Masakoto Kanezashi

Design of Silica Networks for Development of Highly Permeable Hydrogen Separation Membranes with Hydrothermal Stability

A sol-gel method was applied for the development of highly permeable hydrogen separation membranes using bis(triethoxysilyl)ethane (BTESE) as a silica precursor. Hybrid silica membranes showed quite high hydrogen permeance (1 x 10(-5) mol m(-2) s(-1) Pa(-1)) with a high H(2)-to-SF(6) selectivity of 1000 because of loose organic-inorganic silica networks. Hybrid silica membranes were found to show high hydrothermal stability due to the presence of Si-C-C-Si bonds in silica networks.

Microporous inorganic membranes for high temperature hydrogen purification

The general mechanisms of gas separation in microporous inorganic membranes are reviewed in this article. Emphasis has been placed on discussing the requirements of membrane pore structure and material properties for high temperature hydrogen separation from other small gases involved in processes of hydrogen production from fossil fuels. The recent research progresses in developing the crystalline zeolite membranes, and amorphous silica-based membranes for high temperature hydrogen separation are critically reviewed. The fundamental issues associated with the zeolite and silica membranes relevant to the practical applications are analyzed based on the relationships between the separation performance and membrane structural and chemical properties.

Development of Robust Organosilica Membranes for Reverse Osmosis

Hybrid organically bridged silica membranes have attracted considerable attention because of their high performances in a variety of applications. Development of robust reverse osmosis (RO) membranes to withstand aggressive operating conditions is still a major challenge. Here, a new type of microporous organosilica membrane has been developed and applied in reverse osmosis. Sol-gel derived organosilica RO membranes reject isopropanol with rejection higher than 95%, demonstrating superior molecular sieving ability for neutral solutes of low molecular weight. Due to the introduction of an inherently stable hybrid network structure, the membrane withstands higher temperatures in comparison with commercial polyamide RO membranes, and is resistant to water to at least 90 °C with no obvious changes in filtration performance. Furthermore, both an accelerated chlorine-resistance test and Fourier transform infrared analysis confirm excellent chlorine stability in this material, which demonstrates promise for a new generation of chlorine-resistant RO membrane materials.

Permeation Characteristics of Electrolytes and Neutral Solutes through Titania Nanofiltration Membranes at High Temperatures

Nanoporous titania membranes with controlled pore sizes ranging from 0.7 to 2.5 nm, which had molecular weight cutoffs (MWCO) ranging from 500 to 2000, were successfully prepared by sol-gel processing, and the transport characteristics were evaluated across a temperature range of 30-80 degrees C. With increasing temperature, the permeate flux increased 2- to 3-fold, depending on the pore size. The water permeation mechanism was found to be different from viscous flow and was explained by the state of the water (free water/bound water/nonfreezing water) inside confined pores. The rejection of neutral solutes such as raffinose, the separation mechanism of which is molecular sieving (steric hindrance), decreased with temperature whereas that of electrolytes (MgCl(2) and NaCl), the separation mechanism of which is the charge effect (Donnan exclusion), was approximately constant. The temperature dependence of neutral and electrolyte solutes was analyzed using the Spiegler-Kedem equation by combining the Arrhenius equations for diffusivity and viscosity, which we obtained DeltaE(m), the activation energy of diffusion, after eliminating the effect of viscosity. For large DeltaE(m), which corresponds to the rejection of neutral solutes on the basis of molecular sieving, rejection decreased with temperature but remained unchanged for small DeltaE(m), which corresponds to the rejection of electrolytes based on the charge effect.

Nickel‐Doped Silica Membranes for Separation of Helium from Organic Gas Mixtures

Abstract: One of the problems in the use of inorganic silica membranes is their instability against water or water vapor, a problem that results from the dissolution and rearrangements of silica networks. In this work Ni(NO3)-6H2O was added to silica sol for fabrication of Ni-doped silica membranes by sol-gel techniques in order to prevent the densification of amorphous silica networks in a humid atmosphere at 50-3()0°C. A fresh Ni-doped silica membrane (Si/Ni = 2/1) fired at 500 C showed a large He permeance of about 2.6 × 10−5 [m3 (STP)/(m2 ·s · kPa)] with a selectivity of 600 (He/CH4) at 300’C. After the Ni-doped silica membrane was left in humid air (40°C, 60% RH) for 4 days, the He permeance decreased slightly (by 5%) with a larger selectivity of 800 (He/CH4) at 300’C. However, little change was observed in the activation energy of He permeation, suggesting that nickel oxides added to silica can preferably prevent the densification of silica networks through which only H2 and He can permeate. Humid He and CH4 showed smaller permeabilities, especially at temperatures below 150°C, than those of dry gases because of condensed and/or adsorbed H20 molecules in silica networks and on grain boundaries. Separation of He/CH4 mixtures with the fresh Ni-doped silica membrane (Si/Ni = 2/1) at 300’C gave relatively good results and coincided well with the predicted values with the ideal permeance ratio, 600.

Extremely thin Pd–silica mixed-matrix membranes with nano-dispersion for improved hydrogen permeability

Pd-silica mixed-matrix membranes with superior H(2) permeability and hydrothermal stability at high temperatures were successfully fabricated using a sol-gel method. The Pd-silica layer was quite thin (100-200 nm) and small Pd particles (several nm) dispersed well in an amorphous silica matrix.

Tailoring the affinity of organosilica membranes by introducing polarizable ethenylene bridges and aqueous ozone modification.

Bis(triethoxysilyl)ethylene (BTESEthy) was used as a novel precursor to develop a microporous organosilica membrane via the sol-gel technique. Water sorption measurements confirmed that ethenylene-bridged BTESEthy networks had a higher affinity for water than that of ethane-bridged organosilica materials. High permeance of CO2 with high CO2/N2 selectivity was explained relative to the strong CO2 adsorption on the network with π-bond electrons. The introduction of polarizable and rigid ethenylene bridges in the network structure led to improved water permeability and high NaCl rejection (>98.5%) in reverse osmosis (RO). Moreover, the aqueous ozone modification promoted significant improvement in the water permeability of the membrane. After 60 min of ozone exposure, the water permeability reached 1.1 × 10(-12) m(3)/(m(2) s Pa), which is close to that of a commercial seawater RO membrane. Meanwhile, molecular weight cutoff measurements indicated a gradual increase in the effective pore size with ozone modification, which may present new options for fine-tuning of membrane pore sizes.

New Insights into the Microstructure-Separation Properties of Organosilica Membranes with Ethane, Ethylene, and Acetylene Bridges

Microporous organosilica membranes with ethane, ethylene, and acetylene bridges have been developed and the extensive microstructural characterization has been discussed in relation with separation properties of the membrane. The organosilica network structure and the membrane performances can be controlled by adjusting the flexibility, size, and electronic structure of the bridging groups. A relatively narrow size distribution was obtained for the novel acetylene-bridged sol by optimizing the sol synthesis. Incorporation of larger rigid bridges into organosilica networks resulted in a looser microstructure of the membrane, which was quantitatively evaluated by N2 sorption and positron annihilation lifetime (PAL) measurements. Molecular weight cutoff (MWCO) measurements indicated that the acetylene-bridged membrane had a larger effective separation pore size than ethane- and ethylene-bridged membranes, leading to a relatively low NaCl rejection in reverse osmosis. In quantum chemical calculations, a more open pore structure and increased polarization was observed for the acetylene-bridged networks, which led to a significant improvement in water permeability. The present study will offer new insight into design of high-performance molecular separation membranes.

Insight into the pore tuning of triazine-based nitrogen-rich organoalkoxysilane membranes for use in water desalination

A promising new triazine-based nitrogen-rich organosilica (TTESPT) membrane has been developed for molecular separation processes in gas (gas separation) and liquid phases (reverse osmosis (RO)). By adjusting the H2O/TTESPT molar ratio, we found a promising technique for tuning the pore network of TTESPT membranes. An increase in the H2O/TTESPT molar ratio from 60 to 240 fully hydrolyzed all the ethoxide groups in the TTESPT membrane, which reduced the size of the pores in the silica pore network. A TTESPT membrane with a high H2O/TTESPT molar ratio exhibited a high degree of selectivity for H2/SF6 (greater than 4000) at a permeation temperature of 200 °C. This membrane also demonstrated high sodium chloride (NaCl) rejection (>98.5%) with water permeability of >1 × 10−12 m3 m−2 s−1 Pa−1 under operating conditions of 1 MPa and 60 °C during a RO experiment. As the operating temperature was increased from 25 to 60 °C, the NaCl rejection was constant without displaying the characteristic flux deterioration. This showed that the membrane retained a stable hybrid network structure.

Graphene nanosheets supporting Ru nanoparticles with controlled nanoarchitectures form a high-performance catalyst for COx-free hydrogen production from ammonia

To date, Ru is the most active single-metal catalyst known for ammonia decomposition, but its catalytic activity is support-dependent and structure-sensitive. Therefore, a unique support-anchored Ru nanoparticle with controllable size and morphology would be particularly important for high catalytic performance. In this work, we describe Ru nanoparticles supported by two-dimensional graphene nanosheets with a controlled nanoarchitecture that forms a novel composite catalyst that is capable of a high degree of ammonia decomposition. This high-quality Ru/graphene nanocomposite material was obtained via a cosolvent method (CS-Ru/graphene), in which ethylene glycol simultaneously acted as a solvent and a reductant, while water served only as a cosolvent. The abundant oxygen-containing functional groups of graphene oxide played extremely important roles in the growth of Ru nanoparticles on the resultant graphene nanosheets, as they promoted Ru nucleation and acted as anchor sites for the Ru nanoparticles. Moreover, the use of water as a cosolvent was an effective way to tune the Ru particle size and morphology and aid in the loading of the nanocomposite, resulting in dramatically enhanced catalytic activity in comparison with a composite prepared by using ethylene glycol as a single solvent (SS-Ru/graphene). The exceptional catalytic performance of CS-Ru/graphene was mainly ascribed to the novel graphene support that simultaneously combines a large specific surface area with excellent electronic conductivity, but also to the highly dispersive Ru nanoparticles that made up the nanocomposite with a controlled morphology and an optimal size.