Variable-Temperature EPR Studies of Illinois No. 6 Coal Treated with Donor and Acceptor Molecules

Abstract

Variable-temperature EPR studies of Illinois No. 6 coal, its pyridine extract, and samples of each after treatment with known donor and acceptor molecules are reported. The purpose of the study was to explore the origin of the EPR signals near g ) 2 and to elucidate the nature of noncovalently bonded interactions in coal. Curie Law behavior is exhibited for each sample, indicating that the EPR signals are dominated by doublet state species. No evidence for thermally accessible, low-lying triplet states, such as those found in some charge-transfer complexes, was found. Infrared spectroscopy suggests, however, that electron transfer from the coal does occur after treatment with electron acceptors such as TCNQ and TCNE. EPR studies of the Illinois No. 6 coal samples after treatment with the known electron donor TTF revealed the formation of the TTF radical cation.

Pathway of TCNE Interaction with Coal To Enhance Its Solubility in the NMP−CS2 Mixed Solvent

“…After testing more than 20 additives, including electron acceptors and donors, tetracyanoethylene (TCNE) was found to be the most effective increasing the coal solubility to ∼80% for Upper Freeport and Zaozhuang coals. − However, the mechanism by which enhanced solubilization occurs is still not clear. Previous studies of the mechanism have concentrated on charge-transfer complex formation between TCNE and coal, ignoring the role of the solvent. − In this work, we report a reaction of TCNE with NMP related to the mechanism of TCNE enhancement of coal solubility.…”

“…Previous studies of the mechanism have concentrated on charge-transfer complex formation between TCNE and coal, ignoring the role of the solvent. [6][7][8][9] In this work, we report a reaction of TCNE with NMP related to the mechanism of TCNE enhancement of coal solubility.…”

Effect of Addition of Various Salts on Coal Extraction with Carbon Disulfide/N-Methyl-2-pyrrolidinone Mixed Solvent

“…6 coal demonstrate that the increase in the spin concentration by the addition of electron acceptors is not due to the formations of new paramagnetic centers, i.e., thermally accessible triplet state arising from charge-transfer interactions. 7 These results indicate that there is no experimental evidence for the formation of a chargetransfer complex between coal and electron acceptors. Thus the formation of the charge-transfer complex between the coal and the electron acceptor does not seem to be the plausible explanation for enhancing coal solubilities.…”

Ethylenediamine-Assisted Solvent Extraction of Coal in N-Methyl-2-pyrrolidone: Synergistic Effect of Ethylenediamine on Extraction of Coal in N-Methyl-2-pyrrolidone

“…It has been reported recently 56 that enhancement in extractability of coals in NMP+CS 2 system in the presence of additives may not be due to disruption of charge-transfer interactions. It may be due to the induced polarizability of aromatic systems of coal, thereby disrupting stable coal−coal interactions including π−π and van der Waals interactions and steric hindrance may prevent the disruption of charge-transfer interactions. , Painter has suggested that CS 2 limits any self-associations of NMP thereby allowing NMP to extract enhanced amount of coal . We suggest that the preswelling and the expansion of the matrix by EDA may reduce steric hindrance to the disruption of charge-transfer interactions by NMP under reflux conditions thereby resulting in enhanced extraction yields.…”