Study On The Ionothermal Synthesis Of ZSM-22 Zeolite Molecular Sieves

As an effective catalyst,ZSM-22 plays an important role,such as selective catalytic cracking,hydrocarbon isomerization and methanol-to-hydrocarbon.Some traditional synthes of the ZSM-22,such as hydrothermal method,mechanochemical synthesis and seed-assisted approach have appeared.Currently,with the development of ionic liquids,ionothermal synthesis has become a new approach.One of the biggest challenges still remains to synthesis pure ZSM-22 under static conditions.Because ZSM-22 is a dynamic controlled metastable structure,it is prone to crystallize to form ZSM-5 and ZSM-34 symbiotic phases at higher temperature.In this study,tetraethylorthosilicate（TEOS）and ionic liquid（IL）as the raw material,ZSM-22 is synthesized by the dry gel liquid-phase conversion assisted ionic liquid.Different synthesis parameters,such as the types of ionic liquid,hydrolytic environment,were investigated and the optimum synthetic conditions were refined.Al-ZSM-22 zeolite was synthesized by adding the aluminum source with the same synthetic method.Different mole ratios effect of SiO₂/Al₂O₃ and hydrolytic environment were also investigated.The structure of the pure-silica ZSM-22 was successfully obtained under optimal synthesis condition,which are n（Na₂O）/n（SiO₂）=19,n（[Bmin][Cl]）/n（SiO₂）=35,n（H₂O）/n（SiO₂）=40,crystal temperature and time at 160゜C for 24 h.Using different anion of ionic liquids,all the samples appeared TON topology structure and different morphologies.The ZSM-22 has better crystallization under acidic hydrolytic environment of TEOS.ZSM-5 is synthesized from acid catalytic,and then Al-ZSM-22 is synthesized under alkaline condition when aluminum source was added and n（SiO₂）/n（Al₂O₃）=200.The ionic liquid plays the structure-directing role in the synthesis ZSM-22 by TG FTIR and so on.First,the ionic liquid interacts with the initial gel to guide the ordered structure of the framework species.After aging,ionic liquid are stored in dry gel,ionic liquids was decomposed after calcination and ZSM-22 zeolite TON topology is intact.