Simulation study on the adsorption characteristics of CO₂ and CH₄ by oxygen-containing functional groups on coal surface

ABSTRACT

To investigate the adsorption mechanism of CO₂ and CH₄ with oxygen-containing functional groups in coal, the structural models of coal with different functional groups of carboxyl, hydroxyl, carbonyl, and ether bonds were constructed using Materials Studio software, and the adsorption isotherms, heat of adsorption, adsorption energy, energy distribution, and adsorption configurations of CO₂ and CH₄ adsorbed by different functional group structures were analyzed using the giant regular GCMC method. The results showed that the presence of carboxyl, hydroxyl, and carbonyl functional groups will promote the adsorption of CO₂ by coal, and the intermolecular interaction energies of the model with the addition of carboxyl, hydroxyl, and carbonyl groups, and CO₂ increased by 70.37%, 33.67%, and 14.26%, respectively. The order of the adsorption strength of the five structures is: AC-COOH > AC-OH > AC-O > AC > AC-OCH₃, which indicates that the influence of oxygen-containing functional groups on the adsorption performance of CO₂ by coal mainly depends on polarity. The presence of carboxyl, hydroxyl, and carbonyl functional groups weakens the adsorption of CH₄ on coal, and the interaction energy between the model and gas molecules with the addition of carboxyl, hydroxyl, carbonyl, and ether bonds reduced by 41.83%, 36.14%, 26.22%, and 80.21%, respectively. The order of the adsorption strength of the five structures is: AC > AC-O > AC-OH > AC-COOH > AC-OCH₃, which indicates that the effect of oxygen-containing functional groups on the adsorption of CH₄ on coal mainly depends on hydrophobicity; the introduction of ether-bonded functional groups does not favor the adsorption of CO₂ and CH₄ molecules on coal. It indicates that the ether bond has a certain repulsive effect on CO₂ and CH₄ molecules. In different functionalized coal structures with the same carbon atom skeleton, there are different adsorption capacities for CH₄ as well as CO₂, but in the same functionalized structure, the adsorption magnitude relationship is CO₂ > CH₄, indicating that the coal body structure interacts with CO₂ more than CH₄.

KEYWORDS:

• Coal
• oxygen-containing functional group
• Monte Carlo method
• CO₂/CH₄ adsorption
• density distribution

Acknowledgments

The authors are grateful to the financial support from the National Natural Science Foundation of China (No. 51774170). Thanks to all the reviewers and editors for their work.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the National Natural Science Foundation of China