含水合物CH4-H2O体系中溶解甲烷的拉曼光谱原位监测

In-situ Raman Observation of Dissolved CH_4 in Hydrate-bearing CH_4—H_2O System

利用低温高压反应舱模拟海底水合物生成环境,采用原位拉曼光谱技术在线测定含水合物CH_4—H_2O体系中溶解甲烷的拉曼光谱,基于相关理论模型建立了溶解甲烷的拉曼光谱工作曲线(相关系数为0.999 77),定量分析了水合物形成后体系温度、压力对溶解甲烷浓度的影响。结果表明,拉曼光谱技术可准确测定溶解甲烷的浓度,实测溶解甲烷浓度值与理论计算值相吻合,相对误差小于5%。当体系中水合物形成后,温度对溶解甲烷的影响占主导作用,压力影响相对较弱,溶解甲烷浓度随温度升高显著增大,随压力升高而减小;而在气-液两相的情况下,温度与压力对体系内溶解甲烷浓度的影响正好相反。这很好地阐明了在天然气水合物稳定域内、外溶解甲烷浓度的变化特征。

A reaction tank with low temperature and high pressure is designed to form gas hydrate in the seabed environment, and in situ Raman spectroscopy is used for measuring the dissolved methane in a hydrate-bearing CH4-H2O system. A Raman spectrum working curve of dissolved methane is estab- lished （the correlation coefficient r = 0. 999 77） based on the relevant theory models. The effects of temperature and pressure on the dissolved methane concentration are analyzed quantitatively after hydrate formation. The results show that Raman technique can accurately measure the concentration of dissolved methane, and the experimental data agree well with theoretical calculations with a relative er- ror less than 5~. After gas hydrate formation in the system, the temperature affects the dissolved methane concentration dominantly, while the pressure effect is relatively weak. The dissolved methane concentrations increase sharply with the increase of temperatures and decrease with the pressures in- crease. However, in a gas-liquid system, the effects of the temperature and pressure on the dissolved methane concentrations are just opposite. It shows a good illustration of the dissolved methane charac- teristics inside and outside of marine gas hydrate stability zone.