Condensation processes of carbon dioxide in high-pressure methane gas: A microscopic study of the dynamic behavior of nucleation, dissolution, and crystallization

This study analyzes the condensation and crystallization behavior of high-pressure methane and carbon dioxide (CH4-CO2) binary gases on the heat exchanger surfaces through microscopic molecular simulations. The results indicated that increasing the wall energy enhances the phonon coupling between CH4 molecules and copper atoms at the interface, significantly improving heat transfer at the fully wetted interface during initial condensation, from 6.34 × 108 W/m2 to 8.78 × 109 W/m2. In the condensation of CH4-CO2 gas, the nucleation rate increases with the CO2 content, rising from 6.77 × 1032/(m3·s) to 8.55 × 1032/(m3·s), promoting cluster merging. As the temperature decreases, the stability of the CO2 clusters in the initially condensed clusters is low, and some CO2 molecules detach from the clusters and dissolve in liquid CH4. With further temperature reduction and the influence of cryogenic environment, free CO2 gradually aggregates toward the CO2 clusters, promoting their growth and resulting in the cluster structure to be denser and undergoes an ordered evolution. These results reveal the dynamic paths of CO2 aggregation and crystallization during CH4 condensation, providing a theoretical basis for regulating CO2 crystallization behavior in PLNG technology.