Investigation of microscopic mechanisms for carbon dioxide homogeneous crystallization during pressurized liquefaction of natural gas

Clarifying the dynamic mechanism of carbon dioxide (CO2) crystallization is of great significance for effectively regulating the crystallization behavior of CO2 during natural gas pressurized liquefaction. Therefore, this paper investigates the microscopic behavior of liquid CO2 crystallization under different temperature conditions and cooling rates by molecular dynamics simulation. It analyzes the dynamic characteristics of crystal nuclei formation and growth, elucidating the influence mechanism of temperature on the homogeneous crystallization of CO2. The results show that, in a cryogenic environment, the homogeneous crystallization process of CO2 undergoes two stages, densification and ordering, where C atoms gradually transit from a disordered liquid distribution to an ordered crystalline arrangement. An appropriate temperature helps balance intermolecular interactions and diffusion movement capacity, which are crucial for the crystal nuclei formation and growth. Under cryogenic conditions, after nucleation occurs, a transitional phase is required before rapid growth can commence. Additionally, as the cooling rate decreases, the distribution characteristics of C atoms shift from disorder to order, slower cooling rates facilitate the crystal formation and structural stabilization and increase the nucleation temperature, thereby shortening the transition time for the nucleation to enter the rapid growth stage.