以三氯乙烯为供氢剂将四氯化碳转化为氯仿

Converting carbon tetrachloride to chloroform by using trichloroethene as hydrogen donor

四氯化碳(CTC)是甲烷氯化物生产的副产品,也是一种消耗臭氧层物质(ODS),将其转化为氯仿,可同时实现ODS的生产淘汰和资源化循环利用。本文开发了一种以四丁基氟化铵(TBAF)为相转移催化剂、K2CO3为助催化剂、三氯乙烯为供氢剂将CTC转化为氯仿的新方法,研究了温度、催化剂种类和用量对反应的影响,考察了反应动力学特征及反应放大效应。结果表明:在碱性条件下,三氯乙烯的酸性H原子可与四氯化碳发生取代反应,生成四氯乙烯和氯仿;反应速率随相转移催化剂用量的增加以及助催化剂碱性的增强而提高;循环使用过程中催化剂活性的降低与TBAF中氟离子的取代反应消耗有关;表观反应速率符合拟一级反应动力学模型,过程放大效应不明显。在优化反应条件下(30~60℃,9g CTC,10mmol三氯乙烯,1mmol TBAF,10mmol K2CO3,0.5h),三氯乙烯被完全转化,氯仿选择性大于95%。

Carbon tetrachloride(CTC)is a byproduct of chloromethanes industry and an ozone-depleting substance(ODS).Its conversion to chloroform can achieve both ODS production phaseout and recycled resource utilization.A new method for converting CTC to chloroform was developed by using tetrabutylammonium fluoride(TBAF)as phase transfer catalyst,K2CO3 as co-catalyst and trichloroethylene as hydrogen donor.The effect of temperature,composition and usage of the catalysts on the reaction was studied,and the reaction kinetics and the scale-up effect were investigated.The results showed that radical substitution took place between CTC and the acidic H-atom of trichloroethylene under basic conditions,forming tetrachloroethene and chloroform.The reaction rate increased with increasing usage and basicity of the catalysts.The catalytic activity of the catalysts declines slightly in the recycled uses due to the partial fluorination of polychlorinated alkanes by TBAF.The overall reaction rate followed the pseudo-first order model with insignificant scale-up effect.Under optimal conditions(30-60℃,9g CTC,10mmol trichloroethylene,1 mmol TBAF,10 mmol K2CO3,0.5 h),trichloroethene can be converted completely with over 95%chloroform selectivity.