Vertically aligned double wall carbon nanotube arrays adsorbent for pure and mixture adsorption of H2S, ethylbenzene and carbon monoxide, grand canonical Monte Carlo simulation

In this study, pure and ternary adsorption of hydrogen sulfide (H2S), 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 H2S 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 H2S 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 H2S 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 H2S 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 H2S/CO selectivity are greater than EB/H2S selectivity. In addition, at smaller nanotube distances H2S/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 > H2S > CO suggesting that ethylbenzene interaction with nanotube arrays was strongest. Although H2S has a greater dipole moment and smaller molecular dimension, EB adsorption at higher nanotube distance is greater than H2S by at least 50% probably because EB is less volatile. [Display omitted] •H2S and CO form multi-layer around the nanotube walls, while ethylbenzene adsorbs uniformly.•Greater Isosteric heat of adsorption of ethylbenzene showed strong interactions with the nanotubes.•At lower nanotube distances the H2S adsorption is higher than ethylbenzene because ethylbenzene more steric hindrances.•Higher adsorption of ethylbenzene than H2S at higher distance suggested the effect of ethylbenzene less volatility.•Similarity of ethylbenzene to nanotube is responsible for its higher adsorption at higher nanotube distances.