Mechanism Research And Application Process Of Catalytic Ozonation For Degradation Of4-chlorophenol

According to the transformation requirements concerning coal chemical industry put forward in China’s12th Five-Year Plan, the focus of coal chemical wastewater treatment has been changed from the previous meeting emission standards to advanced treatment and recycled utilization. Currently, coal chemical industry generally adopts the biological treatment of A/A/O. The effluent still contains a lot of refractory organic pollutants, such as phenols, nitrogen heterocyclic materials, which are difficult to be reused for water recycling system. As one of advanced oxidation processes (AOPs), heterogeneous catalytic ozonation under moderate experimental conditions is believed to exert great impact on treating wastewater that contains refractory organic pollutants.In order to solve the problems of inefficient utilization of ozone and unsatisfactory treatment effect as well as other issues in traditional ozone oxidation technology, the research aims to establish a three-phase fluidized bed for the system of heterogeneous catalytic ozonation which has a good industrial application prospect, develops supported catalysts, investigates the performance factors and conditions of the reaction system on organics degradation, discusses and analyses the mechanism of heterogeneous catalytic ozonation and degradation, and lays the foundation for heterogeneous catalytic ozonation system to apply to the advanced treatment of coal chemical industry.In the process of establishing heterogeneous catalytic ozonation system, the research compares the catalytic activity of different active components and screens out manganese oxide catalyst which has higher degradation performance. By virtue of intensive study on the relationship between the catalytic performance and the type of carriers, load precursors, dipping concentration, calcinations temperature and time and other catalyst preparation conditions, it is indicated that the preparation conditions have the great influence on the morphololgy of the catalyst surface, surface structure, elements, surface morphology structure and the number of surface hydroxyl. MnOx/γ-A12O3/TiO2catalyst (MAT), which is prepared under the circumstance of manganese nitrate as precursors and γ-A12O3/TiO2as the carrier, has a good catalytic degradation performance. The surface of MAT, in the form of MnO2, Mn2O3crystal structure, owns abundant hydroxyl groups and higher zero potential point (pHzpc).Three-phase fluidized bed is established for the degradation of4-chlorophenol (4-CP) by heterogeneous catalytic ozonation in this research. O3/MAT system has good catalytic degradation performance, efficient effect of organic removal and high degree of mineralization. With the increase of catalyst mass, ozone concentration, the initial pH value and water temperature, the removal efficiency of4-CP gradually is improved in O3/MAT system. With the increase of4-CP concentration, the performance of degradation is decreased. In addition, the common cations Na+, K+, Mn2+, Zn2+, Cu2+, Fe2+, Fe3+, Al3+and inorganic anions Cl-, CO32-, HCO3-, SO42-, H2PO4-, HPO42-, PO43-in the water have enforcing or inhibiting effect on O3/MAT system.The research on the degradation mechanism of heterogeneous catalytic ozonation demonstrates that the abundant hydroxyl groups on the catalyst surface and higher pHzpc have a positive effect on ozone decomposition in the system. The radical inhibitor tert-butanol (TBA) significantly inhabites4-CP degradation, indicating that4-CP degradation in O3/MAT system complys to·OH oxidation mechanism. This paper determines the production of·OH, H2O2,·O2-in the system and studies the relationship between the production and the surface hydroxyl phosphate inhibitors, and the result shows that the generation of·OH, H2O2,·O2-are effectively promoted by adding MAT in the water. There were abundant hydroxyl groups on the surface of MAT catalyst, which are active in ozone decomposition and leading to generate more·OH.·OH is a key factor in generating H2O2, while·O2-determines the generation of·OH.4-CP degradation in O3/MAT system undergos the hydroxylation of aromatic ring, the transformation of aromatics to aliphatics by destruction of ring structures and the oxidation of the aliphatic chains. Organic carboxylic acid and aromatic compounds are major intermediate products of the oxidation, which include p-benzoquinone, hydroquinone,4-chlorocatechol,4-chlororesorcinol,(E,E)-2,4-hexadienal, malic acid, malonic acid, oxalic acid, acetic acid, formic acid, etc.In order to improve the utilization of ozone and the degradation efficiency as well as aiming at the advanced treatment of coal chemical industry, it is established a heterogeneous catalytic ozonation system by the form of an exhaust gas cascade recirculation. TOC, COD, BOD, UV254, chroma of the wastewater are different in different periods. The continuous flow system of heterogeneous catalytic ozonation shows favorable treatment and has a certain resistance to organic load capability. Heterogeneous catalytic ozonation system has an effective removal of phenols, ketones, environmental hormone substances, heterocyclic, and other nitrogen-containing organic compounds in the effluent of coal chemical industry.Heterogeneous catalytic ozonation system is established with higher utilization of ozone, which has an effective removal and mineralization for refractory organic pollutants. The system has certain guiding significance for the employing of ozone oxidation technology in actual treatment of wastewater and broad application prospects.