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Membranes
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Catalysis in Membrane Reactors 2022
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Catalysis in Membrane Reactors 2022

A special issue of Membranes (ISSN 2077-0375). This special issue belongs to the section "Membrane Chemistry".

Deadline for manuscript submissions: closed (30 November 2022) | Viewed by 22954

Special Issue Editors

Prof. Dr. Norikazu Nishiyama

E-Mail Website
Guest Editor
Graduate School of Engineering Science, Osaka University, 1-3 Machikaneyama, Toyonaka, Osaka 560-8531, Japan
Interests: zeolite membrane; carbon membrane; adsorbents; zeolite catalysts
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Shigeyuki Uemiya

E-Mail Website
Guest Editor
Department of Chemistry and Biomolecular Science, Gifu University, 1-1 Yanagido, Gifu 501-1193, Japan
Interests: hydrogen separation; hydrogen production; membrane reactor; catalyst; palladium membrane; silica membrane; molecular sieve; renewable energy
Special Issues, Collections and Topics in MDPI journals
Dr. Nobuo Hara

E-Mail Website
Guest Editor
Research Institute for Chemical Process Technology, National Institute of Advanced Industrial Science and Technology (AIST), Central 5, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan
Interests: gas separation membrane; MOF membrane; membrane process; separation process; process design; process optimization

Special Issue Information

Dear Colleagues,

The 15th International Conference on Catalysis in Membrane Reactors (ICCMR-15) will be held from July 31 to August 4, 2022. It is jointly organized by The Membrane Society of Japan, The Society of Chemical Engineers, Japan, Waseda University.

Scientific program will cover:

  1. Membrane Reactors
    1. Chemical processes
    2. Photo-catalysis
    3. Bio-catalysis
    4. Micro-scaled membrane reactor
    5. Ion conducting membrane reactors
    6. Process system
    7. Modelling and simulation
  2. Materials
    1. Catalysts
    2. Membranes
    ・Polymer
    ・Dense membranes (metallic, ion-conducting)
    ・Porous membranes (zeolite, silica, carbon, MOF, metal oxides)

This Special Issue of Membranes will provide an opportunity to deeply display advances in membrane reactors and the catalysis process. We invite attendees of the “ICCMR-15” to submit their high-quality manuscripts to this Special Issue.

Suitable contributions from other interested professionals are also welcome.

We look forward to your participation and to meeting you in Tokyo in the summer of 2022.

Prof. Dr. Norikazu Nishiyama
Prof. Dr. Shigeyuki Uemiya
Dr. Nobuo Hara
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Membranes is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Published Papers (13 papers)

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Research

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25 pages, 6479 KiB  
Article
Optimization of Small-Scale Hydrogen Production with Membrane Reactors
by Michele Ongis, Gioele Di Marcoberardino, Mattia Baiguini, Fausto Gallucci and Marco Binotti
Membranes 2023, 13(3), 331; https://doi.org/10.3390/membranes13030331 - 14 Mar 2023
Cited by 4 | Viewed by 1840
Abstract
In the pathway towards decarbonization, hydrogen can provide valid support in different sectors, such as transportation, iron and steel industries, and domestic heating, concurrently reducing air pollution. Thanks to its versatility, hydrogen can be produced in different ways, among which steam reforming of [...] Read more.
In the pathway towards decarbonization, hydrogen can provide valid support in different sectors, such as transportation, iron and steel industries, and domestic heating, concurrently reducing air pollution. Thanks to its versatility, hydrogen can be produced in different ways, among which steam reforming of natural gas is still the most commonly used method. Today, less than 0.7% of global hydrogen production can be considered low-carbon-emission. Among the various solutions under investigation for low-carbon hydrogen production, membrane reactor technology has the potential, especially at a small scale, to efficiently convert biogas into green hydrogen, leading to a substantial process intensification. Fluidized bed membrane reactors for autothermal reforming of biogas have reached industrial maturity. Reliable modelling support is thus necessary to develop their full potential. In this work, a mathematical model of the reactor is used to provide guidelines for their design and operations in off-design conditions. The analysis shows the influence of temperature, pressures, catalyst and steam amounts, and inlet temperature. Moreover, the influence of different membrane lengths, numbers, and pitches is investigated. From the results, guidelines are provided to properly design the geometry to obtain a set recovery factor value and hydrogen production. For a given reactor geometry and fluidization velocity, operating the reactor at 12 bar and the permeate-side pressure of 0.1 bar while increasing reactor temperature from 450 to 500 °C leads to an increase of 33% in hydrogen production and about 40% in HRF. At a reactor temperature of 500 °C, going from 8 to 20 bar inside the reactor doubled hydrogen production with a loss in recovery factor of about 16%. With the reactor at 12 bar, a vacuum pressure of 0.5 bar reduces hydrogen production by 43% and HRF by 45%. With the given catalyst, it is sufficient to have only 20% of solids filled into the reactor being catalytic particles. With the fixed operating conditions, it is worth mentioning that by adding membranes and maintaining the same spacing, it is possible to increase hydrogen production proportionally to the membrane area, maintaining the same HRF. Full article
(This article belongs to the Special Issue Catalysis in Membrane Reactors 2022)
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11 pages, 2603 KiB  
Article
Esterification of Acetic Acid by Flow-Type Membrane Reactor with AEI Zeolite Membrane
by Yuma Sekine, Motomu Sakai and Masahiko Matsukata
Membranes 2023, 13(1), 111; https://doi.org/10.3390/membranes13010111 - 14 Jan 2023
Cited by 3 | Viewed by 1699
Abstract
AEI-type zeolite membrane for dehydration was prepared, and a flow-type membrane reactor for the esterification of acetic acid and ethanol by AEI membrane was developed. A synthesized AEI membrane had suitable molecular sieving property for gas separation (H2/i-butane and [...] Read more.
AEI-type zeolite membrane for dehydration was prepared, and a flow-type membrane reactor for the esterification of acetic acid and ethanol by AEI membrane was developed. A synthesized AEI membrane had suitable molecular sieving property for gas separation (H2/i-butane and CO2/CH4) and pervaporation (H2O/acetic acid). AEI membrane showed H2O permeance of 6.2 × 10−7 mol m−2 s−1 Pa−1 with a separation factor of 67 at 363 K for the equimolar mixture of H2O/acetic acid. AEI membrane maintained stable performance under acidic conditions. The yield of ethyl acetate at 363 K in a flow-type membrane reactor with AEI membrane successfully exceeded the equilibrium of 69.1%, reaching 89.0%. The flow rate of feed solution strongly affected the conversion of acetic acid and the space–time yield (STY) of ethyl acetate. Due to the more significant proportion of water selectively removed from the reaction system at a lower feed flow rate, the thermodynamic equilibrium shifted significantly, resulting in higher conversions. In contrast, STY increased with increasing feed flow rate. Our flow-type membrane reactor exhibited a relatively large STY of 430 kg m−3 h−1 compared with the batch-type membrane reactor previously reported. Full article
(This article belongs to the Special Issue Catalysis in Membrane Reactors 2022)
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17 pages, 4110 KiB  
Article
Platinum Nanoparticles Immobilized on Electrospun Membranes for Catalytic Oxidation of Volatile Organic Compounds
by Karel Soukup, Pavel Topka, Jaroslav Kupčík and Olga Solcova
Membranes 2023, 13(1), 110; https://doi.org/10.3390/membranes13010110 - 14 Jan 2023
Cited by 1 | Viewed by 1376
Abstract
Structured catalytic membranes with high porosity and a low pressure drop are particularly suitable for industrial processes carried out at high space velocities. One of these processes is the catalytic total oxidation of volatile organic compounds, which is an economically feasible and environmentally [...] Read more.
Structured catalytic membranes with high porosity and a low pressure drop are particularly suitable for industrial processes carried out at high space velocities. One of these processes is the catalytic total oxidation of volatile organic compounds, which is an economically feasible and environmentally friendly way of emission abatement. Noble metal catalysts are typically preferred due to high activity and stability. In this paper, the preparation of a thermally stable polybenzimidazole electrospun membrane, which can be used as a support for a platinum catalyst applicable in the total oxidation of volatile organic compounds, is reported for the first time. In contrast to commercial pelletized catalysts, high porosity of the membrane allowed for easy accessibility of the platinum active sites to the reactants and the catalytic bed exhibited a low pressure drop. We have shown that the preparation conditions can be tuned in order to obtain catalysts with a desired platinum particle size. In the gas-phase oxidation of ethanol, acetone, and toluene, the catalysts with Pt particle sizes 2.1 nm and 26 nm exhibited a lower catalytic activity than that with a Pt particle size of 12 nm. Catalysts with a Pt particle size of 2.1 nm and 12 nm were prepared by equilibrium adsorption, and the higher catalytic activity of the latter catalyst was ascribed to more reactive adsorbed oxygen species on larger Pt nanoparticles. On the other hand, the catalyst with a Pt particle size of 26 nm was prepared by a solvent evaporation method and contained less active polycrystalline platinum. Last but not least, the catalyst containing only 0.08 wt.% of platinum achieved high conversion (90%) of all the model volatile organic compounds at moderate temperatures (lower than 335 °C), which is important for reducing the costs of the abatement technology. Full article
(This article belongs to the Special Issue Catalysis in Membrane Reactors 2022)
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14 pages, 2669 KiB  
Article
Preparation and Permeation Properties of a pH-Responsive Polyacrylic Acid Coated Porous Alumina Membrane
by Takafumi Sato, Kotomi Makino, Shingo Tamesue, Gakuto Ishiura and Naotsugu Itoh
Membranes 2023, 13(1), 82; https://doi.org/10.3390/membranes13010082 - 09 Jan 2023
Cited by 2 | Viewed by 1659
Abstract
A pH-responsive membrane is expected to be used for applications such as drug delivery, controlling chemical release, bioprocessing, and water treatment. Polyacrylic acid (PAA) is a pH-responsive polymer that swells at high pH. A tubular α-alumina porous support was coated with PAA by [...] Read more.
A pH-responsive membrane is expected to be used for applications such as drug delivery, controlling chemical release, bioprocessing, and water treatment. Polyacrylic acid (PAA) is a pH-responsive polymer that swells at high pH. A tubular α-alumina porous support was coated with PAA by grafting to introduce appropriate functional groups, followed by polymerization with acrylic acid. The permeances of acetic acid, lactic acid, phenol, and caffeine were evaluated by circulating water inside the membrane, measuring the concentration of species that permeated into the water, and analyzing the results with the permeation model. The permeance of all species decreased with increasing pH, and that of phenol was the largest among these species. At high pH, the PAA carboxy group in the membrane dissociated into carboxy ions and protons, causing the swelling of PAA due to electrical repulsion between the negative charges of the PAA chain, which decreased the pore size of the membrane and suppressed permeation. Furthermore, the electrical repulsion between negatively charged species and the PAA membrane also suppressed the permeation. The results of this study demonstrated that the PAA-coated α-alumina porous support functioned as a pH-responsive membrane. Full article
(This article belongs to the Special Issue Catalysis in Membrane Reactors 2022)
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12 pages, 3922 KiB  
Article
Evaluation of FAU-type Zeolite Membrane Stability in Transesterification Reaction Conditions
by Ayumi Ikeda, Wakako Matsuura, Chie Abe, Sean-Thomas Bourne Lundin and Yasuhisa Hasegawa
Membranes 2023, 13(1), 68; https://doi.org/10.3390/membranes13010068 - 05 Jan 2023
Viewed by 1276
Abstract
The transesterification conversion of methyl ether can be enhanced by the removal of the byproduct methanol using methanol permselective faujasite (FAU-type) zeolite membranes. However, the authors previously observed that the methanol flux during the transesterification reaction was lower than the predicted flux. Therefore, [...] Read more.
The transesterification conversion of methyl ether can be enhanced by the removal of the byproduct methanol using methanol permselective faujasite (FAU-type) zeolite membranes. However, the authors previously observed that the methanol flux during the transesterification reaction was lower than the predicted flux. Therefore, this study investigated the stability of FAU-type zeolite membranes in the presence of organic components associated with the transesterification reaction of methyl hexanoate and 1-hexanol. The stability was defined in terms of changes in methanol permeance and zeolite structure. The effect of reaction components (methanol, 1-hexanol, methyl hexanoate, and hexyl hexanoate) on the FAU-type zeolite structure and the methanol permeation performance of the FAU-type zeolite membranes were evaluated to find the component causing the lower methanol flux. From these results, two esters were found to adsorb strongly on the FAU-type zeolite. The methanol flux of the FAU-type zeolite membrane was examined after vapor exposure of each of the four reaction chemicals at 373 K for 8 h. In the case of methyl hexanoate and hexyl hexanoate vapor exposure, the methanol flux was reduced by about 75% compared to the initial flux of 15 kg m−2 h−1. These results indicated methanol permeation performance was inhibited by the adsorption of esters. Full article
(This article belongs to the Special Issue Catalysis in Membrane Reactors 2022)
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15 pages, 3472 KiB  
Article
Estimation of CO2 Separation Performances through CHA-Type Zeolite Membranes Using Molecular Simulation
by Yasuhisa Hasegawa, Mayumi Natsui, Chie Abe, Ayumi Ikeda and Sean-Thomas B. Lundin
Membranes 2023, 13(1), 60; https://doi.org/10.3390/membranes13010060 - 03 Jan 2023
Viewed by 1228
Abstract
Chabazite (CHA)-type zeolite membranes are a potential material for CO2 separations because of their small pore aperture, large pore volume, and low aluminum content. In this study, the permeation and separation properties were evaluated using a molecular simulation technique with a focus [...] Read more.
Chabazite (CHA)-type zeolite membranes are a potential material for CO2 separations because of their small pore aperture, large pore volume, and low aluminum content. In this study, the permeation and separation properties were evaluated using a molecular simulation technique with a focus on improving the CO2 separation performance. The adsorption isotherms of CO2 and CH4 on CHA-type zeolite with Si/Al = 18.2 were predicted by grand canonical Monte Carlo, and the diffusivities in zeolite micropores were simulated by molecular dynamics. The CO2 separation performance of the CHA-type zeolite membrane was estimated by a Maxwell–Stefan equation, accounting for mass transfer through the support tube. The results indicated that the permeances of CO2 and CH4 were influenced mainly by the porosity of the support, with the CO2 permeance reduced due to preferential adsorption with increasing pressure drop. In contrast, it was important for estimation of the CH4 permeance to predict the amounts of adsorbed CH4. Using molecular simulation and the Maxwell–Stefan equation is shown to be a useful technique for estimating the permeation properties of zeolite membranes, although some problems such as predicting accurate adsorption terms remain. Full article
(This article belongs to the Special Issue Catalysis in Membrane Reactors 2022)
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18 pages, 4045 KiB  
Article
Hydrothermal Stability of Hydrogen-Selective Carbon–Ceramic Membranes Derived from Polybenzoxazine-Modified Silica–Zirconia
by Sulaiman Oladipo Lawal, Hiroki Nagasawa, Toshinori Tsuru and Masakoto Kanezashi
Membranes 2023, 13(1), 30; https://doi.org/10.3390/membranes13010030 - 26 Dec 2022
Cited by 2 | Viewed by 1552
Abstract
This work investigated the long-term hydrothermal performance of composite carbon-SiO2-ZrO2 membranes. A carbon-SiO2-ZrO2 composite was formed from the inert pyrolysis of SiO2-ZrO2-polybenzoxazine resin. The carbon-SiO2-ZrO2 composites prepared at 550 and [...] Read more.
This work investigated the long-term hydrothermal performance of composite carbon-SiO2-ZrO2 membranes. A carbon-SiO2-ZrO2 composite was formed from the inert pyrolysis of SiO2-ZrO2-polybenzoxazine resin. The carbon-SiO2-ZrO2 composites prepared at 550 and 750 °C had different surface and microstructural properties. A carbon-SiO2-ZrO2 membrane fabricated at 750 °C exhibited H2 selectivity over CO2, N2, and CH4 of 27, 139, and 1026, respectively, that were higher than those of a membrane fabricated at 550 °C (5, 12, and 11, respectively). In addition to maintaining high H2 permeance and selectivity, the carbon-SiO2-ZrO2 membrane fabricated at 750 °C also showed better stability under hydrothermal conditions at steam partial pressures of 90 (30 mol%) and 150 kPa (50 mol%) compared with the membrane fabricated at 500 °C. This was attributed to the complete pyrolytic and ceramic transformation of the microstructure after pyrolysis at 750 °C. This work thus demonstrates the promise of carbon-SiO2-ZrO2 membranes for H2 separation under severe hydrothermal conditions. Full article
(This article belongs to the Special Issue Catalysis in Membrane Reactors 2022)
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9 pages, 3662 KiB  
Article
An Experimental Study of a Zeolite Membrane Reactor for Reverse Water Gas Shift
by Motomu Sakai, Kyoka Tanaka and Masahiko Matsukata
Membranes 2022, 12(12), 1272; https://doi.org/10.3390/membranes12121272 - 15 Dec 2022
Cited by 3 | Viewed by 1534
Abstract
Reverse water gas shift (RWGS) is attracting attention as one of the promising technologies for CO2 conversion. Selective removal of H2O from the reaction system can improve the CO2 conversion beyond the equilibrium conversion of RWGS in a conventional [...] Read more.
Reverse water gas shift (RWGS) is attracting attention as one of the promising technologies for CO2 conversion. Selective removal of H2O from the reaction system can improve the CO2 conversion beyond the equilibrium conversion of RWGS in a conventional reactor. In this study, a conventional plug-flow reactor without membrane, and two types of RWGS membrane reactors using ZSM-5 membranes, were developed. The yield of CO without membrane (Case 1) was almost the same as the equilibrium conversion. A membrane reactor (Case 2) showed a CO yield 2–3% above that of a conventional reactor. From the results, the effectiveness of the dehydration membrane reactor for RWGS was verified. In addition, CO yield was further increased in the reactor made up of the combination of conventional reactor and membrane reactor (Case 3). For example, the CO yields in Cases 1, 2, and 3 at 560 K were 21.8, 24.9, and 29.0%, respectively. Although the CO yield increased in Case 2, a large amount of raw materials penetrated through the membrane to the permeation side, and was lost. In Case 3, H2 and CO2 permeation through the membrane were suppressed because of the existence of H2O, resulting in the prevention of the leakage of raw material, and contributing to the high CO yield. Full article
(This article belongs to the Special Issue Catalysis in Membrane Reactors 2022)
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13 pages, 3355 KiB  
Article
Improved Esterification of Citric Acid and n-Butanol Using a Dense and Acid-Resistant Beta Zeolite Membrane
by Zhengquan Yang, Mingyu Peng, Yu Li, Xiaowei Wu, Tian Gui, Yuqin Li, Fei Zhang, Xiangshu Chen and Hidetoshi Kita
Membranes 2022, 12(12), 1269; https://doi.org/10.3390/membranes12121269 - 15 Dec 2022
Cited by 2 | Viewed by 1430
Abstract
In this work, a dense and acid-resistant beta zeolite membrane was applied to improve the esterification of citric acid and n-butanol, for the first time. Through the continuous removal of the by-product water via pervaporation (PV), the conversion of citric acid was significantly [...] Read more.
In this work, a dense and acid-resistant beta zeolite membrane was applied to improve the esterification of citric acid and n-butanol, for the first time. Through the continuous removal of the by-product water via pervaporation (PV), the conversion of citric acid was significantly enhanced from 71.7% to 99.2% using p-Toluenesulfonic acid (PTSA) as catalyst. PTSA was a well-known strong acid, and the membrane kept almost no change after PV-esterification, indicating the superior acid resistance of beta zeolite membrane. Compared to the use of acid-resistant MOR zeolite membrane by PV-esterification, a consistently higher conversion of citric acid was obtained using a high-flux beta zeolite membrane. The results showed that high water permeation on the beta zeolite membrane, with good acid resistance, had a strong promoting effect on esterification, leading to an improved conversion. In addition, the citric acid conversion of 97.7% could still be achieved by PV-esterification at a low reaction temperature of 388 K. Full article
(This article belongs to the Special Issue Catalysis in Membrane Reactors 2022)
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23 pages, 7734 KiB  
Article
Fluidized Bed Membrane Reactor for the Direct Dehydrogenation of Propane: Proof of Concept
by Camilla Brencio, Luca Di Felice and Fausto Gallucci
Membranes 2022, 12(12), 1211; https://doi.org/10.3390/membranes12121211 - 30 Nov 2022
Cited by 3 | Viewed by 2005
Abstract
In this work, the fluidized bed membrane reactor (FBMR) technology for the direct dehydrogenation of propane (PDH) was demonstrated at a laboratory scale. Double-skinned PdAg membranes were used to selectively remove H2 during dehydrogenation tests over PtSnK/Al2O3 catalyst under [...] Read more.
In this work, the fluidized bed membrane reactor (FBMR) technology for the direct dehydrogenation of propane (PDH) was demonstrated at a laboratory scale. Double-skinned PdAg membranes were used to selectively remove H2 during dehydrogenation tests over PtSnK/Al2O3 catalyst under fluidization. The performance of the fluidized bed membrane reactor was experimentally investigated and compared with the conventional fluidized bed reactor (FBR) by varying the superficial gas velocity over the minimum fluidization velocity under fixed operating conditions (i.e., 500 °C, 2 bar and feed composition of 30vol% C3H8-70vol% N2). The results obtained in this work confirmed the potential for improving the PDH performance using the FBMR system. An increase in the initial propane conversion of c.a. 20% was observed, going from 19.5% in the FBR to almost 25% in the FBMR. The hydrogen recovery factor displayed a decrease from 70% to values below 50%, due to the membrane coking under alkene exposure. Despites this, the hydrogen extraction from the reaction environment shifted the thermodynamic equilibrium of the dehydrogenation reaction and achieved an average increase of 43% in propylene yields. Full article
(This article belongs to the Special Issue Catalysis in Membrane Reactors 2022)
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18 pages, 8535 KiB  
Article
Effects of the Water Matrix on the Degradation of Micropollutants by a Photocatalytic Ceramic Membrane
by Shuyana A. Heredia Deba, Bas A. Wols, Doekle R. Yntema and Rob G. H. Lammertink
Membranes 2022, 12(10), 1004; https://doi.org/10.3390/membranes12101004 - 16 Oct 2022
Cited by 4 | Viewed by 1944
Abstract
The consumption of pharmaceuticals has increased the presence of micropollutants (MPs) in the environment. The removal and degradation of pharmaceutical mixtures in different water matrices are thus of significant importance. The photocatalytic degradation of four micropollutants—diclofenac (DCF), iopamidol (INN), methylene blue (MB), and [...] Read more.
The consumption of pharmaceuticals has increased the presence of micropollutants (MPs) in the environment. The removal and degradation of pharmaceutical mixtures in different water matrices are thus of significant importance. The photocatalytic degradation of four micropollutants—diclofenac (DCF), iopamidol (INN), methylene blue (MB), and metoprolol (MTP)—have been analyzed in this study by using a photocatalytic ceramic membrane. We experimentally analyzed the degradation rate by using several water matrices by changing the feed composition of micropollutants in the mixture (from mg· L−1 to μg·L−1), adding different concentrations of inorganic compounds (NaHCO3 and NaCl), and by using tap water. A maximum degradation of 97% for DCF and MTP, and 85% for INN was observed in a micropollutants (MPs) mixture in tap water at environmentally relevant feed concentrations [1–6 μg·L−1]o; and 86% for MB in an MPs mixture [1–3 mg·L−1]o with 100 mg·L−1 of NaCl. This work provides further insights into the applicability of photocatalytic membranes and illustrates the importance of the water matrix to the photocatalytic degradation of micropollutants. Full article
(This article belongs to the Special Issue Catalysis in Membrane Reactors 2022)
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16 pages, 3797 KiB  
Article
The Effect of C/Si Ratio and Fluorine Doping on the Gas Permeation Properties of Pendant-Type and Bridged-Type Organosilica Membranes
by Ikram Rana, Takahiro Nagaoka, Hiroki Nagasawa, Toshinori Tsuru and Masakoto Kanezashi
Membranes 2022, 12(10), 991; https://doi.org/10.3390/membranes12100991 - 13 Oct 2022
Viewed by 1509
Abstract
A series of pendant–type alkoxysilane structures with various carbon numbers (C1–C8) were used to fabricate sol–gel derived organosilica membranes to evaluate the effects of the C/Si ratio and fluorine doping. Initially, this investigation was focused on the effect that [...] Read more.
A series of pendant–type alkoxysilane structures with various carbon numbers (C1–C8) were used to fabricate sol–gel derived organosilica membranes to evaluate the effects of the C/Si ratio and fluorine doping. Initially, this investigation was focused on the effect that carbon-linking (pendant–type) units exert on a microporous structure and how this affects the gas-permeation properties of pendant–type organosilica membranes. Gas permeation results were compared with those of bridged–type organosilica membranes (C1–C8). Network pore size evaluation was conducted based on the selectivity of H2/N2 and the activation energy (Ep) of H2 permeation. Consequently, Ep (H2) was increased as the C/Si ratio increased from C1 to C8, which could have been due to the aggregation of pendant side chains that occupied the available micropore channel space and resulted in the reduced pore size. By comparison, these permeation results indicate that pendant–type organosilica membranes showed a somewhat loose network structure in comparison with bridged–type organosilica membranes by following the lower values of activation energies (Ep). Subsequently, we also evaluated the effect that fluorine doping (NH4F) exerts on pendant−type [methytriethoxysilane (MTES), propyltrimethoxysilane (PTMS)] and bridged-type [1,2–bis(triethoxysilyl)methane (BTESM) bis(triethoxysilyl)propane (BTESP)] organosilica structures with similar carbon numbers (C1 and C3). The gas-permeation properties of F–doped pendant network structures revealed values for pore size, H2/N2 selectivity, and Ep (H2) that were comparable to those of pristine organosilica membranes. This could be ascribed to the pendant side chains, which might have hindered the effectiveness of fluorine in pendant–type organosilica structures. The F–doped bridged–type organosilica (BTESM and BTESP) membranes, on the other hand, exhibited a looser network formation as the fluorine concentration increased. Full article
(This article belongs to the Special Issue Catalysis in Membrane Reactors 2022)
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Review

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30 pages, 11682 KiB  
Review
Recent Progress in Silicon Carbide-Based Membranes for Gas Separation
by Qing Wang, Rongfei Zhou and Toshinori Tsuru
Membranes 2022, 12(12), 1255; https://doi.org/10.3390/membranes12121255 - 12 Dec 2022
Cited by 6 | Viewed by 2831
Abstract
The scale of research for developing and applying silicon carbide (SiC) membranes for gas separation has rapidly expanded over the last few decades. Given its importance, this review summarizes the progress on SiC membranes for gas separation by focusing on SiC membrane preparation [...] Read more.
The scale of research for developing and applying silicon carbide (SiC) membranes for gas separation has rapidly expanded over the last few decades. Given its importance, this review summarizes the progress on SiC membranes for gas separation by focusing on SiC membrane preparation approaches and their application. The precursor-derived ceramic approaches for preparing SiC membranes include chemical vapor deposition (CVD)/chemical vapor infiltration (CVI) deposition and pyrolysis of polymeric precursor. Generally, SiC membranes formed using the CVD/CVI deposition route have dense structures, making such membranes suitable for small-molecule gas separation. On the contrary, pyrolysis of a polymeric precursor is the most common and promising route for preparing SiC membranes, which includes the steps of precursor selection, coating/shaping, curing for cross-linking, and pyrolysis. Among these steps, the precursor, curing method, and pyrolysis temperature significantly impact the final microstructures and separation performance of membranes. Based on our discussion of these influencing factors, there is now a good understanding of the evolution of membrane microstructures and how to control membrane microstructures according to the application purpose. In addition, the thermal stability, oxidation resistance, hydrothermal stability, and chemical resistance of the SiC membranes are described. Due to their robust advantages and high separation performance, SiC membranes are the most promising candidates for high-temperature gas separation. Overall, this review will provide meaningful insight and guidance for developing SiC membranes and achieving excellent gas separation performance. Full article
(This article belongs to the Special Issue Catalysis in Membrane Reactors 2022)
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