溴离子对NDMA前体物Chlortoluron的氯化降解特性影响

Influences of Bromide Ions upon Chlorination Characteristics of Chlortoluron as Precursor of NDMA

研究了不同pH下,投加不同浓度的外加溴离子时,NDMA前体物—Chlortoluron的氯化动力学降解情况.实验结果表明,在pH分别为6,7,10,Chlortoluron浓度为9.4μmol·L-1,Cl2浓度为188.0μmol·L-1的条件下,控制投加不同浓度的溴离子时,Chlortoluron的降解仍然符合拟一级动力学模型.当pH分别为6,7时,Chlortoluron的降解速率随着外加溴离子浓度的增加而增大,外加溴离子浓度相同时,偏酸性的环境使Chlortoluron的降解速率更快,这可能与反应体系中HOBr的生成有关.当pH为10时,溴离子浓度的变化对Chlortoluron的降解速率没有显著影响,可能是ClO-与Br-基本不发生反应,从而没有生成HOBr.根据对反应体系的动力学分析,求解了在本实验条件下,不同pH时拟一级反应动力学常数kobs与[Br2]/[Cl2]的线性关系,进而通过求解常微分方程组计算了HOBr与Chlortoluron的反应速率常数(k5=(1.95±0.44)×105).这也从动力学的角度解释了外加溴离子时Chlortoluron氯化速率显著增大的原因.

The chlorination kinetics of Nnitrosodimethylamine(NDMA) precursor, Chlortoluron, controlling different concentrations of bromine ions under different pH,was investigated in this study.Results show that degradation of Chlortoluron still meets pseudo first order dynamic model when different dosages of bromine ions are controlled at scheduled pH of 6,7,10(concentrations of Chlortoluron and Cl2 are 9.4μmol·L-1 and 188.0μmol· L-1,respectively).The degradation rate of Chlortoluron increases with concentrations of bromide ions at pH6 and 7. Chlortoluron degrades faster under more acidic conditions. This phenomena are probably related to the generation of HOBr in the system.Nevertheless,when pH is 10,variation of bromide ions has no significant impact on the degradation rate,which may be attributed to non-reaction of ClO-and Br-and no generation of HOBr.Based on the kinetics analysis,this study obtains the linear relationship between kobs and [Br2 ]/[Cl2 ]at these pH conditions.Then by solving ordinary differential equations,the reaction rate constant of HOBr and Chlortoluron is calculated(k5 =(1.95±0.44)× 105).Simultaneously,from viewpoint of dynamics,this relatively far high rate constant also explains the distinct faster degradation rate of Chlortoluron with the presence of bromine ions.