Vertically aligned double wall carbon nanotube arrays adsorbent for pure and mixture adsorption of HS, ethylbenzene and carbon monoxide, grand canonical Monte Carlo simulation.

In this study, pure and ternary adsorption of hydrogen sulfide (HS), ethylbenzene (EB), and carbon monoxide (CO) on different arrays of zigzag double wall carbon nanotube was investigated using grand canonical Monte Carlo simulations. The internal diameters of nanotube were fixed at 2r = 50.17 Å while nanotube wall distances were different values from d = 0 Å to d = 150 Å. Pure simulation results indicated that adsorption quantity of HS and EB in low pressure ranges of P = 1.9 bar to P = 3.1 bar was at least 100% more than CO adsorption quantities. At high pressure ranges of P = 23.1 bar to P = 38.2 bar HS adsorption was greater than EB and CO by about 200 molecules per unit cell (UC) at low nanotube distances. This was related to smaller kinetic diameter and greater dipole moment of HS compared to EB and CO. At higher nanotube distance the effect of size however disappears and all three gases approach to adsorption quantity of about 800 molecules/UC. Graphical representation of adsorption areas showed that HS and CO form multilayer adsorption around nanotube inner and outer walls while EB fill the whole space uniformly without any congestion around the walls. Ternary adsorption results EB/CO and HS/CO selectivity are greater than EB/HS selectivity. In addition, at smaller nanotube distances HS/CO selectivity is generally higher than EB/CO selectivity, which at higher nanotube distance the order becomes revers suggesting that size dependent effects on adsorption vanishes. Isosteric heat of adsorption shows that the order of EB > HS > CO suggesting that ethylbenzene interaction with nanotube arrays was strongest. Although HS has a greater dipole moment and smaller molecular dimension, EB adsorption at higher nanotube distance is greater than HS by at least 50% probably because EB is less volatile.