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

Abstract

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 twocompartment semibatch reactor in acidic electrolytes (0.1 and 0.5 M H 2 SO 4 ) 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 H 2 SO 4 and 0.5 M H 2 SO 4 . 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 H 2 SO 4 , and 30.6% of products were undesirable in 0.1 M H 2 SO 4 . N 2 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 H 2 SO 4 compared to 0.1 M H 2 SO 4 , a higher yield to MF was reached in 0.5 M H 2 SO 4 than in 0.1 M H 2 SO 4 due to the beneficial impact of nitrogen sparging and the higher electrochemical production rate of MF.

Speciation of potential-dependent fouling on copper foil electrodes during electrochemical hydrogenation and hydrogenolysis of furfural in strong acid

“…This decrease in selectivity was due to the rate of homogeneous side reactions exceeding the rate of FA production. 19 At −700 mV RHE, the selectivity towards MF dropped early on during ECH1 but then remained constant. The selectivity of MF after 30 minutes on ECH1 was 28.2% and dropped to 22.8% at 3 hours.…”

“…The mass balance is the accounting of quantified products FF, FA, and MF, and did not reach 100% due to homogeneous acidic side reactions or fouling. 15,17,19,20 Fig. 2a–c shows that the mass balance closure at −560 mV RHE decreased with time throughout ECH, but the decrease was less severe with subsequent ECH.…”

“…This was because the side reactions were concentration dependent. 19,20 At the end of ECH, the mass balance was found to be 65.9%, 73.7%, and 82.9% when run at −560 mV RHE with consecutive use. A similar trend was shown when ECH was run at −700 mV RHE (Fig.…”

Recent Advances in Metallic Catalyst Materials for Electrochemical Upgrading of Furfurals to Drop‐in Biofuels: A Mini Review

“…electrolytes; however, these reactions can lead to side effects such as the polymerization of furanic compounds. [28,66] This section focus on the polymerization of furanics and its implications will be elucidated.…”

“…Unambiguously, the electrocatalytic reactions of Furfural and 5‐HMF in metallic electrodes to produce biofuels require acidic electrolytes; however, these reactions can lead to side effects such as the polymerization of furanic compounds. [ 28,66 ] This section focus on the polymerization of furanics and its implications will be elucidated.…”