二甲基一氯硅烷和三氯氢硅的热氯化反应及机理研究

Study on thermal chlorination and mechanism of chlorodimethylsilane and trichlorosilane

去除三氯氢硅(SiHCl_(3))中的碳杂质可提高多晶硅的纯度,但SiHCl_(3)和二甲基一氯硅烷[(CH_(3))_(2)SiHCl]的沸点极为接近,在精馏过程中易形成共沸物。因此,SiHCl_(3)中的(CH_(3))_(2)SiHCl较难去除。提出以Cl_(2)为氯源,通过热氯化反应将(CH_(3))_(2)SiHCl转化为高沸点的甲基氯硅烷,以增大相对挥发度,便于后续精馏除杂。但(CH_(3))_(2)SiHCl和SiHCl_(3)会同时发生氯化反应,为此,探究了两者转化率随温度的变化。结果表明,在60℃、120 min时,(CH_(3))_(2)SiHCl的转化率为53.1%,SiHCl_(3)的转化率为14.3%,(CH_(3))_(2)SiHCl的转化率最佳。最后,通过密度泛函理论计算分析了反应路径,确定了反应机理。SiHCl_(3)、(CH_(3))_(2)SiHCl氯化反应的能垒差在于Cl_(2)与SiCl_(3)·、(CH_(3))_(2)SiCl·反应的能垒,且Cl_(2)与SiCl_(3)·反应的能垒比与(CH_(3))_(2)SiCl·反应的能垒高60.4 kJ/mol。

Removal of carbon impurities from trichlorosilane(SiHCl_(3))can improve the purity of polysilicon.However,the points of chlorodimethylsilane[(CH_(3))_(2)SiHCl]and SiHCl_(3)are very close,and azeotrope is easily formed in the distillation process.Therefore,(CH_(3))_(2)SiHCl in SiHCl_(3)is difficult to remove.It was proposed to use Cl_(2)as the chlorine source to convert(CH_(3))_(2)SiHCl into high boiling methyl chlorosilane through thermal chlorination reaction to increase the relative volatility and facilitate the distillation.However,SiHCl_(3)and(CH_(3))_(2)SiHCl were chlorinated at same time.Therefore,the change of the conversion of the two with temperature was investigated.The results showed that the conversions of(CH_(3))_(2)SiHCl and SiHCl_(3)were 53.1%and 14.3%at 60℃and 120 min,and the selectivity of(CH_(3))_(2)SiHCl was the best.Finally,the reaction path was calculated and analyzed by density functional theory,and the reaction mechanism was determined.The difference between the reactions of SiHCl_(3)and(CH_(3))_(2)SiHCl resulted from the different energy barriers for the reactions of the SiCl_(3)·and(CH_(3))_(2)SiCl·radicals with Cl_(2).The energy barrier of the reaction of SiCl_(3)·with Cl_(2)was 60.4 kJ/mol higher than that of the reaction of(CH_(3))_(2)SiCl·.