显微激光拉曼光谱测定甲烷水合物的水合指数

甲烷水合物是由甲烷气体分子与水分子在低温高压下形成的一种笼型结构化合物，广泛存在于海底陆架区和陆地冻土区，被认为是一种潜在的能源资源。在水合物的晶格中，水分子在氢键的作用下形成大小不同的笼子，甲烷分子可分别进入大笼(51262)和小笼(512)中。在自行研制的实验装置上，分别合成了一系列不同体系下的甲烷水合物，包括十二烷基硫酸钠(SDS)水溶液-甲烷体系、冰粉-甲烷体系以及冰粉-不同粒度砂-甲烷体系。对这些甲烷水合物样品进行了激光拉曼光谱分析，测定了其水合指数，笼占有率等结构参数。结果表明，这些甲烷水合物都为Ⅰ型结构，其水合指数和笼占有率基本不受沉积物粒径大小的影响。在3种体系中生成的水合物，大笼中甲烷分子基本占满，占有率大于97%;小笼中甲烷分子占有率为80%～86%，测得的水合指数为6.05～6.15。

Determination of Hydration Number of Methane Hydrates Using Micro-Laser Raman Spectroscopy

Methane hydrates are clathrate compounds that are formed by methane molecules and water molecules under low tem-perature and high pressure conditions. It was found that methane hydrates exist widely in sea-shelf floor and permafrost, and are considered as a potential energy resource. In the crystal lattice of clathrate hydrate, the water molecules form both large cages (5~(12)6~2) and small cages (5~(12)) under the interaction of the hydrogen-hydrogen bond. In this paper, the authors designed a set of experimental apparatus for methane hydrates formation. Based on this equipment, the authors synthesized a series of methane hydrates in various systems in laboratory, including SDS solution (3% Wt) and methane, powdered ice and methane, and pow-dered ice and methane and natural sand with various sizes (i.e. 250-350,180-250, 125-180 and 63-90 μm), under different tem-perature and pressure. The authors also designed a small device which was proved to be convenient for Raman determination of the methane hydrates. Raman spectroscopy was used to analyze the methane hydrates and to measure the structural parameters such as hydration numbers and cage occupancies. The results show that the methane hydrate samples are all in structure Ⅰ type, and hydration numbers and cage occupancies are almost independent of the sediment sizes. In the three systems, the large cages of methane hydrate samples are nearly full occupied, with the occupancy ratios larger than 97%, whereas the small cages be-tween 80% and 86%. The hydration numbers of these methane hydrate samples are between 6.05 and 6.15.