Viscosity of heavy n -alkanes and diffusion of gases therein based on molecular dynamics simulations and empirical correlations

Μakrodimitri, Zoi Α.; Heller, Andreas; Koller, Thomas M.; Rausch, Michael H.; Fleys, Matthieu; Bos, A.N.R.; Laan, Gerard P. van der; Fröba, Andreas P.; Economou, Ioannis G.

doi:10.1016/j.jct.2015.07.026

Cited by 23 publications

(31 citation statements)

References 53 publications

(82 reference statements)

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“…Makrodimitri et al. 19 built a new macroscopic model based on pure simulation data entirely to predict self-diffusion coefficients in n-alkanes. A comparison between simulated and predicted diffusion coefficient values showed the proposed model could predict the diffusivity well.…”

Section: Introductionmentioning

confidence: 99%

Formaldehyde diffusion within crystalline and amorphous cellulose at different temperatures and electric fields: A molecular dynamics study

Chen

2017

Indoor and Built Environment

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To provide a microcosmic theoretical support for the reduction of formaldehyde in building material, the diffusion process was investigated by molecular dynamics simulation. In addition, the diffusion model of formaldehyde molecules in crystalline and amorphous cellulose was built, and diffusion coefficients at different temperatures and electric fields were studied. The simulation temperature was from 293 to 393 K and electric field was from 0 to 400 kV/m. Diffusion coefficient increased with greater temperature and electric field both in crystalline and amorphous region. However, the diffusion coefficient in amorphous region could be ignored for it was two orders of magnitude lower than diffusion coefficient in crystalline region. The relationship between diffusion coefficient and temperature, and the relationship between diffusion coefficient and electric field were obtained by simulation, verified by the experiment. Temperature was shown to have a significant contribution to formaldehyde diffusion than electric field. Compared with experimental studies, the molecular dynamics simulation could only analyse the diffusion coefficient qualitatively because of the difference between micro-scale and macro-scale.

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Section: Introductionmentioning

confidence: 99%

Formaldehyde diffusion within crystalline and amorphous cellulose at different temperatures and electric fields: A molecular dynamics study

Chen

2017

Indoor and Built Environment

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“…A common theme in the successful entries was the use of an allatom force field, which has been shown previously to be important for accurate viscosity predictions of long-chain hydrocarbons. 28 Several other studies have used MD simulations to investigate the viscosity of hydrocarbon mixtures; [37][38][39][40][41][42][43][44][45][46] however, only a few of these have calculated viscosities at elevated pressure. In a recent study, Verma et al 42 studied the viscosity of n-octane + n-dodecane and n-hexadecane + ndecylbenzene binary mixtures up to 200 MPa using the Green-Kubo method.…”

Section: Introductionmentioning

confidence: 99%

Probing the high-pressure viscosity of hydrocarbon mixtures using molecular dynamics simulations

Kondratyuk

Pisarev

Ewen

2020

The Journal of Chemical Physics

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Computational predictions of the high-pressure viscosity of hydrocarbon mixtures could accelerate the development of fuels and lubricants with improved performance. In this study, we use molecular dynamics simulations to study the viscosity and density of methylcyclohexane, 1-methylnaphthalene, and their binary mixtures at 323 K and pressures of up to 500 MPa. The simulation results are in excellent agreement with previous experiments available up to 100 MPa for both pure compounds (200 MPa for 1-methylnaphthalene) as well as the binary mixtures. For 1-methylnaphthalene, the viscosity initially increases slower-than-exponential with pressure before it reaches an inflection point and then increases faster-than-exponential. The inflection point (300 MPa) occurs at a pressure slightly below the one at which 1-methylnaphthalene is expected to enter the supercooled phase (400 MPa). For methylcyclohexane, the increase in viscosity with pressure is slower-than-exponential over the entire pressure range studied. The binary mixtures show intermediate pressure-viscosity responses between the two pure cases. The applicability of equations commonly used to describe the pressure dependence of viscosity, as well as the viscosity of binary mixtures, is evaluated against the computational predictions.

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“…The QENS technique is sensitive to a diffusion displacement distance up to a few nanometers and therefore it is mainly applied to measure diffusion in microporous media. , PFG NMR has been applied to measure diffusion in both bulk liquid − and liquids confined in porous media. , It can follow diffusion displacement distance over micrometers and therefore is suitable for studying diffusion in commercial mesoporous catalysts. Molecular dynamics (MD) simulations have been applied to predict the diffusivity of H 2 , CO, and H 2 O dissolved in heavy n -alkane mixtures. − To date, only diffusion in bulk n -alkane mixtures has been predicted using MD simulations. − In summary, experimental measurements and MD simulations have only addressed the diffusion of FT-relevant gases dissolved in bulk liquid solvents of single-component n -alkanes and n -alkane mixtures. Furthermore, the n -alkane mixtures considered have contained relatively few components ,, compared to the composition of the real FT wax .…”

Section: Introductionmentioning

confidence: 99%

“…Molecular dynamics (MD) simulations have been applied to predict the diffusivity of H 2 , CO, and H 2 O dissolved in heavy n -alkane mixtures. − To date, only diffusion in bulk n -alkane mixtures has been predicted using MD simulations. − In summary, experimental measurements and MD simulations have only addressed the diffusion of FT-relevant gases dissolved in bulk liquid solvents of single-component n -alkanes and n -alkane mixtures. Furthermore, the n -alkane mixtures considered have contained relatively few components ,, compared to the composition of the real FT wax . To date, only one study of dissolved gas diffusion in bulk FT wax has been reported …”

Section: Introductionmentioning

confidence: 99%

“…There are generally three types of theoretical model or correlation used to describe and predict solute diffusion in liquid solvents; these are Arrhenius-type correlations, , correlations where the solvent effect on diffusion is characterized by its viscosity ,, of which the Wilke–Chang correlation is perhaps the most widely used, and the rough hard sphere (RHS) model. ,− , The RHS model has been used to describe systems in which the size of the solute molecules is significantly smaller than that of the solvent molecules − and has been shown to perform well in predicting the diffusivities of dissolved gases in liquid solvents. ,, It is therefore a sensible choice of model to consider for use regarding the diffusion of small solute molecules of H 2 and CO within large solvent molecules of wax. The RHS model treats the molecules in the system as hard spheres and their motion is modeled by extending the kinetic theory of gases to liquids, resulting in the following expression: , where β is a model parameter that characterizes the interaction between solute and solvent molecules, V is the molar volume of the solvent, and V D is a model parameter proportional to the close-packed molecular volume of the solvent. , …”

Section: Introductionmentioning

confidence: 99%

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Experimental Determination of H₂ and CO Diffusion Coefficients in a Wax Mixture Confined in a Porous Titania Catalyst Support

et al. 2020

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The ability to measure and predict molecular diffusion coefficients in multicomponent mixtures is not only of fundamental scientific interest but also of significant relevance in understanding how catalytic processes proceed. In the present work, the direct measurement of the molecular diffusion of H 2 and CO gas-phase species diffusing in n-alkane mixtures using pulsed-field gradient (PFG) nuclear magnetic resonance (NMR) methods is reported. The work is of direct relevance to Fischer−Tropsch (FT) catalysis, with the measurements being made of the gas−wax system with the wax in both the bulk liquid state and when confined within a titania catalyst support, at temperatures and pressures typical of low-temperature FT synthesis. Molecular diffusion coefficients of H 2 and CO within wax-saturated porous titania in the range (1.00−2.43) × 10 −8 and (6.44− 8.50) × 10 −9 m 2 s −1 , respectively, were measured in the temperature range of 140− 240 and 200−240 °C for H 2 and CO, respectively, at a pressure of 40 bar. The wax mixture was typical of a wax produced during FT catalysis and had a molar average carbon number of 36. It is shown that the hydrogen diffusion coefficient within this wax mixture is consistent, to within experimental error, with the hydrogen diffusion coefficient measured in pure single-component nhexatriacontane (n-C 36 ) wax; this result held with the waxes in the bulk liquid state and when confined within the porous titania. The tortuosity of the porous titania was also measured using PFG NMR and found to be 1.77; this value is independent of temperature. The ability of existing correlations to predict these experimentally determined data was then critically evaluated. Although the Wilke−Chang correlation was found to underestimate the molecular diffusion coefficients of both H 2 and CO diffusing in the wax in both the bulk state and when confined within the porous titania, parameterized correlations based on the rough hard sphere model, having accounted for the experimentally determined tortuosity factor, predicted the H 2 and CO diffusion within bulk and confined wax to within 3%.

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Viscosity of heavy n -alkanes and diffusion of gases therein based on molecular dynamics simulations and empirical correlations

Cited by 23 publications

References 53 publications

Formaldehyde diffusion within crystalline and amorphous cellulose at different temperatures and electric fields: A molecular dynamics study

Formaldehyde diffusion within crystalline and amorphous cellulose at different temperatures and electric fields: A molecular dynamics study

Probing the high-pressure viscosity of hydrocarbon mixtures using molecular dynamics simulations

Experimental Determination of H₂ and CO Diffusion Coefficients in a Wax Mixture Confined in a Porous Titania Catalyst Support

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Viscosity of heavy n -alkanes and diffusion of gases therein based on molecular dynamics simulations and empirical correlations

Cited by 23 publications

References 53 publications

Formaldehyde diffusion within crystalline and amorphous cellulose at different temperatures and electric fields: A molecular dynamics study

Formaldehyde diffusion within crystalline and amorphous cellulose at different temperatures and electric fields: A molecular dynamics study

Probing the high-pressure viscosity of hydrocarbon mixtures using molecular dynamics simulations

Experimental Determination of H2 and CO Diffusion Coefficients in a Wax Mixture Confined in a Porous Titania Catalyst Support

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Experimental Determination of H₂ and CO Diffusion Coefficients in a Wax Mixture Confined in a Porous Titania Catalyst Support