Research On Deoxygenating And Aromatization Mechanism Of "Thermal-Dissolution Based Carbon Enrichment" Treatment Of Biomass And Electrochemical Applications Of Products

The energy utilization of biomass is an effective way to achieve carbon peaking and carbon neutrality.However,the diversity among lignocellulosic biomasses and their high oxygen contents are the key issues limiting their efficient utilizations.A novel method termed‘Thermal-dissolution based carbon enrichment（TDCE）’was therefore proposed to convert biomasses under non-polar organic solvent into the Extract with high carbon content,low oxygen content,low ash content and thermoplasticity,and the Residue with high heating values.However,the correlated mechanism involving deoxygenation and aromatization remained unknown,and the use of Residue was restricted by its high ash content.Consequently,this dissertation systematically investigated the underlying reaction kinetics and mechanism of TDCE method,and proposed an electrochemical conversion way of Residue through activation modifications.Detailed and in-depth research works were subsequently carried out as following.The correlations between influential factors and product yields were discussed using machine learning algorithms for the accurate acquisition of predicted yields under multiple conditions.Results showed that the correlation coefficients of Residue,Extract and Gas were 0.97,0.93 and 0.92,respectively,proving the reliability of the machine learning algorithm.Moreover,the yield of Extract,which is the target product,was directly related to the temperature,residence time,volatile matter and carbon contents of biomass,but inversely related to the ash content of the feedstock.Therefore,the optimal Extract yield can be obtained using biomasses with carbon contents between 55%and 70%,volatile contents ranging from 85%to 95%and ash contents lower than 15%when the TDCE temperature exceeded 350 ^oC.A multi-dimentional kinetic method was proposed combining the machine learning algorithm and lumped reaction model for the dynamic acquisition of kinetic parameters of TDCE products concerning continuous variations of the temperature.Results showed a three-stage and regular variation of kinetic parameters concerning each product:（1）The first stage ranged from 275 ^oC to 300 ^oC,the rate constant of the controlling reaction which related to the conversion from Residue to Liquid was 0.0063 min^-1;（2）The second stage ranged from 300 ^oC to 325 ^oC with the dominant reaction being the conversion from Residue to Extract with a rate constant of 0.0044 min^-1;（3）The last stage ranged between 325 ^oC and 350 ^oC,and corresponding controlling reaction was ascribed to the conversion from Extract to Gas with a rate constant of 0.0041 min^-1.The evolutions of biomass characteristics under dynamic heating and isothermal stages were revealed using the cellulose as the representative.Results showed that the cellulose was physically dissolved in the solvent before 275 ^oC.Severe dehydration and depolymerization reactions occurred thereafter when temperature increased to 325 ^oC,and the cellulose was converted into furanic polymers with 55%of the aromatic rings and dissolved organic compounds rich with furanic structures and ether bonds.Further increment of temperature and residence time led to the slight aromatization of undissolved furanic rings into benzene rings in the Residue,and a massive aromatization of dissolved furanic structures into the Extract.In light of its high carbon and ash contents,the Residue was utilized as the precursor for the electrode of supercapacitors after activation modifications.Results showed that the activated Residue exhibited the highest specific surface area（2746 m²/g）among all the modified bio-chars with unique hierarchical structures,which guaranteed its superiority in the electrochemical properties of its corresponding electrode.In fact,the Residue-based electrode presented a high specific capacitance of 228.9 F/g,a high capacitance retention ratio of 72.1%at a current density of 10 A/g,and a low transfer resistance of 0.38Ω,which was the best among all the electrodes thus proving the feasibility of the utilization method.In summary,this research provided new ideals and theories on the efficient thermo-conversion of biomasses,and theoretically supported the comprehensive industrial application of TDCE technology.