显微激光拉曼光谱测定天然气水合物的方法研究

Study on Determination Method of Natural Gas Hydrates by Micro-Laser Raman Spectroscopy

天然气水合物是由烃类气体在一定的温度和压力下与水作用生成的一种非化学计量的笼型晶体化合物,显微激光拉曼光谱是测定其水合指数、笼占有率等结构参数的重要手段。天然气水合物极易分解,不能在常温常压下进行分析测试。本文针对天然气水合物的特性,研制了一套适合显微激光拉曼光谱法测定水合物的小型装置,将样品放入液氮罐中,定期加入液氮(-196℃)保存,确保在测定的过程中甲烷水合物保持稳定状态,解决了肉眼不可见水合物的微观识别问题。对实验合成的一系列不同体系的甲烷水合物和我国海域和陆域的水合物样品进行了分析,探讨了水合物样品的合成、保存和处理方法,研究了拉曼光谱测试条件,揭示不同条件下形成的水合物笼型结构特征。分析结果表明,对同一样品,测定水合指数的相对标准偏差小于1%,方法准确可靠,经分析南海神弧海域水合物为典型Ⅰ型结构的水合物,祁连山冻土区水合物为Ⅱ型结构的水合物,可为我国天然气水合物研究提供必要的结构信息。

Natural gas hydrates are non-stoichiometric clathrate compounds that are formed by hydrocarbon gases and water molecules under the conditions of low temperature and high pressure.Micro-laser Raman Spectroscopy is applied as an important method to measure structural parameters（e.g.hydration number,cage occupancy）.Since the gas hydrate sample readily decomposes,it cannot be measured under normal temperature and pressure.In this paper,we describe a small instrument that has been designed to use Micro-laser Raman spectroscopy at low temperature and pressure for gas hydrates.Our work focuses on the synthesis,preservation and pre-treatment methods of hydrate samples and optimizing parameters of the instrument.The method was verified by repeatedly measuring hydration numbers of the same sample with RSD less than 1%.The results show that the method is accurate and reliable and can be used to identify the structure of simple hydrates.This method has been applied to measure natural gas hydrate samples recovered from the Shenhu area of the South China Sea and also Qilian mountain permafrost with satisfying results.