| Benzoic acid is an important organic chemical raw material, with a wide range of applications in pharmaceutical, food, chemical and other aspects. However, Benzoic acid waste water, containing benzoic acid, benzyl alcohol, benzene formaldehyde, toluene, and other aromatic organic compounds, produced in the production process. High concentrations of these organics, with a strong toxic and acidic corrosive, will cause great pollution to environment if discharged directly. Based on the characteristics of the wastewater, extraction-Fenton treatment process was proposed. Firstly, the production of raw materials toluene was used as the extraction solvent extraction tertiary wastewater to remove organic pollutants in waste water, the organic phase was into reused the reactor, and the wastewater treated by extraction was used Fenton advanced oxidation technology to make the water compliance. The characters of degradation of Benzoic acid were investigated by Fenton reagent.Firstly, the degradation of benzoic acid was studied in the homogeneous Fenton system. The effects of pH value, dosage of H2O2 and Fe2+, and initial concentration of benzoic acid on removal efficiency were investigated. Results demonstrated that at optimum pH=3.0 and room temperature, the removal efficiency of benzoic acid and TOC reached 100.0% and 41.9% respectively after 60 mins when the best economical dosage of H2O2 was the theoretical quantity of 12.3mmol/L and optimum molar ratio H2O2:Fe2+ was 30:1. The maximum removal efficiency of TOC arrived at 45.4% when the initial concentration of benzoic acid was 200mg/L. Above this concentration, it was suggested to take advantage of sequential H2O2 dosing to obtain high removal efficiency of benzoic acid.Fe2+ was fixed in a carrier in order to overcome the shortcomings of high operating costs, a narrow pH range and difficult recycle of Fe2+ in homogeneous Fenton system. Fe-AC catalysts using coconut shell granular activated carbon as carriers were prepared by impregnation method and the factors of catalyst preparation were analyzed by orthogonal, results demonstrated that the particle size of catalyst activity is the most important factor, followed by the calcination temperature and calcination time. Taking the characterizations of TG-DSC, BET, XRD and SEM into account, conditions for catalyst preparation were decided, AC particle size of 60 to 100 mesh, calcination temperature of 300℃ and calcination time of 4 h.Then the degradation of benzoic acid was studied in the heterogeneous Fenton system. Results indicated that at optimum pH=3.0, the removal efficiency of benzoic TOC reached 76.76% respectively after the adsorption of 210mins and the reaction of 90mins when the best economical dosage of H2O2 was half of the theoretical quantity of 6.15mmol/L and catalyst dosage was 1 g/L.Finally, HPLC and UV-visible spectrophotometer were used to study the degradation process. The study found that intermediates were acidic, which were generated in the degradation process of Fenton. Referring some literature, a possible degradation of benzoic course was suggested, benzoic was firstly attacked by·OH, p-hydroxybenzoic acid and m-hydroxybenzoic acid were generated, then low molecular weight acid generator, CO2 and H2O were produced by the further oxidation of hexadiene-hydroxybenzoic acid. |
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