Modified silicone–PVDF composite hollow‐fiber membrane preparation and its application in VOC separation

Polydimethylsiloxane^vi–poly(vinylidene fluoride) (PDMS^vi–PVDF) composite membranes were prepared using asymmetric PVDF hollow‐fiber membranes as the substrate where a very thin layer of silicone‐based coating material was deposited via a developed dip coating method. The preparation of the composite membranes under various conditions were investigated. In the optimal coating procedure, homogenous and stable oligo‐PDMS^vi coating layers as thin as 1–2 μm were successfully deposited on the surface of PVDF membranes. The developed PDMS^vi–PVDF composite membranes were applied for separation of a wide variety of volatile organic compounds (benzene, chloroform, acetone, ethyl acetate, and toluene). The results showed that the PDMS^vi–PVDF hollow‐fiber composite membranes that had been developed exhibited very high removal efficiency (>96%) for all the VOCs examined under favorable operating conditions. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Effect of TEP content in cooling bath on porous structure,crystalline and mechanical properties of PVDF hollow fiber membranes

Poly (vinylidene fluoride) (PVDF) hollow fiber membranes were prepared by adding triethyl phosphate (TEP) to the cooling water bath in a modified thermally induced phase separation process. The effect of TEP content in the cooling bath on the porous structure, crystallinity, thermal and mechanical properties of PVDF hollow fiber membranes was investigated. The melting temperature and crystallinity of the membranes were determined using differential scanning calorimetry. The crystalline and cross‐section morphology of the hollow fiber membranes were investigated using wide angle X‐ray diffraction and scanning electron microscopy. The resulting membrane exhibited a nearly symmetric structure. The results showed that the TEP content in the cooling bath had a crucial role on the membrane formation, which was also confirmed from the morphology and mechanical properties of the hollow fibers. The porosity, average pore size, crystallinity, Young's modulus, max stress, and elongation at breakage of the hollow fiber membranes can be related to the amount of TEP in the cooling bath. Better pore connectivity was obtained in hollow fiber membranes when the weight ratio of TEP to water was 40:60. POLYM. ENG. SCI., 54:2207–2214, 2014. © 2013 Society of Plastics Engineers     

Preparation and properties of PVDF/PVA hollow fiber membranes

On principle of polymer blend phase separation, PVDF/PVA hollow fiber membranes were prepared using phase inversion method. The membrane morphology and performance varied with the blending ratio. The PVDF/PVA blends showed incompatibility by the results of dynamic mechanical analysis (DMA) and infrared attenuated total reflection (FTIR-ATR) sampling technique. Based on bursting pressure and tensile strengths results, we suggest that the mechanical properties of PVDF/PVA blend membranes are worse than that of PVDF membrane. PVA can improve the hydrophilicity of PVDF/PVA hollow fiber membranes, which could be illuminated by the decrease in contact angle, the increase in equilibrium water content (EWC) and the variety in dynamic moisture regain. The pure water flux increases while the rejection ratio decreases with PVA content increasing. Moreover, PVA can improve the anti-fouling property of PVDF/PVA hollow fiber membranes, which could be illuminated by the result of increase coefficient of resistance.     

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.     

PVDF树脂的物性对中空纤维膜性能的影响

采用了不同特性粘度的PVDF树脂,通过非溶剂致相分离法(NIPS)制备了相应的PVDF中空纤维膜。通过力学性能、纯水通量、牛血清白蛋白(BSA)截留率等性能测试发现,不同特性粘度的PVDF树脂制备的中空纤维膜的性能差异较大。随着PVDF特性粘度的增加,PVDF中空纤维膜的拉伸强度及断裂伸长率逐渐增加,纯水通量逐渐降低,BSA截留率先降低后增加。通过扫描电镜(SEM)进一步发现,随着PVDF特性粘度的增加,PVDF树脂制备的中空纤维膜,其海绵层上的孔状结构逐渐减少且变小。     

基于仿生矿化的PTFE中空纤维膜亲水改性研究

由于聚四氟乙烯(PTFE)材料具有强疏水性和极低的表面能,使得PTFE中空纤维膜润湿性差,难以处理水性溶液,限制了其应用过程和领域,因此开展PTFE中空纤维膜亲水化改性研究具有重要的现实意义。利用仿生矿化技术对PTFE中空纤维膜进行表面改性,研究了不同矿化工艺对膜亲水性能的影响,并对改性前后PTFE中空纤维膜的官能团、水通量、气通量、孔径及孔径分布进行了表征。研究表明,仿生矿化能够提高PTFE中空纤维膜的亲水性和水通量,同时由于碳酸钙分子进入膜孔内部,使孔径分布更加均匀,平均孔径和气通量减小。     

Dye removal using hydrophobic polyvinylidene fluoride hollow fibre composite membrane by vacuum membrane distillation

Hydrophobic polyvinylidene fluoride (PVDF) hollow fibre composite membranes were prepared by the dilute solution coating process to build a special surface structure that was similar to the dual micro‐nano structure on the lotus leaf. Poly(vinylidene fluoride‐co‐hexafluoropropene) was chosen as the hydrophobic polymer candidate in dilute solution. Membrane morphology and surface hydrophobicity were evaluated by scanning electron microscopy and dynamic water contact angle measurement. The prepared PVDF hollow fibre membranes were employed to separate dyes (Congo Red and Methylene Blue) from water by vacuum membrane distillation. The effects of operational conditions (feed temperature, vacuum pressure and feed flow rate) on the vacuum membrane distillation performance of different PVDF membranes were investigated. The results indicated that the water contact angle values of PVDF composite membrane surfaces improved from 93.6° to 130.8°, which was mainly attributed to the formation of micro‐nano rods. This structure was similar to the dual micro‐nano structure on the lotus leaf. Under test feed temperature, vacuum pressure and feed flow rate conditions, the dye rejection rate of Congo Red and Methylene Blue by the hydrophobic PVDF hollow fibre membrane remained above 99.5% and 99%, which was higher than that of the pristine PVDF membrane (99% and 98%, respectively). In addition, the hydrophobic PVDF hollow fibre composite membrane showed higher permeation flux under different conditions compared with the pristine PVDF membrane, which was attributed to membrane surface hydrophobicity and the electrostatic interactions between dyes and the PVDF membrane surface.     

Investigation of an Ozone Membrane Contactor System

Ozone mass transfer rates were determined for nine expanded porous Teflon membranes that had different pore size, thickness, and pore volume, a nonporous Teflon membrane, and a PVDF membrane. The mass transfer coefficient was 7.6 ± 0.5 × 10^?5 m/s at Re of 2000 for all membranes tested even though pore sizes ranged from 0.07 to 6 μm and thickness from 0.076 to 0.25 mm. Mass transfer increased with liquid side Reynolds number. Therefore, it is likely that ozone mass transfer is liquid phase controlling and not membrane limited. For a hypothetical case of 4000 m³/d and 2 mg/L ozone transferred, plate and frame membrane and hollow fiber contactors are approximately one and two orders of magnitude smaller, respectively, than fine-bubble diffusers.     

酚酞型聚醚砜对聚偏氟乙烯中空纤维膜结构及性能的影响

以二苯甲酮和N,N-二甲基乙酰胺为稀释剂,酚酞型聚醚砜(PES-C)为添加剂,通过热致相分离法制备了聚偏氟乙烯(PVDF)中空纤维膜。采用扫描电镜观察了膜的结构,测试了膜的纯水通量。在膜生物反应器(MBR)中测试了膜的污水通量和出水的化学需氧量及氨氮指标。该法制得的膜具有较为致密的皮层结构和疏松的支撑层结构,添加质量分数为2%的PES-C制备的PVDF膜与PVDF膜相比纯水通量增加60%,污水通量增加37.8%,出水COD去除率增加了3.32%,NH4+—N去除率增加了2.2%,且MBR出水达到排放标准。     

用于处理染料废水的PVDF/TPU共混中空纤维膜的制备

采用相转化法制备PVDF／TPU共混中空纤维膜,以PVP为添加剂可以改善成膜性能。通过水通量超滤实验、牛血清白蛋白截留实验、扫描电子显微镜表征膜的表面与截面结构分析得出铸膜液中纤维膜的质量分数为16％,m（PVDF）：m（11Pu）为80：20,添加5％PVP时制备的膜的综合性能最佳。对不同的溶液包括BSA、PVPK30、PEG10000、染料活性艳蓝KN-R进行截留实验分析膜过滤性能。在pH范围为1—14时,膜的水通量及截留率均无明显变化,说明PVDF／TPU共混中空纤维膜具有良好的抗酸、碱性。用清水冲洗10min后,膜污染的恢复率即可达到86．5％,膜的抗污染性能良好。     

Removal of Volatile Organic Compounds from Water by Pervaporation Using Polyetherimide-Polyethersulfone Blend Hollow Fiber Membranes

Abstract

Removal of volatile organic compounds (VOCs) such as 1,2-dichloroethane, trichloroethylene, chlorobenzene and toluene from water solutions through polyetherimide (PEI)-polyethersulfone (PES) blend hollow fiber membranes was investigated by pervaporation (PV) in this work. The separation performances of the membranes were researched by varying the spinning conditions (such as coagulation temperature and air gap distance) for the preparation of the hollow fibers and the operation conditions (such as velocity, concentration, and temperature of feed liquids). For the PEI-PES blend hollow fiber membrane prepared when the air gap was 7 cm and the temperature of coagulation bath was 45°C, it possessed high selectivity to the aqueous solutions containing 0.04 wt.% of VOCs at 20°C. The separation factors to 1,2-dichloroethane, trichloroethylene, chlorobenzene and toluene were 7069, 5759, 3952, and 3205, respectively. It was found that the pervaporation performance of the blend hollow fiber membrane was strongly related to the molecular size of the VOCs. The order of the selectivities was 1,2-dichloroethane > trichloroethylene > chlorobenzene > toluene.     

聚乙烯亚胺（PEI）络合一超滤处理水中Cu舢过程中的膜污染

该文依据膜流动电位及zeta电位的测定原理设计了一套试验装置,可对中空纤维膜的流动电位进行测定。通过该装置研究了聚偏氟乙烯（PvDF）中空纤维超滤膜的动电现象在聚乙烯亚胺（PEI）络合一超滤处理水中Cu^2＋过程中的作用及规律,以此分析膜污染发生的过程与机理,为如何减轻和清洗超滤膜污染提供了依据。     

Microporous polyvinylidene fluoride hollow fiber membrane contactors for CO2 stripping: Effect of PEG-400 in spinning dope

In order to develop the structure of microporous PVDF membranes, PEG-400 was introduced into the polymer dope as a non-solvent additive. The hollow fiber membranes were prepared via a wet phase-inversion process and then used in the membrane contactor modules for CO₂ stripping from water. By addition of different amounts of PEG-400, cloud points of the polymer dope were obtained to examine phase-inversion behavior. From FESEM analysis, the membrane structure changed from a finger-like to an approximately sponge-like morphology with the addition of 4 wt.% of PEG-400. The prepared membranes presented smaller mean pore size (0.13 μm) and significantly higher wetting pressure (550 kPa) compared to the plain membrane. From CO₂ stripping test, at water velocity of 0.4 m/s, the PVDF membranes prepared by 4% PEG-400 demonstrated an approximate CO₂ stripping flux of 4.5 × 10⁻⁵ (mol/m² s) which is 125% higher than the flux of the plain membrane. It could be concluded that structurally developed hydrophobic PVDF hollow fiber membranes can be prepared by a controlled phase-inversion process to enhance the performance of gas–liquid membrane contactor.     

添加剂和凝结剂温度对用无溶剂致相位分离法生产高性能PVDF/聚醚F127混合中空光纤膜的影响(英文)

Poly(vinylidene fluoride)(PVDF) has become one of the most popular materials for membrane prepara-tion via nonsolvent induced phase separation(NIPS) process.In this study,an amphiphilic block copolymer,Plu-ronic F127,has been used as both a pore-former and a surface-modifier in the fabrication of PVDF hollow fiber membranes to enhance the membrane permeability and hydrophilicity.The effects of 2nd additive and coagulant temperature on the formation of PVDF/Pluronic F127 membranes have also been investigated.The as-spun hollow fibers were characterized in terms of cross-sectional morphology,pure water permeation(PWP),relative molecular mass cut-off(MWCO),membrane chemistry,and hydrophilicity.It was observed that the addition of Pluronic F127 significantly increased the PWP of as-spun fibers,while the membrane contact angle was reduced.However,the size of macrovoids in the membranes was undesirably large.The addition of a 2nd additive,including lithium chlo-ride(LiCl) and water,or an increase in coagulant temperature was found to effectively suppress the macrovoid for-mation in the Pluronic-containing membranes.In addition,the use of LiCl as a 2nd additive also further enhanced the PWP and hydrophilicity of the membranes,while the surface pore size became smaller.PVDF hollow fiber with a PWP as high as 2530 L?m?2?h?1?MPa?1,a MWCO of 53000 and a contact angle of 71° was successfully fabricated with 3%(by mass) of Pluronic F127 and 3%(by mass) of LiCl at a coagulant temperature of 25 °C,which shows better performance as compared with most of PVDF hollow fiber membranes made by NIPS method.     

纺丝条件对PVDF/PVC中空纤维膜性能的影响

采用干-湿法纺丝工艺制备PVDF/PVC共混中空纤维膜,通过对水通量、孔径、截留率等的测试,研究了挤出速率、芯液流量、干纺程对PVDF/PVC中空纤维膜性能及结构的影响,并进行了详细的理论分析。试验结果表明挤出速率与膜通量存在最大值,芯液流量与膜通量及截留率呈线性关系,干纺程的影响效果跟挤出速率类似。可以通过改变纺丝条件来制备性能不同的中空纤维膜。     

PVDF-TiO2复合中空纤维膜的制备与表征

将纳米二氧化钛(TiO₂)粒子与4类制膜添加剂复配处理,采用相转化法制备聚偏氟乙烯(PVDF)-TiO₂复合中空纤维膜,讨论了纳米TiO₂粒子对复合膜结构和性能的影响。通过扫描电子显微镜、X射线衍射、能谱分析、热重分析、拉伸试验、接触角测定和超滤实验分别表征了复合膜的微观孔结构、晶相结构和复合均匀性、热稳定性、机械性能、亲水性、超滤性能以及抗污染性能。结果表明：通过添加TiO₂粒子复配添加剂,复合膜的性能得到有效改善。复配添加剂中w(TiO₂)为2%(占PVDF固含量的质量分数)时,纯水通量由348 L/(m²·h)提高至377 L/(m²·h),牛血清蛋白截留率由68%提高至90%,断裂强度和抗污染性能提高,复合膜综合性能优异。     

真空膜蒸馏法分离乙醇溶液的研究

采用聚偏氟乙烯复合中空纤维膜制作膜组件,制备小型实验装置用来分离从低浓度到高浓度的乙醇溶液,研究探讨了进料温度、料液流速、料液浓度、真空度对膜通量和分离因子的影响.进料温度升高时,膜通量及分离因子均增大.冷侧真空度的增加,通量呈线性增长,但分离因子减小.料液流速对膜通量和分离因子的影响温和.结果表明,真空膜蒸馏适用于浓...     

Effect of the Addition of Fructose on the Pervaporation of Ethanol/Water Mixtures by Silicone-Rubber-Coated Polyethersulfone Membranes

Abstract

Composite hollow fiber membranes were prepared by coating polyethersulfone hollow fibers with silicone rubber. The hollow fiber membranes so produced were found to be water selective when they were used for the separation of feed ethanol/water mixtures by pervaporation. When fructose was added to feed ethanol/water mixtures, a decrease in permeation rate and an increase in water selectivity were observed. The decrease in the permeation rate was possible to assume, but the noticed increase in water selectivity was against our expectation, since the vapor pressure of water decreases while that of ethanol increases when sugars are added to mixtures of ethanol and water. Water selectivity of the membrane was enhanced with an increase in the amount of fructose in the feed.     

Fabrication and characterization of hydrophobic PVDF hollow fiber membranes for desalination through direct contact membrane distillation

The mixture of inorganic salt LiCl and soluble polymer polyethylene glycol (PEG) 1500 as non-solvent additive was introduced to fabricate hydrophobic hollow fiber membrane of polyvinylidene fluoride (PVDF) by phase inversion process, using N,N-dimethylacetamide (DMAc) as solvent and tap water as the coagulation medium. Compared with other three membranes from PVDF/DMAc, PVDF/DMAc/LiCl and PVDF/DMAc/PEG 1500 dope solution, it can be observed obviously by scanning electron microscope (SEM) that the membrane spun from PVDF/DMAc/LiCl/PEG 1500 dope had longer finger-like cavities, ultra-thin skins, narrow pore size distribution and porous network sponge-like structure owing to the synergistic effect of LiCl and PEG 1500. Besides, the membrane also exhibited high porosity and good hydrophobicity. During the desalination process of 3.5 wt% sodium chloride solution through direct contact membrane distillation (DCMD), the permeate flux achieved 40.5 kg/m² h and the rejection of NaCl maintained 99.99% with the feed solution at 81.8 °C and the cold distillate water at 20.0 °C, this performance is comparable or even higher than most of the previous reports. Furthermore, a 200 h continuously desalination experiment showed that the membrane had stable permeate flux and solute rejection, indicating that the as-spun PVDF hollow fiber membrane may be of great potential to be utilized in the DCMD process.