Effect of addition of salts on coal extraction in CS₂/NMP mixed solvent

The effect of addition of various salts on the extraction of seven different kinds of coals with carbon disulfide-N-methyl-2-pyrrolidinone (CS₂-NMP) mixed solvent (1:1 by volume) was investigated. Addition of some salts considerably increased the extraction yield for several coals. For Upper Freeport coal, in particular, the addition of a very small amount (0.25 mol/kg-coal) of tetrabutylammoniumfluoride increased the extraction yield from 60 to 84%. The effect of a kind of anions on the extraction yield was also examined. It was found that the charge density of anion is responsible for the increase of the extraction yields. The fractionations of the extracts using pyridine indicate that the extracts obtained with the additive contain heavier constituents than those without the additive.