【作者】 刘烨；

【导师】 阳永荣； 王靖岱；

【作者基本信息】 浙江大学 ， 化学工程， 2010， 硕士

【摘要】 丙烯传统的生产路线是石油原料的催化裂解。由于世界石油总量有限,国际原油价格不断上涨,导致丙烯生产成本不断升高,制约了丙烯工业的发展。甲醇制烯烃(MTP)技术是指以煤/天然气合成的甲醇为原料,生产低碳烯烃的化工技术。随着甲醇生产的日益规模化,成本日趋降低,甲醇制丙烯成为最有希望替代石油原料制烯烃的工艺路线。近年来,MTP技术成为学术和工业界研究的热点。MTP技术的关键之一在于催化剂的活性和选择性,其研究的重点集中在催化剂的制备和后处理。ZSM-5是目前发现的对甲醇转化制丙烯反应丙烯选择性最高的催化剂。分子筛催化反应性能与其物性密切相关,因此可以通过不同合成、改性方法对ZSM-5分子筛的形貌、孔结构、酸性质进行调控,从而提高其在MTP反应中的催化性能,本论文分别通过金属原位改性ZSM-5、基质(高岭土)原位晶化ZSM-5和低浓度表面活性剂原位晶化ZSM-5等三种不同方法得到ZSM-5分子筛,继而考察产物分子筛的物性结构及其MTP反应的催化反应性能。论文开展的研究工作和得到的主要结论如下:第一部分,系统研究了Cs、Ca、Mg、Fe、Zn、Ti、Ni七种不同金属元素对改性ZSM-5分子筛物性的影响,并获得了具有最佳MTP反应性能的金属杂原子改性ZSM-5。首先,采用Cs、Ca、Mg、Fe、Zn、Ti、Ni七种不同金属元素,在水热条件下原位合成ZSM-5分子筛。其次,对不同金属元素原位合成的ZSM-5催化剂进行MTP反应测评,结果显示,Ca-ZSM-5对丙烯选择性最高,Mg-ZSM-5次之,这可能与Ca-ZSM-5具有较多的B酸酸性位及较大的平均孔径尺寸有关。最后,以Fe-ZSM-5体系为例,比较了原位改性、离子交换改性和浸渍改性方法的金属负载量,结果表明,原位改性法金属元素进入分子筛的量最少,离子交换法次之,浸渍法对金属的负载量最多。第二部分,首次将高岭土原位合成分子筛技术应用于MTP反应,并得到了具有较高丙烯选择性的多功能ZSM-5分子筛催化剂。首先,分别在静态晶化和动态晶化条件下研究比较了基质原位合成ZSM-5分子筛晶型随反应时间的变化情况。由于动态搅拌加快了晶化体系的传质、传热过程,使得动态晶化条件下的晶相转化过程快于静态晶化条件下的晶相转化过程,且随着反应时间的增加,分子筛晶型由ZSM-5转晶为MOR,经历方沸石中间相。其次,针对动态晶化体系,进一步考察基质对产物分子筛物性的影响,并比较偏土、尖晶石两种基质原位合成ZSM-5的物性差别,以指导工业应用。分析结果表明,基质原位合成的ZSM-5晶粒尺寸小、中强B酸丰富,且形成微孔-介孔-大孔的多级孔道结构。最后,通过MTP反应考评ZSM-5晶粒的催化反应性能发现,基质原位合成ZSM-5可以显著提高MTP反应中丙烯的选择性,其中偏土原位合成ZSM-5增产丙烯效果更为明显,这与偏土、尖晶石合成的ZSM-5分子筛在形貌、孔分布和酸性质上存在的差异有关。第三部分,首次将低浓度表面活性剂(CTAB)原位合成ZSM-5应用于MTP反应,系统研究了CTAB加入量对产物ZSM-5物性及MTP反应性能的影响。通过表征分析可知,加入表面活性剂后,产物ZSM-5分子筛的结晶度与参比ZSM-5分子筛相比有所降低,并形成小晶粒结构,比表面积增大。与此同时,系统考察CTAB占总投料量质量分数分别为0.5%、1.8%、4.2%时对产物ZSM-5的物性变化及MTP反应性能的影响,结果表明,按总投料量质量分数的0.5%及4.2%加入表面活性剂原位合成的ZSM-5分子筛的中强B酸量显著增加。对CTAB原位合成的ZSM-5分子筛进行MTP反应性能测试,按总投料量的4.2%加入CTAB,产物分子筛最有利于MTP反应丙烯的生成,并能够提高ZSM-5分子筛的稳定性,有效抑制氢转移反应。更多还原

【Abstract】 Propylene is traditionally produced by petroleum cracking. However, due to the rising price of petroleum caused by its scarce resources, the development of propylene industry is highly restricted. Methanol to propylene (MTP) technology refers to a new method that based on coal /natural gas for producing propylene. With the increasing scale and lower cost of methanol production, MTP is the most promising technology that would substitute the traditional oil route for producing propylene. Thus, MTP has been received intensive study in recent years in both academic and industry fields. One of the key points in methanol to propylene technology is the activity and selectivity of catalyst, which makes the synthesis and post-processing of catalyst an important part.ZSM-5 has the highest propylene selectivity compared with other catalysts in methanol to propylene process. Former researches indicated that the catalyst’s catalytic performance is closely related to its physical property. Therefore, the catalytic activity of ZSM-5 in MTP reaction can be enhanced by adjusting its morphology, pore structure and acid property by different synthesis and modification methods. The research of this paper examined the physical properties of in-situ synthesis of ZSM-5 in three different systems—ZSM-5 made by metal elements incorporation, ZSM-5 made from matrix and ZSM-5 made from surfactant. Their catalytic activities in methanol to propylene process were also tested. The main research work and conclusions of the paper are as follows:The first part systematicly examined the effects of Cs、Ca、Mg、Fe、Zn、Ti、Ni bringing on the properties of product ZSM-5 and the metallic element modified ZSM-5 with the best MTP performance was obtained. First, Cs, Ca, Mg, Fe, Zn, Ti, and Ni etc. seven different metal elements were used hydrothermal in-situ synthesis of ZSM-5. Secondly, ZSM-5 zeolites made by different metal elements incorporation were tested by MTP reaction for their catalytic performance. The results showed that: Ca-ZSM-5 had the highest propylene selectivity, which may relate to its more B-acid sites and larger average pore size. Finally, the comparison among in-situ modification method, ion exchange modification method and impregnation modification method were made toward Fe-ZSM-5 system. It showed that catalyst treated by in-situ modification method contained minimal amount of metal elements, then followed by ion exchange modification method. Impregnation modification method loaded most content of metal elements.In the second part, the kaolin in-situ synthesis technology was used in MTP reaction for the first time. Multi-functional ZSM-5 zeolite catalyst with high propylene selectivity was obtained. Firstly, changes of matrix in-situ synthesis of ZSM-5 crystal structure with the reaction time were compared under both static and dynamic reaction conditions. It was found that the crystal phase transformation process under dynamic reaction condition was much faster than that under static reaction condition. This might caused by the speeding up of the mass and heat transfer process from dynamic mixing in dynamic reaction condition. And in the crystallization process, ZSM-5 crystal was first formed and then transformed into MOR crystal with analcime as mid-phase. Then, the effect of matrix bringing on the physical properties was further examined, and the difference between metakaolin and spinel in-situ synthesis of ZSM-5 zeolites was investigated for industry application. The results showed that matrix in-situ synthesis of ZSM-5 had small crystal size. Besides, they exhibited a gradient pore distribution and increased medium BrOnsted acid sites. By conducting MTP reaction, both metakaolin co-synthesis ZSM-5 and spinel co-synthesis ZSM-5 exhibited high selectivity for propylene. Metakaolin co-synthesis ZSM-5 showed better catalytic activity toward MTP reaction which might owning to its unique morphology、pore structure and acid properties.The third part of the paper applied low concentration of surfactant (CTAB) to in-situ synthesis of ZSM-5 for the first time, and systematicly investigated the effects of both the properties and MTP reaction performances of ZSM-5 zeolite made by different CTAB amount. Through the characteristic analysis, it was found that after adding surfactant in the synthesis system, the crystallinity of the product zeolites decreased when compared with that of regular ZSM-5. Besides, smaller crystal size and larger specific surface area were also formed. For the acid property, samples with surfactant accounting for 0.5% and 4.2% mass fraction of total investment has more B acid sites. By conducting methanol to propylene reaction, the product zeolite with surfactant account for 4.2% mass fraction of total investment might greatly enhance propylene yield、strengthen product zeolite stability and resist hydrogen transfer reaction efficiently.更多还原