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K+ Exchanged Zeolite ZK-4 as a Highly Selective Sorbent for CO2
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.ORCID iD: 0000-0002-0323-0210
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2014 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 30, no 32, 9682-9690 p.Article in journal (Refereed) Published
Abstract [en]

Adsorbents with high capacity and selectivity for adsorption of CO2 are currently being investigated for applications in adsorption-driven separation of CO2 from flue gas. An adsorbent with a particularly high CO2-over-N-2 selectivity and high capacity was tested here. Zeolite ZK-4 (Si:Al similar to 1.3:1), which had the same structure as zeolite A (LTA), showed a high CO2 capacity of 4.85 mmol/g (273 K, 101 kPa) in its Na+ form. When approximately 26 at % of the extraframework cations were exchanged for K+ (NaK-ZK-4), the material still adsorbed a large amount of CO2 (4.35 mmol/g, 273 K, 101 kPa), but the N-2 uptake became negligible (<0.03 mmol/g, 273 K, 101 kPa). The majority of the CO2 was physisorbed on zeolite ZK-4 as quantified by consecutive volumetric adsorption measurements. The rate of physisorption of CO2 was fast, even for the highly selective sample. The molecular details of the sorption of CO2 were revealed as well. Computer modeling (Monte Carlo, molecular dynamics simulations, and quantum chemical calculations) allowed us to partly predict the behavior of fully K+ exchanged zeolite K-ZK-4 upon adsorption of CO2 and N-2 for Si:Al ratios up to 4:1. Zeolite K-ZK-4 with Si:Al ratios below 23:1 restricted the diffusion of CO2 and N-2 across the cages. These simulations could not probe the delicate details of the molecular sieving of CO2 over N-2. Still, this study indicates that zeolites NaK-ZK-4 and K-ZK-4 could be appealing adsorbents with high CO2 uptake (similar to 4 mmol/g, 101 kPa, 273 K) and a kinetically enhanced CO2-over-N-2 selectivity.

Place, publisher, year, edition, pages
2014. Vol. 30, no 32, 9682-9690 p.
National Category
Materials Chemistry
Identifiers
URN: urn:nbn:se:su:diva-102335DOI: 10.1021/la502897pISI: 000340701300007OAI: oai:DiVA.org:su-102335DiVA: diva2:709618
Available from: 2014-04-02 Created: 2014-04-02 Last updated: 2017-12-05Bibliographically approved
In thesis
1. Narrow-pore zeolites and zeolite-like adsorbents for CO2 separation
Open this publication in new window or tab >>Narrow-pore zeolites and zeolite-like adsorbents for CO2 separation
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

A range of porous solid adsorbents were synthesised and their ability to separate and capture carbon dioxide (CO2) from gas mixtures was examined. CO2 separation from flue gas – a type of exhaust gas from fossil fuel combustion that consists of CO2 mixed with mainly nitrogen and biogas (consists of CO2 mixed with mainly methane) were explicitly considered. The selected adsorbents were chosen partly due to their narrow pore sizes. Narrow pores can differentiate gas molecules of different sizes via a kinetic separation mechanism: a large gas molecule should find it more difficult to enter a narrow pore. CO2 has the smallest kinetic diameter in zeolites when compared with the other two gases in this study. Narrow pore adsorbents can therefore, show enhanced kinetic selectivity to adsorb CO2 from a gas mixture.

The adsorbents tested in this study included mixed cation zeolite A, zeolite ZK-4, a range of aluminophosphates and silicoaluminophosphates, as well as two types of titanium silicates (ETS-4, CTS-1). These adsorbents were compared with one another from different aspects such as CO2 capacity, CO2 selectivity, cyclic performance, working capacity, cost of synthesis, etc. Each of the tested adsorbents has its advantages and disadvantages. Serval phosphates were identified as potentially good CO2 adsorbents, but the high cost of their synthesis must be addressed in order to develop these adsorbents for applications.

Place, publisher, year, edition, pages
Stockholm: Department of Materials and Environmental Chemistry (MMK), Stockholm University, 2014. 94 p.
Keyword
CO2 separation, zeolites, phosphates, titanium silicates, ion exchange, flue gas CO2 capture, biogas upgrading
National Category
Materials Chemistry
Research subject
Materials Chemistry
Identifiers
urn:nbn:se:su:diva-101629 (URN)978-91-7447-877-8 (ISBN)
Public defence
2014-04-28, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 10:00 (English)
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Note

At the time of the doctoral defence the following papers were unpublished and had a status as follows: Papers 4-8: Manuscripts.

Available from: 2014-04-06 Created: 2014-03-12 Last updated: 2014-04-02Bibliographically approved

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