Synthesis Of Modified HZSM-5 Zeolite And Their Catalytic Performances In Aromatization Of Methanol

Aromatics,especially light aromatics?benzene,toluene and xylene,known as BTX?are important basic chemical raw material,its derivatives are widely used for many industries not only synthetic resins,synthetic detergents,synthetic rubber,but also medicines,pesticides,explosives and specialty chemicals.Based on present energy situation in our country which is abundant with coal and lack petroleum and gas,and faced with the problems of excessive methanol production capacity and output and insufficient aromatic hydrocarbon supply in China,the catalytic conversion of methanol to aromatics?MTA?,which is an important nonpetroleum route,has very important practical value and considerable market prospects.In order to develope high-efficient catalysts with high BTX selectivity and long lifetime,modified HZSM-5 catalysts were prepared,moreover,the relationship between the properties of catalysts and the catalytic performance of MTA was studied.In particular,the main contents and the results are as follows:1.HZSM-5 catalysts modified by Zn,Ga,La species were prepared by equal volume impregnation followed by ultrasonic.They werecharacterized by XRD,N2 adsorption-desorption,NH3-TPD and Py-IR technologies,moreover,the crystalline structure,pore structure,acid amount and acid type of modified HZSM-5 catalysts were also discussed.Finally they were used for the MTA reaction,the effects of metal modification on MTA conversion,aromatics selectivity and carbon number distribution of aromatic hydrocarbons were studied emphatically.The results indicated that:?1?The introduction of metal species?Zn,Ga,La?will not destroy the crystalline structure of HZSM-5 zeolites;?2?The dehydroaromatization species were formed on the surface of HZSM-5catalysts with the introduction of metal species?Zn,Ga,La?,which increased the content of total aromatic hydrocarbons in MTA reaction products;?3?La/HZSM-5 zeolites had the highest selectivities of C9 and C10 aromatic hydrocarbons;?4?Zn/HZSM-5 zeolites had the highest selectivities of C6-C8 aromatic hydrocarbons?BTX?,and Zn species were the best active metal species for methanol aromatization.2.Zn/HZSM-5,P/HZSM-5 and Zn-P/HZSM-5 catalysts were prepared by the modification with Zn Si F6 and H3PO4 solution.They were characterized by XRD,N2 adsorption-desorption,NH3-TPD,Py-IR,FTIR,SEM,27 Al MAS NMR,31 P MAS NMR and TG technologies,moreover,the crystalline structure,pore structure,acid amount,acid type,coordinative state of aluminium,surface phosphorus species and carbon deposition of modified HZSM-5 catalysts were also discussed.Finally they were used for the MTA reaction,the results indicated that:?1?The modification of phosphoric acid impregnation caused the dealumination of HZSM-5 framework,as a result,the crystallinity of P/HZSM-5 catalyst decreased accordingly;?2?The total Lewis acid sites of P/HZSM-5zeolite significantly reduced,in particular,the strong Lewis acid sites decreased sharply,while the weak Lewis acid sites increased.At the sametime,the Si?OH?Al bonds of HZSM-5 framework were destroyed with the modification of phosphoric acid impregnation,the strong Bronsted acid sites reduced accordingly,this process was accompanied by the formation of Si-OH,which caused the increase of weak Bronsted acid sites;?3?The modification of phosphoric acid impregnation significantly reduced the carbon deposition of HZSM-5 catalyst;?4?The activity of catalytic cracking was inhibited,however,the activities of oligomerization,cyclization and hydrogen transfer were promoted with the modification of phosphoric acid impregnation;?5?The Zn-2P/HZSM-5 catalysts exhibited high BTX selectivity and better catalytic stability,in particular,the BTX selectivity of Zn-2P/HZSM-5 catalysts could reach as high as 46.76% in 6 hour of reaction,moreover,the selectivity of BTX was still more than 20% after 330 h reaction at T = 400 ?,P = 0.1 MPa,WHSV = 0.7 h^-1.