Microporous Polypropylene Hollow Fiber Membrane Research Articles

Process Scale‐Up of an Energy‐Efficient Membrane Solvent Extraction Process for Rare Earth Recycling from Electronic Wastes

This study reports the process scale‐up and long‐term performance of an energy‐efficient and cost‐effective membrane solvent extraction (MSX) process for separation and recovery of high purity rare earth oxides (REOs) from scrap permanent magnets (SPMs). The rare earth elements (REEs), including dysprosium, neodymium, and praseodymium, are recovered from SPMs using a neutral extractant, tetraoctyl diglycolamide (TODGA) embedded in a microporous polypropylene hollow fiber membrane module. The MSX process performance is demonstrated with bench scale module with membrane surface area of 1.4 m2 to industrial scale modules with membrane surface area of up to 20 m2 to enable the processing of up to 1 ton month−1 of SPMs. The purity and the yield of the recovered REOs are >99.5 wt% and >95%, respectively. The average extraction rate of REOs is >10 g m−2 hr−1. A skid of MSX system is assembled with a membrane area of 40 m2. The MSX skid successfully recovers REOs with a capacity of 300 kg REOs/month. Finally, it is determined that the organic phase containing the extractant maintains its performance up to 250 h. The results suggest that the MSX process is an economically viable and environmentally friendly process for separation and recovery of REOs from electronic wastes.

Comprehensive insights into performance of water gap and air gap membrane distillation modules using hollow fiber membranes

A commercially available microporous polypropylene hollow fiber membranes were employed for air gap and water gap membrane distillation (i.e., AGMD and WGMD, respectively) processes. In both configurations, the outer surface of commercially available dense polypropylene hollow fibers was used as the condensing surface of the permeate. The performance levels of the AGMD and WGMD processes utilizing microporous polyvinylidene fluoride membranes fabricated in-house were compared with those using polypropylene membranes. Under the given specific operating conditions, the maximum mean permeation flux values in AGMD and WGMD using polypropylene hollow fiber membranes were approximately 24 and 27 kg/m2h, respectively. In addition, theoretical studies on AGMD and WGMD using the designed hollow fiber module configuration were performed. The predicted results were found to well agree with the experimental results, thus verifying their validity. Moreover, parametric studies were conducted to identify the optimum evaporation-to-condensation surface area ratio (i.e., optimum numbers of hollow fiber membranes and hollow fiber condensers) in terms of specific energy consumption.

Optimizing SO2 Adsorption from Flue Gas Using Microporous Polypropylene Hollow Fiber Membrane Contactor

This study optimized the operational parameters of removing SO2 from flue gas via a polymeric hollow fiber membrane contactor (HFMC) using the response surface methodology (RSM). The distilled water and polypropylene hollow fibers were applied as the adsorbent and membrane material, respectively. Three experimental parameters were chosen as independent variables: liquid flow rate, gas flow rate, and initial SO2 concentration. The SO2 removal efficiency was significantly affected by the initial SO2 concentration. The optimal ratio of liquid-to-gas flow rate was found to be 0.25 to reach maximum separation efficiency (98.81%). The optimal value of the liquid flow rate was 33 l/h, and the optimal gas flow rate was 131 l/h. The effect of CO2 presence, module length, fibers number, temperature, and the adsorbent nature were also investigated under optimal values obtained for the ratio of liquid-to-gas flow rate. Results indicated that CO2 presence in the flue gas slightly affects SO2 removal using water as an absorbent in HFCM. Furthermore, it was indicated that the SO2 removal efficiency was a function of the flue gas temperature and number of fibers: it decreased as the temperature rose from 20 to 50°C and the fiber numbers increased from 300 to 1000. This study offers a model to predict the efficiency of SO2 removal using HFMC under different conditions and provides the ground to further explore the industrial applications of this technology.

Desflurane and sevoflurane concentrations in blood passing through the oxygenator during cardiopulmonary bypass: a randomized prospective pilot study.

PurposeVolatile anesthetics (VAs) protect myocardial cells in cardiovascular surgery. A recent clinical trial of cardiopulmonary bypass (CPB) surgery reported no significant difference in mortality rates between the use of VAs and total intravenous anesthetics at 1 year postoperatively. However, oxygenator function may affect the VA pharmacokinetics. Thus, we measured the VA blood concentrations during CPB in patients managed with four different microporous polypropylene hollow fiber membrane oxygenators.MethodsTwenty-four patients scheduled for elective CPB were randomly allocated to one of the two VA groups (desflurane and sevoflurane groups) and, then, randomly divided into one of four oxygenator groups: Terumo, LivaNova, Medtronic, and Senko (n = 3). Additionally, in each VA group, three patients were randomly selected and redundantly allocated to the human lung group (for control blood VA concentration without oxygenator). Blood samples collected 20 min after starting 6.0 vol% desflurane or 1.7 vol% sevoflurane were analyzed using gas chromatography. Oxygenator-related complications and structural changes in the membrane surface of each oxygenator after surgery were evaluated.ResultsThe mean (standard deviation) concentrations of desflurane and sevoflurane in the human lung were 182.4 (23.2) and 54.0 (9.6) μg/ml, respectively; not significantly different from those in the four oxygenator groups. No oxygenator-related complications occurred. Structural changes in membrane fibers did not occur after clinical use, except for difficulty in image acquisition with Senko products.ConclusionOur results demonstrated that the blood concentrations of desflurane and sevoflurane passing through oxygenators used during CPB were similar to those in the human lung control.Electronic supplementary materialThe online version of this article (10.1007/s00540-020-02844-1) contains supplementary material, which is available to authorized users.

Experimental investigation and mathematical modeling of CO2 sequestration from CO2/CH4 gaseous mixture using MEA and TEA aqueous absorbents through polypropylene hollow fiber membrane contactor

In the current study, experimental and mathematical results of a counter-current contact between CO2/CH4 gaseous mixture and aqueous liquid absorbents (MEA and TEA) through a microporous polypropylene hollow fiber membrane contactor are presented to evaluate the sequestration percentage of CO2 acidic pollutant from gaseous mixture. One of the aims of this paper is to experimentally and mathematically study the effects of gas flow rate, aqueous liquid absorbents' flow rate and also inlet CO2 concentration on the removal efficiency of CO2. In order to carry out this, a two dimensional mathematical model is developed to predict the experimental results. The experimental results show that MEA absorbent has higher superiority for efficient removal of CO2 acidic gas compared to TEA absorbent. Based on the experimental results, the sequestration efficiency of CO2 from gaseous mixture applying MEA and TEA aqueous absorbents is about 92% and 62%, respectively. The simulated results of CO2 sequestration in wide ranges of gas flow rate, inlet CO2 concentration and liquid absorbents' flow rate demonstrate an excellent agreement with those of experimentally measured ones with average absolute relative errors (AAREs) of 4.3%, 4.4% and 3.6% for employing MEA and 6.9%, 3.4% and 5.2% for using TEA absorbents, respectively. Additionally, this article aims to study the influence of momentous operational parameters such as number of fibers, module length and also membrane porosity and tortuosity on the CO2 separation efficiency. Based on the experimental and the numerical simulated results, increase in the gas flow rate, the membrane tortuosity and the CO2 inlet concentration significantly deteriorates the sequestration efficiency of CO2 while increment of the fibers counts, the membrane module length, the membrane porosity and the liquid flow rate positively encourages the CO2 sequestration percentage.

Application of pseudo-emulsion-based hollow fiber strip dispersion for the extraction of p-nitrophenol from aqueous solutions

ABSTRACTThe extraction of p-nitrophenol (PNP) from aqueous solutions through a pseudo-emulsion hollow fiber strip dispersion (PEHFSD) system was conducted in a microporous hydrophobic polypropylene hollow fiber membrane contactor. For the optimization of the process variables, face-centered central composite design (FCCD) has been used. It was observed that initial feed concentration, carrier composition and stripping phase concentration were the three FCCD factors, which influenced the nitrophenol extraction. Using the optimized process conditions for the separation of PNP, experiments were also performed for the separation of other nitrophenols through PEHFSD system. By the FCCD design and analysis, almost 99% extraction of all three nitrophenols was achieved at optimum conditions. A mass transfer model was also developed and aqueous and membrane resistances were evaluated as 196.46 s cm−1 and 50.14 s cm−1, respectively.

Cadmium(II) transfer using (TiOAC) ionic liquid as carrier in a smart liquid membrane technology

The transfer of cadmium(II) from acidic chloride solutions through a smart liquid membrane technology was investigated in a microporous polypropylene hollow fiber membrane contactor. The organic solution of tri-isooactylammonium chloride (TiOAC) in Exxsol D100 was used as carrier. The acidic chloride feed solution containing the metal was passed through the tube side, and the pseudo-emulsion of the organic solution and NH4OH was passed through the shell side in counter-current mode, using a unique contactor in the process. In the pseudo-emulsion based hollow fiber membrane with strip dispersion (PEHFMSD) technology, the aqueous strip solutions of ammonium hydroxide are dispersed in the organic solutions in a tank with a mixing arrangement to provide a strip dispersion. This strip dispersion circulates from the tank to the membrane module to provide constant supply of the organic solution to the membrane pores. Different hydrodynamic and chemical variables, such as variation in feed acidity, metal concentration in the feed, carrier concentration in the organic phase, variation in feed, strip and organic phase volume ratios and variation in the feed and pseudo-emulsion flows, were investigated. Mass transfer coefficients were calculated from experimental data.

Surface modification of polypropylene membrane by polyethylene glycol graft polymerization

Polypropylene hollow fiber microporous membranes have been used in a wide range of applications, including blood oxygenator. The hydrophobic feature of the polypropylene surface causes membrane fouling. To minimize fouling, a modification consisting of three steps: surface activation in H2 and O2 plasma, membrane immersion in polyethylene glycol (PEG) and plasma graft polymerization was performed. The membranes were characterized by contact angle measurement, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), tensile test, scanning electron microscopy (SEM) and atomic force microscopy (AFM). Oxygen transfer of modified membranes was also tested. The stability of grafted PEG was measured in water and in phosphate buffer saline (PBS) at 37°C. Blood compatibility of modified surfaces was evaluated by the platelet adhesion method. Water contact angel reduction from 110° to 72° demonstrates the enhanced hydrophilicity, and XPS results verify the presence of oxygenated functional groups due to the peak existence in 286eV as a result of PEG grafting. The results clearly indicate that plasma graft-polymerization of PEG is an effective way for antifouling improvement of polypropylene membranes. Also, the results show that oxygen transfer changes in PEG grafted membranes are not significant.

Preparation of Polypropylene and Polysulfone Composite Ultrafiltration Membrane though Physical Coating Method

Polypropylene/polysulfone composite ultrafiltration membrane was prepared though coating method using microporous polypropylene hollow fiber membrane as a support layer and polysulfone membrane as a functional layer. Membranes of different pore sizes were prepared by L-S phase translation though changing the concentration of PS. The properties of the composite membrane include water flux and rejections of PEG-2000 were studies. The flux of 78 L/m2h and 98 % rejection was achieved at PS concentration of 11%, Polyvinylpyrrolidone of 4 %, liquid phase coagulation time of 3 hours.

Membrane extraction for detoxification of biomass hydrolysates

Membrane extraction was used for the removal of sulfuric acid, acetic acid, 5-hydroxymethyl furfural and furfural from corn stover hydrolyzed with dilute sulfuric acid. Microporous polypropylene hollow fiber membranes were used. The organic extractant consisted of 15% Alamine 336 in: octanol, a 50:50 mixture of oleyl alcohol:octanol or oleyl alcohol. Rapid removal of sulfuric acid, 5-hydroxymethyl and furfural was observed. The rate of acetic acid removal decreased as the pH of the hydrolysate increased. Regeneration of the organic extractant was achieved by back extraction into an aqueous phase containing NaOH and ethanol. A cleaning protocol consisting of flushing the hydrolysate compartment with NaOH and the organic phase compartment with pure organic phase enabled regeneration and reuse of the module. Ethanol yields from hydrolysates detoxified by membrane extraction using 15% Alamine 336 in oleyl alcohol were about 10% higher than those from hydrolysates detoxified using ammonium hydroxide treatment.

Surface modification of polypropylene membrane to improve antifouling characteristics in a submerged membrane-bioreactor: Ar plasma treatment

To improve the antifouling characteristics of polypropylene hollow fiber microporous membranes in a submerged membrane-bioreactor for wastewater treatment, the surface-modification was conducted by Ar plasma treatment. Surface hydrophilicity was assessed by water contact angle measurements. The advancing and receding water contact angles reduced after the surface modification, and hysteresis between the advancing and receding water contact angles was enlarged after Ar plasma treatment due to the increased surface roughness after surface plasma treatment. After continuous operation in a submerged membrane-bioreactor for about 55 h, the flux recovery after water cleaning and the flux ratio after fouling were improved by 20.0 and 143.0%, while the reduction of flux was reduced by 28.6% for the surface modified membrane after 1 min Ar plasma treatment, compared to those of the unmodified membrane. Morphological observations showed that the mean membrane pore size after Ar plasma treatment reduced as a result of the deposition of the etched species; after it was used in the submerged membrane-bioreactor, the further decline of the mean membrane pore size was caused by the deposition of foulants. X-ray photoelectron spectroscopy and infrared spectroscopy confirmed that proteins and polysaccharide-like substances were the main foulants in the precipitate.

Comparative analysis of CO 2 separation from flue gas by membrane gas absorption technology and chemical absorption technology in China

This paper firstly evaluated the CO 2 absorption performance of a membrane gas absorption system (MAS) and chemical absorption system (CAS) using the overall mass transfer coefficient ( K G a V) as a basis for comparison. MAS selected microporous polypropylene (PP) hollow fiber membrane contactors to capture CO 2 from the simulated flue gas while CAS used a randomly packed column containing stainless Pall packing. Aqueous monoethanolamine (MEA) solution was adopted in both absorbers. Experimental results show that if the fresh membranes were tested, MAS has the higher K G a V values than that of CAS. However, when all the membrane pores were completely wetted or 50% pores were plugged, CAS inversely performs better than MAS in terms of K G a V values. In addition, the economic performance of MAS and CAS was also estimated. Results indicate that if the real operational time of membrane module is reduced to less than the critical value affected by the membrane price, the CO 2 captured cost of MAS is inversely higher than that of CAS. Therefore, the current well-accepted statement that MAS is superior to CAS in any case may be somewhat arbitrary unless membrane pore-wetting and pore-plugging problems, how to reduce the membrane price and how to prolong the membrane lifetime can be solved perfectly in the future.

Antibacterial effect of surface-functionalized polypropylene hollow fiber membrane from surface-initiated atom transfer radical polymerization

Microporous polypropylene (PP) hollow fiber (PPHF) membranes with surface-grafted block copolymer brushes of poly(ethylene glycol) monomethacrylate (PEGMA) and 2-(dimethylamino)ethyl methacrylate (DMAEMA) (PPHF- g-(PPEGMA- b-PDMAEMA)) were prepared via consecutive surface-initiated atom transfer radical polymerization (ATRP). The effective pore size of the surface modified PPHF membranes could be adjusted by controlling the graft chain length, or the ATRP time. Quaternization of the tertiary amine groups of the PDMAEMA block with 1-bromododecane gave rise to a high concentration of quaternary amine salt (QAS) on the PPHF membrane surface. The antibacterial effect of the quaternized PPHF- g-(PPEGMA- b-PDMAEMA) membrane was assayed with Escherichia coli ( E. coli, a Gram-negative bacterium) and Staphylococcus aureus ( S. aureus, a Gram-positive bacterium) cultures. In addition to bactericidal properties, the functionalized membrane surface also exhibited anti-fouling effect for bacteria due to the hydrophilic nature of the P(PEGMA) block on the PPHF- g-(PPEGMA- b-PDMAEMA) membrane. The permanence of antibacterial effect of the functionalized PPHF membrane was also demonstrated in repeated applications of the quaternized PPHF- g-(P(PEGMA)- b-PDMAEMA) membrane.

Surface modification of polypropylene microporous membrane to improve its antifouling characteristics in an SMBR: Air plasma treatment

Polypropylene hollow fiber microporous membranes (PPHFMMs) were surface-modified by air plasma treatment. Morphological changes on the membrane surface were characterized by field emission scanning electron microscopy (FE-SEM). The change of surface wettability was monitored by contact angle measurements. The static water contact angle of the modified membrane reduced obviously with the increase of plasma treatment time. The relative pure water flux for the modified membranes increased with plasma treatment time up to 2 min, and then it decreased with further increase of plasma treatment time. Decreases in the tensile strength and the rate of tensile elongation at break of the modified membranes were also observed. The antifouling characteristics of the membranes in a submerged membrane-bioreactor (SMBR) for wastewater treatment were investigated. After continuous operation in the SMBR for about 110 h, flux recoveries after water and caustic cleaning are 11.66 and 34.99% higher for the 4 and 2 min air plasma treated membrane than those of the unmodified membrane. Result indicated that reversible fouling was only weakly dependent on membrane surface chemistry; in contrast, irreversible fouling exhibited a marked dependence on surface chemistry.

Mitigated membrane fouling in an SMBR by surface modification

Fouling is a major obstacle in membrane processes applied in membrane bioreactor. To improve the antifouling characteristics of polypropylene hollow fiber microporous membranes (PPHFMMs) in a submerged membrane bioreactor (SMBR), the PPHFMMs were surface modified by NH 3, CO 2 plasma treatment, photoinduced graft polymerization of acrylamide and acrylic acid. The structural and morphological changes on the membrane surface were characterized by X-ray photoelectron spectroscopy (XPS), attenuated total reflection-Fourier transform infrared spectroscopy (FT-IR/ATR) and field emission scanning electron microscopy (FE-SEM). The change of surface wettability was monitored by contact angle measurements. The results of XPS and FT-IR/ATR clearly indicated the successful modification on the membrane surface. The static water contact angle of the modified membrane reduced obviously. The antifouling characteristics of the modified membranes in an SMBR were evaluated. The modified membranes showed better filtration performances in the submerged membrane bioreactor than the unmodified one, and the acrylic acid-grafted membrane presented the best antifouling characteristics. The results demonstrated that (1) the surface carboxyl-containing membranes were better than the surface amido-containing membranes; (2) surface-grafted membranes were better than the plasma-treated membranes.

Photoinduced graft polymerization to improve antifouling characteristics of an SMBR

Hydrophobic polypropylene hollow fiber microporous membranes (PPHFMMs) were surface-modified by photoinduced graft polymerization of 2-aminoethyl methacrylate (AEMA), which were characterized by attenuated total reflection—Fourier transform infrared spectroscopy (FT-IR/ATR), X-ray photoelectron spectroscopy (XPS), and field emission scanning electron microscopy (FE-SEM). Water contact angle was measured by the sessile drop method. The results of FT-IR/ATR and XPS clearly indicated that AEMA was grafted on the membrane surface. The water contact angle on the modified membrane was 50.3° lower than that of the unmodified membrane. The antifouling characteristics in a submerged membrane bioreactor (SMBR) were investigated. After continuous operation in the SMBR for about 65 h, reduction from pure water flux was 3.03% lower, flux recovery after water and caustic cleaning were 28.01 and 48.95% higher for the AEMA grafted PPHFMM with a grafting degree of 5.67 wt.% than those of the unmodified membrane, flux ratio after fouling was 1.78 times for the modified membrane with a grafting degree of 7.30 wt.% of the unmodified one.

Surface modification of polypropylene microporous membrane to improve its antifouling characteristics in an SMBR: N 2 plasma treatment

Fouling is the major obstacle in membrane processes applied in water and wastewater treatment. The polypropylene hollow fiber microporous membranes (PPHFMMs) were surface modified by N 2 low-temperature plasma treatment to improve the antifouling characteristics. Morphological changes on the membrane surface were characterized by field emission scanning electron microscopy (FE-SEM). The change of surface wettability was monitored by contact angle measurements. The static water contact angle of the modified membrane reduced obviously; the relative pure water flux of the modified membranes increased with the increase of plasma treatment time. To assess the relation between plasma treatment and membrane fouling in a submerged membrane bioreactor (SMBR), filtration of activated sludge was carried out by using synthetic wastewater. After continuous operation in the SMBR for about 90 h, flux recoveries for the N 2 plasma-treated PPHFMM for 8 min were 62.9% and 67.8% higher than those of the virgin membrane after water and NaOH cleaning. The irreversible fouling resistance decreased after plasma treatment.

Vacuum assisted removal of volatile to semi volatile organic contaminants from water using hollow fiber membrane contactors: II: A hybrid numerical-analytical modeling approach

Applying a new hybrid numerical and analytical approach in the finite element simulator RockFlow/GeoSys for hydraulic flow and mass transport, the efficiency of the removal of organic contaminants from water using a microporous polypropylene hollow fiber membrane module (HFM) was accurately modeled for a large range of operating conditions. The modeling results were validated against 177 experimental measurements under a wide range of operating conditions for 12 organic compounds with different diffusion coefficients and a wide variety of Henry's law constants, from Naphthalene at circa 0.017 to 1,1-dichloroethene with circa 1.19. The hybrid numerical analytical approach enables prediction of the removal efficiencies within a few minutes, whereas a pure numerical approach would require several hours to days due to numerical stability controls. The input parameters for the model are defined by the geometry of the HFM and the operating conditions, no empirical formulations are applied. This model allows the investigation of the main factors controlling the removal characteristics, e.g., the dependency on Henry's law coefficient, gas side diffusional resistance, and aqueous diffusion limitation, and also enables the efficient design of further organic removal systems based on the HFM technology.

Vacuum assisted removal of volatile to semi-volatile organic contaminants from water using hollow fiber membrane contactors: I: Experimental results

Removal of 12 organic contaminants from water using a microporous polypropylene hollow fiber membrane (HFM) module was studied under low strip gas flow to water flow ratios (≤5:1). Removal efficiencies were found to be strongly dependent on the Henry's law constants indicating a substantial mass transfer resistance on the gas side. Vacuum can be either used to increase removal efficiencies, or to decrease the amount of strip gas that has to be treated without sacrificing efficiency.

Photoinduced graft polymerization of acrylamide on polypropylene microporous membranes for the improvement of antifouling characteristics in a submerged membrane-bioreactor

Polypropylene hollow fiber microporous membranes (PPHFMMs) were surface-modified by the photoinduced graft polymerization of acrylamide (AAm). Structural and morphological changes on the membrane surface were characterized by attenuated total reflection-Fourier transform infrared spectroscopy (FT-IR/ATR) 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 FT-IR/ATR indicated the successful graft polymerization of AAm onto the membrane surface. Water contact angle of the modified membrane decreased with the increase of the grafting degree. It showed 34.9° for the modified membrane with a grafting degree of 278.4 wt.%, nearly 94° lower than that of the nascent one. The antifouling characteristics of the PPHFMMs before and after surface modification were assessed by the filtration of activated sludge in a submerged membrane bioreactor for synthetic wastewater treatment. It demonstrated that after continuous operation for about 42 h, the flux recovery were 36.9, 63.7% and the relative flux ratio were 1.00, 1.32 for the nascent and modified PPHFMMs, respectively.