【作者】 孙秀良；

【导师】 陈标华； 黄崇品；

【作者基本信息】 北京化工大学 ， 化学工程与技术， 2009， 博士

【摘要】 β分子筛是一种具有独特的三维十二元环大孔结构的高硅沸石,拥有优异的催化性能和极为重要的工业应用价值,迫切需要大幅度地改善现有分子筛合成技术,降低合成成本。因此,本论文对廉价合成β分子筛技术进行了研究,并在此基础上展开对分子筛合成机理的研究,为沸石合成提供理论意义和实际指导。本论文首先采用广泛应用的动态水热合成法和气相法合成了β分子筛,进而,通过对蒸汽相法制备干胶过程的改进和采用廉价模板剂TEABr,获得了一种新的廉价体系合成方法-固相合成法。XRD、SEM及FT-IR表征结果表明固相法合成β分子筛晶形良好。与动态水热法、蒸汽法相比,固相合成法工艺简单,成本较低。考察了β分子筛固相合成过程中晶化温度、晶化时间、碱度和模板剂用量对产物结晶度的影响。结果表明：当选用SiO2作为硅源,NaAlO2作为铝源,TEABr作为模板剂时,较优工艺条件为：(SiO2/Al2O3=30), OH-/SiO2=0.40, TEABr/SiO2=0.15,添加晶种4%(与硅源总质量相比),晶化温度为130℃,晶化时间为4天,合成的β分子筛晶形良好,丝光杂晶峰强度较低。对固相合成的β分子筛进行中试放大生产,得到的晶化产物结晶度较高,杂峰较低。对β分子筛进行了酸性和孔结构表征,结果说明微量的丝光沸石对整体的β分子筛的酸性和孔结构影响不大。在固定床微反应器上考察了固相法合成的β分子筛对烯烃的异构化能力。实验结果表明,β分子筛具有较高的异构化产物收率和较好的丙烯收率,水热老化处理后仍保持了烯烃异构化能力。较低硅铝比的β分子筛具有较高异构化活性和较差的芳构化能力。将中试产品作为助剂添加到主催化剂中进行催化裂化反应(特别适用于重质烃油,通常为渣油),有较高的进料转化率、液收和丙烯产率。通过量子化学计算方法分别模拟β和丝光沸石的合成初期硅酸根和铝酸根单体之间的缩聚过程,采用B3LYP方法和6-31+G(d, p)基组,计算结果表明：模板剂TEA+在合成过程中起到降低反应活化位垒的作用,使二聚体的活化能降低了9 kJ/mol。在二聚体向p和丝光沸石的三聚体q2Al的转化过程中,β和丝光沸石的硅铝酸根缩聚都遵循一步成键机理,合成丝光沸石三聚体的活化能为70 kJ/mol,当存在TEA+时,活化能降低为67.2 kJ/mol,说明TEA+对丝光沸石的合成影响有限；而合成p分子筛的三聚体的活化能为102.3 kJ/mol,当存在TEA+时,活化能降低为53.1 kJ/mol,降幅明显,说明TEA+十分有利于β分子筛的合成。为了进一步考察在实验中得不到的β分子筛酸性的重要信息,在密度泛函的B3LYP/6-31G(d, p)水平上,研究了β分子筛中Al和Brφnsted酸的落位及其酸性强度。根据Al(OSiH3)4--TEA+的主.客体相互作用能、Al/Si和(Al,H)/Si替代能、去质化能、O-H伸缩振动频率和碱性探针分子NH3在β分子筛酸性位的吸附能的计算,结果表明：β分子筛中的骨架Al和Brφsted酸有利于落位在T5和T6位,不利于落位在T1和T3位。A15-O14-Si9位置的酸性最强,A17-O3-Si1的酸性最弱。更多还原

【Abstract】 Zeoliteβis one of the aluminosilicate materials with three-dimensional system of interconnected 12-membered ring large-pored channels structure and high silica crystalline. Zeoliteβhad shown outstanding catalytic properties in some chemical and petrochemical processes.It is an important target to improve this zeolites synthesis technology for extensively decreasing the cost. So, the new cost-effectively synthetic method was studied, and in order to carry out the guidance and predict of the prepatation technique of new type zeolite, we have studied the synthesis mechanism of zeolite.In the present work, the thdrohermal synthesis synthetic method and DGC method are used to synthesisβzeolite firstly. By the betterment on the process of dry gel conversion of steam-assisted synthesis and introducing a cheap template TEABr, a new cost-effectively synthetic method is obtained. XRD,SEM and FT-IR indicate that the structure of zeoliteβby cost-effectively synthesis is good. Compared with steam-assisted synthesis and hydrothermal synthesis, solid-phase synthesis is promising and economical,which simplifies the synthetic process and reduce the costs. In this paper, the effect of crystallization temperature, crystallization time, alkalinity, the amount of template on the crystallinity of products is studied. The results indicate that when SiO2 is used as silicic source, NaAlO2 as aluminium source, TEABr as template, the best condition of technics is (SiO2/Al2O3=30):OH-/SiO2=0.40,TEABr/SiO2=0.15,4% crystal introduced (compared with the total mass of silicic source),130℃as crystallization temperature、4 days as crystallization time.On this condition, the structure of zeoliteβis good and the intensity of MOR is lower. Large scale repeats the result of small scale, and the crystallinity of products is higher and MOR is lower.The acidity and pore structrure of prepared samples were also characterized, respectively. The characterization results indicated that the acidity and the pore structure of the synthesized zeolite were pretty consistent with those of the standard zeoliteβ, though a trace of stray crystal of mordenite was observed.βzeolites with different Si/Al ratio were prepared and investigated in the fixed-bed microreactor. It is found that,βzeolite with Si/Al ratio of 30 exhibits higer catalytic activity for isomerization.After hydrothermal treateded at 800℃for,βzeolite maintain excellent stability and catalytic activity for n-hexene isomerization. The product of large scale as assistant catalyzer is introduced into main catalyzer for FCC reaction (especially heavy Oil, usually petroleum residue),which can obtain more propylene and improve the amount of translation of raw material and liquid. The mechanism of zeolite growth of the early stages of P and MOR zeolites are investigated by the quantum chemical calculation. The condensations of silicic acid with aluminate in alkaline environment are studied using the density-functional theory, at the 6-31+G (d, p) basis sets. The calculated results show that the activation energy of TEA+ is decreased by 9 kJ/mol.The mechanism of q2 Al species ofβand MOR zeolites are investigated. The calculated results show that theβand MOR formation of Si-O-Al linkage can proceed via a single-step process.The calculated activation energie of q2Al specie on MOR zeolite is 70 kJ/mol; and it is 67.2 kJ/mol with TEA+ in synthesis process.The calculated activation energie onβzeolite are 102.3 kJ/mol,and it is 53.1 kJ/mol with TEA+ in synthesis process.It is indicated that the synthesis ofβzeolite using TEA+ are easier.In order to understand the important information of P zeolite, Density functional theory (DFT) has been applied to study the distribution of the framework aluminum atoms at nine inequivalent T sites and the acidity of Brφnsted acid in P zeolite.The calculation was carried out at B3LYP/6-31G (d, p) level based on the 5T,8T and 22 T cluster model.According to the interaction energies between zeolite framework and TEA+, the calculated Al/Si substitution, the calculated (Al, H)/Si substitution, proton affinity, and the adsorbing energies of ammonia (NH3),it was proposed that the most favorable sites for Al substitution locate at are T5 and T6 sites,the acidity of A15-O14-Si9 is the highest in the preferable Brφnsted acid sites,and the A17-O3-Si1 site is the lowest.更多还原