【作者】 卢春山；

【导师】 李小年；

【作者基本信息】 浙江工业大学 ， 工业催化， 2012， 博士

【摘要】 催化卤代芳香硝基化合物加氢还原生成卤代芳胺是最重要的有机反应之一,在精细化学品合成中有着重要的地位。但是,卤代芳香硝基化合物在加氢还原过程中极易发生氢解脱卤现象。因此,提高反应选择性一直是卤代芳香硝基化合物加氢还原反应的重要研究课题。前人提出了许多抑制脱卤的方法,至今仅有在有机溶剂中添加抑制剂的雷尼镍催化液相加氢技术在工业上获得了广泛应用。易燃的雷尼镍催化剂在液相催化加氢生产过程一直存在着安全隐患。另外,在现有的液相催化加氢工艺中大量使用有机溶剂,造成溶剂回收需要消耗大量的能量、且有机溶剂的易燃和易致毒性质影响了生态环境及劳动者的身体健康。因此,开展金属催化剂在卤代芳香硝基化合物加氢还原生成卤代芳胺反应中的催化性能和溶剂效应研究,提高反应目标产物选择性、减少溶剂使用等,对于研发环境友好的卤代芳胺催化合成技术及工艺具有重要的现实意义。论文针对在有机溶剂中雷尼镍催化卤代芳香硝基化合物液相加氢合成卤代芳胺工艺技术中,催化剂和抑制剂混合投料存在抑制脱卤效果和产物选择性不稳定,以及直接将脱卤抑制剂加入到反应体系中容易残留在产品中的不足。利用配位络合原理对雷尼镍催化剂进行电子特性改性预处理,预处理剂双氰胺分子中的C=N键选择性地吸附在雷尼镍催化剂表面上的易致脱氯的路易斯酸活性位“Ni-H+”上,并与之发生较强的相互作用,可以有效钝化引起C-Cl键活化的路易斯酸性位,显著降低脱氯氢解的可能性。当双氰胺处理液浓度大于0.15 mol/L时(催化剂：双氰胺水溶液比例为0.15:1 g/m1),75克6-氯-2-硝基甲苯完全转化时间仅需65分钟左右,3-氯-2-甲基苯胺选择性超过了99.9%。与催化剂和抑制剂混合投料方式比较,3-氯-2-甲基苯胺的纯度提高了一个数量级。氢气的传质效率和催化剂解离吸附氢气性能是影响镍基催化剂上芳香硝基化合物催化加氢性能的至关重要因素。氢气传质效率或者催化剂解离吸附氢气性能较弱,将无法保证持续不断提供足够量的活泼H与硝基物或者中间态反应,吸附停留在催化剂表面的大量的硝基物或者中间态就会沿着其它路径生成各种副产物。对于氯代芳香硝基化合物来说,这些中间产物同样可以发生脱卤氢解反应。因此,抑制脱卤的关键不在于毒化催化剂降低催化活性,而是应尽量提高催化剂的氢气解离吸附性能和提高氢气的传质速率,消除催化剂表面上存在的可以活化C-X键的活性位。论文针对目前有溶剂液相催化加氢工艺中,普遍使用易燃易爆的雷尼镍、甲醇溶剂以及氢气等,存在严重的安全隐患和环境不友好的现象,利用氯代芳香硝基化合物及其相应的氯代苯胺的低熔点特性,开展了无溶剂条件下炭载大粒径钯催化氯代芳香硝基化合物液相加氢合成氯代苯胺反应性能的研究。Pd2+离子与卤素离子可形成不同稳定性的钯金属络合物。配位络合于活性炭表面卤化物离子的[PdCl4-nXn]2-可被卤素离子与活性炭表面形成的双电子荷层结构还原生成零价Pd,并成核于活性炭表面。双电子荷层结构中卤素离子与活性炭表面双键作用程度越强,钯金属越易还原。晶体生长速度与还原速度的相对快慢决定了钯粒子的大小。活性炭经2.5 mol/l碘化钾处理剂预处理后,炭载钯催化剂平均Pd粒径可达35 nm,且分布均匀,表现出很强的低负载低分散性能。在383 K、1.0 MPa、1200 r/min、无溶剂反应条件下,6-氯-2-硝基甲苯加氢合成3-氯-2-甲基苯胺选择性超过99.9%。在反应速率不高于32.5 molCNT/(molPd min)时,温度和压力对脱氯选择性的影响可以忽略。无溶剂条件下,炭载大粒径钯催化剂在6-氯-2-硝基甲苯及其它卤代芳香硝基化合物液相加氢反应中表现出了良好的催化活性、选择性和稳定性。循环使用10次以上,催化剂仍无明显失活现象。无溶剂液相催化加氢有效抑制脱氯可能与高粘度的反应介质对氢气扩散的抑制作用、水与更易于脱氯的产物氯代苯胺在催化剂表面活性位上的竞争吸附以及大粒径金属粒子具有较大的配位数和较少的缺电子原子有关。更多还原

【Abstract】 The selective hydrogenation of aromatic halonitro compounds to the corresponding aromatic haloamines is one of the most essential transformations in the synthesis of fine chemicals and intermediates. Although many efforts have been made to minimize dehalogenation, up to now, it remains a big challenge to completely avoid the hydrodehalogenation as a result of the electron donating effect of amino groups in the aromatic ring. In addition, most of the hydrogenation processes entail the use of organic solvents including methanol or alcohol etc, which plays an important part in dissolution, mass and heat transfer, solvation effect and so forth. However, organic solvents are hazardous in terms of toxicity, waste generation and flammability, especially in the presence of ignitable Raney Ni and noble metal catalysts. Thus removal of solvents and trace impurities is highly significant to achieve green production of aromatic haloamines.On the base of the existing problem and deficiency aforementioned, we reported the catalytic performance of Ni catalyst modified with minute quantity of organic amine compounds in the selective hydrogenation of chloronitrobenzenes to chloroanilines. There is a strong interaction between the electron-deficient Lewis acid site characterized as Ni-H+ specie on the surface of Raney Ni catalyst and the nitrogen atom in organic amine molecule with high electronegativity. And then C-Cl bond would not be polarized and activated. The hydrodechlorination side reaction would be inhibited. Over RND-4 catalyst, the selectivity to 3-chloro-2-methylaniline reached up to 99.96% when the 6-chloro-2-nitrotoluene hydrogenation was fully accomplished within 64 min. The amount of hydrodechlorination by-product in the 6-chloro-2-nitrotoluene hydrogenation over modified Ni catalyst was 10 times lower than that over unmodified Raney Ni catalyst. Furthermore, the selectivity to chloroanilines was, to a large extent, depended on the hydrogen diffusion and dissociative adsorption of hydrogen on the catalyst surface efficiently. We think that the superior selectivity for the selective hydrogenation of chloronitrobenzenes to chloroanilines could not be obtained, unless the catalyst possesses excellent dissociative adsorption hydrogen and the catalytic sites in favor of the hydrodehalogenation are covered or deactivated.Selective hydrogenation of aromatic halonitro compounds to aromatic haloamines is usually carried out in methanol solvent, which is hazardous in terms of toxicity, flammability and waste generation. Aromatic haloamines and the corresponding aromatic halonitro compounds have the relatively low melting points, which provide a possibility to carry out catalytic hydrogenation under solvent-free conditions. Whereas much less effort have been paid to the study on the catalytic hydrogenation in solvent-free. In the present work, we prepared a series of Pd/C catalysts with different Pd particles sizes, through the pretreatment of activated carbon with halogen ions solution. The sizes of Pd particles were dependent on the electrical double layer built up with halogen ions and the activated carbon. The Pd/C catalyst with the average Pd particles size of 35 nm and a narrow particle size distribution could be prepared after the activated carbon was pretreated with KI aqueous solution (2.5 mol/l). Compared with the hydrogenation in organic solvent, the selectivity to the desired product of catalytic hydrogeantion of 6-chloro-2-nitrotoluene and some other aromatic halonitro compounds over Pd/C(Ⅰ) catalyst could reach up to as high as 99.9% under solvent-free conditions. Furthermore, Pd/C catalyst could be recovered and reused more than 10 times without any notable loss of catalytic activity and selectivity. The results infer that the larger Pd particles with narrow particle size distribution, hydrogen diffusion, and the competitive adsorption of water and aromatic haloamines on the catalyst surface could be responsible for the almost complete suppression hydrodehalogenation.更多还原