Design Guidelines for Membrane-separated Organic Electrosynthesis: The Case of Adiponitrile Production
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The on-going efforts to transition from thermal to electricity-driven processes can enable the easy integration of renewable energy sources and sustainable practices in chemical manufacturing. Organic electrosynthetic processes are key players in this transition, but face important challenges regarding selectivity and energy efficiency. Although membrane-separated flow reactors can help address these issues, a deeper understanding of membrane behavior in organic electrosynthesis electrolytes is required. In this study, 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), and later assess the advantages of their implementation in flow reactors for organic electrosynthesis. This is done in the context of 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 x 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 electrosynthesis processes makes the insights from this work a significant step in the development of sustainable electrochemical manufacturing processes.