Studies On Catalysts For Gas-Phase Catalytic Dehydrochlorination Of 1,1,2-Trichloroethane

Polychlorinated ethanes such as 1,1,2-trichloroethane and 1,1,2,2-tetrachloro ethane have been used for decades as chemical intermediates,solvents,degrea sing agents,and paint removers.Both compounds have adverse health effects on the liver,the kidneys,and the nervous and immune systems.Due to impr oper disposal practices and accidental releases,these contaminants are widely distributed in groundwater and soils.Therefore,how to deal with the issue of polychlorinated ethylene is an important issue.At present,it is an effective method to convert polychlorinated ethylene into olefin to by catalytic cracking of HCI,in which the catalyst plays an important role.This paper mainly studies the catalysts which can remove HCl from 1,1,2-trichloroethane?TCE?by the way of gas phase catalytic cracking.And then we can design and select Zn/SiO₂ catalyst and Cr-based catalysts which are of good catalytic performance and high selectivity for the production of cis-1,2-vinyl chloride?cis-1,2-DCE?.We study the influence of precursor types,catalyst loading,calcination temperature,airspeed,reaction temperature which will have some impact on the conversion and selectivity of 1,1,2-trichloroethane?TCE?dechlorination,by phase analysis of xray diffraction?XRD?,Thermogravimetric Analysis-Differential Thermal Analysis?TG-DTA?,scanning electron microscope?SEM?,Transmission Electron Microscope?TEM?,specific surface area?BET?,X-ray photoelectron spectroscopy?XPS?,Raman spectra?Raman?,Ammonia-programmed temperature control?NH3-TPD?,Hydrogen-programmed temperature reduction?H2-TPR?and a series of characterization to explore the factors influencing of TCE dechlorination reaction activity,selectivity and deactivation,as well as explore the mechanism of TCE dechlorination.The research contents and results of this thesis are summarized as follows:1.A series of SiO₂-supported fourth periodic transition metal nitrate catalysts?M/SiO₂?were prepared by an impregnation method for the dehydrochlorination of 1,1,2-trichloroethane?TCE?in gas phase.Among these M/SiO₂ catalysts,Zn/SiO₂ had the best catalytic activity with the highest TCE conversion?ca.98%?,as well as excellent selectivity of cis-1,2-dichloroethylene?82%?at the reaction temperature of 350?.By increasing zinc loading,the conversion of TCE using Zn/SiO₂ catalyst was gradually improved,which was in agreement with the total acidity amount in Zn/SiO₂ catalyst.Associated the specific activity and specific acidity Zn/SiO₂ catalyst with different Zn loadings,it was found that the higher specific acidity contributed to the higher specific activity.This may indicate that the acid center of Zn/SiO₂ was the catalytic active site for the dehydrochlorination of TCE reaction.Mainly due to the coke deposition on the catalyst surface.,Zn/SiO₂ catalyst could be deactivated,in the process of this dehydrochlorination reaction.Catalysts with low Zn loading had stronger acid sites which resulted in more coke formation on the catalyst.It is showed that the strong acid sites on the surface is the prime cause of coke deposition and inactivation2.It was prepared by coprecipitation of Cr?NO₃?₃ and NH3-H2O obtained CrOx catalysts at different calcination temperatures.Comparing with the air traffic control experiment,we found that CrOx catalyst work at low temperature on the dehydrochlorination of 1,1,2-trichloroethane?TCE?,At a lower temperature of 250? it have achieve 98%conversion and 90%selectivity of cis-DCE.Through XRD and H2-TPR characterization,it can be found that the catalysts with different valence states were produced by calcination at different temperatures,and the higher the calcination temperature,the higher the content of the low valence Cr.We got CrO,catalyst in the roasting temperature at 450?,which had the highest conversion rate of 98%at the low reaction temperature of 250?,for its larger specific surface area,the amount of acid and more stronger acid strength influence.Moreover,calcination can produce more stronger acid center in order to generate more cis-1,2-dichloroethen.