生物质低温脱氧及其与热解过程的关联耦合机制研究

Low-temperature deoxygenation, generally referring to the biomass thermal pretreatment below 390 ℃, may find potential extensive application in the reduction of moisture and oxygen content in biomass resources, as well as the improvement embodied in materialized structure and thermal chemical reactivity, which is beneficial for subsequent thermal conversion processes. A deep study into the deoxygenation process, in particular the deoxygenation mechanism, is therefore emerging as the key issue to be addressed in the area of biomass thermal conversion. Since pyrolysis is regarded as one of the main approaches to attain comprehensive high-quality utilization of biomass resources, it is of significant importance to investigate the correlated coupling mechanism between low-temperature deoxygenation and subsequent pyrolysis processes. With a combination of experimental study, theoretical analysis and simulation serving as research tools, this project sets typical agricultural straw in China as the research object. Proceeding from the molecular organization and structure, with due consideration of raw material characteristics, fiber composition, rupture of key perssad and precipitated path of oxygen, the project deeply reveals the evolvement mechanism of straw physical & chemical structure within the deoxygenation process and unveils the modulation mechanism of product quality. The emphasis is laid on the deoxygenation mechanism in this process. In the perspective of synthetical promotion of pyrolytic tristate products quality, coupling mechanism of low-temperature deoxygenation with the subsequent pyrolysis processes that are based on comprehensive enrichment of tristate products is studied, accompanied by a dynamic life cycle analysis (LCA) approach employed for optimization analysis of the comprehensive systematic energy efficiency. The outcome will contribute greatly to the establishment of theories & controlling method for both biomass thermal pretreatment and efficient pyrolytic conversion. This will be fully supportive for offering scientific guidelines to the development of high-quality utilization technologies in biomass field, as well as accelerating large-scale and high-quality exploitation of biomass resources in China.

低温脱氧，通常指390℃以下的生物质热预处理方式，能降低生物质含水量和含氧量，改善物化结构，提高热化学反应性，对后续热转化过程有益。而热解是实现生物质高质化利用的主要途径之一，深入研究低温脱氧过程机理，尤其是脱氧机制，及其与后续热解的关联耦合机制是生物质热转化领域的关键问题。本项目以我国典型农业秸秆为研究对象，采用实验研究、理论分析与模拟研究相结合，基于生物质分子组成和结构，从原料特性、纤维组成、关键基团的断裂、氧元素的析出路径等角度，深入揭示秸秆低温脱氧过程理化结构的演变机制和产物品质的调变机理，并把重点放在脱氧机制上；进而从热解产物有效成分综合富集的角度，研究其与后续热解过程关联耦合机制，并采用动态生命周期的方法对系统综合能效进行优化分析，其研究结果将有助生物质热预处理及热解高效转化理论与控制方法的建立，从而为生物质高质化利用技术的发展提供科学的依据，促进我国生物质资源高质化利用。

低温脱氧可脱除生物质中的水分和过多的氧，同时提高生物质的能量密度和改善生物质的可磨性。鉴于此，本研究对生物质的脱氧特性以及脱氧对生物质热解液化的影响进行了深入分析，并结合脱氧过程中生物质理化结构的演变揭示了生物质低温脱氧机制。经过大量的试验研究和理论分析，该研究对生物质的高效预处理以及生物质的高质化利用提供了理论指导和可靠的科学参考。.研究了生物质模型组分以及天然生物质的低温脱氧过程特性。研究发现，在低温脱氧过程中，半纤维素快速失重（228-317℃），O主要以H2O和CO2的形式析出，纤维素的脱氧温度较高（314-390℃），O的主要析出形式以CO和CO2为主，而木质素在低温脱氧过程中失重较少，O主要以H2O的形式析出，玉米秆与棉秆具有相近的反应区间（220~385℃），O以H2O、CO和CO2等形式析出。.低温脱氧过程中，半纤维素从230℃开始主要发生C-O官能团和OH的脱除，320℃时反应完全；纤维素在290℃后，OH和C-O官能团消失，同时生成大量的C=C、C=O官能团；木质素原样具有较高的OH、C-O以及C=C官能团，随着处理温度升高，木质素各含氧官能团缓慢裂解脱除；棉秆在290℃后主要发生的是OH的脱除，而玉米秆则主要发生脱羰反应。.半纤维素主要脱氧温度区间为230-260˚C，脱除了64.48%的氧，纤维素为290-320℃，脱除了46.32%的氧，木质素脱氧效果不明显，390℃时仅脱除14.80%的氧，玉米秆和棉秆的主要脱氧区间分别在在260-390℃和260-350℃，分别脱除了65.49%和55.10%的氧；随脱氧温度的升高，热值升高趋势也很明显，390℃处理后，纤维素、半纤维素、木质素、玉米秆、棉秆热值分别提升了47.09%、58.71%、10.58%、31.88%、36.39%。.借助快速热解反应试验平台对脱氧生物质的快速热解液化特性进行了研究。研究表明，较低温度脱氧处理（200-290℃）仅降低了生物质热解油的产率，较高温度脱氧处理（320-390℃）还减少了热解油中含氧有机物的种类和产量，提高了芳烃类物质的产量以及选择性。.以生态热力学的理论和方法为基础，对低温脱氧后生物质热解多联产系统的温室气体排放、化石能源投入、可再生性、生态足迹和环境影响等进行系统的分析与评价。结果表明，生物质热解多联产系统具有较好的可再生性，低碳效应和可持续性。