【作者】 姚燕；

【导师】 骆仲泱； 周劲松； 倪明江；

【作者基本信息】 浙江大学 ， 环境工程， 2008， 博士

【摘要】 生物质快速热裂解技术由于能够高效生产液体燃料潜在替代品——生物质热解油(生物油),近些年来受到国内外研究者的广泛关注。然而生物油稳定性差、水分含量高、粘度大和具有腐蚀性,难以直接利用,低品位已成为制约生物质快速热裂解技术商业化发展的主要瓶颈,当前生物油提质改性的基础理论研究是该领域的重点与难点。基于此,本文结合国家自然科学基金,对生物油改性技术进行了系统的研究。对现有生物油分离技术评价的基础上,选用先进的分子蒸馏技术,在避免热敏性生物油结焦的情况下,成功将生物油预分离为轻、中和重质三种馏分,轻质和中质馏分的产率之和达85 wt%,回收率高达97%,是其它蒸馏方式无可比拟的先进技术。对三种馏分理化性质进行深入的分析,得到轻质馏分具有含水量高、流动性好、酸性强和稳定性差的特点,其主要由易挥发低沸点酮、醛以及羧酸等化合物组成;中质馏分产率低,含水量少,具有一定流动性,化学成分以酚类为主;重质馏分在常温下近似固态,无水分,热值较高,不含低沸点成分。依据化学族类,将各馏分的成分归类,探讨蒸馏温度与馏分化学成分的内在联系,以及运用统计方法,评价分子蒸馏在生物油分离方面的应用性。通过热重分析仪开展低升温速率下氮气和空气气氛中生物油三馏分的热裂解动力学研究,结合国内外文献和馏分的理化性质,分析热失重过程TG和DTG曲线的变化趋势。在此基础上建立生物油表观动力学模型,进行热裂解动力学参数求解,模型计算结果与试验结果拟合良好。对酸性强的轻质馏分进行酯化精制研究。首先在玻璃反应釜中以乙酸和乙醇酯化为模型反应,设计正交试验,确定三种不同强酸性阳离子交换树脂催化酯化的最佳反应工况。然后在模型反应的基础上,开展轻质馏分在同种催化剂作用下的酯化精制研究。经过酯化后,馏分的物理性质得到一定改善,GC-MS对产物成分的鉴定发现有5种酯类化合物生成,同时还会伴随有大量缩醛和少量醚类化合物。最后结合文献分析,提出了阳离子交换树脂催化生物油轻质馏分的酯化反应机理。针对轻质馏分稳定性差的缺点,开展负载型贵金属催化剂Ru/γ-Al2O3低温下催化加氢试验研究。选取具有代表性的七种模型化合物,在不同反应温度、氢气压力和进料速率下进行加氢试验,获得模化物加氢反应途径。然后,研究同样反应条件下真实馏分的加氢.讨论反应条件与产物分布的内在联系。通过凝胶渗透色谱的分析结果可知,经过加氢精制后的轻质馏分,稳定性有所提高。最后根据DFT理论建立的分子电荷密度模型,利用商业软件Material Studio中Dmol3模块的PW91方法对模型化合物1-羟基-2-丙酮、糠醛、丁子香酚、乙酸等的反应活性和稳定性进行理论研究;得到分子的前线轨道能量EHOMO、ELUMO以及△E(ELUMO-EHOMO),Mulliken电荷布居和Fukui指数等数据判断加氢反应活性位,并预测加氢反应途径和产物,与试验结果较好吻合。量子化学的研究为生物油加氢机理研究提供理论支持。更多还原

【Abstract】 The bio-oils produced by fast pyrolysis of wood has the potential to used as a substitute for traditional liquid fuel, such as gasoline and diesel oil; however, the crude bio-oils appear to be not good in quality just because of it’s high water content, instability and corrosion. Here, mechanism study of bio-oil upgrading was performed to improve the quality of bio-oils under the support of National Natural Science Foundation of China.On the basis of an assessment of the existing separation technologies, molecular distillation method is chosen to separate bio-oil into three fractions: light, medium and heavy fraction. Experimental results showed that molecular distillation technology was particularly suitable for bio-oil separation because the maximum yield of light and mid fraction could reach up to 85% and no obvious coke and polymerization were found.Based on the analysis of physical and chemical properties of bio-oil, light fraction has the property of strong acidity, poor stability and good fluidness, which is mainly composed of ketones, aldehydes and acids; medium fraction has less mobility and low water content, which accounts for small part of bio-oil; and heavy fraction, without volatile substance, appears in black solid and relatively high in heat value. The effect of distillation temperature on chemical composition of each fraction was studied according to the chemical composition category. Moreover, statistical calculation showed that molecular distillation is successful in the bio-oil separation. A series of experiments on pyrolysis kinetics of three fractions were done on a thermogravimetric balance to measure weight loss curves both in the air and nitrogen at a low heating rate. The change of TG and DTG curves were well explained according to the physical and chemical characterization of each fraction. The kinetic models of fractions pyrolysis were brought forward and the dynamic parameters were obtained. The kinetic model is in good agreement with experimental data. On the basis of model reaction study of acetic acid and ethanol, the research on the esterification of bio-oil was carried out on three kinds of strong acidic cation exchange resins. The catalytic esterification improved light fraction in physical characterization. The analysis of gas chromatography-mass Spectrometry showed that the chemical properties of bio-oil after upgrading were different from original oil in which most of volatile organic acids were converted into esters. Besides that, acetalization of some components in bio-oil was promoted by the strong acidic catalyst simultaneously. Hydrotreatment of light fraction was performed on the model compounds and light fraction under the catalysis of Ru/γ-Al2O3 catalyst. Seven model compounds were hydrogenated to determine the reaction mechanism of main components of light fraction. The effect of reaction parameters on the product distribution was also investigated based on the experiment of hydrogenation of light fraction. It was found that mild hydrogenation over Ru/γ-Al2O3 can significantly reduce instability of light fraction.The activity and stability of 1-hydroxy-2-propanone, furfural, eugenol and acetic acid were studied by DMol3 program. And the parameters of the geometry, atomic net charges, the atomic frontier electron densities and Fukui index were obtained. The reaction process and products deduce from the calculation were well consonant with experimental results.更多还原