Alkylation Of Toluene Into Para-xylene Over Aggregate ZSM-5

The technology of toluene alkylation with methanol produces highly selective paraxylene by shape selective catalysis,using relatively abundant toluene in petrochemical industry and cheap methanol in coal chemical industry as raw materials.ZSM-5 molecular sieve is used as the common catalyst in the reaction.However,the equilibrium composition of o-xylene,m-xylene and p-xylene is produced on the ZSM-5 with low silica-alumina ratio.The selectivity and stability of p-xylene can be improved by multi-step composite modification,but the preparation cycle of the catalyst is long and the repeatability is poor.In order to achieve the unification of para-xylene selectivity and catalyst stability,and simplify the preparation process,ZSM-5 with different silica-alumina ratio was synthesized in the thesis.The results are shown as follows.The aggregate ZSM-5 with different silica-alumina ratio was synthesized with low cost.And the influences of silica-aluminum ratio,forming method and amount of binder in extrusion molding were studied.Compared with compression molding,aggregate ZSM-5 by extrusion dispersed the active sites with the addition of a binder,thus improving the selectivity of PX.When the additive amount of?-Al₂O₃ is 13%of the total mass of the catalyst,the selectivity of PX is the highest,and the catalyst have the best performance.When the silica-alumina ratio of the molecular sieve is 75,the acidity and acid amount of ZSM-5 are favorable for obtaining the higher selectivity of PX,and the selectivity of PX is over 55%.The selectivity of PX can be promoted by modified ZSM-5 with single La₂O₃,P₂O₅ or SiO₂,and the selectivity of PX increased with the loading amount of modifier.When the loading amount of P₂O₅ is 10%,the selectivity of PX can reach more than 80%,and the activity and stability of the catalyst performed better.The selectivity of PX can be improved with the use of SiO₂ extrudates,but partial channels of ZSM-5 were blocked and the deactivation of the catalyst was accelerated with the excessive usage of SiO₂ during extrusion.However,the catalyst dealt with converting dry glue to S-1,have the better performance.Contrast with molecular sieves treated with low concentration of NaOH,the treatment with high concentration of NaOH reduces the number of mesopores of ZSM-5,and the selectivity of PX is higher after 10%P₂O₅ modification.The catalyst was treated with 1 mol/L alkali to increase the conversion of toluene.After that,the catalyst was modified with 10%P₂O₅ and 0.15%Pt.The modified catalyst was applied to the reaction,resulting in a PX selectivity of 96%,and the catalyst did not deactivate for 505h.Therefore,the catalyst with high activity,selectivity and stability was obtained.