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摘要: 采用热重-微商热重(TG-DTG)技术研究了蕲艾绒在氮气气氛中的热分解行为及其非等温动力学, 结果发现蕲艾绒的热分解过程分为两个阶段: 第一阶段失重率为3.75%, 主要为蕲艾绒中水分和少量挥发性油类物质的损失, 第二阶段失重率为71.12%, 主要为挥发性的油类物质和木质纤维物质的热分解。使用单重扫描速率法Achar微分方程和Coats-Redfern积分方程求出其动力学参数, 得到了蕲艾绒热分解反应的控制机理函数, 并利用多重扫描速率法的Kissinger方程、Flynn-Wall-Ozawa方程和Starink方程对其动力学参数进行验证, 得到其热分解过程属于F3(三级反应)机理控制, 机理函数f(α)=0.5(1-α)3、g(α)=(1-α)-2-1, 表观活化能(E)为124.76 kJ/mol、指前因子(A)为5.78×1010 s-1, 并确定蕲艾绒热分解非等温动力学方程为: dα/dt=(5.78×1010/β)×(0.5×(1-α)3)×exp(-15 006/T)。根据其热分解动力学参数进行估算, 得出蕲艾绒在室温下的贮存期为4~5年。Abstract: The thermal decomposition behavior and non-isothermal kinetics of Artemisia vulgaris L. in nitrogen were studied by thermogravimetric-differential thermogravimetric(TG-DTG) technique. The results showed that its thermal decomposition was divided into two-step process. In the first stage, the weight loss rate was 3.75%, which was mainly the weight loss of water and a small amount of volatile oil in A. vulgaris L.. In the second stage, the weight loss rate was 71.12%, which was mainly the thermal decomposition of volatile oils and lignocellulose. Meanwhile, the kinetic parameters of A. vulgaris L. were obtained using the Achar differential equation and Coats-Redfern integral equation of the single scanning method, and its control mechanism function of the thermal decomposition was determined. The kinetic parameters were verified by Kissinger equation, Flynn-Wall-Ozawa equation and Starink equation of the multiple scanning rate method. It was found that the thermal decomposition process belonged to the F3(third-order reaction) mechanism control, and the mechanism function f(α)=0.5(1-α)3, g(α)=(1-α)-2-1. The apparent activation energy and the pre-exponential factor were 124.76 kJ/mol and 5.78×1010 s-1, respectively. The thermal decomposition non-isothermal kinetic equation of A. vulgaris L. was dα/dt=(5.78×1010/β)×(0.5×(1-α)3)×exp(-15 006/T). According to the estimation of thermal decomposition kinetic parameters, the shelf-life of A. vulgaris L. was 4-5 years at room temperature.
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Key words:
- Artemisia vulgaris L. /
- thermal decomposition /
- non-isothermal kinetics /
- shelf-life
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图 1 蕲艾绒在10 K/min升温速率下的TG-DTG曲线
Figure 1. TG-DTG curves of A. vulgaris at heating rate of 10 K/min
图 2 不同升温速率下蕲艾绒的TG-DTG曲线
Figure 2. TG-DTG curves of A. vulgaris at different heating rates
表 1 蕲艾绒热分解的基本数据(β=10 K/min)
Table 1. Base data for thermal decomposition of A. vulgaris(β=10 K/min)
序号 No. T/K α dα/dT 序号 No. T/K α dα/dT 1 458.8 0.003 0.036 19 603.8 0.625 7.969 2 477.5 0.008 0.195 20 607.5 0.677 6.930 3 492.2 0.014 0.349 21 611.2 0.722 5.262 5 518.1 0.047 1.048 23 626.1 0.793 1.339 6 529.3 0.072 1.309 24 637.3 0.818 0.968 7 540.5 0.102 1.634 25 652.2 0.839 0.665 8 547.9 0.126 1.780 26 667.1 0.860 0.695 9 555.3 0.150 2.228 27 682.0 0.877 0.585 10 566.5 0.204 3.127 28 704.3 0.901 0.539 11 574.0 0.255 4.162 29 723.0 0.920 0.608 12 577.7 0.280 4.625 30 745.4 0.094 0.338 13 581.5 0.317 5.339 31 767.8 0.953 0.296 14 585.2 0.358 6.125 32 794.0 0.967 0.151 15 588.9 0.401 6.792 33 820.2 0.975 0.162 16 592.6 0.453 7.670 34 846.4 0.980 0.115 17 596.3 0.507 8.227 35 883.8 0.989 0.109 18 600.0 0.567 8.297 36 921.5 0.996 0.127 
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表 2 蕲艾绒热分解动力学数据分析结果
Table 2. Analysis results of thermal decomposition kinetic analysis for A. vulgaris
反应机理reaction mechanism 符号symbol Achar Coats-Redfern E/(kJ·mol-1) lnA r E/(kJ·mol-1) lnA r 随机成核random nucleation A1.5 11.13 3.51 0.391 5 24.04 1.66 0.847 1 随机成核random nucleation A2 2.43 1.63 0.100 4 15.34 -0.38 0.798 1 随机成核random nucleation A3 -6.27 -0.36 0.270 7 6.63 -2.81 0.635 0 随机成核random nucleation A4 -10.63 -1.45 0.441 4 2.28 -4.67 0.339 9 一维扩散one-dimensional diffusion D1 21.22 3.71 0.311 4 63.37 8.33 0.794 2 二维扩散two-dimensional diffusion D2 36.36 6.53 0.509 2 70.03 9.32 0.823 3 三维扩散three-dimensional diffusion D3 59.43 10.28 0.735 9 80.62 10.42 0.867 0 四维扩散four-dimensional diffusion D4 44.64 6.91 0.604 2 73.36 8.64 0.838 1 一级反应first order reaction F1 28.53 7.10 0.675 7 41.44 5.38 0.882 4 二级反应second order reaction F2 72.90 17.21 0.947 4 70.68 12.52 0.981 2 三级反应third order reaction F3 117.28 28.02 0.974 4 108.04 22.04 0.990 7 幂函数定律power function law P1 -43.65 -8.92 0.843 1 1.50 -5.97 0.209 3 相边界反应phase boundary reaction R2 6.34 1.35 0.171 1 32.29 2.34 0.800 3 相边界反应phase boundary reaction R3 13.74 2.63 0.368 9 34.93 2.62 0.827 5
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表 3 不同方法求解的热分解动力学参数
Table 3. Thermal decomposition kinetic parameters solved by different methods
方法 methods E/(kJ·mol-1) lnA 相关系数 correlation coefficient Achar 117.28 28.02 0.974 Coats-Redfern 125.61 22.04 0.991 Kissinger 125.61 24.29 0.998 Flynn-Wall-Ozawa 128.76 — 0.998 Starink 126.60 — 0.998 平均值 average 124.76 24.78 0.992
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表 4 不同温度下蕲艾绒贮存期的估算值
Table 4. The estimated value of the shelf-life of A. vulgaris at different temperatures
温度/℃
temperature反应速率常数(k)
reaction rate constant负对数(pk)
negative logarithm贮存期/年
shelf-life-25 3.157×10-16 15.50 4~5 0 8.000×10-14 13.10 4~5 25 8.017×10-12 11.10 4~5 30 1.838×10-11 10.74 4~5 35 4.103×10-11 10.39 3 40 8.924×10-11 10.05 3
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