BeschreibungThe mass transfer between two demixed phases plays an essential role in fluid separations as it defines the residence time in an apparatus. During the process design of these separation processes, the interface is often considered as an area of zero thickness with an unsteadiness in all physical properties. It is assumed, that the interface itself plays no role in mass transfer . But density functional theories  show, that there could be an enrichment of one component in equilibrium. The question arises, if these enrichments have an influence on the mass transfer across the interface.
To answer this question, the density gradient theory  (DGT) can help to analyze the interfacial mass transfer. The DGT provides an expression for the Helmholtz free energy of a non-uniform system which is a function of the local composition and its gradients There are many works in literature which investigate the interfacial tension and the concentration profile across the interface with help of the DGT . In our work, we want to show the application of the instationary form of the DGT in combination with a GE-model to examine the mass transfer in liquid-liquid systems  and compare it to experimental data. In order to obtain the experimental data, it is necessary to operate in a vessel with a defined interface and ideally mixed phases. This is fulfilled in a Nitsch cell .
At first we examine the mass transfer in the classical extraction system toluene-water with acetone, ethanol and tetrahydrofuran as transferring components. All of these components show an enrichment in the interface on differently high levels as calculated by DGT. It could be shown experimentally that the equilibration time corresponds with the level of enrichment of the transferring component and that the DGT can be used to model the mass transfer across the interface. Based on these findings, we show how the DGT can be used in a Computational fluid dynamics framework to model such phenomena as the demixing of liquid-liquid systems and the drop coalescence.
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|Zeitraum||11 Mai 2019|
|Ereignistitel||Properties and Phase Equilibria for Product and Process Desgin|