麻栎木热解过程的热质变化行为及其动力学

Heat and Mass Change Behavior and Kinetics of Quercus acutissima Wood Pyrolysis

为了解麻栎木热解特性,采用TGA/DSC同步热分析仪对其热解过程的失重机制和热行为进行了研究,采用Flynn-Wall-Ozawa(FWO)法和Kissinger-Akahira-Sunose(KAS)法计算了该过程的表观活化能,通过Malek方法得到了麻栎木热解最概然机理函数。研究结果表明:麻栎木的热解过程分为干燥、预热、挥发分析出和炭化4个阶段,在挥发分析出阶段质量损失最大,达71.24%。麻栎木热解过程既包括吸热反应也包括放热反应,随着升温速率的增加,其TG曲线和DTG曲线均向高温方向移动。FWO法和KAS法计算得到的表观活化能(E)范围分别为226.79~258.17 kJ/mol和229.22~260.8 kJ/mol,相关系数(R^(2))均在0.94以上,E随转化率变化趋势一致。Malek法计算结果表明:麻栎木热解机理在转化率小于0.5时符合三维扩散机理(Jander方程);在转化率大于0.5时符合成核生长机理(Avrami-Erofeev方程,n=3/2)。

In order to well know the pyrolysis characteristics of Quercus acutissima wood,the weightlessness mechanism and thermal behavior of pyrolysis process were analyzed by thermogravimetric analysis,the apparent activation energy of pyrolysis process was calculated through Flynn-Wall-Ozawa(FWO)model and Kissinger-Akahira-Sunose(KAS)model,and the most probable mechanism function was obtained based on Malek method.The results show that the pyrolysis processes can be divided into four stages:dry,preheating,volatile fraction removal and carbonization.The weight loss in the volatile fraction removal stage accounts for 71.24%of the weight loss of total pyrolysis process.The pyrolysis process of quercus acutissima includes both endothermic and exothermic reactions.With the increase of heat rate,TG curves and DTG curves move towards high temperature.The apparent activation energies obtained by FWO model and that of KAS model range from 226.79-258.17 kJ/mol and 229.22-260.8 kJ/mol,respectively,while the trend of the apparent activation energies from above two models are similar.Coefficients of determination are above 0.94.The result from the Malek method shows that the three-dimensional diffusion model(Jander equation)is dominant when the conversion is lower than 0.5,and nuclei formation model(Avrami-Erofeev equation,n=3/2)is dominant when the conversion is higher than 0.5.