Inorganic Membranes Research Articles

Semi-hollow LTA zeolite membrane for water permeation in simulated CO2 hydrogenation to methanol

Linde Type A (LTA) zeolite is an effective inorganic water permeable membrane material due to its inherent Na+-gated water-conducting mechanism. Although dense LTA membranes show excellent water selective permeability, the water permeability rate still needs to be improved to drive the CO2 hydrogenation reaction towards methanol production. In this work, we prepared a water-conducting LTA membrane with well-distributed non-penetrative macroholes, resulting in a cheese-like structure that combines the advantages of micro-nanochannels for high water selective permeability and macroholes for quick water diffusion. These semi-hollow (SH)-LTA membranes with different thicknesses and number of macroholes were fabricated via a steam-assisted method by adjusting the amount of water in the precursor solution. The optimized SH-LTA membranes presented an average water permeance of 8.57 × 10−7 mol m−2 s−1 Pa−1 at 200 °C along with CH3OH, H2, and CO2 permeances of 3.24 × 10−9, 7.92 × 10−12, and 4.32 × 10−12 mol m−2 s−1 Pa−1, respectively. The membrane stability was verified under continuous mixture gas permeation tests for 10 h between 200 and 300 °C. The dissolution-recrystallization route of the SH morphology was confirmed following comprehensive characterizations and complemented by molecular dynamics simulations to elucidate the superior water separation behavior in SH-LTA membrane in comparison with pristine LTA membrane.

Inorganic nanoparticles-modified polyvinyl chloride separation membrane and enhanced anti-fouling performance

Porous nanomaterials are important additives in the preparation of high-performance separation membranes. To prepare two nanocomposites, mesoporous silicon dioxide (MCM-41) as a carrier and zinc acetate as a zinc source, Zinc oxide-loaded mesoporous silicon dioxide (ZPP-MCM) was prepared by using polydopamine (PDA) and Polyethylenimine (PEI) as water-soluble ligands, and zinc oxide-loaded mesoporous silicon dioxide (εZI-MCM) were prepared by using iminodiacetic acid (IDA) as water-soluble ligands and coated with ε-poly-l-lysine HCl. The two nanocomposites were blended into polyvinyl chloride (PVC) membranes as modifiers. The results show that the overall porosity of the composite membrane is increased. However, the surface roughness of the composite membrane is decreased with narrow pore size distribution, which was favourable for selective filtration. εZI-MCM nanoparticles can be evenly distributed on the film due to their excellent dispersion, which solves the problem of uneven distribution of nanoparticles on the film, and the surface of the prepared composite film is relatively flat. In addition, introducing the nanoparticles significantly improves the surface hydrophilicity and water flux of the composite membrane. In the experiments of pure water flux and bovine serum albumin (SBA) flux, the flat film with nanoparticles shows higher flux than pure PVC films. The addition of nano-composites further improves the anti-fouling performance and flux recovery ratio of the modified PVC membrane, and the recovery ratio of flux was more than 90%. This work exhibits that Porous nanomaterials have successfully modified the hydrophobic PVC membrane, affording good anti-fouling performance.

The advances development of proton exchange membrane with high proton conductivity and balanced stability in fuel cells

AbstractIn the proton exchange membrane fuel cell, proton exchange membrane (PEM) serves as both the main conductor of protons and the fuel‐blocking membrane. Thus, high proton conductivity and excellent stability are expected for PEMs at the same time. According to chemical structure, this review divides PEM into three groups. Recently, high‐performance PEM has been made possible by controlling chemical structure, organic–inorganic hybrid composite membranes, and nanofiber composite membranes. One of them, nanofiber composite membranes, is distinguished by long‐range order and is capable of achieving both strong proton conductivity with exceptional stability. The high‐performance PEM has been accomplished by the presence of an acid‐rich layer, acid–base interaction, and proton transport channel in PEMs are also summarized in this paper. We believe that our discussion will help the researcher create high‐performance PEM and pave the way for further developments in the field of energy materials as a whole.

Interfacial assembling of flexible silica membranes with high chlorine resistance for dye separation

Inorganic membranes have gained extensive attention due to their more uniform pore size, higher flux, and better chemical stability over traditional polymeric membranes. However, the development of inorganic membranes still faces substantial obstacles in the form of a difficult preparation procedure and the high cost of a large-scale synthesis. Herein, a facile interfacial assembly strategy is designed to prepare flexible silica membranes by the close and strong packing of ultra-small nanoparticles via crosslinking with trimesoyl chloride. Profiting from the extremely small size and tight packing of silica nanoparticles, the permeance of flexible silica membrane with a uniform pore size of 3.4 nm exceeds 210 L m−2 h−1 MPa−1, which is nearly 11 times higher than the polyamide membrane simultaneously ensuring the rejection effect. Meanwhile, the flexible silica membrane has no performance deterioration after exposure to 50000 ppm h of chlorine (NaOCl), indicating its excellent chlorine resistance. The facile interfacial assembly strategy applied for the synthesis of the membrane is highly reproducible and scalable (high-performance silica membrane with 100 cm2 has been obtained), which has overall flexibility after the curvature of 100 m−1, paving the way for the development of future applications.

Mechanistic formulation of inorganic membranes at the air-liquid interface.

Freestanding functional inorganic membranes, beyond the limits of their organic and polymeric counterparts1, may unlock the potentials of advanced separation2, catalysis3, sensors4,5, memories6, optical filtering7 and ionic conductors8,9. However, the brittle nature of most inorganic materials, and the lack of surface unsaturated linkages10, mean that it is difficult to form continuous membranes through conventional top-down mouldings and/or bottom-up syntheses11. Up to now, only a few specific inorganic membranes have been fabricated from predeposited films by selective removal of sacrificial substrates4-6,8,9. Here we demonstrate a strategy to switch nucleation preferences in aqueous systems of inorganic precursors, resulting in the formation of various ultrathin inorganic membranes at the air-liquid interface. Mechanistic study shows that membrane growth depends on the kinematic evolution of floating building blocks, which helps to derive the phase diagram based on geometrical connectivity. This insight provides general synthetic guidance towards any unexplored membranes, as well as the principle of tuning membrane thickness and through-hole parameters. Beyond understanding a complex dynamic system, this study comprehensively expands the traditional notion of membranes in terms of composition, structure and functionality.

A method to make inorganic membranes on the surface of aqueous solutions

A method to make inorganic membranes on the surface of aqueous solutions

Equilibrium shift, poisoning prevention, and selectivity enhancement in catalysis via dehydration of polymeric membranes

Generation of water as a byproduct in chemical reactions is often detrimental because it lowers the yield of the target product. Although several water removal methods, using absorbents, inorganic membranes, and additional dehydration reactions, have been proposed, there is an increasing demand for a stable and simple system that can selectively remove water over a wide range of reaction temperatures. Herein we report a thermally rearranged polybenzoxazole hollow fiber membrane with good water permselectivity and stability at reaction temperatures of up to 400 °C. Common reaction engineering challenges, such as those due to equilibrium limits, catalyst deactivation, and water-based side reactions, have been addressed using this membrane in a reactor.

Novel Inorganic Membranes Based on Magnetite-Containing Silica Porous Glasses for Ultrafiltration: Structure and Sorption Properties

Porous glasses (PGs) obtained from sodium borosilicate (NBS) phase-separated glasses via leaching are promising inorganic membranes. Introducing Fe2O3 into NBS glasses imparts ferrimagnetic properties due to magnetite crystallization. Leaching of such glasses leads to the formation of magnetic PGs with interesting electro-surface characteristics. This work aimed to investigate the process of obtaining magnetite-containing PGs from NBS glasses depending on silica content, using XRPD and Raman spectroscopy, studying the PG membranes' structural characteristics and their sorption properties with respect to methylene blue (MB). Obtained PGs were characterized by a polymodal distribution of mesopores and a small number of micropores with specific surface area values of 32-135 m2/g and an average mesopore diameter of 5-41 nm. The kinetic data were analyzed using pseudo-first-order, pseudo-second-order, and intra-particle diffusion equations. The equilibrium isotherms were fitted with Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich models. MB adsorption was found to be a complex process. The glass with the highest specific surface area demonstrated the maximum sorption capacity (10.5 mg/g). The pore size of PGs allowed them to be considered potential novel magnetic membranes for ultrafiltration.

Deep Study on Fouling Modelling of Ultrafiltration Membranes Used for OMW Treatment: Comparison Between Semi-empirical Models, Response Surface, and Artificial Neural Networks

Olive oil production generates a large amount of wastewater called olive mill wastewater. This paper presents the study of the effect of transmembrane pressure and cross flow velocity on the decrease in permeate flux of different ultrafiltration membranes (material and pore size) when treating a two-phase olive mill wastewater (olive oil washing wastewater). Both semi-empirical models (Hermia models adapted to tangential filtration, combined model, and series resistance model), as well as statistical and machine learning methods (response surface methodology and artificial neural networks), were studied. Regarding the Hermia model, despite the good fit, the main drawback is that it does not consider the possibility that these mechanisms occur simultaneously in the same process. According to the accuracy of the fit of the models, in terms of R2 and SD, both the series resistance model and the combined model were able to represent the experimental data well. This indicates that both cake layer formation and pore blockage contributed to membrane fouling. The inorganic membranes showed a greater tendency to irreversible fouling, with higher values of the Ra/RT (adsorption/total resistance) ratio. Response surface methodology ANOVA showed that both cross flow velocity and transmembrane pressure are significant variables with respect to permeate flux for all membranes studied. Regarding artificial neural networks, the tansig function presented better results than the selu function, all presenting high R2, ranging from 0.96 to 0.99. However, the comparison of all the analyzed models showed that depending on the membrane, one model fits better than the others. Finally, through this work, it was possible to provide a better understanding of the data modelling of different ultrafiltration membranes used for the treatment of olive mill wastewater.

Long-lifetime water-washable ceramic catalyst filter for air purification

Particulate matter (PM) and volatile organic compounds (VOCs) are recognised as hazardous air pollutants threatening human health. Disposable filters are generally used for air purification despite frequent replacement and waste generation problems. However, the development of a novel regenerable and robust filter for long-term use is a huge challenge. Here, we report on a new class of facile water-washing regenerable ceramic catalyst filters (CCFs), developed to simultaneously remove PM (>95%) and VOCs (>82%) in single-pass and maximized space efficiency by coating the inner and outer filter channels with an inorganic membrane and a Cu2O/TiO2 photocatalyst, respectively. The CCFs reveal four-fold increase in the maximum dust loading capacity (approximately 20 g/L) in relation to conventional filters (5 g/L), and can be reused after ten regeneration capability with simple water washing retaining initial PM and VOC removal performances. Thus, the CCFs can be well-suited for indoor and outdoor air purification for 20 years, which shows a huge increase in lifetime compared to the 6-month lifespan of conventional filters. Finally, we believe that the development and implementation of CCFs for air purification can open new avenues for sustainable technology through renewability and zero-waste generation.

Effect of bio-electrochemical systems on the removal of organic and inorganic membrane fouling from anaerobic membrane bioreactors

To alleviate the fouling of membrane bioreactors, a coupling system was constructed in which a conductive membrane served as the anode of a bio-electrochemical system, whereas ordinary carbon felt served as the cathode. The membrane module showed approximately 90 % performance for wastewater chemical oxygen demand removal. As the external resistance increased from 50 to 1500 Ω, the number of operating days increased from 25 to 62. The respective concentrations of polysaccharide and protein on R-1500 membrane surface were 6.81- and 2.05-fold greater than the concentrations on the R-50 membrane, and the concentration of Ca2+ on the surface of the R-50 membrane was 1.48-fold greater than the concentration on the R-1500 membrane. Therefore, inorganic fouling is the main type of membrane fouling in coupled systems with low external resistance. For coupled systems with higher external resistance, severe organic fouling eventually causes membrane blockage. Variance partitioning analysis showed that the micro-electric field contributed to 95.34 % of the effect on the control of membrane fouling, significantly greater than the 67.19 % contributed by the current. Therefore, in the system where organic and inorganic fouling coexists, appropriate enhanced field strength (increase in external resistance) is particularly important for membrane fouling control.

Carbon nanotubes@fly ash Janus composite membrane prepared from fly ash and waste plastics for efficient solar membrane distillation

Janus membranes have attracted many attentions due to their unique and excellent properties endowed by their asymmetric structure and chemical composition. In this study, a novel carbon nanotubes (CNTs)@fly ash Janus composite membrane with hierarchically oriented straight pores, prepared in two steps using industrial solid waste fly ash and white pollutant waste plastic as raw materials, is introduced into the field of solar membrane distillation. The fly ash membrane is fabricated by the combined phase tape inversion casting and sintering method, and CNTs are then in-situ grown on one side of the as-sintered fly ash membrane via the chemical vapor deposition technique to form CNTs@fly ash Janus membrane. The as-prepared Janus inorganic membrane exhibits good hydrophobicity with a contact angle of 133° as well as excellent gas permeability of 0.51 ± 0.01 × 107 L m−2 h−1 bar−1. When this membrane is used for solar membrane distillation, its interfacial evaporation rate can reach to 1.94 ± 0.01 kg m−2h−1 under one solar intensity, which is 2.19 times that of traditional natural evaporation. Coupled with its lower cost and environmental benefits, this novel Janus membrane is a potential hydrophobic separation membrane to achieve near-zero solid waste emission and efficient seawater desalination.

Research progress and prospects on hydrogen separation membranes

Abstract Membrane separation technologies, with a broad application prospect in the field of hydrogen separation, are characterized by the simplicity of the devices, high energy efficiency and environmental friendliness. The performance of separation membranes is the primary factor that determines the efficiency of hydrogen separation. Therefore, the development of hydrogen separation membranes is always a research focus. This paper presents and reviews the research developments and features of organic membranes, inorganic membranes and hybrid matrix membranes for hydrogen separations. First, the characterization methods of key index parameters of membrane materials are presented. Second, the performance parameters of different types of membrane are compared. Finally, the trend of technological development of different types of membrane materials is forecast.

Enhancement of hydrogen clean energy production from greenhouse gas by in-situ hydrogen separation with a cobalt-silica membrane

Methane steam reforming is a representative reaction to convert carbon-rich fuel to carbon-free fuel. However, the thermodynamic equilibrium limits the conversion from methane to hydrogen. Separating hydrogen in-situ from hydrocarbon reforming reactions by inorganic membranes is an effective way to overcome the thermodynamic equilibrium, which improves the conversion of the reforming reactions and the efficiency of hydrogen production. Silica-based membrane, due to its size sieving effect, could separate hydrogen molecules from other larger gases at high temperatures, but the poor hydrothermal stability of silica in steam conditions remains a challenge for the application in hydrogen production. In this study, to improve the hydrothermal stability cobalt was doped in silica membrane precursors with varying ratios. After a series of characterizations by dynamic light scattering, Fourier Transform Infrared spectroscopy, X-ray diffraction, nitrogen adsorption and Scanning Electron Microscope, a cobalt-silica membrane with a cobalt/silicon ratio of 1/4 was fabricated by dip-coating technique. At 500 °C the membrane delivered helium permeance of 9.37 × 10−8 mol m−2 s−1 Pa−1, helium/nitrogen perm-selectivity of 258.48, and helium/carbon dioxide perm-selectivity of 242.19. The membrane was then employed in methane steam reforming for in-situ hydrogen separation to enhance methane conversion and hydrogen production. Raising the reaction temperature favors the performance of the membrane reactor, but temperature over 550 °C was still challenging due to hydrothermal stability issue. Increasing reaction pressure from 0 to 0.3 MPa favored methane conversion, but pressure over 0.4 MPa led to concentration polarization. Steam to carbon (S/C) ratio of 3 was suitable to avoid nickel/alumina catalyst coking and methane dilution. Reducing the gas hourly space velocity (GHSV) ensured sufficient residence time for methane and favored methane conversion. At T = 500 °C, Δp = 0.3 MPa, S/C = 3 and GHSV = 30 ml g−1 h−1, the membrane elevated the methane conversion from 45.36% (without membrane) to 83.71%. With a cobalt-silica membrane 4.32 ml min−1 of hydrogen was continuously produced with a purity of 82.12 vol% compared to 2.34 ml min−1 of hydrogen with a purity of 65.0 vol% in the case without a membrane. As expected, the micro-morphology of the cobalt-doped membrane after the 20-day steam reforming test showed little visible change in scanning electron microscope. The reduction of pore volume was only 15% as compared to 25% for pure silica material. This membrane demonstrated promising potential in the efficient production of hydrogen.

Preparation of metakaolin-based geopolymer membrane and its application in black liquor treatment

In recent years, inorganic membrane filtration technology has become the most promising treatment option for treating papermaking black liquor and recovering lignin from black liquor. However, the preparation of most inorganic membranes requires sintering or high-cost raw materials, which leads to high cost in the application of black liquor treatment and lignin recovery. For this reason, in this study, a no-sintering, low-cost metakaolin-based geopolymer membranes (MGM) was prepared at room temperature using steel mesh with good ductility and processability as the substrate. The effects of slag doping on the mechanical properties, microstructure and separation properties of MGM were investigated. The results concluded that when the mass ratio of slag to metakaolin is 1:10 (MGM-10), the membrane has the best comprehensive performance. The compressive strength and pure water flux of MGM-10 were 23.94 MPa and 286.62 kg m−2 h−1, respectively. In the application of black liquor treatment and lignin separation and recovery from black liquor, MGM-10 showed excellent separation performance by removing 96% of TSS, 91.75% of COD and 98.97% of BL from black liquor after primary filtration. Compared with ceramic membranes prepared by sintering, MGM has cheaper raw materials and lower energy consumption, which is more promising for industrial scale applications.

膜工学研究を振り返って– 膜を創る

Last time, the author described the study of membrane fouling and the transport equation for membrane permeation. This time, the author would like to introduce his research on creating membranes. Polymer membranes and inorganic membranes have been developed. The polymer membranes are negatively and positively charged ultrafiltration membranes, which are polysulfone membranes with sulfonic acid groups and quaternary ammonium groups. The charged membranes have a complex separation mechanism, that is combination of separation by membrane pores and by charge repulsion between the membrane and solute. It was possible to separate not only salts but also various substances such as amino acids, peptides, and proteins. The transport equations of charged membranes were also studied. Inorganic membranes are mainly silica membranes produced by chemical vapor deposition, and zeolite membranes have also been produced, but they will not be introduced here. The author started with low–temperature deposition using ozone, and finally deposited membranes at high temperature (600 ℃) using various silica sources, and was able to obtain high–performance membranes. Since the advantages of inorganic membranes can be applied to membrane reactors, membrane reactors have been applied to steam reforming of methane, dehydrogenation of cyclohexane and methylcyclohexane, and thermal decomposition of hydrogen sulfide. In particular, the cyclohexane dehydrogenation membrane reactor operated continuously for 1,054 hours, and a small membrane reactor equipped with six 50 cm membranes was also developed.

Hematite based ultrafiltration membrane prepared from pyrrhotite ash waste for textile wastewater treatment

An α-Fe2O3 ultrafiltration (UF) inorganic membrane was synthesized based on pyrrhotite ash solid waste resulting from mining activities and natural clay via spreading a metal–organic complex sheet on a microfiltration (MF) ceramic support. The MF-support was prepared by mixing pyrrhotite ash with natural clay. The pyrrhotite ash was also deployed in the preparation of the metal–organic complex. The membrane composition, structure, morphology were studied via X-ray diffraction, scanning electron microscopy respectively, and operating parameters such as water permeability, and flexural strength were also investigated. The MF support showed a water permeability of 2.37 × 10−6 m3/s. m2. kPa while the UF membrane exhibited a permeability of 2.49 × 10−7 m3/s. m2. kPa. Furthermore, the elaborated MF support and UF membrane were tested in the treatment of two types of textile wastewaters of reactive and dispersed nature. The results showed that the combination of the MF support and UF membrane in cascade filtration led to an elimination rate of 99% and 94% of turbidity and chemical oxygen demand, respectively, in the case of the two chosen wastewaters.

Rational design of a flexible inorganic composite membrane with an interconnected porous structure as a high-performance lithium ion capacitor electrode

The synergistic effect of multiple components (Cu, Cu2O and CuO) in CuxONWs and the high bonding strength between the three materials in a CGA membrane anode markedly improve the capacitance and cycling performance of lithium-ion capacitors.

Cation-selective layered silicon oxide membranes for power generation

Inorganic two-dimensional membranes offer a new approach to modulating mass transport at the nanoscale. These membranes, which can harness the van der Waals gap as a nanochannel and address persistent challenges in organic membranes, are limited to a few material libraries, such as graphene, graphene oxide, molybdenum disulfide, and boron nitride. Here we report for the first time the development of cation-selective layered silicon oxide membranes, in which the nanochannels, specifically the van der Waals gap, can allow cation diffusion flux to generate an electromotive force for a long time. Considering the abundance and well-known properties of silicon oxide, this inorganic membrane can provide a promising route for membrane separation in a variety of applications.

Synthesis and Acidity Study of Mixed MFI-MORD Type Zeolite

Zeolites of various nature are widely used in the chemical industry, the fuel and energy sector of the economy as sorbents, catalysts and materials for the creation of inorganic membranes for various purposes. At the same time, it is possible to change the acid properties of the surface of zeolites both by varying the ratio of silicon to aluminum or silicon to phosphorus, and by joint synthesis of zeolites of various types with different acidic properties. The presented article provides a method for the sequential production of a zeolite of a mixed structure type MFI and mordenite. Synthesis of the original MFI type zeolite was carried out using seed grains by the hydrothermal method for 72 hours, followed by washing and drying of the zeolite. To obtain a layer of mordenite on the surface of the MFI type zeolite, the initial zeolite was pretreated with alkali and then treated with n-butylamine. In this way, nine samples of zeolite with different acidic surface properties were obtained. Determination of the acidic properties of the surface was carried out by the method of ammonia chemisorption followed by its desorption from the surface of the zeolite. For this purpose, the test sample was loaded into a quartz cuvette, purged with argon at a temperature of 800°С, after which the temperature dropped to 150°С, and the surface of the zeolite was treated with ammonia. Subsequently, the test sample was heated up to 800°С with registration of desorption curves. The amount of adsorbed ammonia was carried out according to previously prepared calibration curves. The synthesized samples of zeolites had different acidity from 0.48 to 0.72 mmol(NH3)/g(sample). In this case, the total acidity of the samples correlated with the ratio of silicon to aluminum in the zeolite samples. Also, depending on the ratio of the MFI and mordenite structures in the zeolite sample, it is possible to vary not only the number, but also the strength of the formed acid sites. So, an increase in the content of mordenite contributes to an increase in the strength of acid centers. The developed method for the synthesis of mixed structure zeolites of the MFI type mordenite made it possible to control the surface acidity of the synthesized samples.