Facilitated Diffusion of Methane in Pores with a Higher Aromaticity

Shale gas, which was recently discovered with a large reserve, has invoked wide interest as an alternative energy resource of natural gas. However, little is known about the molecular properties of shale gas (mainly methane) confined in the nanopores of shale, such as their diffusivity, which is essential for its exploitation and utilization. We study here the diffusivity of methane using 1H pulsed field gradient (PFG) NMR and theoretical modeling. Following analysis of the physicochemical properties of shale, a well-ordered mesoporous silica material (SBA-15) modified with organic functional groups is employed to model the mesopores observed in the shale and to study the fundamental behavior of shale gas. The results demonstrate that methane moves faster in the pores modified with the aromatic phenyl groups than those with nonaromatic cyclohexyl groups, suggesting a higher diffusivity of methane with increasing maturity of shale.