Modeling Competing Kinetics between Electrochemical Reduction of Furfural on Copper and Homogeneous Side Reactions in Acid

The understanding of electrochemical reactions for the hydrogenation and hydrogenolysis (ECH) of biomass derived species is important to design and adapt electrochemical reactors to generate desired chemicals sustainably at high yield. In this work, the ECH of furfural (FF) over Cu foil catalysts to furfuryl alcohol (FA) and 2-methylfuran (MF) was studied in a two-compartment semibatch reactor in acidic electrolytes (0.1 and 0.5 M H2SO4) with nitrogen sparging. We found that FA and MF underwent side reactions that follow first order kinetics with respect to the FA and MF concentrations in 0.1 M H2SO4 and 0.5 M H2SO4. MF evaporation from the catholyte in the presence of nitrogen sparging followed a first order dependence with the concentration of MF in the catholyte. Our previous work showed the ECH of FF over Cu followed noncompetitive Langmuir–Hinshelwood models. A kinetic model was developed to consider the electrochemical reactions, nonelectrochemical side reactions, and the evaporation of MF to investigate the competition between these three contributions to the mass balances. Insights were provided by using the model to consider two hypothetical cases where 1) evaporation of MF did not occur, and 2) side reactions did not occur, and a third realistic case where evaporation of MF and side reactions occurred. The model showed that without gas sparging promoting MF evaporation, 81.5% of products were undesirable at 98.5% FF conversion in 0.5 M H2SO4, and 30.6% of products were undesirable in 0.1 M H2SO4. N2 sparging in the catholyte lowered the concentration of MF in the catholyte with a corresponding increase to the concentration in the solvent trap, where side reactions did not occur, allowing for increased MF yields. We showed that despite the faster side reactions to MF in 0.5 M H2SO4 compared to 0.1 M H2SO4, a higher yield to MF was reached in 0.5 M H2SO4 than in 0.1 M H2SO4 due to the beneficial impact of nitrogen sparging and the higher electrochemical production rate of MF.