Highly Selective Conversion Of Lignin And Its Model Compounds Into Aromatic Chemicals

The depletion of fossil fuels and the growing demand of energy and chemicals necessitate the research of renewable energy.Biomass is the only renewable organic carbon resource in nature,which holds advantages in producing value-added products and fuels.As an important component of biomass,lignin accounts for 10-35%by weight,and up to 40%by energy in biomass.However,due to its complex structure and the robust bonds,only a small fraction of lignin has been utilized in low-value commercial applications.Effective cleavage of C-O bond in lignin and its model compounds is of great importance for the transfomation of lignin into high-value platform chemicals and fuels.In chapter 2,the transformation of guaiacol,a dominated lignin model compound,at 300 ^oC in supercritical alcohol system over H₂WO₄ is investigated.The conversion is complete and 16.7%aromatic ethers as well as 80.0%alkylphenols are obtained.Tert-butylphenols are main products with a high selectivity.The total selectivity of 2,6-di-tert-butylphenol and 2,6-di-tert-butyl-4-ethylphenol is as high as 63.7%,which accounts for almost 88.7%of the tert-butylphenols in the product.We examine the reaction system and the catalyst in detail and propose the possible reaction pathways.The results indicate that WO₃ plays a key role on the conversion of guaiacol.At the same time,the acid sites on the H₂WO₄ catalyst favor the production of tert-butylphenols.In chapter 3,WO₃/γ-Al₂O₃ catalyst is prepared by incipient-wetness impregnation method,and is applied to the depolymerization of enzymatic hydrolysis lignin in supercritical ethanol.It is found that the enzymatic hydrolysis lignin is transformed into aromatic ethers,alkylphenols and aromatic esters.Compared with WO₃ and H₂WO₄ catalysts,WO₃/γ-Al₂O₃ catalyst shows a higher activity.In addition,ethanol is the most effective solvent for the lignin depolymerization.Recycle tests show that the WO₃/γ-Al₂O₃ catalyst keeps a high catalytic activity even though it was repeated after used for three times.