Insight into the dissolution of lignite with ionic liquid [Bmim]cl

•[Bmim]Cl pretreatment is accompanied by the generation and reaction of free radicals.•[Bmim]Cl pretreatment increases the contents of carboxyl and ether bonds.•[Bmim]Cl pretreatment reduces the content of hydrogen bond.•[Bmim]Cl pretreatment breaks the cross-linked structure of lignite. Ionic liqui...

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Bibliographic Details
Published in:Fuel (Guildford) 2020-02, Vol.262, p.116679, Article 116679
Main Authors: Han, Song, Yu, Wenhao, Zhang, Hao, Lei, Zhiping, Shui, Hengfu, Ren, Shibiao, Wang, Zhicai, chong Yan, Jing, Li, Zhanku, Kong, Ying, Kang, Shigang, Pan, Chunxiu
Format: Article
Language:English
Subjects:
Bonding strength
Coal
Electron spin
Electron spin resonance
Fourier analysis
Fourier transforms
Free radicals
Functional groups
Hydrogen bonding
Hydrogen bonds
Infrared analysis
Ionic liquid pretreatment
Ionic liquids
Ions
Lignite
Oxygen-containing functional groups
Pretreatment
Radical
Solvents
Spectroscopy
Spectrum analysis
Temperature
Thermogravimetric analysis
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Summary:•[Bmim]Cl pretreatment is accompanied by the generation and reaction of free radicals.•[Bmim]Cl pretreatment increases the contents of carboxyl and ether bonds.•[Bmim]Cl pretreatment reduces the content of hydrogen bond.•[Bmim]Cl pretreatment breaks the cross-linked structure of lignite. Ionic liquid as a green solvent have shown good performance in coal and biomass pretreatment, but the effects of ionic liquids pretreatment on the coal structures is still not properly understood. In this work, the changes of radical concentration in lignite during the pretreatment with ionic liquid 1-butyl-3-methyl-imidazolium chloride [Bmim]Cl were investigated by the electron spin-resonance spectroscopy (ESR) in detail and the effect of ionic liquid pretreatment on the change of coal structure was investigated by the diffuse reflectance infrared fourier transform spectroscopy (DRIFT) and thermogravimetric analysis (TGA). It was found that the pretreatment temperature and the ratio of [Bmim]Cl to lignite had a great impact on the radical concentration of lignite. The radical concentration of lignite decreased when the pretreatment temperature lower than 100 °C, which was attributed to the coupling of free radicals dissolved from coals. When the pretreatment temperature was higher than 100 °C, the radical concentration of lignite increased, which was attributed to the cleavage of weak bonds in lignite. It was also found that pretreatment with ionic liquid can fracture the oxygen-containing functional groups in the coal can be dissociated after pretreatment with ionic liquids, which leads to an increase in the content of carboxyl and ether bonds and a decrease in the content of hydrogen bonds.
ISSN:0016-2361
1873-7153
DOI:10.1016/j.fuel.2019.116679