Synthesis and characterization of PVC-TFC hollow fibers for forward osmosis application

Forward osmosis (FO) is considered among the most encouraging water desalination processes as a result of its high performance and low energy demand. Thin-film composite (TFC) hollow fibers (HF) were synthesized and examined in the FO process. Three different concentrations of polyvinyl chloride (PVC) support polymer were fabricated via the phase inversion technique. The polyamide layer was synthesized on the outer surface of the PVC-HF substrate via interfacial polymerization (IP) reaction. To the best of our knowledge, PVC HF was used in this research for the first time as a support for TFC-FO membranes. PVC HFs have high-quality specifications that are expected to have outstanding performance in TFC-FO applications, especially for water desalination. The obtained membranes were characterized using contact angle measurement, scanning electron microscopy, atomic force microscope and Fourier-transform Infrared. The performance of the PVC-TFC HF was examined in the FO under standard conditions. Results showed that the membrane fabricated with a lower concentration of PVC substrate exhibited higher water flux in comparison to the higher concentration PVC membrane. Changing the concentration of PVC from 15% to 18% reduced water flux from 25 to 13 L m⁻² h⁻¹; however, salt flux also decreased from 8 to 3 g m⁻² h⁻¹.     

Facile modification of aliphatic polyketone-based thin-film composite membrane for three-dimensional and comprehensive antifouling in active-layer-facing-draw-solution mode

The application of “active-layer-facing-draw-solution” (AL-DS) mode, which allows a considerably high water flux in forward osmosis (FO) processes, is hindered by severe fouling occurring within the porous support of the FO membranes. We designed a series of “three-dimensionally” antifouling FO membranes by an extremely convenient and scalable approach, by using in situ reduced aliphatic polyketone (PK) membranes (rPK) and the silver-nanoparticles-immobilized rPK-Ag membranes as the substrates for thin-film composite (TFC) FO membrane preparation. This modification imparted enhanced hydrophilicity compared with the original PK-TFC membrane, without affecting the morphology and transport properties. Benefiting from the three-dimensional antifouling structure, the modified TFC membranes (i.e., rPK-TFC and rPK-Ag-TFC membranes) demonstrated excellent and comprehensive fouling resistance towards a variety of organic foulants, as well as biofouling resistance towards Escherichia coli. These results provide useful insights into the fabrication of antifouling FO membranes for water purification purposes and pressure retarded osmosis (PRO) process.     

Feasibility of using polycarbonate as a substrate of thin film composite membrane in forward osmosis

In the present study, thin film composite (TFC) forward osmosis (FO) membranes with polycarbonate (PC (and polyether sulfone (PES) as substrates were fabricated to investigate the impact of the structural parameters of substrate on the performance of the membranes. Firstly, the substrates were prepared by Loeb-Sourirajan method. Characterization techniques including FESEM, contact angle measurement, pure water flux, gas permeability test, and tensile test were applied to investigate the properties of the substrates. After preparing suitable substrates, active layers were fabricated via interfacial polymerization (IP) technique. The performance and characterization test showed that PC is a relatively hydrophilic polymer with a good property for using as a substrate of FO TFC membrane but as the result of gas permeability test show, this membrane has large surface pore size in comparison with PES membrane. Mean pore size of PC and PES membrane is 378 and 139 nm, respectively. Also, the results show that the effective surface porosity of PC (285, 1/m) is more than PES (213, 1/m) substrate.     

Developing thin‐film‐composite forward osmosis membranes on the PES/SPSf substrate through interfacial polymerization

A new scheme has been developed to fabricate high‐performance forward osmosis (FO) membranes through the interfacial polymerization reaction on porous polymeric supports. p‐Phenylenediamine and 1,3,5‐trimesoylchloride were adopted as the monomers for the in‐situ polycondensation reaction to form a thin aromatic polyamide selective layer of 150 nm in thickness on the substrate surface, a lab‐made polyethersulfone (PES)/sulfonated polysulfone (SPSf)‐alloyed porous membrane with enhanced hydrophilicity. Under FO tests, the FO membrane achieved a higher water flux of 69.8 LMH when against deionized water and 25.2 LMH when against a model 3.5 wt % NaCl solution under 5.0 M NaCl as the draw solution in the pressure‐retarded osmosis mode. The PES/SPSf thin‐film‐composite (TFC)‐FO membrane has a smaller structural parameter S of 238 μm than those reported data. The morphology and topology of substrates and TFC‐FO membranes have been studied by means of atomic force microscopy and scanning electronic microscopy. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

国际正渗透膜技术研讨会IFOS2016回顾：正渗透可行吗?

回顾了2016年底在悉尼召开的国际正渗透研讨会的主要内容,概括了近年来正渗透技术研究和应用的最新进展。在膜材料方面,提高水通量应着重于降低支撑层结构参数,而不是提高分离层的渗透性能。提高分离层的截留率和耐污染性是提高膜性能的关键。对于各种类型的驱动溶质而言,无机盐很可能是最为现实可靠的驱动溶质。正渗透技术在渗透稀释和与其他分离技术的耦合过程处理高含盐污染水源中有潜在应用,然而渗透能发电在短期很难成为主流的新兴能源。     

Molecular design of the cellulose ester-based forward osmosis membranes for desalination

This work has investigated the fundamental science of phase inversion and formation mechanism of cellulose ester membranes at the interface between polymer and casting substrate. It also explores the desired membrane preparation conditions for forward osmosis (FO) applications. With the aid of positron annihilation lifetime spectroscopy (PALS), the similarity in physicochemical properties between the polymer and the substrate was found to play a significant role in determining the porosity of the bottom interfacial layer. The structure of the dense interfacial layer was also strongly dependent on membrane thickness and solvent composition. Experimental results surprisingly reveal that the original pore size of the as-cast membrane plays a critical role determining the final performance of the subsequent annealed membrane independently of annealing temperature and time. In addition, since a threshold pore size exists during annealing above which pores become difficult to downsize, we have found that a thin dense selective layer integrated in an asymmetric membrane may not always be the best option for FO. A balanced membrane structure consisting of a thin porous support and a thin dense selective layer has been developed for FO, which shows a low internal concentration polarization (ICP) and a relatively high water flux when seawater was employed as the feed.     

Thin film composite forward osmosis membranes with poly(2‐hydroxyethyl methacrylate) grafted nano‐TiO2 as additive in substrate

The poly(2‐hydroxyethyl methacrylate) grafted titanium dioxide nanoparticles were synthesized and added to the substrate of flat‐sheet thin film composite forward osmosis (TFC‐FO) membranes. The hydrophilicity of substrate was improved, which was advantageous to enhance the water flux of TFC‐FO membranes. The membranes containing a 3 wt % TiO₂‐PHEMA in the substrate exhibited a finger‐like structure combined with sponge‐like structure, while those with lower or without TiO₂‐PHEMA content showed fully finger‐like structures. As for FO performance, the TFC‐FO membranes with 3 wt % TiO₂‐PHEMA content achieved the highest water flux of 42.8 LMH and 24.2 LMH against the DI water using 2M NaCl as the draw solution tested under the active layer against draw solution (AL‐DS) mode and active layer against feed solution (AL‐FS) mode, respectively. It was proven that the hydrophilic property of membrane substrates was a strong factor influencing the water flux in FO tests. Furthermore, the structural parameter was remarkably decreased with an increase of TiO₂‐PHEMA content in membrane substrate, indicating the reducing of internal concentration polarization. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43719.     

Poly(vinyl) alcohol coating of the support layer of reverse osmosis membranes to enhance performance in forward osmosis

Membrane hydrophilicity influences the transport of water through the membrane in osmotically driven separations such as forward osmosis. In this paper, we coated the polysulfone support layer of two types of commercially available reverse osmosis membranes (brackish water and seawater) with hydrophilic polyvinyl alcohol (PVA). The aim of this was to increase the support layer hydrophilicity and, correspondingly, the rate of water transport through the membrane. Previous work with polydopamine coatings of the polysulfone support of reverse osmosis membranes has yielded promising results. In this work, we explore more readily available materials. Specifically, we studied the effects of two different PVA crosslinking agents – maleic acid and glutaraldehyde – on the resultant membrane properties and osmotic performance. For seawater membranes we found that PVA crosslinked to a limited degree with maleic acid creates a significant improvement in water flux in RO and FO systems, as compared to membranes with PVA crosslinked by glutaraldehyde. However, brackish water membranes did not have comparably significant changes in membrane performance. We conclude that the smaller pores of the brackish water membrane become clogged, and this effect is magnified by the lack of fractional free volume available within PVA that is highly crosslinked with glutaraldehyde.     

刮刀厚度对聚酰胺正渗透复合膜性能的影响

为考察正渗透过程基膜厚度对膜水通量的作用,有效地提高膜的综合性能,采用浓度2 mol/L的NaCl作为汲取液、去离子水为原料液作为评价系统,考察了刮刀厚度不同对正渗透复合膜性能的影响。结果表明,以筛孔80μm的筛网作为支撑材料,当采用厚度为45μm的刮刀所制备的超滤膜作为支撑材料时,制备所得的正渗透复合膜性能为佳,结构参数S可低至1.086 mm;并具有最好的稳定性以及最佳的污染冲洗恢复效果。     

Fabrication of fullerenol-incorporated thin-film nanocomposite forward osmosis membranes for improved desalination performances

Development and use of novel membranes for forward osmosis (FO) applications have gained popularity throughout the world. To enhance FO membrane performance, a novel thin-film nanocomposite membrane was fabricated by interfacial polymerization incorporating Fullerenol (C₆₀(OH)_n) nanomaterial, having n in the range of 24–28 into the active layer. Different concentrations of fullerenol loading (100, 200, 400, and 800 ppm) were added to the top skin layer. The structural and surface properties of the pure thin-film composite membrane (TFC) and fullerenol-incorporated thin-film nanocomposite (FTFC) membranes, were characterized by ATR-FTIR, SEM, and AFM. FO performance and separation properties were evaluated in terms of water flux, reverse salt flux, antifouling propensity, water permeability and salt permeability for all TFC and FTFC membranes. Osmotic performance tests showed that FTFC membranes achieved higher water flux and reverse salt flux selectivity compared with those of TFC membranes. The FTFC membrane with a fullerenol loading of 400 ppm exhibited a water flux of 26.1 L m^?2 h^?1 (LMH), which is 83.03% higher than that of the TFC membrane with a specific reverse salt flux of 0.18 g/L using 1 M sodium chloride draw solution against deionized water in FO mode. The fullerenol incorporation in FTFC membranes also contributed to a decreased fouling propensity.     

正渗透膜材料的研究进展

正渗透技术因其低能耗、耐污染等优势受到国际和国内众多学者的关注,尤其近几年来,取得了迅速发展。本文对正渗透过程中的影响因素以及浓差极化现象作了简要分析,结果表明,内浓差极化是影响正渗透技术效率低下的重要因素,而制备适当的膜材料是有效改善内浓差极化的关键技术。回顾了正渗透分离技术在国内外的发展历程,通过不懈的探索和研发,先后成功制备得到不同材料和结构的正渗透膜。重点讲述膜材料在正渗透领域所取得的最新研究进展,最后指出众多正渗透膜材料由于条件限制难以推广应用,希望在未来的研究过程中突破这项技术难题,缩短科研理论与实际应用之间的差距,在膜材料的实际应用方面取得创新性成果。     

Fabrication of innovative forward osmosis membranes via multilayered interfacial polymerization on electrospun nanofibers

Practical application of forward osmosis (FO) membranes is beset by low water flux and vulnerability of selective polyamide (PA) layers. Herein, novel composite membranes were fabricated with multilayered PA via cyclic interfacial polymerization (IP) on electrospun polyethersulfone (PES) nanofiber substrates to realize high performance FO. The membrane fabrication conditions were optimized detailedly with respect to the morphologies, physicochemical properties, and FO performances. It is indicated that the PES concentration has great impacts on the morphology, thickness, and fiber diameter of the electrospun substrates and the optimal concentration is proved to be 26 wt %. After multilayered IP, the membrane thickness, surface hydrophilicity, and mechanical strength increased with IP cycles. The optimized FO membranes with two PA layers show much higher water flux and membrane selectivity compared with the commercial thin film composite membranes, holding great promise for water purification and seawater desalination. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47247.     

Thin-film composite forward osmosis membrane prepared from polyvinyl chloride/cellulose carbamate substrate and its potential application in brackish water desalination

Synthesized by the reaction between α-cellulose and m-tolyl isocyanate (MTI), cellulose carbamate (CC) was blended with polyvinyl chloride (PVC) to fabricate substrates for thin-film composite (TFC) forward osmosis (FO) membranes. The introduction of CC into substrates improved both membrane structure and performance. The substrates exhibited higher porosity and hydrophilicity, and better connective pore structure; while rejection layer exhibited better morphology but limited cross-linked degree decrease after the introduction of CC. According to the results, the CC blend ratio of 10% was the optimal ratio. With this blend ratio, the TFC-10 membrane presented favorable water permeability (1.86 LMH/bar) and structure parameter (337 μm), which resulted in excellent FO performance (water flux with a value of 40.40 LMH and specific salt flux with a value of 0.099 g/L under rejection layer faces draw solution [DS] mode when 1 M NaCl and deionized water were utilized as DS and feed solution). In addition, the TFC-10 membrane showed good water flux and low-sulfate ion leakage in the potential application of brackish water desalination.     

聚苯乙烯磺酸钠掺杂正渗透膜的制备及其性能

通过两步无皂乳液聚合法,改变第二步对苯乙烯磺酸钠的加入量,制备表面携带磺酸根基团量不同的纳米粒子（PSS）,并将其应用于正渗透（FO）膜的制备。采用红外光谱仪（FTIR）和光电子能谱仪（XPS）表征粒子组成,通过扫描电子显微镜（SEM）表征膜的表面和断面形貌,测定膜孔隙率和亲水性,考察表面磺酸根量不同的聚合物粒子对膜结构性能的影响。结果表明,PSS的引入能提高膜的孔隙率,改善膜的亲水性,且随着粒子表面携带的磺酸根基团量增多,膜的孔隙率与亲水性也随之提高。这是因为PSS粒子可以支撑内部孔道,且表面携带的亲水基团-SO3Na可以提高膜的亲水性,影响活性层的形成。所制备的FO膜性能也得到相应改善,水通量达到了61.1L/(m²·h),为纯聚砜膜的2.8倍,盐截留率达到93.2%,J_s/J_v值仅为0.31g/L,性能得到极大提升。     

支撑层对硅橡胶复合膜渗透汽化分离性能的影响

引言 为了扩大渗透汽化技术的应用领域,科研工作者需要进一步增强渗透汽化膜的分离性能.从工业化的观点而言,用于实际应用的渗透汽化膜大多是复合膜,它由选择层(或分离层)和支撑层组成.一般认为,选择层决定着复合膜的选择性和通量,支撑层起支撑和机械稳定作用.Nijhuis[1]在从甲苯-水体系中分离甲苯的过程中对均质膜和以聚砜为支撑层的复合膜的分离性能进行了比较;Sturken[2]分别用聚醚酰亚胺和聚偏氟乙烯为支撑层的硅橡胶膜从二氯乙烷-水体系中提取二氯乙烷,他们得到了相同的结论:支撑层的影响可以忽略.然而Scholz[3],Heinzelmann[4],Rautenbach[5],Borges[6],Vankelecom[7],Farooq[8],Lipnizki[9]等均在各自研究中发现,由于基膜和分离层的物理化学性质以及制膜方法等众多因素的存在使得支撑层在一定程度上影响复合膜的分离性能;Feng[10]对均质硅橡胶膜和有微孔支撑层的硅橡胶复合膜的分离性能进行了比较,发现均质硅橡胶膜优先透过异丙醇,而有微孔亲水性支撑层的硅橡胶复合膜则优先透过水,这表明在一定的情况下,支撑层甚至起主导作用并能够决定复合膜的分离性能.因此,通过系统研究以不同多孔材料为支撑层的复合膜对有机物-水溶液的分离性能的影响,能够找到最优的复合膜支撑层,从而能够提高复合膜的分离性能.然而,至今关于支撑层对渗透汽化膜分离性能影响的系统研究仍相当少.     

The influence of membrane formation parameters on structural morphology and performance of PES/PDMS composite membrane for gas separation

In this study, influence of membrane preparation parameters on structural morphology and performance of polyethersulfone/polydimethylsiloxane (PES/PDMS) composite membrane was investigated for gas separation. Asymmetric PES flat sheet membranes were composed by phase inversion method and used as supports. PES composite membranes were fabricated by coating silicone rubber as selective layer on the top surface of support. Effects of different concentrations of PES and PDMS, solvent type, and support thickness on membrane performance were investigated for separation of oxygen from nitrogen. The optimized superior membrane was further modified using polyvinylidenfluoride, methanol and ethanol as additives in PES solutions and/or in water coagulation bath to promote the membrane capability. The results showed that addition of ethanol and methanol in cast solution and coagulation bath can greatly affect the morphology and hence the performance of the prepared membranes. The permeance changes have the contrary trend with solubility parameter difference between solvent and nonsolvent mixture, for instance when this parameter difference was lowest, higher permeance was obtained. Support and coating polymer concentration can control the permeance. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

High performance forward osmosis cellulose acetate (CA) membrane modified by polyvinyl alcohol and polydopamine

Cellulose acetate (CA) is a low cost and readily available material widely used in forward osmosis (FO) membranes. However, the performance of pure CA membranes is not good enough in salt separation and the traditional modification methods are generally multistep and difficult to control. In this paper, we reported high performance cellulose acetate (CA) composite forward osmosis (FO) membranes modified with polyvinyl alcohol (PVA) and polydopamine (PDA). PVA was first cross-linked onto the surface of CA membranes, and then PDA was coated with a rapid deposition method. The membranes were characterized with respect to membrane chemistry (FTIR and XPS), surface properties comprising wettability (by water contact angle), and osmosis performance. The modified membrane coated by PVA and PDA shown better hydrophilicity and exhibited 16.72 LMH osmotic water flux and 0.14 mMH reverse solute flux with DI water as feed solution and 2.0 M NaCl as draw solution and active layer facing the feed solution. This simple and highly effective modification method makes it as an excellent candidate for further exploration for FO.     

Morphological controlling of CTA forward osmosis membrane using different solvent-nonsolvent compositions in first coagulation bath

Cellulose triacetate (CTA) membranes were fabricated via a modified nonsolvent induced phase separation (NIPS) method. Different solvent-nonsolvent compositions in first coagulation bath (FCB) were introduced to optimize CTA membrane structures. The effects of FCB compositions, immersion time and mass ratio of solvent (N-methyl-2-pyrrolidone, NMP) and nonsolvent (water, ethanol, ethylene glycol and glycerol) on membrane morphology and performance were systematically investigated. Prospective membranes with a dense bottom layer and a scaffold-like top layer were obtained under room temperature, owing to the low relative energy difference (RED) between nonsolvent and polymer as well as the high viscosity of FCBs. A high water flux J_v (12.6 L m^?2 h^?1) and a low reserve salt flux J_s (1.32 g m^?2 h^?1) were obtained in the optimized membrane, with a structural parameter S of 119 μm. Compared with membranes prepared via conventional NIPS method and commercial CTA forward osmosis (FO) membranes, a remarkable improvement of J_s/J_v value and S value was achieved, indicating membranes with single dense-layer structure might suffer less from internal concentration polymerization (ICP) which is the main obstacle for the development of FO process. This study might help us pave the way to design superior CTA membrane structures for forward osmosis application.     

Thin-film composite forward osmosis membranes with substrate layer composed of polysulfone blended with PEG or polysulfone grafted PEG methyl ether methacrylate

To advance commercial application of forward osmosis (FO), we investigated the effects of two additives on the performance of polysulfone (PSf) based FO membranes: one is poly(ethylene glycol) (PEG), and another is PSf grafted with PEG methyl ether methacrylate (PSf-g-PEGMA). PSf blended with PEG or PSf-g-PEGMA was used to form a substrate layer, and then polyamide was formed on a support layer by interfacial polymerization. In this study, NaCl (1 mol?L⁻¹) and deionized water were used as the draw solution and the feed solution, respectively. With the increase of PEG content from 0 to 15 wt-%, FO water flux declined by 23.4% to 59.3% compared to a PSf TFC FO membrane. With the increase of PSf-g-PEGMA from 0 to 15 wt-%, the membrane flux showed almost no change at first and then declined by about 52.0% and 50.4%. The PSf with 5 wt-% PSf-g-PEGMA FO membrane showed a higher pure water flux of 8.74 L?m⁻²?h⁻¹ than the commercial HTI membranes (6–8 L?m⁻²?h⁻¹) under the FO mode. Our study suggests that hydrophobic interface is very important for the formation of polyamide, and a small amount of PSf-g-PEGMA can maintain a good condition for the formation of polyamide and reduce internal concentration polarization.     

Composite ceramic membranes from natural aluminosilicates for microfiltration applications

This work concerns to the development and characterisation of support, active layer and tubular composite membranes (CM) from natural aluminosilicates as principal components (clay, bentonite, feldspar, quartz, alumina). The selection of these raw materials was primarily based on their low cost and they are locally produced. In the substrates preparation, the effect of materials compositions, additives, particle sizes, paste rheological properties, and drying-sintering temperatures was investigated. The consolidated ceramic substrates were characterised by SEM, DTA–TG, X-Ray diffraction, Hg intrusion, mechanical resistance, and water flux measurements. Extrusion has been used as the forming process of tubular support. The CM was fabricated depositing a thin active layer by slip-casting method on the support. The CM sintered at 1200 °C showed the best structural characteristics, porosities of 50%, active layer pore size between 0.08 and 0.55 μm. The CM hydraulic permeabilities (10–274 L/h m² kPa) were comparable and greater than several inorganic commercial membranes and CM obtained from other researches. The CM microfiltration effectiveness was tested with different substances from food industry, i.e. slaughterhouse wastewater treatment and goat milk pasteurisation. The obtained results, insoluble residue rejections (100%) and high bacterial removal (87–99%), make the ceramic CM suitable for microfiltration processes.