Support For Composite Membranes Research Articles

Adsorption of steroid hormone micropollutant by polyethersulfone ultrafiltration membranes with varying morphology

The effective removal of micropollutants necessitates the use of dense membranes, such as thin-film composite (TFC) reverse osmosis (RO) and nanofiltration (NF) membranes. TFCs have a polyamide active layer interfacially polymerized on a support layer that is typically made of polysulfone (PSu) or polyethersulfone (PES). Retention by NF and RO is often incomplete because micropollutants are adsorbed to the polymer material and subsequently permeate via a combination of convection and diffusion, which evidences a breakthrough curve. When describing breakthrough phenomena, the role of the support membrane is commonly neglected, even though the adsorption in this layer can be significant. This work investigated the adsorption of steroid hormone micropollutants (17β-estradiol, E2) by fabricated and commercial PES ultrafiltration membranes with varying morphology.By increasing the coagulation bath temperature between 10 and 70 °C, the pure water permeability increased from 13 to 3800 L/m2·h−1·bar−1, and consequently, the average pore size rose from 12 to 191 nm. The fabricated membranes with smaller pore sizes showed higher E2 removal via adsorption which can be attributed to the higher internal surface area. The adsorbed mass of fabricated PES membranes (using dimethylformamide (coded as PDG) and N-methyl-2-pyrrolidone (coded as PNG) and PES (Istanbul Technical University (ITU), with non-woven supports) varies from 0.30 to 0.60, 0.27–0.60 and 1–1.2 ng·cm−2, respectively. These values are lower than the adsorbed masses with commercial Biomax (Millipore Inc.) membranes (0.5–2.0 ng·cm−2). Ultrafiltration membranes used as support for composite membranes, nanofiltration or as filters in sample preparation benefit from lower micropollutant adsorption.

Polyvinyl chloride-based membranes: A review on fabrication techniques, applications and future perspectives

• Review of recent developments in application and modification of PVC membranes. • Various PVC membranes with their preparation methods and applications are reviewed. • Commercial PVC membranes are reviewed and future perspective are discussed. The present study offers an overview of the recent developments in the application and modification of PVC membranes, focusing on some applications such as water and wastewater treatment, ion exchange, gas separation, pervaporation, electromembrane extraction, and support of composite membranes. For this purpose, an introduction to different types of the PVC polymers is provided first, and then, the application of PVC in the membrane fabrication is discussed. Various PVC membranes with their preparation methods and applications are reviewed and a detailed study is done on the modification methods of the PVC membranes. A deep literature review is performed to report the basics for selecting an appropriate method and membrane fabrication system with required processing conditions to produce membranes with desired morphology, performance and stability. Finally, the commercial PVC membranes are overviewed and the challenges and future perspective of these membranes are discussed.

Preparation and Microstructure Control of PMDA/ODA Polyimide Hollow Fibers

Poly(4,4'-oxydiphenylene pyromellitimide) (PMDA/ODA) hollow fiber membranes with regular morphologies have been successfully prepared through a two-step dry-jet wet spinning method. The morphologies of polyimide (PI) hollow fibers were regulated via adjusting the major spinning parameters, including dope/bore flow rate ratio, bore fluid composition, coagulation bath temperature and air gap distance. SEM results show that the morphologies of PI hollow fibers strongly depended on the spinning conditions, and fibers with regular asymmetric structures were finally obtained. The fiber wall thickened with the increase of dope/bore flow rate ratio, and the fibers could well self-support when the dope/bore flow rate ratio ranged from 3:1 to 4:1. While higher DMAc content in the bore fluid was conducive to the formation of finger-like voids, reduced amount of DMAc would result in smaller finger-like voids and thereby lower overall porosities as well as better mechanical properties. Moreover, the finger-like voids and surface defects could be effectively prevented by lowering the coagulation bath temperature or extending the air gap distance. Gas separation and mechanical properties of the hollow fibers were found closely related to these morphological changes. On such basis, regular PI hollow fibers with different microstructures and Young’s modulus up to 1040 MPa were successfully fabricated. The prepared polyimide hollow fibers are promising candidates for fine separation under high temperature and high pressure or can be employed as the support of composite membranes.

Supported liquid membrane extraction of nickel using stable composite SPEEK/PVDF support impregnated with a sustainable liquid membrane

A sustainable and stable supported liquid membrane (SLM) extraction of nickel was developed via impregnation of sustainable liquid membrane in the composite membrane support consisting of polyvinylidene fluoride (PVDF) and sulfonated poly (ether ether ketone) (SPEEK). Bis-2-ethylhexyl phosphate (D2EHPA), 1-octanol, refined palm oil and sulfuric acid were employed as extractant, synergist extractant, diluent and strippant, respectively. Variables studied including effect of refined palm oil compositions as well as the configurations and thicknesses of SPEEK. Lifespan of SLM was evaluated by recycling the composite membrane support. Results revealed that upon using 100% refined palm oil, about 100% of nickel was extracted and recovered in 10 and 14 h, respectively. Composite SPEEK/PVDF stabilized SLM by reducing liquid membrane loss from 47 to 23% upon applying SPEEK at the feed side of PVDF support. High permeability and flux values were obtained at 9.26 x 10−4 cms−1 and 6.48 x 10−7 molcm−2s−1 when increasing SPEEK thickness from 0.025 to 0.055 mm, respectively. The lifespan of SLM was extended up to ninth cycles with low weight loss percentage of the impregnated composite membrane (8%). In conclusion, the SPEEK/PVDF impregnated with refined palm oil has improved the stability of SLM extraction of nickel ions from industrial wastewater.

Application and modification of polysulfone membranes

Abstract Polysulfone (PSf) is a favorite polymer for the production of membrane due to its excellent physicochemical properties, including thermal stability; good chemical resistance to different materials such as different bases, acids, and chlorine; sufficient mechanical strength; and good processability. The present study offers an overview of the recent development in the application and modification of PSf membranes, focusing on some applications such as water and wastewater treatment, membrane distillation, pollutant removal, gas separation, separator for lithium ion battery, and support of composite membranes. In general, there are two major difficulties in the use of membranes made of PSf: membrane fouling and membrane wetting. Therefore, PSf membrane with good anticompaction and antifouling properties is reviewed. Finally, important issues related to the modification of PSf membranes for real applications are discussed. This article provides an intelligent direction for the progress of PSf membranes in the future.

Norepinephrine modified thin film composite membranes for forward osmosis

Surface modification has been demonstrated as a valuable method for improving hydrophilicity of surfaces. A number of approaches have been used for facile modification of support layer chemistry including the use of polydopamine. In this work, norepinephrine is used as an alternative monomer to dopamine for surface modification. The chemistry of norepinephrine allows for a wider array of coating conditions and tighter control of deposition. This study compares surface modification through the application of polydopamine and polynorepinephrine on thin film composite membrane support layers for use in forward osmosis. It was found that polynorepinephrine under ambient conditions performs equally well as a polydopamine modified membrane. Controlling the rate of polynorepinephrine formation by using ammonium persulfate, an oxidizing agent, provided an additional lever for tuning the modification process speed.

Graphene oxide incorporated polysulfone substrate for the fabrication of flat-sheet thin-film composite forward osmosis membranes

The preparation and performances of the newly synthesized thin film composite (TFC) forward osmosis (FO) membranes with graphene oxide (GO)-modified support layer are presented in this study. GO nanosheets were incorporated in the polysulfone (PSf) to obtain PSf/GO composite membrane support layer. Polyamide (PA) active layer was subsequently formed on the PSf/GO by interfacial polymerization to obtain the TFC-FO membranes. Results reveal that at an optimal amount of GO addition (0.25wt%), a PSf/GO composite support layer with favorable structural property measured in terms of thickness, porosity and pore size can be achieved. The optimum incorporation of GO in the PSF support layer not only significantly improved water permeability but also allowed effective PA layer formation, in comparison to that of pure PSf support layer which had much lower water permeability. Thus, a TFC-FO membrane with high water flux (19.77Lm−2h−1 against 6.08Lm−2h−1 for pure PSf) and reverse flux selectivity (5.75Lg−1 against 3.36Lg−1 for pure PSf) was obtained under the active layer facing the feed solution or AL-FS membrane orientation. Besides the improved structural properties (reduced structural parameter, S) of the support layer, enhanced support hydrophilicity also contributed to the improved water permeability of the membrane. Beyond a certain point of GO addition (≥0.5wt%), the poor dispersion of GO in dope solution and significant structure change resulted in lower water permeation and weaker mechanical properties in support as well as FO flux/selectivity of consequent TFC membrane. Overall, this study suggests that GO modification of membrane supports could be a promising technique to improve the performances of TFC-FO membranes.

Incorporation of zinc for fabrication of low-cost spinel-based composite ceramic membrane support to achieve its stabilization

In order to reduce environment risk of zinc, a spinel-based porous membrane support was prepared by the high-temperature reaction of zinc and bauxite mineral. The phase evolution process, shrinkage, porosity, mechanical property, pore size distribution, gas permeation flux and microstructure were systematically studied. The XRD results, based on a Zn/Al stoichiometric composition of 1/2, show a formation of ZnAl2O4 structure starting from 1000°C and then accomplished at 1300°C. For spinel-based composite membrane, shrinkage and porosity are mainly influenced by a combination of an expansion induced by ZnAl2O4 formation and a general densification due to amorphous liquid SiO2. The highest porosity, as high as 44%, is observed in ZnAl4 membrane support among all the investigated compositions. Compared with pure bauxite (Al), ZnAl4 composite membrane support is reinforced by ZnAl2O4 phase and inter-locked mullite crystals, which is proved by the empirical strength–porosity relationships. Also, an increase in average pore diameter and gas flux can be observed in ZnAl4. A prolonged leaching experiment reveals the zinc can be successfully incorporated into ceramic membrane support via formation of ZnAl2O4, which has substantially better resistance toward acidic attack.

Siloxane 유-무기 복합막 제조와 투과증발법을 이용한 Acetone-Butanol-Ethanol (ABE) 용액에서 부탄올의 분리

본 연구에서는 투과증발 공정에서 지지체에 따른 투과특성의 차이를 알아보기 위해 고분자 지지체 복합막과 세라믹 지지체 복합막을 제조하였다. 고분자 지지체로는 polyvinylidene fluoride (PVDF)를 사용하였으며 세라믹 지지체로는 <TEX>$a-Al_2O_3$</TEX> 를 사용하였다. 활성층으로는 각각의 지지체에 고무상 고분자인 polydimethoxysilane (PDMS)를 코팅하였다. 제조한 복합막의 구조와 특성을 살펴보기 위해 SEM, contact angle, XPS로 분석하였으며, 이를 투과증발 공정에 적용하여 다성분계의 혼합용액에서 복합막의 지지체에 따른 투과 특성을 알아보았다. 투과 증발 실험 결과 세라믹 지지체 복합막의 투과 플럭스는 <TEX>$250.87g/m^2h$</TEX>로 고분자 지지체 복합막의 <TEX>$159.64g/m^2h$</TEX> 보다 높은 투과 플럭스를 나타내었다. 그러나 선택도의 경우 고분자 지지체 복합막이 31.98로 20.66인 세라믹 지지체 복합막보다 더 높게 나타나는 것을 확인하였다. In this paper, polymer composite membranes and ceramic composite membranes were prepared in order to compare differences in pervaporation performances relative to the support layers. PVDF was used for the polymer support layers, and <TEX>$a-Al_2O_3$</TEX> was used for the ceramic support layers. For active layer was coated for PDMS, which is a rubbery polymer. The characterization of membranes were analysed by SEM, contact angle, and XPS. We studied performances relative to the composite membrane support layers in the ABE mixture solutions. The results of the pervaporation, the flux of the ceramic composite membrane was shown to be <TEX>$250.87g/m^2h$</TEX>, which was higher than that of polymer composite membranes, at <TEX>$195.64g/m^2h$</TEX>. However, it was determined that the separation factor of the polymer composite membranes was 31.98 which were higher than that of the ceramic composite membranes, at 20.66.

Nanofibers in thin-film composite membrane support layers: Enabling expanded application of forward and pressure retarded osmosis

Re-engineering the support layers of membranes for forward and pressure retarded osmosis is critical for making these technologies commercially viable. Real-world applications of forward and pressure retarded osmosis, especially those involving natural and waste waters, will require membranes to withstand significant stresses. Therefore, structural changes to the support layer, which are necessary in minimizing internal concentration polarization, must not compromise its critical abilities to resist mechanical stress and provide a suitable surface for the interfacial polymerization of a robust and selective active layer. Electrospinning can provide nanofibers for support layers to potentially overcome the limitations of traditional membrane fabrication techniques in fulfilling these challenging design criteria. In this work, we present the fabrication and evaluation of thin-film composite membranes composed of electrospun polyethylene terephthalate nanofibers, a phase separation formed microporous polysulfone layer, and a polyamide selective layer formed by interfacial polymerization. These membranes have active and support layer transport properties that are suitable for engineered osmosis, with water permeability of 1.13Lm−2h−1bar−1 (3.14×10−7ms−1bar−1), salt permeability of 0.23Lm−2h−1 (6.4×10−8ms−1), and a structural parameter of 651μm. Relevant and easily reproducible tests for membrane resistance to mechanical stress were performed. The use of electrospun fibers in the support layer enhanced membrane resistance to delamination at high cross-flow velocities because the 340nm diameter electrospun fibers enmesh with the microporous polysulfone layer. A broader discussion of the most promising approaches for using electrospun materials to improve membranes for engineered osmosis is provided.

Surface modification of thin film composite membrane support layers with polydopamine: Enabling use of reverse osmosis membranes in pressure retarded osmosis

Previous investigations of forward osmosis and pressure retarded osmosis identified asymmetric membrane support layer hydrophilicity as critical to obtain high water flux. In this study, the support layers of two commercially available thin film composite reverse osmosis membranes were modified to enhance their hydrophilicity. The membrane support layers were coated with polydopamine, a novel bio-inspired hydrophilic polymer. This resulted in increased hydrophilicity and a corresponding increase in ‘wetted porosity’ and reduced internal concentration polarization. The modified membranes were then characterized for contact angle, salt rejection, hydraulic permeability, salt flux, and osmotic flux. The results were promising, indicating that the modified reverse osmosis membranes exhibited an eight to fifteen fold increase in flux performance under test conditions when compared to baseline control data. This modification method, which is scalable, has the potential to enable the use of existing thin film composite membranes for all engineered osmosis applications.

Relating performance of thin-film composite forward osmosis membranes to support layer formation and structure

Osmotically driven membrane processes have the potential to treat impaired water sources, desalinate sea/brackish waters, and sustainably produce energy. The development of a membrane tailored for these processes is essential to advance the technology to the point that it is commercially viable. Here, a systematic investigation of the influence of thin-film composite membrane support layer structure on forward osmosis performance is conducted. The membranes consist of a selective polyamide active layer formed by interfacial polymerization on top of a polysulfone support layer fabricated by phase separation. By systematically varying the conditions used during the casting of the polysulfone layer, an array of support layers with differing structures was produced. The role that solvent quality, dope polymer concentration, fabric layer wetting, and casting blade gate height play in the support layer structure formation was investigated. Using a 1 M NaCl draw solution and a deionized water feed, water fluxes ranging from 4 to 25 L m −2 h −1 with consistently high salt rejection (>95.5%) were produced. The relationship between membrane structure and performance was analyzed. This study confirms the hypothesis that the optimal forward osmosis membrane consists of a mixed-structure support layer, where a thin sponge-like layer sits on top of highly porous macrovoids. Both the active layer transport properties and the support layer structural characteristics need to be optimized in order to fabricate a high performance forward osmosis membrane.

Membranes of poly(ether imide) and nanodispersed silica

Organic–inorganic hybrids of poly(ether imide) and silica were prepared by in situ growth of the inorganic network by hydrolysis and condensation of TEOS. The dispersion of the inorganic and organic phase was possible in the nanoscale with addition of amino silane as shown by field emission electron microscopy and atomic force microscopy. An increase of T g of dense films was detected by differential scanning calorimetry with incorporation of the inorganic component. Membranes with quite different morphologies were prepared by phase inversion with different TEOS concentrations. Their performance as support of composite membranes for vapor separation was evaluated under pressures of 80 bar, confirming the advantage of the introduction of the inorganic component.

Strengthened porous alumina membrane tube prepared by means of internal anodic oxidation

A method for preparing an anodic aluminum oxide tube with a much higher mechanical strength than before was developed, where anodic oxidation was carried out from the inside of an aluminum tube (internal anodizing method). It was considered that the internal stress remaining in the alumina layer, which was formed in the course of the internal anodizing, resulted in a considerable improvement of compressive strength against external pressure. As a matter of fact, the tube could withstand at least up to 0.98 MPa of transmembrane pressure, which corresponded to 32.6 MPa in terms of breaking pressure. The tubular alumina membrane obtained had straight mesopores of 20–25 nm in diameter and, therefore, showed the Knudsen permselectivity for inorganic gases. Such a strengthened alumina tube is expected to be used as a porous membrane or as a support for composite membranes.