396 / 2018-10-10 14:32:33

Raman spetroscopic study on ternary model coal mine methane hydrates

coal mine methane, gas hydrate, Raman spectroscopy, micro-parameter

矿井瓦斯与煤与瓦斯突出 > 煤矿瓦斯

Abstract: The micro features of coal mine methane (CMM) hydrates, synthesized with three gas samples (CH4/C2H6/N2,G1=43﹕47﹕10,G2=60﹕30﹕10,G3=74﹕16﹕10) in a self-made transparent high-pressure cell at 275.15 K and 5 MPa were investigated using Raman spectroscopy. As a discriminator, the vibrational band frequencies in the C-C regions of the recorded hydrate Raman spectra for C2H6 show that G1~G3 hydrates are structure I (sI). The three principal parameters used to study the micro features of the model CMM hydrates, including cavity occupancies, hydrate guest compositions and hydration numbers, were calculated. The large cavity occupancies for C2H6 constantly decrease from 85.12% to 79.32%, while the small cavity occupancies for CH4 have a continual increase from 73.75% to 96.42%. However, CH4 competes with C2H6 on entering the large cavities for their large cavity occupancies of 12.79%~17.31%. The cavity occupancies of N2 are less than 1.2%. The hydrate composition calculations show that the molar fractions of C2H6 are the maximum. Hydration numbers ranging from 6.221 to 6.00. Based on the hydrate guest compositions and hydration numbers, the molecular formulas of the three CMM hydrates are presented.