Hexamethylenediamine Carbamate And Catalytic Synthesis Of 1,6-hexamethylene Carbamate

Many non-phosgene routes were promoted to synthesize hexane-l,6-diisocyanate(HDI) in order to overcome instinct drawbacks in traditional phosgene route. The most promising industrial route was thermal cleavage method including two setps. Intermediate dimethyl hexane-1,6-diyldicarbamate(HDC) synthysis was the key step in above thermal cleavage method. This works using methanol as solvent, methyl carbamate (MC) as carbonyl reagent and1,6-hexamethylenediamine (HDA) as material successfully synthesis HDC in the reactor. The catalytic activities of various catalysts were investigated. The reaction conditions in HDC synthesis was optimized after the optimal catalyst was selected. The conversion of catalyst and possible reaction mechanism were futher researched. The research details and main conclusions were listed as follows:1. HDC was successfully synthesis in hydrothermal reactor with a magnetic stirring from methyl MC and HDA using methanol as solvent. HDC products were qualitatively analyzed by GC-MS and FTIR. The desired, inermidiate products and byproduct was quantatively by gas chromatography using propyl benzene as an inernal standard.2. The effect of initial Zn、Fe ion concentration in exchange solution on exchange degree of modified4A、13X、ZSM-5and beta zeolites was researched. The results indicated with an increase of initial ion concentration, the exchange degree of modified zeolites increased gradually. By controlling the initial ion concentration of exchange solution, a batch of Z、Fe modified zeolites with a certain exchange degree were prepared.3. A seriers of catalysts, including prepared Z、Fe modified zeolites, commom solid acid and base, part of the transition metal oxides and lead oxysalts, were screend to catalytic HDC synthesis. The results indicated modified zeolites showed bad catalytic behavior, the yield of HDC was below20%. Solid acid Al2O3could not promote the reaction, while solid base CaO also behaved poor catalytic activity. Transition metal oxides catalytic activities were different, about67%yield of HDC was reached when the best ZnO was employed. Nano-ZnO which has smaller size could not futhur promote HDC yield. The Sb oxide at a low valency showed better catalytic than that at a high valency, the yield of HDC was65%. Lead compounds showed high activity; about 60-90%HDC yields were obtained. PbO2exhibited the highest activity; the yield of HDC reached93%, mean-while, only1.2%yield of intermediate HAC and2.1%yield of byproduct polyurea were produced.4. The optimal reaction conditons were obtained after investigation, the optimal reaction termperature was190℃; the optimal reaction time was6h; the optimal amont of PbO2was10%wt.5. Under the optimum reactions conditions, the PbO2reusebility was futher investigated. The results indicated the activity of PbO2dropped after first run, from93%to72%. The XRD and FTIRcharacterization results indicated that PbO2catalyst has been converted into PbCO3through intermediate Pb2OCO3in the reaction process. This conversion may be the reason for the reduction of PbO2catalytic activity.6. PbO2was pretreatment by solvent and reagents. The XRD characterization indicated that methanol played the role to make PbO2converted into Pb2OCO3, while MC and HDA together promoted Pb2OCO3further converted into PbCO3.7. There might be some active position in lead oxides which could activate carbonyl. An addition-eliminatino reaction happened on HDA, product HDC was produced through two urea intermediates over two catalytic cycles.