臭氧降解水中邻苯二甲酸二甲酯的动力学及影响因素

利用臭氧(O3)降解含较高浓度邻苯二甲酸二甲酯(DMP)的模拟废水,采用竞争动力学法,以硝基苯为参比有机物,获得了DMP与O3及羟基自由基(·OH)的反应速率常数,研究了·OH抑制剂叔丁醇(TBA)、pH和多种离子对O3降解DMP效果的影响.结果表明,O3降解DMP符合拟一级动力学,DMP与O3的反应速率常数kO3-DMP为(0.064±0.014)L.(mol·s)-1,与·OH的反应速率常数k·OH-DMP为3.59×109L.(mol·s)-1;O3降解DMP过程中,生成的羧酸类中间产物使弱酸或弱碱性反应液的pH下降,但不足以影响强酸或强碱性反应液的pH;降解过程中产生大量中间产物使COD的去除率滞后于DMP的降解率,且部分中间产物不易被矿化;较低浓度的TBA不足以抑制·OH与DMP反应,当TBA的浓度增大到DMP的90.21倍时,DMP的降解率由98.7%降为8.8%,已经基本抑制了·OH与DMP的反应;用磷酸盐缓冲溶液调节反应液pH,DMP的降解效果优于用NaOH/H2SO4调节;水中常见低浓度阴阳离子对DMP的降解效果没有影响,高浓度SO24-、NO3-和HPO24-对DMP降解效果的影响相对较小,高浓度Cl-和HCO3-对DMP的降解有抑制作用,且HCO3-的影响大于Cl-,当Cl-和HCO3-的浓度分别为7 097 mg·L-1和6 093 mg·L-1时,反应40 min,DMP降解率分别为50.5%和26.2%.

Kinetics and Influencing Factors of Dimethyl Phthalate Degradation in Aqueous Solution by Ozonation

The rate constants for the reaction of higher concentrations of DMP with ozone and hydroxyl radical (·OH) were determined by competition kinetics method, in which nitrobenzene (NB) was selected as the reference organic compound. The effects of·OH inhibitor tert-butyl alcohol, pH and a variety of ions on the degradation of DMP were discussed. Experimental results showed that the degradation of DMP by ozonation followed pseudo-first-order kinetics. The rate constants of DMP with ozone and·OH were (0.064±0.014) L·(mol·s)^-1 and 3.59×10⁹ L·(mol·s)^-1, respectively. The system pH decreased due to the carboxylic acids intermediates generated by ozonation at initial pH of 6.08 and 9.07, but the system pH was stabilized in strong alkali or acidic solution. A large number of intermediates resulted in the removal rate of COD lagging behind the degradation efficiency of DMP, and part of the intermediates were difficult to be mineralized. The reaction of DMP with·OH was not inhibited by lower concentrations of tert-butyl alcohol. But the reaction was inhibited when the concentration of tert-butyl alcohol was 90.21 times as high as that of DMP, and the degradation efficiency of DMP decreased from 98.7% to 8.8%. The degradation efficiency of DMP was higher with phosphate buffer solution for pH adjustment than NaOH/H₂SO₄ solution. Low concentrations of cations and anions had no effects on the degradation efficiency of DMP. High concentrations of SO₄^2-, NO₃^- and HPO₄^2- had no remarkable effects on ozonation. But high concentrations of Cl^- and HCO₃^- inhibited the degradation and the inhibitory effect of HCO₃^- was stronger than Cl^-. The degradation efficiency of DMP was only 50.5% and 26.2%, respectively, after 40 min under 7097 mg·L^-1 of Cl^- and 6093 mg·L^-1of HCO₃^-.