| Lignocellulosic biomass is considered to be one of the most sustainable and renewable enrgy resources that can displace a significant fraction of current petroleum supplies. In some other areas, it can also be used to produce material. However, the key points of biomass utilization is, economically, clean, and highly efficient separation of lignin in the whole macromolecular, and then to make high-value added products, In this study, tamarix and eucalyptus are used as raw materials to study the structure of the main components. Organic solvents, alkali solutions, and ionic liquid-based systems were used to isolate lignin from the biomass. The yields, structure characteristic and physical-chemical properties of the lignin fractions were fully investigated. We focus on the dissolution of biomass in ionic liquds (ILs)-organic solvents systems and selectively isolation the lignin fraction. At the same time, the ILs-water system was fistly introduced into the lignin dissolution and regeneration process. The dissolution mechanism and flowchart were given, and the structure of the regenerated lignin as high value-added products was studied.Different organic solvents and alkali solutions were used to dissolve the tamarix wood powder and isolate the lignin fraction. It was found that the alkali-soluble lignin showed uniform structure and contained a high amount of G type lignin, but the organosolv-lignin is rich in S type lignin. The HSQC results indicated that the main linkages of organoslv-lignin was β-O-4’aryl ether structure, which was amount to73%of the total side chains, followed by lower amounts of β-β’resinol-type (19%of total side chains), trace amounts of β-5’phenylcoumaran (3%), and β-1’spirodienone-type (3%) substructures. The organosolv-lignin showed a higher thermal stability than the alkali-soluble lignin, and this was probably owing to the high molecular weight of the organosolv-lignin.The gentle milling technique was used to isolate the ball-milled wood lignin (MWL). The organosolv-lignin (OL) and alkali-lignin (AL) were successively isolated from the biomass by organic solvents and sodium hydroxide solution. The yields of MWL, OL, and AL were6.7%,17.7%and15.3%(based on Klason lignin), respectively. It was found that the OL fraction was associated with a low amount of carbohydrate (0.79%) as compared to the alkali lignin (1.86%), indicating that the ethanol containing NaOH solution was effective in cleaving the ester and ether bonds between lignin and hemicelluloses. GPC results showed different molecular weights for MWL (2395g/mol), OL (3415g/mol), and AL (1870g/mol). The2D NMR analysis showed that the lignin fraction was GSH type lignin, including the main linkages of β-O-4’(68.4-79.0%, relative amount), β-β’(17.3-22.3%), phenylcoumaran β-5’(2.2-5.6%), and spirodienone linkages (1.5-5.0%). The acetylation occurred at the γ position of the β-O-4’substructure, which amount to7.9%.Results showed that the acid insoluble lignin and the total sugar contents of the binderless board (BB) increased by13.5%and8.9%compared to the original material, respectively, which was in favor of the physical properties of binderless board. The BB showed high internal bond (IB) strength of1.81MPa, which was satisfied the Chinese Standard GB/T11718-2009(0.6MPa). HSQC results indicated an increase of β-O-4’linkages (69.2%) in the EMAL of BB, revealing that the condensation reaction occurred during hot pressing.31P NMR analysis showed that lignin containing S units is preferentially condensed by hot pressing over those containing G units, and G units are easier to degrade than S units. The decomposition and recondensation of lignin were two competitiveness reactions during hot pressing. The study showed a high reference value in binderless board production.Lignin was extracted by the cheap imidazolium acesulfamate IL1-butyl-3-methylimidazolium acesulfamate [Bmim][Ace] from the wood powder. The resulting carbohydrate enriched materials were subsequently extracted with70%ethanol containing1M NaOH. Results showed that the yield of alkaline ethanol lignin (AEL,8.0-23.3%) was relatively higher than that of IL-organic solvents lignin (IOL,11.5-15.4%, based on the Klason lignin content). The increased yield was due to the different conductivities of the co-solvents affected by dielectric constants (ε) of the organic solvetns. It was found that a low dielectric constant of organic solvent resulted in a high yield of lignin. To achieve environmentally friendly biomass processing, the recovery and reuse of ILs is one of the main challenges. The IL used was recycled with the average yield over94.6%, and the structure and properties of the IL was unchanged.Lignin was dissolved in several imidazoulium-based ionic liquids, and subsequently regenerated using ethanol-water mixtures or water, respectively. Results showed that acidic water was effective in precipitating lignin than water or ethanol-water mixture or ehthanol. The degradation ability of ILs followed the order of [Emim][OAc]>[Bmim][HSO4]>[Bmim]Cl>[Bmim][BF4]. The degradation and condensation reactions are both exist in the lignin dissolution and regenerated process. The decreased S/G ratio of regenerated lignin was probably owing to the demethoxylation reaction of S type lignin under the acidic condition. Meanwhile, the demethoxylation of S type lignin leads to increase of G type lignin, which contains more phenolic OH groups. It was also found that the regenerated lignin obtained at high temperatures exhibited higher thermal stability than that obtained at low temperatures. SEM images showed a regular uniform structure of lignin droplets of regenerated lignin ranged from4.5-10.8μm in diameter. The compact structure and alveolate surface of lignin caused by the dissolution and regeneration of ILs suggest a functional material of lignin;ILs-water system was firstly used in lignin dissolution and regeneration, and the mechanism of lignin dissolution was studied. Water was effective in precipitating lignin than the ethanol-water mixture or ethanol. Measurement of lignin yield of different proportions of [Emim][OAc]-water mixtures suggested two different modes with ILs-water system treatment. It was found that the yield of lignin increased with increasing [Emim][OAc] content from5%to65%, implying that water plays a leading role in the system. It should be noted that the yields of lignin decreased in66-100wt%aqueous [Emim][OAc], where ionic liquid is believed to play a major role in the degradation process. GPC results showed that the Mw of regenerated lignin ranged from560to790g/mol. The Mw of regenerated lignin from the pure IL was580g/mol. It can be deduced that a certain amount of water could replace partial ILs and benefit the lignin degradation. The solubilized compounds in ILs were identified by GC-MS analysis. It is believed that the interaction energy of IL-lignin tends to decrease, and the hydrogen bonds between ILs and lignin is weaken or even destroyed by the addition of water. |
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