Study On The Catalyst In The Hydrogenation Process Of Silicon Tetrachloride

A certain amount of SiCl₄ was generated as a by-product during the production of polysilicon.With the expansion of the market,the discharge of SiCl₄ grows continuously.In order to reduce the negative impact of SiCl₄ on photovoltaic and lower the operation cost of polysilicon production,it is of significance to study effective treatment method for Si Cl₄ .As a main technology of reducing SiCl₄ ,hydrogenation technology mainly include“hot hydrogenation technology”and“cold hydrogenation technology”.Cold hydrogenation technology was widely used in polysilicon production in domestic due to its low consumption,high operation controlling and high stability.In view of the low conversion efficiency of SiCl₄ to SiHCl₃ by cold hydrogenation technology,catalysts were always added to improve the conversion rate.In this paper,the main research object was copper-based catalysts,nickel-based catalysts,iron-based catalysts,cobalt-based catalysts,molybdenum-based catalysts,etc.And preparation of catalysts,active evaluation,mechanism research of SiCl₄ hydrogenation technology,the role of catalyst on SiCl₄ hydrogenation process,as well as the determination of parameters of hydrogenation technology are analyzed and studied.Based on preparation and testing of catalyst mentioned above,it was concluded that nickel-based catalysts was with the highest stability during the whole reaction process.In contrast,copper-based catalysts appeared a certain sintering phenomenon,and pore channel of iron-based catalysts gradually disappeared with temperature below 500?,and water in structure took off quickly with temperature above 500?.Cobalt-based catalysts played the best role only when the temperature was higher than 680?.Research on the reaction mechanism of Si Cl₄ hydrogenation technology showed that the copper chloride crystals with higher energy could absorb a chloride ion from SiCl₄ ,and thus make the silicon chloride bond stretched until break.At the same time,SiCl₄ turned into silicon trichloride radicals,and then generated Si HCl₃ and a hydrogen ion by capturing a hydrogen atom from hydrogen molecule.After that,hydrochloric acid was synthesized by free hydrogen ion and chloride ion absorbed by copper chloride.Subsequently,hydrochloric acid molecules desorbed from surface of copper chloride,and absorption of SiCl₄ by copper chloride reoccurred.The optimum condition of SiCl₄ hydrogenation process were pressure 25atm,550?and raw material ratio 4.The impacts of four different kinds of catalysts on the conversion rate of SiCl₄ hydrogenation technology were analyzed.And it was found that the conversion rate was the highest,at 25.8%,when copper-based catalysts were added,following by nickel-based catalysts.When iron-based catalysts,cobalt-based catalysts and molybdenum-based catalysts were added,the conversion rate was very low.Copper and nickel catalyst was applied to large test equipment and operated for a month continuously.It was detected that average conversion rate was 22.54%using copper-base catalysts and 18.54%using nickel-based catalysts.In view of the relatively higher conversion rate of copper-based catalysts,the application of copper-based catalysts were very promising in SiCl₄ recycling.