Synthesis Of Beta Zeolite Membranes And Its Acid Catalytic Activity

Beta zeolite is a large-pore silicon-rich zeolite with 12-rings channels,and it is well-known for its special three-dimensional structure and its excellent catalytic properties.For Beta zeolite,a large amount of template is always used in the sysnthesis system.But the template will remain in the structure of zeolite and reduce the useablity.As usual,high temperature??29?723 K?combustion is traditionally employed to remove these templates,but it often results into damage of local crystal structure and decrease of acidity.In this paper,we use catalytic hydrocracking technology to remove templates at a mild temperature?613K?.This approach shows high efficiency on template removal and maintains local structure of zeolites while the high temperature combustion turns framework Al into extra-framework Al and reduce its acid activity.The catalytic performance of esterification for ethyl acetate is also proved this result.This approach plays an important guiding role in removing template for zeolite and zeolite membrane.Although Beta zeolite has excellent catalytic activity,its micropore size is only about0.55-0.65nm,some molecule with large size cannot enter the channels,and they can only react with the active center on the surface.So its catalytic activity is limited.For this,we get hierachical beta zeolite through alkali treatment by TEAOH?Tetraethyl ammonium hydroxide?.The sharacterization results show that,hierachical beta zeolite has more framework Al and its pore size increases to about 1nm.Besides these,hierachical beta zeolite has better catalytic activity and stability.So,we can say that,the alkali treatment by TEAOH can not only make the hierachical structure,but also adjust the framework which can increase the acid activity of beta zeolite.Different from normal Beta zeolite seed,we get other Beta zeolite seeds with different size and status,and then we synthesise different zeolite membrane by using different seed.With adding the polymer PDDA,the zeolite seed has the same size than normal seed while the particle become agglomerate.Synthesis zeolite membrane by this agglomerate seed has a better result.The memebrane shows superior defect-free structure and better permeation,they meas a better usablity of zeolite membrane.In order to find the application of zeolite membrane in thick water filtration,we assemble the pressurized filtration unit with blank?-Al₂O₃ ceramic tube,then we explore the relationship between the pressure and flux of thick water and the permeation of fresh water.Our research show that,under a certain flow rate,the permeation flux is positively correlated with the thick water pressure,but it`s different under a certain pressure.Under a high pressure,middle flow rate is beneficial to high permeation flux,but the permeation flux is positively correlated with the thick water flow rate under a low pressure.In addition,we find the blank ceramic tube is easily blocked by the thick water,so the pretreatment of thick water before filtration is very necessary.These results provide a reference for the application of the zeolite membrane in water filtration.