Properties Of Hollow Fiber Membranes Research Articles

Spinning of Polysulfone Hollow Fiber Membranes Using Constant Dope Solution Composition: Viscosity Control via Temperature.

The dope solution viscosity is an important parameter that largely determines the properties of hollow fiber membranes. In the literature available today, the change in viscosity is carried out only by changing the quantitative and/or qualitative dope solution compositions. However, such an important spinning parameter as temperature should significantly affect the dope solution viscosity. For the first time, the influence of the dope solution viscosity of a constant composition on polysulfone hollow fiber membrane properties was studied. The hollow fiber membranes were obtained by the phase separation method induced by a non-solvent (NIPS). The change in the dope solution temperature was carried out in the temperature range of 17-27 °C, providing a dope solution viscosity range of 34.3-21.6 Pa∙s. This work shows that even in such a narrow temperature range, the properties of polysulfone hollow fiber membranes change significantly. With a decrease in the viscosity in this temperature range, the wall thickness of the hollow fiber membrane decreases by 2.8 times; the permeance for the individual gases He and CO2 increases by 1.6-1.8 times, respectively; the ideal selectivity decreases by 1.12 times; the mean flow pore size increases by 1.63 times; and the surface porosity increases about 3 times.

Physical and Mechanical Properties of Hollow Fiber Membranes and Technological Parameters of the Gas Separation Process.

The porous layer of composite and asymmetric hollow fiber membranes acts as a support and is exposed to strong mechanical stresses. The effect of external pressure on the polymer structure and, as a consequence, the separation characteristics of the membrane remains unsolved. Based on the solution of the Lamé approach to the calculation of the stress state of a hollow cylinder, a method of calculation was proposed for hollow fiber membranes. Calculations were based on the approximation of the isotropic nature of the physical and mechanical characteristics of the selective layer and substrate. Permissible deformation of the membrane’s selective layer was determined from the linear sector of strain-on-stress dependence, where Hooke’s law was performed. For these calculations, commercial polyethersulfone membranes were chosen with an inner and/or outer selective layer and with the following values of Young’s modulus of 2650 and 72 MPa for the selective and porous layers, respectively. The results obtained indicate that the dependence of the maximum allowable operating pressure on the substrate thickness asymptotically trends to a certain maximum value for a given membrane. Presented data showed that membranes with outer selective layer can be operated at higher working pressure. Optimal parameters for hollow fiber gas separation membrane systems should be realized, solving the optimization problem and taking into account the influence of operating, physicochemical and physicomechanical parameters on each other.

Effect of different PVDF and additives on the properties of hollow fiber membranes contactors for CO2 separation

AbstractIn the present work, different poly(vinil fluoride) (PVDF) were selected for preparing membranes, based on the fact that they are able to form polymer solutions with different viscosities. This characteristic can affect spinning, as well as, mass transfer between the polymer solution and precipitation bath; therefore, each PVDF solution can differently affect membrane formation. The effect of different additives in the polymer solutions was also investigated. Flat sheet and hollow fiber membranes were characterized by Scanning Electron Microscopy analysis, contact angle, gas permeation, porosity, and membrane gas–liquid contactor tests, aiming carbon dioxide removal. The hollow fibers prepared by the polymer which formed a less viscous solution (named PVDF‐I) had a faster light transmittance decay, which started around 150 s before the more viscous solution (PVDF‐II). Hollow fibers obtained using PVDF‐I and propionic acid, in the polymer solution, presented the best gas–liquid contactor performance. CO2 removal increased from 21 to 35.1%, for PVDF‐II and PVDF‐I, respectively, using aqueous diethanolamine solution, as absorbent liquid. In conclusion, even though PVDF‐I and PVDF‐II membranes were obtained by using the same spinning conditions and experimental methodology, the difference between the polymers properties certainly affected the final membrane morphology and transport properties.

Effect of the molecular weight and its distribution of polyvinylidene fluoride on the relationship between the spinning process, microstructure and properties of hollow fiber membranes via thermally induced phase separation

Polyvinylidene fluoride (PVDF) is an important material in the preparation of ultrafiltration membranes via the thermally induced phase separation (TIPS) method. In this paper, four PVDF hollow fiber membranes with different molecular weights were prepared via the TIPS method by using dibutyl phthalate and dioctyl phthalate as a mixed diluent. The relationship between the molecular weight of PVDF and its distribution, phase separation, crystallization behavior and spinning process has been systematically studied. The effects of three factors on the microstructure and properties of the PVDF membrane have been analyzed. The flow behaviors of the PVDF/diluent and PVDF melt were tested by a capillary rheometer and a melt flow rate instrument, respectively. A phase diagram of the membrane solution was determined by thermal polarizing microscope and differential scanning calorimetry. The crystallization behavior and angle of orientation of the membrane were tested by using a differential scanning calorimeter and a sound velocity orientation measurement instrument. The microstructures, such as the pore structure and crystalline grain structure, were observed by field emission scanning electron microscopy. Meanwhile, the properties of the membrane were examined from the view of water flux, porosity and tensile testing. The results showed that changes in the polymer molecular weights affected not only the dynamics but also the thermodynamics of phase separation in membrane formation. As the PVDF molecular weight increased, the phase separation region increased, but the membrane structure became denser. A wide molecular weight distribution easily produced large pores. Then, the water flux decreased first and then increased.

Incorporation of silica grafted silver nanoparticles into polyvinyl chloride/polycarbonate hollow fiber membranes for pharmaceutical wastewater treatment

Polyvinyl chloride/polycarbonate hollow fiber membranes incorporated with modified silver nanoparticles were prepared by wet spinning method. Fabricated membranes were then characterized by FESEM, EDX, TGA, contact angle, pure water flux and mechanical tests. It was found that the addition of modified silver nanoparticles changed the structure of hollow fiber membranes and the size of macrovoids in the middle layer decreased whereas the thickness of sponge-like outer layer increased. The results of EDX analysis showed that the modified silver nanoparticles were dispersed uniformly throughout the membranes. In addition, degradation temperature of the membranes increased as the content of nanoparticles increased which shows that thermal resistance of membranes was improved. The number of pores on the membrane surface increased due to the presence of nanoparticles but mean pore radius decreased. Addition of modified nanoparticles also improved hydrophilicity, tensile strength and elongation of hollow fiber membranes. The membranes were finally used in a membrane bioreactor system with pharmaceutical wastewater feed during 28days and the results revealed that incorporation of modified silver nanoparticles enhanced antifouling properties of hollow fiber membranes. Moreover, pure water flux and COD removal as the criteria of membrane performance increased simultaneously.

Improvement of anti-biofouling properties of hollow fiber membranes with bismuth-BAL chelates (BisBAL)

ABSTRACTIn this study, hollow fiber membranes with and without bismuth dimercaptopropanol (Bis-BAL) additive were fabricated. Membranes were characterized in terms of permeability, surface properties, anti-biofouling and antibacterial properties. Membranes were operated in a lab-scale submerged membrane bioreactor (MBR). During the MBR operation, flux, chemical oxygen demand, volatile suspended solids and suspended solids were calculated for 30 days. Results showed that extracellular polymeric substance and soluble microbial product amounts were decreased in BisBAL-containing membranes. BisBAL-added membranes had the ability to inhibit the growth of Escherichia coli. BisBAL as an additive for membranes was found to be an effective, cheap alternative for enhancing anti-biofouling properties of the membranes.

Polydimethylsiloxane/postmodified MIL‐53 composite layer coated on asymmetric hollow fiber membrane for improving gas separation performance

ABSTRACTComposite layer containing postmodified MIL‐53 (P‐MIL‐53) was exploited to be coated on as‐fabricated asymmetric hollow fiber membrane for improving gas separation performance. The morphology and pore size distribution of P‐MIL‐53 particles were characterized by SEM and N2 adsorption isotherm. The EDX mapping and FTIR spectra were performed to confirm the presence of P‐MIL‐53 deposited on the outer surface of hollow fiber membranes. The results of pure gas permeation measurement indicated that incorporation of P‐MIL‐53 particles in coating layer could improve permeation properties of hollow fiber membranes. By varying coating times and P‐MIL‐53 content, the membrane coated with PDMS/15%P‐MIL‐53 composite by three times achieved best performance. Compared to pure PDMS coated membrane, CO2 permeance was enhanced from 29.96 GPU to 40.24 GPU and ideal selectivity of CO2/N2 and CO2/CH4 also increased from 23.28 and 26.95 to 28.08 and 32.03, respectively. The gas transport through composite membrane was governed by solution‐diffusion mechanism and CO2 preferential adsorption of P‐MIL‐53 contributed to considerable increase of CO2 solubility resulting in accelerated permeation rate. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44999.

Investigation on the effect of spinning conditions on the properties of hollow fiber membrane for hemodialysis application

ABSTRACTPolyethersulfone (PES) hollow fiber membranes were fabricated via the dry‐wet phase inversion spinning technique, aiming to produce an asymmetric, micro porous ultrafiltration hollow‐fiber specifically for hemodialysis membrane. The objective of this study is to investigate the effect of spinning conditions on the morphological and permeation properties of the fabricated membrane. Among the parameters that were studied in this work are air gap distance, dope extrusion rate, bore fluid flow rate, and the take‐up speed. The contact angle was measured to determine the hydrophilicity of the fibers. Membrane with sufficient hydrophilicity properties is desired for hemodialysis application to avoid fouling and increase its biocompatibility. The influences of the hollow fiber's morphology (i.e., diameter and wall thickness) on the performance of the membranes were evaluated by pure water flux and BSA rejection. The experimental results showed that the dope extrusion rate to bore fluid flow rate ratio should be maintained at 1:1 ratio to produce a perfectly rounded asymmetric hollow fiber membrane. Moreover, the flux of the hollow fiber spun at higher air gap distance had better flux than the one spun at lower air gap distance. Furthermore, spinning asymmetric hollow fiber membranes at high air gap distance helps to produce a thin and porous skin layer, leading to a better flux but a relatively low percentage of rejection for BSA separation. Findings from this study would serve as primary data which will be a useful guide for fabricating a high performance hemodialysis hollow fiber membrane. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43633.

Preparation and properties of hollow fiber membranes for removing virus and bacteria.

In this study, polysulfone hollow fiber membrane was successfully prepared by phase inversion method for separation of virus and bacteria. When we prepare the hollow fiber membrane, we controlled various factors such as the polymer concentration, air gap and internal coagulation to investigate effect to membrane property. Morphology of surface and cross section of membrane were measured by field emission scanning electron microscope (FE-SEM). Water flux of membrane was measured using test modules. Mean pore diameter of membrane was calculated using rejection of polystyrene (PS) latex beads for separation of virus and bacteria. Flux and mean flow pore diameter of prepared membrane show 800 L/mh, 0.03 μm at 1.0 kgf/cm2. The bacteria removal performance of prepared UF membranes was over 6 logs

Preparation of PVDF/CaCO3composite hollow fiber membrane via a thermally induced phase separation method

The spinnabiliy of polyvinylidene fluoride (PVDF)/CaCO3 microparticle dope solution were explored via a thermally induced phase separation process, and composite hollow fiber (CHF) membranes were prepared successfully. The experiment results showed that the self-supporting property of CHF got improved after adding CaCO3 at low concentration of PVDF, so the control of spinning process became easy. The effects of CaCO3 on the structure and properties of hollow fiber membrane were investigated in terms of morphology, water flux, porosity, breakage strength, and crystallization. The results indicated that CHF presented a uniform bicontinuous structure. The permeability and porosity of CHF increased obviously when CaCO3 was removed by acid, while the breakage strength decreased slightly. CHF presented a good drying stability. POLYM. COMPOS., 34:1204–1210, 2013. © 2013 Society of Plastics Engineers

Investigation of transport and mechanical properties of hollow fiber membranes containing ionic liquids for pre-combustion carbon dioxide capture

Polymeric hollow fiber supported ionic liquid membranes were fabricated utilizing Matrimid® and 1-hexyl-3-methylimidalzolium bis(trifluoromethylsulfonyl)imide ([hmim][Tf2N]) as the selected polymeric and ionic liquid materials, respectively. The fibers were spun via a dry–wet nonsolvent-induced phase separation procedure, employing a single layer spinneret extrusion system. Four different types of membranes were fabricated using four morphologically different hollow fiber supports. These membranes take advantage of the fiber morphology combined with a supported ionic liquid to enable more efficient mass transfer than flat membranes. Initially the membranes had a low separation performance for CO2/H2; however, upon changing the porosity and support morphology, better permeance and selectivity were achieved. Transport properties of CO2 and H2 are reported for hollow fiber membranes containing an ionic liquid in the temperature range from 37 to 150°C. The glass transition temperature, Young's modulus, and tensile strength are also reported. The volume fractions of polymer, macro-voids, and micro-voids were determined using a combination of density measurements and an SEM image analysis technique. These quantities were then used to calculate both the bulk fiber porosity and the porosity of the micro-porous region. The surface porosity was also estimated by image analysis. It was observed that the transport and mechanical properties of the fiber were influenced by porosity.

Modelling of vacuum membrane distillation

A new method of measuring the properties of hollow fibre membranes for modelling purposes was developed. Measuring the gas permeability as a function of membrane length and extrapolating to zero length provided enough membrane material information for modelling the flux. These values resulted in the predicted Vacuum Membrane Distillation (VMD) flux within the experimental errors (±5%) for different velocities. The predicted results at different temperatures were mostly within the experimental variation range. However, the error (<10%) was greater at the highest temperature tested, perhaps due to water evaporation in the feed tank. Additionally both the modelling and experimental results show that the flux in VMD was independent of the module packing density under the presented conditions. The results also show that the mathematical model predictions agree well with the experimental results of short experimental duration (1–2h).

Zirconium stabilized Ba 0.5Sr 0.5(Co 0.8− xZr x)Fe 0.2O 3− α perovskite hollow fibre membranes for oxygen separation

Ba 0.5Sr 0.5(Co 0.8− x Zr x )Fe 0.2O 3− α ( x = 0.0–0.3) (BSCZxF) ceramic powders were synthesized via an improved EDTA-citric acid complexing method. The BSCZxF ( x = 0.05, 0.1, 0.2) perovskite hollow fibre membranes were fabricated from the powders through a phase-version/sintering technique. The oxygen permeation properties of the hollow fibre membranes were measured under air/He gradients at 700–950 °C. Experimental results have shown that the composites with x = 0.05–0.20 Zr-doping content exhibit pure cubic perovskite structure but the BSCZ 0.30F oxide contains impurity phases. Due to the substitution of zirconium in Co sites, the phase stability, the mechanical strength and the densification properties of the BSCZxF hollow fibre membranes are improved noticeably. However, the oxygen permeation flux of the BSCZxF membranes decreases with increased activation energy as the Zr-doping content is increased from 0.05 to 0.20. The suitable Zr-doping content should be around x = 0.1 in order to obtain both high permeation fluxes and high permeation stability.

Membrane fouling properties of hollow fiber membranes prepared from cellulose acetate derivatives

Three types of hollow fiber membrane were prepared from cellulose acetate (CA), cellulose acetate butyrate (CAB), and cellulose acetate propionate (CAP) via the thermally induced phase separation (TIPS) method. The three membranes had almost the same water permeability, surface roughness and zeta potential. However, hydrophilicities clearly differed between the three membranes, decreasing in the order CA > CAB > CAP. Hydrophilicity, surface roughness, zeta potential, water permeability, solute rejection and other membrane properties affect membrane fouling and the latter is quite complex. In this work, the effect of changes in membrane hydrophilicity on fouling behavior was investigated, while other membrane properties were kept virtually constant. The most hydrophilic membrane, CA, showed the highest antifouling properties for humic acid and BSA. In addition, backwashing was most effective with the CA membrane. Thus, a hydrophilic membrane surface was useful for backwashing as well as reducing flux decline.

Preparation of PVDF Hollow Fiber Membranes Using SiO2 Particles: The Effect of Acid and Alkali Treatment on the Membrane Performances

This work presents the preparation of PVDF hollow fiber membranes using SiO2 particles as an additive via a conventional immersion precipitation method. The asymmetric membrane formed consists of a uniform distribution of finger-like structure near the inner layer with sponge-like structure near the outer layer. SiO2 particles were removed from the spun membranes by a treatment using either sodium hydroxide (NaOH) solution or hydrofluoric (HF) acid. Both the NaOH solution and HF acid treatments have resulted in PVDF hollow fiber membranes with enhanced water permeability of up to 748.4 L/m2·h and 690.7 L/m2·h, respectively. HF acid was found to be more efficient in dissolving SiO2 and subsequently washing the particles out of the membrane for only 10 min compared to the treatment with NaOH solution, which took almost 1 h for complete removal. Mechanical properties of hollow fiber membrane treated with HF acid was found to be almost unaffected and showed a much better ductile behavior compared to the origi...

Characterization and pervaporation dehydration of heat-treatment PAN hollow fiber membranes

In this study, heat-treated polyacrylonitrile (PAN) hollow fiber membranes have been used to investigate the pervaporation performances of aqueous ethanol solution. The heat-treated PAN hollow fiber membranes were prepared by heat treating the as-spun PAN precursor hollow fiber membranes at 120, 160 and 210°C for 12h under air atmosphere, respectively. Scanning electron microscopy (SEM), Fourier transform infrared (FT-IR), simultaneous thermal analysis/mass spectrometry (TA/MS) and thermogravimetric analysis (TGA) are used to characterize the properties of hollow fiber membranes. The 90wt.% aqueous ethanol solution at 25°C has been used to investigate the pervaporation performances through hollow fiber membrane. Furthermore, in this investigation, we also use the positron annihilation spectroscopy (PAS) to identify the effect of heat-treatment on free volume variation of PAN hollow fiber membranes. To our knowledge, it is the pioneering work for PAS analysis technique used in hollow fiber membranes. The results have shown that the pervaporation performances of PAN hollow fiber membrane can be improved by heat-treatment. The permeation rate decreases while water content in permeate increases with increasing heat-treatment temperature. These phenomena might be due to that after heat-treating, the PAN hollow fiber membrane morphology becomes denser and the free volume of PAN polymer chain is reduced. Finally, heat-treated PAN/polyethylene glycol (PEG)10K blended hollow fiber membranes are also fabricated to investigate the pervaporation performance of aqueous ethanol solution. It has shown that the permeation rate as well as water content in permeate increases with increasing heat-treatment temperature. These phenomena can be interpreted that some of the PEG10K in hollow fiber membrane matrix has burnt away by heat-treating, and the occupied space of PEG10K would lead water molecules more easy to permeate. The long-term pervaporation stability of 210°C heat-treated PAN hollow fiber membranes was also investigated in this study. It has shown that the long-term pervaporation stability can last at least 250 days.

Phosphorylcholine-modified poly(ethylene- co-vinyl alcohol) microporous membranes with improved protein-adsorption-resistance property

This paper describes a facile and novel approach for the surface modification of poly(ethylene- co-vinyl alcohol) (EVOH) microporous membranes by introducing phosphorylcholine (PC) groups. Chemical changes of the membrane surface were characterized by attenuated total reflectance Fourier transform infrared spectroscopy (ATR/FT-IR) and X-ray photoelectron spectroscopy (XPS). Results revealed that PC groups have been successfully introduced to the EVOH membrane surface. The morphologies and mechanical properties of hollow fiber membranes were examined by scanning electron microscope (SEM), environmental SEM (ESEM), and tensile tester, which indicated that the modification had exerted little effect on the bulk structure of hollow fiber membranes. The surface properties of membranes were characterized by water-contact angle and protein adsorption measurements. It was found that the hydrophilicity was effectively improved and the bovine serum albumin adsorption was significantly suppressed by introducing PC groups onto the EVOH membrane surface. Finally, permeation fluxes of pure water and γ-globulin solution were measured to further evaluate the protein-adsorption-resistance property for the studied membranes. Results showed that PC-modified EVOH membranes had higher pure water fluxes with enhanced flux recovery and reduced flux loss from protein adsorptive fouling.

Measurement of hollow fiber membrane transport properties in hemodialyzers

Determination of the transport properties of hollow fiber membranes contained within modern hemodialyzers is indispensable for assessing device design and optimizing the hemodialysis process. To measure these transport properties, a new and simplified experimental system employing dialyzer mini-modules was developed. In comparison to a full-size dialyzer, the advantages of using mini-modules for experimental purposes are: (1) each hollow fiber is assured to be patent; (2) interaction among the fibers is negligible. Mini-module dimensions were 15 cm (length) and 1.2 cm (diameter) and each device contained 10 hollow fibers. A special syringe pump was used to ensure the steady flow in the experiments. We applied this system to measure hydraulic permeability ( L p), the diffusive permeability ( P s) and reflection coefficient ( σ) of four solutes (urea, creatinine, vancomycin and inulin), for several different types of hollow fiber membranes. These determinations allowed mean pore sizes to be calculated, and these measurements were in close agreement with estimates obtained by SEM image analysis. This approach provides fundamental transport property data necessary for optimal membrane and, ultimately, dialyzer design.

Effect of nonsolvents on properties of spinning solutions and polyethersulfone hollow fiber ultrafiltration membranes

The relationship among the presence of nonsolvent additives, the rheological behavior of spinning solutions and properties of hollow fiber membranes was studied. The additives tested were water, polyvinylpyrrolidone (PVP) and polyethylene glycol (PEG), and the base mixture was polyethersulfone/ N-methyl-2-pyrrolidone (PES–NMP). In addition the effect of combining water and PVP or PEG was also studied. Membranes were prepared using a spinneret having two concentric orifices. The internal coagulant used as well as the nonsolvent from the coagulation bath were both water at 28°C and 30°C, respectively. Rheological properties of polymer solutions were evaluated using a rheometer Haake RV 20. Changes on composition of spin-solutions were also evaluated in terms of membrane water permeability, solute rejection and membrane structure observed using scanning electron microscopy (SEM). Experimental results from this work showed that spinning solutions containing any of the three additives behave as Newtonian fluids in the range of shearing rates tested. The addition of water, PVP or PEG to the base PES–NMP solution increased its viscosity and this effect was independent of the type of additive used. A direct relation between viscosity of casting solutions and membrane thickness was found. However, rheological properties (viscosity and normal stress difference) could not be used to explain differences on membrane water flux (MWF) when using different additives at the same concentration. The addition of any of the three additives generally increased MWF. The extent of this increment seemed to be more related to changes on membrane porosity than changes on pore sizes induced by the nature and concentration of the additive used.