硅源用量对SAPO-18分子筛合成及催化性能的影响

采用水热合成法,以N,N-二异丙基乙胺为模板剂合成SAPO-18分子筛,并用X射线衍射、X射线荧光光谱、扫描电子显微镜、NH3程序升温脱附及N2吸附-脱附等对其结构进行表征,系统研究合成凝胶中硅源用量对SAPO-18分子筛合成及其在甲醇制烯烃反应中催化性能的影响。结果表明,在晶化温度453 K、晶化时间96 h和合成凝胶中0.3≤n(Si O2)∶n(Al2O3)≤1.2条件下,能合成出纯相的SAPO-18分子筛,其中,当n(Si O2)∶n(Al2O3)=0.6,在反应时间135 min时,合成的SAPO-18分子筛具有较高的双烯选择性(乙烯+丙烯)。合成凝胶中硅源的用量对SAPO-18分子筛酸性有显著影响,适当增加分子筛中强酸比有助于提高乙烯和丙烯选择性,但缩短催化剂寿命。

Effect of SiO2 amounts on synthesis of SAPO-18 molecular sieves and their catalytic properties

Using N,N-diisopropylenthylamine as the structure-directing agent,SAPO-18 molecular sieves were synthesized by hydrothermal method.The physicochemical properties of the as-prepared molecular sieves were characterized by XRD,XRF,SEM,NH₃-TPD and N₂ adsorption-desorption.The effect of silicon amounts on physicochemical properties and catalytic performance of SAPO-18 molecular sieves in MTO reaction was investigated.The results showed that under the condition of crystallization temperature 453 K,crystallization time 96 h,and 0.3≤n(SiO₂)∶n(Al₂O₃)≤1.2 in initial gel,pure SAPO-18 molecular sieve was obtained;SAPO-18 molecular sieve prepared with n(SiO₂)∶n(Al₂O₃)=0.6 had the highest selectivity to (ethylene+propylene) under reaction time 135 min.The silicon amounts in initial gel had remarkable influence on the acidity of SAPO-18 molecular sieves.Increasing appropriately the ratio of strong acid in molecular sieves helped to improve the selectivity to ethylene and propylene,but shortened the service time of the catalyst.