Quantitative analysis of gas hydrates using Raman spectroscopy

A calibration protocol to quantify the compositional information of gas hydrates using Raman spectroscopy is proposed. Structure I pure CH4-, CO2- and C2H6-hydrates in their deuterated and hydrogenated forms with known cage occupancies were investigated by Raman spectroscopy. Raman scattering cross sections of CH4 in the large and small cages were found to be very similar, but not identical. Some C2H6 bands of C2H6-hydrate were tentatively reassigned or newly reported and assigned. Our results show that the relative cross sections of guest vibrational modes in the deuterated hydrate are in agreement with those in the hydrogenated hydrate, whereas they are considerably different from those in fluid phase. Using our Raman quantification factors, the relative cage occupancies can now be determined more reliably in CH4-hydrates. Moreover, with additional assumptions, the absolute cage occupancies, the bulk guest composition and hydration number of pure or mixed gas hydrates become accessible by Raman spectroscopy. (c) 2013 American Institute of Chemical Engineers AIChE J, 59: 21552167, 2013