【作者】 马利勇；

【导师】 陈丰秋； 程党国；

【作者基本信息】 浙江大学 ， 工业催化， 2012， 博士

【摘要】 乙烯、丙烯等低碳烯烃作为石油化工的重要基础原料,在石油化学工业中起着举足轻重的作用。其传统生产方式主要通过管式炉蒸汽裂解法制备得到。然而随着丙烯衍生物需求量的增加,通过蒸汽裂解法联产得到的丙烯产量远不能满足国内外市场对丙烯日益增长的需要。此外蒸汽热裂解技术还存在能耗和设备投资过高、裂解原料选择范围较窄、环境污染较为严重等问题。因此,近年来低碳烯烃的原料和工艺正向多元化方向发展,一些新的工艺技术不断涌现。在探索替代传统的蒸汽热裂解制取低碳烯烃的诸多研究中,烃类催化裂解制低碳烯烃是最具有发展前景的方法之一。影响催化裂解的因素除原料组成、操作条件和反应装置外,其中研究和开发具备良好催化性能的催化剂是该技术的关键。分子筛经改性后可获得合理的孔道结构和合适的酸性质,是一类最有研发前景的轻烃催化裂解催化剂。因此,本文首先对各种分子筛进行了孔道结构和酸性质的表征分析,并以正庚烷的催化裂解为模型反应,考察了分子筛的催化轻烃裂解反应性能,探索了分子筛的催化性能与催化剂的孔道结构和酸性质的内在关系。研究表明分子筛含有适当的酸量和酸强度以及一定的微介孔比率有利于提高正庚烷的转化率以及乙烯和丙烯的选择性。在此基础上考察了硅铝摩尔比和均相反应器转速对ZSM-5分子筛催化性能的影响。发现高硅ZSM-5较弱的酸性和酸强度可以抑制氢转移反应的发生,有利于丙烯选择性的提高。均相反应器转速的增大使得ZSM-5分子筛的晶粒变小,酸性变强,其催化性能显著提高。其次,系统研究了Y203改性对ZSM-5分子筛物化性能的影响。主要考察了Y203含量、焙烧温度以及ZSM-5硅铝比对Y203改性ZSM-5分子筛催化性能的影响。同时采用一种有别于ZSM-5的ZRP-1分子筛为载体,制备得到了一系列Y203改性的ZRP-1分子筛,考察了Y203改性对ZRP-1分子筛物化性能及其对正庚烷催化性能的影响。结果表明,Y2O3-ZSM-5和Y2O3-ZRP-1的物化性质随着Y203含量的增加产生了显著的变化。当Y203含量较低时,酸性质较孔结构变化更为明显；而当Y203含量较高时,催化剂为核壳结构式的多级孔催化剂,其孔道结构和酸性质都产生了显著的变化。此外焙烧温度和ZSM-5分子筛的硅铝比对Y2O3-ZSM-5的孔道结构和酸性质的影响作用明显。研究认为选择合适硅铝比的ZSM-5分子筛对其进行Y203改性,有望获得稳定性好、催化性能优异的催化剂。最后,本文采用水热合成法,首次合成得到了HZSM-5-ZRP-1多级孔分子筛。讨论了ZRP-1含量和加入方式对HZSM-5-ZRP-1多级孔分子筛催化性能的影响。考察了Hβ、HY和丝光沸石含量分别对HZSM-5-Hp、HZSM-5-HY和HZSM-5-Mordenite多级孔分子筛的孔道结构和酸性质的影响。结果表明,HZSM-5-ZRP-1多级孔分子筛的孔结构性质明显有别单一的HZSM-5和ZRP-1。其微孔和介孔之间的比率重新得到了调整。不同含量的Hβ、 HY和丝光沸石的加入也使得相对应的HZSM-5-Hβ、HZSM-5-HY和HZSM-5-Mordenite多级孔分子筛的孔道结构各不相同。HZSM-5-ZRP-1多级孔分子筛的酸性质基本位于HZSM-5和ZRP-1之间,但其强酸位的酸强度明显要高于HZSM-5和ZRP-1,其酸位L/B的比率也明显要大于ZRP-1和HZSM-5本身。HZSM-5-Hβ、HZSM-5-HY和HZSM-5-Mordenite多级孔分子筛的酸性质有别于HZSM-5和各自所对应的分子筛,不仅催化剂的酸量和酸强度发生了变化,而且产生了新的酸位。实验结果表明在ZSM-5合成体系中加入适量的ZRP-1、Hβ、HY和丝光沸石,可以显著提高催化剂的活性以及乙烯和丙烯的选择性。更多还原

【Abstract】 Light alkene (ethylene, propylene, etc.) as the important chemical raw materials are produced mainly by thermal cracking of naphtha in the current chemical industry. Nowadays, the traditional methods for propylene production cannot satisfy the growing demand of high quality petrochemical materials. Therefore, some new technologies have been studied and developed, in which catalytic cracking of hydrocarbons to produce ethylene and propylene has been considered as one of the most effective technologies to produce light olefins since it can not only reduce reaction temperature but also adjust the product distributions compare with conventional thermal cracking process. In addition, more propylene can be obtained in catalytic cracking reaction, which can satisfy the increasing demand of propylene driven primarily by the high growth rate of polypropylene. In numerous factors, the development of catalysts with good performances is the key of studies on catalytic cracking.Molecular sieve has been considered as one of the most effective catatyst for catalytic cracking of light hydrocarbons. Therefore, in the present work, firstly, the catalytic performance of the zeolites with different pore structures and acid properties were investigated in cracking of n-heptane. The relationship between the catalytic performance of the zeolites and pore structures was disccussed as well as the acidic properties. It was found that the suitable acid properties, such as the strength and amount of acid sites and the appropriate ratio of microporosity/mesoporosity of catalysts were favorable for enthancing the conversion of n-heptane and selectivity of ethylene and propylene. In addition, the effect of SiO2/Al2O3ratio and rotating speed of homogeneous reactor in the process of ZSM-5synthesis was tested. The results indicated that ZSM-5with higher SSiO2/Al2O3ratio were helpful for the selectivity of propylene, because their lower strength and amount of acid sites suppressed the secondarty reaction of the alkenes. High silica ZSM-5with smaller particles had stronger acidic properties and showed better catalytic performance. Secondly, the physicochemical properties and catalytic performances of Y2O3-ZSM-5and Y2O3-ZRP-1were investigated, the effect of different Y2O3loading amounts、calcination temperature and SiO2/Al2O3ratio of ZSM-5on the Y2O3-ZSM-5were discussed. The results indicated that the physicochemical properties and catalytic performances of Y2O3-ZSM-5and Y2O3-ZRP-1samples were quite different from those of ZSM-5and ZRP-1, respectively. Their acid properties changed apparently compared with the physical properties in condition of lower Y2O3loading amounts, in this case, the acid properties were considered as the principal factor for their catalytic performances. On the other hand, both of the acid properties and pore structures simultaneously changed in the presence of relatively high Y2O3loading amounts. Accordingly the conversion of n-heptane and distributions of products were also changed. The reason should due to the integrated zeolite structures and suitable acid properties. It was also found that the calcination temperature and SiO2/Al2O3ratio had effect on the Y2O3-ZSM-5performance.Besides, a series of HZSM-5-ZRP-1hierarchical molecular sieve was synthesized by adding different contents of ZRP-1to the procedure of hydrothermal synthesis of ZSM-5. Analogously, HZSM-5-Hβ、HZSM-5-HY and HZSM-5-Mordenite were also obtained. It was indicated that the physicochemical properties and catalytic performances of ZSM-5-ZRP-1samples are quite different from those of HZSM-5or ZRP-1. ZSM-5-ZRP-1samples have a lot of mesopores and suitable amount of B+L acid sites compared with HZSM-5or ZRP-1as well as higher L/B ratio. The properties of HZSM-5-Hβ、HZSM-5-HY and HZSM-5-Mordenite had a significant change, not only changed the physical properties, but also the acid properties, such as the strength and amount of acid sites. Moreover, new acid site was formed. The results indicated that the higher conversion of n-heptane and selectivitiy of olefins (ethylene plus propylene) were obtained over ZSM-5-ZRP-1samples as well as HZSM-5-Hβ、HZSM-5-HY and HZSM-5-Mordenite hierarchical molecular sieve.更多还原