Study On The Technology Of Microwave-enhanced Synthesis Of Y-type Molecular Sieves

At present,the recovery processes of the spent fluid catalytic cracking（spent FCC）catalyst have many disadvantages,such as complex process,low removal rates of contaminant metals,and long crystallization time in the synthesis process.Therefore,the microwave heating technology is used to enhance the harmless handle of spent FCC catalyst in this work.And by comparing the mechanism of pure matter synthesis in microwave field,microwave heating technology is used to enhance the process of pure matter synthesis.Specifically,a microwave controlled leaching process has been employed to improve the removal efficiency of contaminant metals SFCC catalyst without destroying the zeolite-Y framework.The principle lies in the microwave energy that can selectively and quickly act on the contaminant metals and the polar molecules of the leaching solvent.The activated SFCC catalyst is then used as an aluminum source to synthesize zeolite-Y under microwave heating.Using the characteristics of microwave selectivity,efficiency and rapidity,the synthetic molecular sieves of pure materials were systematically studied.In this work,the characterization,which involves distribution,migration and speciation of contaminant metals in spent FCC catalyst,has been studied.By adopting the system experiment,the comparison experiment,a new recovering process of the spent FCC catalyst under microwave heating is proposed.In addition,the intensification mechanism of reactions between the spent catalyst and the solvent is revealed under microwave heating.（1）The deposition mechanism of contaminant metals in SFCC catalyst is successfully revealed.The results show that the contaminant metals deposit on the outer layer of the spent catalyst particles,forming 1.5-3μm deep contaminated layers.Fe and Ni mainly accumulate at and near the particle surface through the surface deposition mechanism.V eventually distributes throughout the catalyst particle through the mechanism of deposition before migration.Compared with Fe,Ni penetrates deeper into the SFCC particle.During the poisoning of the catalyst particles,Si migrates from the inside to the surface,and then combines with the contaminant metals Fe and Ni deposited on the particle surface.（2）The results of zeolite-Y synthesis show that microwave treatment can promote the high-temperature synthesis of Y-type zeolite with the advantages of shorter crystallization time and product properties of the produced Y-type zeolite.Specifically,under the optimized conditions,such as input ratio of Si/Al of 4,microwave heating temperature of 150℃,crystallization time of 0.5 h,pure Y-type zeolite is synthesized with BET specific surface area of 645 m²/g and the total pore volume is 0.322 cm³/g.Microwave-assisted acid activation process can facilitate the formation of the activeγ-Al₂O₃,which is promising for the synthesis of zeolite-Y.Compared with the inactivated SFCC catalyst,the activated SFCC catalyst has a larger specific surface area and a lower contaminant metal content.The specific surface areas of SFCC catalyst after activation by hydrochloric acid and oxalic acid show that a better activation by hydrochloric acid compared to oxalic acid in the microwave field.In addition,increasing the synthesis temperature and prolonging the crystallization time favor the growth of zeolite-Y crystal particles,however,zeolite-Y partially transforms into zeolite-P.The priority of different aluminum sources in zeolite-Y synthesis is:hydrochloric acid activated SFCC catalyst>oxalic acid activated SFCC catalyst>inactivated SFCC catalyst.