(437e) Molecular Simulation Studies of CO2 Adsorption From Mixtures of N2, CH4, and H2O by Microporous Carbon

Carbon capture combined with CO₂ utilization and sequestration offers the possibility to reduce CO₂ emissions in the near future, while allowing for a continued use of fossil fuels. Adsorption of CO₂/CH₄, CO₂/N₂, and CO₂/H₂O mixtures has been studied in the current work. In the case of carbon capture, our studies show that functionalized carbon-based sorbents may be competitive with other sorbents in terms of the pure CO₂ adsorption capacity by modifying the surface functionality. The separation of CO₂ from CO₂/N₂ and CO₂/H₂O gas mixtures is involved in carbon capture for flue gas applications. In the case of carbon storage in coal and the organic matrix of gas shale, CO₂ injection into coalbeds and gas shale reservoirs may enhance subsequent methane (CH₄) recovery while simultaneously storing CO₂; therefore, the adsorption mixtures of CO₂/CH₄ is involved in CO₂ enhanced coalbed methane recovery (CO₂-ECBM) and shale gas productions. In this work, complex pore structures for general carbon-based porous materials and natural organic materials were modeled as a collection of independent, non-interconnected, functionalized graphitic slit pores with surface heterogeneities. Together with Bader charge analysis, electronic structure calculations coupled with van der Waals-inclusive corrections can provide the initial framework comprising both the geometry and corresponding charge information required to carry out statistical-based molecular simulations. Grand canonical Monte Carlo simulations are carried out to determine the adsorption isotherms and selectivity of CO₂ from CO₂/N₂ and CO₂/CH₄ gas mixtures at temperature/pressure conditions relevant to carbon capture and storage applications. The polarity induced by the surface functionalities and the interactions between the surface and the non-polar/polar molecules have been investigated. Molecular simulations of the adsorption of CO₂/CH₄ and CO₂/N₂ mixtures show that CO₂ preferentially adsorbs on oxygen-containing functionalized graphitic surfaces with an induced polarity due to the strong quadrupole moment of CO₂ compared with that of N₂ and the weak octupole moment of CH₄. For the mixtures where CO₂ has a stronger polarity, the difference in the quadrupole moment of the mixture component results in a different surface occupancy on the same surface, and the oxygen-containing functionalized surfaces not only increase the total adsorption of CO₂, but also enhance the separation selectivity of a given gas mixture. The investigation of different polar surfaces also shows that surface chemistry is tunable thereby influencing the selectivity and allowing for control of CO₂ separation based upon adsorption processes.