Study On Wet Oxidation Of Phenol By Hollow Spheres Supported Catalysts

The organic pollutants in wastewaters can cause many severe environmental problems, which also waste the limited natural water resources. So it is a very important mission to remove the organic pollutants and reuse water. Wet oxidation developed in 1950's provides a new method for wastewater treatment. Compare with traditional treatments such as incineration, biological ,wet oxidation is more appropriate for disposing high concentration toxic wastewater. Many developed countries have regarded the wet oxidation as high-technology for the secondary treatment of sewage, and a number of wet air oxidation industrial wastewater treatment plants have emerged. With development of catalysis science, using catalysts in the process of wet air oxidation resulted in the technology of Catalytic Wet Oxidation (CWO), which appears to be a very promising new technology for high conversion of organic pollutants.The catalysts in wet air oxidation can be divided into noble metal catalysts and non-noble metal catalysts according to the active component. Catalytic wet oxidation can also be divided into Wet Air Oxidation (CWAO) and Advanced Oxidation Process (AOPs) according to oxidants. Generally, the oxidant of CWAO is oxygen or air, whereas the oxidant of AOPs is hydrogen peroxide, ozone, etc. In this thesis, some novel non-noble metal catalysts were prepared and used to catalytically oxide the phenol solution by CWAO and AOPs technology. The main contents of this paper include:Using ethyl silicate as silicon resource, nitric acid as hydrolyzing catalyst, silicon dioxide hollow microspheres were successfully prepared by emulsion/sol-gel technology. With further impregnation and calcination, the non-noble mental catalysts were finally prepared. The structure of the catalysts was studied by SEM, XRD, TPR and nitrogen adsorption-desorption etc. With CuO/SiO₂ and CuO-CeO₂/SiO₂ as catalysts, high concentration of phenol solution (COD = 3000mg / L) was wet air oxidized in autoclave. The effect of experiment condition such as temperature, oxygen partial pressure and pH value were studied by the single factor and orthogonal experiments. The results show that CuO/SiO₂ has better catalysis effect. Under 170℃, oxygen partial pressure 1.5MPa and the amount of the catalyst 0.2g, COD removal rate can attain 93.2%. And temperature is the most important factor for CWAO.The further oxidation process using hydrogen peroxide as oxidant was carried out at normal pressure. The effect of different temperature, reaction time and amount of hydrogen peroxide was studied by using non-noble CuO/SiO₂, MnO₂/SiO₂ and CuO-CeO₂/SiO₂ as catalyst. Experiment results prove that CuO/SiO₂ catalyst has good catalytic effect in the presence of hydrogen peroxide. The influence of temperature on the catalytic effects is obvious: as temperature increases, COD removal rate also increases. The intermediate sampling is more acidic than that of catalytic wet air oxidation. That is to say, decarboxylation of intermediates is relatively easy in CWO process, while carboxylic acids accumulate in CWPO process.