The Role of Noncovalent Bonding in Coal

Stenberg, Virgil I.; Baltisberger, R.J.; Patal, Kundan M.; Raman, K.; Woolsey, Neil F.

doi:10.1016/b978-0-12-150702-2.50009-8

Cited by 14 publications

(12 citation statements)

References 83 publications

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“…The OH−π hydrogen bond in preasphaltenes disappearing at higher temperatures than in asphaltenes may be attributed to the higher aromaticity of preasphaltenes. The larger the size of an aromatic ring, the stronger is the interaction between OH and π electrons . OH−ether O hydrogen bond is the most stable during pyrolysis.…”

Section: Resultsmentioning

confidence: 99%

Observation of the Type of Hydrogen Bonds in Coal by FTIR

1998

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It is hard to distinguish the type of hydrogen bonds formed by hydroxyl groups by normal FTIR methods because of the interference of water in samples. In this work, a method is proposed for the clear observation of the types of hydrogen bonds by FTIR. The method involves the evaporation of water in a vacuum chamber with CaF2 windows (vacuum level, 4 × 10-3 kPa) followed by in situ scanning of the IR spectrum. Five types of hydrogen bonds were found in coal and its extracts. The hydroxyl groups in coal mainly exist as self-associated OH and OH−N hydrogen-bonded pairs. The thermal stability of these hydrogen bonds was investigated by means of in-situ pyrolysis FTIR. It follows the order of OH−ether O > self-associated OH ≈ cyclic OH > OH−N > OH−π.

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Section: Resultsmentioning

confidence: 99%

Observation of the Type of Hydrogen Bonds in Coal by FTIR

1998

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“…Hydrogen bonding is an important coal−solvent interaction. , Hydroxyl, ether oxygen, pyridine nitrogen, and pyrrolic N−H and π electrons on the aromatic rings are specific sites that are able to form hydrogen bonds with hydroxyl in coal molecules . When hydrogen-bonding-accepting solvents, such as THF, cyclohexanone, pyridine, and NMP are used, the hydrogen bonding mainly occurs between hydroxyl in coal and solvent.…”

Section: Resultsmentioning

confidence: 99%

Role of Noncovalent Bonding in Swelling of Coal

1998

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The effects of coal-solvent interactions and coal-coal interactions on coal swelling were investigated to clarify the role of noncovalent bonds in coal swelling in polar and nonpolar solvents. It is found that the swelling of coal is different from that of a covalently cross-linked polymer and is caused by both covalent cross-links and noncovalent cross-links (or some physical associations). Coal-solvent hydrogen bonding plays an important role in determining the swelling of coal in polar solvents. Coal swelling increases with stronger hydrogen-bonding solvents and with more hydroxyl sites in coal. Increased swelling is accomplished by conversion of carboxylate to carboxyl in lignite through acid washing and by hydrolysis of weak ether and ester bonds in bituminous coal to increase hydroxyl content. Coal swelling in nonpolar solvents is mainly controlled by coal-coal interactions. The low swelling of lignite in nonpolar solvents is attributed to strong ionic forces. On the other hand, hydrogen bonds, charge-transfer interactions, and π-π interactions are the predominant noncovalent coal-coal interactions in bituminous coal and restrain the solvent swelling of the coals. Some coal-coal interactions can be dissociated by acid washing or solvent extraction, e.g., acid pretreatment removes the ionic forces, solvent extraction with hydrogen bonding solvents dissociates hydrogen bonds, etc. For the cyclohexanone-extracted coal, swelling reaches the maximum value at carbon contents of 81.6 and 82.3 wt % for Fugu and Shuangyashan coal, respectively, which implies that the coal-coal interactions are the weakest in this rank of coal. In addition, the decrease of swelling after CS 2 -N-methyl-2-pyrrolidinone (NMP) extraction of Shenbei lignite was found to be attributed to the coordination of N and O in NMP with metal ions in the coal.

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“…1), which should be related to the reductive character of the process conducted in this reaction system. The solubility of coals in typical organic solvents depends on the so-called secondary coal structure, whose most important component is the network of hydrogen bonds [24]. As a result of both reductive and non-reductive alkylation, the hydroxyl groups are Oalkylated, which weakens the hydrogen bonds and leads to increased solubility.…”

Section: Resultsmentioning

confidence: 99%

Composition of extraction products from alkylated high-sulphur coals

2003

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Products of reductive and non-reductive methylation of two high-sulphur coals (Mequinenza and Illinois No. 6) have been extracted by dichloromethane. It has been established that the e¯ciency of the transformation of coal to the products soluble in CH 2 Cl 2 is higher for coals subjected to non-reductive methylation by the Liotta method than for those after reduction in the potassium=liquid ammonia system. The extracts and the extraction residues were subjected to elemental analysis, IR spectroscopy, and AP-TPR (Atmospheric PressureTemperature Programmed Reduction) measurements. It has been shown that the main species undergoing extraction by CH 2 Cl 2 are aliphatic compounds or aromatic structures of low degree of condensation. The e¬ect of the extraction on the sulphur groups in coal has been discussed.

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The Role of Noncovalent Bonding in Coal

Cited by 14 publications

References 83 publications

Observation of the Type of Hydrogen Bonds in Coal by FTIR

Observation of the Type of Hydrogen Bonds in Coal by FTIR

Role of Noncovalent Bonding in Swelling of Coal

Composition of extraction products from alkylated high-sulphur coals

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