Kinetics and Mechanism of Catalytic Oxidation of 5-Methylfurfural to 2,5-Furandicarboxylic Acid with Co/Mn/Br Catalyst

2,5-Furandicarboxylic acid (FDCA), a versatile platform chemical, can be widely used for synthesizing various polymers and has the potential to replace terephthalic acid in the green polymer industry. To replace part of the relatively expensive and chemically unstable 5-hydroxymethylfurfural (HMF), 5-methylfurfural (MF) was used as the starting material for preparing FDCA. The aerobic oxidation of MF to FDCA over the Co/Mn/Br catalyst system was investigated in both batch and semicontinuous reactors with acetic acid as solvent. On the basis of free-radical chain reaction mechanism, a fractional kinetic model was developed to describe the oxidation process of MF to FDCA and the relevant model parameters were determined by data fitting using the least-squares method. Under the same reaction conditions, the FDCA yield of 73.5% and purity of 99.5% were achieved, lower than those of HMF oxidation to FDCA. The influence of stirring rates was evaluated to eliminate the liquid-gas transfer resistance. Furthermore, the effects of substrate concentration, reaction temperature, and catalyst concentration on the reaction rate were investigated systematically. Finally, the developed fractional kinetic model was proved to be reliable for predicting the product distribution satisfactorily by the semicontinuous experiments. The kinetic data and reactor model play an essential role in the optimization for industrially producing FDCA.