Effects of Layer-Charge Distribution of 2:1 Clay Minerals on Methane Hydrate Formation: A Molecular Dynamics Simulation Study

• Published in: Langmuir
• Main Authors: Li, Yun, Chen, Meng, Liu, Chanjuan, Song, Hongzhe, Yuan, Peng, Zhang, Baifa, Liu, Dong, Du, Peixin
• Format: Report
• Language: English
• Published: AMER CHEMICAL SOC 2020
• Subjects: CARBON-DIOXIDE HYDRATE; CO2 HYDRATE; CH4 HYDRATE; X-RAY; NUCLEATION; MONTMORILLONITE; PHASE; WATER; SURFACES; STABILITY; Chemistry; Materials Science; Multidisciplinary; Physical; Methane hydrate
• Online Access: http://ir.giec.ac.cn/handle/344007/27045; https://doi.org/10.1021/acs.langmuir.0c00183

Molecular dynamics simulations were used to investigate the effects of the external surface of a 2:1 clay mineral with different charge amounts and charge locations on CH4 hydrate formation. The results showed that 5(12), 5(12)6(2), 5(12)6(3), and 5(12)6(4) were formed away from the clay mineral surface. The surface of the clay mineral with high-and low-charge layers was occupied by Na+ to form various distributions of outer-and inner-sphere hydration structures, respectively. The adsorbed Na+ on the high-charge layer surface reduced the H2O activity by disturbing the hydrogen bond network, resulting in low tetrahedral arrangement of H2O molecules near the layer surface, which inhibited CH4 hydrate formation. However, more CH4 molecules were adsorbed onto the vacancy in the Si-O rings of a neutral-charge layer to form semicage structures. Thus, the order parameter of H2O molecules near this surface indicated that the arrangement of H2O molecules resulted in a more optimal tetrahedral structure for CH4 hydrate formation than that near the negatively charged layer surface. Different nucleation mechanisms of the CH4 hydrate on external surfaces of clay mineral models were observed. For clay minerals with negatively charged layers (i.e., high and low charge), the homogeneous nucleation of the CH4 hydrate occurred away from the surface. For a clay mineral with a neutralcharge layer, the CH4 hydrate could nucleate either in the bulk-like solution homogeneously or at the clay mineral-H2O interface heterogeneously.