Quantitative Analysis of the Hydration Process of Mine Gas Mixture Based on Raman Spectroscopy

The research on micro crystal structure of mine gas hydrate is especially significant for the technology of gas hydrate separation. Using Raman spectroscopy to observe hydration process of 3 kinds of mine gas mixture on line which contains high concentration of carbon dioxide, this experiment obtained the information of the hydrate crystals including large and small cage occupancy. Meanwhile obtained the hydration number indirectly based on the statistical thermodynamic model of van der Waals and Platteeuw. The results show that cage occupancy and hydration number of mine gas hydrates change little during different growth stages. The large cages of hydrate phases are nearly full occupied by carbon dioxide and methane molecules together, with the occupancy ratios between 97. 70% and 98. 68%. Most of the guest molecules in large cages is carbon dioxide (78. 58% similar to 94. 09%) and only a few (4. 52%similar to 19. 12%) is filled with methane, it is because carbon dioxide concentration in the gas sample is higher than methane and there is competition between them. However the small cage occupancy ratios is generally low in the range from 17. 93% to 82. 41%, and the guest molecules are all methane. With the increase of methane concentration in gas sample, the cage occupancy both large and small which methane occupied has increased, meanwhile the large cage occupancy which methane occupied is lower than small cage. The hydration numbers of mine gas hydrate during different growth stages are between 6. 13 and 7 33 Small cage occupancy has increased with the increase of methane concentration, this lead to hydration number decreases. Because of the uneven distribution of hydrate growth, the hydration numbers of 3 kinds of gas samples show irregular change during different growth stages.