Catalytic Degradation and Mineralization of Phenol by Immobilized Active Iron Oxides and Their Applications

• Main Authors: Chun-Ping Huang, 黃君平
• Other Authors: Yao-Hui Huang
• Format: Others
• Language: en_US
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/80022328502103993876

博士 === 國立成功大學 === 化學工程學系碩博士班 === 97 === This study is aimed to better understand the interactions among organic compounds (azo-dye and phenol), oxidants (H2O2 and O2) and catalysts (iron oxides and iron ions). Firstly, the degradation of phenol by hydrogen peroxide in the presence of four kinds of iron oxides is compared to find the most active catalyst. Secondly, the interactions (dissolution of iron) and reactions (redox) between the oxidative intermediates of phenol (such as hydroquinones and oxalic acid) and iron oxide are investigated. Also, the operation parameters (such as pH, temperature, system loading and concentration of oxidants), which may affect the degradation efficiency of organic compounds, are also studied. Furthermore, the degradation and the mineralization performance were enhanced by a photo-reactor. Also, the recycle life of iron oxide catalyst was increased by the photo-reactor. Finally, kinetics and reasonable reaction mechanism of the system are proposed. Comparison study of the reactivity of iron oxides reveals that the immobilized iron oxides, namely SiG1 and SiG2, were efficient for the degradation of phenol in the presence of hydrogen peroxide (100% of phenol was degraded). SiG1 and SiG2 exhibited high reactivity for the reductive dissolution process in the presence of hydroquinones (catechol and 1,4-hydroquinone); a critical condition, in which the reductive dissolution was very inefficient, was found at solution pH 5. Furthermore, the redox reactions between iron species and hydroquinones implied that oxidants for the degradation of phenol were not only H2O2, hydroxyl radical, but also Fe(III) species. Thermal effect (temperature) is an important parameter for the decomposition of H2O2 and for the degradation of azo-dye reactive black B (RBB), and a two-stage rate law was proposed to describe the degradation kinetics of RBB. Moreover, the mineralization of phenol is quite inefficient in dark system (< 40% TOC removal efficiency) because the mineralization was retarded by oxalic acid. Also, iron species leaching from the surface of the immobilized iron oxides due to the accumulation of oxalic acid in the absence of irradiation. In order to improve the mineralization efficiency of phenol, a water-flow type photo-fluidized bed (photo-FBR) was designed to mineralize phenol and to minimize iron leaching. Successfully, the mineralization of phenol (about 98% TOC removal efficiency) and minimization of iron leaching (< 5 mg/L) were achieved in the photo-FBR. An interesting phenomenon was observed that the variation of solution pH also reflected the degree of mineralization. The result also means that the mineralization level of phenol in this system can be conveniently derived by the observation of solution pH variation. In addition to acidic and basic reagents, there is a savings of more than 40% of the H2O2 for the mineralization of phenol in photo-FBR. This also indicates that the cost of applied acid, base and H2O2 in industrial wastewater treatment can be dramatically reduced. The photolysis of SiG2-oxalate produces ferrous ions and carbon dioxide radical anions. The decomposition of oxalic acid consumes iron(III) species and dissolved oxygen. The application of UV/SiG-oxalate process is able to degrade phenol and to increase degradation efficiency at solution pH 5. The catalyses mechanisms of SiG1 and SiG2 for the degradation of phenol in the presence/absence light were proposed. The kinetics of iron dissolution by oxalic acid, iron reductive dissolution by catechol, H2O2 decomposition and RBB degradation by SiG2/H2O2 were investigated, also the kinetics parameters were obtained.