麻馨, 杨佳宝, 周健, 秦玉才, 宋丽娟. 无溶剂法合成小晶粒ZSM-5及丁烯催化裂解性能[J]. 燃料化学学报(中英文). DOI: 10.3724/2097-213X.2024.JFCT.0011
引用本文: 麻馨, 杨佳宝, 周健, 秦玉才, 宋丽娟. 无溶剂法合成小晶粒ZSM-5及丁烯催化裂解性能[J]. 燃料化学学报(中英文). DOI: 10.3724/2097-213X.2024.JFCT.0011
MA Xin, YANG Jiabao, ZHOU Jian, QIN Yucai, SONG Lijuan. Synthesis of small crystal ZSM-5 zeolite by solvent-free method and catalytic cracking performance of butene[J]. Journal of Fuel Chemistry and Technology. DOI: 10.3724/2097-213X.2024.JFCT.0011
Citation: MA Xin, YANG Jiabao, ZHOU Jian, QIN Yucai, SONG Lijuan. Synthesis of small crystal ZSM-5 zeolite by solvent-free method and catalytic cracking performance of butene[J]. Journal of Fuel Chemistry and Technology. DOI: 10.3724/2097-213X.2024.JFCT.0011

无溶剂法合成小晶粒ZSM-5及丁烯催化裂解性能

Synthesis of small crystal ZSM-5 zeolite by solvent-free method and catalytic cracking performance of butene

  • 摘要: 采用无溶剂法合成了四种不同硅铝比的小晶粒ZSM-5分子筛,运用XRD、SEM和N2吸附-脱附等温线等对其晶体结构和织构性质进行了表征,并运用NH3-TPD和Py-FTIR探究了分子筛的酸性质,考察了ZSM-5分子筛的丁烯催化裂解反应性能。结果表明,无溶剂法合成的H型ZSM-5分子筛晶粒呈近球形,粒径(约160 nm)分布均匀。C4烯烃裂解性能与文献已报道水热合成小晶粒ZSM-5分子筛相当,随硅铝比增加丁烯催化裂解活性降低,但乙烯和丙烯选择性明显提高。根据产物分析证实低硅铝比的ZSM-5分子筛较高的酸密度会导致烯烃分子通过氢转移反应生成烷烃,从而降低目标产物的选择性。

     

    Abstract: Catalytic cracking is one of the important paths to achieve high value-added applications of C4 hydrocarbon resources, and ZSM-5 zeolite is the most concerned catalytic material in the industrial application and research and development fields for C4 olefin catalytic cracking technology. In this work, four types of small crystal ZSM-5 zeolites with different silicon aluminum ratios have been synthesized using a solvent-free method. The crystal structure and texture properties were characterized using XRD, SEM, and N2 adsorption isotherms. The acid properties of these zeolites were investigated using NH3-TPD and Py-FTIR, and key catalytic performance indicators such as butene conversion rate, product distribution, and hydrogen transfer index were systematically examined. The correlation between the acid properties of the zeolites and the butene conversion reaction pathway was systematically analyzed, with a focus on exploring the effect of acid density on product selectivity by regulating hydrogen transfer reaction. The research results indicate that the four H-ZSM-5 zeolites synthesized by solvent-free method have nearly spherical crystal with uniform particle size distribution (about 160 nm). Compared with the reported hydrothermal synthesis of small grain ZSM-5 zeolites in literature, the small grain ZSM-5 zeolites synthesized by solvent-free method showed significantly higher ethylene selectivity when the C4 olefin conversion rate is slightly higher. Moreover, as the silicon aluminum ratio increased, the catalytic cracking activity of butene decreased, but the selectivity for ethylene and propylene increased significantly. Based on the analysis of product distribution and reaction pathways, it is inferred that the reaction pathways for catalytic conversion of butene on ZSM-5 samples with different silicon aluminum ratios are different. Among them, the acid density on ZSM-5 zeolites with low silicon aluminum ratios increases, and the synergistic effect between adjacent B acid centers in the pores facilitates the occurrence of hydrogen transfer reactions based on bimolecular mechanisms. This leads to the formation of alkanes through hydrogen transfer reactions of the light olefin product molecules produced by cracking reaction, thereby reducing the selectivity of light olefins in the target product. The single acid center catalytic conversion efficiency of ZSM-5 zeolite with high silicon aluminum ratio is significantly higher than that of low silicon aluminum ratio zeolite. It is proposed that the catalytic cracking pathway of butene on ZSM-5 zeolite is that butene or it’s isomers first oligomerizes on the B acid center to form C8 carbocation intermediate, and then undergoes β-cracking to produce propylene/ethylene and C5 carbocation intermediate. The catalytic cracking of ZSM-5 zeolite with high silicon aluminum ratio is more conducive to the direct cracking of C5 carbocation intermediate into ethylene and propylene products. In addition, the samples with high silicon aluminum ratios are prone to undergo single-molecule acid catalyzed isomerization reactions of the butene skeleton or double bonds, resulting in more butene isomers. Furthermore, the deactivation rate of small crystal ZSM-5 zeolite is relatively low. This is because the reduction in crystal size helps the carbon deposition precursor to rapidly diffuse out of the zeolite crystal, slowing down the catalyst's carbon deposition deactivation rate and preventing rapid deactivation. The research results and conclusions of this article not only provide important data support for the development of efficient catalytic cracking ZSM-5 zeolite materials, but also have important guiding significance for understanding the regulatory mechanism of product distribution in the cracking process of C4 olefins.

     

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