FTIR Analysis of the Correlation Between the Pyrolysis Characteristics and Molecular Structure of Ultrasonic Extraction Derived From Mid-Temperature Pitch
1. College of Chemical Engineering, University of Science and Technology Liaoning, Anshan 114051, China
2. Key Laboratory of Chemical Metallurgy Liaoning Province, University of Science and Technology Liaoning, Anshan 114051, China
Abstract：The regulation of molecular structure and thermal conversion behavior of coal tar pitch is the key to preparing high-quality coal tar pitch-based carbon materials. In order to further clarify the relationship between pyrolysis behavior and molecular structure of coal tar pitch, 8 kinds of extracts derived from Medium temperature pitch (AGMP) were extracted by ultrasonic extraction with 8 kinds of organic solvents at room temperature in this paper. The PeakFit v4.12 software was used to perform peak fitting the infrared spectra of the extracts in four regions of 700~900, 1 000~1 800, 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 the extracts. FTIR spectra analysis shows that the 8 extracts are complex compounds composed of condensed aromatic ring structures mainly comprised of aliphatic hydrocarbon side chains containing oxygen and nitrogen and other heteroatoms. Moreover, due to the difference in the extractant’s structure, the extract’s molecular structure parameters are also slightly different. The extract obtained from the linear structure extractant has a higher content of chain hydrocarbons (I5), and the extract obtained from the ring structure extractant has more aromatic rings substituted structures (I6). Thermogravimetric analysis (TGA) was used to study the thermal weight loss behavior of 8 extracts at different heating rates (3, 6, 10, 15 K·min-1). Under the condition of equal conversion rate without considering the reaction mechanism, the pyrolytic activation energy (Ea) were calculated and analyzed using the Flynn-Wall-Ozawa method and Kissingr-Akahira-Sunose method. The results indicated that the eight extracts’ pyrolytic activation energies ranged from 78 to 116 kJ·mol-1, which are closely related to the structure and content of functional groups. The structural parameters of the extracts obtained by IR quantitative are correlated with the pyrolysis activation energy. The fitting results of the one-element linear equation Ea=f(Ii) between the structural parameters of the extracts and the pyrolysis activation energy found that the aromaticity index (I3) and the degree of branching (I5) are the two main indicators that determine the pyrolysis activation energy of the extracts. The fitting results of positive and negative correlation between the pyrolysis activation energy with every single index (Ii) indicate the difficulty of the structure being destroyed by pyrolysis. Considering the interaction of various infrared structural parameters, the fitting relationship model between the Ea of AGMP extracts and the infrared spectral structure indexes was shown as followed: Ea=-4 294.53I1+73 812.16I2+207 673.32I3-20 324.20I4-168.56I5+857.86I6. The results, which combined analysis of FTIR spectra, reveal more details about thermal characterization and kinetic characterization and they can be expected to lead to a well-understood coal tar pitch’s pyrolysis.
[1] Granda M, Blanco C, Alvarez P，et al. Chem. Rev., 2014, 114(3): 1608.
[2] Xing B L, Zhang C T, Liu Q R，et al. J. Alloys Compd.，2019, (795)：91.
[3] Li L, Lin X C, Zhang Y K，et al. J. Anal. Appl. Pyrolysis, 2020, 150(9): 104889.
[4] Guo J G, Li X K, Xu H T，et al. Energy & Fuels, 2020, 34(5): 6474.
[5] Yang H W, Yao T, Guo L，et al. Energy Sources, Part A, 2018, 40(5): 493.
[6] Solomon P R, Serio M A, Suuberg E M，et al. Progress in Energy and Combustionence, 1992, 18(2): 133.
[7] Zhu H Q, Zhao H R, Wei H Y，et al. Combust. Flame, 2020, 216: 354.
[8] WENG Shi-fu(翁诗甫). Fourier Translation Infrared Spectroscopy(傅里叶变换红外光谱分析). 2nd ed.(第2版). Beijing: Chemical Industry Press(北京：化学工业出版社), 2010.
[9] ZHANG Xiu-xia, LÜ Xiao-xue, ZHOU Zhi-jun, et al(张秀霞, 吕晓雪, 周志军, 等). Journal of Fuel Chemistry and Technology(燃料化学学报), 2020, 48(9): 1035.
[10] Song H J, Liu G R, Wu J H，et al. Fuel Process. Technol., 2017, 156: 454.
[11] Liu P, Zhang D X, Wang L L，et al. Appl. Energy, 2016, (163): 254.
[12] Yan C Q, Huang W D, Ma J M, et al. Constr. Build. Mater, 2020, 233: 117708.
[13] Hua Z J, Wang Q, Jia C X, et al. Energy Sci. Eng., 2019, 7(3): 912.
[14] Aslan D I, Özoğul B, Ceylan S, et al. Bioresour. Technol., 2018, 258: 105.
