Decomposition of a Lignin Model Compound under Hydrothermal Conditions

TLDR

Lignin, the second most abundant aromatic polymer in wood biomass, is a promising alternative source of chemical compounds due to its oxygen‑based functional groups. The study aimed to propose a reaction mechanism for guaiacol decomposition under hydrothermal conditions. Guaiacol was reacted in supercritical water (653–673 K, varying pressures, argon atmosphere) in a batch reactor, and a severity parameter combining temperature and time monitored its decomposition. Decomposition yielded catechol (≈40.7 wt %), phenol (≈14.2 wt %), and o‑cresol (≈4.5 wt %), with higher severity increasing guaiacol consumption and product formation, suggesting the process could underpin efficient wood biomass conversion.

Abstract

Abstract Lignin, which is the second most abundant polymeric aromatic organic substance in wood biomass after cellulose, and contains many oxygen‐based functional groups, has been proposed as an alternative source of chemical compounds. Guaiacol, a model compound for lignin, was reacted in supercritical water using a batch‐type reactor at temperatures of 653–673 K and various pressures under an argon atmosphere. The effects of temperature and reaction time at the same pressure were combined into a single severity parameter that was used to monitor the decomposition of guaiacol to its derived compounds. The main products in aqueous solution were catechol, phenol, and o ‐cresol. The amounts present approached 40.73 wt %, 14.18 wt %, and 4.45 wt %, respectively. With an increase in the reaction time at the same conditions, the amount of guaiacol decreased and the quantity of derived compounds of guaiacol increased. Based on the experimental results, a reaction mechanism for the decomposition of guaiacol was proposed. The process investigated in this study may form the basis for an efficient method of wood biomass decomposition.