Research On Aromatization Of Methyl Vinyl Ether On Cu/Al₂O₃ And HZSM-5 Catalysts

Aromatic hydrocarbons are a significant class of basic chemical raw materials,primarily produced from petroleum and coal at present.Over the past decade,China has actively promoted the development of the coal chemical industry.Industrialization of coal-to-olefin processes using methanol as an intermediate has achieved remarkable success.Breakthroughs have also been made in methanol-to-aromatic hydrocarbon.Furthermore,the acetylene-based chemical synthesis utilizing calcium carbide remains the mainstay of polyvinyl chloride production in China.Our team’s preliminary research demonstrates that methanol and calcium carbide can efficiently synthesize methyl vinyl ether（MVE,CH₂=CHOCH₃）under mild conditions.MVE contains both C=C bonds and aliphatic ether bonds.The oxygen atom in the aliphatic ether bond,with non-bonding electrons,engages in a p-πconjugation with the C=C bond,forming resonating structures with activeαandβcarbon atoms.The molecular structure of MVE indicates its potential for further downstream product synthesis through hydrogenation and self-cyclization.This paper aims to explore the catalytic conversion behavior of MVE,particularly its aromatization,to provide a theoretical basis for establishing new pathways for downstream product synthesis combining coal-based carbon one and carbon two.This thesis studied the hydrogenation and hydrogen-free aromatization of MVE using a fixed-bed reactor.The main parts of the study are as follows:1.Screening catalysts for hydrogenation and hydrogen-free aromatization,evaluating the impact of active components,carriers,and temperatures on MVE’s reaction.2.Investigating the structure-activity relationship of MVE to produce hexamethylbenzene under hydrogenation conditions using Cu/Al₂O₃,assessing reaction conditions,Cu loading’s influence on hexamethylbenzene yield.3.Exploring the hydrogen-free production of toluene/xylene from MVE using ZSM-5,investigating the effects of reaction conditions and Si/Al ratio on toluene/xylene yield.The main conclusions are as follows:（1）At temperatures between 400-450 ^oC,MVE,under hydrogenation conditions using Cu O/Al₂O₃ catalyst,can produce hexamethylbenzene.At 400^oC,with a V_H2/V_MVE ratio of 23 and a gas hourly space velocity（GHSV）of1835 h^-1,the carbon yield of hexamethylbenzene can reach 10.4%.This yield is approximately 6%higher compared to the existing naphtha pathway.The reaction pathway involves the initial hydrogenative cracking of MVE to yield acetaldehyde and methanol,which further transform into hexamethylbenzene.Cu⁰ facilitates the production of C₃₊aldehydes/ketones and hexamethylbenzene,while Cu⁺promotes MVE polymerization.（2）In the absence of hydrogen,at temperatures between 400-450 ^oC,MVE can be transformed on HZSM-5 into single-ring aromatic hydrocarbons like BTX,C2-C4 olefins,and acetaldehyde.The yield of the product is influenced by the Si/Al ratio（i.e.,acidity）within the HZSM-5.Stronger catalyst acidity favors the formation of toluene and xylene,whereas weaker catalyst acidity results in higher acetaldehyde yields.Under optimal reaction conditions,the carbon yields for BTX and C2-C4 olefins reach 47%and 30%,respectively.Notably,toluene and xylene achieve a high carbon yield of 40%,which is approximately 15%higher compared to the current methanol aromatization pathway.Deactivated catalysts can be regenerated in situ through oxidation treatment at 500 ^oC.The toluene and xylene yields from five cycles of regenerated catalysts reach approximately 31%.At temperatures below 300 ^oC,the surface polymerization and deposition of MVE on HZSM-5 prevent the formation of aromatic hydrocarbons.（3）At temperatures below 300 ^oC,Pt/Al₂O₃ catalyzes the hydrogenation of C=C bonds,primarily producing methyl ethyl ether,with a carbon yield of 59%at 200 ^oC.In the range of 400-450 ^oC,Pt/Al₂O₃ catalyzes the hydrodeoxygenation of MVE,yielding gaseous hydrocarbons with carbon yields ranging from 88%to 95%.Additionally,Cu O/Mg O,Cu-Zn/Al₂O₃,and Cu O/Ce O₂ catalyzed the hydrogenation of both C=C bonds and aliphatic ether bonds,yielding methanol and dimethyl ether with a total carbon yield of 8-27%at 270 ^oC.On the other hand,Cu O/Al₂O₃ and Cu O/Ti O₂ catalyzed the cleavage and hydrogenation of aliphatic ether and C=C bonds,respectively,yielding 13-15%carbon for ethanol at 250 ^oC.（4）In the absence of a catalyst,the reaction of MVE at 450 ^oC results in the formation of dimethoxyethane without hydrogen and,in the presence of hydrogen,the generation of gaseous hydrocarbons and acetaldehyde.Between400-450 ^oC,on Al₂O₃,MVE transforms into hexamethylbenzene,though yielding less compared to Cu O/Al₂O₃ under hydrogenation conditions.Below300 ^oC,metal oxides,sulfides,and weakly acidic catalysts hydrolyze MVE to produce methanol,dimethyl ether,and acetaldehyde,independent of the reaction atmosphere.Strong acids induce the polymerization of MVE.