Interfacial phenomena and mass transfer

doi:10.1016/0009-2509(66)85099-6

Chemical Engineering Science

Volume 21, Issue 11, November 1966, Pages 1039-1046

https://doi.org/10.1016/0009-2509(66)85099-6 Get rights and content

Abstract

This paper contributes to the study of interfacial phenomena with respect to mass transfer in three ways:

(1) Solutes are classified quantitatively according to their ability to impede or promote movement of a free interface. Within this scheme the influence of concentration of the solute on the obstruction of movement can also be explained.

(2) Interfacial movement induced by differences in interfacial tension is divided into two categories: large scale and micro scale movement. The importance of this differentiation is stressed in a discussion on observations of growing droplets to which or from which a solute is transferred.

(3) A schlieren optical study of the microscale behaviour of the interface during extraction revealed that the mean cell size and the penetration depth are of the same order of magnitude. This fact could be made acceptable. From this the ratio of the rates of mass transfer with and without cells could be estimated; the predicted values of this ratio, 2 to 3, are in accordance with published results.

Résumé

Cet article apporte une contribution à l'étude des phénomènes interfaciaux en liaison avec le transfert de masse sur trois points:

(1) Les solutés sont quantitativement classés selon leur aptitude à freiner ou à provoquer le mouvement d'un interface libre. Ce schéma permet de plus d'expliquer l'influence de la concentration du soluté sur les caractériques du mouvement.

(2) Les mouvements interfaciaux dus à des différences de tension interfaciale sont classés en deux catégories: les mouvements à grande échelle, et à micro échelle. L'importance de cette différentiation est mise en évidence dans une discussion sur des observations de grossissement de gouttes qui reçoivent ou donnent un soluté.

(3) Une étude optique “schlieren” du comportement à micro échelle de l'interface pendant une extraction a montré que la taille moyenne des cellules et la profondeur de pénétration sont du même ordre de grandeur. Les auteurs ont pu rendre compte de ce fait. Ils en ont déduit une estimation du rapport des vitesses de transfert de masse avec et sans cellules; les valeurs prévues de ce rapport, 2 à 3, sont en accord avec dés résultats publiés.

Zusammenfassung

Dies ist ein Beitrag zur Erfassung von Phasengrenzerscheinungen beim Stoffaustausch, und zwar in dreifacher Hinsicht:

(1) Die gelösten Komponenten werden je nach ihrer Fähigkeit, die Bewegung freier Phasengrenzen zu hemmen oder zu beschleunigen, quantitativ geordnet; dabei wird auch der Konzentrationseinfluβ auf diese Erscheinungen erfaβt.

(2) Die Phasengrenzbewegungen aufgrund von Unterschie den der Oberflächenspannung lassen sich in zwei Gruppen zusammenfassen: ausgedehnte Verschiebungen und kleine Schwingungen. Diese wichtige Unterscheidung ergibt sich aus der Beobachtung von Flüssigkeitselementen, aus denen oder zu denen das Gelöste übertragen wird.

(3) Aus schlierenoptischen Untersuchungen von Phasengrenzen bei Extraktionsvorgängen ergibt sicht, daβ die Zellenabmessungen und die Eindringtiefe von gleicher Gröβenordnung sind. Daraus läβt sich das Verhältnis der Austauschgeschwindigkeiten mit und ohne Zellen abschätzen, dieser Wert liegt zwischen 2 und 3 und stimmt mit Literaturangaben überein.

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A new study of electrically induced disturbances and mass transfer at a liquid-liquid interface as a means of process intensification is presented. Visualization of electrically induced disturbances during mass transfer of ethanol from an aqueous phase into an extracting solvent, n-decanol is demonstrated. Mass transfer rates were measured for extraction of ethanol from an aqueous electrically charged pendant droplet into a continuous phase of n-decanol. In a second part, mass transfer rates of ethanol into n-decanol across a planar interface in the presence of a DC electrical field are presented. Thirdly, results are presented of electrostatic spraying of aqueous enzyme solutions into an immiscible triglyceride ester oil phase. The effect of electrical field on specific interfacial rate of reaction was determined. The first part of the study demonstrated the positive effect of electrical disturbance on mass transfer rate from the pendant droplet. Time dependent mass transfer was also shown, consistent with earlier mass transfer studies with uncharged pendant drops. The mass transfer study using the planar interface provided further confirmation of the positive effect of electrically induced interfacial turbulence on mass transfer. The experimental data are successfully compared with simulations based on rigorous numerical solutions of the controlling equations. The visual disturbance pattern at the interface and rates of mass transfer were accurately predicted. The reactor experiments clearly show a significant positive effect of electrical charge on the specific rate of hydrolysis. This latter finding opens up the possibility of intensification of enzymatic catalytic activity using electrical fields. The potential for electrically induced enhancement of other reaction systems involving liquid-liquid interfaces such as in the case of phase-transfer catalysis is highlighted.
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The experimental evidence of this self-similarity is displayed in Fig. 20b. Here we transform the different curves for the temporal evolution of the pattern size measured by Bakker et al. [64] in the system isobutanol/water with acetic acid as diffusing species. For convenience, a relative initial concentration (based on the experiment with the highest initial concentration of c0 = 0.8 mol/l) is used to scale length and time as this is the only varying parameter which influences ∆σ.
According to the seminal theory by Sternling and Scriven [1], solutal Marangoni convection during mass transfer of surface-active solutes may occur as either oscillatory or stationary instability. With strong support of Manuel G. Velarde, a combined initiative of experimental works, in particular to mention those of Linde, Wierschem and coworkers, and theory has enabled a classification of dominant wave types of the oscillatory mode and their interactions. In this way a rather comprehensive understanding of the nonlinear evolution of the oscillatory instability could be achieved. A comparably advanced state-of-the-art with respect to the stationary counterpart seemed to be out of reach a short time ago. Recent developments on both the numerical and experimental side, in combination with assessing an extensive number of older experiments, now allow one to draw a more unified picture. By reviewing these works, we show that three main building blocks exist during the nonlinear evolution: roll cells, relaxation oscillations and relaxation oscillations waves. What is frequently called interfacial turbulence results from the interaction between these partly coexisting basic patterns which may additionally occur in different hierarchy levels. The second focus of this review lies on the practical importance of such convection patterns concerning their influence on mass transfer characteristics. Particular attention is paid here to the interaction between Marangoni and buoyancy effects which frequently complicates the pattern formation even more. To shed more light on these dependencies, new simulations regarding the limiting case of stabilizing density stratification and vanishing buoyancy are incorporated.
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¹: Present address: Caltex Petroleum Mij., Pernis, The Netherlands.

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Interfacial phenomena and mass transfer

Abstract

Résumé

Zusammenfassung

Chem. Engng Sci.

Chem. Engng Sci.

Ind. Engng Chem.

A.I.Ch.E. Jl.

A.I.Ch.E. Jl.

Kolloidzschr.