油茶壳热解反应动力学和热力学研究

Reaction kinetics and thermodynamics during pyrolysis of camellia oleifera shell

安全处理油茶壳并将其转化为生物燃料回收能源,对于实现油茶壳资源化利用具有重要意义。基于油茶壳与低阶煤共热解特性以及共热解过程存在协同效应,利用热重分析法对油茶壳热解过程中反应动力学和热力学特性进行相关研究,并采用热重分析实验考察不同升温速率(5℃/min、10℃/min、15℃/min和20℃/min)下油茶壳的热失重特性曲线变化规律。结果表明,随着升温速率的增加,失重曲线向高温方向偏移,存在明显的滞后现象,失重速率曲线上失重峰峰值温度也明显存在向高温偏移现象。利用Friedman(FM)、Ozawa-Flynn-Wall(OFW)和Kissinger-Akahira-Sunose(KAS)该3种等转化率法模型对热解过程的表观活化能进行计算。3种模型计算所得到的表观活化能变化趋势相同,均随转化率的增加而不断增大。利用OFW模型对热力学函数进行计算,结果发现,随转化率的增加,指前因子(A)、焓变(ΔH)和熵变(ΔS)呈不断增大的趋势,在等转化率的情况下ΔH和ΔS随升温速率的加快稍有降低;吉布斯自由能(ΔG)的变化随转化率的增加并不明显且稍有降低,但在相同转化率时,ΔG与升温速率呈正相关性。

To efficiently convert camellia oleifera shell into biofuel for energy recovery using pyrolysis methods,it is of great significance to understand the kinetics and thermodynamics of the pyrolysis processes.Based on the co-pyrolytic characteristics of camellia oleifera shell with low-rank coal and their synergistic effect during the co-pyrolysis process,the reaction kinetics and thermodynamic properties of the pyrolysis were investigated using the thermogravimetric analysis(TGA).The thermal degradation experiments were conducted at different heating rates(5℃/min,10℃/min,15℃/min and 20℃/min),and the thermal loss characteristic curves of the camellia oleifera shell were obtained.The results observed showed that with the increase in heating rate,the TG curves moved towards the higher temperature region,named as the thermal lag effect,and the temperature corresponding to the DTG peaks also tended to shift to the highertemperature region.The apparent activation energies of the pyrolysis process were calculated with three isoconversional methods,namely,the Friedman(FM)model,the Ozawa-Flynn-Wall(OFW)model and the Kissinger-Akahira-Sunose(KAS)model,and the apparent activation energies all exhibited the same trends,which increased as the conversion increased.With the OFW model,the relative thermodynamic functions were acquired.It was found that for the same heating rate,the pre-exponential factor(A),enthalpy change(ΔH)and entropy change(ΔS)all increased as the conversion rates increased,whileΔH andΔS decreased slightly with the increase in heating rate under the same conversion rates.The change in Gibbs free energy(ΔG)was not obvious with the increase in conversion rates,which only slightly decreased.However,for the same conversion rate,ΔG increased linearly with the heating rate.