Chemical Characterization of Coal Tar−Water Interfacial Films

Abstract

Semigelatinous interfacial films, which may influence the fluid mechanic and mass transfer properties of coal tar in porous media, have been observed to form in coal tar−water systems when coal tars are aged in water under quiescent conditions for a few days. Samples of the interfacial film were isolated after aging for a period of 1 year and compared to the bulk coal tar using GC/MS, 13 C-NMR, 1 H-NMR, and FTIR techniques. The results showed that these films were very similar in organic composition to the bulk coal tar with no significant enrichment, depletion, or polymerization of tar components. The notable difference in the composition of the film material was the presence of water bound to coal tar constituents by weak, reversible bonds. FTIR analysis of a sample of coal tar film kept in contact with deuterated water showed that the water molecules bound to the coal tar constituents would slowly interchange with water molecules that were not bound. Similar bonding of water molecules and coal tar constituents was observed in coal tar−water emulsions. These results suggest that the semigelatinous film formed at the coal tar−water interface is similar to a thin emulsion layer.