SAPO-18分子筛催化不同烯烃裂解性能研究

发布时间：2018-03-24 18:20

  本文选题：SAPO-18分子筛　切入点：1-丁烯　出处：《东北石油大学》2017年硕士论文

【摘要】：丙烯作为原材料在石油化工企业中有着不可或缺的地位。随着工业的迅猛发展,中国已经步入亚洲乃至全球丙烯生产及消费大国的行列。但在丙烯的供需上还存在巨大缺口,所以利用烯烃催化裂化产生高经济价值的丙烯工艺受到广泛关注。现今石化行业中所应用的裂解烯烃催化剂ZSM-5具备良好的裂解活性,但多环芳烃的选择性较高,没有达到令人满意的丙烯选择性。因此,研究具备高丙烯选择性的催化剂有着更为重要的意义。首先,本文合成了不同Si含量的SAPO-18分子筛,并且利用了XRD、SEM、NH3-TPD技术手段进行了分子筛表征分析。通过微型固定床反应器评价了代表不同结构的H-ZSM-5(MFI)、H-Beta(*BEA)、SAPO-18(AEI)系列分子筛催化1-丁烯裂解性能。实验结果表明:分子筛的结构和酸性对反应结果都有明显影响,增加分子筛酸量会提高1-丁烯的转化率,但酸量过高会引发氢转移、芳构化等副反应导致丙烯选择性降低;分子筛孔口大小、孔道结构决定了可以获得的最高丙烯选择性。本文还进行了SAPO-18分子筛催化1-己烯、1-辛烯裂解评价实验,并比较1-丁烯、1-己烯与1-辛烯裂解产物分布。实验结果发现:烯烃碳链的长度会影响SAPO-18分子筛催化烯烃裂解性能。1-丁烯与1-己烯容易扩散到分子筛笼内发生裂解反应;1-辛烯在SAPO-18分子筛的八元环孔口发生了更强烈地吸附,导致1-辛烯扩散进入笼内进一步裂解速率明显下降。通过TG手段对裂解反应后的分子筛积碳进行了分析,实验结果表明:裂解反应过程中烯烃采用的裂解方式不同,分子筛的积碳量有着明显的差异。SAPO-18分子筛催化1-己烯、1-辛烯采用单分子裂解方式生成易扩散的小分子,缩减了积碳前驱体产生的机率,因此积碳量相对少。而SAPO-18分子筛催化1-丁烯采用双分子二聚裂解方式,尽管二聚裂解方式提高了丙烯收率,但二聚裂解过程中会产生大分子芳烃物质,其无法从分子筛笼内扩散加快了积碳的生成。最后,考察了不同反应温度和反应空速对SAPO-18分子筛催化1-丁烯、1-己烯与1-辛烯裂解反应的影响,实验结果表明:在反应温度为500℃,1-丁烯空速为3.5h-1时,SAPO-18分子筛在1-丁烯催化裂解反应表现出较好的催化性能。在反应温度为500℃,催化剂填料为1g,进料气速为20ml/min,1-己烯与混合气配比为2.5:1;1-辛烯与混合气配比为1:1时,1-己烯、1-辛烯在SAPO-18分子筛上催化裂解反应表现出较好的催化结果。
[Abstract]:Propylene, as a raw material, plays an indispensable role in petrochemical enterprises. With the rapid development of industry, China has stepped into the ranks of Asian and even global propene producing and consuming countries. However, there is still a huge gap in the supply and demand of propylene. Therefore, the process of producing high economic value propylene by olefin catalytic cracking has attracted wide attention. Nowadays, the olefin cracking catalyst ZSM-5 used in petrochemical industry has good cracking activity, but the selectivity of polycyclic aromatic hydrocarbons (PAHs) is high. Therefore, it is more important to study catalysts with high propylene selectivity. Firstly, SAPO-18 molecular sieves with different Si content have been synthesized. The molecular sieve was characterized and analyzed by XRDX SEMN NH3-TPD. The catalytic properties of H-ZSM-5 MFI (H-BetaEI) series, representing different structures, for 1-butene cracking were evaluated by means of micro-fixed-bed reactor. The experimental results showed that the structure of the molecular sieve was characterized by SAPO-18AEI. And acidity have a significant effect on the results of the reaction, The conversion of 1-butene can be increased by increasing the acid content of molecular sieve, but the hydrogen transfer will be initiated when the acid content is too high, the selectivity of propene will be decreased due to the side reactions such as aromatization, and the pore size of molecular sieve will be decreased. The highest selectivity of propylene was determined by pore structure. The evaluation experiment of 1-hexene 1-octene cracking catalyzed by SAPO-18 molecular sieve was also carried out. The distribution of 1-butene 1-hexene and 1-octene pyrolysis products were compared. The results showed that the length of olefins carbon chain affected the cracking performance of olefin catalyzed by SAPO-18 molecular sieve .1-butene and 1-hexene easily diffused into the molecular sieve cage to produce cracking. The reaction of 1-octene adsorbed more strongly at the octa-ring pore of SAPO-18 molecular sieve. As a result, the further cracking rate of 1-octene diffusion into the cage was significantly decreased. The carbon deposition of molecular sieve after pyrolysis was analyzed by TG. The experimental results showed that the cracking modes of olefin were different during the cracking reaction. The carbon content of molecular sieve has obvious difference. SAPO-18 molecular sieve catalyzes 1-hexene 1-octene to form easily diffusing small molecule by single molecule cracking, which reduces the probability of producing carbon precursor. Therefore, the amount of carbon deposition is relatively small, while SAPO-18 molecular sieve catalyzes 1-butene by bimolecular dimerization, although dimeric cracking improves the yield of propylene, macromolecular aromatics are produced in the process of dimeric cracking. The formation of carbon was accelerated by the impossibility of diffusion from the molecular sieve cage. Finally, the effects of reaction temperature and space velocity on the cracking of 1-butene 1-hexene and 1-octene catalyzed by SAPO-18 molecular sieve were investigated. The experimental results show that when the reaction temperature is 500 鈩，

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