热分析法研究五倍子醛的热稳定性及其分解动力学

Study on Thermal Stability and Decomposition Kinetics of Gallic Aldehyde by Thermal Analysis

采用热重法,以氮气为保护气,分别在5、10、15、20℃/min的升温速率下,测得五倍子醛的热重-微分热重(TG-DTG)曲线,并在10℃/min的升温速率下测得样品的差示扫描量热(DSC)曲线。结合热失重数据和五倍子醛结构对其分解机理进行推断和验证,并运用双外推法对五倍子醛的热解动力学进行分析,求得原始状态和热平衡态下的动力学参数。研究结果表明,五倍子醛晶体在升温过程中先经历了非结合水和结合水的受热挥发阶段,然后在163℃之后发生热分解,分子中醛基断裂失去1分子的CO;随着升温速率的升高,五倍子醛的分解反应向高温区域移动,最大失重速率依次减小;热解活化能Eα为286.21 kJ/mol,指前因子lnA为70.21,热解机理函数g(α)=[-ln(1-α)]2/3,反应级数n=2/3;热解活化能随转化率的增加逐渐减小;经动力学参数推断,在室温(25℃)下,五倍子醛的贮存期为4～5年。

Gallic aldehyde was heated up by thermogravimetry from room temperature to 700 ℃ at different heating rates（5,10,15,20 ℃/min） under nitrogen atmosphere while its DSC curve was obtained by differential scanning calorimetry at 10 ℃/min.The thermal decomposition mechanism was inferred in accordance with its weight loss and molecular structure while kinetic parameters in thermal equilibrium and original reaction conditions were calculated by double extrapolated method.Experimental results showed that after the volatilization of unbound and bound water,one molecule CO was lost due to the cracking of the aldehyde group.The decomposition reaction of gallic aldehyde was pushed to high temperatures with the increase of heating rates,and the maximum weight loss rate decreased in turn.The activation energy（Eα） of pyrolysis was 286.21 kJ/mol while pre-exponential factor（lnA） was 70.21.The pyrolysis mechanism function was g（α）=[-ln（1-α）]2/3 with reaction order（n） of 2/3.Pyrolysis activation energy decreased with the increase of conversion ratio.According to its kinetic parameters,the shelflives of gallic aldehyde was 4-5 years at room temperature.