Improving base catalyzed lignin depolymerization by avoiding lignin repolymerization

Base catalyzed depolymerization was studied to revalorize lignin into monomeric phenolic compounds focusing in avoiding repolymerization phenomenon in order to improve oil yield. In this sense, two capping agents were evaluated in the oxidation of organosolv olive tree pruning lignin. Lignin to capping agent ratio was varied in order to establish its influence on phenolic oil yield and composition. The obtained phenolic products (oil) and by-products (char and residual lignin) were characterized to determine their composition and yield. Boric acid and phenol behaviors were completely different concerning their effect on the nature of the obtained products and on products yields. Boric acid avoided repolymerization although the active fragments seemed to prone to char formation instead of increasing oil monomeric compounds yield. Interestingly, phenol capping agent was proved to favor phenolic compounds production and at the same time, to avoid repolymerization phenomenon. The optimum capping agent to lignin ratio depended on the nature of the added capping agent since their action in lignin base catalyzed depolymerization was totally different.