The adsorption behaviour of CH4 on microporous carbons: effects of surface heterogeneity

Abstract

The effects of chemical and structural surface heterogeneity on the CH4 adsorption behaviour on microporous carbons have been investigated using a hybrid theoretical approach, including the use of density functional theory (DFT), molecular dynamics (MD), and grand canonical Monte Carlo (GCMC) simulations. Bader charge analysis is first performed to analyze the surface atomic partial charges. The CH4 adsorption densities in defective and functionalized graphite slit pores are lower than that in the perfect pore according to the MD simulations. Finally, the CH4 adsorption isotherms for the perfect, defective and functionalized slit pores are analyzed using the GCMC simulations in combination with the DFT and MD results. For pores with a defective surface, the adsorption capacities decrease; the embedded functional groups decrease the adsorption capacity at low pressure and enhance it at high pressure. Our results demonstrate the significant effects of chemical and structural surface heterogeneity on the CH4 adsorption and provide a systematic approach to understand the gas adsorption behaviour.

Oil adsorption in shale nanopores and its effect on recoverable oil-in-place

“…MD, a computer simulation of physical movements of atoms and molecules, exhibits unparalleled merits in the theoretical investigation on the thermodynamic properties of nanomaterials and transport behaviors at the nanoscale, which increasingly appeals to many researchers in the adsorption field (Ambrose et al, 2012;Dunne and Manos, 2010;Jin et al, 2014;Rajabbeigi et al, 2009). Interested readers can find a more detailed discussion of this approach in Frenkel and Smit (2001) and Griebel et al (2007).…”

Competitive adsorption of a binary CO2–CH4mixture in nanoporous carbons: effects of edge-functionalization

“…For COOH-NPC, two strong electronegative O atoms slightly weaken the CH 4 adsorption, whereas for the other NPCs, edge-functionalization has little positive effect on the CH 4 absolute adsorption capacity, which is different from the negative effect of surface-functionalization on CH 4 adsorption density and excess adsorption amount. 1,20 Fig . 3 shows that the absolute adsorption isotherms of CH 4 and CO 2 exhibit type-I Langmuir adsorption behaviour, which is a typical characteristic of nanoporous materials.…”

“…Fig. 4 shows the adsorption selectivity of CO 2 from an equimolar CO 2 /CH 4 mixture in edge-functionalized NPCs at low (0-5 MPa) and high (5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) pressures at 298, 313, and 373 K. In Fig. 4, the selectivity of CO 2 over CH 4 in NPC is ~2, which is well consistent with that in the perfect graphite slit pore as reported by Wilcox 1 and that in mesoporous carbon as reported by Lu 48 .…”

“…[12][13][14][15][16][17][18][19][20][21][22] Jain et al [15][16][17] developed a new molecular modeling on NPCs by using the reverse Monte Carlo (RMC) method, and found that the calculated adsorption amount and isosteric heat were in good agreement with the experimental results. Brochard et al 18 studied the competitive adsorption of binary CO 2 /CH 4 mixture in NPCs, and described the desorption behavior of CH 4 with the CO 2 -injection in detail.…”

The influence factors for gas adsorption with different ranks of coals

“…But it can be seen that the V L is smaller compared to the other stages (Figure 4(a)). It is mainly ascribed to the existence of numerous oxygen-containing functional groups within coal during this stage (Billemont et al, 2014;Hao et al, 2013;Jin et al, 2014), which has an inhibitory effect on gas adsorption , leading to the smaller V L . For P L , these values are relatively larger, suggesting that the desorption capacity is stronger (R o,max < 1.1%) (Figure 4(b)).…”