Sustainion® Outperforms Nafion And Fumasep FAB

Sustainion® Membranes create a more facile route for the electrochemical production of Adiponitrile – the largest organic electrosynthesis in industry

Sustainion® outperforms other commercial membranes (Nafion and Fumasep FAB) in the electrohydrodimerization of acrylonitrile to adiponitrile

The electrosynthesis of ADN is the largest-volume organic electrochemical transformation – accounting for >500 K tons of ADN production annually. Significant advances on ion-conducting membranes was the motivation for this study titled “Insights into membrane-separated organic electrosynthesis: the case of adiponitrile electrochemical production” recently published in Reaction Chemistry & Engineering. They wanted to check if using state of the art ion exchange membranes in the aforementioned organic flow reactors could yield to better performance.

Specifically, 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) was evaluated. Permeabilities between 0.4–1.2 × 106 cm2 s1 towards organic molecules led to low crossover of organics and improved reactor selectivity. Undivided flow reactors exhibited charge transport limitations and parasitic redox reactions leading to 48% reactor selectivity (40 mA cm−2 and 4 V).

In the case of Nafion membranes, the addition of dilute organic concentrations leads to a decrease in the size of ion-conducting domains, which results in a drop in conductivity. As the concentration of organics increases, these domains are expanded, increasing membrane conductivity. Correspondingly, selectivities of 77% (20 mA cm2 and 2.7 V) were obtained with Nafion separated reactors.

The two AEMs tested, Sustainion and Fumasep FAB, display a similar trend on conductivity, but Sustainion had the weakest conductivity dependence on organic concentration and correspondingly recorded the best at 81% (40 mA cm−2 and 3 V). Overall, Sustainion led to a lower cell resistance than the FAB membrane, which is likely the result of Sustainion’s higher ionic conductivity in organic containing electrolytes.

Fig. 1 Effect of AN concentration on membrane conductivity for Sustainion and Fumasep FAB AEMs at 25 °C. The electrolyte contained 0.5 M Na3PO4, 0.02 M TBA hydroxide, and 0.03 M EDTA.

The permeability of organic species was low which also helps explain the improved selectivity with respect to undivided reactors. The demonstrated improvement in energy efficiency for continuous organic electrosynthetic processes especially when in conjunction with using an AEM such as Sustainion makes the insights from this work a significant step in the development of sustainable electrochemical manufacturing processes.

(a)    Steady state polarization curve and (b) selectivity obtainedwith AEM-separated flow reactors (the standard deviation on all thereported selectivity was <4%). The catholyte contained 0.6 M AN, 0.5M Na3PO4, 0.03 M EDTA, and 0.02 M TBA hydroxide, while the anolyte consisted of 1 M NaOH

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