Research On Degradation Of Coking Desulfurizing Wastewater In Supercritical Oxidation System Via Ir-Ta Catalyst

Coking desulfurization wastewater is a kind of high concentrated industrial wastewater which produced during gas purification process in coke oven, and contains massive mount of organics and inorganic salt. It occupys a large proportion and impacts water treatment system intensively, tranditional treatment technologies are rather difficult and ineffective. As higher pollutant emission standard promulgated, green and efficient processing method needs to developed. Supercritical catalytic oxidation is a novel and effective technology for degradation of high organic concentration industry wastewater. Choose coking desulfurization wastewater from gas desulfurization process of WISCO coking plant and analyse the water quality. Based on the summary of research around the world, the novel supercritical catalytic oxidation of coking desulfurization wastewater was investigated. The main conclusions are as follows.(1) Using titanium plate as support, the specific surface area of support was increased by electrochemical corrosion. The support coated with Ir-Ta active component, and then roasted at high-temperature to produce Ir-Ta/Ti catalysts with specific surface area of 52.63 m2/g. The catalysts were characterized by XRD, BET, TG-MS, SEM and XRF. The optimum preparation conditions were conclued: Oven dried at 120? for 10-15 min and roasted in muffle furnace at 150? for 10 min after each coating, sintered in muffle furnace with 500? for 1 h the last time.(2) Using honeycomb cordierite as support, the specific surface area of the substrate was increased by acid corrosion. The support coated with Ir-Ta active component after surface strengthening and modifing, then roasted at high-temperature to produce Ir-Ta/AlCe-Cord catalysts with specific surface area 37.27 m2/g. The catalysts were characterized by XRD, BET, TG-MS, SEM and XRF. The optimum preparation conditions were conclued: honeycomb cordierite support was corrroded by 20% oxalic acid soution for 1 h, dried at 120? for 2 h and roasted at 500? for 4 h. The surface strengthening and modification process was conducted at 120? for 1 h and roasted at 500? for 4 h. During Ir-Ta active component loading process, the drying temperature was 120? for 10-15 min each time, and then roasted at 500? for 10 min each time, sintered in muffle furnace with 500? for 1 h the last time.(3) The influence of different factors(catalyst, temperature, pressure, reaction time and oxygen ratio) on the removal efficiency of COD and NH3-N in the desulfurization wastewater were investigated,the results showed that the degradation of pollutants(especially NH3-N) was significantly increased by the use of catalysts, the results can be attributed to the degradation of NH3-N on the active component of IrO2. The removal efficiency of COD and NH3-N increased with the improvement of temperature, residence time and oxygen ratio, but the reaction pressure has little effect on the removal rate of COD and NH3-N.(4) The factors of the supercritical water oxidation for coking desulphurizing wastewater treatment were optimized by response surface methodology(RSM). The quadratic regression model of COD and NH3-N removal efficiency was established by central composite design(CCD). The effects of interaction of significance were investigated by RSM. Based on the achievement of emission standard, choose lower reaction temperature and pressure. The optimum parameters within the experimental range were: 440?, 24 MPa, 1 min and oxygen excess ratio of 2. With optimized condition, the removal efficiency of COD and NH3-N via Ir-Ta/Ti catalyst were 99.89% and 98.55%, respectively. The removal efficiency of COD and NH3-N via Ir-Ta/AlCe-Cord catalyst were 99.73% and 98.41%, respectively. The error between actual and predicted values based on model calculations was less then 5%, which indicated the the obtained models were feasible and reliable for the optimization of supercritical catalytic oxidation process for coking desulfurization wastewater treatment.(5) The removal kinetics of COD under different conditions were studied, under the conditions of temperature at 380-460 ?, pressure at 24 MPa and oxygen excess ratio of 2, the reaction activation energy(Ea) and preexponential factors(A) with Ir-Ta/Ti catalyst were 45.18 kJ/mol and 54.05 s-1, respectively. The reaction activation energy(Ea) and preexponential factors(A) with Ir-Ta/AlCe-Cord catalyst were 48.11kJ/mol and 97.51 s-1, respectively. The reaction activation energy(Ea) and preexponential factors(A) with non-catalyst were 100.59 k J/mol and 27.9×104 s-1, respectively. The results showed that the addition of catalysts can significantly reduce the reaction activation energy, decrease reaction temperature and improve the degradation rate of organics.(6) With Materials Studio based on Quantum chemistry and density functional theory, the transformation process of Quinoline and Pyidine in the supercritical catalytic oxidation process was assumed and the possible degradation pathway was obtained. The results are validated by GC-MS detection.