Synthesis,Characterization And Catalytic Performance Of The NaY Molecular Sieves With The Controllable Small Particle Size

NaY molecular sieves as a basic catalyst have been widely used in hydrogenation cracking, catalytic cracking and isomerization of petroleum refining processes.However, the average particle size of industrial NaY molecular sieves is generally about 1 ?m, large grain, which results in a significantly decreased mass transport and diffusion rate of the guest species and also affect the catalytic activity. Silane coupling agent due to its unique reactive groups can prevent the further growth of the crystal in NaY synthesis system, which is useful to obtain NaY molecular sieve with controllable particle size. Therefore, we just use cheap and non-toxic silane coupling agents as partial silicon source to synthesize NaY molecular sieves with controllable small particle size by directing agent method. This thesis mainly focuses on the synthesis, structure, characterization and catalytic performance of cumene cracking of NaY molecular sieves with small particle size, the results obtained are as follows:Using silica sol and methyltriethoxysilane(MTS) as silicon source in the directing agent synthesis system, the factors affecting dosage of silane coupling agents(MTS), crystallization temperature, crystallization time and water content on the synthesis of NaY molecular sieves with the controllable small particle size were investigated in detail. The structure and morphology of the synthesized samples were characterized by means of XRD, FT-IR, Water Contact Angle, SEM, N2adsorption-desorption(BET), and ICP. The results indicated that the NaY molecular sieves(Si O2/Al2O3=3~4) with the controllable small particle size(100~300 nm) were successfully synthesized using MTS as partial silicon source, when adding amount of MTS was 2 m L, crystallization temperature of 100 ? for 5 hours, 17.4 m L of water.NaY molecular sieves have the most uniform average particle size of about 180 nm,high relative crystallinity, the micropore surface area of 798 m2g-1 and micropore volume of 0.31 cm3g-1Combining the above mentioned synthetic conditions(17.4 m L of water,crystallization temperature of 100 ? for 5 h), with X-ray diffraction(XRD),scanning electron microscope(SEM) and other characterization methods, the effects of dosage of diethoxydimethylsilane(DMTS) on the particle size and structure performance of NaY molecular sieves were investigated in detail. The results indicated that the crystallinity and particle size of NaY molecular sieves decreased with the increasing of the methyl groups, when adding amount of DMTS was 1.8 m L(the same molar with 2 m L MTS), which has the most uniform average particle size of about 150 nm, high relative crystallinity, the micropore surface area of 704 m2g-1 and micropore volume of 0.27 cm3g-1, and the size was more uniform. However, the molarratio of Si O2 to Al2O3 of synthetic samples was low; resulting in poor thermal stability during the NH4+ exchange and calcination process, which showed that it was not suitable for catalytic cracking of cumene.Based on the above research results, the NaY molecular sieves(Si O2/Al2O3=4.8~5.6) with the uniform particle size(1.0~1.8 ?m) and high-silica were hydrothermally synthesized by direct method using MTS as additive. Combining with X-ray diffraction(XRD), scanning electron microscope(SEM), FT-IR and Al-NMR and other characterization methods, the effects of dosage of MTS and crystallization temperature on structure and performance of NaY molecular sieves were investigated in detail. The results showed that the introduction of MTS could improve the ratio of Si O2/Al2O3 of NaY molecular sieves. Compared with directing agent method, NaY molecular sieves synthesized by direct method has higher thermal stability, showing that the catalytic cracking of cucume has higher catalytic activity.The optimum reaction conditions were obtained such as amount of MTS added was0.2 m L, the ground size of the catalysts was around 40~60 mesh, and reaction temperature of 350 ?. Meanwhile, the best catalytic performance achieved was as high as 86.3 % at the beginning of the reaction and maintained up to 40 % even after the reaction for 400 minutes more.