In-situ Synthesis For Increasing NaY Zeolite Framework Si/Al And Study On Catalytic Cracking Performance

The synthesis of high-silica Y-type zeolite is beneficial to control the structural stability,structural flexibility,pore structure distribution and surface properties（hydrophilicity,acid-base）of Y zeolite,which further affects its catalytic cracking performance.In addition,the accurate determination of the framework Si/Al ratio also has important research significance for the synthesis of high-silica Y zeolite.Compared with the traditional control strategy of Si/Al ratio（post-treatment dealumination technology and the use of organic templates）,the in-situ method of adjusting the Si/Al ratio of the zeolite can not only maintain its structural integrity and good crystallinity,but also cut the synthesis cost and avoid environmental pollution.In this desertation,the experiment ultilized in-situ synthesis method with the condition of commercial Y zeolite seed crystals as structure directing agent,from the aspects of aluminum inhibition and silicon supplementation,exploring the effects,including the type、dosage and synthesis conditions（reaction temperature,time,etc.）of the silicon source,on the crystallinity and Si/Al ratio of zeolite.Firstly,pure phase high-silica Y zeolite was synthesized using sodium silicate as the silicon source and commercial Y zeolite as the structure directing agent.The specific research contents include the following two aspects:1.Inhibition of Al from:Using Zn ions to inhibit Al ions from entering into the zeolite framework;Adjust the number and position of Al sites in zeolite framework by reducing the Na⁺concentration;Increasing the ratio of Si/Al by using inorganic template NH₄⁺instead of organic cations.2.Improving the entrance of Si into the framework:Using H₂O₂ as the initiator of hydroxyl radicals to enhance the formation of Si-O-Si bonds;Use the method of gradually adding silicon source to the reaction solution to increase the content of silicon in the product;Adjusting the synthesis conditions（reaction temperature,time,silicon supplement method,etc.）to obtain Y zeolite with high crystallinity and high Si/Al.The Si/Al ratio is increased from 1.6 to 2.7 by reducing the Na⁺concentration and the coupling method of silicon supplementation.The synthesized Na Y zeolite was ion-exchanged to HY,and then dealuminized to obtain USY.Tetrahydronaphthalene was used as raw material for catalytic cracking reaction（The reaction temperature was 500℃）.The reaction results show that HY-2.4 has suitable acidity and crystallinity,exhibiting good catalytic performance.In order to further increase the Si/Al ratio of Y zeolite,organic molecules were ultilized to synthesize Na Y with a high Si/Al ratio,which is specifically divided into the following two aspects:1.Organic template:using tetraethylammonium hydroxide and tetrabutylammonium hydroxide to improve Si/Al,and exploring the influence of NH₃.H₂O concentration respectively;2.Organic silicon source:using 1,2-bis（triethoxy）（Silicon-based）ethane replaces sodium silicate as the silicon source,exploring the feed ratio of the two silicon sources,adoptimg the same way of replenishing silicon to improve Si/Al.By reducing the Na⁺concentration and using organic silicon source coupling,Si/Al ratio reached 4.6.The HY was obtained by ion exchange of Na Y and then treated with dealumination post-treatment to obtain USY.In the catalytic cracking reaction with tetralin as a model compound,the conversion rate of HY-4.6 has been increased with a small extent.