【作者】 苏肇秦；

【导师】 蒋建新；

【作者基本信息】 北京林业大学 ， 林产化学加工工程， 2012， 硕士

【摘要】 胡枝子是一种豆科灌木,其来源广泛、生长迅速、生物质含量高等特性使之成为了一种非常具有前景的生物乙醇生产原料。本文以胡枝子茎秆为原料,先进行低强度蒸汽爆破(1.25MPa,4min),再使用碱性过氧化氢脱除木质素。处理后的固相经水洗后进行酶水解以考察预处理的效果；液相进行半纤维素和木质素的提取,以分析预处理过程对结构的影响。1.25MPa,4min蒸汽爆破对胡枝子原料化学组分的改变并不明显,除半纤维素发生明显的降解外,纤维素、木质素和抽提物的含量并没有发生大的改变。细胞壁结构在蒸汽爆破之后发生少量的破损,但纤维之间的粘结依旧很紧密,纤维素的可及度不高。在随后的过氧化氢处理中,通过控制底物浓度、过氧化氢用量、温度、反应时间和乙醇用量等因素考察反应条件对木质素脱除量的影响。单因素实验得到的最优条件是底物浓度3.3%、过氧化氢用量0.6g H202/g底物、反应时间24h、温度60℃,此条件下脱去了蒸汽爆破后物料中73.20%的木素。过氧化氢处理对木质素的脱除率最高可以达到88.41%。进行三组过氧化氢脱木素处理,分别得到木质素含量为15%、10%和5%的物料,其酶水解后葡萄糖产量分别为431.8、491.2和432.6mg/g原始原料。随着木素脱除程度的增加,纤维素组分的结晶度上升(50.4%-53.1%),聚合度下降(333.9-229.3),细胞壁结构变得疏松,露出了大量的纤维。木质素组分通过凝胶色谱分析、红外光谱分析、和热分析发现其结构发生了改变,主要是由过氧化氢在碱性条件下生成的活性因子攻击木素分子造成的解聚作用和处理强度继续增加后木素小分子与大分子之间发生的缩合反应。缩合反应将木质素的分子量升高到18,919g/mol,同时增加了木质素热处理后的剩余物质量(从26%上升到31%)。对半纤维素组分进行凝胶色谱分析、糖分析、红外光谱和核磁共振波谱分析之后发现,木素的脱除过程中除去了大量半纤维素,并使其发生降解(分子量从14,090g/mol下降到9062g/mol)。木质素脱除、分离和提取纤维素组分及半纤维素组分的过程中,原料的整体回收率最高可以达到88%,说明本研究中的预处理方法可以在提高酶水解得率的同时进行低损耗的组分分离,从而实现原料全组分的综合利用。更多还原

【Abstract】 Lespedeza crytobotrya is a perennial shrub species of the leguminous genus Lespedeza. The most important advantages of L. crytobotrya with respect to its use as a substrate for bioconversion to ethanol are that it has superior growth characteristics relative to other species and that its stalks contain a relatively large amount of carbohydrate. A combination of low severity steam explosion (1.25MPa,4min) and alkaline peroxide post-treatment of Lespedeza stalks was investigated in order to improve enzymatic digestibility of cellulose, and the removed lignin and hemicellulose were isolated from the filtration after this process.Steam explosion did not significantly change the composition of Lespedeza materials except for hemicellulose. The samples obtained by steam explosion were found to be slightly smoother and looser than the raw material through scanning electron microscopy images.In the post-treatment by alkaline peroxide, the experimental sets included variations in substrate concentration, peroxide content, time, temperature and ethanol content for investigating the delignification. The optimal reaction condition got from single factor experiments was substrate concentration3.3%, peroxide content0.6g H2O2/g substrate,24h, and60℃, resulting in a remove of73.20%of lignin from steam-pretreated material. The maximum delignification reached88.41%as the lignin content of sample was only5%.Samples with lignin content of15%,10%, and5%were produced by alkaline peroxide treatment for analyzing the influence of delignification on cellulose digestibility and the structure of lignin and hemicellulose. The cellulose-rich fractions were characterized by scanning electron microscopy and X-ray diffraction, illustrating a smoother surface, a looser structure, an rising crystalline index (from50.4%to53.1%), and a declining degree of polymerization (from333.9to229.3) with the increase of delignification severity. The glucose yield of the3cellulose-rich fractions were431.8、491.2和432.6mg/g raw material, respectively. The isolated lignin preparations were characterized by gel permeation chromatography, Fourier transform infrared spectroscopy, and thermogravimetric analysis/differential thermal analysis. Depolymerization and condensation occurred during the alkaline peroxide treatment. Condensation increased the thermal stability of lignin (mass of pyrolysis residue went up from26to 31%), and the average molecular weight rose to18,919g/mol with the increase of delignification severity. The isolated hemicellulos preparations were characterized by gel permeation chromatography, Fourier transform infrared spectroscopy,’H NMR spectroscopy. Almost all of the hemicellulose was removed from the material, and was further degraded as the average molecular weight was decreased from14,090to9,062g/mol.The maximum value of solid recovery in those three procedures reached88%, indicating that the consecutive pretreatment conducted in this research can not only enhance the enzymatic hydrolysis of lespedeza stalks, but also achieve the isolation and utilization of full composition with minimal loss.更多还原