Influence of Microwave Heating on LiquidLiquid Phase Inversion and Temperature Rates for Immiscible Mixtures

Abstract

Time dependencies of component temperatures for mixtures of immiscible liquids during microwave heating were studied for acetonitrile-cyclohexane and water-toluene. For the first time, we report microwave induced liquid-liquid phase inversion for acetonitrile-cyclohexane mixture: acetonitrile layer was initially at the bottom of the mixture, after 10 sec of microwave heating its density decreased and it inverted to the top of the mixture for the remainder of the microwave heating. This phase inversion could not be achieved by conventional radiant heating. The maximum rate of temperature growth for the polar component of the mixtures was 2 - 5 times larger than for the non-polar component. This suggests that microwave energy is absorbed by polar liquids (water or acetonitrile) and heat is transferred into the non-polar liquid (toluene or cyclohexane) in the mixture by conduction (in case of cyclohexane) or conduction and convection (in case of toluene). Comparison between experimental data and semi-empirical mathematical models, proposed in [Kennedy et at., 2009] showed good correlation. Average relative error between theoretical and experimental results did not exceed 7%. These results can be used to model the temperature kinetics of components for other multiphase mixtures.

On buoyancy driven mixing by volumetric microwave energy deposition

“…It is believed that VED can aid material mixing processes through buoyancy (pressure gradient) acting on the variation in density. Furthermore, VED may enhance mixing rates (stirring and molecular), and can thus significantly affect local reaction rates and efficiency in chemically reactive systems [15][16][17]. As such, there is a need for experimental data to validate mathematical models of the VED process.…”

“…the RT instability was generated below the boiling points of the fluids used. The interaction of two dielectric fluids under microwave heating was examined by Kennedy et al [16,17], however, only immiscible fluids were examined. The work of [14] was the first investigation of mixing of two miscible fluids by VED, and set the stage for the current study.…”