Optimization Of Preparation Process Of Carbonized Sludge And Catalytic Oxidation Of NO At Room Temperature

As one of the main air pollutants that cause great harm to human living environment and physical health,NO_x emission control has become an international research hotspot.For controlling the emission of NO with ambient temperature and high O₂ content,the typical selective catalytic reduction（SCR）technology is not suitable anymore.The catalytic oxidation of NO（CONO）over carbon-based active materials at ambient temperature has gained much attention.Through this technology,NO can be oxidized to NO₂ at ambient temperature and high O₂ content,and recycled in form of nitric acid or nitrate.Due to the great environmental and economic benefits,this technology has a broad application prospect.Experimental research on CONO at ambient temperature over sludge char（SC）prepared from municipal sludge by certain technological means was conducted in the previous stage of research.The results show that the carbonized sludge has a certain carbon content and complex pore structure,which has the ability to become a carbon-based catalyst or catalyst carrier.The SC denitrification efficiency prepared by pyrolysis+KOH activation+HNO₃ pickling+H₂ reduction is the highest.Based on the above research,this paper optimized the preparation process of carbonized sludge,explored the possibility of sludge pyrolysis and KOH activation at the same time,compared the effects of HCl pickling and HNO₃ pickling on the physical and chemical properties of SC surface,and carried out a series of studies on the CONO on SC at room temperature.The main achievements are as follows:（1）The results indicated that both pyrolysis temperature and KOH activation had great influence on catalytic performance of SC.With the increase of temperature from 600℃to 800℃,the NO conversion of pyrolysis sample increased from 12%to 36%.However,the catalytic activity of KOH-activated SC increased and then decreased with the increase of KOH content.The SC prepared under the pyrolysis temperature of 700℃and the DS/KOH mass ratio of 3:1 showed the best catalytic performance with NO conversion of 56%,and the NO conversion was further increased to 76.5%when the SC was reduced by H₂.（2）At the same concentration,compared with HCl pickling,HNO₃ pickling has greater damage to SC pore wall structure and can destroy a large number of aromatic hydrocarbon structures in SC,resulting in the opening of many C=C double bonds and exposing a large number of active carbon atoms.Meanwhile,HNO₃solution can provide free oxygen and nitrogen,which makes it easier to introduce a large number of oxygen-containing and nitrogen-containing functional groups on SC surface.These oxygen-containing functional groups introduced by HNO₃ pickling can block SC pores to a certain extent and occupy the active site,which is not conducive to the CONO.After H₂ reduction treatment,oxygen-containing functional groups are removed,and the NO conversion rate increases accordingly.The nitrogenous functional groups introduced by HNO₃ pickling increased the alkalinity of SC surface,thus increasing the adsorption capacity of SC to acidic NO_x,which was conducive to the CONO.（3）The CONO over SC at room temperature is mainly influenced by the interaction of micropore structure,active site and surface alkalinity,in which the catalytic oxidation of micropore structure and active site of SC surface plays a major role.Microporous catalysis refers to the production of（NO）₂ polymer by the polymerization of gas phase NO in SC micropores,and then oxidized to NO₂ by gas phase O₂ in the micropores.Surface active site catalysis refers to the formation of C-NO by adsorption of gaseous NO on the active site on the surface of SC,which is then oxidized by gaseous O₂ to adsorbed C-NO₂,and then releases a large amount of gaseous NO₂through a series of complex changes.Surface alkalinity refers to that the introduction of nitrogen-containing functional groups increases SC surface alkalinity,which makes SC have a strong affinity for acidic NOx,resulting in the enhanced adsorption capacity of SC for NO,which is conducive to the CONO.（4）The presence of water vapor has a strong inhibition effect on the CONO over SC,and the sample SC-KOH-HNO₃ shows the worst water resistance,and the NO conversion is reduced by51.8%compared with dry gas at the relative humidity of 10%water vapor.The sample SC-KOH-HCl showed the best water resistance,and the NO conversion was reduced by 35.5%under the relative humidity of 10%water vapor compared with dry gas environment.The water resistance of SC is closely related to the number of oxygen-containing functional groups on its surface.The more oxygen-containing functional groups the SC has,the higher its affinity for water molecules is,and the worse its water resistance is.（5）The sample prepared by KOH pyrolysis/activation+HNO₃ pickling+H₂ reduction has the optimum denitrification performance.When the temperature is 30℃,20%O₂,and NO inlet concentration is 450ppm,the NO conversion rate is as high as 75.6%.Meanwhile,the NO conversion decreases with the increase of the relative humidity of water vapor,and the sample completely fails when the relative humidity is 60%.In addition,the NO conversion rate decreased with the increase of temperature,increased with the increase of NO inlet concentration,and increased with the increase of O₂ concentration.