| Lignocellulosic biomass is a carbon-containing renewable resource with abundant reserves.Converting it into liquid fuels,through thermochemical and biological conversion methods,is of great significance to adjust the energy industry structures,and realize the green sustainable development goals of carbon peak and carbon neutral.Garden waste is rich in lignocellulosic components,and most of them have not been rationally used at present.Therefore,using efficient and intensive treatment technologies to transform garden waste into fuels and high-value chemicals can realize the ecological and economic value of garden waste.In this work,the low-temperature hydrothermal technologies were applied to realize the purpose of converting garden waste into biochar and fuel precursors.Firstly,hydrothermal saccharification of garden waste was studied to prepare fuel ethanol precursors(glucose and xylose)in deep eutectic solvents(DES).Secondly,hydrochar was prepared through high-temperature hydrothermal carbonization of garden waste in DES,and the characteristics and adsorption performance of hydrochar were investigated;Then,the process of preparing fuel precursors with the condensation of the liquid components of hydrothermal carbonization of garden waste and cyclopentanone was investigated based on the preparation of cyclic fuel precursors by the ketone-aldehyde condensation of benzaldehyde and cyclopentanone;Finally,the fuel precursors were subjected to hydrodeoxygenation reaction to realize the transformation to liquid cyclic alkane fuels.The main research content and results are as follows:(1)The low-temperature hydrothermal saccharification of garden waste was performed with acid DES as reaction solvent.The process conditions were optimized and the saccharification mechanism was explored.The results showed that the highest yields of total glucose and total xylose were obtained with 20.93%and 43.57%,respectively,under the condition of the solid-liquid ratio of garden waste to DES was 1:10,the acidity was 2wt%H2SO4,and the saccharification was performed at 120℃ for 2h.DES improved the digestibility of garden waste,promoted the exposure of more lignocellulosic components during the saccharification process.The catalytic performance of DES was further strengthened after sulfuric acid was added,which could promote the effective saccharification of cellulose and hemicellulose into monomers,and cause structural changes in garden waste components to achieve better saccharification accessibility and higher sugar yield.(2)Hydrothennal carbonization of garden waste in high temperature was conducted to prepare garden waste hydrochar(GHC)with DES choline chloride-water(CHCI-H2O)and FeCl3 as catalyst.The effects of temperature,time and metal salt amount on characteristics and adsorption performance of GHC were investigated.The results indicated that the hydrochar(GHCop)with the highest adsorption capacity was obtained by hydrothermal carbonizing garden waste at 180℃ for 5h with 4g FeCl3.The maximum equilibrium adsorption capacity for methylene blue(MB)was 169.19mg g-1 at 270min;The fitting results of adsorption kinetics showed that the adsorption process of GHCop to MB had a better fitting effect on pseudo-second-order kinetic and Freundlich model.The adsorption of MB on GHCop was mainly the result of van der Waals force or weak bonds interaction of physical adsorption.The result of adsorption thermodynamics indicated that the adsorption process of MB on GHCop was spontaneous and endothermic determined by entropy.(3)The condensation of benzaldehyde and cyclopentanone in a DES-containing catalytic system was performed to prepare fuel intermediates.The effects of different temperature,time,catalyst molar ratio and substrate molar ratio on the conversion rate of substrate and the yield of condensation products were investigated.The results indicated that the C12 and C19 fuel precursors prepared by condensation at 80℃ for 120min had the highest selectivity with 49.20%and 15.20%,respectively,and the total yield was 64.37%under the condition of the molar ratio of choline chloride/formic acid(CHCl/Fa)was 1:12,the addition amount of SnCl4·5H2O was 4mmol,the molar ratio of benzaldehyde to cyclopentanone was 1:6.The conversion rate of benzaldehyde was 99.96%.Then,this optimized condition was used to catalyze the condensation of the liquid components of hydrothermal carbonization with cyclopentanone.It was found that the condensation reaction of p-hydroxybenzaldehyde in the components and cyclopentanone produced C13 fuel precursor.The corresponding unsaturated alkanes were obtained after further hydrodeoxygenation of the prepared fuel precursors C12,C13 and C19 with relative selectivities of 37.61%,35.74%and 24.10%,respectively.The Sn4+in SnCl4·5H2O protonated the cyclopentanone and coordinated to form an enol structure and removed water molecules during the condensation process.The benzaldehyde was protonated to cause proton release and electron transfer during the dehydration process,and then condense to form C12.The protonated carbonyl group in the C12 structure continued electron transfer to form an enol structure containing a C=C double bond,which react with benzaldehyde to form C19.The presence of H+in CHCl/Fa enhanced the catalysis of Sn4+and further promoted the condensation process of benzaldehyde and cyclopentanone.In this thesis,garden waste,as a raw material,was used to investigate the process of hydrothermal conversion into biochar and fuel precursors in the DES system.This work developed a new way to realize the utilization of garden waste,and provided certain theoretical support for the technology development of biomass conversion and utilization. |
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