One-step Synthesis Of REY-type Molecular Sieves From Kaolin In Yunnan And A Preliminary Study On Its Kinetics

REY zeolites are widely used in the fields of drying and purification,petroleum refining and catalysis,adsorption and separation due to specific physical and chemical properties.In industrial production,REY zeolites are generally synthesized by chemical reagent and obtained through modification treatment,which will increase the production process and cause serious waste of rare earth resources,and recycling will also increase production cost.The REY zeolites are synthesized by one step hydrothermal method using kaolin as raw material that is rich and cheap in resources,which can reduce the production cost of zeolite while simplifying the synthesis path and making full use of natural resources,and it has extremely important strategic significance for the economic development of kaolin producing areas.Firstly,the calcination modification process of kaolin was studied,and the results showed that:kaolin needs to be heat-treated at 600? for 2 h to obtain modified kaolin under normal calcination conditions,but heat treatment is required at 600? for 30 min under microwave calcination conditions.Considering the energy-saving and high-efficiency of microwave heating treatment,the kaolin under microwave calcination for 30 min was selected as the raw material for the synthesis of REY(RE-La,Y type)zeolites.Secondly,the hydrothermal one-step synthesis of REY zeolites was studied.The single-factor experiment results showed that the best conditions for the synthesis of REY zeolites are that rare earth content was 0.5 g/L,the mixing order was a,the aging temperature of the guding agent was 55? and the time was 60 min,the crystallization temperature was 100? and the time was 24 h.And the silicon-aluminum ratio of the synthesized product is about 4.20 and the content of La2O3 is about 2.74%,which has the framework structure and morphological characteristics of Y zeolites.Finally,preliminary study on the crystallization process kinetics of REY zeolite was carried out,and its apparent nucleation activation energy and apparent crystal growth activation energy were calculated.The nucleation process of synthesizing REY zeolite using modified kaolin as raw material involves the dissolution activation energy of modified kaolin and the activation energy of crystal nucleus formation,while the crystallization process involves the dissolution activation energy of modified kaolin and the formation of crystal nucleus activation energy.Thus,its apparent nucleation activation energy and apparent crystal growth activation energy(En=33.66kJ/moL,Ec=20.07kJ/moL)are greater than the REY zeolite synthesized from chemical reagents(En=10.78 kJ/moL,Ec=10.32 kJ/moL).In summary,the use of an alternative natural mineral raw material-kaolin hydrothermal one-step synthesis of REY zeolite is extremely important for promoting the development of the REY zeolites industry and broadening its application fields.