Synthesis, Characterization And Modification Of Nanosized NaY Zeolite

NaY zeolite is a kind of porous material with distinct structurally three-dimensional framework and very rich surface acid site,which is the main active component of fluidized catalytic cracking catalysts.Nanosized zeolites refer to zeolites below 100 nm,which have larger surface area,shorter pores and better diffusion properties compared with the conventional micrometer zeolites.Therefore,nanosized NaY zeolites have superior catalytic properties than conventional NaY zeolite,such as higher activity in cracking reaction and longer life during catalysis.At present,nanosized NaY zeolites systhesized with various methods uaually have low n?Si?/n?Al?ratio and poor hydrothermal stability,therefore,it is necessary to improve the n?Si?/n?Al?ratio of nanosized NaY zeolites by appropriate post-modification method to use them in industry.In this work,high crystalline nanosized NaY zeolites were hydrothermally systhesized without any stucture-directing agents and templates,using industrial water glass and ludox as the silicon source,sodium aluminate as the aluminum source.Aging conditions,crystallization conditions and mixing methods have a great influence on the performance of synthetic zeolite products.The number of nucleus is less at low aging temperature as silicate ions in water glass are in the form of polygene.But when the aging temperature is too high,it will probably appear a little impurity of P-type zeolite.Aging time is also one of the factors affecting the number of nucleus in the gel.When aging time is too short,the number of nucleus in the gel is insufficient.While the aging time is too long,the nucleus are saturated and connected causing the grow up of molecular sieve particles.Crystallization time mainly affects the crystallinity of the product,crystallization has not yet been completed when the crystallization time is too short,and the crystallinity of the zeolite is low.Crystallinity of the zeolite product was improved with the crystallization time extension,but molecular sieve particles would grow up as the crystallization time is too long.Dynamic crystallization and ultrasonic assisted mixing can make the gel more uniform to prepare smaller molecular sieve products,and then the particle size distribution is more uniform.The optimum reaction conditions are: aging temperature is 60oC,aging time is 4 h,crystallization temperature is 90oC and crystallization time is 28 h.The nano-NaY products are below 100 nm and closely graded as the reaction volume was enlarged to 10 times,which were found to have similar properties to the small volume products.The specific surface area of the nano-NaY products is 961 m²/g,and the extra specific surface area is 82 m²/g.The obtained nanosized NaY zeolites were dealuminated by liquid phase chemical method using ammonium fluorosilicate and oxalic acid as aluminum remover.When the ammonium fluorosilicate is used as the aluminum remover,the main influencing factors are the amount of fluorosilicate,reaction time and reaction temperature.The optimum reaction conditions are:?NH₄?₂SiF₆/ NH₄NaY=0.3,reaction time is 5 h and reaction temperature is 75 oC.As the ammonium fluorosilicate has not only the role of removing aluminum,but also the role of adding silicon,the product can be a high degree of crystallinity in the process of reaction.Using oxalic acid as aluminum remover,its main removal of aluminum is non-skeleton aluminum,the degree of crystallinity of the product is reduced with the increase of oxalic acid usage.It is indicated that the dealuminated nano Y zeolite got higer n?Si?/n?Al?ratio with structural pore,the specific surface area of it is 915 m²/g,and the extra specific surface area is 90 m²/g.The acid sites were decreased by dealumination,and the strong acid sites were increased,therefore it has shown better properties in the pyrolysis of 1,3,5-triisopropylbenzene.