碱改性ZSM-5分子筛及其甲醇芳构化性能

Effect of alkali modification to ZSM-5 zeolite on the aromatization of methanol

利用乙酸钠和柠檬酸钠对ZSM-5分子筛进行脱硅改性处理,并通过XRD、SEM、NH_(3)-TPD、^(27)Al MAS NMR、吡啶吸附红外光谱和N2吸附-脱附等表征手段对ZSM-5分子筛结构、酸量、比表面积及孔体积等物化性质进行表征分析。结果表明,碱改性使分子筛的孔径增加且形成合适的微-介孔结构,同时,使L酸量和B酸量明显降低。当乙酸钠溶液浓度为0.5 mol/L时,改性的分子筛在形成大量介孔结构的同时具有合适的B/L值,使催化剂的寿命延长并展现出最优的催化性能。与微孔ZSM-5相比,使用寿命由20 h延长到74 h,芳烃最高产率从20.97%提高到40.05%。

ZSM-5 zeolites were modified by desilication with sodium acetate and sodium citrate.The physicochemical properties of ZSM-5 zeolites,such as crystal structure,acid content,surface area and pore volume,were characterized by XRD,SEM,NH_(3)-TPD,^(27)Al MAS NMR,pyridine adsorption infrared spectroscopy and N2 adsorption-desorption isotherms.The results indicate that pore size of the zeolite increases and mesoporous structures are formed by alkali modification,and the amount of Lewis and Brönsted acid contents decreases obviously.When the concentration of sodium acetate solution is 0.5 mol/L,the modified zeolite has a suitable B/L value for the aromatization of methanol while forming a large number of mesoporous structures.Compared with microporous ZSM-5,the catalyst life is increased from 20 h to 74 h,and the highest yield of aromatics is increased from 20.97%to 40.05%.