Effects of mesostructured silica catalysts on the depolymerization of organosolv lignin fractionated from woody eucalyptus

• Organosolv lignin was depolymerized with mesostructured silica catalysts.
• Phenolic monomer profiles depended on catalysts, reaction conditions and solvents.
• MCM-41 and SBA-15 were the best two catalysts for the producing of syringol.
• Higher syringol yield was achieved in methanol/water than that in water.
• SBA-15 gave the highest syringol yield (23.0%) in methanol/water (50/50, wt/wt).

Isolated and purified organosolv eucalyptus wood lignin was depolymerized at different temperatures with and without mesostructured silica catalysts (i.e., SBA-15, MCM-41, ZrO2-SBA-15 and ZrO2-MCM-41). It was found that at 300 °C for 1 h with a solid/liquid ratio of 0.0175/1 (w/v), the SBA-15 catalyst with high acidity gave the highest syringol yield of 23.0% in a methanol/water mixture (50/50, wt/wt). Doping with ZrO2 over these catalysts did not increase syringol yield, but increased the total amount of solid residue. Gas chromatography–mass spectrometry (GC–MS) also identified other main phenolic compounds such as 1-(4-hydroxy-3,5-dimethoxyphenyl)-ethanone, 1,2-benzenediol, and 4-hydroxy-3,5-dimethoxy-benzaldehyde. Analysis of the lignin residues with Fourier transform-infrared spectroscopy (FT-IR) indicated decreases in the absorption bands intensities of OH group, CO stretching of syringyl ring and aromatic CH deformation of syringol unit, and an increase in band intensities associated with the guaiacyl ring, confirming the type of products formed.