Green Synthesis Of Magadiite And Recrystallization Of It Into Zeolites

Zeolite is a kind of silica（aluminate）material with a unique pore structure and crystal chemical properties.It is widely used in petrochemical industry,fine chemical industry,environmental chemical industry,and other important areas because of its high specific surface area,strong stability and excellent catalytic performance.In recent years,zeolite prepared by recrystallization of layered silicate magadiite have attracted much attention because of their low cost,short crystallization time,and a small amount of structure-directing agent.However,there are also some problems,such as the low synthesis efficiency of raw material magadiite,need to add structure-directing agent during crystal conversion,lack of researches on zeolite crystal morphology and size control,etc.Therefore,this article based on the green and efficient synthesis of magadiite,aims to synthesize small-crystal zeolite,and explored the changes in structure and morphology of the recrystallization products under template-free conditions.The effect of structure directing agent intercalation on the recrystallization products was investigated.The studies in detail were as follows:（1）The magadiite was synthesized using illite silica residue by steam-assisted conversion（SAC）.The effects of Na₂O/Si O₂ molar ratio,crystallization temperature（T）,crystallization time（t）,synthesis methods and silicon sources on the structure and morphology of the synthesized samples were investigated.The results show that rosette-shaped（12μm）pure phase magadiite with high crystallinity was synthesized under the conditions of n（Na₂O）/n（Si O₂）=0.15,T=170℃,t=16 h.The yield was as high as 86.2%,the thermal stability below 260℃,and it has good adsorption performance for Cu²⁺.（2）Three types of zeolite（MOR,Na P and ANA）were successfully converted in a template-free hydrothermal system using magadiite by steam-assisted synthesis of illite silica residue.The binary crystalline phase diagram is used to analyze the phase transition rule of magadiite in the conversion system.The effects of synthesis parameters（OH^-/Si O₂ molar ratio,Si O₂/Al₂O₃ molar ratio,crystallization time and crystallization temperature）on the structure,morphology and size of mordenite was investigated in detail.The relative crystallinity of mordenite increased with the increase of the OH^-/Si O₂ molar ratio,and increases first and then decreases with the increase of the Si O₂/Al₂O₃ molar ratio;the morphology of the synthesized mordenite is prismatic,and the crystals size increased with the increase of the OH^-/Si O₂ molar ratio and crystallization temperature significantly.The Si O₂/Al₂O₃ molar ratio and crystallization time have no obvious effects on the morphology and size of mordenite.（3）MFI-type zeolite was successfully prepared by the synthesis strategy of intercalation first and then recrystallization using Na-magadiite by steam-assisted synthesis of illite silica residue and H-magadiite exchanged with hydrochloric acid as raw materials.The intercalation results of different organic structure-directing agents on Na/H-magadiite was investigated.The results show that the structure-directing agents was successfully inserted between the magadiite layers,but only the intercalation complex of TPA⁺and magadiite has been successfully transformed into MFI-type zeolite molecular sieve.The morphology of MFI-type zeolite is secondary spherical particles（8～12μm）formed by the accumulation of submicron-sized crystals.