Molecular Dynamics Simulation Of The Effect Of Oily Macromolecular Organics On Stability Of Structure H Hydrate

As a low-carbon and environmentally friendly energy,natural gas is widely used in industrial production and our urban life.The large-scale application of natural gas is inseparable from its efficient storage and transportation.Natural gas storage by hydrate method is recognized as a highly potential and efficient gas storage technology,with the advantages of high efficiency,safety and economy.However,the slow growth rate of hydrate and the low actual gas storage capacity seriously restrict the industrial application of hydrate technology.There are three kinds of clathrate structures formed by gas hydrates.At the same time,compared with type I and type II hydrates,H-type hydrates can store a large number of gas molecules or larger organic molecules,which makes H-type hydrates in gas storage and transportation.The process has a very broad prospect.Exploring efficient and environmentally friendly accelerators to reduce the thermodynamic conditions of H-hydrate formation is of great significance for large-scale storage,transportation and industrial application of natural gas hydrates.Based on the molecular dynamics method,this paper simulates the effects of cycloheptanone(C₇H₁₂O),methylcyclohexane(C₆H₁₁-CH₃)and cycloheptane(C₇H₁₄)on H-type hydrates under ideal conditions under the constant temperature and pressure ensemble（NPT）.The stability and other related properties of the oil are analyzed through the radial distribution function（RDF）,mean square displacement（MSD）,final conformation map,relative concentration（RC）and other related parameters to analyze temperature conditions,pressure conditions,large crystal cavity occupancy and oily state.Effects of macromolecular organics and number of guest methane molecules on the stability of H-form methane hydrate.The details are as follows:（1）Under the constant temperature and constant pressure ensemble（NPT）,the temperature of 290K、300K、310K and 320K,the pressure of 3MPa and 8MPa,cycloheptanone,methylcyclohexane and cycloheptane were studied respectively.The influence of oily macromolecular organics on the stability of H-type methane（CH₄）hydrate model,and it is concluded that C₇H₁₂O,C₆H₁₁-CH₃and C₇H₁₄as guest molecules can occupy the H-type CH₄hydrate large crystal cavity,and the existence of oily macromolecular organics Helps to improve the stability of H-type methane hydrate.Under the action of different oily macromolecules,the order of hydrate stability was cycloheptane>methylcyclohexane>cycloheptanone.（2）Using cycloheptane as a large guest molecule to study the stability of H-type hydrates with different large hole occupancies,under the conditions of temperature of 290K,pressure of 3 MPa and 8 MPa,the study of large hole occupancy is 100%,75%,50%and 25%on the stability of H-hydrate.The study found that when the occupancy rate of macropores is 100%,the hydrate cage structure is well supported by guest molecules and has good stability,but when the occupancy rate of macropores is less than 100%,the hydrate cage structure is unstable.,it is easy to distort and cause the collapse of the hydrate cage structure.（3）Under the conditions of temperature of 290K,pressure of 3MPa and 8MPa,taking cycloheptane as an example,when the number of large guest molecules in the macrocage remains unchanged,the hydrate stability changes with the increase of the number of methane molecules in the macrocage.Condition.It is concluded that when the number of large guest molecules in the large cage is constant,the stability of the hydrate increases with the increase of the number of methane molecules in the large cage,and there can be up to 4methane molecules stably in the large cage,and each of them can be stable.The H-hydrate with 4 methane molecules in the large cage has the highest stability.（4）The stability of H-type coalbed methane hydrate was studied when different proportions of methane and nitrogen were used as small guest molecules.The results show that the different ratios of guest methane molecules and nitrogen molecules have a very direct effect on the stability of the cage structure of H-hydrate.When the ratio between methane molecules and nitrogen molecules is 7:3（28CH₄+12N₂）,the average hydrogen bond length of the H-type hydrate hydrate system is the closest to the initial stable structure,and CBM hydrate is the most stable at this time.