(179b) Influence of Dispersion Conditions on Phase Separation in Liquid Multiphase Systems

Surfactant multiphase systems can be applied as liquid/liquid reaction systems to realise the hydroformylation of long-chained olefins. High and specific yields can be achieved if a rhodium complex is used as homogeneous catalyst. Furthermore, these systems enable fast phase separation and therefore catalyst recycling despite the high amounts of surfactant.

The separation is especially fast if the process parameters are adjusted until a liquid three phase system occurs. Under this conditions, the organic and aqueous excess phases are separated by a surfactant-rich middle phase. The occurrence of the third phase reduces the separation time from hours or even days to several minutes.

The main components of these multiphase systems are water, oil and non-ionic surfactant. To achieve a fundamental understanding of the separation process, the density and viscosity of each phase as well as the interfacial tension between the respective phases are analysed. Furthermore, an endoscope measurement technique and image analysis is applied to investigate the drop size distributions and drop interactions (e.g. single droplets, droplets attached to each other or multiple emulsions). The type of drop interaction is mainly defined by the phase volume fractions and interfacial tensions.

In common two phase systems, the separation time usually increases with decreasing drop sizes. However, the drop interaction cannot be neglected under three phase conditions. It was observed that besides the drop size distributions, the type of drop interaction is the main factor influencing the separation time. Therefore, systems with small drop sizes can sometimes even separate faster than systems with large droplets, if the drop interactions change accordingly.