KR20020016370A - New polyimides and gas separation Membrane - Google Patents

Abstract

PURPOSE: Novel polyimides and gas separation membrane using the same is provided, which has excellent chemical resistance, and thermal resistance, selective permeation capacity to oxygen and carbon dioxide. CONSTITUTION: The novel polyimides represented by chemical formula 1 for selective gas separation is prepared by polycondensation of diamine represented by chemical formula 2 with tetracarboxylic acid anhydride represented by chemical formula 3.

Description

New polyimide and gas separation membrane using the same

The present invention relates to a novel polyimide and a gas separation membrane using the same, and more particularly, to a novel polyimide represented by the following Chemical Formula 1, a method for preparing the same, and a gas separation membrane manufactured using the novel polyimide.

Formula 1

In Formula 1 above:

4 selected from

N is an integer of 1 to 3;

R ₂ and R ₃ each represent an alkyl or haloalkyl group having 1 to 3 carbon atoms, a phenyl group, or a phenyl group substituted with a halogen atom;

Is selected from.

In order to apply the polymer as a commercial gas separation membrane, high gas permeability, high separation characteristics, and excellent thermal mechanical properties are required. High gas permeation properties are typical for polymers with low polymer pull forces, and typical polymers include polydimethylsiloxane (PDMS) and poly (4-methyl-1-pentene). Since the polymers have a low glass transition temperature due to low interchain attraction, special processing conditions are required because they must be crosslinked if they are not used at low application temperatures. On the other hand, polymers with high interchain attraction have high glass transition temperatures and very small gas permeation characteristics.

As a general gas separation membrane material, cellulose acetate is well known. However, cellulose acetate-based separators have many problems due to their low chemical resistance and heat resistance. Polysulfone membranes with improved heat resistance are also unsatisfactory in terms of highly required chemical resistance and permeability.

Accordingly, research and development of a separator made of a polyimide material having excellent mechanical properties and heat resistance and excellent gas permeation characteristics have been performed. In general, polyimide has been reported to have high gas permeation characteristics according to its molecular structural specificity despite the high intermetallic attraction and high glass transition temperature. For example, US Pat. Nos. 3,822,202 (1974) and US Pat. No. 30,351 (1980) describe gas separation processes using semipermeable membranes made from polyimide, polyamide, and polyester, and US Pat. Nos. 4,378,400 and 4,959,151 proposes to separate various gas mixtures using polyimide membranes prepared from biphenyltetracarboxylic anhydride.

It is known that a soluble polyimide can be obtained when hexafluoroisopropylidene 2,2-bis (phthalic anhydride) (hereinafter referred to as "6FDA") is used as the tetracarboxylic anhydride component constituting the polyimide. [JP-A-2160832]. Polyimide obtained by polymerizing 6FDA and aromatic diamine is also known to have high gas permeability and selective permeability [ J. Membr. Sci. 50 , 285 (1990), J. Membr. Sci . 94 , 1-65 (1994)]. This characteristic is because the hexafloorisopropylidene group of 6FDA has a large volume to inhibit the internal segmental motility of the polymer, thereby increasing the rigidity of the main chain, thereby improving the permeability and increasing the gas permeability by suppressing the interaction between molecular chains. As a result, it is judged to exhibit gas diffusion selectivity due to high gas permeability and low molecular chain motility due to large free volume.

In addition, although the phenylene diamine component in which the ortho position is substituted with the alkyl group with respect to the amine functional group and the aromatic polyimide membrane prepared from 6FDA are known to have very high gas permeability [US Patent No. 4,705,545 (1987), Japanese Patent Publication No. 63-111921 and J. Polym. Sci. Polym. Phys. vol 30 , 907-914 (1992), etc., have a problem of low gas permeability. Also, a small amount of 3,3 ', 4,4'-benzophenonetetracarboxylic dianhydride (hereinafter referred to as "BTDA") is a copolymer using phenylenediamine in which both 6FDA and ortho-position are substituted with alkyl groups. It has been suggested that the polyimide in the form of UV can increase the permeation selectivity by inducing crosslinking between polymer chains (US Pat. No. 4,717,393 (1988)). In addition, a technique for preparing a copolymer by mixing diacid anhydride or diamine with phenylene diamine in which all 6FDA or ortho positions are substituted with alkyl groups (US Pat. No. 4,717,394 (1988)), and both 6FDA and ortho positions are alkyl groups Techniques for improving the permeation selectivity by treating polyimide consisting of phenylene diamine substituted with amines (US Pat. No. 4,981,497 (1991)) and the like are known.

However, most of the prior arts known so far have been limited in developing materials having excellent properties such as gas permeability and permeation selectivity of polyimide membranes. Therefore, good gas permeability has low selectivity and selectivity. It has been pointed out that the relatively good one is inferior in its permeability.

Therefore, there is an urgent need to develop a polyimide material having a new structure having higher permeability and high selectivity and a new gas separation membrane using such a new material.

In the present invention, in forming a polyimide from diamine and tetracarboxylic dianhydride, as the above diamine component, a bulky hexafluoroisopropylidene group and 2,4,6-trimethylbenzene group are introduced at the same time; By preparing a novel polyimide using N'-bis (2,4,6-trimethyl-3-aminophenyl) -4,4'-hexafluoroisopropylidene diphthalimide (hereinafter referred to as "BAHD") The present invention has been completed.

Accordingly, an object of the present invention is to provide a gas separation membrane excellent in film forming properties, mechanical strength, heat resistance, and gas separation properties, which is manufactured using the novel polyimide and its manufacturing method, and the novel polyimide as a material. The gas separation membrane of the present invention is used for separation of a mixed gas, and in particular, the permeability of carbon dioxide and oxygen is extremely high, and the permeation selectivity to these gases, nitrogen, and methane is excellent, and thus it is useful for an oxygen load membrane or a selective separation membrane of carbon dioxide.

The polyimide having the following general formula (1) as a repeating unit of the present invention is characterized by the following.

Formula 1

In Formula 1 above: Is as defined above.

Referring to the present invention in more detail as follows.

The novel polyimide of the present invention has a large hexafluorisopropylidene group in the main chain, and is composed of phenylene diamine in which all ortho positions of imide nitrogen atoms are substituted with methyl groups, thereby forming a molecular structure of polyimide having a very high gas permeability. In addition, since the imide groups in the repeating unit of the polymer main chain is twice as large as the general polyimide, the polymer main chain can be rigid to improve high glass transition temperature, separation characteristics, chemical resistance and heat resistance. Therefore, the gas separation membrane prepared from the novel polyimide of the present invention has the effect of having an excellent balance between gas permeability and selectivity.

Referring to the preparation method of the polyimide having the formula 1 as a repeating unit according to the present invention.

Polyimide of the present invention is N, N'-bis (2,4,6-trimethyl-3-aminophenyl) -4,4'-hexafluoroisopropylidene diphthalimide represented by the formula (2) BAHD ") and tetracarboxylic dianhydride represented by the following formula (3) to prepare by equimolar amount condensation polymerization.

In Formula 2 above: Is as defined above.

In addition, the diamine represented by the formula (2), which is characteristically used in the present invention, may be prepared by the preparation method according to the following Scheme 1, and may be 3-nitromethylene (3-NM) by dinitrating and reducing the mesitylene. ) And synthesized by reacting with 6FDA followed by reduction using palladium catalyst and hydrogen.

There is no restriction | limiting in particular in the polymerization method for polyimide synthesis in this invention, It is possible to superpose | polymerize by the method generally performed as a polymerization method of polyimide. As the polymerization solvent, N-methyl-2-pyrrolidone (NMP), N, N'-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), N, N'-dimethylformamide (DMF), etc. may be used. These may be used alone or in combination. The amount of the solvent used for the raw material is not particularly limited, but is usually in a concentration of 70 to 95% by weight. A diamine and tetracarboxylic dianhydride component are mixed, it is made to react at the temperature below room temperature normally for 1 to 5 hours, and a polyamic acid is synthesize | combined. Next, a dehydration ring closing agent such as acetic anhydride, pyridine, or triethylamine is added to the reaction solution, and the reaction is carried out usually at room temperature for 7 to 24 hours to imidize the polyamic acid. In addition, since the polyimide of the present invention is soluble in a phenolic solvent, one step of reacting the polymerization and imide at a time at 150 to 250 ° C. using a mixed solvent of 4-methoxyphenol and phenol, methacresol and chlorophenol, etc. A polymer can also be obtained by the method of obtaining a high molecular weight polyimide by high temperature reaction. At this time, a small amount of benzoic acid, isoquinoline and the like are used as a catalyst. The reaction solution produced after the polymerization is introduced into a large amount of methyl alcohol, and the precipitated polymer is filtered and dried to obtain the polyimide powder of the present invention.

The solution obtained by dissolving 0.5 g of the polyimide prepared by the above production method in 100 mL of N, N'-dimethylacetamide is preferably in the range of 0.3 to 1.5 dL / g of intrinsic viscosity based on the value measured at 30 ° C. If the intrinsic viscosity is too small, the self-support is poor when the gas separation membrane is made, and the mechanical strength is insufficient. In addition, too high mechanical strength makes it difficult to obtain a uniform solution and makes film formation difficult.

On the other hand, the present invention includes a gas separation membrane prepared using a novel polyimide having the formula (1) as a repeating unit as a material, the production of the gas separation membrane can be prepared by various methods.

For example, the polyimide is dissolved in a film forming solution solvent, applied as a uniform film forming solution to a suitable support base material (eg, glass plate, etc.), and then heat treated or heated under reduced pressure, and the solvent is evaporated to form a homogeneous film. The film thickness is preferably in the range of 0.03 to 20 µm, because a sufficiently thin film is required for practical gas permeation performance, that is, a large permeation rate, but there is a possibility that pinholes may occur and mechanical strength may decrease. As the film forming solvent, organic solvents such as N-methyl-2-pyrrolidone, N, N'-dimethyl acetamide, dimethyl sulfoxide, N, N'-dimethylformamide and the like are preferable as in the polymerization reaction. It does not specifically limit as a support base material for apply | coating a film forming liquid, The material which has a smooth surface on the surface of a heat resistant polymer, glass, a metal, a ceramic, etc. can be used. Although the temperature which heats a film forming liquid after apply | coating to a support base material is based on the solvent used for film forming, in the case of the said solvent, it is 80-200 degreeC, Preferably it is 100-150 degreeC. Particularly preferred is to evaporate most of the solvent in such a temperature range and then to 200-300 ° C. to evaporate completely. In addition, it is also possible to form a non-homogeneous film by applying the film forming solution to a supporting base material and then immersing it in a poor solvent in water or polyimide mixed with the organic solvent. There is no restriction on the film formation and the film form thereof, and a composite film may be used. The film shape may be a flat film, a hollow fiber film, or the like.

Such a present invention will be described in more detail based on the following examples, but the present invention is not limited thereto. In addition, the term used in the following Example is defined as follows.

(1) Gas Permeation Coefficient: An index indicating the permeation rate of a gas through a membrane. Measurement data are the values at 25 degreeC and 1 atmosphere.

Barrel = 10 ^-10 cm ³ (STP) cm / cm ² sec cm Hg

In Equation 1: STP represents the volume of gas permeable at 0 ℃, 1 atm conditions; cm represents the thickness of the film; cm ² represents the area of the film; sec represents time in seconds; cmHg represents pressure.

(2) Selectivity: The gas selectivity of a membrane is expressed as the ratio of permeability coefficients measured by individual gases alone with the same membrane. For example, CO ₂ / N ₂ = 50 indicates that the permeation of CO ₂ gas permeated at a rate 50 times higher than that of nitrogen gas. Measurement data are the values at 25 degreeC and 1 atmosphere.

Preparation Example: Synthesis of Monomer

(1) 2,4-dinitromethylene (DNM)

In a 500 mL three-necked flask equipped with a cooler, a dropping funnel, and a stirrer, 250 mL of fuming nitric acid (d = 1.5) was added and cooled using an ice bath. 100 g (0.83 mol) of mesitylene were placed in a dropping funnel and stirred vigorously for 3 to 4 hours with slow addition to the reaction vessel. After completion of the reaction, the nitro compound was separated, washed several times with distilled water and recrystallized in ethanol to obtain 145 g (83%) of pure 2,4-dinitromethylene.

Melting point 85-86 ° C .; ¹ H-NMR (DMSO-d ₆ ) δ 1.95 (s, 3H, —CH ₃ ), 2.1 (s, 6H, —CH ₃ ), 7.3 (s, 1H).

(2) 3-nitromesidine (3-NM)

100 g (0.476 mol) of 2,4-dinitromethylene (DNM) was added to 360 mL of distilled water and heated. Then, 120 g (0.71 mol) of sodium sulfide pentahydrate and 16 g (0.5 mol) of sulfur were added to 360 mL of The solution dissolved in distilled water was added slowly over 2 hours. After addition, the reaction solution was refluxed for 3.5 hours, poured into 6N hydrochloric acid, heated for about 10 minutes, and cooled to 65 ° C. After the reaction solution was filtered and left at about 5 ° C. or less for one day, 3-nitromecidine chloride in the form of needle was precipitated. After filtration and drying, the resultant was dissolved in 500 mL of distilled water at 50 to 60 DEG C, and 40 mL of concentrated hydrochloric acid was added thereto. The addition of concentrated aqueous ammonia solution to alkaline and cooling yielded 65 g (76%) of 3-nitromesidine (3-NM) as a yellow crystalline form.

Melting point 68-70 ° C .; ¹ H-NMR (CDCl ₃ ) δ2.0 (s, 1H, —CH ₃ ), 2.1 (s, 6H, —CH ₃ ), 3.6 (s, 2H, —NH ₂ ), 6.8 (s, 1H).

(3) N, N'-bis (2,4,6-trimethyl-3-nitrophenyl) -4,4'-hexafluorodiphthalimide (BNHD)

Dean-Stark Trap Add 180 mL of acetic acid to a 500 mL three-necked flask, add 18.02 g (0.1 mol) of 3-nitromesidine (3-NM) and 22.21 g (0.05 mol) of 6-FDA, and stir at room temperature and nitrogen stream for 1 hour. I was. The reaction temperature was slowly raised to 118 ° C. and refluxed for 6 hours. After the temperature was cooled to room temperature, 70 mL of cyclohexane was added thereto, and refluxed again for 12 hours to remove water generated during the reaction. After removing 60 mL of acetic acid as a solvent and cooling to room temperature, N, N'-bis (2,4,6-trimethyl-3-nitrophenyl) -4,4'-hexafluorodiphthalimide (BNHD) Obtained as a precipitate. The precipitate was washed with water, dried and reprecipitated in methanol to give 34 g (96%) of pure BNHD.

Melting point 297-299 ° C .; ¹ H-NMR (CDCl ₃ ) δ2.08 (s, 6H, -CH ₃ ), 2.17 (s, 6H, -CH ₃ ), 2.32 (s, 6H, -CH ₃ ), 7.15 (s, 2H), 7.92-7.95 (m, 4H), 8.04-8.07 (d, 2H).

(4) N, N'-bis (2,4,6-trimethyl-3-aminophenyll) -4,4'-hexafluorodiphthalimide (BAHD)

10 g (13.01 mmol) of N, N'-bis (2,4,6-trimethyl-3-nitrophenyl) -4,4'-hexafluorodiphthalimide (BNHD) was dissolved in 200 mL of DMF, 1 g of 10% Pd / C was placed in a hydrogen reactor, and reacted at 50 ° C. at a pressure of 3 atm for 48 hours. After the reaction, the resultant was filtered to remove Pd / C, and the filtered reaction solution was distilled to remove DMF, followed by pure N, N'-bis (2,4,6-trimethyl-3) using a mixed solvent of n-hexane and ethyl acetate. -Aminophenyll) -4,4'-hexafluoro diphthalimide (BAHD) was obtained.

Melting point 182-184 ° C .; Yield about 60%; ¹ H-NMR (DMSO-d ₆ ) δ 1.83 (s, 6H, -CH ₃ ), 1.90 (s, 6H, -CH ₃ ), 2.11 (s, 6H, -CH ₃ ), 4.64 (s, 4H -NH ₂ ), 6.83 (s, 2H), 7.90-7.73 (d, 4H), 8.12-8.15 (d, 2H).

Example Synthesis of Polymer

In a 100 mL four-necked flask with a stirrer, thermometer and cooling tube, add 37 mL of m-cresol, 5.999 g (8.465 mmol) AATB, 2.151 g (8.465 mmol) pyromellitic dianhydride and 1-2 drops of isoquinoline. The reaction was carried out for 3 hours at ℃. The temperature was slowly raised to 195 ° C. and nitrogen was blown while refluxing for 8 hours to remove the produced water. After the reaction was completed, the temperature was slowly cooled to room temperature, and then precipitated in excess methanol. The precipitate was washed with methanol and then dried in a 120 ° C. vacuum dryer to prepare a polyimide powder. The yield was 95% and the intrinsic viscosity measured at 30 ° C. at a concentration of 0.5 g / dL using N, N′-dimethylacetamide (DMAc) as a solvent was 0.98 dL / g. 100 mL of 10 wt% N, N'-dimethylacetamide (DMAc) solution in which 0.5 g of this polyimide powder is dissolved is applied onto a glass plate and heated under vacuum at 200 to 300 DEG C for 5 hours to completely remove the solvent. It was. In addition, the viscosity, glass transition temperature and gas permeation characteristics of the prepared polyimide are shown in Table 1 and Table 2.

Examples 2-6

By the same method as in Example 1, except that tetracarboxylic dianhydride was changed to prepare a polyimide. In addition, the viscosity, glass transition temperature and gas permeation characteristics of the prepared polyimide are shown in Table 1 and Table 2.

Comparative example

In a 100 mL four-necked flask with stirrer, thermometer, cooling tube, 37 mL of m-cresol, 1.272 g (8.465 mmol) of 2,4,6-trimethyl-1,3-phenylenediamine, 3.7604 g (8.465 mmol) of 6FDA, and 1 to 2 drops of isoquinoline were added and reacted at 70 ° C. for 3 hours. The temperature was slowly raised to 200 ° C. and nitrogen was blown while refluxing for 10 hours to remove the produced water. After the reaction was completed, the temperature was slowly cooled to room temperature, and then precipitated in excess methanol. The precipitate was washed with methanol and then dried in a 150 ° C. vacuum dryer to prepare a polyimide powder. The yield was 93% and the intrinsic viscosity measured at 30 ° C. at a concentration of 0.5 g / dL using N, N′-dimethylacetamide (DMAc) as a solvent was 0.55 dL / g. 100 mL of 10 wt% N, N'-dimethylacetamide (DMAc) solution in which 0.5 g of this polyimide powder is dissolved is applied onto a glass plate, and is heated under vacuum at 200 to 300 ° C for 7 hours to completely remove the solvent. It was. In addition, the viscosity, glass transition temperature and gas permeation characteristics of the prepared polyimide are shown in Table 1 and Table 2.

The novel polyimide according to the present invention is an soluble polyimide having excellent mechanical strength that can be practically used, and has an advantage of making filming and hollow fiber extremely easy. In addition, the novel polyimide of the present invention has a large hexafluorisopropylidene group in the main chain, and is composed of phenylene diamine in which all ortho positions of nitrogen atoms of the imide are substituted with methyl groups. It has a molecular structure and the imide groups in the repeating unit of the polymer main chain is twice as large as the general polyimide, which makes the polymer main chain rigid, thereby improving high glass transition temperature, separation characteristics and heat resistance. Therefore, the gas separation membrane prepared by using the novel polyimide of the present invention has an effect of excellent balance between gas permeability and selectivity.

Claims (4)

The polyimide having the following formula (1) as a repeating unit. Formula 1 In Formula 1 above: 4 selected from N is an integer of 1 to 3; R ₂ and R ₃ each represent an alkyl or haloalkyl group having 1 to 3 carbon atoms, a phenyl group, or a phenyl group substituted with a halogen atom; Is selected from. A method for producing a polyimide having the following formula (1) as a repeating unit by condensation polymerization of a diamine represented by the following formula (2) and a tetracarboxylic anhydride represented by the following formula (3). Formula 2 Formula 3 Formula 1 In the above formula: Is as defined in claim 1 above. Gas separation membrane, characterized in that prepared by using a polyimide having a formula 1 as a repeating unit. Formula 1 In Formula 1 above: Is as defined in claim 1. 4. The gas separation membrane of claim 3, wherein the separation membrane is a flat membrane or a hollow fiber membrane.