Synthesis And Depolymerization Of Lignin Model Compounds

Lignin as macromolecular polymer is rich in aromatic ring units,making the most of lignin can effectively alleviate the dilemma of increasing exhaustion of fossil energy,and lignin can be a source of renewable aromatic compounds by depolymerization reaction of it.However,due to the complex structure of lignin,and a large number of carbon-carbon bonds will be generated during the extraction process,the chemical properties of lignin will be more stable,so the depolymerization of lignin will become more difficult.Therefore,the design,synthesis and depolymerization of lignin model compounds and the depolymerization of Kraft lignin by different catalytic conditions have been studied in this paper.The main research contents and results are as follows:(1)β-5 dimeric lignin model compound was synthesized from isoeugenol;aβ-O-4 dimeric model compound was synthesized by six-step reaction using 3-methoxy-4-hydroxyacetophenone as the raw material,the β-O-4 bond is the most abundant bond in lignin;a novel tetrameric model compound was synthesized from acetylbiphenyl as a raw material,this compound contains four different bond types:α-O-4,β-O-4,β-5 and 5-5 bonds.The structures of the above three model compounds were characterized by gas chromatography-mass spectrometry(GC/MS)and nuclear magnetic resonance spectroscopy(NMR).The molecular weights and the structures of these compounds were consistent with the target products;(2)According to the different bond types of the model compounds,suitable catalysts(such as Ru/C,Ru/MgAl2O4,NiW/C,FeOOH/C,Pt/Al2O3,etc.)and optimal reaction conditions were used to depolymerize the above three model compounds.The depolymerization products were analyzed by gas chromatography-mass spectrometry.The results showed that the β-5 bond was completely broken under the severe reaction conditions of FeOOH/C catalyst,while the a-O-4 bond andβ-O-4 bond can be broken under all the catalytic reaction conditions.But the catalysts used in this paper could not break the 5-5 bond in the tetrameric model compound;(3)The depolymerization process of Kraft lignin were carried out by Ru/C,NiW/C and FeOOH/C as catalysts,and the depolymerization products were analyzed by GC/MS.The results showed that the depolymerization ability of the three catalysts drop successively from FeOOH/C,Ru/C to NiW/C.And the FeOOH/C catalyst can break the carbon-carbon bond in lignin,which is consistent with the conclusion of the depolymerization of lignin model compounds.