Density Functional Theory Study On Trace Hg~0 Removal Of Flue Gas By Halogen Modified Rice Husk Char

Mercury pollution from coal-fired power stations is highly toxic and persistent in the environment,threatening human life and health,and has attracted worldwide attention.At present,the commonly used treatment method is to spray activated carbon into the flue gas as a trace amount of Hg⁰ adsorbent.It is important to look for efficient,inexpensive,and renewable adsorbents instead of high-cost activated carbon.In this paper,the waste by-product rice husk char from the chaff gasification power plant is used as a mercury removal sorbent,and the efficiency of removing Hg⁰ can be improved by practical and feasible modification methods,which can save energy,reduce cost and reduce environmental pollution.In order to deeply investigate the influencing factors of trace Hg⁰ in flue gas from modified rice husk char,based on the fixed bed experimental device,the performance of trace Hg⁰ adsorption of rice husk char and activated carbon before and after modification was compared and studied.The effect of different halogens and density of halogen on the adsorption of trace Hg⁰ of modified rice husk char.The physicochemical properties of rice husk char coke before and after modification were determined by specific surface area and pore structure analysis?BET?and Fourier transform infrared spectroscopy?FTIR?,such as the characteristics of rice husk char pyrostructure,oxygen-containing functional groups,halogen atoms.The conclusions of the load form and the possible oxidation products of Hg⁰ are used to analyze the reasons for the difference in the performance of mercury removal.The results show that the mercury removal performance of rice husk char is much lower than that of activated carbon.The results confirm the advantages of activated carbon adsorbent in pore structure.At this time,physical adsorption is dominant;while after loading halogen,rice husk char and activated carbon The mercury removal performance is greatly improved,which means that the carbon-based adsorbent after halogen loading is mainly chemical adsorption;the mercury removal performance of three different halogen-modified rice husk char is arranged from small to large:chlorine modified rice husk char?RHCCl?-3)<bromo modified rice husk char?RHCBr-3?<iodine modified rice husk char?RHCI-3?;and with the increase of halogen concentration,the better the mercury removal performance of modified rice husk char adsorbent.In order to further verify the experimental conclusions,the Gaussian software was used to establish the relevant configuration for simulation calculation.From the microscopic point of view,the effects of unsaturated active sites,oxygen-containing functional groups,different halogens and halogen concentrations were studied to systematically reveal the modification.The microscopic mechanism of rice husk char and Hg⁰.Firstly,the effect of unsaturated active sites on Hg⁰ adsorption by rice husk char configuration was studied.In the quantum chemical density functional theory?DFT?B3LYP method and the 6-31G?d?-D3/Lanl2dz mixed basis set,the rice husk char focal configuration and activated carbon configuration were established and optimized,and the unsaturated active sites were explored and compared.The microscopic process of adsorbing Hg⁰ on both configurations is studied.It can be seen from the calculation that the Hg⁰ adsorption reaction of rice husk char configuration and activated carbon configuration is a physical adsorption process,and the adsorption energy of activated carbon is larger than that of rice husk char,which confirms the mercury removal of activated carbon.The reason for the strong performance.Secondly,the effect of oxygen-containing functional groups on Hg⁰ adsorption by rice husk char configuration was studied.The adsorption energy of preliminary adsorption reaction with Hg⁰ after embedding different oxygen-containing functional groups in the rice husk char focal configuration was calculated.The results showed that the order of influence was:carbonyl>hydroxy>carboxy>furan;At the same time,taking the most oxidizable carbonyl as an example,from the viewpoint of chemical adsorption,the activation energy of the oxide formed by the reaction is large,which means that HgO will not be the main product of the removal of trace Hg⁰ from rice husk char,that is,Chemical adsorption does not occupy a major position in the effect of oxygen functional groups on rice husk char.Again,the effect of different halogens on the adsorption of Hg⁰ on the configuration of modified rice husk char oxygen-containing functional groups was investigated.Based on the molecular configuration of the oxygen-containing functional group of rice husk char,the reaction path to Hg⁰ when different halogens were loaded in the configuration was studied.The results of calculation of adsorption energy and activation energy showed that HgX was formed by modified rice husk char?X=Cl,Br?.I)The required activation energy is:RHC-Cl>RHC-Br>RHC-I,that is,the most difficult to generate HgCl under the same conditions is the easiest to generate HgI,which is also consistent with the experimental results;The adsorption energy is:RHC-Cl>RHC-Br>RHC-I,that is,the reaction is most likely to generate HgI but relatively easier to decompose,the most difficult to form HgCl but relatively more stable;and the rice husk char oxygen-containing functional configuration?RHC-4?The adsorption energy of the produced product HgCl is slightly larger than the surface configuration of rice husk char?RHC-5?,which means that the oxygen-containing functional group promotes the mercury removal performance of rice husk char to some extent.Finally,the effect of halogen concentration on the adsorption of Hg⁰ on the modified oxygen-containing functional group of rice husk char was studied.After clearing the reaction path of HgCl and HgCl₂ on the modified rice husk char,the results show that the activation energy required to form HgCl₂ is much larger than that of HgCl.It is easier to form HgCl and HgCl₂ is more difficult.The oxide formed by rice husk char adsorption of Hg⁰ is mainly HgCl.In addition,by comparing the adsorption energy with the mayer bond level,it can be seen that the loading of halogen on rice husk char can enhance the initial physical adsorption,and further convert Hg⁰ into chemical adsorption.Moreover,more halogen can also promote the chemisorption of Hg⁰,that is,the increase of halogen concentration promotes the adsorption of modified rice husk char to trace Hg⁰.