Effect of Conditioning Ultrafiltration Membranes on their Performances in Electrodialysis with Ultrafiltration Membrane

Abstract

A recent alternative method based on ultrafiltration membrane stacked in an electrodialysis cell was recently used for the separation of bio‐active high added value charged molecules, such as peptides and polyphenols. However, the ultrafiltration membranes which are uncharged membranes present lower electrical conductivity, in comparison with conventional ion‐exchange membranes. The purpose of this study was to evaluate the effect of conditioning ultrafiltration membranes of different molecular weight cut‐off (MWCO) (10, 20, 50, and 100 kDa) in solution with different ionic strength (distilled water and 0.1 M NaCl_(aq)) on their electrodialytic properties. It appeared that the conditioning solution could have a major impact on the electrical conductivity value of an ultrafiltration membrane and that the final conductivity value after soaking increased with an increase in molecular weight cut‐off. However, the soaking period and solution had no effect on membrane thickness. Furthermore, the electrical conductivity of the membrane was increased after an electrodialysis with ultrafiltration membranes process of a salt solution.     

Resolution of Racemic Propranolol in Liquid Membranes Containing TA‐β‐cyclodextrin

Abstract

The pharmacological properties of propranolol enantiomers are quite different, the β‐adrenergic blocking activity resides in the (S)‐(?) isomer, while the (R)‐(+)‐enantiomer has only a membrane stabilizing effect. The inherent chirality of cyclodextrins (CDs) allows them to form diastereomeric complexes. In this work, a peracetylated β‐CD (TA‐β‐CD) that preferentially interacts with the (S)‐(?) isomer of propranolol was used. Two liquid membranes, bulk liquid membrane (BLM) and supported liquid membrane (SLM) were tested. A recovery of 30% and a enantiomeric excess of 12% were obtained, using a SLM with 10 mM of propranolol and a pH gradient between feed and stripping phases.     

Separation Behavior of Composite Polyamide Membranes from Mixed Amines: Effects of Interfacial Reaction Condition and Chemical Post-Treatment

Abstract

Composite polyamide membranes are prepared using in-situ interfacial polymerization using mixed amine system comprising 1,4-phenylene diamine and pipperazine. Separation performance of the membranes are studied as a function of the concentration of amine and acid chloride, the concentration ratio of the amines, nature of the acid chloride, and the presence of surfactant and acid acceptor in the aqueous reagent. The effect of esterification and hydrazide reactions involving residual carboxylic acid groups in the polymeric membranes on the co-polymeric composite membrane performance is also studied. The membrane performance can be tailored easily by conversion of the residual reactive functional groups in post-treatment.     

A Study on Triple-Membrane-Separator (TMS) Process to Treat Aqueous Effluents Containing Uranium

Abstract

An effective process incorporated with the novel membrane separation technology was developed to recover uranium from the filtrate effluent of uranium dioxide conversion processes. The prominent feature of the process is that it utilizes separation characteristics of three different types of membranes as follow: separation of uranium species from effluent of high fluoride content by ultrafiltration membrane, separation of uranium species from effluent of low fluoride content by reverse osmosis membrane, precipitation of uranium species with hydrogen peroxide, and filtration of uranium bearing precipitates by microfiltration membrane. The process is simple and feasible for treatment of liquid waste containing both soluble and suspended uranium species. The recovery of uranium can achieve 95% and the treated effluents meet the current environmental standards.     

Separation and Fractionation of Macromolecular Solutions by Ultrafiltration

Abstract

The present state-of-the-art of membrane ultrafiltration with reference to macromolecular fractionations is reviewed. Ultrafiltration is now a widely used technique, both in the laboratory and industrial applications, which stems from the development of asymmetric membranes followed by the recognition of the importance of fluid mechanical and mass transfer processes and their management through equipment design and fluid-flow practices. However, large-scale fractionation of macromolecular mixtures or solutions such as proteins has not yet been feasible. This inability is attributable to a number of factors, viz., concentration polarization and fouling processes which may also be coupled with limitations imposed by nonuniform pore size as well as protein–protein (solute) interactions, the latter being determined by the solution chemistry. It is now well recognized that boundary-layer and interfacial effects, in general, are extremely important in membrane applications, as evidenced by a number of manifestations. Several models have been put forward to explain the effects of concentration polarization, whereas membrane-fouling owing to solute-membrane interactions and membrane pore-obstruction or secondary membrane formation via macrosolute deposition, thus causing major changes in effective pore size distribution and therefore effecting inevitable changes in membrane characteristics, have hardly been considered in detail in ultrafiltration transport modeling. Nevertheless, the recognition of the importance of surface and colloid chemical phenomena in governing membrane performance has focused attention upon techniques of membrane modification and feed solution properties control as the key to ultrafiltration applications. These are particularly important for macro-molecular fractionations which depend upon a reasonably clear understanding of the mechanisms of the various processes and which emerge from a good deal of basic or fundamental research.     

Poisoning of Liquid Membrane Carriers in Extraction of Metal Ions

Abstract

In the extraction of desired metal (scandium, mixed rare earths) ions using chelating extractants (TTA, HDEHP) as liquid membrane carriers, the carriers will become poisoned owing to the presence of even minute quantity of certain high ionic potential ions in the feed solution. The reason for the poisoning of carriers is that those ions have so much greater affinity than the desired ions for the membrane carrier that the ion-carrier coordination compound cannot be stripped at the interior interface of the membrane and gradually no more free carrier transports any metal ions across the membrane. The calculated results are in agreement with the experiments, and methods to avoid the poisoning are given in the paper.     

Determination of Some Characteristic Parameters of Treated Cellophane Membranes

Abstract

Membrane potential, water permeation, and electrical resistance of a cellophane membrane treated with NaOH and HC1 solutions have been measured. Some membrane properties, such as permselectivity, hydraulic permeability, and fixed charge concentration in the membrane, were calculated. Variation of hydraulic permeability and the concentration of fixed charge in the membrane with temperature have been also studied. In order to determine the influence of treatment, membrane potentials were measured for a untreated and three differently treated cellophane membranes. A comparation of the fixed charge concentration and permselectivity for treated and untreated membranes was also made. Variation of perm selectivity with concentration was obtained.     

The Effect of Pulsatile Flows on the Transport Across Membranes: An Analytical and Experimental Study

Abstract

Pulsatile flows have shown to increase the permeation flux in reverse osmosis studies and to reduce fouling that exists in using membranes for separation processes. However, this study demonstrates that permeation from the inside of a hollow fiber with a membrane boundary to the outside decreases once pulsations are added to the inside of the membranes. The increase in the axial flux due to the flow pulsations are the reason for the increased permeation in reverse osmosis and the decrease in transport from inside to outside. An analytical model for a two‐dimensional system is presented along with experimental results in separating oxygen from air using polycarbonate based hollow fiber membranes.     

Effect of Plasticizer on Carrier-Mediated Transport of Zinc Ion through Cellulose Triacetate Membranes

Abstract

In practical applications of liquid membranes containing a mobile camer, three main types of membranes have been studied: liquid surfactant, supported liquid, and solvent polymeric membranes (2-6). In these membranes the solvent polymeric membrane which consists of a polymer film containing a plasticizer generally exhibits a low ionic permeability compared with the other types of membranes, although it has a high stability and durability. This is because the transference of the carrier in the membrane is depressed by its high viscosity and high electrical resistance. Accordingly, the ionic permeability may be improved by selecting an appropriate plasticizer.     

Studies of Ion Transport through a Liquid Membrane by Using Crown Ethers

Abstract

Studies on ion transport through a liquid membrane system composed of two extraction processes have been carried out. Kinetic models based on extraction processes with consideration of the controlled parameters were developed for mediated ion transport through liquid membranes, especially those using crown ethers as the ion carrier. A study of the concentration change in the receiving or source phase envisages the determination of the equilibrium constant by a kinetic method corresponding to the chemical reaction at the interface as well as the maximum initial flux through the membrane. The equilibrium constant values determined by the kinetic process were checked by the solvent extraction method.     

Opportunities for Membrane Technologies in the Treatment of Mining and Mineral Process Streams and Effluents∗

Abstract

The membrane separation technologies of microfiltration, ultrafiltration, nanofiltration, and reverse osmosis are suitable for treating many dilute streams and effluents generated in mining and mineral processing. Membrane technologies are capable of treating these dilute streams in order to produce clean permeate water for recycle and a concentrate that can potentially be used for valuable metals recovery. Membrane technologies can be utilized alone, or in combination with other techniques as a polishing step, in these separation processes. A review of potential applications of membranes for the treatment of different process streams and effluents for water recycling and pollution control is given here. Although membranes may not be optimum in all applications, these technologies are recognized in the mining sector for the many potential advantages they can provide.

     

Nanofiltration of Magnesium Chloride,Sodium Carbonate,and Calcium Sulphate in Salt Solutions

Abstract

Nanofiltration (NF) membranes have been employed in pre‐treatment unit operations in both thermal and membrane seawater desalination processes. This has resulted in reduction of chemicals used in pretreatment processes as well as lowering the energy consumption and water production cost and, therefore, has led to a more environmentally friendly processes. In order to predict NF membrane performance, a systematic study on the filtration performance of selected commercial NF membranes against brackish water and seawater is required. In this study, three commercial nanofiltration membranes (NF90, NF270, N30F) have been used to treat highly concentrated different salts solutions (MgCl₂, Na₂CO₃, and CaSO₄) at salinity level similar to that of brackish water and seawater. The main parameters studied in this paper are salt concentration and feed pressure. The experimental data were correlated and analysed using the Spiegler‐Kedem model. In particular, the reflection coefficient (σ) of all studied membranes and the solute permeability (P_s) have been determined for all membranes and at different salinity levels of studied salts. All the studied membranes fitted the model well for all investigated salts except the experimental data of MgCl₂ using N30F membrane, which did not fit well at low rejection. The results showed that NF90 produced a high rejection around 97% for all salts with medium permeate flux while NF270 gave a high flux with medium rejection and N30F gave low rejection and flux.     

Effect of Film Aging on the Pervaporation Properties of Latex Membranes

Abstract

Latex membranes have recently been investigated for their application in pervaporation separation processes. Acrylonitrile-butyl acrylate copolymer latex membrane showed selective permeation to water in pervaporation with water-ethanol mixtures. Different from solvent-cast membranes, the pervaporation properties of latex membranes were found to change with the membrane aging time or under different aging conditions. It is shown that aging leads to better membrane fusion, thus decreasing the permeation rate and increasing the separation factor. Aging the membrane in a medium which keeps the latex particle from good fusion would cause a high permeation rate but a low separation factor. Based on our observations, a comprehensive transport mechanism of the permeant through latex membranes during pervaporation is proposed.     

Suppression of Osmotic Distillation in Gas Membrane Processes

Abstract

Suppression of osmotic distillation of water is important for the commercial scale application of gas membranes. We have equalized the water vapor pressure on either side of the membrane by increasing the temperature of the stream with the lower water vapor pressure. The experimentally determined temperature gradient is many times larger than predicted from water vapor pressure–temperature data. The larger temperature gradient may be explained by considering the heat flux across the membrane. The economic viability of adjusting the temperature of the feed and strip streams to suppresses water vapor transport depends on the additional energy costs involved.     

New Matrix Materials for Molten Electrolyte Membranes

Abstract

An electrochemical flue gas desulfurization process has been developed and shown to remove 98+% of SO₂ from simulated flue gas (0.3% SO₂) by flow past an electrolyte-filled membrane. An applied electric field preferentially removes SO₂ and produces a concentrated by-product stream of SO₃. The only reagent required for the process is electricity; this permits the process to have favorable economics.

The electrolyte is retained by a matrix of inert powder which forms a membrane. The matrix is designed to retain the molten electrolyte and prevent electrode pore flooding; flooding reduces interfacial area and increases the electrical requirements. New membrane formulations have been tested for increased electrolyte retention; the preparation of membranes with borosilicate glass or zeolites as the matrix is presented. The capillary action of the zeolite is higher than that of the porous electrodes. This enables the process to operate with a higher mass transfer area, allowing higher current densities. Polarization is compared with that of a MgO-based membrane.     

Instability Mechanisms of Supported Liquid Membranes

ABSTRACT

Supported liquid membranes (SLMs) have the ability to selectively separate low concentrations of metal and other ions from solution, and are therefore suited to waste treatment and process recycling operations. However, their application has been limited by their low flux and limited life. The extraction of copper across a supported liquid membrane using Acorga P5100 as the carrier was investigated. The effect of membrane liquid composition, and in particular its rheology on membrane stability and mass transfer, is discussed and modeled. Membrane instability mechanisms are discussed with reference to the proposed model and its effect in relation to the design of membrane units.     

Application of Cr(VI) transport across the polymer inclusion membrane with calixresorcin[4]arene derivative as ion carrier

ABSTRACT

In this study, the experiments were performed to evaluate the Cr(VI) removal efficiency by transport across the polymer inclusion membrane with calixresorcin[4]arene derivative as ion carrier. The several influence factors such as carrier concentration, the amount of plasticizer in the membrane as well the effect of acid type and its concentration in source phase and the membrane stability were investigated. It was found that the immobilized calixresorcin[4]arene derivative in membranes effectively extracted chromium from acidic media. Under optimized conditions, the Cr(VI) removal efficiency was 98.4%.     

Conduction and Mass Transfer in Reinforced Cation Exchange Membranes

Abstract

The transport of sodium chloride and calcium chloride through two types of reinforced perfluorinated cation exchange membranes under an electrical field gradient was studied to determine the effect of calcium ion interferences to sodium ion migration. Electromigration-electroosmosis experiments were performed in a diaphragm cell. The concentration of all ions in each half cell was maintained constant by a feedback mechanism. For single salt experiments, the salt flux of calcium ions was half the salt flux for sodium ions. The water flux was higher for the membrane with the greater reinforcement. The effect of two cations competing for migration to the membrane matrix was studied by experiments utilizing a feedback mechanism for each cation. The flux ratio of sodium ions to calcium ions decreased as the concentration of calcium chloride was increased for experiments where the solutions contained mixtures of sodium chloride and calcium chloride.

The electrical conductivity of the membranes was measured using in a diaphragm cell having one movable electrode, allowing for resistance measurements at different path lengths. The resistivity for the membranes in solutions having only one cation was greater for calcium chloride solutions than for sodium chloride solutions. The resistivity of the more reinforced membrane was greater. For a mixture of sodium and calcium ions, as the calcium ion content decreased and the sodium ion concentration was held constant, an increase in resistivity was observed.     

Electrical Properties of Modified Aromatic Polyamide Membranes

Abstract

The effects of chemical structure on the values of different electrical parameters measured with novel aromatic polyamide (aramid) membranes were studied. Poly-(isophthalamides) containing pendant groups were considered since they can be transformed into dense membranes, suitable for the determination of characteristic transport parameters such as ion transport numbers, electrical resistances and capacitances. Measurements were carried out with the membranes in contact with different NaCl and MgCl₂ solutions. Results show that resistance values are strongly dependent on concentration, but membrane capacitance is almost constant for the whole range of concentrations studied (10^?3 < C(N) < 5 × 10²). The ionic permeabilities in the membrane were determined from membrane potential and resistance results. The presence of polar side substituents causes lower resistivity in modified polyamides compared with the unsubstituted parent, and the higher the polarity of the substitutent, the lower the resistivity. This trend is valid for both NaCl and MgCl₂ solutions.     

Carrier-Mediated Transport of Rare Earth Ions through Supported Liquid Membranes

Abstract

Fluxes of rare earth ions (Sc³⁺, Y³⁺, La³⁺, Sm³⁺, and Lu³⁺) across supported liquid membranes using mixtures of nitrophenyl octyl, heptyl, or phenyl ethers and tris(2-n-butoxyethyl) phosphate (TBEP) as solvents and some β-diketones as carriers were determined. The effects of membrane composition, pH of the source phase, and carrier concentration on the flux are demonstrated. The effect of membrane composition is further discussed from the values of the membrane potential and the viscosity and electrical conductivity of the solvents. A maximal flux of lanthanum is observed for the membranes by using mixtures consisting of equal volumes of the nitrophenol derivative and TBEP. The fluxes of the rare earths, except scandium, decrease rapidly with decreasing pH difference between the source and receiving phases. The difference in flux among the rare earths, except scandium, is small. The flux increases in the carrier order benzoyl- > thenoyl- > furoyltrifluoroacetones. The lanthanum flux is proportional to the carrier concentration.