Innovative hydrophobic/hydrophilic perfluoropolyether (PFPE)/polyvinylidene fluoride (PVDF) composite membrane for vacuum membrane distillation

Though membrane distillation (MD) has gained more and more attention in the field of desalination, the wetting phenomenon was still a non-negligible problem. In this work, a method combined dip-coating and UV in situ polymerization for preparing hydrophobic/hydrophilic perfluoropolyether (PFPE)/polyvinylidene fluoride composite membranes. This composite membrane consisted of a top thin hydrophobic coating layer and hydrophilic substrate membrane. In terms of anti-wetting properties, contact angle and liquid entry pressure of all composite membranes (except for those based on 0.45 μm) exceeded 160° and 0.3 MPa, respectively. In particular, the desalination performance was tested in vacuum membrane distillation tests by feeding 3.5% (mass) saline solution (NaCl) at 60 ℃. The composite membranes with larger support pore size and lower PFPE content had higher membrane distillation flux. And for stability tests (testing the 0.22 μm membrane coated by 5% (mass) PFPE), the highest MD flux 29.08 kg·m^-2·h^-1 and stable salt rejection (over 99.99%) during the period. Except that, the effects of coating material concentration and pore sizes of substrate membrane were also investigated for surface morphology and topography, porosity, mechanical strength and pore size characteristics. This work provided a simple and effective alternative to prepare excellent hydrophobic composite membranes for MD applications.     

Hydrophilic modification of high‐strength polyvinylidene fluoride hollow fiber membrane

The polyvinylidene fluoride (PVDF)/polyvinyl alcohol (PVA) polymer solutions were coated on the outer surface of PVDF matrix hollow fiber membrane. On the principle of the homogeneous‐reinforced (HR) membrane technology, the reinforced PVDF/PVA (RFA) hollow fiber membranes prepared through the dry‐wet spinning method. The performance of the RFA membranes varies with the PVA concentration in the polymer solution and is characterized in terms of pure water flux (PWF), porosity, a mechanical strength test, and morphology observations by a scanning electron microscopy (SEM). The results of this study indicate that PVA can apparently improve the hydrophilicity of the PVDF hollow fiber membranes. The growing enrichment of the hydrophilic components PVA on the membrane surface is determined by X‐ray photoelectron spectroscopy. The RFA membranes have a favorable interfacial bonding between the coating layer (PVDF/PVA) and the matrix membrane (PVDF hollow fiber membrane), as shown by SEM. The elongation at break of the RFA membranes increases much more than that of the matrix membrane that is endowed with the better flexibility of the membrane performance. PWF decreases much more compared with that of the matrix membrane. The RFA membranes have a lower flux decline degree during the process of protein solution and ink solution filtration compared with that of the matrix membrane. POLYM. ENG. SCI., 54:276–287, 2014. © 2013 Society of Plastics Engineers     

聚偏氟乙烯/聚二甲基硅氧烷渗透气化膜在丁醇分离中的应用

通过相转化法制备PVDF多孔支撑膜,在其上涂覆致密的PDMS分离层制备得到PVDF/PDMS复合膜,用于丁醇的分离纯化。以丁醇水溶液为原料液,流速为1.6 L·min^-1,丁醇浓度为15 g·L^-1,温度为37℃时, PVDF/PDMS复合膜的总通量为158.2 g·m^-2·h^-1,分离因子为17.3。向丁醇水溶液中按丁醇：丙酮：乙醇比例为6：3：1添加丙酮和乙醇模拟发酵液,PVDF/PDMS复合膜的总通量升高到189.5 g·m^-2·h^-1,分离因子降低到14.8。进一步考察了以丙酮-丁醇-乙醇（ABE）发酵液为原料液的渗透气化膜分离性能,发酵液中不存在菌体时,PVDF/PDMS复合膜的总通量和分离因子分别为120.2 g·m^-2·h^-1和19.7,而菌体存在时,复合膜的总通量和分离因子分别为122.1 g·m^-2·h^-1和16.7。与PDMS均质膜相比,PVDF/PDMS复合膜在丁醇分离过程中的分离性能有了显著的提升, 具有潜在的应用价值。     

Vacuum membrane distillation simulation of desalination using polypropylene hydrophobic microporous membrane

Numerical simulation is an effective method to get the optimal operating parameters in the chemical engineering process. In this work, the transport mechanism of vacuum membrane distillation (VMD) process was simulated and predicted by mathematical model, which was established based on the convective heat transfer coefficient, and 0.5M aqueous NaCl solution was concentrated with isotactic polypropylene (iPP) hydrophobic microporous membrane prepared via thermally induced phase separation (TIPS) in the VMD process. The as‐presented mathematical model simulated the effects of different operating parameters on the VMD performances for aqueous NaCl solution, such as feed temperature, feed flow rate, absolute pressure of membrane permeate side, temperature coefficient, membrane thickness, and porosity. A comparison between experimental data and simulated data was also considered to verify the proposed mathematical model. Additionally, the salt rejection of aqueous NaCl solution production water in VMD was higher than 99.9%. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41632.     

太阳能光热-光电中空纤维真空膜蒸馏系统理论与实验研究

自主设计并搭建了太阳能光热-光电中空纤维膜蒸馏系统,太阳能光热采用面积1.82 m²真空管集热系统,光伏发电采用面积1.63 m²多晶硅电池板。实验方面,研究了不同工况下,热料液在不同流动方式时膜通量的差异;研究了在不同跟踪方式下太阳辐照度对系统性能的影响。结果表明：料液在管程流动的膜通量大于壳程的膜通量,且进口料液温度取50~70℃之间为宜;自动跟踪下膜组件入口温度比非跟踪高2~3℃,可以延长膜蒸馏系统运行时间1~2 h,且在相同的自然环境下,自动跟踪方式最大膜通量8.89 kg/(m²·h)远高于非跟踪方式时4.26 kg/(m²·h)。理论方面,分析了以水为工质的中空纤维膜蒸馏的传热和传质过程,建立了传热传质理论计算数学模型;分析了辐照强度、膜表面温差、膜丝内表面传热系数、传热与传质通量的定量关系,计算了膜面温度与理论膜通量,对比了实验值与理论值。系统运行稳定,能量综合利用效率高,性能可靠,为工程应用奠定了理论和实验基础。     

Improvement of porous polyvinylidene fluoride-co-hexafluropropylene hollow fiber membranes for sweeping gas membrane distillation of ethylene glycol solution

Porous polyvinylidene fluoride-co-hexafluropropylene (PVDF-HFP) hollow fiber membranes were fabricated through a wet spinning process. In order to improve the membrane structure, composition of the polymer solution was adjusted by studying ternary phase diagrams of polymer/solvent/non-solvent. The prepared membranes were used for sweeping gas membrane distillation (SGMD) of 20 wt% ethylene glycol (EG) aqueous solution. The membranes were characterized by different tests such as N₂ permeation, overall porosity, critical water entry pressure (CEP_w), water contact angle and collapsing pressure. From FESEM examination, addition of 3 wt% glycerol in the PVDF-HFP solution, produced membranes with smaller finger-likes cavities, higher surface porosity and smaller pore sizes. Increasing the polymer concentration up to 21 wt% resulted in a dense spongy structure which could significantly reduce the N₂ permeance. The membrane prepared by 3 wt% glycerol and 17 wt% polymer demonstrated an improved structure with mean pore size of 18 nm and a high surface porosity of 872 m⁻¹. CEP_w of 350 kPa and overall porosity of 84% were also obtained for the improved membrane. Collapsing pressure of the membranes relatively improved by increasing the polymer concentration. From the SGMD test, the developed membrane represented a maximum permeate flux of 28 kg·m⁻²·h⁻¹ which is almost 19% higher than the flux of plain membrane. During 120 h of a long-term SGMD operation, a gradual flux reduction of 30% was noticed. In addition, EG rejection reduced from 100% to around 99.5% during 120 h of the operation.     

Improvement of porous polyvinylidene fluoride-co-hexafluropropylene hollow fiber membranes for sweeping gas membrane distillation of ethylene glycol solution

Porous polyvinylidene fluoride-co-hexafluropropylene (PVDF-HFP) hollow fiber membranes were fabricated through a wet spinning process. In order to improve the membrane structure, composition of the polymer solution was adjusted by studying ternary phase diagrams of polymer/solvent/non-solvent. The prepared membranes were used for sweeping gas membrane distillation (SGMD) of 20 wt% ethylene glycol (EG) aqueous solution. The membranes were characterized by different tests such as N₂ permeation, overall porosity, critical water entry pressure (CEP_w), water contact angle and collapsing pressure. From FESEM examination, addition of 3 wt% glycerol in the PVDF-HFP solution, produced membranes with smaller finger-likes cavities, higher surface porosity and smaller pore sizes. Increasing the polymer concentration up to 21 wt% resulted in a dense spongy structure which could significantly reduce the N₂ permeance. The membrane prepared by 3 wt% glycerol and 17 wt% polymer demonstrated an improved structure with mean pore size of 18 nm and a high surface porosity of 872 m^-1. CEP_w of 350 kPa and overall porosity of 84% were also obtained for the improved membrane. Collapsing pressure of the membranes relatively improved by increasing the polymer concentration. From the SGMD test, the developed membrane represented a maximum permeate flux of 28 kg·m^-2·h^-1 which is almost 19% higher than the flux of plain membrane. During 120 h of a long-term SGMD operation, a gradual flux reduction of 30% was noticed. In addition, EG rejection reduced from 100% to around 99.5% during 120 h of the operation.     

Exploring the spinning and operations of multibore hollow fiber membranes for vacuum membrane distillation

Hollow fiber membranes with a multibore configuration have demonstrated their advantages with high mechanical strength, easy module fabrication, and excellent stability for membrane distillation (MD). In this work, the microstructure of multibore fibers was optimized for vacuum MD (VMD). A microstructure consisting of a tight liquid contact surface and a fully porous cross‐section is proposed and fabricated to maximize the wetting resistance and VMD desalination performance. The new membrane exhibited a high VMD flux of 71.8 L m^?2 h^?1 with a 78°C model seawater feed. Investigations were also carried to examine various effects of VMD operational conditions on desalination performance. The 7‐bore membrane showed higher flux and superior thermal efficiency under the VMD configuration than the direct contact MD configuration. Different from the traditional single‐bore hollow fiber, the VMD flux of multibore membrane at the lumen‐side feed configuration was higher than that of the shell‐side feed due to the additional evaporation surface of multibore geometry. © 2013 American Institute of Chemical Engineers AIChE J, 60: 1078–1090, 2014     

Treatment of wastewater containing oil using phosphorylated silica nanotubes (PSNTs)/polyvinylidene fluoride (PVDF) composite membrane

PVDF membranes are broadly applied in many fields owing to their good physicochemical stability, resistance to oxidation and chlorine. However when treating with wastewater, PVDF membranes are easily contaminated by pollutant, degrading their properties due to the hydrophobicity and poor anti-compaction capabilities, which can result in the decline of flux and lifespan of the membrane and limit their application in large scale. To enhance the integrative capabilities of PVDF membrane, phosphorylated silica nanotubes (PSNTs) were doped to PVDF to prepare a novel PSNTs/PVDF composite membrane through a phase inversion technique. The PSNTs/PVDF composite membranes were exposed to wastewater containing oil, and the effects of doped materials, operating pressure and operating temperature on fluxes were researched. The optimum parameters are: operating pressure is 0.1 MPa, operating temperature 25 °C. Through physical flushing and chemical cleaning, the PSNTs/PVDF membranes could still keep a high permeation flux and long lifetime. Finally, the interaction mechanism between PSNTs and PVDF membrane, the anti-fouling mechanism of PSNTs/PVDF composite membrane were explored and analyzed. The results show that the hydrophilicity, anti-fouling and anti-compaction properties of composite membrane can be obviously enhanced and hence the PSNTs/PVDF composite membrane is desirable in the treatment of wastewater containing oil and sewage.     

Preparation and characterization of polyvinylidene fluoride hollow fiber membranes for ultrafiltration

Polyvinylidene fluoride (PVDF) hollow fiber membranes were prepared using the solvent spinning method. N,N-dimethylacetamide was the solvent and ethylene glycol was employed as non-solvent additive. The effect of the concentration of ethylene glycol in the PVDF spinning solution as well as the effect of ethanol either in the internal or the external coagulant on the morphology of the hollow fibers was investigated. The prepared membranes were characterized in terms of the liquid entry pressure of water measurements, the gas permeation tests, the scanning electron microscopy, the atomic force microscopy, and the solute transport experiments. Ultrafiltration experiments were conducted using polyethylene glycol and polyethylene oxides of different molecular weights cut-off as solutes. A comparative analysis was made between the membrane characteristic parameters obtained from the different characterization techniques.     

Cadmium removal using hollow fiber membrane with organic extradant

Removal of cadmium ion by using a hollow fiber module is investigated experimentally, and organic extradant is applied to enhance the removal rate. The roles of pH, flow rates of the aqueous phase and the organic phase, initial concentration of cadmium ion and coexisting metals are investigated to find an optimum operating condition of the module. The experimental outcome indicates that the best performance is yielded with pH of 4 and the flow rate of aqueous phase in tube side flow controls mass transfer rate. In addition, the initial concentration of 100 ppm gives the best removal. Effect of coexisting component is negligible except Zn and Cu when both of them are present at the same time.     

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.     

增强型聚偏氟乙烯微孔膜的研制

通过相转化法制备无纺布支撑的增强型聚偏氟乙烯微孔膜,确定二甲基乙酰胺(DMAC)为溶剂,氯化锂为第二添加剂,以水作为凝胶浴.研究了添加剂组成和浓度、凝胶浴组成和浓度、凝胶浴温度、热处理条件等因素对聚偏氟乙烯膜性能的影响.     

污染聚偏氟乙烯中空纤维超滤膜的超声清洗

中空纤维超滤膜污染和清洗影响膜处理废水工艺的经济性及可运行性.研究了平板浸没式超声处理器（40 kHz）与2000 mg·L^-1柠檬酸清洗剂对中石化某水处理厂污染聚偏氟乙烯超滤膜的清洗效果.利用自定义的除垢率和扫描电镜对清洗结果进行表征并用过滤通量来验证.证明超声对超滤膜的清洗效果显著.单根膜清洗除垢率比不加超声时提高了25%,达到80%左右,且没有破坏膜的表面和结构.得到本批污染膜及自制污染膜组件的优化清洗工艺及超声参数为：频率40 kHz、声强2200 W·m^-2、超声处理时间30 min.未使用反向冲清洗,仅切向气流结合超声清洗膜面,清洗后的通量从原来污染组件的0.0368 cm³·cm^-2·min^-1增加到0.1254 cm³·cm^-2·min^-1,恢复到相当于新膜初始通量的72.5%,通量增加率达到241%.进一步证明了超声清洗膜的可行性和有效性.     

基于聚偏氟乙烯复合结构色材料的制备与性能

以聚偏氟乙烯(PVDF)为黏结剂，将其填充于三维PS@SiO₂光子晶体中，锁定PS@SiO₂微球组装的有序阵列，成功构建了结构稳定且柔韧的新型PVDF/PS@SiO₂结构色材料。使用纳米粒度与电位分析仪对PS@SiO₂微球的多分散性指数以及Zeta电位进行了测试，采用SEM、TEM、固体紫外-可见光谱仪、预置式色牢度摩擦仪及拉伸测试仪对PVDF/PS@SiO₂结构色材料的形貌、光学性质及稳定性进行了表征和测试。结果表明，该结构色材料在摩擦测试100次后，结构保持稳定，颜色稳定存在。同时材料易于图案化，具有优异的抗拉伸性能和柔性，材料的拉伸断裂应力达到22.28 MPa，断裂应变为28.49%，在卷曲100次后，依旧保持微观结构稳定。     

减压膜蒸馏浓缩盐水溶液的研究现状

减压膜蒸馏技术是一种新型膜分离技术,在许多领域中呈现出明显优势。综述了减压膜蒸馏技术浓缩盐水溶液的研究现状,分析了影响分离性能的相关因素以及该技术在处理浓盐水中的应用效果,指出了减压膜蒸馏技术浓缩盐水溶液的应用前景。     

改性聚偏氟乙烯膜污染清洗技术及发展趋势

介绍了聚偏氟乙烯（PVDF）膜污染的机制.介绍了改性PVDF膜污染清洗及清洗原理.分析了改性PVDF膜清洗技术的发展趋势.     

Numerical simulation studies on heat and mass transfer using vacuum membrane distillation

A general 2D mathematical model was developed to simulate the purification of water from volatile organic compounds (VOCs) via vacuum membrane distillation (VMD) process in hollow fiber membrane contactors. The model was developed for hydrophobic membrane material conditions, taking into consideration axial and radial diffusion in the tube, membrane and compartments of the contactor and was simplified to the two‐dimensional structure with a single porous membrane wall. The simulation has studied the mass and heat transfer of VMD system in the porous media, in which aqueous volatile organic solution was considered as an incompressible and steady fluid. Effect of the downstream pressure on the removal of 1, 1, 1‐trichloroethane (TCA) was studied to validation of simulation results with experimental data that it was obtained from literature. The temperature, Reynolds number, and total mass flux (convective and diffusive) distribution of TCA are determined in the membrane module. POLYM. ENG. SCI., 54:2553–2559, 2014. © 2013 Society of Plastics Engineers     

Hydrophobic SiO2 nanoparticle-induced polyvinylidene fluoride crystal phase inversion to enhance permeability of thin film composite membrane

Thin film composite (TFC) membrane can get rid of small molecular contaminants and salts with a very high efficiency, thus exhibiting promising potential for addressing the emerging problem of a clean water shortage. In this work, a new type of TFC membrane was prepared by interfacial polymerization of two monomers (MPD and TMC) on surface of SiO₂/polyvinylidene fluoride (PVDF) substrate. The maximum flux of 3.16 L m⁻² h⁻¹ Bar⁻¹ was achieved for the optimized hydrophobic SiO₂ nanoparticles well dispersed in PVDF substrate, which is 2.6 times higher than that of 1.21 L m⁻² h⁻¹ Bar⁻¹ for the commercial cellulose triacetate reverse osmosis membrane. The improved performance of TFC membrane could be attributed to the higher compaction resistance of SiO₂/PVDF substrate. Further analysis revealed that PVDF crystal phase inversion induced by superhydrophobic SiO₂ nanoparticles obviously enhanced the intramolecular and intermolecular hydrogen bonds between PVDF polymer molecules. Additionally, the narrower finger-like pore size and thicker pore wall of SiO₂/PVDF substrate also played significant roles in enhancing the compaction resistance of PVDF membrane. This work also provides a proof-of-concept demonstration of high permeability substrates for effective flux enhancement of TFC membranes. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48204.     

聚偏氟乙烯超滤膜亲水改性研究进展

膜污染会缩短超滤膜的使用寿命,增加由于水力清洗、化学清洗以及膜组件更换而产生的费用。为减少运行成本,有必要对膜污染加以控制。膜污染与原水中污染物的性质和膜本身的性质密切相关。亲水性膜具有水通量高、抗污染性能好的特点,因而提高超滤膜的亲水性是提高膜的水通量和控制膜污染的重要方法之一。简要介绍了具有良好化学稳定性、耐辐射性、耐热性的聚偏氟乙烯膜的表面亲水改性和共混亲水改性的研究进展,指出通过不同的改性方式,聚偏氟乙烯膜都能够实现亲水性的增强。