多级孔ZSM-5的合成及其在甲醇制芳烃（MTA）中的应用

发布时间：2018-08-09 12:36

【摘要】：在工业中被广泛应用的芳烃,主要依赖于传统的汽油衍生技术。由于我国富煤少油,国内生产能力严重不足,我国的芳烃主要依赖进口。基于以上原因,国内芳烃供求关系严重失衡,价格也居高不下,寻求的一种新的芳烃非石油生产工艺迫在眉睫。随着我国甲醇工业的高速发展,甲醇生产能力也飞速发展,但是甲醇的后续生产工艺开发远没有赶上甲醇发展的速度,目前甲醇生产设备开工率低,价格低廉,开发甲醇的下游工艺也迫在眉睫。近些年兴起的甲醇制芳烃工艺很好的缓解了甲醇和芳烃的供求矛盾,对我国也具有很重大的战略意义。目前甲醇制芳烃反应主要存在BTX(苯,甲苯,二甲苯)选择率不高,催化剂稳定性不强等问题。针对BTX选择率低问题,目前主要采用负载金属的方法解决,目前以负载Zn的效果最佳。由于反应机理的模糊不清,对BTX选择性相关问题的研究遇到严重的瓶颈。另外一方面,对于催化剂稳定性问题,研究者们主要采用引入介孔的方法来解决。但是依然存在这样或那样的问题,仍需要做进一步的研究。本文从引入介孔的方向出发,尝试了使用糖原或苯基三乙氧基硅烷为模板剂来制备多级孔ZSM-5,以期望其在甲醇制芳烃中的优良表现。首先,本课题尝试将糖原作为模板剂制备多级孔ZSM-5并探究其在甲醇制芳烃中的性能表现。XRD表征结果发现,分子筛的结晶度并没有因为糖原的存在而受到太大的影响;N_2吸附脱附表征结果显示糖原确实有促进介孔生成的作用;SEM结果表明糖原的存在阻碍了晶体生长的维度从而改变了晶体的形貌,这也很可能是糖原有助于介孔生成的深层次原因;NH3-TPD结果显示糖原也影响了分子筛酸的生成及其强度分布。本课题还比较了糖原对催化剂在甲醇制芳烃中的性能表现,结果显示糖原对催化剂稳定性改善并不是非常的明显,这很可能是因为硬模板糖原的水溶性差,在结晶过程中不能很好的靠近前驱体,从而导致生成的介孔不能够很好地靠近晶体表面,难以很好的起到改善质量传递的作用。BTX选择率也从19.55%提高到23.84%,这很可能是由于酸性质以及较大的介孔比表面积所引起的。不过糖原确实很好的起到了引入介孔的作用,也在一定程度上改善了催化剂的催化性能。为了避免再出现上述硬模板水溶性差导致的易发生相分离的问题,本课题选取了不易与前驱体发生相分离(水溶性好)的苯基三乙氧基硅烷作为模板剂。本课题以此为模板剂成功制备了多级孔ZSM-5,并在甲醇制芳烃反应中表现出了很不错的催化性能。本文还通过调变模板剂的加入量,来探求其加入量与催化性能之间的关系。本课题发现催化剂稳定性随模板剂的量的增多呈现出先增后减的趋势,催化剂寿命最高可达到126 h,而BTX选择率则逐渐增加,最高可达33.01%。为了探求催化剂不同催化性能的原因,本课题对催化剂做了一系列分析表征。N_2吸附脱附表征结果显示介孔数量和介孔比表面积与催化剂稳定性均呈现出相同的趋势;热重结果也表明当其适量时确实明显改善了催化剂的抗积碳性能;SEM和NH3-TPD结果也表明它确实也影响了分子筛的形貌以及酸性质;XRD结果显示适量的模板剂对分子筛结晶度并无太大的影响,但是当其过量时分子筛结晶明显受到了影响。由于苯基三乙氧基硅烷较好的水溶性,并且也参与分子筛骨架的搭建,本课题通过这种物质将有机基团(苯环)嫁接于分子筛表面,很好的避免了相分离。本课题通过这种方式引进的介孔可以很好地改善催化剂的质量传递,从而增强了催化剂的稳定性。
[Abstract]:Aromatics, which are widely used in industry, mainly depend on the traditional gasoline derivation technology. Because of our country's rich coal and less oil and serious shortage of domestic production capacity, the aromatics in our country are mainly dependent on imports. Based on the above reasons, the domestic aromatics supply and demand relationship is seriously unbalanced and the price is also high, a new aromatics non petroleum production process is sought. With the rapid development of methanol industry in China and the rapid development of methanol production capacity, the development of methanol production technology is far from the speed of methanol development. At present, the production of methanol equipment is low and the price is low. The downstream process of methanol development is also urgent. The aromatics process which has been developed by methanol is very good in recent years. It also alleviates the contradiction between the supply and demand of methanol and aromatics, which is also of great strategic significance to our country. At present, the reaction of methanol to aromatic hydrocarbons is mainly BTX (benzene, toluene, xylene), the selectivity of BTX is not high, and the stability of the catalyst is not strong. At present, the method of metal loading is mainly used to solve the problem of low selectivity of the catalyst. At present, the effect of load Zn is at present. Because of the ambiguity of the reaction mechanism, the study of BTX selectivity related problems encountered serious bottlenecks. On the other hand, the researchers mainly adopted mesoporous methods to solve the problem of catalyst stability. However, further research still needs to be done. In the direction, we tried to use glycogen or phenyl triethoxy silane as a template to prepare multilevel pore ZSM-5, so as to expect its excellent performance in methanol aromatics. First, we tried to prepare multilevel hole ZSM-5 by using glycogen as a template and explore its performance in methanol to aromatics,.XRD characterization results and molecular sieves. The crystallinity was not greatly influenced by the presence of glycogen; the results of N_2 adsorption desorption showed that glycogen did promote mesoporous formation; SEM results showed that the presence of glycogen hindered the dimension of crystal growth and changed the morphology of the crystal, which was also probably the deep cause of glycogen to facilitate mesoporous formation; NH3- TPD results show that glycogen also affects the formation and intensity distribution of molecular sieve acid. The performance of glycogen in methanol to aromatics is also compared. The results show that the stability of the catalyst is not very obvious. This is probably due to the poor water solubility of the hard template glycogen, which can not be very good during the crystallization process. It is close to the precursor so that the mesoporous pores can not be well close to the crystal surface, and it is difficult to improve the mass transfer by improving the selection rate of.BTX from 19.55% to 23.84%, which is probably due to the acid properties and the larger mesoporous surface area. In order to avoid the problem of the easy phase separation caused by the poor water solubility of the above hard templates, this topic selected the phenyl triethoxy silane which is not easy to separate from the precursor (water solubility) as a template. This topic is a successful preparation of the template. The multilevel hole ZSM-5 has shown good catalytic performance in the reaction of methanol to aromatics. The relationship between the addition amount of the modulating agent and the catalytic performance is also explored in this paper. It is found that the stability of the catalyst increases first and then decreases with the increase of the amount of the template, and the life span of the catalyst is up to the highest. To 126 h, the selection rate of BTX increased gradually, up to 33.01%. in order to find the reasons for the catalytic performance of the catalyst. A series of analysis and characterization of.N_2 adsorption desorption showed that the number of mesoporous and the surface area of the mesoporous ratio showed the same trend as the stability of the catalyst. SEM and NH3-TPD results also showed that it did also affect the morphology and acid properties of molecular sieves. XRD results showed that a proper amount of templates had no significant influence on the crystallinity of molecular sieves, but the crystallization of molecular sieves was obviously affected when they were excessive. Silane is well water-soluble and also participates in the construction of molecular sieve framework. This subject grafted the organic group (benzene ring) on the surface of molecular sieve through this material. It is good to avoid phase separation. The mesoporous mesopore introduced in this way can improve the mass transfer of the catalyst so as to enhance the stability of the catalyst.
【学位授予单位】：太原理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TQ241;O643.36

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