| With the depletion of fossil fuels such as coal and petroleum,biomass as a renewable resource has the advantages of extensive sources and huge output,and its resource utilization effectively alleviates the current crisis of energy and material.As an emerging thermochemical conversion method,hydrothermal carbonization(HTC)directly utilizes the waste biomass with a high moisture content and low energy density.In this study,some typical waste biomasses were used as the raw materials,and the hydrothennal carbonization(HTC)method was adopted for high-quality products geneneration.The series of experiments were carried out including catalytic HTC and co-hydrothermal carbonization to prepare high-quality solid fuel;co-hydrothermal carbonization to produce rich-nutrient hydrochar;and hydrothermal carbonization to produce high-performance adsorbent,and some potential reaction mechanisms and product regulation methods for multi-functional materials were explored,and the feasibility of hydrothermal carbonization of low-value biomass to produce high-quality multi-functional hydrochar was evaluated.The specific research content and the main conclusions are listed as follows:(1)Using lignocellulosic biomass as raw material,on the basis of preliminary hydrothermal carbonization experiments,hydrothermal carbonization process was enhanced by adding exogenous homogeneous catalysts such as FeCl3,CaO and the autocatalysis of hydrothermal liquid product recycling.The results indicated that the addition of exogenous catalyst increased the carbonization degree of hydrochar and reduced the content of volatile matter.On the other hand,GC/MS results showed that the addition of FeCl3 and other catalysts increased the formation of formic acid,acetic acid,levulinic acid,5-hydroxymcthyl-furfural and other products in the liquid phase.In addition,when the aqueous phase product in the hydrothermal carbonization process was used as processing water,the hydrochar yield and energy efficiency were significantly improved by the autocatalyst of small-molecule compounds such as acetic acid.(2)A series of co-hydrothermal carbonization of lignocellulosic biomass and waste polyvinyl chloride plastic was conducted to produce solid fuel.The parameters of hydrothermal carbonization temperature and the mixing ratio of raw materials on the carbon conversion and dichlorination were examined.By combining SEM,FTIR etc.to analyze the morphology and chemical structure of hydrochar,the mechanisms of carbonization and dechlorination in HTC were explored.With the help of TG/DTG and Py-GC/MS methods,the combustion and pyrolysis properties of hydrochar as the solid fuel were studied.The co-hydrothermal carbonization significantly improved the fuel quality of hydrochar.With the increasing of hydrothermal carbonization temperature,the carbon contents in hydrochar increased from 47.59%(200?)to 74.26%(280?),and the chlorine content decreased from 31.96%to 3.98%.At the hydrothermal temperature of 240?,the calorific values of hydrochar obtained by hydrothermal carbonization were increased from 21.03 MJ/kg to 26.90 MJ/kg,29.66 MJ/kg,29.78 MJ/kg(3:1,1:1,1:3,PS/PVCS),respectively.Py-GC/MS analysis indicated that the co-hydrothermal carbonization promoted the generation of the aliphatic and alicyclic hydrocarbon compounds in the pyrolysis of hydrochar product.(3)Lignocellulosic biomass and dewatered sludge were hydrothermally co-carbonized for the generation of soil amendment.In hydrothermal carbonization,the transformation of nutrient elements such as carbon,nitrogen and phosphorus and the interaction mechanism between two feedstocks were investigated.The physicochemical properties of solid products as soil amendments were investigated by the methods of SEM,FTIR,Boehm's titration,CP-MAS 13C NMR and the species of nitrogen and phosphorus.It was found that the co-hydrothermal carbonization had obvious synergistic effects on promoting the formation of solid hydrochar products.At the mixing ratio of 1:1,the obtained hydrochar had a high synergistic coefficient,the hydrochar yield reached 58.11%,the carbon retention efficiency was 66.56%,the organic matter retention efficiency was 57.48%,and the synergistic coefficients were 8.41%,14.92%and 13.09%,respectively.The chemical structure analysis results showed that co-hydrothermal carbonization significantly improved the degree of coalification and the density of highly active-oxygen containing functional groups with a good soil improvement characteristic.The results of transformation and the speciation of nitrogen and phosphorus indicated that the co-hydrothermal carbonization had a certain synergistic effect on nitrogen and phosphorus immobilization,which increased the contents of nutrient elements in hydrochar and reduced the loss of nitrogen and phosphorus when it was used as a slow nutrient-releasing fertilizer.(4)Lignocellulosic biomass was used as a raw material to prepare high-performance adsorbent by combining hydrothermal carbonization and subsequent acid/base modification methods,and the potential mechanism of enhanced adsorption of modified hydrochar was explored by BET,FTIR and XPS.It was found that the hydrochar prepared by hydrothermal carbonization could produce high-performance adsorbent for Cr(VI)ion by low concentration alkali modification,and its adsorption effect was better than that of acid modification.At 25?,the adsorption capacity of Cr(VI)in the liquid phase with hydrochar modified by low concentration alkali(0.05 N)was 200.46%higher than that of raw material(15.27 mg/g).The yield of modified hydrochar adsorbent was 47.61%,which was much higher than that of activated carbon prepared by traditional pyrolysis-activation method.The adsorption kinetics results showed that pseudo-second-order kinetic model was better to describe the adsorption kinetics of modified hydrochar on Cr(VI).The adsorption of modified hydrochar on Cr(VI)was fitted to Freundlich isotherm.Thermodynamic analysis showed that the adsorption process was a spontaneously endothermic reaction.The pore structure,surface functional groups and elemental chemical states of hydrochar materials were characterized by BET,FTIR and XPS.It was found that the modified hydrochar had more abundant functional groups,which enhanced the adsorption performance.In summary,hydrothermal carbonization is a highly efficient method for upgrading biomass to high-value products.Based on the physical and chemical properties of different biomass(biomass components,nitrogen,phosphorus,chlorine content etc.),by adopting feedstocks blending,exogenous catalysis,process water autocatalysis,and post-modification,the high-quality solid hydrochar fuel,nutrient-rich soil amendment and high-performance adsorbent could be obtained.Relevant research results could provide a theoretical basis and technical guidance for the preparation of high value-added products from biomass via hydrothermal carbonized. |
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