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Temporal coarse graining of CO2 and N2 diffusion in Zeolite NaKA; from the quantum scale to the macroscopic
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).ORCID iD: 0000-0002-0323-0210
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
Uppsala universitet, Institutionen för fysik och astronomi.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The kinetic CO2-over-N2 sieving capabilities in narrow pore zeolite are dependent on the free energy barriers of diffusion between the zeolite pores, which can be fine-tuned by altering the framework composition. An ab initio level of theory is necessary to accurately compute the energy barriers, while it is desirable to predict the macroscopic scale diffusion for industrial applications. Using spatially constrained ab initio molecu- lar dynamics on the ps time scale, the free energy barriers of diffusion can be predicted for different local pore properties in order to identify those that are rate determining for the pore-to-pore diffusion. Specifically, we investigate the effects of the Na+-to-K+ exchange at the different cation sites and the CO2 loading. These computed energy barriers are then used as input for the Kinetic Monte Carlo method, coarse-graining the dynamic simulation steps to the pore-to-pore diffusion. With this approach we simulate how the identified rate determining properties as well as the application of skin layer surface defects affect the diffusion driven uptake in a realistic powder particle model on a macroscopic time scale. Finally, we suggest a model by combining these effects, which provides an excellent agreement with the experimental CO2 and N2 uptake behaviors presented by Liu et al.

Keyword [en]
Kinetic Monte Carlo, Density Functional Theory, molecular sieving, Zeolite A, LTA, Linde Type A, cation exchange, diffusion, multiscale modeling, gas separation, gas adsorption, swing adsorption, ab initio, molecular dynamics, AIMD, DFT, KMC
National Category
Physical Chemistry
Research subject
Physical Chemistry
Identifiers
URN: urn:nbn:se:su:diva-113019OAI: oai:DiVA.org:su-113019DiVA: diva2:782415
Available from: 2015-01-21 Created: 2015-01-21 Last updated: 2016-01-29Bibliographically approved
In thesis
1. Multiscale Modeling of Molecular Sieving in LTA-type Zeolites: From the Quantum Level to the Macroscopic
Open this publication in new window or tab >>Multiscale Modeling of Molecular Sieving in LTA-type Zeolites: From the Quantum Level to the Macroscopic
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

LTA-type zeolites with narrow window apertures coinciding with the approximate size of small gaseous molecules such as CO2 and N2 are interesting candidates for adsorbents with swing adsorption technologies due to their molecular sieving capabilities and otherwise attractive properties. These sieving capabilities are dependent on the energy barriers of diffusion between the zeolite pores, which can be fine-tuned by altering the framework composition. An ab initio level of theory is necessary to accurately describe specific gas-zeolite interaction and diffusion properties, while it is desirable to predict the macroscopic scale diffusion for industrial applications. Hence, a multiscale modeling approach is necessary to describe the molecular sieving phenomena exhaustively.

In this thesis, we use several different modeling methods on different length and time scales to describe the diffusion driven uptake and separation of CO2 and N2 in Zeolite NaKA. A combination of classical force field based modeling methods are used to show the importance of taking into account both thermodynamic, as well as, kinetic effects when modeling gas uptake in narrow pore zeolites where the gas diffusion is to some extent hindered. For a more detailed investigation of the gas molecules’ pore-to-pore dynamics in the material, we present a procedure to compute the free energy barriers of diffusion using spatially constrained ab initio Molecular Dynamics. With this procedure, we seek to identify diffusion rate determining local properties of the Zeolite NaKA pores, including the Na+-to-K+ exchange at different ion sites and the presence of additional CO2 molecules in the pores. This energy barrier information is then used as input for the Kinetic Monte Carlo method, allowing us to simulate and compare these and other effects on the diffusion driven uptake using a realistic powder particle model on macroscopic timescales.

Place, publisher, year, edition, pages
Stockholm: Department of Materials and Environmental Chemistry, Stockholm University, 2015. 76 p.
Keyword
CO2 separation, carbon capture, kinetic sieving, Zeolite A, Zeolite NaKA, cation exchange, temporal coarse graining, Kinetic Monte Carlo, Molecular Dynamics, AIMD, DFT
National Category
Physical Chemistry
Research subject
Physical Chemistry
Identifiers
urn:nbn:se:su:diva-113024 (URN)978-91-7649-081-5 (ISBN)
Public defence
2015-02-20, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.

Available from: 2015-01-28 Created: 2015-01-21 Last updated: 2015-01-28Bibliographically approved

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