模式拟合法和无模式函数法对月桂酸热解行为及机理的研究

doi:10.3969/j.issn.1001-1803.2021.04.001

摘要/Abstract

摘要：

通过综合热分析实验研究了月桂酸粉体在氮气及空气气氛下的热解动力学行为。实验结果表明,氮气气氛中30 µm月桂酸粉体快速热解气化,无燃烧放热反应。而不同升温速率条件下,空气气氛中月桂酸粉体的热解包括快速热解氧化及残余物质缓慢热解氧化两个阶段。运用模式拟合法（Coats-Redfern法）求解氮气与空气气氛中月桂酸主要热解阶段的动力学参数,并描述其热解反应机理。结果表明氮气与空气气氛中月桂酸的快速热解阶段均遵循一维相界面反应模型（R1模型）,且氮气气氛中月桂酸热解的表观活化能（9.1 kJ/mol）和指前因子（8.606 1）均较低,表明月桂酸的氧化放热行为抑制了热解反应,但对其热解机理无明显影响,且在升温速率为15 ℃/min时,相同温度条件下,月桂酸在氮气气氛中热解的转化率高于空气气氛。同时运用无模式函数法（Flynn-Wall-Ozawa法和Kissinger-Akahira-Sunose法）对空气气氛中月桂酸不同转化率α下的表观活化能进行解算,两种方法的计算结果与模式拟合法计算结果较为接近,可得空气气氛下月桂酸的平均表观活化能为14.82 kJ/mol;且在10%~80%转化率范围内,月桂酸快速热解氧化阶段的表观活化能随转化率的变化趋势较为平缓,进而验证了月桂酸热解遵循一维相界面反应机理的可靠性。

关键词: 月桂酸, 热解, 模式拟合法, 无模式函数法, 动力学

Abstract:

The pyrolysis kinetics of lauric acid powder in nitrogen and air was studied by comprehensive thermal analysis. The experimental results showed that 30 µm lauric acid powder was rapidly pyrolyzed and gasified in nitrogen atmosphere without exothermic combustion reaction. At different heating rates, the pyrolysis of lauric acid powder in air included two stages: fast pyrolysis and slow pyrolysis. The kinetic parameters of lauric acid pyrolysis in nitrogen and air atmosphere were solved by means of Coats-Redfern method, and the pyrolysis mechanism was described. The results showed that, the rapid pyrolysis of lauric acid in nitrogen and air atmosphere followed the one-dimensional reaction model at phase interface （R1 model）; the apparent activation energy （9.1 kJ/mol） and pre-exponential factor （8.606 1） of lauric acid pyrolysis in nitrogen atmosphere were relatively low, indicating that the oxidation and exothermic behavior of lauric acid inhibited the pyrolysis reaction, but had no obvious effect on its pyrolysis mechanism; when the heating rate was 15 ℃/min, at the same temperature, the conversion of lauric acid pyrolysis in nitrogen atmosphere was higher than that in air atmosphere. The apparent activation energy of lauric acid for different conversion α in air atmosphere was also calculated by using the methods of model-free functions （Flynn-Wall-Ozawa method and Kissinger-Akahira-Sunose method）. The results obtained by the two methods were close to those by the model-fitting method. The average apparent activation energy of lauric acid in air atmosphere was 14.82 kJ/mol; in the range of 10%~80% conversion, the apparent activation energy in the oxidation stage of rapid pyrolysis showed a gentle change with the conversion, which verified that the pyrolysis of lauric acid followed the one-dimensional phase-interface reaction mechanism.

Key words: lauric acid, pyrolysis, model-fitting method, model-free method, kinetics

中图分类号:

TQ645.6

张公妍,张延松,陈昆,张新燕,黄兴旺. 模式拟合法和无模式函数法对月桂酸热解行为及机理的研究[J]. 日用化学工业, 2021, 51(4): 265-271.

ZHANG Gong-yan,ZHANG Yan-song,CHEN Kun,ZHANG Xin-yan,HUANG Xing-wang. Study on the behavior and mechanism of pyrolysis of lauric acid bymodel-fitting and model-free methods[J]. China Surfactant Detergent & Cosmetics, 2021, 51(4): 265-271.

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	机理函数	符号	f（α）	G（α）
化学反应机理	1级	F1	1-α	-ln （1-α）
	1.5级	F1.5	（1-α）^3/2	2[（1-α） ^-1/2-1]
	2级	F2	（1-α）²	（1-α） ^-1-1
	3级	F3	（1-α）³	1/2[（1-α） ^-2-1]
	4级	F4	（1-α）⁴	1/3[（1-α） ^-3-1]
相界面反应机理	一维	R1	1	α
	二维	R2	2 （1-α）^1/2	1- （1-α）^1/2
	三维	R3	3 （1-α）^2/3	1- （1-α）^1/3
随机成核与生长反应机理	Arrami-Erofeev, n=2	A2	2 （1-α）[-ln （1-α）] ^1/2	[-ln （1-α）] ^1/2
	Arrami-Erofeev, n=3	A3	3 （1-α）[-ln （1-α）] ^2/3	[-ln （1-α）] ^1/3
	Arrami-Erofeev, n=4	A4	4 （1-α）[-ln （1-α）] ^3/4	[-ln （1-α）] ^1/4

氮气气氛快速热解气化阶段			空气气氛快速热解氧化阶段
活化能 E/（kJ·mol^-1）	指前因子A/min^-1	相关系数R²	活化能 E/（kJ·mol^-1）	指前因子A/min^-1	相关系数R²
9.1	8.606 1	0.988 9	14.2	49.734 9	0.991 2

转化率/%	Flynn-Wall-Ozawa		Kissinger-Akahira-Sunose
转化率/%	E/（kJ·mol^-1）	R²	E/（kJ·mol^-1）	R²
10	14.01	0.996 3	11.39	0.994 4
20	15.26	0.991 2	12.44	0.986 0
30	16.08	0.988 9	13.14	0.982 7
40	16.57	0.987 4	13.54	0.980 2
50	17.01	0.988 3	13.92	0.981 7
60	17.52	0.987 4	14.38	0.980 5
70	18.16	0.992 0	14.97	0.987 8
80	18.43	0.994 8	15.19	0.992 2
平均值	16.63	—	13.62	—