The mechanism of H2O in the superheated steam affecting pyrolysis of the kaolinite-associated kerogen

Abstract

In this work, ReaxFF molecular dynamics (MD) simulation was adopted to investigate the effect of superheated steam on the conversion of the kaolinite-associated Barkol kerogen (BLK) and reveal the corresponding mechanism. The ReaxFF simulated weight loss rate (DTG) and release tendency of H2O, H2 and CO2 for BLK and the kaolinite-associated BLK agreed well with the results of Py-MS experiments. H-rich rate, double bond equivalents (DBEs), and hydrocarbon content were adopted to assess the quality of C5-C40, and configurations of C40+ were extracted to investigate the characteristics of residues. And the H2Osteam- and kaolinite-involved (steam refers to the superheated steam) reactions were analyzed. The results indicate that B- and L-acid sites of kaolinite co-catalyzed decomposition of BLK into heavy oil and shale gas in the kaolinite-pyrolysis system, and in steam/kaolinite-pyrolysis system, H2Osteam further promoted decomposition of BLK into higher quality shale oil, especially for C5-C13 components, remaining higher aromatic and porous residues. And this enhanced effect of H2Osteam is attributed to kaolinite and the induced decomposition of H2Osteam molecules and their participation as reactants in reactions in two aspects: i) interaction between kaolinite and H2Osteam, on one hand, inhibited formation of L-acids and facilitated generation of B-acids to catalyze carbocation ion reactions process, further weakened dehydrogenation of organics catalyzed by L-acid sites, and enhanced cracking of residues catalyzed by B-acaid sites, on the other hand, promoted decomposition of H2Osteam molecules to form H-rich environment and further weakened dehydrogenation of organics; ii) attacking Car directly, H2Osteam promoted shedding of alkyl side chains and ring-opening of aromatics to increase the –CH2– content in shale oil. This paper provides theoretical guidance for further understanding mechanism of H2Osteam on pyrolysis of kaolinite-associated kerogen and corresponding catalyst development and preparation.