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Keywords = counter-diffusion CVD

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14 pages, 32813 KB  
Article
The Evaluation of Counter Diffusion CVD Silica Membrane Formation Process by In Situ Analysis of Diffusion Carrier Gas
by Katsunori Ishii and Mikihiro Nomura
Membranes 2022, 12(2), 102; https://doi.org/10.3390/membranes12020102 - 18 Jan 2022
Cited by 4 | Viewed by 3439
Abstract
A new evaluation method for preparing silica membranes by counter diffusion chemical vapor deposition (CVD) was proposed. This is the first attempt to provide new insights, such as the decomposition products, membrane selectivity, and precursor reactivity. The permeation of the carrier gas used [...] Read more.
A new evaluation method for preparing silica membranes by counter diffusion chemical vapor deposition (CVD) was proposed. This is the first attempt to provide new insights, such as the decomposition products, membrane selectivity, and precursor reactivity. The permeation of the carrier gas used for supplying a silica precursor was quantified during the deposition reaction by using a mass spectrometer. Membrane formation processes were evaluated by the decrease of the permeation of the carrier gas derived from pore blocking of the silica deposition. The membrane formation processes were compared for each deposition condition and precursor, and the apparent silica deposition rates from the precursors such as tetramethoxysilane (TMOS), hexyltrimethoxysilane (HTMOS), or tetraethoxysilane (TEOS) were investigated by changing the deposition temperature at 400–600 °C. The apparent deposition rates increased with the deposition temperature. The apparent activation energies of the carrier gas through the TMOS, HTMOS, and TEOS derived membranes were 44.3, 49.4, and 71.0 kJ mol−1, respectively. The deposition reaction of the CVD silica membrane depends on the alkoxy group of the silica precursors. Full article
(This article belongs to the Special Issue State-of-the-Art Membrane Science and Technology in Japan 2021, 2022)
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11 pages, 3361 KB  
Article
Permeation Properties of Ions through Inorganic Silica-Based Membranes
by Junko Yoshiura, Katsunori Ishii, Yuta Saito, Takaya Nagataki, Yuhei Nagataki, Ayumi Ikeda and Mikihiro Nomura
Membranes 2020, 10(2), 27; https://doi.org/10.3390/membranes10020027 - 8 Feb 2020
Cited by 7 | Viewed by 4405
Abstract
The development of inorganic membranes has mainly found applicability in liquid separation technologies. However, only a few reports cite the permeation and separation of liquids through inorganic nanofiltration membranes compared with the more popular microfiltration membranes. Herein, we prepared silica membranes using 3,3,3-trifluoropropyltrimethoxysilane [...] Read more.
The development of inorganic membranes has mainly found applicability in liquid separation technologies. However, only a few reports cite the permeation and separation of liquids through inorganic nanofiltration membranes compared with the more popular microfiltration membranes. Herein, we prepared silica membranes using 3,3,3-trifluoropropyltrimethoxysilane (TFPrTMOS) to investigate its liquid permeance performance using four different ion solutions (i.e., NaCl, Na2SO4, MgCl2, and MgSO4). The TFPrTMOS-derived membranes were deposited above a temperature of 175 °C, where the deposition behavior of TFPrTMOS was dependent on the organic functional groups decomposition temperature. The highest membrane rejection was from NaCl at 91.0% when deposited at 200 °C. For anions, the SO42− rejections were the greatest. It was also possible to separate monovalent and divalent anions, as the negatively charged groups on the membrane surfaces retained pore sizes >1.48 nm. Ions were also easily separated by molecular sieving below a pore size of 0.50 nm. For the TFPrTMOS-derived membrane deposited at 175 °C, glucose showed 67% rejection, which was higher than that achieved through the propyltrimethoxysilane membrane. We infer that charge exclusion might be due to the dissociation of hydroxyl groups resulting from decomposition of organic groups. Pore size and organic functional group decomposition were found to be important for ion permeation. Full article
(This article belongs to the Special Issue Mass Transfer in Membranes)
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11 pages, 3978 KB  
Article
Development of CVD Silica Membranes Having High Hydrogen Permeance and Steam Durability and a Membrane Reactor for a Water Gas Shift Reaction
by Ryoichi Nishida, Toshiki Tago, Takashi Saitoh, Masahiro Seshimo and Shin-ichi Nakao
Membranes 2019, 9(11), 140; https://doi.org/10.3390/membranes9110140 - 30 Oct 2019
Cited by 8 | Viewed by 4411
Abstract
Water gas shift reaction of carbon monoxide (CO) with membrane reactors should be a promising method for hydrogen mass-production because of its high CO conversion, high hydrogen purity and low carbon dioxide emission. For developing such membrane reactors, we need hydrogen permselective membranes [...] Read more.
Water gas shift reaction of carbon monoxide (CO) with membrane reactors should be a promising method for hydrogen mass-production because of its high CO conversion, high hydrogen purity and low carbon dioxide emission. For developing such membrane reactors, we need hydrogen permselective membranes with high hydrogen permeance with order of 10−6 mol m−2 s−1 Pa−1 at 573 K and high steam durability. In this study, we have optimized the kind of substrates, precursors, vapor concentration, and chemical vapor deposition (CVD) time using the counter-diffusion CVD method for developing such membranes. The developed membrane prepared from hexamethyldisiloxane has a hydrogen permeance of 1.29 × 10−6 mol m−2 s−1 Pa−1 at 573 K and high steam durability. We also conducted water gas shift reactions with membrane reactors installed the developed silica membranes. The results indicated that reactions proceed efficiently with the conversion around 95–97%, hydrogen purity around 94%, and hydrogen recovery around 60% at space velocity (SV) 7000. Full article
(This article belongs to the Special Issue Preparation, Characterization and Application of Silica-Based Membranes)
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12 pages, 4252 KB  
Article
Silica-Based RO Membranes for Separation of Acidic Solution
by Katsunori Ishii, Ayumi Ikeda, Toshichika Takeuchi, Junko Yoshiura and Mikihiro Nomura
Membranes 2019, 9(8), 94; https://doi.org/10.3390/membranes9080094 - 1 Aug 2019
Cited by 10 | Viewed by 5212
Abstract
The development of acid separation membranes is important. Silica-based reverse osmosis (RO) membranes for sulfuric acid (H2SO4) solution separation were developed by using a counter diffusion chemical vapor deposition (CVD) method. Diphenyldimethoxysilane (DPhDMOS) was used as a silica precursor. [...] Read more.
The development of acid separation membranes is important. Silica-based reverse osmosis (RO) membranes for sulfuric acid (H2SO4) solution separation were developed by using a counter diffusion chemical vapor deposition (CVD) method. Diphenyldimethoxysilane (DPhDMOS) was used as a silica precursor. The deposited membrane showed the H2SO4 rejection of 81% with a total flux of 5.8 kg m−2 h−1 from the 10−3 mol L−1 of H2SO4. The γ-alumina substrate was damaged by the permeation of the H2SO4 solution. In order to improve acid stability, the silica substrates were developed. The acid stability was checked by the gas permeation tests after immersing in 1 mol L−1 of the H2SO4 solution for 24 h. The N2 permeance decreased by 11% with the acid treatment through the silica substrate, while the permeance decreased to 94% through the γ-alumina substrate. The flux and the rejection through the DPhDMOS-derived membrane on the silica substrate were stable in the 70 wt % H2SO4 solution. Full article
(This article belongs to the Special Issue Preparation, Characterization and Application of Silica-Based Membranes)
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