硅改性拟薄水铝石合成SAPO-34分子筛的研究

SAPO-34分子筛常用于甲醇制烯烃（MTO）反应中。以硅酸钠、硝酸铝和氨水为原料采用碱滴酸加料方式制备一种硅改性拟薄水铝石,再以硅改性拟薄水铝石为硅源和铝源、磷酸（H₃PO₄）为磷源、四乙基氢氧化铵（TEAOH）为模板剂采用水热合成法制备SAPO-34分子筛。采用XRD、SEM、FT-IR、NH₃-TPD等表征手段对合成的硅改性拟薄水铝石及SAPO-34分子筛进行表征并对其MTO催化性能进行评价。结果表明,在硅铝物质的量比为0.08~0.5时,硅的引入对合成纯相拟薄水铝石无影响,但硅的引入量对拟薄水铝石的结晶度及形貌有一定影响；在硅铝物质的量比为0.2~0.5时,以硅改性拟薄水铝石为硅源和铝源可以合成纯相SAPO-34分子筛,MTO催化反应甲醇转化率可达99%以上,双烯选择性最高达87%以上,并拥有较高的乙烯选择性。

Study on synthesis of SAPO-34 molecular sieve by silicon-modified pseudo-boehmite

SAPO-34 molecular sieve is often used in methanol to olefin（MTO） reaction.Using sodium silicate,aluminum nitrate and ammonia as raw materials,a silicon modified pseudo boehmite was prepared by alkali dropping to acid feeding method,and then SAPO-34 molecular sieve was prepared by hydrothermal synthesis method with silicon modified pseudo boehmite as silicon source and aluminum source,phosphoric acid（H₃PO₄） as phosphorus source,tetraethyl ammonium hydroxide（TEAOH） as template.The synthesized silica modified pseudo boehmite and SAPO-34 molecular sieve were characterized by XRD,SEM,FT-IR and NH₃-TPD,and their MTO catalytic properties were evaluated.The results showed that when the molar ratio of silicon to aluminum was 0.08~0.5,the introduction of silicon had no effect on the synthesis of pure pseudo boehmite,but the amount of silicon had a certain effect on the crystallinity and morphology of pseudo boehmite.When the amount molar ratio of silicon to aluminum was 0.2~0.5,pure SAPO-34 molecular sieve could be synthesized with silicon modified pseudo boehmite as silicon source and aluminum source.The methanol conversion rate of MTO catalytic reaction could reach more than 99%,the diene selectivity could reach more than 87%,and it had high ethylene selectivity.