The
adsorption of hydrocarbon (pure CH4 and C2H6) on illitic clay was investigated at temperatures of
333, 363, and 393 K (60, 90, and 120 °C) over a range of pressures
up to 30 MPa using grand canonical Monte Carlo (GCMC) simulations.
We first discussed the comparability of molecular simulation results
with experimental measurements. Our results indicate that molecular
simulation results of the
excess adsorption are comparable with the experimental measurements
if they are both expressed per unit surface area available for adsorption
instead of per unit mass. The gas density profiles indicate that the
adsorption of CH4 and C2H6 is mainly
affected by the clay surface layers. In micropores smaller than 2
nm, the overlapping of the interaction of the simulated pore walls
with the gas results in enhanced density peaks. For pore sizes of
2 nm or larger, the overlapping effect is significantly reduced, and
the height of the gas density peak close to the surfaces is no longer
affected by pore sizes. The maximum excess adsorption of illite for
C2H6 is almost twice that for CH4 due to the stronger interaction between illite and C2H6 than between illite and CH4, but the saturation
capacity (maximum loading) is the same for both. Our findings may
provide some insights into gas adsorption behavior in illite-bearing
shales and give some guidance for improving experimental prediction.
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