Abstract

Synergistic Effect of Ultrasound Irradiation in Micro-structured Electrochemical Reactors

Simon Kuhn, Associate Professor, Katholieke Universiteit Leuven

Organic electrochemistry enables a broad variety of reactions, and electrochemical transformations in general have the potential to replace traditional catalytically activated reactions for e.g. heterocycle synthesis. At the same time, new developments in small-scale flow reactors have increasingly gained attention as convenient tools for more efficient syntheses compared to traditional batch procedures. Small-scale flow reactors provide uniform residence times, well-defined flow patterns, and precise temperature control. Their advantage for electrochemical reactions in particular is their large surface to volume ratio and the reduced ohmic resistance. This minimizes supporting electrolyte requirements so that less purification steps are required and enables green chemistry. However, one of the challenges that needs to be overcome to establish continuous micro-scale electrochemical reactors is that due to their prevailing laminar flow profile, species transport, which occurs normal to the flow direction between the electrodes, is rather slow. This drastically limits the achievable throughput of electrochemical microreactors. In this contribution, we will present the design of an electrochemical reactor with integrated ultrasound actuators. The acoustic irradiation will lead to a synergistic effect which increases species transport between the electrodes via acoustic streaming. To guide the efficient design and integration of the piezoelectric actuators, we developed an analytical model which calculates the transmission of the piezoelectric actuator vibration to the liquid flowing in the reactor. Depending on the frequency at which the actuators are driven, a standing sound wave is excited in the channel. In this resonance mode, the acoustic pressure will strongly couple with the fluid, leading to a secondary flow structure with vortical motions, strongly enhancing species transport (acoustic streaming). As a proof-of-principle, this reactor is applied to achieve controlled electrolyte-free atom transfer radical polymerization of methyl acrylate.