In situ Raman Spectroscopic Observation of Micro-Processes of Methane Hydrate Formation and Dissociation
LIU Chang-ling1，2，YE Yu-guang1，2，MENG Qing-guo1，Lü Wan-jun3，WANG Fei-fei3
1. Key Laboratory of Marine Hydrocarbon Resources and Environmental Geology, Ministry of Land and Resources, Qingdao 266071, China 2. Qingdao Institute of Marine Geology, Qingdao 266071, China 3. Faculty of Resources, China University of Geosciences, Wuhan 430074, China
Abstract：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.
Key words：Methane hydrate;Laser Raman spectroscopy;High pressure capillary;Formation and decomposition
[1] Wu N Y, Zhang H Q, Su X. Terra Nostra, 2007, (1-2): 236. [2] Zhu Y H, Zhang Y Q, Wen H J, et al. Acta Geological Sinica(English Edition), 2010, 84(1): 1. [3] LIU Chang-ling, YE Yu-guang, MENG Qing-guo, et al(刘昌岭, 业渝光, 孟庆国, 等). Acta Chimica Sinica(化学学报), 2010, 68(22): 2320. [4] MEI Dong-hai, LIAO Jian, WANG Lu-kun(梅东海, 廖 健, 王璐琨). Journal of Chemical Engineering of Chinese Universities(高校化学工程学报), 1997, 11(3): 113. [5] QIU Jun-hong, GUO Tian-min(裘俊红, 郭天民). Acta Petrolei Sinica(石油学报), 1998, 14(1): 125. [6] SUN Zhi-gao, FAN Shuan-shi(孙志高，樊栓狮). Xi’an Jiaotong University Xuebao(西安交通大学学报), 2002，36(1): 16. [7] ZHENG Xin, SUN Zhi-gao(郑 新, 孙志高). Natural Gas Industry(天然气工业), 2003, 23(1): 95. [8] Chen Q, Liu C L, Ye Y G. Journal of Nature Gas Chemistry, 2009, 18(2): 217. [9] UchidaT, Takeya S, Kamata Y, et al. J. Phys. Chem., 2002, 106: 12426. [10] Lu H, Seo Y T, Lee J W, et al. Nature, 2007, 445, 18: 303. [11] Lu H, Moudrakovski I, Riedel M, et al. J. Geophys. Res., 2005, 110: B10204. [12] Chazallon B, Focsa C, Charlou J L, et al. Chemical Geology, 2007, 244: 175. [13] Lu W J, Chou I M, Burruss R C, et al. Appl. Spectrosc., 2006, 60(2): 122. [14] Sum A K, Burruss R C, Sloan E D. J. Phys. Chem. B, 1997, 101: 7371. [15] Subramanian S, Sloan E. D. Fluid Phase Equilib, 1999, 158: 831. [16] Shicks J M, Ripmeester J A. Angew. Chem. Int. Ed., 2004, 43: 3310. [17] MENG Qing-guo，LIU Chang-ling, YE Yu-guang, et al. (孟庆国，刘昌岭, 业渝光, 等). Natural Gas Industry(天然气工业), 2010, 30(6): 117. [18] Link D D, Ladner E P, Elsen H A. Fluid Phase Equilibria, 2003, 211: 1. [19] Zhang B Y, Wu Q, Sun D L. Journal of China University of Mining & Technology, 2008, 18(1): 018.
