Preparation Of Supported Zinc Acetate Catalyst And Its Application In Methyl N-phenyl Carbamate Synthesis

Methyl N-phenyl carbamate(MPC) is the intermediate of4,4，-diphenylmethanedisocyanate(MDI) by the cleaning non-phosgene method. There are two bottlenecks in theindustrialization of MPC production with "green chemical" dimethyl carbonate(DMC) andaniline as raw material. The first one is that the homogeneous catalyst is prone to deactiveeasily and is very difficult to be regenerate, in sprite of its higher catalytic activity. Theother one is that the catalyst of solid phase show low activity and selectivity. Therefore, theimmobilization of Zn(OAc)2and co-preparation of MPC and Nanometer ZnO are studied inthis paper.Zn(OAc)2/SiO2catalyst was prepared by incipient impregnation process. WhenZn(OAc)2loading was30wt%and Zn(OAc)2/SiO2was calcined at300℃, it showed thebetter activity. The aniline conversion and methyl N-phenyl carbamate(MPC) yield were98.1%and93.8%, respectively. The activity of Zn(OAc)2/SiO2catalyst was slightly lowerthan the homogeneous Zn(OAc)2, but its stability was improved significantly.The anilineconversion and MPC yield were decreased to64.3%and38.1%after Zn(OAc)2/SiO2wasused for five times. The characterization results suggest the cause for its better stability wasthe formation of Si-O-Zn bonds by the interaction between Zn(OAc)2and SiO2, whichwould increase the steric hindrance of Zn2+.Additionally, the other cause was thedehydration of methanol and hydroxyl group on the surface of SiO2.Zn(OAc)2/SiO2catalyst was prepared by reaction impregnation process, in which bothZn(OAc)2/SiO2catalyst and MPC were obtained after the reaction between aniline anddimethyl carbonate catalyzed by Zn(OAc)2. In the process,most of Zn(OAc)2/SiO2wasadsorbed onto the surface of SiO2, gradually. Zn existed in three forms of Zn(OAc)2、ZnOand Zn5(OH)6(CO3)2on the surface of Zn(OAc)2/SiO2. When the reaction temperature is170℃, reaction time is7h, and the mass ratio of Zn(OAc)2to SiO2is1, the catalystexhibited the better activity. The aniline conversion and MPC yield were96.3%and96.0%,respectively. Compared with incipient impregnation process, Zn(OAc)2was dispersed wellon the surface of SiO2together with a good stability. After Zn(OAc)2/SiO2was used foreight times, aniline conversion and MPC yield could reach81.6%and64.1%, respectively.Based on the idea of co-preparation of MPC and nanometer ZnO, a new method for preparation of nanometer ZnO was investigated. Different morphology and nano size ofZnO were prepared. Under the reaction condition of aniline conversion and MPC yieldbeing more than99%, polyhedral spherical ZnO with the average particle size of6-7nm androd-like ZnO with the aspect ratio of13:1were obtained, respectively.