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Optimized cesium and potassium ion-exchanged zeolites A and X granules for biogas upgrading
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
Department of Energy Conversion, Technical University of Denmark, Roskilde 4000, Denmark.
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.ORCID iD: 0000-0003-4888-6237
2018 (English)In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 8, no 65, p. 37277-37285Article in journal (Refereed) Published
Abstract [en]

Partially ion-exchanged zeolites A and X binderless granules were evaluated for CO2 separation from CH4. The CO2 adsorption capacity and CO2-over-CH4 selectivity of binderless zeolites A and X granules were optimized by partial exchange of cations with K+ and Cs+, while retaining the mechanical strength of 1.3 MPa and 2 MPa, respectively. Single gas CO2 and CH4 adsorption isotherms were recorded on zeolites A and X granules and used to estimate the co-adsorption of CO2–CH4 using ideal adsorbed solution theory (IAST). The IAST co-adsorption analysis showed that the partially ion-exchanged binderless zeolites A and X granules had a high CO2-over-CH4 selectivity of 1775 and 525 respectively, at 100 kPa and 298 K. Optimally ion-exchanged zeolite X granules retained 97% of CO2 uptake capacity, 3.8 mmol g−1, after 5 breakthrough adsorption–desorption cycles while for zeolite A ion-exchanged granules the reduction in CO2 uptake capacity was found to be 18%; CO2uptake capacity of 3.4 mmol g−1. The mass transfer analysis of breakthrough experimental data showed that the ion-exchanged zeolite X had offered a higher mass transfer coefficient, (κ) through the adsorption column compared to zeolite A; 0.41 and 0.13 m s−1 for NaK4.5Cs0.3X and CaK2.5Cs0.2A, respectively

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2018. Vol. 8, no 65, p. 37277-37285
National Category
Other Materials Engineering
Research subject
Engineering Materials
Identifiers
URN: urn:nbn:se:ltu:diva-71679DOI: 10.1039/C8RA08004FISI: 000450973500034Scopus ID: 2-s2.0-85056892674OAI: oai:DiVA.org:ltu-71679DiVA, id: diva2:1264575
Note

Validerad;2018;Nivå 2;2018-11-20 (johcin) 

Available from: 2018-11-20 Created: 2018-11-20 Last updated: 2019-05-07Bibliographically approved
In thesis
1. Tailoring of adsorptive properties of zeolites for biogas upgrading
Open this publication in new window or tab >>Tailoring of adsorptive properties of zeolites for biogas upgrading
2019 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Biogas is a promising alternative fuel with low CO2 emissions and high market potential due to the abundance of organic biomass. Despite being a renewable form of energy, biogas consists of 40-45% CO2, which lowers its calorific value [1]. Various porous materials have been tailored to adsorb CO2 gas from the biogas stream to obtain 95-97% biomethane. Zeolites are one of the promising porous materials that can contribute remarkably in the upgrading process by selectively adsorbing the CO2 gas from biogas [2].

The aim of this thesis is to develop hierarchical structures by novel approaches to enhance their CO2 adsorptive properties. The first part of the study addresses the tailoring of zeolites NaX and CaA binderless beads using the ion-exchange process to acquire high CO2 adsorption capacities of 5.1 mmol/g and 4.3 mmol/g at 298 K with the high mechanical strength of 2 MPa and 1.3 MPa respectively. The ion-exchange process was optimized for NaX and CaA zeolite to obtain high CO2-over-CH4 selectivity of 525 and 1775 respectively. The breakthrough experiments show that the partially ion-exchanged zeolite NaX has high mass transfer kinetics with a CO2 uptake rate of 2.8 mg of CO2/g/s as compared to the zeolite CaA binderless beads.

The second part dealt with the structuring of zeolites using freeze granulation and electrospinning techniques. The freeze granulation process was optimized to form granules of 2-3 mm in diameter from NaX and CaA zeolite powder. The CO2-over-CH4 selectivities were investigated using Henry’s law and it shows that the NaX granules offer high selectivity of 214 than the CaA granule, 172 at 273 K and 100 kPa. No physical damage was observed when the granules were subjected to five cyclic breakthrough adsorption-desorption experiments at 4 bar. In addition, NaX granules offer a high uptake rate of 3.6 mg of CO2/g/s with a mass transfer coefficient of 1.3 m/s as compared to the CaA granules.

To move further in structuring techniques, electrospinning was used to fabricate hierarchical porous structures. ZSM-5 nanofibers composites were developed from the ZSM-5 nanopowder and polyvinylpyrrolidone (PVP) polymer. Two-step post thermal treatments were carried out: Pre-oxidation and carbonization on ZSM-5 nanofibers composites to form mechanically strong composite structures. The post-carbonized structures showed a 30.4% increase in specific BET surface area than the ZSM-5 nanopowder with the CO2 uptake of 2.15 mmol/g. To investigate the CO2 separation properties, secondary pellet structures were developed with a tensile strength up to 6.46 MPa. The CO2 uptake rate for pellets was 2.3 mg of CO2/g/s without any performance decay after the first cycle with the simulated mass transfer coefficient of 1.24 m/s.

[1] J Wang. Decentralized biogas technology of anaerobic digestion and farm ecosystem: Opportunities and challenges, Front.Energy Res. 2 (2014).

[2] RV Siriwardane, M- Shen, EP Fisher, J Losch. Adsorption of CO 2 on zeolites at moderate temperatures, Energy Fuels. 19 (2005) 1153-1159.

Place, publisher, year, edition, pages
Luleå University of Technology, 2019
Series
Licentiate thesis / Luleå University of Technology, ISSN 1402-1757
National Category
Engineering and Technology Other Materials Engineering
Research subject
Engineering Materials
Identifiers
urn:nbn:se:ltu:diva-73868 (URN)978-91-7790-388-8 (ISBN)978-91-7790-389-5 (ISBN)
Presentation
2019-06-12, E-231, Luleå University of Technology, Luleå, 10:00 (English)
Opponent
Supervisors
Available from: 2019-05-07 Created: 2019-05-07 Last updated: 2019-06-14Bibliographically approved

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Narang, KritikaAkhtar, Farid

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