摘要
现阶段,我国对氯苯胺生产方法及技术落后,生产规模小。多数是采用传统的铁粉、硫化碱等还原法,对环境污染严重。而贵金属催化加氢法由于对环境友好,产品纯度高而备受关注。以活性炭负载贵金属制得催化剂的研究已有报道,但关于活性炭负载铑的制备及其催化对氯硝基苯加氢的研究很少,存在较大的研究空间。
本论文以对氯硝基苯加氢合成对氯苯胺为研究背景,以开发制备高性能的Rh/C加氢催化剂为主要目标,系统的研究了活性炭负载铑制得的催化剂在对氯硝基苯加氢反应中应用的可行性。论文通过对活性炭进行不同方法的预处理后再负载铑制得催化剂,分析了影响Rh/C催化剂催化性能的主要因素；考察了第二金属的添加对催化剂催化性能的影响；探讨了Rh/C催化剂催化对氯硝基苯加氢反应寿命和失活机理；并与国外Alfa公司制备的Rh/C催化剂进行比较,为Rh/C催化剂的深入研究奠定了基础。
1.采用浸渍法制备了Rh/C催化剂,研究了活性炭的预处理、Rh的负载量、还原剂、还原方法、pH值等对Rh/C催化剂催化对氯硝基苯加氢反应性能的影响。结果表明：降低活性炭表面酸性基团总含量后负载Rh制得的催化剂活性升高。在处理活性炭的过程中,氢氧化钠的加入量对其表面基团有一定的影响。加入少量的氢氧化钠,不能完全中和表面酸性基团；加入过多会中和所有酸性基团,同时碱性位增多,对氯苯胺的收率下降。在制备Rh/C催化剂的过程中,Rh的负载量对催化剂催化对氯硝基苯加氢反应影响很大,最佳的负载量应该控制的0.7%-1%之间。在液相还原时,水合肼还原效果没甲醛好,其制备的催化剂活性降低,甲醛是比较理想的还原剂。通过加氢还原制得的催化剂金属的分散度比液相甲醛还原制得的高,加氢高温还原更有利于金属的分散。通氢还原制备的催化剂在活性上高于甲醛还原制得的催化剂并且其寿命比甲醛还原制得的催化剂寿命长。
2.考察了双金属催化齐(?)Rh-M/C(M:Cs.Fe.Co.Ni.Cu)催化对氯硝基苯加氢的反应性能,探讨了浸渍顺序和第二金属的负载量对Rh-M/C催化剂性能的影响。此外,还研究了Rh-M/C双金属催化剂催化对氯硝基苯加氢反应的最佳反应温度,时间和催化剂用量。结果表明：第二金属的添加相比单金属催化剂其活性提高,在三小时的反应时间里就能使对氯苯胺的收率达到99%以上。第二金属的类型及浸渍方法对催化剂的影响很大,不同的金属、不同的浸渍方法对催化剂的影响不同。共浸渍法制备的RhCs/C双金属催化剂效果最好。
3.考察了磷酸对Rh/C催化剂寿命的影响并对催化剂的失活机理进行了研究,比较了Rh/C和Rh-M/C的催化寿命。结果表明：Rh/C催化剂经反应一次后,继续反应活性明显下降。在制备过程中加入一定量的磷酸,催化剂的寿命明显增强。磷酸的加入能增强贵金属和载体之间的相互作用,增加催化剂的寿命,但磷酸的加入也造成Rh在载体上分散度降低,同时磷酸加入过多会直接影响催化剂的活性。催化剂反应三次后其比表面积,孔容都下降,载体表面发生坍塌堵塞覆盖Rh。双金属催化剂不仅能改善催化剂的活性,减少反应时间,控制脱氯率,在寿命上也比单金属催化剂长。
4.对自制5%Rh/C催化剂和国外Alfa公司制得的5%Rh/C催化剂进行比较。通过对氯硝基苯加氢反应和α-蒎烯加氢制蒎烷反应的活性评价及各种表征手段进行对比。结果表明：自制Rh/C-B催化剂的产物收率最高,经反应后其收率有所下降；自制Rh/C-C催化剂的催化活性比较高,但其对应产物收率不高；进口催化剂的活性和Rh/C-C催化剂接近,其对应收率比Rh/C-C催化剂的好。
At present, the production method and technicals for chlorinated aniline of our country fall behind and the production scale is small. Most is using reduction method of traditional iron powder, Sodium SulpHide etc,therefore causing serious environmental pollution. However hydrogenation by precious metals catalysis is been concerned due to friendly to environment, high purity. The catalyst prepared by loading precious metal on activated carbon has been reported, but the preparation about loading rhodium on activated carbon and the research about catalytic hydrogenation of nitrobenzene chlorinated are rarely, existing biggish research space.
The research background of this work is synthesis chloro aniline using chlorine nitrobenzene hydrogenation, with development high-performance Rh/C hydrogenation catalyst for the main goal, researching the feasibility of activated carbon loading precious metal rhodium catalysts in the application of chlorinated nitrobenzene hydrogenation reaction systematically. The catalysts were prepared by loading precious metals rhodium on the active carbon which was treating with different methods. Further we analyzed the primary factors which influence the catalytic performance of precious metal rhodium loading activated carbon catalysts, studying the effect of adding second kind of metal on the catalytic performance, discussing the deactivation mechanism of Rh/C catalytic hydrogenation of chlorinated nitrobenzene, and compared with the Rh/C catalyst which was prepared by Alfa company, and laying a foundation for the in-depth study of Rh/C noble metal catalysts.
1. Rh/C catalysts were prepared by impregnation method, and researching the active carbon pretreatments, loading contents of Rh, reductants, reduction methods, pH values on the properties of hydrogenation reaction of chlorine nitrobenzene using Rh/C as catalysts. Results show that the acid treatment was not good for loading precious metal rhodium, the Rh/C prepared by loading precious metals rhodium after reducing total content of surface acidity groups on the carbon, the catalytic activity was increased. In the process of treating activated carbon, the addition amount of sodium hydroxide influences its surface groups. Too little addition of Sodium hydroxide, processing surface acidity groups was not thorough enough, Excessive, all the acidic group was neutralizing, and alkaline bits increased, the yield of chloro aniline declined. In the process of preparation of Rh/C catalyst, the loading contents of precious metals strongly influence the hydrogenation reaction of chlorine nitrobenzene, the best contents should be controlled 0.7%～1%. In liquid pHase reduction, hydrazine hydrate was against the reduction of Rh, and catalytic activity is very low, formaldehyde is an ideal reductant. The metal dispersion of catalysts through hydrogenation was better than liquid formaldehyde reduction, high temperature hydrogenation reduction is better for the dispersion of metal. The catalysts prepared by hydrogenation reduction were more active and had longer life than the catalysts prepared by formaldehyde reduction.
2. Studying the dual metal catalysts Rh-M/C (M:Cs, Fe, Co, Ni, Cu) for the catalytic performance of hydrogenation reaction of chlorine nitrobenzene, discussing the effect of sequence of impregnation and the second kind of metal on the catalytic properties of Rh-M/C. In addition, the optimum reaction temperature, time and the dosage of catalyst of hydrogenation of chlorine nitrobenzene were also studied. Results show that:compared with single metal catalyst, the addition of second metal improved activity, the yield of chloro aniline can reach 99% in three hours of reaction time. The type of second metal and the impregnation method strongly influence the catalysts, the effects of catalysts were different with different metals and different impregnation methods. The Rh-Cs/C prepared by co-impregnation method was best.
3. The effect of pHospHoric acid on the life of Rh/C catalyst and the deactivation mechanism has been studied, comparing the catalytic life of Rh/C and Rh-M/C. Results show that:After Rh/C reacting one time, the reaction activity significantly declined if continue using. After adding a certain volume of pHospHoric acid in the process of preparation, the catalytic life time was obviously increased. The addition of pHospHoric acid can enhance the interaction between precious metals and carrier, increase the catalyst life, but also causes the decline of the dispersion of rhodium. Excessive pHospHoric acid addition amount will directly influence the activity of catalysts. After three times reaction, the specific surface area, pore volume were decreased, the surface of carrier collapsed, or covering the precious metal. Dual metal catalysts can not only improve activity of catalysts, decline reaction time, control the ratio of taking of chlorine, but also increase catalyst life.
4. Compared with the homemade Rh/C catalyst and Rh/C catalyst prepared by Alfa company. Through the evaluing the reaction activity of hydrogenation of chlorine nitrobenzene reaction, and hydrogenation of alpHa pinene and comparing various characterization methods.Results show that:the self-made Rh/C-B catalysts, had highest yield and after reacting its yield decreased; the activity Rh/C-C was higher, but its corresponding product yield was not high; the activity of imported catalyst and Rh/C-C catalyst were close, but its corresponding yield was better than self-made Rh/C-C catalyst.
引文
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