Composite Hollow Fiber Membranes Research Articles

Nafion-PTFE hollow fiber composite membranes for ammonia removal and recovery using an aqueous-organic membrane contactor

• A novel aqueous-organic membrane contactor process was applied. • The novel membrane contactor process was more favorable to treat low-ammonia-content feeds. • Accompanying water transport was avoided. Nafion-PTFE hollow fiber composite membranes were applied in the ammonia removal and recovery with a novel aqueous-organic membrane contactor (AOMC) process, in which an aqueous solution and an organic solution were separated by the composite membrane. A kerosene-diluted di-(2-ethylhexyl) phosphoric acid (D2EHPA) solution was used to receive the ammonia, which could be recycled and reused after regeneration by the stripping agent (a dilute solution of H 2 SO 4 , HNO 3 , or H 3 PO 4 ). The new-type membrane contactor can avoid the accompanying water transport in conventional membrane contactors. The effects of experimental factors including the pH, the velocity and the initial ammonia concentration of the feed on the overall mass transfer of the ammonia were investigated. Meanwhile, how the regeneration experiment parameters influenced the stripping ratio was also studied. The results showed that the AOMC process was more favorable to treat ammonia feed with low ammonia concentrations. The ammonia removal could be over 99% under certain conditions. Additionally, the ammonia was concentrated 26.4 times after four cycles. It was found that the accompanying water transport was non-negligible in the traditional aqueous-aqueous membrane contactor (AAMC) process when treating ammonia feed of low concentrations, with the maximum water flux two orders of magnitude higher than ammonia.

Ultra-strong polymeric hollow fiber membranes for saline dewatering and desalination

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.

Thin-film composite hollow-fiber nanofiltration membranes prepared from benzonitrile containing disulfonated poly(arylene ether sulfone) random copolymers coated onto polyphenylene oxide support membranes

A new method for the preparation of chemically robust thin-film composite hollow-fiber (TFC-HF) nanofiltration membranes through a dip-coating process is reported. A negatively charged disulfonated poly(arylene ether sulfone) random copolymer (SPN-20) containing highly polar benzonitrile groups was utilized as a separation layer in a TFC-HF membrane. Only four polar aprotic solvents, N-methyl-2-pyrrolidone (NMP), dimethyl acetamide (DMAc), dimethyl formamide (DMF), and dimethyl sulfoxide (DMSO), proved to be good solvents for SPN-20 possibly due to its rigid chemical backbone and strong intermolecular interactions. In order to avoid dissolution or irreversible swelling of the polymeric supports in the dip-coating process, a polyphenylene oxide (PPO) hollow-fiber membrane was introduced as a novel substrate for TFC-HF fabrications. Solubility investigation using a framework of Hansen solubility parameters (HSPs) revealed that the PPO membrane is a suitable substrate for coating the SPN-20 copolymer due to its tolerance of polar aprotic solvents. By using DMSO as a coating solvent for the SPN-20 copolymer, TFC-HF membranes were successfully prepared with neither dissolution nor any damage to PPO supports. The dip-coating and drying processes were analyzed in detail to optimize the thickness and separation performance of TFC-HF membranes. The resultant membranes showed excellent rejection of Na2SO4 (>98%) and an almost 100% rejection of negatively charged dyes along with a reasonable level of pure water flux (1.0–10.3 [L∙m−2∙h−1∙bar−1]).

Innovative Adsorbents and Membranes Tested for High CO2 Content NG Separation at CO2CRC’s Otway International Test Centre

The CO2CRC, in collaboration with The University of Melbourne (UoM) and the University of New South Wales (UNSW), tested two novel CO2 capture technologies aimed for both on-shore and off-shore natural gas applications. The tests involved materials testing in a state-of-the-art experimental capture rig at CO2CRC’s Otway International Test Centre followed by simulation and techno-economic activities for scaled up facilities. The goal was to develop robust and compact technology for high pressure natural gas separation over a range of adjusted high CO2 concentrations mimicking various gas field conditions. The tests were conducted for adsorbents and membranes in a high-pressure rig incorporating both pressure swing adsorption (PSA) and membrane technologies. It was found that adsorption, a second-generation technology with a low footprint is very suitable for natural gas separation with higher separation efficiency, contrary to the general perception. The stable separation performance of the thin film composite hollow fibre membranes was particularly encouraging among all membranes tested. This paper will discuss novel adsorbent and membrane development and their quantitative performance in the test campaigns followed by suggested next steps in the TRL towards commercial application. It is anticipated further research and testing at higher Technology Readiness Level (TRL) levels 5/6 would be necessary to make them commercial ready. These technologies, if successful, would facilitate developing new gas fields to recover methane in a cost-effective manner which is currently uneconomical with conventional technologies.

Fabrication and characterization of composite hollow fibre membrane derived from hydroxyapatite cow bone and kaolin

Due to its superior behaviour, membrane separation has been applied widely towards water and wastewater treatment. Compare to polymeric counterparts, ceramic membrane has become innovation technology nowadays as it can be used both separation and adsorption application. The conventional ceramic membrane made from alumina, however, in view of its high-cost output. As a result, exploring to a cheap ceramic material derived from clay and waste is gaining attention. In this study, hydroxyapatite derived from cow bone waste and kaolin were used as the main materials for the fabrication of ceramic hollow fibre membrane via phase inversion and sintering technique. The membrane composition was varied through kaolin:hydroxyapatite ration into three composition (40:0, 0:40, 20:20). Result showed the ceramic membrane fabricated from 20 wt% kaolin and 20 wt% hydroxyapatite induces excellent performance at water flux of 10168.5 L/m².h and mechanical strength at 13.33 MPa.

Fabrication of Polydimethysiloxane (PDMS) Dense Layer on Polyetherimide (PEI) Hollow Fiber Support for the Efficient CO2/N2 Separation Membranes.

The development of thin layer on hollow-fiber substrate has drawn great attention in the gas-separation process. In this work, polydimethysiloxane (PDMS)/polyetherimide (PEI) hollow-fiber membranes were prepared by using the dip-coating method. The prepared membranes were characterized by Scanning Electron Microscope (SEM), energy-dispersive X-ray spectroscopy (EDX), and gas permeance measurements. The concentration of PDMS solution and coating time revealed an important influence on the gas permeance and the thickness of the PDMS layer. It was confirmed from the SEM and EDX results that the PDMS layer’s thickness and the atomic content of silicon in the selective layer increased with the growth in coating time and the concentration of PDMS solution. The composite hollow-fiber membrane prepared from 15 wt% PDMS solution at 10 min coating time showed the best gas-separation performance with CO2 permeance of 51 GPU and CO2/N2 ideal selectivity of 21.

High loading and high-selectivity H2 purification using SBC@ZIF based thin film composite hollow fiber membranes

Membrane-based separation systems have been widely explored for hydrogen production and purification in the development of next-generation fuels. In this work, we propose a thin film composite hollow fiber membrane (TFCHFM) for H2 purification, incorporating poly(styrene-co-butadiene) copolymers (SBC, 4% butadiene, for flexibility and ease of processing) and ZIF-8 nanoparticles. The TFC was supported on a PEI-based hollow fiber substrate. SBC containing a flexible butadiene segment showed enhanced compatibility through π-π interactions. The morphology of ZIF-8 was altered from a cubic shape to a smaller spherical shape by altering the molar ratio of NH4+/Zn2+. The gas separation mechanism of the ZIF-8 based TFC membrane was predicted by the Maxwell model. In the binary gas permeation test (5 vol% H2), the H2 permeance and H2/CH4 selectivity of TFCHFMs were 6.85 GPU and 152.20, respectively, with 50 wt% ZIF-8 loading. We believe that the high loading weight (50 wt% ZIF-8) and H2/CH4 selectivity presented here are unprecedented for ZIF-8 based TFC membranes reported in the literature.

Optimization of interfacial polymerization to fabricate thin-film composite hollow fiber membranes in modules for brackish water reverse osmosis

The development of commercial-scale thin-film composite (TFC) hollow fiber membranes and modules for reverse osmosis (RO) has been lagging behind spiral wound TFC flat-sheet membranes and modules for many years. The delay arises from the challenges of synthesizing a defect-free polyamide selective layer on hollow fibers in modules. In order to solve this problem, a novel interfacial polymerization method is presented in this work to fabricate 1-inch TFC hollow fiber membrane modules for RO applications. By circulating the m-phenylenediamine (MPD) solution on the lumen side under a positive pressure and circulating the trimesoyl chloride (TMC) solution at the atmosphere pressure, a strong, uniform and defect-free polyamide selective layer is formed on the inner surface of hollow fiber membranes in modules. Under pressure, not only MPD monomers are evenly distributed on the inner surface of each hollow fiber substrate in modules, but also sufficient MPD monomers can retain in the substrate pores for further reaction with TMC monomers. The best RO performance obtained by this newly developed TFC hollow fiber membrane module has a water permeability of 4.49 L m−2 h−1 bar−1 and a NaCl rejection of ~99%, using a feed solution of 1000 ppm NaCl under a transmembrane pressure of 20 bar. The novel interfacial polymerization method may provide useful insights to fabricate TFC hollow fiber membrane modules for desalination of brackish water.

Optimization of TFC-PES hollow fiber membranes for reverse osmosis (RO) and osmotically assisted reverse osmosis (OARO) applications

The osmotically assisted reverse osmosis (OARO) has been recently proposed to increase the water recovery of the reverse osmosis (RO) process, in which RO has reached its limitations. Strong membranes are essential for both OARO and RO processes. Here, we have developed high mechanical strength thin-film composite (TFC) hollow fiber membranes for both RO and OARO processes. The newly developed TFC hollow fiber membranes consist of a polyamide layer synthesized via interfacial polymerization on the inner surface of PES hollow fiber substrates that have been optimized by controlling the bore and dope fluid flow rates, fiber dimension and morphology. The TFC-PES hollow fiber membranes have a pure water permeability (PWP) of around 2.5–3 L/(m2 h bar) (LMH/bar) and a NaCl rejection of around 97.5–98% for brackish water desalination at 20 bar. The water permeability drops from 2.15 to 0.06 LMH/bar when the NaCl concentration increases from 0.035 mol/L (2000 ppm) to 1.2 mol/L at 30 bar for OARO due to the concentrative and dilutive concentration polarization (ECP and ICP) that decreases the effective driving force. The structural parameter (S) and burst pressure (PB) of the newly developed membranes increase from 550 to 800 μm and from 47 to 104 bar, respectively, with an increase in the dope to bore flow rate ratio (D/B ratio) because of the thicker substrate wall and reduction in porosity. The optimal TFC-PES hollow fiber membrane for OARO has a burst pressure of 95 bar, structural parameter of 795 μm and water permeability of 0.09 LMH/bar when using 1.2 mol/L NaCl for OARO. To the best of our knowledge, this inner-selective TFC-PES hollow fiber membrane has the highest burst pressure to date, it has impressive high mechanical strength and good RO and OARO performance.

Porous Hydrophobic-Hydrophilic Composite Hollow Fiber and Flat Membranes Prepared by Plasma Polymerization for Direct Contact Membrane Distillation.

High water vapor flux at low brine temperatures without surface fouling is needed in membrane distillation-based desalination. Brine crossflow over surface-modified hydrophobic hollow fiber membranes (HFMs) yielded fouling-free operation with supersaturated solutions of scaling salts and their precipitates. Surface modification involved an ultrathin porous polyfluorosiloxane or polysiloxane coating deposited on the outside of porous polypropylene (PP) HFMs by plasma polymerization. The outside of hydrophilic MicroPES HFMs of polyethersulfone was also coated by an ultrathin coating of porous plasma-polymerized polyfluorosiloxane or polysiloxane rendering the surface hydrophobic. Direct contact membrane distillation-based desalination performances of these HFMs were determined and compared with porous PP-based HFMs. Salt concentrations of 1, 10, and 20 wt% were used. Leak rates were determined at low pressures. Surface and cross-sections of two kinds of coated HFMs were investigated by scanning electron microscopy. The HFMs based on water-wetted MicroPES substrate offered a very thin gas gap in the hydrophobic surface coating yielding a high flux of 26.4–27.6 kg/m2-h with 1 wt% feed brine at 70 °C. The fluxes of HFMs on porous PP substrates having a long vapor diffusion path were significantly lower. Coated HFM performances have been compared with flat hydrophilic membranes of polyvinylidene fluoride having a similar plasma-polymerized hydrophobic polyfluorosiloxane coating.

Covalently immobilized cobalt Phthalocyanine@MWCNT PDMS hollow fiber membrane for highly selective, reversible and bio-inspired oxygen transport

Facilitated oxygen transport is an effective strategy for the oxygen transport that may enhance the oxygen permeance and its selectivity, which may provide oxygen rich permeate that can be used in medical applications as in the present COVID-19 pandemic situation for providing the sufficient oxygen to the patients. This study presents the bio-inspired oxygen transport by covalently bonded Cobalt Phthalocyanine complex anchored on multi walled carbon nanotube (MWCNT) via axial ligand, incorporated in PDMS hollow fiber membranes with 0.05, 0.1, 0.5 and 1.0 wt % loadings. Successful functionalization of MWCNT was confirmed by Raman spectroscopy and X-ray photoelectron spectroscopy. The membranes were thoroughly characterized by using FE-SEM with elemental mapping, ATR-IR, DSC and TGA analysis. It demonstrated facilitated oxygen transport through the covalently immobilized Cobalt complex of the membrane with high oxygen permeance of 49 GPU as well as exceptional oxygen selectivity of 17 at 0.5 wt % Cobalt Phthalocyanine@ MWCNT loading. These values are highest among the known Cobalt complex based hollow fiber composite membranes in the literature suggesting its best utility in selective oxygen concentration for practical applications.

Second interfacial polymerization of thin‐film composite hollow fibers with amine‐cyclodextrins for pervaporation dehydration

AbstractHigh performance thin‐film composite (TFC) hollow fiber membranes have been developed for pervaporation dehydration by second interfacial polymerization (SIP) modification with three kinds of amine‐functionalized β‐cyclodextrin (amine‐CDs), which were synthesized by modifying β‐CD with ammonia, ethylenediamine (EDA), and tris(2‐aminoethyl)amine, respectively. The chemical properties of amine‐CDs and SIP‐modified TFC membranes were characterized by various techniques. The effects of amine‐CD type and SIP parameters (pH or concentration of CD‐EDA solution) were studied systematically to acquire the optimized selective layer of TFC membranes for ethanol dehydration. Among all SIP‐modified TFC membranes, the one with SIP by 2 wt% CD‐EDA aqueous solution (pH = 2) exhibited the most outstanding separation performance with a ultrahigh permeation flux (3,018.0 ± 12.0 g/m2 hr) and permeate concentration (98.7 ± 0.2 wt% water) at 50°C (equivalent to separation factor of 415), contributed by the effectively incorporated CD with rich hydrophilic functional groups and intrinsic nanocavities facilitating the passage of water molecules.

In-situ synthesis of PA/PVDF composite hollow fiber membranes with an outer selective structure for efficient fractionation of low-molecular-weight dyes-salts

A polyamide/poly(vinylidene fluoride) composite hollow fiber membrane (HFM) was designed by in situ interfacial polymerization (IP) during the fiber spinning process. Using a piperazine aqueous solution as the bore fluid and a dual-bath coagulation, the PA outer layer was formed via IP of the PIP in the bore fluid and TMC in the second reactive bath during phase inversion process. Chemical structure, membrane morphology and surface property were characterized by using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscope (XPS), scanning electron microscope (SEM), and zeta potential. The effects of several parameters involved in the membrane fabrication (e.g., piperazine concentration, bore fluid flow rate, residence time and heat treatment temperature) on the morphology and performance of resultant composite HFMs were investigated. The composite HFM showed a performance that is comparable favorably with conventional nanofiltration membranes in terms of showed water permeability (10.2 L/m2·h·bar), high rejection to dyes (i.e., 100% for CR and EBT, 99.99% for RhB and MB, 98.3% for MO) and low salt rejections (NaCl 6.2%). Moreover, the newly developed composite HFM showed good stability and flux recovery with simple water rinsing for treatment of simulated textile wastewater. This work is expected to provide a new approach to designing composite HFMs for the treatment and reuse of textile wastewater.

The Effects of PEI Hollow Fiber Substrate Characteristics on PDMS/PEI Hollow Fiber Membranes for CO2/N2 Separation.

The CO2 separation from flue gas based on membrane technology has drawn great attention in the last few decades. In this work, polyetherimide (PEI) hollow fibers were fabricated by using a dry-jet-wet spinning technique. Subsequently, the composite hollow fiber membranes were prepared by dip coating of polydimethylsiloxane (PDMS) selective layer on the outer surface of PEI hollow fibers. The hollow fibers spun from various spinning conditions were fully characterized. The influence of hollow fiber substrates on the CO2/N2 separation performance of PDMS/PEI composite membranes was estimated by gas permeance and ideal selectivity. The prepared composite membrane where the hollow fiber substrate was spun from 20 wt% of dope solution, 12 mL/min of bore fluid (water) flow rate exhibited the highest ideal selectivity equal to 21.3 with CO2 permeance of 59 GPU. It was found that the dope concentration, bore fluid flow rate and bore fluid composition affect the porous structure, surface morphology and dimension of hollow fibers. The bore fluid composition significantly influenced the gas permeance and ideal selectivity of the PDMS/PEI composite membrane. The prepared PDMS/PEI composite membranes possess comparable CO2/N2 separation performance to literature ones.

Performance, fouling and cleaning of a thin film composite hollow fiber membrane during fertiliser-drawn forward osmosis process for micro-polluted water

Analysis of occurrence and cleaning regeneration of organic/inorganic fouled FO membranes in the FDFO process and related mechanisms.

Improved CO2/CH4 separation performance of mixed‐matrix membrane by adding ZIF‐7‐NH2 nanocrystals

AbstractMembrane‐based technology is an attractive alternative in terms of CO2 separation. Pebax‐based membranes are regarded as potential candidates for CO2 separation due to the favorable interaction between its poly (ethylene oxide) chains with CO2 molecules and inorganic fillers. However, the separation performance for CO2/CH4 mixture is still suffered from the moderate gas permeability and selectivity. To overcome this problem, in this work, amino‐functionalized zeolite imidazolate framework (ZIF‐7‐NH2) nanocrystals were used as fillers to blend with Pebax 1657 for fabricating mixed‐matrix membranes (MMMs). XRD, Brunauer–Emmett–Teller (BET), scanning electron microscope, and 1H nuclear magnetic resonance characterization indicated that ZIF‐7‐NH2 with the highest crystallinity was synthesized. Fourier transform infrared spectroscopy, thermogravimetric analysis, differential scanning calorimetry (DSC), and Young's modulus showed that it has good interfacial interaction. Gas separation test results showed that both the CO2 permeability and CO2/CH4 selectivity of the 31 wt% ZIF‐7‐NH2/Pebax MMMs increased by 80 and 170%, respectively. The improved performance is attributed to the addition of ZIF‐7‐NH2 nanocrystals and the favorable interfacial interactions between the polymer and ZIF‐7‐NH2 nanocrystals. Furthermore, the polyvinylidene fluoride supported hollow fiber composite membranes also exhibit the long‐term stability for CO2/CH4 separation.

Thin film composite hollow fibre membrane for pharmaceutical concentration and solvent recovery

A 100-piece hollow fibre thin-film composite membrane module was successfully developed for pharmaceutical concentration and solvent recovery. To increase its packing density, thinner P84 polyimide hollow fibre substrates were spun using a smaller spinneret. The substrates were subsequently cross-linked with hexamethylene diamine to achieve organic solvent resistance. An MPD-based thin-film composite was synthesized through interfacial polymerisation to increase selectivity for solutes of less than 300 Da. The thin-film composite was then solvent-activated using N,N-dimethylformamide to increase its solvent permeability. The resulting membrane exhibited excellent performance with 24.2 l m−2 h−1 bar−1 acetone permeability and 90.1% methyl red (269 Da) rejection. In addition, the solvent-activated membrane maintained its performance for prolonged period, demonstrating the scalability of the thin-film composite fabrication process and stability of solvent-activated membranes. The membrane was also able to concentrate levofloxacin (361 Da) from 500 ppm to 20,000 ppm in acetone using a batch process, showing promising results for pharmaceutical applications.

Highly permeable thin film composite hollow fiber membranes for brackish water desalination by incorporating amino functionalized carbon quantum dots and hypochlorite treatment

A novel strategy has been demonstrated to synergistically improve the separation performance of thin film composite (TFC) hollow fiber membranes for brackish water reverse osmosis (BWRO) desalination. It consists of two steps. Firstly, a series of amino functionalized carbon quantum dots (CQDs) were synthesized and incorporated into the polyamide layer of TFC membranes. The modified TFC membrane with the optimal amino functionalized CQDs has a pure water permeability (PWP) of 5.50 LMH/bar and a NaCl rejection of 98.0% against a 2000 ppm NaCl feed solution at 15 bar. Comparing with the unmodified TFC membrane, the modified TFC membrane has a 42.1% higher PWP without compromising the salt rejection. Then the modified TFC membrane was treated by a sodium hypochlorite solution at different concentrations. Chlorine was bonded to the polyamide layers, enhancing their repulsion against charged solutes and making the polyamide network less cross-linked. As a result, both PWP and NaCl rejection of the TFC membranes could be improved. After being treated with a sodium hypochlorite aqueous solution at 4000 ppm for 3h, the aforementioned modified TFC membrane displays a PWP of 10.13 LMH/bar and a NaCl rejection of 98.9% against a 2000 ppm NaCl solution at 15 bar, which demonstrates a great potential for brackish water desalination. This study may mark a milestone for the development of future BWRO membranes based on the use of amino functionalized CQDs and hypochlorite treatment.

Fabrication and characterization of a novel Nafion‐PTFE composite hollow fiber membrane

AbstractNafion has been widely used in electrochemistry, but there are only a few reports on its application in other fields, such as, gas separation, even though it exhibits good performance. The primary reason for that is the high cost of Nafion and making a composite membrane with a thin Nafion layer is a potential solution to solve this problem. In this study, a novel Nafion‐PTFE composite hollow fiber membrane, which had a thin (~5 μm) and detect‐free Nafion layer on PTFE surface, without Nafion filling substrate pores was developed, differing from the reported ones in which Nafion resin was required to impregnate into porous PTFE membrane as thorough as possible to ensure the ion conductivity and operation stability. The surface morphology, crystallite, solubility in ethanol/water mixture, and water uptake of membranes were systemically investigated. The gas permeance tests were also conducted. The permeances of different gasses of prepared composite membranes were significantly enhanced compared with the commercial membranes due to the decrease of Nafion thicknesses, while the selectivity remained the same, verifying the detect‐free structure of Nafion layer on PTFE substrate. This study provided a good reference for the preparation and application of low‐cost Nafion composite membranes.

Nafion-PTFE hollow fiber composite membranes for improvement of anti-fouling and anti-wetting properties in vacuum membrane distillation

Nafion-PTFE hollow fiber composite membranes were fabricated and applied in vacuum membrane distillation (VMD) process to improve the anti-fouling and anti-wetting performance in the presence of oil and surfactant. The composite membrane exhibited an underwater super-oilphobic property according to the contact angle test. The VMD performance when treating saline feed containing 3.5 wt% NaCl and 1000 ppm mineral oil for the composite membrane behaved a stable flux for 40 h. In construct, an immediate and sharply-declined flux was observed for the pristine PTFE, indicating the significant improvement in the anti-fouling property. Meanwhile, the composite membrane also alleviated the wetting phenomena caused by the surfactant comparing with the pristine PTFE membrane, and the Nafion-PTFE composite membrane behaves a stable flux and high salt rejection higher than 99.99% for 60 h treating saline feed containing O/W emulsions. The pressure depression effect of the Nafion layer on the mass transfer was analyzed. It was found that the depression could be reduced with the increasing of the feed temperature and the enhancement of the corresponding effective pore diameter of the Nafion layer, that the pressure depression factor decreased from 0.23 to 0.04 with the feed temperature increasing from 60 °C to 75 °C.