Ozonation and Homogeneous Catalytic Ozonation of Acetic Acid
|School||Zhejiang University of Technology|
|Keywords||homogeneous catalytic ozonation Ti(Ⅳ) hydrogen peroxide acetic acid kinetics degradation efficiency Fe(Ⅱ) catalytic mechanism|
The physical chemistry properties of ozone and its application in water treatment are reviewed, and the emphasis of discussion is put on homogeneous catalytic ozonation technology developing recently. On the basis of the present research situation of ozonation in water treatment and its existing shortcomings, the research target and main task of this work are proposed. The contents of this paper mainly include three parts: degradation of acetic acid by Ti（Ⅳ）-catalyzed H2O2/O3; characteristics of kinetics of acetic acid degradation by Ti（Ⅳ）/H2O2/O3; different metallic ions catalytic ozonation of acetic acid. The above results are of significance for the practical application of Ti（Ⅳ）/ H2O2/O3 in water or wastewater treatment.In chapterⅣ, the effect of Ti（Ⅳ） on the efficiency of acetic acid degradation by H2O2/O3 was investigated under acidic conditions. The process parameters were optimized, and the degradation mechanism was also analyzed. The results indicated that addition of Ti（Ⅳ） could promote greatly the oxidation of acetic acid by H2O2/O3 at pH 2.8, and that the removal rate of acetic acid reached 52.0% in 30 min for Ti（Ⅳ）/H2O2/O3 and only 5.6% for H2O2/O3. When Ti（Ⅳ） and H2O2 concentrations were 6 mg·L-1 and 120 mg·L-1, Ti（Ⅳ）/H2O2/O3 had the highest efficiency（52.0%）. The effect of pH on the efficiency of Ti（Ⅳ） /H2O2/O3 was not significant, which might attribute to the existence of specific initiator for various pH values. In view of the shortcomings and characteristics of H2O2/O3, Ti（Ⅳ）/H2O2/O3 system that can be a complement to H2O2/O3 process, is suitable for application in acid solution. The test by using tert-butyl alcohol showed that acetic acid degradation by Ti（Ⅳ）/H2O2/O3 followed a hydroxyl radical-type mechanism. The values of H2O2/O3 and Ti（Ⅳ）/H2O2/O3 calculated by the relative method were 5.548×10-9 and 2.128×10-7, respectively, indicating that Ti（Ⅳ）/H2O2/O3 could generate more hydroxyl radicals. RctIn chapterⅤ, the kinetic of acetic acid degradation by Ti（Ⅳ）/H2O2/O3 was investigated, and the influences of different parameters on the removal rate of catalytic ozonation were discussed. The results showed that, the initial concentration of acetic acid affected degradation process, and the rate constants of degradation were found to decrease with increasing of the initial concentration of acetic acid. Under different pH values, the degradation of acetic acid followed a pseudo-first-order kinetic model for both H2O2/O3 and Ti（Ⅳ）/H2O2/O3, and the apparent reaction rate constants both increased with the increase of pH value. The comparison of kinetic rate constants obtained from these two systems showed that Ti（Ⅳ）/H2O2/O3 system was more suitable for application in acid solution. The increase of Ti（Ⅳ） and H2O2 concentrations accelerated the removal rate of acetic acid within a suitable range. After optimization, the mass concentration ratio of HAc: Ti（Ⅳ） was 50:3, the dosage of H2O2: Ti（Ⅳ） should be controlled less than 40.In chapterⅥ, a comparative study on Ti（Ⅳ）, Fe（Ⅱ） catalytic ozonation of acetic acid was evaluated. And their catalytic mechanisms were also analyzed. The results showed that, at pH 2.8, both M（metallic ions）/O3 and M/H2O2 systems had no remarkable effect on the degradation of acetic acid. But in M/H2O2/O3 systems, Fe（Ⅱ）/H2O2/O3 system showed limited degradation efficiency of acetic acid, and Ti（Ⅳ）/H2O2/O3 system had high efficiency. The degradation rate of acetic acid by intermittent adding of H2O2 is better than that by an pre-adding. At pH 5, M/O3 system also had no significant effect on the degradation of acetic acid. Compared with H2O2/O3 system, Fe（Ⅱ）/H2O2/O3 system had no higher removal efficiency of acetic acid , but Ti（Ⅳ）/H2O2/O3 system enhance the removal rate of acetic acid by 29%. These results indicated that, the Ti（Ⅳ）/H2O2/O3 system has high application potential in water treatment, likely becoming an new technology which can removal refractory organic pollutants efficiently and economically.