Liberation of molecular hydrogen (H2) and methane (CH4) during non-isothermal pyrolysis of shales and coals: Systematics and quantification

Based on previous research on H2 generation mechanisms, different evolution pathways are proposed to explain the observed H2 release patterns. For shales, the dominant mechanism shifts from cracking of hetero-bonds and demethylation in Group A towards aromatization and condensation in Groups B and C. In coals, aromatization and condensation are considered to be the predominant H2 evolution mechanisms. The molar yields of H2 correlate like the CH4 yields with the TOC and Rock-Eval S2 values of the samples, indicating a purely organic origin. The results have implications for hydrogen balance considerations during thermal maturation of coals and gas/oil shales.