Synthesis Of 2, 6-dimethylnaphthalene By Methylation Of Methylnaphthalene On Modified Zeolite Catalysts

The compound 2,6-dimethylnaphthylene(2,6-DMN) is used as a precursor of 2,6-naphthalene dicarboxylic acid in the manufacture of high performance polyester resins such as polyethylene naphthalate polymer(PEN),because 2,6-DMN is easily oxidized to 2,6-naphthalene dicarboxylic acid compared with other presursos such as 2,6-diisopropylnaphthalene or 2-methyl-6-isobutyrylnaphthalenes.there have been many expected PEN's applications to film and bottle uses,such as long time recording type video film,Advanced Photo System ,hot fill containers,refillable bottles and tire codes because of its good physical properties in strength,thermal resistance and gas barrier property .However,PEN have heretofore been too expensive to expand its market cleanly because of few effective processes for the 2,6-DMNcommercilization .In this article the process for preparing 2,6-DMN by methylation of 2-monmethylnaphthalene on zeolite catalysts is employed .our works included the following contents :the technology of extruding zeolite catalysts ,the modification of zeolite catalysts and the application in the reaction of methylation of 2-monmethylnaphalene,and discussion on reaction conditions which influence the carbonization on the used zeolite catalysts and so on.1) Factors which infuence the mechanical strength of the zeolite catalysts such as H P during extruding are discussed.High mechnical strength zeolite catalyst can be prepared by properly adjusting the factors.2) The hight conversion of 2-MN and selectivity of the 2,6-DMN in the methylation on H 3 zeolite in the following conditions :at the reaction temperature 350-400癈;the prepared weight ratio of 2-MN to methanol is hi the range of 3:1 to 4:1 ;the flux of carrier gas N2 is in the range of 2 to 4 ml/min.3) Campared with HZSM-5 and HY ,on H P zeolite catalyst the result of methylation is best though among the three zeolite catalysts HZSM-5 shows the highest selectivity,and HY zeolite the highest conversion of 2-MN.4) The discussion of the methylation of 2-MN with methanol on various kinds of modified H P zeolite catalysts is studied .The modified zeolite catalysts exhibited lower initial methylation activities ,higher selectivies to 2,6+l,6-DMN,and longer catalyst lives than unmodified zeolitecatalyst.This is ascribed to the decrease in acidic properties and acid siteson the internal or external surface zeolites crystallites and the pore sizes of zeolites.5) The catalyst deactivity is mainly caused by the coke deposit on catalysts.The coke decreases with the reduce in reaction temperature ,the ratio of methanol to 2-MN and acidic properties and acid site on the zeolite crystallites.