Fabrication Of Hollow Fiber Membranes Research Articles

The Comparison of Polyethersulfone (PES)/N-Methyl 2-Pyrrolidone (NMP) on the Fabrication of Hollow Fiber Membranes with Commercial Membranes for Applications Hemodialysis

The decrease in kidney function is caused by an increase in creatinine and urea levels in the blood; this is the cause of chronic kidney failure (GGK) in patients. Hemodialysis membrane technology is an alternative treatment for chronic renal failure by separating dissolved components in the blood, such as creatinine and urea, using dialysate fluid by passing through the membrane pores. Therefore, the characteristics of hemodialysis membranes become essential to meet the requirements of a dialyzer. This study aimed to compare the features of the resulting hemodialysis membrane with several commercial membranes. In this study, there were four kinds of commercial membranes used, namely F8HPS, FX80, LO PS 15, and Nipro Elisio 15-H, were compared with membrane products that have variations in the composition of polyethylene (PES) using N-methyl-2-pyrolidone (NMP) solvents are 22.5; 24; and 25%. The membrane manufacturing method uses nonsolvent-induced precipitation (NISP). The resulting hollow fiber membrane is characterized by surface morphology using a scanning electron microscope (SEM), functional groups (FT-IR), and tensile test analysis (DMA). The results showed that the composition of PES/NMP is 25%, close to the characteristics of Nipro Elisio 15-H.

Lowering spinning temperature for polyketone (PK) hollow fiber membrane fabrication with low-toxic diluent system via thermally induced phase separation

Due to the excellent solvent resistance properties of polyketone (PK), the traditional non-solvent induced phase separation (NIPS) preparation process is both highly toxic and complex. In this work, we successfully and efficiently prepared PK hollow fiber membranes using the thermally induced phase separation (TIPS) method, capitalizing on a low-toxicity diluent system of polyethylene glycol 300 (PEG300) and triethylene glycol (TEG). Moreover, by simply adding TEG to the diluent, we achieved a reduction in the spinning temperature, resulting in membranes that display an interconnected structure formed through the liquid-liquid phase separation process. We systematically investigated the impact of the TEG ratio in the diluent, PK concentration, and propylene carbonate (PC) ratio in the bore liquid on the phase diagram, membrane morphology, and characteristics of PK membranes. Increasing the PC ratio in the bore liquid significantly improves the inner surface porosity due to PC penetration into the dope solution, leading to high water permeability. Additionally, the resulting PK membrane exhibits exceptional resistance to organic solvents. This work introduces a novel approach to lower the spinning temperature for PK membrane preparation in the TIPS process while preserving the membrane structure and properties.

A novel organic solvent-free method for manufacturing polyethersulfone hollow fiber membranes using melt extrusion

Hollow fiber membranes are traditionally manufactured using the spinning process, which takes advantage of the phase separation/inversion for the creation of a porous structure. In this work, the use of melt extrusion led to the fabrication of hollow fiber membranes without the use of organic solvents. Following post-treatment, the fabricated partially dense fibers are transformed into porous fibers. In detail, ternary blends of polyethersulfone/poly(ethylene glycol)/poly(N-vinyl pyrrolidone) (PESU/PEG/PVP) were developed by combining a solvent-free liquid mixture of PEG/PVP into PESU. Using a single screw extruder, this blend was melted and extruded using an annular slit nozzle where PEG functioned as a plasticizer, i.e., decreased processing temperatures, while PVP aided in retaining the hollow fiber geometry. These hollow fibers were comprised of uniformly closed pores, occurring due to the expansion and formation of bubbles of evaporating PEG nucleated by PVP during extrusion. By immersing these fibers into an aqueous solution of sodium hypochlorite (NaOCl), PEG and PVP were removed, which led to an open porous structure with pore sizes between 100 nm and 1 μm throughout the membrane. The outer surfaces of the hollow fibers were found to contain a higher PVP content than the inner surface. As PVP and PESU are miscible, i.e., blended in a single phase, treatment with NaOCl led to the creation of open pores on the outer surface with pore sizes between 10 and 150 nm, thus deeming the outer surface functional as a separation layer. The effect of blend composition, extrusion settings, and post-treatment parameters on membrane morphology, water flux, thermal characteristics, and tensile strength was studied, while after the modification, near-pristine PESU membranes were pursued. A water-flux of 28 L/h m2 bar and a molecular weight cut-off (MWCO) of 90%, 75%, and 40% for poly(ethylene oxide) of an average of 1000 kDa, 400 kDa, and 100 kDa molecular weight, respectively, proved that via extrusion it is possible to produce hollow fiber membranes for ultrafiltration without the use of organic solvents.

Effect of Molecular Weight and Chemical Structure of Terminal Groups on the Properties of Porous Hollow Fiber Polysulfone Membranes

For the first time, polysulfones (PSFs) were synthesized with chlorine and hydroxyl terminal groups and studied for the task of producing porous hollow fiber membranes. The synthesis was carried out in dimethylacetamide (DMAc) at various excesses of 2,2-bis(4-hydroxyphenyl)propane (Bisphenol A) and 4,4'-dichlorodiphenylsulfone, as well as at an equimolar ratio of monomers in various aprotic solvents. The synthesized polymers were studied by nuclear magnetic resonance (NMR), differential scanning calorimetry, gel permeation chromatography (GPC), and the coagulation values of 2 wt.% PSF polymer solutions in N-methyl-2-pyrollidone were determined. According to GPC data, PSFs were obtained in a wide range of molecular weights Mw from 22 to 128 kg/mol. NMR analysis confirmed the presence of terminal groups of a certain type in accordance with the use of the corresponding monomer excess in the synthesis process. Based on the obtained results on the dynamic viscosity of dope solutions, promising samples of the synthesized PSF were selected to produce porous hollow fiber membranes. The selected polymers had predominantly -OH terminal groups and their molecular weight was in the range of 55-79 kg/mol. It was found that porous hollow fiber membrane from PSF with Mw 65 kg/mol (synthesized in DMAc with an excess of Bisphenol A 1%) has a high helium permeability of 45 m3/m2∙h∙bar and selectivity α (He/N2) = 2.3. This membrane is a good candidate to be used as a porous support for thin-film composite hollow fiber membrane fabrication.

Open Pore Ultrafiltration Hollow Fiber Membrane Fabrication Method via Dual Pore Former with Dual Dope Solution Phase.

Hollow-fiber membranes are widely used in various fields of membrane processes because of their numerous properties, e.g., large surface area, high packing density, mass production with uniform quality, obvious end-of-life indicators, and so on. However, it is difficult to control the pores and internal properties of hollow-fiber membranes due to their inherent structure: a hollow inside surrounded by a wall membrane. Herein, we aimed to control pores and the internal structure of hollow-fiber membranes by fabricating a dual layer using a dual nozzle. Two different pore formers, polyethylene glycol (PEG) and polyvinyl pyrrolidone (PVP), were separately prepared in the dope solutions and used for spinning the dual layer. Our results show that nanoscale pores could be formed on the lumen side (26.8-33.2 nm), and the open pores continuously increased in size toward the shell side. Due to robust pore structure, our fabricated membrane exhibited a remarkable water permeability of 296.2 ± 5.7 L/m2·h·bar and an extremely low BSA loss rate of 0.06 ± 0.02%, i.e., a high BSA retention of 99.94%. In consideration of these properties, the studied membranes are well-suited for use in either water treatment or hemodialysis. Overall, our membranes could be considered for the latter application with a high urea clearance of 257.6 mL/min, which is comparable with commercial membranes.

Fabrication of hollow fiber membranes with different inner diameters for enhanced uremic toxins removal in hemodialysis: Exploring from high-flux to high molecular weight retention onset classes

Developing a hemodialysis membrane that sufficiently removes both small-sized toxins and the middle molecule is essential. Protein-bound uremic toxins (PBUTs) are involved in an increased risk of cardiovascular events and mortality; however, their removal pathway has not been explored yet. Herein, this work aimed to fabricate novel hemodialysis membranes under different inner diameters (ID) with approaching two classes: high-flux (M#1, M#2) and high molecular weight retention onset (MWRO) (M#3, M#4). The results showed that membrane with smaller ID (M#1: 218 μm) performed a superior removal of small molecules i.e., urea: 266,394 mg/m2 and creatinine: 11,985 mg/m2. Spinning conditions, such as bore and dope solution flowrate, had a significant impact on pore size distribution, porosity, and dimensions, but not entirely on the membrane structure. These factors are crucial to govern the efficiency of uremic toxin clearance and the level of protein loss/leaking. Consequently, a high MWRO of M#4 at 13,998 Da favored enhanced removal of middle molecules, resulting in lysozyme removal of 5120 mg/m2 and a high sieving coefficient of β2-microglobulin (0.91). A minimized loss (2.46 g/session) and minor leaking (0.08 g/session) of protein were attained in M#4 e.g., MWRO class. Notably, we first explored the removal pathway of protein-bound uremic toxins (PBUTs) with i) Free Form-PBUTs removal by diffusion ii) Free Form-PBUTs removal by adsorption iii) Bovine serum albumin (BSA)-PBUTs conjugate adsorption on a membrane, and iv) Leaking of BSA-PBUTs conjugate to the dialysate. Our high-flux and MWRO membranes removed hippuric acid of 2911 mg/m2; 3476 mg/m2, indoxyl sulfate of 1640 mg/m2; 1452 mg/m2, p-cresol of 3,1469 mg/m2; 3702 mg/m2, respectively. Overall, our study proposes a promising membrane for hemodialysis application that exhibited either higher flux or high molecular weight retention onset compared to commercial membranes. Their properties facilitate an increase in the removal of middle molecules but still retain a minimized loss of protein and minor leakage.

High‐Performance Zeolitic Hollow‐Fiber Membranes by a Viscosity‐Confined Dry Gel Conversion Process for Gas Separation

Zeolite membranes show great potential for gas and hydrocarbon separations, but high manufacturing cost has been one of the main hurdles in their industrial application. Here we demonstrate a method termed viscosity-confined dry gel conversion (VCDGC) for zeolite hollow fiber membrane fabrication. We demonstrate in detail the VCDGC synthesis of small-pore CHA zeolite membranes. Extensive permeation measurements reveal that dry gel-processed CHA zeolite hollow fiber membranes have excellent gas and hydrocarbon separation characteristics well exceeding or comparable to current membranes. Medium-pore MFI membranes are also fabricated, and their favorable hydrocarbon separation characteristics indicate the versatility and reliability of the VCDGC method.

High-Performance Zeolitic Hollow-Fiber Membranes by a Viscosity-Confined Dry Gel Conversion Process for Gas Separation.

Zeolite membranes show great potential for gas and hydrocarbon separations, but high manufacturing cost has been one of the main hurdles in their industrial application. Here we demonstrate a method termed viscosity-confined dry gel conversion (VCDGC) for zeolite hollow fiber membrane fabrication. We demonstrate in detail the VCDGC synthesis of small-pore CHA zeolite membranes. Extensive permeation measurements reveal that dry gel-processed CHA zeolite hollow fiber membranes have excellent gas and hydrocarbon separation characteristics well exceeding or comparable to current membranes. Medium-pore MFI membranes are also fabricated, and their favorable hydrocarbon separation characteristics indicate the versatility and reliability of the VCDGC method.

Rotation-in-a-Spinneret integrates static mixers inside hollow fiber membranes

Turbulence promoters boost the efficiency of membrane applications suffering from mass transfer limitations. To counteract these mass transfer limitations, static mixers were established for flat sheet and tubular membrane geometries. However, the combination of static mixers with hollow fiber membranes has not been possible because of tedious assembly into modules consisting of small-sized and fragile hollow fiber membranes. Here, we introduce a scalable hollow fiber membrane fabrication methodology overcoming said tedious assembly challenges. It comprises the simultaneous fabrication and integration of static mixers inside hollow fiber membranes by a single-step spinning process. Conceptually, this process builds upon our Rotation-in-a-Spinneret platform technology featuring a microstructured 3D printed hollow fiber spinneret. In particular, we integrate a rotating microstructured needle into the spinneret for extruding a static mixer into the nascent hollow fiber membrane. Specifically designed spinning parameters enabled us to engineer twisted tape-shaped static mixers with an adjustable pitch and pitch direction. The emerging Static-Mixer-Membranes exhibit a separate arrangement of both components with an inner diameter below 2.5mm. Characteristic membrane properties are independent of the needle rotation and static mixer integration. Static mixers introduce secondary flow evolution proven by pressure drop manipulation and streamline visualization. Ultimately, two application show cases – oxygenation and CO2 capture with gas–liquid membrane contactors – reveal improved transmembrane gas fluxes up to 440%. The static mixer pitch controls these improvements demonstrating process intensification. Additionally, the technique enabled fabricating nanoparticle-equipped static mixers for improved static mixer shaping and potentially catalytic functionality.

Optimization of Nanofiltration Hollow Fiber Membrane Fabrication Process Based on Response Surface Method

Layer-by-layer (LBL) self-assembly technology has become a new research hotspot in the fabrication of nanofiltration membranes in recent years. However, there is a lack of a systematic approach for the assessment of influencing factors during the membrane fabrication process. In this study, the process optimization of LBL deposition was performed by a two-step statistical method. The multiple linear regression was performed on the results of single-factor experiments to determine the major influencing factors on membrane performance, including the concentration of Poly (allylamine hydrochloride) (PAH), glutaraldehyde, and the NaCl concentration in PAH solution. The Box–Behnken response surface method was then used to analyze the interactions between the selected factors, while their correlation with the membrane performance was obtained by polynomial fitting. The R2 value of the regression models (0.97 and 0.94) was in good agreement with the adjusted R2 value (0.93 and 0.86), indicating that the quadratic response models were adequate enough to predict the membrane performance. The optimal process parameters were finally determined through dual-response surface analysis to achieve both high membrane permeability of 14.3 LMH·MPa−1 and MgSO4 rejection rate of 90.22%.

Investigation on the effects of air gap distance on the formation of cellulose triacetate hollow fiber membrane for CO2 and CH4 gases permeation

CO2 removal is essential for the sweetening process of sour natural gas in order to meet the desired specifications for natural gas to be utilized and transported. CO2 separation from natural gas stream can be achieved through the application of membrane technology which will enable natural gas to be suitable for commercial use. Cellulose triacetate (CTA) is a well-known polymer material for CO2 removal due to its high affinity towards CO2. As compared to flat sheet membranes, hollow fiber configuration is preferable due to its large surface to unit volume ratio and self-supporting characteristics, therefore making it a superior choice compared to other configurations. In this work, fabrication of hollow fiber membranes by employing CTA as a polymer for the separation of CO2 and CH4 gases is focused. During fabrication, the air gap distance was varied from 1 cm to 7 cm. Following that, the morphology of the resulting fibers was investigated by using a scanning electron microscope (SEM). Next, the CO2 and CH4 gas permeation, and CO2/CH4 gas pair selectivity of the resultant HFMs were assessed using a custom-built gas permeation test rig. In addition, post-treatment of HFM with polydimethylsiloxane (PDMS) was also carried out. Then, the gas permeation and gas pair selectivity of the resultant hollow fiber membranes before and after the PDMS coating were compared. The optimum gas permeation performance of CTA HFM was obtained at an air gap distance of 3 cm and a feed pressure of 3 bar as it yielded the highest CO2 permeance of 78.77 GPU and CO2/CH4 gas pair selectivity of 2.80. Whereas for PDMS coated CTA HFM, fibers spun at air gap distance of 1 cm demonstrated the highest CO2 permeance of 14.85 GPU and CO2/CH4 selectivity of 2.54 at feed pressure of 9 bar.

Modeling and Optimization of Spinning Parameters on Selectivity of Polysulfone Hollow Fiber Membrane for CO2/CH4 Separation

Hollow fiber membrane (HFM) and related technologies have recently become highly in demand and widely used in most industries and other areas recently. HFM could be used in different functions, from water and gas treatment to blood and medical applications. The paper describes the modeling of the effects of the spinning condition of a nonporous HFM on the membrane’s characteristics with the use of an automated hollow fiber fabrication system. An integrated, systematic experimental strategy based on the design of experiments was used to elaborate the effects of each parameter on selectivity. To obtain and sustain a satisfactory, significant selectivity of HFM, an automated system controlled the parameters during the fabrication process. The parameters involved in the fabrication of HFM and used in modeling are dope flow rate, bore flow rate, draw force, and air gap, which are considered inputs to fabricate polysulfone membrane. The fabrication process is improved by automating and instrumenting fabrication systems. An empirical model of the effects of fabrication parameters on the selectivity of the membrane is extracted experimentally. The mathematical model effectively explains the selectivity of CO2/CH4 with 95% fit.

Formation of electrically conductive hollow fiber membranes via crossflow deposition of carbon nanotubes – Addressing the conductivity/permeability trade-off

Electrically conductive membranes (ECMs) have significant potential for enhanced membrane separations. While most of the existing studies on ECMs have focused on flat sheet membranes, it is the hollow fiber membrane format that is the preferred format for large-scale treatment applications. While ECMs in hollow fiber format are emerging, existing approaches tend towards extremes of membrane conductivity or permeability without considering the trade-off between these metrics. We aim to understand and optimize this trade-off by studying the effect of the normal (pressure, lift) and tangential (shear) forces associated with conductive coating deposition. A suspension of functionalized single walled/double walled carbon nanotubes (SW/DWCNTs) in solution containing sodium dodecyl sulfate and polyvinyl alcohol was pressure deposited in crossflow along the active lumen surface of polyethersulfone microfiltration membranes. The impact of the crossflow deposition parameters affecting surface forces (feed pressure, crossflow velocity) were quantified according to both membrane permeability and conductivity in a 22 design-of-experiments study. Unexpectedly, the highest membrane permeability (~2900 LMH/bar) and conductivity (~670 S/m) and were obtained at the high feed pressure and high crossflow velocity condition. A Robeson-like plot was generated that demonstrates a trade-off between composite membrane permeability and conductivity for 29 CNT-coated hollow fiber membranes fabricated at various SW/DWCNT concentrations, crossflow velocities, and applied pressures. Measured conductivities (up to 2500 S/m) and permeabilities (up to 6000 LMH/bar) for the CNT-coated hollow fiber membranes were several orders of magnitude higher than previous conductive hollow fibers, indicating the substantial benefits of crossflow deposition. The electrically conductive hollow fiber membrane fabrication technique developed herein will be useful in a variety of conductive membrane applications including fouling prevention, enhanced removal of charged particles, and integrated membrane sensing capabilities.

Macrovoid-free high performance polybenzimidazole hollow fiber membranes for elevated temperature H2/CO2 separations

Thermally robust membranes are required for H2 production and carbon capture from hydrocarbon fuel derived synthesis (syn) gas. Polybenzimidaole (PBI) materials have exceptional thermal, chemical and mechanical characteristics and high H2 perm-selectivity for efficient syngas separations at process relevant conditions. The large gas volumes processed mandate the use of a high-throughput, small footprint hollow fiber membrane (HFM) platform. In this work, an industrially attractive spinning protocol is developed to fabricate PBI HFMs with unprecedented H2/CO2 separation performance. A unique dope composition incorporating an acetonitrile diluent is discovered enabling asymmetric macro-void free PBI HFM fabrication using a water coagulant. The influences of dope viscosity, coagulant chemistry, and air gap on HFM morphology are evaluated. Elevated temperature (up to 350 °C) H2 permeances of 400 GPU with H2/CO2 selectivities > 20 are achieved. This unprecedented separation performance is a ground breaking achievement at temperatures traditionally considered out-of-reach for polymeric membranes.

Fabrication of Hollow Fiber Membranes Using Highly Viscous Liquids as Internal Coagulants

Ethylene glycol (EG) and its derivatives were proposed as internal coagulants to spin hollow fiber membranes of the commercial polymer poly(ether imide) (PEI) and compared with water. The thermodynamic and kinetic characteristics of the polymer–solvent–nonsolvent systems were analyzed. The morphology and ultrafiltration performance of the resultant membranes were investigated. Water leads to a fast precipitation rate while a slow process is obtained for EG derivatives because of their high viscosity, large molecular size, and weak nonsolvent capability. The hollow fibers prepared with EG derivatives as bore fluids have thinner walls, which promote less resistance to the permeant transport. High rejections of bovine serum albumin (66 kg/mol), ovalbumin (45 kg/mol), and α-lactalbumin (14 kg/mol) were detected. The good performance combined with the nontoxicity of the EG derivatives makes them promising coagulants for membrane fabrication.

Thin film nanocomposite nanofiltration hollow fiber membrane fabrication and characterization by electrochemical impedance spectroscopy

Nano-TiO2 nanoparticles were incorporated into thin film nanocomposites (TFN) formed on hollow fiber support membranes composed of a blend of polysulfone and multi-walled carbon nanotubes. Three different TiO2 nanoparticles (0.01%, 0.05% and 0.2% w/v) in the thin film composite were investigated. Formation of the nanocomposite polyamide layer was confirmed by the results of FTIR and scanning electron microscopy. Double-layer capacitance values obtained from electrochemical impedance spectroscopy results showed that effective surface area of the membranes was enhance by the incorporation of nano-TiO2. Nanofiltration membrane performance was examined using solutions of MgSO4 and NaCl under cross-flow system with hollow fiber nanofiltration modules. Fouling of the membrane was evaluated with solutions of humic and tannic acids. The permeate flux of TFN 0.05 composite membranes was improved nearly 12 times with the incorporation of TiO2 with rejections of MgSO4 and NaCl salts of 22% and 5%, respectively. The rejections of the NF membranes for HA and TA were 84% and 74%, respectively, with improved antifouling properties compared to the thin film composite membrane without TiO2, the latter being attributed to increased hydrophilicity of membrane surface.

Preliminary Characterization of Corn Cob Ash as an Alternative Material for Ceramic Hollow Fiber Membrane (CHFM/CCA)

Currently, exchanging trends in the expensive usage of ceramic materials such as alumina, zirconia etc. into economical ceramic raw sources have been studied extensively over the last decade for various technological applications. Despite the fact that this ceramic compound or elements offer a great performance and stability, especially at high temperature and corrosive or acidic conditions, the basic commercial price of this compound which is a little bit higher have hindered the used of these materials. Thus interest in fabricating of bio-ceramic membrane using corn cob ash, an agricultural by product not only offered the development of new low cost materials but also able to enhance better properties and performance. The suitability of corn cob ash as an alternative material for ceramic hollow fiber membrane fabrication (CHFM/CCA) as a main substrate was investigated via combined phase inversion and sintering technique based on several controlled operating parameters. The effects of selected bore fluid (5, 10, 15 and 20 mL/min) and different sintering temperature (800˚C, 900˚C, 1000˚C, 1100˚C) towards membrane structure and properties were observed and studied. Interestingly, analysis of the SEM morphology showed that the potential of the main constituents of corn cob ash which highly consisted of silica, alumina and calcium oxide are able to improve the properties of CHFM/CCA by lowering sintering temperature (1000˚C) as compared to the standard CHFM bodies which normally has sintering temperature higher than 1200 oC. Thus, the used of corn cob ash not only able to enhance better ceramic properties but also able to reduce sintering temperature. Reduction in energy consumption with slightly reduced sintering temperature also will offer a better sustainable process through recycling abundant waste materials as well as the emphasis on the green resources. In respect, the bio-material of corn cob ash is capable to replace the commercial ceramic membrane materials for membrane applications by considering the availability of this agro waste product as the main crops in most countries in the world.

Fabrication of Hollow Fiber Membrane from Polyarylate–Polyarylate Block Copolymer for Air Separation

A process has been developed for spinning asymmetric hollow fiber membranes from a polyarylate–polyarylate block copolymer having a separation factor for pure gases in the oxygen–nitrogen pair of α(O2/N2) = 6.3 and an oxygen permeance coefficient of 2.4 Barrer. The effect of the polymer molecular weight, the composition of the dope solution, and the spinning parameters on the gas transport properties of the hollow fiber membrane and its geometry has been studied. The use of a polymer with a molecular weight of 67 kDa, as well as the introduction of surfactants into the dope solution, has made it possible to prepare samples of defect-free membranes with an oxygen permeance of 120 L(STP)/(m2 h bar) and a separation factor of α(O2/N2) = 6.5, which correspond to the selective layer thickness of 60 nm.

Ion-Exchanged SAPO-34 Membranes for Krypton-Xenon Separation: Control of Permeation Properties and Fabrication of Hollow Fiber Membranes.

Separation of radioisotope 85Kr from 136Xe is of importance in used nuclear fuel reprocessing. Membrane separation based on zeolite molecular sieves such as chabazite SAPO-34 is an attractive alternative to energy-intensive cryogenic distillation. We report the synthesis of SAPO-34 membranes with considerably enhanced performance via thickness reduction based upon control of a steam-assisted vapor-solid conversion technique followed by ion exchange with alkali metal cations. The reduction of membrane thickness leads to a large increase in Kr permeance from 7.5 to 26.3 gas permeation units (GPU) with ideal Kr/Xe selectivities >20 at 298 K. Cation-exchanged membranes show large (>50%) increases in selectivity at ambient or slight subambient conditions. The adsorption, diffusion, and permeation characteristics of ion-exchanged SAPO-34 materials and membranes are investigated in detail, with potassium-exchanged SAPO-34 membranes showing particularly attractive performance. We then demonstrate the fabrication of selective SAPO-34 membranes on α-alumina hollow fibers.

Preparation of Hollow Fiber Membranes by Nonsolvent Induced Phase Separation along with Hydrogen Gas Formation Using a Single Orifice Spinneret

AbstractTraditional nonsolvent induced phase separation (NIPS) process for fabrication of hollow fiber membranes (HFMs) faces challenges, like design and manufacture of spinneret with two concentric orifices to provide parallel and continuous feed of polymer solution and bore fluid at specific rates. These factors limit the use of traditional technique to produce HFMs. Here, a new direct spinning method for fabricating HFMs by feeding a polymer solution, containing a gas producing agent using single orifice spinneret is reported. Polysulfone‐dimethylacetamide solution containing NaBH4 is extruded through a stainless‐steel needle (single orifice spinneret) into HCl aqueous solution (coagulation bath) at specific rates. Effects of polysulfone concentration, temperature, and pH of coagulant bath on structure and performance of the HFMs are investigated. Synergy between hydrogen from NaBH4 hydrolysis and NIPS process benefits fabrication of HFMs with good hollow bore structure and high porous wall. The prepared HFMs show good dye separation.