Microstructure-Dependent Gas Adsorption: Accurate Predictions of Methane Uptake in Nanoporous Carbons

Journal Article · Wed Jan 01 00:00:00 EST 2014 · Journal of Chemical Theory and Computation

DOI:https://doi.org/10.1021/ct400875n· OSTI ID:1116484

Ihm, Yungok ^[1]; Cooper, Valentino R ^[2]; Gallego, Nidia C ^[2]; Contescu, Cristian I ^[2]; Morris, James R ^[2]

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1. University of Tennessee (UTK) and Oak Ridge National Laboratory (ORNL)
2. ORNL

We demonstrate a successful, efficient framework for predicting gas adsorption properties in real materials based on first-principles calculations, with a specific comparison of experiment and theory for methane adsorption in activated carbons. These carbon materials have different pore size distributions, leading to a variety of uptake characteristics. Utilizing these distributions, we accurately predict experimental uptakes and heats of adsorption without empirical potentials or lengthy simulations. We demonstrate that materials with smaller pores have higher heats of adsorption, leading to a higher gas density in these pores. This pore-size dependence must be accounted for, in order to predict and understand the adsorption behavior. The theoretical approach combines: (1) ab initio calculations with a van der Waals density functional to determine adsorbent-adsorbate interactions, and (2) a thermodynamic method that predicts equilibrium adsorption densities by directly incorporating the calculated potential energy surface in a slit pore model. The predicted uptake at P=20 bar and T=298 K is in excellent agreement for all five activated carbon materials used. This approach uses only the pore-size distribution as an input, with no fitting parameters or empirical adsorbent-adsorbate interactions, and thus can be easily applied to other adsorbent-adsorbate combinations.

• Research Organization: Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• DOE Contract Number: DE-AC05-00OR22725
• OSTI ID: 1116484
• Journal Information: Journal of Chemical Theory and Computation, Vol. 10, Issue 1; ISSN 1549-9618
• Publisher: American Chemical Society
• Country of Publication: United States
• Language: English