High Efficient Deconstruction Of Lignocellulose By Deep Eutectic Solvent And The Application Of The Deconstructed Components

With the depletion of fossil fuels and the increasing demand for energy,it have been become the tendency of global energy development to exploit the eco-and renewable energy materials.Particular attention has been put in replacing the fossil fuels and petroleum-based derivatives with the abundant,renewable and biodegradable lignocellulose that are more environmentally friendly,improving the environmental benefits and alleviating the pressure from conventional energy shortage.But the biomass recalcitrance caused by the hierarchical structure at multiple scales and the complex structure-activity relationship of lignocellulosic components hinders the modification and functionalization of lignocellulose.Therefore,it is crucial to break the biomass recalcitrance and deconstruct lignocellulose matrix to improve the high-value functional applications of the deconstructed lignocellulosic components.However,there still exists tremendous challenges:1)the low efficiency of lignocellulose deconstruction;2)the difficulty of tailoring green and low cost solvent;3)the tedious step of the multifunctional applications of deconstructed components.Here,the low-cost and abundant lignocellulose as starting materials was deconstructed by the cheap and environmental friendly deep eutectic solvents(DESs).The interactions among different DESs are explored at the molecular level through a combined theoretical calculation and experimental analysis.Furtherly,we also analyze the effect of the DESs’ interactions on the efficiency of lignocellulose deconstruction.The principle of acid multi-site solvent is proposed to design the novel DESs to improve the efficiency of lignocellulose deconstruction toward the comprehensive utilizations and functional applications of lignocellulose.The main work and results of this thesis are as follows:(1)DESs prepared from Choline Chloride(ChCl)as hydrogen bond acceptor(HBA)and three hydrogen bond donors(HBD)-oxalic acid,glycerol and urea-were evaluated for treatment of poplar.The molecular interactions of different DESs system(e.g.,hydrogen bond acidity,hydrogen bond acceptability)were explored by density functional theory calculation(DFT)and Kamlet-Taft solvatochromic parameters.The results indicated that both of all DESs exists anionic hydrogen bonds and cationic hydrogen bonds between HBA and HBD.ChCl/oxalic acid DES has the largest hydrogen acidity and hydrogen bond acceptability,followed by ChCl/urea and ChCl/glycerol.Accordingly,ChCl/oxalic acid displayed the highest lignin fractionation efficiency,up to 90%.ChCl/glycerol possessing the lowest hydrogen acidity and hydrogen bond acceptability has poorest efficiency of lignin removal(<4%).(2)In terms of the intrinsic structural-activity relationship of lignin,we explored the ineffective separation of lignin by choline chloride/glycerol DES.A novel three-component DES(3C-DES,ChCl/glycerol/AlCl3·6H2O)with double hydrogen bond acceptor was designed based on an acidic multisite coordination theory to improve the efficiency of lignocellulose deconstruction in ChCl/glycerol DES.The Lewis acid properties and the multiple Cl-site of AlCl3·6H2O can enhance the hydrogen bond acidity(α=1.99)and hydrogen bond acceptability(β=0.68)of ChCl/glycerol DES,allowing it to efficiently cleave both the H-bonds and ether bonds in lignin.Therefore,the lignin fractionation efficiency was significa ntly improved from 3.61%to 95.46%,and the lignin purity reached 94±0.45%.(3)Based on an acidic multisite coordination theory,this work designed the novel and single hydrogen-bond-acceptor glycerol/AlCl3·6H2O DES that is featured with high hydrogen bond acidity(α=1.9)and high hydrogen bond acceptability(β=0.66)to deconstruct lignocellulose and convert the cellulose resuides.The lignin removal efficiency is 71.8%and cellulose residues is 55%by such glycerol/AlCl3·6H2O DES at 110℃ for 4 hours.Meanwhile,it accompanied with synchronous preparation of fluorescent carbon quantum dot during lignocellulose deconstruction process.Furthermore,the cellulose residues were converted into the uniform amorphous carbon sphere with uniform size around 5.8-6.1 μm via carbonization reaction(160℃ for 4 hours)in glycerol/AlCl3·6H2O DES.(4)Lignin component was in-situ and fast removed from wood using ChCl/oxalic acid DES,which can eliminate the light absorption of lignin and brownish color of wood without destroying the cellulose skeleton structure.And then it can be further compounded with refractive index matching epoxy by vacuum impregnation to prepare the optical transparent wood.The obtained transparent wood has a high tensile strength(58 MPa)and bending strength(123 MPa),improved optical transmittance(90%)as well as effective light management,which is potential to apply in energy-efficient building.(5)The high-performance macromolecular film(denote as lignocellulosic film)was fabricated by two step strategy:first,the deconstruction of lignocellulose by a combined ChCl/oxalic acid DES treatment and mechanical ultrasound;second,the structural recombination of the fibrillated cellulose and lignin components.Cellulose has the mutual entanglement by massive hydrogen bond.The intertwining cellulose reinforced by a percolating lignin network.Therefore,the obtained lignocellulosic film demonstrates the integrated features of high mechanical strength(80 MPa),improved thermal properties(thermal degradation temperature of 343℃)and water stability(water contact angle of 98.1°),excellent degradability(the complete degradation of lignocellulosic film after 47 days of burial in the soil).