Study on thermal decomposition characteristics and kinetics of soybean

doi:10.11949/0438-1157.20200224

Abstract

Abstract:

In this paper, the thermal degradation kinetics of soybean was studied by dynamic thermogravimetry (TGA). The thermal decomposition characteristics and kinetics of soybean under different pyrolysis conditions were explored by changing the heating rate (5, 10, 20 and 40℃/min) and the atmosphere conditions (nitrogen and air). According to the trend of TGA and DTG curves, the pyrolysis of soybean can be divided into four stages: the first two stages correspond to the removal of free water and crystal water, and the last two stages correspond to the secondary decomposition stage and the main decomposition stage of main components (starch, protein and fat). In the latter two stages, due to the presence of oxygen, the thermal decomposition process of soybean appeared different, and the activation energy and carbon residue rate of the reaction decreased. Compared with pyrolysis in nitrogen atmosphere, soybean showed lower activation energy and fire safety in air atmosphere. In this paper, the difference of pyrolysis kinetics of soybean in different atmosphere was studied for the first time, and the intrinsic law of pyrolysis and its fire safety were revealed.

Key words: pyrolysis, biomass, thermodynamics, activation energy, thermogravimetric analysis

摘要：

动态热重分析（TGA）被用来研究大豆的热降解动力学，通过改变大豆热解时的升温速率（5，10，20和40℃/min）以及气氛条件（氮气和空气）探索了大豆在不同热解条件下的热解特性。并结合对相应热解条件下的动力学参数（表观活化能E_k）进行求解，探究了大豆的火灾安全性。结果表明，大豆的热解可以分为四个阶段：前两个阶段对应自由水和结晶水的脱除，后两个阶段对应主要成分（淀粉、蛋白质和脂肪）的次分解阶段和主要分解阶段。后两个阶段，由于氧气的存在，导致大豆的热分解出现了不同的历程，800℃时的残炭率降低。且与氮气气氛下热解相比，大豆在空气气氛下表现出更低的反应活化能和火灾安全性。

关键词: 热解, 生物质, 热力学, 活化能, 热重分析

CLC Number:

O 5551/O 5552

Yifan ZHOU, Congxue YAO, Jingwen WANG, Wenwen GUO, Lei SONG, Xiaowei MU, Yuan HU. Study on thermal decomposition characteristics and kinetics of soybean[J]. CIESC Journal, 2020, 71(S2): 187-194.

周一帆, 姚丛雪, 王靖文, 郭文文, 宋磊, 牧小卫, 胡源. 大豆的热分解特性及其动力学探究[J]. 化工学报, 2020, 71(S2): 187-194.

Figures/Tables 13

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元素	相对含量/ %（atom）
碳（C）	49.41
氢（H）	7.78
氧（O）	37.35
氮（N）	5.63
硫（S）	0.42

元素	相对含量/ %（atom）
碳（C）	49.41
氢（H）	7.78
氧（O）	37.35
氮（N）	5.63
硫（S）	0.42

升温速率/ (℃/min)	气氛	第一阶段		第二阶段		第三阶段		第四阶段		水除外的总失重率/%
升温速率/ (℃/min)	气氛	热解温度/℃	失重率/%	热解温度/℃	失重率/%	热解温度/℃	失重率/%	热解温度/℃	失重率/%	水除外的总失重率/%
5	氮气	RT~173	5	173~248	13	248~321	23	321~497	37	76
5	空气	RT~173	5	173~248	13	248~347	36	347~526	36	89
10	氮气	RT~183	2	183~262	13	262~334	27	334~516	38	79
10	空气	RT~183	2	183~262	13	262~358	39	358~553	39	92
20	氮气	RT~192	6	192~267	13	267~342	26	342~548	35	78
20	空气	RT~192	6	192~267	13	267~371	37	371~568	37	92
40	氮气	RT~209	6	209~282	13	282~358	28	358~560	34	79
40	空气	RT~209	6	209~282	13	282~400	42	400~650	33	93

升温速率/ (℃/min)	气氛	第一阶段		第二阶段		第三阶段		第四阶段		水除外的总失重率/%
升温速率/ (℃/min)	气氛	热解温度/℃	失重率/%	热解温度/℃	失重率/%	热解温度/℃	失重率/%	热解温度/℃	失重率/%	水除外的总失重率/%
5	氮气	RT~173	5	173~248	13	248~321	23	321~497	37	76
5	空气	RT~173	5	173~248	13	248~347	36	347~526	36	89
10	氮气	RT~183	2	183~262	13	262~334	27	334~516	38	79
10	空气	RT~183	2	183~262	13	262~358	39	358~553	39	92
20	氮气	RT~192	6	192~267	13	267~342	26	342~548	35	78
20	空气	RT~192	6	192~267	13	267~371	37	371~568	37	92
40	氮气	RT~209	6	209~282	13	282~358	28	358~560	34	79
40	空气	RT~209	6	209~282	13	282~400	42	400~650	33	93

参数	氮气气氛			空气气氛
参数	失重峰1（235℃）	失重峰2（325℃）	失重峰3（384℃）	失重峰1（235℃）	失重峰2（326℃）	失重峰3（486℃）
R	-0.996	-0.998	-0.996	-0.997	-0.925	-0.795
E /(kJ/mol)	114.761	162.501	128.918	131.869	71.973	48.336