Tensile properties of structural I clathrate hydrates: Role of guest—host hydrogen bonding ability

Abstract

Clathrate hydrates (CHs) are one of the most promising molecular structures in applications of gas capture and storage, and gas separations. Fundamental knowledge of mechanical characteristics of CHs is of crucial importance for assessing gas storage and separations at cold conditions, as well as understanding their stability and formation mechanisms. Here, the tensile mechanical properties of structural I CHs encapsulating a variety of guest species (CH4, NH3, H2S, CH2O, CH3OH, and CH3SH) that have different abilities to form hydrogen (H-) bonds with water molecule are explored by classical molecular dynamics (MD) simulations. All investigated CHs are structurally stable clathrate structures. Basic mechanical properties of CHs including tensile limit and Young's modulus are dominated by the H-bonding ability of host-guest molecules and the guest molecular polarity. CHs containing small CH4, CH2O and H2S guest molecules that possess weak H-bonding ability are mechanically robust clathrate structures and mechanically destabilized via brittle failure on the (1 0 1) plane. However, those entrapping CH3SH, CH3OH, and NH3 that have strong H-bonding ability are mechanically weak molecular structures and mechanically destabilized through ductile failure as a result of gradual global dissociation of clathrate cages.

Strengthening and weakening of methane hydrate by water vacancies

“…Using TIP4P, TIP4P/2005, TIP4P/ICE and TIP4P/EW water models, the tensile strength of defectfree sI methane hydrate is predicted to be around 0.826, 1.135, 1.135 and 0.872 GPa, respectively. The tensile strength of perfect sI methane hydrates predicted by TIP4P, TIP4P/2005, TIP4P/ICE water models are in good agreement with previous data by Shi et al (2018) and Xin et al (2021).…”

“…Using molecular dynamics (MD) simulations, the effects of engineering strain rate, temperature, crystal orientation, guest molecules, cage occupancy and nanovoids on the mechanical properties of clathrate hydrates were examined (Wu et al, 2015;Cao et al, 2020;Xu et al, 2020). It was revealed that the fundamental mechanical properties such as tensile strength limit, fracture strain and destabilization pattern are dominated by the guest molecular property such as size, shape and polarity (Shi et al, 2018;Xin et al, 2021). Moreover, the degree of occupancy of guest molecules in the large 5 12 6 2 cages primarily determines the mechanical strength and elastic limit of clathrate hydrates (Cao et al, 2018).…”

Exploring Guest–Host Interactions in Gas Hydrates: Insights from Quantum Mechanics

“…The effect of the topology of the H-bond network of the host cages was quite substantial. The encapsulation of guest molecules would inevitably lead to the deformation of the cage. − This deformation showed the relative position change of the water molecule in the crystal hydrate. It was not conducive to the overall stability of the hydrate and may even lead to decomposition of the hydrate at the macroscale.…”

“…The simulation results showed that CO 2 accelerated nucleation due to its high solubility. Wu et al − estimated the mechanical characteristics of the hydrate by MD simulation and studied the key influencing factors of the hydrate stability. The results showed that the stability of the gas hydrate depends not only on the size and shape of the guest molecules but also on their polarity.…”

Insights into the mechanical stability of tetrahydrofuran hydrates from experimental, machine learning, and molecular dynamics perspectives

“…25–27,35 Fundamental mechanical parameters like tensile strength, fracture strain, Young's modulus, and failure pattern are influenced by the properties of guest molecules, such as size, shape and polarity. 27,32,33…”