Pretreating lignin with diverse nitrogen sources for the efficient conversion of lignin via microwave-assisted depolymerization

Expanding the range of monomers prepared by lignin depolymerization is of great importance to achieving sustainable and high-value biorefineries. However, there is a trade-off between the fast conversion technology and the slow conversion pathway from lignin to high-value chemicals. Herein, we use microwave-assisted depolymerization technology with low energy consumption and fast reaction speed, and use different nitrogen sources to achieve target liquid products. Different pretreatment strategies modify the dielectric properties of lignin, boosting liquid product conversion efficiency and enhancing biochar application value. Microwave-assisted depolymerization of ammonium paratungstate-lignin mixtures yields substantial amounts of phenols and nitrogenous compounds. Multi-physic field coupled finite element simulations and kinetic analyses revealed that the dielectric disparity between ammonium paratungstate and lignin particles under microwave irradiation triggers a potent interfacial polarization effect. This effect substantially elevates the depolymerization temperature. Additionally, the incorporation of ammonium paratungstate notably decreases the reaction activation energy from 30.15 kJ mol−1 to 25.16 kJ mol−1, thereby enhancing the depolymerization efficiency. This approach enables the one-step conversion of lignin to nitrogen-containing monomers (pyridine, quinoline, aniline) through reactions between lignin side chains/phenolic monomers and amines, offering a viable route for lignin valorization and guiding future production of high-value lignin-derived monomers.