Al-ITQ-13分子筛的碱改性及其催化裂化性能

Alkali Modification of Al-ITQ-13 Zeolite and Its Performances for Catalytic Cracking

以粗孔硅为硅源、拟薄水铝石为铝源直接合成了Al-ITQ-13分子筛原粉,然后利用不同浓度的NaOH溶液对Al-ITQ-13分子筛进行碱改性,并采用XRD、N2吸附-脱附、NH3-TPD和吡啶吸附FTIR等方法对碱改性前后的Al-ITQ-13分子筛进行了表征;以正辛烷催化裂化作为模型反应,考察了碱改性前后Al-ITQ-13分子筛的催化性能。实验结果表明,经碱改性的AlITQ-13分子筛的比表面积、微孔比表面积、总孔体积和微孔体积均有所增大;酸强度降低,中强酸量增加。在500℃、催化剂用量50 mg、0.1 MPa、在线反应15 min的条件下,Al-ITQ-13分子筛的催化活性及乙烯、丙烯选择性与工业ZSM-5分子筛相当,而经0.20 mol/L NaOH溶液处理的Al-ITQ-13分子筛的低碳烯烃(乙烯和丙烯)选择性比未经碱改性的Al-ITQ-13和工业ZSM-5分子筛分别提高了8.10,7.09百分点。

Al-ITQ-13 zeolite was directly synthesized with porous silica as silicon source and pseudo-boehmite as aluminium source,and then modified by NaOH solutions with different concentration.The modified Al-ITQ-13 samples were characterized by means of XRD,N2 adsorptiondesorption,NH3-TPD and pyridine adsorbed FTIR,and used as catalysts in the catalytic cracking of n-octane in a microreactor.The results showed that the Al-ITQ-13 zeolite could be synthesized from cheap silicon source and aluminium source.After the treatment with the alkali,all the BET specific surface area,micropore surface area,pore volume and micropore volume of the Al-ITQ-13 zeolites increased,and the acid strength decreased but the moderately strong acid amount in the modified Al-ITQ-13 zeolites increased.Under the reaction conditions of 500 ℃,catalyst 50 mg,0.1 MPa and time on stream 15 min,the catalytic activity and selectivities to ethylene and propylene of the Al-ITQ-13 catalyst were equivalent to those of the ZSM-5 zeolite.Compared with the Al-ITQ-13 and ZSM-5 catalysts,the light olefin（ethylene and propylene） selectivity on the Al-ITQ-13 zeolite modified with 0.20 mol/L NaOH solution increased by 8.10 and 7.09 percentage point,respectively.