复合分子筛催化烷烃临氢异构化反应性能研究

发布时间：2018-06-10 21:30

  本文选题：复合分子筛 + 临氢异构化　； 参考：《西安石油大学》2017年硕士论文

【摘要】：烷烃临氢异构化是目前生产高辛烷值汽油最有效的手段之一,复合分子筛因具有合适的孔结构、酸性分布以及良好的水热稳定性,成为近年来临氢异构化催化剂载体研究的热点,此外使用非贵金属代替贵金属对复合分子筛进行改性,能够在提高催化剂性能的同时大大降低成本。因此本文在制备出MCM-41/A、MCM-41/B和MCM-41/C三种复合分子筛的基础上分别负载非贵金属对其改性,研究了复合分子筛催化剂的正己烷临氢异构化反应性能,并对其临氢异构化反应机理进行了初步探索。分别以碱处理A、B和C的浆液为部分硅铝源,在水热体系中采用外加硅铝源法分别制备了MCM-41/A、MCM-41/B和MCM-41/C三种复合分子筛,并采用XRD、BET、FT-IR、Py-IR、TEM等手段分别对复合分子筛样品进行了表征。结果表明,合成的复合分子筛均具有良好的微孔和介孔双重孔结构,其比表面积、孔容和平均孔径均明显高于普通沸石分子筛。由Py-IR表征可知,三种复合分子筛均具有L酸和B酸中心,且金属离子的引入使得复合分子筛的酸性再分布,更有利于提高临氢异构化反应性能。此外,合成的复合分子筛均具有良好的热稳定性和水热稳定性。对比研究了非贵金属改性后的上述三种复合分子筛催化剂的正己烷临氢异构化反应性能,M-MCM-41/A催化剂因具有较大的孔结构尺寸及较多的中强酸中心而表现出较高的催化活性和选择性,且反应72 h内正己烷转化率和异构化选择性分别保持在40%和60%左右,表明其反应稳定性良好。同时还考察了还原温度、反应温度、体积空速和金属负载量等因素对正己烷临氢异构化反应性能的影响。结果表明,当还原温度为450℃、反应温度为260℃、体积空速为3 h-1、催化剂的金属负载量为3 wt%时,M-MCM-41/A催化剂的正己烷临氢异构化反应性能较好,正己烷转化率为48.58%,i-C6异构烷烃选择性高达64.45%,液体收率为91.10%。此外还比较了复合分子筛催化剂在临氢和非临氢条件下的正己烷异构化反应性能,与非临氢条件相比,临氢条件下氢气的存在对正己烷转化率无明显影响,但异构化选择性提高了10%~20%,裂化选择性降低了约15%,液体收率也大幅提高,因此临氢异构化较非临氢异构化有更好的反应性能。对反应机理的初步探索表明,复合分子筛催化剂上的正己烷临氢异构化反应遵循正碳离子反应机理,金属离子及分子筛本身的酸中心一起协同构成了异构化反应的活性中心。
[Abstract]:Hydroisomerization of alkanes is one of the most effective methods to produce gasoline with high octane number at present. Because of its suitable pore structure, acid distribution and good hydrothermal stability, the composite molecular sieve has good hydroisomerization. In recent years, it has become a hot topic to study the support of hydroisomerization catalyst. In addition, the use of non-precious metal instead of precious metal to modify composite molecular sieve can greatly reduce the cost while improving the performance of the catalyst. Therefore, on the basis of the preparation of MCM-41 / Agna MCM-41 / B and MCM-41 / C composite molecular sieves, respectively, the non-precious metals were supported to modify them, and the properties of n-hexane hydroisomerization over composite molecular sieve catalysts were studied. The mechanism of hydroisomerization was also studied. Three kinds of composite molecular sieves MCM-41A1- 41B and MCM-41C were prepared in hydrothermal system using the slurry of alkali treated Agna B and C as partial Si-Al source, respectively. The composite molecular sieve samples were characterized by XRDX BETFT-IRPy-IRTEM. The results show that the synthesized composite molecular sieves have good microporous and mesoporous double pore structures, and their specific surface area, pore volume and average pore size are obviously higher than those of ordinary zeolites. The results of Py-IR show that all of the three zeolites have L acid and B acid sites, and the introduction of metal ions makes the acid redistribution of the composite molecular sieves, which is more conducive to improving the performance of hydroisomerization reaction. In addition, the synthesized composite molecular sieves have good thermal stability and hydrothermal stability. The catalytic properties of M-MCM-41 / A catalyst for the isomerization of n-hexane over the above three modified molecular sieve catalysts were compared and studied. Due to their larger pore size and more moderate and strong acid centers, M-MCM-41 / A catalyst exhibited higher catalytic activity. Chemical activity and selectivity, The conversion and isomerization selectivity of n-hexane were about 40% and 60% within 72 h, respectively, which indicated that the reaction was stable. The effects of reduction temperature, reaction temperature, volume space velocity and metal loading on the isomerization of n-hexane were also investigated. The results show that when the reduction temperature is 450 鈩，

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