Preparation And Adsorption Properties Of Porous Carbon Materials From Oxidized Residual Coal

The preparation of high-quality carbon materials from lignite is an effective way to achieve high value-added utilization of lignite.To solve the problem of low utilization rate of lignite,which is directly activated by coal samples to produce carbon materials,hydrogen peroxide method is used to preoxidize lignite to extract by-product fulvic acid and obtain oxygen less residual coal with less volatile matter.The oxygenated coal was activated by two ways of tube furnace and microwave,and carbon materials were prepared with KOH as activator.The structure and properties of carbon materials were characterized by FT-IR,Raman spectroscopy,XRD,thermogravimetric analysis,SEM and specific surface area aperture analyzer.The adsorption properties of carbon materials to methyl orange dyes were investigated.Four isothermal models and three kinetic models were used to explore the mechanism of the adsorption process.Yunnan lignite contains many volatiles,ash,etc.The direct activation and preparation of carbon materials will cause the waste of small molecules,affect the performance of carbon materials and pollute the environment.Hydroxy-hydrogen peroxide pre-oxidation lignite was used to extract small-molecule fulvic acid.The orthogonal experimental results showed that the optimum conditions for extraction of fulvic acid were oxygen-coal ratio of 6,hydrogen peroxide concentration of 23%,reaction temperature of 40°C,reaction time of 30 min,the yield of humic acid was32.72%,and the yield of oxygenated residual coal was 53.54%.In the experiment of activated oxygen-resolved residual coal in the tube furnace for the preparation of carbon materials?CM₁?,combined with the single factor experimental results for orthogonal experiment,obtained the best process conditions for the preparation of CM₁ in the tube furnace as the activation temperature was 600°C,the activation time was 30 min,and the activator ratio was 3.5:1.The iodine adsorption value of CM₁ was 1209.86 mg/g and the yield was 12.46%.In the microwave radiation activation method for preparing carbon materials?CM₂?experiment,combined with the single factor experimental results and response surface experiments,the correlation coefficient of the model obtained by the second-order polynomial regression analysis was 0.8690.The optimum technological condition for the preparation of CM₂ was microwave power 432.54 W,activation time 14 min,activator ratio 3:1,the iodine adsorption value of CM₂ was 1060.06 mg/g,and the yield was 24.56%.The FT-IR analysis of CM₁ and CM₂ showed that CM₁ and CM₂ contained a large number of aromatic rings,and also contained methyl,methylene and hydroxyl functional groups.Compared with the oxygenated residue coal,the proportion of aromatic structure increased and the content of other functional groups decreased significantly.Raman spectra and XRD spectra show that graphite microcrystalline structure obviously presents in the material,and the graphitization degree of CM₁ is lower than CM₂,which is due to the etching of carbon atoms by activator KOH.The results of BET analysis showed that the existence of a large number of pore structures of CM₁ and CM₂ structure,with mostly micropores.The specific surface area of CM₁was 1226.71 m²/g,the pore volume was 0.685cm³/g,and the specific surface area of CM₂ was 1129.11 m²/g,the pore volume was 0.603 cm³/g;the nitrogen adsorption desorption isotherms all showed that the adsorption of II adsorption,that is characteristics of mixed adsorption of microporous and mesoporous,and the pore size distribution is relatively concentrated.The experimental study on the adsorption of methyl orange on carbon materials has guided significance for the practical application of materials.The effect of initial pH and adsorption time on the performance of the material adsorbing methyl orange was discussed.The optimum adsorption pH was 8.0 and the saturation adsorption time was 480 min.The isothermal model and kinetic analysis of carbon materials found that the adsorption process of methyl orange by CM₁ and CM₂ accords with the Freundich model and generally conforms to Tempkin isothermal model.The adsorption process is mainly the combination of physical multilayer adsorption and chemical adsorption.Kinetic analysis showed that the adsorption process of CM₁ and CM₂ on methyl orange followed the pseudo two level adsorption kinetic rate equation model.