Study On Magnetic Catalyst For Catalytic Hydrogenolysis Of Lignin In Alkaline Aqueous System

Lignocellulose is a kind of abundant biomass material obtained from plant on the earth,it consists of cellulose（30-50%）,hemicellulose（20%-40%）and lignin（15%-25%）,some little protein and lipid were also contained.Lignin is the second abundant natu ral polymer material in the plant produced by photosynthesis,formed by the three bas ic Phenylpropanoid units（4-hydroxy-3-methoxyphenylpropane,3,5-dimethoxy-4-hydroxyp henylpropane,4-hydroxyphenylpropane）,the chemical bond between the units are C-O bond and C-C bond.Lignin depolymerization for small molecules production is a kind of popular and potential method to make good use lignin materials,but the traditiona l chemical depolymerization methods are usually high-cost and low-yield.In order to utilize lignin well for the renewable material and energy,we had investigated a high-e fficient and low-cost method for lignin hydrogenolysis.In our experiment,we had obt ained a high monomeric yield with recyclable catalyst in mild reaction condition,we also deduced the reaction mechanism of lignin hydrogenolysis in our reaction conditio n.We synthesized a magnetic catalyst for lignin hydrogenolysis.Loading the traditional noble atom on the surface of the magnetic Fe₃O₄ particles to make a magnetic catalyst Pd@Fe₃O₄.The characterizations of XRD,XPS,SEM indicates that the palladium atom had been loaded on the surface of Fe₃O₄ successfully and the AAS characterization shows that the loading rate of Pd atom is 8.54%.The lignin model compound and bagasse lignin can been depolymerized successfully by using this catalyst.The magnetic catalyst can be separated from the reaction solution easily by extern magnet after applying the Pd@Fe₃O₄ in the reaction.The separated catalyst can be reused for 5 times in lignin hydrogenolysis after simple wash.Lignin hydrogenolysis was performed in the alkaline aqueous,we found the C-O bond in bagasse lignin disappeared through comparing the HSQC picture of bagasse lignin and bagasse lignin hydrogenolysis product,a high monomeric yield（36.4%）was obtained in this reaction system.The sodium hydroxide solution used can promote the lignin’s dissolve and raise the yield of monomers.The hydrogen source was provided by sodium formate because sodium formate can transferred into CO₂ and H₂ after heat.Compared with traditional method,using sodium formate as reducing agent has the advantages of safe and convenient operation.We investigated different reaction temperature and reaction time’s effect on monomer yield,a suitable condition was obtained（150℃,6 h）.We also investigated the reaction mechanism of lignin hydrogenolysis in this condition by using lignin model compound,a possible mechanism was brought up.We divided the lignin hydrogenolysis’s products into 3 parts like alkyl monomers,carboxylic monomers and other monomers（aldehyde,ketone and alcohol）according to their function group on the side chain of benzene.We tried to use simple extraction method to separate each kind of monomers from the products in order to make good use of the produced monomers in the future.We tried to separate the monomers from the mixture by using different solvent（ethyl acetate,hexane）to extract monomer from aqueous with different pH value.Using the EtOAc as the extraction agent can separate the carboxylic monomers from the mixture of the monomeric products when the aqueous solution’s pH value is 8 and the using the hexane as extraction agent can separate alkyl monomers from the mixture of monomeric products when the aqueous solution’s pH value is 10.The separated monomers can be utilized better because of their similar function group.Magnetic catalyst’s usage solved the problem of catalyst’s separation and recycle,a high monomeric yield（36.4%）and low reaction cost were achieved by using alkaline aqueous as reaction’s solvent,the monomeric product’s separation by simple extraction method make the utilization of lignin hydrogenolysis’s products possible.Above all,we optimized the whole procedure of lignin hydrogenolysis in order to make good use of lignin.