Synthesis And Crystallization Mechanism Of Zeolite Beta Via Aerosol-assisted Method

Zeolite beta with three-dimensional 12-memberbed ring channels is widely used in petroleum refining,petrochemical industry and fine chemistry due to its high hydrothermal and chemical stabilities and proper acidity.Hydrothermal method is the most widely used method to synthesize zeolites.The operation and product performance are stable,but plenty of solvent and organic-template are required.To solve the problems of high cost and low yield,the aerosol-assisted method was conducted to synthesize nano-sized zeolite Beta agglomerates and zeolite Beta large crystals with less defect sites.The synthesis conditions and crystallization mechanism were systematically studied.The catalytic performances of Beta zeolites were evaluated via the cracking of 1,3,5-TIPB or IPB.The main contents of this paper are as follows:Firstly,nano-sized zeolite Beta agglomerates were synthesized by the aerosol-assisted method.When SiO₂/Al2O3 is 50,the effects of crystallization temperature,template amount and crystallization time were systematically studied.The optimized synthesis conditions are:T=130?,TEAOH/Si O₂=0.15,t=48h.The zeolites Beta with different Si O₂/Al2O3 ratios exhibit spherical nano-agglomerates with intercrystal pores.The crystallization process followed the liquid-phase mechanism.The catalytic performances were evaluated by the cracking of 1,3,5-TIPB.A comparison between the aerosol sample and the commercial sample indicate its pottential applications in industry.Secondly,zeolite Beta large crystals with less defect sites were synthesized in the ammonium fluoride system.When the SiO₂/Al2O3 is 50,the effects of the crystallization step,crystallization temperature,template and NH4 F amounts were systematically studied.The results show that the optimized synthesis conditions are: TEAOH/SiO₂=0.3,NH4F/SiO₂=0.3,120? crystallized for 24 h then 150? crystallized for 90 h.This indicates that the aerosol-assisted method can accelerate crystallization rate and reduce the amounts of TEAOH and NH4 F.The crystallization mechanism of zeolite Beta synthesized in the ammonium fluoride system was studied.The crystallization was carried out at near neutral pH,and the crystallization process followed the solution mediated solid-phase nucleation mechanism.The sample obtained under the optimum conditions exhibited good catalytic activity and stability in the cracking reaction of IPB due to less defect sites.