Simulations of Binary Mixture Adsorption of Carbon Dioxide and Methane in Carbon Nanotubes:  Temperature, Pressure, and Pore Size Effects

Abstract

Grand canonical Monte Carlo (GCMC) simulations were performed to investigate the adsorption behavior of an equimolar CO2/CH4 mixture in carbon nanotubes (CNTs). Five CNTs [(6, 6), (7, 7), (8, 8), (9, 9), and (10, 10)] with diameters varying from 0.678 to 1.356 nm, seven temperatures (283, 293, 303, 313, 323, 333, 343 K), and seven pressures (1, 5, 10, 15, 20, 25, 30 MPa) were chosen to investigate the effect of temperature, pressure, and pore size on the adsorption behavior. The results show that the CNTs have a preferential adsorption of CO2 in the binary CO2/CH4 mixture. For pore size effect on the adsorption behavior, we found that the adsorption of CO2 is much larger than that of CH4 in the same CNT and that the CO2 adsorption in the CNTs increases dramatically with an increase of CNT's diameter, whereas the absolute amount of adsorbed CH4 changes little with the CNT's pore size. In the investigated temperature and pressure ranges, we observed that in the CNTs with diameters less than 1.1 nm, the temperature and pressure have little effect on the adsorption behavior of the binary mixture, whereas in larger CNTs the adsorption behavior changes with temperature and pressure significantly. In addition, the CNTs demonstrated a higher selectivity of CO2 than other materials (activated carbons, zeolites 13X, and metal−organic frameworks) reported in the literature. For example, in (6, 6) CNT at 343 K and 1 MPa, the selectivity reaches 11.2, larger than that reported in activated carbon. The selectivity in narrow CNTs (<1 nm in diameter) is fluctuating with temperature and pressure, but it remains almost the same in larger CNTs at the investigated temperature and pressure.

Adsorption of CO2/CH4 Mixtures in a Molecular Model of Activated Carbon through Monte Carlo Simulations

“…preferential adsorption towards CO 2 ) significantly increased (Kowalczyk et al 2012). The selectivities in the activated carbon is lower than that obtained on carbon nanotubes (Huang et al 2007), but close to the selectivity in C168 models (Babarao et al 2007). Finally in the coals with large clusters, greater selectivity is observed at low pressures, which tends to decrease with increasing pressure.…”

N-octane diffusivity enhancement via carbon dioxide in silica slit-shaped nanopores – a molecular dynamics simulation

“…2 Understanding the molecular phenomena related to adsorption and transport of CO2-hydrocarbon mixtures in the sub-surface is therefore necessary in order to optimize both CO2 storage capacity, as well as oil and gas production. Despite the vast literature on binary CO2 and CH4 mixtures, [3][4][5] few studies focused on adsorption and dynamics of CO2 mixtures with more economically attractive, higher molecular weight hydrocarbons under confinement. 6,7 We previously conducted extensive molecular dynamics (MD) simulations to study propane adsorption, structure and diffusion in slit-shaped silica pores at sub-, near-, and super-critical conditions.…”

Flue gas adsorption by single-wall carbon nanotubes: A Monte Carlo study

“…20,[26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41] Most of these simulation studies consider classical force fields, but ab initio calculations have also been reported. 19,27,42 The capacity of carbon nanotubes to adsorb pure CO 2 has been tested by computer simulations in isolated 19 and arrays of parallel SWCNTs, 20 as well as isolated 36 and parallel double-walled carbon nanotube bundles.…”

“…19,27,42 The capacity of carbon nanotubes to adsorb pure CO 2 has been tested by computer simulations in isolated 19 and arrays of parallel SWCNTs, 20 as well as isolated 36 and parallel double-walled carbon nanotube bundles. 38,40 On the other hand, CO 2 separation by carbon nanotubes from mixtures has been studied in CO 2 -CH 4 mixtures, 30,39 in presence of water 37 or in CO 2 -N 2 mixtures. 33 This latter study, relevant for CO 2 capture from flue gases, studied the effect of pressure, temperature, and bulk gas composition on the CO 2 adsorption in SWCNTs with diameters between 8 and 10 Å.…”