New composite reverse osmosis membranes made from poly-2-vinylimidazoline

Novel ultra-thin film (UTF) composite reverse osmosis (RO) membranes were fabricated in situ by the interfacial polymerization of poly-2-vinylimidazoline (PVI) precursors and aromatic acid chloride crosslinking agents. The syntheses of three different forms of PVI, which were used as precursors, are described. 3-(Chlorosulphonyl)benzoyl chloride, 3,5-di(chlorosulphonyl)benzoyl chloride and 1,3-benzenedicarbonyl dichloride were used as crosslinking agents. Both flat-sheet and tubular membranes were fabricated and tested for their salt retentions and permeate fluxes. The RO performances of the two sets of tubular membranes PVI I and PVI II crosslinked with 3-(chlorosulphonyl)benzoyl chloride, prepared according to optimized fabrication formulations, were recorded. These were 97.1 ± 0.1% retention; 730 ± 24 lmd flux and 98.2 ± 0.7% retention; 560 ± 150 L/m²/day (lmd) flux, respectively. The RO performances of initial tubular membranes made from PVI III and 3-(chlorosulphonyl)benzoyl chloride was 97.0 ± 1.1% retention and 643 ± 74 lmd flux.     

Optimization of the Fabrication Variables of Poly-2-vinylimidazoline Tubular Reverse Osmosis Membranes

Abstract

The fabrication of tubular poly-2-vinylimidazoline (PVI) composite reverse osmosis (RO) membranes is described. Self-directing optimization experiments were used to derive a formulation for these membranes. Two types of membranes were prepared from two different PVI precursors, each interfacially crosslinked with 3-(chlorosulfonyl)benzoyl chloride. Very good RO properties were exhibited by the “optimized” membranes: in one case 99.4% NaCl retention and a permeate flux of 500 L/m²/d were obtained. Conditions of evaluation were: 2 MPa, 20°C, 2 g/L NaCl feed, 1 m/s linear flow rate.     

用于反渗透复合膜的海绵状结构支撑膜制备研究

通过调节铸膜液中聚砜浓度和非溶剂含量,浸没沉淀法制备海绵状结构的支撑膜,并在支撑膜上界面聚合制备聚酰胺反渗透复合膜。分别对支撑膜及反渗透复合膜的结构和性能进行表征,考察聚砜浓度对支撑膜结构和性能的影响,以及不同结构支撑膜对反渗透复合膜结构和性能的影响。结果显示,随着聚砜浓度的增加,支撑膜表面孔径和孔隙率下降,断面结构变致密,耐压性增强。在不同支撑膜上制备的反渗透复合膜具有不同的通量和脱盐率。综合考虑支撑膜及反渗透复合膜的性能,以聚砜浓度为15%制备的海绵状结构支撑膜更适于作为制备反渗透复合膜的支撑层。     

Reverse osmosis rejection of heavy metal cations

The selective rejection of various heavy metal chloride salts by cellulose acetate reverse osmosis membranes is described. A series of membranes exhibiting NaCl rejection levels of from 26 to 91% is employed.The observed selectivity pattern for divalent metals suggests that ion-water rather than ion-membrane interactions are the controlling factors in cation rejections by cellulose acetate membranes. The partial molal free energies of hydration and the entropies of the ions in solution adequately represent these controlling factors.     

Truly chlorine-resistant polyamide reverse osmosis composite membrane

Truly chlorine-resistant polyamide reverse osmosis composite membranes were prepared by cross-linking the interface of the composite membrane. Such membranes possessed chlorine resistance one order of magnitude more than those of the commercially used polyamide composite membranes. The effect of the degree of cross-linking on chlorine resistance was also described. © 1996 John Wiley & Sons, Inc.     

Preparation of composite reverse osmosis membranes by plasma polymerization of organic compounds. III. Plasma polymers of acetylene/CO/H2O

Reverse osmosis characteristics of composite membranes prepared by the plasma polymerization of acetylene/CO/H₂O mixtures with various ratios of components are investigated; porous film of cellulose nitrate-cellulose acetate is used as the substrate. This monomer system seems to have the following advantages: (1) A relatively short deposition time (1–2 min) is enough to produce reasonably good reverse osmosis membranes; and (2) good chemical stability of membranes can be obtained, especially in the case of chlorine resistance.     

反渗透复合膜(Ⅰ)结构与性能

引言 反渗透被称为"21世纪的净化水技术",具有净化率高、成本低等优点,广泛应用于海水淡化、电厂水处理、纯净水制取等领域.聚酰胺含有酰胺基团(-CO-NH-),亲水性好,且其机械稳定性、热稳定性及水解稳定性均很好,是最典型的反渗透膜材料之一[1-4],与醋酸纤维素反渗透膜相比,它具有脱盐率高、通量大、操作压力要求低等优点.反渗透膜的脱盐率和通量很大程度上取决于膜的表面形态和表面化学结构.     

醇类添加剂影响界面聚合反渗透复合膜性能的机理

在考察间苯二胺和均苯三甲酰氯界面聚合单体浓度对膜性能影响的基础上,研究了在水相反应溶液中添加系列小分子醇类后膜分离性能的变化,添加醇后的聚酰胺反渗透复合膜通量有明显提高,最高增加超过一倍。FTIR结果表明由于醇羟基与酰氯基团反应生成酯键终结聚酰胺分子链的增长,降低网络结构的交联度,利于分子透过。简要分析了通量的增加量与醇的种类以及溶解度各分量之间的关系,当醇与聚酰胺溶解度越接近时,醇更容易溶解透过初生态的聚酰胺膜,与酰氯接触发生反应的机会增加,链终止的可能性就会增大,通量提高得越多。最后,根据实验结果得出结论：在前面最佳制膜工艺的指导下,醇作为水相添加剂且添加量质量分数在5%～10%之间可以有效优化聚酰胺复合膜的性能,制备出高通量的反渗透复合膜。     

Preparation of reverse osmosis membranes by plasma polymerization of organic compounds

The plasma polymerization of organic compounds was used to prepare a composite reverse osmosis membrane which consists of an ultrathin semipermeable membrane formed by plasma polymerization of an organic compound or compounds and a porous substrate. Many nitrogen-containing compounds (aromatic amines, heteroaromatic compounds, aliphatic amines, and nitriles) were found to yield excellent reverse osmosis membranes by plasma polymerization directly onto porous substrates such as Millipore filters, porous polysulfone filters, and porous glass tubes. Factors involved in the preparation of reverse osmosis membranes by plasma polymerization were investigated and discussed. The plasma polymerized membranes have the following unique features: (1) very stable performance independent of salt concentration and applied pressure (practically no water flux decline was observed with many membranes): (2) salt rejection and water flux both increase with time in the initial stage of reverse osmosis (consequently, the performance of the membrane improves with time of operation); (3) very high salt rejection (over 99%) with high water flux (up to 38 gfd) can be obtained with 3.5% NaCl at 1500 psi (membranes perform equally well under conditions of sea water conversion and brakish water treatment).     

Highly permeable reverse osmosis membranes incorporated with hydrophilic polymers of intrinsic microporosity via interfacial polymerization

Enhancing the water permeation while maintaining high salt rejection of existing reverse osmosis (RO) membranes remains a considerable challenge. Herein, we proposed to introduce polymer of intrinsic microporosity, PIM-1, into the selective layer of reverse osmosis membranes to break the trade-off effect between permeability and selectivity. A water-soluble a-LPIM-1 of low-molecular-weight and hydroxyl terminals was synthesized. These designed characteristics endowed it with high solubility and reactivity. Then it was mixed with m-phenylenediamine and together served as aqueous monomer to react with organic monomer of trimesoyl chloride via interfacial polymerization. The characterization results exhibited that more “nodule” rather than “leaf” structure formed on RO membrane surface, which indicated that the introduction of the high free-volume of a-LPIM-1 with three dimensional twisted and folded structure into the selective layer effectively caused the frustrated packing between polymer chains. In virtue of this effect, even with reduced surface roughness and unchanged layer thickness, the water permeability of prepared reverse osmosis membranes increased 2.1 times to 62.8 L·m^-2·h^-1 with acceptable NaCl rejection of 97.6%. This attempt developed a new strategy to break the trade-off effect faced by traditional polyamide reverse osmosis membranes.     

Reverse osmosis by composite charged membranes

The charged membranes were prepared from the sulfonation and amination of SBR resins, and their reverse osmosis performances were investigated. The sulfonated membranes show high salt rejection. This result is in accord with the result of membrane potentials. Relatively excellent membranes were obtained by amination of the sulfonated membranes. This is probably owing to the formation of a dense charged region near the membrane surface; the composite charged membranes of sandwich-type are obtained by this method. The reverse osmosis performances of these membranes from various materials were made clear.     

New thin-film composite reverse osmosis membranes and spiral wound modules

Two new series of thin-film composite reverse osmosis membranes have been developed and fabricated into spiral wound modules. The NTR-7100 series membrane is able to desalt sea and brackish water. The NTR-7250 membrane is designed for use at pressures below 20 kg/cm². The membrane has a very high water permeability and is resistant to chemical and microbiological attack. In particular, the membrane is stable to chlorine, as shown by long-term reverse osmosis tests with tap water containing about 1 ppm of residual chlorine. The membrane has an unusual pattern of solute rejection. Salts containing divalent anions, such as sodium sulphate or magnesium sulfate, are rejected more than 98%; while salts with monovalent anions and bivalent cations, such as magnesium chloride, are rejected about 90% and salts with monovalent anions and cations, such as sodium chloride, are rejected 30–50%. Neutral solutes have relatively high rejection; for example, glucose, 90% and sucrose, <99%.     

The use of direct osmosis tests as complementary experiments to determine the water and salt permeabilities of reinforced cellulose acetate membranes

In this article the use of the direct osmosis test as a complementary experiment to the reverse osmosis test is described. The membranes investigated are cellulose acetate membranes reinforced with mineral fillers. In both tests the same influence of the type of fillers on the water permeability coefficients is found. The salt permeability coefficients indicate the presence of pressure sensitive defects in the reinforced membranes. The direct osmosis test is found to be a suitable test to confirm and predict the membrane properties under reverse osmosis conditions.     

Composite melamine-formaldehyde-furfuralcohol copolymerization membrane for reverse osmosis

The preparation and performance of the new composite reverse osmosis membrane were investigated. The ultrathin semipermeable barrier of the composite melamine-formaldehyde-furfuralcohol copolymerization membrane for reverse osmosis is formed on the porous surface of polysulfone support membrane by copolymerization between melamine-formaldehyde prepolymer and furfuralcohol under sulfuric acid catalyst. In the condition of operation pressure 20 kg/cm² and concentrated water flux 20 L/h, the membrane has 95% rejection and 0.3 m³/m².d flux for 1500 ppm aqueous sodium chloride. The factors affecting the reverse osmosis performance of the composite membrane, such as amount of the prepolymer and catalyst, the temperature of the polymerization and the properties of additives etc, were investigated.     

Composite hollow fiber membranes

Composite polysulfone hollow fibers consisting of a polysulfone porous substrate coated with crosslinked polyethyleneimine (PEI) or furan resin are reported. These composite hollow fibers are analogous to the flat-sheet composite membranes known as NS-100 and NS-200. The surface structure of the porous substrate was rigorously studied before and after coating. Scanning electron microscope observations and reverse osmosis transport studies showed that the support fiber must have surface pore diameters of less than 0.2 μm to obtain a durable composite hollow fiber membrane. The curing process would normally follow in situ condensation of the PEI or the cationic polymerization of the furfuryl alcohol. However, since both the dense layer and surface of the porous substrate contract when exposed to the curing temperature (110–150°C), it was found to be profitable to cure the hollow fiber before applying the coating. When tested in a reverse osmosis rig, PEI/TDI-coated polysulfone hollow fiber bundles displayed 98% salt rejection and a flux of 5–7 gfd for a feed solution of 10,000 ppm NaCl at a hydraulic pressure of 400 psi. A new method of depositing furan resin on the polysulfone hollow fiber is described. The furfuryl alcohol is instantaneously polymerized by exposing the alcohol-soaked fiber to a 60% solution of concentrated sulfuric acid. It has been demonstrated that in such a polymerization procedure a dense, semipermeable layer is formed on top of the porous substrate; the resulting composite hollow fiber membrane yields salt rejections higher than 98% when tested under the above reverse osmosis conditions.     

Influence of metal salts in reaction medium on performance enhancement of novel aliphatic–aromatic-based polyamide thin-film composite osmosis membranes

In this study, we report an easy and novel way to develop high flux aliphatic–aromatic-based thin-film composite (TFC) polyamide osmosis membranes by addition of inorganic metal salts with amine reactants in the reaction system of polyethylene imine (PEI) and 1,3-benzene dicarbonyl chloride. Inorganic metal salts like CuSO₄, NiSO₄, MgSO₄, and Al₂(SO₄)₃ added to block some of the amine groups of PEI through complexation which in turn changes the polycondensation reaction kinetics of amine acid chloride reaction. The prepared membranes were characterized using water contact angle and atomic force microscopy studies and the performances were evaluated both in reverse osmosis and forward osmosis mode. In presence of metal salts in reaction interface, the performance of TFC membranes was greatly enhanced and the optimum metal salt concentration was identified for individual metal salts for maximum performance enhancement. The effects of different anions for same metal ion and different molecular weight of PEI were evaluated on composite polyamide membrane performances. Water permeability (flux) of 63.48 L m^?2 h^?1 was achieved upon inorganic salt addition compared to the unmodified TFC membranes with flux of 42.1 L m^?2 h^?1 at similar salt rejection of ~95%. Based on the new findings, a conceptual model was proposed to explain the role of metal ion in amine solution on the resulting characteristics of aromatic–aliphatic type polyamide–polysulfone composite membrane.     

Reverse osmosis characteristics of composite membranes prepared by plasma polymerization of allylamine. Effects of deposition conditions

A study has been conducted to determine the effects of flow configuration and reaction conditions on the performance of composite reverse osmosis membranes prepared by plasma polymerization of allylamine over a porous polymer substrate. It was established that superior membranes were obtained by using a gas-flow configuration avoiding direct monomer flow over the substrate. High rejections of NaCl could be attained when the plasma-deposited film was sufficiently thick to bridge all of the pores in the substrate. It was observed that in addition to influencing the rate of polymerization, the conditions used to sustain the plasma also affected the reverse osmosis characteristics of the deposited film. The effects of these conditions and other preparation procedures are discussed. Attempts to use infrared spectroscopy and ESCA to identify the relationship between polymer structure and reverse osmosis performance were not successful. ESCA did prove useful, though, in confirming an earlier postulated hypothesis that degradation of reverse osmosis performance is associated with the hydrolysis of nitrogen-containing structures in the plasma-deposited film.     

Recent advances in polymer and polymer composite membranes for reverse and forward osmosis processes

Semipermeable membranes are the core elements for membrane water desalination technologies such as commercial reverse osmosis (RO) process and emerging forward osmosis (FO) process. Structural and chemical properties of the semipermeable membranes determine water flux, salt rejection, fouling resistance, and chemical stability, which greatly impact energy consumption and costs in osmosis separation processes. In recent years, significant progress has been made in the development of high-performance polymer and polymer composite membranes for desalination applications. This paper reviews recent advances in different polymer-based RO and FO desalination membranes in terms of materials and strategies developed for improving properties and performances.     

THERMODYNAMIC MODELING OF SOLUTE TRANSPORT THROUGH REVERSE OSMOSIS MEMBRANE

A new thermodynamic model is developed for water and solute transports through reverse osmosis membranes. The model is featured with rigorous derivations in theoretical development and clearly defined parameters for membrane transport properties. The new model can correctly describe not only the dependence of salt rejection on pressure and salt concentration, but also the non-linearity between water flux and pressure. Comparisons of model simulations with the reported reverse osmosis experiments demonstrate that the parameters in the new model are concentration-independent. This study shows that water and salt transports through reverse osmosis membranes can be satisfactorily described with irreversible thermodynamics.