KR101979683B1 - Thin-film composite membrane for organic solvent nanofiltration and preparation method thereof - Google Patents

Abstract

TECHNICAL FIELD The present invention relates to an ultra-thin composite membrane for organic solvent nanofiltration and a method for producing the same, and more particularly, to a composite membrane comprising a porous support formed of a thermally-converting poly (benzoxazole-imide) copolymer, Membranes and applying them to organic solvent nanofiltration processes.
The ultra-thin composite membrane formed according to the present invention, on which a thin film active layer is formed on a porous thermally-converting poly (benzoxazole-imide) copolymer support, has excellent chemical and thermal stability against an organic solvent and excellent organic solvent nano- In addition, since nanofiltration performance is stably maintained even under high temperature organic solvent conditions, it can be applied to organic solvent nanofiltration membranes in chemical, pharmaceutical or refining industries.

Description

TECHNICAL FIELD [0001] The present invention relates to a thin film composite membrane for organic solvent nanofiltration,

The present invention relates to an ultra-thin composite membrane for organic solvent nanofiltration and a method of manufacturing the same. More particularly, the present invention relates to a method of forming a porous support using a heat conversion poly (benzoxazole-imide) copolymer, The present invention relates to a technique for preparing a composite membrane containing an organic solvent and applying the same to an organic solvent nanofiltration process.

In general, the separation process required in the chemical industry and the pharmaceutical industry is carried out using almost organic solvents, including distillation, crystallization, adsorption, and extraction processes, and thus the demand for organic solvent separation membranes is steadily increasing. However, since most of the conventionally developed or commercialized membranes are manufactured for water treatment or gas separation, there is a limit to maintaining a stable chemical structure in an environment exposed to various organic solvents. Therefore, although there is an industrial demand for the organic solvent separator and its size is not so small, the organic solvent separator has not been developed so far.

However, a composite membrane obtained by forming a polyamide thin film layer on a polyimide support as an organic solvent nanofiltration membrane, a polybenzimidazole membrane and a polyether ether ketone membrane polymerized from tetraamine and dicarboxylic acid, and the like are known. In the case of the filtration membrane, the pore size is also important, but the interaction between the solvent or the solute and the separation membrane affects the performance of the separation membrane, so it is urgent to develop a material having excellent stability to the organic solvent. In addition, polyimide, crosslinked polybenzimidazole, polyetheretherketone membrane, etc., which are conventionally formed in the form of an asymmetric membrane, are often used in limited organic solvents and temperature ranges because they are difficult to obtain an excellent permeability even if they are stable to organic solvents Various types of separator materials, shapes, and improved separation performance are required (Patent Documents 1 and 2).

Further, a heat-converted poly (benzoxazole-imide) copolymer film is prepared by reacting an acid anhydride, ortho-hydroxyamine and an aromatic diamine to obtain a hydroxypolyimide-polyimide copolymer film and heat- , There is no disclosure about the chemical stability of the organic solvent as well as the separation performance of the organic solvent. Thus, application to the organic solvent nanofiltration membrane has not been considered (Non-Patent Document 1).

Accordingly, the inventors of the present invention have conducted studies to expand application fields of thermally-converting poly (benzoxazole-imide) copolymer films having excellent thermal and chemical stability and mechanical properties. As a result, they have found that heat- If the ultra-thin composite membrane can be prepared by forming the membrane of the copolymer on the porous support and forming a thin active layer on the porous support, it can be applied as an organic solvent nanofiltration membrane on the basis of the stability against the organic solvent and the separation performance And finally completed the present invention.

Patent Document 1: US Patent Application Publication No. US 2015/0231572 Patent Document 2 US Patent Publication No. US 2013/0118983

Non-Patent Document 1 Chul Ho Jung et al., J. Membr. Science 350, 301-309 (2010)

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and it is an object of the present invention to provide a method for producing a nanofiltration membrane, which is excellent in chemical and thermal stability to an organic solvent and is excellent in organic solvent nanofiltration performance, The present invention provides an ultra-thin composite membrane for organic solvent nanofiltration and a method of manufacturing the same.

In order to accomplish the above object, the present invention provides a porous thermally-converting poly (benzoxazole-imide) copolymer support having a repeating unit represented by the following formula (1); And an active layer of a thin film formed on the support. The present invention also provides an ultra-thin composite membrane for organic solvent nanofiltration.

≪ Formula 1 >

(Wherein Ar ₁ is an aromatic ring group selected from a substituted or unsubstituted quadrivalent arylene group having 6 to 24 carbon atoms and a substituted or unsubstituted quadrivalent heterocyclic group having 4 to 24 carbon atoms, O, S, CO, SO ₂ , Si (CH ₃ ) ₂ , (CH ₂ ) _p (1 ≦ _P ≦ ₁₀ ), or two or more of them form a condensed ring; ), (CF ₂ ) _q ( ₁ ? _Q ? 10), C (CH ₃ ) ₂ , C (CF ₃ ) ₂ or CO-

Ar ₂ is an aromatic ring group selected from a substituted or unsubstituted divalent arylene group having 6 to 24 carbon atoms and a substituted or unsubstituted divalent heterocyclic group having 4 to 24 carbon atoms and the aromatic ring group is present alone; Two or more of them form a condensed ring with each other; Two or more single bond, O, S, CO, SO 2, Si (CH 3) 2, (CH 2) p (1≤P≤10), (CF 2) q (1≤q≤10), C _{(CH 3) 2, C (} CF 3) is connected to ₂ or CO-NH,

Q is a single bond; _{O, S, CO, SO 2} , Si (CH 3) 2, (CH 2) p (1≤P≤10), (CF 2) q (1≤q≤10), C (CH 3) 2, C _{(CF 3) 2, CO-} NH, C (CH 3) (CF 3), or a substituted or unsubstituted phenylene ring, x, y is 0.1≤x≤0.9, 0.1≤y≤ a molar fraction within each repeating unit 0.9, x + y = 1)

The porous heat conversion poly (benzoxazole-imide) copolymer support is characterized by being an electrospray film.

The thickness of the electrodisplacive film is 10 to 80 탆 and the porosity is 60 to 80%.

Wherein the active layer of the thin film is an aromatic polyamide having a crosslinked structure having a repeating unit represented by the following formula (2).

(2)

The active layer of the thin film has a thickness of 50 to 300 nm.

The present invention also provides a process for preparing a polyimide-polyimide copolymer, which comprises: (I) synthesizing a hydroxy group-containing polyimide-polyimide copolymer by reacting an acid dianhydride, ortho-hydroxy diamine and an aromatic diamine to obtain a polyamic acid solution, followed by azeotropic thermal imidization;

II) forming a polymer solution by dissolving the hydroxy group-containing polyimide-polyimide copolymer of step I) in an organic solvent by electrospinning;

III) obtaining a porous thermally-converting poly (benzoxazole-imide) copolymer support having the repeating units represented by Formula 1 by thermal conversion of the membrane obtained in the step II); And

IV) forming an active layer of an aromatic polyamide thin film having a crosslinked structure having the repeating unit represented by the above formula (2) on the support, and a method of manufacturing an ultra-thin composite membrane for organic solvent nanofiltration.

The acid dianhydride in the step I) is characterized by being represented by the following formula (3).

(3)

(Wherein Ar ₁ is as defined in Formula 1)

The ortho-hydroxydiamine of the step I) is characterized by being represented by the following general formula (4).

≪ Formula 4 >

(Q in Formula 4 is the same as defined in Formula 1)

The aromatic diamine of the step I) is represented by the following general formula (5).

≪ Formula 5 >

(Ar ₂ in the formula (5) is the same as defined in the formula (1)

In the azeotropic thermal imidation of the step I), toluene or xylene is added to the polyamic acid solution, and the mixture is stirred to perform imidization reaction at 160 to 200 ° C for 6 to 24 hours.

The heat conversion in step III) is performed by raising the temperature to 300 to 400 ° C at a rate of 1 to 20 ° C / min in an inert gas atmosphere of high purity, and then maintaining the isothermal state for 1 to 2 hours.

And a step of hydrophilizing the support obtained in the step (III) before the step (IV) is carried out.

The hydrophilization treatment is characterized in that the support obtained in the step (III) is coated with polypodamine.

The active layer of the aromatic polyamide thin film having the crosslinked structure is characterized in that it is formed by the interfacial polymerization reaction of meta-phenylenediamine and trimethoyl chloride.

The ultra-thin composite membrane formed according to the present invention, on which a thin film active layer is formed on a porous thermally-converting poly (benzoxazole-imide) copolymer support, has excellent chemical and thermal stability against an organic solvent and excellent organic solvent nano- In addition, since the nanofiltration performance is stably maintained even under high temperature organic solvent conditions, it can be applied to organic solvent nanofiltration membranes.

1 is a process and a scanning electron microscope (SEM) image of a porous thermally-converting poly (benzoxazole-imide) copolymer support according to Examples 1-9.
Figure 2 is an ATR-IR spectrum of a porous heat-converted poly (benzoxazole-imide) copolymer support prepared according to Examples 1-9.
Figure 3 is an ATR-IR spectrum of a porous heat-converted poly (benzoxazole-imide) copolymer support (a) prepared according to Example 1 and an ultra-thin composite membrane (b) prepared according to Example 10;
4 is a thermogravimetric analysis (TGA) graph showing the thermogravimetric reduction characteristics of the porous heat-converted poly (benzoxazole-imide) copolymer support prepared according to Example 1 according to the thermal conversion conditions.
5 is a graph showing the results of pure solvent permeability test results of a porous heat-converted poly (benzoxazole-imide) copolymer support prepared according to Example 1. Fig.
FIG. 6 is a graph showing changes in morphology and structure in the high-temperature DMF of the porous heat-converted poly (benzoxazole-imide) copolymer support prepared according to Example 1 [(a) (C) scanning electron microscope (SEM) images].
7 is a graph showing the surface of a conventionally-used polysulfone-based composite membrane (a) for reverse osmosis, a cellulose-based ultrathin composite membrane (b) for osmosis and an ultra-thin composite membrane (c) , Active layer, and Total (SEM) image of the membrane.
8 is a graph showing the THF permeability (a) and rejection rate (b) of the ultra-thin composite membrane produced according to Example 10. Fig.
9 is a graph showing the DMF permeability (a) and rejection rate (b) of the ultra-thin composite membrane prepared according to Example 10. Fig.
10 is a graph showing the high-temperature DMF permeability (a) and rejection rate (b) of an ultra-thin composite membrane produced according to Example 10. Fig.
11 is a scanning electron microscope (SEM) image showing morphology before and after use of an organic solvent nanofiltration membrane of an ultra-thin composite membrane prepared according to Example 10. FIG.

In the present invention, a porous heat-converted poly (benzoxazole-imide) copolymer support having a repeating unit represented by the following formula (1); And an active layer of a thin film formed on the support. The present invention also provides an ultra-thin composite membrane for organic solvent nanofiltration.

≪ Formula 1 >

(Wherein Ar ₁ is an aromatic ring group selected from a substituted or unsubstituted quadrivalent arylene group having 6 to 24 carbon atoms and a substituted or unsubstituted quadrivalent heterocyclic group having 4 to 24 carbon atoms, O, S, CO, SO ₂ , Si (CH ₃ ) ₂ , (CH ₂ ) _p (1 ≦ _P ≦ ₁₀ ), or two or more of them form a condensed ring; ), (CF ₂ ) _q ( ₁ ? _Q ? 10), C (CH ₃ ) ₂ , C (CF ₃ ) ₂ or CO-

Ar ₂ is an aromatic ring group selected from a substituted or unsubstituted divalent arylene group having 6 to 24 carbon atoms and a substituted or unsubstituted divalent heterocyclic group having 4 to 24 carbon atoms and the aromatic ring group is present alone; Two or more of them form a condensed ring with each other; Two or more single bond, O, S, CO, SO 2, Si (CH 3) 2, (CH 2) p (1≤P≤10), (CF 2) q (1≤q≤10), C _{(CH 3) 2, C (} CF 3) is connected to ₂ or CO-NH,

Q is a single bond; _{O, S, CO, SO 2} , Si (CH 3) 2, (CH 2) p (1≤P≤10), (CF 2) q (1≤q≤10), C (CH 3) 2, C _{(CF 3) 2, CO-} NH, C (CH 3) (CF 3), or a substituted or unsubstituted phenylene ring, x, y is 0.1≤x≤0.9, 0.1≤y≤ a molar fraction within each repeating unit 0.9, x + y = 1)

The porous thermally-converting poly (benzoxazole-imide) copolymer scaffold has excellent chemical and thermal stability in terms of the structure of the repeating units defined in the above formula (1).

The porous heat-converted poly (benzoxazole-imide) copolymer support is preferably an electrospun film. Generally, electrospinning can deposit hundreds of nano-sized fibers in a bottom-up manner by electrospinning to form a porous support with a thin thickness and interconnected pore structure with high porosity. Accordingly, in the present invention, when the porous thermally-converting poly (benzoxazole-imide) copolymer support is an electrorec- tric membrane, it may preferably have a thickness of 10 to 80 탆 and a porosity of 60 to 80%.

Therefore, in the present invention, the mass transport resistance can be minimized by using a very thin porous support having a thickness of 10 to 80 탆 and an extremely high porosity of 60 to 80% It can be applied to an organic solvent nanofiltration membrane in addition to its excellent chemical and thermal stability.

At this time, if the thickness of the porous support obtained from the electrospray is less than 10 탆, the thickness of the support may be too thin to reduce the mechanical properties, and if the thickness exceeds 80 탆, the mass transfer resistance may increase . If the porosity of the porous support is less than 60%, the separation efficiency of the organic solvent may be deteriorated. If the porosity exceeds 80%, the film formation is not smooth.

The active layer of the thin film formed on the porous support may be a crosslinked aromatic polyamide having a repeating unit represented by the following formula (2).

(2)

At this time, the active layer of the thin film preferably has a thickness of 50 to 300 nm. When the thickness of the active layer is less than 50 nm, it is difficult to withstand a high operating pressure. When the thickness exceeds 300 nm, .

The structure of the poly (benzoxazole-imide) copolymer represented by the above formula (1) is based on the synthesis of a polyimide prepared by imidizing a polyamic acid obtained by reacting an acid dianhydride with a diamine. In addition, the thermally-modified polybenzoxazole can be prepared by a method in which a functional group such as a hydroxyl group in the ortho-position of the aromatic imido linkage attacks an imine ring carbonyl group to form an intermediate of the carboxy- benzoxazole structure, The present invention also provides a method for producing an ultra-thin composite membrane for organic solvent nanofiltration comprising the following steps.

That is, in the present invention, a process for preparing a polyamic acid solution by reacting an acid dianhydride, an ortho-hydroxydiamine and an aromatic diamine, followed by synthesis of a hydroxy group-containing polyimide-polyimide copolymer by an azeotropic thermal imidization process;

II) forming a polymer solution by dissolving the hydroxy group-containing polyimide-polyimide copolymer of step I) in an organic solvent by electrospinning;

III) obtaining a porous thermally-converting poly (benzoxazole-imide) copolymer support having the repeating units represented by Formula 1 by thermal conversion of the membrane obtained in the step II); And

IV) forming an active layer of an aromatic polyamide thin film having a crosslinked structure having the repeating unit represented by the above formula (2) on the support, and a method of manufacturing an ultra-thin composite membrane for organic solvent nanofiltration.

In order to synthesize a polyimide, a polyamic acid must first be obtained by reacting an acid dianhydride with a diamine. In the present invention, a compound represented by the following formula 3 is used as an acid anhydride.

(3)

(Wherein Ar ₁ is as defined in Formula 1)

As the monomer for synthesizing the polyimide, any of the acid dianhydrides may be used as long as they are as defined in the above formula (3). However, considering the fact that the thermal and chemical properties of the polyimide synthesized can be further improved, Hexafluoroisopropylidene phthalic acid dianhydride (6FDA), or 4,4'-oxydiphthalic acid dianhydride (ODPA) is preferably used.

In addition, since the present invention ultimately has a poly (benzoxazole-imide) copolymer structure, attention has been paid to the fact that polybenzoxazole units can be introduced by thermal conversion of ortho-hydroxypolyimide, As the ortho-hydroxy diamine, a compound represented by the following formula (4) is used to synthesize hydroxy polyimide.

≪ Formula 4 >

(Q in Formula 4 is the same as defined in Formula 1)

As the ortho-hydroxydiamine, there can be used any of those as defined in Chemical Formula 4 above. However, considering that the thermal and chemical properties of the polyimide to be synthesized can be further improved, 2,2 (3-amino-4-hydroxyphenyl) hexafluoropropane (APAF) or 3,3'-diamino-4,4'-dihydroxybiphenyl (HAB) .

The present invention also provides a process for producing a hydroxy group-containing polyimide-polyimide copolymer by reacting an acid dianhydride represented by Chemical Formula 3 and an ortho-hydroxy diamine represented by Chemical Formula 4 with an aromatic diamine represented by Chemical Formula 5 as a comonomer, can do.

≪ Formula 5 >

(Ar ₂ in the formula (5) is the same as defined in the formula (1)

As the aromatic diamine, any of the aromatic diamines may be used as long as they are as defined in the above formula (5), but 4,4'-oxydianiline (ODA) or 2,4,6-trimethylphenylenediamine (DAM) .

That is, in step I), the acid dianhydride of Chemical Formula 3, the ortho-hydroxydaramine of Chemical Formula 4, and the aromatic diamine of Chemical Formula 5 are dissolved and stirred in an organic solvent such as N-methylpyrrolidone (NMP) After the solution is obtained, the hydroxy group-containing polyimide-polyimide copolymer represented by the following general formula (1) is synthesized by azeotropic thermal imidization.

≪ General Formula 1 &

(In the general formula 1, Ar ₁ , Ar ₂ , Q, x and y are as defined in the general formula (1)

At this time, in the azeotropic thermal imidization method, toluene or xylene is added to the polyamic acid solution, and the imidization reaction is carried out at 160 to 200 ° C for 6 to 24 hours. During this period, the imide ring is generated and water Is separated as an azeotropic mixture of toluene or xylene.

Next, a polymer solution obtained by dissolving the hydroxy group-containing polyimide-polyimide copolymer of the above step I) represented by the above-mentioned general formula 1 in an organic solvent such as N-methylpyrrolidone (NMP) is subjected to electrospinning I need to make a film.

Subsequently, the hydroxy group-containing polyimide-polyimide copolymer electrospun film is thermally converted to obtain a porous thermally-converting poly (benzoxazole-imide) copolymer support having the repeating unit represented by the above formula (1).

At this time, the heat conversion is performed by raising the temperature to 300-400 DEG C at a rate of 1 to 20 DEG C / min in an inert gas atmosphere of high purity, and then maintaining the isothermal state for 1 to 2 hours.

Finally, an active layer of a crosslinked aromatic polyamide thin film having a repeating unit represented by the above formula (2) is formed on a porous thermally-converting poly (benzoxazole-imide) copolymer support having a repeating unit represented by the above formula Thereby producing an ultra-thin composite membrane for organic solvent nanofiltration, which is the object of the present invention.

On the other hand, in the present invention, before the active layer of the crosslinked aromatic polyamide thin film is formed on the porous thermally-converting poly (benzoxazole-imide) copolymer support, the support is subjected to hydrophilization treatment to smoothly form the active layer of the thin film For the hydrophilization treatment of the support, various known methods such as a PDA coating, a polyvinyl alcohol (PVA) coating or a plasma coating may be used. In particular, the support may be coated with polypodamine It is more preferable to perform hydrophilization treatment.

In one embodiment of the present invention, the porous heat-converted poly (benzoxazole-imide) copolymer support was coated with polypodamine and subjected to hydrophilization treatment. As a result, it was found that the contact angle before coating was about 2 times (ATR-IR) analysis showed that hydroxyl groups and acetal groups were observed, and that the porous heat-converted poly (benzoxazole-imide) copolymer support was coated by polypodamine Could know.

In addition, the active layer of the aromatic polyamide thin film having a crosslinked structure having the repeating unit represented by Formula 2 is formed by interfacial polymerization between meta-phenylenediamine (MPD) and trimethoyl chloride (TMC) according to the following reaction formula .

<Reaction Scheme>

Hereinafter, embodiments according to the present invention will be described in detail with reference to the accompanying drawings.

[Synthesis Example 1] Synthesis of hydroxy group-containing polyimide-polyimide copolymer

5.0 mmol of 3,3'-diamino-4,4'-dihydroxybiphenyl (HAB) and 5.0 mmol of 4,4'-oxydianiline (ODA) were dissolved in 10 ml of anhydrous NMP, 10.0 mmol of 4,4'-oxydiphthalic acid dianhydride (ODPA) dissolved in 10 ml of anhydrous NMP was added thereto. The reaction mixture was stirred at 0 占 폚 for 15 minutes, then allowed to warm to room temperature and allowed to stand overnight to obtain a polyamic acid viscous solution. Next, 20 ml of ortho-xylene was added to the polyamic acid solution, followed by vigorous stirring and heating to carry out imidization at 180 ° C for 6 hours. In this process, the water released by the formation of the imide ring was isolated as the xylene azeotropic mixture. The thus obtained brown solution was cooled to room temperature, immersed in distilled water, washed several times with hot water, and dried in a convection oven at 120 ° C. for 12 hours to obtain a hydroxy group-containing polyimide-polyimide copolymer represented by the following formula And named it ODPA-HAB ₅ -ODA ₅ .

(6)

It was confirmed by ¹ H-NMR and FT-IR data that the hydroxy group-containing polyimide-polyimide copolymer represented by the above-mentioned Synthesis Examples 1 to 6 was synthesized as follows. ^{1 H-NMR (300 MHz,} DMSO- d 6, ppm): 10.41 (s, -OH), 8.10 (d, H ar, J = 8.0Hz), 7.92 (d, H ar, J = 8.0Hz), _{7.85 (s, H ar),} 7.80 (s, H ar), 7.71 (s, H ar), 7.47 (s, H ar), 7.20 (d, H ar, J = 8.3Hz), 7.04 (d, H _ar , J = 8.3 Hz). FT-IR (film): ν (OH) at 3400 cm ^-1 , ν (C═O) at 1786 and 1705 cm ^-1 , Ar (CC) at 1619, 1519 cm ^-1 , imide ν (CN) at 1377 cm ^-1 , imide (CNC) at 1102 and 720 cm ^-1 .

[Synthesis Examples 2 to 9] Synthesis of hydroxy group-containing polyimide-polyimide copolymer

A polyimide-polyimide copolymer containing a hydroxy group was prepared in the same manner as in Synthesis Example 1, and various acid dianhydrides, ortho-hydroxydiamine and aromatic diamines shown in Table 1 below were used as reactants, Was named in the same manner as in Example 1.

Synthetic example Sample name Mole fraction Synthesis Example 2 ODPA-HAB ₈ -ODA ₂ x = 0.8, y = 0.2 Synthesis Example 3 6FDA-APAF ₈ -ODA ₂ x = 0.8, y = 0.2 Synthesis Example 4 6FDA-APAF ₅ -DAM ₅ x = 0.5, y = 0.5 Synthesis Example 5 6FDA-HAB ₅ -ODA ₅ x = 0.5, y = 0.5 Synthesis Example 6 6FDA-HAB ₈ -ODA ₂ x = 0.8, y = 0.2 Synthesis Example 7 6FDA-HAB ₅ -DAM ₅ x = 0.5, y = 0.5 Synthesis Example 8 6FDA-APAF ₂ -ODA ₈ x = 0.2, y = 0.8 Synthesis Example 9 6FDA-APAF ₅ -ODA ₅ x = 0.5, y = 0.5

6FDA (4,4'-hexafluoroisopropylidene phthalic acid dianhydride)

APAF (2,2-bis (3-amino-4-hydroxyphenyl) hexafluoropropane)

DAM (2,4,6-trimethylphenylenediamine)

[Example 1] Production of thermal conversion poly (benzoxazole-imide) copolymer support (electrospray film)

ODPA-HAB ₅ -ODA ₅ obtained from Synthesis Example 1 was dissolved in dimethylacetamide (DMAc) to prepare a 10 wt% solution. 6 ml of the polymer solution was charged into a 10 ml syringe equipped with a 23 G needle and then mounted on a syringe pump of an electrospinning device (ES-robot, NanoNC, Korea) HPI). The obtained electrospun film was put between an alumina plate and a carbon cloth and heated to 400 DEG C at a rate of 3 DEG C / min in a high purity argon gas atmosphere. Thereafter, the isotropic state was maintained at 400 DEG C for 2 hours, (Benzoxazole - imide) copolymer electrospray membrane (PBO) represented by the formula (7) was prepared.

&Lt; Formula 7 >

[ Example  2 to 9] Thermal Conversion Poly ( Benzoxazole - Imide ) Copolymer support ( An electric room )

Thermosetting poly (benzoxazole-imide) copolymer electrospun films were prepared in the same manner as in Example 1 using the samples obtained in Synthesis Examples 2 to 9, and the porosity It can be seen that a nanofiber porous electrodisplacive film was prepared from the manufacturing process of a thermally converted poly (benzoxazole-imide) copolymer support (electrospray membrane) and a scanning electron microscope (SEM) image.

[Example 10] Preparation of an ultra-thin composite membrane comprising a heat-converted poly (benzoxazole-imide) copolymer support

The thermosensitive poly (benzoxazole-imide) copolymer electrospun film prepared in Example 1 was coated with polypodamine (PDA) to be hydrophilized, and then an aqueous solution of 3.5 wt% of meta-phenylenediamine (MPD) The excess amount of the solution was removed, and 0.15% by weight of trimesoyl chloride hexane solution was poured onto the surface of the support to perform interfacial polymerization. The hexane was washed and allowed to stand in the air and cured in an oven at 90 ° C to prepare an ultra-thin composite membrane having a crosslinked polyamide thin film active layer on a thermally-converted poly (benzoxazole-imide) copolymer support (electrospray membrane).

FIG. 2 shows the ATR-IR spectra of the porous heat-converted poly (benzoxazole-imide) copolymer supports prepared according to Examples 1 to 9. The OH stretching peak near 3400 cm ^-1 disappears and two distinct peaks due to the typical benzoxazole ring near 1480 cm ^-1 and 1054 cm ^-1 appear, indicating that the benzoxazole ring was formed during the heat treatment Could know. In addition, the inherent absorption band of the imide is found around 1784 cm ^-1 and 1717 cm ^-1 , and the thermal stability of the aromatic imide linkage ring can be confirmed even at the thermal conversion temperature reaching 400 ° C.

Table 2 shows mechanical properties, average pore size, and porosity of the thermally-converting poly (benzoxazole-imide) copolymer support (electrospray membrane) prepared from Example 1 according to various thicknesses.

Thickness (㎛) Mechanical properties (MD / TD) Average pore size (占 퐉) Porosity (%) Tensile Strength (Mpa) Elongation (%) 20 35/51 11/28 0.22 75 40 23/29 6/13 0.20 64 60 23/34 5/12 0.12 61

Machine direction (MD), transverse direction (TD)

From Table 2, it can be seen that the thermally-converting poly (benzoxazole-imide) copolymer support prepared according to the present invention is much thinner than the thickness of the porous support (100 ~ 200 탆) And the porosity is also very high.

3 shows the ATR-IR spectra of the porous heat-converted poly (benzoxazole-imide) copolymer support (a) prepared according to Example 1 and the ultra-thin composite membrane (b) prepared according to Example 10 Respectively. As shown in FIG. 3, in the case of the ultra-thin composite membrane (b) produced according to Example 10, unlike the porous heat conversion poly (benzoxazole-imide) copolymer support (a) prepared according to Example 1 , 3444 cm ^-1 and 3310 cm ^-1 , respectively. The stretching vibration and the hydrogen bonding of the NH group were confirmed at 1667 cm ^-1 and 1542 cm ^-1 , and the stretching vibration of the C═O group and the plane bending of the NH group were confirmed there was.

4 shows the results of various thermal conversion conditions (375 DEG C for 0.5 hour, 375 DEG C for 1 hour, 375 DEG C for 2 hours, 400 DEG C) for the porous thermally-converting poly (benzoxazole- imide) copolymer support prepared according to Example 1 Deg.] C for 2 hours) as a thermogravimetric analysis (TGA) graph. The thermogravimetric analysis was carried out at a heating rate of 10 ° C / min to 400 ° C, followed by heating at 400 ° C for 2 hours and then heating to 800 ° C again. The weight reduction due to heat conversion is theoretically about 9% when 100% heat conversion is performed, and the weight reduction of pristine is 10% between 40 and 160 minutes as shown in FIG. It can be seen that the heat conversion has proceeded smoothly and the degree of thermal conversion can be calculated inversely from the quantitative weight loss data of the support treated in each heat conversion condition.

FIG. 5 is a graph showing the results of pure solvent permeability test of the porous thermally-converting poly (benzoxazole-imide) copolymer support prepared according to Example 1. FIG. 5, isopropyl alcohol (IPA), distilled water, chloroform, dimethylformamide (DMF), tetrahydrofuran (THF), toluene, acetonitrile, heptane Heptane), it exhibits high pure solvent permeability from not only the chemical resistance of the support but also the high porosity. Therefore, it plays a role as a supporter for organic solvent nanofiltration, and has a chemical resistance and heat resistance It can be applied to organic solvent nanofiltration membrane.

Further, the morphology and structural change of the porous heat-converted poly (benzoxazole-imide) copolymer support prepared according to Example 1 of FIG. 6 in high temperature DMF was observed [(a) (30 ° C, 60 ° C, 90 ° C, 120 ° C), which is the most deteriorated condition, in the DMF solvent, the heat resistance and chemical resistance of the substrate Is not numerically changed, and it can be seen that there is no significant change even with the naked eye and the scanning electron microscope (SEM) image.

7 shows the surface of a conventionally-used polysulfone-based composite membrane (a) for reverse osmosis, a cellulose-based ultrathin composite membrane (b) for osmosis and an ultra-thin composite membrane (c) , Active layer (active layer) and total film (Total). 7, it can be seen that the ultra-thin composite membrane manufactured according to Example 10 of the present invention has a significantly thinner and porous structure than the conventional commercialized polysulfone-based composite membrane for reverse osmosis and cellulose-based ultra thin composite membrane, The thickness of the active layer is also very thin, so that the mass transfer resistance generated inside the composite film can be minimized. Therefore, the ultra thin composite membrane according to Example 10 of the present invention can be expected to have excellent performance as a separation membrane, and can be applied to organic solvent nanofiltration membranes based on excellent heat resistance and chemical resistance of a support.

FIG. 8 is a graph showing the THF permeability (a) and rejection rate (b) of the ultra-thin composite membrane prepared according to Example 10. As shown in FIG. 8, hr using a volumetric cylinder. The volume of the permeate was measured for a certain period of time. The permeate and the feed were sampled in the same manner and the rejection rate was measured using HPLC-UV / Vis. As shown in FIG. 8, it can be seen that the rejection ratio of polystyrene having a high permeability of 5 LMH / bar and a molecular weight of 236 to 1600 g / mol is 99% or more.

FIG. 9 is a graph showing the DMF permeability (a) and rejection rate (b) of the ultra-thin composite membrane prepared according to Example 10. As a result, a polystyrene / DMF solution having a concentration of 2 g / L and a dye (Charge, 249 g / mol), Methylene Orange (+ charge, 327 g / mol), and water were added to the solution at 30 ° C, 30 bar, and 50 L / hr using a volumetric cylinder. Brilliant Blue (+ charge, 826 g / mol). In the measurement, the permeability was calculated by measuring the volume of the permeate for a certain period of time, and the exclusion rate of each dye was observed by UV spectroscopy. As shown in FIG. 9, the high permeability of about 8 LMH / bar can be confirmed, and the rejection profile according to the solute size can be confirmed regardless of the charge.

FIG. 10 is a graph showing the high-temperature DMF permeability (a) and rejection rate (b) of the ultra-thin composite membrane produced according to Example 10. As shown in FIG. 10, ) DMF solvent and showed excellent performance. That is, since the viscosity of the solvent decreases as the temperature of the system increases, the permeability increases while the rejection ratio hardly changes. This indicates that the chemical stability of the active layer and the support is very excellent even at a high temperature, so that only the permeability increases and the rejection rate tends to be maintained. This suggests that the organic solvent nanofiltration membrane can be applied even under such a deteriorated condition.

11 shows a scanning electron microscope (SEM) image obtained by observing the morphology before and after the organic solvent nanofiltration membrane of the ultra-thin composite membrane prepared according to Example 10. As a result, The stability of the ultra-thin composite membrane according to the present invention can be confirmed by showing no significant change in SEM image comparison before and after use as a filtration membrane.

As described above, the ultra-thin composite membrane having the active layer of the thin film formed on the porous thermally-converting poly (benzoxazole-imide) copolymer support produced according to the present invention has excellent chemical and thermal stability against the organic solvent, The filtration performance is excellent, and nanofiltration performance is stably maintained even under high temperature organic solvent conditions, so that it can be applied to organic solvent nanofiltration membranes in chemical, pharmaceutical or refining industries.

Claims (14)

A porous thermally-converting poly (benzoxazole-imide) copolymer support having a repeating unit represented by the following formula (1); And an active layer of a cross-linked aromatic polyamide thin film having a repeating unit represented by the following formula (2) formed on the support.
&Lt; Formula 1 >

(Wherein Ar ₁ is an aromatic ring group selected from a substituted or unsubstituted quadrivalent arylene group having 6 to 24 carbon atoms and a substituted or unsubstituted quadrivalent heterocyclic group having 4 to 24 carbon atoms, O, S, CO, SO ₂ , Si (CH ₃ ) ₂ , (CH ₂ ) _p (1 ≦ _P ≦ ₁₀ ), or two or more of them form a condensed ring; ), (CF ₂ ) _q ( ₁ ? _Q ? 10), C (CH ₃ ) ₂ , C (CF ₃ ) ₂ or CO-
Ar ₂ is an aromatic ring group selected from a substituted or unsubstituted divalent arylene group having 6 to 24 carbon atoms and a substituted or unsubstituted divalent heterocyclic group having 4 to 24 carbon atoms and the aromatic ring group is present alone; Two or more of them form a condensed ring with each other; Two or more single bond, O, S, CO, SO 2, Si (CH 3) 2, (CH 2) p (1≤P≤10), (CF 2) q (1≤q≤10), C _{(CH 3) 2, C (} CF 3) is connected to ₂ or CO-NH,
Q is a single bond; _{O, S, CO, SO 2} , Si (CH 3) 2, (CH 2) p (1≤P≤10), (CF 2) q (1≤q≤10), C (CH 3) 2, C _{(CF 3) 2, CO-} NH, C (CH 3) (CF 3), or a substituted or unsubstituted phenylene ring, x, y is 0.1≤x≤0.9, 0.1≤y≤ a molar fraction within each repeating unit 0.9, x + y = 1)
(2)

The ultra-thin composite membrane for organic solvent nanofiltration according to claim 1, wherein the porous heat-converted poly (benzoxazole-imide) copolymer support is an electrospun film. 3. The ultra-thin composite membrane for organic solvent nanofiltration according to claim 2, wherein the thickness of the electrodisplacive membrane is 10 to 80 mu m and the porosity is 60 to 80%. delete The ultra-thin composite membrane for organic solvent nanofiltration according to claim 1, wherein the active layer of the thin film has a thickness of 50 to 300 nm. I) reacting an acid dianhydride, ortho-hydroxydiamine and an aromatic diamine to obtain a polyamic acid solution, and then synthesizing a hydroxy group-containing polyimide-polyimide copolymer by an azeotropic thermal imidization process;
II) forming a polymer solution by dissolving the hydroxy group-containing polyimide-polyimide copolymer of step I) in an organic solvent by electrospinning;
III) obtaining a porous heat-converted poly (benzoxazole-imide) copolymer support having a repeating unit represented by the general formula (1) according to claim 1 by thermally converting the membrane obtained in the step (II); And
IV) forming an active layer of a cross-linked aromatic polyamide thin film having a repeating unit represented by the general formula (2) described in claim 1 on the support; and forming an ultra-thin composite membrane for organic solvent nanofiltration. 7. The method of claim 6, wherein the acid dianhydride of step I) is represented by the following formula (3).
(3)

(In the general formula Ar ₁ 3 are as defined in formula (I) of claim 1) The method of claim 6, wherein the ortho-hydroxydiamine of the step I) is represented by the following formula (4).
&Lt; Formula 4 >

(Wherein Q in the formula (4) is the same as defined in the formula (1) The method according to claim 6, wherein the aromatic diamine in step I) is represented by the following formula (5).
&Lt; Formula 5 >

(Wherein Ar &lt; ₂ &gt; in the general formula (5) is the same as defined in the general formula (1) 7. The method of claim 6, wherein the azeotropic thermal imidization in step I) comprises adding toluene or xylene to the polyamic acid solution, stirring the solution, and conducting an imidization reaction at 160 to 200 DEG C for 6 to 24 hours (Method for producing ultra thin composite membrane for organic solvent nanofiltration). [7] The method of claim 6, wherein the heat conversion in step III) is performed by raising the temperature to 300 to 400 DEG C at a rate of 1 to 20 DEG C / min in an inert gas atmosphere of high purity and then maintaining an isothermal state for 1 to 2 hours Wherein the organic solvent-based nano-filtration is carried out in the presence of an organic solvent. The method according to claim 6, further comprising, before performing step IV), hydrophilization treatment of the support obtained in step III). 13. The method for producing an ultra-thin composite membrane for organic solvent nanofiltration according to claim 12, wherein the hydrophilic treatment is performed by coating the support obtained in the step (III) with polydodamine. 7. The method of claim 6, wherein the active layer of the aromatic polyamide thin film having the crosslinked structure is formed by interfacial polymerization between meta-phenylenediamine and trimethoyl chloride.

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