【摘要】：氮氧化物(NO_x)是一種主要的大氣污染物,它會引起酸雨、光化學煙霧、臭氧層破壞等諸多環(huán)境問題,近年來日益受到人們的關(guān)注。目前,針對NO_x的脫除,應(yīng)用最廣泛且技術(shù)最成熟的方法是選擇性催化還原法(SCR),其多采用過渡金屬或貴金屬催化劑。而鐵礦石尾礦作為鋼鐵冶金行業(yè)的一種主要固體廢棄物,其中仍含有大量未被利用的金屬元素,如鐵等,若將其制備成催化劑催化還原NO_x,不但可以實現(xiàn)冶金固廢的綜合利用,對于NO_x的減排也具有重要意義。以馬鋼南山礦鐵礦石尾礦作為主要原料制備催化劑,NH_3為還原劑,進行催化還原NO的實驗。建立了催化還原NO實驗的電加熱固定床反應(yīng)裝置,考察了催化劑粒徑、反應(yīng)溫度、焙燒溫度、NO初始濃度、O_2含量、空速、鐵含量、添加MnO_2等因素對NO催化還原效率的影響。同時,對催化劑中的鐵礦石尾礦進行LDPSA、XRF、BET、XRD、SEM、TGA等表征分析,并對催化還原NO進行失活測試及動力學分析。實驗結(jié)果表明,鐵礦石尾礦制備的催化劑對NO具有良好的催化還原性能。在氣體流量為600m L/min,NO初始濃度為600ppm,NH3/NO=1,無O_2存在條件下,溫度低于300℃時催化性能不是很理想,但隨著溫度升高,催化效率迅速升高,500℃時催化效率達到54.8%,550℃時催化效率達到85.4%,600℃時催化效率達到97.5%。催化劑粒徑對催化還原效率有較大影響,平均粒徑10μm催化劑催化效率比平均粒徑300μm催化劑約高20%左右。實驗發(fā)現(xiàn)對催化劑進行焙燒并不能顯著提高其比表面積,450℃以上焙燒處理反而會使催化劑中的Fe_2O_3的衍射峰逐漸變得平緩直至消失,減小對NO的催化還原效率。NO的初始濃度和空速對NO催化效率均有一定的影響,隨著NO初始濃度的升高,催化效率逐漸降低,但這種影響會隨著反應(yīng)溫度的升高而逐漸減小。當氣體總流量從600mL/min增加到800mL/min時,其催化還原效率下降約5%。O_2濃度對催化還原效率影響較大,溫度較低時(350℃),O_2的加入促進了催化還原效率,無O_2時催化效率為3%,通入O_2時催化效率能達到10%以上,但當O_2濃度超過4%時對催化效率幾乎無影響;溫度較高時(500℃),O_2的加入會抑制反應(yīng)的進行,無O_2時催化效率能達到55%左右,通入O_2時催化效率降低到40%以下。實驗發(fā)現(xiàn)鐵含量越高,催化還原效率越高,但鐵含量越高,催化劑在石英砂表面的分散性越差,高溫時容易粘結(jié),影響了對NO的催化效果。鐵礦石尾礦與MnO_2摻混制備的催化劑能有效提高對NO的催化還原效率,在相同溫度時催化效率較高。對鐵礦石尾礦制備的催化劑進行了失活測試,2.0g尾礦在600℃時初始效率達到98%,反應(yīng)3h后仍達到95%,反應(yīng)8h后仍能達到60%以上,反應(yīng)13.5h后催化效率仍能保持在50%以上。對鐵礦石尾礦制備的催化劑催化還原NO的動力學進行了分析,結(jié)果表明,進口NO濃度和O_2濃度對應(yīng)的反應(yīng)級數(shù)分別為0.876和0.248,而NH3的反應(yīng)級數(shù)為零,該催化反應(yīng)的反應(yīng)活化能為87.76kJ/mol。
[Abstract]:Nitrogen oxide (NO_x) is a major atmospheric pollutant, which can cause many environmental problems, such as acid rain, photochemical smog, ozone layer destruction and so on, which has attracted more and more attention in recent years. At present, for the removal of NO_x, the most widely used and the most mature method is selective catalytic reduction method (SCR),). Transition metal or precious metal catalysts are mostly used in (SCR),. Iron ore tailings, as a major solid waste in iron and steel metallurgy industry, still contain a large number of unused metal elements, such as iron, if they are prepared into catalysts for catalytic reduction of NO_x, Not only the comprehensive utilization of metallurgical solid waste can be realized, but also the emission reduction of NO_x is of great significance. The experiment of catalytic reduction of NO was carried out using iron ore tailings of Nanshan Mine of Masteel as main raw material and NH_3 as reducing agent. An electrothermal fixed-bed reactor for catalytic reduction of NO was established. The particle size, reaction temperature, calcination temperature, initial concentration of NO, O _ 2 content, space velocity and iron content were investigated. The effect of adding MnO_2 and other factors on the catalytic reduction efficiency of NO. At the same time, the iron ore tailings in the catalyst were characterized by LDPSA,XRF,BET,XRD,SEM,TGA, and the deactivation test and kinetic analysis of the catalytic reduction NO were carried out. The experimental results show that the catalyst prepared by iron ore tailings has good catalytic reduction performance for NO. When the initial concentration of no is 600 ppm / min, the catalytic performance is not ideal when the temperature is lower than 300 鈩，

本文編號：2321656