显微激光拉曼光谱原位观测甲烷水合物生成与分解的微观过程

摘要

Micro laser Raman spectroscopic technique was used for in situ observation of the micro-processes of methane hydrate formed and decomposed in a high pressure transparent capillary. The changes in clathrate structure of methane hydrate were investigated during these processes. The results show that, during hydrate formation, the Raman peak(2 917 cm-1 )of methane gas gradually splits into two peaks (2 905 and 2 915 cm-1 ) representing large and small cages, respectively, suggesting that the dissolved methane molecules go into two different chemical environments. In the meantime, the hydrogen bonds interaction is strengthened because water is changing from liquid to solid state gradually. As a result, the O-H stretching vibrations of water shift to lower wavenumber. During the decomposition process of methane hydrates, the Raman peaks of the methane molecules both in the large and small cages gradually clear up, and finally turn into a single peak of methane gas. The experimental results show that laser Raman spectroscopy can accurately demonstrate some relevant information of hydrate crystal structure changes during the formation and dissociation processes of methane hydrate.%采用显微激光拉曼光谱技术对高压透明毛细管中甲烷水合物的生成与分解的微观过程进行了原位观测,初步探讨了甲烷水合物笼型结构的变化规律.结果表明,甲烷水合物在生成过程中,甲烷分子的拉曼峰(2 917 cm-1)逐渐分裂为两个峰(2 905和2 915 cm-1),表明溶解态甲烷分子从单一的化学环境进入了两个有差异的化学环境中,这两个峰分别代表着水合物的大笼和小笼.同时,水的氢键作用由其液态向固态的转化而得到加强,使O-H键伸缩振动向低波数迁移.在甲烷水合物的分解过程中,大小笼中甲烷分子的拉曼双峰逐渐消解,并最终转化成单一的甲烷气体峰.显微激光拉曼光谱可以准确捕捉水合物生成与分解过程中其笼型结构变化的相关信息.