Valorization of waste lignin: Efficient and steady production of liquid fuels

Efficient lignin depolymerization is crucial in the generation of valuable liquid fuels and mono-phenols for enhancing the utilization and sustainability of biomass resources. However, the complicated three-dimensional structure of lignin, the propensity for intermediate products to condense, and an overreliance on high-pressure hydrogen in depolymerization reactions pose major challenges. In this regard, we prepared a La and Ru modified Y zeolite (Ru2La0.5/HYo) and employed isopropanol (IPA) as an in situ hydrogen donor for the efficient conversion of lignin without requiring an external hydrogen source. Ru2La0.5/HYo selectively activates and decomposes IPA, constantly liberating H2 for lignin degradation. The Ru-mediated synergy between the L-acid and hydrogenation active sites stabilizes the active intermediate and inhibits condensation, thereby balancing the depolymerization and condensation rates. La coordination with the alumina in the molecular sieve limits Al leaching, preventing zeolite deactivation during the reaction and enabling lignin depolymerization to proceed steadily. After four consecutive trials, no significant decline in activity is unobserved. After a 12 h reaction at 290 degrees C, the oxygen content dropped from 29.69 % to 15.47 %, and the higher heating value (HHV) improved from 25.41 to 34.65 MJ/kg. Extending the period to 24 h resulted in a 93.80 % yield of liquid product and a 63.68 % yield of petroleum ether soluble (PES) product, allowing lignin to be upgraded for liquid fuels generation.