Effects of membrane hydrophilicity on the removal of a trihalomethane via micellar-enhanced ultrafiltration process

Micellar-enhanced ultrafiltration (MEUF) process was explored for obtaining pure water from an aqueous solution containing small amount of trihalomethanes (THMs). A homologous series of polyethylene glycol alkylether was used as nonionic surfactant. To understand effects of membrane hydrophilicity on the performance of MEUF process, membranes for the ultrafiltration were prepared from polysulfone blends containing various amount of a hydrophilic copolymer, poly(1-vinylpyrrolidone-co-acrylonitrile) (P(VP-AN)). An increase in the permeate flux was observed with an increase of the membrane hydrophilicity. The performance of MEUF process in removing THM and surfactant was shown to depend on the membrane characteristics, surfactant characteristics, and operating pressure. The rejections of THM and surfactant were increased with increasing hydrophobicity of surfactant and hydrophilicity of membrane. The rejections of THM examined with hydrophilic membranes were increased with increasing operating pressure, while those examined with hydrophobic membranes were decreased with increasing operating pressure. THM included in water could be removed up to 99% via MEUF process. The performance of MEUF examined with hydrophilic membranes could be explained with the rejection of micelles containing THM, while that examined with hydrophobic membranes could be explained with hydrophobic interactions between surfactant and membrane materials.     

Removal of cadmium ions using micellar-enhanced ultrafiltration with mixed anionic-nonionic surfactants

Micellar-enhanced ultrafiltration (MEUF) was used to remove cadmium ions from wastewater efficiently. In this study the nonionic surfactants polyoxyethyleneglycol dodecyl ether (Brij35) and polyoxyethylene octyl phenyl ether (TritonX-100) were for micellar-enhanced ultrafiltration to lower the dosage of the anionic surfactant sodium dodecyl sulfate (SDS). The surfactant critical micelle concentration (CMC) and the degree of micelle counterion binding were investigated. The effects of nonionic surfactant addition on the efficiency of cadmium removal, the residual quantities of surfactant, the permeate flux and the secondary membrane resistance were investigated. A comparison between MEUF with SDS and MEUF with mixed anionic–nonionic surfactants was undertaken. The results show that the addition of Brij35 or TritonX-100 reduced the CMC of SDS and the degree of counterion binding for the micelles. Due to these variations the Cd²⁺ rejection efficiency was at a maximum when the Brij35:SDS and the TritonX-100:SDS molar ratio was 0.5. The Cd²⁺ rejection efficiency in MEUF with SDS is higher than for MEUF with mixed surfactants when the total dose of surfactant is constant. The permeate flux of MEUF with SDS is higher than that for MEUF with mixed surfactants while the secondary resistance of MEUF with SDS is less than that of MEUF with mixed surfactants.     

Improved MEUF removal of naphthenic acids from produced water

Naphthenic acids are naturally occurring organics in produced waters from oil recovery operations. In principle, these contaminants can be removed using micellar-enhanced ultrafiltration (MEUF), which is an effective technique for the removal of organic contaminants from water streams. In this work, we show that the amphiphilic nature of the naphthenic acids contributed to decreasing the critical micelle concentration (CMC) of cetylpyridinium chloride (CPC), a widely used surfactant in MEUF. This reduction in CMC allowed a decrease in the CPC dosage required to attain certain removal of the organics, and hence, improved the performance of traditional MEUF as a result of reducing back contamination and potential fouling of the membrane. The effect of CPC feed concentration, and the concentration and carbon number of the naphthenic acids on permeate flux, recovery ratio and percent rejection of CPC and naphthenic acids were explored over a range of trans-membrane pressure. The MEUF setup employed hydrophilic polyacrylonitrile (PAN) hollow fiber membrane with 13 kDa MWCO, since it allowed for high permeate flux and contaminant rejection.     

Nonlinear two-phase equilibrium model for the binding of arsenic anions to cationic micelles

The binding of arsenic ions to cationic cetylpyridinium chloride (CPC) micelles has been investigated using the semiequilibrium dialysis (SED) technique. In SED experiments, it has been shown that CPC micelles are very effective in binding arsenic ions in the retentate. At the studied pH (pH 8), the unbound and bound arsenic exists primarily as divalent anions (HAsO₄²⁻) while CPC molecules exist as monovalent cations. Therefore, arsenic ions are bound electrostatically to the cationic micelle. The resultant colloid is large enough not to pass through the dialysis membrane, producing a rejection greater than 99.59%. The concentration of the unbound arsenic anions passing through the dialysis membrane is practically the same as the permeate concentration of these species in the analogous micellar-enhanced ultrafiltration (MEUF) experiments. Therefore, a nonlinear equilibrium model which combines thermodynamic relations, charge balance equations, and material balance equations with the Oosawa two-phase polyelectrolyte theory has been developed to correlate the binding of arsenic to CPC micelles in SED and MEUF. It was shown that the equilibrium model successfully accounts for the experimental data in both SED and MEUF in the absence and presence of monovalent (HCO₃¹⁻) and divalent co-ions (HPO₄²⁻). Because of their small sizes (less than 10 nm), micelles should retain their equilibrium shapes in the presence of hydrodynamic shear typically attained in most dynamic processes. Therefore, the equilibrium model can be used to predict separation efficiencies in other ultrafiltration units such as in crossflow ultrafiltration processes.     

Micellar-enhanced ultrafiltration of cadmium ions with anionic–nonionic surfactants

Micellar-enhanced ultrafiltration (MEUF), a surfactant-based separation process, is promising in removing multivalent metal ions from aqueous solutions. The micellar-enhanced ultrafiltration of cadmium from aqueous solution was studied in systems of anionic surfactant and mixed anionic/nonionic surfactants. The micelle sizes and zeta potentials were investigated by dynamic light scattering measurements. The effects of feed surfactant concentration, cadmium concentration and the molar ratio of nonionic surfactants to sodium dodecyl sulfate (SDS) on the cadmium removal efficiency, the rejection of SDS and nonionic surfactants and the permeate flux were investigated. The rejection efficiencies of cadmium in the MEUF operation were enhanced with higher SDS concentration and moderate Cd concentration. When SDS concentration was fixed at 3 mM, the optimal ranges of the molar ratios of nonionic surfactants to SDS for the removal of cadmium were 0.4–0.7 for Brij 35 and 0.5–0.7 for Triton X-100, respectively. With the addition of nonionic surfactants, the SDS dosage and the SDS concentration in the permeate were reduced efficiently.     

Resistance in series model for micellar enhanced ultrafiltration of eosin dye

A study has been performed to quantify the extent of flux decline during micellar enhanced ultrafiltration (MEUF) of an acid dye (eosin red) using hexadecyl (cetyl) pyridinium chloride as the cationic surfactant. Effects of the operating conditions, e.g., transmembrane pressure drop and feed-surfactant-to-dye ratio, on the permeate flux profile and observed retention have been investigated in an unstirred batch ultrafiltration (UF) cell. A simple resistance-in-series model has been used to quantify the flux decline. From the flux decline history, it has been found that the membrane permeability decreases rapidly due to reversible pore blocking and further flux decline is caused by the growth of a gel-type layer over the membrane surface. The different resistances and growth kinetics of the gel layer have been investigated as functions of the operating conditions.     

Effect of operating parameters on selective separation of heavy metals from binary mixtures via polymer enhanced ultrafiltration

Performance of continuous polymer enhanced ultrafiltration (PEUF) method was investigated for removal of mercury and cadmium from binary mixtures. This method includes the addition of polyethyleneimine (PEI) as a water soluble polymer to bind the metals, which was followed by ultrafiltration operation performed on both laboratory and pilot scale systems. The influence of various operating parameters such as temperature, metal/polymer ratio, presence of calcium ions and pH on retention of metals and permeate flux was investigated. To investigate the possibility of selective separation of mercury and cadmium, experiments were conducted for binary solutions at different pH and loading ratios. It was seen that the retention of mercury decreased and permeate flux increased when the temperature increased. The increased pH and decreased metal/polymer ratio, loading (L), resulted in higher retention of both metals. Shapes of retention vs. pH or L curves were very similar for both metals. Retentions stay almost constant at a value very close to unity until a critical L or pH value was reached, then, R decreases almost linearly with L or pH. However, retention of cadmium was affected more than that of mercury as the pH decreased and L increased. This leads to the selective separation of mercury and cadmium. At low pH values (about 5) and at high L values (about 0.3), mercury was removed by ultrafiltration operation while almost all cadmium passed through the membrane. At pH 5.5 and cadmium/polymer ratio about 0.35 and mercury/polymer ratio about 0.39, the highest separation factor was obtained as 49.     

Determination of equilibrium distribution constants of phenol between surfactant micelles and water using ultrafiltering centrifuge tubes

Equilibrium distribution constants, K_s, of phenol between surfactant micelles and water have been determined by micellar enhanced ultrafiltration (MEUF) using commercial ultrafiltering centrifuge tubes. Three surfactants: sodium dodecyl sulphate (SDS), polyoxyethylene 20 cetyl ether (C16E20) and cetylpiridinium chloride (CPC) were tested with a 10 000 molecular weight cut off (MWCO) membrane. Additionally, membranes of 5000 and 30 000 MWCO were used for CPC. A phenomenological mathematical model has been proposed for the batch MEUF process and checked with the experimental permeate or retentate composition. The model is based on two assumptions: monomeric molecules are not rejected by the membrane and the rejection of micelles is independent of the retentate concentration. The measured micelles rejections for different surfactants and the equivalent molecular weight of the micelles are correlated and they are not significantly affected by the addition of phenol. The estimates of K_s for SDS and CPC agree with previously reported values determined by other methods. K_s values for CPC, calculated using 5000, 10 000 and 30 000 MWCO membranes, have not been significantly different. K_s estimate has allowed to predict the phenol permeate concentration measured in continuous tangential MEUF experiments.     

Removal of tetramethyl ammonium hydroxide from synthetic liquid wastes of electronic industry through micellar enhanced ultrafiltration

In this paper, the separation of tetramethyl ammonium hydroxide (TMAH) from synthetic liquid wastes of electronic industry is carried out by using a micellar enhanced ultrafiltration (MEUF) process. This treatment represents the first step of an integrated process, aimed at the recovery of TMAH and surfactant and water reuse. The laboratory tests are carried out with an ultrafiltration module using initial solutions having a concentration of pollutant equal to 2?g/L and by adding sodium dodecyl sulfate as a surfactant, at a concentration in the range 4–10?mM/L, that is, under and above its critical micellar concentration (CMC). The experiments have been carried out at a fixed temperature of 25°C. The obtained results showed that very good percentage removals of TMAH are achieved (99%), especially when the surfactant was above the CMC.     

Comparison of polysulfone and ceramic membranes for the separation of phenol in micellar-enhanced ultrafiltration

Micellar-enhanced ultrafiltration (MEUF) of phenol and a cationic surfactant, cetylpyridinium chloride (CPC), is studied using two polysulfone membranes of 5- and 50-kDa molecular weight cutoff (MWCO) and two ceramic membranes of 15- and 50-kDa MWCO. Filtrations are run under laminar cross-flow and steady-state conditions. The effect of operation variables (pressure and retentate flux) and membrane properties (nature and MWCO) on permeate flux, surfactant, and phenol rejections is analyzed. The permeate flux depends, among other variables, on the fouling favored by membrane-micelle interactions, which are strongest in the 50-kDa MWCO ceramic membrane. On the other hand, surfactant rejection is mainly determined by the pore size and influenced by the pressure for both 50-kDa MWCO membranes. An equilibrium distribution constant, K(s), of phenol between surfactant micelles and water is calculated. Its value is not significantly affected by operation conditions and membrane type. K(s) is also approximately 20% lower than the value determined in a previous work with batch dead-end ultrafiltration.     

Molecular and Morphological Designs of High Performance Polymeric Membranes

Currently, membrane separation techniques, such as reverse osmosis and ultrafiltration, play an important role in industrial separation technology. To develop high performance polymeric membranes, it is essential to design the molecular and morphological structures of the membranes for their specific applications. In the reverse osmosis field, we have developed several kinds of composite membranes for specific uses. Applications include ultrapure water production, seawater desalination, softening and desalination of brackish water, and recovery of valuable substances. In the course of development, thin-film composite membrane materials and membrane morphology have been analyzed intensively and are becoming clearer. These results enable us to control membrane performance by an optimum combination of membrane materials and membrane morphology. The morphological structure and chemical structure of the composite membranes were designed to optimize the performance of both the ultrathin layer and the supporting substrate layer for each membrane's application. As ultrafiltration is expanding to various fields, requirements for membrane performance have become more severe, especially for 1) sharpness of molecular weight cutoff, 2) solvent and high temperature resistance, and 3) fouling resistance (low nonspecific protein adsorption). To satisfy these requirements, we have developed a new ultrafiltration membrane. Owing to the high resistivity and hydrophilicity of its chemical structure, the membrane shows excellent solvent and high temperature resistance as well as fouling resistance. In addition, sharp molecular cutoff was realized by controlling membrane morphology.     

Micellar enhanced ultrafiltration of phenol in synthetic wastewater using polysulfone spiral membrane

The micellar enhanced ultrafiltration (MEUF) of phenol in synthetic wastewater using two polysulfone spiral membranes of 6- and 10-kDa molecule weight cut-off (MWCO) and cetylpyridinium chloride (CPC) as cationic surfactant was studied. The effects on the permeate flux, permeate and retentate concentrations of phenol and CPC of various factors in the practical application of MEUF were studied, including surfactant and phenol concentrations, retentate flux, operating pressure, temperature and electrolyte. It was found that these two membranes could adsorb free phenol so the concentration of permeate phenol was lower than that of free phenol. The retentate phenol concentration kept increasing, then decreased slightly with the increase of the feed CPC concentration. Retentate flux and temperature had great effect on the performance of MEUF, and operating pressure did not. The addition of sodium carbonate (Na₂CO₃) could increase the retentate phenol concentration and decrease the permeate concentrations of phenol and CPC significantly.     

Electrodialysis with ultrafiltration membranes for peptide separation

A number of bioactive peptides find their potential applications in food or pharmaceutical industry; however, there arise some limitations of their large-scale production to satisfy market demands. Although pressure-driven membrane processes are able of continuous production and separation of peptides, these technologies often demonstrate insufficient selectivity. Electrophoresis is a well-known purification process characterized by high resolution of separated species but it is limited by relatively low production capacity. On the other hand, electromembrane processes offer high production capacity but their limitation is the size of separated molecules. Electrodialysis with inserted ultrafiltration membranes is an alternative method of peptide separation into fractions, their concentration and possibly demineralization at the same time to achieve large production quantities. It is a hybrid process combining conventional electrodialysis and electrophoresis principles using ultrafiltration membranes. These membranes serve as a molecular barrier separating two types of solution while the driving force remains electric potential difference. This article offers state-of-the-art summary in the field of bioactive peptide separation and fractionation by electrodialysis with ultrafiltration membranes.     

Micellar enhanced ultrafiltration of phenolic derivatives from their mixtures

Micellar enhanced ultrafiltration (MEUF) of different phenolic derivatives including meta-nitrophenol (MNP), catechol (CC), para-nitrophenol (PNP), and beta-napthol (BN) in their binary mixture has been studied. A 1:1 ratio of the mixture of (i) MNP with CC and (ii) PNP with BN is taken for the MEUF experiments using a cationic surfactant, namely, cetyl(hexadecyl)pyridinium chloride (CPC). An organic polyamide membrane with molecular weight cutoff of 1000 is used. Experiments are conducted using an unstirred batch cell and a continuous cross-flow cell. The effects of various operating conditions, e.g., concentrations of surfactant and solute in the feed, transmembrane pressure drop, and cross-flow rate (for cross-flow experiments) on the permeate flux and the observed retention of each solute have been studied in detail. The retention of solutes without using the surfactant varies from 3 to 15% only at a typical feed solute concentration of 0.09 kg/m3, whereas, under the same operating pressure (345 kPa), retention at the end of the experiment increases to about 66 to 99.8% depending on the nature of solute in the batch cell using surfactant micelles (10 kg/m3). Retention of solutes is less in the case of the two-component feed solution compared to the single-component feed solution. An increase in flux to the range of 9 to 16% is realized in cross-flow experiments compared to batch cell flux after one hour of operation.     

Investigations of properties and binding forms of cadmium and nickel in protein extracts by ultra-/diafiltration, photometry and atomic absorption spectrometry

A combination of a special ultrafiltration procedure with photometry and atomic absorption spectrometry for application in the speciation analysis of protein containing solutions is described, allowing not only the determination of qualitative distribution patterns of metal species but also the quantitative characterization of metal species. According to these investigations, exemplified by cadmium and nickel species in protein extracts of bean seeds, it is demonstrated how to use this method. The results show that cadium and nickel have completely different binding mechanisms in these seeds. Furthermore, these investigations lead to the result that the application of membrane separation techniques in speciation analysis is not limited to the separation into molecular weight ranges only. Much more, they are useful techniques in combination with detection methods to obtain information about binding strength and the complexing ability of different matrices to bind heavy metals.     

Concentration polarization,separation factor,and Peclet number in membrane processes

Concentration polarization affects almost all the membrane separation processes and can be the cause of a substantial reduction in the separation factor and flux. A generalized equation relating the modified Peclet number to the concentration polarization occurring in the boundary layer is proposed and shown applicable to the majority of membrane separation processes like gas separations, reverse osmosis, ultrafiltration, pervaporation, and dissolved gas permeation in liquid. The membrane permeability, separation factor (or solute rejection), membrane thickness, boundary layer mass transfer coefficient, and Henry's law coefficient are the factors that determine the extent of polarization. An analysis is presented to offer a clean division of the hydrodynamic effect from the pure membrane property for membrane separation processes of liquid phases. Also the effect of membrane thickness on polarization is discussed. An attempt has been made to reconcile the different approaches taken for different membrane processes in the literature. Experimental data from widely different sources illustrate and confirm the present theory for pervaporative separation of dilute solutions of volatile organic compounds, dissolved gas permeation, and ultrafiltration of proteins and carbowax. Specific suggestions are made to obtain independent experimental measurements of the Peclet number and polarization index in terms of measurable quantities like the actual and intrinsic separation factors.     

Polyphenylsulfone/multiwalled carbon nanotubes mixed ultrafiltration membranes: Fabrication,characterization and removal of heavy metals Pb2+, Hg2+, and Cd2+ from aqueous solutions

Polyphenylsulfone/multiwalled carbon nanotubes/polyvinylpyrrolidone/1-methyl-2-pyrrolidone mixed matrix ultrafiltration flat-sheet membranes were fabricated via phase inversion process to inspect the heavy metals separation efficacy from aqueous media. Fabricated membranes cross-sectional morphological changes and the topographical alterations were assessed with Scanning electron microscopy (SEM) and atomic force microscopy (AFM). Particularly, MWCNTs assisted membranes exhibited better permeability ability as well as heavy metal removal enactment than virgin membrane. The dead-end filter unit was engaged in current research to examine the permeability and heavy metal removal competence of membranes. With the continuous enhancement of MWCNTs wt% in a polymer matrix, significant enhancement was observed with pure water flux study, from 41.69 L/m² h to >185 L/m² h as well as with the heavy metals separation study. Added additive MWCNTs can impact the pore sizes in membranes. The heavy metal separation results achieved, the membrane with 0.3 wt% of MWCNTs (PCNT-3) exhibited >98%, >76% and >72% for Pb²⁺, Hg²⁺ and Cd²⁺ ions, respectively. Overall, MWCNTs introduced PPSU membranes exposed best outcomes with heavy metals contained wastewater treatment.     

抗污染PVA/PVDF电纺纳米纤维复合超滤膜的制备及过滤性能

以聚对苯二甲酸二醇酯(PET)无纺布为基底,聚偏氟乙烯(PVDF)纳米纤维为支撑层,聚乙烯醇(PVA)纳米纤维膜为分离层,采用静电纺丝法制备超滤膜,并用水/丙酮混合溶液对复合纳米纤维膜表面进行溶液处理,再加入戊二醛交联改性得到致密分离层.采用扫描电子显微镜(SEM)和红外光谱(FTIR)表征了复合超滤膜的表面,用水接触角(WCA)表征复合超滤膜的亲水性.在0.02 MPa恒压下死端过滤油/水乳液,测试复合超滤膜的过滤性能.结果表明,最优条件下制备的复合超滤膜死端过滤油/水乳液的通量为(42.50±4.78)L/(m~2·h),截留率达到(95.72±0.33)%;循环使用5次后,依然具有较好的过滤性能,常压下死端过滤复合超滤膜的纯水通量为(3469±28)L/(m~2·h).     

分离液体的膜

本文概述了7种以高分子为膜材料、用于混合液体分离的膜分离过程,即离子交换膜与电渗析、反渗透、超滤、微孔过滤、膜萃取、渗透汽化和膜蒸馏。对其原理、高分子膜材料、应用和发展趋向作了简要介绍;并阐述了我国膜分离发展的现状和展望。