Increase of the extraction yields of coals by the addition of aromatic amines

The effect of the addition of aromatic amines on the yields of the extracti on of Argonne Premium coals with carbon disulfide-N-methylpyrrolidinone (CS 2-NMP) mixed solvent (1:1 by volume) was investigated. The addition of a ve ry small amount (25 mg/g-coal) of p-phenylenediamine (p-PDA) increased the extraction yield of Upper Freeport (UF) coal from 51.4 to 81.3%. The solven t fractionation of the extracts obtained shows that the increase in the yie ld was caused mainly by the increase of the heaviest fraction, i.e. pyridin e insoluble fraction (PI), and not that of the lighter pyridine soluble fra ction, p-PDA was also found to increase the solubility of PI in the CS2-NMP mixed solvent. These behaviors of p-PDA are very similar to those already observed by the addition of tetracyanoethylene, and can be explained by the breaking of the associates among coal molecules through the interaction of the amines with coal. The extraction yields of other Argonne Premium coals than UF coal also increased their extraction yields, but only slightly. Th e results obtained from the addition of various aromatic amines with differ ent structure and electron donatability suggest that the hydrogen bonds, no t electron donor-acceptor interaction, of the amines with coal seem to be r esponsible for the solubility enhancements of the coals and extracts. Effec t of water on the extraction yield was also examined. (C) 2000 Elsevier Sci ence Ltd. All rights reserved.