Theoretical Analysis on Thermal Pyrolysis of Major Compositions in Tree Leaves | 树叶组成的热解反应及热稳定性的理论解析

Chinese. 采用多组分平行反应模型并结合非线性最小二乘拟合技术,对树叶在惰性氛围中的热重（TG）试验结果进行动力学过程的解析,理论上跟踪各组分的热解特性和规律。结果表明：随着温度的提升,树叶经历脱水、挥发油类物质析出、半纤维素、纤维素以及木质素的依次降解并形成焦炭（即固定碳）等过程。温度150℃后树叶的热失重速率（DTG）曲线的变化特征主要由半纤维素、纤维素以及木质素的热解叠加而成,与木材中主要成分的热解现象相似。半纤维素热解几乎完全生成气体,对碳形成的贡献很小;纤维素则稍有不同。木质素对固定碳的含量贡献最大。相应地,半纤维素和纤维素的份额对应工业分析中的挥发分含量,而固定碳含量则取决于木质素所占的比例。工业分析中挥发分的含量高意味着对应材料的热稳定性差,即可燃性强;对于固定碳的含量来说则正好相反。研究结果为评估植物的热稳定性以及防火树种的筛选提供了重要的依据。

English. The thermo-gravimetric（TG） measurements of leaves in inert atmosphere was analysed by using a multi-component parallel reaction model in conjunction with a non-linear least-square fitting technique,which allowed for close observation on the contribution of individual chemical compositions to the pyrolysis process.The result showed that,with increasing temperature,the leaves experienced both physical and chemical processes,including dehydration,precipitation of volatile oil,successive pyrolysis of hemicellulose,cellulose and lignin,and the formation of chars（fixed carbon）.The trend in the DTG curves over 150 ℃ was mainly a comprehensive result of the mass loss caused by thermal decomposition of hemicellulose,cellulose and lignin,which are similar to those appearing in the pyrolysis of the core compositions in wood.The hemicellulose primarily generated gases during pyrolysis,making little contribution to the formation of carbon,whereas the cellulosic compositions in leaves were slightly different.The lignin had predominated contribution to the formation of the carbon by pyrolysis.As a result,the amounts of hemicellulose and cellulose retained by a leaf mainly corresponded to the content of the volatile matter determined by the proximate analysis,while the content of fixed carbon very much relied on the portion of lignin stored in a leaf.A higher content of volatile matter in a leaf implies a relatively poorer thermal stability of the solid,and hence pointing to a higher flammability of the material;while for the content of fixed carbon is in the opposite.The established recognition would provide an important basis for evaluating the thermal stability of tree leaves and identifying fire-resistant tree species for fire prevention in forest areas.