(591b) Transport Processes in Micellar Three Phase Systems

Authors: 
Paul, N., Technische Universität Berlin
Schulz, J. M., TU Berlin
Kraume, M., Technical University Berlin

Combining the advantages of the homogeneous and heterogeneous catalysis is the main goal of tunable solvent systems. Homogeneous conditions shall be achieved throughout the reaction period and heterogeneous conditions shall be adjusted within the separation process. Micellar multiphase systems are examples for tunable solvent systems which can be applied to increase the reaction rates of reactions in liquid/liquid systems. Furthermore, these systems fulfil many principles of the “green chemistry” e.g. using water as a solvent, reducing the waste production etc. The highest reaction rates and the fastest separation were achieved when a micellar three phase system was created (aqueous phase, organic phase and a microemulsion phase). Due to the occurrence of a new phase and the presence of interfacial active molecules an additional mass transfer resistance arises, which again affects the reaction rate and the separation process. For the design of the separation process the phase separation itself and the liquid/liquid mass transfer must be quantified.

A special test cell was designed in this work. Due to the low interfacial tensions occurring in micellar systems single drop experiments could not be applied. A modified “Nitsch test cell” was designed to determine the liquid/liquid mass transfer and the phase separation (coalescence). All experiments were conducted in the same test system: water/1-dodecene, but different non-ionic surfactants (pure surfactants and surfactants in technical grade) were used. To gain a fundamental understanding of the occurring influences on the transport processes caused by the interfacial active molecules the interfacial phenomena were observed detailly. The interfacial tension, the interfacial rheology and the structure at the interface was quantified by applying different measurement techniques (atomic force microscopy, determination of the Brewster angle etc.)

Under three phase conditions the fastest phase separation was observed. Within this temperature range for three phase conditions a minimum of the separation time occurred. This was observed for all different surfactants, which were applied in this work. At the temperature of the fastest phase separation the liquid/liquid mass transfer rate was also at the highest, although this temperature was not the highest. The modified test cell which was designed for this work is made out of glass to provide an optical accessibility. Therefore, at certain temperatures cloudy interfaces were observed. Under these conditions the lowest liquid/liquid mass transfer rates and the slowest phase separation were determined. The determination of the interfacial phenomena proved the creation of a highly viscous microemulsion phase which resulted in a high additional mass transfer resistance. Furthermore, this layer decreased the separation velocity. For the design of a separation process these results must be taken into consideration; otherwise the liquid/liquid mass transfer is overestimated and the separation time is underestimated.