Study On A Cleaner Preparation Method Of Biochar/Activated Carbon From Furfural Residues

Furfural residues are usually produced from corncob as an industrial-biomass waste of acid catalysis.A large amount of furfural residues with subacidity and high moisture content are accumulated and stored in the open,occupying a significant amount of land and posing a serious threat to the ecological environment,causing water,air,and soil pollution.However,furfural residues are rich in cellulose and lignin,making this material a promising precursor for the production of porous carbon materials by pyrolysis.Porous carbon materials with high surface area,void-containing structure,and stable chemical properties can be used for water control and catalysis.However,there are some fundamental problems presented by traditional physical activation methods,such as secondary pollution caused by pyrolysis gas emission,low activation efficiency of activators,and requirement of a long mixing time.To avoid the disadvantages of traditional activation methods,the goal of this study was to develop a novel strategy for the utilization of this material,in which biochar/activated carbon is prepared via pyrolysis gas and molten salt pyrolysis in a novel sequencing integration system.Activated carbon activation was performed by H₂O,CO₂,and KOH for the same batch of corncob-furfural residue.The influences on activated carbon of activation temperature,activation time,and dosage of activator were studied.The results showed that the surface areas of activated carbon prepared with H₂O were 456 to 655 m²/g,the total pore volumes were 0.31 to 0.36 cm³/g,the mesopore pore volumes were approximately the same as the micropore pore volumes,with a ratio of the micropore pore volume to the total pore volume of 60.4%.Activated carbon prepared with CO₂ was microporous,and the ratio of micropore volume reached 91.3%.The surface area?618?995 m²/g?and total pore volume?0.42?0.48 cm³/g?of the CO₂-activated materials were higher than those activated by H₂O.Activated carbon prepared with KOH showed excellent nitrogen adsorption capacity and good economic value.The specific surface areas ranged from 409?3376 m²/g,total pore volume was between 0.32 to 2.14 cm³/g,and micropores accounted for 85.5%.Activation temperature and the amount of added activator were the main determinants of the properties of activated carbon.Analysis of activation method provided the scientific basis for the preparation of activated carbon materials from furfural residues,and some of this analysis is presented in a later chapter.A strategy for the self-activation of biochar from furfural residues using recycled pyrolysis gas was presented.This strategy resolves the issue of pyrolysis gas secondary pollution and provides improved resource utilization.The influences of preparation parameters on the resulting biochar were studied by varying the pyrolysis-gas flow rate,activation time,and temperature.The results indicated that the highest surface area of the biochar was 567 m²/g,the total pore volume was 0.38 cm³/g,the ratio of the mesopore pore volume to the total pore volume reached 39.2%,and the specific surface area per gram furfural residue was 176.90 m²/g.There was a significant effect of pyrolysis gas flow rate and activation time on the development of specific surface area and the resulting pores of the biochar.The dosage of activator was determined by pyrolysis gas flow rate and activation time.Excessive activation reaction and pore collapse resulted for pyrolysis gas velocity that was too fast and a long activation time,ultimately decreasing the performance of the biochar.The CO volume fraction of the pyrolysis gas ranged from 34.7 to 62.3%and the CO₂ volume fraction ranged from 48.3%to 12.2%under different conditions of pyrolysis-gas flow rate,activation time,and temperature.The calorific values of pyrolysis gas changed from 8.8 MJ/m³ to 14.0 MJ/m³,suggesting its potential for use as gas fuel for industrial use.These results demonstrated the feasibility of treatment of furfural residues to produce microporous and mesoporous biochar.Overall,this new self-activation method meets the development requirements of a cyclic economy with cleaner production.A novel sequencing integration reactor that combined the carbonization and activation processes in a single process was developed to produce high-quality porous carbon from furfural residues.Additionally,the traditional solution impregnation method was replaced by a dot-dipping molten salt method,to avoid the low activation efficiency of activator and long mixing time of traditional physical and chemical activation methods.To determine the mixing and activation mechanism,systematic studies on the effects of soaking and carbonization time,activation temperature,and time on the properties of porous carbon were measured.The electrochemical properties of the activated carbon as electrode materials for supercapacitors were investigated by cyclic voltammetry,galvanostatic charge/discharge,and electrochemical impedance spectroscopy.The mixture of potassium hydroxide molten salt and pyrolysis char was a physical and chemical coupling process.The corrosion reaction between pyrolysis char and potassium hydroxide molten salt promoted the molten entry and loading rates.The mixing time of the molten salt method was 3 min,1/400 as long as the KOH method.The mass of load molten salt was 1.73 g/g,higher than that obtained by the traditional method?0.43 g/g?.The micropores in the porous carbon had a large surface area of over 2494 m²/g with a total pore volume of 1.51 cm³/g and a ratio of micropore volume of 79.3%.The activated carbon-based electrode exhibited higher capacitance of 210.2 F/g with 96.3%capacity retention after 10,000 cycles at 5 A/g in 6 M KOH electrolyte,and the energy density was 52.6 Wh/Kg at a power density of 251.0 W/Kg.The electrochemical properties were higher than those of most carbon material-based supercapacitors,suggesting the potential application of these materials in energy conservation and storage.A lower activator dosage,shorter mixing and preparation time,and higher activation effect were observed for the molten salt activation method.Overall,the new method is green,conserves energy,and a pollution-free activation method.The pyrolysis gas coupling molten salt activation method was designed to resolve the problem of molten salt ultimate load capacity,which limits the performance improvement of activated carbon.The results show production of activated carbons with a specific surface area of 2458 m²/g and total volume of 1.58 cm³/g,for a yield of 19.9%.The pore size distribution of activated carbon ranged from 0.6?3 nm,and the resulting material was microporous activated carbon?82.9%?.The average calorific value of pyrolysis gas after activation was 9.9 MJ/m³,lower than pyrolysis gas activation alone.This result was because the molten salt occupied the most space inside of pores,which could limit the pyrolysis gas for activation.The adsorption capacity for methylene blue of activated carbon was 647.1 mg/g,and the adsorption data showed a good fit to the Langmuir model with maximum monolayer adsorption capacity.Activated carbons with higher specific surface area and abundant pore structures were prepared using a green activator,avoiding the disadvantages of the potassium hydroxide molten salt method.