WO2014194228A1 - Application de nanotubes de carbone ou de particules de carbone sur des matériaux polymères à fibres creuses - Google Patents

Application de nanotubes de carbone ou de particules de carbone sur des matériaux polymères à fibres creuses Download PDF

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Publication number
WO2014194228A1
WO2014194228A1 PCT/US2014/040289 US2014040289W WO2014194228A1 WO 2014194228 A1 WO2014194228 A1 WO 2014194228A1 US 2014040289 W US2014040289 W US 2014040289W WO 2014194228 A1 WO2014194228 A1 WO 2014194228A1
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hollow fiber
polymeric hollow
cnt
carbon
carbon nanotubes
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PCT/US2014/040289
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English (en)
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Kellogg J. SCHWAB
Haiou HUANG
Benoit TYCHENE
David Howard FAIRBROTHER
Joseph G. JACANGELO
Gaurav AJMANI
Miranda LAHR
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The Johns Hopkins University
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/02—Inorganic material
    • B01D71/021—Carbon
    • B01D71/0212—Carbon nanotubes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D65/00—Accessories or auxiliary operations, in general, for separation processes or apparatus using semi-permeable membranes
    • B01D65/08—Prevention of membrane fouling or of concentration polarisation
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
    • B01D67/0081—After-treatment of organic or inorganic membranes
    • B01D67/0088—Physical treatment with compounds, e.g. swelling, coating or impregnation
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/06—Organic material
    • B01D71/66—Polymers having sulfur in the main chain, with or without nitrogen, oxygen or carbon only
    • B01D71/68—Polysulfones; Polyethersulfones
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/44—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2303/00—Specific treatment goals
    • C02F2303/16—Regeneration of sorbents, filters
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2305/00—Use of specific compounds during water treatment
    • C02F2305/08—Nanoparticles or nanotubes

Definitions

  • nanomaterials such as nanosilver, nano-scale metal oxides, and carbon nanotubes (CNTs)
  • CNTs carbon nanotubes
  • CNTs are particularly well suited to positively impact water treatment as transformative components in the design of new nano-enabled environmental technologies based on separation processes (adsorption, filtration, and the like).
  • CNT surfaces also can be selectively functionalized to enhance sorption properties by introducing specific functional groups.
  • CNTs are effective at removing hydrophobic organic chemicals, H. Li, et al, Chem. Commun. (2010); J. Heo, et al., Water Sci. Technol. (2011); and CD. Vecitis, et al, J. Phys. Chem. C (2011), heavy metals, T.
  • the high surface area and conductivity also enables CNT mats to function as three-dimensional porous electrodes. This characteristic has opened up the possibility of using redox reactions to destroy contaminants when they adsorb onto CNT mats, augmenting sorption as a means for contaminant removal.
  • CNTs to enhance a membrane's fouling resistance is further aided by their chemical stability towards harsh chemicals, such as sodium
  • hypochlorite used to control organic fouling and prevent biofilm formation on membrane surfaces during water purification. J.S. Baker, L.Y. Dudley, Desalination (1998); and A. Subramani, E.M.V. Hoek, Desalination (2010). Membranes modified by CNT mats clearly hold significant promise for improving the energy efficiency and sustainability of next-generation membranes for water purification.
  • CNTs have been used to create membranes by growing vertically aligned CNTs, J.K. Holt, et al., Science (2006), and by forming CNT -polymer composites, where the CNTs are incorporated within a porous polymeric matrix.
  • CNTs have been used to create membranes by growing vertically aligned CNTs, J.K. Holt, et al., Science (2006), and by forming CNT -polymer composites, where the CNTs are incorporated within a porous polymeric matrix.
  • CNT- composite membranes show no major improvement, in terms of water flux and separation characteristics, compared to available commercial membranes.
  • Mechanically stable CNTs also have recently been successfully grafted onto the surface of cellulose nitrate membranes as a minor (20% maximum) component of a matrix containing poly(vinyl) alcohol and succinic acid.
  • membrane processes for full-scale water treatment mainly operate with hollow fiber membranes made out of materials, such as polyvinylidene fluoride (PVDF) and polyether sulfone (PES), D. Furukawa, A Global Perspective of Low Pressure Membranes, National Water Research Institute, Fountain Valley, California, 2008, studies of hybrid CNT membranes have concentrated on flat sheet membrane configurations. S. Steiner, et al, Carbon (2012).
  • Hollow fiber, low pressure membranes may be operated in either an inside- out (active layer on the inner surface) or outside-in (active layer on the outer surface) configuration. LPMs are a physical barrier for contaminant removal, G.P.
  • the presently disclosed subject matter provides a method for preparing a carbon mat on an inner surface of a polymeric hollow fiber membrane, the method comprising: (a) providing a plurality of carbon nanotubes and/or carbon particles; (b) suspending the plurality of carbon nanotubes and/or carbon particles in a solution to form a suspension of carbon nanotubes and/or carbon particles; (c) providing one or more polymeric hollow fiber membranes, wherein the one or more polymeric hollow fiber membranes have at least one open end in fluid communication with a lumen, and wherein the lumen defines an inner surface of the one or more polymeric hollow fiber membranes; (d) dispensing the suspension of carbon nanotubes and/or carbon particles in the at least one open end of the one or more polymeric hollow fiber membranes; and (e) filtering the suspension of carbon nanotubes and/or carbon particles through the one or more polymeric hollow fiber
  • the presently disclosed subject matter provides a polymeric hollow fiber membrane prepared by the presently disclosed methods, wherein the polymeric hollow fiber membrane has a carbon mat deposited on an inner surface thereof.
  • the presently disclosed subject matter provides a method for filtering an effluent, the method comprising passing the effluent through a polymeric hollow fiber membrane having a carbon mat deposited on an inner surface thereof.
  • FIG. 1 depicts preparation of a CNT mat by filtering a CNT suspension through a hollow fiber membrane from the "inside out.”
  • Membrane before loading (Left).
  • Modified membrane (Right);
  • FIGS. 2A and 2B show variation in TMP (bar) vs. Filtration time (min) during the preparation of MWCNT mats on the inner surface of HF-PVDF (A) and HF-PES (B) hollow fiber membranes.
  • Stage 1 Filtration of the MWCNT suspension through the membrane from the "inside out”.
  • Stage 2 Filtration of Milli-Q water through the membrane following MWCNT loading;
  • FIGS. 3 A and 3B are SEM images of CNT mats created on the inner surface of (A) PVDF and (B) PES hollow fiber membranes.
  • the white arrows show the mat depth on each membrane (depth corresponding to 1 1 g m "2 mass loading);
  • FIGS. 4A and 4B show mass of MWCNTs released from HF-PVDF -CNT (A) and HF-PES-CNT (B) membranes during a sequence of backwashing steps where the flow direction was reversed (i.e., from the "outside in”). Results are shown for
  • FIGS. 5 A and 5B are SEM pictures of MWCNT mats on the inner surface of PVDF (A l and A2) and PES (B l and B2) hollow fiber membranes after the membranes were backwashed.
  • Al and B2 are zoomed out SEM images that show the cross section of the modified hollow fibers.
  • A2 and B2 SEM images show the detailed nature of the membrane/MWCNT interface;
  • FIGS. 6A and 6B show TMP increase (P-PO) during the filtration of a 5 ppm alginate suspension through (A) PVDF and (B) PES virgin and MWCNT modified hollow fiber membranes.
  • the flux of alginate was held constant at 67 L h "1 m ⁇ 2 .
  • the vertical arrows indicate times at which the membrane was backwashed with the permeate at 134 L h "1 m ⁇ 2 .
  • Data are shown for four cycles of 80 min filtration followed by 6 min backwashes;
  • FIG. 7 shows a representative loading procedure used to create a CNT mat on the inner surface of HF-PVDF membrane (HF-PVDF-CNT);
  • FIG. 8 is UV-Vis spectra showing that in the region between 800 nm to 900 nm there is no absorbance from the surfactant (Triton-X), but absorbance from CNTs is still observed in this region;
  • FIG. 9 is a calibration curve showing how the absorbance in the 800-nm to 900-nm range is related to MWCNT mass concentration
  • FIG. 10 is UV-Vis spectra showing that in the region between 800 nm to 900 nm there is no absorbance from SRNOM;
  • FIG. 1 1 shows backwashing of CNT mats created on the outer surface of a HF-PVDF membrane with Milli-Q water. The darkening of the solution and the appearance of 'white' regions on the membrane's surface during backwashing highlight the mat's hydraulic instability;
  • FIG. 12 is a graph showing the variation in transmembrane pressure (TMP) during SRNOM filtration
  • FIG. 13 is a visual analysis of CNTs released from the least stable HF-PES- CNT membrane studied during several different backwashing steps. For comparison an example of a CNT feed solution used to create the mats also is shown;
  • FIG. 14 shows and high resolution SEM images of Powder Activated Carbon (PAC) mats created on the inner surface of PVDF hollow fiber membranes.
  • PAC Powder Activated Carbon
  • Novel membrane technologies for water purification are urgently needed to meet the increasing demand for clean industrial water and safe drinking water.
  • CNT carbon nanotube
  • the carbon mat structure is established by filtering a SWCNT and/or
  • MWCNT and/or carbon particle suspension through the lumen of hollow polymeric fibers using an inside-out process.
  • the CNTs and carbon particles are rejected by the porous polymer and accumulate at the inner surface of the HFMs, thereby creating a stable, highly porous carbon mat structure.
  • the presently disclosed carbon-coated HFMs exhibit, depending on the CNT and/or carbon particle and HFM properties, high fouling resistance and high separation capacities for both chemical and biological contaminants.
  • the confined volume inside each fiber lumen and the symmetric geometry of the hollow tube restricts CNT or carbon particle resuspension and improves the stability of the carbon mat structure without the need of additional process or chemical addition.
  • the carbon mat structure inside a HFM shows superb hydraulic and chemical stability and remains stable following backwashing and chemical cleaning.
  • the stability of the presently disclosed carbon mats can be determined, for example, from scanning electron microscopy images of the hybrid membranes and by quantifying the mass of carbon lost during prolonged backwashing, hydraulic stress, and exposure to harsh chemical cleaning agents. Compared to virgin membranes, the presently disclosed carbon-modified membranes exhibited improved fouling
  • the presently disclosed integrated CNT -HFM composites contain electrical conductive properties conducive to charge-associated contaminant removal and membrane cleaning processes.
  • the presently disclosed methods provide filters with high fouling resistance and high contaminant (both chemical and biological) removal efficiency that remain stable following backwashing and chemical cleaning. These capabilities will improve the capacity of impurity removal, as well as decrease power requirements for filtration separation, and offer the potential to
  • 11 1232-00258.P12108-02 provide considerable cost savings to the end users when applying treatment. Accordingly, the development of stable carbon mat structures onto polymeric materials provides a sustainable, scalable technique to dramatically improve the capacity and sustainability of filtration separation.
  • carbon-HFMs can be used including, but not limited to, water and wastewater treatment, water reuse, medical procedures and treatments (e.g., kidney dialysis), industrial processes (e.g., microchip processing, food production, and the like), and analytical processes (e.g., solid phase microextraction, electrical sensors, and the like).
  • the presently disclosed subject matter also provides a non-metallic electrical conductance material for use in separation processes and power transfer.
  • the presently disclosed subject matter provides a method for preparing a carbon mat on an inner surface of a polymeric hollow fiber membrane, the method comprising: (a) providing a plurality of carbon nanotubes and/or carbon particles; (b) suspending the plurality of carbon nanotubes and/or carbon particles in a solution to form a suspension of carbon nanotubes and/or carbon particles; (c) providing one or more polymeric hollow fiber membranes 100, wherein the one or more polymeric hollow fiber membranes 100 have at least one open end 110 in fluid communication with a lumen 120 and at least one dead end 130, and wherein the lumen 120 defines an inner surface 140 of the one or more polymeric hollow fiber membranes 100; (d) dispensing the suspension 150 of carbon nanotubes and/or carbon particles in the at least one open end 110 of the one or more polymeric hollow fiber membranes 100; and (e) filtering the suspension 150 of carbon nanotubes and/or carbon particles through the one or more polymeric hollow fiber membranes 100
  • the plurality of carbon nanotubes comprise multi- walled carbon nanotubes.
  • Multi-walled nanotubes comprise, in some embodiments, multiple rolled layers of concentric tubes of graphene or a single sheet of graphite is rolled in around itself, for example, like a scroll of parchment or a rolled newspaper.
  • the plurality of carbon nanotubes comprise single- walled carbon nanotubes.
  • a single-walled carbon nanotube can include a one-atom thick layer of graphite, e.g., graphene, that can be wrapped into a seamless cylinder.
  • the plurality of carbon nanotubes have a diameter from about 50 nm to about 80 nm. In other embodiments, the plurality of carbon nanotubes have a length from about 10 ⁇ to about 20 ⁇ . In still other embodiments, the plurality of carbon nanotubes have a specific surface area of about 60 m 2 g 1 . In further embodiments, the plurality of carbon nanotubes comprise unfunctionalized carbon nanotubes.
  • the carbon particles comprise powdered activated carbon particles.
  • Common polymeric hollow fiber membranes include, but are not limited to, polymers or copolymers selected from the group consisting of cellulose acetate (CA), nitrocellulose (CN), cellulose esters (CE), polysulfone (PS), polyether sulfone (PES), polyacrilonitrile (PAN), polyamide, polyimide, polyethylene (PE), polypropylene (PP),
  • PTFE polytetrafluoroethylene
  • PVDF polyvinylidene fluoride
  • PVC polyvinylchloride
  • Criteria for selecting polymeric hollow fiber membranes suitable for use with the presently disclosed methods and compositions can include, but are not limited to, a desired binding affinity for compounds to be separated, an ability to withstand the required cleaning conditions, rigidity, stereoregularity, crystallinity, glass transition temperature, polarity of its functional groups, hydrophilicity or hydrophobicity (e.g., related to surface free energy), presence of ionic charge, chemical or thermal resistance, density, porosity, and an ability to bind the carbon nanofiber mat deposited therein, in addition to practical considerations, such as cost and availability.
  • the one or polymeric hollow fiber membranes are hydrophilic.
  • the one or more hydrophilic polymeric hollow fiber membranes comprise polyether sulfone (PES).
  • the one or more polymeric hollow fiber membranes have a nominal pore size of about 0.03 ⁇ . In other embodiments, the one or more polymeric hollow fiber membranes are
  • 11 1232-00258.P12108-02 capable of sustaining a maximum flux of pure water flux of about 1200 ⁇ 120 L h 1 m " 2 bar 1 .
  • the one or more polymeric hollow fiber membranes are hydrophobic.
  • the one or more polymeric hollow fiber membranes comprise polyvinylidene fluoride (PVDF).
  • PVDF polyvinylidene fluoride
  • the one or more polymeric hollow fiber membranes have a nominal pore size of about 0.1 ⁇ .
  • the one or more polymeric hollow fiber membranes are capable of sustaining a maximum flux of pure water of about 655 ⁇ 85 L h "1 m ⁇ 2 bar "1 .
  • the carbon mat comprises powdered activated carbon (PAC).
  • Activated carbon is a form of carbon comprising small, low- volume pores that result in an increase in surface area available for adsorption. Due to its high degree of microporosity, one gram of activated carbon can have a surface area in excess of 500 m 2 . An activation level sufficient for useful application may be attained solely from high surface area; however, further chemical treatment can enhance its adsorption properties .
  • Active carbons can be made in particulate form as powders or fine granules less than about 1.0 mm in size.
  • Powdered active carbon (PAC) is made up of crushed or ground carbon particles, 95-100% of which will pass through a designated mesh sieve. Particle sizes corresponding to an 80-mesh sieve (0.177 mm) and smaller are designated as PAC.
  • the solution in which the carbon mat is prepared comprises an aqueous solution.
  • the aqueous solution comprises a non-ionic surfactant.
  • the method comprises sonicating the solution of carbon nanotubes for a period of time.
  • the presently disclosed subject matter provides a polymeric hollow fiber membrane having a carbon nanotube mat deposited on an inner surface thereof.
  • the polymeric hollow fiber membrane comprises a polymer selected from the group consisting of a hydrophilic polymer and a hydrophobic polymer.
  • the polymeric hollow fiber membrane comprises a polymer selected from the group consisting of polyether sulfone (PES) and polyvinylidene fluoride (PVDF).
  • the polymeric hollow fiber membrane comprises a total mass of carbon nanotubes deposited on the inner surface thereof of about 11 g m "2 .
  • the polymeric hollow fiber membrane comprises an electrical conductance material.
  • the presently disclosed subject matter provides a method for filtering an effluent, the method comprising passing the effluent through a polymeric hollow fiber membrane having a carbon mat deposited on an inner surface thereof.
  • the effluent is selected from the group consisting of water, wastewater, and a biological fluid.
  • the biological fluid comprises blood.
  • the method further comprises an industrial process.
  • the industrial method comprises a process selected from the group consisting of microchip processing and food processing.
  • the presently disclose method further comprises removing anthropogenic and/or naturally occurring substances, e.g., arsenic, from groundwater and the like.
  • anthropogenic and/or naturally occurring substances e.g., arsenic
  • the presently disclosed methods can be used to remove contaminants from a source of water.
  • the method further comprises an analytical process.
  • the analytical process comprises solid phase microextraction.
  • the term "about,” when referring to a value can be meant to encompass variations of, in some embodiments, ⁇ 100% in some embodiments ⁇ 50%, in some embodiments ⁇ 20%, in some embodiments ⁇ 10%, in some embodiments ⁇ 5%, in some embodiments ⁇ 1%, in some embodiments ⁇ 0.5%, and in some embodiments ⁇ 0.1% from the specified amount, as such variations are appropriate to perform the disclosed methods or employ the disclosed compositions.
  • Carbon Nanotubes Commercially available pristine (unfunctionalized) multiwalled CNTs (MWCNTs) were purchased from Cheap Tubes, Inc. (Vermont, USA). According to the manufacturer's specifications, the MWCNTs exhibit
  • 11 1232-00258.P12108-02 diameters ranging from 50 nm to 80 nm and lengths between 10 ⁇ to 20 ⁇ and a specific surface area of 60 m 2 g "1 .
  • MWCNT suspensions Prior to loading, MWCNT suspensions were prepared at a concentration of approximately 750 mg L “1 in Milli-Q water (18 ⁇ cm “1 ) with 0.9 % v/v 3 ⁇ 40 of non-ionic surfactant (Triton X100). To disperse the CNTs, all MWCNT suspensions were sonicated in a water bath sonicator for 30 min (Aquasonic 250HT).
  • Hollow Fiber Membranes Two types of commercially available hollow fiber (HF) membranes were used; PES and PVDF.
  • the PES membranes were hydrophilic with a nominal pore size of 0.03 ⁇ and are capable of sustaining a maximum pure water flux of approximately 1200 ⁇ 120 L h "1 m “2 bar "1 .
  • the PVDF membranes are hydrophobic with a nominal pore size of 0.1 ⁇ and are able to sustain a maximum flux of pure water of approximately 655 ⁇ 85 L h "1 m “2 bar “1 .
  • the HF-PVDF and HF-PES membrane modules were soaked overnight in a 25 %v/v H 2 O isopropanol solution and then attached to the filtration system. Prior to each experiment the module was flushed with Milli-Q water and the pure water flux measured by the flux step method. E. Filloux, et al, Water Res. (2012). A new membrane module was used for each experiment.
  • FIG. 1 summarizes the approach used to create CNT mats on the inner surface virgin HF-PES and HF PVDF membranes.
  • PES and PVDF hollow fiber membranes modified by the addition of CNT mats to their inner surfaces are referred to herein as HF-PES CNT and HF-PVDF-CNT membranes, respectively.
  • CNT mats were created by filtering 13 mL of a 750 mg L "1 CNT suspension through each hollow fiber in the module (6 fibers for HF-PVDF and 4 for HF-PES) in an inside-out mode at a constant filtration flux of 134 L h "1 m "2 using a peristaltic pump (Masterflex L/S, Cole-Palmer, USA).
  • the CNT loading was maintained at approximately 1 1 g m "2 .
  • the CNT loading (mg MWCNT m ⁇ 2 ) was determined by multiplying the MWCNT concentration (mg L "1 ) by the total volume of MWCNT -containing solution filtered through the hollow fibers. This allowed the total mass of MWCNTs (mg) used during the loading process to be calculated. This value was then divided by the inner surface area of the HF-PVDF or HF-PES modules (m 2 ) to obtain the CNT loading (mg MWCNT m "2 ).
  • mat stability was evaluated by reversing the flow of water through HF-PES-CNT and HF-PVDF-CNT membranes using hydraulic backwashing, i.e., outside-in filtration.
  • hydraulic backwashing i.e., outside-in filtration.
  • the mat's stability during each backwashing step was assessed by determining the mass of CNTs dislodged from the mats. This assessment was done by analyzing the concentration of MWCNTs in the backwashed water using UV-Vis spectroscopy (UV-Vis). To determine the concentration (and thereby the mass), of CNTs released during each backwash step by UV-Vis, it is necessary to ensure that all of the CNTs are dispersed. CNT dispersion of any aggregates was accomplished by first adjusting the pH of the backwash solution to 10, as it has been shown previously that high pH improves CNT dispersion. B. Smith, et al., Environ. Sci. Technol. (2009).
  • the correlation between UV absorbance in the 800-nm to 900-nm range and MWCNT mass concentration (mg L "1 ) was determined by conducting separate control studies where known masses of MWCNTs powders were dispersed in Milli-Q with 0.5% Triton X 100 v/v H 2 O (see FIG. 9).
  • the CNT mass released from the mat in any backwash experiment was determined by multiplying the CNT mass concentration determined by UV-Vis by the total volume collected during the backwash.
  • the limit of MWCNT detection was determined by discerning the lowest UV-Vis absorbance value that could be discerned from the baseline (0.01 1 absorbance units). A range of uncertainty in the MWCNT detection limit was then calculated from the uncertainty
  • MWCNT detection was estimated to be between 2.5 - 6.6* 10 "5 mg MWCNT.
  • HF-PVDF-CNT and HF-PES-CNT hollow fiber membranes were imaged using a cold cathode field emission scanning electron microscope (JEOL 6700F, FESEM) with 1.0 nm resolution at 15 keV. Hollow fiber membrane surfaces were imaged after CNT loading and then again after the backwashing steps described in Example 2. Prior to analysis, each membrane sample was dried for 48 hours at room temperature. Cross-sectional images were taken by first cryo-snapping the CNT modified membranes in the presence of liquid nitrogen and then sputter-coating them with platinum to prevent charging during SEM.
  • JEOL 6700F, FESEM cold cathode field emission scanning electron microscope
  • Samples were then mounted vertically onto the side of a sample stub and imaged at various magnifications.
  • the SRNOM suspension was prepared at a concentration of 5 mg L "1 SRNOM diluted in 49 ppm NaHC0 3 , 28 ppm CaS0 4 , 25 ppm MgS0 4 and 1.9 ppm KC1 and was filtered through a HF-PVDF-CNT module at 67 L h "1 m ⁇ 2 in two, 60 minute cycles. In between these two cycles, the HF-PVDF-CNT membrane was backwashed with the permeate at 85 L h _1 m ⁇ 2 .
  • the concentration of CNTs in the permeate and the backwash solutions was determined by the method described in Example 2, also taking advantage of the fact that NOM does not adsorb in the 800-nm to 900-nm region (see FIG. 10). Data from the UV-Vis analysis of the permeate are provided in Table 1.
  • an alginate suspension (5 ppm sodium alginate diluted in 47 ppm aHC0 3 and 380 ppm KC1) was prepared at pH 7 and exhibited a conductivity of approximately 750 ⁇ 8 ⁇ "1 at 20°C.
  • This alginate suspension was filtered through HF PVDF, HF-PES and HF-PVDF-CNT, HF-PES-CNT membranes in dead-end mode, at a constant flux of 67 L h _1 m ⁇ 2 through four cycles of 80 min, with each filtration cycle followed by 6 minutes of backwashing with the permeate at
  • Membrane fouling was evaluated by measuring the rate of TMP increase (d(P t - Po)/dt) versus time during each filtration cycle, where Po is the initial TMP prior to the filtration of the alginate solution and P t is the TMP at time, t.
  • the irreversible fouling was determined after each backwashing step by the pressure increase ( ⁇ ) measured at the onset of the subsequent filtration cycle.
  • FIG. 2 illustrates the change in transmembrane pressure (TMP) observed during the creation of three representative HF-PVDF-CNT (FIG.2-A, left) and three representative HF-PES-CNT (FIG.2-B, right) membranes.
  • TMP transmembrane pressure
  • the average TMP increase is higher for the HF-PVDF membranes (approximately 0.9 bars) than for the HF-PES membranes (approximately 0.5 bars).
  • This difference in behavior between the two types of hollow fiber membranes is consistent with the hypothesis that the TMP increase during Stage 1 is predominantly a result of physical interactions, specifically hydrophobic interactions, between the base membrane and the surfactant present in the feed solution.
  • FIG. 2 shows that for both HF-PVDF-CNT (FIG. 2-A)
  • the last backwash step was chemically cleaning the CNT modified hollow fiber membranes using different solution chemistries.
  • the quantity of CNTs removed during each one of the different chemical treatment steps was small (e.g., less than about 0.05 mg); the most disruptive treatment was the backwash with the synthetic water solution at a flux of 85 L h "1 m "2 .
  • the MWCNT mats formed on the HF-PVDF-CNT and HF-PES-CNT membranes are hydraulically stable, i.e., they are baskwashable.
  • the fraction of MWCNTs lost is less than 1% of the initial MWCNT mass used to create the mats.
  • the HF-PVDF-CNT and HF-PES-CNT membranes exhibited comparable stabilities, which suggest that MWCNT stability is more a function of their structure than specific interactions with the membrane surface.
  • a humic substance (SRNOM; 5 mg C L "1 ) was filtered through a HF-PVDF- CNT membrane at 67 L h "1 m "2 over a two hour period.
  • 3 mL aliquots of the permeate were analyzed by measuring the UV-Vis in the 800-nm to 900-nm region, for any evidence of CNTs.
  • Humic substances exhibit a strong propensity for facilitated transport and for stabilizing CNTs as suspended particles, M.A. Chappell, et al, Environ. Pollut. (2009), and SRNOM filtration is thus a stringent test for CNT stability.
  • the membrane pore size should be relatively large; and (2) the SRNOM should not induce fouling, which would decrease the membrane's effective pore size and the propensity for CNT transport.
  • the HF-PVDF membrane was investigated because of its larger pore size (0.1 ⁇ for HF-PVDF vs. 0.03 ⁇ for HF-PES), as compared to the CNT dimensions (lengths of 10 ⁇ - 20 ⁇ with outer diameters of 50 nm to 80 nm).
  • SRNOM ⁇ 800 Da determined by HPLC-SEC
  • FIG.6-A shows that during each cycle of alginate filtration the rate of TMP increase for the HF-PVDF-CNT membranes decreased considerably compared to the HF-PVDF membranes.
  • the fouling rate in the first cycle as determined by the slope of the pressure increase vs. time in the linear part of the curve, was equal to 2 and 0.8 mbar min "1 for the HF PVDF and HF- PVDF-CNT membranes, respectively.
  • the presence of the CNT mat reduced the fouling rate by about 60% during the first cycle.
  • the presently CNT mats decreased the extent of irreversible fouling.
  • the permeability of the HF-PVDF and HF-PVDF-CNT membranes was 468 Lh bar 1 and 395 Lh " ⁇ ar "1 , respectively.
  • the permeability of the HF-PVDF and HF- PVDF CNT membranes was 655 ⁇ 85 Lrf bar "1 and 434 Lh bar 1 .
  • the irreversible fouling reduced the permeability of the HF-PVDF membranes by 29%, but the HF-PVDF-CNT membrane by only 9%.
  • the CNT mats were, however, less effective at reducing alginate fouling when adsorbed on the inner surface of PES membranes.
  • the fouling rate was 2 mbar min 1 and 1.3 mbar min 1 for the HF-PES and HF-PES-CNT membranes, respectively.
  • the relative improvement of the HF-PES-CNT membrane compared to the HF-PES membrane decreased such that the performance of the HF-PES-CNT and the HF-PES membrane were virtually indistinguishable from one another after three backwash cycles.
  • the extent of irreversible fouling was negligible for either the HF-PES-CNT membrane or the HF-PES membrane.
  • the CNT mats have a greater effect on the performance of the HF-PVDF membranes can be ascribed to the difference in pore- size between the hollow fiber membranes and the CNT mats.
  • the HF-PVDF and HF- PES membranes have pore sizes of approximately about 0.1 ⁇ and less than about 0.03 ⁇ , respectively; the CNT mats have a pore size distribution predominantly in the range of about 0.01 ⁇ to about 0.1 ⁇ , based on previous findings using flat sheet membranes.
  • the CNT mat introduces a new, finer filter that helps to trap particles responsible for clogging/blocking membrane pores.
  • the pore size in the HF-PES membrane is comparable to that in the CNT mat and consequently the CNT
  • 11 1232-00258.P12108-02 mat produced far less of a change in the antifouling properties of the hybrid membrane.
  • Brinket et al. hollow fibers and therefore by inference the CNTs mats, will be mainly subjected to radial and circumferential stresses during filtration, although longitudinal stress can be neglected as the fiber is open on one end.
  • tensile hoop stress which exerts a force that tries to expand the material.
  • a mat created on inner surface of a fiber is subjected to compressive hoop stresses.
  • CNT mats i.e., CNT mats that are backwashable
  • CNT mats can be generated using a simple preparative method on the inner surfaces of hollow fiber membranes, in sharp contrast to the instability of CNT mats deposited either on flat sheet membranes or on the outer surface of the hollow fiber membranes.
  • it is thought that the detailed nature of membrane-CNT interactions is not playing a major role in determining the mat's stability, due to an ability to create stable CNT mats on two membranes (HF-PVDF and HF-PES) with very different physicochemical properties (different hydrophilic properties, pore size, chemical composition, and the like).
  • HF membrane-CNT combinations e.g., single walled and oxidized multiwalled CNTs
  • the stability of different HF membrane-CNT combinations also can be investigated to the extent which the creation of stable CNT mats on the inner surfaces of HFs represents a generalizable phenomenon.
  • the ability of these CNT mats to improve membrane performance can be explored, for example, by comparing longer term antifouling properties, as well as virus and contaminant removal properties of virgin and CNT modified hollow fibers.
  • Related studies can explore the effect of the mat's characteristics including, but not limited to, thickness, type and concentration of CNT, on both hydraulic stability and water purification properties.
  • CNT mats By measuring changes in conductance during operation, CNT mats also could be used to remotely monitor a membrane's integrity and performance in the field, something that is otherwise difficult to do. It should be noted, however, that these advances and potential applications only apply to hollow fiber membranes being operated in an inside-out mode.
  • the presently disclosed subject matter provides a method to generate hydraulically stable, i.e., backwashable, CNT mats on the inner surface of polymeric hollow fiber membranes.
  • the presently disclosed methods involve filtering a CNT suspension through a hollow fiber membrane operating in dead-end mode from the inside-out.
  • the CNT mats do not significantly change the base membranes' permeability, although one attribute is their ability to withstand backwashing, including long term backwashing and hydraulic stress with Milli-Q water and chemical cleaning.
  • the CNT mats lost ⁇ 1% of their initial mass during these backwashing steps as measured by UV-Vis, while the mat's stability was confirmed visually by cross-sectional SEM images taken before and after
  • the surprising stability of the presently disclosed CNT mats is in marked contrast to the hydraulic instability of CNT mats created on the outer surface of hollow fiber membranes or on flat sheet membranes toward even the simplest and least aggressive backwash steps.
  • the potential for the presently disclosed CNT mats to enhance hollow fiber membrane performance characteristics is highlighted by their ability to sustainably improve the anti-fouling resistance of HF-PVDF membranes, through several filtration/cleaning steps.
  • the presently disclosed results open the door to the practical implementation of CNT mats into real world membrane applications, with the potential to improve anti-fouling resistance, as well as contaminant and virus removal capabilities of hollow fiber membranes.

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Engineering & Computer Science (AREA)
  • Inorganic Chemistry (AREA)
  • Materials Engineering (AREA)
  • Nanotechnology (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Hydrology & Water Resources (AREA)
  • Environmental & Geological Engineering (AREA)
  • Water Supply & Treatment (AREA)
  • Organic Chemistry (AREA)
  • Manufacturing & Machinery (AREA)
  • Separation Using Semi-Permeable Membranes (AREA)

Abstract

La présente invention concerne des procédés pour générer des mats de carbone sur la surface intérieure de membranes à fibres creuses, ainsi que de telles membranes à fibres modifiées, et leurs procédés d'utilisation. Un procédé comprend les étapes suivantes : disposer d'une pluralité de nanotubes de carbone et/ou de particules de carbone suspendues dans une solution de manière à former une suspension; disposer d'une ou de plusieurs membranes polymères à fibres creuses, ladite ou lesdites membranes polymères à fibres creuses présentant au moins une extrémité ouverte en communication fluidique avec une lumière, ladite lumière définissant une surface intérieure de ladite ou desdites membranes polymères à fibres creuses; distribuer la suspension dans la au moins une extrémité ouverte de la ou des membranes polymères à fibres creuses et filtrer la suspension de nanotubes et/ou de particules de carbone à travers la ou les membranes polymères à fibres creuses.
PCT/US2014/040289 2013-05-31 2014-05-30 Application de nanotubes de carbone ou de particules de carbone sur des matériaux polymères à fibres creuses WO2014194228A1 (fr)

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CN108311125A (zh) * 2018-01-26 2018-07-24 南京理工大学 基于中空碳纳米材料的固相微萃取涂层及其制备方法
US10421047B2 (en) 2017-02-06 2019-09-24 Baker Hughes, A Ge Company, Llc Composite membranes comprising nanoparticles for liquid filtration
CN114621621A (zh) * 2020-12-14 2022-06-14 清华大学 光吸收体预制液及其制备方法

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US10421047B2 (en) 2017-02-06 2019-09-24 Baker Hughes, A Ge Company, Llc Composite membranes comprising nanoparticles for liquid filtration
CN108311125A (zh) * 2018-01-26 2018-07-24 南京理工大学 基于中空碳纳米材料的固相微萃取涂层及其制备方法
CN108311125B (zh) * 2018-01-26 2020-09-18 南京理工大学 基于中空碳纳米材料的固相微萃取涂层及其制备方法
CN114621621A (zh) * 2020-12-14 2022-06-14 清华大学 光吸收体预制液及其制备方法

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