Heterogeneous condensation mechanism of methane-hexane binary mixture

• Published in: Energy (Oxford) 2022-10, Vol.256, p.124627, Article 124627
• Main Authors: Guo, Dan, Cao, Xuewen, Zhang, Pan, Ding, Gaoya, Liu, Yang, Cao, Hengguang, Bian, Jiang
• Format: Article
• Language: English
• Subjects: Heterogeneous condensation; Methane; Molecular dynamics simulation; n-hexane; Natural gas; Nucleation
• ISSN: 0360-5442
• DOI: 10.1016/j.energy.2022.124627

The condensation mechanism of alkanes is an essential foundation for improving the liquefaction efficiency of natural gas. However, a microscopic understanding of this mechanism is still lacking. This study analyzes the homogeneous and heterogeneous condensation characteristics of methane and explores the influence mechanisms of n-hexane molecules. The results reveal that higher initial pressures cause more intense nucleation stages with more latent heat released. Moreover, changes in the monomer temperature lag behind changes in cluster temperature, which is particularly pronounced in low supersaturation systems. Trace amounts of n-hexane can greatly improve the nucleation rate and liquefaction ratio of methane. The pre-condensed n-hexane clusters serve as a surface for heterogeneous methane nucleation, lowering the nucleation barrier significantly. As the number of n-hexane molecules increases, the nucleation promotion effect is further enhanced. With increased subcooling, the promotion effect lg (J/J0) drops from 17 to approximately 2. Furthermore, the heterogeneous condensation of n-hexane and methane mixture comprises three processes: n-hexane condensation with methane molecular adhesion, methane aggregation on n-hexane nuclei, and surface growth of methane clusters accompanied by n-hexane dissolution. Moreover, methane with lower surface tension always dominates in the cluster surface region. •Condensation mechanism of methane and n-hexane was elucidated at molecular level.•The thermodynamic and kinetic characteristics during condensation were obtained.•Trace amounts of heavy hydrocarbons can promote nucleation of methane vapor.•Methane always dominates in the surface region of binary cluster.