Unveiling atomic mechanism of organic sodium on the inhibition of tar and the release behavior of sodium in Zhundong coal hydropyrolysis via ReaxFF MD simulation

Abstract

In this work, the effect of organic Na on coal hydropyrolysis was investigated at the atomic level by reactive molecular dynamics (ReaxFF MD) simulation, and verified by corresponding hydropyrolysis experiment. Results show that organic Na can reduce the initial temperature of the hydropyrolysis reaction, promote the release of H₂O and volatile gases, and accelerate the decomposition of coal macromolecules. The atomic inhibition mechanism of organic Na on tar formation was revealed, through inhibiting the formation path of tar, promoting tar condensation to coke, and enhancing the release of H₂O and other volatiles in tar. Additionally, through statistical analysis of Na-containing products and tracking real-time reaction trajectories, three primary pathways for the migration and transformation of organic Na were identified. First, organic Na breaks at the O-Na bond to form atomic Na, which then reacts with inorganic components like H₂O and -OH, a process that occurs frequently. The resulting atomic Na combines with gaseous hydrocarbons to form gaseous Na, which is subsequently released. Tar-Na is formed when atomic Na interacts with tar molecules. These findings provided valuable molecular dynamics insights for exploring the sustainable and efficient conversion of high-alkali coal resources.