Investigation on the effect of spinning conditions on the properties of hollow fiber membrane for hemodialysis application

Polyethersulfone (PES) hollow fiber membranes were fabricated via the dry‐wet phase inversion spinning technique, aiming to produce an asymmetric, micro porous ultrafiltration hollow‐fiber specifically for hemodialysis membrane. The objective of this study is to investigate the effect of spinning conditions on the morphological and permeation properties of the fabricated membrane. Among the parameters that were studied in this work are air gap distance, dope extrusion rate, bore fluid flow rate, and the take‐up speed. The contact angle was measured to determine the hydrophilicity of the fibers. Membrane with sufficient hydrophilicity properties is desired for hemodialysis application to avoid fouling and increase its biocompatibility. The influences of the hollow fiber's morphology (i.e., diameter and wall thickness) on the performance of the membranes were evaluated by pure water flux and BSA rejection. The experimental results showed that the dope extrusion rate to bore fluid flow rate ratio should be maintained at 1:1 ratio to produce a perfectly rounded asymmetric hollow fiber membrane. Moreover, the flux of the hollow fiber spun at higher air gap distance had better flux than the one spun at lower air gap distance. Furthermore, spinning asymmetric hollow fiber membranes at high air gap distance helps to produce a thin and porous skin layer, leading to a better flux but a relatively low percentage of rejection for BSA separation. Findings from this study would serve as primary data which will be a useful guide for fabricating a high performance hemodialysis hollow fiber membrane. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43633.     

Preparation of poly(ether sulfone) hollow fiber UF membrane for removal of NOM

In this study, a high performance poly(ether sulfone) (PES) hollow fiber ultrafiltration (UF) membrane has been prepared for removal of natural organic matter (NOM). The membrane was spun from a dope solution containing PES/poly (vinyl pyrrolidone) (PVP 40K)/N‐methyl‐2‐pyrrolidone (NMP) by using a wet‐spinning process. Characterization of the membrane in terms of pure water flux, molecule weight cut‐off (MWCO), and retention for a model humic acid (HA) were conducted, and the fouling resistance was analyzed. The experimental results showed that the membrane had a pure water permeability of 20 × 10^?5 L m^?2 h^?1 Pa^?1 and a nominal MWCO of 6000 Da. The results also showed that the membrane retention for humic acid was over 97% and both productivity and selectivity for HA increased with increasing feed velocity. The PES membrane in this study exhibited a much lower fouling tendency than the commercial polysulfone membrane. SEM images revealed that the membrane had an outer dense skin and a porous inner surface. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 430–435, 2006     

Synthesis and Characterization of Polycarbonate/TiO2 Ultrafiltration Membranes: Critical Flux Determination

A novel polycarbonate (PC) membrane was modified with titanium dioxide via nonsolvent-induced phase separation method to improve its hydrophilicity and antifouling properties in a submerged membrane system for the removal of humic acid (HA) both with and without polyaluminum chloride (PAC) coagulant. The effect of TiO₂ additive on the morphology and performance of the nanocomposite membranes was studied by atomic force microscopy, field emission scanning electron microscopy, energy dispersive X-ray, mechanical properties, water contact angle, porosity, pure water flux, rejection tests, and antifouling parameters. The obtained results revealed that a higher critical flux was achieved by the PC/TiO₂ nanocomposite membrane. The flux recovery ratio of the neat PC membrane increased with the addition of TiO₂ nanoparticles and without PAC coagulant. HA removal for the PC nanocomposite membrane was higher than that of the neat PC membrane with and without PAC coagulant.     

Studies on fouling by natural organic matter (NOM) on polysulfone membranes: Effect of polyethylene glycol (PEG)

Polysulfone membranes were prepared via phase inversion technique by using polyethylene glycol with molecular weights of 400, 1500 and 6000 Da as pore forming agent in dope formulation. The performance of membrane was characterized using humic acid and water sample taken from Sembrong River, Johor, Malaysia was used as natural organic matter sources. Membrane properties were also characterized in terms of mean pore radius, pure water flux, humic acid rejection and fouling resistance. The results indicated that the pure water flux and mean pore radius of membranes increased with the increase of PEG content. Fourier transform infrared spectroscopy results revealed the presence of hydrophilic component in PSf/PEG blend with the significant appearance of O–H peak at 3418.78 cm^− 1. Scanning electron microscopy analysis revealed the presence of finger-like structure for all membranes and the structure intensified as PEG content was increased. The results obtained from the fouling study indicated that the membrane with the lowest PEG content and molecular weight has an excellent performance in mitigating fouling.     

Development of asymmetric BTDA-TDI/MDI (P84) copolyimide flat sheet and hollow fiber membranes for ultrafiltration: Morphology transition and membrane performance

In this paper, the effects of γ-butyrolactone (GBL) weight ratio (w_GBL) and membrane thickness on the formation of asymmetric flat sheet membranes prepared with P84 (BTDA-TDI/MDI co-polyimide)/N-methyl-2-pyrrolidone (NMP)/GBL casting solutions are investigated. With the increase of membrane thickness, the transition of membrane morphology from sponge-like to finger-like structure occurs at critical structure-transition thickness L_c. L_c and the general sponge-like structure thickness (L_gs) increase with w_GBL. For 20 wt.% P84/NMP/GBL casting solution, the membrane morphology changes from finger-like to sponge-like structure at the critical weight ratio of GBL (w^? = 0.69). The membrane morphology and performance of hollow fibers spun with various w_GBL are observed. Compared with the hollow fiber membranes made of 18 wt.% P84/NMP/GBL dope solution with w_GBL = 0.75, the hollow fiber membranes spun with w_GBL = 0.25 present a higher permeation flux and a larger MWCO. As w_GBL increases from 0.25 to 0.75, the membrane morphology transfers from finger-like to sponge-like structure. An increase in shear rate shifts the rejection curves towards left, and lowers the MWCO of hollow fiber membranes. For hollow fiber membranes spun with w_GBL = 0.75, a relatively high permeation flux and a large MWCO are obtained by the wet spinning process.     

Comparative impact of SiO2 and TiO2 nanofillers on the performance of thin-film nanocomposite membranes

Nanoparticle (NP) additions can substantially improve the performance of reverse osmosis and nanofiltration polyamide (PA) membranes. However, the relative impacts of leading additives are poorly understood. In this study, we compare the effects of TiO₂ and SiO₂ NPs as nanofillers in PA membranes with respect to permeate flux and the rejection of organic matter (OM) and salts. Thin-film nanocomposite (TFN) PA membranes were fabricated using similarly sized TiO₂ 15 nm and SiO₂ (10 – 20 nm) NPs, introduced at four different NP concentrations (0.01, 0.05, 0.2, and 0.5% w/v). Compared with PA membranes fabricated without NPs, membranes fabricated with nanofillers improved membranes hydrophilicity, membrane porosity, and consequently the permeability. Permeability was increased by 24 and 58% with the addition of TiO₂ and SiO₂ , respectively. Rejection performance and fouling behavior of the membranes were examined with salt (MgSO₄ and NaCl ) and OM (humic acid [HA] and tannic acid [TA]). The addition of TiO₂ and SiO₂ nanofillers to the PA membranes improved the permeability of these membranes and also increased the rejection of MgSO₄ , especially for TiO₂ membranes. The addition of TiO₂ and SiO₂ to the membranes exhibited a higher flux and lower flux decline ratio than the control membrane in OM solution filtration. TFN membranes' HA and TA rejections were at least 77 and 71%, respectively. The surface change properties of NPs appear to play a dominant role in determining their effects as nanofillers in the composite membrane matrix through a balance of changes produced in membrane pore size and membrane hydrophilicity.     

Structural and performance properties of UV-assisted TiO2 deposited nano-composite PVDF/SPES membranes

In this research, the surface of poly (vinylidene fluoride) (PVDF)/sulfonated polyethersulfone (SPES) blend membrane prepared via immersion precipitation was modified by depositing of TiO₂ nano-particles followed by UV irradiation to activate their photocatalytic property. The membranes were characterized by FTIR, SEM, AFM, contact angle, dead end filtration (pure water flux and BSA solution flux), antifouling analysis and antibacterial activity. The FTIR spectrum confirmed the presence of OH functional groups on the PVDF/SPES membrane structure, which was the key factor for deposition, and self-assembly of TiO₂ nanoparticles on the membrane surface. The SEM and AFM images indicated that the TiO₂ nanoparticles were deposited on the PVDF/SPES membrane. The contact angle measurements showed that the hydrophilicity of PVDF/SPES membrane was strongly improved by TiO₂ deposition and UV irradiation. The filtration results indicated that the initial flux of TiO₂ deposited PVDF/SPES membranes was lower than the initial flux of neat PVDF/SPES membrane. However, the former membranes showed lower flux decline compared to the neat PVDF/SPES membrane. The BSA rejection of modified membranes was improved. The fouling analysis demonstrated that the TiO₂ deposited PVDF/SPES membranes showed the fewer tendencies to fouling. The results of antibacterial study showed that the UV irradiated TiO₂ deposited PVDF/SPES membranes possess high antibacterial property.     

A Comparative study of organic fouling in hollow fiber and spiral wound membranes

The occurrence of flux decline in brackish water reverse osmosis (RO) plants due to dissolved organics is a topic of ongoing research. This type of organic fouling has also been found in seawater RO plants. A study was undertaken to compare organic fouling in hollow fiber and spiral wound membranes using a seawater feed that possessed a high concentration of huraic acid. This study was undertaken at an RO plant on Grand Cayman Island, British West Indies. The feed water came from a sea well and possessed a concentration of humic acid that varied between 35 and 60 mg/l.The hollow fiber membrane was operated at a recovery of 25% while the recovery with the spiral wound membrane varied between 5 and 25%. The performance data which included permeate flow, salt rejection, pressure drops across the membrane and analysis of the membranes for organic fouling were undertaken. This study compared the performance data and organic fouling between the hollow fiber and spiral wound meembranes.     

Removal of dyes by poly(p-phenylene terephthamide)/polyvinylidene fluoride hollow fiber in-situ blend membranes

In order to obtain the compatible poly(p-phenylene terephthalamide) (PPTA)/polyvinylidene fluoride (PVDF) blend membranes, the casting solution was synthesized via the in situ polycondensation process and flat sheet blend membranes were successfully prepared through the immersion precipitation phase inversion method in our previous study. In this study, the polycondensation solution was directly used as the spinning dope to fabricate PPTA/PVDF hollow fiber in-situ blend membrane by the dry-wet spinning technique. Hollow fiber membranes were employed to remove the dyes including Congo red (CR) and methylene blue (MB) from the dyeing liquor. Effects of operation conditions on dye rejection and membrane water flux were investigated. With the increase of operation pressure, feed concentration and feed temperature, dye rejection rates gradually decreased, but the rejection value of CR and MB still remained above 99.5%. On the contrary, the permeation water flux basically increased. During the continuous dye filtration of 300 min, hollow fiber membrane can maintain high dye rejection rates and stable water flux. The combination method of physical backwashing and chemical cleaning can effectively alleviate membrane fouling and recover membrane water flux. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48569.     

Studies on the surface properties of mixed‐matrix membrane and its antifouling properties for humic acid removal

A major factor limiting the use of ultrafiltration (UF) membrane in water treatment process is the membrane fouling by natural organic matter such as humic acid (HA). In this work, neat PVDF and PVDF/TiO₂ mixed‐matrix membranes were prepared and compared in terms of their antifouling properties. Two commercial types of TiO₂ namely PC‐20 and P25 were embedded to prepare the mixed matrix membranes via in situ colloidal precipitation method. The contact angles for the mixed‐matrix membranes were slightly reduced while the zeta potential was increased (more negatively charged) compared with the neat membrane. Filtration of HA with the presence of Ca²⁺ demonstrated that mixed‐matrix membrane could significantly mitigate the fouling tendency compared with the neat membrane with flux ratio (J/J₀) of 0.65, 0.70, and 0.82 for neat PVDF membrane, PVDF/TiO₂ mixed‐matrix membrane embedded with P25 and PC‐20, respectively. PC‐20 with higher anatase polymorphs exhibited better antifouling properties due to its hydrophilicity nature. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Fouling of UF membrane by humic substance: Effects of molecular weight and powder-activated carbon (PAC) pre-treatment

Fouling characteristics of membranes with various molecular weight cut-offs (MWCO) were investigated. The effects of the molecular weights (MW) of humic acids and pre-treatment with PAC on membrane fouling were studied. It was found that the hydraulic resistance caused by fouling materials calculated using cake resistance in series model is a better indicator than the percentage of flux decline to assess the fouling of membranes with various MWCO. The effects of MWCO of membranes and MW of humic acids on membrane fouling can be explained by the different types of fouling mechanisms.     

Polyvinyl alcohol/polysulfone (PVA/PSF) hollow fiber composite membranes for pervaporation separation of ethanol/water solution

Polysulfone (PSF) hollow fiber membranes were spun by phase‐inversion method from 29 wt % solids of 29 : 65 : 6 PSF/NMP/glycerol and 29 : 64 : 7 PSF/DMAc/glycol using 93.5 : 6.5 NMP/water and 94.5 : 5.5 DMAc/water as bore fluids, respectively, while the external coagulant was water. Polyvinyl alcohol/polysulfone (PVA/PSF) hollow fiber composite membranes were prepared after PSF hollow fiber membranes were coated using different PVA aqueous solutions, which were composed of PVA, fatty alcohol polyoxyethylene ether (AEO₉), maleic acid (MAC), and water. Two coating methods (dip coating and vacuum coating) and different heat treatments were discussed. The effects of hollow fiber membrane treatment methods, membrane structures, ethanol solution temperatures, and MAC/PVA ratios on the pervaporation performance of 95 wt % ethanol/water solution were studied. Using the vacuum‐coating method, the suitable MAC/PVA ratio was 0.3 for the preparation of PVA/PSF hollow fiber composite membrane with the sponge‐like membrane structure. Its pervaporation performance was as follows: separation factor (α) was 185 while permeation flux (J) was 30g/m²·h at 50°C. Based on the experimental results, it was found that separation factor (α) of PVA/PSF composite membrane with single finger‐void membrane structure was higher than that with the sponge‐like membrane structure. Therefore, single finger‐void membrane structure as the supported membrane was more suitable than sponge‐like membrane structure for the preparation of PVA/PSF hollow fiber composite membrane. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 247–254, 2005     

Effect of polyethylene glycol molecular weights and concentrations on polyethersulfone hollow fiber ultrafiltration membranes

Polyethersulfone (PES) hollow‐fiber membranes were fabricated using poly(ethyleneglycol) (PEG) with different molecular weights (MW = PEG200, PEG600, PEG2000, PEG6000, and PEG10000) and poly(vinyl pyrrolidone) PVP40000 as additives and N‐methyl‐2‐pyrrolidone (NMP) as a solvent. Asymmetric hollow‐fiber membranes were spun by a wet phase‐inversion method from 25 wt % solids of 20 : 5 : 75 (weight ratio) PES/PEG/NMP or 18 : 7 : 75 of PES/(PEG600 + PVP40000)/NMP solutions, whereas both the bore fluid and the external coagulant were water. Effects of PEG molecular weights and PEG600 concentrations in the dope solution on separation properties, morphology, and mechanical properties of PES hollow‐fiber membranes were investigated. The membrane structures of PES hollow‐fiber membranes including cross section, external surface, and internal surface were characterized by scanning electron microscopy and the mechanical properties of PES hollow‐fiber membranes were discussed. Bovine serum albumin (BSA, MW 67,000), chicken egg albumin (CEA, MW 45,000), and lysozyme (MW 14,400) were used for the measurement of rejection. It was found that with an increase of PEG molecular weights from 200 to 10,000 in the dope solution, membrane structures were changed from double‐layer fingerlike structure to voids in the shape of spheres or ellipsoids; moreover, there were crack phenomena on the internal surfaces and external surfaces of PES hollow‐fiber membranes, pure water permeation fluxes increased from 22.0 to 64.0 L m^?2 h^?1 bar^?1, rejections of three protein for PES/PEG hollow‐fiber membranes were not significant, and changes in mechanical properties were decreased. Besides, with a decrease of PEG600 concentrations in the dope solution, permeation flux and elongation at break decreased, whereas the addition of PVP40000 in the dope solution resulted in more smooth surfaces (internal or external) of PES/(PEG600 + PVP40000) hollow‐fiber membranes than those of PES/PEG hollow‐fiber membranes. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3398–3407, 2004     

微纳米气泡对超滤膜过滤腐植酸污染影响研究

为有效解决超滤过程中因有机物堵塞膜孔导致的膜污染和渗透通量下降问题，提出在对腐植酸（HA）溶液超滤传输及反洗过程中引入微纳米气泡水处理工艺，以强化超滤过程，实验研究了微纳米气泡对超滤膜渗透通量和截留效率的影响以及膜污染去除效果。结果表明在纯水和HA溶液中鼓入微纳米气泡后其归一化通量增大到1.1~1.3，截留效率提高了2.5%~22.0%，微纳米气泡水清洗和反洗后膜通量恢复分别高于纯水21%和25%。     

Cellulose acetate butyrate membrane containing TiO2 nanoparticle: Preparation, characterization and permeation study

Cellulose acetate butyrate/TiO₂ hybrid membranes were prepared via phase inversion by dispersing the TiO₂ nanoparticles in casting solutions. The influence of TiO₂ nanoparticles on the morphology and performance of membranes was investigated. The scanning electron microscope images and experiments of membrane performance showed that the membrane thickness and pure water flux were first increased by adding the TiO₂ nanoparticles to the casting solution up to 4 wt% and then decreased with the addition of further nanoparticles to it. The obtained results indicated that the addition of TiO₂ in the casting solution enhanced the rejection and permeate flux in filtration of bovine serum albumin solution. Furthermore, increasing the TiO₂ nanoparticle concentration in the casting solution increased the flux recovery and consequently decreased the fouling of membrane.     

Preparation and characterization of alumina hollow fiber membranes

With the rapid development of membrane technology in water treatment, there is a growing demand for membrane products with high performance. The inorganic hollow fiber membranes are of great interest due to their high resistance to abrasion, chemical/thermal degradation, and higher surface area/volume ratio therefore they can be utilized in the fields of water treatment. In this study, the alumina (Al₂O₃) hollow fiber membranes were prepared by a combined phase-inversion and sintering method. The organic binder solution (dope) containing suspended Al₂O₃ powders was spun to a hollow fiber precursor, which was then sintered at elevated temperatures in order to obtain the Al₂O₃ hollow fiber membrane. The dope solution consisted of polyethersulfone (PES), Nmethyl-2-pyrrolidone (NMP) and polyvinylpyrrolidone (PVP), which were used as polymer binder, solvent and additive, respectively. The prepared Al₂O₃ hollow fiber membranes were characterized by a scanning electron microscope (SEM) and thermal gravimetric analysis (TG). The effects of the sintering temperature and Al₂O₃/PES ratios on the morphological structure, pure water flux, pore size and porosity of the membranes were also investigated extensively. The results showed that the pure water flux, maximum pore size and porosity of the prepared membranes decreased with the increase in Al₂O₃/PES ratios and sintering temperature. When the Al₂O₃/PES ratio reached 9, the pure water flux and maximum pore size were at 2547 L/m²·h and 1.4 μm, respectively. Under 1600dgC of sintering temperature, the pure water flux and maximum pore size reached 2398 L/(m²·h) and 2.3 μm, respectively. The results showed that the alumina hollow fiber membranes we prepared were suitable for the microfiltration process. The morphology investigation also revealed that the prepared Al₂O₃ hollow fiber membrane retained its’asymmetric structure even after the sintering process.     

Control of organic fouling at two seawater reverse osmosis plants

Organic fouling of seawater Reverse Osmosis (RC) membranes is a phenomenon not well understood; it can result in a loss of membrane productivity and salt rejection properties. Two seawater RO plants using DuPont B-10 hollow fiber permeators had experienced organic fouling and were studied.The two plants used different sources of feedwater; one RO plant at Culebra, Puerto Rico, used open seawater; while the other RO plant at Grand Cayman Island, British West Indies, used a sea well. Both feed water sources possessed high concentrations of soluble organics (40–80mg/1) which were mainly humic acids. In an attempt to remove these organics with in-line cationic polyelectrolyte coagulation, the plants experienced organic fouling which caused excessive loss of productivity and salt rejection; both plants initially failed their acceptance tests.It was discovered that the fouling was actually caused by interactions between the humic acids and in-line cationic, polyelectrolyte coagulants which were not removed by in-dedth and cartridge filtration. Rather than remove the humic acid material, acid addition was initiated and in-line cationic coagulants use discontinued to keep the humic acids soluble. It should be noted that with the open seawater intake ferrous sulfate was still used to remove colloidal material and reduce the SDI. Both plants subsequently have passed their 720-hour acceptance test.Culebra and Grand Cayman plants have now exceeded design specification for both productivity and salt rejection. The aramid hollow fiber permeators on acidified feed have shown 100% rejection of these organics at both 25% and 50% conversion and organic fouling has not been evident.     

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     

Effect of polyvinylpyrrolidone molecular weights on morphology,oil/water separation,mechanical and thermal properties of polyetherimide/polyvinylpyrrolidone hollow fiber membranes

We prepared polyetherimide (PEI) hollow fiber membranes using polyvinylpyrrolidones (PVP) with different molecular weights (PVP 10,000, PVP 40,000, and PVP 1,300,000) as additives for oil/water separation. Asymmetric hollow fiber membranes were fabricated by wet phase inversion technique from 25 wt % or 30 wt % solids of 20 : 5 : 75 or 20 : 10 : 70 (weight ratio) PEI/PVP/N‐metyl‐2‐pyrrolidone (NMP) solutions and a 95 : 5 NMP/water solution was used as bore fluid to eliminate resistance on the internal surface. Effects of PVP molecular weights on morphology, oil‐surfactant‐water separation characteristics, mechanical, and thermal properties of PEI/PVP hollow fiber membranes were investigated. It was found that an increase in PVP molecular weight and percentage in PEI/PVP dope solution resulted in the membrane morphology change from the finger‐like structure to the spongy structure. Without sodium hypochlorite posttreatment, hollow fiber membranes with higher PVP molecular weights had a higher rejection but with a lower water flux. For oil‐surfactant‐water emulsion systems (1600 ppm surfactant of sodium dodecylbenzenesulfonate and 2500 ppm oil of n‐decane), experimental results illustrated that the rejection rates for surfactant, total organic carbon, and oil were 76.1 ≈ 79.8%, 91.0 ≈ 93.0%, and more than 99%, respectively. Based on the glass transition temperature values, PVP existed in hollow fiber membranes and resulted in the hydrophilicity of membranes. In addition, using NaOCl as a posttreatment agent for membranes showed a significant improvement in membrane permeability for PVP with a molecular weight of 1300 K, whereas the elongation at break of the treated hollow fiber membranes decreased significantly. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2220–2233, 1999     

Application of asymmetric Si3N4 hollow fiber membrane for cross-flow microfiltration of oily waste water

The asymmetric morphology of silicon nitride (Si₃N₄) ceramic hollow fiber membrane with a selective spongiform outer layer was optimized by the air gap distance and the internal rate of coagulate for oil/water emulsion microfiltration. The effect of trans-membrane pressure (TMP), feed flow rate (FFR), and pH of the feeding emulsion on the separation performance were determined experimentally. Membrane fouling has increased by dissociation of oil droplets during filtration at high TMP and FFR values. Fouling phenomena were studied based on standard pore blocking model. The pH by affecting the surface charge of the Si₃N₄ hollow fibers and zeta potential of the feed emulsion has also been introduced as a prominent influential factor on separation efficiency. The highest values of permeate flux (390 Lm^?2h^-1) and oil rejection (95%) were recorded in alkaline pH. The fabricated Si₃N₄ ceramic membranes were completely recovered (≤99%) by simple thermal treatment at 400 °C.