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Oxygen bond cleavage and its migration mechanisms during pyrolysis of naomaohu sub-bituminous coal.

Authors :
Gao, Yue
Tian, Yuanyu
Hao, Meilu
Li, Songze
Sun, Lanyi
Liang, Peng
Source :
Journal of Analytical & Applied Pyrolysis. May2024, Vol. 179, pN.PAG-N.PAG. 1p.
Publication Year :
2024

Abstract

Investigating the oxygen bond cleavage and its migration mechanisms during the pyrolysis process of sub-bituminous coals is essential for their classification utilization. The present study employed a fixed-bed pyrolysis technique (temperature range: 350–600 °C) to explore the cleavage of oxygen-containing bonds and subsequent behavior of oxygen migration and transformation during the pyrolysis process of Naomaohu sub-bituminous coal (NSBC). X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy results reveal that the organic oxygen in NSBC predominantly exists as the form of C–O bonds, accounting for 22.81 wt% of the total composition, mainly encompassing hydroxyl, carbonyl, ester, and ether groups. The organic oxygen in the light tar is mainly in the form of phenols, reaching 1.71 wt%, of which methyl substituted phenols is predominant at a final pyrolysis temperature of 600 °C. This can be attributed to the presence of more aryl ether bonds and hydroxyl groups in NSBC, which are prone to cleavage at higher temperatures, resulting in the formation of phenoxyl radicals. Additionally, the higher temperature facilitates the weakening of hydrogen bonds between phenolic hydroxyl groups, thereby enhancing the yield of phenolic compounds. The ester compounds present a decreasing trend with increasing temperature, primarily associated with the cleavage temperature of ester linkers being 350 °C, suggesting that an increase in temperature favors the cleavage of ester bonds. In addition, the cleavage of C–O bonds begins to accelerate significantly during the pyrolysis temperature range of 450–500 °C, subsequently accounting for the pronounced proliferation of phenols within this specific thermal interval. The oxygen content in semi-coke decreased with the increase of temperature, from 85.27 wt% at 350 °C to 37.17 wt% at 600 °C, while the oxygen content in the pyrolysis gas increases from 11.63 wt% at 350 °C to 47.53 wt% at 600 °C, indicating that a significant migration of organic oxygen to the pyrolysis gas during the pyrolysis of NSBC. This study can deepen the understanding of the transformation mechanism of oxygen-containing structure in NSBC pyrolysis process, and provide a theoretical basis for high-grade utilization of low-rank coals. [Display omitted] • Elevated temperatures promote the migration of organic oxygen into volatile products. • The breaking of organic oxygen bonds depends mainly on temperature. • High temperatures favor the breaking of aryl ether bonds to form phenols. • Cleavage of aryl alkyl ethers at 350–450 °C leads to a large increase in alcohols. • The release of volatile oxygenates leads to a reduction in the oxygen content of the coke. [ABSTRACT FROM AUTHOR]

Details

Language :
English
ISSN :
01652370
Volume :
179
Database :
Academic Search Index
Journal :
Journal of Analytical & Applied Pyrolysis
Publication Type :
Academic Journal
Accession number :
177203197
Full Text :
https://doi.org/10.1016/j.jaap.2024.106489