Patent Application
20220220241
Nanofiltration (NF) membranes are defined by effective pore sizes ˜1 nm. They are typically used for removing divalent salts from water and wastewater streams in applications such as water softening. Almost all commercial NF membranes on the market today feature cross-linked polyamide selective layers, prepared by interfacial polymerization. This selective layer chemistry has been used for decades, and as a result, these commercial membranes are very well-optimized and offer reasonably high water permeability along with the desired divalent salt rejection.
However, polyamide selective layers also come with significant limitations inherent to their chemical structure, such as lack of fouling and chlorine resistance. Recently, zwitterions have attracted extensive research in the membrane field due to their hydrophilicity and fouling resistance. Zwitterionic amphiphilic copolymers (ZACs) are documented to self-assemble to create microstructures. And that when ZACs are used as membrane selective layers, fouling resistant membranes with ˜1-2 nm effective pore size etc can be achieved. These membranes were also shown to be highly chlorine resistant.
However, an important feature of these membranes was that they exhibited relatively low salt rejection due to the overall neutral chemistry of the membrane selective layer. Therefore, while ZACs offer promising fouling and chlorine resistance as well as effective pore sizes close to that of NF membranes, their rejection profiles are not sufficient for replacing commercial NF membranes in most applications. Therefore, there is a need to develop high performance membranes that do not have the aforementioned drawbacks.
Provided herein are copolymers comprising pluralities of each of three types of monomeric units: hydrophobic monomeric units, zwitterionic monomeric units, and charged or ionizable monomeric units. Preferably the copolymers are linear, statistical, or random, or all of them. Also provided are thin film composite membranes whose selective layer is comprised of these copolymers. These membranes can be used for several aqueous separations, including but not limited to water treatment, water softening, wastewater treatment, and separation and purification of organic molecules in aqueous solutions. Due to the chemical nature of these copolymers, the membranes exhibit improved resistance to chemical degradation by chlorine and strong resistance to fouling.
In one aspect, provided herein are copolymers, comprising a plurality of zwitterionic monomeric units, a plurality of charged/ionizable monomeric units, and a plurality of hydrophobic monomeric units.
In yet another aspect, provided herein are thin film composite membranes, comprising a porous support, and a thin film of the polymeric material, wherein the pore size of the porous support is larger than the effective pore size of the thin film of the polymer material.
In another aspect, provided herein are methods of size-based selection or exclusion, comprising contacting a solution comprising a plurality of uncharged organic molecules of different sizes with a thin film composite membrane disclosed herein.
In further another aspect, provided herein are methods of charge-based selection or exclusion, comprising contacting a solution comprising a plurality of salts with a thin film composite membrane disclosed herein.
Zwitterionic Amphiphilic Copolymer (CZAC), P(TFEMA-r-SBMA-r-MAA), and schematic description of its self-assembly when coated onto a support to form a membrane selective layer, featuring ˜1-2 nm hydrophilic domains that act as a network of effective nanochannels lined with carboxylate groups.
Disclosed are membranes that combine NF-type selectivity with fouling- and chlorine-resistance by leveraging the self-assembling properties of ZACs and modifying this polymer family to improve salt rejection. Specifically, disclosed are charged zwitterionic amphiphilic copolymers (CZACs) and membranes prepared with CZAC selective layers through scalable manufacturing techniques. The CZACs are random or statistical terpolymers of three types of monomers: hydrophobic monomer, zwitterionic monomer, and acidic/ionizable monomer. Preferably, the copolymers are linear, random, and statistical. The random/statistical architecture of the copolymers and zwitterion-zwitterion attractive forces grant this terpolymer the ability to self-assemble into a bicontinuous network comprised of 1-2 nm hydrophilic (zwitterionic/charged) and hydrophobic nanodomains. Water and other solutes pass through the hydrophilic domains, which act as an effective network of nanochannels with charged walls. This allows the terpolymer to serve as a membrane selective layer. The hydrophilic nanochannel is net charged due to the ionization of the incorporated functional groups (e.g. deprotonation of an acidic repeat unit, protonation of an amine group, dissociation of a sulfonate group), which enhances the rejection of charged solutes and salt ions. Due to the presence of zwitterionic groups, these membranes are highly fouling resistant. The use of a novel polymer chemistry enables high chlorine resistance, with no changes in performance upon exposure to 32,000 ppm.hours of chlorine.
Disclosed is a family of polymeric materials that comprise pluralities of at least three types of repeat units:
The polymers, which are termed “Charged Zwitterionic Amphiphilic Copolymers” (CZACs), may be synthesized from vinyl monomers (e.g., acrylates, methacrylates, acrylamides, styrene derivatives, acrylonitrile) using well-known polymerization methods (e.g., free radical polymerization). The polymers incorporate the three types of repeat units in roughly random/statistical order (as opposed to in large blocks of individual monomers), and have a molecular weight from 20,000 g/mol to 1,000,000 g/mol (preferably from 40,000 g/mol, or 100,000 g/mol to 1,000,000 g/mol). Preferably, the copolymers are linear.
In certain compositions suitable for the application/embodiment described below for membrane selective layers, the CZACs comprise ˜30-80 wt % of the hydrophobic monomer, 1-40 wt % of the charged monomer, and 1-40 wt % of the zwitterionic monomer. Broader ranges of compositions may be of use in other applications.
Exemplary monomers for formation of each type of repeat unit are listed below.
Zwitterionic: Sulfobetaine methacrylate (SBMA)*; methacryloxy phosphoryl choline (MPC); carboxybetaine methacrylate (CBMA); sulfobetaine-2-vinylpyridine; sulfobetaine-4-vinylpyridine; sulfobetaine-vinyl imidazole; and several others comprising sulfobetaine, carboxybetaine, or phosphorylcholine moieties.
Charged/ionizable: Methacrylic acid (MAA)*; acrylic acid; styrene sulfonate; methacrylate, acrylate, acrylamide or styrene derivatives containing carboxylic acid, sulfonate, amine, phosphate, or other ionizable/charged groups
Relatively hydrophobic: 2,2-trifluoroethyl methacrylate (TFEMA)*; other fluorinated acrylates, methacrylates, and acrylamides (e.g., pentafluoropropyl methacrylate, heptafluorobutyl methacrylate, pentafluorophenyl methacrylate); styrene; methyl methacrylate; acrylonitrile; other monomers that fit the above criteria.
Utilities of the polymeric materials are discussed below, particularly in the context of their use as membrane selective layers. However, they can potentially be useful for other applications (e.g., as additives in membrane manufacture, compatibilizers).
The CZACs may be coated onto porous supports by methods understood in the membrane industry (e.g., blade coating, non-solvent induced phase separation (NIPS), spray coating). This results in a thin film composite (TFC) membrane, comprising at least two layers: A porous support with large pores, providing mechanical integrity; and a thin layer (thickness preferably <10 μm, more preferably <3 μm or <1 μm) of the CZAC, serving as the “selective layer” of the membrane. In this embodiment, the CZAC layer typically contains a continuous dense layer of CZAC (i.e., not regular “through-pores” providing pathways for water permeation, with the exception of occasional defects that may appear in processing even if they are not desired); in other words, water should permeate through the CZAC, as the main transport mechanism, rather than through pores/holes in it.
The resultant membranes exhibit size-based separation of neutral organic molecules, but also higher rejection of charged solutes than neutral solutes. This quality is useful for several applications where size-based separation is not sufficient. For example, if full or partial removal of contaminants is desired, the combination of size-based and charge-based rejection offered by these membranes can lead to better effluent quality. Alternatively, these membranes can separate two organic solutes (e.g., amino acids, drug compounds) from each other that differ by the presence of a charged group.
The current membranes can be modified and tuned to increase salt rejection to address reverse osmosis (RO)/desalination processes and engineered osmosis (EO), or to access slightly larger pore sizes to have charge-selective tight ultrafiltration (UF) membranes.
Commercial NF and RO/EO membranes almost universally have cross-linked polyamide selective layers. Such membranes suffer from two major problems: First, they are prone to fouling, requiring several pretreatment steps that impact the cost and energy efficiency of the overall process for desalination. Second, the membranes are highly sensitive to chlorine, which reacts with the selective layer. Chlorination is typically used to kill microorganisms in the incoming water to desalination facilities to prevent biofouling. Due to the chlorine sensitivity of commercial NF and RO membranes, the water is dechlorinated before being fed to the NF or RO units, then chlorinated again before being sent to customers.
The current membranes circumvent both of these issues: Zwitterionic groups are known and demonstrated to be highly resistant to fouling. The membranes are shown to be exceptionally resistant to fouling by an organic stream. Furthermore, the constituent polymers are not inherently prone to attack by chlorine. The membranes are shown to be stable to commercial chlorine bleach.
The membranes may undergo a pore rearrangement when subjected to high-pH buffers. When exposed to a high-pH buffer solution, membranes with some CZAC selective layers exhibit a one-time, irreversible and stable increase in permeability, along with a slight increase in pore size.
In one aspect, provided herein are copolymers, comprising a plurality of zwitterionic monomeric units, a plurality of charged/ionizable monomeric units, and a plurality of hydrophobic monomeric units.
In some embodiments, the molecular weight of the copolymer is 20,000 g/mol to 1,000,000 g/mol. In some embodiments, the molecular weight of the copolymer is 40,000 g/mol to 1,000,000 g/mol. In some embodiments, the molecular weight of the copolymer is 100,000 g/mol to 1,000,000 g/mol.
In some embodiments, the zwitterionic monomeric units constitute 1-40 wt % of the copolymer. In some embodiments, the charged/ionizable monomeric units constitute 1-40 wt % of the copolymer. In some embodiments, the hydrophobic monomeric units constitute 30-80 wt % of the copolymer.
In some embodiments, each of the zwitterionic monomeric units is formed from a monomer comprising sulfobetaine, carboxybetaine, or phosphorylcholine moieties. In some embodiments, each of the zwitterionic monomeric units is formed from a monomer selected from the group consisting of sulfobetaine methacrylate (SBMA), methacryloxy phosphoryl choline (MPC), carboxybetaine methacrylate (CBMA), sulfobetaine-2-vinylpyridine, sulfobetaine-4-vinylpyridine, and sulfobetaine-vinyl imidazole. In some embodiments, each of the zwitterionic monomeric units is formed from sulfobetaine methacrylate (SBMA).
In some embodiments, each of the charged/ionizable monomeric units is formed from a monomer selected from the group consisting of a methacrylate, an acrylate, an acrylamide or a styrene derivative comprising carboxylic acid, sulfonate, phosphate, or amine moieties. In some embodiments, each of the charged/ionizable monomeric units is formed from a monomer selected from the group consisting of methacrylic acid (MAA), acrylic acid, 2-carboxyethyl acrylate, 2-carboxyethyl methacrylate, styrene sulfonate, 3-sulfopropyl acrylate, 3-sulfopropyl methacrylate, 2-acrylamido-2-methyl-1-propanesulfonic acid, 2-(dimethylamino)ethyl methacrylate, 2-(diethylamino)ethyl methacrylate, 2-aminoethyl methacrylate, [2-(methacryloyloxy)ethyl]trimethylammonium chloride, [2-(acryloyloxy)ethyl]trimethylammonium chloride, 2-(diethylamino)ethyl acrylate, 2-(dimethylamino)ethyl acrylate, 3-(dimethylamino)propyl acrylate, N-acryloyl-L-valine, (3-acrylamidopropyl)trimethylammonium chloride, N[3-dimethylamino)propyl]methacrylamide, (2-isopropenylaniline, 4-[N-(methylaminoethyl)aminomethyl]styrene, and (vinylbenzyl)trimethylammonium chloride. In some embodiments, each of the charged/ionizable monomeric units is formed from methacrylic acid (MAA).
In some embodiments, each of the hydrophobic monomeric units is formed from a monomer selected from the group consisting of styrene, methyl methacrylate, acrylonitrile, a fluoroalkyl acrylate, a fluoroaryl acrylate, a fluoroalkyl methacrylate, a fluoroaryl methacrylate, a fluoroalkyl acrylamide, and a fluoroaryl acrylamide. In some embodiments, each of the hydrophobic monomeric units is formed from a monomer selected from the group consisting of a fluoroalkyl acrylate, a fluoroaryl acrylate, a fluoroalkyl methacrylate, a fluoroaryl methacrylate, a fluoroalkyl acrylamide, and a fluoroaryl acrylamide. In some embodiments, each of the hydrophobic monomeric units is formed from a monomer selected from the group consisting of 2,2-trifluoroethyl methacrylate (TFEMA), pentafluoropropyl methacrylate, heptafluorobutyl methacrylate, and pentafluorophenyl methacrylate. In some embodiments, each of the hydrophobic monomeric units is formed from 2,2-trifluoroethyl methacrylate (TFEMA).
In some embodiments, hydrophobic monomeric units are characterized in that a homopolymer formed thereof has a glass transition temperature above room temperature.
In some embodiments, the copolymer is a random copolymer.
In some embodiments, the copolymer is a statistical copolymer.
In some embodiments, the copolymer is a linear copolymer.
In some embodiments, the copolymer is poly((sulfobetaine methacrylate)-random-(methacrylic acid)-random-(2,2-trifluoroethyl methacrylate)).
In another aspect, provide herein are polymeric materials comprising a plurality of the copolymers. In some embodiments, the polymeric material is in the form of a thin film.
In yet another aspect, provided herein are thin film composite membranes, comprising a porous support, and a thin film of the polymeric material, wherein the pore size of the porous support is larger than the pore size of the thin film of the polymer material.
In some embodiments, the thin film of the polymeric material has a thickness of 1 nm to 10 μm. In some embodiments, the thin film of the polymeric material has a thickness of 1 nm to 3 μm. In some embodiments, the thin film of the polymeric material has a thickness of 1 nm to 1 μm.
In some embodiments, the thin film of the polymeric material has an effective pore size of 0.1-5 nm. In some embodiments, the thin film of the polymeric material has an effective pore size of 0.6-3 nm. In some embodiments, the thin film of the polymeric material has an effective pore size of 0.6-2 nm.
In some embodiments, the thin film composite membrane exhibits resistance to fouling by an oil emulsion.
In some embodiments, the thin film composite membrane is stable upon exposure to chlorine bleach (e.g., at pH 4).
In some embodiments, the thin film composite membrane undergoes a one-time, irreversible change in pore size upon exposure to buffers with high pH.
In some embodiments, the thin film composite membrane exhibits size-based selectivity between uncharged organic molecules.
In some embodiments, the thin film composite membrane rejects charged solutes and salts.
In another aspect, provided herein are methods of size-based selection or exclusion, comprising contacting a solution comprising a plurality of uncharged organic molecules of different sizes with a thin film composite membrane disclosed herein.
In further another aspect, provided herein are methods of charge-based selection or exclusion, comprising contacting a solution comprising a plurality of salts with a thin film composite membrane disclosed herein.
In order that the invention described herein may be more fully understood, the following examples are set forth. The examples described in this application are offered to illustrate the compounds, compositions, materials, device, and methods provided herein and are not to be construed in any way as limiting their scope.
In this example, a random/statistical terpolymer of the monomers trifluoroethylmethacrylate (TFEMA), sulfobetaine methacrylate (SBMA), and methacrylic acid (MAA) (a terpolymer comprised of these three components will be generically termed PTFEMA-SBMA-MAA) was synthesized as follows. First, TFEMA and MAA were purified using basic alumina columns. Then DMSO (80 mL), purified TFEMA (5.49 g), SBMA (2.61 g), purified MAA (1.11 g), LiCl (0.090 g), and AIBN (11 mg) were added to a 250 mL flat bottom reaction flask, which was then sealed with a rubber septum. The mixture was then allowed to stir at room temperature for two days to dissolve the zwitterionic monomer. Afterwards, the flask was sealed with a rubber septum, purged with N2 for 40 minutes, and then plunged into a 70° C. oil bath with stirring. After 20 hours, the reaction was terminated by exposure to air and the addition of MEHQ (0.5 g). For precipitation, the viscous polymer solution was then poured into an 800 mL mixture of ethanol and hexane (1:1 volume ratio.) The polymer was then cut into small pieces, and washed via stirring in an 800 mL mixture of ethanol and hexane (1:1 volume ratio) for over 12 hrs. This wash cycle was repeated 2 times. Afterwards, the polymer was left to dry under the hood for around 1 week, and finally dried in a 50° C. vacuum oven for over 24 hours. Yield was calculated as 38%, as determined by the by the weight of the dried polymer. This polymer will be termed PTFEMA-SBMA-MAA-B 1. The composition of the purified polymer was calculated from the 1H-NMR spectrum (
In this example, a random/statistical terpolymer of TFEMA, SBMA, and MAA was synthesized as follows. First, SBMA (2.80 g) and DMSO (87 mL) were added to a 250 mL flat bottom reaction flask. Temperature was raised to 70° C. to dissolve the zwitterionic monomer, and then returned to room temperature. During this the cool-down period, both TFEMA and MAA were purified using basic alumina columns (VWR). Following this, purified TFEMA (4.49 mL), purified MAA (1.86 mL), LiCl (0.10 g), and AIBN (9.8 mg) were added to the reaction flask. Afterwards, the flask was sealed with a rubber septum, purged with N2 for 30 minutes, and then plunged into a 70° C. oil bath with stirring. After 20 hours, the reaction was terminated by exposure to air and the addition of MEHQ (0.7 g) dissolved in approximately 5 mL of DMSO. For precipitation, the viscous polymer solution was then poured into a 900 mL mixture of ethanol and hexane (1:1 volume ratio). The polymer was then cut into small pieces, and washed via stirring in a 900 mL mixture of ethanol and hexane (1:1 volume ratio) for 12 hrs. This wash cycle was repeated 3 times. Afterwards, the polymer was left to dry under the hood for around 1 week, and finally dried in a 50° C. vacuum oven for 4 days. Yield was calculated as 60%, as determined by the by the weight of the dried polymer. This polymer will be termed PTFEMA-SBMA-MAA-B2. The composition of the purified polymer was calculated from the 1H-NMR spectrum (
From the data in
In this example, a TFC membrane was prepared using the polymer described in Example 1A. The copolymer was first dissolved in trifluoroethanol (TFE) at 0.11 g copolymer/mL TFE. The solution was then filtered using a 1 μm glass syringe filter, degassed via heating to 50° C. for 1 hour, and allowed to cool back down to room temperature. Next, a Gardco wire wound rod (wire size 2 ½, which deposits a 6 μm wet film) was used to coat the copolymer solution onto a PES ultrafiltration support membrane (Trisep UE50). After coating, the coated membrane was quickly plunged into a non-solvent bath of isopropyl alcohol (IPA) for 20 minutes, followed by immersion in DI water. This procedure yielded TFC membranes with the selective layer being the PTFEMA-SBMA-terpolymer described in Example 1A.
In this example, a membrane was prepared using the polymer described in Example 1B. The copolymer was first dissolved in trifluoroethanol (TFE) at 0.11 g copolymer/mL TFE. The solution was then filtered using a 1.2 μm glass syringe filter, degassed via heating to 50° C. for 1 hour, and allowed to cool back down to room temperature. Next, a Gardco universal blade applicator with a 20 μm gate setting was used to coat the copolymer solution onto a PES ultrafiltration support membrane (Trisep UE50). After coating, the film of polymer solution was allowed 15 seconds to evaporate. The coated membrane was then plunged into a nonsolvent bath of isopropyl alcohol (IPA) for 20 minutes, followed by immersion in DI water. This procedure yielded thin film composite (TFC) membranes with the selective layer being the PTFEMA-SBMA-MAA-B2 terpolymer described in Example 1B.
Scanning electron microscopy (SEM) was used to observe the cross-section of the TFC membranes described in Example 2A and Example 2B, which allowed for the selective layer thickness and membrane morphology to be analyzed. To prepare the samples, membrane sections were freeze-fractured and sputter-coated with gold-palladium. SEM images of the membrane cross-section were obtained using a Phenom G2 pure tabletop SEM at a 5 kV setting.
In this example, the pure water permeance of the membranes described in Examples 2A and 2B was measured, and compared to membrane prepared from PTFEMA-SBMA. To carry out the experiments, 10 mL Amicon 8010 stirred cells in dead-end mode was used. The membrane swatch area was 4.1 cm2, the stirring speed was 500 RPM, and the pressure was 30 psi for PTFEMA-SBMA-MAA-B 1 membranes and 50 psi for PTFEMA-SBMA-MAA-B2 membranes. To measure membrane permeance, Ohaus Scout Pro scales that were connected to a computer was used. Synchronized measurements of permeate mass versus time allowed for the measurement of membrane flowrate, which allowed for the calculation of membrane permeance. The permeances of PTFEMA-SBMA-MAA-B1 membranes and PTFEMA-SBMA-MAA-B2 membranes was 1.7 L/m2.h.bar (abbreviated as LMH/bar) and 2.5 LMH/bar, respectively (Table 1).
In this example, various neutral solutes were filtered using the membranes described in Example 3B. The purpose of these experiments was to: (1) to demonstrate the ability of membranes described in Example 3B to filter small neutral molecules from solution, and (2) to establish an effective pore size for the membranes described in Example 3B.
Filtration experiments were carried out using 10 mL Amicon 8010 stirred cells in dead-end mode. The membrane swatch area was 4.1 cm2, the stirring speed was 500 RPM, and the pressure was 50 psi for all experiments. The first 1.5 mL of permeate was discarded, and the subsequent 0.7 mL was collected for the measurement of permeate concentration. Permeate concentration was measured using chemical oxygen demand (COD) for sugars, and UV-vis spectroscopy for dyes.
In this example, various ionic solutes were filtered using the TFC membranes described in Example 3B. The purpose of these experiments was: (1) to demonstrate the ability of membranes prepared as described in Example 3B to filter salts from solution, and (2) demonstrate the ability of membranes prepared as described in Example 3B to selectively filter ionic species while passing neutral solutes of the same size.
Filtration experiments were carried out using 10 mL Amicon 8010 stirred cells in dead-end mode. The membrane swatch area was 4.1 cm2, the stirring speed was 500 RPM, and the pressure was 50 psi for all experiments. The first 1.5 mL of permeate was discarded, and the subsequent 0.7 mL was collected for the measurement of permeate concentration. Permeate concentration was measured using a conductivity meter. The data is tabulated in Table 3.
To test the hypothesis that deprotonated MAA grants the membrane with charge selectivity, Na2SO4 is filtered at varying pH (
The effective pKa<4.0 is well below the pKa of 4.78 that is reported for MAA monomer. This implies that MAA is approximately 10 times more reactive when incorporated into the CZAC nanostructure than when in free solution. This contradicted expectations, since it is generally found that confinement leads to reduced MAA reactivity.
In this example, the rejection of dyes and Na2SO4 by the TFC membranes prepared in Example 3A was determined and compared to that of PTFEMA-r-SBMA TFC membranes (termed PTFEMA-SBMA.) The synthesis of PTFEMA-SBMA and fabrication of PTFEMA-SBMA TFC membranes can be found elsewhere. It is noted here that the main difference between PTFEMA-SBMA membranes and PTFEMA-SBMA-MAA membranes is that PTFEMA-SBMA membranes lack MAA, and therefore should have a lower rejection of charged solutes. The purpose of these experiments was to: (1) demonstrate the ability of the PTFEMA-SBMA-MAA-B1 membranes to filter dyes from solutions, a feature which would be useful in applications such dye removal in the textile industry; (2) to further demonstrate the charge selectivity observed with PTFEMA-SBMA-MAA TFC membranes, with PTFEMA-SBMA TFC membranes serving as an appropriate control.
Filtration experiments were carried out using 10 mL Amicon 8010 stirred cells in dead-end mode. The membrane swatch area was 4.1 cm2, the stirring speed was 500 RPM, and the pressure was 27 psi for all experiments. The first 1.8 mL of permeate was discarded, and the subsequent 0.7 mL was collected to measure the concentration of the permeate. Permeate concentration was measured using UV vis spectroscopy for dyes, and conductivity for Na2SO4. The diameter of the dye molecules was obtained by assuming that the dye molecules were spheres of volume Vmolar, where Vmolar is the molar volume of the dye molecule; the molar volume of the dyes was obtained using Molecular Modeling Pro software by ChemSW.
Zwitterions are one of the most fouling resistant materials currently known. This is because the foulant-surface adsorption event that constitutes fouling is limited by the strong hydration shell that surrounds zwitterions (ΔGhydration˜−500 kJ/mol according to simulations). Previous work has shown that membranes comprised of random zwitterionic copolymers are highly fouling resistant, which proves that zwitterions are still able to act as anti-fouling agents from within the confines of the membrane nanostructure. To test if this rule extends to CZAC membranes, dead-end filtration using different model foulants is performed. Commercial NF membranes were used as benchmarks. The membranes were fouled for 24 hours, and the initial flux of the CZAC membrane was matched to that of the benchmark.
In this example, the fouling resistance of the PTFEMA-SBMA-MAA-B2 membrane described in Example 3B was measured using oil-in-water emulsions. The purpose of this was to show that the membranes are fouling resistant, which is a vital feature for any membrane that is pitted against a fouling-prone feedstock.
Fouling experiments were carried out using 10 mL Amicon 8010 stirred cells in dead-end mode. The membrane swatch area was 4.1 cm2, the stirring speed was 500 RPM, and the pressure was 50 psi for all experiments. To measure membrane permeance versus time, we used Ohaus Scout Pro scales that were connected to a computer. Synchronized measurements of permeate mass versus time allowed for the measurement of membrane flowrate, which allowed for the calculation of membrane permeance. The normalized permeance, which is permeance divided by the average DIW permeance before introducing the membrane to foulant, was calculated. Oil emulsions were prepared by blending surfactant, oil, and water together on <high> for 5 minutes. The mass ratio of surfactant: oil was 1:9, and the concentration of oil was 1500 mg/L in the stabilized emulsion. Span80 surfactant was for one fouling experiment, and DC 193 surfactant was used for the other.
In this example, PTFEMA-SBMA-MAA-B1 membrane was exposed to a solution of containing a chlorinated solution, prepared by diluting commercial Clorox bleach and adjusting its pH to an acidic value in agreement with commercial cleaning procedures. The purpose of this was to demonstrate that the PTFEMA-SBMA-MAA-B1 membranes are resistant to chlorine, which would enable the membranes to be cleaned with sodium hypochlorite, a commonplace disinfectant. The polyamide membranes that represent the cornerstone of the NF market are not stable upon exposure to chlorine, which is a major disadvantage of the technology.
To carry out the experiments, 10 mL Amicon 8010 stirred cells in dead-end mode was used. The membrane swatch area was 4.1 cm2, the stirring speed was 500 RPM, and the pressure was 50 psi. To measure membrane permeance, Ohaus Scout Pro scales that were connected to a computer was used. Synchronized measurements of permeate mass versus time allowed for the measurement of membrane flowrate, which allowed for the calculation of membrane permeance. The deionized water permeance of the membrane was measured as described above. The chlorinated solution was prepared by diluting commercial Clorox laundry bleach with deionized water and adjusting its pH to 4 in order to ensure that the vast majority of hypochlorite was hypochlorous acid. The final HClO concentration was estimated to be around 15,000 mg/L. The membrane swatch was exposed to this solution for 1-2 hours. Then, the permeance was measured again.
In this example, the irreversible response of PTFEMA-SBMA-MAA-B1 membranes to bases (termed base rearrangement) was investigated. The purpose of this was to reveal the unique response behavior of membranes derived from this new material. Filtration experiments were carried out using 10 mL Amicon 8010 stirred cells in dead-end mode. The membrane swatch area was 4.1 cm2, the stirring speed was 500 RPM, and the pressure was in the range of 30-50 psi for all experiments.
For the rearrangement seen in
The permeance of the membranes during filtration experiments for Example 2A and Example 2B was consistently measured using a simple mass balance. The results for filtration experiments, which captured 17 different uncharged/charged/dye solutes, is shown in
We also probed at how base-rearranged PTFEMA-SBMA-MAA-B1 membranes respond to basic solutions containing cations other than sodium and potassium (NaOH(aq) contains sodium as the cation; PBS contains sodium and potassium as the cations.) Calcium is known to bind with carboxylate, and so it was though that the binding interaction might have an impact on membrane flux. For this experiment, we measured permeance of a base rearranged PTFEMA-SBMA-MAA-B1 membrane with the feed being a basic (pH=10) solution of CaSO4.
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This application claims the benefit of U.S. Provisional Application No. 62/846,014, filed May 10, 2019, the contents of which are incorporated herein by reference in their entirety.
This invention was made with government support under grants 1508049 and 1553661 awarded by the National Science Foundation. The government has certain rights in the invention.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US20/32068 | 5/8/2020 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62846014 | May 2019 | US |
