Understanding acid-catalysed lignin depolymerisation process by model aromatic compound reaction kinetics

Benzyl phenyl ether (BPE) was used as a model compound to study the mechanism of the α-O-4 bond cleavage in lignin. The selection of solvent (methanol, ethanol, γ-valerolactone, water), catalyst loading (0.5–1.5 wt% of H2SO4) and the effect of the reaction temperature (160–200 °C) on the acidolysis, performed in a batch reactor under an inert atmosphere, were considered. A mathematical model including thermodynamics and reaction kinetics was developed to describe the experimental data and to obtain relevant kinetic parameters. The results indicate that a nucleophile in the system inhibits the tendency of oligomerisation in acidified medium and is one of the decisive factors in determining the ratio between nucleophilic substitution and condensation reactions as well as the ratio between alkoxylated and hydroxyl group bearing products. The reaction rate was linearly dependent on the catalyst loading in aliphatic alcohols, while the temperature dependence was in accordance with the Arrhenius equation.