Structure And Active Center Regulation Of MTW Zeolite And Study On The Alkylation Of Phenol With Tert-butyl Alcohol

Tert-butyl phenol,as an important chemical raw material,were widely used in various fields.However,the contradiction between the increasing demand and backward production technology had aroused widespread concern.The traditional liquid acid catalyst had many problems,which seriously affect the production efficiency and the surrounding environment.In view of the backward production technology of tert-butyl phenol,researchers focus on developing new,efficient and green catalysts.And zeolite was a solid acid catalyst,which had the advantages of adjustable acidity,type-selective catalysis and no pollution.In this thesis,using the MTW zeolite with special one-dimensional linear straight channel system as the catalyst,the reaction between phenol and tert-butyl alcohol was studied based on the porosity and acidity of MTW zeolite,which provided a feasible and effective scheme for the green production process of tert-butyl phenol.Firstly,microporous MTW zeolite precursor was synthesized by hydrothermal method and alkaline treatment was carried out.In the process of alkaline treatment,piperidine was added as structure protective agent and the amount of piperidine added was changed to control the degree of zeolite defect.MTW zeolite with different defect degrees were successfully synthesized by this method,and the crystal form,morphology,acidity and diffusion properties of the defective MTW zeolites were characterized by different characterization methods.By adding protective agent,MTW zeolites not only successfully introduced mesopores,but also protected its activity,and the channel parameters and acidity data showed regular changes.The alkylation of phenol and tert-butyl alcohol was catalyzed by synthesized MTW zeolite to explore the influence of zeolite pores on the reaction.The defective MTW zeolites showed a phenol conversion of～95%and a selectivity of～80%for4-tert-butylphenol.In terms of zeolite lifetime,the defective MTW zeolite had better anti-clogging ability and better reaction stability because of its more mesopores and higher effective diffusion coefficient.Secondly,a series of MTW zeolite with different Si/Al ratios were synthesized by hydrothermal method.The Si-Al ratio of zeolite was adjusted by changing the amount of aluminum source during synthesis,and the crystal form,pore parameters and acidity of this series of zeolite were characterized.It was determined that three MTW zeolite with different acidity were successfully synthesized.Changing the aluminum content had little effect on the crystal form and pore parameters of MTW zeolite,but it had significantly effect on acidity.In the reaction,we found that the higher the acid concentration,the higher the reaction activity,and the reaction activity is obviously affected by the acidity.In addition,MTW zeolite with different acidity correspond to different product distributions,from which the following conclusions can be drawn:low acid concentration is beneficial to the formation of tert-butyl phenyl ether;Medium acid concentration was beneficial to the formation of 2-tert-butylphenol and 4-tert-butylphenol;High acid concentration is beneficial to the formation of 2,4-di-tert-butylphenol.Therefore,acidity is the most important factor affecting this reaction.Thirdly,the MTW zeolite with different mesoporous degrees were synthesized by soft template method,and then these MTW zeolite with different mesoporous degrees was sulfonated to synthesize sulfonic acid MTW zeolite with different acidity.The principle of sulfonation was that there were a lot of silicon hydroxyl groups on the surface of zeolite,some silane coupling agents can react with them,and then the sulfhydryl groups in silane coupling agents are oxidized into sulfonic acid groups by means of oxidation,so that sulfonic acid groups can be successfully introduced into zeolite to finish the sulfonation modification.XRD,XPS,²⁹Si MAS NMR,thermogravimetry and other means confirmed that sulfonic acid group was successfully grafted on the surface of MTW zeolite.Through pyridine infrared adsorption,it was determined that the acidity of MTW zeolite were greatly improved after being modified by sulfoacid.After sulfonation modification,the pore channels of MTW zeolite were blocked to a certain extent,because the large sulfonic acid groups were in the zeolite pore,which certificated that it was necessary to use mesoporous zeolite as grafting carriers.In reaction,the activity of sulfonic MTW zeolite is higher than that of unsulfonated MTW zeolite,and the acidity and catalytic activity of MTW zeolite also increase with the increase of mesoporous degree.In sulfonic acid system,2-tert-butylphenol became the main product（with the selectivity of～54%）,and through literature investigation,we found that this was due to the change of reaction mechanism.From the original Eley-Rideal reaction mechanism（single active state participating in the reaction）to Langmuir-Hinshelwood reaction mechanism（double active state participating in the reaction）,when phenol and tert-butyl alcohol were both adsorbed state,the negative effect of steric hindrance decreased,so that the main product was converted from4-tert-butylphenol to 2-tert-butylphenol.