Insights Provided By Modeling of Electrochemical Hydrogenation and Hydrogenolysis of Furfural on Cu and Side Reactions in Acidic Media

Abstract

Fine chemicals and fuels can be generated by electrochemical methods as an alternative to the currently in place thermocatalytic methods. The thermocatalytic methods require harsher reaction conditions, such as elevated pressures and temperatures, but also requires hydrogen gas as a reactant for reduction reactions which largely is produced by non-sustainable methods which emit high amounts of CO2. Electrochemical methods, in comparison, use in-situ generated protons in lieu of hydrogen gas which reduces the overall CO2 generation. Electrifying the chemical industry will allow for the reduction in anthropogenic CO2 generation by coupling a neutral or negative carbon emitting process with renewable electricity. Furfural (FF) is a biomass derived platform molecule produced at a scale above 300,000 metric tons annually and can used to produce furfuryl alcohol (FA) and 2-methylfuran (MF) through electrochemical hydrogenation and hydrogenolysis (ECH) respectively. FA is a fine chemical that is highly desirable for use in furanic molds, while MF has been identified as a fuel or fuel precursor. In this work, the kinetics of the FF ECH electrochemical system is decoupled and modeled to understand the conversion of FF.In this work, the electrochemical kinetics and non-electrochemical side reactions investigated in our previous works [1,2,3] are modeled to gain further insights into the mass balance and the longer-term phenomena associated with the FF ECH system. The FF ECH system is modeled as three contributing pieces: the ECH reactions, the non-electrochemical side reactions, and the evaporation of MF to the solvent trap for collection. The desired electrochemical reactions were investigated using a 2 compartment H-cell with a Cu flag electrode in the cathode compartment, and connected to a solvent trap held at -15°C. Experimentation was done in 0.1 and 0.5 M H2SO4 with concentrations of FF between 10 and 120 mM FF. The catholyte had a cosolvent of 80:20 vol% water: acetonitrile and was purged with 60mL/min of nitrogen gas. To study the non-electrochemical reactions, vials of electrolyte with FF, FA, and MF in concentrations matching those found in electrochemical experiments were prepared and sample over time without the presence of any electrochemistry. The vial samples over time showed that mass loss occurred for the three furanics, however much more significantly for FA and MF, the two desired products. Lastly, the evaporation of MF from the catholyte to the solvent trap was studied by preparing the H-cell with a known concentration of MF and sampling over time. By modeling the FF ECH system this way, we were able to show the prominence of the competing side reactions and evaporation of MF to the solvent trap which provides insights into the mass balance and performance of the FF ECH system. We find that while the side reactions are more prevalent in the 0.5M H2SO4 than the 0.1M H2SO4, that a higher MF yield is reached due to the evaporation and collection of MF in the solvent trap. A higher FA yield is found in the 0.1M H2SO4 compared to the 0.5M H2SO4.[1] May, Andrew S., Steven M. Watt, and Elizabeth J. Biddinger. "Kinetics of furfural electrochemical hydrogenation and hydrogenolysis in acidic media on copper." Reaction Chemistry & Engineering 6, no. 11 (2021): 2075-2086[2] Jung, Sungyup, and Elizabeth J. Biddinger. "Electrocatalytic hydrogenation and hydrogenolysis of furfural and the impact of homogeneous side reactions of furanic compounds in acidic electrolytes." ACS Sustainable Chemistry & Engineering 4, no. 12 (2016): 6500-6508[3] Jung, Sungyup, and Elizabeth J. Biddinger. "Controlling competitive side reactions in the electrochemical upgrading of furfural to biofuel." Energy Technology 6, no. 7 (2018): 1370-1379