无溶剂条件下氧化锌催化苯氨基甲酸甲酯制备苯异氰酸酯的研究

Zinc Oxide Catalyzed Solvent-Free Synthesis of Phenyl Isocyanate with Methyl N-Phenyl Carbamate

对无溶剂条件下金属氧化物催化苯氨基甲酸甲酯(MPC)热分解制备苯异氰酸酯(PI)的反应进行了研究,控制适宜的加热温度和绝对真空度,产物PI和甲醇以蒸气状态分离出反应器,使分离与热解反应同时进行,再采用分段冷凝的方式将PI和甲醇分离并收集,发现金属氧化物中氧化锌(ZnO)具有较好的催化活性。考察了制备方法对ZnO催化性能的影响,结果表明以碱式碳酸锌热分解制备的ZnO,在400℃焙烧时性能最好。对ZnO催化剂进行了XRD和TEM表征,发现催化剂颗粒大小是影响催化性能的重要因素,最佳的催化剂粒径为40 nm左右。当ZnO用量为MPC用量的1%(wt),在加热温度为200℃,绝对真空度为100 mmHg时,MPC转化率为57.2%,PI选择性为91.1%。与溶剂法相比,该方法可得到更高浓度的目标产物,并减少分离提纯的能耗和污染。

Solvent-free synthesis of phenyl isocyanate （PI） by thermal decomposition of methyl N-phenyl carbamate （MPC） with metal oxides as the catalyst was studied. The temperature and vacuum conditions were kept optimal to obtain PI and methanol vapors,which were then separated and collected by condensation. The results show that zinc oxide （ZnO） has better activity than other metal oxides used and ZnO prepared by calcinating basic zinc carbonate at 400℃ shows best performance. XRD and TEM results show that the particle size of the catalysts has remarkable effect on the catalytic performance, and the optimal particle size is approximately 40 nm. Under the optimum reaction conditions （ZnO/MPC： 1 wt%,heating temperature： 200℃, vacuum value： 100 mmHg）, the conversion of MPC and the selectivity of PI are 57.2% and 91.1%,respectively. Compared with reactions under solvent condition, higher PI concentration can be obtained in the solvent-free method. Moreover, energy consumption and potential pollution can be reduced during separation and purification.