【作者】 刘丽敏；

【导师】 王延吉；

【作者基本信息】 河北工业大学 ， 化学工艺， 2008， 硕士

【摘要】 二苯甲烷二氨基甲酸甲酯(MDC)是生产二苯甲烷二异氰酸酯(MDI)的中间体,MDI是生产聚氨酯的重要原料之一。以碳酸二甲酯(DMC)为原料合成MDI的工艺路线包括苯氨基甲酸甲酯(MPC)的合成、MPC缩合及MDC裂解三步反应。本文针对该工艺路线工序复杂的问题,将MPC合成反应和MPC缩合反应过程集成,并制备了与之相对应的双功能催化剂来实现MDC的一步合成。对苯胺和DMC为原料一步合成MDC的反应体系进行了分析,确定以ZrO2/SiO2作为MPC合成反应的催化剂,H4SiW12O40/SiO2作为MPC缩合反应的催化剂,甲醛溶液作为MPC缩合反应的甲基化试剂,DMC作为集成反应的溶剂。开发出双功能催化剂H4SiW12O40-ZrO2/SiO2,研究了该催化剂上以苯胺、DMC和甲醛为原料一步合成MDC的反应性能。考察了反应时间、反应温度、H4SiW12O40负载量、原料配比等反应条件对催化性能的影响。适宜的反应条件是:n(DMC)/n(苯胺)/n(甲醛)=20/ 1/0.05(摩尔比),ZrO2的负载量为1%,H4SiW12O40的负载量为10%,170℃下反应7h后降温到100℃下反应4.5h。在此反应条件下,MDC的收率为24.9%。采用吡啶吸附红外光谱法对H4SiW12O40-ZrO2/SiO2催化剂的酸类型进行了表征,结果表明其表面同时存在着Lewis酸中心和Br?nsted酸中心,分别用于催化MPC合成反应和MPC缩合反应。对影响H4SiW12O40-ZrO2/SiO2催化剂上一步合成MDC反应性能的因素进行了研究,发现苯胺在H4SiW12O40活性中心上的吸附,是导致MPC难以发生缩合反应的原因。为解决苯胺在H4SiW12O40活性中心上的吸附及H4SiW12O40的流失问题,采用溶胶-凝胶法制备出包覆型的ZrO2/SiO2@H4SiW12O40催化剂。凝胶时间为50h时制备出的包覆型催化剂活性较高,当n(DMC)/n(苯胺)/n(甲醛) =20/1/0.05(摩尔比),170℃下反应7h后降温到100℃下继续反应4.5h时,MDC的收率为9.2%。利用分子模拟软件对反应物及主副产物分子的空间构型和几何参数进行模拟和估算,结果表明所制备的包覆型催化剂能够满足反应物和产物在催化剂孔道内的扩散。与等体积浸渍法制备的负载型催化剂相比,包覆型催化剂对MDC的合成具有较好的稳定性。更多还原

【Abstract】 Methylene diphenyl dicarbamate (MDC) is an intermediate in the synthesis of methylene diphenyl diisocyanate (MDI), and MDI can be used as the raw material for the production of polyurethane. The synthesis of MDI using dimethyl carbonate (DMC) is environmentally friendly. Nevertheless, the process is complicated, for it comprises three steps: synthesis of methyl N-phenyl carbamate (MPC), reaction of MPC with methylenating agents to form MDC, and decomposition of MDC to prepare MDI. If MPC synthesis can be coupled and performed together with its condensation, the process can be greatly simplified. This work reports the one-step synthesis of MDC over bifunctional catalysts.The one-step synthesis of MDC using aniline and DMC as raw materials was studied. ZrO2/SiO2 and H4SiW12O40/SiO2 were used as the catalyst in MPC synthesis and MPC condensation respectively. Formaldehyde was chose as a methylenating agent and DMC could be used as a solvent for the system.A bifunctional catalyst H4SiW12O40-ZrO2/SiO2 was developed for the direct synthesis of MDC from aniline, DMC, and formaldehyde solution. The effects of reaction time, reaction temperature, H4SiW12O40 loading and DMC/aniline/formaldehyde molar ratio were studied. Suitable reaction conditions were as follows: DMC/aniline/formaldehyde molar ratio was 20/1/0.05, ZrO2 loading was 1%, H4SiW12O40 loading was 10%, and reaction temperature was controlled by stages (i.e., reaction at 170℃for 7h and then at 100℃for 4.5h). Under these conditions, the yield of MDC was 24.9%. FT-IR of the catalyst adsorbed with pyridine was carried out to characterize the H4SiW12O40-ZrO2/SiO2. From the result, it could be concluded that Lewis acid sites and Br?nsted acid sites existed on the surface of catalyst at the same time, which were the active sites for MPC synthesis and MPC condensation respectively. It could be conjectured that the acid sites of H4SiW12O40 were occupied by aniline which resulted in the difficulty for MPC condensation with formaldehyde.With a view to reducing the attachment of aniline to the acid site of H4SiW12O40 and H4SiW12O40 leaching, a capsule catalyst ZrO2/SiO2@H4SiW12O40 was prepared through sol-gel process. When gel time was 50h, the catalyst showed high activity. The better reaction conditions were as follows: DMC/aniline/formaldehyde molar ratio was 20/1/0.05, reaction at 170℃for 7h and then at 100℃for 4.5h. Under these conditions, the yield of MDC was 9.2%. The spacial structure and geometrical parameters of reagents and produces were simulated and computed by Material Studio solfware, it showed that reagents and produces could diffuse freely in the pore of catalyst. Compared with H4SiW12O40-ZrO2/SiO2, ZrO2/SiO2@H4SiW12O40 catalyst showed better stability on MDC synthesis.更多还原