【作者】 龙帅；

【导师】 张爱清；

【作者基本信息】 中南民族大学 ， 有机化学， 2009， 硕士

【摘要】 苯部分加氢制环己烯是典型的有机催化反应,无论在理论研究还是在工业生产上,都具有十分重要的意义。环己烯为苯加氢反应的中间产物,但是由于最终产物环己烷的热力学稳定性比环己烯要高得多(环己烷的标准生成热为-153.4 kJ/mol,环己烯的为-63.9 kJ/mol),所以苯加氢反应很难被控制在环己烯阶段,而是大部分生成最终加氢产物环己烷。目前,关于苯加氢制环己烯催化剂研究的最多的为钌系催化剂,由于铂具有更高的加氢活性,所以更难以获得环己烯,因此相关研究甚少。但铂系催化剂的高催化活性、长使用寿命的特点和钌系催化剂供应不足、制备复杂、重复使用效率低的缺点,使得有必要对铂类催化剂在苯部分加氢中的催化活性做进一步探索。本文通过包埋法将有机材料感光性聚酰亚胺(PSPI)和无机材料铂纳米金属簇的特性结合起来形成铂纳米簇/感光性聚酰亚胺(Pt/PSPI)溶胀型膜反应器,对其结构和性能进行表征和分析,并将其应用于苯催化加氢反应中,以期获得高选择性的目标产物环己烯。具体包括以下几个方面的内容:1.采用聚乙烯基吡咯烷酮作为稳定剂,通过微波加热法制备了平均粒子直径为3.7 nm的稳定的铂族金属簇。X-射线衍射分析表明制备的铂金属簇具有良好的晶型和稳定性。微波加热具有辐射时间短和加热均匀的特征,可应用于多种纳米金属簇的制备。2. PSPI是通过传统的两步法由1,5-二(胺基苯基)-1,4-戊二烯-3-酮、3,3’,4,4’-二苯酮四酸二酐和4,4’-二氨基二苯醚经聚合反应制得的。在第一步制得固含量为12 %的聚酰胺酸(PAA)后将分散在N-甲基-2-吡咯烷酮(NMP)中的铂纳米粒子添加至PAA中并搅拌。然后,通过程序升温法分别在80℃、150℃、200℃、250℃、300℃下处理1小时以进一步酰亚胺化得到Pt/PSPI杂化膜。制得的杂化膜Pt含量为5.5 wt.%。由于NMP既是作为制备铂纳米粒子的溶剂,同时也是合成PSPI的溶剂,因此通过包埋法,可将铂纳米粒子高度分散在PSPI膜中。X-射线衍射分析表明,加氢反应前后铂纳米稳定的存在于聚酰亚胺膜中,具有良好的晶型。X-射线光电子能谱分析表明由于铂原子与聚酰亚胺的氮和氧原子发生了络合现象,说明铂与氮、氧原子间存在作用力,减轻了催化活性中心的流失问题。3.以Pt/PSPI杂化膜为催化剂时,苯加氢得到产物环己烯和环己烷,环己烯的产率随着时间的延长而增加,在10h达到最大。以Pt/PSPI杂化膜为催化剂时,随着反应时间的延长,苯的转化率逐渐升高,同时环己烯的选择性呈现先升高后降低的趋势,当反应时间为2h,环己烯的选择性最大,达到72.4%。而当催化剂仅为单纯铂纳米金属簇而无聚酰亚胺膜时,唯一的产物为环己烷。由于在其它反应条件相同的情况下,只有当催化剂为Pt/PSPI,而不是单纯Pt金属簇时,才有产物环己烯的出现,这说明此杂化膜对产物环己烯的形成有着至关重要的影响。溶胀实验结果表明环己烯比苯和环己烷更难溶胀于杂化膜中,因此,我们推测一旦反应生成了环己烯,它会较快地从杂化膜中流溢出来,隔断了与催化氢化活性中心的接触,从而避免了进一步加氢成环己烷的可能性。所以,产物中环己烯的选择性要高于环己烷。更多还原

【Abstract】 Partial hydrogenation of benzene to cyclohexene is a typical organic catalytic reaction and a subject of great interest, from both theoretical and practical aspects. In spite of the fact that cyclohexene is an intermediate product of the benzene hydrogenation, cyclohexane is the end product rather than cyclohexene, owing to the kinetically favouring hydrogenation of cyclohexene to cyclohexane (standard heats of formation of cyclohexane and cyclohexene are -153.4kJ/mol and -63.9kJ/mol respective). At present, ruthenium-based catalysts are the vast majority of catalysts on the benzene hydrogenation to cyclohexene. It is more difficult to obtain cyclohexene as the platinum has a higher hydrogenation activity than ruthenium. So, there are little researchs about it. The platinum-based catalysts have such characteristics as high catalytic activity and long life. And the ruthenium-based catalysts have so many shortcomings like inadequate supply, complexity of preparing, inefficient circular using and so on. Therefore, it is necessary to explore the catalytic activity of the platinum catalyst in the partial hydrogenation of benzene further.In this work, we fabricated Pt nano-cluster /photosensitive polyimide swollen membrane reactor (Pt/PSPI) consisting of inorganic material of monodisperse platinum group nano-clusters and organic material of photosensitive polyimide (PSPI) with the method of embedment. The structure and performance of hybrid membrane were characterized and analyzed. The membrane reactor was used to obtain the high selectivity of cyclohexene in catalytic hydrogenation reaction of benzene.There are three parts to be included in this paper: 1. The stabile platinum metal clusters were obtained with stabilizer Polyvinylpyrrolidone (PVP, K30) and reducing agent glycol by microwave irradiation (MW), which average diameter of particles was 3.7 nm. X-ray diffraction analysis showed the good crystalline form and stability of the platinum metal cluster. The characteristic of MW are short irradiation time and uniform heating. And MW can be applied to prepare a variety of nano-metal cluster.2. It was mixed with 1, 5-bisaminophenyl-1, 4-pentadien-3-one ,3,3’,4,4’-benzophenonetetracarboxylic dianhydride and 4,4’-Diaminodiphenyl ether to synthesize PSPI by traditional two-step method. Polyimide acid (PAA,which solid content was 12%) was prepared in first step, and then the catalysts which dispersed in N-methyl-2-pyrrolidone (NMP) were added to PAA by stirring. Lastly, Pt/PSPI hybrid membranes were obtained by heating 1h in 80℃、150℃、200℃、250℃、300℃respectively for further imiding with the method of temperature programmed. The Pt content of hybrid membrane was 5.5 wt.%. Platinum nano-particles were dispersed uniformly in membrane of PSPI by embedding, thanks to the nano-particles could be dissolved in NMP and the NMP was solvent for synthesis of PSPI. X-ray diffraction analysis showed that Pt nano- particles were stably loaded on polyimide film with good crystal form in pre and post reaction. X-ray photoelectron spectroscopy analysis showed that complex phenomena occurred between platinum atoms and nitrogen or oxygen atoms, which was force between atoms. Thereby it would to reduce the question of losing the catalytic active center.3. The products of benzene hydrogenation were cyclohexene and cyclohexane when the catalyst was Pt/PSPI hybrid membrane. It can be seen that the conversion of benzene and the yield of cyclohexene getting the peak after 10h increased with the time. The highest selectivity of cyclohexene increased at first and then decreased, which exceeded 72% at 2h. There was no cyclohexene in products when the catalyst was only Pt nano-particles without PSPI, and the only product was cyclohexane. The formation of cyclohexene is influenced deeply by hybrid membrane, because the cyclohexene of production only could be found when the catalysts were Pt/PSPI rather than Pt. The experiment results of swollen show that cyclohexene is hard to swollen in hybrid membrane rather than cyclohexane. Accordingly, we can conjecture that the cyclohexene is separated from active center of catalytic hydrogenation and effused from the hybrid membrane so that they cannot be further hydrogenated to cyclohexane, once they appeared in reaction. So the selectivity of cyclohexene is higher than that of cyclohexane.更多还原