【作者】 孙永昌；

【导师】 孙润仓；

【作者基本信息】 北京林业大学 ， 林产化学加工工程， 2014， 博士

【摘要】 生物质不论是转化为材料还是能源,高值化利用的关键还是组分的高效、清洁、经济分离。有效的将三大素以完整分子形式提取出来,各自加以利用,才能达到高值化利用的目的。本文选用柽柳和桉木为原料来开展生物质能源高值化利用研究。针对木质素组分高效、清洁、绿色分离途径和复杂结构性能表征两方面问题进行了系统论述。主要采用有机溶剂体系、碱性溶液体系和离子液体体系对木质素进行提取分离,全面分析了木质素在不同溶剂体系下的溶解规律及物理化学性质；研究了纤维板中木质素在热压过程中的迁移规律,建立了纤维板性能与木质素结构变化的构效关系；提出将离子液体-有机溶剂体系用于木质纤维原料全溶,并将该技术引入到木质素选择性分离研究。同时率先将离子液体-水体系引入到木质素的溶解及降解过程中,提出了降解机理,探索了木质素转化为能源及化学品的高值化利用工艺和机理。为离子液体在木质纤维组分分离及转化方面提供了理论依据。采用有机溶剂、碱性溶液体系分别对木质纤维进行溶解,提取木质素。分析得出有机溶剂能够有效的从柽柳中分离出木质素,该木质素具有较高分子量(1585-4730g/mol)及较多的S型结构单元。碱溶性木质素具有均一的结构单元,含有相对较高含量的G型木质素(guaiacyl units)结构单元。柽柳中有机溶剂木质素的主要连接结构是p-0-4’芳基醚键连接结构,占总木质素样品中侧链含量的相对比例为73%,其次是p-β’、p-5’和β-1’结构连接,分别占19%、3%和2%。有机溶剂木质素具有较高的热稳定性,这与其结构及分子量有直接关系。采用轻度球磨、温和提取磨木木质素MWL的方法,随后用有机溶剂和碱性溶液连续抽提得到细胞壁不同部位的OL(有机溶剂木质素)和AL(碱木质素)。MWL、OL和AL的得率分别为6.7%、17.7%和15.3%。得到有机溶剂木质素糖含量相对较低(0.79%),碱性木质素糖含量较高(1.86%),说明有机溶剂和碱性溶剂提取能够破坏木质素与半纤维素之间绝大部分连接键LCC。二维核磁共振HSQC分析表明柽柳木质素结构为GSH结构类型,主要连接结构p-0-4’占总侧链相对值在68.4-79.0%,β-β’结构含量在17.3-22.3%内,此外,还检测到少量的苯基香豆满(2.2-5.6%)和螺旋二烯酮结构(1.5-5.0%),其中γ位发生乙酰化作用的β-O-4’结构含量最高为7.9%。热压纤维板中酸不溶木质素和总糖含量比原料分别提高了13.5%和8.9%,有利于“无胶粘合”。纤维板的内结合强度高达1.81MPa,远远高于国标要求(0.6MPa)。热压后的纤维板中木质素p-O-4’结构从60.1%上升到69.2%(绝对值),意味着木质素分子之间存在缩合作用。31PNMR分析表明S型木质素结构单元更容易缩合,而G型单元易于解聚。热压过程中木质素的缩合和解聚均存在,是一对竞争性的反应。该发现为深入研究无胶纤维板粘合机理提供参考,具有很高的工业应用前景。从廉价和功能化两个角度出发,合成具有特殊性能的功能化离子液体1-丁基-3-甲基咪唑乙酰磺胺盐[Bmim][Ace],将离子液体-有机溶剂体系引入到木质纤维原料的全溶和木质素的选择性分离,有效提高了木质素得率,为提高木质纤维素的酶解效率“扫清”障碍。结果表明,IL-甲苯体系提取得到的木质素最多。指出木质素得率受有机溶剂介电常数(ε)影响,介电常数越小,木质素得率越高。离子液体-有机溶剂体系增强了木质纤维原料的全溶效果和木质素得率,分析表明离子液体回收率平均在94.6%以上,且结构未发生改变,循环使用3次提取效率未发生较大改变。采用不同离子液体体系对原本木质素进行溶解和再生,探讨降解机理。分析表明,反相溶剂再生木质素的能力顺序为：酸性水溶液>水>>乙醇,离子液体对木质素的降解能力顺序为：[Emim][OAc]>[Bmim][HSO4]>[Bmim]C1>[Bmim][BF4]。降解反应和缩合反应均存在于离子液体对木质素的降解和再生过程中。随反应温度上升,酸性离子液体中S型单元容易脱除甲氧基(-OCH3),导致G型结构单元含量升高,S/G值变小,木质素分子量显著降低(Mw=630g/mo1)。β-0-4’结构的断裂导致非缩合的S和G结构单元中羟基(-OH)含量上升。此外,经过离子液体体系再生后木质素具有“蜂窝”多孔小球结构,这种小分子量的木质素可以用在材料制备领域,如多孔吸附材料等,给木质素应用开辟了新的研究方向。率先将ILs-H20均相体系引入到了木质素溶解及降解过程中。重点分析对木质素的降解能力及降解机理。结果表明：ILs-H20体系对木质素的降解主要分为两个阶段(以离子液体质量分数为5-65%和66-100%划分),在两个阶段中引起降解的主导作用不同。表明水能代替一部分离子液体,有利于木质素降解。创新性的研究了离子液体中木质素降解产物的类型及分子量,总结出木质素在离子液体中降解的主要原因是由于两种不同强度氢键作用力竞争导致。更多还原

【Abstract】 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.更多还原