Selection Of Membrane Material Research Articles

Research on Polyvinylidene Fluoride Hollow Fiber Hemodialyzers

Hemodialysis is the main treatment of acute and chronic renal failure, and the selection of hemodialysis membrane materials is the key factor that determines the curative possibilities. By changing the membrane forming conditions, we have spun polyvinylidene fluoride (PVDF) hollow fiber membranes with the same inner diameters but different wall thicknesses. Via centrifugal moulding, we have also made membranes into dialyzers to study the mechanical performance of the membranes and the dialysis performance of the dialyzers. The results show that the mechanical performance meets the demand of dialysis. For the dialyzers with 30μm fiber walls, the clearance rates of urea and lysozyme are 90% and 75% respectively, and the rejection rate of bovine serum albumin (BSA) comes to 90% plus. The increase of the mass content of the dope solution polyethylene glycol (PEG) from 19% to 22% decreases the rejection rate of BSA.

Removal of Pesticides by Polymer Membranes

Nanofiltration membranes attract attention to take a role of the high performance purification of water. The purification processes with a little energy consumption are enabled by the selection of membrane materials and driving conditions.

Research progress of vanadium redox flow battery for energy storage in China

Principle and characteristics of vanadium redox flow battery (VRB), a novel energy storage system, was introduced. A research and development united laboratory of VRB was founded in Central South University in 2002 with the financial support of Panzhihua Steel Corporation. The laboratory focused their research mainly on the selection and preparation of electrode materials, membrane material and modification, stable concentrated electrolyte producing approach, test cell configuration design and optimization. Some relevant foundation problems, such as state of vanadium in sulfurous acid with various additives, the difference of electrochemical reaction rate in anode and in cathode, the crossover of vanadium ions and so on, have been emphasized. The details of these studies have been given and discussed. A 5 kW VRB stack was fabricated in the laboratory and its performances, especially electrochemical performance such as voltage efficiencies, energy efficiencies, and durability, were fully tested. The results will be shown in the talk. The key technologies of developing VRB, such as to improve the activity of its electrode materials, the stability of electrolyte and selectivity of separator, were also discussed. In addition, the research progresses in other laboratories in China were briefly introduced.

Introduction to membranes: Membrane selection

In the second of a series of articles, Graeme Pearce looks at the factors influencing selection when choosing membranes working with water and wastewater, aiming to provide an understanding of the factors which influence the selection of membrane material for commercial products

Layer-by-Layer Assembled Semipermeable Membrane for Amperometric Glucose Sensors

The performance of implantable glucose sensors is closely related to the behavior of the outer membrane. Such membranes govern the diffusion characteristics of glucose and, correspondingly, the sensitivity of the sensors. This manuscript discusses the selection of various membrane materials and their effect on the device response. Sensors were fabricated utilizing a 50-microm platinum wire followed by immobilization of the glucose oxidase (GO(X)) enzyme. Sequential adsorption of various ionic species via a layer-by-layer process created devices coated with bilayers of humic acids/ferric cations (HAs/Fe(3+)), humic acids/poly(diallyldimethylammonium chloride) (HAs/PDDA), and poly(styrene sulfonate)/poly(diallyldimethylammonium chloride) (PSS/PDDA). The in vitro amperometric response of the sensors was determined at 0.7 V vs an Ag/AgCl reference electrode in phosphate-buffered saline (37 degrees C) for various glucose concentrations. The diffusion coefficients of glucose and hydrogen peroxide (H(2)O(2)) through these membranes were calculated and analyzed. Outer membranes based on the sequential deposition of bilayers of HAs/Fe(3+), HAs/PDDA, and PSS/PDDA were grown successfully on immobilized layers of GO(X). The amperometric response and reversibility upon changing the in vitro concentration of glucose were investigated. Through alteration of the number of bilayers of the outer membrane, it was possible to modulate the diffusion of glucose toward the sensor as a result of its flux-limiting characteristics. Semipermeable membranes based on five HAs/Fe(3+) bilayers exhibited a superior behavior with a minimum hysterisis response to glucose cycling and a lesser current saturation at hyperglycemic glucose concentrations because of a more balanced inward diffusion of glucose and outward diffusion of H(2)O(2).

Effect of Film Thickness on the Gas-Permeation Characteristics of Glassy Polymer Membranes

Films made from three glassy polymerspolysulfone, poly(2,6-dimethyl-1,4-phenylene oxide), and a commercial polyimide known as Matrimidwere prepared in thicknesses ranging from 0.4 μm to 60 μm, and their permeabilities to oxygen, nitrogen, and methane were monitored for more than a year. These films exhibited substantial decreases in permeability with time, because of volume relaxation that is due to physical aging, which is a reversible process. The observed permeability coefficients were originally greater than the literature values for thick, or so-called “bulk” films, but eventually decreased well below these values. The rate of the aging effect becomes greater the thinner the film. The implications of this observation for practical membrane gas separation processes and the selection of membrane materials based on thick film data are discussed.

Material Aspects of the Design and Operation of Direct Borohydride Fuel Cells

AbstractThe direct borohydride fuel cell (DBFC) has attracted increasing interest as a potential high power source for mobile and portable applications. Engineering design plays an important role in the development of the DBFC. This paper reports data for the selection of anode, cathode, and membrane materials for the DBFC. The best DBFC performance is achieved with a Au anode, a Pt cathode, and a 3541P ion exchange membrane. The use of non‐precious catalysts, e.g., Ag, leads to promising results.

Selection of membrane materials for separation of H2-containing mixtures: Database analysis

Correlation between the chemical structure and transport characteristics of polyimides that are used for separation of hydrogen-containing mixtures is analyzed. The effect of various functional groups (keto-, oxy-, methoxy-, amino-, and others) in polyimides is considered in detail. The group-contribution method is demonstrated to be efficient for prediction of the transport properties of new polyimides and for the search for new promising diamine-dianhydride combinations. The empirical analysis of the database accumulated at the Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, confirms the perspectiveness of further investigations of new membrane materials for separation of H2-CH4 and H2-CO gas pairs.

Selection and crosslinking modification of membrane material for FCC gasoline desulfurization

Selection and modification of membrane material is important fundamental research for fluid catalytic cracking (FCC) gasoline desulfurization by membrane process. Solubility parameters of FCC gasoline components and typical polymeric membrane materials were calculated and given out. For thiophene species, which are the primary ones in FCC gasoline, solubility parameters were about 19–21 (J/cm 3) 1/2, while about 14–15 (J/cm 3) 1/2 for most hydrocarbon species in FCC gasoline. The distinct difference in solubility parameter between the two typical species was just the key to fulfill the separation. By the study and analysis of solubility parameter theory, pervaporation (PV) performance and membrane preparation, polyethylene glycol (PEG) was determined as the promising membrane material for gasoline desulfurization. In spite of its desulfurization capacity, PEG needs modification for its easier swelling and unstable PV performance. According to the comparison on PV performance of PEG before and after modification as well as the swelling experiments, crosslinking was an effective modification way for PEG membrane applied in gasoline desulfurization. After crosslinking, not only the sulfur enrichment factor increased distinctly, but also the membrane performance was stable which was the most important point for practical application. Sulfur enrichment factor increased with the increase of amount of crosslinking agent and crosslinking time, while total permeation flux decreased. Unfavorable results occurred with exorbitant crosslinking resulted form excessive crosslinking agent and overlong crosslinking time. Since sulfur enrichment factor was for key consideration, 16% of crosslinking agent amount and 60 min of crosslinking time were more practical.

Prediction of Activities of Small Molecules in Polymer Membrane Materials Using the Group Contribution Equation of State

Estimation of the activities or solubility of small molecules in polymers is essential in a number of process applications such as the mixture separation by polymeric membrane, polymeric membrane preparation, polymer preparation, especially, the selection of membrane material for a predefined separation process. The VTPR EoS-GE group contribution model has been used to predict the activities of water, alkane, and aromatic small molecules in poly(vinyl alcohol), poly(dimethyl siloxane), and polyisobutylene polymeric membrane materials. The influence of temperature and the molar mass of polymer on the activities of small molecules in the polymeric membrane are discussed. It has been shown that the results predicted by the VTPR EoS-GE model are good agreement with the experimental ones, and the total average deviation between the experimental and the calculated is no more than 3%. It should be expected that the VTPR EoS-GE group contribution model could be applied to the polymeric membrane material selection, to the polymeric membrane preparation processes and to the polymeric material preparation processes.

Influence of the filtration modes on colloid adsorption on the membrane in submerged membrane bioreactor

The influence of three different filtration modes on the colloid adsorption in a submerged membrane bioreactor (SMBR) was evaluated and the feasibility for the characterization of the colloid adsorption on the membrane using a modified Freundlich isothermal adsorption equation q e = X / A = a C e 1 / n was also explored in this study. Under the same operating conditions, the adsorption equations determined in this study were 0.519 C e 1.1623 , 7.416 C e 0.7305 and 2.590 C e 1.0449 for modes of vacuum pump dragging with air back washing, vacuum and suction pumps dragging without air back washing, respectively. Compared with the filtration mode of suction pump or vacuum pump dragging without air back washing, the mode of 10 min vacuum pump dragging with 5 min air back washing could reduce the colloid adsorption. The results also demonstrated the modified Freundlich isothermal adsorption equation, q e = X / A = a C e 1/ n , was applicable to characterize the colloid adsorption on the membrane in the SMBR. Except the characterization of colloid adsorption, this approach also could be used for the optimization of operational conditions, the selection of membrane materials and the evaluation of module configuration, consequently alleviating the membrane fouling in a SMBR.

The use of ultrafiltration for treatment of spent solventcleaning rinses from nickel-plating operations: membrane material selection study

Solvent-resistant hollow-fiber OF membranes were selected by measurement of fiber swelling and treatability studies on spent solvent cleaning rinse. The experimental results indicated that the membranes made of both cellulose acetate (CA) and polyacrylonitrile (PAN) materials could tolerate the solvent present and were suitable for treating the spent solvent rinses, whereas polyethersulfone and polysulfone membranes were not suitable. The CA membrane had the lowest fouling tendency when treating the spent solvent rinse. The results also showed that retentions of the emulsified solvent and oil-grease for the CA membrane were above 96% and 80%, respectively, and the PAN membrane had better retention than the CA membrane. It was hypothesized that there might be a critical micellar concentration for oil-grease for the PAN membrane.

Aroma compounds recovery of tropical fruit juice by pervaporation: membrane material selection and process evaluation

In the present work, aroma recovery of tropical fruit juice by pervaporation process was investigated using model solutes and different kinds of composite membranes. As feed solution, binary and quaternary synthetic aqueous solutions were used, as well as the single strength and the clarified pineapple juices. Composite membranes (flat or hollow fiber), prepared in laboratory or commercial ones, were used for comparison. The water permeability and the overall mass transfer coefficient for each organic solute were determined. The experimental pervaporation results were used as input for a simulation of a permeation unit, allowing a preliminary comparison of the different membranes investigated. Experimental and simulation results indicated that EPDM membranes presented the best performance.

Theoretical formulation of the diffusion through a slab—theory validation

A new theoretical approach to diffusion through a slab and its convection out of the slab is developed. The resulted general model is based on the following assumptions. The transport is a one-dimensional. The diffusion coefficient, the membrane thickness and the temperature are constants. The fluxes in or out of the slab are proportional to concentration differences at the slab interfaces with the concentrations in the two volumes of both sides of the slab. No restrictions are set on the size of the two volumes, on the solute concentrations either in the slab or in the two volumes, as well as on the stirring intensity (natural to perfect forced convection) of the solutions in the two volumes. The formulation in general is exact, except the initial condition. It has been approximately satisfied using the residual approximation method. The general model is validated by its reduction to special cases covering the whole range of its parameters. The general model is reduced to existing analytical studies and well agrees to existing data covering other parts of the parameter ranges. The generality of the model is useful in a wide variety of applications such as separation technology, conducting diffusion experiments, membrane material selection, packaging, pharmaceutical and agricultural applications, as well as other applications which obey the above restrictions underlying the general model.

Membrane based electrostatic precipitation

Legislation from the US EPA aimed at governing the release of particles smaller than 2.5 mm into the atmosphere will have a major impact on coal-fired power plants across the USA. Researchers lead by Professor Hajrudin Pasic at Ohio University have come up with a unique design for wet and dry electrostatic precipitators (ESP) that relies on membrane technology to efficiently capture small particles. In this article, some recent results related to particle collection and removal efficiencies, selection of membrane materials and other relevant issues, as well as comparisons with existing ESP technologies are presented.

Preparation of a bioartificial kidney using tubular epithelial cells, and an evaluation of Na+ active transport and morphological changes

We intend to develop a bioartificial kidney using tubular epithelial cells and artificial membranes, and to evaluate the reabsorptive function of the confluent layers. Madin-Darby canine kidney (MDCK) cells were cultured on a nucleopore polycarbonate membrane for up to 4 weeks after confluence to examine the influence of culture period on their properties, such as the localization of Na+/K+-ATPase and active Na+ transport. The results were as follows. Ouabain-sensitive Na+ active transport declined at 3 to 4 weeks after confluence in each matrix. The localization of Na+/K+-ATPase indicated depolarization in the cell membrane 3 to 4 weeks after confluence. Prolongation of the culture period increased the formation of an upheaving cell mass after the formation of the confluent monolayer. Scanning electron microscopy revealed fewer microvilli and more flat cells after 3 to 4 weeks of confluency. We conclude that the decline of Na+ active transport in the MDCK cells was due to both the formation of multilayers and a decline of cell function throughout the long period of culture following the formation of the confluent monolayers. Further study for selection of membrane material, the extracellular matrix, and species of cells should be continued.

Strategy for Selection of Composite Membrane Materials

A method to identify polymers that are potentially useful for membrane separations has been developed by examining gas chromatography (GC) retention data. Promising stationary phases were identified, and polymers with similar structures were obtained and deposited into inorganic supports. Polymers were identified to separate ketones and alcohols from hydrocarbons. The polymer/inorganic composite membranes synthesized for this research were characterized by IR spectroscopy and scanning electron microscopy. Favorable fluxes and high separations factors were achieved for several composite materials.

Liquid Separation by Membrane Pervaporation: A Review

Pervaporation is one of the most active areas in membrane research, and the pervaporation process has been shown to be an indispensable component for chemical separations. In this paper, the recent development in pervaporation membranes and pervaporation processes is reviewed, and some outstanding questions involved in membrane pervaporation are discussed with emphasis on the following issues: mass transport in the membrane, membrane material selection, concentration polarization in the boundary layer, pressure buildup in hollow fiber membranes, asymmetric and composite membranes, and the activation energy for permeation. We attempt to provide insight into this dynamic field and to highlight some of the outstanding problems yet to be solved or clarified.

Aqueous—organic membrane bioreactors. Part I. A guide to membrane selection

The influence of membrane pore structure on the ease with which an aqueous-organic interface can be maintained in the plane of the membrane of a two-phase membrane reactor is discussed. Four factors affecting the pressure required to cause breakthrough of the non-wetting phase have been identified: (i) membrane pore size, (ii) asymmetry of membrane pore structure, (iii) the placement of the wetting liquid when an asymmetric membrane is used, and (iv) a change in the wetting characteristics of the membrane as the reaction progresses. The fourth factor is particularly important since two phase biocatalytic reactions frequently involve surface active reactants and/or products. It is shown that the ideal pattern of surfactant-membrane interactions - which is reflected by the desired direction of change in the angle of contact between the wetting liquid and the membrane - depends on the second and third factors. An experiment is suggested to assess the importance of the various factors and a set of rules of thumb have been presented to assist in the selection of membrane material and type. The importance of correctly identifying the wetting liquid when an amphiphilic membrane polymer is used has been pointed out.

A Simple Method for Prediction of Gas Permeability of Polymers from Their Molecular Structure

A method for the prediction of gas permeabilities (P) through polymers from their chemical structure has been developed on the basis of the ratio of molar free volume to molar cohesive energy, V(f)/E(coh). The permeation of small gas molecules through polymer membranes is dependent on the chain packing density measured by V(f) and segmental motion of polymer chains measured by E(coh). But no simple relationship between P and V(f) or E(coh) alone was found. The permeability data of more than 60 polymers covering 7 orders of magnitude for six gases have been treated with linear regression analysis. All plots of log P vs. V(f)/E(coh) gave good straight lines. It is also found that a linear relationship holds when plotting both the intercepts and slopes of log P vs. V(f)/E(coh) lines against square of the diameters of gas molecules. Therefore, the permeabilities of all the non-swelling gases through a great variety of polymers can be estimated using two correlations above. Moreover, this method is more accurate than others in the literature and may found useful for the selection of gas separation or barrier membrane materials.