Construction of Lignin-Based Heterogeneous Acid Catalysts with an Excellent Performance for the Acetalization of Biomass-Based Furfural and Glycerol

Catalytic upgrading of furfural plays a critical role in the synthesis of biofuels and valuable chemicals in biorefineries. Meanwhile, the attention for valorization of the byproduct (i.e., glycerol) from biodiesel production and the byproduct (i.e., lignosulfonate) from the paper industry has been rising rapidly. Herein, a series of lignin-based heterogeneous acid catalysts (i.e., LCA, LoPA, and LoPAS) were prepared from sodium lignosulfonate via different methods and then applied for the acetalization of furfural and glycerol in biobased 2-methyltetrahydrofuran to afford cyclic acetals, which are excellent oxygenated fuel additives. Interestingly, the LoPAS catalyst, prepared by phenol-formaldehyde condensation, ion exchange, and subsequent sulfonation methods, exhibited a remarkable performance at 50 °C for 1 h, giving a 74.2% total yield of cyclic acetals at 77.9% furfural conversion. Based on catalytic results and characterization analysis, the relationships between the catalyst structure/properties and the catalytic performance were elucidated. The high acid density and good hydrophobicity of LoPAS are responsible for its excellent performance. Moreover, the LoPAS catalyst was proved to be universal in the acetalization of various biobased furanic compounds and alcohols. This work merges furfural valorization and high-value utilization of glycerol as well as lignosulfonate in a biobased solvent, which is expected to ignite novel ideas for achieving a fully renewable resource utilization.