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| Study on the Correlation Between Pyrolysis Characteristics and Molecular Structure of Lignite Thermal Extract |
| YAN Li-dong1, ZHU Ya-ming1*, CHENG Jun-xia1, GAO Li-juan1, BAI Yong-hui2, ZHAO Xue-fei1* |
1. College of Chemical Engineering, University of Science and Technology Liaoning, Anshan 114051, China
2. State Key Laboratory of High-Efficiency Utilization of Coal and Green Chemical Engineering, Ningxia University, Yinchuan 750021, China
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Abstract Pyrolysis extraction was one of the effective ways of high value-added utilization of low-rank coal. It was significant to clarify the pyrolysis characteristics of a thermal extraction for clean and efficient conversion of low-rank coal. The relationship between pyrolysis activation energy and the molecular structure of escaped gas in Lignite extract (CPW) has been researched by the technology of a thermogravimetric analyzer coupled with Fourier transform infrared spectrometer (TG-FTIR) and the method of peak fitting. In this work, the CPW has been used as the raw material, and the non-isothermal kinetics of CPW was studied by the TG method. Under the condition of equal conversion rate without considering the reaction mechanism, the pyrolytic activation energy (Ea) of CPW was calculated and analyzed using the Flynn-Wall-Ozawa method and Kissinger-Akahira-Sunose method. The results indicated: that the pyrolytic activation energies of CPW ranged from 94.04 to 177.40 kJ·mol-1 when the conversion rate (α) was between 0.2 and 0.8, and the average value of activation energy was 130.01 kJ·mol-1. Moreover, with the increase conversion rate, activation energy also increased. The Peak Fit software was used to perform peak fitting of the infrared spectra of CPW in four regions of 700~900, 1 100~1 800, 2 800~3 000 and 3 000~3 100 cm-1 to achieve the fine structure information about various functional groups. In addition, six molecular structure parameters (I1~I6) were introduced to characterize the relationship between molecular structure and pyrolysis activation energy of CPW when the conversion rate was 0.20≤α≤0.80. The results showed that: It is closely related to molecular structure and pyrolysis activation energy of CPW during the different reaction stages. It showed a good linear relationship between the pyrolysis activation energy and molecular structure parameters, including the degree of branching (I1), aromaticity index (I3), degree of substitute (I6), and the linearity R2 is 0.903 4, 0.744 7 and 0.803 1, respectively. The six molecular structure parameters and pyrolysis activation energy (Ea) were analyzed by linear regression at the same conversion rate. The fitting relationship model between the Ea of CPW and the molecular structure indexes was shown as follows: Ea=124.91-88.75I1-318.84I2-19.19I3+40.29I4-14.28I5+1 272.33I6 (R2 up to 0.999 9). Based on the TG-FTIR experiment, the molecular structure parameters and pyrolysis activation energy of CPW were analyzed, which helped to clarify the pyrolysis process and thermal conversion behavior of CPW. They provided the certain theoretical basis for the high value-added utilization of lignite.
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Received: 2022-01-15
Accepted: 2022-06-04
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Corresponding Authors:
ZHU Ya-ming, ZHAO Xue-fei
E-mail: zhao_xuefei@sohu.com；zhuyaming0504@163.com
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