Depolymerization of Organosolv Lignin to Valuable Chemicals over Homogeneous and Heterogeneous Acid Catalysts

Study on lignin conversion to industrial-needed chemicals has been recently developing by using acid depolymerization process. In this work, depolymerization of organosolv lignin was investigated at 250 °C for 1 h in methanol with and without presence of homogeneous and heterogeneous acid catalysts. In addition, the effect of reaction temperature (200, 250, 300, and 350 °C) was studied for maximizing the total yields of phenolic compounds. Significant differences in terms of lignin conversion, liquid fraction (oil products), residual lignin (RL) fraction, and solid residue (char) were also observed. The results show that H-Y zeolite (SiO2/Al2O3 = 10) gave the highest lignin conversion (80.70%) and the yields of total aromatic monomers (1.02%) with the maximum product distribution of vanillin (0.40%). Under the conditions of 300 °C for 1 h in the presence of H-Y zeolite (SiO2/Al2O3 = 10), maximum lignin conversion of 92.58% with total phenolic compound yield of 6.02% can be achieved. The individual monomeric phenols composed of 4-ethylguaiacol (1.37%), guaiacol (1.23%), 4-ethylphenol (1.23%), syringol (1.09%), phenol (0.68%), and vanillin (0.22%). These results suggest that catalytic depolymerization of organosolv lignin is a promising way for production of valuable chemicals.