Advancing Sustainable Nylon Production Through Electrosynthesis—Elucidating Reaction Mechanisms at Electrode Interfaces and Enabling Bio-Derived Polymers

The chemical industry, particularly organic chemical manufacturing, is a significant contributor to global greenhouse gas emissions, with traditional processes relying heavily on fossil fuels and operating under energy-intensive conditions. Transitioning to electrosynthesis offers a promising path for integrating renewable electricity and accelerating the decarbonization of large-scale chemical processes. This is especially relevant in the production of Nylon 6,6, a crucial polymer reliant on adiponitrile (ADN) as a key precursor.<br/>Our research focuses on two critical aspects of sustainable ADN production: (1) improving the performance and understanding of the electrochemical hydrodimerization of acrylonitrile (AN), one of the largest electro-organic reactions practiced in industry, and (2) optimizing the electrochemical synthesis of ADN from biomass-derived precursors.<br/>In the first approach, we investigate the role of tetraalkylammonium (TAA) salts as supporting electrolytes in the electrochemical hydrodimerization of AN. By manipulating the molecular size and concentration of TAA ions, we observed improvements in ADN selectivity and production efficiency, primarily influenced by the mass transport of organic reactants to the electrical double layer (EDL). Combining an electrochemical flow cell with attenuated total reflection Fourier-transform infrared (FTIR) spectroscopy revealed that TAA ions significantly increase the local concentration of AN near the electrode, correlating with improved ADN selectivity. Kinetic isotope effect (KIE) studies and electron paramagnetic resonance (EPR) spectroscopy provide insights into the reaction mechanism, suggesting that hydrogen transfer to AN is a rate-determining step and that ADN production partially occurs through the coupling of free AN radicals in solution.<br/>In the second approach, we propose a sustainable pathway utilizing renewable glutamic acid from protein waste hydrolysis. Glutamic acid is transformed into 3-cyanopropanoic acid (CPA), followed by ADN synthesis via Kolbe electrolysis. Our study employs a hierarchical electrochemical reaction engineering strategy, combining high-throughput experimentation with detailed studies to identify optimal conditions and elucidate factors controlling reaction pathways. Results show that platinum electrodes favor ADN formation, while graphite electrodes promote AN production. Under optimized conditions, a Faradaic efficiency of 40% towards ADN at current densities up to 500 mA cm-2 is achievable.<br/>The guidelines obtained from these studies apply to various electrochemical decarboxylation reactions and AN electrohydrodimerization, informing the development and optimization of sustainable electro-organic manufacturing processes in the chemical industry.