Influence of minerals and iron on natural gases generation during pyrolysis of type-III kerogen

Pyrolysis experiments in a closed system were conducted on kerogen (isolated from a low mature coal sample) either in the presence or absence of clay minerals, iron-bearing minerals, transition metal and their mixture, respectively. The generated gases were collected and analyzed for chemical compositions by using gas chromatography and mass spectrometer; the solid residues were also quantitatively collected and analyzed for iron species using Mössbauer spectroscopy. These experiments revealed that the hydrocarbon gases generation from kerogen was significantly increased by catalysis of minerals and transition metal (iron). The generation of hydrocarbon gases could be potentially increased by 0.1-1.5 times in the presence of minerals and iron, and the catalytic efficiency was in the order of kerogen + mixed catalysts > kerogen + pyrite > kerogen + smectite > kerogen + iron > kerogen. The dryness ratios, including ethene/ethane, propene/propane, isobutane/n-butane and isopentane/n-pentane, were all decreased due to the catalysis of smectite, pyrite and mixed catalysts, and slightly increased with iron addition. The conversion of pyrite into pyrrhotite and elemental sulfur started at 300 °C during the experiments, for which pyrite might be as an inducer indirectly via sulfur and thus enhance the free radical formation and improve the hydrocarbon yield.