【作者】 徐玉福；

【导师】 胡献国；

【作者基本信息】 合肥工业大学 ， 环保装备及环境监测工程， 2012， 博士

【摘要】 随着传统化石能源逐渐枯竭以及社会可持续发展形势的日益需求,开发新型可再生替代能源成为大势所趋。生物质能源是一种可再生的清洁能源,其中藻类生物质由于其生物量大,繁殖速度快,不占耕地等优势已成为近年生物质能源研究的重点对象。采用热化学转化技术将其转变成发动机代用燃料——生物油,已成为该研究领域的前沿和热点问题之一。然而,针对我国淡水湖泊中经常出现的两种典型生物质微藻——小球藻(俗称“绿藻”)和螺旋藻(俗称“蓝藻”)热液化制备微藻生物油的系统研究尚处于探索阶段,微藻生物油的性能改善方法与措施也有待进一步的研究。同时,生物油的摩擦学特性直接关系着发动机的润滑效率和使用寿命。因此,本文主要从小球藻和螺旋藻热液化制备微藻生物油与提质改性及其摩擦学特性等方面开展相关的研究,旨在为发展新一代发动机代用燃料,为微藻生物油在内燃机上的应用打下一定的基础。具体的研究内容包括以下几个方面：首先,对小球藻和螺旋藻进行了成分等基本物性分析,并通过稀土负载的HZSM-5催化剂对其进行了催化热解,掌握了其热解动力学行为。研究表明,与HZSM-5相比,除La(Ⅱ)/HZSM-5外,其余稀土负载后的催化剂(Ce(Ⅰ)/HZSM-5, Ce(Ⅱ)/HZSM-5, Pr-Nd/HZSM-5和La(Ⅰ)/HZSM-5)对小球藻和螺旋藻都有降低热解活化能的催化作用,其中Ce(Ⅰ)/HZSM-5对小球藻催化效果最佳,Ce(Ⅱ)/HZSM-5对螺旋藻催化效果最好。与HZSM-5相比,它们对热解活化能的降低幅度分别达到47.1%和43.1%,显示了良好的稀土改性催化效果,也为微藻的高效催化液化提供了参考。其次,系统探讨了小球藻催化液化制备生物油的影响规律及其液化机理。考察了催化剂、液化条件等因素对液化行为的影响,测试了生物油的基本物性及其燃烧性能,采用乳化技术对小球藻生物油进行提质改性研究,并应用发动机缸套-活塞环摩擦磨损实验方法探讨了生物油提质前后对缸套-活塞环摩擦学特性的影响,分析其摩擦磨损机理。结果表明,采用Ce(Ⅰ)/HZSM-5催化不仅可增加小球藻生物油产率,还可以改变液化产物的分子组成,特别是可以提高生物油H/C比,降低O/C比,增加碳氢化合物的含量。小球藻的优化液化反应条件为：采用5wt%的Ce(Ⅰ)/HZSM-5为催化剂,在300℃水热条件下催化液化20min,小球藻和溶剂水的料液比为1:10g·mL-1。此条件下生物油产率达39.87%,生物油热值达26.09MJ·kg-1。小球藻生物油的主要成分为醇类、酯类、环烷烃、烯烃、苯衍生物等,经过乳化提质改性后,生物油的基本物性有所改善,热值提高,腐蚀磨损性能得到改善。摩擦学特性的改善归因于油品中的有机物在摩擦过程中在摩擦副表面的吸附、挤压形成的润滑膜,以及腐蚀性成分被稀释所致。然后,研究了螺旋藻催化液化制备生物油的影响规律,分析了生物油的基本物性及其燃烧性能,以催化酯化技术对螺旋藻生物油进行提质改性研究,考察了油品对缸套-活塞环摩擦学特性的影响,分析了其摩擦磨损机理。结果表明,螺旋藻优化的液化催化剂为5wt%的Ce(Ⅱ)/HZSM-5,最高生物油产率达49.71%。螺旋藻生物油的主要成分为羧酸、酮、烯烃、酰胺、醚、酯以及部分环状含N化合物,其中其酸类成分较大,造成其酸值较高,达21.79mgKOH·g-1。经过催化酯化提质后,生物油中酸类成分及含量明显下降,酯类成分增多,生物油的基本物性有所改善,H/C比提高、O/C比降低,热值有较大提高,酯化后油品的摩擦学性能较酯化前明显好转,其中分别采用KF/Al2O3和KF/HZSM-5催化乙醇和甲醇酯化后的油品AEO、HEO、AMO和HMO的平均摩擦系数比反应前分别降低22.52%、9.91%、21.64%和11.41%,磨损量也有不同程度的降低。能谱分析(EDS)和X-射线光电子能谱(XPS)测试结果表明,油品中的有机物在摩擦副表面吸附、挤压形成润滑油膜,以及摩擦生成的Fe2O3化学反应膜,特别是酯化后生物油中的酯基(-COOR)、烷基等被沉积到摩擦面共同起到抗磨减摩作用。最后,分别采用水热液化以及超临界流体液化方法,研究了小球藻和螺旋藻共液化制备生物油的行为及其摩擦学特性。结果表明,水热环境下当小球藻和螺旋藻质量比较接近时共液化具有一定的协同效果,La203是一种相对较好的水热共液化催化剂；超/亚临界醇溶剂体系中微藻的共液化生物油产率有显著提高,在超临界甲醇和超临界乙醇体系中的共液化生物油产率达74.71%和64.43%,是水热环境下最高液化率的2-3倍；共液化生物油的主要成分为醇类、醚类、烃类、芳香族、酯、酮、酸、醛类以及部分含氮化合物等组成的复杂混合物；在超临界流体环境下,醇类不但起到了液化溶剂作用,还充当了反应原料,对产物有一定的酯化改质作用：和水溶剂无催化条件相比,采用La2O3催化或通过超/亚临界醇类体系制备的共液化生物油具有较高的H/C比和热值,同时O/C比和酸值下降,综合性能显著提升。四球摩擦磨损实验结果表明,在15W-40柴油机油中添加10wt%共液化生物油后,油品的摩擦系数及磨损量显著下降,最大降幅分别可达61.8%和32.2%,表明共液化生物油具有良好的润滑效果。分析表明,在摩擦过程中油品有机物中C-C, C-OH, C=O,-COOR等成分在摩擦副表面的吸附、挤压形成的润滑膜,摩擦生成的Fe203化学反应膜,并与部分含N化合物以C-NH2形式沉积到摩擦面以及摩擦形成FeN化学反应膜共同起到润滑作用,显示了良好的应用前景。更多还原

【Abstract】 With the gradual depletion of traditional fossil energy sources and the increasing demand for the sustainable development of society, the development of new, renewable, alternative energy sources has become a general trend. Biomass is a clean, renewable energy source. In recent years, algal biomass has become the focus of biomass energy for such advantages as large quantity, fast propagation, and lack of occupied farmland. The thermochemical conversion technology for the transformation of microalgae into bio-oil as an alternative fuel for engines has become a research frontier and is the focus of this study.Most freshwater lakes in China contain two kinds of typical microalgae biomass:Chlorella (commonly known as "green algae") and Spirulina (commonly known as "blue algae"). However, the systemic thermal liquefaction of these microalgae remains at the exploratory stage. In addition, the performance of microalgae bio-oil, including its tribological properties and upgrading methods, should be further explored because the lubricative efficiency and service life of engines are significantly affected by the tribological behavior of bio-oil.In this paper, related studies on the preparation, upgrading, and tribological properties of the bio-oil derived from Chlorella and Spirulina via thermochemical liquefaction are conducted. This study aims to establish an experimental basis for the development of a new generation of biomass liquid fuels and to promote the application of microalgae bio-oil in internal combustion engines. The specific research topics include the following aspects:First, the basic physical properties including the components of Chlorella and Spirulina were studied. The rare earth-loaded HZSM-5catalysts were prepared via catalytic pyrolysis of the microalgae, and the pyrolysis kinetic behavior was investigated. The results indicate that compared with HZSM-5, except for La(Ⅱ)/HZSM-5, the load of rare-earth catalysts such as Ce(I)/HZSM-5, Ce(Ⅱ)/HZSM-5, Pr-Nd/HZSM-5, and La(Ⅰ)/HZSM-5can lower the catalytic pyrolysis activation energy of Chlorella and Spirulina. Ce(Ⅰ)/HZSM-5has the best catalystic effect for Chlorella, whereas Ce(Ⅱ)/HZSM-5has the best catalytic effect for Spirulina. Pyrolysis activation energy decreased by47.1%and43.1%for Chlorella and Spirulina, respectively. The results show the efficiency of the rare-earth modified catalysts and provide a reference for algae biomass catalytic liquefaction.Second, the catalytic liquefaction preparation and mechanisms of bio-oil from Chlorella were studied systematically. The effects of the catalyst, liquefaction conditions, and other factors on the liquefaction behavior of the microalgae biomass were analyzed. The basic physical properties and combustion performance of bio-oil were tested. Emulsion technology was used to upgrade the Chlorella bio-oil. The piston ring-cylinder friction of the engine as well as wear experiments were used to simulate the changes of wear when fuel is injected into the cylinder wall in internal combustion engines and to analyze the mechanism of friction. The results show that the use of Ce(Ⅰ)/HZSM-5as a catalyst for liquefying Chlorella not only increases the liquefaction yield but also changes the molecular composition of the liquefied products. Moreover, the use of this catalyst can increase the hydrogen-to-carbon (H/C) ratio, reduce the oxygen-to-carbon (O/C) ratio, and increase the hydrocarbon content of the liquefied products. The optimal reaction conditions include: the selection of5wt%Ce(I)/HZSM-5as catalyst, Chlorella-to-solvent volume ratio of1:10g-mL"1, and reaction at300℃for20min. The maximum liquefaction yield reached39.87%, and the heating value of final bio-fuel reached26.09MJ-kg-1. The main components of the bio-fuel from Chlorella are alcohol, ester derivatives, and a number of hydrocarbons. The basic properties, calorific value, corrosion, and wear performance of Chlorella bio-oil improved after emulsion. A better lubricity of the upgrading bio-oil was attributed to organics during oil adsorption on the friction surface to form a lubricant film while the corrosion components in the oil were diluted.Third, the catalytic liquefaction regularity of bio-oil from Spirulina was investigated systematically. Moreover, the basic physiochemical properties and combustion performance of the Spirulina bio-oil were analyzed. Catalytic esterification technologies were used to upgrade the Spirulina bio-oil. The piston ring-cylinder friction of the engine as well as wear experiments were used to test the lubricant performance of the fuels, and the friction mechanism was also investigated. The results indicate that the optimal liquefaction catalyst for Spirulina is Ce(Ⅱ)/HZSM-5at5wt%. The maximum liquefaction yield can reach49.71%. The main components of Spirulina bio-oil are carboxylic acids, ketones, olefins, amides, ethers, esters, and a number of ring compounds that contain N. Spirulina bio-oil has a high acid value of approximately21.79mg KOH·g-1. The acid components of Spirulina bio-oil decreased, whereas the ester components increased evidently after catalytic esterification. Moreover, the basic physical properties of the bio-oil improved; the H/C ratio increased, the O/C ratio decreased, and the calorific value improved significantly. The lubricity of bio-oil after esterification significantly improved. The average coefficient of friction of the esterified fuel such as AEO, HEO, AMO, and HMO were decreased by22.52%,9.91%,21.64%, and11.41%, respectively, and the wear amount decreased as well. Energy dispersive spectroscopy and X-ray photoelectron spectroscopy showed that the adsorption and extrusion of organics on the surface of the friction pairs to form a lubricant film and a tribochemical reaction film such as Fe2O3, especially the ester (-COOR) and alkyl groups of esterified bio-oil, were deposited onto the friction surface, all of which play an antifriction and wear reduction roles.Finally, hydrothermal liquefaction and supercritical fluid liquefaction methods were employed to study the behavior and performance of the co-liquefaction of bio-oil obtained from Chlorella and Spirulina. The studies show the synergistic effects of the co-liquefaction when the quality of Chlorella and Spirulina are close at the hydrothermal liquefaction process. La2—3is an efficient liquefaction catalyst of hydrothermal liquefaction. Super/sub-critical methanol and alcohol can remarkably enhance the co-liquefaction yield of microalgae up to approximately74.71%and64.43%, respectively. These values are approximately two to three times of the maximum yield of hydrothermal liquefaction. The main components of co-liquefaction bio-oil are complex mixtures including alcohols, ethers, hydrocarbons, aromatics, esters, ketones, acids, aldehydes, and a number of nitrogen-containing compounds. Alcohols not only serve as a liquefaction solvent but also act as a reactant and an esterification modifier in a supercritical fluid environment. Compared with the case wherein water is used as a solvent without La2O3as catalyst or the case wherein a super/sub-critical alcohol system is adopted for co-liquefaction of bio-oil from microalgae, the H/C ratio and calorific value of alcohol increased, whereas the O/C ratio and the acid value decreased. The comprehensive performance improved significantly. Four-ball tribometer results show that the co-liquefaction bio-oil has efficient tribological effects because of the reduction in the friction coefficient and wear volume, in which the maximum decreasing range is approximately61.8%and32.2%, respectively, when10wt%bio-oil is added to the15W-40diesel engine oil. The results show that organic groups such as C-C, C-OH, C=O, and-COOR are adsorbed on the friction surface and react with the Fe of the steel substrate to form the lubricant film that also contains Fe2O3. The N-containing compounds deposited on the friction surface in the form of C-NH2and FeN tribochemical reaction films altogether play a lubrication role, which shows good application potential.更多还原