Ozonation And Homogeneous Catalytic Ozonation Of Acetic Acid

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.