Advances in Continuous Flow Production of 5-(Hydroxymethyl)furfural, 2,5-Furandicarboxylic Acid, 2,5-Diformylfuran, and 2,5-Dimethylfuran

The synthesis of biobased molecules from biomass to produce fine chemicals, fuels, and commodity chemicals offers a sustainable alternative to petrochemical-based products. Biomass is rich in carbohydrates, which can be converted to 5-(hydroxymethyl)furfural (HMF), a highly functionalized platform molecule. Chemical modifications of HMF can yield other valuable molecules such as 2,5-furandicarboxylic acid (FDCA), 2,5-diformylfuran (DFF), and 2,5-dimethylfuran (DMF). FDCA and DFF are typically obtained by the catalytic oxidation of HMF, usually over metal catalysts, and serve as polymer precursors. DMF, which can be blended with gasoline due to its similar octane number and energy density, is produced by the hydrogenation of HMF, typically with the assistance of metallic catalysts. Laboratory-scale synthesis of these platform chemicals has primarily been performed under batch conditions by using various solvents and catalysts. However, scaling up production requires more effort to make synthesis pathways as economical and efficient as petrochemical processes. One promising approach is the use of continuous-flow reactors, which offer advantages in heat and mass transfer. These reactors facilitate the simple separation of products from solid catalysts and can be used for complex reactions. This review focuses on the laboratory-scale synthesis of HMF in continuous-flow reactors and its conversion into platform chemicals, such as FDCA, DFF, and DMF, through oxidation, hydrogenation, and hydrogenolysis reactions.