Depolymerization of organosolv lignin to aromatic compounds over Cu-doped porous metal oxides

Isolated, solvent-extracted lignin from candlenut (Aleurites moluccana) biomass was subjected to catalytic depolymerization in methanol with an added pressure of H₂, using a porous metal oxide catalyst (PMO) derived from a Cu-doped hydrotalcite-like precursor. The Cu-PMO was effective in converting low-molecular weight lignin into simple mixtures of aromatic products in high yield, without char formation. Gel permeation chromatography was used to track changes in molecular weight as a result of the catalytic treatments and product mixtures were characterized by ¹H and ¹³C NMR spectroscopy. In the temperature range 140-220 °C, unusual C9 catechols were obtained with high selectivity. Lignin conversion of >90% and recovery of methanol-soluble products in yields of was >70% was seen at 180 °C with optimized catalyst and biomass loadings. At 140 °C, 4-(3-hydroxypropyl)- catechol was the major product and could be isolated in high purity.