KR102538247B1 - Hollow fiber composite membrane, manufacturing method thereof, gas separation membrane comprising the hollow fiber composite membrane - Google Patents

Abstract

The present invention relates to a hollow fiber composite membrane, a method for manufacturing the same, and a gas separation membrane including the hollow fiber composite membrane, and more particularly, to a microporous inorganic filler encapsulated with polydopamine on the inner surface of a porous support hollow fiber membrane by interfacial polymerization. By manufacturing a hollow fiber composite membrane on which a polyamide layer containing is formed, the specific surface area is increased, and the gas permeability and selectivity can be remarkably improved by facilitating the passage and adsorption of gas molecules through the uniform dispersion of the inorganic filler. . In addition, a uniform composite film can be formed even with a small amount of inorganic filler, and price competitiveness can be maximized.

Description

Hollow fiber composite membrane, manufacturing method thereof, gas separation membrane comprising the hollow fiber composite membrane

The present invention relates to a hollow fiber composite membrane, a manufacturing method thereof, and a gas separation membrane including the hollow fiber composite membrane.

For the past 30 years, the membrane process has been used as a key element in various fields such as chemical, desalination plants, food and beverage industries, pharmaceutical industries, and gas purification, as it has advantages such as high energy efficiency, simple operation method, and reliability compared to other separation and purification technologies. has been developed

In the case of a general membrane process such as gas separation or reverse osmosis process, there is a trade-off phenomenon between permeability and selectivity. A separation membrane material having permeability and selectivity is required. Among these membranes, organic polymer membranes in particular have been used in many separation processes because they are easy to select from various materials having various physico-chemical properties according to the purpose of separation and have low cost in manufacturing the membranes.

In the separation process, many efforts have been made to improve permeability or selectivity. Among these studies, MMMs (mixed matrix membranes) prepared by adding microporous materials or inorganic materials with high permeability characteristics to organic polymers as additives have been used. Therefore, many studies are in progress to increase permeability and selectivity for gas separation performance.

Among them, gas separation through the manufacture of MMMs using a porous metal-organic framework (MOF) has been studied a lot. As an example, H ₂ /CO ₂ by mixing MOF with poly(acrylic acid) (PAA) An excellent result was obtained with a selectivity of 20.3, and a high selectivity of 21.03 for H ₂ /CO ₂ was also obtained by coating polydimethylsiloxane (PDMS) with MOF on a polysulfone hollow fiber membrane support. got

In addition, in another study, CO ₂ permeability for CO ₂ /CH ₄ separation was 15 Barrer through MMMs obtained by incorporating COFs (covalent organic frameworks), a porous material, into Matrimid-5218, and selectivity for CO ₂ /CH ₄ was 32 was obtained with excellent results. In addition to this, ZIF-8 (Zeolitic imidazolate framework-8) can be used in various applications such as Polysulfone, PVC-g-POEM, PIM-1 (polymer intrinsic microporosity-1), polybenzimidazole, and Matrimid-5218. Research on the use of MMMs obtained by mixing with polymers for gas separation such as H ₂ , CO ₂ , N ₂ , and CH ₄ is also being conducted.

As such, various organic-inorganic materials are being used as materials for MMMs, and thin film nanocomposites are obtained by grafting various inorganic materials to organic polymers to obtain a film without losing the nanoporous characteristics of inorganic materials. , TFN), many studies have been conducted. Methods for fixing inorganic materials to a separator are representative methods of preparing a membrane after mixing inorganic materials in a polymer solution state or forming a coating layer in which inorganic materials are adsorbed in the form of a thin film on the surface of a polymer support, and the solution mixing method is mainly used. It became.

However, in the case of a dense membrane formed by the solution mixing method, it is difficult to uniformly distribute the inorganic filler, so most of the added nanoparticles do not act as a separation factor affecting permeability/selectivity. There is a problem not In addition, since a large amount of inorganic materials are used in membrane-casting, there is a problem in that price competitiveness is low.

Therefore, it is necessary to develop a new technology capable of supplementing the problems of the existing solution mixing method while forming a thin film nanocomposite containing an inorganic material and an organic polymer.

Korean Patent Registration No. 10-1920716

In order to solve the above problems, the present invention is to provide a hollow fiber composite membrane in which a polyamide layer containing a microporous inorganic filler encapsulated with polydopamine is formed on the inner surface of the porous support hollow fiber membrane by interfacial polymerization. to be

In addition, an object of the present invention is to provide a gas separation membrane having improved gas permeability and selectivity, including a hollow fiber composite membrane.

In addition, an object of the present invention is to provide a method for manufacturing a hollow fiber composite membrane using an interfacial polymerization method.

The present invention is a porous support hollow fiber membrane; and a polyamide layer formed on the inner surface of the porous support hollow fiber membrane and including a microporous inorganic filler encapsulated with polydopamine, wherein the microporous inorganic filler is a titanosilicate (Engelhard titanosilicate- 4, ETS-4) to provide a hollow fiber composite membrane.

[Formula 1]

Na ₉ Si ₁₂ Ti ₅ O ₃₅ (OH) xH ₂ O

(In Formula 1, x is an integer from 1 to 20.)

In addition, the present invention provides a gas separation membrane including the hollow fiber composite membrane.

In addition, the present invention comprises the steps of preparing a porous support hollow fiber membrane; Preparing a titanosilicate (Engelhard titanosilicate-4, ETS-4) composed of Formula 1; preparing a microporous inorganic filler encapsulated with polydopamine by mixing polydopamine with the titanosilicate; Preparing a hollow fiber composite membrane having a polyamide layer by injecting a microporous inorganic filler encapsulated with polydopamine, an aqueous monomer solution, and an organic monomer solution on an inner surface of the porous support hollow fiber membrane and conducting an interfacial polymerization reaction; and heat-treating the hollow fiber composite membrane.

[Formula 1]

Na ₉ Si ₁₂ Ti ₅ O ₃₅ (OH) xH ₂ O

(In Formula 1, x is an integer from 1 to 20.)

The hollow fiber composite membrane according to the present invention increases the specific surface area by preparing a hollow fiber composite membrane in which a polyamide layer containing a microporous inorganic filler encapsulated with polydopamine is formed on the inner surface of the porous support hollow fiber membrane by interfacial polymerization, The uniform dispersion of the inorganic filler facilitates the passage and adsorption of gas molecules, thereby remarkably improving gas permeability and selectivity. In addition, a uniform composite film can be formed even with a small amount of inorganic filler, and price competitiveness can be maximized.

The effects of the present invention are not limited to the effects mentioned above. It should be understood that the effects of the present invention include all effects that can be inferred from the following description.

1 is a view schematically showing a process of forming a hollow fiber composite membrane according to the present invention.
2 is an XRD graph of ETS-4 prepared in Example 1 of the present invention.
Figure 3 shows the results of SEM (a) and EDX analysis (b) of ETS-4 prepared in Example 1 of the present invention.
Figure 4 shows Si (c), Ti (d), N (e), O (f), Si as a result of TEM (a, b) and EDX mapping of PD-ETS-4 prepared in Example 1 of the present invention. , Ti, N and O are shown in the elemental image (g).
5 is a TGA result graph of ETS-4 and PD-ETS-4 prepared in Example 1 of the present invention.
6 is a graph showing the results of ATR-FTIR spectrum analysis of PD-ETS-4, PES hollow fiber membranes, PT, and ETS-4-PT prepared in Example 1 and Comparative Examples 1 to 3 of the present invention.
7 is a graph showing the results of XPS analysis for the PES hollow fiber membrane (a) prepared in Comparative Example 1 and the PD-ETS-4-PT (b) prepared in Example 1 of the present invention.
8 is a PES hollow fiber membrane (a, e), PT (b, f), ETS-4-PT (c, g), PD-ETS-4 prepared in Comparative Examples 1 to 3 and Example 1 of the present invention (d, h), FE-SEM cross-sectional and surface images of immobilized ETS-4 nanoparticles (i) and EDX analysis results of immobilized ETS-4 nanoparticles are shown.
9 shows AFM contact angles and three-dimensional images of PES hollow fiber membranes, PT, ETS-4-PT, and PD-ETS-4 prepared in Comparative Examples 1 to 3 and Example 1 of the present invention.
10 is CO ₂ gas permeability (a) according to operating pressure (0.2 to 2.0 bar) for PT, ETS-PT, and PD-ETS-4 prepared in Comparative Examples 2 and 3 and Example 1 of the present invention, and operation N ₂ gas permeability as a function of pressure (b), permeability of various gases (H ₂ , CO ₂ , N ₂ , CH ₄ ) as a function of gas kinetic diameter (c), CO ₂ /N ₂ ideal gas selectivity as a function of operating pressure (d), these are graphs as a result of analyzing various ideal gas selectivities (e) and H ₂ /CO ₂ selectivity (f) according to H ₂ permeability.

Hereinafter, the present invention will be described in detail with examples and drawings.

The present invention relates to a hollow fiber composite membrane, a manufacturing method thereof, and a gas separation membrane including the hollow fiber composite membrane.

As described above, the existing thin film nanocomposite was formed into a thin film by a solution mixing method, but it was difficult to uniformly distribute the inorganic filler, so it was not easy to act as a separation factor affecting gas permeability and selectivity. However, there was a problem in that a large amount of inorganic materials was used, and price competitiveness was low.

Therefore, in the present invention, in order to compensate for these disadvantages, the hollow fiber composite membrane is prepared by preparing a hollow fiber composite membrane in which a polyamide layer containing a microporous inorganic filler encapsulated with polydopamine is formed on the inner surface of the porous support hollow fiber membrane by interfacial polymerization. The gas permeability and selectivity can be remarkably improved by increasing the surface area and facilitating the passage and adsorption of gas molecules through the uniform dispersion of the inorganic filler. In addition, by forming a polyamide layer including an inorganic filler with a nanometer thickness, a uniform composite film can be formed even with a small amount of inorganic filler, and price competitiveness can be maximized.

Specifically, the present invention is a porous support hollow fiber membrane; and a polyamide layer formed on the inner surface of the porous support hollow fiber membrane and including a microporous inorganic filler encapsulated with polydopamine, wherein the microporous inorganic filler is a titanosilicate (Engelhard titanosilicate- 4, ETS-4) to provide a hollow fiber composite membrane.

[Formula 1]

Na ₉ Si ₁₂ Ti ₅ O ₃₅ (OH) xH ₂ O

(In Formula 1, x is an integer from 1 to 20.)

The porous support hollow fiber membrane has a much larger specific surface area per unit volume than other types of separation membranes, enabling high gas permeability and being applicable to large-scale processes. In addition, by forming a polyamide layer including an inorganic filler having high gas permeability and selectivity on the inner surface of the porous support hollow fiber membrane, there is an advantage of having excellent gas permeability and selectivity applicable to an actual gas separation process.

The porous support hollow fiber membrane may be made of at least one polymer selected from the group consisting of polyethersulfone, polysulfone, polyetherimide, polyimide, polycarbonate, polyacrylonitrile, and cellulose acetate. Preferably, the porous support hollow fiber membrane may be polyethersulfone, polysulfone, or a mixture thereof, and most preferably may be polyethersulfone. Compared to other polymers, the polyethersulfone has a high gas permeability due to high attraction between polymers, but may have relatively high selectivity despite low gas permeability.

The porous support hollow fiber membrane may have an inner diameter of 100 to 400 μm and an average thickness of 100 μm to 300 μm, preferably an inner diameter of 200 to 300 μm and an average thickness of 100 to 200 μm. At this time, when the inner diameter and average thickness of the porous support hollow fiber membrane do not satisfy both of the above ranges, the surface area through which gas molecules are permeated and adsorbed is reduced, and the inorganic filler is not uniformly distributed on the surface, resulting in increased gas permeability and selectivity. may be lowered

The titanosilicate (Engelhard titanosilicate-4, ETS-4) represented by Chemical Formula 1 may have a Si/Ti weight ratio of 2 to 4, preferably 2.5 to 3.5, and most preferably 3.0 to 3.2. When the weight ratio of Si/Ti satisfies the above range, permeability and selectivity of gas molecules can be increased, and it can exhibit potential as an ideal gas permeation separation membrane material.

In addition, the titanosilicate may have a pore diameter of 0.3 to 0.4 nm. The titanosilicate is composed of corner-sharing SiO ₄ tetrahedral and TiO ₆ octahedral structures. This uniform pore diameter as well as a high specific surface area can absorb gas molecules with a diameter smaller than the pore size of molecular sieving, H ₂ O, N ₂ , NH with a pore diameter smaller than 0.3 nm ₃ , H ₂ S, and SO ₂ molecules can be adsorbed. In particular, H ₂ permeability and H ₂ /CO ₂ selectivity can be significantly improved. Using these characteristics, the titanosilicate (ETS-4) has the advantage of being applicable to various fields such as fuel cells, pervaporation, and water vapor separation.

The titanosilicate maximizes interaction and interfacial polymerization with the polymers forming the polyamide layer, and prevents aggregation between the titanosilicate nanoparticles by mutual electrostatic repulsion to evenly disperse them in the polyamide layer. It is preferable to encapsulate the surface of the titanosilicate with positively charged polydopamine by self polymerization. The polydopamine (PD) is extracted from marine mussels and can form interactions with organic and inorganic surfaces through strong covalent and non-covalent interactions.

In other words, in the hollow fiber composite membrane, when gas molecules pass only through the titanosilicate (ETS-4) particles of the polyamide layer, it can exhibit characteristics as an efficient gas permeation membrane of a mixed matrix membrane (MMM). If poor interaction occurs between the titanosilicate (ETS-4) and the polyamide layer, gas molecules do not permeate through the titanosilicate (ETS-4), but bypass the titanosilicate (tortuous pathway) and mix. Permeation occurs through voids existing in the matrix membrane, and in this case, there is a problem of causing low gas selectivity. Accordingly, polydopamine, which is extracted from marine mussels and can form interactions with organic and inorganic surfaces through strong covalent and non-covalent interactions, is polymerized to encapsulate the titanosilicate (ETS-4) in encapsulated form This can minimize problems caused by voids.

The polydopamine may be included in an amount of 1 to 5% by weight, preferably 2 to 4% by weight, and most preferably 3% by weight, based on 100% by weight of the microporous inorganic filler. At this time, if the content of the polydopamine is less than 1% by weight, it may be difficult to evenly encapsulate the surface of the microporous inorganic filler with a uniform thickness, and conversely, if it exceeds 5% by weight, the pores of the microporous inorganic filler are blocked to increase the permeability. may cause degradation.

The polyamide layer is interfacial polymerization by condensation between polyethylenimine, an aqueous monomer, and 1,3,5-benzenetricarbonyl trichloride, an organic monomer (1,3,5-benzenetricarbonyl trichloride). It can be formed by interfacial polymerization (IP) method. More specifically, the polyamide layer contains polyethyleneimine and 1,3,5-benzenetricarbonyltrichloride in a 1 to 5:1 molar ratio, preferably 1.5 to 4 molar ratio, more preferably 1.8 to 3 molar ratio, most Preferably, it may be formed by interfacial polymerization at a molar ratio of 2:1.

The polyamide layer contains 0.05 to 1% by weight, preferably 0.08 to 0.7% by weight, more preferably 0.09 to 0.5% by weight, most preferably 0.1 to 0.3% by weight of the microporous inorganic filler based on 100% by weight of the polyamide layer. % by weight. At this time, if the content of the microporous inorganic filler is less than 0.05% by weight, the gas permeability and selectivity may be significantly reduced due to the selective absorption of gas molecules and the reduction in the passage of movement. Selectivity cannot be expected, and there is a problem of low price competitiveness.

The polyamide layer may have a thickness of 50 to 200 nm, preferably 60 to 140 nm, more preferably 80 to 110 nm, and most preferably 96 to 97 nm. At this time, if the thickness of the polyamide layer is less than 50 nm, the area for adsorbing gas molecules is reduced and gas selectivity may be lowered. may be lowered

As such, the hollow fiber composite membrane may have facilitated transport properties toward CO ₂ through gas permeation experiments for H ₂ , CO ₂ , N ₂ , _and CH ₄ , and the titanosilicate In particular, the H ₂ permeability and H ₂ /CO ₂ selectivity can be significantly improved by the molecular sieving effect of (ETS-4).

1 is a view schematically showing a process of forming a hollow fiber composite membrane according to the present invention. Referring to FIG. 1, the interface by condensation reaction between polyethylenimine and 1,3,5-benzenetricarbonyl trichloride on the inner surface of the porous support hollow fiber membrane It shows that a polyamide layer was formed by polymerization. In addition, in the polyamide layer, the microporous inorganic filler (ETS-4) encapsulated with polydopamine is uniformly and evenly dispersed by mutual bonding with the polyethylenimine and 1,3,5-benzene tricarbonyl trichloride. show what has happened

Meanwhile, the present invention provides a gas separation membrane including the hollow fiber composite membrane.

In addition, the present invention comprises the steps of preparing a porous support hollow fiber membrane; Preparing a titanosilicate (Engelhard titanosilicate-4, ETS-4) composed of Formula 1; preparing a microporous inorganic filler encapsulated with polydopamine by mixing polydopamine with the titanosilicate; Preparing a hollow fiber composite membrane having a polyamide layer by injecting a microporous inorganic filler encapsulated with polydopamine, an aqueous monomer solution, and an organic monomer solution on an inner surface of the porous support hollow fiber membrane and conducting an interfacial polymerization reaction; and heat-treating the hollow fiber composite membrane.

[Formula 1]

Na ₉ Si ₁₂ Ti ₅ O ₃₅ (OH) xH ₂ O

(In Formula 1, x is an integer from 1 to 20.)

The preparing of the porous support hollow fiber membrane may include preparing a dope solution by mixing a polymer, a pore former, and an organic solvent; supplying the dope solution to a spinning nozzle and then discharging it to manufacture a hollow fiber; contacting the discharged hollow fiber with an internal coagulant to form a porous support hollow fiber membrane; and washing and then drying the porous support hollow fiber membrane.

In the step of preparing the dope solution, the polymer may be at least one selected from the group consisting of polyethersulfone, polysulfone, polyetherimide, polyimide, polycarbonate, polyacrylonitrile, and cellulose acetate. Preferably, the porous support hollow fiber membrane may be polyethersulfone, polysulfone, or a mixture thereof, and most preferably may be polyethersulfone.

The pore forming agent may be at least one selected from the group consisting of lithium chloride (LiCl), polyethylene glycol (PEG), and polyvinylpyrrolidone (PVP), and preferably may be lithium chloride (LiCl). The pore former may serve to increase the porosity of the porous support hollow fiber membrane and control the pore size within a certain range.

In the step of preparing the dope solution, the dope solution may include 16 to 22% by weight of a polymer, 4 to 8% by weight of a pore former, and 70 to 80% by weight of an organic solvent.

The internal coagulant may serve to form pores in the membrane through interaction with the organic solvent in the dope solution and solidify to form a porous support hollow fiber membrane, and any solvent having a hydroxy group (-OH) functional group can be used. It is possible, but it is preferable to use at least one selected from the group consisting of water, ethanol, propanol and butanol.

In the step of preparing the titanosilicate, a mixed solution having a molar composition of 5H ₂ O ₂ : 0.5TiO ₂ : 10SiO ₂ : 18NaOH: 675H ₂ O can be prepared by mixing a titanium trichloride solution, a hydrogen peroxide solution, and a sodium silicate solution in distilled water. there is. The mixed solution may be dried at a temperature of 180 to 230 °C for 40 to 55 hours to form crystallized titanosilicate.

In the step of preparing the microporous inorganic filler encapsulated with polydopamine, polydopamine is added to the titanosilicate, mixed for 1 to 3 hours using a magnetic stirrer, and then allowed to react at room temperature for 20 to 26 hours. In this case, the polydopamine may be mixed in an amount of 1 to 5% by weight, preferably 2 to 4% by weight, and most preferably 3% by weight, based on 100% by weight of the microporous inorganic filler.

In the step of manufacturing the hollow fiber composite membrane, interfacial polymerization (IP) is one of the ways to easily obtain a thin-film composite (TFC) membrane, and the aqueous monomer (amine-based compound) and the organic monomer (chloride-based) A polyamide layer can be formed at the interface between the aqueous solution and the organic solvent by condensation polymerization between the compounds). At this time, the interfacial polymerization has the advantage of simple polymerization and the use of various monomers compared to conventional dip-coating, spray coating, and spin coating methods, and the interfacial polymerization method The dense thin film layer obtained by can have high gas selectivity.

In the step of preparing the hollow fiber composite membrane, the aqueous monomer solution may include polyethyleneimine, and the organic monomer solution may include 1,3,5-benzenetricarbonyltrichloride. At this time, the aqueous monomer solution and the organic monomer solution are interfacially polymerized at a molar ratio of 1 to 5:1, preferably at a molar ratio of 1.5 to 4, more preferably at a molar ratio of 1.8 to 3, and most preferably at a molar ratio of 2:1 to obtain polyamide. can be synthesized.

In the step of preparing the hollow fiber composite membrane, the microporous inorganic filler encapsulated with polydopamine is 0.05 to 1% by weight, preferably 0.08 to 0.7% by weight, more preferably 0.09 to 0.09% by weight, based on 100% by weight of the polyamide layer. 0.5% by weight, most preferably 0.1 to 0.3% by weight.

In the heat treatment of the hollow fiber composite membrane, the heat treatment may be performed at 60 to 100 °C for 5 to 20 minutes, preferably at 70 to 90 °C for 8 to 12 minutes. At this time, if both the heat treatment temperature and time conditions are not satisfied, the solvent remaining in the polyamide layer may not be sufficiently removed, and it is important to sufficiently remove the solvent because the remaining solvent causes structural changes in the polyamide layer. do.

Hereinafter, the present invention will be described in detail by examples, but the present invention is not limited by the following examples.

Example 1

(1) Manufacture of PES hollow fiber membrane

As shown in Table 1 below, a polymer dope solution for preparing a PES hollow fiber membrane was prepared by mixing PES, LiCl as a pore forming agent, and NMP as a solvent at a ratio of 18:5:77% by weight, respectively. Specifically, the PES polymer (Ultrason E6020P, BASF, Germany, MW=58,000 g/mol) was mixed with LiCl (lithium chloride sigma Aldrich, USA) under NMP (N-methylpyrrolidone, SAMCHUM CHEMICALS, Korea) solvent at 160 rpm under 3 A dope solution having the composition shown in Table 1 was prepared by stirring at about 160 rpm at 60 °C for 1 day. Then, the dope solution was put into a vacuum pump, and bubbles in the dope solution were removed for one day. Thereafter, the dope solution is moved to a spinneret (0.12/0.5 mm) through a micron filter using a gear pump, and distilled water (DI water), an internal coagulant, is passed through a HPLC pump (Series pump). , Lab alliance, USA). The hollow fiber spun through the spinneret undergoes complete phase conversion in the primary coagulation bath, and after going through the secondary coagulation bath and washing in the winder bath, the spun hollow fiber membrane is left with residual solvent. In order to remove the PES hollow fiber membrane as a porous support, it was washed with 50 cm ³ /min of flowing water in a washing batch for one week and then completely dried in a constant temperature drying room (313 K).

(2) Synthesis of ETS-4 and polydopamine-encapsulated ETS-4 (PD-ETS-4)

(2-1) Synthesis of ETS-4

ETS-4 with a mineral zeolite octahedral/tetrahedral framework was synthesized as follows. That is, after dissolving sodium hydroxide (Aldrich, 97%) in distilled water, a titanium trichloride solution (Aldrich, ca. 10 wt% in 20 to 30 wt% HCl) was slowly mixed and stirred for 30 minutes. A hydrogen peroxide solution and a sodium silicate solution (Aldrich, 27% SiO ₂ , 14% NaOH) were added to the formed white precipitate and reacted for 30 minutes to obtain 5H ₂ O ₂ : 0.5TiO ₂ : 10SiO ₂ : 18NaOH: 675 moles of H ₂ O A solution having the composition was obtained and the resulting solution was crystallized at 210° C. for 2 days in a 500 mL Teflon-coated autoclave. The synthesized product was cooled and washed several times with distilled water, and then the particle size was adjusted using an attrition mill to obtain ETS-4 as a final product.

(2-2) Synthesis of polydopamine-encapsulated ETS-4 (PD-ETS-4)

To encapsulate the synthesized ETS-4, spontaneous polymerization was performed in an alkaline aqueous solution using dopamine (Aldrich). Specifically, grained ETS-4 nanoparticles were mixed with 3% by weight of dopamine in a buffer solution (1.0 M Tris HCl, pH 8.5), stirred for 2 hours using a magnetic stirrer, and then stored at room temperature for 24 hours. . The PD-encapsulated ETS-4 particles were washed several times until the pH was neutral, and then the synthesized PD-ETS-4 was separated by centrifugation at 4000 RPM.

(3) Manufacture of hollow fiber composite membrane (PD-ETS-4)

The prepared PES hollow fiber membrane was used as a support for the TFN membrane. An amine-based PEI (polyethylenimine, branched, Sigma-Aldrich) was used as an aqueous monomer, and a chlorine-based TMC (1,3,5-Benzenetricarbonyl trichloride, Sigma-Aldrich) was used as an organic monomer, and as a solvent n-Hexane (99.9%, Ducsan) was used.

The composition of the TFN membrane through interfacial polymerization is shown in Table 2 below. After manufacturing the manufactured PES hollow fiber membrane as a module, each PEI and TMC monomer was supplied using a syringe pump as follows. That is, ETS-4 (PD-ETS-4) encapsulated with polydopamine and an aqueous monomer solution (PEI) were injected onto the PES hollow fiber membrane support for 1 minute, followed by nitrogen gas purging for 1 minute. Then, after injecting the organic monomer solution (TMC) for 1 minute, nitrogen gas purging was performed for another 1 minute. At this time, the polydopamine-encapsulated ETS-4 (PD-ETS-4) is a mixed matrix film on the inner surface of the PES hollow fiber by interfacial polymerization by the reaction of PEI, an aqueous monomer, with TMC, an organic monomer. A polyamide layer was formed in the form of membranes (MMM) to prepare a hollow fiber composite membrane (PD-ETS-4). Then, after stabilizing the polyamide layer formed by mixing PEI and TMC at room temperature for 1 hour, heat treatment was performed in an oven at 80 °C for 10 minutes. Residual solvent was removed using distilled water after the drying process. That is, an interfacial polymerization reaction occurred instantaneously to form a polyamide layer on the inner surface of the PES hollow fiber membrane.

Comparative Examples 1 to 3

As shown in Table 2 below, Comparative Example 1 was carried out in the same manner as Example 1, but a PES hollow fiber membrane was prepared.

Comparative Example 2 was carried out in the same manner as Example 1, but a polyamide film was prepared by interfacial polymerization by reaction of PEI, an aqueous monomer, with TMC, an organic monomer.

Comparative Example 3 was carried out in the same manner as Example 1, except that ETS-4 not encapsulated with polydopamine was used, and a polyamide membrane was prepared by interfacial polymerization by reaction of PEI, an aqueous monomer, with TMC, an organic monomer.

Experimental Example 1: XRD, SEM and EDX analysis of ETS-4

XRD, FE-SEM (Field Emission Scanning Electron Microscope) and EDX (Energy-dispersive X-ray spectroscopy) analyzes were performed to confirm the structure of ETS-4 prepared in Example 1, and the results are shown in FIGS. 3.

2 is an XRD graph of ETS-4 prepared in Example 1 above. Referring to FIG. 2, specific diffraction peaks of ETS-4 were observed in the 2θ ranges of 7.5 °, 12.7 ° and 30.0 °, respectively, which were consistent with the values reported in previous studies.

3 shows the results of SEM (a) and EDX analysis (b) of ETS-4 prepared in Example 1 above. Referring to FIG. 3, it was confirmed through FE-SEM that the ETS-4 particles were dumbbell-like, and it was also confirmed that they had the same shape as those reported in previous studies. In addition, through EDX analysis, the Si/Ti ratio of ETS-4 was observed to be about 3.0, which was almost consistent with the values of 2.7 to 2.9 reported in previous studies.

Experimental Example 2: TEM, EDX mapping and TGA analysis of PD-ETS-4

TEM and EDX (Energy-dispersive X-ray spectroscopy) mapping and TGA (Thermogravimetric analysis) analysis were performed to confirm the structure, elemental distribution, and thermal characteristics of PD-ETS-4 prepared in Example 1, and the results is shown in Figures 4 and 5.

4 shows Si(c), Ti(d), N(e), O(f), Si, Ti as a result of TEM (a, b) and EDX mapping of PD-ETS-4 prepared in Example 1 above. , N and O are shown in the elemental image (g). Referring to FIG. 4, it was confirmed that ETS-4 having a width of about 30 nm was surrounded by polydopamine (PD) (red circles in FIGS. 3a and 5b). In addition, it was confirmed through EDX mapping that the boundary layer between Si and Ti was clearly divided (Figs. 3c and 3d), and it was confirmed that the N and O peaks included in the PD were evenly distributed (Figs. 3e to 3g).

5 is a TGA result graph of ETS-4 and PD-ETS-4 prepared in Example 1 above. Referring to FIG. 5, it was confirmed that loss of loosely bound moisture occurred in the range of 30 to 100 ° C. at the beginning of the analysis. After that, it was confirmed that the weight loss of pure ETS-4 and PD-ETS-4 continued from 200 ℃ to 250 ℃ temperature range. It was found that ETS-4 lost its crystallinity due to the loss of structural water and collapsed into an amorphous material.

In addition, in the case of the pure ETS-4, a weight loss of about 15% by weight was exhibited by thermal decomposition up to 250 ° C., whereas in the case of the PD-ETS-4 sample, a weight loss of about 30% by weight was exhibited at the same temperature range. It was found that this was caused by decomposition of OH- and -NH ₂ functional groups of polydopamine in addition to the loss of structural water mentioned above. In addition, in the case of the PD-ETS-4, a gradual weight loss was shown up to 800 ° C., which was found to be due to the thermal decomposition of polydopamine.

Experimental Example 3: ATR-FTIR, XRD, FE-SEM and AFM surface analysis of hollow fiber composite membranes

The structure analysis of PD-ETS-4, PES hollow fiber membrane, PT, and ETS-4-PT prepared in Example 1 and Comparative Examples 1 to 3 was performed by ATR-FTIR, XRD, FE-SEM and AFM surface analysis , The results are shown in Table 3 and Figures 6 to 9.

6 is a graph showing the results of ATR-FTIR spectrum analysis of PD-ETS-4, PES hollow fiber membrane, PT, and ETS-4-PT prepared in Example 1 and Comparative Examples 1 to 3. Referring to FIG. 6, in the case of the ETS-4, a peak due to scissors (scissoring) of absorbed water molecules appeared in the 1650 cm ^-1 region, and at 986 cm ^-1 and 913 cm ^-1 , respectively, Si- Peaks due to stretching vibration of O-Si and Si-O-Ti bonds were confirmed.

In addition, in the case of the PD-ETS-4 (PD-ETS), the characteristic Si-O-Si and Si-O-Ti peaks (986, 913 cm ^-1 ) caused by ETS-4 and PD (polydopamine) were observed at 3200 Peaks due to stretching of -OH and NH groups in the area of cm ^-1 were confirmed. In addition, characteristic C=O and CO peaks due to PD were confirmed at 1630 cm ^-1 and 1295 cm ^-1 . Through this, it was confirmed that ETS-4 was successfully encapsulated by polydopamine.

In addition, in the case of Comparative Example 2 (PT) prepared only through interfacial polymerization without ETS-4, it was confirmed that a peak not found in the pure PES support appeared at 1665 cm ^-1 in the IR spectrum. This is due to the amide group of the polyamide generated from interfacial polymerization, and it was found that interfacial polymerization occurred successfully.

On the other hand, in the case of Example 1 (PD-ETS-PT), the main peaks caused by the pure ETS-4 and the hollow fiber composite membrane overlapped, and the amount of ETS-4 used was very small (0.2% by weight compared to PEI). Therefore, it was not possible to confirm clear peaks due to the stretching vibration of the Si-O-Si and Si-O-Ti groups of ETS-4 through the IR spectrum.

7 is a graph showing XPS analysis results for the PES hollow fiber membrane (a) prepared in Comparative Example 1 and the PD-ETS-4-PT (b) prepared in Example 1. Referring to FIG. 7, as a result of comparing C _1s core level spectra of Comparative Example 1 (PES hollow fiber membrane) and Example 1 (PD-ETS-4-PT) at binding energies of 280 to 290 eV, the In the case of Comparative Example 1 (PES hollow fiber membrane), a main peak corresponding to the binding energy of CC and CH appeared at 283.5 eV, and peaks corresponding to the binding of benzene and CO appeared at 284.3 eV and 285.8 eV. could

On the other hand, in the case of Example 1 (PD-ETS-4-PT), the peak at 286.6 eV due to the CO carbon of PES appeared strongly, and at 286.7 eV, the carbonyl peak of NC=O was newly generated. The presence of an amide bond was confirmed. Through this, it was confirmed through the peak of C _1s in XPS that the hollow fiber composite membrane was successfully manufactured.

In addition, the cross-section and surface of the hollow fiber composite membrane formed by the interfacial polymerization method were analyzed through FE-SEM, and the results are shown in FIG. 8 .

8 is a PES hollow fiber membrane (a, e), PT (b, f), ETS-4-PT (c, g), and PD-ETS-4 (d) prepared in Comparative Examples 1 to 3 and Example 1 , h), FE-SEM cross-sectional and surface images of the immobilized ETS-4 nanoparticles (i) and EDX analysis results of the immobilized ETS-4 nanoparticles. Referring to FIG. 8, in the case of Comparative Example 2 (PT) (b, f), after polymerization between PEI and TMC on Comparative Example 1 (PES hollow fiber membrane) (a, e) having a porous surface Formation of the selective layer was confirmed through cross-section and surface images. In addition, in the case of Comparative Example 3 (ETS-4-PT) (c, g), it was confirmed that the thickness of the coating layer on the surface of the membrane increased from 68.8 nm to 100 nm by the additional addition of ETS-4 nanoparticles. Through this, it was confirmed that the ETS-4 particles were successfully incorporated into the selective layer and a polyamide layer was formed by interfacial polymerization (FIG. 8b to 8d).

In addition, the separators of Comparative Example 3 (ETS-4-PT) and Example 1 (PD-ETS-PT) have a thickness of 100 nm and 96.9 nm, respectively, and a similar selective layer thickness. It was confirmed through analysis (FIG. 8c, 8d). It was found that this was because the ETS-4 content was prepared according to the same concentration and nanoparticle content during the manufacture of the two separators.

However, in the surface analysis image, it was confirmed that the separator of Example 1 (PD-ETS-PT) was more evenly dispersed (FIG. 8h). It was found that this was because the aggregation between ETS-4 nanoparticles was suppressed by reciprocal electrostatic repulsion in the case of ETS-4 encapsulated with polydopamine having a positive charge. In addition, as a result of confirming the EDX analysis result of ETS-4 incorporated in the polyamide layer, it was possible to confirm the peaks of Si and Ti detected from ETS-4, through which it was confirmed that the TFN hollow fiber membrane was successfully manufactured. (FIG. 8j).

In addition, the root mean square roughness (Rq), average roughness (Ra), and maximum roughness (Rmax) of each separator through AFM surface analysis were calculated and compared. The results are shown in FIG. 9 .

9 shows the contact angle and three-dimensional images of AFM for the PES hollow fiber membranes, PT, ETS-4-PT, and PD-ETS-4 prepared in Comparative Examples 1 to 3 and Example 1. Referring to FIG. 9, it was confirmed that the average roughness increased after interfacial polymerization and incorporation of ETS-4 as a whole. In addition, despite the fact that Comparative Example 3 (ETS-4-PT) and Example 1 (PD-ETS-PT) have the same ETS-4 incorporation conditions, Example 1 (PD-ETS-PT) It shows a higher roughness, and through this, it can be seen that Example 1 (PD-ETS-PT) spreads well on the surface without agglomeration, which is consistent with the results shown in the previous SEM image.

In addition, the surface interface energy of the surface of the separator before and after interfacial polymerization was calculated, and the results are shown in Table 3.

Referring to Table 3, in the case of Comparative Example 1, after interfacial polymerization at 106.6 mJ/m ² , as in Comparative Example 2, it was confirmed that a higher surface interface energy was exhibited at 118.5 mJ/m ² , and then ETS-4 A higher value of 128.2 mJ/m ² than PT was shown in Example 1 (PD-ETS-PT) with additional incorporation. It was found that the increase in average surface roughness and interfacial energy could contribute to increasing the gas permeability by increasing the surface area of the separator.

Experimental Example 4: Gas Separation Performance Analysis of Hollow Fiber Composite Membrane

For the PD-ETS-4, PT, and ETS-PT prepared in Example 1 and Comparative Examples 2 and 3, permeation experiments for various gases such as CO ₂ and H ₂ , N ₂ , CH ₄ were analyzed. Results are shown in FIG. 10 .

A module was manufactured for the gas separation experiment of the manufactured hollow fiber composite membrane, and the operating conditions of the manufactured module are shown in Table 4. The experiment was conducted while changing the pressure at an operating pressure of 0.1 to 2.0 bar, and at this time, the operating temperature was maintained at 25 ° C by air circulation inside the oven. The gas permeated through the hollow fiber composite membrane module was measured using a bubble flow meter (Holiba VP-1), and the permeability of the permeated gas was calculated using Equation 1 below.

[Equation 1]

Here, Q _P is the permeate flow rate of gas passing through the membrane, ΔP is the pressure difference in the membrane, and A is the effective cross-sectional area of the membrane. The permeance unit is expressed as mol/(m ² s Pa) or cm ³ (STP)/(cm ² cmHg sec) in the SI system. However, here P is more widely used as gas permeation units (GPU), i.e. 1 GPU = 1 x 10 ^-6 cm ³ (STP)/(cm ² ㅇ cmHg ㅇ sec). The ideal selectivity of the permeated single gas was calculated as in Equation 2 below.

[Equation 2]

10 shows the CO ₂ gas permeability (a) according to the operating pressure (0.2 to 2.0 bar) for PT, ETS-PT, and PD-ETS-4 prepared in Comparative Examples 2 and 3 and Example 1, and (b) permeability of various gases (H ₂ , CO ₂ , N ₂ , CH ₄ ) as a function of gas kinetic diameter (c), CO _{2 /} N ₂ ideal gas selectivity as a function of operating pressure (d) ), various ideal gas selectivities (e), and H ₂ /CO ₂ selectivity (f) according to H ₂ permeability.

Referring to (a) and (b) of FIG. 10, as a result of observing the permeation characteristics of CO ₂ and N ₂ according to the change in the operating pressure in the range of 0.25 to 2.0 bar in the dry state of each membrane at 25 ° C, the operating pressure As N _{2 increases, the permeability of N 2} increases slightly due to the increase in diffusivity according to the increase in pressure, but CO ₂ shows the opposite trend of facilitated transport. That is, as can be seen in (d) of FIG. 10, the PD-ETS-PT membrane has the highest CO ₂ permeability with ~17 GPU and CO ₂ /N ₂ selectivity of ~34 at low pressure (0.25 bar). showed up The reason for this facilitated transport property can be found from PEI and PDA used in the manufacture of hollow fiber composite membranes.

That is, PEI is a polymer having a repeating unit composed of two methylene spacers, and has a large amount of primary, secondary, and tertiary amine groups with strong affinity to CO ₂ molecules, and PD also has a large number of primary and secondary amine groups, such secondary and tertiary amines can react with CO ₂ in a dry state as shown in Schemes 1 and 2 below, respectively. That is, the interaction of secondary amines follows the mechanism by zwitterion formation, and tertiary amines do not follow zwitterion deprotonation for CO ₂ interaction, but electrostatic attraction and van der Waals force mechanism can be followed.

[Scheme 1] Secondary amine reaction

Step 1: R ₂ NH + CO ₂ ↔ R ₂ NH + COO ^-

Step 2: R ₂ NH ⁺ COO ^- + R ₂ NH ↔ R ₂ N COO ^- + : R ₂ NH ⁺

[Scheme 2] Secondary amine reaction

Step 1: R ₃ N + CO ₂ ↔ R ₃ N ⁺ COO ^-

Step 2: R ₃ NH ⁺ COO ^- + R ₃ N ↔ R ₂ N COO ^- + : R ₄ N

Such an amine functional group can be a good carrier according to the increase in CO ₂ solubility, and can obtain higher permeability and selectivity through a catalyzed transport mechanism of CO ₂ through a reversible reaction. However, an increase in the operating pressure causes saturation of the adsorption capacity of the CO ₂ carrier, which means that a typical permeation trend is shown at the operating pressure point of 1.5 bar.

In particular, the reason why the membrane of Example 1 (PD-ETS-PT) exhibits high permeability compared to other membranes can be explained by the dissolution diffusion model among the separation mechanisms of the membrane. In particular, the permeability of the separation membrane may be determined according to hydrophilicity, thickness, crosslinking density, and permeation path. In the case of CO ₂ , since it is a condensable gas, it may be affected by solubility. Example 1 (PD-ETS-PT) showed a clear difference compared to other separators in the hydrophilicity change of the separator surface and the surface interface energy calculation result through the thickness and contact angle of the separator through FE-SEM. Through this, it was confirmed that interfacial polymerization and the addition of ETS-4 had a positive effect on CO ₂ permeability improvement by increasing the solubility in preparing the hollow fiber composite membrane.

On the other hand, in the case of N ₂ permeability results, it was confirmed that the permeability decreased according to the type of membrane in the order of Comparative Example 2 (PT), Comparative Example 3 (ETS-PT), and Example 1 (PD-ETS-PT). That is, in the case of Comparative Example 2 (PT), it was confirmed that the N ₂ permeability decreased from about 1.4 to 0.5 GPU at an operating pressure of 1.0 bar according to the addition of ETS-4 when preparing TFN using the interfacial polymerization (IP) method. . As mentioned above, ETS-4 has a pore size of about 3 to 4 Å, and in the case of N ₂ (3.64 Å, 3.8 Å), which has a relatively large kinetic diameter and collision diameter, there is a difference in gas diffusivity. Therefore, permeation is relatively effectively restricted, and this feature is clearly shown in the hydrogen permeability of FIG. 10(c).

Referring to (c) of FIG. 10, the permeability of H ₂ , CO ₂ , N ₂ , CH ₄ single gas at an operating pressure of 2 bar is shown, and as a result of the permeation experiment, the pore size is larger than that of ETS-4. In the case of small H ₂ (2.89 Å), it was confirmed that a high transmission tendency of about 50 to 60 GPU was shown.

Comparing the gas permeability of Comparative Example 3 (ETS-PT) in which PD was not encapsulated in ETS-4 and Example 1 (PD-ETS-PT) in which PD was encapsulated, the Comparative Example at an operating pressure of 2 bar 3 (ETS-PT), in the case of Example 1 (PD-ETS-PT), H ₂ transmittance was lower by about 5 GPU, and based on N ₂ transmittance, 0.86 and 0.6 GPU, respectively, compared to Example 1 (PD-ETS-PT). -ETS-PT) was found to have lower permeability. This is due to the encapsulation effect of ETS-4 using PD and can be explained as follows. As mentioned above, MMM can obtain ideal permeability and selectivity for gas molecules when inorganic materials such as ETS-4 pass only through inorganic materials, not through defects or pin-holes between polymer separators. And it was found.

Accordingly, polydopamine (PD), which enables the formation of strong covalent and non-covalent bonds with various organic and inorganic materials, lowers the aggregation effect of inorganic materials between ETS-4 and polyamide formed by interfacial polymerization, thereby dispersing and nanoparticles in the separator. Porous properties could be maintained. In addition, it was confirmed that the cohesive force between the polyamide layer produced by interfacial polymerization and the ETS-4 particles was improved, so that the gas molecules did not bypass the inorganic material but used the inside of ETS-4 as a migration path. As a result, compared to Comparative Example 3 (ETS-PT) in which PD was not encapsulated in ETS-4, in the case of Example 1 (PD-ETS-PT), there was a slight loss in terms of permeability, but improved selectivity. was obtained (c and e in FIG. 10).

10(f) shows the H ₂ /CO ₂ permeability-selectivity of polymer membranes such as PIMs, TR, and polybenzimidazole (PBI), which are representative gas separation polymers, and MMM including MOF and ZIF, based on the results of the permeation experiment. This is the result of comparing with the GPU unit. In the case of the PIM membrane, about 650 to 7800 GPU shows a very high permeability and a H ₂ /CO ₂ selectivity of about 2, and the TR membrane shows a trend of 20 to 6000 GPU and H ₂ /CO ₂ 0.6 to 8.5. In addition, in the case of MOF and ZIP, which are MMM base separators, selectivity tended to be 1500 and 7031 GPU, respectively, and 20 and 18.4 H ₂ /CO ₂ , respectively. In addition, the hollow fiber membrane using the ETS-4 shows a relatively low selectivity of about 60 GPU, but the H ₂ /CO ₂ selectivity shows a high result of 13, and MMM separation membrane by molecular sieving in the future Its applicability to

As described above, in the present invention, the gas permeability of ETS-4 nanoparticles was confirmed, ETS-4 synthesis and encapsulation of ETS-4 were performed using polydopamine, and the synthesized ETS-4 was synthesized with PEI on a PES hollow fiber membrane. A hollow fiber composite membrane was prepared using TMC.

The synthesized ETS-4 was confirmed for its physical and chemical structure through XRD, SEM, EDX, and TEM, and in the case of TFN, the incorporation of ETS-4 was confirmed through SEM, FT-IR, and XPS. In addition, the permeability of various gases was confirmed using the hollow fiber composite membrane, and the enhanced transport permeability was shown during CO ₂ separation by PEI and PD. In addition, the molecular sieve effect according to the size of the kinetic diameter of gas molecules due to the structural characteristics (pore size) of ETS-4 was confirmed. As a result, it was confirmed that the maximum single gas hydrogen permeability was about 80 GPU, and the H ₂ /CO ₂ ideal gas selectivity was 13. Through this, it was found that ETS-4 is a promising inorganic material for gas separation according to the motion diameter due to its structural characteristics and can be applied to various fields.

Claims (14)

A porous support hollow fiber membrane comprising hollow fibers; and
A polyamide layer formed on the inner surface of the hollow fibers included in the porous support hollow fiber membrane and containing a microporous inorganic filler encapsulated with polydopamine;
The hollow fiber composite membrane wherein the microporous inorganic filler is titanosilicate (Engelhard titanosilicate-4, ETS-4) composed of Formula 1 below.
[Formula 1]
Na ₉ Si ₁₂ Ti ₅ O ₃₅ (OH) xH ₂ O
(In Formula 1, x is an integer from 1 to 20.)
According to claim 1,
The porous support hollow fiber membrane is made of one or more polymers selected from the group consisting of polyethersulfone, polysulfone, polyetherimide, polyimide, polycarbonate, polyacrylonitrile and cellulose acetate.
According to claim 1,
The porous support hollow fiber membrane has an inner diameter of 100 to 400 μm and an average thickness of 100 to 300 μm.
According to claim 1,
The titanosilicate has a weight ratio of Si / Ti of 2 to 4 and a pore diameter of 0.3 to 0.4 nm.
According to claim 1,
The hollow fiber composite membrane comprising 1 to 5% by weight of the polydopamine based on 100% by weight of the microporous inorganic filler.
According to claim 1,
The polyamide layer is a hollow fiber composite membrane formed by interfacial polymerization of polyethyleneimine and 1,3,5-benzenetricarbonyltrichloride in a molar ratio of 1 to 5: 1.
According to claim 1,
The hollow fiber composite membrane, wherein the polyamide layer contains 0.05 to 1% by weight of a microporous inorganic filler based on 100% by weight of the polyamide layer.
According to claim 1,
The polyamide layer is a hollow fiber composite membrane having a thickness of 50 to 200 nm.
A gas separation membrane comprising the hollow fiber composite membrane of any one of claims 1 to 8.
Preparing a porous support hollow fiber membrane comprising a hollow fiber;
Preparing a titanosilicate (Engelhard titanosilicate-4, ETS-4) composed of Formula 1;
preparing a microporous inorganic filler encapsulated with polydopamine by mixing polydopamine with the titanosilicate;
A microporous inorganic filler encapsulated with polydopamine, an aqueous monomer solution, and an organic monomer solution are injected into the hollow fibers included in the porous support hollow fiber membrane, and interfacial polymerization is performed to form a polyamide layer on the inner surface of the hollow fibers. Preparing a hollow fiber composite membrane; and
heat-treating the hollow fiber composite membrane;
Method for producing a hollow fiber composite membrane comprising a.
[Formula 1]
Na ₉ Si ₁₂ Ti ₅ O ₃₅ (OH) xH ₂ O
(In Formula 1, x is an integer from 1 to 20.)
According to claim 10,
The step of preparing the porous support hollow fiber membrane,
preparing a dope solution by mixing a polymer, a pore former, and an organic solvent; supplying the dope solution to a spinning nozzle and then discharging it to manufacture a hollow fiber;
contacting the discharged hollow fiber with an internal coagulant to form a porous support hollow fiber membrane; and
washing and drying the porous support hollow fiber membrane;
Method for producing a hollow fiber composite membrane further comprising a.
According to claim 10,
The aqueous monomer solution is a method for producing a hollow fiber composite membrane comprising polyethyleneimine.
According to claim 10,
The method of manufacturing a hollow fiber composite membrane, wherein the organic monomer solution contains 1,3,5-benzenetricarbonyltrichloride.
According to claim 10,
In the step of heat-treating the hollow fiber composite membrane, the heat treatment is performed at 60 to 100 ° C. for 5 to 20 minutes.

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