| Majorities of bamboo processing residues are discarded or burned directly in China without efficient utilization.The conversion of these bamboo processing residues into high-value-added bamboo charcoal by thermochemical conversion can not only reduce the atomospheric pollution caused by direct combustion to the environment,but also upgrade the biomass waste into green energy,chemicals,and materials.Therefore,clean production of value added bamboo charcoal has its theoretical significance and practical application and has received extensive attention.This dissertation aims at converting moso bamboo particles into hydrochars with high calorific value,carbon spheres with homogeneous particle size distribution and porous carbon materials through hydrothermal carbonization.Effects of temperature,pressure and residence time on the physicochemical properties and surface morphology of the produced hydrochar were studied.The pathway of hemicellulose,cellulose and lignin degradation during hydrothermal carbonization process were also elaborated.Methods for preparing engineered hydrochar material with potassium permanganate modification were explored.Effect of acid ion on the formation of homogenous carbon microspheres was studied as well.At last,technology for preparing porous carbon material was developed aiming at the problems of pollution and high energy consumption during traditional hydrochar activation process.This dissertation potentially provides experience and technical support for the further research and development for functional modification and controllable synthesis of hydrochar materials.(1)Torrefaction and hydrothermal carbonization were employed for processing bamboo residues,which effectively improved the end production quality.Results showed that dry torrefaction was beneficial in improving the mass yield(61.6 to 92.8%),energy yield(74.9 to 93.8%),and energy efficiency(30.5 to 40.4%),while hydrothermal carbonization produced bamboo hydrochar with higher calorific value(28.29?29.30 MJ/kg)and more fixed carbon content(63.1?68.6%).Hydrochars produced at 260 and 300? were found having smaller particle size(50%of the particles were smaller than 84.5 ?m),higher bulk density(0.25 to 0.29 g/cm3)and excellent hydrophobicity(moisture absorption of 1.60 to 2.49%).As temperature increased,the quality yield,energy yield and volatile content decreased,whereas the calorific value,fixed carbon content,hydrophobicity and pyrolytic stability increased.At the meantime,the disappearance of the specific peak at around 1730 cm-1 in FTIR spectral revealed changes on the surface functional group of hydrochar and torrefied product.Besides,with temperature increasing,the total pore volume decreased as well as the hydrophobicity enhanced,which prevented the solid fuel from deteriorating.(2)Experiments were carried out to study the effect of feedstock concentration(solid to liquid ratio),reaction temperature,pressure,and residence time on the properties of hydrochar.Results showed that the reaction temperature had the greatest influence on the properties of hydrochar.The higher the temperature,the more completed the decomposition of hemicellulose and cellulose;the deeper the degree of carbonization;the higher the fixed carbon content;the lower the volatile content;and the greater the calorific value.The calorific value of hydrochar produced at 260? was greater than 28 MJ/kg,which has reached standard coal's calorific value.The effect of residence time on the properties of hydrochar is less than that of reaction temperature.When the reaction temperature is low(220?),the residence time will deepen the degree of carbonization,and the increase of various energy indicators is slightly larger.While the reaction temperature is high(260 and 300?),the residence time has less effect on the properties of hydrochar.However,for the lab-scale hydrothermal reactor,the feedstock concentration and reaction pressure had little effect on the properties of hydrochar.Comprehensively taken the quality and energy consumption into consideration,the optimal hydrothermal carbonization condition was set to temperature at 260?,residence time at 1 h,feedstock concentration at 50 g/L,and no external pressure applied.(3)A novel approach was developed to prepare engineered hydrochar from potassium permanganate treated bamboo residues through hydrothermal carbonization.The effect of potassium permanganate concentration on the physicochemical properties,hydrophobicity and morphology of engineered hydrochar material under different temperature conditions was studied.The hydrochar yields were within a specified range of 61.8?67.8%at 180? and 39.8?45.0%at 260?,respectively.The higher temperature led to the higher C content,lower H/C and O/C ratio,whereas the ash content increased with increasing potassium permanganate concentration,causing the increase of solid yield as well as the decrease of C content.Pseudo-second kinetic model was optimal to describe bamboo hydrochar's hygroscopic dynamic,and the engineered hydrochar produced at 260? and 1.0 wt%concentration obtained the better hydrophobicity of 0.82%.SEM-EDS and XRD analysis confirmed the existence of manganese carbonate on the surface of engineered hydrochar,from which we inferred the chemical complexation between potassium permanganate and hydrochar.(4)Three commonly used inorganic strong acids(hydrochloric acid,sulfuric acid,and nitric acid)were introduced into hydrothermal carbonization system as catalysts to prepare homogenous carbon microspheres as well as engineered hydrochars loaded with sulfonic acid groups.Hydrochar produced at 220? with hydrochloric acid and sulfuric acid catalysts had high calorific value of 26.75 and 25.00 MJ/kg,respectively,which can be comparable with normal hydrochar produced at higher temperature.When the hydrothermal carbonization temperature is 220?,existence of hydrochloric acid and nitric acid can effectively overcome the agglomeration phenomenon of hydrochar,forming carbon microspheres with particle sizes of 8?10 ?m and about 0.2 ?m,respectively.As temperature increased,the carbon microspheres continued growing,while cross-linking of carbon microspheres occurred in some locality.Sulfuric acid catalyzed hydrothermal carbonization formed irregularly shaped engineered hydrochar particles,and introduced sulfonic acid groups on the surface of the engineered hydrochar particles.Engineered hydrochar with sulfonic acid groups can be used as cellulose hydrolysis catalyst and solid acid catalyst carrier.Carbon microspheres produced by hydrothermal carbonization with inorganic acid catalysts could achieve the quality of normal hydrochars produced at higher temperature,thus saving energy consumption and having better economic benefits.(5)Three commonly used strong bases(potassium hydroxide,sodium hydroxide,and potassium carbonate)were added as catalysts into hydrothermal carbonization reaction system of moso bamboo particles.Alkali treated hydrochars were then pyrolyzed at a high-temperature to prepare porous carbon material.Amongst all,the pore-forming effect of potassium carbonate combined with high-temperature pyrolysis was the best.The BET specific surface area and total pore volume reached 307.4 m2/g and 0.167 cm3/g,respectively. |
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