Conventional Polymeric Membranes Research Articles

Sbnd]SO3H functionalized UiO-66 nanocrystals in Polysulfone based mixed matrix membranes: Synthesis and application for efficient CO2 capture

Functionalized mixed matrix membranes (MMMs) have the potential to upgrade the separation performance of conventional polymeric membranes while as yet keeping their processing benefits and lower costs. This study investigated the highly stable zirconium based metal-organic framework UiO-66 functionalized with sulfonic group, which was grafted by silane coupling agent mercaptopropyl trimethoxysilane. Sulfonic group imparted high separation properties to UiO-66. Polysulfone (PSf) was used as a polymer matrix and MMMs were synthesized for non-functionalized and functionalized UiO-66; and their results were compared. The characterization and permeation results ascribed that functionalized UiO-66 adhered well with the PSf matrix. The results demonstrated that increasing sulfonic group concentration resulted in higher selectivities owing to their high affinity towards CO2 gas molecules. The MMMs exhibited high CO2 permeabilities and selectivities under pure and mixed gas conditions; and proved this material promising for CO2 separation. In order to evaluate the practical commercial viability of these MMMs, investigation was conducted under different temperatures and compared with existing literature.

Biofouling-resistant nanocellulose layer in hierarchical polymeric membranes: Synthesis, characterization and performance

In this study, we developed a hierarchical thin-film nanofibrous composite (TFNC) membrane with electrospun mat as substrate and hydrophilic nanocellulose as the antifouling barrier layer. We found that, due to the super-hydrophilic nature of the nanocellulose, the contact angle of the barrier layer (20−28°) decreased rapidly with time and reached nearly zero after a few seconds, whereby the membrane flux were remarkably higher (52L.m−2.h−1) than conventional polymeric membranes (4−14L.m−2.h−1) at a very low transmembrane pressure of 0.5 psi. In addition, the membrane surface was considerably more negatively-charged due to the high concentration of carboxylate groups, resulting in higher repulsive electrostatic forces between the barrier layer and the model foulant. As a result, the nanocellulose-based hierarchical membranes exhibited a lower fouling tendency (<10%) and a higher degree of protein rejection ratio compared with the conventional membranes (fouling tendency >30%). The effect of the nanocellulose layer thickness on the membrane fouling was also examined and it was demonstrated that the nanocellulose barrier layer thickness had a significant effect on the membrane fouling. The higher flux, lower fouling, and good rejection properties of this membrane system suggest nanocellulose is a promising barrier material for filtration membranes for water purification and other separation processes.

DDR-type zeolite membrane: A novel CO2 separation technology for enhanced oil recovery

JGC Corporation (JGC) and NGK Insulators, Ltd. (NGK) have been developing the world’s largest DDR-type zeolite membrane to meet the practical needs of CO2/hydrocarbon separation in the natural gas and CO2 Enhanced Oil Recovery (CO2-EOR) industries.DDR-type zeolite has desirable nano-size pores for CO2/hydrocarbon separation. NGK has developed a thin, defect-free DDR-type zeolite membrane with a monolithic structure. This membrane is prepared onto the inner surface of a cylindrical monolithic alumina substrate having 30 channels with a diameter and length of 30 mm and 160 mm, respectively. CO2 permselectivity over CH4 of the monolithic membrane was investigated using the binary gas mixture of 61–67 mol% CO2 and 33–39 mol% CH4 at 44–46 °C with up to 8.0 MPa G as the feed pressure. The CO2 permeability reached 1973 Barrer (6.6 × 10−13 mol m m−2 s−1 Pa−1) while the separation factor of CO2/CH4 exceeded 140 at the transmembrane pressure difference of 2.5 MPa. This CO2 permeability decreased to 1154 Barrer (3.9 × 10−13 mol m m−2 s−1 Pa−1) at the transmembrane pressure difference of 7.0 MPa; however, the separation factor of CO2/CH4 was still as high as 90. In order to understand the stability of the monolithic membrane, the change in the permeability of CO2 and CH4 with time was measured at 58–60 °C with transmembrane pressure difference of 7.4–7.7 MPa using the binary gas mixture of 65–71 mol% CO2 and 29–35 mol% CH4 for 140 h. During the gas permeation test, the CO2 permeability was almost constant while CH4 permeability slightly decreased. As a result, the separation factor of CO2/CH4 was maintained at the initial value.Based on the experimental results, we evaluated the potential applicability of the DDR-type zeolite membrane compared to the conventional polymer membrane for a CO2 recovery process in a CO2-EOR project where CO2 is often separated from the associated gas for re-use. We assumed that the associated gas contains 70 mol% CO2 and 30 mol% CH4 at a pressure of 4.0 MPa G while the specification of CO2 purity in the permeate gas was 95 mol% at a pressure of 0.3 MPa G. When this associated gas is treated using a single-stage membrane process, only 49% of CO2 was recovered by a membrane having a CO2/CH4 separation factor of 12.5 like a typical polymer membrane. On the other hand, membranes having CO2/CH4 separation factors of 80–100 could recover 98–99% of CO2 while more than 96 mol% purity of CH4 was obtained at the retentate side. This simulation study indicated that the highly selective membrane like the DDR-type zeolite membrane can recover not only high purity CO2 for CO2-EOR projects, but also make available CH4 for use or sale. This high purity CH4 brings additional benefit to the CO2-EOR operators.

Hydrophobic ceramic capillary membranes for versatile virus filtration

In this study, we present hydrophobic yttria-stabilized zirconia capillary membranes conditioned for virus filtration. These macroporous ceramic filters (d50 = 150 nm) efficiently extract viruses regardless of their surface charge with high throughput rates. For hydrophobic functionalization of the ceramic membranes we used two different silanes, n-hexyltriethoxysilane (HTS, C6-chain) and n-octyltriethoxysilane (OTS, C8-chain), in three different molarities. The virus retention of the membranes is tested in dead-end mode by intracapillary virus feeding using two small bacteriophages as model species: MS2 and PhiX174. Virus retention increases most strongly for hydrophobic capillaries functionalized with 0.05 M OTS, showing a virtually complete retention with log-reduction values (LRVs) of ~ 9 for both bacteriophages compared to the non-functionalized membrane with LRVs of 0.3 ± 0.1 for MS2 and 3.4 ± 0.2 for PhiX174. The functionalized membranes allow a high membrane flux of ~ 150 L/(m2hbar), with throughput rates up to ~ 400 L/(m2 h) while maintaining high filtration efficiency. Even under varying feed conditions using only mono- or divalent salt ions or pH values ranging from 3 to 9, retention capacities of the capillary membranes are high. Accordingly, such hydrophobic ceramic membranes offer a versatile alternative to conventional polymeric membranes for virus removal with greatly improved membrane flux.

Micropatterned Ultrathin MOF Membranes with Enhanced Molecular Sieving Property

AbstractMetal–organic frameworks (MOFs) are attractive crystalline materials for membranes due to their diverse crystalline pore structures and molecular separation properties. However, the fabrication cost is relatively high compared to conventional polymeric membranes. The concern of the cost could be eased if they are part of a value‐added device, for example, as the key separation unit in a lab‐on‐a‐chip device. This study demonstrates the feasibility of miniaturization of MOF membranes by patterning the membrane surface, a necessary step for MOF membranes to be used in compact devices. Water‐stable ultrathin UiO‐66 membranes with a thickness down to 250 nm on a substrate with a complex pattern were grown. The patterned membranes showed a 100 % improvement in the apparent permeation flux over conventional flat‐UiO‐66 membranes without compromising the molecular separation property, indicating the complexity of a surface would not be a formidable obstacle to the MOF membrane fabrication.

Micropatterned Ultrathin MOF Membranes with Enhanced Molecular Sieving Property.

Metal–organic frameworks (MOFs) are attractive crystalline materials for membranes due to their diverse crystalline pore structures and molecular separation properties. However, the fabrication cost is relatively high compared to conventional polymeric membranes. The concern of the cost could be eased if they are part of a value‐added device, for example, as the key separation unit in a lab‐on‐a‐chip device. This study demonstrates the feasibility of miniaturization of MOF membranes by patterning the membrane surface, a necessary step for MOF membranes to be used in compact devices. Water‐stable ultrathin UiO‐66 membranes with a thickness down to 250 nm on a substrate with a complex pattern were grown. The patterned membranes showed a 100 % improvement in the apparent permeation flux over conventional flat‐UiO‐66 membranes without compromising the molecular separation property, indicating the complexity of a surface would not be a formidable obstacle to the MOF membrane fabrication.

Modeling Permeation through Mixed-Matrix Membranes: A Review

Over the past three decades, mixed-matrix membranes (MMMs), comprising an inorganic filler phase embedded in a polymer matrix, have emerged as a promising alternative to overcome limitations of conventional polymer and inorganic membranes. However, while much effort has been devoted to MMMs in practice, their modeling is largely based on early theories for transport in composites. These theories consider uniform transport properties and driving force, and thus models for the permeability in MMMs often perform unsatisfactorily when compared to experimental permeation data. In this work, we review existing theories for permeation in MMMs and discuss their fundamental assumptions and limitations with the aim of providing future directions permitting new models to consider realistic MMM operating conditions. Furthermore, we compare predictions of popular permeation models against available experimental and simulation-based permeation data, and discuss the suitability of these models for predicting MMM permeability under typical operating conditions.

Efficient removal of As(III) by Cu nanoparticles intercalated in carbon nanotube membranes for drinking water treatment

Arsenic contamination is threatening drinking water safety in many areas around the world. Among different arsenic species in water, arsenite or As(III) is the most difficult one to remove due to its neutrality in drinking water. Therefore, development of novel materials is warranted for efficient As(III) removal. Herein, novel nanocomposite materials were facilely prepared by intercalating Cu nanoparticles into carboxylated/hydroxylated carbon nanotubes (CNT) deposited on top of a conventional polymeric membrane. The as-prepared membrane possessed high pure water permeability (4639–4854 L m−2 h−1 bar−1) and capability to remove more than 90% of As(III) at transmembrane pressures below 0.01 bar, which is plausible for gravity-driven membrane (GDM) filtration applications. Compared to Fe-based materials reported in the literature, the Cu/CNT nanocomposite membranes exhibited robustness in removing As(III) at a pH range of 5–9 and in the presence of chloride, nitrate, bicarbonate, sulfate and natural organic matter. A mechanical investigation suggests that the filtration process involves direct adsorption of As(III) onto Cu/CNT composites. As(V) species were also produced due to oxidation of As(III) by dissolved oxygen under the catalysis of Cu and adsorbed by Cu/CNT composites. Overall, the novel Cu/CNT nanocomposite membranes exhibit promising potentials in As(III) removal from contaminated water, and are worth of further investigation for their suitability in drinking water treatment.

Performance of Mixed Matrix Membranes Containing Porous Two-Dimensional (2D) and Three-Dimensional (3D) Fillers for CO2 Separation: A Review

Application of conventional polymeric membranes in CO2 separation processes are limited by the existing trade-off between permeability and selectivity represented by the renowned upper bound. Addition of porous nanofillers in polymeric membranes is a promising approach to transcend the upper bound, owing to their superior separation capabilities. Porous nanofillers entice increased attention over nonporous counterparts due to their inherent CO2 uptake capacities and secondary transport pathways when added to polymer matrices. Infinite possibilities of tuning the porous architecture of these nanofillers also facilitate simultaneous enhancement of permeability, selectivity and stability features of the membrane conveniently heading in the direction towards industrial realization. This review focuses on presenting a complete synopsis of inherent capacities of several porous nanofillers, like metal organic frameworks (MOFs), Zeolites, and porous organic frameworks (POFs) and the effects on their addition to polymeric membranes. Gas permeation performances of select hybrids with these three-dimensional (3D) fillers and porous nanosheets have been summarized and discussed with respect to each type. Consequently, the benefits and shortcomings of each class of materials have been outlined and future research directions concerning the hybrids with 3D fillers have been suggested.

(Keynote) Ionic Liquids for Improved Separations

Synthetic membranes are important for many separation applications, such as the separation and purification of atmospheric gases for medical and industrial use, and salt removal from seawater in regions lacking fresh water sources. Unlike mesh filters used to separate large solid particles from a fluid (i.e., via phase difference), membranes used to separate molecular species from one another (i.e., a chemical separation) are required to perform a more difficult process, given the size scale and level of mixing of the components. Membranes perform chemical separations generally based on their morphology (i.e., whether they are dense or porous). Dense (i.e., nonporous) membranes operate by the solution-diffusion (S-D) mechanism in which one molecular species is separated from another by the difference in their abilities to be dissolved in the membrane material and their ability to diffuse through it. The keys to designing porous membrane materials for chemical separations are the ability to generate uniform pores with the correct size on the molecular level and that are continuous across the membrane. If there is a distribution of pore sizes, most of the molecules will pass through the largest pores accessible, thereby compromising selectivity. Because of the benefits of membrane-based chemical separations over other methods (e.g., smaller device footprints, lower energy use compared to distillation), there has been recent interest in applying membranes to new separation problems, as well as improving membrane materials used in existing separations. Consequently, there is a need for better membrane materials in general (i.e., with better selectivity, better productivity, longer life and operational stability, increased operating temperature range, use in chemically challenging environments, and the ability to adjust materials properties and performance for a given application). We have focused our research on novel material platforms that provide some advantages compared to conventional membranes. One approach is to use room-temperature ionic liquids (RTILs) in various morphologies as membranes. RTILs have unique physiochemical properties, such as negligible vapor pressure, high thermal stability, and intrinsic solubility for certain gases, which make them unique in terms of organic liquids and solvents. In comparison to conventional polymeric membranes, RTILs perform gas separations due to solubility differences. They can also be converted to polymerizable molecules, thus allowing promising RTILs to be polymerized into solid-state materials. Thus, they can be converted to various morphologies as membranes while maintaining the inherent selectivity of the material. These materials have all the advantages listed earlier. They can be prepared as polymer films, composite structures with ionic liquid within the structure and gels. The wide range of morphologies and chemical structures possible for RTILs allows for designing materials that not only have the desired physicochemical properties but also the mechanical properties needed to produce viable membranes. We have prepared polymerized RTIL-based membranes that can be used for selective gas separations, as membrane separators in electrochemical devices, as catalytic membranes, and as “breathable” barrier materials against chemical warfare agents and toxic industrial chemicals.

High Water Flux with Ions Sieving in a Desalination 2D Sub-Nanoporous Boron Nitride Material.

Over the past decades, desalination by reverse osmosis (RO) membranes has attracted increasing attention. Although RO has proven its efficiency, it remains, however, relatively costly because of the use of high-pressure pumps and the low water permeability of conventional cross-linked polymer membranes. One route to improve the desalination performance consists of using membranes made from sub-nanoporous boron nitride (sNBN) monolayers. Indeed, by using molecular dynamics simulations, we report here that the water permeability of such sNBN membranes far exceeds that of conventional RO polymer membranes and is even higher than that of nanoporous graphene while the ion rejection remains close to 100%. At the same time, the molecular mechanism of water and ion transport through sNBN has been elucidated, with special attention paid to the impact of ions on water permeability through sNBN membranes.

Progress of Nanocomposite Membranes for Water Treatment.

The use of membrane-based technologies has been applied for water treatment applications; however, the limitations of conventional polymeric membranes have led to the addition of inorganic fillers to enhance their performance. In recent years, nanocomposite membranes have greatly attracted the attention of scientists for water treatment applications such as wastewater treatment, water purification, removal of microorganisms, chemical compounds, heavy metals, etc. The incorporation of different nanofillers, such as carbon nanotubes, zinc oxide, graphene oxide, silver and copper nanoparticles, titanium dioxide, 2D materials, and some other novel nano-scale materials into polymeric membranes have provided great advances, e.g., enhancing on hydrophilicity, suppressing the accumulation of pollutants and foulants, enhancing rejection efficiencies and improving mechanical properties and thermal stabilities. Thereby, the aim of this work is to provide up-to-date information related to those novel nanocomposite membranes and their contribution for water treatment applications.

A porous ceramic membrane tailored high-temperature supercapacitor

The supercapacitor that can operate at high-temperature are promising for markedly increase in capacitance because of accelerated charge movement. However, the state-of-the-art polymer-based membranes will decompose at high temperature. Inspired by solid oxide fuel cells, we present here the experimental realization of high-temperature supercapacitors (HTSCs) tailored with porous ceramic separator fabricated by yttria-stabilized zirconia (YSZ) and nickel oxide (NiO). Using activated carbon electrode and supporting electrolyte from potassium hydroxide (KOH) aqueous solution, a category of symmetrical HTSCs are built in comparison with a conventional polymer membrane based device. The dependence of capacitance performance on temperature is carefully studied, yielding a maximized specific capacitance of 272 F g−1 at 90 °C for the optimized HTSC tailored by NiO/YSZ membrane. Moreover, the resultant HTSC has relatively high durability when suffer repeated measurement over 1000 cycles at 90 °C, while the polymer membrane based supercapacitor shows significant reduction in capacitance at 60 °C. The high capacitance along with durability demonstrates NiO/YSZ membrane tailored HTSCs are promising in future advanced energy storage devices.

Water and ion sorption, diffusion, and transport in graphene oxide membranes revisited

Graphene oxide (GO) membranes show promising separation performance, including high water permeation rate and rejection of ions or molecules larger than the interlayer distance of adjacent GO sheets. However, the fundamental water and small ion transport properties of GO membranes are still debated due to the heterogeneity of the physical and chemical structures of GO sheets. Here, we report the sorption, diffusion, and permeation properties of water and ions in GO membranes. The water permeability coefficient of GO membranes is in the range 3.0 × 10−7–1.0 × 10−6cm2/s and strongly depends on the flake size, the oxidation level, and the drying process. This value is not as high as reported in the literature and is similar to that of polymeric materials used for desalination, such as polyamide. Unexpectedly, a high water partition coefficient (0.93) was observed in GO membranes compared to those of other hydrophilic polymers. This contributes to the water permeability based on a solution-diffusion mechanism. Consequently, the water diffusivity of GO membranes is lower than that of hydrophilic polymers with similar water permeability due to the high tortuosity caused by its lamellar structure. In this study, we showed that GO membranes exhibited unique ion selective sorption and permeation behaviors compared to conventional polymeric membrane materials. The physical and chemical modifications of GO membranes strongly affect the transport properties of water and ions, indicating the possibility of the further improvement in the separation performances of GO-based membrane materials for liquid separation.

Oxygen permselectivities through supramolecular polymer membranes prepared by highly selective photocyclic aromatization of poly(substituted acetylene)

In order to estimate oxygen permselectivities through a supramolecular polymer membrane for the first time, we prepared three kinds of composite membranes consisting of a supramolecular polymer membrane and a conventional organic polymer membrane. Supramolecular polymer membranes were prepared by using highly selective photocyclic aromatization of poly(substituted acetylene)s. It was found that the supramolecular polymer membrane had oxygen permselectivity (α = PO2/PN2) around three in spite of its low molecular weight.

Electrospun Membranes for Desalination and Water/Wastewater Treatment: A Comprehensive Review

Polymeric nanofbers, specifcally fabricated by electrospinning, offer viable means useful for a wide range of applications such as health, energy and environmental issues. However, among the mentioned sectors, desalination and water/wastewater treatment applications have been highlighted during the past decade. This article focuses on the present status and recent development of electrospun nanofbrous membranes and their potential impact in two major areas, i.e., desalination and water/wastewater treatment. Specifc applications for desalination and high-quality water/wastewater treatment, including pressure-driven and osmotic membrane processes (MF, UF, NF, FO, etc.), thermal-driven membrane processes, coalescing fltration and adsorptive application of nanofbers, are described. Also, benefts, limitations and challenges are discussed, comprehensively. Electrospun membranes can play a critical role in improving membrane-based desalination and water/wastewater treatment systems. These fltration elements with 3D inter-connected structures will be shown to have interesting and crucial advantages over conventional polymeric membranes in terms of performance, cost and energy savings. This article also highlights the prospects of electrospun membranes and specifcally provides the state-of-the-art applications in the water industry.

Gas Separation Process for CO2 Removal from Natural Gas with DDR-type Zeolite Membrane

The DDR-type zeolite membrane (DDR Membrane) with an aperture of 0.36 × 0.44nm was formed on a porous alumina substrate by hydrothermal process. We have succeeded in scaling up the DDR Membrane element into a large monolithic structure with a diameter and length of 180mm and 1,000mm, respectively. The CO2/CH4 selectivity exceeded 100 for mixed gas of 70 mol% CO2 at 8.0 MPag, 45 degC. This high selectivity improves hydrocarbon recovery compared to the conventional polymeric membrane. The DDR Membrane is suitable for CO2 separation for high CO2 natural gas fields.

Integrated pyrolucite fluidized bed-membrane hybrid process for improved iron and manganese control in drinking water

Newly developed ceramic membrane technologies offer numerous advantages over the conventional polymeric membranes. This work proposes a new configuration, an integrated pyrolucite fluidized bed (PFB)-ceramic MF/UF hybrid process, for improved iron and manganese control in drinking water. A pilot-scale study was undertaken to evaluate the performance of this process with respect to iron and manganese control as well as membrane fouling. In addition, the fouling of commercially available ceramic membranes in conventional preoxidation-MF/UF process was compared with the hybrid process configuration. In this regard, a series of experiments were conducted under different influent water quality and operating conditions. Fouling mechanisms and reversibility were analyzed using blocking law and resistance-in-series models. The results evidenced that the flux rate and the concentration of calcium and humic acids in the feed water have a substantial impact on the filtration behavior of both membranes. The model for constant flux compressible cake formation well described the rise in transmembrane pressure. The compressibility of the filter cake substantially increased in the presence of 2 mg/L humic acids. The presence of calcium ions caused significant aggregation of manganese dioxide and humic acid which severely impacted the extent of membrane fouling. The PFB pretreatment properly alleviated membrane fouling by removing more than 75% and 95% of iron and manganese, respectively.

Highly permeable zeolite imidazolate framework composite membranes fabricated via a chelation-assisted interfacial reaction

The preparation of high-permselectivity membranes is still a challenging task due to the limitations of conventional polymeric membranes.

High-performance of modified Al2O3 hollow fiber membranes for CO2 absorption at room temperature

To the best of our knowledge, we demonstrate for the first time that modified inorganic hollow fiber membrane contactor can be successfully used for the absorption of CO2 from a gas mixture using aqueous solutions of monoethanolamine (MEA) at room temperature with extraordinary results. The fluoroalkylsilanized Al2O3 hollow fiber membrane contactors containing a high-symmetric distribution of morphological elements showed higher permeability for the CO2. A CO2 absorption flux of about 5.4×10−3molm−2s−1 was achieved with a single symmetric ceramic membrane, which is considerably higher compared to other conventional polymeric membrane for CO2 absorption into MEA solutions.