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Excessive discharges of chemical dyes have led to severe contamination of seawater, resulting in significant ecological damage. Thermo-osmotic energy conversion technology, which purifies wastewater and generates electricity under temperature gradients, has garnered considerable interest from researchers. However, the operational efficiency of thermo-osmotic energy conversion is inherently limited by the effective membrane area, and conventional systems typically employ flat membranes as separators, resulting in suboptimal performance for the same floorage. In this study, we introduce a novel system that combines thermo-osmotic energy conversion technology with hollow fiber membranes that possess a high effective membrane area, thereby achieving optimized performance. Driven by the temperature gradient, the water in the dye solution condenses outside the membrane and converted from vapor to liquid. The continuous accumulation of condensed water generates pressure and drives a water turbine for sustainable power generation. Our results demonstrate that at temperature gradient of 40 °C, the system can achieve the power output of 16.75 Wm−3 and the freshwater production rate of 70.29 kg m−3 h−1 under ideal conditions. This study presents a novel water-electricity co-production system based on low-grade waste heat recovery for dye solution treatment, which extends the applicability of thermo-osmotic energy conversion technology and improves its practicality. • Hollow fiber membrane combined thermal-osmosis hybrid system was proposed. • Simultaneous generation of freshwater and electricity was achieved under dye solution. • Optimal operating conditions for the system are discussed. • A theoretical model was developed to optimize water and electricity output of the system. [ABSTRACT FROM AUTHOR]

Batch reverse osmosis (RO) is a desalination process that can follow the osmotic pressure of gradually concentrating feed to achieve high energy efficiency. Its limitation of treating high-salinity (> 7 % wt.) feed can be overcome by making both sides of the membrane saline, reducing the osmotic pressure difference across the membrane. This osmotically assisted approach performs best with the streams in counterflow. To increase recovery, we propose the first temporally multi-staged batch counterflow process. A pressure exchanger design allows the use of atmospheric pressure tanks for gradually concentrating and diluting the two streams. To achieve temporal multi-staging, we run multiple batches using the same hollow fiber membrane but varied salinities, and ensure that the volume and salinity of the diluting feed at the end of each stage stabilizes to a cyclically steady process. The diluted feed produced at the end of the first stage matches the feed salinity of seawater RO, and increases the overall recovery significantly. Using a reduced order model that captures internal and external concentration polarization, we predict a 4.24 kWh / m 3 specific energy consumption (41.8 % second law efficiency), operating at 84.39 % volumetric recovery of seawater with a 2.12 LMH time-averaged counterflow RO flux. • First multi-stage batch counterflow reverse osmosis process. • Temporal multi-staging significantly reduces component count. • Internally unsteady but cyclically steady operation • Uses pressure exchanger and atmospheric tanks for low downtime • High energy efficiency and higher flux than other OARO processes [ABSTRACT FROM AUTHOR]

This study focused on the development of pressure retarded osmosis (PRO) thin film composite (TFC) membranes for enhanced osmotic power using hollow fiber polyethersulfone (PES) support structure modified by incorporating hydrophilic graphene oxide (GO) nanosheets. The GO loadings in the hollow fiber substrates were varied to improve water flux performances without compromising the mechanical strength. GO embedded (≤0.2 wt%) PES hollow fiber supports revealed noticeable improvements in pure water permeability, improved structural morphologies, as well as the hydrophilicity within the support layer, without deteriorating the mechanical properties. The GO (0.2 wt%)-incorporated TFC-PRO membrane appeared to have an initial PRO flux (without any applied pressure) of 43.74 L m−2 h−1, lower specific reverse salt flux of 0.04 g L−1 and structural parameter (S) of 522 μm, significantly better than the control membrane. The maximum power density of 14.6 W m−2 was achieved at an operating pressure of 16.5 bar under the condition of DI water and 1 M NaCl as feed and draw solutions, respectively. The results obtained in this study indicate that modification of PRO hollow fiber support layer by incorporating nanoparticles such as GO nanosheet can be a useful tool to improve the PRO performance. Unlabelled Image • Mixed-matrix PES/GO hollow fiber supports were fabricated for TFC PRO membranes. • A small amount of GO incorporation in support layer improved PRO performances. • GO-incorporated membrane support revealed competitive mechanical properties. • The power density of 14.6 W m−2 was achieved with GO (0.2 wt%) added PRO membrane. [ABSTRACT FROM AUTHOR]

Abstract The current study assesses the technical feasibility of using a thermoresponsive polyelectrolyte draw solution (DS) in a Forward Osmosis (FO) desalination pilot scale system of 10 m3/day capacity. The FO system utilized a commercial spiral wound hollow fiber FO membrane and ethylene oxide-propylene oxide copolymer as DS. This study evaluated the effect of DS flow rate and feed solution flow rates on the net water recovery and product water flow rates of the system. The osmotic pressure distribution of polyelectrolyte DS at different sections of the HF module was greatly influenced by DS flow rate. The study revealed that the DS had great potential to generate the high osmotic pressure (Δπ) difference in the various compartments of the HF module. The reliability of the FO pilot plant was proved over a long run without any severe FO membrane fouling with total dissolved solids of product water at 143 ppm and water recovery of 30%. The selected DS showed its potentiality towards the installation of commercial-scale FO desalination plant by witnessing its low viscosity and easy phase separation at a moderately lower temperature of 85 °C in the coalesce DS regeneration system. Graphical abstract Unlabelled Image Highlights • Polyelectrolyte DS having thermo-responsive property was tested in a pilot scale FO system. • Performance of the DS mainly relies on the flow rates of the DS and FS. • High flow rate of DS resulted in overall high-water flux and product flow rate. • Increased FS flow rate increases the rate of dilution of the FS to increase the driving force of the process. • Study recommends further research on development of DS with >45 °C phase transition temperature. [ABSTRACT FROM AUTHOR]

Abstract Forward osmosis (FO)-based water treatment and desalination processes have attracted increasing attention to address the global water crisis, but its practical application is restricted by the lack of FO membranes with high permeability and selectivity. In this work, an all nanocarbon-based FO membrane was successfully fabricated via constructing reduced graphene oxide (RGO) on a carbon nanotube (CNT) hollow fiber substrate via electrophoretic deposition coupling with chemical reduction processes. Due to the ultra-low friction and well-defined interlayer spacing, the RGO active layer provided high water permeability and ion selectivity. Meanwhile, the high porosity and good wettability ensured the CNT hollow fiber substrate with low internal concentration polarization, and thus increasing water flux. During against DI water feed using 0.5 M NaCl draw solution, the prepared RGO/CNT membrane presented an outstanding water flux of 22.6 LMH, which is 3.3 times higher than that of the commercial membrane. Meanwhile, its reverse salt flux was only 1.6 gMH in comparison to 2.2 gMH for the commercial membrane. These results indicate that the all nanocarbon-based membrane is an alternative membrane for providing clean water in the FO process. Graphical abstract Unlabelled Image Highlights • Preparation of all nanocarbon-based hollow fiber membrane • Controllable thickness of reduced graphene oxide active layer • Low internal concentration polarization in high porous and hydrophilic substrate • High water flux and low reverse salt flux during forward osmosis process [ABSTRACT FROM AUTHOR]

Hollow fiber membranes have shown great promise as a platform for osmotic processes such as forward osmosis (FO) and pressure retarded osmosis (PRO). Numerous hollow fiber FO membranes have been designed by academic researchers around the world. However, few of these designs have made it to full scale production. In this study, we report on the newly launched Aquaporin Inside™ hollow fiber FO membrane from Aquaporin A/S, Denmark. These membranes were tested in miniature modules under various osmotic testing conditions. With incorporating biomimetic aquaporin proteins as “water channel” in the selective layer, these membranes exhibited excellent FO performance with water flux of 21 LMH, reverse salt flux of 3.6 gMH and specific reverse salt flux of 0.18 g/L in PRO mode with 1 M NaCl and deionized water as draw and feed solutions, respectively. The structure parameter was determined to be 210.5 ± 55.5  μm , which is one of the lowest S values reported for thin film composite hollow fiber membranes. [ABSTRACT FROM AUTHOR]

Polyvinylidene fluoride (PVDF)/polytetrafluoroethylene (PTFE) hollow fiber membranes were developed via thermally induced phase separation (TIPS) method for direct contact membrane distillation (DCMD). The effects of PTFE addition on the thermal behavior of the dope mixtures and membrane formation were investigated. It was found that the crystallization of PVDF was significantly enhanced with increased nucleation sites provided by PTFE particles, leading to promoted formation of smaller spherulites in a greater density. Furthermore, the improved uniformity and increased amount of cavity between the spherical crystallites coherently facilitated the formation of smaller pores ranging from 0.08 to 0.12 μm. With certain PTFE loading, the membranes exhibited improved porosity, water permeability and hydrophobicity as well as enhanced tensile strength of 9.4 ± 0.3 MPa. To examine the DCMD performance, the membranes were tested under various conditions using 3.5 wt% NaCl solution. A stable permeation flux of 28.3 kg m − 2 h − 1 at the feed temperature of 60 °C with 99.99% NaCl rejection for over 50 h of operation was achieved, which is comparable with similar type of PVDF membranes while the newly developed membrane exhibited better mechanical strength. This study suggests that the as-spun PVDF/PTFE hollow fiber membranes have potential for DCMD applications. [ABSTRACT FROM AUTHOR]

In this study, hydrophobic asymmetric SiO 2 -PDMS-PVDF hollow fiber membranes were prepared for the vacuum membrane distillation (VMD). To make PVDF dope solution, hydrophobic nano-fumed silica (SiO 2 ) and polydimethylsiloxane (PDMS) were used. The effects of SiO 2 concentration on membrane parameters such as membrane morphology, hydrophobicity, porosity, thickness, pore size, liquid entry pressure, burst pressure, Fourier transformed infrared spectroscopy, thermal property, mechanical property and permeability were investigated. With the increasing of nano-particle concentration, membrane hydrophobicity, mechanical property and thermal stability improved. Furthermore, membrane VMD properties under various operation conditions were studied, the membranes showed a stable substantial flux of 44.27 LMH and a stable high salt rejection of over 99.9% under the optimum operation conditions of 75 °C, 35 g/L, 87 kPa, and 50 L/h. The results of our research demonstrated that the prepared hydrophobic asymmetric SiO 2 -PDMS-PVDF hollow fiber membranes not only had high permeability and good anti-wetting property but also exhibited a satisfying stability for the vacuum membrane distillation of desalination. [ABSTRACT FROM AUTHOR]

We have developed a thin-film composite (TFC) hollow fiber (HF) forward osmosis (FO) membrane using a polyketone HF membrane as a support. To investigate the effect of the diameter of the HF support membrane on the resulting FO performance of the TFC-HF-FO membrane, two-types of HFs with different inner diameters (HF-A: 347 μm and HF-B: 609 μm) were used. The FO performance of the prepared TFC membranes was measured and then analyzed using intrinsic membrane parameters obtained by an FO fitting method. These intrinsic parameters can be used to estimate the experimental data under various operating conditions. The prepared TFC-FO membrane using the HF with smaller diameter (TFC-FO (HF-A)) showed higher FO flux and better mechanical properties than those of the membrane prepared using the HF with larger diameter (TFC-FO (HF-B)), while higher operational pumping energy consumption is necessary because of higher bore-side pressure drop. Barlow's equation and the Hagen-Poiseuille equation were used to analyze the experimental data on the maximum burst pressure and the data on bore-side pressure drop of the prepared TFC FO membranes, respectively. The prepared TFC-FO membrane using the HF with smaller diameter showed one of highest FO fluxes yet reported in the literature. [ABSTRACT FROM AUTHOR]

The fabrication of loose nanofiltration (LNF) membranes for effective separation of dye/salt wastewater mixtures remains a great challenge. In this study, a new method for preparing a LNF membrane is proposed by combining co-extrusion technology and chemical cross-linking. Poly(styrene maleic anhydride (PSMA), an amphipathic copolymer was first entrapped onto the outer surface of poly(vinylidene fluoride) (PVDF) hollow fiber membranes (HFMs) by spinning using a triple orifice spinneret. Subsequently, the prepared PVDF/PSMA membranes were cross-linked using polyethylenimine (PEI) or poly(allylamine hydrochloride) (PAH). Finally, the chemical structure, morphology, hydrophilicity, zeta potential, and pore size were studied systematically. The small pore size and strong positive charge of the prepared membranes contributed to the high rejection of various dyes (>99 %) and low salt rejection (<8.5 %). The prepared membranes also exhibited excellent stability during long-term filtration. Antifouling experiments demonstrated that the prepared LNF membrane had good fouling reduction properties against bovine serum albumin (BSA) and lysozyme (LYZ). This study provides new perspectives for the design of useful LNF HFMs for the treatment of dye/salt wastewater mixtures. [Display omitted] • Loose nanofiltration membrane was developed via co-extrusion technology followed by chemical cross-linking. • High rejection of various dyes and low salt rejection was achieved. • The as-prepared LNF membrane showed excellent stability during long-term filtration. • Good antifouling properties for lysozyme [ABSTRACT FROM AUTHOR]

In this study, the process of air gap membrane distillation (AGMD) supplemented by a vacuum pump was developed to eliminate the disadvantage of the air gap and to improve the process performance. The vacuum-air gap membrane distillation (V-AGMD) process was evaluated by comparing with the AGMD process while varying operating conditions such as the feed inlet temperature, feed flow rate, cooling water temperature and feed salt concentration. The optimal operating conditions were obtained by orthogonal experiments of the AGMD and V-AGMD processes. It was found that the vacuum pump could promote the permeate flux (P F ), thermal efficiency (η), gained output ratio (GOR) and performance ratio (PR). Under the optimal conditions, a feed flow rate of 4 l/min and feed inlet temperature of 50 °C, P F and GOR could be increased by 24.96% and 14.29%, respectively, from AGMD to V-AGMD. While the feed inlet temperature at 80 °C, cooling water temperature at 20 °C and feed salt concentration at 253 ppm, PR and η increased about 15.25% and 11.99% at 2 l/min and 4 l/min, respectively. The results of this work proved that improving the performance of the AGMD process is possible by using a supplementary vacuum pump. [ABSTRACT FROM AUTHOR]

Experimental results show that the cross-flow hollow fiber membrane contactor is the controlling component of the humidification dehumidification desalination system performance. Three sets of main operating conditions sensitivity analyses are performed numerically, including solution conditions (temperature, salinity, flow rate), air conditions (temperature, relative humidity, flow rate) and dimensionless parameters (number of heat transfer units, flow rate ratio of solution to air). Increasing flow rate ratio can effectively promote freshwater production rate before flow rate ratio reaches a critical value of 6.0. It is useful to improve moisture effectiveness by increasing number of heat transfer units. Solution inlet temperature has an exponential promoting effect on membrane flux, which is consistent with the exponential upward trend of the solution phase equilibrium humidity. Membrane flux increases dramatically at first and then slowly after solution flow rate exceeds 228 kg/h and air flow rate exceeds 57 kg/h. Ambient air with high temperature and relative humidity as well as the high salinity of the solution will slightly degrade the membrane flux. • A two-dimensional mathematical model was established for cross-flow hollow fiber membrane contactor. • Humidification characteristic of membrane humidifier and the dehumidification characteristic of condenser were expounded. • Effects of comprehensive operating parameters on transmembrane water flux and humidification effectiveness were analyzed. • Optimal design of membrane contactor operating conditions was performed. [ABSTRACT FROM AUTHOR]

Self-heating membrane distillation has been considered as an alternative technology to alleviate water crisis, while the unsatisfactory energy efficiency and distillate flux limit the practical application. Herein, an all-in-one conductive hollow fiber membrane without supporting layer was fabricated, in which carbon nanotube (CNT) guaranteed the rapid electro-thermal conversion and polydimethylsiloxane (PDMS) endowed the composite membrane with superhydrophobicity to enhance membrane stability. The narrow channel of the hollow fiber membrane encircled the feed solution in a localized space to achieve efficient vaporization, which was benefit for both high higher distillate flux and low energy requirement. As a result, the CNT/PDMS hollow fiber membrane obtained a high distillate flux of 24.27 ± 0.89 kg m−2 h−1 and salt rejection rate > 99.9 % under 2.5 W input power with a flow rate of 12.81 mm s−1. Meanwhile, this membrane displayed a superior salt-resistance with increasing of the feed solution concentration from 10 g L−1 to 100 g L−1. For actual seawater desalination, the concentration of representative ions in collected water met the requirement standard of soft drinking water, indicating a great feasibility in practical application. Thus, this energy-efficient hollow fiber membrane provides a promising avenue to fabricate high-performance self-heating membrane for membrane distillation. [Display omitted] • An all-in-one CNT hollow fiber membrane for self-heating membrane distillation. • Overall conductive and narrow channel are beneficial to enhance performance. • As high as 24 ± 0.89 kg m−2 h−1 of distillate flux was obtained. • CNTs/PDMS membrane display a great feasibility in seawater desalination. [ABSTRACT FROM AUTHOR]

Desalination with forward osmosis (FO) membranes is an attractive method, achieving an efficiency superior to that of reverse osmosis (RO), which has been improved for many decades, is difficult. Although many FO membranes have been developed, there are no guidelines in membrane development to make FO highly efficient. This paper quantitatively investigates whether FO desalination can be potentially superior to RO desalination, and, where so, we uncover the range of required membrane properties. The results show that it is difficult for the FO method with current hollow fiber modules to exhibit process performance superior to that of the present RO method with spiral-type membranes. However, if the water permeability of such membranes can be increased threefold, then the energy consumption of FO desalination can be reduced to 70 % of that of RO desalination. Thus, this study proposes guidelines regarding membrane properties, such as support layer thickness, water permeability, and rejection performance, which will be required when FO membranes are further advanced in the future. [Display omitted] • The forward osmosis (FO) desalination process with hollow fiber membranes was simulated. • The FO desalination process with the present membrane properties cannot outperform the RO process. • The FO desalination process surpasses the RO process in the case of higher membrane permeability. • Energy consumption of the FO desalination process can be reduced to 70 % of the RO process. • This study provides important guidelines for the design of the FO hollow fiber membranes. [ABSTRACT FROM AUTHOR]

Poly(tetrafluoroethylene-co-hexafluoropropylene)(FEP) hydrophobic hollow fiber membranes were prepared through melt spinning method. The performances and structures of membrane samples with different stretching ratios were investigated. It can be seen that the increased stretching ratios (nascent, 50%, 100% and 150%) brought about obvious interfacial microvoids (IFMs) which improved the membrane's porosity, while decreased the liquid entry pressure (LEP) and mechanical strength. In addition, the FEP hollow fiber membranes exhibited strong hydrophobicity, excellent chemical and thermal stability owing to its perfluoro structure. Therefore, the performances of membrane samples were measured by vacuum membrane distillation (VMD) using alkaline aqueous with high temperature. The results showed that the FEP hollow fiber membranes' salt rejections achieved as high as 99.0%. In addition, the MD flux, salt rejection and mechanical strength kept stable in the strong alkaline aqueous (NaOH concentration of 300 g/L, 80 °C) through a long term operation of 48 h. However, the compared poly(vinylidenefluoride) (PVDF) hollow fiber membrane exhibited weak alkaline and thermal endurance with obvious decrease of mechanical strength and salt rejection. Therefore, this study indicated that the obtained FEP hollow fiber membrane could be used in the VMD which exhibited satisfying salt rejection. [ABSTRACT FROM AUTHOR]

Air-bubbling vacuum membrane distillation (AVMD) process was designed to boost the heat and mass transfer in membrane distillation (MD). Both effect of flow pattern on the performance of AVMD process and the heat and mass transfer mechanism in this process were studied in this paper. The results showed that the performance of VMD was improved obviously by air-bubbling method. The flux was doubled at certain feed velocity and gas/liquid proportion. The study showed that flow pattern was the key factor affecting the mass and heat transfer efficiencies. The heat transfer coefficients, corresponding to the two main flow patterns in AVMD process, bubbly flow h f b u b = 1.7527 R e t p 0.4215 P r 1 3 μ b / μ w 0.14 λ / d and slug flow h f s l u = 0.0632 R e t p 1.0420 P r 1 3 μ b / μ w 0.14 λ / d , were obtained and employed in the modeling of AVMD process. The modeling results showed that the theoretical prediction of flux aligned with experimental results well, in which the error was within ± 5%. Both variations of Temperature Polarization Coefficient ( TPC ) and Concentration Polarization Coefficient ( CPC ) in AVMD process were studied based on the obtained correlations. And the result showed that both TPC and CPC were significantly influenced by the flow patterns. [ABSTRACT FROM AUTHOR]

A positively charged polyamide composite nanofiltration (NF) hollow fiber membrane for lithium and magnesium separation was fabricated by the interfacial polymerization of 1,4-Bis(3-aminopropyl)piperazine (DAPP) and trimesoyl chloride (TMC) on the polyacrylonitrile (PAN) ultrafiltration hollow fiber membrane. The chemical structure, morphology and surface charge of the composite membrane were characterized by using ATR-FTIR, XPS, SEM, AFM and zeta potential analyzer. The performance of the composite membrane was tested with various salts in aqueous solution (2000 ppm) at the operating pressure of 0.3 MPa. The results showed that the membrane performance was related to the changes of the monomer content in the aqueous phase rather than that in the organic phase. Furthermore, the salt rejection order of the membrane was MgCl 2 > MgSO 4 > NaCl ≥ LiCl. The difference between the rejections of MgCl 2 and LiCl reached to 47.5%. The zeta potential measurements indicated that the surface of the resultant membrane was positively charged at pH values below 9.5. Moreover, the mass ratio of Mg 2 + /Li + decreased from initial 20:1 in the feed of 2.0 g/L MgCl 2 and LiCl mixture to 7.7:1 in the permeate after the filtration by the composite membrane. [ABSTRACT FROM AUTHOR]

Recently, forward osmosis (FO) has received much attention as an advanced water treatment technology. Although the FO process has begun to spread widely worldwide, it still has some problems – such as the low water permeation rate compared with those required for some applications – that must be solved for its commercial application. To achieve the higher water flux and lower reverse salt flux, pressure assisted osmosis (PAO), in which pressure is applied to a feed solution (FS), has recently been proposed. In this work, experiments were carried out to investigate membrane structures and operating conditions in the PAO process by using three types of cellulose triacetate (CTA) — hollow fiber (HF) membranes. The HF membranes are preferable in the FO process because a high packing density and a large specific surface area can be obtained in the HF module. In addition, the HF membrane module has four ports and does not require a spacer between the membranes. The effects of the applied pressure, the draw solution concentration, and the structure parameter of the HF membranes on the PAO performance were investigated. The water flux in the PAO process was theoretically analyzed. The calculated results satisfactorily agreed with experimental data. [ABSTRACT FROM AUTHOR]

In the present study, PANI (polyaniline)-nanofibers were synthesized by interfacial polymerization technique, dispersed in n-Methyl-2-Pyrrolidone (NMP) solvent and blended with PVP (Polyvinylpyrrolidone)/PSf (Polysulfone) for preparing the novel hollow fiber membrane by dry–wet spinning technique. The newly prepared nanocomposite ultrafiltration hollow fiber membrane is characterized by Scanning Electron Microscope (SEM), Contact Angle, Zeta Potential and Differential Scanning Calorimeter (DSC). Filtration studies are conducted to measure the membrane pure water flux (PWF), rejection of hazardous dye (Reactive Red 120) and fouling resistance. The maximum rejections are obtained for M 0.5 membrane with 99.25% rejection of RR120 hazardous dye at 2 bar pressure. The pure water flux, percentage rejection, antifouling property and thermal resistance increased with an increase in PANI-nanofiber concentration. The contact angle of the membrane decreased with increasing PANI-nanofiber concentration, which indicated increased hydrophilicity of the new membranes. [ABSTRACT FROM AUTHOR]

Pilot scale studies were performed to investigate how CNTs might affect hollow fiber membrane (HF) resistance to stress. Further, this research explored how the addition of CNTs into membrane solutions affected trends associated with changes in conventional HF spinning parameters. Nanocomposite polymer solutions were formed by adding functionalized multiwalled carbon nanotubes (MWCNTs) (0.2 wt.%, 0.4 wt.% and 0.8 wt.%) and PES. Membranes were fabricated under three different air residence times (1.875 s, 0.935 s, and 0 s) by changing either the air gap (15 cm or 0 cm) or the fiber take-up speed (0.16 m/s or 0.08 m/s). Subsequently, HF membranes were characterized according to their porosity, permeability, contact angle, and tensile strength. As expected, stress resistance and Young's Modulus increased up to 125% and 118% for certain membranes containing CNTs, respectively. Shorter air residence times caused significant porosity increases and large permeability decreases in the membranes containing CNTs. Finally, the effect of the de-mixing rate was more pronounced in nanocomposite membranes, while the effect of take-up speed was more pronounced in pristine membranes. This study establishes the potential for CNTs to improve the mechanical properties of HF membranes, and serves as the first demonstration of industrial-scale production of CNT-polymer HF membranes. [ABSTRACT FROM AUTHOR]

Vacuum membrane distillation (VMD) has received considerable attention from both academia and industry. During VMD, the liquid-vapor interface is supported by a porous hydrophobic membrane to prevent wetting of the membrane pores and allow only vapor to pass through. Therefore, it is advantageous for the production of high-purity water by desalination, and improving the membrane performance has attracted significant attention. In this work, we present a facile method of modifying polyvinylidene difluoride (PVDF) membranes with a fluorine-containing ionic liquid (BPPF6) to improve the membrane hydrophobicity and antiwetting and antifouling properties. The dynamic water contact angle of the membrane increased from 124.5 ± 0.3° to 136.7 ± 0.1°, and the VMD water flux increased by 14.2% for treating 3.5 wt% NaCl aqueous solution at 45 °C. Enhancement of hydrophobicity and water flux by facile coating of ionic liquid. [Display omitted] • Facile coating method to improve hydrophobicity of PVDF membrane • Mitigated pore blocking by IL coating method • Water flux during membrane distillation process improved by hydrophobic coating • Improved anti-wetting and anti-fouling properties by lowering surface free energy [ABSTRACT FROM AUTHOR]

Abstract: The layer-by-layer (LBL) polyelectrolyte deposition was applied on polyethersulfone (PES) hollow fiber ultrafiltration membrane to prepare nanofiltration (NF) membrane for low pressure water softening application for the first time. The effects of polyelectrolyte type and molecular weight (MW), deposited bilayer number, polyelectrolyte solution pH and supporting electrolyte concentration on the performance of resultant membranes were studied thoroughly. Experiments revealed that the pH of the polyelectrolyte solution and supporting electrolyte concentration presented the most notable effects. For weak poly-cations, Poly(ethylenimine) (PEI) and Poly(allylamine hydrochloride) (PAH), the solution pH affected the membrane performance significantly, and high water permeability and divalent cation rejection were obtained at optimum pH values. Using a low concentration of supporting electrolyte at underneath layers was proved to be an effective way to increase water permeability while maintaining high salt rejection. A salt water flux (SWP) of 12LMH/bar and 94% Mg2+ rejection was obtained by depositing only two bilayers of PSS/PAH polyelectrolytes on the PES substrate, while for the 3000ppm mixed salt solution, the water permeability was 11LMH/bar with Mg2+ and Ca2+ rejection as high as 90%. These promising results demonstrate that LBL technique is potentially applicable for preparing low-pressure water softening hollow fiber membranes. [Copyright &y& Elsevier]

Abstract: Based on the operational performance of hollow fiber membrane, backflushing flow (BF) and backflushing pressure (BP), the two key parameters of cleaning in line (CIL) were experimentally investigated in this paper. It was assumed that the optimal parameters should meet the requirement for delivering cleaning agents to the most distant fiber surface. Based on Hagen-Poiseuille theory, the equation derivation of the CIL operation shows that when the membrane backflushing flow (pressure) is fixed, the corresponding BF and BP have an optimal value range which the design of the BF and BP could base on. The permeability recovery of cleaning with sodium hypochlorite, assessed at low and high flow (pressure), indicated that operation at a more conservative flow (pressure) could conserve energy. With the flow (pressure) increased experimentally, an interesting phenomenon was found that the effective backflushing length first presents a short increase followed by a downswing. Meanwhile, the effect was investigated to prove that as fiber length increased, the backflushing time also increased. Moreover, when taking into account both the flux recovery and hysteresis time, operation with constant flow outperformed that with constant pressure under the optimal parameters. Finally, a mathematic model was developed to verify the former conclusion by comparing the theoretical value with the experimental value. [Copyright &y& Elsevier]

Abstract: Homogeneous-reinforced (HR) polyvinyl chloride (PVC) hollow fiber membranes consisting of coating layer and matrix layer were fabricated via coating process. The mixtures of polymer solutions were uniformly coated on the homogeneous PVC matrix membrane which was prepared by melt-spinning method. The influences of PVC concentration and poly(ethylene glycol) (PEG) molecular weight in polymer solutions on structure and performance of HR membranes were investigated. The results showed that the HR PVC membranes had a dense and smooth outer surface compared with matrix membrane. The maximum pure water flux and protein permeation flux of HR PVC membranes were obtained as the PVC concentration reached to 10wt.% and PEG molecular weight was 2000. The increase of PVC concentration and PEG molecular weight brought about the increase of protein rejection rate and the decrease of membrane porosity. The high flux recovery rate (>85.00%) indicated that the HR membranes had excellent anti-fouling property. Moreover, the HR PVC membranes had a favorable interfacial bonding force between the coating layer and matrix membrane. The tensile strength of HR membranes decreased slightly compared with matrix membrane and was nearly 19MPa, but the elongation at break was opposite which was nearly 102%. [Copyright &y& Elsevier]

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 Na 2 SO 4 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. [Display omitted] • The novel PA/(PES/PVDF) hollow fiber TFC membranes were developed via a simple and scalable procedure. • Fabrication parameters on the structures and properties of the resultant TFC membrane were investigated. • Pure water permeability of 13.8 L/m2·h·bar was approximately two times higher than that of conventional TFC membrane. • The membranes exhibited excellent stability, backwash ability and anti-fouling ability. [ABSTRACT FROM AUTHOR]

A commercially available microporous polypropylene hollow fiber membranes were employed for air gap and water gap membrane distillation (i.e., AGMD and WGMD, respectively) processes. In both configurations, the outer surface of commercially available dense polypropylene hollow fibers was used as the condensing surface of the permeate. The performance levels of the AGMD and WGMD processes utilizing microporous polyvinylidene fluoride membranes fabricated in-house were compared with those using polypropylene membranes. Under the given specific operating conditions, the maximum mean permeation flux values in AGMD and WGMD using polypropylene hollow fiber membranes were approximately 24 and 27 kg/m2h, respectively. In addition, theoretical studies on AGMD and WGMD using the designed hollow fiber module configuration were performed. The predicted results were found to well agree with the experimental results, thus verifying their validity. Moreover, parametric studies were conducted to identify the optimum evaporation-to-condensation surface area ratio (i.e., optimum numbers of hollow fiber membranes and hollow fiber condensers) in terms of specific energy consumption. [Display omitted] • WGMD and AGMD processes using hollow fibers have been demonstrated. • Dense polypropylene hollow fibers are employed to condense the permeate. • Hollow fiber membranes and condensers are arranged in a single shell. • Theoretical models of AGMD and WGMD using hollow fibers are developed. • Optimal configurations of AGMD and WGMD using hollow fibers have been identified. [ABSTRACT FROM AUTHOR]

The dominant market for lithium-ion batteries (LIBs) in China has driven lithium chemicals with foreseeable growth in demand. Lithium extraction from salt-lake brine in China with high Mg2+/Li+ ratio has become one of the key challenges in the separation of Mg2+ and Li+. In this study, we introduce here an unprecedented, highly permselective nanofiltration hollow fiber membrane prepared by layer-by-layer (LBL) deposition as a novel alternative for Mg2+/Li+ separation. Poly(styrene sulfonate) and poly(allylamine hydrochloride) were deposited alternatively on a tailor-made ultrafiltration hollow fiber support and crosslinking with glutaric dialdehyde. The pure water permeability of LBL NF membrane was 18.4 L m−2 h−1 bar−1. Under the synergistic effect of size sieving and Donnan exclusion effect, it also achieved promising results when tested with simulated brine. The rejection rate of Mg2+ was as high as 99%, and the rejection rate of Li+ was as low as −60%, with a separation factor of 74 was observed, setting a record of permselectivity for Mg2+/Li+ separation for engineerable membranes. This research has paved a new road for the engineering application of LBL nanofiltration membranes for mono and bivalent ion separation. • LBL nanofiltration hollow fiber membrane was used for Mg2+/Li+ separation for the first time. • Exceedingly high permselectivity was observed using PSS/PAH pairs in LBL assembly. • Size sieving was identified as the key factor for Mg2+/Li+ separation. [ABSTRACT FROM AUTHOR]

Abstract: The membrane flux curve characteristics of cross-flow hollow fiber membrane in direct contact membrane distillation (DCMD) were investigated under various experimental conditions. The results indicate that the increase of feed inlet temperature diminishes the impact of the feed concentration on the flux. Both a low feed inlet temperature and a high feed flow rate lead to a high membrane thermal efficiency. Various operating parameters interact with each other in DCMD process. The feed and distillate inlet temperatures influence the flux mainly by changing temperature difference between two sides of the membrane. The feed flow rate influences the flux mainly by changing the temperature polarization at feed side. The distillate flow rate influences the flux mainly by changing the residence time of the distillate in hollow fiber membrane as well as by impacting the temperature polarization in a certain extent. Consequently, different flux curve characteristics are formed respectively under different operating conditions. This study is helpful to understand the DCMD characteristics. [Copyright &y& Elsevier]

Abstract: pH- and thermo‐sensitive polyethersulfone (PES) hollow fiber membranes were prepared for the first time by blending a terpolymer of poly(N-isopropylacrylamide-co-methacrylic acid-co-methyl methacrylate) (P(NIPAAm-MAA-MMA)) via dry–wet spinning technique based on a liquid–liquid phase separation. The terpolymer was synthesized via free radical solution polymerization. Scanning electron microscopy (SEM) results indicated that the membrane morphology had been altered after the introduction of the terpolymer. The modified PES hollow fiber membranes showed pH-sensitivity, and the pH-valve effect was observed at the pH value between 7.0 and 10.0; the modified PES membranes also showed thermo-sensitivity, the hydrodynamic permeability changed slightly while the pore sizes changed significantly when the temperature increased, which indicated that the modified membranes could be used for thermo-sensitivity separation, but not suitable for thermo-sensitivity hydrodynamic permeability control. The membranes also showed excellent pH- and thermo-reversibilities. [Copyright &y& Elsevier]

Abstract: Modification of polypropylene (PP) hollow fiber microfiltration membranes for nanofiltration through dip-coating sodium carboxymethyl cellulose (CMCNa) skin layer followed by cross-linking with AlCl3 was investigated in this study. Modification parameters were studied to optimize the membrane performance and the obtained modified membranes were characterized in terms of surface and permeation properties. It was found that the surface property and solute separation capability of the PP hollow fiber membrane were significantly improved by coating CMCNa surface layer, and the optimized modified membrane took on a composite structure with a hydrophilic selective skin layer having an isoelectric point of pH 3.7. The composite layer was negatively charged at neutral pH and was relatively looser in acidic pH compared with that in basic or neutral. Permeation tests revealed that the desired modified membrane possessed a molecular weight cut-off (MWCO) of 760Da and a high pure water permeability of 10.8l/m2 hbar, and exhibited rejections to salts following the order of MgCl2

Abstract: In this study, pH-sensitive polyethersulfone (PES) hollow fiber membrane was prepared by blending a copolymer of poly (styrene-alt-maleic anhydride) (PSMA). The PSMA alternating copolymer was synthesized by a traditional synthetic route, and was characterized by Fourier transform infrared spectroscopy (FTIR) analysis, nuclear magnetic resonance (1H NMR) and gel permeation chromatography technique (GPC). The PES/PSMA membrane was then transformed to carboxylic PES/PSMA-H carboxylic membrane using sodium hydroxide solution, by which the anhydride groups were transformed to carboxyl groups, and the modified membranes showed excellent pH-sensitivity and pH-reversibility. Furthermore, the alternating copolymer modified PES hollow fiber membranes showed evident hysteresis of water flux, for which it would take several hours to reach the equilibrium state. [Copyright &y& Elsevier]

Abstract: The aim of the present study was to thoroughly investigate the effect of alkali metal counter-ions (Li, Na, K and Rb) of PFSA on the formation, morphology and performances of polyvinylidenefluoride (PVDF)/perfluorosulfonic acid (PFSA-M) hollow fiber membranes. It is found that the homogeneous region in the ternary phase diagram of the PVDF–PFSA–M/NMP/H2O systems shrinks and the precipitation rate increases when varying the counter-ions of PFSA in the order of Li, Na and K. The double finger-like structure and the cavities can be evidently developed with increasing the radius of the counter-ions of the spun PVDF/PFSA-M membranes. The pure water permeability (J W) and mean effective pore size of the PVDF/PFSA-M membranes first increase from counter-ion Li, Na to K and then slightly decrease for Rb. In addition, the highest J W value of 96.5L M−2 H−1 bar−1 was obtained for the PVDF/PFSA-K membrane with a MWCO of 86kDa. XRD patterns and FTIR-ATR spectra verify the exclusive formation of β crystalline phase structure in the as-spun PVDF/PFSA-M membranes. The PVDF/PFSA-Li membrane has better Young''s modulus and tensile strength than that of other PVDF/PFSA-M fibers. [Copyright &y& Elsevier]

Abstract: In this paper, the effects of γ-butyrolactone (GBL) weight ratio (w GBL) and membrane thickness on the formation of asymmetric flat sheet membranes prepared with P84 (BTDA-TDI/MDI co-polyimide)/N-methyl-2-pyrrolidone (NMP)/GBL casting solutions are investigated. With the increase of membrane thickness, the transition of membrane morphology from sponge-like to finger-like structure occurs at critical structure-transition thickness Lc. Lc and the general sponge-like structure thickness (Lgs) increase with w GBL. For 20wt.% P84/NMP/GBL casting solution, the membrane morphology changes from finger-like to sponge-like structure at the critical weight ratio of GBL (w ⁎ =0.69). The membrane morphology and performance of hollow fibers spun with various w GBL are observed. Compared with the hollow fiber membranes made of 18wt.% P84/NMP/GBL dope solution with w GBL =0.75, the hollow fiber membranes spun with w GBL =0.25 present a higher permeation flux and a larger MWCO. As w GBL increases from 0.25 to 0.75, the membrane morphology transfers from finger-like to sponge-like structure. An increase in shear rate shifts the rejection curves towards left, and lowers the MWCO of hollow fiber membranes. For hollow fiber membranes spun with w GBL =0.75, a relatively high permeation flux and a large MWCO are obtained by the wet spinning process. [Copyright &y& Elsevier]

Abstract: A novel method was proposed to improve the hydrophilicity and permeation of poly (vinyl chloride)/polyacrylonitrile/SiO2 (PVC/PAN/SiO2) composite hollow fiber membranes (HFMs) by the interfacial hydrolysis of PAN between PVC and SiO2. PVC/PAN/SiO2 composite HFMs were prepared by phase inversion method, using water as inner and outer coagulation. Sodium hydroxide solution was fed to the composite HFMs to introduce hydrolysis reaction. The Fourier transform infrared spectroscopy (FTIR), bubble point pore diameter and scanning electron micrograph (SEM) were used to characterize the chemical, pore size and morphological changes of the membranes. The changes of permeation performance and mechanical properties were also investigated. Water contact angle (WCA) and protein filtration were employed to evaluate the hydrophilicity and the anti-fouling performance of the membranes. The alkaline hydrolysis occurred in the composite HFMs, both water permeation and the anti-fouling performance were improved while mechanical strength was still kept at a high level. [Copyright &y& Elsevier]

Abstract: The pH-sensitivity of two kinds of polyethersulfone (PES) hollow fiber membranes modified by two random copolymers, poly (acrylonitrile-co-acrylic acid) (P(AN-AA)) and poly(acrylonitrile-co-methyl acrylic acid) (P(AN-MAA)), was studied. The P(AN-AA) and P(AN-MAA) copolymers which had the same hydrophobic chains, comparable amounts of carboxyl groups but different hydrophilic chains, were synthesized via free radical polymerization and characterized by FT-IR, element analysis and 1H NMR. The copolymers could be directly blended with polyethersulfone to prepare hollow fiber membranes by dry–wet spinning technique. Both of the two copolymer modified PES hollow fiber membranes showed evident pH sensitivity. The flux variation for the P(AN-AA) modified PES hollow fiber was larger than that for the P(AN-MAA) between the pH values 2.0 and 11.0, since the ted the dissociation of the carboxyl, and further affected the pH sensitivity of the modified hollow fiber membranes. [Copyright &y& Elsevier]

Abstract: Polyvinyl butyral (PVB) hollow fiber membranes were prepared via wet-spinning method using polyvinylpyrrolidone (PVP) as additive. The effects of PVP and PVB concentration, bore fluid composition on the membrane formation were investigated by viscosity, light transmission, scanning electron microscopy (SEM) and ultrafiltration respectively. Results revealed that PVB and PVP have a good miscibility. Addition of PVP mainly changed the kinetic property of the dope, such as the increased viscosity, the delayed demixing, etc. The cross-sections of the resulting membranes showed a similar asymmetric structure. Ultrafiltration showed that the rejection of membrane increased, but the flux firstly increased then decreased with an increase in PVP concentration. The low PVB concentration in the dope caused a loose cross-sectional morphology, which improved the water flux of membrane. Moreover notable difference occurred at the internal surface of PVB hollow fiber membrane when N,N-dimethulacetamide (DMAc) was added to the bore fluid. As a result, membrane exhibited a high flux with no significant change in retention performance. [Copyright &y& Elsevier]