The effect of the biomass components lignin, cellulose and hemicellulose on TGA and fixed bed pyrolysis
The effect of the biomass components lignin, cellulose and hemicellulose on TGA and fixed bed pyrolysis
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DOI：
10.1016/j.jaap.2013.01.012
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发表时间：
2013-05-01
影响因子：
6
通讯作者：
Laborie, Marie-Pierre
中科院分区：
文献类型：
--
作者：
Burhenne, Luisa;Messmer, Jonas;Laborie, Marie-Pierre
生物质的热化学转化在过去几十年中得到了广泛的研究。对于热化学转化过程（如固定床热解）的设计、优化和建模，对热解的正确理解至关重要。然而，大多数类型的生物质分解成气体，液体和固体馏分的机理仍然是未知的，因为热解的复杂性和生物质组成的差异，本研究的目的是找到三个广泛使用的生物质原料的热解行为的特征差异，以优化工业固定床热解的性能。这一目标分三步实现。首先，在热重分析仪（TGA）中研究了三种生物质热解过程中的挥发分动力学。然后，一个一步多组分热解模型与三个独立的平行反应半纤维素，纤维素和木质素的推导出相关的动力学与单组分的分解，并确定它们的量在生物质样品。在最后一步中，在实验室规模的固定床反应器中对研究结果进行了测试，以证明其在工业过程中的适用性。它们分别代表具有高纤维素、半纤维素和木质素含量的生物质。由于木质素是这三种生物质组分中最稳定和最复杂的，它的量被认为是热化学分解过程中的主要控制因素，云杉木材与树皮的热重（TG）曲线被发现移动到约20 K的温度比秸秆和油菜秸秆的TG曲线。这一结果表明，木质生物质的分解需要更高的活化能，木质生物质含有比秸秆更高的量和不同类型的木质素。从负一阶导数曲线（DTG）可以看出，木材的分解过程分为三个阶段：半纤维素分解过程中的肩峰、纤维素分解过程中的峰值和木质素分解过程中的小幅度上升。通过比较，两种草本生物量类型在较低温度下仅分两个阶段分解。草本和木本生物质样品的分解分别在约830 K和900 K下完成，仅留下灰分的固体残留物。衍生的热解模型估计的组成和描述的脱挥发分曲线的每种生物质的工业过程中有足够的精度，虽然相同的活化能集，从文献中，用于每种生物质。在固定床热解实验中，发现类似的特性，在TGA实验。草本生物质具有较高的纤维素和半纤维素含量分解速度更快，并产生了更大的馏分的气体产物比木质素含量较高的木本生物质。根据每次实验后进行的产物分布的评估，木质生物质热解导致比草本生物质热解更大比例的固体产物。我们的结论是，工业固定床热解可以优化不同的生物质原料与纤维素，半纤维素和木质素的特定组合物。(C)2013爱思唯尔有限公司版权所有。
Thermochemical conversion of biomass has been studied extensively over the last decades. For the design, optimization and modeling of thermochemical conversion processes, such as fixed bed pyrolysis, a sound understanding of pyrolysis is essential. However, the decomposition mechanism of most biomass types into gaseous, liquid, and solid fractions is still unknown because of the complexity of pyrolysis and differences in biomass composition.The aim of this study was to find characteristic differences in the pyrolysis behavior of three widely used biomass feedstocks to optimize the performance of industrial fixed bed pyrolysis. This aim was achieved in three steps. First, devolatilization kinetics during pyrolysis of three biomass types was investigated in a thermogravimetric analyzer (TGA). Then, a one-step multi-component pyrolysis model with three independent parallel reactions for hemicellulose, cellulose and lignin was derived to correlate the kinetics with single component decomposition and to identify their amount in the biomass sample. In a final step, the findings were tested in a fixed bed reactor at laboratory scale to prove applicability in industrial processes.Three types of biomass were chosen for this investigation: wheat straw, rape straw and spruce wood with bark. They represent biomass with a high cellulose, hemicellulose and lignin content, respectively. Since lignin is the most stable and complex of these three biomass components, its amount is assumed to be the main controlling factor in the thermochemical decomposition process.The thermogravimetric (TG) curve of spruce wood with bark was found to shift to about 20 K higher temperatures compared to the TG curves of straw and rape straw. This result indicates that a higher activation energy is needed to decompose woody biomass, which contains a higher amount and a different type of lignin than straw. Three wood decomposition phases were distinguished from the negative first derivatives curves (DTG): a shoulder during hemicellulose decomposition, a peak during cellulose decomposition and a smaller rise during lignin decomposition. By comparison both herbaceous biomass types decomposed in only two phases at lower temperatures. The decomposition of the herbaceous, and woody biomass samples was completed at about 830 K and 900 K, respectively, leaving only a solid residue of ash. The derived pyrolysis model estimated the composition and described the devolatilization curves of each biomass with sufficient accuracy for industrial processes, although the same activation energy set, taken from the literature, was used for each biomass. In the fixed bed pyrolysis experiments similar characteristics were found to those in the TGA experiments. Herbaceous biomass with a higher cellulose and hemicellulose content decomposed faster and produced a larger fraction of gaseous products than woody biomass with a higher lignin content. According to the assessment of the product distribution, performed after each experiment, woody biomass pyrolysis led to a larger fraction of solid products than herbaceous biomass pyrolysis. We conclude that industrial fixed bed pyrolysis can be optimized for different biomass feedstocks with a specific composition of cellulose, hemicellulose and lignin. (C) 2013 Elsevier B.V. All rights reserved.