Computational simulation of fluorinated methane derivatives in type I clathrate hydrate

• Published in: Journal of molecular liquids Vol. 314; p. 113783
• Main Authors: Fernández-Fernández, Ángel M., Piñeiro, Manuel M., Pérez-Rodríguez, Martín
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.09.2020
• Subjects: Clathrate; Electronic DFT; Energy barrier; HFC; Inter-cage transition; Type I hydrate; Type I hydrate; Clathrate; Electronic DFT; HFC; Energy barrier; Inter-cage transition
• ISSN: 0167-7322; 1873-3166
• DOI: 10.1016/j.molliq.2020.113783

We have performed quantum mechanical simulations of methane and derivative fluorocarbon gases (CH4, CH3F, CHF3, CF4) as guest molecules inside type I clathrate hydrate, in order to assess the stability of the clathrate and the ability of the guest gas to diffuse through the water crystalline lattice. Our results confirm the suspected high stability of the clathrate and the great difficulty for the gas molecules to move through the faces of the water polyhedra. We have found that the diffusion along the clathrate channels is thermodynamically allowed, but its probability is quite low due to the high energy barriers the guest molecule has to overcome. The water lattice has to be heavily deformed in order to allow the transport of the guest. Interestingly, those barriers get significantly reduced from their expected maxima, due to the reordering of water H-bonds and the temporal formation of new H-bonds with guest molecule F atoms. This phenomenon may have important implications in the long term stability, and also in the selectivity of the hydrate with respect to other guests of similar sizes. [Display omitted] •Quantum simulations of type I hydrates of CH4, CH3F, CHF3 and CF4 are discussed.•Inter-cage transition barriers are of the order of about a hundred kJ mol−1.•Transitions depend on redistribution of hydrogen bonds in the inter-cage water ring.•Diffusion in type I hydrates results in the order: CH3F > CH4 > CHF3 > CF4.