From excess to absolute adsorption isotherm: The effect of the adsorbed density

H Ghasemzadeh and S Babaei and S Tesson and J Azamat and M Ostadhassan, CHEMICAL ENGINEERING JOURNAL, 425, 131495 (2021).

DOI: 10.1016/j.cej.2021.131495

Estimating an accurate quantity of adsorbed density to calculate the absolute adsorption in shale reservoirs is critical for production, sequestration, and enhanced oil recovery purposes. Recent studies have shown that assuming a constant adsorbed density can generate erroneous results. Despite efforts to estimate the adsorbed density via methane density profile, there isn't a consensus to select the appropriate range. In this study, hybrid molecular dynamics/grand canonical Monte Carlo (MD/GCMC) simulations for investigating the methane adsorbed density in graphene layers with different pore widths (0.7-6 nm), temperatures (303.15-348.15 K), and pressures (0-40 MPa) under 13 different systems based on the methane density profile were used. Also, helium expansion and helium probe were utilized to calculate the accessible pore volume. The results showed that various ranges that are chosen from the methane density profile for calculating the adsorbed density have a significant effect on the trend and estimation of the absolute adsorption isotherm. It was found that adsorbed density calculated with a starting point of the effective pore width obtained from the helium probe would be the most appropriate one when the helium probe is used to calculate the accessible pore volume in the excess adsorption isotherm.

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