Study On Catalytic Supercritical Water Oxidation Of P-Nitrophenol Wastewater

p-Nitrophenol is a serious toxic organic compound, which can cause serious pollution in water, and it has been included in the china environment priority-controlling pollutant blacklist. It is difficult to completely decompose p-nitrophenol by traditional wastewater treatments such as biodegradation, physical method or chemical oxidation method. Supercritical water oxidation (SCWO) is the promising technology for the treatment of organic-contained wastewater. In this paper, the catalytic supercritical water oxidation of p-nitrophenol is investigated.The preparation of heterogeneous catalysts was studied systematically, the preparation methods and conditions were determined. The optimum preparation conditions of supported Mn2O3/Ti-Al composite oxide catalyst were as following: Mn2O3/Ti-Al composite oxide was as carrier, on which the aqueous solution manganese nitrate was impregnated by the incipient wetness impregnation method, loading of Mn2O3 15wt.%, impregnated time 18h, dried at 120℃for 4h, calcined at 600℃for 4h. The catalysts were characterized by the techniques of XRD, BET and activity evaluation.According to the properly designed experiments, the possible catalytic mechanism of manganese oxide for supercritical water oxidation was researched. It was proposed that the synergism of the adsorbed oxygen species and the lattice oxygen species could become the catalytic oxidation mechanism during reaction, which could interpret the phase transformation of catalysts.In this thesis, the supported Mn2O3/Ti-Al oxide composite catalyst was employed for the p-nitrophenol oxidation in SCWO, and the effects of temperature, pressure, oxygen excess degree and residence time on the decomposition of p-nitrophenol were investigated. The removal rate of p-nitrophenol was increased with the raising of the four factors, the influence of temperature was comparatively obvious, the oxygen excess degree and residence time had appropriate values. The optimized experiment conditions for SCWO of p-nitrophenol were 420℃, 26MPa, the oxygen excess degree 20 and the residence time more than 6s. Under these conditions, the concentration of p-nitrophenol was reached to 1.7mg/L, and TOC value was 8.4mg/L, both of which met the demands of first grade of national discharge standard (GB8978-1996).The catalytic decomposition mechanism was investigated by means of GC-MS. The main intermediate products detected were: p-benzoquinone, phenol, o-nitrophenol, hydroquinone, 2-phenoxyphenol, 4-phenoxyphenol, dibenzofuran and 2-nitrodibenzofuran, etc. Meanwhile, the possible oxidative degradation routes of p-nitrophenol were proposed.