Polyacrylonitrile Hollow Fiber Research Articles

Development of polyethersulfone and polyacrylonitrile hollow fiber membranes for clarification of surface water and fungal enzyme broth

Hollow fiber membranes are of great commercial interest with several applications at the forefront of research to carryout bioseparations, drinking water purification, wastewater treatment besides liquid phase separations and gaseous separations. An experimental study was carried out to synthesize hollow fiber membranes from polyethersulfone (PES) and polyacrylonitrile (PAN) polymers to fabricate modules for surface water treatment and clarification of fungal enzyme broth. Design drawings of a manual hollow fiber spinning machine and spinneret were prepared to fabricate the necessary equipment for extrusion of hollow fibers. Effect of various spinning conditions on specific macroscopic fiber properties, such as outer diameter and wall thickness and membrane pore structure was studied. Concentrations of 15–20 wt% PES in n-methylpyrrolidone (NMP) and PAN in dimethyl formamide (DMF) solvents with important additives and pore formers were prepared. These polymer solutions were extruded through the spinneret and subjected to phase inversion in a water bath. The membranes were characterized by scanning electron microscopy (SEM) and pure water flux studies. PAN and PES exhibited 99.8 and 95.4% turbidity rejection. PAN exhibited a 5 log reduction of Escherichia coli bacteria for surface water treatment at a low hydraulic pressure of 1 bar with a flux of 54.2 L/m2 h at a water recovery of 80% whereas PES gave a flux of 36.6 L/m2 h with 4 log reduction of E. coli. PAN and PES membranes exhibited 54.9 and 69.3% xylanase enzyme recoveries from fungal broth at reasonable flux with turbidity rejection of 94.8 and 95.7% respectively.

Experimental investigation of aligned groove formation on the inner surface of polyacrylonitrile hollow fiber membrane

The fabrication of textured hollow fiber membrane (HFM) such as fibers with aligned grooves on the inner surface is of great interest especially for nerve regeneration applications. Grooved polyacrylonitrile (PAN) HFMs have been successfully fabricated using a dry-jet wet spinning process. Aligned grooves are formed on the HFM inner surface due to process-induced instability under selected fabrication conditions (air gap distance, polymer solution concentration, and polymer solution and nonsolvent flow rates). The influence of different fabrication conditions has been experimentally investigated to appreciate their relationship with the groove formability. It is found that HFMs with aligned grooves on the inner surface can be fabricated within an identified groove forming region, which is defined by the air gap distance, polymer solution concentration, and polymer solution and nonsolvent flow rates; and within the groove forming region, the number of grooves increases with the air gap distance from 1 to 20cm, and it decreases with the polymer solution concentration and flow rate. The number of grooves is not sensitive to the inner nonsolvent flow rate.

Hollow Fiber Membrane Decorated with Ag/MWNTs: Toward Effective Water Disinfection and Biofouling Control

The currently applied disinfection methods during water treatment provide effective solutions to kill pathogens, but also generate harmful byproducts, which are required to be treated with additional efforts. In this work, an alternative and safer water disinfection system consisting of silver nanoparticle/multiwalled carbon nanotubes (Ag/MWNTs) coated on a polyacrylonitrile (PAN) hollow fiber membrane, Ag/MWNTs/PAN, has been developed. Silver nanoparticles of controlled sizes were coated on polyethylene glycol-grafted MWNTs. Ag/MWNTs were then covalently coated on the external surface of a chemically modified PAN hollow fiber membrane to act as a disinfection barrier. A continuous filtration test using E. coli containing feedwater was conducted for the pristine PAN and Ag/MWNTs/PAN composite membranes. The Ag/MWNT coating significantly enhanced the antimicrobial activities and antifouling properties of the membrane against E. coli. Under the continuous filtration mode using E. coli feedwater, the relative flux drop over Ag/MWNTs/PAN was 6%, which was significantly lower than that over the pristine PAN (55%) at 20 h of filtration. The presence of the Ag/MWNT disinfection layer effectively inhibited the growth of bacteria in the filtration module and prevented the formation of biofilm on the surface of the membrane. Such distinctive antimicrobial properties of the composite membrane is attributed to the proper dispersion of silver nanoparticles on the external surface of the membrane, leading to direct contact with bacterium cells.

Effect of Spinning Conditions on the Morphology of Polyacrylonitrile Hollow Fiber Membranes

In this paper dry-wet spinning technique was used during the preparation of dialysis hollow fiber membranes, three-component solution polyacrylonitrile(PAN)/dimethylformamide (DMF)/Water was chosen as the basic materials. The macro and micro-morphology of the hollow fibers were observed by microscopy and SEM. The influence of some important spinning parameters such as spinning pressure, inner pressure and spinneret aperture was investigated. The appearance of some big bores in the outer surface and multilayer structure in the cross section of the hollow fibers was discussed based on phase transition theory. The results show that the spinneret dimension is the key factor that determines the macrostructure of the membrane, the bigger the spinneret aperture the bigger the fiber size; the inner, outer membrane diameters and wall thickness increase with the spinning pressure; the inner, outer membrane diameters increase and the wall thickness decreases with the inner pressure; Concentric spinneret with proper aperture must be used to obtain satisfactory fibers.

Time dependent solid-state 13C NMR study on alkaline hydrolysis of polyacrylonitrile hollow fiber ultrafiltration membranes

The effects of alkaline hydrolysis on the chemical structure of polyacrylonitrile (PAN) hollow fiber ultrafiltration (UF) membrane were studied using solid-state 13C NMR spectroscopy. The PAN membrane was hydrolyzed in an NaOH solution of pH 13, which is generally used in water industry for anti-fouling treatments of UF membranes but is much weaker than the alkaline concentrations (0.5–2.5N) used so far in conventional 13C NMR studies. All of the carbon sites of the PAN were characterized by the solid-state 1H–13C CPMAS and HETCOR NMR spectra. Upon the alkaline treatments, the chemical conversion from the cyano functional groups of the PAN to the carboxylates was observed. The analysis of the 13C CPMAS NMR spectra obtained as a function of the treatment time for 4–96h showed that the chemical modification occurred very rapidly in the early stage (≤6h) of the reaction but then proceeded slowly up to 96h. The relative amount of the hydrolyzed acrylonitrile units after 96h of the reaction at room temperature was estimated to be only 3.8%. We suggested that the alkaline hydrolysis of the PAN membrane proceeds at two distinct rates, a rapid conversion of the cyano groups on or near the membrane surface and a slow conversion of the bulk.

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.

Investigation of post-treatment effect on morphology and pervaporation performance of PEG added PAN hollow fiber membranes

In this study, hydrophilic additive, polyethylene glycol (PEG) was added in polyacrylonitrile (PAN)/ N,N-dimethylformamide (DMF) dope solution to fabricate PAN hollow fiber membrane via wet-spinning process to investigate the effect of post-treatment on the morphology and pervaporation performance of PAN hollow fiber membrane. The post-treatment includes two processes, a water bath post-treatment for 4 h at various temperatures and a dry air oven heat-treatment at 120°C for 12 h. The morphology of the hollow fiber membranes were observed with scanning electron microscope (SEM). The results show that after heat-treatment, 200 g/mole molecular weight of PEG 200 is more suitable to add in the PAN dope to fabricate the aqueous isopropanol (IPA) solution dehydration use PAN hollow fiber membrane by comparing with PEG series of additives. The porosity of the outer edge of PAN pristine hollow fiber membrane increases with increasing PEG 200 content in PAN dope solution. After post-treating the PEG-added PAN hollow fiber membrane in water bath, PEG could be leached out from the hollow fiber membrane matrix and the annealed effect might be occurred. Moreover, the pervaporation performance of 90 wt.% aqueous IPA solution through dry-air heat-treated PAN hollow fiber membranes were also investigated. By comparing with water bath post-treated-free PAN hollow fiber membranes, the water bath post-treated hollow fiber membranes have shown lower permeation rate and a little higher water content in permeate.

Carbon nanofibers with nanoporosity and hollow channels from binary polyacrylonitrile systems

Carbon nanofibers with new structural features, e.g. nanoporosity, hollow, U-shape cross-section, were generated by utilizing the phase separation behavior of polymer additive with polyacrylonitrile (PAN). The approach involved the formation of precursor fibers by electrospinning of binary mixtures of PAN with poly(ethylene oxide) (PEO), cellulose acetate (CA) or poly(methyl methacrylate) (PMMA), the removal of the polymer and the carbonization of the remaining PAN. The carbon nanofiber yield was ca 50% of PAN in all cases. Nanoporous carbon nanofibers with an average diameter of 100 nm were generated from the water treated PAN/PEO precursors. Multi-channel hollow fibers (90–190 nm diameters) were produced from the acetone treated PAN/CA precursors. Carbon fibers produced from the chloroform treated PAN/PMMA precursors were 250–400 nm in diameters and consisted of varied hollow structures, i.e., hollow and U-shape cross-sections from those containing 30% and 50% PAN, respectively, and multi-channel hollow fibers from the 70/30 PAN/PMMA precursor. Carbonization of equal-mass PAN/PMMA as-spun fibers also produced similarly U-shape cross-sections as the chloroform treated ones, showing promise of direct carbonization. This simple and yet versatile approach to create new structural features in carbonized fibers has shown to depend on the distinct phase separation as well as the pyrolytic behaviors of the second polymer component.

Improved MEUF removal of naphthenic acids from produced water

Naphthenic acids are naturally occurring organics in produced waters from oil recovery operations. In principle, these contaminants can be removed using micellar-enhanced ultrafiltration (MEUF), which is an effective technique for the removal of organic contaminants from water streams. In this work, we show that the amphiphilic nature of the naphthenic acids contributed to decreasing the critical micelle concentration (CMC) of cetylpyridinium chloride (CPC), a widely used surfactant in MEUF. This reduction in CMC allowed a decrease in the CPC dosage required to attain certain removal of the organics, and hence, improved the performance of traditional MEUF as a result of reducing back contamination and potential fouling of the membrane. The effect of CPC feed concentration, and the concentration and carbon number of the naphthenic acids on permeate flux, recovery ratio and percent rejection of CPC and naphthenic acids were explored over a range of trans-membrane pressure. The MEUF setup employed hydrophilic polyacrylonitrile (PAN) hollow fiber membrane with 13 kDa MWCO, since it allowed for high permeate flux and contaminant rejection.

Preparation and pH‐sensitivity of polyacrylonitrile (PAN) based porous hollow gel fibers

AbstractPolyacrylonitrile based porous hollow gel fibers were prepared from PAN hollow fibers by oxidation and subsequent alkaline treatment. Fourier‐transform infrared (FTIR), X‐ray diffraction, and scanning electron microscope (SEM) analyses showed that the PAN porous hollow gel fiber was a kind of amphoteric fiber due to the combination of cationic groups of pyridyl and anionic groups of carboxyl; after gelation the hollow channel and finger‐like pores on the fiber walls were conserved. The effects of cyclization reaction degree, alkaline solution concentration, and alkaline treatment time on the mechanical properties or pH‐sensitive behavior of the porous hollow gel fibers were investigated. The elongation/contraction behavior was studied in detail. It was found that the gel fiber exhibited a large swelling in an alkaline solution and contracting in an acid solution; the swelling change in length was above 90%; the responsive time of elongation/contraction was less than 20 s; the maximum contraction force was 20 N/cm2; and pH‐sensitivity was reversible. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Perfluorosulfonic acid—Tetraethoxysilane/polyacrylonitrile (PFSA‐TEOS/PAN) hollow fiber composite membranes prepared for pervaporation dehydration of ethyl acetate–water solutions

AbstractPreparation of organic‐inorganic composite membranes and their pervaporation (PV) permeation and separation characteristics for the aqueous solution of ethyl acetate were described. Polyacrylonitrile (PAN) hollow fiber ultrafiltration membrane as support membrane, the mixtures of perfluorosulfonic acid (PFSA) and tetraethoxysilane (TEOS) by the sol‐gel reaction as the coating solution, the PFSA‐TEOS/PAN hollow fiber composite membranes by the different annealing conditions were prepared. The swelling of PFSA in ethyl acetate aqueous solutions was inhibited with addition of TEOS. The PFSA‐TEOS/PAN composite membranes containing up to 30 wt % TEOS in coating solution exhibited high selectivity towards water, then the selectivity decreased and permeation flux increased with increasing the TEOS concentration more than 30 wt %. When the PFSA‐TEOS/PAN composite membranes were annealed, the separation factor increased with increasing annealing temperature and time. Higher annealing temperature and longer annealing time promoted the crosslinking reaction between PFSA and TEOS in PFSA‐TEOS/PAN composite membranes, leading to the enhanced selectivity towards water. For the PFSA/PAN and PFSA‐TEOS/PAN composite membrane with 5 and 30 wt % TEOS annealed at 90°C for 12 h, their PV performance of aqueous solution 98 wt % ethyl acetate were as follows: the separation factors were 30.8, 254 and 496, while their permeation flux were 1430, 513 and 205 g/m2 h at 40°C, respectively. In addition, the PV performance of PFSA‐TEOS/PAN composite membranes was investigated at different feed solution temperature and concentration. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Role of naphthenic acid contaminants in the removal of p-xylene from synthetic produced water by MEUF

The high demand for water in oil sands operations in addition to the shortage of fresh water resources mandate continuous search for reliable and cost effective water treatment technologies. Micellar-enhanced ultrafiltration (MEUF) is potentially applicable to produced water treatment. MEUF is, however, susceptible to membrane plugging and back contamination, especially at high surfactant dosages. Recent investigations showed that addition of small amounts of a non-ionic surfactant to an ionic surfactant solution reduces the critical micellar concentration (CMC) of the mixed surfactant solution, and consequently reduces the surfactant dosage required to achieve certain removal of contaminants using MEUF. In the present study a naphthenic acid, octanoic acid, typically existing in produced water is shown to play a similar role as the non-ionic surfactant when added to the cationic surfactant cetylpyridinium chloride (CPC). Cross-flow MEUF using three different molecular weight cutoffs (MWCOs) of polyacrylonitrile (PAN) hollow fiber membranes was used to treat synthetic produced water containing p-xylene. The mixed CPC/octanoic acid solution removed comparable percentages of p-xylene contaminant at much lower concentrations of CPC. Decreasing CPC concentration in the feed resulted in less fouling and higher permeate flux and reduced back contamination. This, in turn, enhanced the performance of MEUF.

Hydrolysis of olive oil catalyzed by surfactant-coatedCandida rugosa lipase in a hollow fiber membrane reactor

In this study, we invetigated the hydrolysis of olive oil catalyzed by a surfactant-coatedCandida rugosa lipase in a hydrophilic polyacrylonitrile hollow fiber membrane reactor and then compared the results to those using the native lipase. The organic phase was passed through the hollow inner fibers of the reactor and consisted of either the coated lipase and olive oil dissolved in isooctane or the coated lipase dissolved in pure olive oil. The aqueous phase was pumped through the outer space. After 12 h and with conditions of 30°C, 0.12 mg enzyme/mL and 0.62 M olive oil, the substrate conversion of the coated lipase reached 60%. This was twice the conversion for the same amount of native lipase that was pre-immobilized on the membrane surface. When using pure olive oil, after 12 h the substrate conversion of the coated lipase was 50%. which was 1.4 times higher than that of the native lipase.

Effect of draw ratio and coagulant composition on polyacrylonitrile hollow fiber membranes

Asymmetric polyacrylonitrile (PAN) hollow fiber membranes were fabricated via the dry-jet wet spinning process. The effects of the draw ratio and the DMF content in the coagulation bath on the mechanical properties, permeation, and morphology were investigated. The external surface and cross-section of the resulting hollow fibers were examined using a scanning electron microscope (SEM) and the thermal properties were measured. Additional characterization using X-ray and porosity measurement suggested the improvement in molecular orientation. The results show that the maximum draw ratio increased with the DMF content in the coagulant. The pure water permeability increased while the retention decreased with the increase of the draw ratio. On the other hand, both the permeability and the retention increased with the DMF content.

Pilot study on the treatment of spent solvent cleaning rinse in metal plating

Abstract Pilot trials on a spent solvent cleaning rinse from a nickel-plating operation were conducted using polyacrylonitrile hollow-fiber UF membranes. The results indicated that the membrane pore size and operating conditions were important factors for treating the emulsified spent solvent rinse. Retention of TOC increased with a decrease in membrane pore size or product recovery. TOC retention also increased with increase of feed velocity. Flux declines of membranes of MWCO 13 K and 50 K over time showed the same trend and their stabilized fluxes were 12 and 60 L m −2 h −1 at 0.1 MPa, respectively. The results also showed that retention of TOC and oil/grease for the membrane of MWCO 13 K was above 95.1% and 72.5%, respectively. It was hypothesized that there might be a critical micellar concentration for the emulsified solvent or oil/grease.

Effect of bore liquid temperature and dope concentration on mechanical properties and permeation performance of polyacrylonitrile hollow fibers

Asymmetric polyacrylonitrile (PAN) hollow fiber membranes were fabricated via the dry-jet wet spinning process. Water at various temperatures was used as the bore liquid. The effects of the dope concentration and the bore liquid temperature on the hollow fiber mechanical properties and permeation performance were investigated. The internal surface and cross-section of the resulting hollow fibers were examined using a scanning electron microscopy (SEM), porosity ( ɛ) and the mechanical properties were measured. Dextran of four molecular weights was used to measure the retention. The results show that the tensile strength increased with the dope concentration of polymer and the decrease of bore liquid temperature. In addition, hollow fibers spun from higher dope concentration using lower bore liquid temperature would exhibit lower hydraulic permeability and higher retention.

Heat-treatment effect on the morphology and pervaporation performances of asymmetric PAN hollow fiber membranes

The influence of heat-treatment conditions on the morphology and pervaporation performances of aqueous isopropanol (IPA) solution through wet spinning prepared polyacrylonitrile (PAN) hollow fiber membranes were investigated. At heat-treatment temperature higher than 210 °C, dehydrogenation and cyclization reaction of the PAN molecular occurred during the heat-treatment process. The SEMs observation depicts that the morphology of heat-treated PAN hollow fiber membranes was denser with increasing the heat-treatment temperature. The permeation rate and water concentration in the permeate for a 90 wt.% aqueous isopropanol solution through the heat-treated PAN hollow fiber membranes at 120 °C for 12 h were 186 g/m 2 h and 99.2 wt.%, respectively.

The effects of carbonization time on the properties and structure of PAN-based activated carbon hollow fiber

Polyacrylonitrile (PAN) hollow fibers were pretreated with ammonium dibasic phosphate, then further oxidized in air, carbonized in nitrogen and activated with carbon dioxide. The effects of carbonization time of PAN hollow fiber precursor on the microstructure, specific surface, pore-size distribution and adsorption properties of PAN-based carbon hollow fiber (PAN-CHF) and PAN-based activated carbon hollow fiber (PAN-ACHF) were studied in this work. After the activation process, the surface area of the PAN-ACHF increased very remarkably, reaches 506 m2⋅g− 1, when fibers are carbonized at 900∘C for 70 min and activated at 800∘C for 40 min. The different adsorption ratios to two adsorbates including creatinine and VB12 reflect the number of micropores and mesopores in PAN-ACHF. The dominant pore sizes of mesopores in PAN-ACHF range from 2 to 5 nm

Adsorption properties of polyacrylonitrile-based activated carbon hollow fiber

In this work, polyacrylonitrile (PAN) hollow fibers are pretreated with ammonium dibasic phosphate and then further oxidized in air, carbonized in nitrogen, and activated with carbon dioxide. The adsorption properties of the resultant activated carbon hollow fibers (ACHF) prepared in different conditions were studied. The results show that the adsorption properties of ACHF change regularly with preparing conditions of ACHF. The different adsorption ratios to three adsorbates reflect the number of micropores and mesopores in PAN-based ACHF. Pretreatment with phosphate can increase the number of mesopores. Proper oxidation temperature and time can increase the number of micropores and mesopores. When carbonization temperature is more than 900°C and carbonization time ranges from 50 to 90 min, the number of micropores and mesopores, especially mesopores, greatly increases. Compared with other treatments, activation treatment greatly increases the number of micropores and mesopores, and the dominant pore sizes of mesopores in PAN-based ACHF are from 2 to 10 nm. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 602–607, 2004

Characterization and inhibitory effect of antibacterial PAN-based hollow fiber loaded with silver nitrate

Silver-loading polyacrylonitrile hollow fiber was spun via the dry jet–wet spinning technique from a dope containing 0.5 wt.% silver nitrate. The morphology of the resulting hollow fibers was examined using a scanning electron microscope (SEM) and Ag content in the fiber was measured using an inductively coupled plasma (ICP) atomic emission spectrometer. These hollow fibers had a five-layer structure and dense inner and outer surfaces. The average pore size was 20 nm and the silver content was 0.19 wt.% for the nascent hollow fibers. After flushing with water for 60 days, the silver content in the hollow fibers decreased to 0.1 wt.%, and still showed antibacterial activity against Escherichia coli and Staphylococcus aureus. On the other hand, by permeating water through the hollow fibers, silver content was decreased faster and may require periodical replenish.