Visual Representation of Carbon Dioxide Adsorption in a Low-Volatile Bituminous Coal Molecular Model

Carbon dioxide can be sequestered in unmineable coal seams to aid in mitigating global climate change, while concurrently CH 4 can be desorbed from the coal seam and used as a domestic energy source. In this work, a previously constructed molecular representation was used to simulate several processes that occur during sequestration, such as sorption capacities of CO 2 and CH 4, CO 2 -induced swelling, contraction because of CH 4 and water loss, and the pore-blocking role of moisture. This is carried out by calculating the energy minima of the molecular model with different amounts of CO 2, CH 4, and H 2 O. The model used is large (>22 000 atoms) and contains a molecular-weight distribution, so that it has the flexibility to be used by other researchers and for other purposes in the future. In the low-level molecular modeling presented here, it was anticipated that CO 2 would be adsorbed more readily than CH 4, that swelling would be anisotropic, greater perpendicular to the bedding plane because of the rank of this coal, and finally, that, with the addition of moisture, CO 2 capacity in the coal would be reduced. As expected with this high-rank coal, there was swelling when CO 2 perturbed the structure of approximately 5%. It was found that, on the basis of the interconnected pore structure and molecular sizes, CO 2 was able to access 12.4% more of the pore volume (as defined by helium) than CH 4, in the rigid molecular representation. With water as stationary molecules, mostly hydrogen bound to the coal oxygen functionality, pore access decreased by 5.1% of the pore volume for CO 2 accessibility and 4.7% of the pore volume for CH 4 accessibility.