Depolymerization of Different Organosolv Lignins in Supercritical Methanol, Ethanol, and Acetone To Produce Phenolic Monomers

Olive tree pruning was delignified by organosolv processes (acetosolv, formosolv, and acetosolv/formosolv) to extract different lignins. The obtained lignins (acetosolv lignin (AL), formosolv lignin (FL), and acetosolv/formosolv lignin (AFL)) were depolymerized using three different solvents (methanol, ethanol, and acetone) under supercritical conditions in a batch reactor to produce high value-added compounds. The recovered products (oil, char, and residual lignin) were analyzed in order to determine their composition and to know the influence of employed solvent and lignin. Lignin was successfully depolymerized in all cases, and the molecular weight of residual lignin was significantly reduced compared to raw lignin. The obtained oil had numerous phenolic monomers, with syringol and guaiacol being the main products in all studied cases. Depolymerization of AFL led to maximum yield of oil (38.04%), and acetone was the best solvent in terms of phenolic monomers production.