Asymmetric Polyethersulfone Membranes Research Articles

Surface characterization and Remazol Red adsorption by asymmetric polyethersulfone membranes modified by polyelectrolyte complexes

AbstractPolyethersulfone (PES) membranes containing 4‐fluorophenyl sulfone‐terminated poly(diallylpiperidinium hexafluorophosphate)‐sulfonated poly(ethylene terephthalate) polyelectrolyte complexes (PECs) were obtained via phase inversion using three different methods that enabled the complexation of polyelectrolytes (PELs) to occur before, after, and during membrane formation. Atomic force microscopy‐infrared spectroscopy analysis revealed varying concentrations of the polyanion depending on the preparation method and confirmed the presence of PECs in the membranes, highlighting an increase in surface roughness. Zeta potential measurements demonstrated positive surface charges for the membrane comprising PES and the polycation. The reduction in zeta potential in PEC membranes corresponded with the neutralization of positive groups by sulfonated poly(ethylene terephthalate. Scanning electron microscopy micrographs depicted surface imperfections in PEC membranes, emphasizing the influence of PECs on membrane surfaces. The water contact angle decreased, indicating increased hydrophilicity in PEC membranes. Additionally, dye adsorption results showcased significant adsorption, with the membranes absorbing at least 60% of Remazol Red from an aqueous solution. Notably, the Blend membrane outperformed others, exhibiting an exceptional adsorption rate exceeding 92%.

An asymmetric polyether sulfone membrane as an efficient separator in aluminium–graphite batteries with EMIMCl/AlCl3 electrolyte

This work demonstrates the superior performance of a 160 μm PES membrane as a separator in an aprotic aluminum–graphite battery compared to a cell with a 260 μm glass fiber separator, paving the way for further developments and market entry.

Glycerol-tailored asymmetric polyethersulfone membranes with uniform ion transport for stable lithium metal batteries

Advancing the performance and stability of lithium metal batteries is crucial for future energy storage devices. One of the major challenges for practical applications of Li metal batteries is to mitigate the formation of Li dendrites during cycling. In this work, we prepared a series of asymmetrically structured polyethersulfone (PES) membranes, consisting of a nanoporous skin layer and a bulk with macrovoids, by incorporating different amounts of glycerol during membrane preparation. Under optimal conditions, the asymmetric PES membrane made with 1.2 wt% of glycerol (PES-G1.2) possesses a thin skin layer with a uniform nanopore distribution, which is ideal for regulating the ion flux near the Li anode surface, thus suppressing Li dendrite formation. Our results demonstrate that the PES-G1.2 possesses exceptional ionic conductivity of 1.76 mS cm−1, Li+ transference number of 0.52, and high compatibility with Li electrode. Additionally, the Li/PES-G1.2/LiFePO4 cells also present a remarkable rate capability with specific capacity of 150 mAh g−1 at 0.2 C and 81 mAh g−1 at 10 C, respectively, and 90 % of capacity can be retained after 100 charge-discharge cycles under 0.2 C. These findings shed light on the unique properties of asymmetric porous membrane as well as its promising potential for applications in lithium metal batteries.

Highly permeable novel PDMS coated asymmetric polyethersulfone membranes loaded with SAPO-34 zeolite for carbon dioxide separation

Novel asymmetric polyethersulfone membranes loaded with SAPO-34 particles were prepared using phase inversion technique and then surface coated with PDMS using spin coating method. The mixed matrix membranes were then characterized by FTIR, TGA, SEM-EDX and gas permeation analysis. Effect of SAPO-34 loading alongwith operating pressure was also analyzed on gas permeation properties of both coated and uncoated membranes. SAPO-34 loading resulted in improvement of permeability of all the gases without much decrease in CO2 ideal selectivity with respect to methane and nitrogen whereas PDMS coating resulted in improvement of ideal selectivity of CO2 at the expense of decrease of permeance of all the gases. It was found that PDMS coated PES membrane, loaded with 30 wt.% SAPO-34, having thickness of 45 µm, demonstrated high CO2 permeance of 641.77 GPU, CO2/CH4 ideal selectivity of 4.45 and CO2/N2 ideal selectivity of 12.45, respectively at 20 bar and 25 °C. It was found that the performance of this membrane crossed the Robeson upper bound limit 2008 for CO2/N2 separation whereas for CO2/CH4 separation it crossed the previous upper bound limit 1991. Finally, the performance of this membrane was also analyzed under mixed gas conditions for CO2/CH4 separation at high pressure.

Morphological changes in asymmetric PES membranes by addition of polyurethanes: A thermodynamic and experimental study

The effect of adding two types of polyurethane (PU) namely: polyether urethane (ETPU) and polyester urethane (ESPU), on polyether sulfone (PES) blend membrane is investigated. The morphology of the prepared membranes is studied by phase diagram. For this purpose, Hansen solubility parameters are calculated by Van Krevelen and Hoy methods, and the ternary and quaternary phase diagrams for the prepared membranes are produced using Flory Huggins theory. The membranes are prepared by phase inversion method. Different tests such as permeability, water contact angle, FTIR and SEM images are carried out to determine the membranes' characteristics. The results indicate that porosity and gas permeability of PES blend membranes increase by addition of PU as an additive. The PES/ETPU blend membrane has higher permeability and porosity in comparison with the PES/ESPU due to higher compatibility of the polymers and lower de-mixing rate between solvent and non-solvent in PES/ESPU membrane. It should be mentioned that by increasing the additive concentration, viscosity increases and high viscosity acts as a barrier to mass transfer between the solvent and non-solvent. Therefore, the delayed de-mixing rate reduces pore size and permeability.

Solid phase extraction membranes with submicron multifunctional adsorbent particles

Asymmetric polyethersulfone membranes with submicron particles comprising crosslinked poly(glycidyl methacrylate-co-2-acrylamido-2-methylpropane sulfonic acid) were prepared by a combination of a traditional liquid phase inversion process for making membranes with photopolymerization and crosslinking of functional monomers included in the casting solution. Scanning electron microscope images of the membrane cross-section revealed a hybrid structure with an interconnected network of submicron particles embedded within the porous polyethersulfone support. Permeation of toluidine blue solutions through non-functionalized membranes showed a dramatic effect of 2-acrylamido-2-methylpropane sulfonic acid concentration in the casting solution on the dynamic adsorption performance. The epoxide groups present in glycidyl methacrylate copolymer were transformed into amine functionalities by ring opening under alkaline conditions. Permeation of dilute Cu2+ solutions through functionalized membranes demonstrated that the plate height for some of these membranes was an order of magnitude smaller than for commercial particle-filled membranes used in solid phase extraction.

Evaluation of fouling mechanisms in asymmetric microfiltration membranes using advanced imaging

This contribution details the use of advanced microscopy to study the fouling of asymmetric polyethersulfone membranes during the microfiltration of protein (casein), polyphenol (tannic acid), and polysaccharide (β-cyclodextrin) mixtures to better understand the solute–solute and solute–membrane interactions leading to fouling. Fluorescently labeled probes were used to visualize the fouling profiles of individual components within the wet membrane structure with confocal laser scanning microscopy (CLSM). Cross-sectional CLSM imaging provided information on the location and extent of fouling throughout the entire thickness of the PES membrane, overcoming the depth of penetration limit observed by researchers in previous studies. Quantitative analysis of the cross-sectional CLSM images provided a measurement of the masses of foulants deposited throughout the membrane. Moreover, flux decline data were collected for different mixtures of casein, tannic acid and β-cyclodextrin (model foulants) and were analyzed with standard fouling models to determine the fouling mechanisms at play when processing different combinations of foulants. Results from model analysis of flux data were compared with the quantitative visual analysis of the correspondent CLSM images. This approach, which couples visual and performance measurements, is expected to provide a better understanding of the causes of fouling that, in turn, is expected to aid in the design of new membranes with tailored structure or surface chemistries that prevent the deposition of the foulants in “prone to foul” regions.

Fabrication of asymmetric polyethersulfone membranes for separation of carbon dioxide from methane using polyetherimide as polymeric additive

Polyetherimide (PEI) was used as a polymeric additive for preparing an asymmetric polyethersulfone (PES) membrane for the separation of CO2 from CH4. In pure gas experiments, the higher skin layer thickness and the lower porosity of the sub layer for the membrane prepared from the polymer blend with the composition of 98:2 lead to an increase in CO2/CH4 selectivity and a decrease in the CO2 permeance in contrast with a pristine PES. For higher PEI contents, the higher fractional free volume of the membranes improves the gas permeance and reduces the CO2/CH4 selectivity. The incorporation of PEI in PES reduces the CO2 sorption in PES via decreasing the non-equilibrium free volume and imparts antiplasticization properties to the membrane.

Novel membrane adsorbers incorporating functionalized polyglycidyl methacrylate

Asymmetric polyethersulfone membranes with submicron particles comprising crosslinked glycidyl methacrylate copolymer were prepared by a combination of a traditional immersion precipitation process for making membranes with photopolymerization and crosslinking of functional monomers included in the casting solution. As the concentration of polymerizable monomers increased the original macrovoid structure was replaced by a hybrid morphology with microglobules typical of macroporous methacrylate adsorbers embedded within microporous structure with no significant effects on water permeability. The epoxide groups present in glycidyl methacrylate copolymer were transformed into amine functionalities by ring opening under alkaline conditions. Permeation of Orange G solution at low transmembrane pressures was used to demonstrate suitability of these novel membranes for membrane adsorption.

Fixed facilitated transport of CO2 through integrally-skinned asymmetric polyethersulfone membrane using a novel synthesized Poly (acrylonitrile-co-N, N-Dimethylaminopropyl acrylamide)

In the current study, a novel water insoluble Poly (acrylonitrile-co-N, N-Dimethylaminopropyl acrylamide) [PAN-PDMAPAM] copolymer was synthesized and employed as a CO2 carrier in an integrally-skinned asymmetric polyethersulfone (PES) membrane. The membranes provided the facilitated transport in addition to the solution–diffusion mechanism in PES membranes for the separation of CO2 from CH4. Differential Scanning Calorimetry was used for investigating the change in the glass transition temperature of the PES and miscibility of the PES and synthesized PAN-PDMAPAM. Scanning Electron Microscopy (SEM) and porosity measurement were used to study the effect of PAN-PDMAPAM on the membrane morphology. The effects of the synthesized PAN-PDMAPAM on the gas sorption capacity and the dual-mode parameter of the PES membranes were studied using sorption isotherms. The addition of PAN-PDMAPAM changes the morphology, increases the CO2 sorption capacity and decreases the glass transition temperature (Tg) as well as Langmuir sorption sites of the prepared PES membranes. An improvement can be seen in the plasticization when the PAN-PDMAPAM concentration was 0.5 and 1wt.%. Introducing the PAN-PDMAPAM in PES membranes significantly improves the membrane performance including CO2 permeance and CO2/CH4 selectivity because of the incorporation of the facilitated transport of CO2. The addition of PAN-PDMAPAM in the PES membranes changes the behavior of the PES membrane against the feed temperature and the feed pressure. It was shown that the application of PES/PAN-PDMAPAM membranes is limited to ambient temperature because at the elevated temperatures, the equilibrium constant of the facilitated transport reaction is small, and hence the permeation of CO2 decreases.

Preparation of modified polyethersulfone membranes using variation in coagulation bath temperature and addition of hydrophilic surfactant

In this study, novel asymmetric polyethersulfone membranes were prepared from PES/PEG/Tween-20/NMP system via immersion precipitation. Pure water was used as gelation media. Simultaneous effects of variation in coagulation bath temperature (CBT) and addition of Tween-20 on morphology, wettabiliy, pure water permeation flux (PWF) and bovine serum albumin (BSA) rejection of the prepared membranes were studied by scanning electron microscopy (SEM), atomic force microscopy (AFM), contact angle measuring instrument and experimental set up. The obtained results indicate that the small addition of surfactants in the casting solution along with using the lowest level of CBT increases hydrophilicity of the PES membranes. Also it was found out that addition of Tween-20 in the casting solution along with increasing the CBT incites the formation of the bigger pores on the top surface and results in the formation of membranes with higher porosity in the sublayer.

Synthesis and characterization of asymmetric polyethersulfone membranes: effects of concentration and polarity of nonsolvent additives on morphology and performance of the membranes

AbstractIn this study, effects of methanol, ethanol and 1‐propanol as variable nonsolvent additives (NSAs) on the morphology and performance of flat sheet asymmetric polyethersulfone (PES) membranes were investigated. The membranes were prepared from PES/Polyvinylpyrrolidone (PVP)/N‐methyl‐2‐pyrrolidone (NMP) system via phase inversion. The obtained results indicate that with the addition of NSAs to the casting solution, the membrane morphology changes slowly from macrovoids to an asymmetric structure with finger‐like pores. By increasing the NSAs concentrations in the casting solution and decreasing their polarities, the membrane structure changes from finger‐like pores to sponge. The AFM and SEM images reveal that addition of NSA to the casting solution decreases the pore size of the prepared membranes and reduces the pure water flux and BSA solution flux, while increasing the protein rejection. Surface analysis of the membranes showed that mean pore size and surface porosity of the prepared membranes with NSAs in the casting solution are smaller compared with those of the membrane prepared with no NSA. Pure water flux and BSA solution flux through the membranes decrease and BSA rejection increases with increase in the concentration of NSAs and decrease in their polarity. Finally, it can be concluded that the Tg values of the PES membranes increase by addition of NSAs to the casting solution. Copyright © 2009 John Wiley & Sons, Ltd.

Membrane stripping: Desorption of carbon dioxide from alkali solvents

Membrane stripping of carbon dioxide from an aqueous 30% (w/w) potassium carbonate solvent was achieved using two types of polymeric flat sheet microporous membranes; a polytetrofluoroethylene (PTFE) membrane and an asymmetric polyether sulfone membrane with a proprietary hydrophobic surface coating. Both membranes were tested at stripping temperatures of 60–100 °C. The asymmetric membrane performed well at all temperatures. However, the mass transfer performance of the PTFE membrane was not sustained at higher temperatures, probably as a result of pore wetting by solvent intrusion. Calculations suggested that up to 72% of the membrane was wetted. In industrial applications, the use of higher temperatures could also lead to condensation of water vapour in the membrane support structure.

Preparation and characterization of hyperthin-skinned and high performances asymmetric polyethersulfone membrane for gas separation

Defect-free high performance membranes for O 2/N 2 separation were prepared by coating the porous polyethersulphone (PES) membrane of hyperthin-skin layer with silicone rubber. The combined effects of fabrication parameters in dry/wet phase inversion process and of the casting dope rheology enabled improved of membrane performance in O 2 and N 2 separation, i.e. the optimum range was found to be from 149 to 447 s − 1 and 10 to 14 s, respectively, for the shear rate and the evaporation time to prepare the hyperthin-skinned asymmetric polyethersulfone membranes. The optimum polymer concentration was 32 wt.% , 61 wt.% and 7 wt.% for PES, 1-methyl-2-pyrrolidone and water respectively. The thinnest skin layer thickness was 538 ± 95.6 Å. Evaporation time and casting shear have been identified as the dominant fabrication parameters in controlling skin layer thickness and skin integrity.

Gas permselection properties in silicone-coated asymmetric polyethersulfone membranes

The gas permeation properties of H2, He, CO2, O2, and N2 through silicone-coated polyethersulfone (PESf) asymmetric hollow-fiber membranes with different structures were investigated as a function of pressure and temperature and compared with those of PESf dense membrane and silicone rubber (PDMS) membrane. The PESf asymmetric hollow-fiber membranes were prepared from spinning solutions containing N-methyl-2-pyrrolidone as a solvent, with ethanol, 1-propanol, or water as a nonsolvent-additive. Water was also used as both an internal and an external coagulant. A thin silicone rubber film was coated on the external surface of dried PESf hollow-fiber membranes. The apparent structure characteristics of the separation layer (thickness, porosity, and mean pore size) of the asymmetric membranes were determined by gas permeation method and their cross-section morphologies were examined with a scanning electron microscope. The results reveal that the gas pressure normalized fluxes of the five gases in the three silicone-coated PESf asymmetric membranes are nearly independent of pressure and did not exhibit the dual-mode behavior. The activation energies of permeation in the silicone-coated asymmetric membranes may be larger or smaller than those of PESf dense membrane, which is controlled by the membrane physical structure (skin layer and sublayer structure). Permselectivities for the gas pairs H2/N2, He/N2, CO2/N2, and O2/N2 are also presented and their temperature dependency addressed. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 837–846, 1997

Micellar ultrafiltration in an unstirred batch cell at constant flux

An unsteady mass-transfer model is developed to describe the ultrafiltration of micellar surfactant solutions in an unstirred batch cell at constant flux. Excellent agreement between the model and new experiments for asymmetric polyethersulfone membranes [5000 and 50,000 molecular weight cutoff (MWCO)] with aqueous hexadecyl (=cetyl)pyridinium chloride (CPC) solutions in 0.01 M NaCl allows quantitative characterization of the intrinsic membrane rejection properties for both surfactant monomer and micelles, and supports the physics at the membrane surface presumed in the model. The 5000 MWCO membrane rejects all of the micelles (hydrodynamic radius ≈2.5 nm) and most of the singly dispersed surfactant molecules, or monomers (hydrodynamic radius ≈0.42 nm); the intrinsic rejection coefficient of this membrane for micelles is 1.0 and for monomers 0.80. For the 50,000 MWCO membrane, two pore types are necessary to explain the observations. The small-pore intrinsic rejection coefficients for monomers and micelles are 0.75 and 1.0, respectively, while the large-pore rejection coefficients are 0.4 and 0.85, respectively. At least 88% of the permeate flow for the 50,000 MWCO membrane is through pores that completely reject micelles. More of the monomers and micelles are sieved by the membranes than is expected from their advertised molecular weight cutoffs. Calculations of intrinsic rejection using estimates of pore and solute size indicate qualitatively that repulsive electrostatic interactions and surfactant adsorption significantly influence rejection.

Gas transport through homogeneous and asymmetric polyethersulfone membranes

AbstractBoth homogeneous and asymmetric polyethersulfone (PES) membranes were prepared by solvent casting. The sorption and permeation behavior of CO2, O2, and N2 using these two kinds of cast PES membranes and commercially available homogeneous PES film was investigated to extract the pressure dependence of gas permeability and the permselectivity for CO2 relative to N2, and to confirm the validity of the working assumption that a skin layer in an asymmetric membrane can be essentially replaced by a thick homogeneous dense membrane. The pressure dependence of the mean permeability coefficient to CO2 in homogeneous membranes obeys the dual‐mode mobility model. The ideal separation factor for CO2 relative to N2 at an upstream pressure of 0.5 MPa attains ca. 40, while the permeability to CO2 is about 2.7 Barrer at the same upstream pressure. The same separation factor in asymmetric membranes amounts to 35. The diffusion behavior for the skin layer in an asymmetric membrane with a thin skin layer can be simulated approximately by that in a homogeneous dense membrane. © 1993 John Wiley & Sons, Inc.

Effect of membrane structure and protein concentration on the osmotic reflection coefficient

Although there have been a number of important studies of the protein filtration reflection coefficient (or sieving coefficient) for asymmetric ultrafiltration membranes, there have been no corresponding studies of the protein osmotic reflection coefficient and its effect on solvent flux. We have obtained experimental data for the bovine serum albumin osmotic reflection coefficient for asymmetric polyethersulfone membranes with nominal molecular weight cut-offs from 30,000 to 1,000,000. The overall osmotic reflection coefficients for these membranes were smaller than the reflection coefficients of the skin layer due to the substantial diffusive resistance provided by the membrane support structure. The results for the skin layer were in relatively good agreement with available hydrodynamic models, suitably modified to account for the effects of protein adsorption and for the presence of a pore size distribution. The osmotic reflection coefficients decreased with increasing bulk protein concentration, with the concentration dependence somewhat larger than that predicted by available theoretical analyses. The osmotic reflection coefficients were in relatively good agreement with literature values for the corresponding filtration reflection coefficients, with the slightly smaller values for the osmotic reflection coefficients probably reflecting the variation in pore size within the ultrathin skin of these asymmetric membranes.

Dextran transport through asymmetric ultrafiltration membranes: Comparison with hydrodynamic models

Although dextran sieving is often used to evaluate the pore size characteristics of the ultrafiltration membranes, there is still considerable disagreement regarding the proper interpretation of these sieving measurements. We obtained experimental data for the transport of polydisperse dextrans through asymmetric polyethersulfone membranes of differing molecular weight cut-off in a stirred ultrafiltration device. Gel permeation chromatography is used to evaluate the actual sieving coefficient as a function of dextran molecular weight from data for the bulk and filtrate concentrations, with the bulk mass transport effects evaluated using a stagnant film model. There is no evidence of any dextran deformation even at fluxes as high as 10−4 m/sec. The flux dependence of the actual sieving coefficients is in good agreement with membrane transport theory, allowing the evaluation of both the hindered diffusivities and asymptotic sieving coefficients as a function of dextran molecular weight. The results are shown to be in good agreement with available hydrodynamic models for spherical solutes in cylindrical pores with the effective solute to pore size ratio evaluated using a partitioning model which implicitly accounts for the membrane pore size distribution.