CO_(2)水合物生长特性的分子动力学模拟

Molecular dynamics simulations of growth characteristics of CO_(2) hydrate

采用分子动力学对CO_(2)水合物生长进行模拟并分析其变化规律,探究了CO_(2)水合物晶体生长的微观过程以及不同温度、压力条件对水合物生长特性的影响机理.CO_(2)水合物的生长是从已有晶胞附近向外扩散并逐具有序性的过程,水分子间逐渐形成四面体氢键与CO_(2)共同形成完整的水合物笼.另外,CO_(2)水合物生长需要合适的过冷度,在压力为30 MPa、温度范围265 K至275 K,水合物笼型晶胞可正常生成,并且温度越低,生成速率越快;在高温290 K和300 K时,体系分子运动加剧,水合物笼直接散开.此外,在温度为270 K、不同压力条件下,发现相较温度而言,由于CO_(2)溶解度随压力变化的不明显性,导致CO_(2)水合物增长速度伴随压力的变化相对不敏感.

The growth of CO_(2)hydrate was simulated and its variation was analyzed by using molecular dynamics simulations.The microscopic process of CO_(2)hydrate crystal growth and the mechanism of different temperature and pressure conditions on the growth characteristics of hydrate were explored.The growth of CO_(2)hydrate is a process of diffusing outward from the existing unit cell and gradually becoming ordered.In this process,water molecules gradually form tetrahedral hydrogen bonds and form complete cages with CO_(2).Additionally,the growth of CO_(2)hydrate requires a suitable degree of supercooling.At pressure of 30 MPa and a temperature range of 265 K to 275 K,hydrate cages can grow normally,and the lower the temperature,the faster the growth rate.At high temperatures of 290 K and 300 K,the hydrate cages spread out directly due to the intensified molecular movement of the systems.In addition,at temperature of 270 K and different pressures,it is found that compared with temperature,due to the invisibility of CO_(2)solubility with pressure changes,the growth rate of CO_(2)hydrate with pressure changes is relatively insensitive.