【作者】 李芳；

【导师】 王延吉；

【作者基本信息】 河北工业大学 ， 化学工艺， 2007， 博士

【摘要】 二苯甲烷二异氰酸酯（MDI）是生产聚氨酯的重要原料。以苯胺和碳酸二甲酯为原料合成MDI属于非光气法工艺。它由苯氨基甲酸甲酯合成、缩合及裂解等三步反应构成。该工艺目前存在使用均相催化剂和多步反应等问题。为此,本文针对合成苯氨基甲酸甲酯用新型高效多相催化剂和苯氨基甲酸甲酯合成与其缩合反应耦合实现两步反应一步化过程进行了系统研究。采用气相色谱-质谱联用仪对苯胺与碳酸二甲酯合成苯氨基甲酸甲酯反应体系中的组分进行了定性分析,确定了两种未知副产物:N,N-二甲基苯胺和邻（或对）甲基苯氨基甲酸甲酯;建立了利用液相色谱对该反应体系组分的定量分析方法,实现了反应体系中主副产物的全分析。对苯胺和碳酸二甲酯反应体系进行了热力学分析,其中主反应以及合成N-甲基苯胺和N,N-二甲基苯胺的反应是放热反应,而合成二苯基脲的反应是吸热反应;合成N-甲基苯胺和N,N-二甲基苯胺的反应在热力学上是主反应的主要竞争反应。制备出了用于苯氨基甲酸甲酯合成反应的纳米氧化锆新型催化剂。研究了溶胶-凝胶法制备条件对ZrO₂粒径、晶相和比表面的影响规律,并对溶胶-凝胶时间、尿素/ZrOCl₂比值、ZrOCl₂浓度、醋酸浓度及焙烧温度等制备因素与ZrO₂粒径、四方晶相比例及比表面等催化剂性质进行了定量关联;考察了纳米ZrO₂粒径与其酸量的关系,发现酸量随粒径减小而单调上升,且在15nm左右呈突变趋势;将纳米ZrO₂用于催化合成苯氨基甲酸甲酯反应,对催化反应性能与ZrO₂粒径和四方晶相比例进行了定量关联,发现在小粒径、四方晶相比例高的ZrO₂上苯胺转化率和苯氨基甲酸甲酯选择性较高。开发出了用于苯氨基甲酸甲酯合成反应的新型高效多相催化剂ZrO₂/SiO₂。考察了ZrO₂负载量和焙烧温度对ZrO₂/SiO₂催化反应性能的影响,在ZrO₂负载量为1 wt%、573 K焙烧2 h时,ZrO₂/SiO₂催化剂具有较好的活性;采用XRD、XPS、NH3-TPD、吡啶吸附红外光谱等对催化剂进行了表征,ZrO₂与SiO₂载体间的相互作用形成了Si-O-Zr键;负载后的ZrO₂催化剂酸量和弱酸中心的比例显著提高,且以L酸中心为主;通过催化剂性质与其反应性能的关联,认为苯氨基甲酸甲酯合成反应在弱L酸中心上进行;在优化的反应条件下,苯胺转化率为98.6%,苯氨基甲酸甲酯收率为79.8%。提出了ZrO₂/SiO₂催化剂上苯氨基甲酸甲酯合成反应机理,建立了反应动力学方程。利用原位红外光谱方法研究了ZrO₂/SiO₂催化碳酸二甲酯与苯胺反应的机理。首先,碳酸二甲酯的羰基和催化剂表面的L酸中心相互作用形成化学吸附,然后亲核试剂苯胺进攻被活化的羰基上的C原子,发生双分子亲核取代反应（SN2）。基于该反应机理,利用在线红外分析系统React IR IC-10研究了ZrO₂/SiO₂催化剂上碳酸二甲酯和苯胺合成苯氨基甲酸甲酯反应的动力学,其中表面反应为反应速率的控制步骤,动力学方程为:设计并制备出了用于苯氨基甲酸甲酯合成反应的新型催化剂ZnO-TiO₂。n（Ti）/n（Zn）为2且673 K焙烧的ZnO-TiO₂对于苯氨基甲酸甲酯合成具有较好的催化活性。苯胺转化率和苯氨基甲酸甲酯收率最高分别为96.9%和66.7%;将催化剂表征结果和反应性能进行了关联,发现Zn₂TiO₄和ZnTiO3晶相的形成提供了苯氨基甲酸甲酯合成反应所需的L酸中心;ZnO-TiO₂催化剂具有较好的稳定性,失活催化剂通过简单焙烧即可再生。建立了由苯氨基甲酸甲酯合成反应及其缩合制二苯甲烷二氨基甲酸甲酯（MDC）反应构成的微观尺度集成系统,实现了由苯胺、碳酸二甲酯、甲醛为初始原料一步直接合成MDC。设计制备出双功能催化剂H₄SiW₁₂O₄₀- ZrO₂/SiO₂。在n（DMC） / n（苯胺） / n（甲醛）=20 / 1 / 0.05（摩尔比）,H₄SiW₁₂O₄₀的负载量10 wt%,443 K下反应7 h后降温到373 K下继续反应4.5 h的条件下,MDC收率为24.9%。更多还原

【Abstract】 Methylene diphenyl diisocyanate （MDI） is an important raw material for the production of polyurethane. The synthesis of MDI from aniline and dimethyl carbonate （DMC） belongs to the non-phosgene route, and is composed of synthesis of methyl N-phenyl carbamate （MPC）, condensation of MPC with formaldehyde to methylene diphenyl carbamate （MDC） and decomposition of MDC to MDI. However, this method has some drawbacks that to be deal with, such as the usage of homogeneous catalyst and the multistep process to obtain MDI, etc. In this paper, the novel efficient heterogeneous catalyst for MPC synthesis and the coupling of MPC synthesis with its condensation, that is to say, the one-pot synthesis of MDC from aniline and DMC, were studied systematically.The qualitative analysis of the reaction system of aniline and DMC was carried out by a gas chromatography-mass spectrometry （GC-MS）, and two unknown by-products were determined as N,N-dimethyl aniline （DMA） and methyl 2-methylphenylcarbamate （or methyl 4-methylphenylcarbamate）. The quantitative analysis method for the reaction system was developed using a reversed-phase high performance liquid chromatography and all the components could be separated well.The thermodynamics analysis of the reaction system of DMC and aniline showed that the main reaction and two side reactions, the formation of N-methyl aniline （NMA） and DMA, were exothermal. While,the synthesis of diphenylurea was endothermic reaction. In addition, the synthesis of NMA and DMA were more competitive than the synthesis of MPC in thermodynamics.A novel nano-sized ZrO₂ catalyst for MPC synthesis was prepared through sol-gel process. The influence of preparation conditions on particle size, crystal phase and specific surface area was studied. The preparation conditions, such as sol-gel time, molar ratio of urea to ZrOCl₂, ZrOCl₂ concentration, acetic acid concentration and calcination temperature was correlated quantitatively with the nature of ZrO₂ catalyst, such as particle size, content of tetragonal ZrO₂ and the specific surface area. The influence of ZrO₂ particle size on its acidic nature was explored. It was found that the acid amounts decreased monotonously with the particle size increasing, and there was an instant change around 15 nm. The synthesis of MPC was evaluated over nano-sized ZrO₂ catalyst, and high aniline conversion and MPC selectivity were obtained over ZrO₂ with small size and high content of tetragonal phase.A novel supported ZrO₂/SiO₂ catalyst for MPC synthesis was developed based on the abovementioned study. When ZrO₂ loading was 1 wt% and the catalyst was calcined at 573 K for 2 h, it showed high activity. XRD, XPS, NH3-TPD and FT-IR of the catalyst adsorbed with pyridine were carried out to characterize the supported catalyst. From the results, it can be concluded that the formation of Si-O-Zr bonds was due to the interaction between ZrO₂ and SiO₂. The acid amounts and the content of weak acid sites on the surface of ZrO₂/SiO₂ increased obviously than that of ZrO₂, and Lewis acid sites were dominant. Aniline conversion is 98.6% and MPC yield is 79.8% under the optimized reaction conditions.The reaction scheme of DMC and aniline over ZrO₂/SiO₂ catalyst was proposed and studied by in-situ FT-IR. Firstly, DMC adsorbed on the surface of ZrO₂/SiO₂ catalyst, and C atom in carbonyl group became more electropositive. Then,aniline, the nucleophilic reagent, attacked the C atom and bimolecular nucleophilic substitution （SN2） took place. Based on the reaction scheme, kinetics of MPC synthesis over ZrO₂/SiO₂ catalyst was studied by Reactor IR IC-10. The surface reaction was the control step of reaction rate, and the kinetic equation was as follows.A novel heterogeneous catalyst, ZnO-TiO₂ was designed and prepared for MPC synthesis. ZnO-TiO₂ catalyst, calcined at 673 K, with n（Ti）/n（Zn） equaling to 2 exhibited a better activity. Aniline conversion was 96.9% and MPC yield was 66.7%. The characterization results and catalytic activity was correlated. It was found that the formation of ZnTiO3 and Zn₂TiO₄ provided the Lewis acid sites for MPC synthesis. Furthermore, ZnO-TiO₂ showed better stability, and its catalytic activity could be reactivated almost completely just by calcination.The integrated reaction system of MPC synthesis with its condensation to MDC in microscale was set up. A bifunctional catalyst, H₄SiW₁₂O₄₀-ZrO₂/SiO₂, was designed and prepared for the one-pot synthesis of MDC using aniline, DMC and formaldehyde as raw material. The better reaction conditions were as follows: n（DMC）/n（aniline）/n（formaldehyde） = 20/1/0.1（molar ratio）, H₄SiW₁₂O₄₀ load was 10 wt% and the reaction temperature was designed by stages, namely, maintaining 443 K for 7 h and then cooling down to 373 K for 4.5 h. Under above conditions, the MDC yield was 24.9%.更多还原