Microporous Polypropylene Hollow Fiber Membrane Research Articles

Microbial degradation of phenol in high-salinity solutions in suspensions and hollow fiber membrane contactors

A microporous polypropylene (PP) hollow fiber membrane contactor was used as a bioreactor to degrade phenol in aqueous solutions by Pseudomonas putida BCRC 14365 at 30 °C. The fibers were pre-wetted by ethanol to make them more hydrophilic. The initial cell density was fixed at 0.025 g l −1. The effects of added NaCl concentration (0–1.78 M) and pH (3–8) in substrate solution on the biodegradation were studied. The experimental results by suspended cells were discussed. It was shown that the cells in microporous hollow fibers were unable to tolerate substrate solution pH to a larger range than those in suspensions. The suspended cells grew well on 100 mg l −1 of phenol only at NaCl concentrations below 0.44 M. However, the cells in microporous hollow fibers could completely degrade 500 mg l −1 of phenol in solutions containing NaCl concentration up to 1.52 M, which was due to the enhanced tolerance limit to salinity effect by the membrane-attached biofilms and the sufficiently slow mass transfer of NaCl through the membrane pores.

Improvement of the antifouling characteristics for polypropylene microporous membranes by the sequential photoinduced graft polymerization of acrylic acid

Surface modification of polypropylene hollow fiber microporous membranes (PPHFMMs) was performed by a sequential photoinduced graft polymerization of acrylic acid (AA) from water solution. Structural and morphological changes on the membrane surface were characterized by attenuated total reflection-Fourier transform infrared spectroscopy (ATR/FT-IR) and field emission scanning electron microscopy (FE-SEM). Water contact angles of the membrane surfaces were also measured by the sessile drop method. Results of ATR/FT-IR indicated the successful graft polymerization of AA onto the membrane surface. Water contact angle of the modified membrane decreased with the increase of the grafting degree (GD). It showed 68° for the grafted membrane with a GD of 45.8 wt.%, nearly 61° lower than that of the nascent one. The pure water fluxes of the studied membranes depending on GD and pH value were studied. It was found that the pure water flux increased with the increase of GD and the decrease of pH value. The antifouling characteristics for the PPHFMMs before and after surface modification were assessed by the filtration of activated sludge in a submerged membrane bioreactor for synthetic wastewater treatment. Results demonstrated that after continuous operation for about 85 h, the flux recovery was 13.7% and 25.4% while the flux ratio was 1.00 and 2.52 for the nascent and grafted PPHFMMs, respectively.

Surface modification of polypropylene microporous membranes to improve their antifouling property in MBR: NH 3 plasma treatment

To improve the antifouling property of polypropylene hollow fiber microporous membranes (PPHFMMs) in a membrane bioreactor (MBR) for wastewater treatment, PPHFMMs were subjected to surface modification by NH 3 plasma treatment. Structural and morphological changes of the membranes were characterized by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Water contact angle, which reflects the hydrophilicity of the membrane surface, was measured by the sessile drop method. Results of XPS clearly indicated that the plasma treatment introduced nitrogen- and oxygen-containing polar groups on the membrane surface. The water contact angle of the modified membrane reduced with the decrease of the initial NH 3 pressure in the plasma reactor. To assess the relation between the plasma treatment and the membrane fouling in an MBR, membrane filtration for activated sludge was carried out using synthetic wastewater. PPHFMMs after NH 3 plasma treatment showed better flux recovery after cleaning than that of the unmodified membrane. Under the operating conditions with 8–12 h hydraulic retention time and 6.2 g/L sludge concentration in the MBR, the removal efficiency of COD and NH 3–N was above 95% and around 60%, respectively, for a 350 mg/L COD and a 10–15 mg/L NH 3–N fed to the bioreactor.

Application of Hollow Fiber Contactor in Nondispersive Solvent Extraction of Pu(IV) by TBP

Data on dispersion‐free solvent extraction (DFSX) of Pu(IV) from acidic nitrate media using microporous hydrophobic polypropylene hollow fiber membrane contactor with tri‐n‐butylphosphate (TBP) employing as an extractant are being presented. The DFSX operation was carried out with various concentration of TBP in n‐dodecane by passing acidic feed containing Pu (IV) through the tube side at the flow rate of 5.83 cm3 s−1 and organic extractant through the shell side at the flow rate of 1.53 cm3s−1. Extraction studies were performed under different hydrodynamic conditions and the overall mass‐transfer coefficient was evaluated with countercurrent flow condition. It was possible to extract and concentrate Pu(IV) from aqueous phase by employing this technique. For back extracting the Pu, uranous nitrate and hydroxylamine hydrochloride solution as strippants were examined, which flowed through the tube side (flow rate: 6.11 cm3 s−1) and the loaded organic was passed through the shell side with the flow rate of 1.66 cm3s−1. Results revealed that ∼80% of Pu(IV) from oxalate supernatant waste could be extracted by utilizing this technique.

Surface modification of polypropylene microporous membrane to improve its antifouling property in MBR: CO 2 plasma treatment

To improve the antifouling property of polypropylene hollow fiber microporous membranes (PPHFMMs) in a membrane-bioreactor (MBR) for wastewater treatment, the PPHFMMs were subjected to surface modification by CO 2 plasma treatment. Structural and morphological changes on the membrane surface were characterized by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Water contact angle, which reflects the hydrophilicity of the membrane surface, was measured by the sessile drop method. Results of XPS clearly indicated that the plasma treatment introduced oxygen containing polar groups on the membrane surface. The static water contact angle of the modified membrane reduced obviously at first and then kept almost constant with the increase of CO 2 plasma treatment time. To assess the relation between the plasma treatment and the membrane fouling in a MBR, filtration for activated sludge was carried out using synthetic wastewater. The PPHFMMs after CO 2 plasma treatment showed better flux recovery after cleaning than that of the unmodified membrane. Fouling index (FI) for the CO 2 plasma treated PPHFMMs was lower than that of the unmodified PPHFMM.

Removal of Aqueous Phase Trichloroethylene Using Membrane Air Stripping Contactors

This work investigates the use of membrane air-stripping (MAS) contactors containing microporous polypropylene hollow-fiber membranes to remove volatile organic compounds from water into the gas phase. Experiments using countercurrent and cross-flow flow configurations to remove trichloroethylene (TCE) from water into air were performed. The effects of influent TCE concentration, liquid and gas flow rates, and air-to-water ratio were investigated. In each case studied, it was found that mass transfer in MAS contactors is controlled by liquid-phase resistance. Maximum removal of TCE was obtained at air-to-water ratios that were significantly lower than those required for conventional packed-tower stripping. Mathematical models based on empirical correlations for the liquid-phase convective mass transfer coefficients were developed and validated with experimental data, and subsequently used to perform simulations of full-scale MAS contactors. At the operating conditions explored, full-scale cross-flow contactors were shown to be superior to countercurrent-flow contactors: for the same gas and liquid flow rates and number of fibers, cross-flow contactors removed more than 95% of the original TCE in the feed liquid whereas countercurrent-flow contactors removed less than 50%. In comparison with packed-tower stripping, MAS contactors are shown to be an alternative feasible technology.

Degradation of hydroxylated compounds using laccase and horseradish peroxidase immobilized on microporous polypropylene hollow fiber membranes

Microporous polypropylene hollow fiber membranes (HF) impregnated with horseradish peroxidase (HRP) and laccase were used to study the degradation of selected hydroxylated aromatic compounds (3,4-dimethylphenols, 4-ethylphenol, 2-hydroxy-1,2,3,4-tetrahydronaphthalene, 2-hydroxy-decahydronaphthalene and 4-hydroxy-biphenyl). It was found that, with the exception of 2-hydroxy-decahydronaphthalene, all substrates were efficiently degraded (50–100% within 48 h). In preliminary investigations, the transport behavior of the analytes through the membranes before and after enzyme immobilization was studied in batch experiments. In addition, a continuous-flow hollow fiber membrane device was used to examine the degradation performance of the immobilized enzymes on the substrates. It was successfully demonstrated that freshly prepared radish juice can be used to replace the commercially available horseradish peroxidase. The method of overall monitoring used was a combination of solid-phase microextraction/gas chromatography/mass spectrometry (SPME–GC–MS).

Hydrodynamically stable adhesion of endothelial cells onto a polypropylene hollow fiber membrane by modification with adhesive protein.

The effect on the adhesion of endothelial cells of immobilization of adhesion proteins onto a microporous polypropylene hollow fiber membrane for a conventional artificial lung was investigated with the aim of constructing a hybrid artificial lung bearing endothelial cells on the modified membrane. The membrane was modified by adsorption or covalent bonding of adhesion proteins of fibronectin, gelatin, or Pronectin. The density of adherent cells on the membrane modified by adsorption of or covalent bonding with fibronectin reached 1 x 10(5) cells/cm(2) after 1 day of incubation, which corresponds to the confluent cell density in a conventional culture dish, while the cell densities on the membranes modifieds with gelatin and Pronectin were 1-5 x 10(4) cells/cm(2) and 0.5-1 x 10(4) cells/cm(2), respectively. The loading of hydrodynamic shear force (0.23 N/m(2)) for 30 min to the membranes bearing endothelial cells had little effect on the density of adhered cells. The membrane covalently bonded with fibronectin could well maintain a high cell density even after the loading of a higher shear force of 1.15 N/m(2) for 180 min, however, at this level of shear force 49% of adhered cells on the fibronectin-adsorbed membrane were lost after 30 min. A partial cardiopulmonary bypass in rats employing the hybrid artificial lung model composed of a polypropylene hollow fiber membrane covalently bonded with fibronectin and endothelial cell adhesion showed the inhibition of tumor necrosis factor-Alpha release and an increase in IL-10 concentration in the circulating blood compared with that employing an artificial lung without cells. Long-term partial cardiopulmonary bypass employing the hybrid artificial lung model should be studied further.

Surface Modification of Microporous Polypropylene Membranes by Plasma-Induced Graft Polymerization of α-Allyl Glucoside

To change the surface property from hydrophobic to hydrophilic and to improve the antifouling property, the N2-plasma-induced graft polymerization of sugar-containing monomer [α-allyl glucoside (AG) in this work] was carried out on microporous polypropylene hollow fiber membranes (PPHFMs) for the first time. The chemical and morphological changes of the membrane surface were confirmed by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, pure-water contact-angle, and protein adsorption measurements. It was found that the AG grafting degree increased slightly with the increase of AG monomer concentration for coating and adsorption on the membrane surface, and then it decreased when the AG concentration exceeded 0.25 g/mL. The static contact angle of pure water on the grafted membrane decreased significantly from 120 to 36° with the increase of the AG grafting degree from 0 to 3.46 wt %, which indicated that the membrane surface was distinctly changed fr...

The air-phase mass tranfer resistance in the lumen of a hollow fiber at low air flow

Removal of volatile organic compounds (VOCs) from water/wastewater by membrane air stripping (MAS) was studied using microporous polypropylene hollow fiber membrane modules. Chloroform was used as model organic compound. The mass transfer of organic compound from feed solution to air stream was studied with liquid cross-flow on the shell side and airflow in the lumen of hollow fibers. The Graetz numbers for airflows in the lumen of the fibers in this study ranged from 3.1×10 −3 to 6.9×10 −3. For such low Graetz numbers, the widely used Lévéque’s [Annales de Mines 12 (13/14) (1928) 201] model was found to be inapplicable. An alternative model is presented to predict the mass transfer resistance. This model was found to be useful, particularly when the airflow rate on the lumen side of the hollow fiber is very low.

Microporous polypropylene hollow fiber membranes: Part II. Pervaporation separation of water/ethanol mixtures by the poly(acrylic acid) grafted membranes

Polypropylene hollow fiber membranes grafted with poly(acrylic acid) were used for water–ethanol separation by pervaporation. The effects of grafting degree of poly(acrylic acid) (PAA), the cross-linking degree of the grafted-PAA, the sodium counter-ions as well as the operation temperature and the ethanol concentration in feed mixtures on pervaporation properties were investigated. It was found that water-permselective pervaporation membranes could be prepared by the grafting polymerization of acrylic acid on microporous polypropylene hollow fiber membrane surface. The separation factor increased with the increase of grafting degree of PAA in the range of 20–70 wt.%. Incorporating counter-ions as well as multifunctional comonomer into the grafted chains could improve the selectivity but sacrificed the permeation flux. The separation factor of the counter-ion containing membrane decreased according to the sequence Al 3+ > K + > Ca 2+ > Na + > Li + and the permeation flux increased following the sequence Al 3+ < Ca 2+ < K + < Na + < Li +. Remarkable increase in permeation flux without decrease in separation factor was observed for Al 3+ as counter-ion in this membrane. These results might be ascribed to the increase of packing density and the decrease of swelling degree of grafted layer on the membrane surface.

Mass transport in the membrane air-stripping process using microporous polypropylene hollow fibers: effect of toluene in aqueous feed

Membrane air-stripping (MAS), using microporous polypropylene hollow fiber membrane modules, is one of the most promising processes for removal and recovery of volatile organic compounds (VOCs) from water/wastewater. In this work, aqueous feed containing VOCs was allowed to cross-flow on the shell side, whereas air flowed through the lumen of fibers. Chloroform, toluene and their mixture were used as model VOCs. The effects of presence of toluene alone and in mixture with chloroform in aqueous feed on the mass transport of VOCs through the membrane are reported. It was found that Henry’s law constants (HLCs) for toluene as well as chloroform did not change significantly in mixtures. The tests showed that higher toluene adsorption than that of chloroform on the fibers. It appeared that toluene blocked the pores partially, due to its strong affinity for the membrane material, resulting in substantially reduced mass transport.

Effects of nucleating agents on preparation of polypropylene hollow fiber membranes by melt spinning process

Microporous polypropylene hollow fiber membrane was fabricated from isotactic polypropylenesoybean oil system by melt spinning process. Addition of nucleating agent accelerated the crystallization rate and elevated the crystallization temperature. Nucleating agent increased the number of nuclei and spherulites, which offered more inter-spherulitic amorphous sites for stretching. Benzoic acid, adipic acid, and dibenzylidene sorbitol were selected as nucleating agents, and their characteristics and effects were investigated by thermal and optical analyses. Spherulite growth and micropore formation characteristics were correlated with the kind of nucleating agent. Benzoic acid and adipic acid showed the remarkable nucleating effect, while dibenzylidene sorbitol was less effective than those. Nucleating agents also helped the sample have uniform microporous structure. Increase of nucleating agent composition enhanced the nucleation effect to some extent. Nucleating agents played very important roles in enhancing the membrane porosity and water flux.

Microporous polypropylene hollow fiber membrane: Part I. Surface modification by the graft polymerization of acrylic acid

Surface modification of microporous polypropylene hollow fiber membranes was performed by graft polymerization of acrylic acid. The effects of temperature, polymerization medium, monomer concentration and multifunctional cross-linker on the graft polymerization were studied. The grafting degree on the polypropylene membrane can be greatly increased upon the addition of divinylbenzene (DVB). Scanning electron microscopy (SEM) pictures demonstrated that PAA grafted mainly on the surface of the membrane. Mercury porosimetry analysis revealed that the grafting also took place within the pores. Contact angle and absorbed water measurements showed excellent wetting properties with water for the grafted membranes. The grafted membrane did not show high flux for ultrapure water because the grafting of AA plugs the pores of the membrane.

A study of mass transfer in the membrane air-stripping process using microporous polyproplylene hollow fibers

The mass transfer of water and chloroform in membrane air-stripping (MAS) was studied using a microporous polypropylene hollow fiber membrane module, with air flow on the lumen side and liquid cross-flow on the shell side. Water transport experiments showed that its mass transport decreased significantly when the membrane had been in contact with water for prolonged periods. It was hypothesized that the increased mass transfer resistance was due to water condensation in a fraction of the membrane pores. MAS of chloroform from aqueous solutions confirmed the additional mass transfer resistance with prior exposure to water. It was concluded that membrane pores were either completely air-filled or partially wetted with water during the MAS process. Existing models are able to predict the performance only for either completely air-filled or liquid-filled pores. A modified model was proposed to take into account the diffusion through partially wetted pores. The model described the data well. This hypothesis also provided a plausible explanation to the conflicting literature values of the membrane mass transfer resistance. It was found that the membrane mass transfer resistance of the partially wetted pores is two orders of magnitude higher than that of air-filled pores. The overall mass transfer coefficient was constant for initial feed chloroform concentrations ranging from 50 to 1000 ppm.

Lipase-facilitated separation of organic acids in a hollow fiber contained liquid membrane module

A lipase-facilitated selective and continuous separation of difficult-to-separate mixtures of organic acids has been developed in a hollow fiber contained liquid membrane (HFCLM) device. The device consists of a well-mixed two-fiber-set hydrophobic microporous polypropylene hollow fiber membrane module where lipase from Candida rugosa (CRL) and lipase from porcine pancreas (PPL) were immobilized on the internal diameter of two identical sets of hollow fibers, respectively. The module shell side contained 20 v/v% octanol in n-heptane acting as the organic liquid membrane between the two commingled fiber sets. Two systems of model acid mixtures were selected to demonstrate this technique: (1) phenylacetic acid (PAA) and mandelic acids (MAs); (2) PAA and 6-aminopenicillanic acid (6-APA). Aqueous feed solution containing the acid mixtures and ethanol flowed through one fiber set; a stripping aqueous solution flowed through the second fiber set and was highly enriched in PAA. The separation factors of PAA over MAs and PAA over 6-APA were as high as 20 and 10, respectively. The esterification kinetics of PAA and ethanol catalyzed by CRL in batch experiment yielded V max and K m′ values to be 0.139 mmol/(h(mmol) CRL) and 62.2 mM, respectively. Much higher enzyme activities and enzyme stability were achieved in the HFCLM device due to immobilization of the lipases on the hydrophobic membrane surface where the organic–aqueous interface was immobilized and the ester produced was simultaneously transferred into the organic liquid membrane. The transport rate of PAA in the HFCLM device was 224 times higher than the V max measured in batch experiments.

Microporous hollow fiber membranes formed from blends of isotactic and atactic polypropylene

A novel process to prepare microporous hollow fiber membranes is proposed. Fibers of blends of isotactic polypropylene (i-PP) and atactic polypropylene (a-PP) spun under high take-up draw ratio are found to be elastic. Small angle X-ray scattering (SAXS) observation indicates that fibers have row-nucleated lamella structure normal to the fiber direction. Microporous polypropylene hollow fiber membranes were obtained from the fibers by extraction of atactic polypropylene and cool-stretching. The membranes have smaller pore size and higher permeability than those of traditional stretch method. The mechanism of micropore formation is discussed.

Kinetic analysis of the vacuum membrane distillation of chloroform from aqueous solutions

In this work, the vacuum membrane distillation (VMD) technology has been applied to the removal of chloroform from a dilute aqueous stream. Microporous polypropylene hollow fiber membranes were used to immobilize the liquid–vapor interface. The influence of the following operational variables was experimentally studied: (i) initial chloroform concentration in the feed (212–2012 mg/l), (ii) feed flow rate in the laminar flow regime (0.23–0.98 l/min) and in the transition to the turbulent flow regime (2.7–8 l/min), (iii) temperature (5–47.5°C) and vacuum pressure in the permeate side (7 and 14 mm Hg). The mathematical model proposed to describe the kinetic results includes the mass balance to the feed tank and the mass balance to the VMD module. In the laminar regime the solution of the continuity mass conservation equation makes the diffusion coefficient of chloroform in the aqueous phase the only parameter needed to describe the separation rates. In the turbulent flow regime, a macroscopic mass balance including an overall mass transfer coefficient that accounts both for liquid film diffusion and membrane mass transport was developed. It was found that only at higher Reynolds numbers within the turbulent flow regime the resistance to mass transfer in the membrane had influence on the overall mass transfer coefficient.

Hollow-Fiber Affinity Partitioning Chromatography Using Affinity-Based Reversed Micelles as Stationary Phase

An organic phase containing reversed micelles of Cibacron Blue F-3GA modified lecithin (CB-lecithin) was attached to microporous polypropylene hollow-fiber membranes. This led to the formation of a hollow-fiber column with immobilized dye-affinity reversed micelles within the membrane pores as the stationary phase. This column for chromatographic separation of proteins was called hollow-fiber affinity partitioning chromatography (HFAPC). With a column of 3 mL in net hollow fiber volume, lysozyme and bovine serum albumin (BSA) could be completely separated, and HFAPC experiments with overloaded lysozyme/BSA mixtures yielded a lysozyme fraction with a purity of 93.5% and a high yield. Furthermore, lysozyme was purified by the HFAPC from a crude chicken egg-white solution containing 9.56 mg proteins with a recovery yield of 98.2%. The purity of the lysozyme fraction was increased by 47.4-fold, reaching 85.3% of the total proteins.

Membrane Air Stripping: A Process for Removal of Organics from Aqueous Solutions

ABSTRACT The membrane air-stripping (MAS) process using microporous polypropylene hollow fiber membranes has shown potential for the removal of volatile organics from aqueous streams over conventional treatment processes, particularly in reducing the size of the equipment. This paper reviews the theoretical aspects and experimental investigations on the performance of these membranes in terms of overall mass transfer capabilities in the removal of organics from aqueous solutions. The reported findings of the effectof pH, ozone, chlorine, influence of packing density and possible fouling on the performance of these hollow fibers membranes are presented. The fate of the stripped air is discussed. Other possible applications as well as the future research needs are highlighted, along with a critical assessment of the reported work.