Study On Green Synthesis Route Of Zeolite Beta From Kenyaite

Zeolite beta has unique structure and good physical chemical properties,which makes it widely used in metallurgy,electronics,petrochemical and other industries.In this paper,the high crystallinity zeolite beta was successfully obtained from layered silicate kenyaite by hydrothermal and solvent-free methods under OSDA-free,seed-directed conditions.To get a better understanding of the change of secondary structural unit and the crystallization behavior during crystallization by using XRD,SEM,FT-IR,EDS,N2 adsorption,solid-state nuclear magnetic spectroscopy.Compared with the traditional method,the synthesis of zeolite beta with kenyaite has high efficiency and high selectivity,which provides a new thought for the study of zeolite mechanism.Specific research is as follows:The pure zeolite beta was synthesized using kenyaite as raw material by hydrothermal method under OSDA-free,seed-directed conditions.The optimal reaction conditions were as follows: the reactant composition was H₂O : Na₂O : SiO₂ : Al₂O₃ = 180 : 0.48 : 1 : 0.0167,25 wt% seed crystals and crystallized at 125 ℃ for 36 h.The seed and kenyaite dissolved during the crystallization process under alkaline hydrothermal conditions,and the residual seed provided the active surface for zeolite beta,which promoted the nucleation and growth of zeolite beta.The five-membered ring and six-membered ring structures in kenyaite are partially preserved,and the five-membered rings are connected to each other to form four-membered rings structure.With the continuous consumption of kenyaite,zeolite beta continued to nucleate and grow gradually.In the OSDA-free and solvent-free system,pure zeolite beta was obtained by crystallizing from kenyaite as the raw material.The optimal reaction conditions were: as follows: the reactant composition was Na₂O:SiO₂ : Al₂O₃ = 2.4 : 8 : 1,20 wt% seed crystals and crystallized at 115 ℃ for 8 h.The structure of aluminosilicate continues to depolymerize under alkaline heating conditions,and the five-membered and six-membered ring structures of kenyaite are partially retained,and are continuously rearranged to form new four-membered rings that are connected to each other form the framework structural unit of zeolite beta and eventually form zeolite beta.This method improves the yield of zeolite,avoids the generation of harmful gases and high pressure.It opens the way to the development of a highly sustainable green zeolite synthesis route.A batch reactor was used to evaluate the reactivity of the synthesized zeolite beta in the preparation of cyclohexene by dehydration of cyclohexanol.At the heating temperature of 220 ℃,8.00 g cyclohexanol and 0.40 g catalyst were added,and the highest conversion rate of cyclohexanol was 61.0 % and the purity of cyclohexene was above 99.0 %.The experimental results show that zeolite beta has good acid catalytic activity,high selectivity and good cyclability,and is a green,efficient and cheap solid acid catalyst with good application prospect.