Porous Hollow Fiber Research Articles

The effect of the production method on the mechanical strength of an alumina porous hollow fiber

The mechanical strength of inorganic porous hollow fibers is an important property and is strongly affected by the production method. Three production methods for fibers are compared: non-solvent induced phase separation (NIPS), bio-ionic gelation with an internal multivalent ion source (BIG-I), and with an external ion source (BIG-E). The BIG-E fibers show insufficient mechanical integrity for strength analysis. Fibers prepared via BIG-I have a larger bending strength compared to fibers prepared using NIPS or BIG-E, combined with a larger scatter in their strength data. The large scatter likely originates from surface deformations present in the fiber wall, which can be reduced by further optimization of the production method. Statistical models are fitted to the measured strength data. The NIPS and BIG-I production methods yield fibers of which the strength distribution follows the Weibull model, presuming failure occurs at the weakest link.

Electrospray Ionization-Ion Mobility Spectrometry in the Negative Mode Combined with Hollow Fiber Liquid–Liquid–Liquid Microextraction for the Determination of Diclofenac in Urine and Plasma Samples

The combination of hollow fiber liquid–liquid–liquid microextraction and electrospray ionization-ion mobility spectrometry (ESI-IMS) was used for the analysis of diclofenac in biological samples. Diclofenac was extracted from an acidic aqueous sample into methanol as an acceptor phase, through n-dodecane impregnated in the hollow fiber pores. The extracted drug was detected with ESI-IMS in the negative mode. Extraction parameters including pH of donor phase, stirring rate, sample ionic strength, temperature and extraction time were studied. The linearity of the method for the determination of diclofenac was in the range of 100–2000 and 60–2000 µg L−1 for plasma and urine, respectively. The detection limit of the method was also 34 and 21 µg L−1 in the plasma and urine, respectively. The applicability of the method for analyzing the analyte in biological samples was investigated. The method was also applied to analysis of urine and plasma of a healthy volunteer after oral administration of diclofenac.

Solvent bar microextraction using a reverse micelle containing extraction phase for the determination of warfarin from human plasma by high-performance liquid chromatography

For the first time, solvent bar microextraction using a reverse micelle RMM-SBME as extraction phase was developed for extraction of warfarin in human plasma sample. The reverse micelle of a cationic surfactant (hexadecyltrimethylammonium bromide) in 1-octanol was applied as supported and acceptor phase in SBME. In this process, the analyte was extracted from aqueous samples into a reverse micelle impregnated and also filled in the wall pores and lumen the polypropylene hollow fiber membrane by the electrostatic interactions between the analyte and the surfactant head groups. The influences of fundamental parameters affecting extraction efficiency of warfarin including sample solution pH, surfactant concentration and extraction time were studied using central composite design optimization method. The analysis of extracted analyte was performed by high performance liquid chromatography with ultra violet detector.Under the optimum condition, the sample containing 40ngmL−1 of warfarin was extracted with extraction recovery of 97.8% that pertained to enrichment factor of 260. A good linearity over a concentration range 1–600ngmL−1 with correlation coefficient value of 0.9989 was provided by the current method. Limits of detection and inner and inter-day relative standard deviation were 0.3ngmL−1 and less than 4.4%, respectively. This method was compared to conventional SBME, and illustrated higher extraction efficiency. The method needs minimal sample preparation time since the porous hollow fiber membrane prevents from being extracted potential interfering materials, acts as a filter, and any extra cleanup was not required. The method with bar of 3cm and acceptor phase volume of 8.5μL is environmentally green/friendly method. The proposed method was successfully applied for the preconcentration and determination of warfarin in plasma sample.

An automated lab-scale flue gas permeation membrane testing system at the National Carbon Capture Center

A constant pressure, mixed gas permeation testing skid was deployed at the National Carbon Capture Center to test membrane performance when continuously exposed to slipstream post-combustion flue gas. Small, laboratory scale membranes can be loaded for testing and the degree of automation allowed the skid to be run unattended for several weeks at a time. In this report, we share our experience in commissioning the skid and quantifying CO2, N2 and O2 permeances of several membranes during the first round of testing. Dense films of polydimethylsiloxane and poly(bistrifluoroethoxyphosphazene) were tested with flue gas for approximately 20h each. In addition, we successfully tested four thin film composite hollow fiber membranes made by a dip coating process, consisting of porous Torlon hollow fibers coated with a selective layer of poly(bistrifluoroethoxyphosphazene) or its mixed matrix with a metal organic framework SIFSIX-Cu-2i filler particles. Initial results suggest the polydimethylsiloxane showed comparable results to the literature data, but the coated hollow fiber membranes have lower CO2 permeances relative to N2 or O2 permeances compared to their performance under idealized, dry, contaminant-free mixed gas conditions. While quantification of H2O permeance was performed, we found it was affected by concentration polarization even with small membrane area and a low stage cut.

Polysulfone porous hollow fiber membranes for ethylene-ethane separation in gas-liquid membrane contactor

Abstract Separation of olefin from paraffin having same carbon number is one of the most energy intensive separations in petrochemical processes. Employing gas-liquid membrane contactors for olefin/paraffin separation is very attractive. In the present work, the membrane contactor ethylene/ethane separation was investigated based on porous asymmetric polysulfone hollow fiber membranes having mesoporous (dav ∼ 2 nm) skin layer structure in contrast to conventional ultrafiltration membranes (dav ∼ 50–100 nm). Also, the membranes selective layer surface was modified to increase its hydrophobic properties expecting that pore size and surface properties tailoring prevents liquid absorbent penetration into membrane pores. The membrane contactor performance was studied under various operating parameters such as absorbent (aqueous AgNO3) solution concentration and gas and liquid flow rates. Ethylene permeance value was 185 L/(m2 h bar), which is at the level of the best results available in literature for porous membranes, at ethylene recovery rate up to 39%, which is three times higher than that in literature. Modified membranes were characterized after membrane contactor experiments. SEM, EDX and XRD analysis as well as gas permeance measurements showed that silver nitrate crystals deposition in the membranes pore space occurs. However, no noticeable change of membrane contactor performance was observed during two months of experiments on ethylene/ethane separation.

Nano-grained SnO2/Li4Ti5O12 composite hollow fibers via sol-gel/ electrospinning as anode material for Li- ion batteries

The high capacity of SnO2 (tin oxide) and high rate capability of Li4Ti5O12 (lithium titanate, LTO) were pooled together for engineering a composite Li ion anode material in hollow fiber edifice by sol-gel/electrospinning. The electrospun porous precursor composite hollow fibers (CHFs) were heat treated either in air (SnO2/LTOA) or argon (SnO2/LTOAr) atmosphere to control grain size, porosity and presence of Ti3+ content. The morphological study performed using Field Emission Scanning Electron Microscopy and Transmission Electron Microscopy revealed smaller grain size (5–10 nm) for SnO2/LTOAr CHFs. Further, X-Ray Diffraction and X- Ray Photoelectron Spectroscopy studies illustrated a significant variation in the crystallinity and the elemental oxidation states in these CHFs respectively. Brunauer-Emmett-Teller measurements exposed the presence of high surface area and pore volume in SnO2/LTOAr CHFs. Further, the half-cell galvanostatic charge-discharge performances of SnO2/LTOAr CHFs at 1 C rate revealed a stable specific capacity of 300 mA h/g for 110 cycles with 90% capacity retention. The stable and high capacity of SnO2/LTOAr CHFs were corroborated to the presence of smaller grain size, high porosity and conductive Ti3+ providing faster lithium ion diffusion when compared to SnO2/LTOA CHFs. Electrochemical Impedance Spectroscopy study confirmed low impedances in SnO2/LTOAr CHFs due to low charge transfer and electrolyte resistances. Moreover, Li ion full-cell study performed using LiFePO4 (LFP) cathode (3 V), delivered a specific capacity of 230 mAh/g at 0.1 C rates. The excellent electrochemical performance of SnO2/LTOAr CHFs in both half-cell and full-cell modes illustrated the significance of sol-gel/electrospinning in synthesizing high performance Lithium ion batteries in a cost effective and scalable way.

Membrane-Based Technologies in the Pharmaceutical Industry and Continuous Production of Polymer-Coated Crystals/Particles.

Membrane technologies are of increasing importance in a variety of separation and purification applications involving liquid phases and gaseous mixtures. Although the most widely used applications at this time are in water treatment including desalination, there are many applications in chemical, food, healthcare, paper and petrochemical industries. This brief review is concerned with existing and emerging applications of various membrane technologies in the pharmaceutical and biopharmaceutical industry. The goal of this review article is to identify important membrane processes and techniques which are being used or proposed to be used in the pharmaceutical and biopharmaceutical operations. How novel membrane processes can be useful for delivery of crystalline/particulate drugs is also of interest. Membrane separation technologies are extensively used in downstream processes for bio-pharmaceutical separation and purification operations via microfiltration, ultrafiltration and diafiltration. Also the new technique of membrane chromatography allows efficient purification of monoclonal antibodies. Membrane filtration techniques of reverse osmosis and nanofiltration are being combined with bioreactors and advanced oxidation processes to treat wastewaters from pharmaceutical plants. Nanofiltration with organic solvent-stable membranes can implement solvent exchange and catalyst recovery during organic solvent-based drug synthesis of pharmaceutical compounds/intermediates. Membranes in the form of hollow fibers can be conveniently used to implement crystallization of pharmaceutical compounds. The novel crystallization methods of solid hollow fiber cooling crystallizer (SHFCC) and porous hollow fiber anti-solvent crystallization (PHFAC) are being developed to provide efficient methods for continuous production of polymer-coated drug crystals in the area of drug delivery. This brief review provides a general introduction to various applications of membrane technologies in the pharmaceutical/biopharmaceutical industry with special emphasis on novel membrane techniques for pharmaceutical applications. The method of coating a drug particle with a polymer using the SHFCC method is stable and ready for scale-up for operation over an extended period.

Continuous Flow Processing of ZIF-8 Membranes on Polymeric Porous Hollow Fiber Supports for CO2 Capture.

We have utilized an environmentally friendly synthesis approach for the accelerated growth of a selective inorganic membrane on a polymeric hollow fiber support for postcombustion carbon capture. Specifically, continuous defect-free ZIF-8 thin films were grown and anchored using continuous flow synthesis on the outer surface of porous supports using water as solvent. These membranes demonstrated CO2 permeance of 22 GPU and the highest reported CO2/N2 selectivity of 52 for a continuous flow synthesized ZIF-8 membrane.

Simultaneous speciation of inorganic chromium(III) and chromium(VI) by hollow-fiber-based liquid-phase microextraction coupled with HPLC-UV.

The speciation of chromium(VI) and chromium(III) was investigated by using hollow fiber liquid-phase microextraction based on two immiscible organic solvents followed by high performance liquid chromatography with ultraviolet detection. In this method, chromium(VI) and chromium(III) reacted with ammonium pyrrolidine dithiocarbamate to produce hydrophobic complexes. Subsequently, the complexes were first extracted into a thin layer of organic solvent (n-dodecane) present in the pores of a porous hollow fiber, and then into a μL volume of an organic acceptor (methanol) located inside the lumen of the hollow fiber. Then, the extracting organic phase was injected into the separation column of the high-performance liquid chromatograph for the analysis of both chromium species. Effective parameters on extraction were optimized using one-variable-at-a-time method and central composite design. Under optimized conditions, a linear range of 0.25-100 and 0.5-100 μg/L (R2 > 0.998), the limits of detection of (S/N = 3) 0.08 and 0.1 μg/L and a preconcentration factor of 625 and 556 were achieved for chromium(VI) and chromium(III), respectively. The method was successfully applied to the speciation and determination of chromium species in different water samples and satisfactory results were obtained.

Application of modified hollow fiber liquid phase microextraction in conjunction with chromatography-electron capture detection for quantification of acrylamide in waste water samples at ultra-trace levels

Herein, a simple and sensitive method was successfully developed for the extraction and quantification of acrylamide in water samples. Initially, acrylamide was derivatized through a bromination process. Subsequently, a modified hollow-fiber liquid-phase microextraction was applied for the extraction of the brominated acrylamide from a 10-ml portion of an aqueous sample. Briefly, in this method, the derivatized acrylamide (2,3-dibromopropionamide) was extracted from the aqueous sample into a thin layer of an organic solvent sustained in pores of a porous hollow fiber. Then, it was back-extracted using a small volume of organic acceptor solution (acetonitril, 25μl) located inside the lumen of the hollow fiber followed by gas chromatography–electron capture detection (GC–ECD). The optimal conditions were examined for the extraction of the analyte such as: the organic solvent: dihexyl ether+10% tri-n-octyl phosphine oxide; stirring rate: 750rpm; no salt addition and 30min extraction time. These optimal extraction conditions allowed excellent enrichment factor values for the method. Enrichment factor, detection limit (S/N=3) and dynamic linear range of 60, 2ngL−1 and 50–1000ngL−1 to be determined for the analyte. The relative standard deviations (RSD%) representing precision of the method were in the range of 2.2–5.8 based on the average of three measurements. Accuracy of the method was tested by the relative recovery experiments on spiked samples, with results ranging from 93 to 108%. Finally, the method proved to be simple, rapid, and cost-effective for routine screen of acrylamide-contaminated highly-complicated untreated waste water samples.

Porous polyethersulfone hollow fiber membrane in oily wastewater treatment

Porous polyethersulfone hollow fiber membrane in oily wastewater treatment

The mechanical strength of a ceramic porous hollow fiber

The mechanical strength of inorganic porous hollow fibers is a critical constraint that limits their wide scale application. Various methods, including 3-point bending, 4-point bending, and diametrical compression are used for the quantification of the mechanical strength. Here, we show that these methods cannot be used in an interchangeable manner. For large sets of alumina hollow fibers, the parameters describing the cumulative probability of failure functions depend on the type of measurement, i.e., 3 or 4-point, the span size, and the measurement geometry. This implies that reporting data on mechanical properties of inorganic hollow fibers requires that extensive information about the experimental details is provided, and that a direct quantitative comparison between datasets is unjustifiable. The mechanical strength of the alumina hollow fibers tends to follow a normal distribution, or log-normal distribution, instead of the often used Weibull distribution. Monte Carlo simulations demonstrate that, especially at small sample set sizes, it is difficult to accurately determine the shape of the probability distribution. However, detailed knowledge of the type and the shape of this distribution function is essential when mechanical strength values are to be used in further design.

Porous polyethersulfone hollow fiber membrane in CO2 separation process via membrane contactor - The effect of nonsolvent additives

A membrane contactor (MC) is used for natural gas sweetening and wastewater treatment with a membrane that is acting as a separating barrier between two phases, usually liquid and gas. The performance of membrane is governed by parameters such as pore size, porosity, tortuosity and surface hydrophobicity, which can be controlled by a number of methods. Addition of nonsolvents to spinning solution is known to be one of such methods. In this study, the effects of low molecular weight additives as phase inversion promoters on the morphology of polyethersulfone hollow fiber membranes and their performance in gas-liquid MC processes were investigated. It was found that among the six nonsolvent additives under study, addition of water resulted in the highest CO2 flux, by decreasing the thermodynamic stability of polymer solution and maintaining high solvent-nonsolvent exchange rate.

Porous hollow fiber membranes with varying hydrophobic–hydrophilic surface properties for gas–liquid membrane contactors

In relation to the demand for asymmetric porous hollow fiber membranes to be used in gas–liquid membrane contactors designed for operation in organic media, polysulfone membranes of this type have been prepared and subsequently modified to impart oleophobic properties to their surface. The structure and properties of the membranes have been characterized using various techniques, such as optical and scanning electron microscopy, and by measuring contact angles and the permeability of helium, carbon dioxide, and hexane. The surface properties of the membranes have been modified by etching with a mixture of hydrogen peroxide and sulfuric acid or coating with a perfluorinated acrylic copolymer. In the latter case, modified membrane samples have shown a significant reduction in wettability with both water and organic liquids. The hexane permeability data indicate the absence of hexane flow through the membrane modified with perfluorinated acrylic copolymer until a gauge pressure of about 1 atm. The results of the study lead to the conclusion that these membranes can find use in gas–liquid membrane contactors, e.g., for the removal of dissolved gases from liquid hydrocarbons.

Preparation and characterization of inner-pressure hollow fiber composite membrane via two-way coating technique for CO2/CH4 separation

High-selectivity inner-pressure hollow fiber composite (HFC) membrane for CO2/CH4 separation was prepared through the Two-way coating (TWC) technique. The blends of poly(vinylamine) (PVAm)/polyvinyl alcohol (PVA) were coated onto porous hollow fiber polysulfone (PSF) ultrafiltration (UF) membrane with an effective membrane area of 0.4 m2. The effects of fabrication parameters on the permselectivity of the resultant HFC membrane were investigated and the optimum preparation conditions were obtained as follows: coating time for 30 min and air blowing time for 30 min after the coating. The prepared HFC membrane showed the typical characteristic of fixed carrier membrane with a high selectivity of CO2 and CH4: the separation factor of CO2/CH4 (40 vol% CO2 at 25 °C and 0.2 MPa) was 36.6 and the CO2 permeability was 56.3 GPU. Field emission scanning electron microscopy (FESEM) images indicated that the HFC membrane prepared by TWC technique had a uniform coating layer along the whole hollow fiber. Membrane permselectivity showed almost no difference between different membrane sections. The HFC membrane showed a good stability during the continuous testing process of 540 h. And the HFC membrane preserved at 30 °C and 40 % humidity exhibited a good durability with a basically unchanged separation factor after 30 days.

An innovative method for analysis of Pb (II) in rice, milk and water samples based on TiO2 reinforced caprylic acid hollow fiber solid/liquid phase microextraction.

In the present study, nano-sized titanium oxides were applied for preconcentration and determination of Pb(II) in aqueous samples using hollow fiber based solid-liquid phase microextraction (HF-SLPME) combined with flame atomic absorption spectrometry (FAAS). In this work, the nanoparticles dispersed in caprylic acid as an extraction solvent was placed into a polypropylene porous hollow fiber segment supported by capillary forces and sonification. This membrane was in direct contact with solutions containing Pb (II). The effect of experimental conditions on the extraction, such as pH, stirring rate, sample volume, and extraction time were optimized. Under the optimal conditions, the performance of the proposed method was investigated for the determination of Pb (II) in food and water samples. The method was linear in the range of 0.6-3000μgmL-1. The relative standard deviations and relative recovery of Pb (II) was 4.9% and 99.3%, respectively (n=5).

Hollow fiber integrated microfluidic platforms for in vitro Co-culture of multiple cell types.

This study demonstrates a rapid prototyping approach for fabricating and integrating porous hollow fibers (HFs) into microfluidic device. Integration of HF can enhance mass transfer and recapitulate tubular shapes for tissue-engineered environments. We demonstrate the integration of single or multiple HFs, which can give the users the flexibility to control the total surface area for tissue development. We also present three microfluidic designs to enable different co-culture conditions such as the ability to co-culture multiple cell types simultaneously on a flat and tubular surface, or inside the lumen of multiple HFs. Additionally, we introduce a pressurized cell seeding process that can allow the cells to uniformly adhere on the inner surface of HFs without losing their viabilities. Co-cultures of lung epithelial cells and microvascular endothelial cells were demonstrated on the different platforms for at least five days. Overall, these platforms provide new opportunities for co-culturing of multiple cell types in a single device to reconstruct native tissue micro-environment for biomedical and tissue engineering research.

Modification of polysulfone porous hollow fiber membranes by air plasma treatment

Air plasma treatment was used to enhance the surface hydrophilic properties of the polysulfone porous hollow fiber membranes prepared via a dry-wet phase invertion technique in the free spinning mode in air. Membranes prepared had porous asymmetric structure with macroporous support on the shell side and fine-porous selective layer on the lumen side. The wettability of the inner membrane surfaces were checked by contact angle measurements and FTIR was used to compare the surfaces before and after plasma treatment. Membrane morphology was examined with confocal scanning laser microscopy (CSLM). Contact angle measurements confirm that air plasma treatment affords improvement in the wettability of polysulfone membranes and FTIR results show that air plasmas chemically modify the lumen side membrane surface, however, there is no significant change in membranes chemical structure after modification. CSLM data obtained, as well as gas permeability (He and CO2) measurements show that after plasma treatment pore etching occurs.

Effect of hydrophobic modification on carbon dioxide absorption using porous alumina (Al2O3) hollow fiber membrane contactor

Porous alumina (Al2O3) hollow fiber membranes were successfully prepared using phase inversion spinning and sintering technique. Hydrophilic surface of porous Al2O3 hollow fiber membrane was modified with a fluoroalkylsilane (FAS) solution that was used as hydrophobic agent for treating the surface of Al2O3 hollow fiber membranes. The unmodified and modified porous Al2O3 membranes were characterized using scanning electron microscopy, mercury porosimetry, gas permeation testing equipment, energy-dispersive X-ray spectroscopy, thermogravimetric analysis, and the contact angle analyzer. The hydrophobicity of the porous Al2O3 hollow fiber membrane increased with increasing FAS coating time. The effect of the FAS coating on the CO2 absorption performance was also investigated. As a result, the CO2 absorption flux decreased with increasing FAS coating time. In particular, these experiments revealed that 2h coating was sufficient to obtain an optimal hydrophobic protection against the wetting process of the Al2O3 hollow fiber membrane pores. In addition, the best performance for CO2 absorption flux was achieved with the Al2O3 hollow fiber membrane modified for 2h coating. The maximum CO2 absorption flux of surface modified Al2O3 hollow fiber membrane was 6.022×10−3mol/m2s with a liquid flow rate of 50ml/min at room temperature. Finally, a 50-hours-long stability test demonstrates that the modified porous Al2O3 hollow fiber membranes are stable and promising for membrane contactors.

Preconcentration and determination of naproxen in water samples by functionalized multi-walled carbon nanotubes hollow fiber solid phase microextraction—HPLC

A simple, sensitive and selective solid phase microextraction with hollow fiber-supported multi-walled carbon nanotube functionalization reinforced sol–gel combined HPLC method was proposed for the determination of naproxen in tap, well and river water samples. In this method, functionalized multi-walled carbon nanotubes (MWCNTs) were prepared and held in pores of hollow fiber with sol–gel technology by immersion of polypropylene hollow fiber segment into the sol of the functionalized MWCNTs/silica composite and ultrasonically treated at room temperature. Effect of main parameters such as volume of donor phase, pH, extraction time, desorption time, type of desorption solvent, sample ionic strength and stirring rate were studied. Under optimum conditions, linearity was observed in the range of 0.03–500 ng/mL, with correlation coefficients of 0.997. The relative standard deviation for three replicate determinations of 50 ng/mL of naproxen was 4.3%. Limit of detection and pre-concentration factor were 0.008 ng/mL and 198, respectively. In order to check the applicability of the proposed method, it was used to determine trace levels of naproxen in different water samples.