Catalytic Isomeirization Of 2,5-dichlorotoluene And Thermodynamic Analysis

Series products of toluene chlorination are important fine chemical raw materials.In the derivativesoftoluenechlorination,2,6-dichlorotoluene,2,4-dichlorotoluene,2,3-dichlorotoluene and 3,4-dichlorotoluene have high market price and are widely used in preparing medicine,pesticides,dyes and other fine chemical intermediates.Nevertheless,2,5-dichlorotoluene is single-purpose and cheap.It leads to the bright future of dichlorotoluene isomerization in commercial application.In our present paper,the catalytic technique of 2,5-dichlorotoluene isomerization and conversion was investigated,including isomerization of 2,5-dichlorotoluene catalyzed by H types of zeolites,conversion of 2,5-dichlorotoluene catalyzed by metal-modified Hβ（SiO₂/Al₂O₃=25）zeolite and isomerization and redistribution of 2,5-dichlorotoluene over AlCl₃ with thermodynamic analysis.The effects of reaction parameters,such as types of catalyst,catalyst amounts,reaction temperatures,liquid hourly space velocity of raw material,types of carrier gas,types of loading metal,amount of loading metal and so on.And the reaction mechanisms would be investigated based on the experimental data.1.SevenkindsofHtypeszeolites:Hβ（SiO₂/Al₂O₃=25）,HZSM-5（SiO₂/Al₂O₃=25/80/260）,HY（SiO₂/Al₂O₃=5/7/11）were used as catalysts in the isomerization of 2,5-dichlorotoluene.The experimental results revealed that the total acid amounts and acid strength had an obvious effect on the isomerization of 2,5-dichlorotoluene.Zeolite Hβ（SiO₂/Al₂O₃=25）hadafavorableeffectonconverting2,5-dichlorotolueneto2,6-dichlorotoluene.When the zeolite Hβ（SiO₂/Al₂O₃=25）was used as catalyst,reaction temperature was 350^oC and liquid hourly space velocity of 2,5-dichlorotoluene was 0.6 hr^-1,the conversion of2,5-dichlorotoluenewas22.9%,andtheselectivitiesof2,6-dichlorotoluene,2,4-dichlorotoluene,2,3-dichlorotoluene,3,4-dichlorotoluene,chlorobenzene,dichlorobenzene and xylene dichloride were 9.2%,14.9%,3.9%,2.2%,4.3%,37.6%,and24.3%,respectively.2.Metal-modified Hβ（SiO₂/Al₂O₃=25）catalysts were synthesized by wet impregnation method and applied to the conversion of 2,5-dichlorotoluene.The experimental results revealed that after modified with metallic Ag or Cu,the total acid amount was improved.In the N₂ atmosphere,2,5-dichlorotoluene was converted to dichlorobenzene,2,6-dichlorotoluene,2,4-dichlorotoluene and xylene dichloride with the isomerization and redistribution of2,5-dichlorotoluene catalyzed by Hβ,Ag/Hβand Cu/Hβ,and Ag/Hβcatalysts with higher total acid amounts favored the formation of 2,4-dichlorotoluene when the reaction temperature was310 ^oC or 350 ^oC.In the H₂ atmosphere,catalysts Ag/Hβand Cu/Hβfavored the hydrogenation of 2,5-dichlorotoluene to dichlorobenzene.When the Hβ（SiO₂/Al₂O₃=25）was modified with 10%（wt%）metallic Cu was used as catalyst,the reaction temperature was 350 ^oC,the liquid hourly space velocity of2,5-dichlorotoluene was 0.2 hr^-11 and in the H₂ atmosphere,the conversion of2,5-dichlorotoluenewas44.1%,andtheselectivitiesof2,6-dichlorotoluene,2,4-dichlorotoluene,2,3-dichlorotoluene,3,4-dichlorotoluene,chlorobenzene,dichlorobenzene and xylene dichloride were 14.3%,16.0%,1.8%,2.4%,13.3%,42.1%,and9.3%,respectively.3.The products distribution,conversion activity and thermodynamic of the isomerization of 2,5-dichlorotoluene（2,5-DCT）catalyzed over 30%-50%mass fraction of AlCl₃ at392.15-452.15 K was studied and five dependent isomerizations of 2,5-DCT were considered in our paper.The?_rG_m⁰ of dependent reactions（R1-5）in the isomerization of2,5-dichlorotoluene over AlCl₃ were greater than zero which revealed that R1-5 were all endothermic reactions.When the dependent reactions arrived the equilibrium,the conversion of2,5-dichlorotoluene was ca.77.5%,and the selectivities of 2,6-dichlorotoluene,2,4-dichlorotoluene,2,3-dichlorotoluene,3,4-dichlorotoluene,chlorobenzene,dichlorobenzene and xylene dichloride were ca.7.3%,20.9%,2.9%,4.3%,12.3%,0.6%,24.8%and 26.3%,respectively.