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Fe-ZSM-5催化剂上N2O直接氧化苯制苯酚

Direct Oxidation of Benzene to Phenol by N2O Over Fe-ZSM-5 Catalysts

作者: 专业:物理化学 导师:朱伟东 年度:2010 学位:硕士  院校: 浙江师范大学

Keywords

N2O, benzene, phenol, Fe-ZSM-5, mesozeolites

        苯酚是重要的有机化工中间体和化工原料,主要用于制造酚醛树脂,双酚A及己内酰胺。目前工业生产苯酚最主要的方法为异丙苯法,该法最大的缺点在于生产苯酚的同时副产等摩尔市场需求量相对较小的丙酮,因而苯酚的生产受到丙酮市场价格的制约。与传统方法生产苯酚相比,更为经济、环保的苯直接催化氧化制取苯酚(BTOP)新工艺逐渐受到学术界与工业界的重视。其中美国Solutia公司和俄罗斯Boreskov催化研究所共同研究开发的以N2O为氧化剂,Fe-ZSM-5分子筛为催化剂苯羟基化制取苯酚的AlphOx工艺最具吸引力。该工艺不仅可以利用己二酸工业生产中的废N2O,还可将苯酚生产装置与己二酸生产装置有效整合,所得苯酚选择性高,是环境友好型化学过程。然而中试表明,Fe-ZSM-5催化剂连续运转周期较差,离工业化仍有一定距离。这主要是因为Fe-ZSM-5是一种微孔材料,反应物苯和产物苯酚在催化剂孔道中的传递受到限制,易造成催化剂积炭失活所致。对沸石进行后处理来提高其传质性能在炼油工业中一直受到研究者的重视,一般采用的方法是水热处理或酸处理脱除分子筛骨架Al产生介孔。然而脱Al可能部分堵塞分子筛孔道,不能明显改善沸石的传质性能。最近发展的一种改性方法是碱处理,通过选择性控制脱Si使分子筛产生介孔,并与微孔保持相通,从而缩短了分子在沸石微孔孔道中的扩散距离,可提高沸石的传质性能。碱处理改性后,材料晶体的微孔结构及酸性基本没有发生变化,介孔的产生有利于物质的传递,而微孔作为一种微反应器,不仅提供了反应活性中心或吸附位,而且对分子的形状和大小具有选择性。因此,碱处理是一种得到介孔沸石分子筛的有效方式,然而其对Fe-ZSM-5催化剂进行改性并应用于BTOP催化反应,目前研究鲜见。因此,我们主要比较了通过碱处理得到Fe-ZSM-5介孔分子筛与母体分子筛在苯直接氧化制苯酚反应中的催化性能,全文主要结果总结如下:1)研究了液态离子交换法和同晶取代法制备的Fe-ZSM-5催化剂上的苯羟基化反应。发现同晶取代法合成的Fe-ZSM-5催化剂经过碱处理后表现出较高的活性与稳定性。进而考察了影响Fe-ZSM-5催化剂BTOP反应活性的碱处理条件,如温度、时间和浓度等。最优的碱处理条件为0.3MNaOH、80℃、2h,在此基础上得到的最佳催化剂,在320℃反应温度下,苯的初始转化率为22.1%,反应3h后仍维持在20%。这首次证明了碱处理改性的Fe-ZSM-5在BTOP反应中十分有效。碱处理并未改变Fe(Ⅲ)存在状态,然而,碱处理所产生的介孔可明显改善分子筛的传质性能,这是碱处理改性的Fe-ZSM-5催化剂具有优越的BTOP催化反应性能的原因。2)通过碱处理后再水蒸汽处理改性Fe-ZSM-5催化剂,其活性不如仅用碱处理改性的催化剂,这是因为在水蒸汽处理过程中许多Fe物种转变为Fe3+xOy低聚颗粒物,对此通过TEM和UV-vis表征进行了证实。而且,通过N2吸附表征说明,经过碱处理结合水蒸汽处理改性Fe-ZSM-5分子筛,其比表面积和微孔体积都有所降低,这可能是导致其BTOP反应活性较低的原因。
    Phenol is an important organic chemical intermediate and chemical raw material, mainly used in the manufacture of phenolic resin, bisphenol A and caprolactam. At present, the most important method for industrial production of phenol is the so-called cumene process. However, this process has some fundamental and inevitable disadvantages: acetone as byproduct produced in a 1:1 stoichiometry, which in terms of market demand is much smaller than phenol. Therefore, the productivity of phenol via this technology is influenced by the market price of acetone coproduced.Compared with traditional methods, advanced technologies for direct oxidation of benzene to phenol (BTOP) with economical and environmentally friendly advantages have attracted more attention in both academic and industrial affiliations. The Alphox process developed by Solutia company in USA and Boreskov Institute of Catalysis in Russia together is the most attractive process for phenol production. In the Alphox process N2O is used as oxidant, for hydroxylation of benzene to phenol over Fe-ZSM-5 catalysts. The process can not only make a good use of the waste N2O generated in the industrial production of adipic acid, but also be able to integrate effectively phenol production plant with adipic acid production plant, combined with a high selectivity for phenol. Therefore, this is considered as an eco-friendly chemical process. However, the pilot tests of the Alphox process show that the used Fe-ZSM-5 catalysts are unstable and there is still some distance away from industrialization. This is due to the zeolite Fe-ZSM-5 is of microporous material, in which there are some strong mass transfer limitations available for the reactant benzene and the product phenol, easily leading to the catalyst deactivation. To improve mass-transfer properties of zeolites via post-treatments in the refining industry has attracted researchers’attention for years, and in general, hydrothermal-or acid-treatments (dealimination) are used to create mesopores in zeolite crystals. However, recently some experimental investigation has proven that dealuminated species could block the interconnections between created mesopores and zeolite micropores. This cannot, in principle, improve the mass-transport properties of zeolites. On the other hand, recently, a method, the so-called alkaline treatment, has been proved that mesopores formed by extracting framework silicon selectively are connected with micropores, resulting in a reduction of the diffusion path length of molecules through zeolite micropores The micropores structure of crystalline materials and acidity maintain the same after alkaline treatment while larger mesopores offer a molecule transfer path. Micropores can serve as "micro-reactors", which can offer active species or adsorptive sites, and have a molecular sieving effect. Therefore, alkaline treatment is an efficient manner to improve the mass-transfer properties of zeolites. Up to now, to our knowledge, however, research on alkaline treatment for the improvement of Fe-ZSM-5 mass-transfer properties and its application in the BTOP reaction has been very limited.Therefore, our strategy in this work is to compare the catalytic properties of mesoporous Fe-ZSM-5 zeolites obtained via alkaline treatment with those of parent zeolites for the BTOP reaction. The main results in this thesis are summarized as follows:1) The hydroxylation of benzene to phenol over Fe-ZSM-5 catalysts has been investigated. Fe-ZSM-5 catalysts were prepared with ion-exchange and isomorphously substituted methods. Alkali-treated Fe-ZSM-5 catalysts prepared by the isomorphously substituted method show the higher activity and stability. Furthermore, the effects of alkaline treatment conditions such as temperature, duration, and concentration on the activity of the resulted catalyst in the BTOP reaction have been studied. The optimized alkaline treatment conditions are 0.3 M NaOH at 80℃for 2 h, under which the prepared catalyst used in the BTOP reaction shows that the initial conversion of benzene is 22.1% and the conversion still has 20% after the 3-hour continuous reaction at 320℃. This for the first time demonstrates that the mesoporous Fe-ZSM-5 zeolite obtained via alkaline treatment has better catalytic properties in the BTOP reaction, compared to the parent catalyst Fe-ZSM-5. The state of Fe(III) is not altered upon alkaline treatment while the mass-transfer properties of the alkali-treated zeolites are significantly improved, resulting in a better catalytic performance for the BTOP reaction.2) The Fe-ZSM-5 prepared via first alkaline-treatment and then steam-treatment has a lower catalytic activity in the BTOP reaction, compared to the catalyst obtained via only alkaline-treatment. This is due to the transformation of Fe species into oligonuclear Fe3+xOy species during steam-treatment, confirmed by the TEM and UV-vis characterizations. Additionally, the N2 adsorption characterization shows that it is also found that the Fe-ZSM-5 obtained via first alkaline-treatment and then steam-treatment has a lower BET surface area and a smaller micropore volume, perhaps also leading to a lower catalytic activity for the BTOP reaction.
        

Fe-ZSM-5催化剂上N_2O直接氧化苯制苯酚

摘要3-5
ABSTRACT5-7
目录8-10
第一章 文献综述10-24
    1.1 引言10
    1.2 直接法制备苯酚催化新工艺10-16
        1.2.1 H_2O_2氧化法11-13
        1.2.2 O_2 氧化法13-14
        1.2.3 N_2O氧化法14-16
    1.3 Fe-ZSM-5分子筛催化剂的改性16-22
        1.3.1 调整分子筛表面的酸强度和酸密度16-18
        1.3.2 控制引入铁的量18-19
        1.3.3 拓宽分子筛的孔道体系19-22
    1.4 课题研究意义和论文构思22-24
        1.4.1 课题研究意义22-23
        1.4.2 论文构思23-24
第二章 实验部分24-36
    2.1 引言24
    2.2 实验部分24-35
        2.2.1 Fe-ZSM-5沸石分子筛催化剂的制备及改性25-29
        2.2.2 分子筛催化剂表征29-30
        2.2.3 催化反应性能评价30-35
    2.3 小结35-36
第三章 结果与讨论36-68
    3.1 引言36-37
    3.2 实验室合成的Fe-ZSM-5改性、表征与评价37-59
        3.2.1 BTOP催化反应评价条件的优化37-39
        3.2.2 Fe-ZSM-5催化剂的筛选39-42
        3.2.3 Fe-ZSM-5催化剂的表征42-45
        3.2.4 改性Fe-ZSM-5催化剂BTOP反应性能研究45-51
        3.2.5 改性Fe-ZSM-5催化剂的表征51-58
        3.2.6 实验室合成的Fe-ZSM-5及其改性应用小结58-59
    3.3 商品H-ZSM-5为载体制备的Fe-ZSM-5改性、表征与评价59-66
        3.3.1 晶体结构的测定59-60
        3.3.2 形貌特征的观察60-61
        3.3.3 Fe(Ⅲ)物种的分析61-62
        3.3.4 孔结构的测定62-64
        3.3.5 催化剂的BTOP反应性能测试64-66
        3.3.6 商品H-ZSM-5为载体制备的Fe-ZSM-5及其改性应用小结66
    3.4 本章小结66-68
第四章 总结与展望68-70
    4.1 全文总结68-69
    4.2 课题展望69-70
参考文献70-78
攻读学位期间取得的研究成果78-80
致谢80-81
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