Insights into membrane-separated organic electrosynthesis: the case of adiponitrile electrochemical production

Abstract

Organic electrosynthetic processes are key players in the integration of renewable energy in chemical manufacturing, but face important challenges in selectivity and energy efficiency. Although membrane-separated flow reactors can help address these issues, a deeper understanding of membrane behavior in organic-containing electrolytes is required. We evaluate the effect of organic reactants on the conductivity and permeability of one cation exchange membrane (Nafion 117) and two anion exchange membranes (Sustainion and Fumasep FAB), to later assess the advantages of their implementation in flow reactors for the electrohydrodimerization of acrylonitrile to adiponitrile – the largest organic electrosynthesis in industry. The presence of organic molecules led to important losses in membrane conductivity, however no significant contribution to reactor overpotential was observed from their implementation in membrane-separated reactors. Furthermore, permeabilities between 0.4–1.2 × 10⁻⁶ cm² s⁻¹ towards organic molecules led to low crossover of organics and improved reactor selectivity. Undivided reactors yielded selectivities as high as 48% (40 mA cm⁻² and 4 V), while selectivities of 77% (20 mA cm⁻² and 2.7 V) and 81% (40 mA cm⁻² and 3 V) were obtained with Nafion and Sustainion-separated reactors, respectively. The demonstrated improvement in energy efficiency for continuous organic electrosynthetic processes makes the insights from this work a significant step in the development of sustainable electrochemical manufacturing processes.