【作者】 李维尊；

【导师】 鞠美庭；

【作者基本信息】 南开大学 ， 环境管理与经济， 2013， 博士

【摘要】 随着科技的进步,人民生活水平的提高,人类对环境的要求越来越高。然而伴随着农作物产量的提高,城市绿化面积的增加,以秸秆、麦草、园林绿化垃圾为代表的木质纤维素类生物质固废的处理成为当前的棘手问题。当前对于生物质固废的处理主要是焚烧、堆置、填埋等。然而这些处理方式均对环境产生一定影响。例如长期堆置的生物质固废在雨水冲刷下,污染物会进入地表水和地下水,污染水体；生物质被填埋后随时间的推移而发酵产生渗滤液污染地下水同时还产生沼气严重威胁周围群众的人身财产安全；当前对生物质固废的焚烧主要是分散露天焚烧,造成严重的空气污染,尤其是冬季焚烧,是造成冬季雾霾的主要因素,此外焚烧秸秆产生的浓烟严重影响交通安全同时易引发火灾,严重威胁人身财产安全。生物质固废中的主要成分为纤维素、半纤维素和木质素,其中纤维素被半纤维素和木质素所包裹,并与半纤维素和木质素共同形成一种三维网状结构,从而使得其难于溶解于水和常规有机溶剂中。然而纤维素具有可再生性、热稳定性、易生物降解、环境友好等优点而被广泛应用。离子液体作为一种新型绿色有机溶剂于2002年被引入到纤维素领域。由于其具有极低的蒸汽压、良好的热稳定性、不燃烧、易于回收、结构性质可调等优点迅速引起学者们的关注。由于离子液体能够很好的溶解纤维素,并使纤维素易于从离子液体体系中再生出来,从而成为纤维素的一个全新方向。本论文以纤维素和北方广泛分布的结缕草为原料,针对纤维素的特性开发新型离子液体,研究离子液体对纤维素的溶解情况,在上述研究的基础上分析探讨了离子液体对纤维素的溶解机制,进而将其应用于结缕草并进行纤维素的提取、再生研究。主要研究结果如下：(1)根据纤维素特性设计离子液体的结构特征,并合成了对纤维素有较强溶解能力的1-烯丙基-3-甲基咪唑氯盐([AMIM]C1)和1-烯丙基-3-甲基咪唑醋酸盐([AMIM][OAc])离子液体,并利用NMR、13CNMR以及FT-IR技术对合成产物进行结构分析并确认为所要获得的离子液体。对合成的两种离子液体应用TG-DTG技术,其热分解温度均在200。C以上,具有很好的热稳定性。在20℃至70oC的温度范围内测定了上述离子液体的密度(ρ)、粘度(η)和电导率(σ)数据。测定结果表明,随着温度的增加,离子液体的密度略有降低,粘度明显降低,电导率增大。在相同温度下,阴离子体积的增大将会使离子液体的密度升高、粘度和电导率下降。离子液体[AMIM]C1和[AMIM][OAc]的密度随温度的变化可采用Tait方程进行描述；其粘度随温度的变化可采用Arrhenius方程进行描述；离子液体[AMIM]C1和[AMIM][OAc]的电导率随温度的变化无法用一种方程进行很好的拟合,即氯盐离子液体更适合用VFT方程描述而醋酸盐离子液体更适合于Arrhenius方程。(2)利用所合成的两种离子液体进行微晶纤维素及滤纸纤维素的溶解研究。利用POM技术测定了纤维素在离子液体([AMIM]C1和[AMIM][OAc])中的溶解度。试验表明,醋酸根具有很强的给电子能力从而导致在相同的阳离子条件下,其与纤维素形成氢键的能力强于氯离子；针对同一种阴离子,咪唑类阳离子的侧链得电子能力越强,其越容易与纤维素的羟基结合形成氢键。氢键的不稳定性决定了随着温度的升高,纤维素在离子液体中的溶解度增大。(3)利用1H NMR、13C NMR、FT-IR以及TG-DTG技术分析确认了再生离子液体的结构及热稳定性,试验证实再生后的离子液体保持原有性质,并未因再生而发生变化,通过研究离子液体的再生产率表明离子液体是一种优良的可再生溶剂,在某种程度上降低了其应用成本,具有广阔的应用前景。(4)利用FT-IR、固体超导13C NMR及XRD技术分析再生前后的纤维素变化情况,证实了离子液体是纤维素的直接溶剂,溶解在离子液体中的纤维素不发生衍生化反应。然而在溶解过程中,离子液体破坏了纤维素原有结构,造成再生纤维素结晶度降低。通过XRD分析表明,经过溶解再生的纤维素,晶型结构发生明显变化,但是通过TG-DTG分析表明,这一变化并未影响再生纤维素的热化学性质,仍具有很好的热稳定性。(5)根据试验研究结果以及当前研究进展分析探讨了离子液体对纤维素的溶解机理,阴阳离子对纤维素溶解的作用以及纤维素在离子液体中的再生机理。离子液体与纤维素通过氢键的溶解机制可由经典EDA理论进行解释。离子液体中的阴离子具有较强的电负性,对羟基氢的吸引力强,从而成为破坏纤维素分子内和分子间氢键的主要因素,直接决定了离子液体溶解纤维素的能力；阳离子基团的离域π键使得阳离子基团的H(2)质子化明显,从而使其成为电子受体,能够接受来自羟基氧的孤对电子,因此促进纤维素的溶解。纤维素在再生过程中自身氢键重新组合是随机的,主要依据O-H…O之间的距离,因此其再生过程是无序的,也就无法形成原生纤维素晶型,由此解释了经过再生的纤维素晶型由纤维素I向着纤维素II方向转变,而从分子势能角度可认为,纤维素II是纤维素I的稳定形态。(6)利用离子液体溶解再生结缕草中纤维素的研究。通过对结缕草应用不同的预处理技术(高温高压水预处理、高温高压氨水预处理和NaOH溶液预处理),研究预处理前后结缕草中纤维素在离子液体[AMIM]C1和[AMIM][OAc]中的溶解及提取情况。利用SEM技术证实预处理能够明显破坏木质纤维素的三维结构,提高离子液体对纤维素的提取能力；而碱性的增强能够提高离子液体对结缕草中纤维素的溶解效率。利用FT-IR、固体超导13C NMR及XRD等技术,分析研究了经离子液体提取的再生纤维素,经拟合表明再生纤维素结晶度下降且从纤维素I转变为纤维素II,在此过程中未发生衍生化反应。随着预处理碱性的增强,再生纤维素的结晶度降低。利用TG-DTG技术表明了经离子液体再生的纤维素其热稳定性与原生纤维素相同,保持较高水平。更多还原

【Abstract】 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.更多还原