| In the background of the Carbn Peaking and Carbon Neutrality Goals and the clean utilization of coal in the international community,and at a time when environmental protection and quality of life have reached new heights,coal is inevitably transformed from a kind of fuel to a carbon material,and coal-based activated carbon is one of the most important options,ultrafine coal-based activated carbon has attracted attention due to a series of outstanding properties,but reports on the preparation of ultrafine coal-based activated carbon are scarce.In this paper,a fuzzy evaluation model based on Analytic Hierarchy Process was used to obtain the optimum process conditions for ultrafine pulverization of Ningxia anthracite,the precursor was prepared by mechanical-chemical method,and the ultrafine coal-based activated carbon was prepared by one-step method followed by,the evolution of the microstructure and the mechanism of adsorption of Methylene Blue were investigated in depth,which provided a new method for the preparation of ultrafine coal-based activated carbon and a theoretical basis for its later modification.The research on ultra-fine comminution of anthracite by planetary mill using a fuzzy comprehensive evaluation model based on Analytic Hierarchy Process shows that a new membership function for the maximum particle size dmax can be constructed through four steps:"mapping","variable interchange and modelling","normalisation" and"refinement" based on the comminution kinetics data,which can represent the actual variation of the index better.The optimum ultrafine grinding process is the speed of 250 rpm,the specific surface area of the medium of 85.34 m2/kg,the concentration of 0.8 g/mL,and the importance of each factor in the order is the concentration,speed and specific surface area of the medium.The ultrafine comminution process conforms to the n-order kinetic model,with agglomeration and mechanochemical interactions occurring during the comminution process.The research on the preparation of ultrafine coal-based activated carbon by mechanical-chemical method showed that the optimum conditions for the charring and activation process were:the heating rate of 7?/min,charring temperature of 650?,charring for 2 h,the mass ratio of KOH to raw coal(abbreviated as KOH:C mass ratio)of 1.5,activation temperature of 850?,and activation time of 1.5 h.The ultrafine activated carbon obtained under these conditions increased the adsorption of methylene blue by 94.08 mg/g compared with the ultrafine activated carbon obtained by preparing granular activated carbon under the same conditions first and then crushing.With the increase of KOH:C mass ratio,the degree of oxygen enrichment of ultrafine coal-based activated carbon increased and then decreased,the degree of orientation of aromatic lamellae gradually increased and then decreased,the change pattern of amorphous carbon content was not obvious,the total volume of mesopores and macropores generally showed increasing and then decreasing,the fractal dimension of mesopore pore size distribution firstly decreased and then increased,the specific surface area of multi-point BET gradually increased and the adsorption capacity firstly increased and then decreased.As the activation temperature increases,the fractal dimension of the oxygen-containing functional groups and mesopore pore size distribution does not change significantly,the aromatic lamellae become more and more oriented and the content of amorphous carbon gradually decreases,but the high temperature causes the erosion of ordered carbon,the total volume of mesopores and macropores first increases and then decreases,and the adsorption capacity first increases and then slightly decreases.The longer the activation time,the more the volume of mesopores and macropores increases,the fractal dimension of the mesopore distribution decreases and then increases,and the adsorption capacity increases and then decreases.The interlayer spacing between the aromatic flakes of ultrafine coal-based activated carbon activated for 1 h and above was close to that of pure graphite at 0.34 nm.The activation reaction was relatively fast,with the product reaching 90.58%of the maximum BET specific surface area at 0.5 h activation.The microstructural evolution of the ultrafine coal-based activated carbon preparation process shows that KOH contributes to the evolution of the size of the crushed product to a smaller particle size,and has a certain ash-reducing effect,while"agglomeration" still exists in the process.The increase in interlayer spacing of the precursor aromatic lamellae and the decrease in the average number of aromatic layers in the stack provide favourable conditions for the insertion of KOH into the carbon layers,and the increase in oxygen enrichment provides more active sites,all of which are conducive to the preparation of more porous ultrafine activated carbon.Throughout the preparation process,the amount of pore space first decreases and then increases by an order of magnitude,and the degree of oxygen enrichment first increases slightly and then increases greatly.The amorphous carbon gradually evolves into graphitic carbon and the defects in the hybrid carbon structure gradually decrease.The benzene ring substitution evolves towards multiple substitution and the hydrogen bonding formed by the selfconjugated-OH gradually decreases.Experimental research on the adsorption of methylene blue shows that the adsorption of methylene blue molecules by ultrafine coal-based activated carbon is a physicalchemical adsorption,with capillary coalescence occurring during the process,following the Bangham kinetic model and the Langmuir-Freundlich adsorption isotherm model.The methylene blue molecules are adsorbed on the surface of the activated carbon by ?? conjugation with different benzene ring substitutions,by hydrogen bonding with hydroxyl OH,by electrostatic interaction with carboxyl groups,and by using N atoms as contact points.The adsorption showed a multivariate linear relationship with the fractal dimension of the multipoint BET specific surface area and mesopore pore size distribution.Molecular simulation studies of adsorbed methylene blue showed that the peak adsorption concentration occurred near 6 ? on the pore surface,and the adsorption concentration in the hollow region of the pore was about 2/5 to 1/3 of the peak.Both hydroxyl and carboxyl groups have adsorption effect on methylene blue molecules,and the carboxyl group adsorption effect is stronger;Van der Waals force plays a dominant role in the adsorption process,and its contribution is>60%;the contribution of electrostatic force in the adsorption of methylene blue molecules is greater in the carboxyl group model compared with the hydroxyl model.In summary,a new membership function was constructed by using the crushing kinetic data,and then the ultra-fine crushing process was optimized by the AHP-FUZZY model,the ultrafine coal-based activated carbon is prepared by mechanical-chemical method,and the influence of different factors on products'performance and structure was explored,the microstructure evolution of anthracite coal to precursor and ultra-fine activated carbon was analyzed from both physical and chemical aspects,and the mechanism of adsorption of methylene blue molecules by ultrafine coal-based activated carbon was revealed in both experimental and molecular simulation.It provided new ideas for the preparation of ultrafine coal-based activated carbon,and theoretical basis and reference for its modification and improvement.Figure[88]table[46]reference[198]... |
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