PNNL

Abstract

In situ high pressure infrared (IR), 13C Bloch decay magic angle spinning nuclear magnetic resonance (MAS NMR), and exchange correlation (EXSY) NMR spectroscopic data acquired at T = 323 K and Pfluid = 90 bars CH4 pressure show that CH4 occurs in the interlayer nano-pores of smectite clays, in pores between the clay particles (inter-particle pores), and in bulk fluid likely in the head space of the NMR rotors. All three CH4 environments interact with the clay surfaces and are in dynamic exchange on 100 to 104 Hz rates. The 13CH4 chemical shifts for these three environments are well resolved, with the 13C shift becoming more positive with decreasing physical space accessible by the CH4. This effect is most pronounced for interlayer adsorbed CH4, where the layer charge, size of the charge balancing cation, and relative humidity of the fluid all influence the interlayer pore size, 13CH4 chemical shift, and the amount of interlayer CH4 adsorbed. Layer charge exhibits the strongest influence. 2D EXSY NMR spectra of dry Cs-Laponite® show that CH4 is exchanging among all three environments, with interlayer CH4 exchanging with inter-particle/bulk CH4 at a broad range of frequencies between 104 to 100 Hz, while inter-particle/bulk CH4 exchange occurs at