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Adsorption and Mass Transport in Zeolite Membranes
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.ORCID iD: 0000-0002-7792-1348
2022 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Zeolites are commonly used as adsorbents and catalysts in the industry due to their well-defined pores of molecular dimensions. Zeolites offer porous structure, which consists of interlinked alumina and silica tetrahedra with shared oxygen atoms. Zeolites can also be prepared as intergrown films on porous supports, which results in zeolite membranes. CHA and MFI are two promising zeolites that can be used as membranes for biogas and syngas separation and upgrading since their pore size is suitable.

Membrane technology is considered an energy-lean gas separation method that offers a straightforward process with compact equipment and high efficiency. Compared with polymeric membranes, zeolite membranes offer higher permeance and stability due to their porous structure and ceramic nature. Since zeolite membranes are expensive and a higher flux would reduce the needed membrane area, thin membranes with high flux are of great interest. However, to enable the design of zeolite membrane processes, it is vital to enhance the fundamental understanding of the mass transport in the materials.

In this study, zeolite membranes of different types, i.e., CHA and MFI, were evaluated for separation of various gas mixtures. MFI disc membranes were evaluated for the separation of equimolar CO2/H2 mixtures under both dry and humid conditions, as well as for the separation of ternary CH4/N2/He mixtures. High selectivity and high CO2 fluxes were observed during CO2/H2 separation under both dry and humid conditions. The MFI disc membrane also displayed a high performance for separation of ternary CH4/N2/He mixtures. The results indicated that MFI membranes are promising candidates for separation of CO2 from the gas mixtures and for helium recovery from natural gas. Tubular CHA membranes, with lengths of 10 and 50 cm, were also investigated for CO2/CH4 separation under industrially relevant conditions. A maximum CO2/CH4 separation selectivity of 198 combined with a CO2 permeance of 14×10-7 mol/(m2·s·Pa) was observed for humid gas. The results verified the feasibility of these membranes for industrial gas separations.

After verifying the high performance of CHA zeolite membranes for gas separation under industrial conditions, CHA zeolite crystals with various Si/Al ratios were synthesized and the adsorption of CO2 and CH4 in the materials were studied. Subsequently, the mass transport through ultra-thin MFI and CHA zeolite disc membranes was measured and a model accounting for the adsorption and diffusion through the surface barriers and in the pores was developed. The model was successfully fitted to both single component and mixture permeation data. The fitted model indicates that the mass transport through ultra-thin membranes is controlled by the surface barriers. It revealed that the surface barrier is a surface diffusion process at the pore mouth with an activation energy that is higher than for the surface diffusion in the pores. Furthermore, the fitted model indicated that the high selectivity of CHA membranes is mostly due to a highly selective surface barrier and, to a lesser extent, is a result of adsorption selectivity.

In the last part of the work, a process for upgrading biogas was designed by using the developed model. The process was compared with a process based on hollow fiber polymeric membranes. It was concluded that the zeolite membrane processes were much more compact and had a much lower demand for electricity than the polymeric membrane process.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2022.
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
National Category
Chemical Engineering
Research subject
Chemical Technology
Identifiers
URN: urn:nbn:se:ltu:diva-89354ISBN: 978-91-8048-032-1 (print)ISBN: 978-91-8048-033-8 (electronic)OAI: oai:DiVA.org:ltu-89354DiVA, id: diva2:1639202
Public defence
2022-04-22, E632, Luleå tekniska universitet (LTU), E-huset, Luleå, 10:00 (English)
Opponent
Supervisors
Available from: 2022-02-21 Created: 2022-02-20 Last updated: 2022-04-01Bibliographically approved
List of papers
1. The origin of the surface barrier in nanoporous materials
Open this publication in new window or tab >>The origin of the surface barrier in nanoporous materials
2022 (English)In: Journal of Membrane Science, ISSN 0376-7388, E-ISSN 1873-3123, Vol. 641, article id 119893Article in journal (Refereed) Published
Abstract [en]

Surface barriers are influencing the mass transfer in nanopores, but their origin is unclear and can be quite different in different materials. For MFI and CHA membranes studied here, we show that the surface barrier may be a surface diffusion process with higher activation energy than the surface diffusion process in the pores, but other possible mechanisms such as pore blocking and pore narrowing has not been ruled out. The higher activation energy is probably a result of less interaction between adsorbed molecules at the pore mouth than inside the pores, i.e. the barrier is simply a geometrical effect in these materials. For pure components at low concentration in MFI zeolite, we found that barrier is proportional to the product of the molecular weight and heat of desorption. For MFI and CHA zeolite, we observed that the barrier is a function of concentration and approach zero at high concentration and that the barriers of the components become more similar due to interaction between the components in mixtures, which explains the high and selective mass transfer displayed by these nanoporous materials at high concentration.

Place, publisher, year, edition, pages
Elsevier, 2022
Keywords
Surface barrier, Nanoporous materials, Mass transfer, Surface diffusion, Activation energy
National Category
Chemical Process Engineering
Research subject
Chemical Technology
Identifiers
urn:nbn:se:ltu:diva-87194 (URN)10.1016/j.memsci.2021.119893 (DOI)000705871700004 ()2-s2.0-85115774975 (Scopus ID)
Funder
Swedish Research CouncilSwedish Research Council FormasBio4Energy
Note

Validerad;2021;Nivå 2;2021-10-01 (alebob)

Available from: 2021-09-23 Created: 2021-09-23 Last updated: 2022-02-20Bibliographically approved
2. Mass transport of CO2 over CH4 controlled by the selective surface barrier in ultra-thin CHA membranes
Open this publication in new window or tab >>Mass transport of CO2 over CH4 controlled by the selective surface barrier in ultra-thin CHA membranes
2022 (English)In: Microporous and Mesoporous Materials, ISSN 1387-1811, E-ISSN 1873-3093, Vol. 332, article id 111716Article in journal (Refereed) Published
Abstract [en]

The adsorption and mass transport of CO2 and CH4 in CHA zeolite were studied experimentally. First, large and well-defined CHA crystals with varying Si/Al ratios and morphologies ideal for adsorption studies were prepared. Then, adsorption isotherms were measured, and adsorption parameters were estimated from the data. In the next step, permeation experiments for pure components and mixtures were conducted for a defect-free CHA membrane with a Si/Al ratio of 80 and a thickness of 600 nm over a wide temperature range. A maximum selectivity of 243 in combination with a CO2 permeance of 70 × 10−7 mol/(m2 s Pa) was observed for a feed of an equimolar CO2/CH4 mixture at 273 K and 5.5 bar. Finally, a simple model accounting for adsorption and diffusion through the surface barriers and the interior of the pores of the membrane was fitted to the permeation data. The fitted model indicated that the surface barrier was a surface diffusion process at the pore mouth with higher activation energy than the diffusion process within the pores. The model also showed that the highly selective mass transport in the membrane was mostly a result of a selective surface barrier and, to a lesser extent, a result of adsorption selectivity.

Place, publisher, year, edition, pages
Elsevier, 2022
Keywords
Activation energy, Adsorption, Mass transport, Surface barrier, Surface diffusion
National Category
Chemical Process Engineering
Research subject
Chemical Technology
Identifiers
urn:nbn:se:ltu:diva-89075 (URN)10.1016/j.micromeso.2022.111716 (DOI)000761764300006 ()2-s2.0-85123872231 (Scopus ID)
Funder
Swedish Research Council FormasSwedish Research CouncilBio4Energy
Note

Validerad;2022;Nivå 2;2022-02-21 (hanlid)

Available from: 2022-02-01 Created: 2022-02-01 Last updated: 2022-07-04Bibliographically approved
3. High performance fluoride MFI membranes for efficient CO2/H2 separation
Open this publication in new window or tab >>High performance fluoride MFI membranes for efficient CO2/H2 separation
2020 (English)In: Journal of Membrane Science, ISSN 0376-7388, E-ISSN 1873-3123, Vol. 616, article id 118623Article in journal (Refereed) Published
Abstract [en]

In the present work, ultra-thin MFI zeolite membranes with a thickness of about 450 nm prepared in fluoride media were evaluated for separation of equimolar CO2/H2 gas mixtures. Both dry and humid mixtures were evaluated. For dry gas mixtures, the membrane selectivity increased from 13 to 45 when the temperature decreased from 318 to 285 K, and CO2 flux was very high and almost constant at 4 mol m−2 s−1, corresponding to CO2 permeance of 100 × 10−7 mol m−2 s−1 Pa−1 (29851 GPU). For humid gas mixtures with a partial pressure of water of 3.5 kPa, the CO2 flux decreased from 3.27 to 0.10 mol m−2 s−1 when the temperature decreased from 316 to 288 K. The corresponding CO2 permeance decreased from 79 to 2.5 × 10−7 mol m−2 s−1 Pa−1 (from 23582 to 746 GPU). At the highest temperature 318 K, the CO2/Hseparation selectivity was slightly higher for the humid gas mixture. For the humid gas mixture, the CO2 flux increased from 3.27 to 3.76 mol m−2 s−1 at 318 K and from 0.52 to 0.90 mol m−2 s−1 at 296 K when the permeate pressure was reduced from atmospheric to vacuum, respectively. The separation selectivity of CO2/H2 was almost not affected by the permeate pressure. The results show that ultra-thin fluoride MFI zeolite membranes are promising candidates for separation of CO2 from dry or humid synthesis gas.

Place, publisher, year, edition, pages
Elsevier, 2020
Keywords
MFI zeolite Membrane, Fluoride membrane, CO2 separation, Synthesis gas, Humid gas
National Category
Chemical Process Engineering
Research subject
Chemical Technology
Identifiers
urn:nbn:se:ltu:diva-80491 (URN)10.1016/j.memsci.2020.118623 (DOI)000571498900001 ()2-s2.0-85089593990 (Scopus ID)
Note

Validerad;2020;Nivå 2;2020-08-26 (alebob)

Available from: 2020-08-20 Created: 2020-08-20 Last updated: 2022-02-20Bibliographically approved
4. Recovery of helium from natural gas using MFI membranes
Open this publication in new window or tab >>Recovery of helium from natural gas using MFI membranes
Show others...
2022 (English)In: Journal of Membrane Science, ISSN 0376-7388, E-ISSN 1873-3123, Vol. 644, article id 120113Article in journal (Refereed) Published
Abstract [en]

The development of more efficient technology for the production of helium from natural gas is pressing as the current resources are dwindling. In the present work, ultra-thin MFI membranes were evaluated for the separation of an equimolar CH4/N2/He mixture in a wide temperature range 120–293K. The membrane was highly selective towards CH4 and N2 at all the investigated conditions, which resulted in a helium rich retentate. The observed selectivity should be a result of selective adsorption of CH4 and N2. A maximum (CH4+N2)/He separation factor of 152 was observed at 153 K and a feed pressure of 3 bar and a permeate pressure of 0.2 bar. At these conditions, separation factors were 265 and 38 for CH4/He and N2/He, respectively, and the CH4 and N2 fluxes were 1.12 and 0.16 mol/(m2⋅s), respectively. To the best of our knowledge, these are the best results reported in the open literature for the recovery of helium from natural gas using membrane technology. The high selectivity and flux indicated that the ultra-thin MFI membranes are a promising candidate for efficient helium production from natural gas.

Place, publisher, year, edition, pages
Elsevier, 2022
Keywords
High-flux MFI membrane, Natural gas, Helium production, Methane, Nitrogen
National Category
Chemical Process Engineering
Research subject
Chemical Technology
Identifiers
urn:nbn:se:ltu:diva-87961 (URN)10.1016/j.memsci.2021.120113 (DOI)000788512800002 ()2-s2.0-85119933714 (Scopus ID)
Funder
Swedish Research CouncilSwedish Research Council FormasThe Kempe Foundations, JCK-1904.1Bio4Energy
Note

Validerad;2022;Nivå 2;2022-03-04 (hanlid)

Available from: 2021-11-22 Created: 2021-11-22 Last updated: 2022-05-12Bibliographically approved
5. Highly permeable and selective tubular zeolite CHA membranes
Open this publication in new window or tab >>Highly permeable and selective tubular zeolite CHA membranes
2019 (English)In: Journal of Membrane Science, ISSN 0376-7388, E-ISSN 1873-3123, Vol. 588, article id 117224Article in journal (Refereed) Published
Abstract [en]

Highly permeable and selective tubular zeolite CHA membranes with a thickness of about 450 nm and a length of 100 mm and an inner diameter of 7 mm were evaluated by single gas permeation experiments and for separation of an equimolar CO2/CH4 mixture. The membranes displayed high H2 and CO2 single gas permeances of 55 × 10−7 mol m−2 s−1 Pa−1 and 94 × 10−7 mol m−2 s−1 Pa−1, respectively, and a very low SF6 permeance of 3 × 10−9 mol m−2 s−1 Pa−1. The highest observed mixture separation factor was 99 with CO2 permeance of 60 × 10−7 mol m−2 s−1 Pa−1 at a feed pressure of 5 bar and permeate pressure of 0.12 bar. The corresponding CO2flux was 1.46 mol m−2 s−1. The highest observed flux was 1.98 mol m−2 s−1 with a separation factor of 52 at a feed pressure of 10 bar and permeate pressure of 0.12 bar at room temperature. To the best of our knowledge, this is the first report describing highly permeable and selective tubular CHA membranes. The results indicate that the membranes have a great potential for industrial separation of CO2from natural gas and biogas.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Tubular zeolite CHA membrane, Gas separation, High permeance, Biogas, Natural gas
National Category
Chemical Process Engineering
Research subject
Chemical Technology
Identifiers
urn:nbn:se:ltu:diva-75258 (URN)10.1016/j.memsci.2019.117224 (DOI)000481577200017 ()2-s2.0-85068362145 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-07-08 (johcin)

Available from: 2019-07-08 Created: 2019-07-08 Last updated: 2022-06-01Bibliographically approved
6. Industrially relevant CHA membranes for CO2/CH4 separation
Open this publication in new window or tab >>Industrially relevant CHA membranes for CO2/CH4 separation
2022 (English)In: Journal of Membrane Science, ISSN 0376-7388, E-ISSN 1873-3123, Vol. 641, article id 119888Article in journal (Refereed) Published
Abstract [en]

In the present work, single channel tubular zeolite CHA membranes with a length of 50 cm and a membrane area of 100 cm2 were evaluated by SEM and permeation experiments with single components and industrially relevant humid mixtures. The membranes comprised well-intergrown and smooth CHA films with a thickness of <500 nm supported on the inside of a highly porous tube. For single component permeation, a very low SF6 permeance of 4.5 × 10−10 mol/(m2‧s‧Pa) was observed, which indicated nearly defect free membranes. On the contrary, the membranes displayed a very high CO2 permeance of 128 × 10−7 mol/(m2‧s‧Pa), which illustrated the very high permeability of the CHA pores. Finally, the membranes displayed excellent selectivity for separation of industrially relevant CO2/CH4/H2O mixtures, which was attributed to selective interaction between the CO2 molecules and the polar water molecules in the pores. The highest observed CO2/CH4 separation selectivity was as high as 198 in combination with a CO2 permeance of 14 × 10−7 mol/(m2‧s‧Pa) at a feed pressure of 600 kPa (including 2.2 kPa water) and 293K. The corresponding CO2 flux was 0.39 mol/(m2‧s) and the corresponding CO2/CH4 separation factor was 162. The observed membrane performance was reduced by concentration polarisation due to the limited feed flow in the experimental setup. The corresponding selectivity and CO2 permeance corrected for concentration polarisation were as high as 236 and 16 × 10−7 mol/(m2‧s‧Pa), and the corrected CO2 flux was 0.44 mol/(m2‧s) and corrected separation factor was 198. An estimate showed that even at a low feed pressure of 500 kPa, it would be sufficient with as few as 64 membranes for processing of a feed of 100 Nm3/h raw biogas, i.e. the capacity of a typical biogas plant at a large farm, to biomethane with high purity. These results illustrated that the membranes are promising candidates for industrial separation of CO2 from e.g. natural gas and biogas.

Place, publisher, year, edition, pages
Elsevier, 2022
Keywords
Tubular zeolite CHA membrane, Scale-up, Industrially relevant gas separation, Natural gas, Biogas
National Category
Chemical Process Engineering
Research subject
Chemical Technology
Identifiers
urn:nbn:se:ltu:diva-87332 (URN)10.1016/j.memsci.2021.119888 (DOI)000705872500002 ()2-s2.0-85115369262 (Scopus ID)
Funder
Swedish Research CouncilSwedish Research Council FormasThe Kempe Foundations, JCK-1904.1Bio4Energy
Note

Validerad;2021;Nivå 2;2021-10-04 (alebob)

Available from: 2021-10-04 Created: 2021-10-04 Last updated: 2022-02-20Bibliographically approved
7. Zeolite Membrane Process for Industrial CO2/CH4 Separation
Open this publication in new window or tab >>Zeolite Membrane Process for Industrial CO2/CH4 Separation
2022 (English)In: Chemical Engineering Journal, ISSN 1385-8947, E-ISSN 1873-3212, Vol. 446, no 4, article id 137223Article in journal (Refereed) Published
Abstract [en]

Zeolite membrane processes were designed for biogas upgrading for feed pressures ranging from 5 to 20 bar and compared with corresponding polymeric membrane processes. The mass transfer through zeolite membranes was estimated by a model accounting for adsorption and diffusion through the surface barriers and the interior of the pores, while the mass transfer through polymeric membranes was estimated using reported permeances for commercial polymeric membranes. The zeolite membranes displayed approximately three orders of magnitude higher permeance and up to 7 times higher selectivity. To reach a low methane loss, two and three membrane stages were needed for zeolite and polymeric membranes, respectively, because of the differences in selectivity. Due to the higher selectivity, the electricity need for the zeolite membrane process was only 50–60% of that for the corresponding polymeric membrane process. As a result of the much higher permeability, the zeolite membrane processes were much more compact than the equivalent polymeric membrane processes. The estimated cost for zeolite membranes prepared in small scale including modules was much lower than the cost for industrially produced polymeric membranes including modules.

Place, publisher, year, edition, pages
Elsevier, 2022
Keywords
Biogas, Natural gas, Membrane, Zeolite membrane, Polymeric membrane
National Category
Chemical Engineering
Research subject
Chemical Technology
Identifiers
urn:nbn:se:ltu:diva-89112 (URN)10.1016/j.cej.2022.137223 (DOI)000833417800001 ()2-s2.0-85131690439 (Scopus ID)
Funder
Swedish Research CouncilSwedish Research Council FormasBio4Energy
Note

Validerad;2022;Nivå 2;2022-06-22 (hanlid)

Available from: 2022-02-04 Created: 2022-02-04 Last updated: 2022-08-11Bibliographically approved

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