Coal Tar Dissolution in Water-Miscible Solvents: Experimental Evaluation

Coal tar, a dense nonaqueous phase liquid (NAPL), is a common subsurface contaminant at sites of former manufactured gas plants. A proposed remediation technology is water-miscible solvent extraction, which requires understanding of the effect of water-miscible solvents on the solubility of coal tar. This study investigated this effect and the extent to which multicomponent coal tar could be represented as a pseudocomponent in thermodynamic modeling. The coal tar used in this study showed a predominance of polycyclic aromatic hydrocarbons with no single compound accounting for more than 4% (wt). The bulk solubility of coal tar in water was estimated to be 16 mg/L using composition data and Raoult's law assumption for aqueous solubility. For three solvents, n-butylamine, acetone, and 2-propanol, equilibrium phase compositions of two-phase coal tar/solvent/water mixtures were experimentally determined using radiolabeled materials and are presented as ternary phase diagrams. Results showed n-butylamine to be a good water-miscible solvent for coal tar dissolution. The validity of thermodynamic modeling of coal tar as a pseudocomponent was explored by examining the liquid-liquid solute partitioning of naphthalene, phenanthrene and pyrene and by assessing the effect of solvent extraction on coal tar phase composition. It was found that coal tar partitions as a pseudocomponent in systems with appreciable solvent, but not in systems with only coal tar and water.