Effect Of Guest Molecules On Mechanical Properties Of SⅠ-type Clathrate Hydrates

Natural gas hydrate is a non-stoichiometric ice-like crystalline compound with a cage structure,commonly known as "flammable ice".Natural gas hydrate in nature is mainly formed by methane gas and water molecules in a low temperature and high pressure environment,so it usually exists in deep-sea sediments and permafrost regions.Natural gas hydrate is considered as a potential energy source in the future and has caused extensive research in various countries around the world.In addition to being a new type of mining energy,the unique molecular structure of natural gas hydrate also involves many hot research issues,such as gas storage,separation,and transportation.Therefore,studies on the formation process and stability of natural gas hydrates have attracted the attention of scholars from various countries.Based on the study of natural gas hydrates at home and abroad,this paper carried out molecular dynamics simulation of uniaxial tensile load on sI hydrate.The mechanical stability of hydrates containing different guest molecules is mainly studied,and the effects of guest molecules on the structure and mechanical properties of hydrates are analyzed.This paper first discusses the influence of the geometric configuration and motion of the guest molecule on the mechanical properties of the hydrate structure.The study found that the potential energy of the interaction between the guest molecule and the host water molecule is mainly related to the free movement of the guest molecule in the cage.For linear structure molecules such as CO2,as the strain increases,the rotation of the molecules in the@512 and@ 51262LP cage is Confinement in the direction of tensile load results in a decrease in potential energy,and the effect of this limitation will decrease with increasing temperature.Different cage types have different sensitivity to tensile load.Generally,large cages containing guest molecules in hydrates are more stable under tensile load.Under the same strain,the deformation of the O…O…O bond angle in the hydrate is more sensitive than the deformation of the O…O…O bond length and plays a more critical role in the destruction of the cage.Next,this article focuses on the influence of the ability of the guest molecule to form hydrogen bonds on the mechanical stability of the hydrate structure.Through analysis of the simulation results,it is found that the more the number of hydrogen bonds formed between the main water molecules of the sI gas hydrate,The better the mechanical stability.The stronger the ability of the guest molecule to form hydrogen bonds,the new hydrogen bonds will be formed with surrounding water molecules,resulting in a reduction in the number of hydrogen bonds between the host water molecules.Through a series of snapshot observations of the hydrate stretching process,it was found that the guest molecule hydrate with weak hydrogen bonding ability was mainly deformed on the(101)crystal plane.The formation of guest molecular hydrates with strong hydrogen bonding ability is mainly concentrated at the water molecular nodes of the cage.As the tensile load increases,the stress at the apex becomes more concentrated,then deformation occurs at each node in the hydrate structure,and largescale dissociation and destruction begin.