Study On The Synthesis Of CF₃I Via Vapor-phase Catalytic Reaction Of CHF₃ With I₂

CHF3 is the major by-product during the manufacture of CHClF2(R22,HCFC-22),and it has the second highest global warming potential among all the greenhouse gases.CHF3 is a potent and synthetic greenhouse gas with global warming potential of 11,700 times(for a 100-year time horizon)higher than carbon dioxide.It necessitates the research and development of potential routes for the treatment of CHF3 and other synthetic greenhouse gases.Trifluoroiodomethane(CF3I)has drawn growing attention as a promising replacement for halon in the application of fire extinguishing agent,freezing medium and etching gas since its short atmospheric lifetime and low global warming potential(GWP).Therefore,investigation of vapor-phase catalytic reaction of CF3I is of industrial value.This thesis mainly investigated the pyrolysis of CHF3 over activated carbon,especially the role of surface oxygen groups.The effect of La on Rb-K/AC catalyst and the influence of catalyst carriers on the performance of CF3I synthesis were investigated.The amount and type of surface oxygen groups of activated carbons,acidic-basic property of catalyst surface and the structure of graphite were characterized by energy dispersive spectrometer(EDS),X-ray diffraction(XRD),BET surface area analysis,C02-TPD and so on.The results are as follows:1.Effect of surface oxygen groups on the pyrolysis of CHF3 and CHClF2 over activated carbonsThe results confirm that following different treatments,the concentration of surface oxygen groups on activated carbons varies dramatically.These surface groups play important roles in decomposition of CHF3 and the product profiles.It is suggested that carboxylic groups are responsible for the formation of CF3 and ultimately the product C2F6 which is resulted from the coupling the CF3,while the interaction between CHF3 and hydroxyl or carbonyl groups leads to the total destruction of CHW3 and production of CO and C02.Pyrolysis of CHClF2 over activated carbon confirms that surface oxygen groups have no noticeable influence on the performance of CF2.By contrast,pure carbon surface is responsible for the disproportion of CF2 and formation of CF3.2.The effect of La on the performance of Rb-K/AC catalyst for trifluoroiodomethane synthesisThe results show that the intensity and the amount of basic sites on the catalyst were enhanced following the addition of La.As La affects the interaction between the Rb-K and support,improved dispersion of the active components is achieved.In addition,La is confirmed to be on of the active phases for CF3I synthesis.3.KF/HSAG catalyst for the synthesis of CF3I.Although HSAG(High Surface Area Graphite)is more stable than AC,the activity of KF/HSAG catalyst is lower than that of KF/AC as the surface area.is low compared with AC.In order to improve the activity and dispersion of KF,ball-milling and ultrasonic assisted impregnation were also attempted to prepare KF/HSAG catalyst.Hoever,no improved activity was observed.