Research Of Activity Regulation And Catalytic Performance Of TS-1 Titanium Silicalite Zeolite

“Environmental-friendly technology”is the key direction of the current chemical production process.Propylene oxide and epichlorohydrin are all important chemical raw materials.Currently,the production of propylene oxide and epichlorohydrin in domestic adopt the traditional high-pollution chlorohydrin method.The olefin epoxidation system using TS-1titanium silicalite zeolite as catalyst and H₂O₂ as oxidant,has been paid great attention and became one of the most promising systems for industrial applications,for its mild reaction conditions,high product selectivity and without pollution problems.TS-1 titanium silicalite zeolite as the core of the olefin epoxidation reaction,it has excellent catalytic oxidation performance.The traditional synthesis method has a high production cost,however,low-cost synthesis system easily leads to an increase of the grain size;the hydrolysis rate of the titanium source and the silicon source difficult to match and cause a large amount of non-framework titanium;at the same time,the confinement effect of micropores also prevent the diffusion of product molecules.The above factors inhibited the catalytic performance of TS-1 zeolite and severely restricted its industrial application.Therefore,research and development of TS-1titanium silicalite zeolite with low preparation cost,high framework titanium content,and small crystal size while having hierarchical structure is the premise and basis for the promotion of clean production and industrial upgrading of propylene oxide and other products.In this paper,in the low-cost synthesis system,the hydrolysis rate of titanium source and silicon source is firstly matched by the adjustment of the synthesis parameters;by adding seed and steam-assisted crystallization method to prepare nanosized TS-1 with only tetra-coordinate Ti species and uniform particle size.The small crystal grains can increase the specific surface areas of the molecular sieve to exhibit more active sites,and small crystal grains also reduce the diffusion resistance of the b-axis straight channel,thereby improving the reaction performance of olefin epoxidation.On the basis,hierarchical TS-1 were prepared in different ways to improve the diffusion performance of the olefine epoxidation reaction by regulating the pore structure,which provides a design and theoretical basis for the synthesis of hierarchical nanosized TS-1.The as-synthesized nanosized TS-1 as parents was modified by post-treatment with different solutions to obtain hierarchical TS-1,the mechanism of modification was explored.The results show that the modification with Na₂CO₃ solution will cause the collapse of the framework and the loss of Ti due to the reverse reaction of crystallization;the modification with TPAOH solution changes the coordination state of Ti in the framework,and leads to the occurence of Ti which has no benefit for catalytic effect;the post-modification with pure NH₄F solution can produce abundant mesopores in the intracrystalline,the hydrophobicity of the molecular sieve after treatment increased,and the catalytic performance in the propylene epoxidation is significantly enhanced.The soluble starch was used as hard template and adopted a space-filling method to prepare hierarchical nanosized TS-1.The pH of the crystallization system can be adjusted during the preparation process to obtaining a TS-1 zeolite with rich tetra-coordinate Ti species.For the allyl chloride epoxidation,the sample with the starch/SiO₂?mass ratio of 0.4?exhibited the outstanding catalytic performance.Through the regulation of the synthetic chemical environment,the Kirkendall growth effect can be used to realize the preparation of nanoscale TS-1 crystals with hierarchical structure in one step without the presence of additional mesoporous templating agents.The optimized preparation conditions can be obtained by investigating the synthesis parameters,and controllable preparation of the particle size and pore size,and high yield can be realized,it can provide theoretical guidance for the large-scale synthesis of hierarchical zeolite.