Selective Catalytic Oxidation Of NH₃at Low Temperature On Low Concentration Ammonia Containing Waste Gas

NH3is widely applied to industrial production as a kind of chemical raw material. At the same time, the environmental pollution caused by the emissions contained NH3has been getting more and more attention. Refrigeration industry, fertilizer and other emissions of large volume, low concentration NH3gas need purification. And hydrogen cyanide mixed waste gas purification technology and equipment of yellow phosphorus tail gas ("863Program" key projects) in low concentration NH3, HCN catalytic hydrolysis product in the same need to get purification treatment. NH3selective catalytic oxidation (NH3-SCO) catalyst extremely hard won more than90%of NH3conversion and higher than90%N2selectivity simultaneously at150℃. So the research from two aspects, respectively, to study low temperature selective catalyst for the N2and water and NH3two-step method two steps low temperature catalytic oxidation system, hoping to waste gas of low concentration NH3under the condition of less than150℃into N2and H2O.This article carries out the research work of the system aims at the core of the catalyst in low temperature NH3-SCO-carrier and active component. The experimental research on catalysts for selective catalytic oxidation of NH3and two-step method, catalyst carrier and active component and so on have been studied in the experiment of selection, and considering the adding ratio of active components, additives and catalyst preparation conditions, reaction conditions and other factors affect the performance of catalysts. Selecting out the best selective catalytic oxidation of ammonia and apply to step method research of catalysts was based on the analysis of the influence factors of the catalytic performance, optimization of the catalyst and the activity of catalyst characterization analysis and so on.NH3-SCO at low temperature results show that catalysts using C-TiO2(carbon-titanium dioxide) as carrier and using Cu as the active compound has a much higher activity than usings Al2O3, CNTs and TiO2as carriers. This is caused by the better dispersion and the existence of carbon layer, catalyst containing more kinds of active component, which is advantageous to the O2adsorption and activation. Based on the experimental, Cu-Co/C-TiO2can be a promising catalyst for the NH3-SCO. After optimization, Cu-Co/C-TiO2(roasting in the muffle furnace, Cu/Co=10%:10%(mass percent)) in the O2content in the reaction system under the condition of1%has the best catalytic oxidation performance. And the removal rate of NH3, NO yield and NO2yield are75%,19%and1%at175℃, respectively.Selective catalytic oxidation of NH3experimental results show that the removal rate of NH3is still difficult to achieve ideal removal level, therefore, on the basis of the previous research practice the two footwork experiment. First, reaction system used NH3-SCO catalyst to make part of NH3selective catalytic oxidation to NO and NO2at low temperature, and to make the ratio of the second catalyst of NH3and NOx is about1:1. Then the reaction system used the ideal selective catalytic reduction (NO-SCR) catalyst removal of NOx and NH3to generate N2and H2O, and achieve the purpose of purifying NH3. In order to obtain ideal NH3-SCO catalyst, the research changed the ratio of active components, the adding of rare earth elements. The NH3-SCO catalyst in the reaction gas can at150℃of NH3and the ratio of NOx is about1:1. For the previous studies and relevant literatures reading, we chose MnOx as the second catalyst for two footwork experiment. Two-step method research results show that the NH3purification at low temperature is feasible. It’s found that the catalyst prepared by ultrasonic impregnation method, under muffle furnace roasting,1%Ce-1%La-10%Cu-10%Co/C-TiO2meet two steps reaction system requirement.1%Ce-1%La-10%Cu-10%Co/C-TiO2+MnOx reaction system can obtained the removal rate of NH3higher than90%and NO yield less than1%at150℃. And a second step catalyst stability test results showed that:when the reaction proceeds to20h after removal rate of NH3from90%to about80%gradually, the yield of NO increased slightly, but the catalysts performance was till stable after33h.