A Continuous-Flow Electrochemical Taylor Vortex Reactor: A Laboratory-Scale High-Throughput Flow Reactor with Enhanced Mixing for Scalable Electrosynthesis

Abstract

We report the development of a small footprint continuous electrochemical Taylor vortex reactor capable of processing kilogram quantities of material per day. This report builds upon our previous development of a scalable photochemical Taylor vortex reactor (Org. Process Res. Dev. 2017, 21, 1042; 2020, 24, 201–206). It describes a static and rotating electrode system that allows for enhanced mixing within the annular gap between the electrodes. We demonstrate that the size of the annular gap and the rotation speed of the electrode are important for both conversion of the substrate and selectivity of the product exemplified using the methoxylation of N-formylpyrrolidine. The employment of a cooling jacket was necessary for scaling the reaction in order to manage the heat generated by electrodes at higher currents (up to 30 A, >270 mA cm–2) allowing multimole productivity per day of methoxylation product to be achieved. The electrochemical oxidation of thioanisole was also studied, and it was demonstrated that the reactor has the performance to produce up to 400 g day–1 of either of the corresponding sulfoxide or sulfone while maintaining a very high reaction selectivity (>97%) to the desired product. This development completes a suite of vortex reactor designs that can be used for photo-, thermal-, or electrochemistry, all of which decouple residence time from mixing. This opens up the possibility of performing continuous multistep reactions at scale with flexibility in optimizing processes.

High-Productivity Single-Pass Electrochemical Birch Reduction of Naphthalenes in a Continuous Flow Electrochemical Taylor Vortex Reactor

“…A schematic of the reactor is depicted in Figure 2 , and a full piping diagram showing the overall setup is detailed in the Supporting Information. Unpublished experiments to measure the residence time distribution in our original electrochemical Taylor vortex reactor with a carbon outer electrode 51 indicated that the mean residence time was only slightly longer than the value estimated by dividing the reactor volume by the volumetric flow rate. The lengthening of the time may well be due to the adsorption of the Rose Bengal dye used in the experiment to the porous carbon electrode.…”

“…Our original report, 51 focused on electrochemical oxidation, used a graphite tube as the outer anode of the reactor. Here, however, as a sacrificial anode is required for this type of reduction reaction, other materials were considered for the electrodes; indeed, when the reduction reaction was run with the graphite anode, no reaction took place.…”

“…55 Moreover, the increase in the rotation speed of the inner cylinder is expected to increase mixing efficiency within the gap and enhance the electrochemical reaction. Our original report, 52 focused on electrochemical oxidation, used a graphite tube as the outer anode of the reactor. Here, however, as a sacrificial anode is required for this type of reduction reaction, other materials were considered for the electrodes; indeed, when the reduction reaction was run with the graphite anode, no reaction took place.…”

“…The power supply was operated in constant current mode, where the desired current was set for each experiment and the maximum voltage was set to 30 V. The electrochemical vortex reactor was described previously and was used without change except for the static outer electrode materials. 51 The reaction solution was delivered by a JASCO PU-4180HPLC pump. The solution was removed from the reactor using a Cole Parmer Masterflex L/S peristaltic pump.…”

“… 43 − 49 One reactor type that had been under-utilized for synthetic electrochemistry is the Taylor vortex reactor. 50 Recently, we reported an electrochemical flow Taylor vortex reactor 51 that consists of a tubular electrode (anode—graphite) with a rotating cylinder (cathode—stainless steel) on the inside that serves as the second electrode. This reactor design builds on our successful photochemical vortex reactor designs reported previously.…”