Boosting the valorization of biomass and green electrons to chemical building blocks: A study on the kinetics and mass transfer during the electrochemical conversion of HMF to FDCA in a microreactor

Electrochemical conversion of biomass-derived 5-hydroxymethyl-furfural (HMF) to 2,5-furandicarboxylic acid (FDCA), the building block of bio-based plastics, is an attractive process that leverages renewable electrons and carbon resources. The process offers the potential to increase energy and cost efficiency by combining mild reaction conditions with high activity and selectivity. This study elucidates the mechanism and reaction kinetics of HMF electrochemical oxidation over Ni(OH)2/NiOOH, and their implications on the reactor design. The reaction is studied in a parallel plate electrochemical microreactor using Ni plates as the working and counter electrodes. The work presents mass transfer characterization of the reactor and a thorough parametric study. Nearly complete conversion and current efficiency are obtained at pH 13, cell potential of 1.7 V, and unprecedentedly short residence time of <380s. Taking advantage of the flow microreactor, mass transfer- and reaction- limited regimes are decoupled, and a kinetic model is developed for the first time in the literature. The kinetics model, showing a good agreement with the experimental results, suggested that the reaction proceeds through adsorption of HMF and the intermediates over NiOOH. Finally, the effect of mass transfer characteristics of the reactor on the process is evaluated for various cell configurations.