KR20160011851A - Fluorinated thermally rearranged polymer gas separation membrane for separation of natural gas and preparation method thereof - Google Patents

Abstract

The present invention relates to a fluorinated thermally rearranged polymer gas separation membrane, and to a production method thereof. The fluorinated thermally rearranged polymer gas separation membrane can be applied in the separation of natural gas and is produced by a fluorinated thermally rearranged polymer membrane by a direct fluorination method using a thermally rearranged polymer membrane derived from polyimide or a polyimide copolymer which is obtained from acid dianhydride and aromatic diamine having at least one functional group occupying an ortho position. The fluorinated thermally rearranged polymer gas separation membrane which is used in the separation of natural gas and is produced according to the present invention retains high gas permeability which is an inherent characteristic of a thermally polymer membrane. Thus, the commercialization of the membrane is possible as a gas separation membrane for the separation of natural gas has excellent selectability of nitrogen, carbon dioxide, or helium with respect to methane.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a fluorinated thermally-reversible polymer gas separation membrane for separating natural gas,

The present invention relates to a fluorinated thermal conversion polymer gas separation membrane for natural gas separation and a method for producing the same, and more particularly, to a fluorinated thermal conversion polymer gas separation membrane for natural gas separation, which comprises a polyimide or polyimide copolymer obtained from an aromatic diamine and an acid anhydride having at least one functional group at an ortho- The present invention relates to a fluorinated thermal conversion polymer membrane capable of producing a fluorinated thermal conversion polymer membrane by direct fluorination of a thermal conversion polymer membrane and applying it to natural gas separation, and a production method thereof.

Recently, membrane-based gas separation has attracted attention as a rapidly growing separation technology in response to its importance. Gas separation using these membranes has several advantages, such as lower energy consumption and operating cost, but higher process availability than conventional separation processes. In particular, since the 1980s, a lot of basic research using organic polymer membranes has been conducted, but conventional polymers show relatively low mass transport rates due to the general properties of providing efficient packing in the polymer chain space with little micropores.

On the other hand, polymers with a high level of free volume, known as microporous organic polymers, are emerging as one of the strong candidates in the separation process due to their ability to adsorb to small gas molecules and their enhanced diffusion capability. Therefore, attention is focused on the fact that inherent microporous polymers based on a rigid ladder-like structure having a twisted region that prevents effective packing of polymer chain spaces exhibit relatively high gas permeability and selectivity, and thus, organic polymers Various researches are under way to develop.

Among these studies, attempts have been actively made to apply stiff glassy wholly aromatic organic polymers such as polybenzoxazole, polybenzimidazole, or polybenzthiazole, which have excellent thermal, mechanical and chemical properties, as gas separation membranes, Most of the polymers are insoluble in common organic solvents, and thus it has been difficult to prepare membranes by a simple and practical solvent casting method. Therefore, in order to overcome this difficulty, the inventors of the present invention have recently found that polybenzoxazole membranes can be prepared by thermal conversion of polyimide having hydroxy groups in the orthosilicate position, compared with conventional polybenzoxazole membranes prepared by the solvent casting method The permeability of carbon dioxide has been reported to be 10 to 100 times higher. However, the selectivity of carbon dioxide / methane (CO ₂ / CH ₄ ) is still comparable to that of conventional commercialized cellulose acetate membranes and there is room for improvement One).

Further, the inventors of the present invention is poly-hydroxyimide - already converted heat to the heat treatment to stop de copolymers polybenzoxazole - already manufactured film de copolymers, although hanba applied it to the gas separation, from a commercial perspective, CO ₂ / CH ₄ mixed gas and the like, the selectivity of carbon dioxide to methane did not reach a satisfactory level of about 19.4 to 38.7 (Patent Document 1).

Thermally-converted polybenzoxazole membranes and polybenzoxazole-pyrrolone copolymer membranes for gas separation have also been developed, but this is limited to improving oxygen selectivity to gas permeability and nitrogen for oxygen / nitrogen mixed gases Further studies have been required on the selective separation of natural gas, which is a mixer mainly composed of methane (Patent Document 2).

Accordingly, the inventors of the present invention have found that when the surfaces of various heat-converted polymer membranes as described above are treated with fluorine, the selectivity of nitrogen, carbon dioxide, or helium to methane increases remarkably while maintaining high gas permeability inherent to the heat- The present invention has been completed.

Patent Document 1 Registration No. 10-0932765 Patent Document 2: Japanese Patent Application Laid-Open No. 10-2006-0085845

Non-Patent Document 1 Y.M. Lee et al., Science 318, 254-258 (2007)

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 separating natural gas, A polymer gas separation membrane and a method of manufacturing the same.

In order to accomplish the above object, the present invention provides a polyimide-based thermally-converting polymer membrane comprising a polyimide having a hydroxyl group, a thiol group or an amino group, or a polyimide having a hydroxyl group, a thiol group or an amino group, A fluorinated thermal conversion polymer gas separation membrane for fluorine-treated natural gas separation is provided.

The polyimide having a hydroxyl group, a thiol group or an amino group has a repeating unit represented by the following formula (1) or (2).

&Lt; Formula 1 > < EMI ID =

(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), (CF 2) q} (1≤q≤10), C (CH 3) 2, C (CF 3) 2 or are connected to the CO-NH, Q is a single bond or; 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 , and _{CO-NH, C (CH 3} ) (CF 3), or a substituted or unsubstituted phenylene ring, Y may be an OH, SH or NH _2, the same or different from each other)

The polyimide copolymer comprising a polyimide having a hydroxyl group, a thiol group or an amino group has a repeating unit represented by the following formula (3) or (4).

(3)

&Lt; Formula 4 >

(Wherein Ar _{1 ,} Q and Y are as defined in formula (1) or (2), Ar ₂ is a substituted or unsubstituted divalent arylene group having 6 to 24 carbon atoms and a substituted or unsubstituted divalent carbon number an aromatic group selected from a heterocyclic group of 4 to 24, where the aromatic group is independently present or; two or more form a condensed ring with each other, or; a single bond, two or more, 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 or CO-NH M and l are the mole fractions in the repeating units, 0.1? M? 0.9, 0.1? L? 0.9, and m + l = 1,

The thermal conversion polymer membrane may be a polybenzoxazole film, a polybenzothiazole film, a polypyrrole film, a polybenzoxazole-imide copolymer film, a polybenzothiazole-imide copolymer film, a polypyrrolone-imide copolymer film, a poly Benzoxazole-benzothiazole copolymer film, polybenzoxazole-pyrrolone copolymer film, and polybenzothiazole-pyrrolone copolymer film.

The fluorinated thermal conversion polymer gas separation membrane has a fluorination degree of 1 to 100%.

The natural gas separation is characterized in that a mixed gas of N ₂ / CH ₄ , CO ₂ / CH ₄ or He / CH ₄ is used.

The present invention also relates to i) an aromatic diamine having an acid anhydride and a hydroxyl group, a thiol group or an amino group; A polyimide having a hydroxyl group, a thiol group or an amino group by reacting an aromatic dianhydride having an acid anhydride with a hydroxyl group, a thiol group or an amino group and an aromatic diamine as a comonomer to obtain a polyamic acid solution and then imidizing the polyamic acid solution; Or a polyimide copolymer containing the polyimide;

ii) obtaining a heat-converted polymer membrane by casting or electrospinning a polyimide copolymer synthesized in step i) or a polyimide copolymer containing the polyimide in an organic solvent; And

and iii) fluorinating the surface of the thermally-reversible polymer membrane obtained in the step ii). The present invention also provides a method for producing a fluorinated thermal conversion polymer gas separation membrane for separating natural gas.

The acid dianhydride in step i) is characterized by being represented by the following general formula (1).

&Lt; General Formula 1 &

(In the general formula 1, Ar ₁ is as defined in the above formulas 1 to 4)

The aromatic diamine having a hydroxyl group, a thiol group or an amino group in the step i) is represented by the following formula 2 or 3:

&Lt; General Formula 2 > < General Formula 3 &

(In the general formula 2 or 3, Q and Y are as defined in the above formulas 1 to 4)

The aromatic diamine as the comonomer in the step i) is characterized by being represented by the following general formula (4).

&Lt; General Formula 4 &

(In the general formula 4, Ar ₂ is the same as defined in the above formulas 1 to 4)

The imidization in the step i) is performed by an azeotropic thermal imidization method.

The azeotropic thermal imidization method is characterized in that toluene or xylene is added to a polyamic acid solution and the mixture is stirred to perform an imidation reaction at 180 to 200 ° C for 6 to 12 hours.

The heat treatment in the step ii) is performed by raising the temperature to 300 to 450 ° C at a temperature raising rate of 1 to 20 ° C / min in an inert gas atmosphere of high purity, and then maintaining an isothermal state for 0.1 to 12 hours.

The thermal conversion polymer membrane in step ii) may be selected from the group consisting of a polybenzoxazole film, a polybenzothiazole film, a polypyrrole film, a polybenzoxazole-imide copolymer film, a polybenzothiazole-imide copolymer film, a polypyrrolone- A polybenzoxazole-pyrrolone copolymer film, a polybenzothiazole-pyrrolone copolymer film, a polybenzoxazole-benzothiazole copolymer film, a polybenzoxazole-pyrrolone copolymer film and a polybenzothiazole-pyrrolone copolymer film.

The fluorination treatment in step iii) is performed by a direct fluorination method using a mixed gas containing 1 ppm to 1 volume% of fluorine gas.

The mixed gas is characterized by containing fluorine gas and diluted gas of nitrogen, argon or helium.

The fluorine treatment is performed for 1 minute to 24 hours.

The fluorinated thermal conversion polymer gas separation membrane has a fluorination degree of 1 to 100%.

The natural gas separation is characterized in that a mixed gas of N ₂ / CH ₄ , CO ₂ / CH ₄ or He / CH ₄ is used.

The fluorinated thermal conversion polymer gas separation membrane for natural gas separation according to the present invention has excellent gas permeability of inherently high thermal conversion polymer membrane and excellent selectivity of nitrogen, carbon dioxide or helium to methane, Can be commercialized.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing the F-NMR spectrum of a fluorinated thermally-converted polybenzoxazole-imide copolymer film prepared from Example 4 (120 minutes of fluorine treatment) of the present invention, together with those of fluorine-untreated Comparative Example 1. FIG.
2 is a dynamic mechanical analysis (DMA) spectrum of a fluorinated thermally-converted polybenzoxazole-imide copolymer film prepared from Example 6 of the present invention.
3 is a graph showing the selectivity (CO ₂ / CH ₄ ) of carbon dioxide to methane according to the fluorine treatment time and the permeability of carbon dioxide in Examples 1 to 4 and Comparative Example 1;
4 is a graph showing the selectivity (CO ₂ / CH ₄ ) of carbon dioxide to methane according to fluorine treatment time and permeability of carbon dioxide in Examples 5 to 8 and Comparative Example 2;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a fluorinated thermal conversion polymer gas separator for natural gas separation according to the present invention and a method for producing the same will be described in detail with reference to the embodiments and the accompanying drawings.

The present invention provides a polyimide having a hydroxyl group, a thiol group, or an amino group, or a polyimide copolymer-derived thermal conversion polymer membrane having a fluorine-treated surface, and a fluorinated thermal conversion polymer gas separation membrane for separating natural gas.

In general, a polyimide or polyimide copolymer is widely used as a gas separation membrane. In particular, a polyimide obtained by reacting an aromatic dianhydride having at least one functional group such as a hydroxyl group, a thiol group or an amino group at an ortho position with an acid anhydride, The copolymer is thermally converted by a simple heat treatment process and its structure is changed, and thus it has recently been attracting attention as a gas separation membrane material.

That is, the structure such as this thermal conversion polymer film density is decreased while passing through a thermal conversion process, according to the fine pores increases and a significant increase in the free volume fraction (fractional free volume), also increased interplanar distance (d -spacing) But it is difficult to overcome the trade-off relationship between gas permeability and selectivity, which is an obstacle to commercialization due to the lack of selectivity to a specific gas.

Therefore, in the present invention, a simple process of improving the selectivity and treating the surface of the thermally-converted polymer membrane with fluorine, based on a thermally-converted polymer membrane having excellent gas permeability, produces methane gas from a gas mixture mainly composed of methane, It was possible to obtain a fluorinated heat conversion polymer gas separation membrane for natural gas separation which has remarkably improved selectivity for the gas.

First, in the present invention, a polyimide having a repeating unit represented by the following formula (1) or (2) is used as a polyimide having a hydroxyl group, a thiol group, or an amino group, which is a precursor for obtaining a heat conversion polymer.

&Lt; Formula 1 > < EMI ID =

(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), (CF 2) q} (1≤q≤10), C (CH 3) 2, C (CF 3) 2 or are connected to the CO-NH, Q is a single bond or; 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 , and _{CO-NH, C (CH 3} ) (CF 3), or a substituted or unsubstituted phenylene ring, Y may be an OH, SH or NH _2, the same or different from each other)

In the case where Y is a hydroxyl group (OH) in a polyimide having a repeating unit represented by the formula (1) or (2), the polyimide is thermally converted to polybenzoxazole, and when Y is a thiol group (SH) Polybenzothiazolyl, or when Y is an amino group (NH _{2 )} , the structure is thermally converted to polypyrrolone.

Further, as a polyimide copolymer containing a hydroxy group, a thiol group or a polyimide having an amino group, which is another precursor for obtaining a heat conversion polymer, a polyimide copolymer having a repeating unit represented by the following general formula (3) or (4) Use coalescence.

(3)

&Lt; Formula 4 >

(Wherein Ar _1, Q and Y are as defined in formula (1) or (2), Ar ₂ is a substituted or unsubstituted divalent arylene group having 6 to 24 carbon atoms and a substituted or unsubstituted divalent carbon number an aromatic group selected from a heterocyclic group of 4 to 24, where the aromatic group is independently present or; two or more form a condensed ring with each other, or; a single bond, two or more, 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 or CO-NH M and l are the mole fractions in the repeating units, 0.1? M? 0.9, 0.1? L? 0.9, and m + l = 1,

The polyimide copolymer having a repeating unit represented by the formula (3) or (4) is thermally converted to a polybenzoxazole-imide copolymer, a polybenzothiazole-imide copolymer or a polypyrrolone- When the structure is changed to a copolymer and the hydroxyl group, the thiol group or the amino group is different from the functional group in the ortho position in each imide structural unit constituting the repeating unit, it is thermally converted to polybenzoxazole- Benzothiazole copolymers, polybenzoxazole-pyrrolone copolymers or polybenzothiazole-pyrrolone copolymers.

Therefore, the thermal conversion polymer membrane according to the present invention can be used as a polymer electrolyte membrane such as a polybenzoxazole film, a polybenzothiazole film, a polypyrroleone film, a polybenzoxazole-imide copolymer film, a polybenzothiazole-imide copolymer film, a polypyrrolone- A polybenzoxazole-pyrrolone copolymer film, a polybenzoxazole-benzothiazole copolymer film, a polybenzoxazole-pyrrolone copolymer film and a polybenzothiazole-pyrrolone copolymer film, and among these, A polybenzoxazole-imide copolymer film or a polybenzoxazole-pyrrolone copolymer film is more preferable.

Further, the fluorinated thermal conversion polymeric gas separation membrane of the present invention wherein the surface of the thermally-reversible polymer membrane is fluorine-treated has a fluorination degree (in terms of% of fluorine atoms relative to the content of carbon atoms) of 1 to 100% , And more preferably, the degree of fluorination may be 10 to 70%.

Also, the fluorinated thermal conversion polymer gas separation membrane of the present invention is useful for selectively separating a specific gas from a mixed gas such as natural gas containing methane gas as a main component. Particularly, N ₂ / CH ₄ , CO ₂ / CH ₄ or He / CH ₄ mixed gas is preferable not only for gas permeability but also for nitrogen, carbon dioxide or helium to methane, which is very excellent.

Also, in the present invention, i) an aromatic diamine having an acid anhydride and a hydroxyl group, a thiol group or an amino group; A polyimide having a hydroxyl group, a thiol group or an amino group by reacting an aromatic dianhydride having an acid anhydride with a hydroxyl group, a thiol group or an amino group and an aromatic diamine as a comonomer to obtain a polyamic acid solution and then imidizing the polyamic acid solution; Or a polyimide copolymer containing the polyimide;

ii) obtaining a heat-converted polymer membrane by casting or electrospinning a polyimide copolymer synthesized in step i) or a polyimide copolymer containing the polyimide in an organic solvent; And

and iii) fluorinating the surface of the thermally-reversible polymer membrane obtained in the step ii). The present invention also provides a method for producing a fluorinated thermal conversion polymer gas separation membrane for separating natural gas.

Generally, in order to synthesize a polyimide, a polyamic acid must be obtained by reacting an acid anhydride with a diamine. In the present invention, a compound represented by the following Formula 1 is used as an acid anhydride.

&Lt; General Formula 1 &

(In the general formula 1, Ar ₁ is as defined in the above formulas 1 to 4)

As the monomers for synthesizing the polyimide or polyimide copolymer, any of the acid dianhydrides can be used without limitation as long as they are as defined in the general formula 1. However, it is possible to further improve the thermal and chemical properties of the synthesized polyimide It is preferable to use 4,4'-hexafluoroisopropylidene phthalic acid dianhydride (6FDA) having a fluorine group.

As the aromatic diamine having a hydroxyl group, a thiol group or an amino group, a compound represented by the following Formula 2 or 3 is used.

&Lt; General Formula 2 > < General Formula 3 &

(In the general formula 2 or 3, Q and Y are as defined in the above formulas 1 to 4)

The aromatic diamine having a hydroxyl group, a thiol group or an amino group, which is another monomer for synthesizing a polyimide or polyimide copolymer, may be any of those as defined in <Formula 2> or <Formula 3> However, an aromatic diamine having a hydroxyl group or an amino group at the ortho position is preferably used. Particularly, in consideration of the fact that the aromatic diamine having a hydroxyl group at the ortho position can further improve the thermal and chemical properties of the polyimide synthesized, 2,2-bis (3-amino-4-hydroxyphenyl It is more preferable to use 3,3-diaminobenzidine (DAB) as the aromatic diamine having an amino group at the ortho position, and more preferably 3,3-dihydroxybenzidine (DAB) .

Further, in the present invention, a polyimide copolymer can be synthesized by using an aromatic diamine represented by the following formula 4 as a comonomer, and as the aromatic diamine which is a comonomer, as defined in the following <Formula 4> Any of them can be used without limitation. However, the lower the cost, the more preferable the use of 2,4,6-trimethyl-phenylenediamine (DAM) because the cost of the whole process is reduced in mass production.

&Lt; General Formula 4 &

(In the general formula 4, Ar ₂ is the same as defined in the above formulas 1 to 4)

That is, in step i), an acid dianhydride of the general formula (1) and an aromatic diamine having a hydroxyl group, thiol group or amino group of the general formula (2) or the general formula (3) A polyimide having a hydroxyl group, a thiol group or an amino group by imidizing an aromatic diamine together with an organic solvent such as N-methylpyrrolidone (NMP) to obtain a polyamic acid solution and stirring; Or a polyimide copolymer containing the polyimide is synthesized. In this case, the imidization reaction may be any known imidization method, but it is preferable that the imidization reaction is performed by azeotropic thermal imidization in consideration of the physical properties of the polyimide or polyimide copolymer to be synthesized , Toluene or xylene is added to the polyamic acid solution, and the mixture is stirred to perform imidization reaction at 180 to 200 ° C for 6 to 12 hours. During this period, the water is released while the imide ring is formed and the toluene or xylene And separated as a mixture.

Next, a polyimide having a hydroxyl group, a thiol group or an amino group synthesized in the step i) or a polyimide copolymer containing the polyimide is dissolved in an organic solvent such as N-methylpyrrolidone (NMP) Cast or electrospun, and then heat-treated to obtain a thermally-converted polymer film.

The heat treatment is performed by raising the temperature to 300 to 450 DEG C at a temperature rising rate of 1 to 20 DEG C / min in an inert gas atmosphere of high purity and then maintaining an isothermal state for 0.1 to 12 hours, preferably at 400 to 450 DEG C for 30 minutes Heat treatment for ~ 2 hours. If the heat treatment temperature is less than 300 ° C, the gas permeability may be lowered due to deterioration of the polymer membrane due to the residual solvent during the film formation. If the heat treatment temperature exceeds 450 ° C, the properties of the polymer membrane may deteriorate due to carbonization of the polymer membrane. Problems can arise.

By subjecting to the heat treatment step, a polybenzoxazole film, a polybenzothiazole film, a polypyrrole film, a polybenzoxazole-imide copolymer film, a polybenzothiazole-imide copolymer film, a polypyrrolone-imide copolymer film, A polybenzoxazole-benzothiazole copolymer film, a polybenzoxazole-pyrrolone copolymer film, and a polybenzothiazole-pyrrolone copolymer film is obtained.

Finally, as one of the key technical features of the present invention, the surface of the thermal conversion polymer membrane is subjected to fluorine treatment to produce a fluorinated thermal conversion polymer gas separation membrane for separating natural gas.

The fluorine treatment is to treat the surface of the heat-converted polymer membrane using fluorine gas. There is no particular limitation on the method, but a direct fluorination method in which a fluorine gas of a certain concentration is directly injected and treated is fluorine-treated by a simple process .

In this case, since a high concentration of fluorine gas is directly injected into the heat conversion polymer membrane, damage may occur to the polymer membrane. Therefore, a mixed gas obtained by mixing a diluent gas with a fluorine gas is used. As the diluent gas, An inert gas such as argon or helium is preferably used.

Therefore, the fluorine treatment is preferably carried out for 1 minute to 24 hours using a mixed gas containing 1 ppm to 1% by volume of fluorine gas so that the degree of fluorination of the target fluorine-containing heat converting polymer membrane is 1 to 100% It is preferable that the fluorination degree is 10 to 70%. On the other hand, the fluorination temperature and pressure are not particularly limited. However, considering the high reactivity and economical efficiency of fluorine, it is sufficient to perform at normal temperature and atmospheric pressure.

As a result of the fluorine treatment, the hydrogen groups in the aromatic or aliphatic chain of the thermal conversion polymer are directly substituted with fluorine groups, or the fluorine atoms directly interfere with the fluorine atoms and the fluorine atoms partially cover or block the pores of the thermally- The fluorinated heat conversion polymer membrane produced according to the present invention has a high gas permeability as well as a markedly increased selectivity.

Hereinafter, specific embodiments will be described in detail with reference to the accompanying drawings.

[Example 1] Production of fluorinated thermally-converted polybenzoxazole-imide copolymer film

(Step I) Synthesis of Ortho-Hydroxypolyimide Copolymer

5 mmol of 3,3-dihydroxybenzidine (HAB) and 5 mmol of 2,4,6-trimethyl-phenylenediamine (DAM) were dissolved in 10 ml of anhydrous NMP, cooled to 0 ° C and dissolved in 10 ml of anhydrous NMP 10 mmol of 4,4'-hexafluoroisopropylidene phthalic acid dianhydride (6FDA) 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 a distillation shoe, washed several times with hot water, and dried in a convection oven at 120 ° C. for 12 hours to obtain an ortho-hydroxypolyimide copolymer represented by the following formula Was synthesized.

&Lt; Formula 5 >

(X and y in the above formula (5) are mole fractions in the repeating unit, x = 0.5 and y = 0.5)

The synthesis of the ortho-hydroxypolyimide copolymer represented by Formula 5 in the above Step I was confirmed by ¹ H-NMR and FT-IR data 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 , (CF) at 1299-1135 cm ^-1 , imide (CNC) at 1102 and 720 cm ^-1 .

(II) Preparation of heat-converted polybenzoxazole-imide copolymer membranes

The ortho-hydroxypolyimide copolymer represented by Formula 5 synthesized in Step I was dissolved in NMP to prepare a 15 wt% polymer solution, which was then cast on a glass plate. This was placed in a vacuum oven and maintained at 100 ° C, 150 ° C and 200 ° C for one hour, respectively, and the remaining NMP was evaporated and dried to form a film. The film thus formed was cut into a 3 cm x 3 cm piece and placed between quartz plates to prevent deformation of the film due to temperature rise in the muffle furnace. The sample was heated to 425 DEG C at a heating rate of 5 DEG C / min in a high-purity argon gas atmosphere, and maintained in an isothermal state for 30 minutes. After the heat treatment, the muffle furnace was gradually cooled to room temperature at a cooling rate of less than 10 DEG C / min to prepare a heat-converted polybenzoxazole-imide copolymer film represented by the following formula (6).

(6)

 (Wherein x and y are as defined in Chemical Formula 5)

The thermal conversion represented by the <Formula 6> prepared in step II polybenzoxazole-imide copolymer membrane The analysis of the ATR-IR spectrum disappear and the OH stretching peak appearing near 3400 cm ^-1, 1480 cm ^{- 1} and 1054 cm ^-1 , indicating that the benzoxazole ring was formed during the heat treatment process. In addition, the inherent absorption band of the imide was found around 1784 cm ^-1 and 1717 cm ^-1 , and the thermal stability of the aromatic imide linkage ring was confirmed even at the heat treatment temperature reaching 425 ° C.

(III) Preparation of Fluorinated Thermal Conversion Polybenzoxazole-imide Copolymer Membrane

The heat-converted polybenzoxazole-imide copolymer film represented by the formula (6) prepared in the step (II) was immersed in an oven where the fluorination reaction occurred, and fixed. The fluorine gas had a concentration of 500 ppm , And the surface of the copolymer membrane was treated by injecting a mixed gas diluted with a high purity nitrogen gas for 30 minutes to prepare a fluorinated thermally converted polybenzoxazole-imide copolymer film.

[Examples 2 to 4] Preparation of fluorinated thermally-converted polybenzoxazole-imide copolymer film

Except that the fluorine treatment time was changed to 60 minutes, 90 minutes, and 120 minutes, respectively, the fluorinated heat converted polybenzoxazole-imide copolymer films were prepared through the same procedures as those in steps I to III of Example 1 .

[Examples 5 to 8] Production of fluorinated heat-converted polybenzoxazole-imide copolymer film

Examples 1 to 4 were repeated except that 2,2-bis (3-amino-4-hydroxyphenyl) hexafluoropropane (APAF) was used in place of 3,3-dihydroxybenzidine (HAB) The fluorinated thermally-converted polybenzoxazole-imide copolymer film was prepared.

[Examples 9 to 12] Preparation of fluorinated heat-converted polybenzoxazole-pyrrolone copolymer film

(Step I) Preparation of Ortho-Hydroxyortho-Aminopolyimide Copolymer Membrane

5 mmol of 3,3-diaminobenzidine (DAB) and 5 mmol of 3,3-dihydroxybenzidine (HAB) were dissolved in 5 ml of anhydrous NMP and cooled to 15 ° C. To this were added 4,4 '-Hexafluoroisopropylidene phthalic acid 10 mmol of anhydride (6FDA) was added dropwise to the dropping funnel and the reaction was allowed to drop slowly. This viscous solution was cast on a glass plate and placed in a vacuum oven at 100 ° C, 150 ° C, 200 ° C and 250 ° C for one hour, The remaining NMP was evaporated and dried to prepare an ortho-hydroxysso-aminopolyimide copolymer membrane represented by the following formula (7).

&Lt; Formula 7 >

(X and y in the formula (7) are mole fractions in the repeating unit, x = 0.5 and y = 0.5)

(II) Preparation of heat-converted polybenzoxazole-pyrrolone copolymer membranes

The film thus formed was cut to a size of 3 cm x 3 cm and placed between quartz plates to prevent deformation of the film due to temperature rise in the muffle furnace. The sample was heated to 450 DEG C at a rate of 5 DEG C / min in a high-purity argon gas atmosphere, and maintained in an isothermal state for 30 minutes. After the heat treatment, the muffle furnace was gradually cooled to room temperature at a cooling rate of less than 10 DEG C / min to prepare a thermally-converted polybenzoxazole-pyrrolone copolymer film represented by the following formula (8).

(8)

( III  Step) Fluorination Thermal Conversion Polybenzoxazole - Pyrrolone Copolymer film  Produce

The heat-converted polybenzoxazole-pyrrolone copolymer film represented by the formula (8) prepared in the above step II was subjected to fluorination treatment in the same manner as in step III of Examples 1 to 4 to obtain a fluorinated thermally-converted polybenzoxazole-pyrrolone To prepare a copolymer film.

[Comparative Examples 1 to 3] Production of fluorine-free heat-converted polybenzoxazole-imide copolymer film

In Comparative Examples 1 to 3, only steps I and II of Examples 1 to 4, Examples 5 to 8, and Examples 9 to 12 were carried out in the same manner to obtain a fluorine-free heat-converted polybenzoxazole-imide copolymer membrane .

1 shows the F-NMR spectrum of a fluorinated thermally-converted polybenzoxazole-imide copolymer film (6FDA-HAB-DAM) prepared from Example 4 (120 minutes of fluorine treatment) of the present invention, As shown in FIG. 1, as shown in FIG. 1, a fluorine peak was found in the vicinity of -165 ppm in the fluorine-decomposing thermally-converting polybenzoxazole-imide copolymer film of the fluorine-treated Example 4, (A large peak near -60 ppm is due to the fluorine atom of 6FDA).

2 is a graph showing the mechanical properties of a fluorine-decomposing polybenzoxazole-imide copolymer film (6FDA-APAF-DAM) prepared from Example 6 (60 minutes of fluorine treatment) (a) storage modulus, (b) tan delta], as shown in FIG. 2, the spectrum obtained by performing the fluorination heat conversion It can be seen that the storage modulus of the polybenzoxazole-imide copolymer film according to the temperature was greatly improved as compared with the fluorine-free heat-converted polybenzoxazole-imide copolymer film of Comparative Example 2. [ Therefore, it can be seen that the fluorine treatment improves the mechanical properties without greatly affecting the structure and chain of the polymer.

Further, in order to confirm the gas separation performance of the fluorinated heat-converted polyimide copolymer film prepared in Examples 1 to 12 and the fluorine-free heat-converted polyimide copolymer films prepared in Comparative Examples 1 to 3, The results of measurement of the permeability of hydrogen, carbon dioxide, nitrogen and methane gas and the selectivities of nitrogen, carbon dioxide and helium to methane from these mixed gases are shown in the following Tables 1 and 2.

Sample Gas permeability (barrer) ^a He H ₂ CO ₂ N ₂ CH ₄ Example 1 256 249 92 5.1 1.2 Example 2 200 214 59 2.6 0.6 Example 3 250 216 41 1.7 0.5 Example 4 196 186 28 1.3 0.4 Example 5 179 183 31 1.7 0.4 Example 6 290 301 115 5.2 1.7 Example 7 179 156 20 1.6 0.3 Example 8 300 253 51 2.9 0.6 Example 9 170 193 81 3.6 1.0 Example 10 242 303 151 7.0 2.4 Example 11 175 177 36 1.6 0.4 Example 12 124 126 11 0.54 0.3 Comparative Example 1 195 254 207 10 7.8 Comparative Example 2 313 333 331 15 12 Comparative Example 3 173 192 144 6.0 4.2

^a 1 barrr = 10 ^-10 cm ³ (STP) cm / (s cm ² cmHg)

Sample Selectivity ^b N ₂ / CH ₄ CO ₂ / CH ₄ He / CH ₄ Example 1 4.3 75 213 Example 2 4.3 95 333 Example 3 3.4 87 500 Example 4 3.3 73 490 Example 5 4.3 78 448 Example 6 3.1 69 171 Example 7 5.3 71 597 Example 8 4.8 87 500 Example 9 3.6 76 170 Example 10 2.9 63 101 Example 11 4.0 84 438 Example 12 2.6 54 413 Comparative Example 1 1.3 26 25 Comparative Example 2 1.4 28 26 Comparative Example 3 1.4 35 41

^b selectivity is the ratio of the permeability of the two gases

3 shows the selectivity (CO ₂ / CH ₄ ) of carbon dioxide to methane according to the fluorine treatment time and the permeability of carbon dioxide in Examples 1 to 4 and Comparative Example 1, And the selectivity (CO ₂ / CH ₄ ) of carbon dioxide to methane according to the fluorine treatment time and the permeability of carbon dioxide in Example 2, respectively.

As shown in Tables 1 and 2 and FIGS. 3 and 4, as the fluorine treatment time increases, the permeability of other gases such as carbon dioxide tends to decline as a whole, while the fluorinated heat conversion polymer gas separator (CO ₂ / CH ₄ ) and selectivity to nitrogen (N ₂ / CH ₄ ) for methane are 3 to 4 times higher than those of the thermally-converted polymer membranes not treated with fluorine, (He / CH ₄ ) of helium is significantly increased up to about 24 times.

Therefore, the fluorinated thermal conversion polymer gas separation membrane produced from the present invention is expected to have a very high selectivity for methane from a mixed gas such as natural gas containing methane as a main component, so that it can be commercialized by applying it to natural gas separation will be.

Claims (19)

A polyimide having a hydroxyl group, a thiol group, or an amino group, or a polyimide copolymer containing a polyimide having a hydroxyl group, a thiol group, or an amino group, is fluorinated on the surface of the heat-converted polymer membrane, . The fluorinated thermal conversion polymer gas separation membrane for natural gas separation according to claim 1, wherein the polyimide having a hydroxyl group, a thiol group or an amino group has a repeating unit represented by the following formula (1) or (2)
&Lt; Formula 1 >< EMI ID =

(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), (CF 2) q} (1≤q≤10), C (CH 3) 2, C (CF 3) 2 or are connected to the CO-NH, Q is a single bond or; 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 , and _{CO-NH, C (CH 3} ) (CF 3), or a substituted or unsubstituted phenylene ring, Y may be an OH, SH or NH _2, the same or different from each other) The polyimide copolymer according to claim 1, wherein the polyimide copolymer comprising a polyimide having a hydroxyl group, a thiol group or an amino group has a repeating unit represented by the following Chemical Formula 3 or 4: Fluorinated Thermal Conversion Polymer Gas Membrane.
(3)

&Lt; Formula 4 >

(Wherein Ar _{1 ,} Q and Y are as defined in claim 2, Ar ₂ is a substituted or unsubstituted divalent arylene group having 6 to 24 carbon atoms and a substituted or unsubstituted divalent group having 4 to 20 carbon atoms, O, S, CO, SO ₂ , Si ((CH _{2) n C} (O) O), and the aromatic ring group may be independently selected from the group consisting of _{CH 3) 2, (CH 2} ) p (1≤P≤10), (CF 2) q (1≤q≤10), C (CH 3) 2, C (CF 3) 2 , or connection to the CO-NH M and l are the mole fractions in the repeating units, 0.1? M? 0.9, 0.1? L? 0.9, and m + l = 1) The method of claim 1, wherein the thermal conversion polymer membrane is a polybenzoxazole membrane, a polybenzothiazole membrane, a polypyrrole membrane, a polybenzoxazole-imide copolymer membrane, a polybenzothiazole-imide copolymer membrane, A polybenzoxazole-pyrrolone copolymer film, and a polybenzothiazole-pyrrolone copolymer film, wherein the polybenzoxazole-pyrrolone copolymer film is at least one selected from the group consisting of polybenzoxazole-benzothiazole copolymer films, polybenzoxazole- Fluorinated Thermal Conversion Polymer Gas Separation Membrane for Natural Gas Separation. The fluorinated thermal conversion polymer gas separation membrane according to any one of claims 1 to 4, wherein the fluorinated thermal conversion polymer gas separation membrane has a fluorination degree of 1 to 100%. The fluorinated thermal conversion polymer gas separation membrane for natural gas separation according to claim 5, wherein the natural gas separation is performed on N ₂ / CH ₄ , CO ₂ / CH ₄ or He / CH ₄ mixed gas. i) an aromatic diamine having an acid anhydride and a hydroxyl group, a thiol group or an amino group; A polyimide having a hydroxyl group, a thiol group or an amino group by reacting an aromatic dianhydride having an acid anhydride with a hydroxyl group, a thiol group or an amino group and an aromatic diamine as a comonomer to obtain a polyamic acid solution and then imidizing the polyamic acid solution; Or a polyimide copolymer containing the polyimide;
ii) obtaining a heat-converted polymer membrane by casting or electrospinning a polyimide copolymer synthesized in step i) or a polyimide copolymer containing the polyimide in an organic solvent; And
and iii) fluorinating the surface of the heat-converted polymer membrane obtained in the step ii). [8] The method according to claim 7, wherein the acid dianhydride in step i) is represented by the following general formula (1).
&Lt; General Formula 1 &

(In the general formula 1, Ar ₁ is the same as defined in claim 2) The method of claim 7, wherein the aromatic diamine having a hydroxyl group, a thiol group or an amino group in step i) is represented by the following general formula (2) or (3) (2).
&Lt; General Formula 2 >< General Formula 3 &

(In the general formula 2 or 3, Q and Y are the same as defined in claim 2) The process according to claim 7, wherein the aromatic diamine as the comonomer in step i) is represented by the following general formula (4).
&Lt; General Formula 4 &

(In the general formula 4, Ar < ₂ > is the same as defined in claim 3) [8] The method of claim 7, wherein the imidization in step i) is performed by an azeotropic thermal imidization method. 12. The method of claim 11, wherein the azeotropic thermal imidization is carried out by adding toluene or xylene to the polyamic acid solution, stirring the mixture at 180 to 200 DEG C for 6 to 12 hours, Process for the preparation of fluorinated thermal conversion polymeric gas separation membranes. [7] The method of claim 7, wherein the heat treatment in step ii) is performed by raising the temperature to 300 to 450 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 0.1 to 12 hours Wherein the fluorinated thermal conversion polymer gas separating membrane for natural gas separation is produced. [7] The method of claim 7, wherein the thermal conversion polymer membrane in step ii) is selected from the group consisting of polybenzoxazole, polybenzothiazole, polypyrrole, polybenzoxazole-imide copolymer, polybenzothiazole- A polybenzimidazole copolymer, a polybenzimidazole copolymer, a polypyrrolone-imide copolymer film, a polybenzoxazole-benzothiazole copolymer film, a polybenzoxazole-pyrrolone copolymer film and a polybenzothiazole-pyrrolone copolymer film Wherein the fluorine-containing thermally-decomposable polymer gas separator is a fluorine-containing thermally decomposable polymer gas separator. The fluorinated thermal conversion polymer gas for separating natural gas according to claim 7, wherein the fluorine treatment in step iii) is carried out by a direct fluorination method using a mixed gas containing 1 ppm to 1 vol% (2). 16. The method of claim 15, wherein the mixed gas comprises fluorine gas and diluent gas of nitrogen, argon or helium. 16. The method of claim 15, wherein the fluorine treatment is performed for 1 minute to 24 hours. The process for producing a fluorinated thermal conversion polymer gas separation membrane according to any one of claims 7 to 17, wherein the fluorinated heat conversion polymer gas separation membrane has a fluorination degree of 1 to 100%. The method of claim 18, wherein the natural gas separation is performed on a mixed gas of N ₂ / CH ₄ , CO ₂ / CH _4, or He / CH _4. .

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