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.