Membrane Separation Research Articles

Membrane Separations in Biomass Processing.

The development of integrated biorefineries and the greater utilization of biomass resources to reduce dependence on fossil fuel-derived products require research emphasis not just on conversion strategies but also on improving separations associated with biorefining. A significant roadblock towards developing biorefineries is the lack of effective separation techniques evidenced by the lack of literature in this area. Additionally, high conversion yields may only be realized if effective separations generate feedstock of sufficient purity - this makes research into biomass conversion strategies all the more critical. In this review, the challenges associated with biomass separations are discussed, followed by an overview of the most appropriate separation strategies for processing biomass. One of the unit operations most appealing for biorefining, membrane separations (MS), is then considered along with a review of the recent literature utilizing this technique in biomass processing.

Transformations of Critical Lithium Ores to Battery-Grade Materials: From Mine to Precursors

The escalating demand for lithium has intensified the need to process critical lithium ores into battery-grade materials efficiently. This review paper overviews the transformation processes and cost of converting critical lithium ores, primarily spodumene and brine, into high-purity battery-grade precursors. We systematically examine the study findings on various approaches for lithium recovery from spodumene and brine. Dense media separation (DMS) and froth flotation are the most often used processes for spodumene beneficiation. Magnetic separation (MS) and ore gravity concentration techniques in spodumene processing have also been considered. To produce battery-grade lithium salts, the beneficiated-concentrated spodumene must be treated further, with or without heat, in the presence of acidic or alkaline media. As a result, various pyro and hydrometallurgical techniques have been explored. Moreover, the process of extracting lithium from brine through precipitation, liquid–liquid extraction, and polymer inclusion membrane separation employing different organic, inorganic, and composite polymer sorbents has also been reviewed.

Machine Learnable Language for the Chemical Space of Nanopores Enables Structure-Property Relationships in Nanoporous 2D Materials.

The synthesis of nanoporous two-dimensional (2D) materials has revolutionized fields such as membrane separations, DNA sequencing, and osmotic power harvesting. Nanopores in 2D materials significantly modulate their optoelectronic, magnetic, and barrier properties. However, the large number of possible nanopore isomers makes their study onerous, while the lack of machine-learnable representations stymies progress toward structure-property relationships. Here, we develop a language for nanopores in 2D materials, called STring Representation Of Nanopore Geometry (STRONG), that opens the field of 2D nanopore informatics. We show that STRONGs are naturally suited for machine learning via recurrent neural networks, predicting formation energies/times of arbitrary nanopores and transport barriers for CO2, N2, and O2 gas molecules, enabling structure-property relationships. The machine learning models enable the discovery of specific nanopore topologies to separate CO2/N2, O2/CO2, and O2/N2 gas mixtures with high selectivity ratios. We also enable the rapid enumeration of unique configurations of stable, functionalized nanopores in 2D materials via STRONGs, allowing systematic searching of the vast chemical space of nanopores. Using the STRONGs approach, we find that a mix of hydrogen and quinone functionalization results in the most stable functionalized nanopore configuration in graphene, a discovery made feasible by expedited chemical space exploration. Additionally, we also unravel the STRONGs approach as ∼1000 times faster than graph theory algorithms to distinguish nanopore shapes. These advances in the language-based representation of 2D nanopores will accelerate the tailored design of nanoporous materials.

Covalent organic framework membranes with vertically aligned nanorods for efficient separation of rare metal ions

Covalent organic frameworks (COFs) have emerged as promising platforms for membrane separations, while remaining challenging for separating ions in a fast and selective way. Here, we propose a concept of COF membranes with vertically aligned nanorods for efficient separation of rare metal ions. A quaternary ammonium-functionalized monomer is rationally designed to synthesize COF layers on porous substrates via interfacial synthesis. The COF layers possess an asymmetric structure, in which the upper part displays vertically aligned nanorods, while the lower part exhibits an ultrathin dense layer. The vertically aligned nanorods enlarge contact areas to harvest water and monovalent ions, and the ultrathin dense layer enables both high permeability and selectivity. The resulting membranes exhibit exceptional separation performances, for instance, a Cs+ permeation rate of 0.33 mol m−2 h−1, close to the value in porous substrates, and selectivities with Cs+/La3+ up to 75.9 and 69.8 in single and binary systems, highlighting the great potentials in the separation of rare metal ions.

Enhancing industrial wastewater treatment: Magnetite-embedded matrix membrane for efficient tetrahydrofuran separation by pervaporation and vapor permeation techniques

The treatment of industrial wastewater is crucial for recovering water of high purity, especially considering its significance in mitigating environmental pollution and ensuring sustainable water resources. This study focuses on the purification of industrial wastewater, emphasizing the separation of tetrahydrofuran (THF) from aqueous solutions using membrane-based techniques. Composite membranes incorporating magnetic nanomaterial (magnetite) within a sodium alginate matrix were synthesized and evaluated for their effectiveness in purifying water from THF mixtures. Both Pervaporation (PV) and Vapor Permeation (VP) processes were employed, with thorough analysis conducted on the impact of magnetite content on permeate purity. The study identified optimal magnetite content for industrial wastewater treatment and developed a new membrane composition based on these findings. The VP process’s performance was evaluated by determining the permeation flux and separation factor. The highest separation factor of 460 was obtained for an 80% wt. THF-water solution in the VP process. Using these findings, the optimal magnetite content for industrial wastewater treatment was identified, and a new membrane composition was developed. The activation energies for the permeation of THF through the NaAlg-Fe20 membrane were found to be 10.50 kcal/mol and 7 kcal/mol for the VP and PV processes, respectively.

Optimization of the Helium Extraction Process from Natural Gas with Integrated Cryogenic–Membrane Separation

Optimization of the Helium Extraction Process from Natural Gas with Integrated Cryogenic–Membrane Separation

Electrospun PVDF/PVP Fibrous Membrane with Photocatalytic and Superhydrophilic Properties.

Membrane separation technology is used to treat environmental wastewater, but during the treatment process, the occurrence of membrane fouling greatly affects the treatment efficiency. To address this phenomenon, improve membrane antipollution capabilities, and treat organic wastewater, photocatalysis and membrane separation technology have been coupled, forming a suitable and promising treatment method. Here, we propose a simple strategy to prepare a polyvinylidene fluoride/polyvinyl pyrrolidone nitrogen-doped titanium dioxide fibrous membrane (PVDF/PVP N-doped TiO2 fibrous membrane). The experimental results showed that PVDF and PVP mixed spinning made the fibrous membrane have a unique microstructure, and the superhydrophobic PVDF fibrous membrane was changed into superhydrophilic. In addition, electrospraying technology was used to attach TiO2 nanoparticles (NPs) to the fiber, and nitrogen (N) was doped in this process to improve the photocatalytic activity of the fibrous membrane. Finally, methyl blue solution was used as the target organic pollutant. Under the irradiation of a xenon lamp, 90.05% of methyl blue was removed within 90 min, indicating that the membrane had good photocatalytic performance. In a water contact angle test, the PVDF/PVP N-doped TiO2 fibrous membrane showed superhydrophilicity. The design of a fibrous membrane with high photocatalytic activity and superhydrophilicity properties has great potential for practical application in the purification of industrial wastewater.

The Impact of Adsorption Property Modification by Crosslinkers on Graphene Oxide Membrane Separation Performance

The health risks associated with the presence of heavy metals in drinking water can be severe. To address this issue, membrane separation technology is one of the consolidated alternatives. Inorganic, porous membranes were found in applications where low energy consumption is highly desirable. The selectivity of these membranes is attained by functionalisation. Graphene oxide functionalised membrane technology is promising for removing heavy metal ions. This work summarises, discusses and presents the relationship between adsorption and overall membrane separation process performance for heavy metal ions removal from wastewater when a graphene oxide-functionalised membrane is used. The separation performance depends on the hydrophobic interactions of the membrane and the solute. The electrostatic interaction between the negatively charged membrane surface and positively charged metal ions facilitates the adsorption, leading to the rejection of these metal ions. The influences of the chemical nature of the modifiers of graphene oxide layers are highlighted.

Boronate affinity metal–organic frameworks molecularly imprinted membranes with hierarchical porous channels for the selective separation of naringin

Naringin (NRG), known as an important natural flavoniod compounds, exhibits excellent phamaceutical value and clinical application prospect. However, the main obstacle to the isolation and purification of NRG is the low concentration and complexity of the extraction system. Herein, a new kind of hierarchical porous metal–organic frameworks (MOFs) based molecularly imprinted membranes (PBMMA-MIMs) for the specific separation of NRG. The prepared PBMMA-MIMs showed the fast adsorption kinetics (within 120 min). Moreover, the abundant boronic acid imprinted recognition sits and hydrophilic hierarchical porous MOFs improved the adsorption capacity (the maximum adsorption amounts 57.39 μmol/g) and exhibited selective NRG adsorption (imprinting factor 2.31) with efficiency over 91.69 % after seven adsorption–desorption cycles. In addition, the coarse NRG could be effectively extracted to a promising purity of 93.13 % via PBMMA-MIMs. This study provides new insights into the design molecularly imprinted membranes via environmentally friendly synthesis route for the preparation for enriching high-value flavoniods, achieving efficient purification rate of agricultural wastes for pollution control, and promoting the sustainable reuse in complex agricultural wastewater.

Uranium removal from contaminated groundwater using goethite-loaded composite microporous membrane

In this study, we have coupled adsorption and membrane separation for the removal of uranium from contaminated groundwater in environmentally relevant conditions at low energy requirements. This study mainly focuses on elucidating uranium, U(VI), adsorption mechanisms using surface complexation modeling approach in a novel goethite-loaded composite microfiltration membrane (GLM). This experiment involved immobilizing goethite nanorods in a microporous (0.22 μm pore size) poly (vinylidene fluoride) (PVDF) membrane. The effect of varying goethite loading and hydraulic residence time on U(VI) removal was investigated at field-relevant pH (i.e. pH 8.5). U(VI) adsorption (i.e. 4.95 μg·mg−1) was optimum at a goethite loading 1.20 mg·cm−2. The effect of varying hydraulic residence time had no impact on U(VI) removal which was also confirmed via performing batch adsorption kinetic experiments. GLM membrane loaded at 1.2 mg·cm−2 could treat 275 L of U(VI) contaminated water having 200 μg of U L−1 below WHO drinking water limit (i.e. 30 μg of U L−1) with 1 m2 of membrane surface area with a adsorption capacity of 6.12 μg·mg−1. Varying the pH of aqueous solution, containing U(VI) from pH 4.0 to pH 10.0, showed a significant impact on uranium uptake ranging from 0.7 μg·mg−1 to 2.63 μg·mg−1 by the composite membrane. The adsorption mechanism of uranium onto goethite was explained via the formation of bidentate surface complexes using the Surface Complexation Model (SCM). The results of batch pH edge experiments and SCM have been compared with pH experiments performed using GLM. The results of SCM predicted the batch pH edge experiment within a RMSE of 0.055. The trend of U(VI) removal in membrane experiments was observed to be similar to that of batch pH edge experiments and was well predicted SCM model. Our results showed that the novel goethite-loaded membrane has the potential for the effective removal of uranium with a lower specific energy consumption.

Construction of Co-Modified MXene/PES Catalytic Membrane for Effective Separation and Degradation of Tetracycline Antibiotics in Aqueous Solutions

The application of antibiotics has advanced modern medicine significantly. However, the abuse and discharge of antibiotics have led to substantial antibiotic residues in water, posing great harm to natural organisms and humans. To address the problem of antibiotic degradation, this study developed a novel catalytic membrane by depositing Co catalysts onto MXene nanosheets and fabricating the polyethersulfone composite (Co@MXene/PES) using vacuum-assisted self-assembly. The dual role of MXene as both a carrier for Co atoms and an enhancer of interlayer spacing led to improved flux and catalytic degradation capabilities of the membrane. Experimental results confirmed that the Co@MXene/PES membrane effectively degraded antibiotics through peroxymonosulfate activation, achieving up to 95.51% degradation at a cobalt concentration of 0.01 mg/mL. The membrane demonstrated excellent antibacterial properties, minimal flux loss after repeated use, and robust anti-fouling performance, making it a promising solution for efficient antibiotic removal and stable water treatment.

Microplastics in wastewater plants: A review of sources, characteristics, distribution and removal technologies

Microplastics (MPs) are widespread in everyday life, and since wastewater treatment plants (WWTPs) serve as an important route for MPs to enter natural water bodies, a thorough understanding of the distribution and removal of MPs in wastewater treatment plants is of great importance. This article provides a comprehensive overview of the measured distribution of MPs and the current status of their removal in wastewater treatment plants. The main sources of MPs in wastewater treatment plants are personal care products in domestic wastewater, textile clothing and industrial wastewater made from plastics, textile factories and the friction of road tires. The MPs that entered the sewage treatment plant were predominantly in the form of fibers, fragments, granular MPs and other types of MPs. The size of MPs is divided into three categories: <0.5 mm, 0.5–1 mm and 1–5 mm. At all treatment stages in wastewater plants, 56.8–88.4 % of MPs are removed in primary treatment, but the primary sedimentation and degreasing stages remove most MPs. The efficiency of the activated sludge process for secondary treatment is inconsistent and is generally between 42.1 and 99.2 %. The coagulation, filtration and disinfection stages of tertiary treatment all have some MPs removal capacity. In addition, novel removal technologies are also described, such as modified filtration technology, membrane separation technology, electroflocculation, sol-gel and photocatalysis. These novel removal technologies can further limit the entry of microplastics into natural water bodies through sewage treatment plants and improved sewage treatment processes help reduce the risk of MPs entering the natural environment through sewage treatment plants. This article will provide reference for the distribution and removal of microplastics in various levels of WWTPs.

Innovative thermal crosslinked polyimide gas separation membrane with highly selective and resistance to physical aging base on phenyl ethynyl

In this study, a high performance phenyl ethynyl thermal crosslinked 6FDA-based polyimide (CR-4ETA-x) was developed, which has high gas permeability and selectivity, resistance to physical aging. By introducing 4,4′-(Acetylene-1,2-diyl) diphthalic anhydride (4ETA) monomer into the polyimide structure, the thermal crosslinking precursor membrane was formed. The precursor membrane was heat treated at 440℃ to obtain CR-4ETA-x. After heat treatment, we detected the olefin radical in the crosslinked membrane by electron paramagnetic resonance, which proved that the polyimide network was formed. This allows the crosslinked membrane to have greater d-spacing, higher rigidity, and BET surface area. The CO2 permeability of CR-4ETA-5% is 4114 barrer and the CO2/CH4 selectivity is 19.22. Compared to 6FDA-DAM, the CO2 permeability increased by 477% while the selectivity decreased by only 17%. CR-4ETA-20% shows the CO2 permeability of 3560 Barrer and CO2/CH4 selectivity of 21.1 in CO2/CH4 mixed-gas. After 60 days of aging the permeability maintenance of CR-4ETA-20% were 88%, 84%, 83% and 91% for O2, N2, CO2 and CH4. In addition, in the long-term stability test of more than 100 h, the separation performance of CR-4ETA-20% did not decrease significantly. However, CR-4ETA-x also has limitations, such as poor stability in alkaline environments and lower gas permeability than some advanced carbon molecular sieve membranes. In general, the method of phenyl ethynyl thermal crosslinking provides an effective way for the development of CO2 separation membranes with possible applications.

Efficient conversion from food waste to composite carbon source through rapid fermentation and ceramic membrane filtration

Anaerobic fermentation of food waste (FW) produces a broth rich in small-molecule organic substances, which has the potential as a composite carbon source for denitrification in wastewater treatment. In this study, the idea was tested by optimizing the fermentation process at different hydraulic residence time (HRT), refining fermentation broth through ceramic membrane filtration, and comparing the performance of fermentation filtrate and other commercial carbon sources. A short HRT of 3 days was a suitable fermentation condition with 88% polysaccharide degradation. Acetic acid contributed 40% of soluble chemical oxygen demand in the fermentation broth, followed by ethanol, propanol, lactic acid, and propionic acid, and the five products accounted for 80%. Ceramic membrane filtration can recover more than 70% of dissolved organic matter and more than 60% of small molecular organic matter and simultaneously remove 99% of SS, 41% of total nitrogen, and 62% of total phosphorus. At the rapid degradation stage, the denitrification rates reached 6.68–10.39 mg NOx−-N/(g VSS·h), which was on par with commercial carbon sources. The short fermentation and the rapid membrane separation were integrated to create an efficient treatment system, which provided a feasible pathway to utilize FW combining wastewater treatment.

Optimizing Membrane Performance using Various Filler Materials in Membrane Fabrication for Enhancing Gas Separation Efficiency: A Review

The membrane technology has been receiving significant interest in both research and industrial applications, particularly in the separation of CO2/CH4. These methods, as published, aim to overcome the limitations of pure polymeric membranes and offer an alternative approach in separation techniques where membrane technology can overcome the constraints of conventional methods such as Solid Phase Extraction (SPE) and Liquid-Liquid Extraction (LLE). Fabricating membranes using fillers as adsorbents can enhance membrane separation performance due to their porous nature. Hence, the selection of suitable fillers is crucial to maximize membrane efficiency in separating analytes. This paper will review 3 types of fillers-metal-organic frameworks, carbonaceous nanomaterials and mesoporous molecular sieves-from various research papers published in recent years. HIGHLIGHTS Additives introduced to polymeric membrane to increase the membrane performances in terms of selectivity and permeability. Short review of materials used for fabrication of mixed matrix membrane. Modification of selected additives used to study its effects on membrane performances. Recent advancement of hybrid additives materials, combining MOF and carbonaceous materials. GRAPHICAL ABSTRACT

Zwitterionic covalent organic framework membranes for efficient liquid molecular separations

Covalent organic frameworks (COFs) featuring uniform topological structure and devisable functionality have emerged as promising membrane materials. The design and precise manipulation of COF membranes with advanced spatial structure to achieve efficient liquid molecular separations are of great necessity. Herein, zwitterionic COF membranes have been in-situ fabricated on porous polymeric substrates using an interfacial polymerization modification strategy. The continuous defect-free COF membranes with two-dimensional in-plane dominant growth can be achieved by optimizing the fabrication parameters including reaction time, monomer concentration, and catalyst concentration. Subsequent zwitterionic modification thereon not only favors the formation of hydrophilic surface but also improves the sieving capability by sheltering effect. Attributed to the synergistic contribution, the optimized zwitterionic COF membrane possesses a superior separation factor of 2839 with the water content in the permeate up to 99.7 wt%, while maintaining a comparable permeation flux of 3309 g m−2 h−1 during the ethanol dehydration process, outperforming most of other representative membranes. Furthermore, the excellent durability of the zwitterionic COF membrane in the ethanol dehydration process and its efficient separation performance towards other alcohol dehydration systems demonstrate its potential practical applications. The easy scalability of the fabrication and regulation method offers crucial guidance for the engineering of advanced COF membranes in efficient liquid molecular separations.

Aminated ZIF‐8 to facilitate CO2 sieving through polyvinyl alcohol/ionic liquid membranes

AbstractCO2 separation technology at low pressure is most desirable in carbon capture projects to mitigate global warming. Facilitated transport membranes offer selective and effective CO2 permeation using a wide range of carbon carriers at low pressure. Porous fillers were recently included as they can carry abundant fixed carriers besides offering open channels for CO2 permeation. This study investigates the effects of amine‐modified zeolitic imidazolate framework‐8 (ZIF‐8) with well‐defined micropores and gas sieving ability in polyvinyl alcohol (PVA) membranes containing an ionic liquid that worked as mobile carriers. The effects of amine‐modified ZIF‐8 and silica nanoparticles on membrane properties and separation performance were also compared. Fourier transform infrared spectra confirmed the incorporation of ZIF‐8, secondary amine, IL anions, and silica nanoparticles in PVA membranes. Energy dispersive analysis showed the good dispersion of inorganic fillers. The amine‐modified silica nanoparticles resulted in higher thermal stability compared to the amine‐modified ZIF‐8 in PVA membranes containing [bmin][Ac] ionic liquid, as shown in the thermogravimetric analysis. However, the CO2 separation performance of PVA membranes containing [bmim][Ac] ionic liquid was improved more significantly by the amine‐modified ZIF‐8 with microporous structure. A CO2/N2 ideal selectivity of 85.65 and CO2 permeance up to 4,502.91 GPU were attained. Unlike the CO2/N2 ideal selectivity, the CO2 permeance was not significantly affected either using [bmin][Ac] or [bmin][BF4]. The humid gas greatly enhanced the CO2 permeance without much changes in the CO2/N2 ideal selectivity due to the promotion of facilitated transport. © 2024 Society of Chemical Industry and John Wiley &amp; Sons, Ltd.

Thin film nanocomposite membranes based on renewable polymer Pebax® and zeolitic imidazolate frameworks for CO2/CH4 separation

This study investigates the impact of integrating Pebax® Rnew® 30R51, a sustainable elastomer-type copolymer material, with zeolitic imidazolate frameworks (ZIFs) to develop advanced membranes for CO2/CH4 gas separation. The fabrication process of ZIF/Pebax® Rnew® 30R51 thin films was optimized to achieve uniform and defect-free thin film composite (TFC) membranes. Crucial membrane properties, including permeability, selectivity and separation efficiency, were analyzed with variations in ZIF type, loading levels, film thickness and operating conditions. Additionally, the resulting TFC and ZIF/Pebax® Rnew® 30R51 thin film nanocomposite (TFN) membranes were subjected to characterization via FTIR, XRD, TGA and SEM to evaluate their physicochemical properties. Nanoparticles of ZIF-8, NH2-ZIF-8 and ZIF-94 were individually added (at 5–15 wt% loadings) to the Pebax® Rnew® 30R51 matrix to develop the CO2 separation efficiency. The pristine TFC membrane showed a 66 GPU CO2 permeance and a 37.5 CO2/CH4 separation selectivity, primarily due to improved CO2 mass transport. Upon inclusion of ZIFs, the CO2 permeance with 5 wt% loadings of ZIF-8, NH2-ZIF-8 and ZIF-94 increased to 148, 99 and 125 GPU, respectively, despite this, the CO2/CH4 separation selectivity maintained at 29.4, 37.0 and 27.0, respectively.

Reversible MOF-Based mixed matrix membranes for SO2/N2 separation: A photo-responsive approach

Fuel consumption for industrial development, SO2 gas emissions are increasing year by year and have become a focal point of air pollution. Membrane separation method photo-responsive materials and MOFs have attracted more and more attention in a variety of fields. This is because the membrane separation method uses less energy and is an uncomplicated process; MOFs have superior gas adsorption capabilities; and the photo-responsive materials are controllable. In this study, mixed matrix membranes are prepared using Uio-66-NH2 and photo-responsive materials CE-Azo-Uio-66 as fillers and Pebax as base membranes. By improving the dissolution-diffusion mechanism for SO2 gas molecules, SO2/N2 gas separation is accomplished. More channels for the mass transport of SO2 gas through the membrane can be created by MOFs increased porosity and larger specific surface area. Secondly, the SO2 adsorption and dissolution-diffusion mechanism of the mixed matrix membrane are strengthened by the grafted SO2 affinity groups on the MOF. Moreover, Pebax/CE-Azo-Uio-66 membranes is not only significantly more permeation selective than Pebax/Uio-66-NH2 membranes, but also shows photo-responsive characteristic. The SO2 permeability and selectivity of Pebax/CE-Azo-Uio-66 mixed matrix membranes at CE-Azo-Uio-66 content of 20 % are increased by 191 % and 179 %, respectively, compared to pure Pebax membranes. It is also found that the SO2 permeability and SO2/N2 selectivity of the membranes show regularly reversible changes at the UV–Vis photoconversion conditions of Pebax/CE-Azo-Uio-66-20 % membranes, indicating the photo-responsive characteristics of mixed matrix membranes that include Azo groups. The SO2 permeability of the Pebax/CE-Azo-Uio-66 membrane is increased by 1300 Barrer and the SO2/N2 selectivity is increased by 350 when the light source is changed from UV to Vis light, achieving a controlled separation of SO2/N2. Besides, the addition of MOF particles significantly enhances the mechanical properties and stability of the membrane.

High Water Permeability Interfacial Polymerized PVDF/EAA Composite Nanofiltration Membrane for Dye Separation

High Water Permeability Interfacial Polymerized PVDF/EAA Composite Nanofiltration Membrane for Dye Separation