Green Method Disassembly Of Lignocellulose For Cellulose And Lignin And Their Conversion

Lignocellulosic biomass,one of the most abundant renewable and promising resources on the earth,is composed of cellulose,hemicellulose and lignin.Lignin is a kind of natural amorphous organic polymer with a three-dimensional network structure formed by a series of carbon-oxygen bonds and carbon-carbon bonds.Lignin,cellulose and hemicellulose form a plant cell wall,which is ubiquitous in biomass resources.In order to dissolve lignin and cellulose selectively under mild conditions and prepare corresponding biomass macromolecule materials,researchers designed and developed inorganic saline compounds and deep eutectic solvents(DESs)systems.Inorganic salt hydrates,such as LiCl-5H2O,LiBr3H2O and LiClO4.3H2O,are used to dissolve cellulose by controlling the condition of the acidity,moisture content and the cationic species of inorganic salts.Zinc chloride salt hydrate has good solubility for cellulose,hemicellulose and other polysaccharides,but limited solubility for lignin,which provides an opportunity for the determination of lignin content in lignocellulose.The deep eutectic solvent(DES)is a transparent mixture with abnormally low freezing point,like ionic liquid solvent system,which can be obtained by composing of at least a kind of hydrogen bond donor(HBD)and the corresponding hydrogen bond acceptor(HBA).These DESs have a series of advantages,such as low price,ease of preparation,non-flammability,non-volatility and recyclability,which make them environmentally friendly.As for DESs,the selectivity of lignin extraction is higher than cellulose.Therefore,the zinc chloride hydrate and a series of DESs using choline as hydrogen bond donor(HBD)were used to selectively dissolve cellulose and lignin in grass and cork wood for the high-value utilization of lignin and cellulose.In the Chapter 2,on the basis of the work of previous senior in our laboratory,Zinc chloride tetrahydrate was used as the solvent to dissolve and hydrolyze hemicellulose and cellulose quickly and completely,while lignin can be remained.In order to prove that the solid residue obtained from the process of lignocellulosic separation under this condition is lignin with a high purity,elemental analysis,thermogravimetric analysis(TGA),infrared spectroscopy,X-ray diffraction(XRD),scanning electron microscopy(SEM),gel permeation chromatography(GPC)and two-dimensional nuclear magnetic resonance(HSQC)were used to characterize the solid.It was found that only a small amount of monosaccharide was detected in different kinds of biomass hydrolysis filtrate,indicating that acid zinc chloride method could almost completely remove the carbohydrate of biomass.In addition,the method also can be applied to different types of lignocellulose,including wheat straw,bamboo powder,rice husk,etc.,not only highly purified lignin,but also high yield of glucose and xylose can be obtained.Which provide a good idea for the lignocellulose decomposition and comprehensive utilization.The lignin extracted by the method of Chapter 2 is used as raw material.In Chapter 3,we synthesized CuFeS,nanocrystals firstly.In the CuFeS2/H2O2 reaction system with the presence of HO·,the conversion rate of lignin can reach more than 85%and the selectivity of oxalic acid more than 30%.As a renewable raw material,the natural lignin could be degraded to carboxylic acids under mild reaction conditions successfully.In the work of Chapter 4,we changed the previous reaction route to completely avoid the zinc ion pollution,using the DESs to dissolve the lignin selectively,while retaining the cellulose framework of Bashar wood.Then the polyacrylic acid(PAA),whose refractive index is close to cellulose,was used as the filling polymer material to prepare transparent wood.According to Sun's work,polychromatic carbon dots were synthesized by using citric acid and urea as raw materials.The white light of mixed carbon dots at 365 nm were obtained with the mass ratio of 1:3:2 of blue carbon dots,green carbon dots and red carbon dots.Finally,carbon dots were introduced into transparent wood to obtain a packaging film suitable for the preparation of white LED.Inspired by the work in Chapter 4,we then explored the preparation of green solvent that can selectively dissolve cellulose,namely choline/L-lysine hydrochloride solution system,in which wheat straw cellulose can be well dissolved to form a uniform solution with long stability.High molecular weight wheat straw cellulose(DP>3000)was successfully dissolved in it,and the solubility can reach 3%?5%.In Chapter 6,on the basis of our work in Chapter 3?we further studied the dissolution process of lignin in DESs and found that three-component DES can dissolve lignin more completely,realizing the Friedel-Crafts reaction in green solvent with DMF as the co-solvent,which has become a promising new generation of green solvent.Dimethoxymethane(FDA)can be used as a cross-linking agent to connect aromatic of lignin,and microporous polymer materials can be obtained through Friedel-Crafts reaction.The products were further carbonized to improve the porosity and used as anode materials for supercapacitors.In summary,in this paper,we use green solvent as a starting point to dissolve,extract and degrade lignin and cellulose from agricultural waste and cork wood.Several biomass-based polymer materials were prepared and DESs were recycled,aiming to realize the green utilization of biomass resources.