Mechanism of CO2 dissolution and crystallization influenced by temperature in the condensation of high-CO2 natural gas: A molecular dynamics study

ZX Wang and BB Wang and Y Wang and J Bian and YH Hua and Q Li and WH Cai, INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER, 253, 127521 (2025).

DOI: 10.1016/j.ijheatmasstransfer.2025.127521

Understanding the crystallization dynamics of CO2 during the condensation of high-CO2 natural gas is crucial for ensuring the safe operation of the pressurized liquefied natural gas (PLNG) process offshore. This study focuses on the condensation process of high-CO2 natural gas, employing molecular dynamics simulations to systematically investigate the coupled condensation nucleation behavior of CH4-CO2. In the high-temperature stage of the CH4-CO2 binary system (10% CO2), when the temperature drops below 170 K, CO2, as the more condensable component, preferentially nucleates, forming initial condensation sites. As the temperature further decreases to below 150 K, rapid CH4-dominated condensation is triggered, enhancing the dissolution capacity of condensation clusters for CO2 and leading to a detachment-dissolution transition for some CO2 molecules. In the lowtemperature stage below 130 K, the reduced solubility of CO2 in liquid CH4 induces reaggregation, driving the secondary crystal growth of CO2 clusters. Furthermore, a low cooling rate extends the condensation relaxation time, facilitating the evolution of CO2 clusters into ordered structures. These findings clarify the evolutionary pathways of CO2 nucleation, dissolution, and reaggregation in liquid CH4 driven by temperature, offering a framework for managing CO2 phase transitions in PLNG systems. This contributes to optimizing the nucleation of high-CO2 natural gas, enhancing the safety and efficiency of offshore natural gas development.

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