Inhibitory Effect of Adsorbed Water on the Transport of Methane in Carbon Nanotubes

Abstract

We investigate the transport diffusion of methane at 300 K and pressures of up to 15 bar in dry and wetted carbon nanotubes (CNTs) having diameters ranging from 0.95 to 2.034 nm using nonequilibrium molecular dynamics (NEMD) simulation. Because of their strong hydrogen bonding, preadsorbed water molecules transport in the form of clusters and block the diffusion of methane, reducing the Onsager coefficient of methane dramatically compared to that in dry CNTs. The reduction in the methane Onsager coefficient is greater in narrower CNTs or at higher water densities. Because the diameter of the water clusters is almost invariant with water density, the Onsager coefficient of water in the (10, 10) CNT increases linearly with water density. It is further found that whereas decreasing the CNT diameter from 2.034 to 0.95 nm enhances the Onsager coefficient of pure methane by about 1 order of magnitude, the Onsager coefficient of water is almost independent of the CNT diameter at a water density of 0.05 g/cm. We propose a theoretical model for the strong dependency of methane diffusion in wetted CNTs on the Onsager coefficient of water, the preadsorbed water density, and the CNT diameter. The model predicts the Onsager coefficients of the methane/water mixture from the Onsager coefficients of the pure components. Our study provides a basic understanding of the coupled diffusion of immiscible components in nanochannels and will facilitate progress in gas storage and carbon capture as well as nanofiltration and biomedical and biotechnological applications.

Adsorption and Diffusion of Carbon Dioxide, Methane, and Their Mixture in Carbon Nanotubes in the Presence of Water

“…Our results are in good agreement with the previous simulation studies. 7,19,24,25 Figure 4 also shows the predictions (lines) of the expression relating D i,self to Đ i derived by Krishna and Paschek (see eq 5). 58 For simplicity, the self-exchange coefficient Đ ii corr is assumed to be CH 4 /CO 2 -loading-independent and used as the fitting parameter.…”

“…9−17 Notably, because of their exceptional properties such as high mechanical strength, large specific surface area, high aspect ratio, and relatively low cost, CNTs are excellent candidates for gas storage and separation processes. 12−17 There have been extensive studies on the adsorption 12−15,18−23 and diffusion 7,19,24,25 properties of CH 4 and CO 2 in CNTs. These studies showed that, at low pressures, a high uptake of CH 4 and CO 2 is achieved in relatively small pores, which can be attributed to the fluid−solid interaction.…”

Impact of Impure Gas on CO2 Capture from Flue Gas Using Carbon Nanotubes: A Molecular Simulation Study

“…In this connection, a host of conventional and emerging nanoporous materials have been invented and explored, including zeolites, activated carbons, metal-organic frameworks (MOFs), and carbon nanotubes (CNTs) [ 3 , 4 , 5 , 6 , 7 , 8 ]. Particularly, CNTs possess large specific surface areas (greater than 1000 m 2 /g) with strong adsorptive affinities, which could be paired with the superior transport properties to further facilitate the adsorption potentials of [ 3 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 ] CNTs for CO 2 capture.…”

Release of methane from nanochannels through displacement using CO2

“…Mahdizadeh et al 17 used grand canonical Monte Carlo (GCMC) simulations to investigate the methane adsorption in single-walled carbon nanotubes (SWCNTs) and their results indicate that SWCNTs can be stylized for methane adsorption. Liu et al 18 explored the diffusion of methane at room temperature under various pressures in dry and wetted CNTs with different diameters through MD simulations. They reported that the diffusion coefficient of methane molecules reduces dramatically in wetted CNTs compared with that in dry CNTs because the low solubility of CH 4 , especially in thin CNTs.…”