Lignin Quaternary Ammonium Phosphotungstate as a Recycle Catalyst for Oxidative Cleavage of Unsaturated Fatty Acids and Soybean Oil

Using H₂O₂ for oxidative cleavage of renewable unsaturated fatty acids (UFA) or plant oil is a green method for preparing biobased mono- and dicarboxylic acids. However, due to the insolubility of UFA or oil in water, organic solvents or unrecyclable surfactants are usually needed to promote the contact between substrates and H₂O₂, which does not meet the Sustainable Development Goals. In this work, a series of lignin quaternary ammonium-supported phosphotungstate catalysts has been designed and prepared. Among these catalysts, HPW-AL₆₅₀₀-QAS₁₆ showed the best catalytic activity for the oxidative cleavage of oleic acid (OA) and soybean oil (SBO) using H₂O₂ as the oxidant without a solvent and additive. This lignin-based catalyst afforded 100% OA and SBO conversion and up to 96.2% azelaic acid (AA), 94.6% nonanoic acid (NA) selectivities for OA and 91.8% AA, and 85.2% NA selectivities for SBO. More importantly, the lignin-based catalyst could be easily recovered and reused at least 5 times without a significant loss in its catalytic activity. These characteristics make the oxidative cleavage of OA and SBO more efficient and environmentally friendly, which may be beneficial for industry applications.