Hollow Fiber Nanofiltration Research Articles

Engineering novel high-flux thin-film composite (TFC) hollow fiber nanofiltration membranes via a facile and scalable coating procedure

A novel defect-free polyamide/(polyether sulfone/poly(vinylidene fluoride)) PA/(PES/PVDF) thin-film composite (TFC) hollow fiber membrane (HFM) with desirable separation characteristics were developed through a facile and scalable coating procedure. By the introduction of piperazine (PIP) monomers into the PES coating solutions, the functional monomer-enriched PES coating layer was formed on the shell side of porous matrix-reinforced hollow fiber (HF) support through phase inversion process. Subsequently, PIP and TMC was interfacial polymerized during the fiber coating line to form a thin and defect-free polyamide (PA) functional layer for TFC HFM with high water permeability. Furthermore, the introduction of aqueous monomers only into the PES layer allowed economizing the cost of membrane manufacturing compared with bulk modification of the membrane substrate. Interestingly, the formation of bowl-like structures endowed the separation layer with higher permeation surface area and thus favored high water permeability. On combining these separation features, the optimized TFC membranes presented a high pure water permeability (PWP) of 13.8 L·m−2·h−1·bar−1, approximately twice than that of conventional TFC membrane, with a satisfying Na2SO4 rejection of 98.2%. Moreover, the PA/(PES/PVDF) TFC HFM exhibited excellent stability, backwash ability and anti-fouling ability, suggesting its huge potential for the water purification. Compared with the conventional two-step IP process on flat sheet membrane, the in-situ IP procedure performed on HF greatly simplifies the manufacturing process, shortens the production period and reduces monomer usage while the high packing density and great surface area per unit volume are obtained. This work may provide a simple and economical strategy for engineering high-performance TFC HFM.

A novel PPTA/PPy composite organic solvent nanofiltration (OSN) membrane prepared by chemical vapor deposition for organic dye wastewater treatment

In this study, a stable and controllable poly(p-phenylene terephthamide)/polypyrrole (PPTA/PPy) composite organic solvent nanofiltration (OSN) hollow fiber membrane was successfully prepared based on the robust chemical vapor deposition (CVD) method. The structure and properties of the prepared PPTA/PPy OSN membranes were studied in detail. Interestingly, after modifying by PPy, SEM showed that the surface of the membrane formed a layer of “Turing-like” structure and evenly covered the surface of the membrane. It was evident that the prepared PPTA/PPy OSN membranes achieved good dye-removal ability with a molecular weight cut-off range from 200 to1000 Da, and the rejection of negative dyes was higher than 93.4%. Especially at high temperature (80 °C) and organic solvent (N,N-dimethylacetamide, DMAc), the PPTA/PPy OSN membranes still exhibited excellent permeation and separation performance. Furthermore, at room temperature, the immersion experiment of the fabricated PPTA/PPy OSN membranes in both ethanol and DMAc for one month also proved the stability of long-term organic solvents. Based on the above results, this work offered a novel PPTA based hollow fiber nanofiltration membrane, which was expected to be applied in thermal and organic dye wastewater treatment.

Confirming NX Filtration's NF capabilities using pilot testing

Pilot projects that use technology from NX Filtration – a company based in The Netherlands that produces membrane products for treating water – are frequently covered in the news pages of Membrane Technology and detailed in the publication's related focus articles. In this issue, we explain how France's Veolia is expanding its pilot testing using NX Filtration's hollow-fibre direct nanofiltration (dNF) technology, and also briefly look at some of the previous pilot programmes, run by other companies, that are based on the Dutch firm's membranes.

Construction of Hollow Fiber Nanofiltration Separation Layer with Bridging Network Structure by Polymer-Anchored Co-Deposition for High-Concentration Heavy Metal Ion Removal

Construction of Hollow Fiber Nanofiltration Separation Layer with Bridging Network Structure by Polymer-Anchored Co-Deposition for High-Concentration Heavy Metal Ion Removal

Advances and Applications of Hollow Fiber Nanofiltration Membranes: A Review.

Hollow fiber nanofiltration (NF) membranes have gained increased attention in recent years, partly driven by the availability of alternatives to polyamide-based dense separation layers. Moreover, the global market for NF has been growing steadily in recent years and is expected to grow even faster. Compared to the traditional spiral-wound configuration, the hollow fiber geometry provides advantages such as low fouling tendencies and effective hydraulic cleaning possibilities. The alternatives to polyamide layers are typically chemically more stable and thus allow operation and cleaning at more extreme conditions. Therefore, these new NF membranes are of interest for use in a variety of applications. In this review, we provide an overview of the applications and emerging opportunities for these membranes. Next to municipal wastewater and drinking water processes, we have put special focus on industrial applications where hollow fiber NF membranes are employed under more strenuous conditions or used to recover specific resources or solutes.

Fabrication of thin-film composite hollow fiber membranes in modules for concentrating pharmaceuticals and separating sulphate from high salinity brine in the chlor-alkali process

Nanofiltration (NF) has been widely used for sulphate removal in chlor-alkali industries and concentrating ingredients in pharmaceutical industries, but the fabrication and applications of thin-film composite (TFC) NF hollow fiber membranes and modules are still lagged behind those NF membranes in other configurations. In this work, the pressure-assisted interfacial polymerization (IP) is employed to fabricate TFC NF hollow fiber membranes in 1-inch modules through tailoring the reaction conditions. By firstly circulating a piperazine (PIP) solution in the lumen side under a positive pressure and then circulating a trimesoyl chloride (TMC) solution at atmosphere pressure, a strong, uniform and defect-free polyamide selective layer is formed on the inner surface of hollow fiber membranes. The optimal TFC NF hollow fiber membranes in 1-inch modules exhibit a pure water permeability of 8.93 L m−2 h−1 bar−1 and a molecular weight cut-off (MWCO) of 175 Da. They also show a rejection of 98.3% to MgSO4 and a high rejection of around 98% to cephalexin (molecular weight = 437 g mol−1). The optimal membranes exhibit a consistent Na2SO4 rejection of ∼85% and nearly no NaCl rejection over a 30-day performance test using a high salinity feed solution containing 200 g/L NaCl and 10 g/L Na2SO4. The impressive performance suggests that the newly developed TFC NF hollow fiber membrane has great potential to be used in the chlor-alkali and pharmaceutical industries.

Two dimensional COFs as ultra-thin interlayer to build TFN hollow fiber nanofiltration membrane for desalination and heavy metal wastewater treatment

An ultra-thin interlayer of two-dimensional covalent organic frameworks (COFs) was in-situ formed on polysulfone hollow fiber (HF) substrate surface to manipulate the interfacial polymerization process for the construction of thin film nanocomposite (TFN) HF nanofiltration (NF) membrane with greatly improved separation performance. p-Phenylenediamine and 1,3,5-Triformylphloroglucinol monomers were used for constructing the COFs interlayer, piperazine and trimethyl chloride were used for the fabrication of the HF NF polyamide skin separation layer. A series of optimization of the membrane preparation conditions were carried out to achieve the good separation performance. The results demonstrated that the two-dimensional COFs nanomaterials could effectively control the pore size distribution and hydrophobicity of the HF substrate surface, realize a uniform distribution of piperazine on the interlayer surface, thus effectively manipulate the interfacial polymerization process. Under the optimal conditions, the rejections of Na2SO4, Cr2(SO4)3, CuSO4, ZnSO4 and MnSO4 can achieve 96.6 %, 95.4 %, 94.3 %, 91.7 % and 91.0 %, respectively, and the water permeance reaches 86.6 L m−2 h−1 MPa−1. Meanwhile, the fabricated TFN HF NF membrane shows good long-term stability, fouling resistance, acid and alkali resistance, as well as chlorine resistance, providing its vast potential for application in desalination and heavy metal wastewater treatment.

Hollow fiber nanofiltration membranes for surface water treatment: Performance evaluation at the pilot scale

Four types of hollow fiber nanofiltration membranes were fabricated and tested during pilot scale treatment of surface water taken from Istanbul Ömerli Lake Reservoir. Membrane types included: polymer thin film composite, reinforced thin film composite, TiO2-polymer thin film nanocomposite, and Aquaporin-polymer reinforced thin film composite. Interfacial polymerization procedure was used to form the polyamide separation layer for all membrane types. The amount of permeate water collected from membranes was controlled by membrane fouling. In terms of productivity, the membranes were ranked as follows: reinforced Aquaporin membrane (6.30 L/m2/h) > TiO2 incorporated membrane (5.69 L/m2/h) > reinforced thin film composite membrane (4.76 L/m2/h) > polymeric thin film composite membrane (3.24 L/m2/h). TiO2-incorporated membranes had the highest initial flux while reinforced thin film composite membranes had the highest removals for each water constituents tested (MgCl2, tannic acid, synthetic lake water, pre-filtered lake water). The study points to the practicability and promise of hollow fiber nanofiltration membranes for surface water treatment applications.

Designing scalable dual-layer composite hollow fiber nanofiltration membranes with fully cross-linked ultrathin functional layer

The treatment of industrial wastewater containing complex foulants demands high efficiency yet cost-effective separation process. The composite hollow fiber nanofiltration membranes suffer from tedious fabrication procedures, impeding the large volume fabrication and application. Herein, we reveal a very simplified designing strategy by polyelectrolyte modification of the co-extruded polyimide/polyethersulphone dual-layer hollow fibers with hierarchical structure and chemistry. The active layer's thickness of the dual-layer hollow fiber substrate is only 800 nm, the thinnest in literature. Compared to integral active single layer hollow fiber, the ultrathin active layer not only leads to over 4 times increase in mechanical flexibility and tenfold reduction in material cost but also enables fully chemical transition from imide to cross-linked polyamide, minimizing the intrinsic hydrolysis tendency of active material. The optimized membranes with a well-defined pore radius of 0.23 nm have 93–95% rejection to Mg2+ and Ca2+ and PWP of 9.1 LMH/bar. Moreover, the composite membranes exhibit backwash ability and stability in the heated feed solutions, which meets the demand for direct treatment of industrial effluents. This work paves the way for the large volume fabrication and application of hollow fiber nanofiltration membranes for treating municipal water, industrial wastewater, and other applications.

Bridging the gap between lab-scale and commercial dimensions of hollow fiber nanofiltration membranes

The development of nanofiltration membranes with hollow fiber geometry is a relatively young field of research in membrane science with only limited, but quickly growing, availability on a commercial scale. These membranes offer promising properties for application in water treatment such as high fouling resistance and low cost compared to Reverse Osmosis membranes. Major differences are found in dimension and operating conditions of hollow fiber nanofiltration membranes used in academia and on an industrial scale. To allow for adequate comparison and prediction of membrane performance, the effect of fiber dimension and operating conditions on process performance needs to be properly understood. A systematic experimental study on MgSO4 retention by hollow fiber nanofiltration membranes was performed to investigate the effect of fiber length and operational conditions on membrane performance. A significant drop in the retention of MgSO4 was observed for 1.5 m long fibers in flux ranges of 20 LMH when reducing crossflow velocity to 0.1 m/s. Transport models were used to describe and predict this behavior. We show that the commonly used mass transport models under predict this decrease in retention. Using different theoretical transport models for the hollow fiber feed phase and reducing dimensional resolution from 2D to 1D and 0D allows for the identification of limitations of the commonly applied analytical mass transfer correlations. To accommodate for this discrepancy found between experimental results and model predictions, a correction factor was derived using the 2D model to specifically account for deviations of these correlations at high permeate recovery values. Our newly developed model makes it possible to accurately predict full scale membrane performance solely based on measured done on small scale membranes, an important precondition for the further development of dense hollow fiber based membranes and processes.

High-Flux Fine Hollow Fiber Nanofiltration Membranes for the Purification of Drinking Water

High-flux fine hollow fiber nanofiltration (HFNF) membranes were prepared by interfacial polymerization (IP) using polysulfone (PSF) ultrafiltration (UF) membranes with an outer diameter of 425 μm ...

Removal of pharmaceuticals and personal care products (PPCPs) and environmental estrogens (EEs) from water using positively charged hollow fiber nanofiltration membrane.

Nanofiltration (NF) membranes show great potential for advanced water treatment, especially for trace organic pollutant removal. The removal efficiency of pharmaceuticals and personal care products (PPCPs) and environmental estrogenic hormones (EEHs) by positively charged hollow fiber NF membranes (PEI-NF) were evaluated. The separation properties were evaluated by changing the operating pressure, temperature, ionic strength, and cation species. A relationship between the physicochemical characteristics of the pharmaceuticals and the NF membrane retention behavior was established. The results showed that the rejection rates of the PEI-NF membrane for the selected PPCPs and EEHs ranged from 81 to ~ 91.26%. For positively (negatively) charged pharmaceutical molecules, the electrostatic repulsion (attraction) effect and steric hindrance were the dominant rejection mechanisms of the PEI-NF membrane. For neutral pharmaceutical molecules, in addition to the size sieving effect, the hydration-induced size increase of hydrophilic substances improved the rejection rates. Both the molecular structure and diffusion coefficient of pharmaceutical molecules influenced their rejection by the PEI-NF membrane to a certain extent. Moreover, the PEI-NF membrane showed a high removal effect for PPCPs and EEHs in water samples from actual tap water plants.

Ionic and pH responsive thin film composite hollow fiber nanofiltration membrane for molecular separation

Ionic and pH responsive thin film composite (TFC) membrane is prepared by interfacial polymerization of lysine and trimesoyl chloride on the out surface of poly (m-phenylene isophthalamide) hollow fiber membrane. Hydrophilicity and strong negative charge of the TFC membrane are obtained by introducing a large amount of carboxylic groups in the cross-linked polyamide network, endorsing the ionic and pH response of the TFC membrane in terms of flux and rejection. The TFC membrane shows almost 100% rejection for Eriochrome black T, with a flux of 35.8 L/m2h (0.2 MPa) at low pH and salt concentration. However, the rejection decreases to 95.8%, and the flux increases more than three times at high pH and salt concentration due to the shift of the interaction in the polyamide network from hydrogen bonding to static-electric repulsion. The responsive TFC membrane also shows great performance in separation of dye-salt mixture and dye mixture.

Green preparation of polyvinylidene fluoride loose nanofiltration hollow fiber membranes with multilayer structure for treating textile wastewater

In this work, polyvinylidene fluoride (PVDF) loose nanofiltration (NF) hollow fiber membranes with multilayer structure were prepared successfully based on a solvent-free process. Graphene oxide (GO) was used to cover the interface pores of the pristine PVDF membranes via vacuum filtration, and polypyrrole (PPy) was polymerized on the surface to further decorate the membrane structure. Interestingly, the modified membranes exhibited a multilayer structure due to synergistic effect of GO and PPy. The structure and property of PVDF loose NF membranes were investigated in detail. After modifying by GO and PPy, the hydrophilicity improved obviously. Moreover, the molecular weight cut off (MWCO) was about 3580 Da, and the smallest pore size of skin layer decreased to 2.5–4 nm. Furthermore, the PVDF loose NF hollow fiber membranes presented a high dye rejection (˃98.5%) for negative dyes, whereas a low salt rejection for NaCl (about 4%), showing a great potential for separating dye/salt accurately. Specifically, there were not any solvent used in all the preparation processes. The work offered a novel strategy for green preparation of loose NF membranes.

High-performance positively charged hollow fiber nanofiltration membranes fabricated via green approach towards polyethyleneimine layer assembly

In this study, high performance positively charged hyper-branched polyethyleneimine (PEI) nanofiltration (NF) layer was assembled successfully on negatively charged polyethersulfone/polyimide (PES/PI) hollow fiber ultrafiltration (UF) membranes under different conditions. In accordance with principles of green chemistry, glutaraldehyde (GA) as cross-linker and purely aqueous solutions were used as a less hazardous alternative compared to, e.g. trimesoyl chloride in an organic solvent. The effects of the surface roughness and charge of the substrate UF membranes, due to the presence of PI, and various fabrication conditions, such as pH of PEI aqueous solution, GA/PEI ratio and crosslinking reaction time, were investigated and discussed. Electron microscopy images revealed the successful assembly of the PEI NF layer at uniform coverage of the PES/PI UF membranes. It was found that the varied preparation conditions drastically affect the membrane surface hydrophilicity, surface zeta potential, permeation flux, and salt rejection. The membrane fabricated at optimum conditions had a molecular weight cut-off of ≤ 400 Da; steric hindrance and Donnan exclusion resulted to achieve salt rejections of 94.2% and 87.4% for MgCl2 and MgSO4, respectively. Moreover, fabricated membranes were tested through three cycles of six-hour filtrations and over 95% flux recovery after the filtration of salts via the backwashing process was recorded.

Preparation and properties of hollow fibre nanofiltration membrane with continuous coffee-ring structure

Polyamide (PA) hollow fibre composite nanofiltration (NF) membranes with a coffee-ring structure and beneficial properties were prepared by adding graphene oxide (GO) into the interfacial polymerization process. The presentation of the coffee-ring structure was attributed to the heterogeneous, finely dispersed multiphase reaction system and the “coffee-stain” effect of the GO solution. When the piperazine concentration was 0.4 wt-%, the trimesoyl chloride concentration was 0.3 wt-%, and the GO concentration was 0.025 wt-%, the prepared NF membranes showed the best separation properties. The permeate flux was 76 L·m−2·h−1, and the rejection rate for MgSO4 was 98.6% at 0.4 MPa. Scanning electron microscopy, atomic force microscopy, and attenuated total reflectance-Fourier transform infrared spectroscopy were used to characterize the chemical structure and morphology of the PA/GO NF membrane. The results showed that GO was successfully entrapped into the PA functional layer. Under neutral operating conditions, the PA/GO membrane showed typical negatively charged NF membrane separation characteristics, and the rejection rate decreased in the order of Na2SO4 > MgSO4 > MgCl2 > NaCl. The PA/GO NF membrane showed better antifouling performance than the PA membrane.

Graphene oxide interlayered thin-film nanocomposite hollow fiber nanofiltration membranes with enhanced aqueous electrolyte separation performance

In this study, a kind of thin-film nanocomposite (TFN) hollow fiber nanofiltration (NF) membranes was fabricated via incorporating graphene oxide (GO) interlayer using the interfacial polymerization (IP) reaction between piperazine (PIP) and trimesoyl chloride (TMC). The surface morphology and cross-sectional structure of the fabricated TFN hollow fiber NF membrane were extensively investigated. The effects of the PIP concentration, species of the aqueous additives, and the GO loading on the structure and performance of the hollow fiber NF membrane were also investigated in detail and the optimal preparation conditions were achieved. Fourier transform infrared spectroscopy (FTIR) confirmed the successful introduction of the GO interlayer into the composite hollow fiber NF membrane. Moreover, the incorporation of GO interlayer helped to reduce the skin thickness of the composite hollow fiber NF membrane remarkably, and thus helped to increase greatly the water permeance while maintaining a high salt rejection. Under an optimal GO loading of 20.0 mg m−2, the TFN hollow fiber NF membrane achieved a water permeance of 80 L m−2 h−1 MPa−1 and a Na2SO4 rejection of 96.1% for 2000 mg L−1 aqueous Na2SO4 solution, much higher than the interlayer-free thin-film composite (TFC) membrane. Meanwhile, the TFN hollow fiber NF membrane showed an excellent selectivity of Na2SO4 over NaCl, as well as good fouling resistance and long-term stability, demonstrating the vast potential in application for the selective separation of monovalent salt and divalent salt.

Bridging the miscibility gap to fabricate delamination-free dual-layer nanofiltration membranes via incorporating fluoro substituted aromatic amine

Delamination of the dual-layer membrane fabricated from immiscible polymers is recognized as the main obstacle to advance the technology. The current work discloses an innovative approach to address the delamination issue by incorporating specific functional groups on the polymer chains. Delamination-free P84®/Ultem® dual-layer hollow fiber nanofiltration membranes were obtained by incorporating 4-Fluoro-2-(trifluoromethyl) benzylamine (FTB) in P84® polyimide. The progressively incorporated FTB on P84® decreases solubility parameter difference and establishes specific intermolecular interactions between the polymer pair which contributes to the interpenetration of molecules at the interfacial region of the dual layers. The interpenetrated network structure at the interfacial region renders the robust integrity of the dual-layer membranes. The one-step fabricated membranes had an over 99% rejection of tetracycline (MW: 444.4 Da) in methanol with pure methanol permeance of 3.7 LMH/bar. The elaborated mechanism may potentially enlarge the scope of selecting immiscible polymers for fabricating dual-layer membranes by molecular designing.

Recovery and purification of potato proteins from potato starch wastewater by hollow fiber separation membrane integrated process

Potato starch wastewater contains high-concentration potato proteins which have great potential in the fields of food and health care. Most researches on potato protein recovery by membrane separation technique are focused on flat sheet or tubular ultrafiltration (UF) and reverse osmosis (RO) membranes and lack the further protein purification and the in-depth discussions on the fouling behavior. In this laboratory-scale study, potato proteins were recovered and purified from the simulated potato starch wastewater by the self-made hollow fiber (HF) UF and nanofiltration (NF) separation membrane integrated process. 85.62% potato proteins with high molecular weight in the potato starch wastewater could be retained by UF membrane and 92.1% potato proteins with low molecular weight were rejected by NF membrane. The concentrated solution after UF and NF filtration was desalinated and purified by diluting the solution eight times and filtering the diluted solution with UF membrane. Both types of HF membranes, UF and NF, suffered the inevitable membrane fouling. After the traditional physical washing and chemical cleaning, water flux of UF and NF membranes can be effectively recovered. The corresponding recovery rates of UF and NF membranes can reach 93.5% and 84.7%, respectively. The hollow fiber UF-NF separation membrane integrated process was proved to be a promising technique of high-purity potato protein recovery from potato starch wastewater.

Design of nanofiltration (NF) hollow fiber membranes made from functionalized bore fluids containing polyethyleneimine (PEI) for heavy metal removal

Effective methods are still lacking for large-scale production of thin-film composite (TFC) hollow fiber membranes made from interfacial polymerization. It is the bottleneck limiting the scale-up of TFC nanofiltration (NF) hollow fiber membranes for wastewater treatments. This study fills the niche in NF hollow fiber production by simplifying the interfacial polymerization process while maintaining the membrane's salt rejection. By blending sulfonated polysulfone (SPSf) in the polyethersulfone (PES) dope solution and using polyethyleneimine (PEI) in the bore fluid for hollow fiber production, amine groups are actively introduced onto membranes. The amine groups can be further modified with various molecules, for instance, poly(acrylic acid) (PAA), glutaraldehyde (GA) and 1,3,5-benzebetricarbonyl chloride (TMC), resulting in precisely designed membranes suitable for heavy metal removal. The best membrane formed in this study has a small mean effective pore size (μp) of 0.57 nm, a molecular weight cut-off (MWCO) of 157 Da and a good pure water permeability (PWP) of 5.14 LMH/bar. It also has over 90% rejections of heavy metal ions, such as Ni2+, Zn2+ and Cu2+. The membrane displays good performance stability in a continuous 96-h operation and in acid washes. The study may provide useful insights in designing TFC NF hollow fiber membranes that are suitable for large-scale production.