Fundamental behavior of benzene–CO2 mutual diffusion coefficients in the critical region of CO2

Nishiumi, Hideo; Kubota, Toshinori

doi:10.1016/j.fluid.2007.07.072

Cited by 12 publications

(10 citation statements)

References 29 publications

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“…Furthermore, in the present study, the deceleration of the Fickian diffusion process with increasing CO 2 mole fraction was found to be more pronounced with increasing temperature. In the literature, ,, such an effect is related to the vicinity to the critical plait point, where the thermodynamic factor and thus D 11 approach zero. However, predictions of the critical temperatures and critical pressures for all studied systems at the various compositions based on the PPR78 EoS indicate that the thermodynamic states associated with the minima for D 11 are still far away from the vicinity to the critical plait point of the mixtures.…”

Section: Resultsmentioning

confidence: 99%

Influence of Liquid Structure on Fickian Diffusion in Binary Mixtures of n-Hexane and Carbon Dioxide Probed by Dynamic Light Scattering, Raman Spectroscopy, and Molecular Dynamics Simulations

et al. 2018

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This study contributes to a fundamental understanding of how the liquid structure in a model system consisting of weakly associative n-hexane ( n-CH) and carbon dioxide (CO) influences the Fickian diffusion process. For this, the benefits of light scattering experiments and molecular dynamics (MD) simulations at macroscopic thermodynamic equilibrium were combined synergistically. Our reference Fickian diffusivities measured by dynamic light scattering (DLS) revealed an unusual trend with increasing CO mole fractions up to about 70 mol %, which agrees with our simulation results. The molecular impacts on the Fickian diffusion were analyzed by MD simulations, where kinetic contributions related to the Maxwell-Stefan (MS) diffusivity and structural contributions quantified by the thermodynamic factor were studied separately. Both the MS diffusivity and the thermodynamic factor indicate the deceleration of Fickian diffusion compared to an ideal mixture behavior. Computed radial distribution functions as well as a significant blue-shift of the CH stretching modes of n-CH identified by Raman spectroscopy show that the slowing down of the diffusion is caused by a structural organization in the binary mixtures over a broad concentration range in the form of self-associated n-CH and CO domains. These networks start to form close to the infinite dilution limits and seem to have their largest extent at a solute-solvent transition point at about 70 mol % CO. The current results not only improve the general understanding of mass diffusion in liquids but also serve to develop sound prediction models for Fick diffusivities.

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Section: Resultsmentioning

confidence: 99%

Influence of Liquid Structure on Fickian Diffusion in Binary Mixtures of n-Hexane and Carbon Dioxide Probed by Dynamic Light Scattering, Raman Spectroscopy, and Molecular Dynamics Simulations

et al. 2018

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“…It was shown recently [17] that the small presence of ethanol can visibly shift parameters of the Widom line. One of the first observations of a change in slope or even the appearance of a V-shaped region on a diffusion curve was reported by Nishiumi& Kubota [18], who attributed this to a decrease in thermodynamic factor. Recent molecular dynamic simulations also showed that the thermodynamic factor in mixtures manifests a deep well in the vicinity of the Widom line [8].…”

Section: Diffusion Of Ethanol In Supercritical Comentioning

confidence: 92%

Diffusion of Quinine with Ethanol as a Co-Solvent in Supercritical CO2

2020

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This study aims at contributing to quinine extraction using supercritical CO2 and ethanol as a co-solvent. The diffusion coefficients of quinine in supercritical CO2 are measured using the Taylor dispersion technique when quinine is pre-dissolved in ethanol. First, the diffusion coefficients of pure ethanol in the supercritical state of CO2 were investigated in order to get a basis for seeing a relative change in the diffusion coefficient with the addition of quinine. We report measurements of the diffusion coefficients of ethanol in scCO2 in the temperature range from 304.3 to 343 K and pressures of 9.5, 10 and 12 MPa. Next, the diffusion coefficients of different amounts of quinine dissolved in ethanol and injected into supercritical CO2 were measured in the same range of temperatures at p = 12 Mpa. At the pressure p = 9.5 MPa, which is close to the critical pressure, the diffusion coefficients were measured at the temperature, T = 343 K, far from the critical value. It was found that the diffusion coefficients are significantly dependent on the amount of quinine in a small range of its content, less than 0.1%. It is quite likely that this behavior is associated with a change in the spatial structure, that is, the formation of clusters or compounds, and a subsequent increase in the molecular weight of the diffusive substance.

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“…The considerable injection volume dependence of the Fick diffusion coefficient reported for solutes like acetone 27 , benzene 28 or naphthalene 29 in supercritical CO 2 in the vicinity of its critical point employing the Taylor dispersion technique can be rationalized when Fig. 2 is observed.…”

Section: Resultsmentioning

confidence: 90%

“…Experimentally, the largest errors for the measured state points are observed in the vicinity of the Widom line, which do not exceed 11%. The presence of a maximum of the Fick diffusion coefficient of an infinitely diluted solute dissolved in supercritical CO 2 has been reported in the literature before 28 , but was challenged by other experimental work 44,45 and the injection volume was identified as one of the factors which affects the density in this region. Further, measurements near the critical point have been commonly associated with the presence of peak tailing 4,45–47 .…”

Section: Resultsmentioning

confidence: 95%

“…Some speculations can be found in the literature about a minimum 27,28,49–51 or slowing down 45,52–54 of the Fick diffusion coefficient of different compounds, such as naphthalene, benzene or acetone, when the critical point of the solvent is approached. From the other side, theoretical estimations based on irreversible thermodynamics and the thermodynamic factor, e.g.…”

Section: Resultsmentioning

confidence: 99%

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Diffusion of methane in supercritical carbon dioxide across the Widom line

Guevara‐Carrion

Ancherbak

Mialdun

et al. 2019

Sci Rep

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Diffusion of methane diluted in supercritical carbon dioxide is studied by experiment and molecular simulation in the temperature range from 292.55 to 332.85 K along the isobars 9.0, 12.5 and 14.7 MPa. Measurements of the Fick diffusion coefficient are carried out with the Taylor dispersion technique. Molecular dynamics simulation and the Green-Kubo formalism are employed to obtain Fick, Maxwell-Stefan and intradiffusion coefficients as well as shear viscosity. The obtained diffusion coefficients are on the order of 10 −8 m 2 /s. The composition, temperature and density dependence of diffusion is analyzed. The Fick diffusion coefficient of methane in carbon dioxide shows an anomaly in the near-critical region. This behavior can be attributed to the crossing of the so-called Widom line, where the supercritical fluid goes through a transition between liquid-like and gas-like states. Further, several classical equations are tested on their ability to predict this behavior and it is found that equations that explicitly include the density are better suited to predict the sharp variation of the diffusion coefficient near the critical region predicted by molecular simulation.

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Fundamental behavior of benzene–CO2 mutual diffusion coefficients in the critical region of CO2

Cited by 12 publications

References 29 publications

Influence of Liquid Structure on Fickian Diffusion in Binary Mixtures of n-Hexane and Carbon Dioxide Probed by Dynamic Light Scattering, Raman Spectroscopy, and Molecular Dynamics Simulations

Influence of Liquid Structure on Fickian Diffusion in Binary Mixtures of n-Hexane and Carbon Dioxide Probed by Dynamic Light Scattering, Raman Spectroscopy, and Molecular Dynamics Simulations

Diffusion of Quinine with Ethanol as a Co-Solvent in Supercritical CO2

Diffusion of methane in supercritical carbon dioxide across the Widom line

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