Investigation into the swelling of Beulah Zap lignite using various organic liquids
Coal is an abundant natural resource having a complex structure. Poly-cyclic aromatic units, entangled aliphatic sidechains, and trapped mineral moieties mesh to create a layered organic material. Subtle differences exist in various types, or ranks, of coal. Differences in water, aromatic carbon, and polar functional group content are common depending on rank. Lignites, the lowest ranked of coals, have low amounts of aromatic carbon and large amounts of moisture and polar functional groups. Having these properties, Beulah Zap lignite from the Argonne Premium Coal Samples Program is an excellent subject to have undergo the most common tool in coal elucidation studies: liquid swelling. Samples of Beulah Zap lignite have been exposed to various liquids, each varying in chemical properties such as geometry, polarity, and aromaticity. Using X-ray scattering, the possible liquid-induced swelling of polycyciic aromatic layers within the coal has been examined. From each scattering pattern taken, phase interference and structural curves were calculated to gain insight into the structural properties of the lignite. The results have then been compared to molecular models of the swelling systems in order to accurately portray the lignite-swelling phenomenon. Results indicate swelling and increased interlayer distance of polycyclic aromatic units in samples exposed to phenol, N-methyl-2-pyrollidinone, aniline, and pyridine. Swelling has not been observed in samples exposed to hexane, acetonitrile, acetone, chlorohexane, ethanol, triethylamine, tetrahydrofuran, and benzene. Molecular modeling of the lignite/liquid systems indicate the presence of a C 9 bilayer for the samples exhibiting no swelling. For those showing swelling behavior, a C9 bilayer intercalated with a liquid molecule fits best with the experimental data.