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植物生物质多孔介质特性与抗降解屏障的破解
Alternative TitlePorous Media Property and Recalcitrance Deconstruction of Plant Biomass
赵军英
Subtype博士
Thesis Advisor陈洪章
2014-04
Degree Grantor中国科学院研究生院
Degree Discipline生物化工
Keyword植物生物质   多孔介质   抗降解屏障   传质   炼制
Abstract植物生物质的资源化利用被认为是解决环境和能源问题、实现人类可持续发展和生态文明的有效途径,但其进化而来的天然结构形成抵抗物理、化学、生物等降解的屏障,导致转化效率低、成本高,因此解析植物生物质的本征结构及其抗降解性并探索预处理破解抗降解屏障的机制是实现植物生物质清洁高效转化的关键科学问题。本论文以玉米秸秆为研究对象,解析植物生物质本征结构和抗降解屏障的本质,并初步探索破解途径及其机制。 1)通过表征玉米秸秆的形貌和孔径分布,揭示玉米秸秆多孔介质的本质:玉米秸秆是一种以细胞壁和胞间物质为固体骨架形成不同孔径孔隙,供流体存在或传递的多孔介质。首先根据玉米秸秆的形态解剖学将其孔径分为5类:大分子毛细孔隙(3~11 nm),细胞壁毛细孔隙(11~100 nm),胞间毛细孔隙(100~1300 nm),细胞腔毛细孔隙(1.3~50 μm),颗粒中毛细孔隙(50~370 μm)。其次通过低场核磁表征毛细孔隙的复水性能,结果表明节、叶片以及髓芯中的薄壁细胞难以复水。玉米秸秆各器官浸泡复水饱和后,几乎没有自由水存在。因此,在反应、产物分离过程中,毛细管中流体的有效驱替是炼制过程的另一个共性关键问题。 2)从进化角度解析植物生物质天然抗降解屏障并通过主成分分析表明,影响酶解的主要因素是分型维数、迂曲度、阈压和突破压力比,而组分对酶解的影响不显著。因此通过预处理改变原有多孔结构,降低阈压分型维数和阈压是提高酶解率的关键。 3)证明汽爆是破解玉米秸秆原有多孔介质(毛细结构及其传质)屏障的有效方式,提出渗流屏障概念。与原玉米秸秆相比,汽爆后孔隙率增加10.12%,逾渗分形维数增加2.11%,孔径增加3.74倍,体积比表面积减小81.79%,弯曲度减小55.27%,最终使得汽爆后玉米秸秆从非饱和状态到渗流过程中三个关键传质参数得到改进:逾渗概率增加21.33%;阈压值降低86.16%;渗透率增加44.16倍。通过多元线性回归分析表明阈压是影响酶解的主导因素。揭示了汽爆通过降低的阈压值破解抗降解屏障,最终提高酶解率。从过程工程角度揭示抗降解屏障本质,提出渗透屏障的概念:植物生物质多孔介质对传质的阻力。 4)解析汽爆或汽爆集成预处理后产生的新物质、新结构对纤维素酶酶活和酶解过程的影响,提出二次抗降解屏障的概念:植物生物质炼制过程中产生的不可逆组成、结构或性能的变化对其酶解或后续转化的抑制或减弱作用。汽爆强度高于3.97时,以及汽爆集成预处理后,形成结构二次抗降解屏障。采用酚类单体模式物证明,酚醛在浓度为0.05~8 g/L时对纤维素酶酶活的有轻微抑制作用,酚酸类物质对纤维素酶酶活的影响与其浓度有关。 5)采用机械分梳装置有效将汽爆玉米秸秆分为维管组织级分和薄壁组织级分。两级分的比表面积、不同状态水(吸湿水、薄膜水、毛管水和自由水)的横向弛豫时间和含量有显著性差异(P<0.05),薄壁组织级分的非自由水含量明显高于维管组织级分。汽爆玉米秸秆经分级得到的薄壁组织级分和维管组织级分可分别作为酶解和制浆原料。机械分梳装置为秸秆分级提供了有效途径。 6)基于植物多孔介质和抗降解屏障特性,提出生物质炼制工程基础问题包括:植物生物质多孔介质基本参数的检测方法和仪器、传质基本理论;植物生物质多孔介质与酶等相互作用的结合理论、作用理论;植物生物质内源性物质对酶等处理介质的促进或抑制机理;植物生物质预处理对不同抗降解屏障的破解机制;植物生物质预处理过程中产生二次抗降解屏障的机制。并指出通过预处理破解植物多孔结构屏障,提高传质速率是提高植物生物质炼制效率的有效措施。
Other AbstractPlant biomass conversion into biobased products has been considered to be an effective way to solve energy and environment problem for human being sustainable development and eco civilization. However, the natural structure of plant biomass formed in the process of evolution is recalcitrant to the hydrolyzing with physical, chemical and biological methods, leading to low conversion efficiency and high cost. Therefore, analyzing the essential structure and the recalcitrance of biomass and exploring the mechanism of deconstructing recalcitrance by pretreatment are crucial to realize plant biomass conversion cleanly and efficiently. This thesis analyzes the essential of structure and recalcitrance of plant biomass, and explores the deconstruction strategy by taking corn stover as example. 1) By characterizing the morpha and pore distribution of corn stover first, its essential structre was revealed: corn stover is a porous media with cell wall and middle lamella as skeleton, forming pore with different diameter for the storage and transport of flow. Pores of corn stover are classified into five classes according to their morpha and diameter: molecule capillary (3~11 nm), cell wall capillary (11~100 nm), cell lamellar capillary (100~1300 nm), cell lumen capillary (1.3~50 μm) and particle capillary (50~370 μm). Secondly, the rehydration property of different capillary was analyzed with low-field nuclear magnetic resonance. Results demonstrated that node, leaf could hardly be rehydrated. When different organs of corn stover were saturated, there was almost no free water. Therefore the transport of flow in capillary was a key problem for plant biomass refining, especially in the process of chemical reaction and products separation. 2) Analyzing biomass recalcitrance in terms of evolution with principle component analysis. Results revealed that the significant factors affecting enzymatic hydrolysis were fractal dimension, tortuosity, threshold pressure and breakthrough pressure ratio instead of components. Results demonstrated that deconstructing the tight structure, reducing threshold pressure fractal dimension and threshold pressure were effective method to increase enzymatic hydrolysis yield. 3) It was proved that steam explosion was an effective technology to deconstruct the tight structure of corn stover, and the concept of seepage recalcitrance was proposed. Compared with the untreated corn stover, after stream explosion, the porosity increased by 10.12%; percolation fractal dimension increased by 2.11%; pore diameter increased by 3.74 times; specific surface area (based on volume) increased by 81.79%;tortuosity decreased by 55.27%. All these changes in structure made the key mass transport parameters during the process from percolation to seepage improve: percolation probability increased by 21.33%; threshold pressure decreased by 86.16%; permeability increased by 44.16 times. By analyzing with multiple factors regression, it was revealed that only threshold pressure related to enzymatic hydrolysis yield significantly. It was revealed that steam explosion enhanced enzymatic hydrolysis by deconstructing the recalcitrance and subsequently reducing the threshold pressure. Finally, the concept of seepage recalcitrance was proposed in terms of process engineering to reveal the essence of biomass recalcitrance: the resistance of porous plant biomass to mass transport. 4) Reveal the effect of new components and new structure resulted from steam explosion or pretreatment integrated with steam explosion on cellulase activity and enzymatic hydrolysis; and proposed the concept of the second biomass recalcitrance: the inhibiting or reducing effect of irreversible component, structure or property changes after pretreatment on enzymatic hydrolysis or subsequent conversion. When the strength of steam explosion was higher than 3.97 or steam explosion was combined with other pretreatment methods, the second biomass recalcitrance was formed.
Language中文
Document Type学位论文
Identifierhttp://ir.ipe.ac.cn/handle/122111/15532
Collection研究所(批量导入)
Recommended Citation
GB/T 7714
赵军英. 植物生物质多孔介质特性与抗降解屏障的破解[D]. 中国科学院研究生院,2014.
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