Controlling Composition And Structure Of Y Zeolite

Rare earth-containing Y zeolite（REY） is widely used in the petroleum refining industry, owing to its favorable acidity, high cracking activity and good hydrothermal stability. With the consumption of rare earth resources and the price of rare earth growing recently, it is necessary to find substitutes for La Y and Ce Y to protect the limited rare earth resources and to lower the cost of REY. In this work, a series of metal modified Y zeolites were prepared from Na Y zeolite by ion-exchage method. The feasibility using these modified Y zeolites as substitutes for Ce Y or La Y was discussed by comparing their properties and structure. Then the structure of Y zeolite was controlled by citric acid-nitric acid modification system.When the concentration of ion-exchange solution was low, Zr Y was prepared and the feasibility using it as potential substitute for Ce Y was studied by investigating its structure parameters, then the optimum ion-exchange condition of Zr4+ was determined by single factor test. Afterwards, a series of Y zeolites were prepared under high concentration of ion-exchange solution. The structure and properties of these different types of Y zeolites were characterized by X-ray diffraction（XRD）, pyridine adsorption IR（Py-IR）, ammonia temperature programmed desorption（NH3-TPD） and nitrogen adsorption-desorption methods. Results show that Y³⁺ is the optimum ion to replace La³⁺ and Ce³⁺. YY has similar acidity but better hydrothermal stability than Ce Y. YY catalyst performed much better than Ce Y catalyst during the heavy oil catalytic cracking test. Compared with La Y, YY possesses similar acidity and hydrothermal stability. The performances of YY catalyst and La Y catalyst show minor difference when the aging condition was mild, however, when the aging time was extended to 16 h, YY catalyst shows a better catalytic performance than La Y catalyst.The bi-metal Y zeolites were obtained by compounding Y³⁺ with La³⁺ or Ce³⁺, and it was found that with the increase of Y³⁺ content, the hydrothermal stability of bi-metal Y zeolites was enhanced, while the acidities show little change. Afterwards, the optimum ion-exchange condition of Y³⁺ was determined by orthogonal experiment and the effect of Y³⁺ content on the structure and properties of Y zeolite was investigated. Then, a tentative exploration on the structure controlling of YY zeolite was carried out under citric acid-nitric acid modification system. Results show that reaction temperature affects the modification effect most, and under appropriate conditions, zeolite with certain mesopore structure can be abtained.