Thin-film Composite Hollow Fiber Membranes Research Articles

PIM-1/PAN Thin-Film Composite Hollow Fiber Membrane as Structured Packings for Isopropanol (IPA)/Water Distillation

In this study, novel polymers of intrinsic microporosity (PIMs)-based hollow fiber structured packings were prepared by a facile pour-coating method and successfully applied as structured packings ...

Thin-film composite hollow fiber membranes incorporated with graphene oxide in polyethersulfone support layers for enhanced osmotic power density

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.

Preparation and characterization of multilayer thin-film composite hollow fiber membranes for helium extraction from its mixtures

The unique and distinctive physico-chemical properties of helium make it an irreplaceable resource in a wide range of applications, including cryogenics. Commercially-produced helium is extracted from natural gas. For the use of a membrane to be viable for the helium extraction and enrichment process, the membrane-based process must be economically competitive against other conventional technologies, and therefore, developments in membrane and optimized process design are crucial. This work demonstrates the successful fabrication of a highly helium-selective multilayer thin-film composite hollow fiber membrane for the enrichment of helium from natural gas. An aromatic polyamide selective layer was formed on top of a mesoporous polyacrylonitrile support by interfacial polymerization, followed by a caulking process to plug defects on the polyamide layer. The permeation and separation properties of the multilayer thin-film composite hollow fiber membrane were characterized using pure and quaternary mixed gases. The effects of feed pressure (up to 300 psig) and stage-cut (1.5–20%) on helium purity and CH4 loss were systematically investigated.

Forward osmosis remediation of high salinity Permian Basin produced water from unconventional oil and gas development

Unconventional oil and gas operations are on the rise, and they are an integral component to meeting the nation's energy needs. Produced water is the primary by-product of oil and gas operations, and it has proven challenging to treat to date. The aim of this study was to evaluate the feasibility of using forward osmosis with thin-film composite hollow fiber membranes as a remediation option for produced water with high total dissolved solids levels from the Permian Basin. Trials consisted of a series of 5 experiments in order to evaluate the performance of the membrane. Three PW samples, each from different locations, were used to conduct the series of experiments and compare the performance of the membranes on samples with TDS levels ranging from 16,000 to 210,000 mg/L. It was concluded that forward osmosis can be used to extract water from high salinity oil field brines and PW. Flux decreased over the course of the trials due to a combination of membrane fouling, concentration polarization, and temperature fluctuations. The flux of the PW was similar to the flux measured for the PW mimic with small difference due to the influence of activity on the osmotic pressure. The flux was also influenced by temperature and the linear velocity of the feed solution and draw solution.

Preparation and characterization of thin film composite membrane for the removal of water vapor from the flue gas at bench scale

Water inadequacy is increasing day by day and researchers are developing several technology to fulfill the pure water demand. Currently membrane technology is coming in big way to save and recovered the water. Herewith we introduce the thin-film composite (TFC) hollow fiber membranes to recover water vapor from flue gas in industrial power plants and it has become a promising technology. TFC membranes were prepared by interfacial polymerization between the aqueous monomer of 3,5-diaminobenzoic acid (DABA) in various concentrations and the organic monomer of trimesoyl chloride (TMC) on inner surface of a polysulfone (PSf) hollow fiber substrate. The selective polyamide layers of TFC membranes were comprehensively characterized by attenuated total reflectance Fourier transformed infrared spectroscopy (ATR-FTIR), field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and water contact angle measurement (WCA). The effect of aqueous monomer concentration on water vapor permeance and selectivity was investigated at lab-scale. As a result, a maximal selectivity of 313, along with 2873 GPU permeance, was obtained using an aqueous monomer concentration of 0.5 wt%; these synthetic conditions were applied for the preparation of bench-scale TFC membranes module. Subsequently, bench-scale experiments using real flue gas were carried out using different operating variables. Consequently, maximal water flux and water vapor removal efficiency (recovery ratio) of 2.3 kg/m2h and 27.7% were obtained. It is possible that the TFC hollow fiber membrane system will be a sustainable approach for water recycling and conservation.

Thin Film Composite and/or Thin Film Nanocomposite Hollow Fiber Membrane for Water Treatment, Pervaporation, and Gas/Vapor Separation.

Thin film composite (TFC) polymeric hollow fiber (HF) membranes are widely used in industrial gas/vapor separations and water treatment. There are many advantages of TFC HF membranes, such as low energy requirements, simplicity of operation, and high specificity. In the present article, a review is made on the progress that has been achieved during the past 15 years in the preparation of the HF substrate and the preparation/modification of the thin selective layer. The review also includes their applications in water treatment, dehydration of alcohols via pervaporation, and gas/vapor separation.

Thin-film composite hollow fiber membrane with inorganic salt additives for high mechanical strength and high power density for pressure-retarded osmosis

Using high salinity draw solutions in pressure retarded osmosis (PRO) demands novel membranes with a higher withstanding pressure and a higher power density to take full advantage of the increased osmotic gradient for greater osmotic energy production. This study highlights novel strategies to design an inner-selective thin-film composite (TFC) PRO hollow fiber membrane with a high operating pressure and a high power density by adding an inorganic salt, CaCl2, to the dope solution and fine-tuning the spinning conditions. An optimal CaCl2 dosage can not only effectively increase the dope viscosity but also reduce the mean pore size and narrow the pore size distribution of the polyethersulfone (PES) hollow fiber substrates. A high flowrate ratio of dope solution to bore fluid greatly enhances the mechanical strength of the PES substrates. The combination of these two strategies results in a more permeable, better-supported and less defective polyamide selective layer after interfacial polymerization. The best newly developed TFC hollow fiber has a power density of 38 W/m2 at 30 bar by using 1.2 M NaCl and deionized water as the feed pair. To our best knowledge, these are the highest power density and operation pressure ever achieved by PRO hollow fiber membranes in the literature. The improved performance will advance the PRO technology closer to commercialization and make osmotic energy more competitive with other renewable energies.

The preparation of polyamide/polyacrylonitrile thin film composite hollow fiber membranes for dehydration of ethanol mixtures

Abstract In this study, Polyamide (PA)/polyacrylonitrile (PAN) thin-film composite (TFC) hollow fiber membranes were fabricated to investigate the dehydration performances of ethanol mixtures by pervaporation. Amine monomers (ethylenediamine (EDA), 1, 6-hexanediamine (HDA), diethylenetriamine (DETA), and tetraethylenepentamine (TEPA)) with difference number of functional groups or chain length were selected to react with trimesoyl chloride (TMC) to prepare a PA dense thin-film onto the surface of asymmetric PAN hollow fiber membranes by way of interfacial polymerization. Attenuated total reflection infrared spectroscopy (FTIR-ATR), scanning electron microscope (SEM), atomic force microscope (AFM), light transmission, contact angle and positron annihilation spectroscopy (PAS) were used to characterize the physicochemical properties, morphologies and microstructure of the PA thin layer. The pervaporation performances of aqueous ethanol solution showed the permeation flux decreased while water content in permeate increased with increasing number of amine groups. The effects of monomer concentration and reaction time on the pervaporation performances of aqueous ethanol solution through TEPA-TMC/PAN TFC hollow fiber membranes were also investigated. A 342.0 ± 22.3 g/m 2 h permeation flux and 97.6 ± 0.3 wt.% water content in permeate were obtained for the pervaporation of 90 wt.% aqueous ethanol solution at 25 °C through the PA/PAN TFC hollow fiber membrane which was fabricated by immersing PAN hollow fiber membrane into 2 wt.% TEPA aqueous solution for 1 min and then contacting 1 wt.% TMC solution for 0.5 min.

Relating osmotic performance of thin film composite hollow fiber membranes to support layer surface pore size

Thin film composite (TFC) membranes are considered a preferred platform for forward osmosis (FO) wherein the selective and support layers can be tailored independently for preferred chemistry and structure. TFC hollow fiber membranes in particular have garnered interest because of their high packing density. In previous studies, TFC hollow fiber membranes were made by forming the selective layer via in-situ interfacial polymerization onto a porous supporting layer. These studies, however, have not examined how the surface properties of the support layer, the pore size in particular, impact the selective layer formation and its properties. In this study, we conducted a systematic investigation on the influence of support layer pore size on the osmotic performance of TFC hollow fiber FO membranes. A series of commercially available ultrafiltration membranes with similar physical and chemical properties but different pore sizes were employed as the support layers. The resulting roughness of the selective layer was found to be dependent on support layer pore size. Osmotic flux tests revealed that the membrane performance is dependent on this roughness with rougher membranes exhibiting higher fluxes in many cases. Aside from elucidating the impact of support layer pore size on osmotic performance, we also demonstrated the potential of making high performance FO membranes using existing commercial hollow fiber ultrafiltration membranes.

Improving CO2 separation performance of thin film composite hollow fiber with Pebax®1657/ionic liquid gel membranes

Blending CO2-selective ionic liquid with block copolymers have been shown to improve the gas separation performance. In this work, defect-free Pebax®1657/[emim][BF4] gel membranes were fabricated in the form of thin film composite hollow-fiber membranes to meet the mechanical stability and high packing density requirement for industrial application. Environmentally benign solvent comprising ethanol/water mixture (70/30 w/w) was selected to allow up to 80wt% IL loading with 300% improvement in CO2 permeability and CO2/N2 and CO2/CH4 selectivities of 36 and 15, respectively. Characterizations of membrane morphological change responding to the IL loading indicated that the preferential interaction between IL and PEO segments was by hydrogen bonding that resulted in decrease in polymer crystallinity, but this interaction inhibited potential interaction with CO2, which lowered the gas permeability below the estimated value. Examinations on the effects of various operating conditions on the TFC gel membranes showed excellent mechanical durability and chemical stability of the membranes and good CO2 separation performance with mixed-gas feed containing traces of water vapor and NOx, suggesting the potential application for CO2 capture with real gas feed. The stability of the high IL-loaded gel membranes with up to 8bar feed pressure also opens up possibility for other industrial gas applications.

Thin film composite hollow fiber membrane for separation in biorefinery

One of the newest applications of the membrane technology is for the separation of sugar component and inhibitor removal during biomass processing in biorefinery. Most of the membranes used in biorefinery were commercially purchased and not specifically customise for the biomass hydrolysate processing. In the current study, a series of thin film composite (TFC) hollow fiber membranes were fabricated to tailor the performance toward xylose/glucose refinement and acetic acid removal in biomass processing. Polysulfone (PSf) hollow fiber membrane support was prepared using 20 wt% PSf, 2 wt% polyvinylpyrrolidone K30 (PVP K30) and 78 wt% dimethylformamide (DMF) through dry/wet spinning process. Three types of aqueous monomers were studied in interfacial polymerisation process, which are piperazine (PIP), triethanolamine (TEOA) and polyethyleneimine (PEI). TFC hollow fiber membrane prepared using TEOA monomer showed the best performance for separation of biomass hydrolysate component. It exhibited rejection value 50.98 ± 4.11 % of xylose, 71.72 ± 3.92 % of glucose and 5.45 ± 1.93 % of acetic acid. This is corresponding to the ideal separation factor of 1.75 ± 0.10 for xylose/glucose, 3.42 ± 0.54 for acetic acid/glucose and 1.95 ± 0.20 for acetic acid/xylose.

Tuning water content in polymer dopes to boost the performance of outer-selective thin-film composite (TFC) hollow fiber membranes for osmotic power generation

The lack of effective membranes greatly hinders the use of pressure retarded osmosis (PRO) to harvest renewable osmotic energy. In comparison to the flat sheet and inner-selective hollow fiber configurations, the development of outer-selective hollow fiber membranes is much slower although it may be more attractive for real PRO applications. This study demonstrates that tuning the water content in polymer dopes can be an effective means to simultaneously enhance the mechanical robustness and water transport properties, boosting the PRO performance of outer-selective thin-film composite (TFC) hollow fiber membranes. Fundamental properties of polymer dopes with different water content and their influence on the hollow fiber supports as well as resultant TFC membranes were systematically investigated. With a low water content of 2wt% in the polymer dope, the newly developed TFC membrane not only has the smallest structural parameter, highest toughness, and largest water permeability among all membranes studied but also displays an impressive peak power density of 10.05W/m2 at 22bar using 1M NaCl and DI water as feeds. To our best knowledge, this is the highest power density of outer-selective TFC PRO hollow fiber membranes reported in the literature. Mathematical models predict that approximately 25% performance increase can be further achieved if the external concentration polarization (ECP) effect is minimized. This study may provide useful insights to design high performance outer-selective TFC hollow fiber membranes for osmotic power generation.

Experimental study of PES/SiO2 based TFC hollow fiber membrane modules for oilfield produced water desalination with low-pressure nanofiltration process

In this study, a PES/SiO2 based thin film composite (TFC) hollow fiber membrane (HFM) was prepared for the oilfield produced water desalination with low-pressure nanofiltration process. The effects of operating parameters including pressure, salt concentration and time, on the salt rejection were investigated. The results showed that the salt rejection increased linearly with an increase in operating pressure from 50psi to 80psi, decreasing slightly with a further increase in pressure to 100psi. The increased salt concentration resulted in a decrease in salt rejection. A solution diffusion theory-based model was proposed to well explain the laboratory testing results.

Evolution of micro-deformation in inner-selective thin film composite hollow fiber membranes and its implications for osmotic power generation

Since thin film composite (TFC) hollow fiber (HF) membranes may experience micro-deformation under high hydraulic pressures in the pressure retarded osmosis (PRO) process due to their polymeric nature and self-supported configuration, this paper aims to elucidate (1) the micro-deformation of polyethersulfone (PES) TFC HF membranes within the pressure range from 0 to 20bar and (2) its effects on water and salt permeability of the polyamide layer, and structure parameter and tortuosity of the substrate layer for osmotic power generation. It is found that pre-stabilization of the TFC HF membranes at a high pressure close to their burst pressures for a certain period of time is a powerful way to maximize their PRO performance. After stabilization at 20bar for 30min, the power density of the PES TFC HF membranes increase from 15.37 to 22.05W/m2 due to the increased membrane surface area, stretched polyamide selective layer (i.e., decreased water transport length and resistance) and decreased membrane structure parameter (i.e., lower tortuosity and internal concentration polarization (ICP)). The intermittent cycle tests have confirmed the sustainability of the enhanced water flux and power density after stabilization of the TFC HF membranes at 20bar without compromising their selectivity.

Interfacial polymerization on PES hollow fiber membranes using mixed diamines for nanofiltration removal of salts containing oxyanions and ferric ions

Thin film composite (TFC) hollow fiber nanofiltration (NF) membranes were fabricated via interfacial polymerization, with mixed diamines of piperazine (PIP) and 2,2′-bis(1-hydroxyl-1-trifluoromethyl-2,2,2-triflutoethyl)-4,4′-methylenedianiline (BHTTM) as water phase and trimesoyl chloride (TMC) as organic phase. Fabricated membranes were characterized for ATR-FTIR, SEM, AFM, and water contact angle. Formation conditions of the selective polyamide layer have been optimized for a good NF membrane performance. The pure water flux of NF membrane prepared under optimized conditions was 31.2L·m−2·h−1 and the rejection for Na2SO4 was 99.7% at 6bar. The rejections of NF membranes for different salts followed the order: Na2SO4>MgSO4>NaCl>MgCl2. The molecular weight cut-off of NF membrane was around 300Da. The performance of NF membranes was stable during a 7-day filtration process for rejecting different species ions including heavy metal ferric ion (FeCl3 and Fe2(SO4)3) and oxyanions (SO42− and HPO42−), in addition to different inorganic salts. Also, the NF membranes exhibited chlorine tolerant property. This work demonstrates the potential of PES outer-selective TFC hollow fiber membranes for desalination or water softening process, provides database to fabricate suitable NF membranes for long-term salts removal and raise a simple technique to form a thin chlorine-tolerant polyamide layer.

Analysis of flux reduction behaviors of PRO hollow fiber membranes: Experiments, mechanisms, and implications

Pressure retarded osmosis (PRO) is a promising technology to harvest renewable osmotic energy using a semipermeable membrane. However, a significant flux reduction has been always observed that severely shrinks the harvestable power to a level only marginally higher or even lower than the economically feasible value. This work focuses on the elucidation of various underlying mechanisms responsible for the flux reduction. First, both inner-selective and outer-selective thin film composite (TFC) hollow fiber membranes are employed to examine how the fundamental internal factors (such as the surface salinity of the selective layer at the feed side (CF,m) and its components) interact with one another under the fixed bulk salinity gradient, resulting in various behaviors of external performance indexes such as water flux, reverse salt flux, and power density. Then, the research is extended to investigate the effects of the growing bulk feed salinity due to the accumulated reverse salt flux along PRO modules. Finally, the insights obtained from the prior two stationary conditions are combined with the advanced nucleation theory to elucidate the dynamic scaling process by visualizing how the multiple fundamental factors (such as local supersaturation, nucleation rate and nuclei size) evolve and interplay with one another in various membrane regimes during the whole scaling process. To our best knowledge, it is the first time that the advanced nucleation theory is applied to study the PRO scaling kinetics in order to provide subtle and clear pictures of the events occurring inside the membrane. This study may provide useful insights to design more suitable TFC hollow fiber membranes and to operate them with enhanced water flux so that the PRO process may become more promising in the near future.

Outer-selective thin film composite (TFC) hollow fiber membranes for osmotic power generation

The pressure-retarded osmosis (PRO) process is a green technique for power generation to respond the world's need of energy sustainability. In this study, we have developed the vital component of the process, i.e. membrane, in the configuration of the outer-selective thin-film composite (TFC) hollow fiber, which is more practical than other configurations in the real applications. The support layer morphology and the formation of the selective polyamide layer have been optimized for a good PRO performance. The results show that the bore fluid with higher amount of the solvent N-methyl-2-pyrrolidone leads to full finger-like hollow fibers, which provide higher flux but lower pressure tolerance. The addition of higher amount of diethylene glycol into the dope solution, improves the pore formation and suppresses the macrovoid formation, while properly lowering the take-up speed increases their wall thickness and pressure tolerance. A simple alcohol-pre-wetting approach on the fiber support leads to a smooth and thin polyamide layer, which is favorable for a high water flux and power density. Its efficiency follows this order: n-propanol>ethanol>methanol>water. The n-propanol pre-wetted TFC membrane can tolerate 17bar with a peak power density of 9.59W/m2 at room temperature, using 1M NaCl solution as the draw solution and DI water as feed. This work demonstrates the potential of outer-selective TFC hollow fiber membranes for energy conversion via PRO process, provides useful database to fabricate suitable support morphology and raise a simple technique to practically form a thin and smooth polyamide layer.

Robust outer-selective thin-film composite polyethersulfone hollow fiber membranes with low reverse salt flux for renewable salinity-gradient energy generation

This study reports outer-selective thin-film composite (TFC) hollow fiber membranes with extremely low reverse salt fluxes and robustness for harvesting salinity-gradient energy from pressure retarded osmosis (PRO) processes. Almost defect-free polyamide layers with impressive low salt permeabilities were synthesized on top of robust polyethersulfone porous supports. The newly developed TFC-II membrane shows a maximum power density of 7.81Wm−2 using 1M NaCl and DI water as feeds at 20bar. Reproducible data obtained in the 2nd and 3rd runs confirm its stability under high hydraulic pressure differences. Comparing to other PRO membranes reported in the literature, the newly developed membrane exhibits not only the smallest slope between water flux decline and ΔP increase but also the lowest ratio of reverse salt flux to water flux. Thus, the effective osmotic driving force could be well maintained even under high pressure operations. For the first time, the effect of feed pressure buildup induced by feed flowrate was evaluated towards PRO performance. A slight increment in feed pressure buildup was found to be beneficial to water flux and power density up to 10.06Wm−2 without comprising the reverse salt flux. We believe this study may open up new perspectives on outer-selective PRO hollow fiber membranes and provide useful insights to understand and design next-generation outer-selective TFC hollow fiber membranes for osmotic power generation.

Green modification of outer selective P84 nanofiltration (NF) hollow fiber membranes for cadmium removal

Outer-selective thin-film composite (TFC) hollow fiber membranes are normally made from interfacial polymerization of m-phenylenediamine (MPD) and trimesoyl chloride (TMC). However, the removal of excess MPD solution and the large consumption of alkane solvents are their technical bottlenecks. In this study, green methods to prepare the outer selective TFC hollow fiber membranes were explored by firstly modifying the membrane substrate with polyethyleneimine (PEI) and then by water soluble small molecules such as glutaraldehyde (GA) and epichlorohydrin (ECH). Using P84 polyimide as the substrate, not only do these modifications decrease substrate's pore size, but also vary surface charge by making the membranes less positively charged. As a result, the resultant membranes have higher rejections against salts such as Na2SO4, NaCl and MgSO4. The PEI and then GA modified membrane has the best separation performance with a NaCl rejection over 90% and a pure water permeability (PWP) of 1.74±0.01Lm−2bar−1h−1. It also shows an impressive rejection to CdCl2 (94%) during long-term stability tests. The CdCl2 rejection remains higher than 90% at operating temperatures from 5 to 60°C. This study may provide useful insights for green manufacturing of outer-selective nanofiltration (NF) hollow fiber membranes.

Engineering design of outer‐selective tribore hollow fiber membranes for forward osmosis and oil‐water separation

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