Study On The Inhibition Of Gel Of Hydrolyzed Chlorosilane Under The High Concentration Of Acidic Condition

Most of the domestic enterprises to adopt the production of polysilicon process with improved Siemens method,the trichlorosilane synthesis process,trichlorosilane distillation process and silicon tetrachloride hydrogenation process produce chlorosilane containing dichlorosilane(SiH2Cl2),trichlorosilane(SiHC1;),silicon tetrachloride(SiCl4),Double silicon atom silane,non-metallic chlorides,metal chlorides,high boiling matter,silicon powder etc.At present,most domestic enterprises use hydrolysis method to dispose chlorosilane,and most of the hydrolysis process of chlorosilane,prone to gel after hydrolysis,decreased mobility in liquid,or even changed to frozen.It affect the subsequent filtration and the separation process,so that the formation of SiO2 and hydrochloric acid is difficult to resource recycling.In this paper,it is difficult to separate the SiO2 and hydrochloric acid products from the hydrolysis of chlorosilane.Study on the factors influencing the preparation of silica under the condition of high concentration hydrochloric acid to hydrolyze chlorosilane on the gelation of hydrolyzate and its essence.The effects of hydrolysis reaction temperature,hydrochloric acid concentration,feed rate and feed vo?me of chlorosilane in high concentration hydrochloric acid were studied.The results showed that the concentration of hydrochloric acid and the ratio of residual liquid to initial hydrochloric acid had significant effect on the gelation time of chlorosilane.The root cause of the gel is the hydrolysis of chlorosilane to produce orthosilicic acid(Si(OH)4),dehydration to produce metasilicic acid,and further dehydration to form silica.In the high concentration hydrochloric acid liquid phase environment,chlorosilane hydrolysis of silica and then combined with the water molecules reverse reaction,the formation of silicic acid(Si(OH)4),and then generate silicic acid cation(Si(OH)4H+),and with S-OH containing silicic acid,silicic acid ions are hydroxyl Condensation,the formation of silicic acid polymer,and then form a gel.Based on the analysis of the influencing factors and the above factors,it was suggested that the electrolyte was added to the high concentration hydrochloric acid,and the hydrolysis of the chlorosilane was carried out under the condition of forming the charged ions in the reaction system to change the hydrolysis of the silica particles.Surface energy,so that the electrostatic repulsion dominated,the formation of silicate ions between the charge mutually exclusive,to block the combination of silicic acid ions,thereby preventing the cationic silicate condensation occurs,play the purpose of anticoagulation.In this paper,an acidic hydrolysis reaction solution was prepared by adding a chlorine salt(NaCl,CaCl2,KCl,BaCl2,MgCl2,NHCl,NHCI,AlCl3)in hydrochloric acid beforehand.Study on the resistant effect of electrolyte,the results show that:The use of alkali metals,alkaline earth metals and other chlorine salts can delay the gel.With the increase of the concentration of electrolyte in the hydrochloric acid,the gel time of the mixed solution increased after the hydrolysis reaction,that is,the anti-coagulation effect was enhanced.When the concentration is too high,the ionic double layer is compressed,the energy barrier gradually decreases,the resistance between ions decreases,van der Waals gravity increases,silicic acid ions began to aggregate.With the increase of electrolyte concentration,gel time becomes shorter,electrolyte anticoagulant effect is weakened;part of the electrolyte concentration is too high to accelerate gel.BaCl2,MgCl2,NH4C1 and AICl3 have a retarding effect on the gel in a certain concentration range,but there are accelerating gel in some concentrations.NaCl,CaCl2,and KCl have a certain delay in gel at different concentrations,anticoagulation effect is better.The anticoagulant effect is the best by adding CaCl2,the adjustable concentration range is wide.In industrial applications,the influence of process concentration fluctuation is small,the anticoagulation is more reliable in industrial application,and more feasible.There was no obvious difference between the silica produced by the hydrolysis of the electrolyte after the addition of the electrolyte and the silica without electrolyte hydrolysis.The particle size test showed that the silica was amorphous in the range of 10?40?m.Therefore,chlorosilane in the high concentration of hydrochloric acid hydrolysis,the use of electrolyte to join to achieve resistance to coagulation,to achieve high concentrations of hydrochloric acid hydrolysis of chlorosilane preparation of ultra-fine silica process continuous.