Base catalyzed depolymerization of lignin: Influence of organosolv lignin nature

Three different lignins obtained from olive tree pruning by organosolv processes (acetosolv, formosolv and acetosolv/formosolv) were depolymerized by alkaline hydrolysis in a batch reactor to produce high value added compounds. Obtained products (oil, coke, residual lignin and gas) were measured and analyzed determining their composition and yield in order to study the changes of the depolymerization process for different organosolv lignin samples. For this purpose, different analytical methods were used (gas chromatography/mass spectroscopy, high performance size exclusion chromatography, pyrolysis–GC–MS, MALDI-TOF). Acetosolv lignin and acetosolv/formosolv lignin gave the highest yield of desired product with 18.48 and 16.25% of oil yield respectively. However, formosolv lignin had the highest proportion of monomeric phenolic compounds in the oil (28.19%). Catechol and its derivatives were the main products in all studied cases, but they were more abundant in the case of formosolv lignin depolymerization. Otherwise, the residual lignin formed during the repolymerization process was the same in both, yield and nature, for all cases.