Hydroxymethylfurfural as an Intermediate of Cellulose Carbonization

Hydrogen bond donor solvents such as aromatic solvents inhibit the secondary degradation of cellulose‐derived primary pyrolysis products. In a previous study, we found that the formation of solid carbonized products was completely inhibited during cellulose pyrolysis in aromatic solvents, with 5‐hydroxymethylfurfural (5‐HMF) recovered in certain yields instead. This indicated that 5‐HMF is an intermediate in cellulose carbonization. To confirm this hypothesis, the thermal reactivity of 5‐HMF was investigated. At 280 °C, pure 5‐HMF polymerized into a hard glassy substance through OH group elimination, but further conversion was slow. When pyrolyzed in the presence of glycerol, a model of coexisting primary pyrolysis products from cellulose, a coupling reaction proceeded. Reactions characteristic of cellulose carbonization then occurred, including the formation of acidic groups and benzene‐type structures in the solid products. These results confirmed the above hypothesis. The molecular mechanism of cellulose carbonization is discussed, focusing on the crystalline nature.