Release of methane from nanochannels through displacement using CO₂

Abstract

The release of methane from nanochannels through displacement using CO2 is investigated through molecular dynamics simulations.

Enhancing the Efficiency of Coal Bed Methane Recovery by Injecting Carbon Dioxide Based on an Anthracite Coal Macromolecular Model and Simulation Methods

“…In micropores, the force of pore walls on both sides for small pores is stronger than for large pores; the CO 2 molecule is more easily adsorbed, which is conducive to displacing CH 4 . The force between the CH 4 molecule and pore walls will be broken, and it will move out from the micropores by injecting CO 2 . , In addition, the molecular diffusion can be inhibited by viscosity and volume expansion and surface roughness in micropores. , During the injection of CO 2 to displace the CH 4 adsorbed in the micropores, the average diffusion rate of CH 4 and CO 2 is slow. In mesopores, owing to the transition from micropores to mesopores, there is a large space for gas molecule migration.…”

“…The average diffusion rate of the CH 4 molecule is reduced from 4.4 × 10 –8 to 1.605 × 10 –8 m 2 /s, decreasing by about 1.7 times. Since the amount of CO 2 injected into the pores increases, the intermolecular van der Waals forces, viscosity, and volume expansion become stronger, which hinder the diffusion rate of CO 2 for displacing CH 4 . , In addition, there is a limited specific surface area in micropores. Increasing the injection amount of CO 2 increases the probability of intermolecular collisions and limits the average diffusion rate for intermolecular collisions .…”

“…Simultaneously, the pore model adsorbs 5 MPa CH 4 . The graphite slit pore is employed to adsorb 10 MPa CO 2 (herein, the temperature for adsorbing CH 4 or CO 2 is set to 303.15 K), and these two adsorption models are connected by a carbon nanotube to construct the displacement model, as shown in Figure . ,,, …”

“…The graphite slit pore is employed to adsorb 10 MPa CO 2 (herein, the temperature for adsorbing CH 4 or CO 2 is set to 303.15 K), and these two adsorption models are connected by a carbon nanotube to construct the displacement model, as shown in Figure 2. 23,36,38,47 In pores, adsorption was decided between the gas−solid and gas− gas interactions by van der Waals forces. 48 In this article, the GCMC method was employed for competitive adsorption simulation and the force field selected was Condensed-phase Optimized Molecular Potentials for Atomistic Simulation Studies.…”

“…Gas adsorption behavior in pores is extremely complex, , which makes an analysis of the competitive adsorption mechanisms of CH 4 /CO 2 difficult. Therefore, scholars have made attempts to investigate the CH 4 /CO 2 competitive adsorption mechanism and how to improve CBM recovery using advanced technology. − Busch et al and Krooss et al observed that the preferential adsorption of CO 2 was greater than that of CH 4 in different coal ranks by experiments, , while they did not clearly explain the microscopic interaction of CH 4 /CO 2 . Following the experimental result, Dang et al reported the CH 4 /CO 2 molecules’ competitive adsorption in brown coal by a molecular simulation; the results demonstrated that the adsorption capacity of CO 2 has an obvious advantage over CH 4 .…”