Chelating water-soluble polymers associated with ultrafiltration membranes for metal ion removal

This article describes the retention properties of commercial chelating water-soluble polymers, for different metal ions in aqueous solution using a liquid-phase polymer-based retention (LPR) technique. The polymers studied were poly(ethyleneimine) or P(EI) (water-free and a 50?% aqueous solution) and poly(ethyleneimine epichlorohydrin) or P(EIE) (a 17?% aqueous solution). These commercial polymers were fractionated by ultrafiltration membranes and then characterized by Fourier-transformed infrared spectroscopy. The extraction process was performed using the following metal ions: Cu²⁺, Cd²⁺, Co²⁺, Ni²⁺, Zn²⁺, Pb²⁺ and Cr³⁺. In the washing studies, we varied the pH (3, 5 and 7) and retention time. The results showed that P(EI) showed high retention for all the metal ions at pH 7 and for selective retention of Cu²⁺ at pH 5, while P(EIE) showed selective retention of Cu²⁺ ions at pH 7. Using the enrichment method, the maximum retention capacity of Cu²⁺ and Cd²⁺ was achieved using a 50?% aqueous solution of P(EI) at pH 5 and 7, respectively. Finally, charge–discharge experiments for Cu²⁺ were analysed by changing the pH from basic to acidic over three cycles. These results showed that it is possible to remove metal ions and regenerate the removal capacity of the polychelatogens using the LPR technique.     

Reverse osmosis with dynamically formed membranes from water-soluble polymers

Membranes were dynamically formed from poly(acrylic acid), poly(1-methyl-2-vinylpyridinium iodide), and methylcellulose on a Millipore filter. The effects of the conditions of membrane formation on reverse osmosis performances and the membrane structure were investigated. The primary factors that affect membrane performance were ascertained to be the kind and concentration of salts and the pH of the preparing solutions, the concentration and the polymerization degree of the membrane materials, the pore size of filters, and the pressure and circulation velocity during membrane formation. Two types of dynamically formed membranes, the membranes inside the filter and the membranes on the filter, were distinguished.     

The performance of ultrafiltration membranes pretreated by polymers

The fouling of ultrafiltration(UF) membranes by protein has been reduced by surface pretreatment with various polymers. In most cases the treatment provided an increase in initial UF flux and a slower flux decline.

The ultrafiltration performance of the treated membranes appears to be influenced by the molecular configuration and size of the polymer as well as its interfacial structure.

Methylcellulose(MC) was found to be the most effective of polymers tested in enhancing UF flux, showing an average flux advantage of 30–40% for first usage. For multiple cycles of usage the benefits increased up to 100% after 5 cycles, due to the reduced amount and reversibility of the fouling protein deposit.     

Water-soluble copolymers in conjunction with ultrafiltration membranes to remove arsenate ions

Water-soluble polymer poly[3-methacryloylamine)propyl)trimethyl ammonium chloride, P(ClMPTA) and the copolymer with 4-vinyl pyridine, poly[(3-methacryloylamine)propyl) trimethylammonium chloride-co-4-vinyl pyridine], P(ClMPTA-co-4VP) were synthesized by radical polymerization, at different feed mole ratios ClMPTA:4VP 1:1, 1:2, and 2:1. The copolymer compositions were determined by FT-IR and H-NMR spectroscopy and analyzed by TG-DSC. The liquid-phase polymer-based retention (LPR) technique was used to study the water-soluble polymers’ arsenic removal properties. The solution’s conductivity properties were evaluated at different pH. The copolymers can bind more selectively divalent anionic arsenic species from an aqueous solution (pH 8 ≥ pH 6 > pH 4). Assays for the mol ratio copolymer: As(V) 75:1, 37.5:1, 20:1, 10:1, and 5:1 at arsenic concentrations of 10 and 37.5 ppm were carried out. Apparently, the behavior of the copolymers with the solution’s pH was similar to pure cationic homopolymer; however, when the retention capacity was expressed as real mass of quaternary ammonium comonomer, the retention values were enhanced for lowest mol ratio 10:1 and 5:1. The retention capacity of exchanger with quaternary ammonium group was improved in presence of a weak base 4-vinyl pyridine comonomer, differently to the behavior showed by those copolymers of ClMPTA with acrylic acid groups as comonomer.     

Water‐soluble polymers: Optimization of arsenate species retention by ultrafiltration

The liquid‐phase polymer‐based retention (LPR) technique was employed to study the retention of arsenate species by poly(vinylbenzyl trimethylammonium chloride), P(ClVBTA), and poly[2‐(acryloyloxy)ethyltrimethylammonium chloride], P(ClAETA). The effect of parameters such as polymer concentration, time exposure, competition of sulfate and phosphate anions, and the use of natural systems as drinking water on the retention of As(V) species was analyzed. The mole ratios of polymer : As(V) of (31 : 1), (20 : 1), (10 : 1), (6 : 1), and (3 : 1) by using the washing method at pH 8 and 6 were assayed. The retention capacity was a function of polymer concentration and pH. The optimum mole ratio of polymer : As(V) was (20 : 1) for all pHs studied and all polymeric structures. The polymer's activity recovery assays were performed by washing at pH 2 and 3. A 95% As(V) elimination was achieved from polymers. A study of competition in the presence of other anions was performed at the same polymer : As(V) ratio (20 : 1). At pH 8 and at the same concentration of arsenate anions, sulfate, and phosphate anions, no important competition on arsenic retention was observed. Assays for P(ClVBTA) at pH 8 and mole ratio of polymer : As(V) (20 : 1), (40 : 1), and (60 : 1) using drinking water showed that the efficiency was higher under these conditions for the three As(V) retention cases. An unbuffered system with drinking water was tested for washing and enrichment methods by determining the maximum saturation capacity of the P(ClVBTA) polymer. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Permeation behavior of dextrans by charged ultrafiltration membranes of polyacrylonitrile photografted with ionic monomers

Charged copolymers, polyacrylonitrile, having grafts of quaternized poly(N,N-dimethylaminoethylmethacrylate) and poly(sodium p-styrenesulfonate), were synthesized by photograft-polymerization. The charged ultrafiltration membranes, which had heterogeneous porous structures, were prepared by casting graft polymer solution containing poly(vinyl alcohol) into water. The permeation of nonionic dextran and anionic dextransulfate through the charged membranes was studied by ultrafiltration in aqueous solution. The molecular weight cutoff characteristics of the charged membrances were obtained using dextrans of various molecular sizes. The permeation behavior was discussed in terms of the charge effect of the graft polymers and electrostatic interaction between the polymers and the solute molecules.     

Hindered diffusion of flexible polymers through polyimide ultrafiltration membranes

The hindered diffusion of polystyrene in dilute solutions of ethyl acetate through polyimide ultrafiltration membranes has been investigated. The present system did not show specific membrane‐solute interactions; furthermore, polystyrene can be considered as a flexible polymer coil. It is shown that the hindered diffusive permeability for monodisperse dilute solutions for a series of molecular weights can be compared well with the diffusive permeability curve of one polydisperse dilute polystyrene solution. In the case of very dilute solutions, the polymer coils have no interaction with each other, and the whole range of molecular‐weight‐dependent permeabilities can be determined from only one measurement. The diffusion behavior of polydisperse solutions through various polyimide membranes has been investigated as well. It was found that the diffusive permeability curve is strongly dependent on the type of membrane, that is, on the pore size distribution. It was not possible to calculate a pore size distribution from diffusion experiments due to mathematical limitations. Nevertheless, it was shown that hindered diffusion measurements are useful to estimate a maximum pore size for each membrane. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1180–1193, 2000     

Methods of fractionating polymers by ultrafiltration

Polyvinylpyrrolidone and dextran polysaccharides have been fractionated by ultrafiltration by using newly developed membranes with sharp molecular weight cutoffs. Three different experimental techniques were employed: (a) batch ultrafiltration by using progressively more retentive membranes; (b) continuous ultrafiltration by using several similar membranes in series; (c) variable pressure ultrafiltration by using a single membrane and varying the applied pressure. Ultrafiltration is shown to be a technique of preparative fraction having the advantages of simplicity, speed, and economy.     

Removal of cadmium from wastewater by enhanced ultrafiltration using surfactants

In order to recover cadmium ion from wastewater, a process based on enhanced ultrafiltration was finalised. The originality of the solution here proposed lies on the coupled use of ceramic membranes and of a surfactant added to the water to be treated. This paper deals with the study of the influence of experimental conditions upon permeation flux and selectivity of the separation. The process is efficient and flexible since a single stage treatment allows to reduce the concentration of cadmium in the effluent by a factor of about 750; this high performance in selectivity is on a par with high fluxes of permeate (roughly 170 L.h.^?1.m^?2 at 25°C and 3 × 10⁵ Pa).     

Slow release of water-soluble salts from polymers

Release rates of NaCl and NaF from mixtures with polystyrene, polyethylene, thermosetting polyester, and crosslinked polyethylene have been studied. Salt/polymer granules were prepared by melt mixing under different conditions. The release process was studied in batch as well as continuous systems. The salt release from polymer into water depends on such parameters as salt content, temperature, water flow rate, and salt particle size.     

Development of ultrafiltration membranes from acrylonitrile co-polymers

Summary Hydrophobic polymer surfaces show higher tendency to protein adsorption and bacteria attachment, thus hydrophobic polymeric membranes foul rapidly in water purification operations. A change in membrane surface properties can reduce fouling; this may be accomplished by increasing the hydrophilicity of the membrane surface, and by using a membrane with smaller pore size. The ultrafiltration membranes were prepared via phase inversion process in our laboratory. Negatively charged hydrophilic ultrafiltration membranes were prepared from acrylonitrile-vinyl acetate (CP16)/Acrylonitrile-vinyl acetate-sodium p-sulfophenyl methallyl ether (CP24). Scanning electron microscopy (SEM) revealed the asymmetric structure of these membranes. The roughness of the surface was measured by atomic force microscopy (AFM). The basic characteristics of these membranes like water permeability, water content and membrane selectivity were also measured. Received: 29 April 2001/Revised version: 14 September 2001/Accepted: 14 September 2001     

电渗析法制备水溶性离子液体

以1-乙基-3-甲基咪唑四氟硼酸盐（［EMIm］BF₄）的制备为例,对四隔室电渗析法制备水溶性离子液体进行了研究。分别考察了操作电压、进料浓度和离子交换膜种类对平均电流效率、能耗和收率3个电渗析过程性能参数的影响。实验结果表明,相比于传统的化学合成法制备离子液体,采用四隔室电渗析法制备水溶性离子液体具有反应条件温和（室温下反应）、反应时间短、反应无须传统有机溶剂（水作反应溶剂）和产物纯度高（最高可达98％）的优点。     

Separation of cation–anion mixture using micellar-enhanced ultrafiltration in a mixed micellar system

Aqueous solution containing copper (cation) and potassium permanganate (anion) was treated by ultrafiltration using mixed micellar system comprising of sodium dodecyl sulfate and cetylpyridinium chloride. Simultaneous separation characteristics of both cation and anion, as well as permeate flux were studied for various operating conditions, namely, transmembrane pressure drop and cross-flow rate. The study was carried over a wide concentration range of both solutes. In the mixture, copper concentration was in the range from 0.05 to 4.0 kg/m³ and that of potassium permanganate was 0.05 to 0.25 kg/m³. Retention of copper was in the range of 90–100% and that of potassium permanganate was 96–99%. Permeate flux was found to be less in the mixed micellar system compared to single surfactant system. A four step chemical treatment process was proposed to recover and reuse the surfactants.     

Preparation of antibacterial polyvinylidene fluoride (PVDF) ultrafiltration membranes with direct addition of N-halamine polymers

In this study, novel antibacterial ultrafiltration polyvinylidene fluoride (PVDF) flat sheet membranes were produced with addition of synthesized N-halamine polymers. The ternary phase diagrams of PVDF and the synthesized polymers with N-methyl-2-pyrrolidone and water systems were prepared. The water flux and BSA rejection performances of the produced membranes were assessed both with and without PVP addition, and compared with a commercial membrane. The produced membranes were characterized with FTIR, XPS, DSC, and SEM analysis. Addition of N-halamine polymers to the membrane structure significantly improved the biocidal performance of the produced membranes against Staphylococcus aureus and Escherichia coli (10⁵ CFU).     

Separation of proteins by charged ultrafiltration membranes

The separation of a protein mixture by charged ultrafiltration membranes was studied. A negatively charged polymer was obtained by sulfonation of polysulfone, and a positively charged polymer was synthesized by chloromethylation of polysulfone and then by quaternization of the amino group. Then, the negatively and positively charged ultrafiltration membranes were cast from solutions of charged polymer/NMP(or DMF)/lithium nitrate. The molecular weight cut-off of the membranes were controlled by the changing casting conditions.

Single protein solutions were ultrafiltrated at the isoelectric point and at another pH level by the use of charged membranes. At the isoelectric point, rejection of the protein was low, while it was high at the pH level which gave the protein the same sign of charge as that of the membrane.

A protein mixture of myoglobin and cytochrome C was separated by the charged ultrafiltration membranes at the isoelectric point of one of the proteins. At the isoelectric point of cytochrome C, myoglobin has a negative charge. Thus myoglobin was rejected with a rejection of about 80% by the negatively charged membrane. At the same time, cytochrome C permeated completely through the membrane. Conversely, at the isoelectric point of myoglobin, cytochrome C has a positive charge and thus it was rejected with a rejection of about 20% by the positively charged membrane. The rejection of myoglobin here was almost zero.     

Complexation of synthetic bilayers with water-soluble polymers

Summary The morphological influence of water-soluble polymers on the aqueous bilayer aggregate (vesicle and/or lamella) of didodecyldimethylammonium bromide was investigated by electron microscopy. Positively charged polymers and uncharged polymers either destroyed the aggregate or was ineffective. On the other hand, the negatively-charged copolymer of acrylamide and acrylate separated the bilayer and produced smaller vesicles.Contribution No. 494 from Department of Organic Synthesis.