(339c) Influence of Surfactants on Mass Transfer and Fluid Dynamics in Disperse Multiphase Systems

Joschka M. Schulz, Matthias Kraume

Technische Universität Berlin, Chair of Chemical and Process Engineering Ackerstraße 76, 13355 Berlin, Germany

matthias.kraume@tu-berlin.de

In liquid/liquid systems the transport processes strongly depend on the characteristics of the interface and the occurring transport phenomena. In many industrial applications surface active substances occur intentionally or as an impurity. By their appearance the behaviour of the liquid/liquid interface changes. Hence, fluid dynamics and mass transfer rates are influenced, which leads (e.g.) to an increase in residence time and hold-up in extraction columns or a decrease in multiphase reaction rates. Since the induced interfacial phenomena such as Marangoni convection or adsorption have contrary effects on the mass transfer in multiphase systems, the prediction of their occurrence and process variables linked to them based on theoretical or empirical equations is a challenging task.

The present work focuses on the interaction between mass transfer and fluid dynamics in disperse liquid/liquid systems in the presence of surfactants. Due to the interaction between the transport processes, fluid dynamic measurements of single droplets can act as an indicator for the prediction of interfacial phenomena and mass transfer rates. For experimental purposes the single drop rising test cell described in Wegener et al. (2007) is used for the measurement of fluid dynamics and mass transfer rates. Additionally, the experimental setup shown in Merker et al. (2017) extending the concept of the rising test cell by adding a vertical traverse system with real-time control is applied, which allows for three-dimensional measurement of shape, velocity and trajectory of the particle during the ascent.

Fig. 1 shows the transient drop rise velocity of single 1-octanol droplets in water for varying surfactant concentrations. Butyldiglycol is chosen as a model surfactant. With increasing surfactant concentration the terminal drop rise velocity decreases from the calculated velocity for a moving interface to the value for rigid spheres. Although the observed effect is in good agreement with the literature, e.g. Wegener et al. (2014), the mass transfer rates show contrary behavior due to the occurrence of Marangoni convection. The investigation aims at a better understanding and prediction of the interaction between the aforementioned transport phenomena by detailed consideration of the drop movement during the ascent.

Figure 1: Experimental transient drop rise velocity of 2 mm 1-octanol droplets in water for different surfactant concentrations. Calculated velocities for the movable and rigid interface are shown for comparison (Feng and Michaelides 2001, Martin 1980).

References

M. Wegener, J. Grünig, J. Stüber, A. R. Paschedag, M. Kraume, Chem. Eng. Sci. 2007, 62, 2067-2078.

D. Merker, L. Böhm, M. Oßberger, P. Klüfers, M. Kraume, Chem. Eng. Technol., 2017, 40, 1391-1399. Z.-G. Feng, E. E. Michaelides, J. Fluids. Eng., 2001, 123, 841-849.

H. Martin, Chem. Ing. Techn., 1980, 52, 199-200.

M. Wegener, N. Paul, M. Kraume, Int. J. Heat Mass Transfer, 2014, 71, 475-495.