Membranes

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17 pages, 9701 KiB

Open AccessArticle

Gas Separation Silica Membranes Prepared by Chemical Vapor Deposition of Methyl-Substituted Silanes

by Harumi Kato, Sean-Thomas B. Lundin, So-Jin Ahn, Atsushi Takagaki, Ryuji Kikuchi and S. Ted Oyama

Membranes 2019, 9(11), 144; https://doi.org/10.3390/membranes9110144 - 03 Nov 2019

Cited by 11 | Viewed by 4513

Abstract

The effect on the gas permeance properties and structural morphology of the presence of methyl functional groups in a silica membrane was studied. Membranes were synthesized via chemical vapor deposition (CVD) at 650 °C and atmospheric pressure using three silicon compounds with differing [...] Read more.

The effect on the gas permeance properties and structural morphology of the presence of methyl functional groups in a silica membrane was studied. Membranes were synthesized via chemical vapor deposition (CVD) at 650 °C and atmospheric pressure using three silicon compounds with differing numbers of methyl- and methoxy-functional groups: tetramethyl orthosilicate (TMOS), methyltrimethoxysilane (MTMOS), and dimethyldimethoxysilane (DMDMOS). The residence time of the silica precursors in the CVD process was adjusted for each precursor and optimized in terms of gas permeance and ideal gas selectivity criteria. Final H₂ permeances at 600 °C for the TMOS-, MTMOS-, and DMDMOS-derived membranes were respectively 1.7 × 10⁻⁷, 2.4 × 10⁻⁷, and 4.4 × 10⁻⁸ mol∙m⁻²∙s⁻¹∙Pa⁻¹ and H₂/N₂ selectivities were 990, 740, and 410. The presence of methyl groups in the membranes fabricated with the MTMOS and DMDMOS precursors was confirmed via Fourier-transform infrared (FTIR) spectroscopy. From FTIR analysis, an increasing methyl signal in the silica structure was correlated with both an improvement in the hydrothermal stability and an increase in the apparent activation energy for hydrogen permeation. In addition, the permeation mechanism for several gas species (He, H₂, Ne, CO₂, N₂, and CH₄) was determined by fitting the gas permeance temperature dependence to one of three models: solid state, gas-translational, or surface diffusion. Full article

(This article belongs to the Special Issue Preparation, Characterization and Application of Silica-Based Membranes)

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11 pages, 3978 KiB

Open AccessArticle

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 7 | Viewed by 3253

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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17 pages, 7472 KiB

Open AccessFeature PaperArticle

Molecular Dynamics Simulation Study of Solid Vibration Permeation in Microporous Amorphous Silica Network Voids

by Tomohisa Yoshioka, Akihiro Nakata, Kuo-Lun Tung, Masakoto Kanezashi and Toshinori Tsuru

Membranes 2019, 9(10), 132; https://doi.org/10.3390/membranes9100132 - 12 Oct 2019

Cited by 8 | Viewed by 3535

Abstract

Microporous silica membranes have silica polymer network voids smaller than 3 Å where only small gas molecules such as helium (2.6 Å) and hydrogen (2.89 Å) can be transported. These silica membranes are highly expected to be available for H₂ separation. In [...] Read more.

Microporous silica membranes have silica polymer network voids smaller than 3 Å where only small gas molecules such as helium (2.6 Å) and hydrogen (2.89 Å) can be transported. These silica membranes are highly expected to be available for H₂ separation. In order to examine gas permeation mechanisms in the silica polymer network voids, factors such as membrane porous structures, gas diffusivity, and gas permeability were studied via membrane permeation molecular dynamics simulation. The thermal motions of silica membrane constituent atoms were examined according to classic harmonic oscillation potential using a suitable amorphous silica structure and non-equilibrium molecular dynamics (NEMD) simulations of gas permeation. The dynamic model successfully simulated the gas permeation characteristics in an amorphous silica membrane with a suitable Hooke’s potential parameter. The introduction of the oscillative thermal motion of the membrane atoms enhanced gas diffusivity. Helium and hydrogen diffusivity and permeability were analyzed using gas translation (GT) and solid vibration (SV) models. The diffusion distance of gas molecules between adsorption sites was around 5.5–7 Å. The solid-type vibration frequencies of gas molecules in the site were on the order of 10¹³ and were reasonably smaller for heavier helium than for hydrogen. Both the GT and SV models could explain the temperature dependency of helium and hydrogen gas diffusivities, but the SV model provided a more realistic geometrical representation of the silica membrane. The SV model also successfully explained gas permeability in an actual silica membrane as well as the virtual amorphous silica membrane. Full article

(This article belongs to the Special Issue Preparation, Characterization and Application of Silica-Based Membranes)

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15 pages, 3430 KiB

Open AccessArticle

Fabrication and Evaluation of Trimethylmethoxysilane (TMMOS)-Derived Membranes for Gas Separation

by Yoshihiro Mise, So-Jin Ahn, Atsushi Takagaki, Ryuji Kikuchi and Shigeo Ted Oyama

Membranes 2019, 9(10), 123; https://doi.org/10.3390/membranes9100123 - 20 Sep 2019

Cited by 8 | Viewed by 3133

Abstract

Gas separation membranes were fabricated with varying trimethylmethoxysilane (TMMOS)/tetraethoxy orthosilicate (TEOS) ratios by a chemical vapor deposition (CVD) method at 650 °C and atmospheric pressure. The membrane had a high H₂ permeance of 8.3 × 10⁻⁷ mol m⁻² s⁻¹ [...] Read more.

Gas separation membranes were fabricated with varying trimethylmethoxysilane (TMMOS)/tetraethoxy orthosilicate (TEOS) ratios by a chemical vapor deposition (CVD) method at 650 °C and atmospheric pressure. The membrane had a high H₂ permeance of 8.3 × 10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹ with H₂/CH₄ selectivity of 140 and H₂/C₂H₆ selectivity of 180 at 300 °C. Fourier transform infrared (FTIR) measurements indicated existence of methyl groups at high preparation temperature (650 °C), which led to a higher hydrothermal stability of the TMMOS-derived membranes than of a pure TEOS-derived membrane. Temperature-dependence measurements of the permeance of various gas species were used to establish a permeation mechanism. It was found that smaller species (He, H₂, and Ne) followed a solid-state diffusion model while larger species (N₂, CO₂, and CH₄) followed a gas translational diffusion model. Full article

(This article belongs to the Special Issue Preparation, Characterization and Application of Silica-Based Membranes)

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14 pages, 4994 KiB

Open AccessArticle

Development of Mass Production Technology of Highly Permeable Nano-Porous Supports for Silica-Based Separation Membranes

by Ken-ichi Sawamura, Shigeru Okamoto and Yoshihiro Todokoro

Membranes 2019, 9(8), 103; https://doi.org/10.3390/membranes9080103 - 16 Aug 2019

Cited by 4 | Viewed by 3014

Abstract

Silica-based membranes show both robust properties and high-permeability, offering us great potential for applying them to harsh conditions where conventional organic membranes cannot work. Despite the increasing number of paper and patents of silica-based membranes, their industrial applications have yet to be fully [...] Read more.

Silica-based membranes show both robust properties and high-permeability, offering us great potential for applying them to harsh conditions where conventional organic membranes cannot work. Despite the increasing number of paper and patents of silica-based membranes, their industrial applications have yet to be fully realized, possibly due to their lack of technologies on scaling-up and mass production. In particular, quality of membrane supports decisively impacts final quality of silica-based separation membranes. In this study, therefore, we have developed mass producing technologies of nano-porous supports (φ 12 mm, length 400 mm) with surface center pore size distribution of 1–10 nm, which are generally used as supports for preparing separation membranes with a pore size of less than 1 nm. The developed mass production apparatuses have enabled us to reproducibly produce nano-porous silica-based supports with high permeance (e.g., N₂ permeance of more than 10⁻⁵ mol m⁻² s⁻¹·Pa⁻¹) minimizing effects of membrane defects less than 0.1% of the total flux. The developed nano-porous supports have enabled us to reproducibly produce silica-based separation membranes with high permeace and selectivity (e.g., H₂ permeance of about 5 × 10⁻⁶ mol m⁻² s⁻¹ Pa⁻¹ and H₂/SF₆ permeance ratio of more than 2000). Full article

(This article belongs to the Special Issue Preparation, Characterization and Application of Silica-Based Membranes)

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12 pages, 4252 KiB

Open AccessArticle

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 - 01 Aug 2019

Cited by 9 | Viewed by 3921

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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13 pages, 6607 KiB

Open AccessArticle

Hydrophobic *BEA-Type Zeolite Membranes on Tubular Silica Supports for Alcohol/Water Separation by Pervaporation

by Kyohei Ueno, Saki Yamada, Toshinari Watanabe, Hideyuki Negishi, Takuya Okuno, Hiromasa Tawarayama, Shinji Ishikawa, Manabu Miyamoto, Shigeyuki Uemiya and Yasunori Oumi

Membranes 2019, 9(7), 86; https://doi.org/10.3390/membranes9070086 - 17 Jul 2019

Cited by 9 | Viewed by 5772

Abstract

Hydrophobic pure-silica *BEA-type zeolite membranes with large pores were prepared on tubular silica supports by hydrothermal synthesis using a secondary growth method and were applied to the separation of alcohol/water mixtures by pervaporation (PV), an alternative energy-efficient process for production of biofuels. Amorphous [...] Read more.

Hydrophobic pure-silica *BEA-type zeolite membranes with large pores were prepared on tubular silica supports by hydrothermal synthesis using a secondary growth method and were applied to the separation of alcohol/water mixtures by pervaporation (PV), an alternative energy-efficient process for production of biofuels. Amorphous pure-silica tubular silica supports, free of Al atoms, were used for preparing the membranes. In this study, the effects of the synthesis conditions, such as the H₂O/SiO₂ and NH₄F/SiO₂ ratios in the synthetic gel, on the membrane formation process and separation performance were systematically investigated. The successfully prepared dense and continuous membranes exhibited alcohol selectivity and high flux for the separation of ethanol/water and butanol/water mixtures. The pure-silica *BEA membranes obtained under optimal conditions (0.08SiO₂:0.5TEAOH:0.7NH₄F:8H₂O) showed high PV performance with a separation factor of 229 and a flux of 0.62 kg·m⁻²·h⁻¹ for a 1 wt % n-butanol/water mixture at 318 K. This result was attributed to the hydrophobicity and large pore size of the pure-silica *BEA membrane. This was the first successful synthesis of hydrophobic large-pore zeolite membranes on tubular supports with alcohol selectivity, and the obtained results could provide new insights into the research on hydrophobic membranes with high permeability. Full article

(This article belongs to the Special Issue Preparation, Characterization and Application of Silica-Based Membranes)

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Review

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24 pages, 10303 KiB

Open AccessFeature PaperReview

Organosilica-Based Membranes in Gas and Liquid-Phase Separation

by Xiuxiu Ren and Toshinori Tsuru

Membranes 2019, 9(9), 107; https://doi.org/10.3390/membranes9090107 - 22 Aug 2019

Cited by 32 | Viewed by 5180

Abstract

Organosilica membranes are a type of novel materials derived from organoalkoxysilane precursors. These membranes have tunable networks, functional properties and excellent hydrothermal stability that allow them to maintain high levels of separation performance for extend periods of time in either a gas-phase with [...] Read more.

Organosilica membranes are a type of novel materials derived from organoalkoxysilane precursors. These membranes have tunable networks, functional properties and excellent hydrothermal stability that allow them to maintain high levels of separation performance for extend periods of time in either a gas-phase with steam or a liquid-phase under high temperature. These attributes make them outperform pure silica membranes. In this review, types of precursors, preparation method, and synthesis factors for the construction of organosilica membranes are covered. The effects that these factors exert on characteristics and performance of these membranes are also discussed. The incorporation of metals, alkoxysilanes, or other functional materials into organosilica membranes is an effective and simple way to improve their hydrothermal stability and achieve preferable chemical properties. These hybrid organosilica membranes have demonstrated effective performance in gas and liquid-phase separation. Full article

(This article belongs to the Special Issue Preparation, Characterization and Application of Silica-Based Membranes)

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