Structural characterization of the solid residue produced by hydrothermal treatment of sunflower stalks and subsequent enzymatic hydrolysis

• After hydrothermal treatment and enzymatic hydrolysis, the solid residues were chemically characterized.
• Ethanol extractives from the solid residue were composed of more than 90% lignin.
• With increasing temperatures, cleavage reactions related to side chain and aryl ether linkages of lignin appeared to be promoted.
• Organic solvent-soluble lignin from 200 °C-solid has higher phenolic hydroxyl groups.
• And, its average molecular weight was lower than that of 180 °C-solid.

This study was to structurally characterize solid residues obtained from sunflower stalks hydrothermally treated at 180 and 200 °C for 30 min, followed by enzymatic hydrolysis. Recovered solid residue were 25.3% and 24.1% of fresh biomass, respectively. Each ethanol soluble fraction could be obtained up to 30% of the solid residue. The fraction from the solid residue at 200 °C was composed of smaller-sized lignin macromolecules with higher phenolic hydroxyl group, but lower aliphatic hydroxyl due to enhanced cleavage reactions related to side chain and aryl ether linkages of lignin, compared to that of the solid residue at 180 °C.