客体分子所处晶穴结构不同对甲烷水合物稳定性的影响

Influence for guest molecules in different cage types on the stability of methane hydrate

采用分子动力学方法模拟了SⅠ型甲烷水合物受热分解微观过程,并对水合物分解过程中不同晶穴结构内客体分子对甲烷水合物稳定性的作用进行了研究.通过最终构象、均方位移和势能等性质的变化规律对分别缺失大晶穴和小晶穴中客体分子的2种水合物体系随模拟温度升高稳定性的变化进行了分析.模拟结果显示,随温度的上升,水合物稳定性逐渐下降直至彻底分解;而水合物分解速度与2种晶穴各自部分晶穴占有率相关,不能简单的通过整体晶穴占有率表示.对比相同注热过程中2种水合物体系分解状况,发现位于大晶穴内的客体分子对水合物稳定性影响更大,缺失大晶穴内客体分子的水合物更容易随温度升高而分解.

Molecular dynamics simulation is used to study the microcosmic process for SⅠ methane hydrate dissociation.The influence of guest molecules in different cage types on the stability of SⅠmethane hydrate is studied.Two different systems of hydrate with similar overall occupancy are elected,one lost the guest molecules in large cage and the other lost the guest molecules in small cage.A series of different analysis include the final conformation,mean square displacements and change of potential energy is used to examine the difference of the stability of two hydrate systems in different temperatures.The results illustrate that when the temperature is increased,the stability of hydrate decrease until dissociated completely,and the dissociation rate of hydrate system is depending on the fractional occupancy of each cage type and cannot be described simply in terms of overall hydrate occupancy.Compared with the dissociation behavior of two hydrate system with similar temperature increase,the guest molecules in large cages have obviously influence on the stability of methane hydrate.Hydrate with empty large cages is easier to be dissociated with the temperature increased.