Structure of some western Anatolia coals investigated by FTIR, Raman, 13C solid state NMR spectroscopy and X-ray diffraction

Abstract

Turkey has one of the largest lignite deposits in Europe but the low calorific values of Turkish lignites dictate new and environmentally safe new utilization technologies for further utilization. Research on coal chemical structures has long been of great interest as a fundamental issue for coal chemistry. Identifying the structures of organic material in lignites is important for lignite conversions to clean liquid fuels and value-added chemicals. Therefore, investigation of chemical and degree of ordered structure present in Turkish lignites is desirable. We report structural information of two coals from the Manisa Soma region, two from the Mugla Yatagan region and one from Kutahya Seyitomer region. FTIR spectra of coal samples contained peaks due to OH and CO functional groups, aliphatic CH, CH2, CH3 and aromatic CC and aromatic-CH structures. Coals with higher fixed carbon were oxidized more after oxidation experiments, as evidenced by the higher intensity of the CO band. Coals that contained higher amounts of nonpolar alkyl and aromatic CC, C-H groups were affected more by the oxidation reactions, which formed high-intensity CO band. XRD investigation revealed crystal structures present in the lignites were arranged slightly to form turbostratic arrangement. The structure of Yatagan region coals was less ordered compared to the other samples. The XRD aromaticity (fa) of the coals ranged between 0.642 and 0.777. Investigations showed that there was a good correlation between calculated structural parameters and maturity of the coals. Raman spectra of the coals revealed that samples contained significant proportions of highly disordered amorphous carbon structures. 13C NMR aromaticities of the coal samples were found between 0.536 and 0.754. Aromaticity values obtained by XRD and NMR methods were in high correlation.