| With the rapid development of industry,the concentration of CO2 in the atmosphere has risen sharply,triggering a series of climate problems.The most effective CO2 reduction method at present is Carbon Capture and Storage(CCS).Activated carbon,as a widely used adsorbent material,provide an effective method for CO2 capture.Activated carbon have the advantages of wide source,low cost,good adsorption properties,low regeneration energy consumption,and no corrosion equipment problems.In this thesis,the agricultural waste-cotton straw was used as raw material to prepare activated carbon and N-doped modification,and its adsorption properties was analyzed.The summaries of the results are as follows:1.Preparation of activated carbon with KOH as activation agent.Orthogonal experiment was designed to investigate the effects of activation time,activation temperature and impregnation ratio on the adsorption properties of activated carbon CO2.From the analysis of the orthogonal experiment,the activation time is the most influential factor on the adsorption properties of activated carbon,followed by the activation temperature and impregnation ratio.The highest adsorption capacity was 2.5659mmol/g at 25? and 1 bar.The optimum preparation conditions were activation temperature 900?,activation time 90min,and impregnation ratio 2:1.By characterization analysis,the specific surface area was 314.38m2/g,the pore volume was 0.175cm3/g,the average pore diameter was 1.272nm,and a mass of pore size was concentrated between 1-2nm.2.In order to further improve the adsorption properties of activated carbon,the surface chemical properties of activated carbon are modified,nitrogen source is introduced,the content of nitrogen in activated carbon is increased,and the adsorption capacity is increased.In this thesis,urea and melamine were used as nitrogen sources to introduce different amounts of nitrogen into activated carbon with different carbonization temperatures.The prepared activated carbon was characterized by scanning electron microscope(SEM),X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FT-IR Spectroscopy),X-ray photoelectron spectroscopy(XPS)and elemental analysis.It was found that nitrogen has been successfully introduced into activated carbon and decomposed into different kinds of nitrogen at high temperature.The activated carbon with the optimum adsorption properties of activated carbon at 25?and 1 bar was MC600-0.4,and the adsorption capacity was 3.8544mmol/g,which was significantly higher than that without N-doped indicating that the introduction of nitrogen source promoted the adsorption properties of activated carbon.It is found that the pyrolysis carbon pore structure caused by the carbonization temperature has a certain influence on the adsorption of N-doped activated carbon.Combined with the pore size distribution of activated carbon,the high micropore ratio has a great effect on the adsorption properties of activated carbon.The adsorption desorption cycle test was carried out 5 times,and the adsorption capacity of the fifth time was 94%of the first time,indicating that the adsorption desorption cycle stability of the nitrogen-doped activated carbon was high.3.The kinetic model was fitted to the prepared activated carbon,and the prepared first-order kinetic model,pseudo-second-order kinetic model and Avrami kinetic model were selected to fit the prepared samples.Among them,the R2 value(0.9778)of the first-order kinetic model is the largest.However,Avrami model was found to better expressed the kinetics of carbon sample and fits well with the experimental over the entire adsorption process.This is confirmed based on higher values of R2(0.9750)and lower values of Aqe(1.21%).In addition,the CO2 uptake at equilibrium predicted by the Avrami model and experimental data are in good agreement with each other suggesting that Avrami model could reasonably describe the adsorption kinetics of carbon sample. |
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