Colloid-enhanced Ultrafiltration Research Articles

Sulfate removal using colloid-enhanced ultrafiltration: performance evaluation and adsorption studies.

Colloid-enhanced ultrafiltration (CEUF), i.e., micellar-enhanced ultrafiltration (MEUF) and polymer-enhanced ultrafiltration (PEUF), was investigated to remove sulfate ions from aqueous solution in batch experiments, using cetyltrimethylammonium (CTAB) and poly(diallydimethylammonium chloride) (PDADMAC) as colloids, respectively. Ultrafiltration performance was evaluated under different initial concentrations of sulfate (0-20 mM) and CTAB/PDADMAC (0-100 mM). The highest retention rate (> 99%) was found in dilute sulfate solutions. At high sulfate concentrations (e.g., 10 mM), a dosage of 50 mM CTAB or PDADMAC can retain approximately 90% of sulfate ions. Though concentration polarization behavior was observed, membrane characterization indicated that the fouling was reversible and membranes can be reused. Furthermore, adsorption equilibrium and kinetics studies show that Freundlich isotherm and pseudo-second-order kinetics can describe the sulfate-colloid interaction, indicating that the surface of absorbents are heterogeneous and the rate-controlling step is chemisorption. Both MEUF and PEUF show potential as effective separation techniques in removing sulfate from aqueous solutions. Under the same conditions examined, PEUF shows advantages over MEUF in its higher retention at lower polymer-to-sulfate ratios, cleaner effluent, and higher adsorption capacity, but compromises on severer flux decline and a tendency of membrane fouling. To overcome this disadvantage, membranes with higher molecular weight cut-off can be used.

Colloid-Enhanced Ultrafiltration of Canola Oil: Effect of Process Conditions and MWCO on Flux, Fouling and Rejections

In the present work, the efficiency of colloid-enhanced ultrafiltration (CEUF) of canola oil miscella was investigated using an anionic surfactant (sodium dodecyl sulfate salt [SDS]), chelating agent (ethylenediaminetetraaceticacid [EDTA]), salt (calcium chloride [CaCl2]) and two molecular weight cutoffs of hydrophobic (polyvinylidene fluoride) membranes (50 and 100 kDa). There were thicker fouled layer on both membrane surfaces for SDS- and EDTA-pretreated samples. The flux reduction of M116 membrane was more than M183 membrane with the all samples except SDS added ones. It was observed that CEUF of EDTA- and SDS-pretreated samples exhibited high efficiency in removing phosphorus. Increasing temperature from 25 to 55C improved the steady-state permeate flux of SDS-pretreated samples to extent of 13 kg/m 2 h. Furthermore, increasing pressure led to increase the permeate flux of pretreated sample except CaCl2 adding ones.

Colloid-enhanced ultrafiltration in removal of traces amounts of borates from water

The use of colloid-enhanced ultrafiltration for boron removal from water is investigated. Biodegradable surfactant, 1,4-sorbitol oleate, was applied to obtain micelles and high molecular weight chitosan to reinforce their stability. Two kind of membranes were compared: neat porous polysulfone membrane and charged porous sulfonated polysylfone membrane; both with similar average pore diameter of 5 nm. The studies revealed that two key factors affect the boron rejection: presence of surfactant in the colloidal mixture and a repulsion effect of sulfone groups on the membrane surface. Both have a positive effect on boron removal.

Inorganic ligand-modified, colloid-enhanced ultrafiltration: A novel method for removing uranium from aqueous solution

Inorganic ligand-modified, colloid-enhanced ultrafiltration (ILM-CEUF) is as a novel membrane-based separation method for selectively removing target ions from aqueous solution. Traditional colloid-enhanced ultrafiltration (CEUF) is a well-established membrane-based separation technique that can be used to separate metal ions from other aqueous solution components. Ligand-modified, colloid-enhanced ultrafiltration (LM-CEUF) uses organic ligands that selectively complex target ions and also associate with a water-soluble colloid, such as a surfactant micelle or polyelectrolyte. The colloid, associated -ligand, and target ion are then concentrated using an ultrafilter, producing a filtrate with a low concentration of the target ion. While traditional LM-CEUF techniques are able to provide quantitative separations of a variety of ionic pollutants, the high costs of the chelating agents make such techniques nonviable in most remediation schemes. This study investigated the replacement of organic ligands with carbonate for the selective removal of U(VI) from aqueous solution. In slightly to moderately basic solutions containing carbonate, UO 2(CO 3) 3 4− can be made to dominate the U(VI) speciation. Using poly(diallyldimethylammonium) chloride, the effectiveness and efficiency of ILM-CEUF for removing U(VI) from other aqueous solution components was investigated as a function of carbonate concentration, pH, and ionic strength. Uranium separations of greater than 99.6% were achieved; even in the presence of large excesses of competing ions. The specific separation of U(VI) from Sr 2+ was also examined.

On the use of colloid-enhanced ultrafiltration in view of enantiomeric enrichments and limiting conditions

We review here the different techniques which have been used during the past twenty years to achieve enantiomer separation, distinguishing between analytical and preparative methods, and stressing upon the place of techniques based on surfactants and colloidal particles. Due to the great progress of membrane technologies, special emphasis will be put on the different attempts resting on the use of ultrafiltration techniques. The main successes in enantiomer separations (or at least enantiomer enrichment) obtained with these techniques involved the formation of a ternary complex including a metal ion (Cu2+ in most cases). Our concern in this work was to investigate the feasibility of performing enantiomer enrichments through micellar ultrafiltration, when only weak enantiomer/selector complexes were formed, not requiring a bridging metal ion. A model system (ephedrine enantiomers and (S)-dodecoxycarbonylvaline micelles as chiral selector), for which successful separations were achieved in micellar electrokinetic chromatography, was tested for this purpose. The lack of significant enrichment tend to demonstrate, that, in such a case, the difference in the binding of the enantiomers to the chiral selector (measured from UV spectroscopy and circular dichroism) is too weak to think about an application of ultrafiltration techniques, even in a multistage mode.

Colloid‐Enhanced Ultrafiltration of Chlorophenols in Wastewater: Part IV. Effect of Added Salt on the Surfactant Leakage in Surfactant Solutions and Surfactant–Polymer Mixtures

The critical aggregation concentration (cac) in surfactant–polymer mixtures approximates a lower limit to the surfactant concentration in the permeate (surfactant leakage) in polyelectrolyte micellar‐enhanced ultrafiltration. Here, the cac was measured at different salinities by using surface tension measurements. It was found that the cac increases slightly with the addition of simple salt, then the cac value decreases at higher salt concentration. The critical micelle concentration (CMC), which approximates surfactant leakage in micellar systems (no polymer), decreases monotonically with increasing salinity for ionic surfactants. The surfactant leakage in colloid‐enhanced ultrafiltration (CEUF) processes is investigated by using a dialysis method in the presence of three phenolic solutes with various degrees of chlorination: 2‐monochlorophenol (MCP), 2,4‐dichlorophenol (DCP), and 2,4,6‐trichlorophenol (TCP). Cetylpyridinium chloride (CPC) or n‐hexadecylpyridinium chloride is used as a cationic surfactant; and sodium poly(styrenesulfonate) (PSS) is used as an anionic polyelectrolyte. The effect of salinity and type of colloid is focused on here. In the absence of added salt, the cac can be over an order of magnitude less than the CMC, as can be surfactant leakage with added polymer. The added salt reduces the surfactant leakage in the micellar solution due to CMC reduction in the presence of electrolyte. In the surfactant–polymer mixture, the surfactant leakage is dramatically affected by salinity.

Colloid-Enhanced Ultrafiltration of Chlorophenols in Wastewater: Part II. Apparent Acid Dissociation Constants of Chlorophenols in Colloid Solutions at Different Ionic Strengths and Effect of pH on Solubilization of Phenolic Compounds

ABSTRACTThe effects of pH, ionic strength, and type of colloid on the efficiency of removal of an organic solute in colloid-enhanced ultrafiltration, as indicated by the tendency of the solute to solubilize into micelles and surfactant–polymer complexes, are investigated in this paper. The apparent acid dissociation constants (Kaapp) of 2-monochlorophenol (MCP), 2,4-dichlorophenol (DCP), and 2,4,6-trichlorophenol (TCP) are determined in surfactant solutions and surfactant–polymer mixtures at different salinities using a spectrophotometric titration technique. The distribution coefficients of charged species and neutral species of MCP and the solubilization of TCP into micelles and into surfactant–polymer aggregates are measured using dialysis methods. Cetylpyridinium chloride (CPC) is the cationic surfactant and sodium polystyrenesulfonate (PSS) is the anionic polymer used. The apparent values of pKa(pKa,app) of the solutes in micellar solution are less than the corresponding values in aqueous solution (pKa,aq), whereas the values of pKa,app for the solutes in the surfactant–polymer mixtures are slightly higher than those in the aqueous and micellar solutions. The pKa,app values increase as salt concentration increases in the micellar solution while remaining almost unchanged in the surfactant–polymer mixtures. In the micellar solutions, the distribution coefficient into the surfactant aggregate of the anionic species of MCP is greater than that of the neutral species, by factors of approximately 30 to 1.5 when salt concentration increases from zero to 0.10 M. However, in the surfactant–polymer mixtures, the distribution coefficient of the neutral species is higher than that of the charged species by factors of 5 to 8 when salt concentration increases from zero to 0.05 M. In the micellar solutions, the distribution coefficients of the neutral species are less dependent on salinity than those of the charged species. The solubilization and solute rejection are influenced by pH, primarily for solutes with low hydrophobicity.

Colloid-Enhanced Ultrafiltration of Chlorophenols in Wastewater: Part III. Effect of Added Salt on Solubilization in Surfactant Solutions and Surfactant–Polymer Mixtures

ABSTRACTThe solubilization of three phenolic solutes in micellar solutions and surfactant–polymer mixtures is studied: 2-monochlorophenol (MCP), 2,4-dichlorophenol (DCP), and 2,4,6-trichlorophenol (TCP). The equilibrium dialysis (ED) technique is used to determine the solubilization equilibrium constant as a function of added NaCl concentration. The added salt enhances the solubilization ability of surfactant micelles, but it only slightly affects the solubilization constant of surfactant–polymer aggregates. The solubilization constant for the surfactant–only systems is greater than that for the surfactant–polymer systems. In the micellar solution, the solute with a low water solubility shows a greater solubilization constant than the solute with a higher water solubility; the solubilization constants increase in the order MCP < DCP < TCP. However, in the surfactant–polymer mixtures, the solubilization constant of DCP can exceed that of TCP due to two opposing effects: ion-dipole interaction, and water solubility or hydrophobicity. Understanding and quantifying this solubilization phenomenon is crucial to optimization of the performance of colloid-enhanced ultrafiltration separation processes.

Purification of Phenolic-Laden Wastewater from the Pulp and Paper Industry by Using Colloid-Enhanced Ultrafiltration

The removal of three phenolic pollutants with variable degrees of chlorination from water was investigated: 2-monochlorophenol (MCP), 2,4-dichlorophenol (DCP), and 2,4,6-trichlorophenol (TCP). These compounds are often found in pulp and paper mill wastewater effluent. Colloid-enhanced ultrafiltration (CEUF) techniques were investigated for wastewater purification. Pollutants can associate with colloids: surfactant micelles or surfactant–polymer complexes solubilize nonionic compounds. In this application of CEUF, the micelles or surfactant–polymer complexes are ultrafiltered from solution with solubilized chlorinated phenol pollutant. An advantage of surfactant–polymer complexes, compared to only surfactants, is reduction of surfactant monomer (unaggregated surfactant) concentration. These surfactant monomers can pass through the ultrafiltration membrane, reducing the purity of the product water. Excellent solute rejections are observed for both micelles and surfactant–polymer complexes, generally exceeding 90% for DCP and TCP, even exceeding 99% in some cases. The ratio of the solubilization constant in micelles to that in surfactant–polymer complexes varied from approximately 1 to 5. In micelles, rejection increases in the orderMCP<DCP<TCP, whereas in the surfactant–polymer system, rejection of the DCP and TCP can sometimes reverse order. The surfactant monomer leakage into the permeate for the surfactant–polymer system is only about 1 to 10% of that for the surfactant micelles, down to very low concentrations approaching 1 μM. Therefore, CEUF using surfactant-only or surfactant–polymer mixtures can be a very effective separation technique to remove chlorinated phenols from wastewater. Surfactant–polymer systems result in lower surfactant leakage, but somewhat poorer rejections of the pollutant. It is anticipated that it will be more difficult to recover the colloid for reuse compared to use of a pure surfactant.

Ligand-Modified Colloid Enhanced Ultrafiltration. Use of Nitrilotriacetic Acid Derivatives for the Selective Removal of Lead from Aqueous Solution

In ligand-modified, colloid-enhanced ultrafiltration (LM-CEUF), a ligand that selectively complexes target ions (e.g., lead) also associates with a water-soluble colloid, such as a surfactant micelle or polyelectrolyte. The colloid, associated ligand, and target ion are then concentrated using ultrafiltration, producing a filtrate with a low concentration of the target ion. Dialysis, ultrafiltration, and potentiometric titration experiments have been used to investigate the effectiveness of four nitrilotriacetic acid (NTA) derivatives in the removal of lead from aqueous solution through LM-CEUF. The ligands are 2-phenyl nitrilotriacetic acid (PNTA), 2-[N, N-di-(carboxymethyl)]amino-octanoic acid (HNTA), 2-[N,N-di-(carboxymethyl)]amino-dodecanoic acid (DNTA), and 2-[N,N-di-(carboxymethyl)]amino-3-sulfopropionic acid (SNTA). The colloids used were the cationic polyelectrolyte poly(diallyldimethylammonium chloride) (PDADMAC) and the cationic surfactant cetylpyridinium nitrate (CPNO3). In equilibrium dialysis and ultrafiltration (UF) experiments, SNTA and PDADMAC systems provided effective lead removal. In semiequilibrium dialysis and UF experiments, DNTA and CPNO3 systems also provided effective lead removal. The effects of pH, ionic strength, competing ions, and colloid concentration were investigated for each ligand system. Ligand protonation constants and ligand–metal stability constants were obtained for SNTA in both water and solutions of PDADMAC and for DNTA in solutions of CPNO3. Ligand regeneration through pH adjustment and metal precipitation with various anions was also demonstrated.

Solubilization by Various Surfactant Solutions and Applications to Separation Technology

Solubilization phenomena of various organic solutes by surfactant solution was reviewed. The interpretation of intramicellar solubilization data obtained from semi-equilibrium dialysis (SED), head-space gas chromatography (HSGC), and solute vapor pressure methods (SVP) are presented for determining equilibrium constants for the solubilization of organic species by aqueous surfactant solutions as well as activity coefficients of both the organic solute and the surfactant within the micelle. The solubilization equilibrium constant of an organic solute in an aqueous micellar solution (K) is defined as the ratio of the mole fraction of organic solute in the micellar 'pseudophase' (X) to the concentration of the unsolubilized monomeric organic solute in the aqueous phase (Cp). The simple empirical expression K=K0 (1-αX+βX2) is used to correlate the solubilization equilibrium constant (K) with the mole fraction of the organic solute in the surfactant aggregates (X). Water-soluble polyelectrolyte/surfactant complexes, involving oppositely charged species, can form at quite low thermodynamic activities of the surfactant. This fact is exploited in colloid-enhanced ultrafiltration separations, where both molecular organic pollutants and toxic ions are to be removed from contaminated aqueous streams.

Use of polyelectrolyte-surfactant complexes in colloid-enhanced ultrafiltration

Water-soluble polyelectrolyte-surfactant complexes, involving oppositely charged species, can form at quite low thermodynamic activities of the surfactant. This fact can be exploited in colloid-enhanced ultrafiltration separations, where both molecular organic pollutants and toxic ions are to be removed from contaminated aqueous streams. Investigations have been made of (a) the solubilization and ultrafiltration of solutions of organic solutes in polymer-surfactant solutions, for comparison with studies of micellar surfactant solutions in the absence of added polymers; (b) the penetration of surfactant through the membrane (leakage of monomer) in dialysis and ultrafiltration experiments; and (c) the utility of polyelectrolytes as ‘scavengers’ for surfactant species that enter the permeate or filtrate in colloid-enhanced ultrafiltration separations. Polyelectrolytes chosen for the studies are sodium poly(styrenesulfonate) and poly(dimethyldiallylammonium chloride); the surfactants are cetylpyridinium chloride (hexadecylpyridinium chloride) and sodium dodecylsulfate. A detailed study has been made of the solubilization and separation of p-tert-butylphenol in aqueous mixtures of sodium poly(styrenesulfonate) and cetylpyridinium chloride, at polyelectrolyte to surfactant mole ratios of two to one.

Solubilization and Separation of p-tert-Butylphenol Using Polyelectrolyte/Surfactant Complexes in Colloid-Enhanced Ultrafiltration

Abstract Water-soluble polyelectrolyte/surfactant complexes, involving oppositely charged species, can form at quite low thermodynamic activities of the surfactant. This fact can be exploited in colloid-enhanced ultrafiltration separations, where both molecular organic pollutants and toxic ions are to be removed from contaminated aqueous streams. Investigations have been made of (a) the solubilization and ultrafiltration of solutions of organic solutes in polymer/surfactant solutions, for comparison with studies of micellar surfactant solutions in the absence of added polymers; (b) the penetration of surfactant through the membrane (leakage of monomer) in dialysis and ultrafiltration experiments; and (c) the utility of polyelectrolytes as scavengers for surfactant species that enter the permeate or filtrate in colloid-enhanced ultrafiltration separations. The polyelectrolyte chosen for the studies is sodium poly(styrenesulfonate) and the surfactant is cetylpyridinium chloride (hexadecylpyridinium chloride). A detailed study has been made of the solubilization and separation of p -tert-butylphenol in aqueous mixtures of sodium poly(styrenesulfonate) and cetylpyridinium chloride, at polyelectrolyte to surfactant mole ratios of two to one and three to one.