On the performance of liquid-liquid Taylor flow electrochemistry in a microreactor – A CFD study

Abstract

A comprehensive understanding of the underlying phenomena (coupled fluid flow, charge transfer, mass transfer and chemical reaction) is fundamental for a proper design, analysis and scale-out of chemical reactors when carrying out multiphase electro-organic transformations. In this study, we have explored the novel combination of organic electrochemical synthesis and computational fluid dynamics (CFD) to perform a systematic theoretical investigation concerning the effect of different operational parameters on the performance of organic-aqueous Taylor flow in electrochemical microreactors. The results indicate that operating at high concentrations of the rate-limiting species (>5 mol⋅m−3 for Di≥10-9 m2⋅s−1; 500 mol⋅m−3 for Di~10-10 m2⋅s−1) is beneficial for the reactor performance. However, excessively high concentrations (>500 mol⋅m−3) do not result in a further improvement in mass transfer and current/voltage relation. Higher diffusivities are also beneficial, but even in this scenario limiting current densities can be found when working at low concentrations. Overall, keeping an internal:external phase electrical conductivity ratio > 1 improves the reactor performance. Working at lower velocities can be beneficial in some scenarios, since higher limiting current densities can be obtained. However, the velocity impact on the reactor performance is not significant in some operating conditions (e.g., at higher concentrations and diffusivities). Finally, working with higher cell potentials is beneficial, but limiting current densities can be encountered at lower concentrations and diffusivities. Variables such as internal phase volume fraction, droplet length and interelectrode distance also have relevant impact on the reactor performance, but are subjected to the same conditioning factors previously mentioned. A comprehensive potential balance was also conducted, showing the relative importance of the activation, Ohmic and concentration overpotentials under different operating conditions. We believe the insights gained herein will be of interest to researchers in both academia and industry to develop more efficient electrochemical flow reactors for liquid–liquid transformations.