【作者】 冯会；

【导师】 山红红；

【作者基本信息】 中国石油大学 ， 化学工程与技术， 2009， 博士

【摘要】 丙烯是一种重要的基本有机合成原料,用来生产聚丙烯、丙烯腈、环氧丙烷等化工产品。丙烯及其衍生物的生产与消费同国民经济的发展密切相关。由于受到丙烯下游衍生物(主要是聚丙烯)需求的驱动,近年来全球丙烯的年需求量一直持续增长,这种发展趋势仍将持续下去,未来全球可能会面临丙烯资源供应紧张的问题。因此增产丙烯成为石化领域研究的热点,主要集中在工艺和催化剂方面。ZSM-5分子筛催化剂广泛应用于催化裂化过程中增产丙烯,其制备大多采用半合成法。半合成法将分子筛和基质用粘结剂粘结后进行喷雾干燥成型,活性组分被分散在基质中,其中部分ZSM-5被基质所包裹,反应物和产物分子的传递、运动必须要经过粘结剂和基质的孔道才能到达活性组分表面,从而降低了活性组分的利用率。基于此,本论文旨在开发新型多产丙烯ZSM-5分子筛催化材料,即在高岭土微球或固体硅胶小球上原位晶化合成ZSM-5分子筛,使反应物分子直接接触活性组分进行反应,进而提高ZSM-5分子筛活性组分的利用率。同时,原位晶化合成法以高岭土或硅胶小球为原料同时制备活性组分和基质,得到的晶化产物可以直接应用于生产。本论文首先研究了在不同焙烧温度下的高岭土微球上ZSM-5分子筛的原位晶化合成。研究发现,产物ZSM-5分子筛的晶化效果与高岭土微球的焙烧处理温度有关。由于高岭土微球在不同焙烧温度下,其微球中含有的具有化学反应活性的SiO2和Al2O3的含量发生变化,而其正是合成ZSM-5分子筛的原料,故最终导致高岭土微球的焙烧温度对ZSM-5分子筛的晶化产生不同程度的影响。详细考察晶化时间、晶化温度、初始凝胶硅铝比及pH值对ZMS-5分子筛晶化的影响,结果表明,晶化时间和晶化温度对于杂晶相态MOR、P型沸石形成的抑制及纯相态、结晶度高ZSM-5分子筛合成起着决定性作用。在本实验条件下,36小时的晶化时间内,提高晶化温度可以得到纯相态、结晶度高的ZSM-5分子筛材料。以此材料为催化裂化增产丙烯助剂,在重油微反装置上,考察了其重油催化裂化反应性能。评价结果表明,高岭土微球上经“原位晶化法”合成的ZSM-5分子筛使丙烯和丁烯的收率增加了4个百分点,对低碳烯烃具有很好的选择性。在高岭土微球上原位晶化合成ZSM-5分子筛研究的基础上,探索了以酸处理高岭土为原料,水热体系中ZSM-5分子筛的合成,目的是最大程度将廉价的高岭土转化为高价值的ZSM-5分子筛。通过XRD、FT-IR、N2吸附脱附技术、SEM及吡啶吸附等手段对合成材料进行表征,结果表明以高岭土为原料得到的ZSM-5分子筛物相单一,结晶度相对较高,具有规整的微孔结构,而且分子筛酸类型以B酸为主,存在少量的L酸,有利于催化裂化反应进行。重油微反评价结果表明这种由高岭土法合成的ZSM-5分子筛催化剂,在添加量为5%的情况下,使丙烯收率增加了近3个百分点,液化气收率增加了6.91个百分点,对丙烯具有较好的选择性,增产丙烯效果明显。本论文还在固体硅胶小球上,以廉价的正丁胺为模板剂,探索了ZSM-5分子筛合成。通过以上相同手段对合成材料进行表征,发现ZSM-5分子筛均匀地生长在硅胶小球的表面,而且硅胶小球的形貌被完整的保留了下来,形成了微孔和大孔复合孔结构的新材料。此外,研究还发现,ZSM-5分子筛的晶体大小可以通过“两段升温晶化法”在0.5-20微米之内进行调变。晶化时间、晶化温度、钠含量和碱含量等合成条件对ZSM-5分子筛的晶化和晶体形貌都会产生一定的影响。以得到的含不同硅铝比的ZSM-5分子筛的硅胶小球作为助剂,重油微反评价结果表明,在添加量为3%的条件下,丙烯收率平均提高3.74个百分点。且随着复合材料中ZSM-5分子筛硅铝比的增加,汽油、柴油收率逐渐增加,同时丙烯、丁烯等低碳烯烃的收率增幅下降,说明低硅铝比的复合材料更适合于增产低碳烯烃。将固体硅胶原位晶化合成ZSM-5分子筛的课题研究进行拓展,本论文还探索了硅胶小球上多级孔ZSM-5分子筛的合成。研究结果表明,以十六烷基三甲基溴化铵和四丙基溴化铵、四丙基氢氧化铵为双重模板剂,采用低温、高温两步晶化法可以成功地在固体硅胶小球上合成多级孔ZSM-5分子筛。这种多级孔ZSM-5分子筛晶体大小为8微米左右,均匀地分布在硅胶小球的表面,而且硅胶小球的形貌被完整地保留下来。通过对这种材料进行物化性能表征,发现这种多级孔ZSM-5分子筛含有类似MCM-41孔道的介孔结构,介孔孔径分布在3纳米左右。通过在多级孔ZSM-5分子筛合成过程中,添加不同量1,3,5-三甲基苯有机溶剂,可以对介孔孔径在3-20纳米之间进行调变。在第二步高温晶化过程中,晶化时间、模板剂的含量及初始凝胶硅铝比等合成因素都会对多级孔ZSM-5分子筛的孔结构产生不同程度的影响。此外,通过对多级孔ZSM-5分子筛形成机理探讨可知,在多级孔ZSM-5分子筛合成过程中,第一步晶化时间的控制是非常重要的,时间过长或过短都不利于多级孔ZSM-5分子筛的合成。最后,采用丙烯齐聚反应作为探针反应,比较了常规ZSM-5分子筛和多级孔ZSM-5分子筛的催化性能差异。反应结果表明,与常规ZSM-5分子筛相比,多级孔ZSM-5分子筛具有高丙烯齐聚转化率,而且对芳香烃和环烷烃具有较高的选择性。更多还原

【Abstract】 Propylene is an important industrial chemical; however, the supply of propylene is not keeping pace with its demand, as a result, research on increasing propylene production has become a topic of interest. ZSM-5 zeolite with three-dimensional sinusoidal and straight channels of molecular dimension was first used by Mobil in 1990s to increase the yield of propylene. This zeolite selectively cracks C7-C13 straight and short branched chain hydrocarbons to C3-C5 olefins. Thus, it increases the yield of light olefins and has become the preferred catalyst or additive for enhancing the yield of propylene in the field of petrochemical processing.The method for in-situ synthesis of ZSM-5 has significant advantages compared to the additive’s traditional preparation. In the traditional method of ZSM-5 additive preparation, the active component ZSM-5 is embedded in a binder or matrix which greatly reduces the contact between the feedstock and the active component. Consequently, the efficiency of ZSM-5 zeolite is decreased. This paper focuses on using the method of in-situ synthesis, in this paper ZSM-5 zeolite is synthesized on the surfaces of kaolin microspheres or silica gel microspheres, thus allowing the feed oil easier access to the active component. Furthermore, because the active component and matrix were obtained together during the synthesis of ZSM-5 zeolite, this ZSM-5 crystallization product can be directly used as an additive in industry.The in-situ synthesis of ZSM-5 zeolite on kaolin microspheres calcined at different temperatures was studied first. The results indicate that the synthesis of ZSM-5 is related to the calcination temperature of kaolin. When the kaolin microspheres were calcined at different temperatures, the amounts of chemically active SiO2 and active Al2O3 in the kaolin microspheres were different. However, the chemically active SiO2 and active Al2O3 are the“nutrients”for the zeolite synthesis; therefore the calcination temperature has an important effect on the synthesis of ZSM-5 zeolite. Some variables, including crystallization time, crystallization temperature, silica to alumina ratio of the initial gel and the pH of the initial gel, were investigated. The results showed that, compare to other variables, crystallization time and crystallization temperature played the most important roles of synthesizing pure, high crystallinity ZSM-5 zeolite. Under our experimental conditions, within a certain hour, increasing crystallization temperature can obtain pure and high crystallinity ZSM-5 zeolite. Using this ZSM-5 zeolite as an additive to an FCC catalyst, catalytic cracking reactions were carried out on a heavy oil micro fixed-bed reactor unit. The results show that by adding 10% of ZSM-5 to the base ZC7300 FCC catalyst, the yields of light olefins such as propylene and butylene increased by approximately four percent. This shows that novel ZSM-5 zeolite has a good selectivity for the light olefins.Based on the above research about the in-situ synthesis of ZSM-5 zeolite on the kaolin microspheres, the hydrothermal synthesis of ZSM-5 zeolite was investigated using acid treated kaolin as a raw material. The objective of this study is to convert cheap kaolin to high value ZSM-5 zeolite completely. The XRD, FT-IR, N2 adsorption-desorption, SEM and Pyridine adsorption techniques were used to characterize the obtained ZSM-5 zeolite. The results show that the ZSM-5 zeolite is pure and has high crystallinity, good micropore structure and more B acid site which favors FCC reactions. The cracking catalytic activity of this ZSM-5 zeolite was studied on a heavy oil micro fixed-bed reactor unit using Daqing VGO as a feedstock. The results indicated that by adding 5% of ZSM-5 to the base ZC7300 FCC catalyst, the yields of propylene and LPG increased by approximately three percent and 6.91 percent, respectively. These results demonstrate that this ZSM-5 zeolite obtained from kaoliin has a good selectivity for propylene and can improve the propylene production effectively.In addition, the in-situ synthesis of ZSM-5 zeolite was studied using n-Butylamine as a structure directing agent. Some characterization techniques, including XRD, FT-IR, N2 adsorption-desorption, SEM and pyridine adsorption, were used to measure the properties of ZSM-5 zeolite. Results show that ZSM-5 zeolite was in-situ synthesized on the silica gel microspheres uniformly, and the shape of the silica gel microspheres was retained, and composite materials with micropore structure and macropore structure were formed. The crystal size of ZSM-5 can be tuned by the method of“two-stage temperature crystallization”within the range of 0.5-20 um. Some synthesis variables, such as crystallization time, crystallization temperature, sodium concentration, alkalinity, have been shown to affect the crystallization and morphologies of ZSM-5 zeolite. Using this novel ZSM-5 zeolite with different silica to alumina ratios as an additive of FCC catalyst, heavy oil catalytic cracking reaction was carried out on a micro fixed-bed reactor. The reaction results indicate that by adding 3% of ZSM-5 to the base ZC7300 FCC catalyst, the yields of propylene increased by 3.74% on average. When silica to alumina ratio was increased, the yields of gasoline and diesel were increased gradually and the yields of light olefins including propylene and butylenes were decreased, showing that the ZSM-5 zeolite with lower silica to alumina ratio is much more suitable for improving the yield of light olefins.Extending the research on in-situ synthesis of ZSM-5 zeolite on the surface of silica gel microspheres, the in-situ synthesis of hierarchical ZSM-5 zeoite was investigated. Results showed that ZSM-5 zeolites with hierarchical porosity were successfully synthesized in-situ on the surface of silica gel microspheres under hydrothermal conditions through cetyltrimethylamnonium bromide (CTAB) and tetrapropylammonium hydroxide (TPAOH) dual templates method. SEM pictures show that the silica gel microspheres were wrapped by a layer of ZSM-5 crystals and the shape of silica gel microspheres was retained very well. TEM pictures and N2 adsorption-desorption data indicate that the ZSM-5 zeolite has intracrystal mesopores with average pore size of 3nm and pore size distribution is only 0.8nm width at half maximum of distribution peak which is very narrow. The pore size can be tuned between 3nm to 20nm by adding the 1, 3, 5-trimethybezene. Catalytic test show that the hierarchical ZSM-5 zeolite catalyst exhibits higher catalytic activity for propylene oligomerization than microporous ZSM-5 zeolite. The high proplylene conversion and aromatic and cycloalkane products selectivity are mainly attributed to the presence of the hierarchical porosity.更多还原