Catalytic Hydrodepolymerization Of Lignin To Produce High Value Added Chemicals

Under the"double-carbon"strategy,biomass as an abundant,renewable carbon-neutral resource has attracted people’s attention.Biomass is mainly composed of cellulose,hemicellulose and lignin.Hemicellulose and cellulose have been well industrialized due to their simple structures.While lignin is a three-dimensional polymer,and its complex structure hinders its industrial application.At present,lignin is still far from industrial application,and the main problem is that the products of lignin depolymerization are various,low selectivity and low yield.In view of the above problems in the utilization of lignin,in this paper,the hydrodepolymerization behavior of corncob lignin in alcohol solution was studied,and the hydrodepolymerization rule of corncob lignin in different solvents such as alkane or water was studied.Dual-function hydrodeoxygenation catalysts with ruthenium and solid acid were constructed,which can directly convert lignin into high-quality bio-based fuel and high value-added chemicals in aqueous solutions.The hydrodeoxygenation of Ru and solid acid bifunctional catalysts not only reduces the complexity of the lignin conversion process and increases the possibility of scale-up of lignin biorefinery,but also provides evidence for the existence of polycyclic structures in lignin.The main research contents and conclusions of this paper are as follows:（1）Based on the rich oxygen-containing functional groups contained in the corncob lignin structure,the catalytic hydrogenation of Ru-based catalysts and the hydrogen donation of alcohol solvents were used to depolymerize lignin into phenolic compounds.At 250^oC,the most phenols（12.7 wt%）could be obtained in ethanol.In addition,4.6 wt%aromatic esters and 2.0 wt%aromatic acids were also obtained.And 1.0 wt%tetralin was detected in the depolymerized products.Combined with the results of ¹³C NMR,we speculated that there were polycyclic structures in lignin.（2）There are also significant differences in the effect of different types of solvents on the hydrodepolymerization of lignin.When alcohols or epoxy compounds were used as solvents,the depolymerization products of lignin were mainly oxygen-containing aromatic compounds.Ru-based catalysts can only break the bonds between the lignin structural units,but have no ability to remove oxygen-containing side chains on the aromatic ring body.However,when alkanes or water were used as solvents,the depolymerization products of lignin were mainly cycloalkanes and arenes.At this time,the Ru-based catalyst showed strong deoxygenation ability.（3）In order to further promote the conversion of corncob lignin,dual-function hydrodeoxygenation catalysts with ruthenium and solid acid were designed to realize the hydrodeoxydepolymerization of lignin.At 280^oC,lignin could be directly converted into hydrocarbon compounds（32.5 wt%）,mainly including methylcyclohexane（2.9 wt%）,ethylcyclohexane（9.4 wt%）and propyl-cyclohexane（6.2 wt%）.After hydrodeoxydepolymerization of lignin,the polarity and boiling point of the depolymerization products were greatly reduced,and the presence of saturated fused ring compounds in the depolymerization product was directly observed by GC-MS,which further proved the existence of polycyclic structure of lignin.