Microwave Enhancement of Extractions and Reactions in Liquid-Liquid Biphasic Systems

Microwaves (MWs) are a powerful technology for electrifying chemical processing and can enable selective heating, which is impossible in conventional systems. This effect was recently ascribed to enhancing liquid-liquid reactive extractions in biomass derivative chemistry. Building on our previous work in which we demonstrated and optimized MW-induced temperature gradients, we investigate the effect of temperature gradients on extraction by experiments and simulations. We demonstrate that the colder organic phase, common to MW heating, induces shifts in solute partitioning and phase behavior. Partitioning can be further tuned by adding salts or by carefully selecting solvent systems as we demonstrate via COSMO-RS calculations. The colder organic phase also leads to Rayleigh instabilities and active buoyancy-driven mixing. These effects, measured experimentally and simulated in COMSOL, can greatly enhance mass transfer rates in liquid-liquid systems. We find that under typical conditions, the enhancement to reactive extractions is minimal. We suggest conditions for more impressive extraction and reactive extractions. Finally, we find that temperature gradients retard humins formation.