulation within a group-contribution formalism: predictions of the fluid-phase behavior and thermodynamic derivative properties of compounds not included in the development of group parameters are demonstrated. The performance of the theory is also critically assessed with predictions of the fluid-phase behavior (vapor-liquid and liquid-liquid equilibria) and excess thermodynamic properties of a variety of binary mixtures, including polymer solutions, where very good agreement with the experimental data is seen, without the need for adjustable mixture parameters.

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“…These results lead later to a further extension of the model to the description of glymes following a similar approach. (Navarro et al 2017) The vapor pressures and liquid densities of several polyethers are depicted in Figure 2 and as it can be seen, soft-SAFT is able to accurately describe such properties. Figure 2 a) shows that the introduction of hydroxyl end-groups within the polyethers structure decreases the vapor pressure of the compound due to the increased hydrogen bonding character of the compound that is retained in the liquid phase.…”

Section: Resultsmentioning

confidence: 91%

“…In molecular based EoS, the adequate selection of a coarse-grained model able to represent the physical features of the different compounds is of an outstanding relevance for the good performance of the equation. soft-SAFT was recently applied by us (Crespo et al 2017;Navarro et al 2017) to accurately describe the vapor-liquid equilibrium (VLE), ppT and second-order derivative properties of several glycols and glymes using a 'simple' but reliable molecular model. The model applied in those works considers the polyethers as LJ chains composed of equal-sized segments with associating sites embedded off-center mimicking each hydroxyl end group (i.e.…”

Section: Molecular Modelsmentioning

confidence: 99%

“…For this reason several polyethers, including glycols, glymes and polymers have been attracting considerable attention as feasible candidates to CO 2 capture but, despite the industrial interest for these compounds, their thermophysical characterization was surprisingly poor. Trying to overcome these gap, aiming to fully characterized this family of compounds a series of studies have been done in the latest years by our groups (Carvalho et al 2015;Crespo et al 2017;Navarro et al 2017). Nonetheless, the CO 2 sorption mechanism in these compounds is still unclear.…”

Section: Introductionmentioning

confidence: 99%

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Soft-SAFT Equation of State as a Valuable Tool for the Design of new CO2 Capture Technologies.

Crespo

Amaral

Dariva

et al. 2017

Day 2 Tue, November 14, 2017

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The design, simulation and/or optimization of new processes rely on the availability of robust and accurate models or equations of state (EoS). However, traditional cubic equations of state (EoS's), traditionally used in many process simulators, fail on describing complex polar and associating behavior of some molecules, leading to unreliable results and hence, poor design and optimization. This problem can be overcome with the use of robust, reliable equations of state. This work belongs to a long term project assessing the performance and usefulness of an advanced EoS (soft-SAFT), as a valuable tool for the description of highly non-ideal systems and thus, for the reliable simulation/design of new technologies. We focus here on assessing the validity of soft-SAFT, a molecular-based EoS, for the development of novel technologies for CO 2 capture using polyether blends as solvent. Within soft-SAFT polyether molecules are modeled as chains with end-groups having an association site, explicitly mimicking the hydroxyl end-groups. The study comprises polyethers, including glymes, and their mixtures with CO2 at different conditions. It is shown that soft-SAFT is able to successfully describe the thermodynamic behavior (e.g. vapor pressures and liquid densities) of these solvents in wide temperature and pressure ranges. Moreover, by explicitly considering the quadrupolar moment of CO 2 , and using one, temperature and pressure independent binary interaction parameter, an accurate description of the gas solubilities in several polyethers was achieved. For glymes, which among polyethers exhibit the highest CO 2 solubilities, such parameter was found to correlate with the molecular weight of the solvent. Finally the equation was used to predict the thermal and pressure cycle capacities of the different solvents. Results presented here reinforce the use of soft-SAFT as a reliable tool for solvent screening, offering reliable predictions of phase equilibria and solubility behavior in a wider number of systems.

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Thermodynamic behaviour of homonuclear and heteronuclear Lennard-Jones chains with association sites from simulation and theory

Cited by 66 publications

References 44 publications

Vapor-liquid interfacial properties of fully flexible Lennard-Jones chains

Vapor-liquid interfacial properties of fully flexible Lennard-Jones chains

Group contribution methodology based on the statistical associating fluid theory for heteronuclear molecules formed from Mie segments

Soft-SAFT Equation of State as a Valuable Tool for the Design of new CO2 Capture Technologies.

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