Study On The Selective Cleavage Of C-O Bond Of Lignite Model Compounds Over Precious Metal Loaded Carbon Catalyst

Lignite retains the lignocellulosic structure of coal-forming plants to a large extent,and the aromatic ring condensed structural units are rich in aromatic ether C-O bridge bonds.These aromatic ring structural monomers are high value-added chemicals.Selective cleavage of aryl ether bonds through catalytic hydrogenation is expected to achieve high added value utilization of lignite.In this thesis,the lignite model compounds are used as research objects,and the catalytic hydrogenolysis performance and reaction mechanism of Pd,Ru and Ni supported on activated carbon on model compounds under different H-sources are investigated.Then,the liquid product obtained from the thermal dissolution of lignite was subjected to catalytic conversion.The composition and relative content of light components in the products before and after the catalytic reaction were analyzed,which provided a theoretical basis and technical support for the preparation of chemicals by hydrocracking of lignite.The comparison of the catalytic hydrogenolytic activity of Pd/AC,Ru/AC and Ni/AC on the model compound benzylphenyl ether?BPE?indicted that the catalytic activity of the noble metals Pd,Ru were significantly higher than that of Ni.It was found that the C-O bond in BPE could be selectively cleaved at room temperature?25 ^oC,0.1 MPa H₂,2 h?.And the yields of the target products,toluene and phenol,were both 100%.The source of active hydrogen in the reaction system was investigated and it was found that at room temperature,all active hydrogen in the system came from H₂.The reaction mechanism of Pd/AC cleavage of C-O bond in BPE at room temperature was proposed:H₂ adsorbed on the Pd site to form active hydrogen radicals?H·?,and then H·reacted with oxygen atoms in BPE,leading to the C-O bond cleavage to produce toluene and phenol.Due to the very mild reaction conditions,it was not enough to hydrogenate the benzene ring.A series of Ru-based catalysts were synthesized by impregnation method,and the catalysts were characterized by BET,XRD and TEM.The results showed that AC has a more developed pore structure,Ru is uniformly dispersed on AC,and the metal particles are smaller.Therefore,Ru/AC showed higher catalytic activity in hydrogenolysis process.In addition,the investigation of different H-sources in the system found that the hydrogenation of benzene ring was serious when H₂ as the H-source.However,the hydrogenation of benzene ring was not obvious when isopropanol?solvent?as the H-source,and the yield of aromatic ring was significantly higher than that of H₂.When the two react together as H-source,all the model compounds reached 100%conversion,which was higher than the conversion when the two react were separately as the H-source,but the benzene ring in the product was severely hydrogenated,and the target product phenol was completely hydrogenated to cyclohexanol.It indicted that in this catalytic reaction,H₂ and isopropanol had a synergistic effect on active hydrogen supply.The reaction mechanism for cleavage of C-O bond in BPE under two different H-sources were proposed:H₂ adsorbs on the Ru site to form H·.Due to the high activity and concentration of H·,not only will it react with the oxygen atoms in BPE to cause the C-O bond cleavage,but also will undergo a hydrogenation reaction with the benzene rings.Isopropanol adsorbs on the Ru site to form H⁺.It tends to react with oxygen atoms to cleave the C-O bond,so that the reaction path eventually tends to hydrogenolysis rather than hydrogenation.Pd/AC and Ru/AC were used in the catalytic hydrogenation of lignite thermal dissolution product.It was found that the relative content of light components in catalytic upgrading product increased significantly.The highest content was aromatics,mainly including benzene,naphthalene,anthracene,phenanthrene and some of their hydrogenation products.It indicted that the catalyst has significant catalytic depolymerization effect on lignite lignite thermal product.Under H₂ conditions,the yield of benzene ring hydrogenation in oil was higher than that under Ar conditions,indicated that H₂ and isopropanol had a synergistic H-donor effect.The relative content of phenols and their hydrogenation products in the product after catalysis was higher than that in the thermal dissolution oil,indicated that the catalyst could effectively cleave the C-O bonds in the macromolecular structure of lignite.The paper has 22 pictures,13 tables,113 references.