Phenolics Production through Catalytic Depolymerization of Alkali Lignin with Metal Chlorides

Lignin is an important renewable source of phenolic products. In this study, alkali lignin was depolymerized to produce phenolic compounds. The effects of catalyst, solvent, reaction time, and reaction temperature on the yields of liquid products and volatile fractions were investigated in detail. Compared with the solvents water and octane, alcohols can significantly promote depolymerization of lignin due to the excellent solubility of the degradation products and intermediates. Under the conditions of 300 degrees C for 2 h in the solvent ethanol, the highest yields of liquid products (75.8 wt%) and volatile fraction (38.1 wt%) were obtained over a ZnCl2 catalyst. Gas chromatograph-mass spectroscopy analysis demonstrated that the volatile fraction was composed of guaiacols (15.09 wt%), phenols (15.79 wt%), and syringols (2.28 wt%). Furthermore, the mechanism for lignin depolymerization is discussed.