【作者】 金少瑾；

【导师】 陈纪忠；

【作者基本信息】 浙江大学 ， 化学工程， 2012， 博士

【摘要】 甲苯是最简单的取代芳烃,其氧化反应是芳烃氧化反应中的典型例子。甲苯氧化产物苯甲醇、苯甲醛和苯甲酸均是有机合成工业中的重要中间体,广泛的应用于农药、香料、医药、染料等领域。目前,甲苯氧化常用的工艺是甲苯液相空气催化氧化法,该工艺具有环境友好、反应条件温和、安全性好等优点。本文采用无卤素和无溶剂的绿色工艺,以纯甲苯为原料,苯甲酸为引发剂,空气为氧化剂,在间歇搅拌式反应釜中,系统研究了Co(acac)2、Co/Mn、[ace-min]Co、CoSBA-15等催化剂对甲苯液相氧化反应的催化性能及其影响规律。以Co(acac)2为催化剂,考察了反应时间、反应温度、催化剂用量、苯甲酸添加量对甲苯液相氧化反应的影响。研究表明,该催化剂的催化活性存在“催化一一抑制”转换现象,有适宜的催化剂用量范围(<0.011w%)。Co(acac)2催化剂的适宜反应温度为165℃,用量仅为0.0044w%时,催化剂寿命即长达6h。反应体系初始无催化剂和苯甲酸时,反应存在明显诱导期。相比于醋酸钴、环烷酸钴等钴盐催化剂,Co(acac)2催化剂具有用量少、催化活性时间长的优点,可有效地减缓钴盐结垢现象。因此,Co(acac)2催化剂对甲苯液相空气氧化反应具有良好的催化性能。探索了二元/三元金属催化体系对甲苯液相氧化反应的协同催化性能,研究了Co/Mn二元催化体系和Co/Mn/Zr三元催化体系对甲苯液相氧化反应的催化性能。结果表明,钴(Ⅱ)锰(Ⅱ)比为1：1是较适宜的催化剂配比。此时,反应选择性相比于全钴催化剂情况下提高了50%。Co/Mn/Zr三元催化体系并不适用于本反应体系。在已有的甲苯液相氧化反应动力学模型基础上,综合考察了苯甲醛、苯甲醇、苯甲酸和苯甲酸苄酯等氧化产物在反应过程中的变化,同时考察了苯甲酸苄酯的逆反应及苯甲酸对反应的促进作用,以此提出了新的反应网络,并根据该反应网络建立了相应的动力学模型。拟合结果表明该动力学模型能较好的描述甲苯液相空气氧化过程中甲苯及各氧化产物的浓度变化。乙酰丙酮钴催化剂相比于环烷酸盐催化剂,能降低甲苯氧化反应的活化能,更有利于反应进行。自行合成了[ace-min]Co催化剂,采用核磁氢谱对其进行表征,并将该催化剂用于甲苯液相氧化反应。研究结果表明[ace-min]Co催化剂首次使用的催化效果与Co(acac)2催化剂相当,[ace-min]Co催化剂再次使用时活性大大降低。钴催化剂失活的主要原因是生成了COC2O4·2H2O沉淀。草酸根的来源有二,分别是从催化剂带入的醋酸转化而来以及烃类过度氧化生成。钴催化剂的沉淀问题在甲苯氧化反应体系中不可避免。自行合成了CoSBA-15分子筛催化剂,采用XRD、N2吸附对其结构进行表征,研究了CoSBA-15分子筛催化剂对甲苯液相氧化反应的催化性能。结果表明,该催化剂能将甲苯选择性的氧化为苯甲醛和苯甲醇,160℃下反应6h,苯甲醛和苯甲醇的选择性之和高于86%。更多还原

【Abstract】 Toluene is the simplest substituted aromatic compound and its oxidation reaction is a typical example of the aromatic hydrocarbon oxidation. The toluene oxidation products, such as benzyl alcohol, benzaldehyde and benzoic acid, are important intermidiates in organic synthesis industry and widely used in pesticides, perfumes, pharmaceuticals, dyes industry and so on. At present, the liquid-phase oxidation of toluene by air is the commonly used process, which is environmentally friendly for its mild reaction conditions and good security. In this paper, the work is to investigate the catalytic activities in the liquid-phase oxidation of pure toluene without halogen and solvent by using Co(acac)2, Co/Mn,[ace-min]Co, CoSBA-15as catalysts separately and benzoic acid as initiator in a stirred tank reactor.Study on aerobic liquid-phase oxidation of toluene with Co(acac)2was investigated and the effects of operation parameters, such as reaction time, reaction temperature, Co concentration, benzoic acid addition were studied. A phenomenon of ’catalyst-inhibitor’transition was found for Co(acac)2catalyst like other Co salt catalyst. The appropriate range of Co(acac)2dosage is<0.011w%. Optimal operation conditions are reaction temperature165℃and Co concentration0.0044w%. At this situation, the life of catalyst can reach6h. There is an obvious induction period when the reaction system was absence of catalyst and benzoic acid. Co(acac)2catalyst has less catalyst dosage and longer lifetime than other Co salt catalysts like Co(OAc)2, etc., which could slow down the cobalt oxalate scaling during reaction. Therefore, Co(acac)2catalyst has a good application prospect as catalyst in liquid-phase oxidation of toluene.The catalytic activities of Co/Mn binary and Co/Mn/Zr ternary catalytic system in toluene liquid-phase oxidation were studied. The results show that the appropriate ratio of Co/Mn is1:1. In this situation, reaction selectivity increase50%compared with only cobalt catalyst. But the Co/Mn/Zr ternary catalyst system does not show the catalytic activities.On the basis of existed kinetic models, we took into account the toluene oxidation products, such as benzyl alcohol, benzaldehyde, benzoic acid and benzyl benzoate, also considered the reverse reaction of benzyl benzoate and promotion of benzoic acid. A new reaction network was proposed, on which a kinetic model was established. The fitting results show that this kinetic model can agree well with the experimental data. Cobalt acetylcaetonate catalyst could reduce activation energy of the reaction of toluene oxidation and make more conducive to the reaction compared to cobalt naphthenate catalyst.[Ace-min]Co catalyst was synthesized successfully, characterized by1H-NMR and used as catalyst for toluene liquid-phase oxidation. The catalytic activity of [ace-min]Co catalyst used for the first time was the same as the Co(acac)2catalyst, but greatly reduced when the [ace-min]Co catalyst was used again. The deactivation of cobalt catalysts is due to the generation of COC2O4·2H2O. And the oxalate ions come from the catalyst and excessive oxidation of hydrocarbon. The precipitation of cobalt catalyst in toluene oxidation is inevitable.Mesoporous CoSBA-15molecular sieves were directly synthesized and characterized using XRD, N2adsorption. CoSBA-15materials were used as catalyst for toluene liquid-phase selective oxidation to benzyl alcohol and benzaldehyde using dioxygen as the oxidant. At160℃, the sum selectivity of benzaldehyde and benzyl alcohol is higher than86%.更多还原