天然气水合物粉晶X射线衍射测试参数优化及分析方法

天然气水合物是由烃类气体和水在低温高压下形成的一种非化学计量的笼型晶体水合物,在常温常压下极易分解,需要在低温条件下对其进行测试。本文针对天然气水合物这一特殊样品,重点研究其粉晶X射线衍射测试条件,系统地探讨了步长、扫描速度、累加次数及测试温度等因素对测试结果的影响,优化了仪器参数,建立了粉晶X射线衍射测试天然气水合物晶体结构的方法,并应用到实验合成的甲烷水合物和我国南海珠江口盆地钻获的天然气水合物样品的晶体结构测试中。结果表明,我国南海珠江口盆地的天然气水合物样品与实验合成的甲烷水合物结构相同,均属立方晶系,为典型的Ⅰ型水合物,晶胞参数分别为11.9309×10~(-10)m和11.9135×10~(-10)m。该技术可准确获得天然气水合物的结构信息,为我国天然气水合物的深入研究提供技术支撑。

Parameter Optimization and Analysis Method for Determination of Natural Gas Hydrate by Powder X-ray Diffraction

Gas hydrate is a form of non-stoichiometric clathrate compound which is produced by hydrocarbon gas molecules and water molecules at high pressure and low temperature. Usually under atmospheric pressure and room temperature, the hydrate sample is easy to decompose and thus the analysis must be carried out at low temperature. The analysis conditions of powder X-ray Diffraction for natural gas hydrate is the focus of this study. The influencing factors (i.e., increment, scan speed, cumulative number, and the temperature) were systematically studied to optimize the analytical parameters. As a result, a powder X-ray Diffraction method to measure the crystal structure of gas hydrate is proposed. This method has been used successfully to measure the crystal structure of the hydrate samples from both the laboratory and the Pearl River Mouth basin in the South China Sea. The results show that the hydrate samples have a similar cubic crystal structure. Both the synthetic methane hydrate in the laboratory and the gas hydrate from the Pearl River Mouth basin in the South China Sea belong to the type I hydrate and have unit cell parameters of 11.9309×10^-10 m and 11.9135×10^-10 m, respectively. This method can be used to obtain the structural information of gas hydrate, and will provide a technical support for further research of gas hydrate in China.