Research And Application Of Microwave-Enhanced ClO₂ Catalytic Oxidation Process

Aim to problems of nonbiodegradable wastewater treatment, micirowave-enhanced advanced oxidation process (MAOP) is founded. Compared with other advanced oxidation processes, microwave enhanced oxidation process has many advantages such as the oxidation speed and the mineralization efficiency are higher, the set-up is simpler, and the operation conditions are more convenient. So it promises to have a wide application in the wastewater treatment. The preparing of heterogeneous catalysts with high activity and stability is one of key techniques in MAOP. In this paper, CuO/γ-Al₂O₃ catalyst and La₂O₃-CuO/γ-Al₂O₃ catalyst were prepared. The catalytic activity of La₂O₃-CuO/γ-Al₂O₃ catalyst was investigated in microwave enhanced ClO₂ catatlytic oxidation process by using phenol and remazol golden yellow dye as as model pollutants.The kinetic and degradation mechanism of remazol golden yellow dye and phenol in MAOP were studied. The formation of hydroxide radical group (·OH) in MAOP was also investigated. The reason of deactivated catalyst La₂O₃-CuO/γ-Al₂O₃ was analyzed and several different regeneration methods were compared. Firstly, CuO/γ-Al₂O₃ was prepared by impregnation-deposition method. The catalytic activity and stability were investigated in MAOP. Because the catalytic activity of CuO/γ-Al₂O₃ decreased fast in the successive runs, La₂O₃-CuO/γ-Al₂O₃ catalyst was prepared by selecting La as doping agent to improve the catalytic activity of CuO/γ-Al₂O₃. According to the structure analysis, Cu exists as CuO and Cu2O in La₂O₃-CuO/γ-Al₂O₃ with the loading amount of 6.748%; La exists as La₂O₃ in La₂O₃-CuO/γ-Al₂O₃ with the loading amount of 0.257%. It proved the surface modification of the carrierγ-Al₂O₃ by the addition of La₂O₃ could reinforce the thermal ability of the support within a certain extent. La₂O₃ could promote the structure of supports and intensify the interaction between active component and support, so that the loading of Cu in the catalyst was improved. Better dispersion and smaller size of CuO crystals could be obtained by La₂O₃, which made the number of active site increased.The process of microwave enhanced chlorine dioxide oxidation treating phenol or remazol golden yellow dye wastewater was investigated by adding La₂O₃-CuO/γ-Al₂O₃ as a catalyst. 100mL synthetic wastewater containing 100 mg/L phenol was treated in MAOP and 91.66% of phenol and 50.35% of total organic carbon (TOC) could be removed under the optimum process conditions: ClO₂ concentration 80 mg/L, microwave power 50 W, contact time 5 min, catalyst dosage 50 g/L, pH 9. Under an optimal condition (ClO₂ concentration 80 mg/L, microwave power 400 W, contact time 1.5 min, catalyst dosage 70 g/L, pH 7), remazol golden yellow dye removal percentage approached 94.03%, corresponding to 67.92% of TOC removal.The reaction kinetics in microwave enhanced ClO₂ catatlytic oxidation process, microwave enhanced ClO₂ oxidation process, traditional waterbath ClO₂ catatlytic oxidation process and traditional waterbath ClO₂ oxidation process were studied. Results suggested that the process between phenol and ClO₂ oxidation reaction accord to first-order reaction for phenol and first-order for chlorine dioxide, the total reaction order was 2. Comparesion of reaction constant in different treatments, it could be concluded in microwave enhanced ClO₂ catatlytic oxidation process microwave irradiation and catalyst work together to improve the reaction rate.The fluorescence technology was applied to detect the regulation of hydroxyl radicals (·OH) created in microwave enhanced ClO₂ catatlytic oxidation process. The results showed that there was no·OH created in ClO₂ oxidation process under room temperature; there were a few hydroxyl radicals created in ClO₂ catatlytic oxidation process under room temperature and microwave enhanced ClO₂ oxidation process; a lot of hydroxyl radicals were created in microwave enhanced ClO₂ catatlytic oxidation process. The mechanisms of organic pollutant degraded in microwave enhanced ClO₂ catatlytic oxidation process could be conluded: organic pollutant were absorbed on the surface of the catalyst, at the same time; microwave was focused on the surface of the catalyst which can absorb microwave. And microwave was transferred heat energy. So the catalyst was heated to very high temperature, which is called hot spot. Then organic pollutant were degraded by·OH which produced by microwave induced ClO₂ under high temperature of the hot spot formed on the surfaced of catalyst in the microwave field.The deactivation reason and regeneration methods of prepared catalysts were also studied in this dissertation. The deactivation was caused by the degradation products of pllutions contained C elements remained on the surface of catalyst and covered the active sites. Microwave radiation regeneration technology was an effective regeneration method; the regenerated catalyst could restore the 91.67% activity of the fresh catalyst with the following working conditions: power of microwave, 500W; exposure time, 30 min; SiC catalyst ratio, 2:1. Studies showed the catalytic activity of regenerated catalyst was very close to initial activity.The improvement of traditional chlorine dioxide oxidation has been realized by combining microwave technology and modifiedγ-Al₂O₃ catalytic oxidation. Compared with traditional ClO₂ oxidation, microwave-assisted ClO₂ catalytic oxidation process can degrade contaminants in short reaction time and with low oxidant dosage, extensive pH range. As a developing process, the microwave enhanced ClO₂ catalytic oxidation process would provide a novel treatment method for the refractory wastewater and would have a broad prospect.