Research On The Preparation Of Vinylidene Fluoride From1-Chloro-1,1-Difluoroethane

Vinylidene fluoride is one of the most important monomers in the fluorine industry, which is mainly used for the production of poly(vinylidene fluoride) and fluoroelastomer. Poly(vinylidene fluoride) is widely used as engineering plastics because of its good comprehensive performance. Fluoroelastomer shows excellent heat resistance, oil resistance, solvent resistance, which is an indispensable basic material in marry applications.Vinylidene fluoride is mainly prepared by pyrolysis of1-chloro-1,1-difluoroethane (HCFC-142b) under high temperature. The influence of temperature and flow rate on the conversion of HCFC-142b and the selectivity of vinylidene fluoride was studied in this dissertation. The conversion of HCFC-142b raised with the enhancement of the reaction temperature and the reduction of flow rate. The selectivity of vinylidene fluoride was improved with the rise of temperature. However, when the temperature reached600℃, the selectivity would be reduced with the appearance of coking. The optimal temperature ranged from550to600℃, and the appropriate flow rate range was0.15to0.6L/min.The products were analy:zed by GC-MS method, and the mainly components were vinylidene fluoride, HCFC-142b, CFCl=CH2and CF3CH3. The reaction path, the thermodynamics data and the activation energies of main reactions in pyrolysis process were studied with the density functional theory (DFT) at the (u)B3LYP level. The activation energy of the dehydrochlorination of HCFC-142b was225.49kJ/mol, while the activation energy of dehydrofluorination was271.15kJ/mol.FeCl3、CuCl2、and NiCl2were supported on activated carbon and used as catalysts. The reaction conversion was improved with the addition of FeCl3and CuCl2, and the catalytic mechanism might be carbonium ion mechanism. However, the service life of the supported catalysts was short, mostly due to the loss of active components and the carbon-laydown on the catalyst surface.The influence of the materials of the cracking tube was also researched in this dissertation. The reaction conversion was improved and the selectivity of vinylidene fluoride was reduced when iron was used as tube material, high conversion and selectivity rate could be obtained when copper was used as tube material.