Selective Extraction And Seperation Of Cellulose From Biomass By Imidazolium-based Ionic Liquid

With the development of technology and the improvement of living standards of the people, people are paying more attention to environmental problems. Along with the improvement of crop yields, however, the increase in the area of urban greening, the treatment of lignocellulosic biomass solid waste such as straw, wheat straw, corn stover, landscaping, has become thorny problems. Commonly, biomass solid waste processing mainly composed of incineration, piling and landfill. However, there are some negative impacts for the treatments of biomass solid waste to the environment. Such as when long-term piled up biomass solid waste was washed by rain, the pollutants would make surface water and groundwater pollution; the leachate and biogas produced by landfilled biomass solid waste fermentation made serious contamination to the groundwater and threatened people’s lives and property; biomass solid waste incineration largely decentralized open-air burning, which is causing serious air pollution, especially the main factor causing the winter haze. Additionally, the smoke from burning straw seriously impact traffic safety, and could lead to fire which threatened people’s lives and property. The main component in the solid waste of biomass is cellulose, hemicelluloses and lignin. Hemicelluloses and lignin wherein the cellulose are wrapped, and together form a three-dimensional structure, which makes biomass difficult to dissolve in water and conventional organic solvents. However, the cellulose has some advantages such as renewable, thermal-stable, easily biodegradable, environmental friendly, etc. These make cellulose widely applied. Ionic liquids as a green organic solvent were introduced into cellulose field in2002. Because of the advantages of very low vapor pressure, good thermal stability, no burning, easily recovery, and structural properties adjustable, ionic liquids were quick aroused concern of scholars. Because of the dissolution and regeneration of cellulose by ionic liquids, a new field was provided for cellulose research. This thesis was mainly focused on cellulose and Zoysia japonica. The ionic liquids were designed according to the characteristics of cellulose. Then we focused on cellulose dissolution by ionic liquids, and then the mechanism of cellulose dissolution by ionic liquid was investigated. Furthermore cellulose in Zoysia japonica was extracted and regenerated. The primary contents and results are described as follows:i.1-Allyl-3-methylimidazolium chloride ([AMIM]C1) and1-allyl-3-methylimidazolium acetate ([AMIM][OAc]) ionic liquid which had a strong ability to dissolve cellulose were designed and synthesized according to the characteristics of cellulose. Meanwhile [AMIM]C1and [AMIM][OAc] ionic liquid were characterized by1H NMR,13C NMR and FT-IR. The synthetic product was subjected to structural analysis, and was recognized as the ionic liquid to be obtained. The ionic liquids synthesized were under TG-DTG analysis, all of them had a thermal decomposition temperature above200℃which showed good thermal stability. The density (ρ), viscosity (η) and conductivity (σ) of the ionic liquids were investigated from20℃to70℃. The results showed that the density was a little decreased, the viscosity was decreased obviously and the conductivity was increased when the temperature increased. Under the same temperature, the density was increased and the viscosity and conductivity were decreased as the volume of anion increased. The variation of density with temperature of ionic liquid [AMIM]C1and [AMIM][OAc] could be described by Tait equation; the variation of viscosity with temperature of ionic liquid [AMIM]C1and [AMIM][OAc] could be described by Arrhenius equation; the variation of conductivity with temperature of ionic liquid [AMIM]C1and [AMIM][OAc] could not be described by an equation to fit. In our research the chloride salt ionic liquid was more suitable for VFT equation and the acetate ionic liquid was more suitable for the Arrhenius equation.ii. The two ionic liquids synthesized were used to investigate the dissolution of microcrystalline cellulose and filter paper. The solubility of cellulose in ionic liquid ([AMIM]C1and [AMIM][OAc]) was determined by POM. The experiments show that the acetate has a strong electron donating ability, so under the same cation conditions, the ability of forming hydrogen bond with the cellulose was stronger than the chloride ion; to the same anion, the stronger of the electron acceptable capacity for the side chain, the easier to combine with the hydroxyl group of the cellulose to form hydrogen bonds. Instability of hydrogen bonds determined that as the temperature risen, the solubility of cellulose in ionic liquids was increased,iii. The structure and thermal-stability of regenerated ionic liquids were confirmed by1H NMR,13C NMR, FT-IR and TG-DTG analysis. The experiments showed the regenerated ionic liquids maintained the characteristics as the fresh. It seemed that ionic liquids could be regenerated and reused which illustrated that ionic liquid was an excellent renewable solvent. In this way the industrial cost would be reduced, so ionic liquids have broad application prospects.iv. The fresh and regenerated cellulose were studied by FT-IR, solid state13C NMR and XRD analysis. The results showed that ionic liquids were the direct solvent to cellulose and there was no derivatization reaction occurred during cellulose dissolution in ionic liquids. However, in the process of dissolution, ionic liquids destroyed the original structure of the cellulose, resulting in lower crystallinity degree of regenerated cellulose. XRD analysis showed that the cellulose structure was changed significantly during cellulose dissolution and regeneration process, but the TG-DTG analysis showed that this transformation did not affect the thermochemical properties of regenerated cellulose. Still, it had a good thermal-stability.v. According to the experiments, the mechanism of cellulose dissolution by ionic liquid was investigated. And the roles of anions and cations were also studied. The mechanisms of hydrogen bond between ionic liquid and cellulose could be explained by classic EDA theory. The anion in the ionic liquid had a strong electronegativity that the hydroxyl hydrogen would be attracted, thereby becoming a major factor in the destruction of inter-and intra-molecule hydrogen bonds in cellulose. The delocalized π bond in cationic group made H(2) protonated significantly, thereby this proton became to electron acceptor which can accept a lone pair of electrons. This was the reason why cellulose dissolution was improved. The re-combination of hydrogen bonds in cellulose during the regeneration process was random, and mainly determined by the distance between OH…O. Therefore the regeneration process was unordered, and would not be able to form the crystalline as the native cellulose that explained the regenerated cellulose polymorph was transformed from cellulose Ⅰ to cellulose Ⅱ. From the perspective of molecular potential energy, cellulose Ⅱ is the stable state of cellulose Ⅰ.vi. Cellulose was extracted and regenerated from Zoysia japonica by ionic liquid Different pretreatment technologies (high-temperature and high-pressure water pretreatment, high-temperature high-pressure ammonia pretreatment and aqueous NaOH pretreatment) were investigated to Zoysia japonica. The cellulose dissolution and regeneration from Zoysia japonica by ionic liquids ([AMIM]C1and [AMIM][OAc]) was study whether the pretreatments were used or not. It was confirmed that pretreatment could significantly undermine the three-dimensional structure of lignocellulose to improve the extraction capacity of ionic liquids by SEM; as alkaline enhanced, the efficiency of ionic liquids for cellulose dissolution from Zoysia japonica was improved. The regenerated cellulose was investigated by FT-IR, solid-state13C NMR and XRD. The fitting curves showed that the crystallinity of regenerated cellulose decreased and transformed from cellulose Ⅰ to cellulose Ⅱ. And there were no derivatizaition reaction occurred in this process. With alkaline enhancements during the pretreatments, the crystallinity of the regenerated cellulose was reduced. The thermal-stability of regenerated cellulose was maintained as the native cellulose with a high level.