Study on polymer degradation and nitrogen migration mechanisms in supercritical water

Polymer drives have been widely used in oilfield extraction, and the presence of polymers increases the complexity and affects the stability of oily sludge. To investigate the efficient and environmentally benign treatment of these polymers, this study employed ReaxFF molecular dynamics simulations to explore the degradation mechanisms of polyacrylamide (PAM) under different reaction conditions, including pyrolysis, supercritical water gasification (SCWG), and supercritical water oxidation (SCWO). The investigation focused on free radical reactions, degradation pathways, product formation mechanisms, and nitrogen transfer pathways. The results indicate that compared to pyrolysis, the ·OH and HO₂• radicals generated by H₂O and O₂ during SCWO more readily attack the carbon atom in the amide group, increasing the amide group detachment efficiency by 129.17 %. A high oxygen concentration enhanced the reaction competitiveness of intermediates with high O/C ratios, leading to a maximum increase of 26.39 % in the conversion of -CHO₃ to CO₂. NH₃ was identified as the predominant nitrogen-containing intermediate. Moreover, at 5000 K, N₂ formation occurred 300 ps earlier than at 3500 K, with the yield doubling.