Ionic reverse osmosis membranes of grafted polyethylene

Membranes of graft copolymers of polyethylene with poly(sodium styrene sulfonate), poly(4-vinylpyridinium methyl bromide), and poly(sodium acrylate) were prepared by using the technique of peroxide grafting. The reverse osmosis characteristics of the membranes were examined as a function of grafting yield. In these membranes, the grafting can be considered as a process of introducing ionic sites, and it depends on the conditions of the grafting reaction, such as monomer concentration and temperature. However, the overall reverse osmosis characteristic is not only dependent on the number of ionic sites introduced but also on the swelling capability of the membrane. Consequently, the salt rejection of grafted membrane of a fixed graft yield depends on the conditions of the grafting reaction. All grafted membranes which have grafting yields above a certain value behave as normal ionic polymer membranes, and their interrelationship of salt rejection and water permeability follow the general dependence found for ionic polymer membranes.     

Asymmetric polivinylidenfluoride (pvdf) radiation grafted membranes: preparation and performance in reverse osmosis application

A new type of reverse osmosis membrane has been synthesized. Membranes were prepared starting from asymmetric PVDF films, obtained by the casting and gelation technique and modified by radiochemical grafting and sulphonation. These membranes were tested in an RO laboratory plant and their performances were determined as a function of preparative parameters.The influences of evaporation time and temperature grafting and solvents were investigated.These membranes exhibit permeabilities as high as 2000 l/m²d and sodium chloride rejections up to 70%.     

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 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.     

Fabrication of reverse‐osmosis membranes for the desalination of underground water via the γ‐radiation grafting of acrylic acid onto polyethylene films

Research has been devoted to the desalination of saline water to fresh water suitable for human demands because of the shortage of water in some countries. Therefore, in this study, reverse‐osmosis membranes were prepared via the γ‐radiation graft copolymerization of acrylic acid onto high‐density and low‐density polyethylene. The factors that could affect the grafting process, such as the solvent type, monomer and inhibitor concentration, and irradiation dose, were investigated to determine the optimum conditions for radiation grafting. The polyethylene grafted acrylic acid copolymers (PAAc‐g‐PE) graft copolymer was characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, and mechanical, rheological, and thermal property testing to illustrate the possibility of practical use in water desalination. The prepared grafted membranes showed significant results in the reverse‐osmosis desalination method with underground saline water. The factors affecting the desalination of water, such as the water flux, operation time, and grafting percentage, were studied. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45410.     

Acrylic acid γ-ray irradiation-grafted nylon 4 membranes

This study was to improve the performances of nylon 4 membranes for washing waste-water treatment of nuclear power plants, e.g., removal of detergent and salt by membranes. The effects of the degree of grafting and ionization on the reverse osmosis performances of acrylic acid (AA)-grafted nylon 4 membranes by γ-ray irradiation modification were investigated. The relationships of operating conditions, such as feed concentrations of salt and detergent, operating temperature, and pressure, and the performances of water flux and solute rejection of the prepared membranes were obtained. Water flux of the prepared membranes was highly sensitive with the operating temperature. It was found that an increase in the operating pressure could increase the water flux and the impaction effect directly. Water flux and salt rejection were significantly improved by both ionized and nonionized AA-grafted nylon 4 membranes compared to ungrafted nylon 4 membranes. Water flux increased rapidly and solute rejection dropped off slightly as the grafted membranes were ionized. The 100% detergent rejection could be obtained by the nonionized AA-grafted nylon 4 membranes with 38.6 and 69.6% degrees of grafting under various operating conditions. Results obtained showed that these modified nylon 4 membranes were usable for washing waste-water treatment of nuclear power plants. © 1993 John Wiley & Sons, Inc.     

Microporous clay membrance materials for reverse osmosis applications. I. Performance characteristics from osmotic studies

Fired clay membranes were prepared from montmorillonite clay and also by incorporating protein (lysozyme) and nylon (copolymer of 6-amino caproic acid) to clay followed by firing these membranes at different temperatures for different durations of time. Osmotic behaviors of the membranes were studied, and the results were correlated to the porosity determined by scanning electron microscope. Reverse osmosis parameters, namely, the reflection coefficient, solute permeability, and rejection coefficient, of the membranes were determined from osmosis experiments. Rejection coefficients as determined from reverse osmosis were compared with those obtained from osmosis experiments.     

Preparation of ultrathin reverse osmosis membranes and the attainment of theoretical salt rejection

Cellulose acetate reverse osmosis membranes, 600–2800 A. thick, have been prepared on glass surfaces by dipping a clean glass plate into a dilute solution of cellulose acetate. After drying, the membranes are floated of onto a water surface and placed on molecular filter supports. Theoretical salt rejections, as calculated from the solution-diffusion model of membrane transport for cellulose acetate, were obtained with imperfection-free membranes.     

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.     

Preparation of asymmetric PTFE membranes and their application in water purification by hyperfiltration

Asymmetric PTFE membranes suitable for purifying and separation by reverse osmosis also in aggressive conditions of the feed were prepared. A technique has been set up in order to obtain the necessary porous supports, using sintering of PTFE emulsions in the presence of salts. The pore distribution, hydraulic permeability, and shape by microscopic observation were investigated. Asymmetric membranes were then prepared by deposition of these porous supports onto dense thin PTFE films. Their properties were checked in a reverse osmosis plant with NaCl, saccharose, chromium, nickel, copper, detergents, and oil emulsions.     

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.     

Cellulose membranes for reverse osmosis part II. Improving RO membranes prepared from non-woody cellulose

Experiments were carried out to minimize the stages of preparing reverse osmosis (RO) desalination membranes at economical cost and to improve the transport properties of RO membranes prepared from non-wood fibrous materials (cotton linters and bagasse pulp) to approach those prepared from imported viscose pulp and purchased cellulose acetate (see Part I). Further study was carried out on examining the effects of long-term testing and subsequent washing of membranes by a special mixture. Finally the quality of the product water reverse osmosis was examined by comparing its water analysis with standard specification for drinking and domestic water.     

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.     

乙烯基桥联有机硅膜的羧基化改性及反渗透性能研究

利用1,2-二(三乙氧基硅基)乙烯(BTESEthy)和硫代苹果酸(MSA)的巯基-烯点击反应对桥联有机硅进行羧基化改性,以管式α-Al₂O₃微滤膜为支撑体制备羧基官能化的桥联有机硅膜。通过傅里叶变换红外光谱(FT-IR)、激光粒度仪(DLS)、智能重量分析仪(IGA)和扫描电镜(SEM)等对膜结构和表面性质进行了表征。量子化学计算表明羧基化改性的有机硅网络拥有更加致密的孔结构和更高的水亲和力。将改性的BTESEthy-MSA膜用于反渗透脱盐,系统考察了BTESEthy-MSA膜反渗透脱盐性能。实验结果表明,与BTESEthy膜相比,羧基化改性的BTESEthy-MSA膜的水渗透率和盐截留率均有所提高。同时,BTESEthy-MSA膜表现出优异的水热稳定性和耐氯性能。在250 h的长期反渗透测试中,BTESEthy-MSA膜的水渗透率高达3.2×10^-13 m³/(m²·s·Pa),NaCl截留率始终保持在94.7%以上。     

Aromatic Polyamide Hydrazide Membranes for Reverse Osmosis Separations

Abstract

Wholly aromatic polyamide hydrazide (PAH) polymers were synthesized by low temperature polycondensation from freshly prepared m-amino benzhydrazide, p-amino benzhydrazide, isophthaloyl chloride, and terephthaloyl chlorides in dimethyl acetamide solvent. A series of film-forming polymers prepared by altering the molar ratios of the reacting monomers was characterized in terms of % moisture regain, η_inh, and x-rays. Asymmetric membranes prepared from selected polymer samples were tested in reverse osmosis test cells, and the pure water permeability and the membrane constant were determined. An optimum meta: para molar ratio of the reacting monomers has been identified for the best performance under reverse osmosis which gave solute separation close to 98% for a feed concentration in the range of seawater. The PAH membranes appear to be potential barrier candidates for treatment of effluents containing ammonium, nitrates, etc. and radioisotopes. Separation data for a few other solute systems were also evaluated and compared with those obtained from cellulose acetate membranes.     

New polymer materials for reverse osmosis membranes

The results of investigations on new polymer materials suitable for reverse osmosis are reported. The studies particularly concerned polypiperazinamides derived from differently structured bicarboxylic acids. Such polyamides show a water permeability that may vary from 0.09 μg cm^?1 sec^?1 to 2.3 μg cm^?1 sec ^?1 depending on the structure.The results obtained from reverse osmosis tests on dense and homogeneous films are described. Anisotropic membranes were prepared from poly(trans-2,5-dimethyl-piperazin-thiofurazanamide). Their properties very closely approach those of the corresponding cellulose acetate membranes. The anisotropic structure of the membranes has been evidenced by stereoscan electron microscope analysis.     

Poly(2-vinylimidazoline) composite reverse osmosis membranes

The preparation of poly(2-vinylimidazoline) (PVI) composite reverse osmosis membranes is described. The membranes were prepared from PVI interfacially crosslinked by the use of 1,3-benzenedicarbonyl chloride, 3-(chlorosulphonyl)benzoyl chloride (A) and 3,5-(dichlorosulphonyl)benzoyl chloride (B), the latter two crosslinking agents being synthesized for the purpose of the study. Initial screening of the reverse osmosis (RO) performance of the membranes are reported on as well as the more detailed testing in the presence of chlorine and at various pH values. Modifications to the PVI/A composite membranes by the addition of hydrophilic fillers is also described.     

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).     

反渗透膜的研究进展与展望

反渗透具有低能耗、高效率等突出优点,是目前应用最为广泛的分离技术之一。反渗透膜的性能是影响反渗透过程效率的决定因素,反渗透膜的研制一直是国内外膜领域的研究热点。特别是近年来,石墨烯、碳纳米管等新型材料展现出优异的水传递行为,成为新型反渗透膜材料的研究热点。本论文回顾了反渗透膜的研制发展历程,介绍了不同单体通过界面聚合反应成膜的研究进展,综述了国内外新型混合基质膜和无机分子筛反渗透膜材料及其成膜研究,最后提出了新型反渗透膜的研究方向。     

Crosslinked poly(hydroxyethyl methacrylate) membranes for desalination by reverse osmosis

A series of crosslinked hydroxyethyl methacrylate (HEMA) membranes for reverse osmosis desalination has been prepared. The crosslinkers used were trimethylol propane trimethacrylate (TPT) or ethylene glycol dimethacrylate (EGD). Membranes were synthesized by polymerizing the monomers as a thin homogeneous film. In addition to reverse osmosis tests, the membranes were also characterized by osmosis experiments and sorption measurements. The reverse osmosis water flux (1500 psi applied pressure, 4% NaCl brine, pH = 5) for these membranes decreases from 0.6 gallonmil/ft²-day (GMFD) to 0.055 GMFD and salt rejection increase from 78% to a maximum of 94% as the amount of TPT is increased from 0 to 11 mole-%. Water contents decrease from 42% to 15% over the same range of crosslinker, but the preferential sorption of water to salt does not vary. Thus, rises in reverse-osmosis semipermeability were found to result from changes in water–salt diffusivity ratios. The mechanism of permselectivity has been interpreted in terms of parallel diffusive fluxes across the membrane of primary H-bonded water and secondary water plus salt ions.