Reverse osmosis separation of inorganic salts using polyvinylalcohol membranes

Permeabilities and fluxes of fifty-four mono-, divalent anions and cations of sodium and chloride salts have been tested under experimental conditions of 50 bar and room temperature through asymmetric polyvinylalcohol membranes crosslinked with formaldehyde. The following percent rejections among these salts are given: sodium salts of divalent anions (70–80%), chloride salts of divalent cations (30–40%), H₂ SO₄ (30%), sodium salts of monovalent monoatomic anions, chloride salts of monovalent cations (15– 30%) and HCl, HNO₃, NaOH, KOH (10–20%). Sodium salts of monovalent polyatomic anions gave higher rejections than those of monovalent monoatomic anions. Higher rejection of divalent anions than that of divalent cations of chloride salts suggests that the membrane surface is negatively charged.     

Reverse osmosis separation of inorganic solutes in aqueous solutions using porous cellulose acetate membranes

Using a modified form of the Born expression for the free energy of ion-solvent interaction, to both the bulk solution phase and the membrane–solution interface, a parameter is obtained to express the repulsion of the ion at the interface. This parameter, called the free energy parameter for ions, is then related to solute transport parameter obtained from reverse osmosis experiments. Numerical values of this free energy parameter have been obtained for six monovalent and four divalent cations and for 12 monovalent anions. Using the experimental data for the reverse osmosis separation of sodium chloride as reference, the utility of the above parameter for predicting solute separation in reverse osmosis is illustrated for 32 other inorganic salts.     

膜集成技术处理氯化法钛白后处理废水的研究

氯化法钛白无机包膜处理工序会产生大量中性废水,其中包含少量钛白粉和水溶性盐,现阶段企业多以外排为主。采用膜集成（陶瓷膜+反渗透膜+纳滤膜）技术对氯化法钛白后处理废水的处理进行研究。将氯化法钛白后处理废水用陶瓷膜过滤,分离回收二氧化钛;将陶瓷膜清液用反渗透膜浓缩,清水回收利用;将反渗透浓液用纳滤膜分离硫酸钠和氯化钠。结果表明：利用陶瓷膜处理氯化法钛白后处理废水,平均通量为650 L/（m ²·h）,浓液中钛白粉质量浓度达到90 g/L以上,清液中钛白粉质量浓度低于0.001 g/L;使用反渗透膜截留清液中的硫酸钠和氯化钠,硫酸钠和氯化钠的截留率为99.5%,浓水中的盐质量分数达到4%以上;浓水中的硫酸钠和氯化钠通过纳滤膜分离,纳滤膜对硫酸钠的截留率为97%,硫酸钠质量分数达到14%以上。     

低压反渗透复合膜NTR—7250的脱盐性能

测定了ＮＴＲ－７２５０膜的脱盐性能。结果表明，该膜水通量约为ＣＡ膜的５倍；脱盐率主要受阴离子控制，并随电荷数递增；水中结垢成分被优先除去，ＳＯ４＾２－，硬度和ＨＣＯ３＾－除去率分别大于９７％，８１％，７６％；该膜抗氧化能力与ＣＡ膜相当，而适用ＰＨ范围更宽，并且可在较高水温下长期使用。     

Nanofiltration thin-film-composite polyesteramide membranes based on bulky diols

Polyesteramide thin-film-composite (TFC) membranes have promise for diafiltration applications due to their relatively good oxidative resistance coupled with the ability to tailor the membrane rejection profile by varying the ester/amide ratio. The incorporation ofester linkages in interfaciallyprepared polyesteramide TFC membranes has been previously shown to increase the oxidation resistance of the membrane. It was also found that polyesteramide TFC membranes incorporating hydroquinone (HQ) or bisphenol-A (Bis-A) had high rejection for monovalent salts, i.e., their rejection profiles matched those of reverse osmosis rather than nanofiltration membranes. We report the properties of polyesteramide TFC membranes incorporating bulky diols such as phenolphthalein (Phe) and terabromobisphenol-A (TBrBis-A). The data were used to correlate the influence of different ester fanctionalities on membrane flux and rejection characteristics. Membranes incorporating TBrBis-A had relativelyhigh rejections for monovalent salts coupled with low water permeance. By contrast, membranes incorporating Phe showed 10 times higher flux and a rejection profile which appears to be of interest for diafiltration applications involving the separation of organics with molecular weight >400 grnol⁻¹ from low-molecular-weight organics and salts. The Phe-based membranes show rejection characteristics for monovalent and multivalent salts typical of negatively charged membranes.     

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.     

Potential use of nanofiltration like-forward osmosis membranes for copper ion removal

The discharge of industrial effluent containing heavy metal ions would cause water pollution if such effluent is not properly treated. In this work, the performance of emerging nanofiltration(NF) like-forward osmosis(FO)membrane was evaluated for its efficiency to remove copper ion from water. Conventionally, copper ion is removed from aqueous solution via adsorption and/or ion-exchange method. The engineered osmosis method as proposed in this work considered four commercial NF membranes(i.e., NF90, DK, NDX and PFO) where their separation performances were accessed using synthetic water sample containing 100 mg·L~(-1) copper ion under FO and pressure retarded osmosis(PRO) orientation. The findings indicated that all membranes could achieve almost complete removal of copper regardless of membrane orientation without applying external driving force.The high removal rates were in good agreement with the outcomes of the membranes tested under pressuredriven mode at 1 MPa. The use of appropriate salts as draw solutes enabled the NF membranes to be employed in engineered osmosis process, achieving a relatively low reverse solute flux. The findings showed that the best performing membrane is PFO membrane in which it achieved N 99.4% copper rejection with very minimum reverse solute flux of 1 g·m~(-2)·h~(-1).     

氧化石墨烯掺杂反渗透混合基质膜制备及性能

由于芳香族聚酰胺反渗透膜在抗污染性以及耐氯性方面存在不足,限制了其在海水淡化等方面的应用。采用往油相中添加氧化石墨烯（GO）的二次界面聚合法改性了商业反渗透膜,评价了GO掺杂反渗透混合基质膜的分离性能和耐氯性能,并用接触角仪、Zeta电位仪、扫描电镜和原子力显微镜等仪器表征了膜的亲水性能、荷电性能以及膜表面形貌。结果表明,GO的添加提高了膜的分离性能、耐氯性能和亲水性能;当GO添加量为30 mg·L^-1时,膜的通量为（77.7±0.9） L·m^-2·h^-1,膜的截留率为97.6%±0.5%,相比商业膜分别提高了38.4%和4.5%。当氯化强度低于4800 mg·L^-1·h时,膜的水通量和盐截留率变化不明显。     

Color control of Japanese soy sauce (shoyu) using membrane technology

The present study systemically decolorized soy sauce using a membrane process to analyze the separation mechanism. An ultrafiltration (UF) membrane (NTU-2120) exhibited only slight decolorization ability. A nanofiltration (NF) membrane with a lower molecular weight cut-off and produced by sulfonated polysulfone (NTR-7400 series) rather than polyvinyl alcohol/polyamide (NTR-7250) had higher decolorization ability. The NF membranes rejected total nitrogen by 17–24%, unsalted soluble solid content by 24–32%, reducing sugar by 25–43%, and amino acids by 10–25%. The NTR-7400 series membrane rejected lactic acid by 6–9%, and pyroglutamic acid by 11–21%; other quality indexes were maintained. In the NF membrane processes, higher rejection of acidic amino acids than neutral and base amino acids was observed. The separation performance was governed by the electrical effect as well as the sieve effect. Soy sauce color could be controlled by blending NF membrane-processed soy sauce with feed soy sauce. Color can be matched to preference in accordance with dishes by suitably blending NF membrane-processed soy sauce with feed soy sauce.     

Reverse osmosis performance of organosilica membranes and comparison with the pervaporation and gas permeation properties

Hybrid organosilica membranes were successfully prepared using bis(triethoxysilyl)ethane (BTESE) and applied to reverse osmosis (RO) desalination. The organosilica membrane calcined at 300^°C almost completely rejected salts and neutral solutes with low‐molecular‐weight. Increasing the operating pressure led to an increase in water flux and salt rejection, while the flux and rejection decreased as salt concentration increased. The water permeation mechanism differed from the viscous flow mechanism. Observed activation energies for permeation were larger for membranes with a smaller pore size, and were considerably larger than the activation energy for water viscosity. The organosilica membranes exhibited exceptional hydrothermal stability in temperature cycles up to 90^°C. The applicability of the generalized solution‐diffusion (SD) model to RO and pervaporation (PV) desalination processes were examined, and the quantitative differences in water permeance were accurately predicted by the application of generalized transport equations. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1298–1307, 2013     

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.     

Preparation of reverse osmosis membranes by surface modification of polymeric films. I. Surface acetylation of cellulose

Surface acetylation of cellophane to afford an asymmetric membrane having high desalination ability (as high as 98% sodium chloride rejection) is described. The films were characterized by multiple-internal-reflectance microscopy (MIR), dyeing tests, light microscopy, and determination of water and sodium chloride transport properties in reverse osmosis cells. Surface modification employing acetyl chloride and acetic anhydride was studied in detail: the influence of the cellophane employed, the degree of cellophane activation, reaction time, reagent concentration, and diluent were assessed. Mixed acetylation reactions are also discussed as well as an evaluation of various postconditioning treatments used to increase desalination.     

PVA/TEOS crosslinked membranes incorporating zinc oxide nanoparticles and sodium alginate to improve reverse osmosis performance for desalination

Pure water is becoming less available with increases in world population, so seawater desalination is becoming more important. For efficient seawater desalination, this paper proposes a novel mixed matrix membrane (MMM) based on the deposition of a poly(vinyl alcohol) (PVA) nanofibrous active layer on a 3-triethoxysilylpropylamine-functionalized cellulose acetate substrate. The active layer is fabricated by utilizing a tetraethyl orthosilicate–crosslinked PVA incorporating zinc oxide nanoparticles (ZnO-NPs) and sodium alginate (NaAlg). The overall reverse osmosis performance of the MMMs is enhanced by the infusion of ZnO-NPs and NaAlg in PVA; we find the optimum concentration for the best performance to be ZnO-NPs at 0.1 wt % and NaAlg at 0.01 wt %. In terms of permeation flux, salt rejection, salt passage, stability, long-term rejection, membrane antifouling, reusability, and chlorine resistance, the proposed MMMs are examined using a dead-end reverse osmosis filtration setup. The results show that the active layer achieves an optimal permeation flux of 34.6 L/m² h, a natural sea salt rejection of 97%, and a chlorine resistance of 93%, suggesting that the proposed MMMs can be useful for seawater desalination. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47559.     

Effects of organic acids on the performance of cellulose triacetate forward osmosis membrane

Forward osmosis (FO) membrane performance was improved using different organic acids (formic acid, acetic acid, lactic acid) for the addition of the casting solution. Scanning electron microscope (SEM) images of all the FO CTA membranes exhibited essentially the membranes have a structure of looking like two dense skin layers and a sponge‐like supporting layer. Additionally, based on the surface roughness values analysis of Atomic Force Microscope (AFM), the membranes with lactic acid, with similar roughness to the membranes without any acid, have bigger roughness than the membranes with formic acid or acetic acid. Furthermore, the water flux of membranes with acids has been improved and the reverse salt flux decreased. The membranes with lactic acid, with an outstanding penetration performance, were utilized to test the performance when 1 mol/L sodium chloride (NaCl), magnesium chloride (MgCl₂)_, magnesium sulfate (MgSO₄), and sodium sulfate (Na₂SO₄) were, respectively, as the draw solutions. The results revealed that the membranes have a higher rejection ratio for MgSO₄. Besides, in the process of separating oil–water mixture, the membranes with the organic acids have a better separation efficiency than the membrane without any acid during FO process and the water flux recovery rate could achieve above 90% insuring the membrane anti‐fouling. POLYM. ENG. SCI., 59:E138–E145, 2019. © 2018 Society of Plastics Engineers     

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。     

Synthesis and crosslinking of partially disulfonated poly(arylene ether sulfone) random copolymers as candidates for chlorine resistant reverse osmosis membranes

Biphenol-based, partially disulfonated poly(arylene ether sulfone)s synthesized by direct copolymerization show promise as potential reverse osmosis membranes. They have excellent chlorine resistance over a wide range of pHs and good anti-protein and anti-oily water fouling behavior. Crosslinking of these copolymers that have high degrees of disulfonation may improve salt rejection of the membranes for reverse osmosis performance. A series of controlled molecular weight, phenoxide-endcapped, 50% disulfonated poly(arylene ether sulfone)s were synthesized. The copolymers were reacted with a multifunctional epoxy resin and crosslinked thermally. The effects on network properties of various factors such as crosslinking time, copolymer molecular weight and epoxy concentration were investigated. The crosslinked membranes were characterized in terms of gel fraction, water uptake, swelling and self-diffusion coefficients of water. The salt rejection of the cured membranes was significantly higher than that for the uncrosslinked copolymer precursors.     

A physicochemical approach for the choice of polymeric membrane materials for water desalination by reverse osmosis

Interfacial properties such as the thickness of interfacial water layer, the distribution coefficient of solute between interfacial and bulk water phases, and the volume of interfacial water per unit mass of polymer material have been identified as relevant physicochemical quantities governing reverse osmosis transport and determined by gas and liquid chromatography methods with respect to different polymeric membrane materials. They are further split into the contribution from the structural component of polymer repeating unit. Force constants A and D for sodium chloride, representing the repulsive force working between membrane surface and solute, have been calculated on the basis of inter-facial properties obtained above. Using these force constants, the pore sizes required to achieve 99.9% of sodium chloride separation are obtained for different polymeric membrane materials. Furthermore, the prediction procedure for the effect of preferentially adsorbed organic molecules on the separation of sodium chloride and product rate is illustrated as a model for “fouling” in the desalination process by reverse osmosis.     

Cellulose triacetate membranes for seawater desalination

Experimental data on reverse osmosis using a sodium chloride solution by cellulose triacetate membranes are presented. The investigation involved studies on the composition of membrane casting solutions and their effects on the performance. A higher polymer concentration (11–13%) is found suitable for production of a uniform and highly salt rejecting membrane. Salt rejection of 99.0% and 4–5 GFD product water flux were obtained at 1000 psi operating pressure using 30,000 ppm TDS seawater in the initial experiments.     

Nanofiltration membranes broaden the use of membrane separation technology

Most reverse osmosis (RO) research has concentrated on the development of single-pass seawater membranes. The success of these high rejection membranes has created interest in other applications requiring less demanding salt rejection, or desiring the elimination of salt from a feed stream (diafiltration), or having severe chemical resistance requirements. All would prefer to operate at lower net driving pressures than demanded by the high rejection membranes. This paper reports on the characteristics of three such tailored membranes. These membranes have been designated as “quo;nanofiltration”quo; membranes to distinguish them from the “quo;hyperfiltration”quo; seawater membranes. The first is XP45, a polyamide membrane with a low sodium chloride rejection that makes it an excellent candidate for applications such as the processing of salty cheese wheys and pharmaceutical preparations. The second is NF70, another polyamide, a low pressure membrane with rejections suited for converting mildly brackish water and organic-laden raw water to potable water that meets WHO standards. The third is XP20, a new developmental membrane for the maintenance of electroless copper plating baths.     

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.