【作者】 杨卿；

【导师】 武书彬；

【作者基本信息】 华南理工大学 ， 制浆造纸工程， 2010， 博士

【摘要】 生物质已被公认为是可再生能源的潜在来源,可以用来替代矿物燃料资源的枯竭。随着化石燃料的消耗和人类对环保的关注,生物质资源的利用已日益引起全世界关注。热解是一种重要的生产能源和交通燃料的热化学转化技术。本实验以麦草为研究对象,通过研究麦草及其三种主要组分在不同热解条件下的热解规律,为实现目标产物的合理调控提供理论指导。本文对麦草中的半纤维素、纤维素和木素的结构分别进行了表征。本实验分离的半纤维素保留了β-D-木糖基、α-L-呋喃阿拉伯糖基结构单元和少量的葡萄糖醛酸;纤维素中主要含有纤维素Iα、纤维素Iβ和少量准晶态纤维素,其结晶度为33.42%;木素是一种具有β-O-4’结构的愈创木酚基-紫丁香基-对羟苯基型木素,其中愈创木酚基结构单元含量较高,而且含有β-5’、β-β’、β-1’和5-5’四种缩合结构单元以及乙烯基醚结构。利用热重分析的方法分别研究了不同升温速率下麦草及其三种主要成分的热解特性,研究结果表明半纤维素比纤维素容易分解,并且两者的热解分别集中在不同的范围内,DTG曲线均只有两个失重峰;而木素的热解发生在一个相当宽的范围内,DTG曲线上出现三个失重峰。当温度超过400℃以后,麦草的热解主要是以木素为主。通过利用Py-GC-MS对麦草及其三种主要成分在四个温度段下的热解产物进行分析,然后初步提出了半纤维素热解形成糠醛以及木素热解形成几种酚型化合物的路径。利用TG-FTIR联用技术,研究了慢速升温速率下麦草及其三种主要成分在热解过程中挥发性气体的释放规律,发现麦草中的半纤维素、纤维素和木素的热解并非是独立地进行的。分别采用Kissinger法、Ozawa法和和分布活化能（DAEM）法对麦草及其三种主要组分热解活化能进行了计算,结果表明:Kissinger法和Ozawa法计算的活化能和频率因子结果比较相近并且Ozawa法的计算结果略高于Kissinger法,但是Kissinge法计算半纤维素和木素动力学参数的拟合程度好于Ozawa法。分布活化能（DAEM）模型不适用于木素的热解动力学分析。本实验利用实验室自行设计的管式炉对麦草及其三种主要组分进行400℃、500℃、600℃、700℃、800℃和900℃的热解研究;通过对气体GC分析表明热解气体主要以H₂、CO、CO₂和CH₄为主,C₂H₄和C₂H₆在一定温度下才存在。GC-MS检测了400℃、600℃和800℃麦草及其三种主要组分热解焦油的主要成分。随着热解温度的提高,除木素外,麦草、半纤维素和纤维素热解焦油的成分差异较大并且热解焦油种类随着热解温度的提高逐渐减少。以600℃热解的固体产物为例,对麦草及其三种主要组分的焦炭进行对比分析。研究结果表明麦草焦炭中的成分主要是以木素热解固体残余物为主本文通过比较三种预处理方法对麦草快速热解特性的影响发现麦草经过热水预处理后热解产物中的苯系物减少同时有利于低分子量化合物的形成。更多还原

【Abstract】 Biomass has been recognized as a potential source for the renewable energy to substitute the declining fossil fuel resources. With the depletion of fossil fuel and the concern of environmental protection, the utilization of biomass resources has attracted increasing worldwide interest. Pyrolysis is a vital thermochemical conversion route for energy and transport fuel production. In this experiment, wheat straw as the research object, theoretical guidance is supplied with studying pyrolysis law of the straw and its three major components in the different pyrolysis conditions to achieve reasonable regulation and control of the target products.In the work, the structural characterization of hemicellulose, cellulose and lignin from was investigated, separately. Hemicellulose isolated in the experiment preserved theβ-D-Xylp andα-L-Araf units as well as a little of glucuronic acid existed, cellulose mainly contained cellulose Iα, cellulose Iβand a few quasi-crystalline cellulose, The lignin was a GSH-lignin withβ-O-4’ structures and several condensed units （β-5’,β-β’,β-1’, 5-5’） and vinyl ether moieties.The thermal decomposition characteristics of the wheat straw and its three major components at different heating rates were explored, which showed that the degradation of hemicellulose was easier than cellulose, both their decomposition focused on different range and only two weight loss peaks appeared in DTG profiles. At pyrolysis temperatures over 400℃, the influence of lignin in wheat straw on wheat straw was obvious during pyrolysis, lignin pyrolysis dominating over that of wheat straw. The pyrolysis products of wheat and its major three components at four phases were analyzed through Py-GC-MS, the pyrolysis pathway of furfura and some kinds of phenol compounds from hemicellulose and lignin, respectively, were also researched. The thermal degradation of hemicellulose, cellulose and lignin in wheat straw was not carried out independently, but there could be interactions, nonetheless the mechanism was not very clear according to the releasing orderliness of volatile gas produced by wheat and its major three components at slow heating rate with TG-FTIR technique.The active energy of wheat straw and its major three components in pyrolysis was determined by Kissinger, Ozawa and DAEM methods, respectively. The activation energy and frequency factor of reckoned by Kissinger and Ozawa formulas were similar and the result of Ozawa method was slightly higher than Kissinger one, while the fitting degree of the Kissinger technique which deduced the active energy of hemicellulose and lignin was better than of the Ozawa one. Distribution of activation energy （DAEM） model did not apply to the thermal decomposition kinetic of lignin. The pyrolysis of wheat straw and its major three components at 400、500、600、700、800 and 900℃was tested on a laboratory-designed tubular furnace.The pyrolysis gas mainly included H₂, CO, CO₂, and CH₄, C₂H₄ and C₂H₆ existed only at certain temperature with GC analysis. The major components of pyrolysis tar from wheat straw and its major three components were detected at 400, 600 and 800℃. As the pyrolysis temperature increased, with the exception of lignin, the pyrolysis tar of wheat straw, hemicellulose and cellulose composition was quite diverse and the sorts of pyrolysis tar gradually reduced. A comparative analysis of coke from wheat straw and its three major components was performed in the case of solid products in pyrolysis at 600℃. Solid residues of pyrolysis from lignin dominated over the main mixture of coke in wheat straw.Benzene series decreased and low molecular weight compounds increased in the pyrolysate after hot water pretreatment of wheat straw were proved by comparing the three kinds of pretreatment methods on fast pyrolysis characteristics of wheat straw.更多还原