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Osmotically assisted reverse osmosis (OARO) has become an emerging membrane technology to tackle the limitations of a reverse osmosis (RO) process for water desalination. A strong membrane that can withstand a high hydraulic pressure is crucial for the OARO process. Here, we develop ultra-strong polymeric thin film composite (TFC) hollow fiber membranes with exceptionally high hydraulic burst pressures of up to 110 bar, while maintaining high pure water permeance of around 3 litre/(m2 h bar) and a NaCl rejection of about 98%. The ultra-strong TFC hollow fiber membranes are achieved mainly by tuning the concentration of the host polymer in spinning dopes and engineering the fiber dimension and morphology. The optimal TFC membranes display promising water permeance under the OR and OARO operation modes. This work may shed new light on the fabrication of ultra-strong TFC hollow fiber membranes for water treatments and desalination. Osmotically assisted reverse osmosis can overcome limitations of the reverse osmosis process but a strong membrane which can withstand a high hydraulic pressure is crucial. Here, the authors develop strong polymer thin film composite hollow fiber membranes with exceptionally high hydraulic burst pressures of up to 110 bar, while maintaining high water permeance and salt rejection. [ABSTRACT FROM AUTHOR]

Abstract Design and fabrication of solvent resistant hollow fiber membranes with great mechanical and thermal stability are highly demanded for sustainable manufacturing in chemical and pharmaceutical industries. Herein, we propose a facile and novel acid doping procedure to synthesize highly stable and selective polybenzimidazole (PBI) hollow fibers for organic solvent nanofiltration for the first time. PBI hollow fibers were spun through a dry-jet wet-spinning method. Subsequently, the hollow fibers were acid doped with a 2 wt% H 2 SO 4 solution so that the acid molecules form hydrogen bonds with the PBI backbone and build an integrated structure which becomes insoluble in organic solvents. Comprehensive characterizations were conducted to study the impact of acid doping on PBI hollow fibers. The acid doping not only reduced the molecular weight cut off (MWCO) of the fibers from 2000 g mol‒1 to 500 g mol‒1 but also significantly enhanced their chemical and mechanical stability, as well as flexibility. In addition, for the first time, the conventional solute‒rejection experiments utilized to determine the MWCO and pore size distribution of membranes in aqueous solutions were modified to estimate them in organic solvents. By using tetracycline/methanol and L-α-lecithin/hexane mixtures as feeds, the newly developed PBI hollow fibers showed rejections of > 98% and permeances of 3.5 and 7.1 L m−2h−1bar−1 towards methanol and hexane, respectively. Therefore, they have great potential for solvent recovery in food and pharmaceutical industries. Highlights • Robust and uniform PBI hollow fiber membranes are produced. • MWCO and pore size distribution of HFMs are calculated in various solvents. • Acid doping technique increases the size sieving ability and chemical stability of HFMs significantly. • Newly developed HFMs show superior performance for food and pharmaceutical applications. [ABSTRACT FROM AUTHOR]

Water vapor in humid air and industrial gases needs to be removed for various applications such as air conditioning, foodstuffs storage, aviation and space flights. Membranes can remove water vapor from gas streams without involving phase change and regeneration. A robust and productive membrane is vital for water vapor removal but it is challenging to produce it. Here we present a defect-free thin film composite (TFC) polydimethylsiloxane (PDMS)/polyacrylonitrile (PAN) hollow fiber membrane with an ultrathin PDMS selective layer of about 260 nm. Different from previous works, the PAN substrate was spun at a high take-up speed of 60 m/min. It has an average of surface pore size of 5.6 nm and superior mechanical properties. After the optimal PDMS coating, the composite membrane shows a N 2 permeance of about 280 GPU, an O 2 /N 2 selectivity of 2.2 and a water vapor permeance ranging from about 800 to 3700 GPU depending on operation conditions. In addition, the PDMS/PAN composite membrane has been tested for 48-hour outer door dehumidification and shown very stable and robust performance with a water vapor removal rate of 65% from the humid air. Besides, the PDMS/PAN composite membrane is not only able to efficiently dry the humid biogas but also upgrade its methane content simultaneously. Therefore, the newly developed TFC composite membrane has great potential for water vapor removal from humid air and various gas streams. [ABSTRACT FROM AUTHOR]

Robust P84 and NH 2 -MWCNT/P84 hollow fiber membranes have been designed by adjusting spinning parameters and then crosslinking them by 1,6-hexanediamine to achieve desirable separation performance for organic solvent nanofiltration (OSN). A weak bore fluid, an adequately high dope flow rate and a small air gap length were required to produce the desired hollow fiber membranes. Compared the neat P84 hollow fiber, the addition of NH 2 -MWCNTs into P84 resulted in an amidation reaction between the imide groups of P84 and the amine groups of NH 2 -MWCNTs, leading to greater mechanical properties and thermal stability as well as higher dope viscosity. Moreover, NH 2 -MWCNT/P84 hollow fibers exhibited great permeances of 4.31, 2.26, 1.45, and 1.17 LMH/bar for acetone, methanol, ethyl acetate, and ethanol, respectively, while having smaller pore sizes with notable rejections. The crosslinked P84 and NH 2 -MWCNT/P84 membranes showed extraordinary rejections of 97.2, and 99.8% to methylene blue (320 g/mol), respectively. Also, the newly developed hollow fibers demonstrated great potential for separating tetracycline/IPA, L-α-lecithin/hexane, and BINAP-Ru(II)/methanol solutions, representing their applicability in the pharmaceutical, food, and petrochemical industries. [ABSTRACT FROM AUTHOR]

Compared to cellulose acetate, silicon rubber, polysulfone, and polyimide, polyethersulfone (PESU) has received much less attention as a commercially viable material for gas separation membranes. This is because PESU has issues of low permeability but rapid physical aging behavior that limit its asymmetric hollow fiber membranes for gas separation applications. To overcome it, a new PESU was synthesized by replacing one diphenyl sulfone unit in the main chains with a bulky and rigid 1,2,4-trimethylbenzene moiety so that the new PESU (referred to as poly trimethyl phenylene ethersulfone (TPESU)) has a greater permeability and less aging behavior. The hollow fiber membranes spun from TPESU dopes exhibit excellent gas separation performance with significantly less aging phenomena. Not only do they have superior O 2 and CO 2 permeance of 16 GPU and 85.1 GPU, respectively, but also possess O 2 /N 2 , CO 2 /N 2 and CO 2 /CH 4 selectivity of 6.5, 34.0 and 35.5, respectively at 25 °C. The pure gases are tested at 3.5 atm except CO 2 at 1 atm. The newly developed TPESU hollow fiber membrane has comparable gas separation performance with those fibers spun from Matrimid. The newly designed TPESU may have great potential as a membrane material for oxygen enrichment, natural gas separation and CO 2 capture. [ABSTRACT FROM AUTHOR]

Abstract: In order to make membrane separation technologies more cost‐competitive with the well‐established processes that are energy intensive for gas/vapor separation, a defect‐free membrane with a high gas permeance is necessary. However, it remains challenging to meet these needs because of the difficulties in developing a suitable material and process that are economical and practical. Herein, a novel and straightforward strategy is presented to produce a defect‐free hollow fiber composite membrane using a highly crosslinked polydimethylsiloxane (PDMS) synthesized by using a postcrosslinking method. The PDMS can be directly coated on a polyacrylonitrile (PAN) membrane substrate, and the resultant PDMS/PAN composite membrane has ultrahigh C3H8 and C3H6 permeances that are higher than 10 000 and 11 000 GPU, respectively, and the corresponding permselectivity of C3H8/N2 and C3H6/N2 are about 21 and 24, respectively. The newly developed methods and materials may open up a new cost‐effective method to fabricate next‐generation composite membranes for the recovery of hydrocarbons, organic vapors, and gases. [ABSTRACT FROM AUTHOR]

The aim of this work is to introduce a new post modification method for polymeric hollow fiber membranes with much-enhanced separation performance for pervaporation dehydration of isopropanol. An ultrathin two-dimensional (2D) ammonia functionalized graphene oxide (NHGO) was vacuum deposited on the shell side of P84 hollow fibers to seal defects without much increasing the overall mass transport resistance. The separation factor of the treated fibers in NHGO solutions for 5 min increased by more than 4 times with a small flux reduction compared to the original fibers. In addition, annealing fibers at low temperatures after the 2D modification further improved separation factor and increased fibers’ long-term stability. For example, a P84 fiber treated for 5 min in NHGO and then annealed at 100 °C exhibited excellent performance. It had a flux of 1914 g m −2 h −1 and a water purity of 99.1% (i.e., a separation factor of 624). These superior properties may arise from three factors: (1) the simultaneous amidation reaction between the polymer matrix and the 2D particles effectively sealed the membrane defects and covalently bonded 2D particles on the surface; (2) the densification of the selective layer during annealing not only increased its selectivity but also reduced membrane swelling; and (3) the partial reduction of certain functional groups of the 2D particles during annealing regulated the pathway for water transport and produced a balanced membrane structure. [ABSTRACT FROM AUTHOR]

Recent development of high performance membranes and advanced modeling have moved the pressure retarded osmosis (PRO) technology closer to commercialization. Nevertheless, a PRO model, that combines the aforementioned two aspects for mathematical quantification and comprehensive assessment of the multi-configured membranes, is still lacking. For the first time, we build a universal platform to analytically evaluate the mass transport of various membrane configurations (i.e., flat sheet (FS), single- and double-skinned hollow fibers (HFs)) for PRO processes. The FS model is found to be applicable for single-skinned HF membranes under laboratory testing conditions. The HF curvature effect needs to be removed when comparing the experimentally determined structural parameter among different membrane configurations. For the double-skinned HF membrane particularly of antifouling interest, the high pressure applied in the fiber lumen side deteriorates the transport properties of its additional skin on the shell side. By considering the foulant build-up as an external cake layer, the advantages of the double-skinned configuration can be mathematically confirmed than the single-skinned one when fouling occurs. [ABSTRACT FROM AUTHOR]

PVDF hollow fiber membranes with a unique sandwich structure and superior wetting resistance have been designed for vacuum membrane distillation (VMD) of seawater desalination in this study. The sandwich structure consists of two sponge-like inner and outer porous layers and a thin middle layer full of small-size macrovoids. The sponge-like structure in the two porous layers is specially designed because it enhances the mechanical strength of hollow fibers with high wetting resistance. This structure is derived from the spinodal liquid-liquid decomposition during phase inversion. Meanwhile, the middle layer of macrovoids is beneficial for VMD flux because they perform as highways for water transport. Comparing to the large size macrovoids, the small-size macrovoids in PVDF hollow fibers are preferred for VMD applications because they would not significantly reduce the membrane mechanical strength. As a result, the newly developed membranes possess impressively high liquid entry pressures (LEPs) of > 3 bar. This study may provide valuable guidelines in designing next generation PVDF hollow fiber membranes for practical VMD applications. [ABSTRACT FROM AUTHOR]

Dual-layer hydrophobic/hydrophilic PVDF/Ultem® hollow fiber membranes with superior mechanical and water transport properties have been prepared via co-extrusion method for vacuum membrane distillation (VMD) of seawater. To fabricate such high-performance dual-layer hollow fibers consisting of two different materials, one must overcome the issues of delamination between the two polymer layers and dense interface morphology. The former would result in a defective membrane, while the latter could significantly increase the substructure resistance for vapor transport. By properly manipulating dope formulation and spinning conditions, we have overcome the first challenge and produced delamination free dual-layer fibers. The second problem is resolved by the addition of Al 2 O 3 nanoparticles into the inner layer dope, which creates micro-porosity on the outer surface of the inner layer. The resultant dual-layer fibers show good mechanical properties, permeation flux and wetting resistance simultaneously under VMD operations. Comparing to the conventional single layer MD fibers, the newly developed VMD hollow fiber containing 15 wt% Al 2 O 3 has 4.5- fold tensile strength (i.e., about 350% increment) with a VMD flux of 45.8 kg/m 2 -h at 70 °C. This study may provide valuable guidelines in designing superior dual-layer PVDF membranes for practical VMD applications of seawater desalination. [ABSTRACT FROM AUTHOR]

High-temperature vapor permeation has a stringent requirement of membrane stability under harsh feed environments. This work reports the design of Teflon AF2400/Ultem composite hollow fiber (HF) membranes for alcohol dehydration via vapor permeation. Fabrication parameters such as Teflon concentration and coating time were systematically investigated. Interestingly, the fabricated composite HF membranes possess an unusual surface with honeycomb-like microstructure patterns. Owing to the Teflon protective layer, the newly developed composite HF shows a promising and stable separation performance with a flux of 4265 gm−2 h−1 and a separation factor of 383 for 95% isopropanol dehydration at 125°C. The composite HF also performs well under extreme vapor feed compositions from 87 to 99 wt % isopropanol. In addition, it exhibits impressive separation performance for the dehydration of ethanol and n-butanol. This work may provide useful insights of designing thermal-stable and high-performance composite polymeric membranes for vapor permeation. © 2016 American Institute of Chemical Engineers AIChE J, 62: 1747-1757, 2016 [ABSTRACT FROM AUTHOR]

• Cup-like SCA4 and STCAss molecules were incorporated into the polyamide network. • Both cup-like calixarenes effectively reduced the reverse solute flux and improved the selectivity of PRO membranes. • 1-inch TFN hollow fiber membrane modules were fabricated for PRO. • The SCA4 incorporated membrane was more efficient in maintaining power density in long-term PRO tests. Osmotic energy is released when mixing solutions with different salinities. Pressure retarded osmosis (PRO) is a promising membrane technology to harvest this osmotic energy. However, the current polymeric PRO membranes suffer from the high reverse solute fluxes during PRO processes, which would dramatically diminish the membrane performance, especially in big membrane modules. In order to control the reverse solute flux, two cup-like calix[ n ]arenes, sulfocalix[4]arene (SCA4) and sulfothiacalix[4]arene (STCAss) were incorporated into the polyamide network to enhance the PRO performance of thin-film nanocomposite (TFN) hollow fiber membranes in 1-inch modules. Due to the unique structures and the enhanced molecular-sieving abilities of both macrocyclic molecules, they were able to effectively improve the selectivity of the resultant TFN hollow fiber membranes. After optimizing the concentration of each nano-filler, it was found that the TFN membrane with 0.20 wt% of STCAss produced a PRO power density of 15.0 W/m2 and a reverse salt flux of 28.3 gMH, while the other containing 0.10 wt% of SCA4 produced a PRO power density of 14.2 W/m2 and a reverse salt flux of 31.6 gMH. In long-term PRO tests at 20 bar, the SCA4-incorporated membrane was more efficient in controlling the concentration polarization (CP) and maintaining the power density comparing to the STCAss membrane because the former has a smaller cavity opening than the latter. This research work may provide useful insights to further design PRO membranes and membrane modules for osmotic power generation. [ABSTRACT FROM AUTHOR]

Outer-selective thin-film composite (TFC) hollow fiber membranes offer advantages like less fiber blockage in the feed stream and high packing density for industrial applications. However, outer-selective TFC hollow fiber membranes are rarely commercially available due to the lack of effective ways to remove residual reactants from fiber's outer surface during interfacial polymerization and form a defect-free polyamide film. A new simplified method to fabricate outer-selective TFC membranes on tribore hollow fiber substrates is reported. Mechanically robust tribore hollow fiber substrates containing three circular-sector channels were first prepared by spinning a P84/ethylene glycol mixed dope solution with delayed demixing at the fiber lumen. The thin wall tribore hollow fibers have a large pure water permeability up to 300 L m−2 h−1 bar−1. Outer-selective TFC tribore hollow fiber membranes were then fabricated by interfacial polymerization with the aid of vacuum sucking to ensure the TFC layer well-attached to the substrate. Under forward osmosis studies, the TFC tribore hollow fiber membrane exhibits a good water flux and a small flux difference between active-to-draw (i.e., the active layer facing the draw solution) and active-to-feed (i.e., the active layer facing the feed solution) modes due to the small internal concentration polarization. A hyperbranched polyglycerol was further grafted on top of the newly developed TFC tribore hollow fiber membranes for oily wastewater treatment. The membrane displays low fouling propensity and can fully recover its water flux after a simple 20-min water wash at 0.5 bar from its lumen side, which makes the membrane preferentially suitable for oil-water separation. © 2015 American Institute of Chemical Engineers AIChE J, 61: 4491-4501, 2015 [ABSTRACT FROM AUTHOR]

Dual-layer hollow fiber membranes were produced from blends of Ultem and polymer of intrinsic microporosity (PIM-1) with enhanced gas permeance. The effects of spinning parameters (take-up speed and air gap distance) on gas separation performance were investigated based on the pristine Ultem. Selected spinning conditions were further adopted for the blend system, achieving defect-free and almost defect-free hollow fibers. Adding PIM results in a higher fractional free volume, 50% increments in gas permeance were observed for Ultem/PIM-1 (95/5) and more than 100% increments for Ultem/PIM-1 (85/15). Both O2/N2 and CO2/CH4 selectivities remained the same for Ultem/PIM-1 (95/5) and above 80% of their respective intrinsic values for Ultem/PIM-1 (85/15). The selective layer thickness ranges from 70 to 120 nm, indicating the successful formation of ultrathin dense layers. Moreover, minimum amounts of the expensive material were consumed, that is, 0.88, 1.7, and 2.3 wt % PIM-1 for Ultem/PIM-1 (95/5), (90/10), and (85/15), respectively. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3848-3858, 2014 [ABSTRACT FROM AUTHOR]

Highlights: [•] Novel thin-film composite (TFC) hollow fiber membranes are molecularly designed and developed. [•] The membrane supports achieve superior tolerance to high pressures up to 23bar. [•] The TFC membranes perform well in pressure retarded osmosis (PRO) process. [•] The effect of flow rate on PRO was investigated for the first time. [Copyright &y& Elsevier]

Abstract: In this study, the development of thin film composite (TFC) pervaporation hollow fiber membranes for biofuel dehydration at high fluxes is presented. The novel membranes consist of a thin selective polyamide layer formed by interfacial polymerization onto a porous polyethersulfone (PES) hollow fiber support that is free of macrovoids. This membrane support was fabricated using the dual-layer co-extrusion technology to design and effectively control the phase inversion during the membrane formation. The macrovoid-free and highly porous morphology of the membrane support is desirable. Not only does it provide excellent membrane strength, but also minimize the mass transfer resistance encountered during the pervaporation process, thus enhancing the total flux. The effects of key fabrication parameters such as drying methods of hollow fiber supports, interfacial polymerization conditions including heat treatment, different alcohols and water as cleaning solvents on membrane formation, membrane morphology and pervaporation performance of the resultant TFC membranes are systematically investigated and elucidated. The surface modification of the TFC membranes with polydopamine or silicone rubber coatings is proposed to simply and effectively enhance the membrane selectivity. The polydopamine-coated and silicone rubber-coated TFC membranes exhibit water separation factors of up to 51 and 60, with substantial high fluxes of 6.6 and 7.5kgm−2 h−1, respectively. The newly developed TFC hollow fiber membranes possess reasonably good selectivity/separation factors and superior permeation fluxes in comparison with most polymeric membranes that have been reported in the open literature. [Copyright &y& Elsevier]

A novel sulfonated polyphenylsulfone (sPPSU)/polyphenylsulfone (PPSU)-based dual-layer hollow fiber membrane with a nanometric thin skin layer has been designed for biofuel dehydration via pervaporation. The thickness of skin selective layer is in the range of 15-90 nm under different spinning conditions measured by positron annihilation spectroscopy (PAS) coupled with a mono-energetic positron beam. The effects of outer-layer dope properties, coagulation temperature, and dope flow rate during spinning were systematically investigated. By tuning these spinning parameters, a high performance sPPSU/PPSU-based dual-layer hollow fiber membrane with desirable morphology was successfully obtained. Particularly owing to its nanometric thin skin layer, a high flux of 3.47 kg/m2h with a separation factor of 156 was achieved for dehydration of an 85 wt % isopropanol aqueous solution at 50°C. After post thermal treatment at 150°C for 2 h, the separation factor was dramatically improved to 687 while flux dropped to 2.30 kg/m2h, which make it comparable to the inorganic membranes. In addition, excellent correlations were found among the results from field emission scanning electron microscopy, PAS spectra, and separation performance. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2943-2956, 2013 [ABSTRACT FROM AUTHOR]

The immiscibility induced phase separation (I2PS) process was introduced as a novel method to fabricate hollow fibers with exceptionally high water permeance and reasonably high water/ethanol selectivity in dehydration of ethanol by pervaporation. As a continuation of the previous work, this study discloses the mechanisms to enhance the performance of hollow fibers spun via I2PS by elucidating the material selection at the inner-layer. Moreover, it revealed the methods to reduce mass-transport resistance by enhancing surface porosity for both inner and outer surfaces to further improve the permeation flux of the membranes. The continuous performance test demonstrates that the fibers spun from the I2PS possess a stable dehydration performance throughout the monitored period of 300 h. A comparison with pervaporation membranes in the literatures verifies the superiority of the membranes spun via I2PS process with the highest water permeation flux of 9.5 kg/m2 h and the permeate water purity of 95.8 wt % at 80°C. © 2013 American Institute of Chemical Engineers AIChE J, 59: 3006-3018, 2013 [ABSTRACT FROM AUTHOR]

Abstract: This study discloses the critical factors that result in the low osmotic efficiency in forward osmosis (FO). Specifically, dual-layer hollow fiber membranes are prepared with newly-synthesized cellulose acetate propionate (CAP) as the outer active layer and commercial cellulose acetate (CA) as the inner sublayer. By carefully analyzing the hollow fiber cross section images, the porosity of the sublayer is found to be nonuniformly distributed at different locations. Viewing the membrane matrix as three consecutive layers, i.e., the active layer, the sublayer and the interface between them, the draw solute concentration profiles within each layer, the osmotic pressure gradients across each layer, and the transport resistance of each layer are determined. One interesting observation is that the active layer of the CAP-CA hollow fibers creates much larger resistance than the interface and the sublayer, indicating that the low osmotic efficiency (i.e., low water flux) is mainly due to the low water permeability of the active layer while internal concentration polarization (ICP) within the sublayer is less important. For any membranes, the active layer–sublayer interface also creates certain transport resistance. These findings provide a valuable reference for the understanding of FO and the design of advanced FO membranes. [Copyright &y& Elsevier]

Abstract: This pioneer study discloses a novel immiscibility induced phase separation (I2PS) process to fabricate high performance dual-layer hollow fiber for dehydration of ethanol via pervaporation. The I2PS process takes the advantages of phase separation phenomena occurring in immiscible blend dopes made of incompatible polymers. The immiscible blend dopes were simultaneously extruded through a triple orifice spinneret and fabricated into dual-layer hollow fibers consisting of an outer protective layer and an inner selective layer. A dense selective layer is formed at the outer-surface of the inner-layer due to the incompatibility between the polymer solutions of both inner and outer-layers as well as the shielding effect of the outer protective layer that provides a sufficient time for the formation of an almost defect-free selective layer during the phase inversion process. It is found that the phase inversion kinetics of the outer-layer dope solutions as well as the nature of outer-layer materials play great roles in determining the morphology of the outer protective layers and subsequently affects the permeance of the resultant hollow fibers. On the other hand, the selectivity of the as-spun fibers was found to be controlled by the outer surface of the inner-layer. The novel dual-layer hollow fiber spun from the combination of cellulose triacetate (CTA) and Ultem® possesses a high water permeance (29.33mol/m2 hkPa) or water flux (1.77kg/m2h at 50°C) coupled with reasonable water/ethanol selectivity (824mol/mol) as compared to the pervaporation membranes available in the literatures. Heat treatment may enhance the selectivity of the aforementioned hollow fibers with some sacrifices of permeance. The present study may illuminate an innovative approach for hollow fiber fabrication in the future. [Copyright &y& Elsevier]

Abstract: Highly constrained by the requirements of high porosity and large pore sizes, traditional single-bore hollow fiber membranes often suffer from easy breakage and performance instability during long-term operations of membrane distillation (MD). In this work, a multi-bore PVDF hollow fiber (MBF) membrane with a lotus root-like geometry was designed and successfully fabricated via the specially designed spinneret and optimized spinning conditions. Various effects of spinning parameters including bore flowrate, dope flowrate and take-up speed were investigated on the membrane macro- and micro-structure, mechanical properties and direct contact membrane distillation (DCMD) performance. The tensile strength characterizations have proven the excellent mechanical rigidity and elasticity of MBF membranes. Even for the MBF membrane with a thin wall of around 40μm, the maximum load was as high as 2.4N. Most importantly, the performance of the DCMD of the MBF membrane was only slightly lower or even comparable to that of single-bore membranes. In addition, the MBF membranes exhibited superior stability in terms of vapor permeation flux and salt rejection during the continuous DCMD experiment with robust operational conditions. We believe this work may have profound implication to the development of mechanically durable membranes not only for membrane distillation MD but also for other membrane applications. [Copyright &y& Elsevier]

Abstract: We have designed and investigated hollow fiber membranes with various configurations and morphologies for water and salt recovery from highly concentrated sodium chloride (NaCl) via direct contact membrane distillation (DCMD) and crystallization. Three types of membranes were fabricated including single-layer polyvinylidene fluoride (PVDF), dual-layer hydrophobic–hydrophobic PVDF and dual-layer hydrophobic–hydrophilic PVDF/polyacrylonitrile (PVDF/PAN) membranes. Compared to dual-layer membranes, the single-layer PVDF membrane exhibited a superior wetting resistance as evidenced by its highest purity of product water (1.1–1.3μScm−1), smallest reduction of membrane permeability (17.7%), and almost complete recovery of membrane permeability after rinsing (99.1%). It was found that membrane pore size and morphology underneath the membrane surface play more important roles to mitigate membrane wetting as compared to membrane wall thickness. As a result, the single-layer membrane possessing a smaller pore size and a cellular mixed-matrix structure outperformed the dual-layer membranes with a globular morphology. The NaCl was recovered from the DCMD retentate solution by means of a cooling crystallizer operated under a batch mode. The supersaturated NaCl ions were uniformly configured into cubical shape crystals. Moreover, preliminary results revealed the feasibility of tailoring the ultimate crystal size distribution (CSD) by adjusting the degree of supersaturation of the crystallized solution through manipulation of the crystallizer cooling profile. [Copyright &y& Elsevier]

High-performance zeolitic imidazolate frameworks (ZIFs)/polybenzimidazole (PBI) nanocomposites are molecularly designed for hydrogen separation at high temperatures, and demonstrate it in a useful configuration as dual-layer hollow fibers for the first time. By incorporating as-synthesized nanoporous ZIF-8 nanoparticles into the high thermal stability but extremely low permeability polybenzimidazole (PBI), the resultant mixed matrix membranes show an impressive enhancement in H2 permeability as high as a hundred times without any significant deduction in H2/CO2 selectivity. The 30/70 ZIF-8/PBI dense membrane has a H2 permeability of 105.4 Barrer and a H2/CO2 selectivity of 12.3. This performance is far superior to ZIF-7/PBI membranes and is the best ever reported data for H2-selective polymeric materials in the literature. Meanwhile, defect-free ZIF-8-PBI/Matrimid dual-layer hollow fibers are successfully fabricated, without post-annealing and coating, by optimizing ZIF-8 nanoparticle loadings, spinning conditions, and solvent-exchange procedures. Two types of hollow fibers targeted at either high H2/CO2 selectivity or high H2 permeance are developed: i) PZM10-I B fibers with a medium H2 permeance of 64.5 GPU (2.16 ×10−8 mol m−2 s−1 Pa−1) at 180°C and a high H2/CO2 selectivity of 12.3, and, ii) PZM33-I B fibers with a high H2 permeance of 202 GPU (6.77 ×10−8 mol m−2 s−1 Pa−1) at 180°C and a medium H2/CO2 selectivity of 7.7. This work not only molecularly designs novel nanocomposite materials for harsh industrial applications, such as syngas and hydrogen production, but also, for the first time, synergistically combines the strengths of both ZIF-8 and PBI for energy-related applications. [ABSTRACT FROM AUTHOR]

Abstract: Operating conditions play a significant role in determining the separation performance of a pervaporation process, because they not only manipulate the driving forces to transport permeants but also affect the physicochemical properties of the pervaporation membrane itself. In this study, fundamental governing equations have been derived to correlate separation performance with system operation conditions and intrinsic separation characteristics of the pervaporation membrane. Polybenzimidazole/polyetherimide (PBI/PEI) dual-layer hollow fiber membranes were chosen to study the pervaporation dehydration of ethylene glycol (EG) under different testing protocols. The effects of operational parameters such as operation temperature, permeate pressure, feed composition and operation duration on performance indicators (flux and separation factor, permeance and selectivity) have been investigated. Experimental results show that an increase in operation temperature results in an increase in flux and selectivity, but a decrease in permeance and separation factor. In addition to other factors, decreasing sorption, less EG–water clusters and lower membrane-EG affinity with increasing temperature, play essential roles for the opposite trends. Both flux and permeance decrease with an increase in permeate pressure, while both separation factor and selectivity have an up-and-down trend. An increase in EG composition in the feed from 50 to 90wt.% results in a lower water flux and permeance, but EG flux and permeance first increase and then decrease. This is due to the combined effect of water-induced membrane swelling and the formation of an EG boundary layer upon the membrane surface. The long-term test up to 33 days proves the membrane durability for EG dehydration. This work may provide useful insights to pervaporation fundamentals, system design and scale up for the EG dehydration. [Copyright &y& Elsevier]

Abstract: We have demonstrated through experimental and theoretical study that membrane sublayer structure has significant influence on the performance in forward osmosis (FO) processes. Cellulose acetate (CA) hollow fiber membranes with different sublayer structures have been fabricated by varying the bore fluid composition during dry-jet wet spinning and then characterized in terms of pore structure of the selective layer, porosity of the sublayer, pure water permeability (PWP) coefficient, salt permeability coefficient and salt rejection. The water flux and reverse salt flux of these membranes are evaluated in the pressure-retarded osmosis (PRO) mode and FO mode. It is observed that varying the sublayer structure does not have apparent influence on the FO performance under the PRO mode but has significant influence on the performance under the FO mode. The different performance under different operation modes is resulted from more severe concentration polarization (CP) in the FO mode. The characteristics of the membrane sublayer structure are the origin of CP phenomenon in the FO mode. Through NF tests and FO tests with low draw solution concentrations on one of the membranes, the reflection coefficients (σ 0) are determined as 0.77 and 0.99 for NaCl and MgCl2 draw solutes, respectively. A low reflection coefficient indicates a low effective driving force in FO processes resulted from serious leakage of draw solutes from the draw solution to the feed. Thus, the reflection coefficient cannot be assumed to be equal to 1 and its significance must be considered when modeling FO performance using NaCl as the draw solute. The theoretical study reveals that the sublayer porosity, tortuosity and thickness have great impact on membrane performance when the draw solution flows against the sublayer. The desired FO membrane should have no sublayer. Since the phase inversed membrane may always have a sublayer, the preferred sublayer has high porosity, low tortuosity and small thickness. However, FO membranes for water reuse may have less structure requirements than those for seawater desalination. [Copyright &y& Elsevier]

Abstract: In this study, the polyvinylidene fluoride (PVDF)/polytetrafluoroethylene (PTFE) composite is used to fabricate hollow fiber membranes for seawater desalination via direct contact membrane distillation (DCMD) application. The incorporation of PTFE particles in the formulated dope solution can efficiently suppress the formation of macrovoids and enhance the outer surface hydrophobicity. Dual-layer hollow fibers with a desirable macrovoid-free morphology and a relatively thin (13±2μm) outer-layer can be obtained via blending 30wt% of PTFE particles in the outer-layer dope. The resultant dual-layer hollow fiber (DL-30) displays a moderately high contact angle of 114.5° and porosity of 81.5%. Compared to the single-layer hollow fiber with 30wt% (SL-30) PFTE particles, the DL-30 fiber exhibits a flux enhancement of approximately 24% that is contributed to the reduction in inner-layer mass transfer resistance. Dual layer membrane configuration with a lower wall thickness as well as larger outer and inner diameters provides even higher water vapor transport is potentially suitable for desalination. Both single- and dual-layer PVDF/PTFE hollow fiber membranes reveal good long-term stability of up to 100h of continuous testing. By utilizing the state-of-the-art dual-layer spinning technology, hollow fiber membranes with better performance (i.e. enhanced flux) and morphology (i.e. macrovoid-free) can be tailored. [Copyright &y& Elsevier]

Abstract: In this study, we have established the fundamental science and engineering of fabricating poly(vinylidene fluoride) (PVDF) asymmetric hollow fiber membranes for ethanol–water separation and elucidated the complicated relationship among membrane morphology, pore size, pore size distribution and separation performance using the concept of the modified pore-flow model proposed in our previous work. The variation of bore-fluid composition, air-gap distance and take-up speed results in membranes with various morphologies ranging from large-finger-like macrovoid to nearly perfect macrovoid-free structures. Interestingly, an increase in air-gap distance or take-up speed not only effectively suppress the formation of macrovoids but also results in the reduction of membrane pore size and the narrowing of pore size distribution, hence leading to the enhancement of membrane performance. The permeation flux is found to be mainly controlled by the overall porosity and the contribution of large pore sizes of the membrane, while the selectivity or separation factor is greatly determined by membrane pore size and pore size distribution, which is consistent with the modified pore-flow model proposed in our previous works. The newly developed PVDF asymmetric hollow fiber membranes demonstrates remarkable high fluxes of 3500–8800gm−2 h−1 and reasonable ethanol–water separation factors of 5–8 compared to existing polymeric-based pervaporation membranes. [Copyright &y& Elsevier]

Abstract: For the first time, the mass transport phenomenon in pervaporation of the ethanol/water system via PVDF asymmetric hollow fiber membranes has been demonstrated through the pore-flow model and a newly modified pore-flow model has been proposed. The modified pore-flow model differs from the pore-flow model by factoring in the contribution of Knudsen flow to vapor transport, which was ignored by the pore-flow model. The correlation of transport parameters to membrane pore size is explored and it is found that the pore size expansion (including the change of membrane surface morphology) is strongly dependent on the solvent in contact. The modified pore-flow model shows a better prediction for the permeate composition than the pore-flow model and both models exhibit an excellent prediction of total permeate mass flux. The significance of Knudsen flow contribution in vapor-phase transport as stated in the modified pore-flow model is discussed from the experimental and theoretical aspects. [ABSTRACT FROM AUTHOR]

Abstract: The aims of this study are to fabricate Extem® hollow fibers with an ultra-thin dense-selective layer for gas separation and to use this brand new amorphous thermoplastic polyetherimide (PEI) as a model material to reveal the fundamentals of hollow fiber membrane fabrication. The evolution of membrane morphology, final dense-selective layer thickness and O2/N2 selectivity from single-layer to dual-layer spinning have been disclosed with an integrated understanding of dope formulation, solution rheology, elongational rate, phase inversion path and co-extrusion method. Without heat treatment, single-layer Extem® hollow fibers are all defective even if the silicon rubber coating is applied due to the substructure resistance. Neither changes in spinning conditions nor increase in polymer concentration could improve the O2/N2 selectivity of single-layer Extem® hollow fibers. By taking the advantages of the characteristics of rapid phase inversion, relatively lower shear and elongational viscosities, dual-layer Extem® hollow fibers with an O2/N2 selectivity of 6.15 and an ultra-thin dense-layer thickness of about 876Å have been successful fabricated for the first time since Extem® was commercialized in 2007. Mainly due to the formation of an ultra-thin dense layer and a porous substructure, the gas permeance of our Extem® hollow fibers is higher than that of Ultem® PEI hollow fibers reported in the literature. [Copyright &y& Elsevier]

Abstract: This study has successfully demonstrated that a proper combination of novel spinneret designs and spinning parameters can effectively counteract the die swell as well as flow instability phenomena, i.e. extrudate distortion, in the hyperbranched polyethersulfone (HPES) hollow fiber spinning. Attempts are also made to unravel the die swell and flow behavior differences between HPES and linear polyethersulfone (LPES) membranes spun using various spinneret designs and spinning conditions. In terms of flow stability, it is revealed that short conical spinnerets with a flow angle of 60° as well as short round flow channel spinneret with a flow angle of 30°, can reduce or eliminate extrudate distortions. Apart from spinneret designs, this study also accentuates the importance of a proper choice of spinning conditions for each specific spinneret to achieve flow stability and reduce die swell, namely: (1) bore fluid composition; (2) dope flow rate; (3) spinning temperature; and (4) take-up speed. Experimental results concluded that a proper combination of spinneret design and these four spinning parameters is the key to stabilize the spinning process. It is found that a high take-up speed spinning and a high non-solvent concentration in the bore fluid can fully eliminate die swell and enhance flow stability in the HPES hollow fiber spinning using short and conical or round spinnerets. [ABSTRACT FROM AUTHOR]

Abstract: Unique ‘micelle-like’ macrovoids have been observed for the first time in the polyvinylidene fluoride-polytetrafluoroethylene (PVDF-PTFE) hollow fiber membranes. FESEM results show that the incorporation of 30 and 40wt% PTFE particles (<1μm) reduces the number of finger-like macrovoids in the membrane matrix, while micelle-like marcovoids (about 10μm in size) are formed when PTFE loading is increased to 50wt% or higher. 50wt% PTFE is the critical particle concentration for micelle-like macrovoid formation. The origins of micelle formation may be attributed to the adhesion and cohesion forces between air bubbles and particles in the supersaturated PTFE solution. A more rigorous degassing of the PVDF-T50 polymer dope solution may enhance the suspension homogeneity and eliminate the micelle-like macrovoid formation. It is therefore concluded that the micelle-like macrovoid formation arises from the agglomeration of gas bubbles upon PTFE particles with the aid of water diffusion and convection during the phase inversion of membrane formation. [Copyright &y& Elsevier]

The influence of elongation and shear rates induced by the geometry of spinnerets on gas performance of PES hollow fiber membranes has been studied. Different elongation and shear rates were introduced in various spinnerets with flow angles of 60°, 75° and 90° by changing the flow rate of dope solution. The PES hollow fiber membranes were fabricated under the wet-spun condition without extra drawing force and their gas performances were tested by using O2 and N2. The flow profiles of dope solution and the elongation and shear rates at the outermost point of the outlet of spinnerets were simulated by the computational fluid dynamics model. A hypothetic mechanism is assumed to explain the effects of elongation and shear rates on the changes of conformation of polymer chain. While trying to correlate the elongation and shear rates with the gas performance of hollow fibers, we have come to some preliminary conclusions that the elongation rate has more contribution portion in permselectivity than in permeance and the shear rate has more contribution portion in permeance than in permselectivity. [Copyright &y& Elsevier]

Simple and versatile modification techniques are highly sought after in the field of membrane science. However, common procedures such as interfacial polymerization require multiple solutions and several steps, particularly when dealing with hollow fiber membranes. In line with strategies laid out for fabricating greener membranes, we report a single-step cross-linking and modification process involving only an aqueous solution of the naturally-occurring tannic acid (TA) and hydrazine for polyacrylonitrile-based hollow fibers. Hydrazine plays a dual role of cross-linking the polyacrylonitrile while forming bonds with TA to yield a robust modification. By simply changing the amount of TA used, hollow fibers with different filtration properties can be obtained, as demonstrated by standard pore size tests using aqueous feeds. TA may even penetrate into the membrane bulk and further improve its mechanical properties. Solvent-related tests such as immersion tests and pure solvent permeation are first conducted for a preliminary understanding of membrane performance. To further demonstrate the efficacy of the one-step modification, organic solvent feeds, such as dyes dissolved in methanol, are employed in nanofiltration tests using these hollow fibers. Long-term tests reveal a stable methanol permeance of 1.2 L m-2 h-1 bar-1 and sustained 100% rejection of Evans Blue (M w = 960.81 g mol-1). Thus, with each reagent playing several roles in this one-step process, a greener yet simple modification method is established for polyacrylonitrile-based membranes and materials. Image 1 • Green membrane fabrication via concurrent crosslinking and tannic acid modification. • Each reagent plays dual roles in enhancing membrane characteristics. • Cross-linked membranes resistant to various organic solvents. • Stable long-term performance and sustained rejection for methanolic Evans Blue feed. [ABSTRACT FROM AUTHOR]

This study provides a novel method for the fabrication and microstructural manipulation of high-performance dual-layer hollow fiber membranes for H 2 /CO 2 separation at elevated temperatures. For the first time, hollow fibers consisting of an outer-selective layer made from polybenzimidazole (PBI) and sulfonated polyphenylsulfone (sPPSU) blends and an inner-support layer made of polysulfone were prepared. sPPSU was chosen because it performed as an ionic-crosslinker towards PBI and it had a higher permeability than PBI. The as-spun hollow fibers were chemically cross-linked by α,α′-dibromo-p-xylene (DBX) and then heat treated to enhance their gas separation performance for H 2 /CO 2 separation. Experiments revealed that sPPSU interacted with PBI at the molecular level and increased the interchain space within PBI, leading to an increment in H 2 permeance. The covalent crosslinking reaction between PBI and DBX resulted in the outer-selective sPPSU/PBI layer with a smaller free volume but a greater H 2 /CO 2 selectivity. The dual-layer hollow fiber membrane cross-linked by 3% DBX and annealed at 120 °C (i.e., HSP-10-3%DBX-120) has a H 2 permeance of 16.7 GPU and an H 2 /CO 2 selectivity of 9.7 at 90 °C and 14 atm. The fabrication of dual-layer hollow fibers may open up a new approach to produce useful membranes for hydrogen purification and CO 2 capture at elevated temperatures. • Dual-layer hollow fiber membranes are fabricated with a miscible polybenzimidazoles (PBI)/polyphenylsulfone (sPPSU) blend as the selective layer and polysulfone as the supporting layer. • The Selective layer of the manufactured hollow fibers is modified using DBX. • The crosslinking of the PBI/sPPSU with DBX tightens its inter-chain packing. • The gas separation performance can be enhanced by tuning the microstructure of the PBI/sPPSU selective layer of the hollow fibers. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract The rapid increases in global population and economic growth have resulted in serious water scarcity in many countries. One of the solutions is to harvest water via dehumidification from ambient air by condensation. However, similar to the traditional air conditioning system, it takes a lot of energy in the condensation process to cool down air to the dew point temperature for dehumidification. Therefore, we propose a combined hollow fiber membrane dehumidification & humidity harvesting system in this study, which not only dehumidifies air but also harvests humidity to generate clean water simultaneously. The driving force for water vapor permeation comes from a dry sweep air combining with a small vacuum pressure of 0.17 bars. The calculation results show that the newly proposed membrane system not only produces fresh cool air but also condenses clean water with minimum energy. It produces 1 m3 fresh cool air at merely 8.0 kJ while the traditional air conditioning system needs 10.55 kJ, which means an energy saving up to 24.3%. Moreover, it also produces by-product clean water. The calculation shows that it consumes only 687.4 kJ to produce 1 kg clean water while it needs 1125 kJ to do the same from the atmospheric air directly. Therefore, the newly proposed membrane system saves 38.9% energy on humidity harvesting. [ABSTRACT FROM AUTHOR]

We have incorporated Na+-functionalized carbon quantum dots (Na-CQDs) into the polyamide layer via interfacial polymerization reaction and developed novel thin film nanocomposite (TFN) hollow fiber membranes for brackish water desalination. Comparing with the conventional thin film composite (TFC) membranes, the TFN membranes comprising Na-CQDs have a larger effective surface area, thinner polyamide layer and more hydrophilic oxygen-containing groups in the polyamide layer. Besides, the interstitial space among the polyamide chains becomes larger due to the presence of Na-CQDs. As a result, the incorporation of 1 wt% Na-CQDs into the polyamide layer could improve the pure water permeability (PWP) of the membranes from 1.74 LMH/bar to 2.56 LMH/bar by 47.1% without compromising their NaCl rejection of 97.7%. Interestingly, stabilization of the TFN hollow fiber membranes containing 1 wt% Na-CQDs at 23 bar could further promote the PWP to 4.27 LMH/bar and the salt rejection to 98.6% under the same testing conditions due to the deformation of the membranes under a high hydraulic pressure. When using a 2000 ppm NaCl aqueous solution as the feed, the optimal water flux and rejection of the newly developed TFN membranes at 15 bar are 57.65 ± 3.26 LMH and 98.6% ± 0.35% respectively. The Na-CQDs incorporated TFN hollow fiber membranes show promising applications in the field of brackish water desalination. Image 1 • Pure water permeability (A value) jumps 47.1% after incorporation of 1 wt% Na-CQDs. • Na-CQDs modify both chemical compositions and morphology of polyamide layers. • High-pressure stabilization of hollow fiber membranes effectively promote Jw and R. • Optimal Jw and R of TFN-(Na-CQDs)-1 achieved at 15 bar are 57.65 LMH and 98.6%. [ABSTRACT FROM AUTHOR]

A novel hybrid system of integrating membrane distillation (MD) and solid hollow fiber cooling crystallization (SHFCC) has been successfully developed for simultaneous production of fresh water and inorganic salt crystals from NaCl brine solutions. Porous PVDF hollow fiber membranes consisting of PTFE particles were spun for the MD subsystem, while non-porous PVDF hollow fibers were fabricated as heat exchangers for the SHFCC subsystem. To optimize the operation parameters, the Taguchi's method was utilized for experiment design including three key factors; namely, feed temperature (T f ), distillated amount (W d ) and water amount to wash away the scallant (W w ). Several response factors were experimentally investigated and their signal-to-noise ratios of each response were calculated to identify the optimal settings of control factors. As a result, the best combined parameters to maximize the crystal harvest took place at W d = 14 g and T f = 50 °C. Narrowly distributed NaCl crystals with a small mean size of 35–45 µm were successfully generated by the hybrid system, and a relatively long-term MD-SHFCC operation of 15 cycles was conducted to verify the system stability and feasibility. The 15-cycle experiments exhibited an impressive average MD water flux of about 8 kg/m 2 h and continuous production of distillate water with a high purity (a NaCl concentration of 0.01 g/L) and NaCl salt crystals with a yield of 64 g per kg feed. [ABSTRACT FROM AUTHOR]

By means of carbon quantum dots incorporation, we have developed novel thin film composite (TFC) membranes for osmotic power generation. The newly developed TFC membrane exhibits a peak power density as high as 34.20 W/m 2 at 23 bar using 1.0 M NaCl and deionized water as the feed pair. To our best knowledge, this is the highest ever power density reported in the literature. The carbon quantum dots (CQDs) are a new class of carbon nanomaterials with advantages of excellent hydrophilicity, low toxicity, environmental friendliness, easy synthesis and low cost. The CQDs are incorporated into the polyamide selective layers via the conventional interfacial polymerization reaction. The effects of incorporating different CQDs and their loadings on membrane morphology, properties and PRO performance have been examined. It is found that the addition of Na + –functionalized CQDs not only increases the existence of hydrophilic oxygen-containing groups and surface area of the polyamide layer, but also changes the morphology with a looser and thinner polyamide network. The TFC membrane comprising 1 wt% Na–CQD-9 has the optimal performance. Compared with the control, the water flux and power density at 23 bar increase from 44.52 to 53.54 LMH and 28.44 to 34.20 W/m 2 respectively, while the reverse salt flux remains unchanged. [ABSTRACT FROM AUTHOR]

A defect-free membrane with a very high gas permeance is greatly attractive to both academia and industry. Thin film composite (TFC) membranes are promising candidates. However, it is always challenging to have a reproducible and up-scalable method to fulfill the needs. Herein, we report a novel and straightforward strategy to fabricate a high-performance hollow fiber composite membrane using a crosslinked polydimethylsiloxane (PDMS) with a high inherent viscosity obtained from a novel post-crosslinking method. The evolution of inherent viscosity with various cross-linking conditions and substrate morphology from different spinning conditions have been investigated. The resultant defect-free composite membrane shows excellent O 2 and CO 2 permeances higher than 1000 and 5000 GPU, respectively; while the corresponding selectivities of O 2 /N 2 and CO 2 /N 2 are about 2 and 11, respectively. The newly developed methods may provide useful insights to fabricate next-generation high-performance composite membranes for gas separation. [ABSTRACT FROM AUTHOR]

For the first time, ultrathin boron bridged graphene oxide (GO) membranes have been successfully constructed on the modified microporous hollow fiber substrates using borates as the cross-linker. Nanochannels within GO layers can be molecularly engineered by manipulating the annealing process and the chemistry of boron bridges. GO framework composite membranes with proper charge properties and size exclusion functionalities have been developed to allow fast water transport and high rejections. Comparing to the pristine GO membrane, boron bridged GO membranes show not only less variations in terms of flux and rejection with annealing temperature, but also high stability during the long term test. Both pore size distribution and X-ray photoelectron spectroscopy were employed to elucidate the fundamental sciences about the evolution of nanochannels and surface chemistry of GO composite membranes with annealing temperature. The newly fabricated boron bridged GO membranes annealed at 65 °C exhibit a water permeability of 6.64–11.66 L m −2 h −1 bar −1 and high rejections of >97% against dyes with molecular weights of 300–1000 Da. The boron bridged GO membranes may have great potential to treat hot and harsh wastewater as well as for water reuse and dye separation industries. [ABSTRACT FROM AUTHOR]

Internal concentration polarization (ICP) and severe irreversible fouling occurring within the porous and tortuous substrates of the forward osmosis (FO) and pressure retarded osmosis (PRO) membranes have significantly hidden their applications for water purification and osmotic power generation. This study experimentally demonstrates that designing a double-skin structure in FO and PRO membranes can effectively control ICP and their fouling propensity. Thin-film composite (TFC) hollow fiber membranes consist of an inner polyamide selective skin and an outer polyamide sealing layer were successfully fabricated by double interfacial polymerizations on a tailored polyethersulfone (PES) fiber substrate (termed as d TFC-PES). Due to the outstanding rejection of the outer polyamide sealing layer, the penetration of inorganic salts and foulants into the substrate is sufficiently blocked. As a result, not only ICP and fouling inside the membrane are effectively minimized, but also sustainable FO and PRO performances are achieved. By using real wastewater contains multiple inorganic salts and organic foulants as the feed, the d TFC-PES membrane shows a quite low flux decline of 29% in FO operations under the PRO mode at an ultrahigh feed recovery of 80%. Under PRO tests for power generation, the membrane power density slightly drops to 90.8% of the initial value after a 12-h test at Δ P =15 bar. In addition, since foulants are primarily accumulated on the surface of the polyamide sealing layer, physically flushing the fouled membrane surface by either freshwater or commercial cleaner Genesol 704 can efficiently restore the water flux back to its initial level with a recovery rate of 87% or 98%, respectively. This study may offer useful insights and meaningful strategies for the development of effective antifouling FO and PRO membranes. [ABSTRACT FROM AUTHOR]

[Display omitted] • CTA/Ultem membranes with superhydrophilic CQDs were successfully prepared. • The effects of CQD concentration on membrane formation and morphology were studied. • The mechanical properties of the CTA/Ultem membranes were reinforced by CQDs. • 0.2CQD_OL showed a flux of 4306 ± 130 g m−2h−1 and a water content of ∼95 wt%. Pervaporative ethanol dehydration is a promising approach to concentrate ethanol from biofuel stocks. In this study, we have fabricated high performance dual-layer cellulose triacetate (CTA)/Ultem hollow fiber membranes incorporated with a small amount of superhydrophilic carbon quantum dots (CQDs) via the immiscibility induced phase separation (I2PS) method. The flow rates of the inner- and outer-layer dopes were firstly optimized. Subsequently, various small amounts of CQDs were added into the inner- and outer-layer dope solutions to explore their impacts on membrane structure and separation performance. It was found that the incorporation of a reasonably small amount of CQDs, whether to the inner or outer layer of I2PS membranes, could significantly enhance the mechanical properties and pervaporation performance by altering their structures. The most effective membrane containing 0.2 wt% CQD in the outer layer (0.2CQD_OL) demonstrated exceptional pervaporation performance. Using an 85 wt% ethanol feed solution, this membrane achieved a total flux of 4306 ± 130 g m−2h−1 (equivalent to a water permeance of 33.28 mol m−2h−1 kPa−1) and a water content of approximately 95 wt% (equivalent to a mole-based selectivity of 153) in the permeate over a 172 hr long-term test. A comparison with literature underscores the superior performance of this newly developed I2PS membrane, particularly in terms of water permeance. In summary, the CQD-embedded CTA/Ultem HF membranes demonstrate substantial potential for industrial applications in the pervaporative ethanol dehydration. [ABSTRACT FROM AUTHOR]

In this work, a novel sandwich-structured hollow fiber membrane has been developed via a specially designed spinneret and optimized spinning conditions. With this specially designed spinneret, the outer layer, which is the most crucial part of the sandwich-structured membrane, is maintained the same as the traditional dual-layer membrane. The inner substrate layer is separated into two layers: (1) an ultra-thin middle layer comprising a high molecular weight polyvinylpyrrolidone (PVP) additive to enhance integration with the outer polybenzimidazole (PBI) selective layer, and (2) an inner-layer to provide strong mechanical strength for the membrane. Experimental results show that a high water permeability and good mechanical strength could be achieved without the expensive post treatment process to remove PVP which was necessary for the dual-layer pressure retarded osmosis (PRO) membranes. By optimizing the composition, the membrane shows a maximum power density of 6.23 W/m 2 at a hydraulic pressure of 22.0 bar when 1 M NaCl and 10 mM NaCl are used as the draw and feed solutions, respectively. To our best knowledge, this is the best phase inversion hollow fiber membrane with an outer selective PBI layer for osmotic power generation. In addition, this is the first work that shows how to fabricate sandwich-structured hollow fiber membranes for various applications. [ABSTRACT FROM AUTHOR]

A novel slow–fast phase separation (SFPS) process is proposed to fabricate the desirable ultrafiltration dual-layer hollow fiber substrate for effective interfacial polymerization. By controlling the ratios of non-solvents to volatile co-solvents in both the outer- and inner-layer dopes, the outer and inner layers undergo slow and fast coagulation, respectively, in the dry-jet wet-spinning co-extrusion process. The inner layer is highly porous for high solvent flux permeation, while the outer layer possesses a surface with nano-sized pores that have a sharp size distribution for effective thin film polymerization. The addition of polyvinylpyrrolidone in the outer dope further reduces the pore size, and enhances surface hydrophilicity as well as mechanical strength. The substrate was cross-linked and subjected to interfacial polymerization for fabricating thin-film composite (TFC) membranes. The effects of the substrate properties of various hollow fiber membranes from the SFPS process on the TFC membrane were systematically investigated in terms of morphology and organic solvent nanofiltration (OSN) performance. The membrane shows a 99.3% rejection of ramazol brilliant blue (MW: 626.54 g mol −1 ) and a methanol flux of 14.4 l m −2 h −1 at 16 bar. [ABSTRACT FROM AUTHOR]

By employing the novel sulfonated polyphenylenesulfone (PPSU) polymer with super-hydrophilic nature as membrane material, triangle-shape tri-bore hollow fiber (TBF) ultrafiltration (UF) membranes have been fabricated via a newly designed dual-layer tri-needle spinneret. The sulfonation degree of PPSU not only plays a key role in forming a fully sponge-like structure, but also enhances membrane hydrophilicity. The separation performance and fouling behavior of the newly developed TBF membranes were systematically studied for oil/water separation. The critical and threshold fluxes of TBF UF membranes were determined as a function of sulfonation degree through pressure stepping experiments. Above threshold fluxes, their UF behaviors were studied under the same experimental conditions to filtrate a 5000 ppm petroleum/water emulsion. Interestingly, the sulfonated TBFs always exhibit higher permeate fluxes and lower total resistance than the pristine PPSU membranes. In addition, analyses by the resistance-in-series model indicate that the sulfonated PPSU membranes display much lower resistances from static foulant adsorption and irreversible fouling. Clearly, the sulfonated membranes become less fouled and easier to regenerate. After UF through TBF membranes, the permeate water appears quite clean with low turbidity and high TOC rejection larger than 95.4%. [ABSTRACT FROM AUTHOR]

For the first time, one novel closed-loop pressure retarded osmosis (PRO) process promoted by an effective hydroacid complex draw solution has been demonstrated for harvesting the renewable salinity-gradient energy. The complex draw solute was molecularly constructed to possess unique characteristics of high osmotic pressure, large molecular size and relative low viscosity, and easy regeneration. Compared to conventional PRO processes, the newly developed closed-loop PRO process exhibits promising advantages of sustainable high power output, negligible internal concentration polarization and low membrane fouling, as well as no problems of feed water pretreatment and brackish water discharge. Employing a highly permeable ( A = 4.30 LMH/bar) and selective ( B = 0.47 LMH) thin film composite PRO hollow fiber membrane, a power density of 16.2 W/m 2 can be achieved with an ultralow reverse solute flux ( J s / J w < 0.062 g L −1 ) at 12 bar when using 1 M complex draw solution and deionized water as feeds. The diluted complex draw solution can be regenerated via a solvent precipitation process, and the outstanding PRO performance could be almost fully recovered. We believe the newly developed closed-loop PRO process shows great potential for salinity-gradient energy capture, although the specific benefits have to be fully defined through energy or cost analysis. [ABSTRACT FROM AUTHOR]

Highlights: [•] PES TFC hollow fibers were fabricated for pressure retarded osmosis. [•] Different macro-structures were found on the hollow fibers. [•] Fibers’ micro-structure determined the mechanical strength and power density. [•] 24.3W/m2 was produced using 1M NaCl and DI water. [ABSTRACT FROM AUTHOR]

This paper investigated the individual effects of reverse salt flux and permeate flux on fouling behaviors of as-spun and annealed polybenzimidazole (PBI)–polyhedral oligomeric silsesquioxane (POSS)/polyacrylonitrile (PAN) hollow fiber membranes under forward osmosis (FO) and pressure retarded osmosis (PRO) processes. Two types of membrane fouling had been studied; namely, inorganic fouling (CaSO4·2H2O gypsum scaling) during FO operations and organic fouling (sodium alginate fouling) during PRO operations. It is found that gypsum scaling on the membrane surface may be inhibited and even eliminated with an increase in reverse MgCl2 flux due to competitive formations of MgSO4° and CaSO4·2H2O. In contrast, the increase of reverse NaCl flux exhibits a slight enhancement on alginate fouling in both FO and PRO processes. Comparing to the reverse salt flux, the permeate flux always plays a dominant role in fouling. Therefore, lesser fouling has been observed on the membrane surface under the pressurized PRO process than FO process because the reduced initial flux mitigates the fouling phenomena more significantly than the enhancement caused by an increase in reverse NaCl flux. [ABSTRACT FROM AUTHOR]

Abstract: The hollow fiber membrane with a multi-bore configuration has attracted much attention in recent years due to ease of potting during module fabrication and improved mechanical stability. The conventional multi-bore hollow fiber consists of seven or three bore channels and a round-shape outer geometry. In this work, novel tri-bore hollow fiber membranes made of Matrimid® and polyethersulfone (PES) materials with regular triangle-shape outer geometry have been fabricated. The fabricated membranes are advantageous in terms of uniform mechanical strength and enhanced permeation properties due to the evenly distributed membrane wall thickness. Experimental results suggest that the combined effects of rapid phase inversion, die swell, outer surface shrinkage and stress balance during the membrane formation are responsible for the unique membrane geometry. The micro-morphology, mechanical strength, pore size distribution and ultra-filtration rejection of the fabricated membranes were examined. We believe this work may provide useful insights for the fabrication of triangle-shape tri-bore membranes with other materials for various applications. [Copyright &y& Elsevier]

Abstract: A dual-layer hollow fiber membrane consisting of copoly(1,5-naphthalene/3,5-benzoic acid-2,2′-bis(3,4-dicarboxyphenyl) hexafluoropropanedimide) (6FDA-NDA/DABA)/polyhedral oligomeric silsesquioxane (POSS) as the outer functional layer and polyetherimide (Ultem®) as the inner support layer has been developed for ethanol hydration via pervaporation. By using lower dope flow rates and optimizing inner dope concentration, the newly developed hollow fiber membranes have desirable morphology consisting of a porous inner layer with low transport resistance and a macrovoid-free selective layer for a superior separation performance. Doppler broadening energy spectra (DBES) have been employed to analyze the depth profile of morphological evolution and examine the thickness of dense selective layer as a function of spinning conditions. Incorporating a small amount (2wt%) of POSS into the selective layer increases its free volume size and diffusion selectivity and hence improves the pervaporation performance of the hybrid membranes. The diffusion mechanism of permeate molecules through polymer chains containing POSS nanoparticles was proposed and verified via FTIR spectra, XRD curves, positron annihilation lifetime (PAL) characterization and vapor sorption tests. Compared to other hollow fiber membranes, the newly developed hollow fibers have a superior flux of 1.9kg/m2 h and a comparable separation factor of 166 for ethanol dehydration. The work may open up a new perspective for the development of next-generation high-performance dual-layer hollow fiber membranes with a POSS embedded selective layer for biofuel separation. [Copyright &y& Elsevier]