Study Of Catalytic Cracking Of High Boiling Chlorosilane At Low Temperature

A large amount of chlorosilane residue is produced during the production of polysilicon using the improved Siemens process.The chlorosilane residue is consist of low boiling residues and high boiling residues,and the high boiling residues involves disilane and polysilane.It is difficult for the polysilicon industry to treat and causes great pollution to the environment.The high boiling residues can be converted into valuable monosilanes by cleaving Si-Si bonds in the presence of hydrogen chloride.It lays the foundation for breaking through the bottleneck of polysilicon industry development,can realize harmless treatment and resource utilization of by-products,and can create economic and social benefits.Low boiling residues with boiling point below 80℃（about 88wt%）and high boiling residues with boiling point between 80℃and 160℃（about 11wt%）are separated from chlorosilane residue.It is found by GC that the low boiling residues is almost composed of Si Cl₄.According to the internal standard curve method and GC-MS,the high boiling residues of 56.42wt%disilane and polysilane mainly consists of Si Cl₄,Si₂Cl₆ and Si₂OCl₆.The impurities of high boiling residues in different temperature range are analyzed by ICP-OES.The results show that the content of impurities in high boiling residues at 80-160℃is small.Low boiling residues with chlorine content of80.61%and high boiling residues with chlorine content of 78.32%are detected by titration.The hydrolysate of chlorosilane residue containing 99.75%Si O₂ is tested by XRF.The effect of the reaction improves with the increasing of reaction temperature and the quantity of catalyst.The reaction apparatus,catalyst type,reaction time and impurity content also influence the reaction.The optimum reaction condition was obtained in a gas-liquid reaction:N,N-dimethylaniline is a better catalyst,reaction temperature is130-135℃,fulx of HCl is 5-9 L/h,catalyst component is 8wt%,the reaction time is 1.5hours and stirred rate is 300r/min.Under the optimum reaction condition,the cleavage ratio and the monosilane yield can reach to 100%and 88.71%.KC134A solid-phase cracking catalyst is used in gas-solid reaction at the reaction temperature of 65-75℃.With sufficient HCl gas,the product yield can reach more than 68%.The structure of each unit in the high boiling residues catalytic cracking process of a company in China was analyzed.Combined with the data provided by the company,when the calculation time is 1 h,the material balances of the total catalytic cracking process and important units were investigated.The whole process can maintain the material balance when approximately 5743 kg of material was fed and approximately5743 kg of material was discharged.