Computer Simulation Study for Functional Group Effect on Methane Adsorption in Porous Silica Glass

In this paper, adsorption of methane on porous silica glass was investigated to see whether functional groups can affect the adsorption behavior. Adsorption isotherms for pores having widths between 7 and 40 angstrom at 283 and 298 K were investigated using a Monte Carlo simulation (MC) method. The model of porous silica glass proposed in this study was assumed to be a finite-length slit pore which consisted of two parallel walls. The tetrahedral structure of SiO4 was used as atomic structure for the wall surface. Hydroxyl was assumed as the surface functional group which allocated either at pore mouth or random with concentration of 5 and 10%. It was found that the concentration of functional group has less significant effect on the adsorption of methane. The adsorption isotherm decreased a bit with an increase of functional group concentration. Effects of functional group position on adsorption isotherm were also investigated, the adsorption isotherm obtained for the random topology was greater than that for the pore mouth topology, due to the pore blocking effects. At the same pore width, the adsorption isotherm at 283K was greater than that at 293K, and this was due to that the adsorption of methane on porous silica glass was a physical adsorption. The initial adsorption of methane shifted to the higher pressure by increasing pore width, and the maximum adsorption capacity decreased with an increase of pore size, because of the pore packing effect.