THE DETERMINATION OF AROMATIC AND ALIPHATIC C-H GROUPS IN COAL USING FOURIER TRANSFORM INFRARED SPECTROSCOPY (VITRINITE, MINERAL ANALYSIS, CARBON-HYDROGEN)

The determination of coal structure is an obdurate problem. Coal is heterogeneous, noncrystalline, and not completely soluble in any known solvent, making spectroscopic analysis of coal especially difficult. The most reasonable data that can be obtained at this time for coal is a quantitative determination of the functional groups present. Using infrared spectroscopy, information can be gained most readily about hydroxyl, aliphatic C-H, and aromatic C-H groups. The availability of Fourier Transform infrared Spectroscopy (FT-IR) has allowed such information to be obtained faster and more precisely than with earlier vintage dispersive instruments. In addition, proton nuclear magnetic resonance spectroscopy (NMR) has been useful in determining the distribution of hydrogen present among chemical functional groups in coal extracts, and thus coals, by assuming a correspondence in structure between the two. The validity of this assumption is discussed.;This method is then applied to a set of 35 whole coals and 41 vitrinite concentrate samples. Infrared absorption coefficients and hydrogen content are determined. Aromatic to aliphatic hydrogen ratios thus obtained are compared to those of other workers. Problems associated with equating infrared band intensities to elemental hydrogen are discussed in depth. The equations used to determine these coefficients are classically ill-conditioned, resulting in a range of solutions for the coefficients. However, the optimum coefficient values obtained for different coal rank subgroups are very similar to the values of the coefficients for the bituminous coal extracts. This justifies the transfer of the bituminous extract coefficients to all of the whole coals.;A method is developed to determine the aromatic and aliphatic C-H content in coal. This involves equating infrared band intensities to elemental hydrogen. This method is initially applied to a set of 11 pyridine coal extracts, also characterized by proton NMR. The NMR measurements of aliphatic and aromatic hydrogen allow direct calibration of the absorption coefficients of appropriate infrared bands. By this means the coefficients determined by relating the infrared band intensities to elemental hydrogen are directly tested. Reasonable agreement between the results from infrared spectroscopy and NMR is obtained.