Effects of hydrothermal treatment on physico-chemcial structures and liquefaction behaviors of lignite

Li, Huan; Wu, Shiyong; Wu, Youqing; Wang, Haiqi; Zhang, Zhimiao; Huang, Sheng; Gao, Jin‐Sheng

doi:10.1016/j.fuel.2019.116636

Cited by 17 publications

(7 citation statements)

References 42 publications

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“…At a low modification temperature, the decomposition of coal was dominant, and the abundant bridge bonds and alkyl side-chain structures in coal were broken, thereby reducing the aliphatic structure. However, with the increase in the modification temperature, the water–gas shift reaction was promoted and a large amount of active hydrogen were generated, thereby enhancing hydrogenation and stabilizing more hydrocarbon radicals, leading to the increase in the aliphatic structure. , SEM analysis results reveal that the CNT content of C-M 280 is higher than that of C-RC, while the content of aliphatic carbon in M 280 is significantly less than that of RC; hence, aliphatic carbon may not be the main carbon source precursors for CNT generation.…”

Section: Resultsmentioning

confidence: 99%

“…Hydromodification of coal in a subcritical-CO system is an important method for tuning the structure and property of coal . In this system, the original cross-links of coal would be broken and a large quantity of active hydrogen is generated by water gas shift reaction, which improves the mobility of radical fragments and promotes the reconstruction of molecules. − It is anticipated that this system could be employed to tailor the coal structure into active precursors. However, little research has so far been dedicated to explore whether and how the hydromodification of coal affects the growth of CNTs in carbon composites.…”

Section: Introductionmentioning

confidence: 99%

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Tuning Lignite Structure via Hydromodification To Promote the Formation of Coal-Based CNTs: Exploration for the Carbon Source of CNTs

et al. 2023

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Although the preparation of coal-based carbon nanotubes (CNTs) has been realized in many studies, the relationship between carbon source structure of coal and CNT growth has not been studied in depth. In this study, we used lignite and KOH as raw material and catalyst and tuned lignite structure via hydrothermal modification to promote the formation of CNTs during catalytic pyrolysis. The main carbon source of CNTs was explored from the change of coal structure and pyrolysis characteristics. The results indicate that the CNT yield of lignite pyrolysis products is only 2.39%, but the CNT yield increases significantly after lignite was hydrothermally modified in a subcritical water–CO system. The graphitization degree, the order degree, and CNT content increase continuously with the increase in modification temperature, and C-M340 has the highest CNT content of 9.41%. Hydromodification promotes the rearrangement of aromatic carbon structures to generate more condensed aromatic rings linked by short aliphatic chains and aromatic ether bonds. The variation of these structures correlates well with the formation of CNTs and leads to the change in the carbon source components released during coal pyrolysis. Compared to lignite, modified coal releases more aromatic compounds, especially polycyclic aromatic hydrocarbons with ≥3 rings and phenols during catalytic pyrolysis, which is conducive to the transformation into carbon clusters and provides carbon sources for CNT growth. In addition, modified coal releases a slightly more carbon-containing gas (CH4 and CO) than lignite, which has a limited effect on the growth of CNTs. This study provides a novel and efficient method for enhancing the growth of CNTs by a molecular tailoring strategy of coal.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Tuning Lignite Structure via Hydromodification To Promote the Formation of Coal-Based CNTs: Exploration for the Carbon Source of CNTs

et al. 2023

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“…Among thermochemical processes capable of upgrading waste and low-value materials, hydrothermal liquefaction (HTL) is a technology that can accommodate a variety of wet and dry feedstocks into an energy-dense product . The potential of the HTL process has been demonstrated in the valorization of renewable waste feedstocks, such as algae, sewage sludges, lignocellulosic wastes, − and non-renewable low-value matter, for example, low-grade coal. − In this latter case, before combustion for electricity combustion, lignite can be converted by HTL to increase the HHV on one side and get an oil crude compatible for fuel production on the other side.…”

Section: Introductionmentioning

confidence: 99%

Lignite and Biomass Waste Hydrothermal Liquefaction Crude Upgrading by Hydrotreatment

et al. 2023

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Hydrothermal liquefaction (HTL) is a promising process for the energetic valorization of low-value feedstocks. However, HTL crude oils are incompatible with the existing fuel standards, making their upgrade imperative. Nonetheless, the hydrotreatment (HDT) of HTL crude oils is still a challenge due to the complex nature of the feedstock. Therefore, this work explores the relationship between the HTL crude oil origin and the HDT conversion. Five HTL crude oils from different feedstocks, namely, oak sawdust, Brewer’s Spent Grain (spent grain), sewage sludge from two origins, and lignite, and their detailed characterization by elemental analysis, 13C and 31P NMR, molecular weight distribution, comprehensive 2D gas chromatography, and SimDis were compared to those of the HDT liquid product. Lignite displayed the highest potential for producing hydrocarbons, particularly monoaromatics and naphthenes, among the feedstocks tested. The capacity of lignite HTL crude oil to be transformed into hydrocarbons was associated with the absence of compounds resistant to HDT in this feedstock. Similarly, oak sawdust also displayed higher selectivity toward aromatic and naphthene hydrocarbons due to the significant concentration of aromatic compounds in the crude oil. In opposition, the sewage sludge and spent-grain crude oils were particularly selective toward aliphatic hydrocarbons, particularly paraffins, produced from aliphatic components, such as amides, in the crude oil. However, these feedstocks were rich in nitrogenated aromatics, for example, carbazole, which are recalcitrant to hydrotreatment and were not fully converted during the reaction. The differences observed in the HDT liquid composition show that the HTL crude oil composition dictates the potential for producing hydrocarbon fuels. Indeed, HTL crude oils rich in aromatic compounds will yield preferentially naphthenes and aromatic hydrocarbons. In opposition, crude oils richer in aliphatic carbon will be more selective toward paraffins. The nature and concentration of heteroatom components must also be considered since these must be imperatively eliminated.

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“…The process enables an improvement in the slurry properties of coal (Yu et al 2012;Fu and Wang 2014;Zhang et al 2018) and can reduce the viscosity of the coal-water slurry. Moreover, hydrothermal treatment not only promotes the hydro-liquefaction activity during coal liquefaction (Li et al 2020) but also increases the coal concentration of the coal-solvent slurry (Inoue et al 2012a, b), which is because of the lower porosity for the treated coal. Furthermore, hydrothermally treated lignite has a greater calorific value (Yu et al 2014;Ullah et al 2018) compared with raw lignite.…”

Section: Introductionmentioning

confidence: 99%

Effect of hydrothermal treatment on the carbon structure of Inner Mongolia lignite

Liu

Zhang

2020

Int J Coal Sci Technol

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Understanding the structural properties of lignite during hydrothermal treatment would aid in predicting the subsequent behavior of coal during the pyrolysis, liquefaction, and gasification processes. Here, hydrothermal treatment of Inner Mongolia lignite (IM) was carried out in a lab autoclave. The distribution of carbon in the lignite was monitored via solid 13C nuclear magnetic resonance spectroscopy, and the functional groups of oxygen in lignite were determined by Fourier transform infrared spectroscopy. The curve-fitting method was used to calculate the content of the functional groups quantitatively. The results show that hydrothermal treatment is an effective method for upgrading the lignite. The side chains of the aromatic ring in lignite are altered, while the main macromolecular structure remains nearly the same. The hydrothermal treatment of IM could be divided into three temperature-dependent stages. The first stage (< 493 K) is the decomposition reaction of oxygen functional groups, where the O/C ratio decreases from 0.203 in raw IM to 0.185 for the IM treated at 493 K. In the second stage (493–533 K), hydrolysis of functional groups and hydrogen transfer between water and lignite occur. Here, the ratio of methylene to methyl increases from 0.871 in IM-493 to 1.241 for IM-533, and the content of quinone generates from the condensation of free phenol increased. The third stage (> 533 K) involves breakage of the covalent bond, and the content of CH4 and CO in the emission gas clearly increase.

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Effects of hydrothermal treatment on physico-chemcial structures and liquefaction behaviors of lignite

Cited by 17 publications

References 42 publications

Tuning Lignite Structure via Hydromodification To Promote the Formation of Coal-Based CNTs: Exploration for the Carbon Source of CNTs

Tuning Lignite Structure via Hydromodification To Promote the Formation of Coal-Based CNTs: Exploration for the Carbon Source of CNTs

Lignite and Biomass Waste Hydrothermal Liquefaction Crude Upgrading by Hydrotreatment

Effect of hydrothermal treatment on the carbon structure of Inner Mongolia lignite

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