芒草细胞壁孔隙度和聚合物特性影响木质纤维高效酶解产糖产醇的研究

发布时间：2021-03-02 12:25

　　芒草是优质的生物能源植物,由于其生物质产量巨大,可用于木质纤维乙醇和相关化学产品的生产。目前纤维素乙醇已作为优良的添加剂加入到汽油中以减少碳排放。纤维素乙醇的生产大体包含三个主要步骤:理化预处理部分裂解植物细胞壁聚合物,纤维素复合酶降解产生可溶性糖,酵母发酵生产乙醇。然而,木质纤维素固有的抗降解屏障,不仅使生产成本高、还会对环境产生第二次污染。木质纤维素的抗降解屏障主要由细胞壁组分,聚合物特性以及复杂细胞壁网络结构共同决定。尽管生物质的孔隙度是决定木质纤维素酶解产糖产醇效率的重要综合因子,但有关植物细胞壁聚合物特性和细胞壁网络是如何影响孔隙度的报导甚少。此外,基于细胞壁结构的多样性,不同的预处理对细胞壁组分、多聚物的特性以及键链接方式的影响尚缺乏一个优化评判标准。本研究首次利用DY 11和DB 15染料代替传统DO 15和DB 1染料作为西蒙染色法的染色剂,并对新染色方法的稳定性及其在测量生物质表面可及性中的应用潜力进行了评估。利用改进后的染色方法,研究了芒草生物质孔隙度对酶解效率的影响。进一步利用四组具有不同细胞壁组分的代表性芒草材料,利用热水预处理（LHW）和酸碱预处理（H

【文章来源】：华中农业大学湖北省 211工程院校 教育部直属院校

【文章页数】：163 页

【学位级别】：博士

【文章目录】：
摘要
Abstract
Abbreviations
1 Introduction
    1.1 Global energy situation
    1.2 Lignocellulose-based biofuels
        1.2.1 Opportunities for lignocellulosic biofuels production
        1.2.2 Challenges for lignocellulosic biofuels production
        1.2.3 Miscanthus,a dedicated bioenergy crop
    1.3 Plant cell wall
    1.4 Cell wall chemistry influencing cellulose accessibility and digestibility
    1.5 Wall polymers and their features influencing cellulose accessibility and digestibility
        1.5.1 Cellulose
        1.5.2 Hemicelluloses
        1.5.3 Lignin
        1.5.4 Pectins
        1.5.5 Proteins
    1.6 Pretreatment for enhancing lignocellulose accessibility and digestibility
        1.6.1 Alkali pretreatment
        1.6.2 Acid pretreatment
        1.6.3 Liquid hot water pretreatment
    1.7 Biomass surface area（porosity）
        1.7.1 Measurements of surface area/porosity
        1.7.2 Simons?Stain
        1.7.3 Congo red stain
        1.7.4 Enzyme adsorption
        1.7.5 Nitrogen adsorption
        1.7.6 Water Retention Value
    1.8 Enzymatic hydrolysis of lignocelluloses
        1.8.1 Inhibition of cellulase enzymes by hemicelluloses/lignin
        1.8.2 Application of additives（surfactants）to alleviate lignin inhibition
    1.9 Yeast fermentation for ethanol production
    1.10 Objectives of the study
2 Methods and materials
    2.1 Collection of plant materials
    2.2 Plant cell wall fractionation
    2.3 Colorimetric assay of hexoses,pentoses and uronic acids
    2.4 Total lignin assay
        2.4.1 Determination of acid-insoluble lignin
        2.4.2 Determination of acid-soluble lignin
    2.5 Quantification of lignin monomers by HPLC
    2.6 Hemicelluloses monosaccharides determination by GC-MS
        2.6.1 Sample preparation
        2.6.2 Standard solutions preparation
        2.6.3 TFA hydrolysis
        2.6.4 Derivatization of monosaccharides to alditol acetates
        2.6.5 GC-MS analytical conditions
    2.7 Detection of cellulose crystallinity index（CrI）
    2.8 Determination of cellulose degree of polymerization（DP）
        2.8.1 Sample preparation
        2.8.2 Cellulose DP assay
    2.9 Biomass characterization by microscopy and spectroscopy
        2.9.1 Scanning electron microscopy（SEM）
        2.9.2 Fourier transform infrared（FTIR）spectroscopy
    2.10 Measurement of biomass porosity
        2.10.1 Solvent exchange drying
        2.10.2 Dye preparation for Simons?stain
        2.10.3 Adsorption studies of Simons?stain
        2.10.4 Simons?stain assay
        2.10.5 Congo red staining
        2.10.6 Enzyme adsorption
        2.10.7 Nitrogen adsorption
        2.10.8 Water retention value
    2.11 Biomass pretreatments and enzymatic saccharification
        2.11.1 LHW pretreatment
2SO₄ pretreatment">        2.11.2 H₂SO₄ pretreatment
        2.11.3 NaOH pretreatment
        2.11.4 Direct enzymatic hydrolysis
        2.11.5 Surfactant-assisted enzymatic hydrolysis
    2.12 Yeast fermentation and ethanol estimation
    2.13 Statistical interpretation of correlation coefficients
3 Results
    3.1 Adsorption studies for optimal parameters of Simons?staining technique
    3.2 Optimal LHW and chemical pretreatments for enhancing biomass enzymatic saccharification
    3.3 Tween-80 co-supply for a complete biomass enzymatic hydrolysis
    3.4 Optimal pretreatments and Tween-80 co-supply for the highest bioethanol production
    3.5 Large extractions of wall polymers under optimal pretreatments
    3.6 Distinct alterations of wall polymer features from optimal pretreatments
    3.7 Characteristic changes of biomass morphology and wall polymer linkages from optimal pretreatments
    3.8 A significant increase of biomass porosity under optimal pretreatments
    3.9 A key factor of biomass porosity on biomass enzymatic saccharification
    3.10 Integrative impact on biomass enzymatic saccharification
    3.11 The mechanism for complete biomass saccharification and highest bioethanol production
4 Discussion
5 Conclusion
6 Summary and future prospects
    6.1 Summary
    6.2 Prospects
References
Appendix1:Reagents/buffers formulation
Appendix2:Regression equations of standard curve
Appendix3:Profile
Appendix4:Publications
Acknowledgement



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