Grenzflächenspannungsmessungen als Baustein verfahrenstechnischer Stofftransportmodellierungen

The interfacial tension is a material parameter describing the interface between two fluid phases. It is also a changing physical value in mass transfer processes beyond equilibrium. Thus, the measurement of change in interfacial tension characterizes adsorption and mass transfer processes at liquid‐liquid interfaces. The units of a pendant drop tensiometer can represent a mini mass transfer cell.     

Methode zur Erfassung von Stofftransport an fluiden Phasengrenzflächen

A finite volume‐based approach to capture mass transfer phenomena at moving fluid interfaces is proposed. The approach is capable of describing two‐phase systems containing several transferred components. Two concentration fields are defined for each transferred component, while each field has physical meaning just in one phase. This two‐field approach allows formulation of space‐ and time‐dependent boundary conditions at the interface. The suggested approach is validated with three test cases describing a single droplet in a continuous liquid phase. Purely diffusive mass transfer is captured very well. The simulation results for the moving system are in good agreement with experimental data.     

Mizellare Extraktion von Zink mit Di(2‐ethylhexyl)phosphorsäure in Gegenwart des Tensids Cetyltrimethylammoniumbromid

Addition of surfactants can influence extraction processes. In the case were the surfactant concentration is above the critical micelles concentration the mass transfer rate increases by the formation of inverse micelles and therefore the micellar extraction mechanism of zinc. The influence of the added surfactant cetyltrimethylammonium bromide (CTAB) on zinc extraction with the cation exchanger di(2‐ethylhexyl)phosphoric acid (D₂EHPA) is analysed based on extraction equilibriums and mass transfer experiments. The observed experimental results are explained phenomenologically.     

Entwicklungsstand und Perspektiven der Modellierung von Transportvorgängen in durchströmten Festbetten

New model equations enable the consistent and accurate calculation of heat transport, mass transport and chemical reactions in packed beds with fluid flow. The main features of this approach are reviewed and summarized, and selected aspects are discussed. The modelling approach may be a good starting point for the development of, for instance, membrane reactors and separation processes such as chromatography or freeze drying for thermally sensitive products.