Process Intensification Approaches to Organic Electrosynthesis: Towards Sustainable Nylon Production

Abstract

The effect of fossil-fuel-derived carbon dioxide (CO2) emissions on the environment has fueled the interest in electrifying the chemical industry through electrochemistry. The implementation of electrochemical processes for the production of large volume chemicals can allow for the direct integration of renewable energy sources into chemical manufacturing. Additionally, these processes provide an opportunity for significant energy efficiency improvements and the introduction of previously unexplored chemical transformations. Although inorganic electrosynthetic processes have been successfully implemented in industry at scale (e.g. chloro-alkali and Aluminum production), the use of electrochemical methods for the production of organic chemicals has been limited, even if their potential impact is significantly larger. In spite of their advantages, organic electrosynthetic processes face common challenges such as limited reactant concentrations in the electrolyte, a complex set of competing organic side reactions, and the narrow electrochemical stability window of aqueous electrolytes.1 The low solubility of organic reactants, together with the use of high current densities that maximize reaction throughput, often result in mass transport limitations that can lower reaction selectivity. As a model case study, this work focuses on the electrohydrodimerization of acrylonitrile (AN) to adiponitrile (ADN), a precursor to Nylon 6,6.2 Although this is considered the largest and most successful organic electrosynthesis implemented in industry, it faces many challenges owing to its limited energy conversion and selectivity. Through a combination of experimental insights and artificial-intelligence-enabled models, we elucidate process intensification guidelines for mass transport enhancement in organic electrosynthesis via electrolyte optimization, complex voltage dosing, and membrane-based electrochemical flow reactors. Moreover, this work explores the development of the sequential electro-hydrogenation of ADN to hexamethylenediamine (HMDA), paving the way for a continuous electrochemical process for the production of Nylon monomers. Our results provide insights on the main challenges faced in organic electrosynthesis, and demonstrate how innovative process intensification approaches can address these challenges and enhance the competitiveness of electrochemical routes for the production of valuable organic chemicals. Blanco, D. E.; Modestino, M. A., Organic Electrosynthesis for Sustainable Chemical Manufacturing. Trends in Chemistry 2019, 1 (1), 8-10.Blanco, D. E.; Dookhith, A. Z.; Modestino, M. A., Enhancing selectivity and efficiency in the electrochemical synthesis of adiponitrile. Reaction Chemistry & Engineering 2019, 4 (1), 8-16.