Methane storage in nanoporous media as observed via high field NMR relaxometry

TL;DR

This study uses high field NMR relaxometry to analyze methane storage in nanoporous Vycor glass, distinguishing free and adsorbed gas fractions across a wide pressure range, with implications for natural gas and hydrogen storage.

Contribution

It demonstrates the application of high field NMR relaxometry to quantify methane storage and adsorption properties in nanoporous media over a broad pressure spectrum.

Findings

Determined methane storage capacity and hydrogen index with high accuracy.

Identified Langmuir and multilayer adsorption regimes.

Quantified the monolayer density and number of adsorbed layers.

Abstract

The storage properties of methane gas in Vycor porous glass (5.7 nm) are characterized in a wide pressure range from 0.7 MPa-89.7 MPa using Nuclear Magnetic Resonance (NMR). We demonstrate the capability of high field NMR relaxometry for the determination of the methane gas storage capacity and the measurement of the Hydrogen Index, to a high degree of accuracy. This helps determine the excess gas in the pore space which can be identified to exhibit Langmuir properties in the low pressure regime of 0.7 MPa to 39.6 Mpa. The Langmuir model enables us to determine the equilibrium density of the monolayer of adsorbed gas to be 8.5% lower than that of liquid methane. We also identify the signatures of multilayer adsorption at the high pressure regime from 39.6 Mpa to 89.7 Mpa and use the Brunauer-Emmet-Teller (BET) theory to determine the number of adsorbed layers of methane gas. We show how these measurements help us differentiate the gas stored in the Vycor pore space into free and adsorbed fractions for the entire pressure range paving way for similar applications such as studying natural gas storage in gas shale rock or hydrogen storage in carbon nanotubes.