Study On Methylation Of Toluene With Methanol Over ZSM-22 Catalysts

p-Xylene(PX)is mainly used for production of terephthalic acid(PTA)and dimethyl terephthalate(DMT),and then for production of polyester,with the rapid development of industrial polyester,the demand of PX is increases with years.Methylation of toluene with methanol over highly shap-selective catalysts to PX is a promising technics for increasing production.Methylation of toluene with methanol to PX was carried out over HZSM-22 as the main active catalyst by means of a fix-bed flow reactor.The catalytic properties of methylation of toluene with methanol to PX over HZSM-22 and HZSM-5 were compared,and the effect of molding method and reacting conditions over HZSM-22 were studied.The catalytic properties of HZSM-22 modified with metallic oxides,non-metallic oxides,nonmetallic oxides and then metallic oxides,water digestion were also studied.According to the study,PX selectivity over HZSM-22 was great higher than it over HZSM-5 in the same reaction conditions,but the catalytic activity was just on the contrary.In the same reaction conditions,the PX selectivity over sheet-shaped HZSM-22 was obviously higher than strip-shaped catalyst,but catalytic activity was almost the same.The experiments showed that the best reaction congditions were:reaction temperature was 430℃,the molar ratio of toluene to methanol was 4:1,WHSV was 6 h^-1,carder gas was N₂,velocity was 25 ml/min,atmospheric pressure.Under this conditions,the toluene conversion was 9.2%and the PX selectivity was 70.5%.With the same loaded amount,the PX selectivity over HZSM-22 catalysts loaded with La₂O₃ was higher than it loaded with MgO,BaO and CaO, and the value was 84.4%.Compared to P₂O₅ modified HZSM-22 catalyst,SiO₂ modified HZSM-22 shows higher PX selectivity,and the value was 76.1%.But HZSM-22 modified with neither metallic oxides nor nonmetallic oxides could obtain high catalytic activity and selectivity simultaneously.SiO₂ modified HZSM-22 and then loadede with La₂O₃ could retain PX selectivity and increase toluene conversion simultaneously.Water digestion HZSM-22 resulted in framework collapse,but SiO₂ modified HZSM-22 and then digested with water could stabilify framework.The value of toluene conversion was 7.3%and PX selectivity was 79.8%over wt.15%SiO₂ loadede HZSM-22 and then water digestion at 120℃temperature.