Oxidative lignin depolymerization using metal supported hydrotalcite catalysts: Effects of process parameters on phenolic compounds distribution

Abstract

High-value utilization of lignin is crucial in further developing biomass refining processes and producing biofuels/chemicals. In this work, lignin depolymerization was examined in a series metal such as Cu, and Co supported on MgAl2O4 hydrotalcite (HT) support catalysts. Different process parameters such as reaction temperature, reaction time, solvents, catalysts amount and reaction environments was evaluated for the selective breaking of the lignin. The structure and morphology of the prepared catalysts were fully characterized by XRD, BET, ICP, TEM, and TPD, methods. Maximum bio-oil was found 72.0 wt% with 10 wt% Co/HT catalyst under inert (N2) atmosphere under methanol solvents at 120 °C for 60 min. reaction time. Whereas when used O2 as reaction environment, the selectivity of the acetosyringone (65%) significantly enhanced with Cu-Co/HT catalyst compared to the nitrogen environment (40.5% with Co/HT) and without catalytic reaction (24.3%). Carbon content remarkably increased in all catalytic liquefaction bio-oils as compared to raw lignin and non-catalytic bio-oil. Higher carbon content (68.5%) was found with Co/HT as compared to no-catalytic and Co-W/HT liquefaction bio-oil. Catalysts stability test showed excellent recyclability. Therefore, in the oxidative environment with the catalysts, lignin was depolymerized into value-able phenolic monomer products.