Ⅰ型CH_(4)/CO_(2)水合物稳定性的分子动力学模拟

Molecular dynamics simulation of stability of type I CH_(4)/CO_(2) hydrate

针对CO_(2)置换CH_(4)水合物,采用分子动力学模拟方法,在NPT系综,温度为253 K,压力为2 MPa条件下,研究了不同晶穴占有率对Ⅰ型CH_(4)水合物和CO_(2)水合物稳定性的影响,分析了水合物的最终构象、径向分布函数、均方根位移和势能变化等。结果表明:CO_(2)水合物在晶穴占有率高于37.5%时,水分子氢键结合形成的笼形结构能保持稳定;晶穴占有率低于37.5%时,水分子无序程度变大导致整体结构不能保持稳定;晶穴占有率在37.5%与62.5%之间时,CH_(4)水合物均发生了不同程度的分解,CO_(2)水合物结构虽然有轻微扭曲,但整体结构依然保持稳定。

For the replacement of CH_(4) in natural gas hydrate by CO_(2),the effects of different hydrate cage occupancy on the stability of typeⅠCH_(4) hydrate and CO_(2) hydrate were studied by molecular dynamics simulation at 253 K and 2 MPa in NPT ensemble.And the final conformation,radial distribution function,root mean square displacement and potential energy change of hydrate were analyzed.The results show that when the hydrate cage occupancy of CO_(2) hydrate is higher than 37.5%,the cage structure formed by hydrogen bonding of water molecules can remain stable.When the hydrate cage occupancy of CO_(2) hydrate is lower than 37.5%,the disorder degree of water molecules becomes larger,resulting in the instability of the overall structure.When the hydrate cage occupancy is between 37.5%and 62.5%,CH_(4) hydrates are decomposed in different degrees,the structure of CO_(2) hydrate is slightly distorted but the overall structure remains stable.