Cleavage of Lignin Model Polymers with Copper-Doped Catalysts in Supercritical Methanol

The rapid worldwide increase in the consumption of fuels and chemicals has led to concern over the depletion of non-renewable resources and the environmental impact of their processing and utilization. Lignin, an abundant plant cell wall polymer that is currently treated as waste, is being considered as a renewable feedstock for the production of chemicals due to its high aromaticity. In our previous work, the Cu-doped porous metal oxides (CuPMO) catalyst has been shown to convert lignin into aromatic compounds, which can potentially be used as platform compounds for chemical synthesis. However, secondary reactions (e.g., arene hydrogenation) to lead to a wide distribution of products limited the usefulness of lignin depolymerization. In order to further understand the mechanisms and kinetics of lignin depolymerization over CuPMO catalyst and better control the undesired reactions, we synthesized β-O-4 linked lignin model polymers, depolymerizing those polymers with CuPMO catalyst and supercritical methanol at 300 °C in as a time-series of 1-9 h. The lignin model polymer and the organic liquids produced have been characterized using chromatography, mass spectrometry, and nuclear magnetic resonance. This suite of analytical methods was conducted in an effort to establish the reaction networks occurring during lignin depolymerization and understand the effect lignin molecular weight and topology has on its depolymerization.