介孔泡沫硅负载钴催化剂的费—托合成反应性能研究

发布时间：2018-04-27 13:50

  本文选题：费-托合成 + 介孔泡沫硅　； 参考：《苏州大学》2016年博士论文

【摘要】：能源短缺和环境污染日益成为当今世界各国关注的焦点。在我国,石油资源相对短缺,近年来石油需求量也急剧增长,日益突出的石油供需矛盾制约了我国经济和社会的发展。利用费-托合成技术把煤、天然气和生物质转化为清洁液体燃料和高附加值化学品是缓解我国石油供需紧张局势和高效利用煤、天然气和生物质的有效途径之一。催化剂是费-托合成技术的核心,对于负载型的费-托合成催化剂,载体是制备催化剂的重要组成部分。有序介孔材料具有比表面积大、孔道结构规整、孔径大小可调等特点,成为常用的费-托合成催化剂载体。介孔泡沫硅(MCF,Mesostructured cellular silica foams)材料除了具有以上特征外,还具有大的孔径和三维互通的孔道结构,有利于物质在孔道中的传输和扩散。因此,本文以MCF为载体,并对其进行改性,系统研究了MCF及改性MCF负载的钴催化剂的费-托合成反应催化性能,该研究为开发反应活性高、选择性和稳定性好的费-托合成催化剂提供了理论参考。本论文主要研究内容如下:(1)以P123为模板剂,苯为微乳剂,正硅酸四乙酯为硅源合成了具有泡沫状孔结构的MCF材料,同时制备了孔径相同但孔道结构不同的SBA-16、KIT-6和SBA-15分子筛,并分别负载了15 wt.%的钴基催化剂,即Co/MCF,Co/SBA-16,Co/KIT-6和Co/SBA-15。结果表明,四种催化剂表现出不同的还原度(39.1%-63.7%)和钴的分散度(9.6%-11.1%),载体的孔结构显著影响钴催化剂的分散度和还原度。具有三维(3D)孔结构的Co/MCF、Co/SBA-16和Co/KIT-6的CO转化率(46.0%-49.4%)明显比二维(2D)孔结构的Co/SBA-15(22.3%)高。同样具有3D孔道结构。催化剂Co/MCF比Co/SBA-16和Co/KIT-6活性高。由于MCF具有3D开放的孔道和大的孔径,有利于合成气和产物在孔道中的扩散,因此催化剂Co/MCF表现出较低的甲烷选择性和高的C5+选择性,其中C20+选择性高达31.5%,明显高于其它催化剂(14.7%-15.8%)。(2)以mcf为载体,柠檬酸为络合剂,通过改变柠檬酸的用量获得了具有不同粒径大小的钴催化剂。结果表明,随着柠檬酸用量的增加,钴的粒径从9.4nm减小到3.9nm,还原度从63.5%降低到49.6%,分散度从10.2%增加到24.6%。当钴粒径为6.9nm时,mcf负载的钴催化剂具有较高的分散度(14.0%)和适当的还原度(54.2%),此时催化剂的co转化率最高(62.7%)。当钴粒径为3.9nm-8.0nm时,反应的tof和钴粒径之间存在线性关系,钴粒径越大,tof值越大,当钴粒径大于8.0nm时,tof保持不变。(3)采用ph值调节法成功制备了铝硅比从0.05到0.3的al-mcf(amcf)载体。结果表明,al以计量比进入到mcf骨架中,而且仍然保持泡沫状介孔结构。负载钴之后,随着铝含量的增加,钴催化剂的分散度从7.5%增加到12.0%。费-托合成反应测试表明:当反应温度为220°c时,含铝催化剂(co/amcfs)的co转化率(31.6%-37.1%)明显高于纯硅mcf负载的钴催化剂(19.5%)。当反应温度为250°c时,co转化率随着铝含量的增加从53.4%增加到57.6%。催化剂co/mcf由于失活较快,导致催化剂具有低的co转化率(30.9%)、高的甲烷选择性(24.3%)和低的c5+选择性(58.4%),这是由于钴的烧结形成难还原的钴硅物种导致了催化剂的失活。催化剂co/mcf-3的液态产物(60.8%)和异构烃选择性(17.4%)最高,这是因为co/amcf-3具有最多的四配位骨架铝和最强的酸性。(4)采用zsm-5晶种组装合成了具有大比表面积,较大双孔孔径的三维泡沫状介孔复合材料z-mcfs,并与相同条件下合成的纯硅mcf进行对比。结果表明,催化剂co/z-mcfs的费-托合成反应活性(76.5%-79.0%)明显高于纯硅mcf负载的催化剂co/mcf(68.1%)。随着zsm-5晶种含量的增加,催化剂co/z-mcfs的活性逐渐增加,c5+选择性降低。当zsm-5晶种含量最高时,催化剂co/z-mcf-3具有最低的失活率,稳定性最好,这归因于催化剂中钴和载体之间的强相互作用。降低反应空速(8nl·h-1·g-1至4nl·h-1·g-1),产物中异构烷烃的比例增加,烯烃减小,烃类产物主要集中在中间馏分(c5-c20),其值为64.2%。(5)以p123为模板剂,环己烷为微乳剂,正硅酸四乙酯为硅源合成了mcf,考察了环己烷的用量、老化温度、铝掺杂对mcf结构和水热稳定性的影响。结果表明,随着环己烷用量的增加,mcf的孔径和孔容增大,比表面积都大于570m2·g-1。当环己烷的用量为12.0g时,样品mcf-2的比表面最大,约为800.7m2·g-1。MCF的孔径和孔容随着老化温度的增加而增大。当老化温度为130°C时,MCF的比表面大于1000 m2·g-1,泡沫状结构最规整。经水热处理12 h后,纯硅MCF的比表面积下降了73.5%,铝掺杂的样品Al-MCF的比表面积仅下降38.7%,表明掺杂铝提高了MCF的水热稳定性。
[Abstract]:Energy shortage and environmental pollution have become the focus of attention of all countries in the world. In China, the shortage of oil resources and the rapid growth of oil demand in recent years, the increasingly prominent contradiction of oil supply and demand has restricted the development of our country's economy and society. The conversion of coal, natural gas and biomass into clean liquid by the use of Fisher technology. Materials and high added value chemicals are one of the effective ways to alleviate the tense situation of petroleum supply and demand and the efficient use of coal, natural gas and biomass. The catalyst is the core of the Fischer Tropsch synthesis technology. For the supported Fischer Tropsch synthesis catalyst, the carrier is an important part of the preparation of the catalyst. The ordered mesoporous material has a large specific surface area and a hole. The channel structure is regular, the size of the aperture is adjustable and so on. It has become a common carrier for the Fischer Tropsch synthesis catalyst. In addition to the above features, MCF, Mesostructured cellular silica foams has a large pore size and a three-dimensional interworking channel structure, which is beneficial to the transport and diffusion of the material in the pass. Therefore, this paper is based on MCF The carrier was modified and the catalytic performance of MCF and modified MCF supported cobalt catalyst was systematically studied. This study provides a theoretical reference for the development of FTIR synthesis catalyst with high reactive activity, selectivity and stability. The main contents of this paper are as follows: (1) P123 as a template, benzene as microemulsion, positive silicon Acid four ethyl ester was used as a silicon source to synthesize a MCF material with a foamy pore structure. At the same time, SBA-16, KIT-6 and SBA-15 molecular sieves with the same pore size but different pore structure were prepared, and 15 wt.% cobalt based catalysts, namely Co/MCF, Co/SBA-16, Co/KIT-6 and Co/SBA-15., showed that four kinds of catalysts showed different reducibility (39.1%-63.). 7%) and the dispersion of cobalt (9.6%-11.1%), the pore structure of the carrier significantly affects the dispersion and reducibility of the cobalt catalyst. The CO conversion rate (46.0%-49.4%) with a three-dimensional (3D) pore structure of Co/MCF, Co/SBA-16 and Co/KIT-6 (46.0%-49.4%) is obviously higher than the Co/SBA-15 (22.3%) of the two-dimensional (2D) pore structure. The same has a 3D pass structure. The activity is high. Because MCF has the open channel and large pore size of 3D, it is beneficial to the diffusion of synthetic gas and products in the channel. Therefore, the catalyst Co/MCF shows low methane selectivity and high C5+ selectivity. The selectivity of C20+ is 31.5%, obviously higher than that of other catalysts (14.7%-15.8%). (2) MCF is the carrier and citric acid is the complexing agent. The cobalt catalyst with different sizes was obtained by changing the dosage of citric acid. The results showed that with the increase of citric acid, the particle size of cobalt decreased from 9.4nm to 3.9nm, the reduction degree decreased from 63.5% to 49.6%, and the dispersion degree increased from 10.2% to 24.6%. when the cobalt particle diameter was 6.9nm, and the cobalt catalyst supported by MCF had a higher dispersion (14%). With the proper degree of reduction (54.2%), the CO conversion rate of the catalyst is the highest (62.7%). When the cobalt particle diameter is 3.9nm-8.0nm, there is a linear relationship between the reaction TOF and the cobalt particle diameter, the greater the cobalt particle diameter, the greater the TOF value, and the TOF remain unchanged when the cobalt particle size is greater than 8.0nm. (3) the al-mcf (AMCF) from 0.05 to 0.3 of aluminum and silicon ratio has been successfully prepared by using the pH value adjustment method. The carrier. The results show that Al is in the MCF framework and still maintains the foamy mesoporous structure. After loading cobalt, with the increase of aluminum content, the dispersion of cobalt catalyst increases from 7.5% to 12.0%. Fischer Tropsch synthesis reaction test shows that when the reaction temperature is 220 C, the CO conversion rate (31.6%-37.1%) of aluminum containing catalyst (co/amcfs) is clear. The cobalt catalyst (19.5%) was significantly higher than the pure silicon MCF load. When the reaction temperature was 250 C, the CO conversion increased from 53.4% to the 57.6%. catalyst co/mcf due to the faster deactivation, resulting in a low CO conversion (30.9%), a high methane selectivity (24.3%) and a low c5+ selectivity (58.4%), which was due to the sintering of cobalt. The cobalt silicon species, which is difficult to reduce, leads to the deactivation of the catalyst. The liquid product (60.8%) of the catalyst co/mcf-3 and the selectivity of isomeric hydrocarbons (17.4%) are the highest, which is because co/amcf-3 has the most four coordination skeleton aluminum and the strongest acidity. (4) the three dimensional foam with a large specific surface area and a large double pore aperture is synthesized by the ZSM-5 crystal assembly. The pore composite material z-mcfs was compared with the pure silicon MCF synthesized under the same conditions. The results showed that the catalyst co/z-mcfs's Fischer Tropsch synthesis reaction activity (76.5%-79.0%) was significantly higher than that of the pure silicon MCF supported catalyst co/mcf (68.1%). With the increase of the ZSM-5 crystal content, the activity of the catalyst co/z-mcfs increased gradually and the c5+ selectivity decreased. When ZSM-5, the selectivity of the catalyst decreased. At the highest grain content, the catalyst co/z-mcf-3 has the lowest inactivation rate and the best stability, which is attributed to the strong interaction between the cobalt and the carrier in the catalyst. The reaction space velocity (8nl. H-1. G-1 to 4nl. H-1. G-1) is reduced, the proportion of ISO paraffin in the product is increased, the alkene is reduced, and the hydrocarbon products are mainly concentrated in the middle fraction (C5-C20). 64.2%. (5) with P123 as a template, cyclohexane as microemulsion and four ethyl orthosilicate as the silicon source, MCF was synthesized. The effect of cyclohexane dosage, aging temperature and aluminum doping on the structure and hydrothermal stability of MCF was investigated. The results showed that the pore diameter and pore volume of MCF increased with the increase of cyclohexane, and the specific surface area was larger than 570m2 g-1. as ring self. When the amount of alkane is 12.0g, the specific surface of the sample mcf-2 is the largest. The pore size of 800.7m2. G-1.MCF and Kong Rong increase with the increase of aging temperature. When the aging temperature is 130 C, the specific surface of MCF is larger than 1000 m2. G-1, and the foam structure is the most regular. After 12 h, the specific surface area of pure silicon MCF decreases by 73.5% and the aluminum doped sample A The specific surface area of l-MCF only decreased by 38.7%, indicating that the doped aluminum increased the hydrothermal stability of MCF.

【学位授予单位】：苏州大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O643.36;TQ529.2
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本文编号：1810990