Hydrocarbon Generation and Chemical Structure Evolution from Confined Pyrolysis of Bituminous Coal

The molecular composition of organic matter formed during pyrolysis is complex. Fourier transform infrared spectroscopy (FTIR) is a good technique to investigate the coal chemical structural evolution. However, reports on the effects of chemical structure on the n-alkane yields and their relative functional groups are scarce in the literature. In our case, the chemical structural evolution process of bituminous coal obtained by pyrolysis at two different heating rates has been analyzed by pyrolysis-gas chromatography (Py-GC) and FTIR. Furthermore, some of the small molecular compounds (e.g., n-alkanes 24 can generate n-alkanes 20 or low-weight compounds) generated by gold-tube pyrolysis were identified using other GC techniques. Biomarkers were analyzed and compared to generated n-alkanes from the gold-tube pyrolysis experiments. We present the results of the relationship between the FTIR parameters and the molecular compositions that were analyzed. A good linear relationship can be seen between the FTIR parameters (C=O, C=C, and C-factor values), the carbon preference index (CPI), and the ratio of the pristane content and n-C₁₇ alkane content (Pr/n-C₁₇). Furthermore, the n-alkane fraction of the pyrolysates, in particular pristane, phytane, n-C₁₇ alkane, and n-C₁₈ alkane, changed upon maturation. Our conclusions indicate that FTIR is applicable as a structural and chemical change probe to explore the pyrolysis process.