Transport properties of mixture of N2 and CH4 in single walled carbon nanotubes

Transport properties of mixture of N

2

and CH

4

in single walled carbon nanotubes

S. Yeganegi*, B. Tahmasbi

Department of Physical and Inorganic Chemistry, Faculty of Chemistry, University of Mazandaran, Babolsar, Iran

Email address: sdyeganegi@gmail.com

Abstract

The high-throughput condor environment now allows many simulations to be performed on related systems, whether the focus is on improving the statistics or on broadening the range of conditions under which these simulations are run. We illustrate the scope of the approach by using Equilibrium Molecular Dynamics (EMD) to calculate self-diffusivities of mixture molecules diffusing through Single Wall Carbon Nanotubes (SWNT).

Keywords: transport properties, molecular dynamic, carbon nanotube.

Introduction

Microporous materials have many industrial applications, most of them based on their ability to condition the diffusion of fluids. Amongst these, Single Wall Carbon Nanotubes (SWNT) have a very interesting properties and are prime candidates for applications such as molecular sieves or membranes and for hydrogen storage.[4]

Molecular transport of fluids through membranes at the nanometer scale is important in many industrial processes including membrane filtration and separation. Carbon nanotubes are potential building blocks for molecular separation membranes, nanofluidic and devices. [1, 6]

Although the diffusion of atoms or small molecules inside SWNT is starting to receive a good deal of attention from the computing modeling community, there are still very few simulations of diffusion in SWNT.

Moa and co-workers [5] simulated the diffusion of organic molecules in nanotube bundles, taking tube flexibility into account with a reactive bond order potential, and showing the influence of pore size on the self-diffusivity.

In this research we present the result of equilibrium simulation of N2/CH4 mixture in carbon nanotubes.

Method

Diffusion is a fundamental mechanism of molecular transport through porous media.

MD simulation we have used classical EMD in NVT ensemble, as implemented in the DL-POLY code for calculate 3D diffusion of N2 and CH4 through single walled carbon nanotubes (SWCNTs) exhibiting various diameters. Also we have studied the effect of rigidity of tube on the diffusity. [2]

The geometry of a SWCNT is described by the nanotube chiral indices, n:m. We have used two different nanotubes chosen to sample helicity and size related influences:

(10,5) , (10:10).

The rigid tubes not require a carbon-carbon interaction potential but the fluid-fluid and fluid-wall interactions have modeled with the cut and shifted Lennard-Jones potential, Eq(1).

σ

¹²

σ

⁶

4 ε

^{i j}

−

^{i j}

, r ≤ r u (r) =

^ij

r r

^cut

ij (1)

0 , r > r

_cut

Where r is the distance between two interacting molecules of species i and j, rcut the cut-off radius (rcut: 2.5σij for all interactions).[3]

Results and Discussion

Calculated diffusion coefficient (Ds /10^-9 m². s^-1) for CH4 and N2 in the rigid (10:10) nanotube at different temperatures are presented in table1.

Temp.(K) N2 CH4

100 6.1500 35.670

300 3.5609 11.419

References:

1. V. P. Sokhan, D. Nicholson, and N. Quirke, " Transport properties of nitrogen in single walled carbon nanotubes," J. chem. Phys, 120, 3855, 2004.

2. H. Rafii-tabar, "Computational modeling of thermo-mechanical and transport properties of carbon Nanotubes,"physics reports, 390, 235, 2004.

3. T. Duren, F. J. Keil, and N. A. Seaton, "Composition dependent transport diffusion coefficients of CH4/CF4 mixtures in carbon nanotubes by non- equilibrium molecular dynamics simulations,"Chemical Engineering Science, 57, 1343, 2002.

4. Z. G. Mao, A. Garg, and S. B. Sinnott,"Molecular dynamics simulations of the dynamic flow through carbon nanotubes", J.

Phys. Chem. B, 104, 4618, 2000.

5. Z. G. Mao, A. Garg, and S. B. Sinnott,"Separation of organic molecular mixtures in carbon nanotubes and bundles: Molecular dynamics simulations", J. Phys. Chem. B, 105, 6916, 2001.

6. S. Yeganegi, and E. pak, "The effect of corrugation of pore wall on the thermal diffusion in nanopores by molecular dynamics simulations", chemical physics, 333, 69, 2007.