Study On Preparation And Properties Of Self-Bonded Zeolite MCM-22 Particles Catalyst

Zeolite catalysts are widely applied in petrochemical industries. Synthetic zeolites and related molecular sieves are generally produced as powders of relatively loosely bonded zeolite. The binder is indispensable in order to produce particles catalyst of optimal dimension and form and having a high mechanical resistance. In such particles catalyst, the fact that the zeolite is diluted with a material that in most instances is inert in the process reduces the effective surface area of the product. Moreover, negative effects, such as blocking of the micropores and active sites by the binder, are pronounced when zeolite powders are prepared by adding an inorganic binder. Therefore, some novel alternative technologies are desired. Self-bonded MCM-22 particles catalyst were in-situ prepared using vapor-phase transport method in this dissertation. And, properties of self-bonded zeolite MCM-22 particles catalyst were investigated by alkylation of benzene and propylene.The characters of the aluminosilicate gel were firstly studied. It was found that self-bonded zeolite MCM-22 particles catalyst could be obtained by dry gel, hydrated gel, and dry powder method when the aluminosilicate gels were prepared using colloidal silica as silica sources, sodium aluminate as aluminum sources. Colloidal silica and sodium aluminate could be dissolved more easily and facilitate preparation self-bonded zeolite MCM-22 particles catalyst when the pH value of the aluminosilicate gel was 10.0. By adding polyethylene glycol to the aluminosilicate gel, the pore size distributions of zeolite particles catalyst could be adjusted.Based on the experimental results of in-situ preparation self-bonded zeolite MCM-22 particles catalyst, the suitable conditions are as follows: the ratio of material is SiO₂:(0.02-0.033)Al₂O₃:(0.09-0.12)Na⁺:1.0HMI: (5-30)H₂O, crystallization temperature 150℃and crystallization periods 168 h. The surplus liquid, chemical properties of which have not change after preparation self-bonded zeolite MCM-22 particles catalyst by the vapor-phase transport method, still contained only hexamethyleneimine and H₂O. Re-adding of hexamethyleneimine and deionized water, the surplus liquid could be reused. It could effectively improve the vapor-phase transport method's disadvantage of a large quantity of waste water and made the vapor-phase transport method become a cleaner process.The as-synthesized products obtained at different crystallization periods were carefully characterized and the crystallization process of self-bonded zeolite MCM-22 particles catalyst was discussed. It was found that the as-synthesized products were amorphous at 48 h and the amorphous phase disappeared at 72 h. The zeolite particles catalyst, prepared by aluminosilicate gel, had been transformed into hierarchical self-bonded zeolite MCM-22 particles catalyst after 168 h of crystallization. The crystallization proceeded via solution phase nucleation mechanism.Compared with the conventional method, the zeolite MCM-22 particles catalyst prepared by the new method, for which the total acid sites, the specific surface area and the average pore diameter reached 1.01×10^-3 mol/g, 486.82 m²/g and 115.85 nm respectively avoided binder accession. The distributions of products were discussed at different reaction conditions in in alkylation of benzene and propylene reaction. In the experiments, self-bonded zeolite MCM-22 particles catalyst possessed excellent reaction stability. The selectivity of cumene increased with increasing the reaction temperature and benzene/propylene ratio, the change of space velocity and reaction time had little influence on the selectivity of products. Self-bonded zeolite MCM-22 particles catalyst were more conducive to the purpose product in alkylation of benzene and propylene reaction. The selectivity of cumene could be improved about 5%. The selectivity of diisopropylbenzene and triisopropylbenzene Gould be reduced about 30% and 60%, respectively.