Understanding the effects of forced and bubble-induced convection in transport-limited organic electrosynthesis

Abstract

Organic electrosynthesis offers a sustainable path to decarbonize the chemical industry by integrating renewable energy into chemical manufacturing. However, achieving the selectivity and energy efficiency required for industrial applications is challenging due to the inherent mass transport limitations of most electro-organic reactions. Convection can mitigate mass transport limitations, but its impact on organic electrochemical processes remains poorly understood. Here we show that the Sherwood number—the ratio of convective mass transport to diffusive mass transport—is a crucial metric to characterize mass transport, determine reactor performance, and enable effective scale-up. We investigate the interplay between mass transport and electrochemical reaction rates under convective flows in the context of the electrosynthesis of adiponitrile, one of the largest organic electrochemical processes in the industry. We use experiments and data-driven predictive models to demonstrate that forced liquid convection and bubble-induced convection produce nearly equivalent mass transport conditions when the corresponding Sherwood numbers are equal. This conclusion shows that the Sherwood number characterizes the mass transport condition independent of the underlying convection mechanism. Moreover, we show that the faradaic efficiency (i.e., the electrochemical selectivity) scales with the Sherwood number for a given current density and reactant concentration. This scalability enables performance to be predicted irrespective of the convection mode employed to enhance mass transport. Our results provide guidelines for the design and selection of convection methods, from lab to industrial scale, and contribute to the development of more sustainable chemical manufacturing processes.