~(13)C Solid-state Nuclear Magnetic Resonance Investigations of Gas Hydrate Structures
Solid State NMR spectroscopy has taken a very prominent place in many spectroscopic techniques employed for the characterization of clathrate hydrates.In this work,we have measured the synthesized ethane gas hydrates by 13C NMR with Magic Angle Spinning(MAS) and High Power 1H Decoupling(HPDEC) at 173 K and atmospheric pressure.Furthermore,we have got the 13C NMR spectra of ethane gas hydrates and propane gas hydrates,and preliminary established the testing method of natural gas hydrate by Solid State 13C NMR spectroscopy.The experimental results show that there is only one resonance line(δ 7.7×10-6) for ethane in the hydrate phase obtained from 13C NMR,while ethane molecules are enclathrated in the sⅠhydrates and only contained in the large cages(51262).The 13C NMR spectra of Propane gas hydrates exhibit tow resonance lines(δ 16.7 and 17.5),which are assigned to methyl carbons and methylene carbons,respectively.Consequently,the propane gas hydrates are determined to be sⅡ hydrates,and propane molecules are only trapped in the large cages(51264).