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

TLDR

Lignin from candlenut was depolymerized in methanol under H₂ pressure using a Cu‑doped porous metal oxide catalyst derived from a hydrotalcite‑like precursor, with GPC monitoring and NMR characterization of the resulting products. The Cu‑PMO catalyst achieved >90 % lignin conversion and >70 % methanol‑soluble product yield, producing high‑yield aromatic mixtures—including selective C9 catechols and 4-(3‑hydroxypropyl)-catechol—without char formation across 140–220 °C.

Abstract

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.