Study On Citric Acid Dealumination And Rare Earth Ion Exchange Modification Of Zeolite NaY

Zeolite Y is widely used as catalytic cracking catalyst due to its rich pore structure and excellent gasoline selectivity.With the refining of crude oil,the problems of poor selectivity and easy deactivation of zeolite Y have become increasingly prominent.Research on modification of synthetic zeolite Y has become a hot spot.The modified Zeolite Y is widely used in Fluidized Catalytic Cracking?FCC?reactions.It is the main component of catalytic activity,selectivity and stability in FCC catalysts,and as an efficient and stable active component in catalysts.The two most commonly used modification methods in the industry are acid dealumination modification and rare earth ion exchange modification.In this paper,citric acid is used as complexing agent for acid dealumination experiments on zeolite NaY,and Y³⁺is used for rare earth ion exchange experiments on zeolite NaY.1.Zeolite NaY was modified with citric acid dealumination.In this paper,citric acid was used as a complexing agent to deal with zeolite NaY.Through changing the citric acid concentration,reaction time,and reaction temperature,the dealumination behavior of NaY molecular sieves in citric acid solution was investigated.The results showed that the concentration of citric acid had the most significant effect on zeolite.When the concentration of citric acid was 0.2 mol/L,the framework silicon-aluminum ratio of zeolite NaY increased by 1.4.In the initial stage of the reaction,the rate of aluminum atoms in the zeolite NaY framework was high,and the chemical silica-alumina ratio and crystallinity of the molecular sieve dropped sharply.With the progress of the reaction time,the chemical silica-alumina ratio and crystallinity of the zeolite have increased,indicating that the framework atoms have been rearranged.The citric acid dealumination of zeolite NaY is not affected by temperature.Compared to zeolite NaY without citric acid treatment,the sample of dealuminized zeolite treated with 0.1 mol/L citric acid for 2hours at 75°C has a 0.6%increase in the framework silicon-aluminum ratio and 17 m²/g of mesoporous specific surface.The dealumination produces a amount of amorphous silica,which can be used as a raw material for the synthesis of other molecular sieves,and provides an important idea for the synthesis of composite molecular sieves.2.Rare earth ion exchange modification of Zeolite NaY.The results show that the acidity of RE-NaY zeolite is gradually strengthened with the increase of rare earth content.After hydrothermal treatment of RE-HY zeolite,it was found that with the increase of the rare earth content,the stability of the zeolite gradually increased,and the retention rate of crystallinity of the zeolite after Y³⁺exchange was higher than that of the zeolite after La³⁺exchange.After conducting many reverse exchange experiments on RE-NaY zeolite with NH₄⁺,it was found that compared with La³⁺,Y³⁺is easily reversely exchanged from the zeolite framework structure,which may be related to its smaller ion radius.3.Combined with XRD,Rietveld refinement method was used to study the migration and positioning of Y³⁺in zeolite.After the Y-NaY zeolite after an ammonium exchange,most of the sodalite cages in which Y³⁺enters the zeolite are positioned at S??,and form coordination with O3.Compared with La³⁺,T-O bond and Y-O3 coordination bond after Y³⁺exchange are shorter.After the RE-NaY zeolite was hydrothermally treated,the acid retention rate of the zeolite after Y³⁺exchange was higher than that of the zeolite after La³⁺exchange.And the dealuminization phenomenon of the zeolite after Y³⁺exchange was not obvious,and the dealuminization phenomenon of the zeolite after La³⁺exchange was serious.In summary,due to the stronger coordination ability between Y³⁺and O atoms,the T-O bond of the molecular sieve is shrunk,which is more conducive to stabilizing the zeolite skeleton structure.