微米级HZSM-5分子筛催化剂在甲苯甲醇烷基化反应中的应用

Shape-selective alkylation of toluene with methanol over modified micron-scale ZSM-5 zeolite

采用浸渍法合成了不同硅铝比、晶粒大小的复合改性HZSM-5分子筛催化剂,采用XRD、SEM、NH3-TPD、TEM和低温N2吸附等手段对改性前后催化剂的结构进行了表征。在小型固定床等温反应器上考察了HZSM-5分子筛催化剂在甲苯与甲醇烷基化反应中的性能。实验结果表明,在反应温度440℃、重时空速2 h^(-1)、n(甲苯)∶n(甲醇)=2、n(H_2)∶n(H_2O)∶n(甲苯+甲醇)=8∶2∶1的优化反应条件下,具有大晶粒、高硅铝比的复合改性HZSM-5分子筛催化剂上甲苯转化率达26.2%、对二甲苯在异构体中的选择性为95.0%;在复合改性HZSM-5分子筛催化剂的基础上引入加氢金属后,催化剂的稳定性明显提高,在相同反应条件下,甲苯转化率为18%~26%,对二甲苯选择性为90%~96%,稳定运行1 700 h后催化剂未出现明显失活的现象。

HZSM-5 zeolite catalysts with different silica-alumina ratio and particle size were modifi ed by impregnation and were characterized by means of XRD,SEM,NH3 TPD,TEM and N2 adsorption. The shape-selective alkylation of toluene with methanol catalyzed by the catalysts was investigated in a continuous flow fixed-bed reactor. The experimental results showed that the modified HZSM-5 zeolite catalysts with large particle size and high silica-alumina ratio had good performances. Under the optimized reaction conditions of temperature 440 ℃,WHSV 2 h^（-1）,n（toluene）∶n（methanol） 2 and n（H2）∶n（H2O）∶n（toluene＋methanol） 8∶2∶1,the conversion of toluene and the selectivity to p-xylene reached 26.2% and 95.0%,respectively. After a precious metal was introduced, the stability of the catalyst was improved,the toluene conversion and the selectivity to p-xylene still were 18%-26% and 90%-96% respectively and during 1 700 h online reaction,no evident catalyst deactivation was found.