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Attapulgite In Situ Crystallization Of Y Zeolite And Its Raw Oil Hydrocracking Performance

Posted on:2012-04-10Degree:MasterType:Thesis
Country:ChinaCandidate:S HuangFull Text:PDF
GTID:2191330335990009Subject:Organic Chemistry
Abstract/Summary:PDF Full Text Request
A Y-type zeolite was successfully synthesized via an in situ crystallization method. The basic principles and the best parameters of the crystallization process were particularly investigated. The attapulgite fluid catalytic cracking (FCC) catalyst was prepared by the ion modification of the Y-type zeolite. Feedstock oil was catalytically cracked on a fixed fluid bed (FFB) using the attapulgite FCC catalyst, and the FCC reaction mechanism and the physical and chemical properties of the feedstock oil were analyzed. The as-synthesized Y-type zeolite and the attapulgite FCC catalyst were characterized by means of scanning electron microscope (SEM), X-ray diffraction (XRD), FT-IR and N2 adsorption-desorption.(1) The SiO2and Al2O3 in attapulgite with Fe3+removed by the acid treatment were activated by the heat treatment, and the properties of the as-obtained product were characterized by XRD, TG-DTA and FT-IR. The effect of the acid treatment with 6 mol/L HC1 on the content of Fe3+ was explored. Great concern was given to the researches on the contents of active SiO2 and A12O3 in calcined attapulgite. The results reveal that the content of Fe3+is below 1.0%after the acid treatment, which meets the requirement of the FCC catalyst. Moreover, the maximum content of active SiO2 is achieved when the calcination temperature is 950℃. It should be noted that the content of Al2O3 decreases rapidly with increasing the calcination temperature and can be neglected at about 950℃. Therefore, the needed A12O3 for the in situ crystallization of attapulgite should be furnished by adding metakaolin.(2) With calcined attapulgite providing active SiO2 and matakaolin providing active A12O3, accompanied by sodium silicate, alkaline solution and directing agent, the Y-type zeolite was successfully synthesized via an in situ crystallization method under hydrothermal conditons. The as-synthesized Y-type zeolite samples were characterized by SEM, XRD, FT-IR and N2 adsorption-desorption techniques. The effects of the crystallization temperature and the ratio of raw materials on the relative crystallinity of the as-synthesized samples were particularly investigated. The results show that the crystallization temperature is the main dynamic factor in the synthesis of the Y-type zeolite. As the crystallization temperature increases, the relative crystallinity of the product improves markedly. When the crystallization temperature raises to 100℃, the high relative crystallinity of the Y-type zeolite is obtained. In the in situ crystallization system, the relative crystallinity of the samples increases with the ratio of n(Si02)/n(Al203) decreasing. Meanwhile, the appropriate alkalinity (n(Na2O)/n(SiO2) and n(Na2O)/n(H2O)) can obviously increase the relative crystallinity of the Y-type zeolite. The optimum ratios of n(SiO2):n(Al2O3), n(Na2O):n(SiO2) and n(H2O):n(Na2O) are 4.7,0.65 and 50, respectively, under which the relative crystallinity of the obtained Y-type zeolite is 53.6%and the molar ratio of silicon/aluminium for the product is 5.28.(3) The calcined attapulgite microspheres, metakaolin microspheres, alkaline solution, sodium silicate and directing reagent with the optimum ratio were put into an auto clave to prepare the Y-type zeolite by in-situ crystallization. The attapulgite FCC catalyst was prepared by NH4+and REC1 modifications of the as-received Y-type zeolite, followed by the calcination and precipitation. The as-prepared attapulgite catalyst samples were characterized by SEM, FT-IR and N2 adsorption-desorption, and their acidities were analyzed by pyridine infrared spectrometer. The charateration results show that the attapulgite FCC catalyst presents regular spherical structure, and the surface of the spheres is covered by the Y-type zeolite evenly, which is the active composition of the FCC catalyst. Moreover, the attapulgite FCC catalyst exhibits a big BET surface area and mesoporous volume. The acid strength and acid density of the attapulgite FCC catalyst are ideal.(4) The mechanism of the catalytic cracking and properties of the feedstock oil were analyzed. Feedstock oil, atmospheric residue and different proportion VR-mixed wax oil were evaluated on FFB. The reaction mechanism analysis of the catalytic cracking reveals that the reaction of the catalytic cracking proceeds with the formation of carbon-cations resulted from the hydrocarbon molecules reacting with the acid canters of that catalyst, followed by many transfer reactions. The FFB evaluation results discloses that both of the FCC catalyst and the properties of the feedstock oil have influences on the degree of the feedstock oil cracking, conversion rate of the feedstock oil, and the yields and distribution of the cracking petrochemical.
Keywords/Search Tags:Fluid catalytic cracking, Attapulgite, In-situ synthesis, Y-type zeolite, Alkalinity, Catalytic cracking reaction mechanism
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