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Multiscale Modeling of Molecular Sieving in LTA-type Zeolites: From the Quantum Level to the Macroscopic
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).ORCID iD: 0000-0002-0323-0210
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 [en]
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: urn:nbn:se:su:diva-113024ISBN: 978-91-7649-081-5 (print)OAI: oai:DiVA.org:su-113024DiVA: diva2:782425
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
List of papers
1. NaKA sorbents with high CO2-over-N2 selectivity and high capacity to adsorb CO2
Open this publication in new window or tab >>NaKA sorbents with high CO2-over-N2 selectivity and high capacity to adsorb CO2
Show others...
2010 (English)In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 46, 4502-4504 p.Article in journal (Refereed) Published
Abstract [en]

The uptake of carbon dioxide and nitrogen gas by zeolite NaKA was studied. A very high ideal CO2-over-N2 selectivity and a high CO2 capacity were observed at an optimal K+ content of 17 at.%. NaKA is a very promising adsorbent for CO2 separation from water-free flue gases.

National Category
Natural Sciences
Identifiers
urn:nbn:se:su:diva-43091 (URN)10.1039/c000900h (DOI)000278824200015 ()
Available from: 2010-09-27 Created: 2010-09-27 Last updated: 2015-01-22Bibliographically approved
2. Role of Ion Mobility in Molecular Sieving of CO2 over N-2 with Zeolite NaKA
Open this publication in new window or tab >>Role of Ion Mobility in Molecular Sieving of CO2 over N-2 with Zeolite NaKA
2013 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, no 46, 24259-24267 p.Article in journal (Refereed) Published
Abstract [en]

Classical molecular dynamics and Grand Canonical Monte Carlo simulations are carried out for sorbates (CO2 and N-2) in zeolite NaKA using a universal type ab initio force field. By combining the results of these simulations, we reproduce the CO2 uptake as a function of the K+ content in the zeolite NaKA as measured experimentally by Liu et al.(1) The experiment yielded an exceptionally high CO2-over-N-2 selectivity of >200 at a specific K+/(K+ + Na+) ratio of 17 atom %. This high selectivity could be attributed to the nonlinear uptake dependency of the K+/(K+ + Na+) ratio measured for both CO2 and N-2. Additionally, our simulations show a strong coupling between the self-diffusion of CO2 and the site-to-site jumping rate of the extra-framework cations. These results show that this nonlinear uptake dependency of CO2 is the result of molecular sieving. Following this, our simulations conclude that contributions must be taken into account when modeling the uptake of this and similar materials both thermodynamic and kinetic with the same functionalities.

National Category
Chemical Sciences
Identifiers
urn:nbn:se:su:diva-98084 (URN)10.1021/jp4048133 (DOI)000327557300020 ()
Funder
Swedish Research Council
Note

AuthorCount:3;

Available from: 2013-12-27 Created: 2013-12-27 Last updated: 2017-12-06Bibliographically approved
3. Free energy barriers for CO2 and N-2 in zeolite NaKA: an ab initio molecular dynamics approach
Open this publication in new window or tab >>Free energy barriers for CO2 and N-2 in zeolite NaKA: an ab initio molecular dynamics approach
2014 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 16, no 1, 166-172 p.Article in journal (Refereed) Published
Abstract [en]

Ab initio Molecular Dynamics (AIMD) is used with spatial constraints to estimate the free energy barriers of diffusion for CO2 and N-2 gas molecules in zeolite NaA and KA. We investigate the extent to which the diffusion of these gas molecules is hindered, in the two separate cases of a smaller Na+ ion or a larger K+ ion blocking the 8-ring pore window. In contrast to classical Molecular Dynamics, AIMD performs these computations accurately and unbiased in the absence of empirical parameterization. Our work has resulted in stable and reliable force profiles. The profiles show that the larger K+ ion effectively blocks the passage of both CO2 and N-2 molecules while the smaller Na+ ion will allow both molecules to pass. These results are a quantitative demonstration of the concept of pore blocking where we compute the effect, which the size of the respective cation occupying the pore window has on diffusive properties of each gas molecule. Hence, this effect can be altered through ion exchange to fine-tune the functionality of a specific zeolite as a molecular sieve.

National Category
Chemical Sciences
Identifiers
urn:nbn:se:su:diva-98265 (URN)10.1039/c3cp52821a (DOI)000327667500018 ()
Note

AuthorCount:3;

Available from: 2014-01-10 Created: 2014-01-03 Last updated: 2017-12-06Bibliographically approved
4. Temporal coarse graining of CO2 and N2 diffusion in Zeolite NaKA; from the quantum scale to the macroscopic
Open this publication in new window or tab >>Temporal coarse graining of CO2 and N2 diffusion in Zeolite NaKA; from the quantum scale to the macroscopic
(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
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:nbn:se:su:diva-113019 (URN)
Available from: 2015-01-21 Created: 2015-01-21 Last updated: 2016-01-29Bibliographically approved

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