Preparation Of Silica By Silicon Tetrachloride Hydrolysis

Polysilicon is the cornerstone of the photovoltaic solar industry, and its demand issharply increased. As with many domestic large-scale polysilicon project launched, manyexcesses of by-products of silicon tetrachloride which is strong corrosive in thedownstream limit the healthy development of polysilicon industry chain. In recent years,many researchers committed to explore new consumption path of silicon tetrachloride, andobtain a suitable particle size distribution of silica by improving gas hydrolysis process ofsilicon tetrachloride. Silica has many properties, such as good chemical stability, highthermostability and nice electrical insulation. Besides, its performance of reinforce andfilling becomes better after silica is modified hydrophobically. While the consumption ofsilicon tetrachloride is extremely limited for little market capacity of gas-phase silica andstrict hydrolysis conditions. Therefore, exploration and research of low-cost, highefficiency hydrolysis process of silicon tetrachloride is particularly important.For solving the problems about gas hydrolysis, a wet route for silicon tetrachloridetreatment is put forward in this paper. Superfine silica powder can be obtained and thehydrogen chloride gas can also be collected and recycled in this process. This papermainly involves the following aspects: hydrolysis of silicon tetrachloride andmorphology control of silica in organic system, hydrolysis of silicon tetrachloride ininorganic salt system, modification and preparation process of silica and desorption ofhydrochloric acid.Firstly, the influence of different organic solvents such as benzene, alkanes and estersand alcohols on hydrolysis of silicon tetrachloride is discussed. The results show thatspecific surfaces of products are smaller in ethanol solvent. Silica solid spherical particleswith good dispersibility are formed in ethanol-water-SDBS system. Silica hollow balls areobtained in ethanol-water-styrene system. Furthermore, in the mixed solvent of ethanoland water, sheet silica is produced when surfactant F-127is3g·l^-1while rodlike silica isformed when the surfactant F-127is12g·l^-1. Meanwhile alveolate silica can be obtainedthrough adding ionic liquids1-butylsulfonic-3-methylimidazolium trifluoromethanesulf-onate to the mixed solvent.Secondly, the "water-hydrochloric acid–inorganic salt” is the better system forhydrolysis of silicon tetrachloride. In this system, filtration performance of the reaction mixture has been improved, and the specific surface area of silica is reduced. The betteroptimal conditions are: the concentration of inorganic salt C as the reaction substrate4.5mol·L^-1, the initial concentration of hydrochloric acid7.1mol·L^-1, silicon tetrachloride0.9mol/（L substrate）, the stirring speed150r·min-1, the reaction temperature45℃, the feedrate0.35mol·h^-1, the aging temperature45℃and the aging time0.5h. Under theseconditions, the particle sizes of products decrease with the reduction of the acidity ofcirculating solution. In addition, nano-silica with good hydrophobic is gained throughhydrolysis of silicon tetrachloride in inorganic salt system which added modifier,and thenits rubber reinforcing performance is improved as well.Finally, the desorption process is studied. It shows that the optimal single strippant iscalcium chloride. And the result of desorption is better with the increasing concentration.The desorption of composite desorbent shows better than single desorbent’s. Thecomposite desorbent consisting of the mass fraction of calcium chloride35%andmagnesium chloride20%has the better desorption about the circulating reaction solution,under this condition more hydrogen chloride gas can be collected.