Abstract The present work studies the effects of the crystallinity level of cellulose on the primary reactions during the slow and fast pyrolysis conducted in a wire-mesh reactor at 40 °C/min and 6000 °C/min, respectively. The sugars present in the water-soluble intermediates were analysed in a chromatogram equipped with a Q-exactive high-resolution mass spectrometer. The products in the washed primary tars were quantified through GC/MS. Slow pyrolysis experiments were also performed in a thermogravimetric analyser at four different heating rates (5, 10, 20 and 40 °C/min). All experimental data was used to develop a modified kinetic model that considers the effects of crystallinity on cellulose pyrolysis, which is based on the cellulose sub-mechanism of the Bio-PoliMi kinetic model. The kinetic parameters of each reaction in the modified model were calibrated using a two-step fitting procedure. The experimental results show that low crystallinity promotes the dehydration reactions in the cellulose solid base and the formation of oligosaccharides in the water-soluble reaction intermediates, increasing the formation of furans and decreasing that of levoglucosan in the final primary tar. The effect of crystallinity on the pyrolysis characteristics of cellulose is weaker during fast pyrolysis than during slow pyrolysis. The isoconversional kinetic approach of cellulose pyrolysis presents a low initial activation energy of the pyrolysis of amorphous cellulose, which is close to the activation energy of cellulose hydrolysis. Assuming that the amorphous region of cellulose decomposition path prefers depolymerization through hydrolysis accompanied by the dehydration of nearby hydroxyl group, the modified kinetic model succeeds to predict the effect of crystallinity on the thermal stability and the yields of char, levoglucosan and furans during cellulose pyrolysis.

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结晶度对纤维素热解影响的实验和动力学建模研究

摘要 目前的工作分别研究了在丝网反应器中以 40 °C/min 和 6000 °C/min 进行的慢速和快速热解过程中纤维素的结晶度水平对初级反应的影响。在配备 Q-exactive 高分辨率质谱仪的色谱图中分析存在于水溶性中间体中的糖。洗涤后的初级焦油中的产物通过 GC/MS 进行定量。还在热重分析仪中以四种不同的加热速率（5、10、20 和 40 °C/min）进行了缓慢热解实验。所有实验数据都用于开发改进的动力学模型，该模型考虑了结晶度对纤维素热解的影响，该模型基于 Bio-PoliMi 动力学模型的纤维素子机制。使用两步拟合程序校准修改模型中每个反应的动力学参数。实验结果表明，低结晶度促进了纤维素固体基质中的脱水反应和水溶性反应中间体中低聚糖的形成，增加了最终初级焦油中呋喃的形成并减少了左旋葡聚糖的形成。结晶度对纤维素热解特性的影响在快速热解过程中比在慢速热解过程中弱。纤维素热解的等转化动力学方法呈现出无定形纤维素热解的低初始活化能，接近纤维素水解的活化能。