Competitive adsorption of CO₂, N₂, and CH₄ in coal-derived asphaltenes, a computational study

Area of Science:

• Geochemistry
• Materials Science
• Environmental Science

Background:

• Greenhouse gas concentrations are rising due to fossil fuel use, driving global warming.
• Coal bed methane (CBM) recovery is a potential strategy, but gas adsorption mechanisms in coal are not fully understood.
• Coal-derived asphaltenes, key components in CBM, play a crucial role in gas adsorption.

Purpose of the Study:

• To investigate the competitive adsorption of carbon dioxide (CO2), methane (CH4), and nitrogen (N2) on functionalized coal-derived asphaltenes.
• To explore the mechanisms of CO2- and N2-enhanced CBM recovery.
• To understand the influence of asphaltene functional groups (CH4, NH, O, S) on gas adsorption.

Main Methods:

• Grand Canonical Monte Carlo (GCMC) simulations for adsorption isotherms.
• Molecular Dynamics (MD) simulations for adsorption processes.
• Density Functional Theory (DFT) calculations for electronic effects and interaction analysis.

Main Results:

• Adsorption is primarily physical (van der Waals interactions), with CO2 showing the highest adsorption energy.
• Higher temperatures reduce gas adsorption capacity.
• Coal-derived asphaltenes display significant selectivity for CO2 over CH4 and N2, especially at elevated temperatures.

Conclusions:

• The studied asphaltene model effectively adsorbs CO2, indicating potential for greenhouse gas mitigation.
• The findings support the use of these asphaltenes in enhanced CBM recovery processes.
• This research offers insights into optimizing CBM extraction while addressing climate change concerns.