Study On The Method Of Stability Evaluation And Preparation Of Low-Mercury Catalyst For Acetylene Hydrochlorination

The preparation of HgCl₂/AC catalyst is the key technique while above 80%of vinyl chloride are produced by process of hydrochlorination of acetylene in China and mercury chloride are used as the catalysts.The stability of HgCl₂/AC catalyst is very important for the life of low-mercury catalysts.The evaluation process for the stability of catalysts consume much time.In order to improve the efficiency of the catalyst development,the present paper studied on the preparation methods and characterization of low-mercury catalyst for acetylene hydrochlorination,to investigate the influence of methods on the catalyst activity and stability.The main results are as followings:1.The methods of the stability evaluation of Low-mercury catalysts were studied for acetylene hydrochlorination reaction.The reaction conditions with gaseous hourly space velocity?GHSV?of 1000 h^-1 and temperature of 180 ^oC can be used as accelerate condition for catalysts screen.The deactivation curve can be fitted by an exponential decay function.The parameter Y₀ in an exponential decay function can be used as stability evaluation index and the conversionof acetylene at 25h(Y₂₅)can be used as intial activity of low mercury catalysts.The effects of experimental condition of the catalysts were studied.It is found that the catalysts can be thermal treated at 250 ^oC for 3h under flow of N₂ to evaluste the thermal stability.Both the above methods can be used to for fast and efficient catalysts screen.2.The deactivation mechanism was studied via detailed characterizations of the fresh and used low-mercury catalyst by the nitrogen sorption,scanning electron microscopy?SEM?,temperature programmed desorption-mass spectrometry?TPD-MS?,temperature programmed oxidation-mass spectrometry?TPO-MS?and thermal gravimetric analysis?TG?.The result shows that deactivation of the low-mercury catalyst are caused by the following reasons:?1?coking;?2?poison by the sulfur;?3?leaching of HgCl₂.And it is found that the coking and poison by the sulfur are the main reason for the low-mercury catalyst.3.The impregnation conditions for low-mercury catalyst were studied.The summarized results the catalytic performance was mainly determined via the HgCl₂%loadings.The preparation conditions only affected the HgCl₂%loadings.The stability and intial activities is not directly related to preparation conditions.The optimal drying condition of low-mercruy catalyst is 120 ^oC,5 h.