Characteristics and potential applications of a novel forward osmosis hollow fiber membrane

There has been a resurgence of interest in forward osmosis (FO) as a potential means of desalination, dewatering and in pressure retarded osmosis, which Sidney Loeb was advocating over 3 decades ago. This paper describes the characteristics and potential applications of a newly developed FO hollow fiber membrane, which was fabricated by interfacial polymerization on the inner surface of a polyethersulfone (PES) hollow fiber. This FO membrane presents excellent intrinsic separation properties, with a water flux of 42.6 L/m² h using 0.5 M NaCl as the draw solution and DI water as the feed with the active layer facing the draw solution orientation at 23 °C. The corresponding ratio of salt flux to water flux was only 0.094 g/L, which is superior to all other FO membranes reported in the open literature. To evaluate different application scenarios, various NaCl solutions (500 ppm (8.6 mM), 1 wt.% (0.17 M) and 3.5 wt.% (0.59 M)) were used as the feed water to test the performance of the FO membrane. The membrane can achieve a water flux of 12.4 L/m² h with 3.5 wt.% NaCl solution as the feed and 2 M NaCl as the draw solution, suggesting it has good potential for seawater desalination.     

Preparation of PET threads reinforced PVDF hollow fiber membrane

PET threads were incorporated in the support layer of hollow fiber membrane in axial direction as a special reinforcement material for the purpose of improving the mechanical properties of PVDF hollow fiber membranes. It was found that the reinforcement threads had a limited effect on the separation-related properties of the membrane, such as porosity and pore size, but the tensile strength of the reinforced membrane was improved several folds. Also, the criterion of choosing reinforced fiber materials was suggested.     

压力温度双敏性聚氨酯中空纤维膜通透性研究

以聚氨基甲酸酯(PU)为基质相,添加成孔剂及二氧化硅粒子,采用熔融纺丝法制得了具有对压力、温度刺激双重敏感的PU中空纤维膜;研究了膜的水通量随压力、温度的变化,对膜表面形貌进行了表征;并考察了中空纤维膜的截留性能。结果表明:制得的PU中空纤维膜为均质膜;膜孔径分布较窄,87.17%的孔集中在0.15～0.20μm。随着压力、温度上升或下降,膜的水通量相应增大或减小,水通量与压力、温度变化有着明显的相关性。经一次过滤,无机粒子清除率达98.52%～99.78%。     

Fabrication and characterization of a novel Nafion-PTFE composite hollow fiber membrane

Nafion has been widely used in electrochemistry, but there are only a few reports on its application in other fields, such as, gas separation, even though it exhibits good performance. The primary reason for that is the high cost of Nafion and making a composite membrane with a thin Nafion layer is a potential solution to solve this problem. In this study, a novel Nafion-PTFE composite hollow fiber membrane, which had a thin (~5 μm) and detect-free Nafion layer on PTFE surface, without Nafion filling substrate pores was developed, differing from the reported ones in which Nafion resin was required to impregnate into porous PTFE membrane as thorough as possible to ensure the ion conductivity and operation stability. The surface morphology, crystallite, solubility in ethanol/water mixture, and water uptake of membranes were systemically investigated. The gas permeance tests were also conducted. The permeances of different gasses of prepared composite membranes were significantly enhanced compared with the commercial membranes due to the decrease of Nafion thicknesses, while the selectivity remained the same, verifying the detect-free structure of Nafion layer on PTFE substrate. This study provided a good reference for the preparation and application of low-cost Nafion composite membranes.     

Preparation and characterization of blend membranes of polyurethane and superfine chitosan powder

A novel kind of asymmetric blend membranes with superfine chitosan powder (SCP) and biomedical polyurethane was prepared by immersion precipitation phase inversion method. Effects of different SCP content on the morphology and properties of the blend membranes were investigated. The result showed that SCP content had little influence on the cross-section structure of the blend membranes, and the cross-section presented a cellular structure. WAXD results revealed that the aggregated structure of SCP remained. With an increment of SCP content, the pore diameter and porosities of blend membranes increased firstly, and then decreased. While, the water absorption rate and water vapor transmission rate were improved remarkably with increasing SCP content. The mechanical testing results indicated that with an increment of SCP ratio, mechanical properties presented a descending trend, whereas all blend membranes exhibited the good elasticity.     

Evaluation of hollow fiber T-type zeolite membrane modules for ethanol dehydration

This work presents the design of hollow fiber T-type zeolite membrane modules with different geometric configurations. The module performances were evaluated by pervaporation dehydration of ethanol/water mixtures. Strong concentration polarization was found for the modules with big membrane bundles. The concen-tration polarization was enhanced at high temperature due to the higher water permeation flux. The increase of feed flow could improve water permeation flux for the membrane modules with small membrane bundle. Computational fluid dynamics was used to visualize the flow field distribution inside of the modules with different configurations. The membrane module with seven bundles exhibited highest separation efficiency due to the uniform distribution of flow rate. The packing density could be 10 times higher than that of the tubular membrane module. The hollow fiber membrane module exhibited good stability for ethanol dehydration.     

Efficient hollow fiber supported liquid membrane system for the removal and preconcentration of Cr(VI) at trace levels

A hollow fiber supported liquid membrane (HFSLM) system for the removal and preconcentration of Cr(VI) has been developed and characterized using Aliquat 336 as carrier. The influence of the chemical composition on the efficiency of the membrane system has been investigated, such as the organic solvent and the stripping composition. Among the stripping reagents tested, a solution of 0.5 M HNO₃ was found to be the most effective to strip Cr(VI) from the loaded organic phase. Moreover, physical parameters such as the stability of the membrane and the operation mode of the module were also evaluated. The results demonstrated the effectiveness of the HFSLM system during 8 non-stop days’ operation. This membrane-based separation system has effectively been used to remove Cr(VI) from different aqueous samples, such as industrial waters and spiked natural waters at μg L⁻¹ levels. Moreover, the system has allowed both the separation and enrichment of the metal and, thus, facilitating the detection of chromate contained in aqueous samples and reducing the volume of polluted water to be treated.     

Catalyst-modified perovskite hollow fiber membrane for oxidative coupling of methane

The catalytic oxidative coupling of methane (OCM) to C2 hydrocarbons (C2H6 and C2H4) represents one of the most effective ways to convert natural gas to more useful products,which can be performed effec-tively using La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) perovskite hollow fiber membrane microreactor.In this work,the effects of adding a thin BaCe0.8Gd0.2O3-δ (BCG) catalyst film onto the inner LSCF fiber surface as the OCM catalyst and a porous Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) perovskite layer onto the outer LSCF surface to improve the oxygen permeation were evaluated.Between 700 ℃ and 1000 ℃,methane conversion increased in the order of uncoated,BCG and BSCF-coated,and BCG-coated LSCF hollow fiber while C2-selectivity and C2-yield increased in the order of BCG and BSCF-coated,uncoated,and BCG-coated LSCF hollow fiber.Oxygen permeation flux at the same temperature range,on the other hand,was enhanced in the order of uncoated,BCG-coated,and BCG and BSCF-coated LSCF hollow fiber,This finding demon-strates the complex interplay between oxygen permeation and OCM performance.The BCG and BSCF-coated hollow fiber was also subjected to thermal cycles between 850 ℃ and 900 ℃ for up to 175 hours during which the fiber showed minor degradation in oxygen permeation fluxes and relatively stable OCM performance.     

Effects of ultrasound parameters on ultrasound-assisted ultrafiltration using cross-flow hollow fiber membrane for Radix astragalus extracts

In this study, the effects of ultrasonic parameters on permeate flux and fouling resistances in the ultrasound-assisted ultrafiltration (UAUF) process of Radix astragalus extracts with hollow fiber membrane (HFM) was investigated. Ultrasonic parameters such as frequency, power and irradiation mode all can significantly affect the flux and fouling during the UAUF process, though the ultrasound power intensity was attenuated to be 10% only from generator. Concentration polarization and cake layer were decreased effectively by the ultrasound irradiation, resulting in a high flux performance. Meanwhile, HFM was susceptible to the irradiation at high power and low frequency compared with a flat sheet membrane. Ultrasound can not only enhance the permeate flux in UAUF but also cause breakage of HFM at an unsuited ultrasound field. It can be applied to the ultrafiltration process with HFM at an appropriate power and frequency.     

Effect of coating and surface modification on water and organic solvent nanofiltration using ceramic hollow fiber membrane

Nanofiltration ceramic hollow fiber membranes were developed to simplify the manufacturing process and improve water and organic solvent permeation performance. The alumina hollow fiber support was prepared by a phase-inversion/sintering method, and a γ-Al₂O₃ sol was coated thereon as a selective layer. Polyvinyl alcohol and ethanol were used as the drying control chemical additive in the coating solution, so that a coating layer could be formed without defects in only one coating step. The coating layer thickness could be adjusted to 0.6–2 μm depending on the coating drawing speed. A sintering temperature of 350 °C was selected to provide both reasonable water permeability (6.91 LMH/bar) and rejection (a molecular weight cutoff of 1000 Da or less) and to form a stable γ-Al₂O₃ phase. In the case of a membrane that was surface-modified with (3-chloropropyl)-trimethoxysilane, the permeability of toluene and hexane was 2.3 and 4.3 LMH/bar, respectively. The newly developed ceramic membrane showed excellent permeability and separation properties, as well as potential effectiveness for organic solvent nanofiltration applications.     

后处理对改性聚氨酯系中空纤维膜压力响应行为的影响

采用熔融纺丝制得改性聚氨酯系中空纤维膜,通过测试水通量随压力的变化研究了拉伸、热处理温度和热处理时间对改性聚氨酯系中空纤维膜压力响应行为的影响。结果表明,所得膜可发生明显的压力响应行为,且拉伸倍数越大,膜的强度越大,压力响应行为越精确;随热处理温度升高,膜的支撑性变差,压力响应行为变弱;随热处理时间延长,膜形变回复率变低,压力响应行为减弱。     

Tailoring the morphology of self-assembled block copolymer hollow fiber membranes

Isoporous asymmetric polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) hollow fiber membranes were successfully made by a dry-jet wet spinning process. Well-defined nanometer-scale pores around 20–40 nm in diameter were tailored on the top surface of the fiber above a non-ordered macroporous layer by combining block copolymer self-assembly and non-solvent induced phase separation (SNIPS). Uniformity of the surface-assembled pores and fiber cross-section morphology was improved by adjusting the solution concentration, solvent composition as well as some important spinning parameters such as bore fluid flow rate, polymer solution flow rate and air gap distance between the spinneret and the precipitation bath. The formation of the well-organized self-assembled pores is a result of the interplay of fast relaxation of the shear-induced oriented block copolymer chains, the rapid evaporation of the solvent mixture on the outer surface and solvent extraction into the bore liquid on the lumen side, and gravity force during spinning. Structural features of the block copolymer solutions were investigated by small-angle X-ray scattering (SAXS) and rheological properties of the solutions were examined as well. The scattering patterns of the optimal solutions for membrane formation indicate a disordered phase which is very close to the disorder-order transition. The nanostructured surface and cross-section morphology of the membranes were characterized by scanning electron microscopy (SEM). The water flux of the membranes was measured and gas permeation was examined to test the pressure stability of the hollow fibers.     

高性能中空纤维超滤膜结构和性能研究

以含二氮杂萘酮结构的聚醚砜酮(PPESK)为膜材料,N-甲基-2-吡咯烷酮为溶剂,一缩二乙二醇、乙二醇甲醚和丁酮为添加剂,采用干-湿相转化技术制备了中空纤维非对称超滤膜。结果表明,聚合物浓度、添加剂类型和添加剂浓度的变化导致了超滤膜的形态逐渐由长而宽的指状孔结构变为海绵状结构,同时也对超滤膜的性能产生了较大的影响,所制得的PPESK超滤膜在0 1MPa的操作压力下对PEG10000的截留率高于95%,纯水通量可高达约159L/(m2·h)。     

液膜技术原理及中空纤维更新液膜

液膜技术可以实现萃取和反萃的耦合,具有独特的分离优势。因为具有非平衡传质的特性,液膜技术传质推动力大,萃取相用量很少。回顾了液膜技术的原理,指出液膜技术的关键在于形成一层厚度薄且相当稳定的液膜相。分析介绍了近年来发展起来的各种液膜技术的优缺点,提出了一种中空纤维更新液膜技术,其体积传质系数比传统萃取塔的大530倍。     

中空纤维膜法制备聚合氯化铝的研究

无机高分子絮凝剂聚合氯化铝(PAC)中的Alb形态质量分数是衡量其絮凝活性的主要指标。如何有效地制备高Alb质量分数的PAC产品已成为研究的重点。文中基于中空纤维膜表面具有大量的微米级微孔这一特点,采用中空纤维膜反应器作为碱液分布器制备PAC,实现了碱液微量连续可控地加入到AlCl3溶液中,从而显著提高了产品中的Alb质量分数。实验优化了制备工艺:碱化度B为2.0,碱液(NaOH)浓度为0.2 mol/L,氯化铝浓度为0.5 mol/L。检测结果表明:膜法制备的聚合氯化铝Alb质量分数可达90.18%,远高于其他方法制备的产品,其对染料模拟废水的絮凝效果远好于工业化产品。     

A novel inorganic hollow fiber membrane reactor for catalytic dehydrogenation of propane

A novel inorganic hollow fiber membrane reactor (iHFMR) has been developed and applied to the catalytic dehydrogenation of propane to propene. Alumina hollow fiber substrates, prepared by a phase inversion/sintering method, possess a unique asymmetric structure that can be characterized by a very porous inner surface from which finger-like voids extend across ∼80% of the fiber cross-section with the remaining 20% consisting of a denser sponge-like outer layer. In contrast to other existing Pd/Ag composite membranes, where an intermediate γ-Al₂O₃ layer is often used to bridge the Pd/Ag layer and the substrate, the Pd/Ag composite membrane prepared in this study was achieved by coating the Pd/Ag layer directly onto the outer surface of the asymmetric substrate. After depositing submicron-sized Pt (0.5 wt %)/γ-alumina catalysts in the finger-like voids of the substrates, a highly compact multifunctional iHFMR was developed. Propane conversion as high as 42% was achieved at the initial stage of the reaction at 723 K. In addition, the space-time yields of the iHFMR were ∼60 times higher than that of a fixed bed reactor, demonstrating advantages of using iHFMR for dehydrogenation reactions. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

中空纤维渗透汽化膜分离研究现状与展望

本文综述了中空纤维渗透汽化膜分离的研究进展,包括中空纤维支撑膜的制备、复合膜的制备方法、中空纤维渗透汽化膜的工业应用和中空纤维渗透汽化膜传质特性等几个方面,对这个方面所存在的问题以及今后发展方向进行了展望.     

Phenol recovery with tributyl phosphate in a hollow fiber membrane contactor: Experimental and model analysis

The extraction and stripping of phenol using a solution of tributyl phosphate in kerosene in a hydrophobic polypropylene hollow fiber membrane contactor has been studied. The effect of the aqueous and the organic phase flow rates on the overall mass transfer coefficient for both extraction and stripping steps was investigated. Experimental values of the overall mass transfer coefficient were determined and compared with predicted values from the resistance in series model. Results showed that the overall mass transfer coefficients for extraction were about one order of magnitude greater than those measured during the stripping process. The experimental values were in good agreement with the predicted values for the extraction module. However, the predicted values were slightly overestimated for the stripping module. The individual mass transfer resistances were analyzed and the rate-controlling steps of mass transfer were also identified in both extraction and stripping modules. The major resistance in extraction and stripping was in the aqueous phase and in the membrane phase, respectively.     

Hydrophobic PVDF hollow fiber membranes with narrow pore size distribution and ultra-thin skin for the fresh water production through membrane distillation

Polyvinylidene fluoride (PVDF) hydrophobic asymmetric hollow fiber membrane was fabricated through the dry-jet wet phase inversion process. It is found that the PVDF hollow fiber has an ultra-thin skin layer and a porous support layer from the morphology study. The fully porous membrane structure has the advantage of decreasing the vapor transport resistance and enhancing the permeation flux. The fabricated PVDF membrane has a mean pore size of in diameter and a narrow pore size distribution. The rough external surface produces an advancing contact angle of 112±3^° with water. During direct contact membrane distillation (MD) of 3.5 wt% salt solution, PVDF hollow fibers produced a water permeation flux of (based on the external diameter of hollow fiber) and a NaCl rejection of 99.99% with a hot salt solution at 79.3 °C and cold distillate water at 17.5 °C. This performance is comparable to or superior to most of commercially available PVDF hollow fiber membranes, indicating that the newly developed PVDF may be suitable for MD applications.     

A TiO2 modified whisker mullite hollow fiber ceramic membrane for high-efficiency oil/water emulsions separation

Design and preparation of membranes with ultrahigh separation performance and antifouling property for oil-in-water (O/W) emulsions remains challenging. In this study, a high flux mullite/TiO₂ ceramic composite membrane was prepared via multi-precipitation of TiO₂ on a whisker mullite hollow fiber support synthesized by combining phase inversion and high-temperature sintering techniques. The results showed that the generated whisker mullite structure improved the permeation flux, and the micro-nano structured TiO₂ functional layer endowed the membrane surface with superhydrophility and stability. The retention of the optimal composite membrane (M20T13) that was soaked in the titanium solution 20 times for 13 min each time for the O/W emulsions like n-hexane, toluene and engine oil maintained over 98 %, and the flux after 6 h filtration was 668.34 L·m⁻²·h⁻¹, 487.25 L·m⁻²·h⁻¹ and 258.66 L·m⁻²·h⁻¹, respectively, much higher than that of the optimal substrate (F3A1, mass ratio of fly ash: Al₂O₃ = 3:1). Moreover, the flux recovery rate of M20T13 was much higher than that of F3A1 after chemical backwashing. This work manifests great potential in O/W treatment fields.