Hydrophilic Ultrafiltration Membranes Research Articles

A facile and scalable fabrication procedure for PVDF-PDA/PEI/SiO2 hollow fiber composite ultrafiltration membranes: Integration of co-deposition and cross-linking

Polyvinylidene fluoride (PVDF) membranes, widely used for their stability, face limitations due to the hardly adjustable pore size in nanoscale and inherent hydrophobicity. To address this, we proposed a co-deposition method incorporating dopamine (DA), polyethyleneimine (PEI), and silicon dioxide (SiO2) nanoparticles with glutaraldehyde cross-linking for precise regulation of pore size and hydrophilicity in PVDF hollow fiber membranes. Notably, the pore diameter reduced from 119.0 ± 3.55 nm to 18.4 ± 0.36 nm, while the contact angle decreased from 107.7° to 40.9°. This simultaneous regulation led to a high-performance PDA/PEI/SiO2-PVDF hydrophilic ultrafiltration membrane with a rejection rate exceeding 99% for 20 nm nanoparticles in a long-term simulated separation experiment while achieving a significant protein permeability of 97% in BSA permeation experiments. Additionally, the membrane demonstrated exceptional long-term stability, offering a novel approach for tuning the performance of ultrafiltration/microfiltration membranes.

Preparation and stability enhancement of anchor bonded 3D-network extracting membrane for nickel extraction

A novel and efficiently anchored 3-dimensional network extracting membrane (3D-NEM) with a thin functional surface layer comprising extraction carrier Bis(2-ethylhexyl) phosphate (D2EHPA) for nickel extraction was designed and studied in this paper. The active sites on the supporting Polytetrafluoroethylene (PTFE) hydrophilic ultrafiltration membrane were introduced by treating PTFE surface with potassium permanganate. Polydimethylsiloxane (PDMS) and Polymethylhydrosiloxane (PMHS) were applied to prepare a 3D network layer which is tightly anchored to the PTFE surface by introducing a crosslinking agent vinyltriethoxysilane (VTES). The prepared 3D-NEM was characterized by SEM, EDS, ATR-IR, XPS and etc. The influence of preparation parameters of 3D-NEM was studied and compared systematically. The optimum preparation conditions of 3D-NEM were based on a PDMS/PMHS/VTES ratio of 2:1:0.1 and a total polysiloxane concentration of 8 wt%. The operation stability test confirmed the average flux of the 3D-NEM in 72h reached 1871.16 mg·m-2·h-1, and only 14.42% flux declined at the end of operation. The proposed designed 3D network structure produced a 5.5 μm-functional extracting layer which has benefits in both effective fixing of D2EHPA and tight anchor to the supporting surface. This work has dual advantages in improving flux and reducing extractant loss compared to supported liquid membrane (SLM) and polymer inclusion membrane (PIM) processes.

Robust and highly hydrophilic ultrafiltration membrane with multi-branched cellulose nanocrystals for permeability-selectivity anti-trade-off property

To overcome challenges associated with the “trade-off” effect and membrane fouling, the high-performance ultrafiltration membranes were prepared by blended multi-branched nanocellulose (Multi CNC) into polyethersulfone (PES) matrix using non-solvent induced phase separation (NIPS) technology. The as-prepared composite ultrafiltration membranes have high hydrophilicity, thicker skin layer and lower negative charge due to the abundant polar groups of carboxyl (COOH) in Multi CNC. As the results, the water flux and Bovine serum albumin (BSA) rejection of the composite membranes with 1 wt% Multi CNC reached to 961.65 L/m2·h and 96.4 %, while the flux and rejection of the original PES membrane was only 702.04 L/m2·h and 86.2 % respectively, thus the “trade-off” was effectively improved by loading of Multi CNC. Moreover, the flux recovery ratio (FRR) of MCP1 (FRR = 74.08 %) was 2.1 times as much as the original PES membranes (FRR = 34.81 %) in the water-BSA-water filtration process, verified that the introduction of Multi CNC could effectively improve the anti-fouling ability of composite membranes. Such hydrophilic composite ultrafiltration membranes with robust mechanical performance could be developed for pharmaceutical and biotechnological industries.

Fabricating novel PVDF-g-IBMA copolymer hydrophilic ultrafiltration membrane for treating papermaking wastewater with good antifouling property.

Ultrafiltration membranes are widely used for the treatment of papermaking wastewater. The antifouling performance of polyvinylidene fluoride (PVDF) ultrafiltration membranes can be improved by changing the hydrophilicity. Here, a novel amphiphilic copolymer material, PVDF grafted with N-isobutoxy methacrylamide (PVDF-g-IBMA), was prepared using ultraviolet-induced Cu(II)-mediated reversible deactivation radical polymerization. The amphipathic copolymer was used to prepare ultrafiltration membrane via NIPS. The prepared PVDF-g-IBMA ultrafiltration membrane was estimated using 1H NMR, FT-IR, and DSC. The contact angle, casting viscosity, and the permeation performance of the PVDF-g-IBMA ultrafiltration membrane were also determined. The pure water flux, bovine serum albumin removal rate, and pure water flux recovery rate of the PVDF-g-IBMA ultrafiltration membrane were 432.8 L·m-2·h-1, 88.4%, and 90.8%, respectively. Furthermore, for the treatment of actual papermaking wastewater, the chemical oxygen demand and turbidity removal rates of the membrane were 61.5% and 92.8%, respectively. The PVDF-g-IBMA amphiphilic copolymer ultrafiltration membrane exhibited good hydrophilicity and antifouling properties, indicating its potential for treating papermaking wastewater.

Re-use of waste cotton textile as an ultrafiltration membrane

Textile industry produces millions of tons of waste annually, which is predominantly incinerated or landfilled. Cotton textile comprises a quarter of total textile production, and although being renewable, its production is highly chemical- and water-intensive, rising the need for effective waste cotton textile recycling. This study presents an investigation whether it is possible to utilize waste cotton textile as a cellulose source for the fabrication of cellulose membranes. The effect of casting thickness and cellulose concentration on the prepared membranes’ performance was studied. Membranes cast from 2 wt% casting solutions exhibited the highest permeabilities of 1.11 and 3.09 m3/(m2·s·Pa) for 300 and 150 μm casting thickness, respectively, but poor adhesion stability and low retention. Membranes cast from solutions of higher concentrations (5, 6, and 7 wt%) resulted in membranes with more stable performance. The permeability values for 300 μm membranes were in the range of 0.27 – 0.39 m3/(m2·s·Pa) and for 150 μm 0.51 – 0.67 m3/(m2·s·Pa). The retention values of these six membranes were relatively close to each other, showing 80 – 92% retention of polyethylene glycol (PEG) 35 kDa. Three most promising membranes (5, 6, and 7 wt% cast at 150μm) were additionally characterized, showing negative zeta potential within −23 – −35 mV range at pH 7 and contact angles of very hydrophilic material (14 – 16°). Overall, the results showed that very hydrophilic ultrafiltration membranes having attractive permeability and retention properties can be made from textile waste. 1 m2 of cotton bed linen is enough to produce approximately 20 m2 of cellulose membrane.

Impact of pilot-scale PSF substrate surface and pore structural properties on tailoring seawater reverse osmosis membrane performance

Recent research pays much attention to the correlations between structural properties of porous substrate and the separation performance of polyamide (PA) thin film composite (TFC) membrane prepared by interfacial polymerization (IP). However, there are limited studies focused on seawater reverse osmosis (SWRO) membrane preparation and optimization. This study reveals profound impacts of substrate surface properties on the separation properties of SWRO membranes, by using different substrates including commercial ultrafiltration (UF) membrane, lab-scale casted polysulfone (PSF) substrate and pilot-scale casted PSF substrates. We demonstrate that the membrane substrates casted using pilot-scale machine led to better SWRO performance than hydrophilic UF membrane or lab-scale casted substrate; and very different SWRO membranes could be made from pilot-scale substrates casted using the same polymer dope solution. These results showed that a high-performance SWRO membrane relies on appropriate substrate possessing the surface properties of relatively hydrophobic, small surface pore size (20-35 nm) and high surface porosity, which directly affect the supply and transport rate of amine for the IP reaction. Our best SWRO membrane exhibits an excellent NaCl rejection of 99.5% together with high water permeance of 1.72 L m−2 h−1 bar−1 under seawater desalination conditions. This work helps pave the way for substrate selection for SWRO membrane fabrication, narrowing the gap between lab-made and commercial SWRO membranes.

Hydrophilic ultrafiltration membranes with surface-bound eosin Y for an integrated synthesis-separation system of aqueous RAFT photopolymerization

The photocatalyst-based ultrafiltration membrane fitted integrated synthesis–separation system holds the promises to bridge the gap between the precision of PET-RAFT polymerization and the efficiency of membrane separation process.

Study of antifouling modified ultrafiltration membrane based on the secondary treated water of urban sewage

Mixtures of polyvinylidene fluoride (PVDF) and polyvinyl alcohol (PVA) containing hydrophilic ultrafiltration membranes were prepared by adding PVA (5 to 30%) to PVDF by the phase inversion method. The hydrophilic contact angle (CA), equilibrium water content, pure water flux and bovine serum albumin retention were studied to assess the membrane performance. The anti-fouling performance of modified membrane to the secondary treated water was evaluated by flux decline, washing recovery rate and fouling resistance analysis. Scanning electron microscopy showed that the cross-section structure of the membranes had finger-like pores, which were well developed and uniformly distributed, and the sub-layer structure was looser and more porous with the increasing content of PVA. The CA gradually decreased. The steady flux was 800 L/m(2) h from P15 to P30, and the BSA retention sharply declined. The ultrafiltration tests for secondary treated water indicated that the main fouling source of the modified membrane was the concentration polarization and cake layer resistance. After physical flushing, the flux recovery ratio of the membrane could reach 100% when the PVA content was 5-15%, which shows excellent anti-pollution performance and good prospects for use in processing wastewater from urban sewage.

Membranes of Poly (Vinyl Butyral) (PVB) or Cationic PVB (CPVB) Blended with Poly (Vinylidene Fluoride) (PVDF) Prepared by a Nonsolvent Induced Phase Separation Method: Miscibility and Hydrophilicity

The synthesized hydrophilic polymers [poly (vinyl butyral) (PVB) and cationic PVB (CPVB)] blended with poly (vinylidene fluoride) (PVDF) were used to fabricate hydrophilic ultrafiltration membranes. A visual inspection method and a glass transition temperature method were applied to study the miscibility of PVDF/PVB and PVDF/CPVB blend systems. The results showed that the PVDF/PVB was an immiscible blend and the PVDF/CPVB was a partially miscible blend. Dynamic contact angle experiments showed that the hydrophilicity of the blend membranes was significantly improved with the addition of PVB and CPVB. The pure water permeation (PWP) of blend membranes increased with the content of PVB and CPVB.

Preparation and Characterization of Hydrophilic Ultrafiltration Membrane with PVDF and PAA Blends

Hydrophilic Polyvinylidene fluoride (PVDF) flat ultrafiltration membranes were prepared by wet-spinning method. The influence of blending ratio ( the mass ratio of PVDF and PAA), polymer concentration on preparation of blending modified hydrophilic PVDF ultrafiltration membranes were investigated, the technical parameters of preparation of hydrophilic PVDF membranes were determined, and hydrophilic PVDF membranes were prepared. Then, hydrophilic PVDF membranes were characterized in terms of IR spectra, contact angle, scanning electron microscopy images, pure water flux and rejection. The results showed that hydrophilic ultrafiltration membrane could be prepared with PAA and PVDF blends, the hydrophilicity improved greatly, and it was better than traditional PVDF membrane.

Temporal variation of NOM and its effects on membrane treatment

Near real‐time monitoring of natural organic matter (NOM) concentration and composition in the upper Mississippi River was performed for 11 months. The monitoring found distinct seasonal trends in dissolved organic carbon (DOC) concentration and ultraviolet light absorbance at 254 nm as well as short‐term (i.e., hours to days) increases that correlated with increases in river discharge during storms and snowmelt. The permeability (i.e., transmembrane pressure‐normalized flux) of hydrophilic ultrafiltration membranes was negatively correlated with river flow (p < 0.01) and raw water specific ultraviolet absorbance (p < 0.01) but not with raw water DOC concentration (p = 0.865). Overall, the potential benefits derived from the increased data provided by an on‐line monitoring system should outweigh the maintenance requirements for such instrumentation. Such data potentially could be used for real‐time control of chemical dosing rates as well as membrane backwash and cleaning schedules.

Sandwich-structured enzyme membrane reactor for efficient conversion of maltose into isomaltooligosaccharides

A novel enzyme membrane reactor with sandwich structure has been developed by confining glucosidase between two sheets of ultrafiltration membranes to effectively convert maltose to isomaltooligosaccharides (IMOs). The hydrophilic ultrafiltration membranes, which were prepared by phase inversion method using PES as bulk polymer and Pluronic F127 as both surface modification and pore formation agent, exhibited the desirable enzyme adsorption-resistant property. The scanning electron microscopy (SEM) photographs showed that two sheets of PES/Pluronic F127 membranes were packed tightly and glucosidase was kept in a free state within a nanoscale space. When the weight ratio of Pluronic F127 to PES was 30%, glucosidase could be completely rejected by the membranes. Due to the sandwich structuring of the membrane reactor and the high hydrophilicity of the PES/Pluronic F127 membrane surface, maltose conversion and yield reached 100% and 58% under the optimum experimental conditions (pH 6.0, 50 degrees C), respectively.

Treatment of stable oil/water emulsion by novel felt-metal supported PVA composite hydrophilic membrane using cross flow ultrafiltration

The novel felt-metal supported PVA composite hydrophilic ultrafiltration membrane was used for the treatment of oil/water(O/W) emulsion. The effects of transmembrane pressure(TMP), cross flow velocity, feed concentration on membrane performance were investigated, and ultrasonic cleaning of the fouled membrane was also investigated. The results show the flux increases with the increase of cross-flow velocity and TMP within the given TMP range from 0.20 MPa to 0.40 MPa. With increase of initial oil concentration increases, the oil rejection increases while the permeate flux decreases. The composite membrane shows more than 90% oil rejection within the initial oil concentration range from 0.05% to 0.50% (mass fraction) at TMP of 0.30 MPa. The fouling of the composite membrane increases rapidly during the initial 20 min at given TMP range from 0.20 MPa to 0.40 MPa, and it increases slowly after 30 min. The results also show that ultrasound is very effective in removing oil fouling of the fouled membrane, and the properties of the composite ultrafiltration membrane can be completely recovered by 10 min of sonication.

Removal of taste and odor model compound (2,4,6-trichloroanisole) by tight ultrafiltration membranes

Taste and odor causing organic compounds of concern to the general public are produced at low concentrations (i.e., ng/L) in surface water. Bench-scale membrane filtration experiments were conducted with 2,4,6-trichloroanisole (TCA), which is of special interest as a model compound due to its very low odor threshold level (i.e., 10 ng/L). Four different tight ultrafiltration (UF) membranes, with different molecular weight cutoffs (MWCO) and hydrophobicities were investigated. The removal of TCA decreased with increasing permeability for all of the UF membranes tested. Relatively hydrophobic UF membranes, even those with higher MWCO and permeability values, exhibited much higher TCA removal efficiencies than relatively hydrophilic UF membranes, both in the presence and absence of hydrophobic natural organic matter (Suwannee River NOM). The adsorption of TCA onto the membrane surfaces/pores through the hydrophobic interaction was found to be important for the efficient removals of TCA by hydrophobic UF membranes, especially those with greater hydrophobicities. The removals of TCA by the tight-UF membranes were affected by two major mechanisms: (1) a convection mechanism for the transmission of TCA through the membrane pores and (2) the adsorption of TCA onto the membrane surfaces/pores through hydrophobic interactions.

A concentration polarization model for the ultrafiltration of nonionic surfactants

A theoretical model has been developed that describes ultrafiltration of nonionic surfactants. The model takes into account the fact that surfactants start to aggregate and form micelles at the critical micelle concentration. The model can be used to predict the performance of the membrane if the transport properties inside and at the membrane surface as well as the surfactant association behavior, are known. Three hydrophilic ultrafiltration membranes, made of regenerated cellulose, were used in the investigation. The cut-offs of the membranes were 10,000, 20,000, and 30,000 Da. The surfactant used in the investigation was the nonionic surfactant Triton X-100. The influence of the concentration of surfactant, transmembrane pressure and pure water flux were studied theoretically and experimentally. From the results presented in this work it can be concluded that the calculated values are in good agreement with experimental data.

Effects of organic solvents on ultrafiltration polyamide membranes for the preparation of oil-in-water emulsions

Hydrophilic ultrafiltration membranes made of polyamide with molecular weight cutoff 10 and 50 kDa have been studied for the preparation of oil-in-water emulsions by a cross-flow membrane emulsification technique. Isooctane and phosphate buffer were used as disperse and continuous phase, respectively. The permeation of apolar isooctane through the polar hydrophilic membrane was achieved by pretreatment of membranes with a gradient of miscible solvents of decreasing polarity to remove water from the pores and replace it with isooctane. Four different procedures were investigated, based on the solvent mixture percentage and contact time with membranes. After pretreatment, the performance of the membranes in terms of pure isooctane permeate flux and emulsion preparation was evaluated. The influence of organic solvents on polyamide (PA) membranes has been studied by SEM analysis, which showed a clear change in the structure and morphology of the thin selective layers. The effects proved stronger for PA 10 kDa than for 50 kDa. In fact, similar pretreatment procedures caused larger pore size and pore size distribution for PA 10 kDa than for 50 kDa. The properties of emulsions in terms of droplet size distribution reflected the membrane pore sizes obtained after pretreatment. The correlation between pore size and droplet size, for the physicochemical and fluid dynamic conditions used, has been evaluated.

Nonaggregating refolding of ribonuclease A using reverse micellar dialysis

A hydrophilic ultrafiltration membrane, regenerated cellulose, facilitates the size-selectable permeability of hydrophilic solutes in reverse micellar solution. By using an ultrafiltration membrane with a molecular weight cutoff of 3,500, we demonstrate a nonaggregating protein refolding technique based on the dialysis of reverse micellar solution. This realizes concurrent removal of denaturants, urea and 2-mercaptoethanol, and the supply of redox reagents, reduced and oxidized glutathione (GSH, GSSG), to promote renaturation of proteins. Two mg/ml ribonuclease A (RNase A) was refolded completely without any dilution and aggregation for 60 h. The refolding behavior of RNase A is strongly influenced by the ratio of GSH and GSSG. Moreover, we recovered 90% of the refolded RNase A from AOT reverse micellar solution with acetone precipitation and beta-cyclodextrin washing. These findings should facilitate the production of a continuous protein refolding membrane reactor.

Preparation of oil-in-water emulsions using polyamide 10 kDa hollow fiber membrane

In this work, asymmetric polyamide hollow fibre membranes having nominal molecular weight cut-off (NMWCO) of 10 kDa, internal diameter of 1.5 (±0.1) mm, and thickness of 0.4 (±0.05) mm have been used to prepare oil-in-water emulsions. Pure isooctane (or isooctane containing naproxen methyl ester) as oil dispersed phase, ultrapure water (or 50 mmol l −1 (50 mM) phosphate buffer pH 7.00) as continuous phase, and sodium dodecil sulphate (SDS) and polyvinyl alcohol (PVA) as emulsifier and stabiliser, respectively, were used. In order to achieve permeation of the apolar organic solvent, isooctane, through the hydrophilic ultrafiltration membrane it was necessary to pre-treat the membrane. The pre-treatment consisted in removing the polar internal liquid phase (water) and substituting it with the apolar solvent. Emulsion with narrow droplet size could be prepared, whose stability did not show any decrease for more than 20 days. Eighty-five percent of dispersed volume was contained in droplets with size of 1.87 (±0.58) μm.

Development of ultrafiltration membranes from acrylonitrile co-polymers

Hydrophobic polymer surfaces show higher tendency to protein adsorption and bacteria attachment, thus hydrophobic polymeric membranes foul rapidly in water purification operations. A change in membrane surface properties can reduce fouling; this may be accomplished by increasing the hydrophilicity of the membrane surface, and by using a membrane with smaller pore size. The ultrafiltration membranes were prepared via phase inversion process in our laboratory. Negatively charged hydrophilic ultrafiltration membranes were prepared from acrylonitrile-vinyl acetate (CP16)/Acrylonitrile-vinyl acetate-sodium p-sulfophenyl methallyl ether (CP24). Scanning electron microscopy (SEM) revealed the asymmetric structure of these membranes. The roughness of the surface was measured by atomic force microscopy (AFM). The basic characteristics of these membranes like water permeability, water content and membrane selectivity were also measured.

A novel reactor concept for the enzymatic reduction of poorly soluble ketones

Reductions of poorly soluble ketones often suffer from low total turnover numbers conferring to the coenzyme and large volumes which are needed for the conversion. The novel emulsion membrane reactor overcomes these limitations. From an emulsion consisting of an organic substrate and an aqueous buffer phase, the aqueous phase is separated selectively by using a hydrophilic ultrafiltration membrane and fed to a subsequent enzyme membrane reactor. The product outflow is recirculated to the emulsion stirred vessel and, due to the partition coefficients, the aqueous phase is recharged with substrate while the product is extracted. This new reactor concept will be compared to the classical enzyme membrane reactor. The latter was operated under the same conditions over a period of 4 months at a space-time yield of 21.2 g l −1 day −1. As a model system the enantioselective reduction of 2-octanone to ( S)-2-octanol (ee > 99.5%) is used, carried out by a carbonyl reductase from Candida parapsilosis. NADH is regenerated by formate dehydrogenase from Candida boidinii. In comparison to the classical enzyme membrane reactor the total turnover number could be increased by a factor 9 using the novel emulsion membrane reactor.