Structural Control of NiO–YSZ/LSCF–YSZ Dual‐Layer Hollow Fiber Membrane for Potential Syngas Production

The objective of this study was to fabricate dual‐layer hollow fiber as a microreactor for potential syngas production via phase inversion‐based co‐extrusion/cosintering process. As the main challenge of phase inversion is the difficulty to obtain defect‐free fiber, this work focuses on the effect of the fabrication parameters, that is, nonsolvent content, sintering temperature and outer‐layer extrusion rate, on the macrostructure of the produced hollow fiber. SEM images confirm that the addition of nonsolvent has successfully minimized the finger‐like formation. At high sintering temperature, more dense hollow fiber was formed while outer‐layer extrusion rate affects the outer layer thickness.     

Preparation and oxygen permeation of U‐shaped perovskite hollow‐fiber membranes

The oxygen permeation of dense U‐shaped perovskite hollow‐fiber membranes based on Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3?δ prepared by a phase inversion spinning process is reported. The perovskite hollow fibers with totally dense wall were obtained with the outer diameter of 1.147 mm and the inner diameter of 0.691 mm. The dependences of the oxygen permeation on the air flow rate on the shell side, the helium flow rate on the core side, the oxygen partial pressures, and the operating temperatures were experimentally investigated. According to the Wagner theory, it follows that the oxygen transport through the U‐shaped hollow‐fiber membrane is controlled by both surface reaction and bulk diffusion at the temperature ranges of 750–950°C. High oxygen permeation flux of 3.0 ml/(min cm²) was kept for about 250 h at 950°C under the conditions of the air feed flow rate of 150 ml/min and the helium flow rate of 50 ml/min. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVDF‐co‐HFP) hollow fiber membranes prepared from PVDF‐co‐HFP/PEG‐600Mw/DMAC solution for membrane distillation

Poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVDF‐co‐HFP) hollow fiber membranes were prepared by using the phase inversion method. The effect of polyethylene glycol (PEG‐600Mw) with different concentrations (i.e., 0, 5, 7, 10, 12, 15, 18, and 20 wt %) as a pore former on the preparation and characterization of PVDF‐co‐HFP hollow fibers was investigated. The hollow fiber membranes were characterized using scanning electron microscopy, atomic force microscopy, and porosity measurement. It was found that there is no significant effect of the PEG concentration on the dimensions of the hollow fibers, whereas the porosity of the hollow fibers increases with increase of PEG concentration. The cross‐sectional structure changed from a sponge‐like structure of the hollow fiber prepared from pure PVDF‐co‐HFP to a finger‐like structure with small sponge‐like layer in the middle of the cross section with increase of PEG concentration. A remarkable undescribed shape of the nodules with different sizes in the outer surfaces, which are denoted as “twisted rope nodules,” was observed. The mean surface roughness of the hollow fiber membranes decreased with an increase of PEG concentration in the polymer solution. The mean pore size of the hollow fibers gradually increased from 99.12 to 368.91 nm with increase of PEG concentration in polymer solution. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

多孔堇青石中空纤维陶瓷膜的制备与表征(英文)

采用相转化和烧结法,通过一步成型制备了新颖的堇青石中空纤维陶瓷膜,并对制备的中空纤维膜微观结构、孔隙率和孔径分布、抗弯强度、纯净水通量和氮气渗透性等结构与性能进行了表征。结果表明:堇青石中空纤维膜为多孔非对称结构,由内部大孔层和外部海绵状多孔层组成。在1360℃保温2h制备的堇青石中空纤维膜孔隙率为39.2%,抗弯强度为76.5MPa。0.10MPa压差下的纯净水和氮气渗透性分别达到61.34m3/(m2·h·MPa)和7824m3/(m2·h·MPa)。实验证明,采用较大粒径的廉价工业级粉体为原料,可制备非对称的中空纤维陶瓷微滤膜。     

Activated carbon‐filled cellulose acetate hollow‐fiber membrane for cell immobilization and phenol degradation

The activated carbon‐filled cellulose acetate (CA) hollow‐fiber membranes were prepared by using phase‐inverse technique and subsequently characterized by scanning electronic microscopy (SEM), atomic force microscopy (AFM), dynamic mechanical analysis (DMA), thermal mechanical analysis (TMA), and tensile analysis. The SEM observation demonstrated that the activated carbon‐filled CA hollow‐fiber membranes possess four‐layer structure, which consists of an external skin dense layer, an external void layer, a central sponge layer, and an internal skin dense layer, whereas the pure CA hollow‐fiber membranes lack the macrovoid layer. As the measurement of AFM, the roughness of both internal and external surface of activated carbon‐filled fibers is much higher than that of pure CA fiber, respectively. Higher Young's modulus and storage modulus of filled membranes indicate that the activated carbon particles were homogeneously dispersed in the polymeric matrix. To investigate the feasibility of the newly developed hollow‐fiber membranes for cell immobilization cells and to evaluate the inhibitory effect of phenol on immobilized cells, Pseudomonas putida ATCC 17484 was chosen to be immobilized on both pure CA and activated carbon‐filled hollow‐fiber membranes. Batch experiments for phenol biodegradation were carried out for both free suspension and immobilized cells at the initial concentration of 1500 mg/L phenol. In the case of free suspension, neither cell growth nor phenol degradation occurred to any measurable extent up to 35 h. We found that both pure CA fiber and activated carbon‐filled fiber immobilization systems can completely degrade the phenol. However, the biodegradation rate of activated carbon‐filled fiber system was higher than that of pure CA fiber system. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 695–707, 2000     

Multichannel mixed‐conducting hollow fiber membranes for oxygen separation

A multichannel mixed‐conducting hollow fiber (MMCHF) membrane, 0.5 wt % Nb₂O₅‐doped SrCo_0.8 Fe_0.2O_3‐δ (SCFNb), has been successfully prepared by phase inversion and sintering technique. The crystalline structure, morphology, sintering behavior, breaking load, and oxygen permeability of the MMCHF membrane were studied systematically. The MMCHF membrane with porous‐dense asymmetrical microstructure was obtained with the outer diameter of 2.46 mm and inner tetra‐bore diameter of 0.80 mm. The breaking load of the MMCHF membrane was 3–6 times that of conventional single‐channel mixed‐conducting hollow fiber membrane. The MMCHF membrane showed a high oxygen flux which was about two times that of symmetric capillary membrane at similar conditions as well as a good long‐term stability under low oxygen partial pressure atmosphere. This work proposed a new configuration for the mixed‐conducting membranes, combining advantages of multichannel tubular membrane technology and conventional hollow fibers. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1969–1976, 2014     

Preparation and characterization of poly(vinyl chloride)/polystyrene/poly(ethylene glycol) hollow‐fiber ultrafiltration membranes

Hollow‐fiber ultrafiltration (UF) membranes were prepared from blends of poly(vinyl chloride) (PVC) and polystyrene (PS) with a dry/wet phase inversion method. Poly(ethylene glycol) (PEG) and N,N‐dimethylacetamide were used as the additive and solvent, respectively. The effects of the PEG concentration in the dope solution as an additive on the cross sections and inner and outer surface morphologies, permeability, and separation performance of the hollow fibers were examined. The mean pore size, pore size distribution, and mean roughness of both the inner and outer surfaces of the produced hollow fibers were determined by atomic force microscopy. Also, the mechanical properties of the hollow‐fiber membranes were investigated. UF experiments were conducted with aqueous solutions of poly(vinyl pyrrolidone) (PVP; K‐90, M_w = 360 kDa). From the results, we found that the PVC/PS hollow‐fiber membranes had two layers with a fingerlike structure. These two layers were changed from a wide and long to a thin and short morphology with increasing PEG concentration. A novel and until now undescribed shape of the nodules in the outer surfaces, which was denoted as a sea‐waves shape, was observed. The outer and inner pore sizes both increased with increasing PEG concentration. The water permeation flux of the hollow fibers increased from 104 to 367 L m^?2 h^?1 bar^?1) at higher PEG concentrations. The PVP rejection reached the highest value at a PEG concentration of 4 wt %, whereas at higher values (from 4 to 9 wt %), the rejection decreased. The same trend was found also for the tensile stress at break, Young's modulus, and elongation at break of the hollow fibers. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 989‐1004, 2013     

Preparation and performance of braid‐reinforced poly(vinyl chloride) hollow fiber membranes

A novel braid‐reinforced (BR) poly(vinyl chloride) (PVC) hollow fiber membrane was fabricated via dry‐wet spinning process. The mixtures of PVC polymer solutions were uniformly coated on the tubular braid which contained polyester (PET) and polyacrylonitrile (PAN) fibers. The influences of braid composition on structure and performance of BR PVC hollow fiber membranes were investigated. The results showed that the prepared BR PVC hollow fiber membranes were composed of two layers which contained separation layer and tubular braid supported layer when the PET and PET/PAN hybrid tubular braids were used as the reinforcement. But the sandwich structure appeared when the PAN tubular braid was used as the reinforcement, which revealed outer separation layer, tubular braid supported layer and the inner polymer layer. The BR PVC hollow fiber membranes that prepared by PET/PAN hybrid tubular braid had favorable interfacial bonding state compared with the membrane prepared by pure PET or PAN tubular braid. The pure water flux of the BR PVC hollow fiber membranes that prepared by the PET/PAN hybrid tubular braid were lower than that prepared by pure PET or PAN tubular braid, but the rejection of Bovine serum albumin was opposite. The tensile strength of prepared BR PVC hollow fiber membrane was higher than 50 MPa. Both of the tensile strength and elongation at break decreased with the increase of the PAN filaments in the PET/PAN hybrid tubular braid. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45068.     

Positively charged hollow‐fiber composite nanofiltration membrane prepared by quaternization crosslinking

Poly(N,N‐dimethylaminoethyl methacrylate) (PDMAEMA) can be crosslinked by interfacial polymerization to develop a positively charged dense network structure. According to this mechanism, a positively charged hollow‐fiber composite nanofiltration (NF) membrane was prepared by quaternization to achieve a crosslinked PDMAEMA gel layer on the outer surface of polysulfone hollow‐fiber ultrafiltration (UF) membranes with a PDMAEMA aqueous solution as a coating solution and p‐xylylene dichloride as an agent. The preparation conditions, including the PDMAEMA concentration, content of additive in the coating solution, catalyzer, alkali, crosslinking temperature, and hollow‐fiber substrate membrane, were studied. Fourier transform infrared spectroscopy and scanning electron microscopy were used to characterize the structure of the membranes. This membrane had a rejection to inorganic salts in aqueous solution. The rejection of MgSO₄ (2 g/L aqueous solution at 0.7 MPa and 25°C) was above 98%, and the flux was about 19.5 L m^?2 h^?1. Moreover, the composite NF membranes showed good stability in the water‐phase filtration process. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Direktes Herstellungsverfahren von Komposit‐Hohlfasermembranen mit sinusförmiger Geometrie

Composite hollow fiber membranes are fabricated in a one‐step process by superimposing the phase inversion process with interfacial polymerization on the lumen side of the fiber. A pulsation module in the bore fluid channel pulsates the bore fluid flow and leads to hollow fiber membranes with sinusoidal geometry. The fabrication of composite hollow fiber membranes with sinusoidal geometry is focus of this work. The sinusoidal geometry leads to reduced concentration polarization effects in membrane applications.     

Rheology behavior of high‐density polyethylene/diluent blends and fabrication of hollow‐fiber membranes via thermally induced phase separation

The phase‐separation behavior of high‐density polyethylene (HDPE)/diluent blends was monitored with a torque variation method (TVM). The torque variation of the molten blends was recorded with a rheometer. It was verified that TVM is an efficient way to detect the thermal phase behavior of a polymer–diluent system. Subsequently, polyethylene hollow‐fiber membranes were fabricated from HDPE/dodecanol/soybean oil blends via thermally induced phase separation. Hollow‐fiber membranes with a dense outer surface of spherulites were observed. Furthermore, the effects of the spinning temperature, air‐gap distance, cold drawing, and HDPE content on the morphology and gas permeability of the resultant membranes were examined. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

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     

一步成型制备非对称多孔YSZ中空纤维陶瓷膜

采用有机相转化与固态粒子烧结法相结合,通过一步成型制备了非对称多孔氧化钇稳定氧化锆(YSZ)中空纤维陶瓷膜。SEM微观结构分析表明,制备的YSZ中空纤维陶瓷膜为非对称多孔结构,中间为多孔海绵状结构,内外两侧为指孔结构,且内外表层平均孔径分别为0.43μm和0.18μm。YSZ中空纤维陶瓷膜抗弯强度和纯净水通量分别为210.5MPa和4.02m~3·m~(-2)·h~(-1)·bar~(-1)。     

Interfacial resistance of dual-layer asymmetric hollow fiber pervaporation membranes formed by co-extrusion

Interface is critical for dual-layer membranes fabricated by co-extrusion and dry-jet wet spinning. In this work, for the first time, the importance of interface structure in overall membrane transport property was revealed by using Polysulfone (outer layer)/Matrimid (inner) dual-layer hollow fibers as a demonstration system. Due to the dope formulations of the two layers, dense skins came into formation at the shell side of Matrimid inner layer facing the interface. The Matrimid inner layer obtained from the dual-layer hollow fiber with the thinnest Polysulfone outer layer exhibited a flux around 1.0 × 10⁻³ kg/m²-s and a separation factor of ~800 in tert-butanol dehydration (feed flow rate 30 L/h, temperature 80 °C, permeate pressure 2 mbar, the same for the other tests). An estimation based on resistance model clearly indicated the dominance of Matrimid inner layer in the overall mass transfer of corresponding dual-layer membrane. As for hollow fibers with the thickest Polysulfone outer layer, the bulk substrate comprising the interfacial dense skin of Matrimid inner layer also displayed significant resistance and appreciable selectivity. Conclusively, the function of interface should not be ignored. The rule for the evolution of interface structure requires further exploration for fully understanding and utilizing the composite membrane by co-extrusion and phase inversion approach.     

New chlorine‐resistant polyamide reverse osmosis membrane with hollow fiber configuration

New asymmetric hollow fiber reverse osmosis (RO) membrane was developed from a new chlorine‐resistant copolyamide [4T‐PIP(30)] with a piperazine moiety by a conventional phase‐separation method. The new 4T‐PIP(30) hollow fiber membrane has the same low‐pressure RO performance as cellulose triacetate hollow fiber membrane (FR = 205 L/m² day, Rj = 99.6%) and superior chlorine resistance as well as pH resistance to conventional aramid RO membranes. Structural analysis and viscoelastic study revealed that the new hollow fiber consisted of a top skin, dense layer, and microporous layer, and that it began to decrease its elasticity at 80°C in water, which is possibly related to its good and stable RO performance around room temperature. Several kinds of RO modules were made from the new hollow fiber membranes, for which RO performances were stable for 2 years in chlorinated feed water desalination (the free residual chlorine ranged from 0.l to 1.1 mg/L). © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 517–527, 2001     

Highly scalable ZIF‐based mixed‐matrix hollow fiber membranes for advanced hydrocarbon separations

ZIF‐8/6FDA‐DAM, a proven mixed‐matrix material that demonstrated remarkably enhanced C₃H₆/C₃H₈ selectivity in dense film geometry, was extended to scalable hollow fiber geometry in the current work. We successfully formed dual‐layer ZIF‐8/6FDA‐DAM mixed‐matrix hollow fiber membranes with ZIF‐8 nanoparticle loading up to 30 wt % using the conventional dry‐jet/wet‐quench fiber spinning technique. The mixed‐matrix hollow fibers showed significantly enhanced C₃H₆/C₃H₈ selectivity that was consistent with mixed‐matrix dense films. Critical variables controlling successful formation of mixed‐matrix hollow fiber membranes with desirable morphology and attractive transport properties were discussed. Furthermore, the effects of coating materials on selectivity recovery of partially defective fibers were investigated. To our best knowledge, this is the first article reporting successful formation of high‐loading mixed‐matrix hollow fiber membranes with significantly enhanced selectivity for separation of condensable olefin/paraffin mixtures. Therefore, it represents a major step in the research area of advanced mixed‐matrix membranes. © 2014 American Institute of Chemical Engineers AIChE J, 60: 2625–2635, 2014     

Fabrication and structural tuning of novel composite hollow fiber membranes for pervaporation

A series of polysiloxaneimide (PSI)/polyetherimide (PEI) composite hollow fibers were fabricated by coextrusion and phase inversion. The hydrophobic PSI outer layer was set as the selective layer which was supported by the PEI inner layer. The PSI was synthesized by polycondensation of 3,3′,4,4′‐Biphenyltetracarboxylic Dianhydride (BPDA) with amino siloxane X‐22‐161A and a chain extender, 1,3‐Bis (3‐aminopropyl) ?1,1,3,3‐tertramethyldisiloxane (BATS). It was found that the macroscopic uniformity of PSI layer was dependent on the dope formulation, coagulant composition and dope flow rate: (1) the higher similarity degree of the solvent(s) for different layers in terms of solubility parameters, (2) the utilization of surfactant as a component in the water coagulant, and (3) higher flow rates of the outer layer dopes, led to the formation of more uniform and smoother PSI outer layer. The maximum outer layer thickness was around 2 μm. The bulk of the PEI layers were porous with finger like macrovoids. The outer surface of the inner PEI layer for some batches of the hollow fibers was confirmed to be porous. The original dual‐layer hollow fibers showed poor pervaporation performance. Post treatment was applied to cure the hollow fiber, delivering composite membranes with performance dominated by the coating material of PDMS. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43324.     

Improved microstructure of asymmetric niobium pentoxide hollow fiber membranes

Asymmetric niobium pentoxide (Nb₂O₅) hollow fiber membranes were prepared by the phase inversion and sintering process at temperatures ranging from 1000 to 1350°C. The effects of extrusion parameters on the morphology and properties of the produced membranes were systematically explored. Asymmetric hollow fibers with regular inner contour were obtained at extrusion flow rates of 15 and 25 ml min⁻¹ of ceramic suspension and internal coagulant, respectively. Hollow fibers sintered at temperatures greater than 1200°C presented modifications in the morphology of Nb₂O₅ grains, which were also evidenced by X-ray diffraction and Raman analyses. Hollow fibers produced with an air gap of 50 mm presented a dense outer sponge-like layer and micro-voids formed from the inner surface. These hollow fibers sintered at 1200°C presented suitable bending resistance and water permeability (24.2 ± 0.60 MPa and 3.00 ± 0.01 L h^-1 m^-2 kPa^-1, respectively). The outer sponge like layer was mitigated when the fibers were produced without air-gap.     

Dynamic layer‐by‐layer self‐assembly of organic–inorganic composite hollow fiber membranes

Multilayer membranes constructed layer‐by‐layer (LbL) is finding increasing importance in many separation applications. The efficient construction of LbL multilayer on to hollow fiber substrates may offer many new opportunities for industrial applications. An organic–inorganic composite hollow fiber membrane has been developed using a dynamic LbL self‐assembly. This poly(acrylic acid)/poly(ethyleneimine) multilayer was dynamically assembled onto the inner surfaces of ceramic hollow fiber porous substrates pretreated by Dynasylan Ameo silane coupling agents. The hollow fibers were subsequently heat crosslinked to obtain stable permselective membranes. The formation of multilayers on the hollow fibers was characterized with a SEM, EDX, an electrokinetic analyzer and IR spectra. The effects of layer number, feed temperature and water content in the feed on the pervaporation performance have been investigated. To the best of our knowledge, this is the first report of LbL assembly of polymer building blocks onto ceramic hollow fiber porous substrates. © 2011 American Institute of Chemical Engineers AIChE J, 58: 3176–3182, 2012     

Structure control of asymmetric poly(vinyl butyral)‐TiO2 composite membrane prepared by nonsolvent induced phase separation

Poly(vinyl butyral) (PVB)‐TiO₂ composite hollow fiber membranes were prepared via nonsolvent induced phase separation (NIPS). The membrane had a skin layer on both the outer and inner surface at the initial stage after membrane preparation. However, the outer surface became porous with the passage of time, as the polymer in the membrane's outer surface was decomposed by the photocatalysis of TiO₂. The initial water permeability increased with the increase of TiO₂ content. Furthermore, for all the membranes, as time elapsed the water permeabilities increased and became constant after about 15 days, which was in accordance with the alteration on the membrane's outer surface. Despite decomposition of the polymer on the outer surface, particle rejection hardly changed because the inner surface kept the original structure. Thus, addition of TiO₂ to the membrane is a useful way to improve water permeability while maintaining particle rejection. The clear asymmetric structure with both porous structure at the outer surface and skin layer at the inner surface was achieved by the addition of TiO₂. Therefore, the addition of TiO₂ is a new method for achieving the high porosity at the outer surface of the hollow fiber membrane. In addition, tensile strength and elasticity kept constant over time and were higher than those of original PVB membranes. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008