Study On The Influence Mechanism Of Feedstock Constitution And Optimization Of Nitrogen Doping During Fruit Peel Hydrothermal Carbonization

The efficient conversion of high-moisture food waste into porous carbon materials can be realized through the hydrothermal carbonization(HTC)-activation process,which is conducive to the efficient treatment and resource utilization of food waste.Citrus peel,the typical food waste in Hubei Province,was selected as the treatment object.Based on the HTC-activation process for preparing porous carbon materials,the complex composition of food waste and the optimization of porous carbon performance were studied in this paper.The key issues to be solved include:(1)Unclear influence mechanism of typical components of feedstock on the physicochemical properties of hydrochar remain unclear.(2)Effective combination of HTC-activation process and nitrogen-doped modification technology to improve the adsorption performance of porous carbon.(3)The differences in the adaptability of the feedstock components to the optimized nitrogen doping method and the mechanism of these components on the modified porous carbon structure.To the above issues,the following research was conducted in this paper:The HTC mechanism of citrus peel was explained according to the effects of typical components,through the hydrothermal experiments based on the content control of components and quantitative fitting analysis.It was found that the differences in carbon content of hydrochar obtained from different feedstocks were little,reflecting the homogenization of hydrothermal carbonization.In the process of HTC,cellulose and hemicellulose promoted the polymerization reaction of furfural and other intermediate products,which increased the furan-containing structure and active oxygen-containing groups in hydrochar.They also facilitated the formation of microspheres on the hydrochar surface,benefitting the activation of hydrochar.Lignin promoted the polymerization of phenolic fragments and the aromatization reaction of carbon-based structure.Therefore,lignin developed the benzene ring structure and ether groups of hydrochar and inhibited the formation of carbonaceous microspheres.A new method for coupling the food waste HTC process of food waste and the nitrogen-doped modification was proposed,and the optimization mechanism of the method at the adsorption capacity of porous carbon was also clarified.Prepared hydrochar from urea-assisted hydrothermal carbonization was activated by KOH to obtain porous carbon with excellent performance.Specific surface area of modified porous carbon reached up to 3053m~2/g.It also possessed great iodine adsorption capacity up to 2252 mg/g and toluene adsorption capacity up to 724 mg/g,which were obviously better than that obtained by conventional methods.The above properties of modified porous carbon were significantly better than those of the porous carbon obtained by conventional methods.In addition,there was a good linear positive relationship between the relative reduction of N content and the relative increment of specific surface area when activated at 500-800 ~oC.This connection indicated that increasing the nitrogen-containing groups of carbon materials effectively improved its pore structure during activation.The inner relation between the typical components of citrus peel and optimization of hydrothermal nitrogen-doping method was clarified,and the optimization mechanism of hemicellulose on hydrochar nitrogenous groups and porous carbon porosity was revealed.During the hydrothermal process with nitrogen doping,hemicellulose greatly increased the nitrogen doping efficiency by promoting the combination of the hydrolysis products and the nitrogenous substances.Hemicellulose mainly developed the formation of the pyrrolic-N/pyridonic-N structure that was important for increasing porosity during activation.In this way,the pore-increasing efficiency of the nitrogen-doped structure was improved,and the porosity of the corresponding porous carbon was developed.Cellulose was adverse to the degradation of feedstock in the hydrothermal nitrogen doping process and inhibited the degree of carbonization.Cellulose content increasing lead to lower efficiency of nitrogen doping,less participation of nitrogenous structure in the activation reaction,and the decrease of porous carbon surface area.Lignin slightly increased the nitrogen-doped structure but inhibited the formation of oxygen-containing groups on hydrochar surface,which had little effect on the total specific surface area of porous carbon.In summary,a high-performance porous carbon adsorbent with well-developed porosity can be prepared through the hydrothermal nitrogen doping and activation processes,when appropriately regulating the composition of food waste.This study provided innovative ideas and theoretical basis for the reduction and high value utilization of food waste.