[Raman spectroscopic studies on CO2-CH4-N2 mixed-gas hydrate system].

Accurate determination of coal mine gas separation product characteristics is the key for gas separation application based on hydrate technology. Gas hydrate was synthesized from two types of gas compositions (CO2-CH4-N2). The separation products were measured by in situ Raman spectroscopy. The crystal structure of mixed-gas hydrate was determined, and the cavity occupancy and hydration index were calculated, based on the object molecular various vibrational mode, "loose cage-tight cage" model and the Raman bands area ratio, combined with the model of van der Waals-Platteeuw. The results show that the mixed-gas hydrates are both structure I for the two gas samples; Large cages of mixed-gas hydrate are nearly occupied by guest molecules, and the large cavity occupancies are 98.57% and 98.52%, respectively; but small cages are not easy to be occupied, and the small cavity occupancies are 29.93% and 33.87%, respectively; hydration index of the two gas samples hydrate is 7.14 and 6.98, respectively, which is greater than the theoretical value of structure I.