Research On Preparation And Characterization As Well As HCL Removal Performance Of Hydrotalcite-Like Adsorbent

Waste incineration is one of the main methods of municipal solid waste treatment.The HClgas in the exhaust gas in the waste incineration induces the environmental pollution,which leads to great inconvenience to the lives of people and the establishment and operation of waste incineration plants.Therefore,investigations on the HClremoval in the exhaust gas of waste incineration are necessary for the waste incineration.The hydrotalcite-like adsorbents can effectively remove HClin the exhaust gas from waste incineration and can be used in pratical project.However the effect of CO₂ in the exhaust gas is not considered,the HClremoval efficiency needs to be increased and the corresponding mechanism needs to be clearer.In present study,the selection,preparation and characterization of hydrotalcite-like adsorbent were studied by experiment and simulation analysis under the support of NSFC.The effects of CO₂ concentration,HClconcentration,particle size,inlet gas velocity and reaction temperature on the HClremoval performance of CaMgAl hydrotalcite-like(CaMgAl-LDOs)adsorbent were studied under CO₂ atmosphere.The effects of the amount of KF,reaction temperature and HClconcentration on the HClremoval performance of CaMgAl-LDOs adsorbent with KF doping were studied.The crystal structure models of hydrotalcite-like adsorbent were established and the mechanism of HClremoval of CaMgAl-LDOs adsorbent was also analyzed according to crystal theory,molecular dynamics(MD)theory and quantum chemistry theory.The main research contents and results are as follows:(1)The selection,preparation and characterization method of hydrotalcite-like adsorbent were proposed.The two parameters of frontier molecular orbital energy and adsorption energy calculated by quantum chemistry were used to determine the material selection of hydrotalcite-like adsorbent.The two-drop co-precipitation method was used to synthesize MgAl,CaAl and CaMgAl-LDOs adsorbents with different metal ratios,and to obtain hydrotalcite-like adsorbents at different calcination temperatures.The method to characterize the crystal structure and chemical properties of hydrotalcite-like adsorbents was proposed based on quantum chemistry theory and by using Materails Studio(MS)software.(2)A fixed-bed HClremoval test system was proposed to carry out the HClremoval test with the hydrotalcite-like adsorbent.The influces of CO₂ concentration,reaction temperature,particle size,HClconcentration and inlet gas velocity on the HClremoval performance of CaMgAl-LDOs adsorbents under CO₂ atmosphere were studied.Some methods such as X-ray powder diffraction(XRD),scanning electron microscopy(SEM)and thermogravimetric analysis(TG)were used to characterize the hydrotalcite-like adsorbents.The results showed that the HClremoval performance of the ternary CaMgAl hydrotalcite-Like adsorbent with the metal ratio of Ca:Mg:Al=2:2:1 is the highest;the HClremoval performance of the hydrotalcite-like adsorbent decreased when the CO₂ concentration increased from 0%to 16%;the HCladsorption capacity of the hydrotalcite-like adsorbent was the largest when the reaction temperature was 600°C;the HClremoval performance of hydrotalcite-like adsorbent was high when its diameter was low in the range of 150?m-850?m;the HClremoval performance of the hydrotalcite-like adsorbent was almost not influced by the HClconcentration change;the HClremoval performance of the hydrotalcite-like adsorbent was highest when the inlet gas velocity was 0.9 L/min.The hydrotalcite-like adsorbent had obvious porous structure and good thermal stability.(3)The KF doping method was used to modify the hydrotalcite-like adsorbent.The effect of KF doping ratios,reaction temperature and HClconcentration on the hydrotalcite-like adsorbent with KF doping were investigated.The HClremoval performance of the hydrotalcite-like adsorbent was characterized and analyzed by XRD,SEM,TG and other methods.The results showed that the HClremoval performance of the CaMgAl-LDOs adsorbent with KF doping(KF/CaMgAl-LDOs)was better than that without KF doping.The HClremoval performance of the KF/CaMgAl-LDOs with 25%KF doping was highest.The HCladsorption capacity of KF/CaMgAl-LDOs with 25%KF doping was highest when the reaction temperature is 600?.The HClremoval performance of KF/CaMgAl-LDOs with 25%KF doping remained stable under different HClconcentrations..The specific surface area and pore volume of the calcined KF/CaMgAl-LDOs sample increased significantly compared with that without calcining.The calcined KF/CaMgAl-LDOs also had a good mesoporous structure and good thermal stability.(4)The crystal structure models of traditional basic adsorbent and hydrotalcite-like adsorbent as well as hydrotalcite-like adsorbent with KF doping were proposed based on the XRD data and the theory of crystallography by using MS software.The adsorption model of hydrotalcite-like adsorbent under CO₂ atmosphere was also constructed.The addition of H₂O or KF increased the lattice constant of crystal structure according to the simulation analysis result.(5)The reaction pathway and mechanism of the HClremoval by CaO adsorbent were determined.The reaction equilibrium constant and reaction rate constant as well as HClremoval performance were investigated under different reaction temperatures according to the quantum chemistry theory and the MD simulation.The results showed that the main reaction pathway between CaO adsorbent and HClwas CaO+HCl?CaClOH,CaClOH+HCl?CaCl₂·H₂O,CaCl₂·H₂O?CaCl₂+H₂O.The reaction equilibrium constant and the reaction rate constant decreased and increased with the increase of reaction temperature,respectively.The HClremoval performance increased first and then decreased when the reaction temperatures increased from 298 K to 1100 K.The adsorbent particles were completely sintered when the reaction temperature was higher than 900 K.The HClremoval performance decreased with the increase of the reaction temperature when it was higher than 900 K for the increase of reaction temperature could not make up for the mass transfer resistance.(6)The mechanisms of the HClremoval performance of CaMgAl-LDOs adsorbent and KF/CaMgAl-LDOs adsorbent were studied by using MS and Gaussian software.The results showed that the HClremoval performance of CaMgAl-LDOs adsorbent increased with the increase of pressure and decrease in the first stage of adsorption with the increase of reaction temperature both under CO₂ atmosphere and without CO₂ atmosphere.The CO₂ molecules preempted part of the active sites originally belonging to HClmolecules,which led to the decrease of the HClremoval performance of CaMgAl-LDOs adsorbents under CO₂ atmosphere.The KF doping increased the alkalinity of gas phase and the adsorption energy between CaMgAl-LDOs adsorbents and HCl,which increased the HClremoval performance of CaMgAl-LDOs adsorbents.