(324d) Microwave Heating of Liquid-Liquid Biphasic Systems

Microwave (MW) technology can be a powerful tool for the intensification of chemical processes and is often recognized for the benefits of high-efficiency and fast and volumetric heat delivery. In multiphase systems, MWs offer the additional advantage of selective heating, which may allow for further improvement of processes such as reactive extractions beyond what is possible in conventional systems. However, limited fundamental understanding of design principles has hindered the effective use of MWs. Further complicating the issue – inadequate temperature measurement strategies often yield misleading results or leave the analysis of topics like selective heating wholly unapproachable. In this work, a commercial single-mode microwave applicator is modified to allow for spatial resolution in temperature measurements, both a continuous-flow microreactor and in batch mode. Simultaneously, corresponding fluid dynamics models are built to simulate temperature profiles. This complementary experimental and computational approach allows us to explore selective MW heating of liquid-liquid biphasic systems. An analytical expression for temperature difference between phases is developed and compared to experimental measurements for various organic solvents in contact with water and various key variables in both batch and continuous flow systems. The agreement between simulations and experiments is excellent. We present design guidelines to tune the selective heating in microwave reactors.