An experimental study of three component gas diffusion

Duncan, J. B.; Toor, H. L.

doi:10.1002/aic.690080112

Cited by 167 publications

(105 citation statements)

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“…(1) Coupling effects in mixture diffusion may cause uphill transport of a component (2) Uphill diffusion results in transient overshoots and serpentine equilibration trajectories (3) Non-ideal phase equilibrium thermodynamics is often the major source of diffusional coupling effects (4) Chemical potential gradients are the proper driving forces for diffusion (5) Uphill transport can be exploited to achieve difficult and unusual separations…”

Section: Key Learning Pointsmentioning

confidence: 99%

Uphill diffusion in multicomponent mixtures

2015

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Molecular diffusion is an omnipresent phenomena that is important in a wide variety of contexts in chemical, physical, and biological processes. In the majority of cases, the diffusion process can be adequately described by Fick's law that postulates a linear relationship between the flux of any species and its own concentration gradient. Most commonly, a component diffuses down the concentration gradient. The major objective of this review is to highlight a very wide variety of situations that cause the uphill transport of one constituent in the mixture. Uphill diffusion may occur in multicomponent mixtures in which the diffusion flux of any species is strongly coupled to that of its partner species. Such coupling effects often arise from strong thermodynamic non-idealities. For a quantitative description we need to use chemical potential gradients as driving forces. The transport of ionic species in aqueous solutions is coupled with its partner ions because of the electro-neutrality constraints; such constraints may accelerate or decelerate a specific ion. When uphill diffusion occurs, we observe transient overshoots during equilibration; the equilibration process follows serpentine trajectories in composition space. For mixtures of liquids, alloys, ceramics and glasses the serpentine trajectories could cause entry into meta-stable composition zones; such entry could result in phenomena such as spinodal decomposition, spontaneous emulsification, and the Ouzo effect. For distillation of multicomponent mixtures that form azeotropes, uphill diffusion may allow crossing of distillation boundaries that are normally forbidden. For mixture separations with microporous adsorbents, uphill diffusion can cause supra-equilibrium loadings to be achieved during transient uptake within crystals; this allows the possibility of over-riding adsorption equilibrium for achieving difficult separations. Key learning points(1) Coupling effects in mixture diffusion may cause uphill transport of a component (2) Uphill diffusion results in transient overshoots and serpentine equilibration trajectories (3) Non-ideal phase equilibrium thermodynamics is often the major source of diffusional coupling effects (4) Chemical potential gradients are the proper driving forces for diffusion (5) Uphill transport can be exploited to achieve difficult and unusual separations

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Section: Key Learning Pointsmentioning

confidence: 99%

Uphill diffusion in multicomponent mixtures

2015

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“…The ternary gaseous diffusion in a Stefan tube is an ideal test problem for the Stefan-Maxwell flux model because of the availability of a closed-form analytical solution and experimental data for concentration profiles along the axis of the tube; ternary diffusion in a Stefan tube has become a classical test problem for the StefanMaxwell flux model (see, e.g., Duncan and Toor 1962, Getzinger and Wilke 1967, Carty and Schrodt 1975, Taylor and Krishna 1993. The present study focuses on the verification and validation of species concentration profiles along the tube as predicted by the Stefan-Maxwell flux model in GOMA.…”

Section: Verification and Validation Of The Stefan-maxwell Flux Modelmentioning

confidence: 99%

Final report on LDRD project: A phenomenological model for multicomponent transport with simultaneous electrochemical reactions in concentrated solutions

Chen¹,

Evans²,

Larson³

et al. 2000

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“…The advantage of the formulation in terms of the entropy variables is not only that the diffusion matrix B(w) is positive definite (which allows us to apply the Lax-Milgram lemma to a linearized version of (12)) but it yields also positive lower and upper bounds for the concentrations. Indeed, inverting (11), we find that (13) c i = e…”

Section: Introductionmentioning

confidence: 99%

“…The model bases upon interspecies force balances, relating the velocities of the species of the mixture. It is well-known that the usual Fickian diffusion model, which states that the flux of a chemical substance is proportional to its concentration gradient, is not able to describe, e.g., uphill or osmotic diffusion phenomena in multicomponent mixtures, as demonstrated experimentally by Duncan and Toor [13]. These phenomena can be modeled by using the theory of nonequilibrium thermodynamics, in which the fluxes are assumed to be linear combinations of the thermodynamic forces [11,Chap.…”

Section: Introductionmentioning

confidence: 99%