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Narrow-pore zeolites and zeolite-like adsorbents for CO2 separation
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
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 [en]
CO2 separation, zeolites, phosphates, titanium silicates, ion exchange, flue gas CO2 capture, biogas upgrading
National Category
Materials Chemistry
Research subject
Materials Chemistry
Identifiers
URN: urn:nbn:se:su:diva-101629ISBN: 978-91-7447-877-8 (print)OAI: oai:DiVA.org:su-101629DiVA: diva2:704661
Public defence
2014-04-28, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 10:00 (English)
Opponent
Supervisors
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At the time of the doctoral defence the following papers were unpublished and had a status as follows: Papers 4-8: Manuscripts.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
List of papers
1. Aluminophosphates for CO2 Separation
Open this publication in new window or tab >>Aluminophosphates for CO2 Separation
2011 (English)In: CHEMSUSCHEM, ISSN 1864-5631, Vol. 4, 91-97 p.Article in journal (Refereed) Published
Abstract [en]

The pressure-swing adsorption method for carbon dioxide capture would ideally be facilitated by adsorbents with a high capacity and a high selectivity for CO(2). Several aluminophosphates with 8-ring window apertures (AlPO(4)-17, AlPO(4)-18, AlPO(4)-53, and AlPO(4)-25) were synthesized by hydrothermal crystallization, calcined, and their CO(2) uptake and CO(2)/N(2) selectivity were studied. CO(2) and N(2) uptake was determined for pressures up to 101 kPa at 273 and 293 K. Langmuir and Toth adsorption models were used to describe the adsorption isotherms. The CO(2) and N(2) uptakes strongly indicated that the squeezed 8-ring windows of certain aluminophosphates can sieve CO(2) from a CO(2) and N(2) gas mixture. Both AlPO(4)-53 and AlPO(4)-25 exhibited a remarkably higher uptake of CO(2) compared to N(2). The hydrophilicity of the AlPO(4) materials was investigated by means of water adsorption, and the results showed that all of the tested aluminophosphates were less water sensitive than a benchmark zeolite (13X). In particular, AlPO(4)-53 and AlPO(4)-25 showed a very low degree of water uptake with up to 20-30% relative humidity. Determination of cyclic adsorption and desorption confirmed the relatively hydrophobic nature of the aluminophosphates, which render them less energy costly for the regeneration of adsorbents.

Place, publisher, year, edition, pages
Wiley-Blackwell, 2011
National Category
Chemical Sciences
Identifiers
urn:nbn:se:su:diva-68149 (URN)10.1002/cssc.201000256 (DOI)000287138900015 ()
Note

authorCount :4

Available from: 2012-01-03 Created: 2012-01-03 Last updated: 2014-04-02Bibliographically approved
2. Silicoaluminophosphates as CO2 sorbents
Open this publication in new window or tab >>Silicoaluminophosphates as CO2 sorbents
2012 (English)In: Microporous and Mesoporous Materials, ISSN 1387-1811, E-ISSN 1873-3093, Vol. 156, 90-96 p.Article in journal (Refereed) Published
Abstract [en]

Silicoaluminophosphates (SAPO-17, SAPO-35, SAPO-56 and SAPO-RHO) synthesised via hydrothermal means are tested for their abilities to adsorb carbon dioxide. These 8-ring microporous phosphates show high capacities to adsorb CO2. SAPO-RHO has a high uptake of CO2 and a very low uptake of N-2 due to its narrow pore window aperture at 273 K. Its significant uptake of N-2 at 77 K is rationalised by a temperature induced shrinkage effect. SAPO-56 has a slightly higher CO2 capacity (5.42 mmol/g, 273 K, 101 kPa) and is less water sensitive than zeolite 13X. Cyclic adsorption and in situ infrared spectroscopy (IR) reveal that SAPOs retain 95% of their original CO2 capacity after six cycles and that adsorption occurs via physisorption. The calculated heat of adsorption for CO2 (at 0.2-0.7 mmol/g loading) on SAPO-56 and SAPO-RHO lies in the physisorption range (similar to 35 kJ/mol). SAPOs, in particular SAPO-56 and SAPO-RHO, possess many desirable properties and are potentially good adsorbents for CO2 capture in swing adsorption processes.

Keyword
Carbon capture, Silicoaluminophosphates, Adsorption, Carbon dioxide, SAPO-56
National Category
Chemical Sciences
Identifiers
urn:nbn:se:su:diva-80024 (URN)10.1016/j.micromeso.2012.02.003 (DOI)000303625200013 ()
Note

AuthorCount:4;

Available from: 2012-09-12 Created: 2012-09-12 Last updated: 2017-12-07Bibliographically approved
3. Adsorption kinetics for CO2 on highly selective zeolites NaKA and nano-NaKA
Open this publication in new window or tab >>Adsorption kinetics for CO2 on highly selective zeolites NaKA and nano-NaKA
Show others...
2013 (English)In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 112, 1326-1336 p.Article in journal (Refereed) Published
Abstract [en]

Carbon dioxide removal from flue gas via swing adsorption processes requires adsorbents with a high CO2 selectivity and capacity. These properties are particularly valuable to reduce the cost of carbon capture and storage (CCS). Zeolite NaKA was studied for its ability to selectively adsorb CO2 from flue gas, as we previously observed that zeolite NaKA, with a K+/(K+ + Na+) ratio of 17 atomic%, was highly selective towards CO2 over N-2 adsorption by tuning the size of the pore window apertures [1]. The reduced pore apertures may, however, retard the adsorption rate of CO2. Here, we studied the kinetics of CO2 adsorption on regularly sized zeolite NaKA and on nano-sized zeolite NaKA. We used in situ infrared (IR) spectroscopy and observed that CO2 physisorbed relatively rapidly. Density functional theory (DFT) was used for quantum chemical calculations, and the results indicated that CO2 molecules bridged across two or three Na+ ions in the samples with no or very small amount of K. When more K+ ions are present the CO2 molecules no longer bridged across multiple metal ions and adopted an end-on configuration. The calculation showed a shift in the stretching vibration frequency of physisorbed CO2 as observed by IR spectroscopy. Nano-sized zeolite NaKA were synthesised and studied to improve the rate of CO2 adsorption, as the diffusion rate typically increases quadratically with decreasing particle size. Still, the CO2 adsorption rate on nano-sized zeolites NaA and NaKA did not increase significantly. For nano-sized zeolite NaA, we speculate that the absence of such an increased rate is an effect from a skin layer that had formed on the nano-sized zeolite NaA, a layer that was possibly related to intergrowths with extremely small crystals on the surface. The apparently slow adsorption kinetics of CO2 on nano-sized zeolite NaKA was more difficult to explain because it could relate to imperfections within the small crystals, remaining water, or other effects. Overall, the CO2 adsorption rates on zeolite NaKA crystals of different sizes were fast and relevant for the time scales required for adsorption based CCS processes, such as vacuum and temperature swing adsorption (VSA/TSA).

Keyword
Carbon dioxide adsorption, Zeolite A, Adsorption kinetics, Diffusion of sorbates, NaKA
National Category
Chemical Sciences
Identifiers
urn:nbn:se:su:diva-100667 (URN)10.1016/j.apenergy.2013.01.017 (DOI)000329377800144 ()
Conference
4th International Conference on Applied Energy (ICAE), Suzhou, China, July 01-04, 2012
Note

AuthorCount:5;

Available from: 2014-02-12 Created: 2014-02-10 Last updated: 2017-11-28Bibliographically approved
4. K+ Exchanged Zeolite ZK-4 as a Highly Selective Sorbent for CO2
Open this publication in new window or tab >>K+ Exchanged Zeolite ZK-4 as a Highly Selective Sorbent for CO2
Show others...
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.

National Category
Materials Chemistry
Identifiers
urn:nbn:se:su:diva-102335 (URN)10.1021/la502897p (DOI)000340701300007 ()
Available from: 2014-04-02 Created: 2014-04-02 Last updated: 2017-12-05Bibliographically approved
5. CO2 separation properties of high silicon zeolite NaK-ZK-4 with Si:Al up to 2.8:1
Open this publication in new window or tab >>CO2 separation properties of high silicon zeolite NaK-ZK-4 with Si:Al up to 2.8:1
(English)Manuscript (preprint) (Other academic)
National Category
Materials Chemistry
Identifiers
urn:nbn:se:su:diva-102339 (URN)
Available from: 2014-04-02 Created: 2014-04-02 Last updated: 2014-04-02
6. CO2 selective NaMg-CTS-1 and its structural formation from the titanium silicate based molecule sieve NaMg-ETS-4 upon dehydration
Open this publication in new window or tab >>CO2 selective NaMg-CTS-1 and its structural formation from the titanium silicate based molecule sieve NaMg-ETS-4 upon dehydration
Show others...
2014 (English)In: Microporous and Mesoporous Materials, ISSN 1387-1811, E-ISSN 1873-3093, Vol. 198, 63-73 p.Article in journal (Other academic) Published
Abstract [en]

A range of titanium silicates (ETS-4 and CTS-1) with interesting gas separation properties were studied as CO2 adsorbents. Some of these adsorbents, in particular NaMg-CTS-1, showed the ability to selectively adsorb CO2-over-N2. Partially exchanged NaM-ETS-4 (M = Mg, Ca, Sr and Ba) were synthesised in the Na+ form and ion exchanged with group 2 cations. All but NaBa-ETS-4 transformed into their CTS-1 counterparts, when these partially exchanged Na-ETS-4 were dehydrated. The transformation from ETS-4 to CTS-1 was monitored and studied extensively using diffraction and spectroscopic techniques. Powder X-ray diffraction allowed us to follow the changes of the unit cell parameters occurred at different temperatures. We combined high energy X-ray total scattering (analysed by pair distribution functions – PDF analysis), electron diffraction, infrared, Raman and Nuclear Magnetic Resonance (NMR) spectroscopy to study the transformation of ETS-4 to CTS-1. We understood that under dehydration steps, there was significant disruption to the Ti–O–Ti chain along the b-axis, which occurred concurrently with the distortion of the double 3-rings alongside of these chains. These changes were partly responsible for the contraction of the ETS-4 framework (and successive transformation to CTS-1). The new information allowed us to understand the interesting structures and sorption properties of these adsorbents

Keyword
CO2 separation, Titanium silicates, ETS-4, Structure determination, Ion exchange
National Category
Materials Chemistry
Identifiers
urn:nbn:se:su:diva-102340 (URN)10.1016/j.micromeso.2014.07.017 (DOI)000341899500010 ()
Note

CO2

Available from: 2014-04-02 Created: 2014-04-02 Last updated: 2017-12-05Bibliographically approved
7. Carbon dioxide separation from methane on highly selective ion exchanged zeolite NaKCsA – a possible sorbent for biogas upgrading
Open this publication in new window or tab >>Carbon dioxide separation from methane on highly selective ion exchanged zeolite NaKCsA – a possible sorbent for biogas upgrading
(English)Manuscript (preprint) (Other academic)
National Category
Materials Chemistry
Identifiers
urn:nbn:se:su:diva-102341 (URN)
Available from: 2014-04-02 Created: 2014-04-02 Last updated: 2014-04-02
8. Spherical aggregates of microporous aluminum phosphates and silicoaluminophosphates and effects of non-traditional mechanism of crystallization
Open this publication in new window or tab >>Spherical aggregates of microporous aluminum phosphates and silicoaluminophosphates and effects of non-traditional mechanism of crystallization
(English)Manuscript (preprint) (Other academic)
National Category
Materials Chemistry
Identifiers
urn:nbn:se:su:diva-102342 (URN)
Available from: 2014-04-02 Created: 2014-04-02 Last updated: 2014-04-02

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