Modification Of ? Zeolite And Catalytic Performance For Esterification Of Maleic Anhydride

Diethyl maleate is an important organic ester by reacting maleic anhydride with n-butyl alcohol,because it is not only a kind of chemical materials but also a comment organic solvent.Hence,it has widely used in industrial production,such as fine chemicals,oil,drugs,plasticisers,food preservatives,cosmetics and paint.Maleic anhydride is produced by a batch process in industries using mineral acid catalysts such as hydrofluoric acid,sulphuric acid.Mineral acid catalysts are highly corrosive and need to be neutralised after the reaction for eliminating enviromental pollution.Therefor,there is a need for ecofriendly heterogeneous catalysts.? Zeolites have a three-dimensional interconnected channel system with 12-member rings,displaying excellent properties like high surface area,high hydrothermal stability,intrinsic acidity,and the ability to confine active metal species in their pores.Hence,? Zeolites are potential heterogeneous catalysts because of the excellent catalytic properties.But,direct synthesized? Zeolites also have many disadvantages,such as less active sites,narrow aperture,low SiO2/Al2O3 ratio,so its application is limited greatly.Therefor,? Zeolites must be modified to improve the catalytic performance and enlarge its application fields.In this paper,the modification of ? Zeolites mainly included acid modification,metal modification and the construction of hierarchical pores.The catalytic performance of modified ? Zeolites were investigated on the esterification of maleic anhydride with n-butyl alcohol.Moreover,the crystal structure and acidity properties of samples were characterized by X ray diffraction(XRD),N2 physical adsorption,Fourier infrared spectrum(FT-TR),Diffuse reflection UV-vis spectrum(DRUV-vis),NH3 temperature programmed desorption(NH3-TPD),X ray fluorescence spectrum(XRF),In-situ infrared spectrum,UV Raman spectrum,etc.In the first,the patent ? Zeolites were treated by a series of different concentration of nitric acid.The experimental results showed that:low concentration nitric acid only could remove extraframework Al species,while high concentration nitric acid could remove extraframework Al species and framework A1 species.After acid modification,the structure and acidity of zeolites both changed significantly.With the increase of nitric acid concentration,the crystallinity,total acid amount,surface area and pore diameter of modified zeolites decreased.To improve the catalytic performance,? zeolites were introduced Sn in surface or framework,named Sn-Beta and Sn-Beta-X,respectively.The experimental results showed that Sn introduced in skelecton had better catalytic activity,conversion of maleic anhydride could reach 98%and yield of diethyl maleate above 97%.This is because Sn entered into zeolite framework formed Sn-O-Si,improving the catalytic activity and stability.In order to improve the mass transfer of ? zeolites,by using cetylt-rimethyl ammonium bromide as structure direct agent and dealuminated ?zeolite as silicon source,hierarchical Sn-Beta zeolites were prepared,which had advantages both of micropore zeolit and mesoporous materials.The results showed that hierarchical Sn-Beta zeolite had best catalytic performance,compared with Sn-Beta and Sn-Beta-X.So what does this show?This illustrates mesoporous is very beneficial.As a result,the acidity properties and porous structure of modified zeolites both affect its catalytic performance.