Types Of Membrane Materials Research Articles

Performance Improvement of Membrane Stress Measurement Equipment through Evaluation of Added Mass of Membrane and Error Correction

One of the most important issues in keeping membrane structures in stable condition is to maintain the proper stress distribution over the membrane. However, it is difficult to determine the quantitative real stress level in the membrane after the completion of the structure. The stress relaxation phenomenon of the membrane and the fluttering effect due to strong wind or ponding caused by precipitation may cause severe damage to the membrane structure itself. Therefore, it is very important to know the magnitude of the existing stress in membrane structures for their maintenance. The authors have proposed a new method for separately estimating the membrane stress in two different directions using sound waves instead of directly measuring the membrane stress. The new method utilizes the resonance phenomenon of the membrane, which is induced by sound excitations given through an audio speaker. During such experiment, the effect of the surrounding air on the vibrating membrane cannot be overlooked in order to assure high measurement precision. In this paper, an evaluation scheme for the added mass of membrane with the effect of air on the vibrating membrane and the correction of measurement error is discussed. In addition, three types of membrane materials are used in the experiment in order to verify the expandability and accuracy of the membrane measurement equipment.

Fabrication of COF-MOF Composite Membranes and Their Highly Selective Separation of H2/CO2.

The search for new types of membrane materials has been of continuous interest in both academia and industry, given their importance in a plethora of applications, particularly for energy-efficient separation technology. In this contribution, we demonstrate for the first time that a metal-organic framework (MOF) can be grown on the covalent-organic framework (COF) membrane to fabricate COF-MOF composite membranes. The resultant COF-MOF composite membranes demonstrate higher separation selectivity of H2/CO2 gas mixtures than the individual COF and MOF membranes. A sound proof for the synergy between two porous materials is the fact that the COF-MOF composite membranes surpass the Robeson upper bound of polymer membranes for mixture separation of a H2/CO2 gas pair and are among the best gas separation MOF membranes reported thus far.

Correlation of bioelectrical impedance analysis phase angle with changes in oxidative stress on end-stage renal disease patients, before, during, and after dialysis

Chronic kidney disease is a condition that promotes oxidative stress. There are conflicting evidence about the role of hemodialysis on oxidative stress, that are mostly related with the various types of membrane materials used, the quality and type of dialysate, the method used, etc. The phase angle (PhA), which is determined with bioelectrical impedance analysis (BIA), measures the functionality of cell membranes. In this study, the correlation of the PhA with parameters of oxidative stress is attempted for the first time. We evaluated parameters of oxidative status as total antioxidant capacity (TAC) in erythrocytes (RBCs) and plasma of patients with ESRD undergoing hemodialysis with low flux synthetic polysulfone membranes. Measurements were recorded from 30 patients (16 men and 14 women) aged 64 ± 14 years before, during, and after dialysis, and in 15 healthy volunteers aged 56 ± 12 years The PhA was obtained by BIA. The plasma TAC increased significantly (41%, p < 0.05). Intracellular TAC noted a non-significant increase. Total antioxidant capacity of the patients before and after hemodialysis was significantly lower from the healthy volunteers (p < 0.05) showing that ESRD patients are at the state of increased oxidative stress. The PhA increased in significantly positive correlation with plasma TAC at the end of hemodialysis. The process of hemodialysis with biocompatible synthetic membranes and bicarbonate dialysate improved plasma TAC. The positive correlation of PhA with extracellular TAC could evolve to a method of oxidative stress estimation by BIA but further research is needed.

Deformation of an elastic capsule in a uniform electric field

The deformation of a thin elastic capsule subjected to a uniform electric field is investigated in the Stokes flow regime. The electrohydrodynamic flow is analyzed using a perfect conductor and a perfect dielectric model for the capsule and the fluid phase, respectively. A theoretical analysis is carried out using an asymptotic expansion in the electric capillary number (Ca) (a ratio of the electric stress to the elastic tension) in the small deformation limit using the finite deformation Hooke’s law. The analysis is used to determine the elasticity of polysiloxane capsules suspended in oil, the deformation of which is obtained using videography. The boundary element method is implemented to seek numerical solutions to the hydrodynamic, elastic, and electrostatics equations. The finite deformation Hooke’s law, the Mooney-Rivlin, and Skalak’s model for elasticity are employed. The effect of electric capillary number, unstressed geometry, and the type of membrane material on the deformation of a capsule is presented in the high Ca number limit using numerical simulation. Capsules synthesized with higher monomer concentration displayed electric stress induced wrinkling process at high electric field strengths. Burst of a capsule is characterized by poration of the polymer membrane, which could be symmetric or asymmetric at the two poles, depending upon the value of the capillary number. The results should be useful in understanding the response of elastic capsules such as red blood cells and polymerized membranes, to an electric field, in applications such as electrodeformation and electroporation. It also provides a theoretical framework for a possible way of determining the elastic parameters of a capsule.

Cellulose membranes are more effective in holding back vital proteins and exhibit less interaction with plasma proteins during hemodialysis

The vast majority of patients with end-stage renal disease are treated with intermittent hemodialysis as a form of renal replacement therapy. To investigate the impact of hemodialysis membrane material on vital protein removal, dialysates from 26 well-characterized hemodialysis patients were collected 5min after beginning, during 5h of treatment, as well as 5min before ending of the dialysis sessions. Dialysis sessions were performed using either modified cellulose (n=12) (low-flux and high flux) or synthetic Polyflux (n=14) (low-flux and high-flux) dialyzer. Protein removal during hemodialysis was quantified and the dialysate proteome patterns were analyzed by 2-DE, MS and Western blot. There was a clear correlation between the type of membrane material and the amount of protein removed. Synthetic Polyflux membranes exhibit strong interaction with plasma proteins resulting in a significantly higher protein loss compared to modified cellulosic membrane. Moreover, the proteomics analysis showed that the removed proteins represented different molecular weight range and different functional groups: transport proteins, protease inhibitors, proteins with role in immune response and regulations, constructive proteins and as a part of HLA immune complex. The effect of this protein removal on hemodialysis treatment outcome should be investigated in further studies.

TANGENTIAL FLOW MICROFILTRATION OF THERMUS AQUATICUS YT-1 LYSATE

The tangential flow microfiltration of Thermus aquaticus YT-1 lysate was investigated. Two membranes of different pore diameter – 0.2 μm PES and 0.65 μm PVDF – were compared. The optimal transmembrane pressure at different flow rates for both membranes was determined. Parameters such as flux through membrane, retention coefficients, rate constants and yields of nucleic acids, polysaccharides, proteins and product Taq DNA polymerase were evaluated. The flux of 0.2 μm pore diameter membrane was shown to be 1.35 times higher as compared with the 0.65 μm pore diameter membrane. A comparison of Taq DNA polymerase yield has revealed the majority of the product to flow through the membrane, but the highest yield of the product (96.3 ±3.7%) has been obtained with the 0.2 μm pore diameter membrane. The type of membrane material was shown to influence the performance of the process. It has been concluded that the 0.2 μm pore diameter membrane is suitable for the clarification of Thermus aquaticus YT-1 lysate. DOI: http://dx.doi.org/10.5755/j01.ct.59.1.1530

ChemInform Abstract: Autotrophic Nitrogen‐Removing Biofilms on Porous and Non‐Porous Membranes

AbstractReview: 59 refs.

Design Consideration of Membrane Structure for Thermal Actuated Micropump

Movable thin film membrane is one of the crucial part in a thermal actuated micropump development that acts as actuator to control the fluid flow. The working principle of this device is due to pressure exchange produced by thermal expansion of air in an isolated chamber. In this paper a deformation analysis of actuator membrane deposited on silicon substrate using Finite Element Analysis (FEM) is reported. The analysis is aimed to study the mechanical and physical behavior of the actuator structure. Parameters such as shape, size, dimension, material and thickness of the membrane are studied to find the optimum design. Correlation between the pressure and membrane structure are also observed. Simulation results show that circular membrane shape gives the largest deflection due to the lowest stress on its edges compared with other shapes of membrane at the same pressure. It is also found that membrane deformation decreases with the increasing of the thickness. However, only suitable deformation will be chosen for the pump application due to the limited chamber space. Comparisons at four types of membrane materials in this analysis indicate that polyimide has the largest deflection. Furthermore, polyimide shows the best capability to handle very hot temperatures since its melting point is very high. It is also elastic, robust and easy to fabricate. From the results, an appropriate membrane parameter selection are important in designing the thermal actuated micropump.

Autotrophic nitrogen‐removing biofilms on porous and non‐porous membranes

The effective removal of nitrogen compounds from wastewater has become a critical issue for treatment plants as the awareness of their negative impact on the environment increased. Autotrophic nitrogen removal has become an interesting alternative to the more conventional heterotrophic processes, as it eliminates the need for an organic carbon addition to the source water and reduces biomass yields. Gas transfer membrane biofilm reactors (MBfR) for nitrification and hydrogen driven denitrification are of special interest as they combine membrane diffusers and biofilms, provide an efficient supply of necessary electron donor for autotrophic removal of ammonia and nitrate, extend solids retention times and retain biomass within the reactor. Subsequently, a wide range of MBfR, which vary based on the type of membrane material and membrane module configuration, are being tested for this purpose. This paper reviews the research to date and also discusses the challenges that still lay ahead before MBfR can be used at treatment plants.

Membrane contactor as a novel technique for separation of iron ions from ilmenite leachant

A novel system based on membrane contactor was applied for separation of iron ions during leaching of ilmenite ore in hydrochloric acid. Separation of iron would enhance leaching of ilmenite and leads to pure titanium products. The used membrane contactor cell consisted of two identical compartments separated by a porous flat sheet membrane. The ilmenite leachant was separated from the residue and placed in one compartment (marked as feed side) and an organic solution containing a selective iron extractant was placed in the other compartment (marked as receive side). Among the several tested organic extractants, trioctylamine (TOA) was found to be effective and selective for extraction of iron ions from solutions of a wide range of hydrochloric acid concentrations. TOA in kerosene and 10% 1-octanole was used as a receive phase in the membrane contactor cell. Two types of membrane materials were tested; polytetrafluoroethylene (PTFE) and polypropylene (PP) with almost similar pore sizes of about 0.5 μm. Multi separation stages by the membrane contactor were applied by replacing the receiving solution with a fresh one after 180 min of separation time. High Fe removal efficiency of about 86% after 4 separation stages using 0.2 μm PP membrane was obtained. The transport mechanism of iron was proposed mainly based on ionpair (R 3NH +FeCl 4 −) formation in the aqueous–membrane interface and its diffusion to the organic pulp through the membrane. The separation of the aqueous and organic solutions by a membrane in this contactor technique overcame the common drawbacks of the solvent extraction such as losses of the organic reagent, emulsion formation and delay of phase separation. In other procedures, the ilmenite slurry suspension was placed as it is in the feed side of the cell to test the possibility of the continuous separation of iron during leaching. The Fe removal efficiency was found to be very low (8% after 3 h) due to fouling of the membrane. A brownish precipitate was observed on the feed side of the membrane and was growing by time leading to slowing down of the Fe transport rate. Thin Film XRD test of membrane fouling showed that Goethite α-FeO(OH), Feroxyhyte ō-FeO(OH) and iron oxy chloride (FeOCl) are the main constituents of the precipitate. In addition, SEM photomicrographs showed that the precipitated particles on the membrane surface are sphere in shape with size ranged from 1 to 2 μm.

Highly selective sulfonated polyethersulfone (SPES)-based membranes with transition metal counterions for hydrogen recovery and natural gas separation

Two types of SPES polymers with different degrees of sulfonation (DS) were synthesized by adjusting the used amount of chlorosulfonic acid and confirmed via elemental analysis and XPS in this work. TGA degradation curves show a difference in the thermal stability between the PES and SPES polymers due to the graft of sulfonic groups. The SPES-H membranes with different DS values were fabricated using a solution-casting method and their gas separation results exhibit a decrease in the permeability and an increase in the selectivity with increasing the degree of sulfonation because of the effect of electrostatic crosslinking. Novel transition metal counterions (i.e. Ag + and Zn 2+) were applied to conduct the ion-exchange treatment of SPES-H polymer samples to change the affinity properties of some specific penetrants in the membrane. EDX data confirm the nearly complete replacement of the proton in the SPES-H sample by metal counterions. The SPES membrane containing Zn 2+ exhibits the best gas separation performance in this study due to a combination of the strong electrostatic crosslinking and the affinity between Zn 2+ and some specific gas molecules (e.g. O 2 and CO 2). Compared to flat dense PES membranes, the SPES membrane containing Zn 2+ exhibits impressive permselectivity increments of approximately 140%, 86%, 18% and 57% for He/N 2, H 2/N 2, O 2/N 2 and CO 2/CH 4 gas pairs, respectively. Both CO 2-induced plasticization tests and CO 2/CH 4 mixed gas measurements have been carried out to examine the applicability of these newly developed SPES membranes with different ion forms in industry. Results prove that this type of membrane material is a promising candidate for hydrogen recovery and natural gas separation.

Power loss and its effect on fuel cell performance

Fuel cell performance and the power are influenced by factors referred to as “power loss”. In fuel cells, there are two kinds of power losses: one is dominated by the electric resistance between the electrodes, which is called as leak resistance, and the other is dominated by mass diffusion between the anode and cathode, i.e. “crossover”. In this work, we analyse the two kinds of power losses and discuss how they influence fuel cell performance. The power loss of a fuel cell caused by crossover is described by a new parameter P leak. The practical performance curve of direct methanol fuel cells using different types of membrane materials are modelled by a mathematical equation describing the power loss and crossover effect. This equation is used to estimate the methanol crossover flux.

Methodology for accelerated pre-selection of UF type of membranes for large scale applications

This paper describes two assessment methods for UF type of membranes for large-scale applications. The combination of those two methods results in quite clear and unambiguous answers to the question what membranes are of interest for long-term testing. With the first method, calld dead-end filtration method, information is generated on the suitability of the membrane and on the combination of the membrane material, the module hydraulics and assembly. With this method the evolution of TMP is monitored upon filtration cycles of 20 minutes with raw water at a flux rate of 120 l/h.m 2, alternated with backwash cycles with permeate of 40 seconds at 1.2 bar negative TMP. The second method, called cross-flow filtration method, gives exclusively information on the suitability of the membrane material. This is being done by the measurement of the absolute value of the so-called “plateau fluxes” in cross-flow mode at 0.2 m/s linear velocity. For this purpose raw water concentrates are being used. Three “open” UF type of membranes, all three in hollow fibre configuration were assessed with these two methods. It was shown that the PSf based membrane (Koch PM100) reached already after 4 filtration cycles a TMP of 1 bar and showed the lowest plateau flux (25 l/h.m 2). This indicated that the membrane suffered from interaction with the raw water. Moreover, it is possible that something was wrong with the hydraulics of this membrane. The two other membranes were PES/PVP based. These membranes showed much less TMP increase over time. The first membrane of this type was X-Flow UFC, the second Stork Friesland Superfil 015-010. It was no problem to operate the first membrane for 18 hours without addition of chemicals for cleaning. The second membrane reached the maximum allowed TMP of 1 bar after 16 hours of operation at the end of the filtration cycle. Moreover, for both membranes a higher plateau flux value (35 l/h.m 2) was found. Both observations indicate that this type of membrane material is much more interesting than PSf. It was also shown the X-Flow membrane gives the lowest absolute TMP values, which is attributed to its higher pure water permeability (740 l/h.m 2.bar) as compared to the Stork Friesland membrane (pure water permeability of 350 l/h.m 2.bar) and the Koch membrane (pure water permeability of 290 l/h.m 2.bar). A last observation was a TMP increase of only 0.1 bar per cycle for the X-Flow membrane, as compared to 0.2 bar for the two others. This observation is in agreement with earlier made FESEM pictures of the inner surfaces. This means that the X-Flow membrane rather acts as a depth filter, whereas the two other membranes act as a surface filter.

Membrane bioreactors for waste gas treatment

This review describes the recent development of membrane reactors for biological treatment of waste gases. In this type of bioreactor gaseous pollutants are transferred through a membrane to the liquid phase, where micro-organisms degrade the pollutants. The membrane bioreactor combines the advantages of membrane devices with the clean technology of biological air purification. Two types of membrane materials can be used for gas–liquid contact: hydrophobic microporous material and dense material, such as silicone rubber. Microporous material generally has a higher permeability, but dense membranes can be advantageous in the case specific selectivity is required. Biomass is generally present as a biofilm on the membrane, but may also be suspended in the liquid phase. In a number of cases the reactor performance appears to be hampered by an unstable biofilm performance and/or by clogging of the liquid channels due to excess biomass formation. So far, membrane bioreactors for waste gas treatment have only been tested on laboratory scale. If the long-term stability of these reactors can be demonstrated, we expect membrane bioreactors to be useful tools in the treatment of gas streams containing poorly water-soluble pollutants and highly chlorinated hydrocarbons, which are difficult to treat with the conventional methods for biofiltration.

Effects of Ultrafiltration Membrane Composition

In a study of the dead‐end ultrafiltration (UF) of an untreated surface water, the effects of different membrane materials and molecular‐weight cutoffs (MWCOs) were evaluated in terms of the removal of total organic carbon (TOC) and turbidity, the development of permeate flux, and the flux recovery after backflushing. Removal of TOC was about 40 percent, independent of the membrane MWCO values investigated. Turbidity removal greater than 98 percent was found for all membranes tested. The rate of flux decline and the magnitude of flux recovery were, however, found to vary significantly, dependent primarily on the type of membrane material. The study showed that a large fraction of organic matter found in surface water should pass through typical UF membranes and that one of the primary technical considerations in using these membranes should be the selection of membrane material.

Effect of dialyzer geometry on granulocyte and complement activation.

During hemodialysis with cuprophan membranes, the complement system as well as leukocytes become activated. In order to clarify the role of dialyzer geometry, the effect of hollow-fiber versus flat-sheet dialyzers and of different surface areas on C3a generation and leukocyte degranulation was investigated. Plasma levels of leukocyte elastase in complex with alpha 1-proteinase inhibitor were significantly increased after 1 h (+55%) and 3 h (+62%) of hemodialysis with flat-sheet dialyzers as compared to hollow-fiber devices. In addition, plasma levels of lactoferrin, released from the specific granules of leukocytes during activation, were significantly higher (+42%) 3 h after the onset of dialysis treatment with flat-sheet than with hollow-fiber dialyzers. With respect to surface area, larger dialyzers tended to cause more release of leukocyte elastase as compared to dialyzers with smaller surface areas, irrespectively of the configuration of the dialyzer used. On the other hand, activation of the complement system, as measured by the generation of C3a-desarg, did not differ with both types of configurations. The same held true for leukopenia, which was almost identical for hollow-fiber and flat-sheet dialyzers. From these findings two lines of evidence emerge: First, not only the type of membrane material used in a dialyzer may influence its biocompatibility, but the geometry of the extracorporeal device also determines the degree of compatibility. Hence, the extent of leukocyte activation correlated with both configuration of the dialyzer and surface area of the membrane.(ABSTRACT TRUNCATED AT 250 WORDS)

Ion-Selective Electrodes

I. INTRODUCTION AND SCOPE The term 'ion-selective electrodes' is applied to a range of membrane electrodes which respond selectively toward one (or several) ionic species in the presence of others. The less-preferred term 'ion-specific' is not favored1 because these electrodes are rarely specific in their response to one ionic species over others, although this is a desirable property sought by the designer of new electrodes. The description membrane is used here in its broadest sense to denote a thin section of electrically conducting material separating two solutions and across which a potential develops. Often the term membrane has associated with it the notion of permeability to a species present in the flanking solutions. However, although this is undoubtedly true with certain porous biological and synthetic membranes, the actual mechanism of electrical conduction in general varies with the type of membrane material; indeed it may change within it.