Nano-zeolite And Its Self-assembly On The Organic Template For The Preparration Of Macroporous Zeolite

In the foreseeable future,fossil fuel is still a major component in energy supply.With the over-exploitation and overuse of crude oil,the quality of crude oil is inevitable to become heavier and worse.Therefore,the optimization of the current oil refining process is becoming an urgent problem to be solved.Zeolite catalyst is widely used in the field of petrochemical industry for cracking,alkylation and heterogeneity because of its high specific surface area,uniform microporous structure,adjustable acid properties and good stability.While its narrow micropore channels also lead to serious diffusion limitation of the small molecules and the non-entry of macromolecules.Therefore,shortening the diffusion path and increasing the external surface area become the main direction of studying zeolite catalytic materials.There are two methods to solve the defects of zeolite materials mentioned above: one is to prepare nano-size zeolite molecular sieves with higher external surface area and shorter micropore length;the other one is to introduce mesoporous or macrospores into conventional micropore zeolite to form hierarchical structure and increase the accessibility of the active sites.But these two solutions also have some limitations: nano zeolite particles are too small to recover after reactions,and hierarchical zeolite is mostly restricted to its high costs.In this paper,we dedicated to prepare zeolite with cheap organic microspheres as template and load nanosized zeolite onto the template surface through self-assembled method in order to form macroporous zeolite accumulated by nano-particles.This method overcomes the difficulties in separation of nano zeolite and expensive cost of mesoporous zeolite.And the product combines the advantages of nano-zeolite and hierarchical zeolite with high external surface area and short diffusion path.Furthermore,its uniform macroporous structure is beneficial for the selective separation of crude oil.So this material possesses a great potential in the catalytic cracking of heavy oil.The research part of this paper is divided into three sections: the preparation of nanosized zeolite,the preparation of organic microsphere template and its application in macroporous material,the assembling of nanosized zeolite on the template.In the chapter of preparation nanosized zeolite,nano-Y and zeolite SOD were prepared by different methods.The preparation of zeolite Y by hydrothermal method and dry-gel method were discussed in detail.Firstly,the preparation of nano-Y zeolite was carried out by template-free method in hydrothermal synthesis,and the influence factors,such as alkalinity,cation concentration and Si/Al ratio in the gel are studied in detail.The morphology,Si/Al ratio and forming progress of synthesized zeolite Y were carefully characterized by XRD,SEM,TEM,NH₃-TPD,FT-IR,N₂ adsorption-desorption and MAS NMR.It suggested that the preparation of this nano-sized zeolite Y has a wild phase interval,and the product was still nano size zeolite and possessed high external surface area after gel ratio was largely adjusted.In the view of the morphologies of nano-Y zeolite,because of the different gel ratio in preparation,it appears in variety of morphologies such as small particles,sheet-like structures,particles assembled spheres like structures and irregularly stacked bulks,and the size and the state of aggregation can be adjusted by changing the gel ratio.In the view of pore structure,all the samples maintained a good microporous structure and their outer surface has been greatly improved with the best surface area up to 186m²/g,the total pore volume of 0.81cm³/g.In the view of Si/Al ratio in framework,the change of the alkalinity and the Si/Al ratio in gel lead to the change of Si/Al ratio in framework,structure stability and acid performance in certain range.In this paper,Y zeolite was prepared by dry-gel method at the temperature of less than 100 ℃ at the first time.The Si/Al ratio and crystallization progress of dry gel and the crystallized samples were analyzed by FT-IR,MAS NMR,TG-DTG and so on.The results showed that some of the primary units structural of Y zeolite have been obtained in the gel,and the Si/Al ratio in these primary structures is obviously lower than the samples after crystallization,It is proved that the aluminum-rich gel is favorable for Y zeolite nucleation,and crystallization process makes more silicon into the framework.The temperature of the zeolite SOD prepared by the dry gel method was reduced to 70 ℃ at the first time.In the chapter of preparation of organic microspheres template,polystyrene（PS）and polymethylmethacrylate（PMMA）microspheres were prepared by emulsion polymerization and soap-free emulsion polymerization respectively.By changing the amount of initiator,monomer and emulsifier used in the solution,the particle size was adjusted continuously within 200 430 nm.To prepare microspheres smaller than 200 nm,some special method was used such as: polymer progress carried out in dilute solution,polymerization interrupted by adding polymerization inhibitor,cooling down,and changing the emulsifier.Those methods made the partical size adjusted in 30²00nm.With those organic microspheres template,some macroporous materials were prepared,such as: three-dimensional ordered macroporous（3DOM）SiO₂,macroporous Al₂O₃ and γ-Al₂O₃,hollow SiO₂.All these materials presented high thermal stability and uniform regular spherical macroporous.After preparation of macroporous zeolite based on the preparation of nano-zeolite and the PS template,the surface properties of PS were firstly characterized,then the way to modify the surface charge was explored,finally the feasibility of combination between template and zeolite was discussed in detail and verified by experiment.The result showed that the microsphere template can be crystallized into the crystal of zeolite for the first time,when the gel of zeolite was modified,and the centrifugal treatment can further increase the spatial limitation of the template to facilitate the preparation of macroporous zeolite.The preparation method of nanometer zeolite in this paper was applied to the preparation of macroporous zeolite.The results showed that:（1）the process of depolymerization and re-polymerization of zeolite and the incompatibility of organic and inorganic phases in zeolite synthesis are the two main factors that hinder the entry of the template into zeolite structure;（2）loose pore wall and regular crystal morphology make the macroporous structure is difficult to present a regular spherical;（3）The zeolite structure with uniform pore size（ 300 nm）can be obtained by combining dry-gel method,modificating conditions and centrifuging appropriatly.