JP2014014728A - Concentration method of carbon dioxide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a concentration method of carbon dioxide in which a high-concentration carbon dioxide is separated from a mixed gas such as natural gas or combustion gas, and which uses a polyamide film suitable for collecting the carbon dioxide.SOLUTION: Mixed gas containing carbon dioxide at partial pressure 0.3 atm or more is permeated through a polyamide film 1, which is made of polyamide including a specific repeating unit and has an oxygen transmission rate of 50(cc/m/24hr/atm/0.1 mm) or less.

Description

  The present invention relates to a method for concentrating carbon dioxide, and in particular, concentrating carbon dioxide using a polyamide film suitable for separating and recovering high concentration carbon dioxide from a mixed gas such as natural gas or combustion gas. Regarding the method.

  In recent years, there has been an increasing demand for separating and concentrating carbon dioxide from natural gas and combustion gas for recovery from the global warming problem. Examples of carbon dioxide separation membranes include carbon membranes (for example, Patent Literature 1), polyimide membranes (for example, Patent Literature 2), ceramic membranes (for example, Patent Literature 3), and the separation principle is a void (free volume). Because of the molecular sieving effect due to the size of the molecules, the smaller size molecules will penetrate the fastest. For example, a mixed gas discharged from a thermal power plant contains hydrogen having a molecular size smaller than that of carbon dioxide, and carbon dioxide cannot be selectively extracted. Further, gas that does not contain hydrogen, such as natural gas, also needs to be dehumidified and removed before separation because it contains water vapor. Therefore, the present situation is that these films can be applied only to a limited gas containing neither hydrogen nor water vapor.

  Methods for separating carbon dioxide containing water vapor include “physical adsorption method” in which polyethylene glycol absorbs it at high pressure and “chemical absorption method” in which amine solvent absorbs it. There is also a problem that the cost for desorbing the carbon dioxide gas is large, and the life of the solvent is short because absorption and desorption of carbon dioxide gas are repeated. In addition, although a part of the research has been carried out to expand the principle of chemical adsorption to membrane separation methods, solvents with affinity for carbon dioxide such as amines, ammonia and carbonates are used as hydrophilic porous membranes and polymers. An example is a liquid film (for example, Patent Documents 4 and 5) that is covered with a matrix and then sandwiched between hydrophobic porous films. In these methods, since the weak base solvent is not fixed, there is a problem in that it precipitates due to pressure or dissolution and causes defects.

  On the other hand, Patent Document 6 shows that polyimide has an affinity for acidic gas. However, polyimide does not have sufficient affinity with carbon dioxide, and the selectivity is low, so that a high concentration of carbon dioxide cannot be obtained. Further, a carbon dioxide separation membrane using a polyamide that is considered to have a relatively high affinity is disclosed in Patent Document 7, which utilizes the molecular sieving effect caused by the voids (free volume) described above. In addition, since the gas barrier property is low and the influence of the affinity of carbon dioxide is small, there are problems similar to those of the above-described carbon film and ceramic film.

JP 2009-34614 A JP-A-3-267130 JP 2009-6260 A JP 2008-36463 A JP-T-2001-519711 JP 2001-137675 A JP 2002-191928 A

  As described above, the currently known method for selectively concentrating carbon dioxide cannot achieve separation of carbon dioxide with low cost, long life and high selectivity.

  Therefore, an object of the present invention is to provide a carbon film that solves the problems of the prior art by using a polymer film that does not lack a carbon dioxide affinity site in a method of concentrating high-concentration carbon dioxide. It is to provide a concentration method.

  In order to concentrate carbon dioxide without losing the carbon dioxide affinity site, the present inventors use a polymer molded body in which structures that selectively permeate carbon dioxide are connected by covalent bonds. It was considered suitable. However, since it is difficult to polymerize a structure having high affinity as used in a liquid membrane to a high molecular weight as it is, high selectivity cannot be achieved by simply increasing the affinity of the polymer chain. I understood that.

  Therefore, as a result of diligent investigation, we applied the so-called gas barrier film technology to suppress the entire gas permeation, and on top of that, by providing a structure with high affinity for carbon dioxide, only carbon dioxide permeates the film. It was found that the desired concentration of carbon dioxide can be achieved.

  The gas barrier film referred to here is a film intended to block gas and is a film having a low gas permeation rate. In order to increase the gas barrier property, it is only necessary to reduce the gap (free volume) between polymer chains derived from the molecular structure, molecular orientation, crystallinity, etc. of the polymer. As such a gas barrier film, for example, An ethylene-polyvinyl alcohol copolymer, polyvinylidene fluoride, oriented crystallized polyamide, polyethylene terephthalate, and the like are known.

  On the other hand, a gas barrier film made of an ethylene-polyvinyl alcohol copolymer having a highly hydrophilic molecular structure is more oxygen or hydrogen than a gas barrier film made of polyvinylidene fluoride or polyethylene terephthalate having a hydrophobic molecular structure. It is known that the permeation rate of the water vapor is small and the permeation rate of water vapor is large. Therefore, the present inventors have considered that a gas barrier film having a small gap (free volume) can only increase the permeation rate of carbon dioxide by using a molecular structure with high affinity for carbon dioxide. Furthermore, in order to increase the carbon dioxide permeation rate by utilizing this affinity, it was considered to use it under high temperature and high humidity conditions in which the diffusion rate increases. This is difficult with a liquid film in which the affinity solvent leaks out.

The present invention has the following configuration. That is,
(1) Chemical formula consists (I) and / or polyamide having a repeating unit represented by formula (II), polyamide film oxygen permeability is less than 50 (cc / m ² /24hr/atm/0.1mm) And a method of concentrating carbon dioxide, wherein a mixed gas containing carbon dioxide at a partial pressure of 0.3 atm or more is permeated.
(Here, Ar ₁ , Ar ₂ , Ar ₃ are each selected from the group consisting of chemical formulas (III) and (IV).
Further, X, Y, Z is _{-O -, - CH 2 -,} - CO -, - CO 2 -, - S -, - SO 2 -, - C (CH 3) 2 - is selected from. )
(2) The carbon dioxide concentration method according to (1), wherein the polyamide film has a thickness of 7 μm or more.
(3) 10% by mole or more of the total number of Ar ₁ , Ar ₂ , and Ar ₃ constituting the polyamide film is selected from the group of chemical formula (III), and the dioxide as described in (1) or (2) Carbon enrichment method.
(4) The carbon dioxide concentration method according to any one of (1) to (3), wherein the Young's modulus of the polyamide film is 3 GPa or more in at least one direction.
(5) The carbon dioxide concentration method according to any one of (1) to (4), wherein carbon dioxide is selectively permeated from a mixed gas of 60 ° C. or higher.
(6) The polyamide film is produced by a solution casting method, and is obtained after heat treatment at 160 ° C. or higher after forming the polyamide film into a film shape (1) to (5) The method for concentrating carbon dioxide according to any one of the above.
(7) The carbon dioxide concentrating method according to any one of (1) to (6), wherein carbon dioxide is selectively permeated from a mixed gas containing hydrogen.
It is.

  The method of concentrating carbon dioxide using the polyamide film of the present invention solves the problems of the prior art and can collect and recover carbon dioxide from the mixed gas to a high concentration.

It is the schematic of the gas separation apparatus used in the Example.

  According to the carbon dioxide concentration method of the present invention, carbon dioxide is preferably concentrated from the mixed gas at a selectivity of 5 or more, more preferably 10 or more, and even more preferably 15 or more. The higher the selectivity of carbon dioxide, the better. If it is less than 5, a high concentration of carbon dioxide cannot be obtained, and it cannot be said that this is an effective concentration method. In the present specification, the selectivity of carbon dioxide means “the partial pressure of a gas other than carbon dioxide in the concentrated gas” with respect to the “ratio of the partial pressure of carbon dioxide to the partial pressure of a gas other than carbon dioxide in the mixed gas”. It is defined on the basis of the ratio of “the ratio of carbon dioxide partial pressure to carbon dioxide”.

  In order to increase the selectivity, it is preferable to increase the gas barrier property and suppress the gas permeation while increasing the affinity with carbon dioxide to facilitate the permeation of carbon dioxide, and the method will be described below. To do.

  Below, the preferable form of the polyamide film used for the concentration method of the carbon dioxide of this invention is demonstrated.

The inventors of the present invention have found that polyamide films are useful as a result of intensive studies on materials that have high affinity with carbon dioxide and can improve gas barrier properties. The reason why the polyamide film has a high affinity with carbon dioxide is not clear, but is thought to be due to the interaction between the amide bond and carbon dioxide. Since the amide bond is a part of the linear chain of the polymer, it is stably present without leaking compared with a liquid film in which a conventional affinity solvent is supported on a polymer matrix, and is uniform in the material. To increase the number of existence. Therefore, the molecular structure of the polyamide film used in the carbon dioxide concentration method of the present invention has a repeating unit represented by the following chemical formula (I) and / or chemical formula (II).
(Here, Ar ₁ , Ar ₂ , Ar ₃ are each selected from the group consisting of chemical formulas (III) and (IV).
Further, X, Y, Z _{is, -O -, - CH 2 -} , - CO -, - CO 2 -, - S -, - SO 2 -, - C (CH 3) 2 - is selected from. )

The polyamide film used in the carbon dioxide concentration method of the present invention is preferably an aromatic polyamide. Specifically, 10 mol% or more of the total number of Ar ₁ , Ar ₂ , and Ar ₃ is represented by the chemical formula (III). It is preferably selected from the group, more preferably 30 mol% or more, and further preferably 80 mol% or more. Furthermore, the aromatic ring represented by the chemical formula (III) has a para-coordination and a meta-coordination, but 50 mol% or more of all aromatics are preferably para-coordination, and 80 mol% or more. Is more preferably para-coordination, and more preferably 90 mol% or more is para-coordination. Increasing the proportion selected from the group of the chemical formula (III) and / or increasing the proportion of the para-coordination increases the heat resistance of the polyamide film and increases the diffusion rate of carbon dioxide. Can be used without breaking even under high pressure conditions.

  Furthermore, some of the hydrogen atoms on the aromatic ring represented by the chemical formula (III) are halogen groups such as fluorine, bromine and chlorine, alkyl groups such as nitro group, methyl group, ethyl group and propyl group, methoxy group, Use of a substance substituted with a substituent such as an alkoxy group such as an ethoxy group or a propoxy group makes it difficult for moisture to be adsorbed to the amide group which is a hygroscopic site due to steric hindrance, thereby improving moisture resistance. It is preferable because it can be used under high-humidity conditions where the diffusion rate increases. Among them, it is more preferable to substitute with chlorine, a methyl group, or a methoxy group because there is almost no deterioration in physical performance and excellent heat resistance.

  When forming a polyamide film, it may be formed into a film so as to impart gas barrier properties by a known method, and it may be melt film formation or solution film formation. The gas barrier film here refers to a so-called non-porous body and a flat molded body having a small void (free volume) and does not include a porous body.

It is known that the gas permeability through the film is influenced by the aforementioned affinity in addition to the voids (free volume) derived from the molecular structure, molecular orientation, crystallinity, etc. If there are large voids such as a solid body, the gas permeates with little influence on molecular orientation, crystallinity, and affinity. The polyamide film used in the carbon dioxide concentration method of the present invention needs to be a film having a small gap and a high gas barrier property in order to effectively utilize the affinity, and the gas barrier property is a single gas having a low affinity with the amide. This can be determined by measuring the transmission speed. Examples of the amide affinity less single gas can be mentioned oxygen, it is necessary that the oxygen permeability of not more than ^{50 (cc / m 2 /24hr/atm/0.1mm)} , 5 (cc / m 2 is preferably /24Hr/atm/0.1Mm) or less, more preferably 0.5 (cc / m ² /24hr/atm/0.1mm) below. The size of the void (free volume) that provides such oxygen permeability can be measured by the positron annihilation method or the like, and the diameter of the void (free volume) is preferably 0.5 nm or less, and 0.4 nm or less. Is more preferably 0.35 nm or less. In order to achieve such a range, it is necessary to form a resin having a specific molecular structure (such as the above-described polyamide or ethylene-polyvinyl alcohol copolymer) under conditions that make it non-porous.

  If it is formed by melt film formation, it becomes a non-porous body. However, when film formation is performed by solution film formation, the solvent part becomes a void in the drying process to remove the solvent present in the resin. It becomes. Therefore, in order to make this porous body a non-porous body, a post-treatment such as a heat treatment will be performed, but if the post-treatment is insufficient, voids of a size that allows gas to easily pass through remain. Gas barrier properties are insufficient. Hereinafter, a step of performing heat treatment will be described as an example of the post-treatment method, but the post-treatment step is not limited to the heat treatment.

  First, in order to make the voids as small as possible, the solvent is dried at a relatively low temperature (for example, in the case of N-methyl-2-pyrrolidone, it is about 80 ° C. to 180 ° C.). Thereafter, vacuum drying or precipitation in water is preferable because the solvent removal rate increases. Next, the heat treatment is preferably performed for 3 minutes or more, so that the voids are further reduced by shrinkage of the resin. The temperature of the heat treatment is preferably as high as possible within a range in which softening or decomposition of the film does not occur although it depends on the structure of the resin. For example, if it is a fully aromatic polyamide, it is preferably 160 ° C. or higher. The temperature is more preferably 200 ° C. or higher and lower than 500 ° C., and further preferably 250 ° C. or higher and lower than 400 ° C.

  In the case of solution casting, it is difficult to improve the gas barrier property because a gas other than carbon dioxide permeates from the gap unless such a post-treatment process is performed. Further, when the heat treatment is performed, the gas barrier property is further improved by increasing the crystallinity or forming a molecular structure in which the voids are reduced due to cross-linking, so that the selectivity of carbon dioxide is also increased.

  The polyamide film used in the carbon dioxide concentration method of the present invention is not particularly limited, but the thickness is preferably 7 μm or more, more preferably 11 μm or more and less than 100 μm, and 18 μm or more and less than 50 μm. More preferably it is. When the thickness is less than 7 μm, the gas barrier property is lowered, so that all the gases are easy to permeate. As a result, the carbon dioxide selectivity is lowered. Therefore, if the thickness is increased to 8 μm or more, 11 μm or more, or 18 μm or more, the gas barrier property becomes high and the gas hardly permeates. However, carbon dioxide dissolves and diffuses into the film due to its high affinity with carbon dioxide. Therefore, the decrease in permeation rate is small, resulting in a high selectivity and a polyamide film suitable for concentration of carbon dioxide. However, if the thickness is too thick, the carbon dioxide permeation rate also decreases, so it is preferably less than 100 μm.

  The polyamide film used in the carbon dioxide concentration method of the present invention is not particularly limited, but the Young's modulus is preferably 3 GPa or more in at least one direction, more preferably 7 GPa or more, and 9 GPa or more. More preferably it is. The Young's modulus can be measured by a method such as ASTM-D882 (1997). The upper limit of the Young's modulus is not particularly limited, but is practically about 25 GPa. If the Young's modulus is high, the rigidity becomes high, so that it is difficult to break even if the pressure of the supply gas is high. In order to increase the Young's modulus, it is conceivable to use an aromatic structure or molecular orientation as described above. In the case of molecular orientation, the orientation is preferably by stretching, and more preferably in the longitudinal and transverse biaxial directions. The method of stretching in the longitudinal and lateral biaxial directions may be either sequential biaxial stretching or simultaneous biaxial stretching. In addition, when molecular orientation is performed, the gas barrier property is increased and the gas permeation rate is reduced. However, the carbon dioxide permeation has a large contribution of affinity as described above, and the permeation rate is difficult to decrease, so that the selectivity is increased. More preferable.

  Below, the supply gas suitable for processing by the carbon dioxide concentration method of the present invention will be described.

  The supply gas used in the carbon dioxide concentration method of the present invention is not particularly limited as long as it is a mixed gas containing carbon dioxide, but a mixed gas containing hydrogen, helium, nitrogen, methane, water vapor, etc. in addition to carbon dioxide. Is mentioned.

  In the carbon dioxide concentration method of the present invention, the partial pressure of carbon dioxide in the supplied mixed gas needs to be 0.3 atm or more. Preferably it is 0.8 atm or more and less than 50 atm, More preferably, it is 1.5 atm or more and less than 20 atm. When the carbon dioxide partial pressure is less than 0.3 atm, it is difficult to increase the partial pressure difference between the supply side and the membrane permeation side, and the carbon dioxide permeation rate may be reduced. In addition, when the carbon dioxide partial pressure is higher than 50 atm, the film may be broken, and when the partial pressure of gases other than carbon dioxide is also high at the same time, the permeation of those gases may be prevented. The selectivity is low without being suppressed. On the other hand, separation with a liquid membrane is difficult to use for a long time because the affinity solvent leaks and the selectivity decreases under conditions where the carbon dioxide partial pressure is as high as 0.3 atm or higher. In the polyamide film of the present invention, the affinity site is bonded as a polymer straight chain, so there is no risk of leakage and stable use is possible.

  The carbon dioxide concentration method of the present invention is not particularly limited in the relative humidity of the supply gas, but is preferably 30% or more, more preferably 40% or more and less than 95%, and more preferably 50% or more. More preferably, it is less than 90%. By setting the relative humidity within this range, carbon dioxide is humidified and easily ionized, and the rate of dissolution in the polyamide film increases, so that the amount of carbon dioxide permeated can be increased. At this time, if the hygroscopicity of the polyamide film is high, deterioration due to swelling occurs, which is not preferable. Therefore, an aromatic polyamide film having high moisture resistance in which chlorine, methyl groups, methoxy groups, etc. are substituted with aromatic rings as described above. It is preferable to use it.

  The carbon dioxide concentration method of the present invention is not particularly limited in the temperature of the supply gas, but is preferably used at 60 ° C. or higher, more preferably 80 ° C. or higher and lower than 190 ° C., and further preferably 110 ° C. It is not lower than 160 ° C. The higher the temperature of the mixed gas, the greater the rate at which carbon dioxide diffuses in the polyamide film, so that the membrane permeation rate of carbon dioxide can be increased and the selectivity can be increased. On the other hand, if the temperature of the mixed gas is too high, the polyamide film may be thermally deformed. Therefore, depending on the heat resistance of the polyamide film to be used, the temperature of the mixed gas is less than 190 ° C or even less than 160 ° C. Preferably there is. Moreover, since the temperature of the mixed gas which can be separated by the amine absorption method is about 30 ° C. to 50 ° C., the method using the polyamide film of the present invention is useful in the range of 60 ° C. or more. In order to increase the heat resistance of the polyamide film, it is preferable to have a structure in which an aromatic is introduced as described above, and more preferably a wholly aromatic polyamide.

  The method for concentrating carbon dioxide of the present invention is useful when hydrogen is contained in a supply gas at a partial pressure of 0.1 atm or more, more preferably 0.5 atm or more, and more preferably 5 atm or more. It is more useful to include. The permeation rate by the polyamide film of the present invention greatly contributes to affinity, and even if hydrogen or helium is mixed in the feed gas, the permeation rate of carbon dioxide is the largest, so the hydrogen in the feed gas is in the above range. It is particularly useful as a method for concentrating carbon dioxide.

[Characteristic measurement method and effect evaluation method]
The characteristic value measurement method and effect evaluation method used in the description of the present invention are as follows.

(1) Separation test of carbon dioxide and helium The selectivity of carbon dioxide was measured using an apparatus schematically shown in FIG. In FIG. 1, a supply gas composed of a mixed gas of carbon dioxide gas and helium gas is supplied to a gas permeable cell 2 installed in a thermostat 4 after adjusting humidity through a humidifier 5. The pressure of the supply gas containing carbon dioxide gas, helium gas and water vapor is measured by a pressure gauge 3. In the gas permeation cell 2, the supply gas is separated into a permeate gas 10 that permeates the film 1 and a non-permeate gas 11 that does not permeate the film 1 under predetermined conditions. The permeate gas 10 is discharged from the gas permeation cell 2 by a sweep gas made of argon, then the pressure is measured by a pressure gauge 9 and the gas composition is analyzed by a gas chromatography 8. Further, the gas composition of the non-permeating gas 11 is analyzed by the gas chromatography 7 after passing through the back pressure valve 6.

In the examples, a mixed gas of carbon dioxide gas and helium gas was humidified to a relative humidity of 80% and supplied to the gas permeable cell 2 in the film, and the film was processed at the treatment temperature, carbon dioxide partial pressure, and helium partial pressure shown in Table 1. The carbon dioxide selectivity (α) of the gas that passed through 1 was calculated. The area of the film 1 used for the test was 0.8 cm ² . Supply gas carbon dioxide partial pressure (P _CO2 ) _f , helium partial pressure (P _He ) _f , permeate gas carbon dioxide partial pressure (P _CO2 ) _p , helium partial pressure (P _He ) _p , selectivity (α) It calculated according to the numerical formulas 1-5 shown below.

P _f in the equation is the supply pressure measured with the pressure gauge 3, P _p is the permeation pressure measured with the pressure gauge 9, and c is the saturated water vapor pressure at the treatment temperature. (X _CO2 ) _f and (X _He ) _f are the concentrations of carbon dioxide and helium in the feed gas, (X _CO2 ) _p and (X _He ) _p are the concentrations of carbon dioxide and helium in the permeate gas, Each was measured by gas chromatography. Here, since the permeation partial pressure is smaller than the supply partial pressure, the measured value of the supply partial pressure is not affected.

<Gas chromatography analysis conditions>
Product: GC390B (Tsukubarika Seiki Co., Ltd.)
Ar carrier gas amount: about 20 ml / min Permeation pressure: 1 atm
Column 1: Silico 1/8 inch x 4 m / MS / Silico 1/8 inch x 2 m
Column 2: UniBeads 2S 1/8 inch × 4m

(2) Film thickness The thickness of the film was determined by the following method using an Anlitz digital micrometer K402B.

  First, sampling was performed in a circular shape having a diameter of 5 cm, and the thickness of the center was measured (point 1). Next, the thickness was measured by moving 1 cm from the position in an arbitrary direction (point 2). Subsequently, the thickness was measured by moving 2 cm from that position in the direction of point 1 (point 3). It was moved to the position of point 1, and the thicknesses of the positions moved by 1 cm in the directions of 90 ° and 270 ° with respect to the straight line obtained by connecting point 2, point 1, and point 3 were measured respectively (point 4, point 5). The total value of the above 5 points was divided by 5 to obtain the film thickness.

(3) Young's modulus According to the method prescribed | regulated to ASTM-D882 (1997), it measured in 23 degreeC and 65% of relative humidity atmosphere using Robot Tensilon (trademark) RTA (made by Orientec). The test piece is 10 mm wide and 50 mm long, and the pulling speed is 300 mm / min. However, the point where the weight passed 0.1 kgf after the start of the test was taken as the origin of elongation. The results were judged as ◎ to × according to the following criteria.
9 GPa or more: ◎
7 GPa or more and less than 9 GPa: O
3 GPa or more and less than 7 GPa: Δ
Less than 3 GPa: ×

(4) Aromatic content rate Of the total number of Ar ₁ , Ar ₂ , and Ar _{3 represented} by formulas (I) and (II), the molar fraction of the structure selected from chemical formula (III) is calculated, and evaluated according to the following criteria: did.
80 mol% or more: ◎
30 mol% or more and less than 80 mol%: O
10 mol% or more and less than 30 mol%: Δ
Less than 10 mol%: ×

(5) Oxygen permeability According to ASTM D-3985, it measured on 25 degreeC and 50% RH conditions using modern control Co., Ltd. oxygen permeability measuring apparatus OX-TRAN100.

(Film formation example 1)
2-chloroparaphenylenediamine corresponding to 100 mol% was dissolved in dehydrated N-methyl-2-pyrrolidone, 2-chloroterephthalic acid chloride corresponding to 99 mol% was added, and polymerization was carried out by stirring for 2 hours. Next, after dissolving 4,4′-diaminodiphenyl sulfone corresponding to 100 mol% in this solution, 3 mol% of polymer units were obtained by block copolymerization of terephthalic acid chloride corresponding to 99 mol% with respect to the polymer units. And further polymerized by stirring for 2 hours. Thereafter, neutralization with lithium carbonate was performed to obtain an aromatic polyamide solution having a polymer concentration of 10% by weight. The polymer solution was cast on a glass plate with a 10 mil applicator and dried at a hot air temperature of 180 ° C. until the film was self-supporting, and then the gel film was peeled from the glass plate. Next, the gel film was fixed to a metal frame, and water extraction such as residual solvent was performed in a water tank. After the water extraction, the moisture on both surfaces of the water-containing film was wiped off with gauze and heat-treated in an oven at 250 ° C. while being fixed to the metal frame to obtain an unoriented film. The unoriented film was stretched 1.3 times in the width direction of the film and 1.1 times in the longitudinal direction at 250 ° C. using a stretcher to obtain a biaxially oriented polyamide film.

(Film formation example 2)
A biaxially oriented polyamide film was obtained in the same manner as in Example 1 except that a 6 mil applicator was used in Example 1.

(Film formation example 3)
A biaxially oriented polyamide film was obtained in the same manner as in Example 1 except that a 4 mil applicator was used in Example 1.

(Film formation example 4)
A biaxially oriented polyamide film was obtained in the same manner as in Film Formation Example 1 except that a 2 mil applicator was used in Film Production Example 1.

(Film formation example 5)
The unoriented film obtained in Film Production Example 1 was used as it was without stretching.

(Film formation example 6)
A nylon resin obtained by copolymerizing nylon 6T / nylon 66 at 75/25% by weight was pressed at a melting temperature of 320 ° C. and 20 MPa using a 60 t press, and held for 2 minutes. Thereafter, it was cooled to 30 ° C. and released from the mold to obtain an unoriented film. The unoriented film was stretched 1.3 times in the width direction of the film and 1.1 times in the longitudinal direction at 110 ° C. using a stretcher to obtain a biaxially oriented polyamide film.

(Film formation example 7)
A biaxially oriented polyamide film was obtained in the same manner as in Example 6 except that nylon 6T / nylon 66 was copolymerized at 55/45% by weight.

(Film formation example 8)
Nylon 6 resin was pressed at a melting temperature of 240 ° C. and 20 MPa using a 60 t press and held for 2 minutes. Thereafter, it was cooled to 30 ° C. and released from the mold to obtain an unoriented film. This unoriented film was stretched 2.3 times in the width direction of the film and 2.1 times in the longitudinal direction at 60 ° C. using a stretcher to obtain a biaxially oriented polyamide film.

(Film formation example 9)
After obtaining a non-oriented film by setting the heat treatment temperature at 180 ° C. in Film Formation Example 1, it was used as it was without being stretched.

(Film formation example 10)
In Example 1 of film formation, the drying temperature and heat treatment temperature were both set to 150 ° C. to obtain an unoriented film, which was used as it was without being stretched.

(Film formation example 11)
Homopolyethylene terephthalate having an intrinsic viscosity of 0.65 was pressed at a melting temperature of 280 ° C. and 20 MPa using a 60 t press, and held there for 2 minutes. Thereafter, it was cooled to 30 ° C. and released from the mold to obtain an unoriented film. This unoriented film was stretched 3.4 times in the film width direction and 3.2 times in the longitudinal direction at 100 ° C. using a stretcher to obtain a biaxially oriented polyethylene terephthalate film.

(Examples 1-7)
Based on the method described above using the polyamide film produced in Film Formation Example 1, carbon dioxide was concentrated under the conditions as shown in Table 1. The results were excellent as shown in Table 1. Water vapor was not detected in the permeated gas.

(Examples 8 to 10)
Based on the method described above using the polyamide film produced in Film Formation Example 2, carbon dioxide was concentrated under the conditions shown in Table 1. The results were excellent as shown in the table. Water vapor was not detected in the permeated gas.

(Examples 11 to 12)
Carbon dioxide was concentrated under the conditions shown in Table 1 based on the method described above using the polyamide film produced in Film Formation Example 3. The results were excellent as shown in the table. Water vapor was not detected in the permeated gas.

(Example 13)
Based on the method described above using the polyamide film produced in Film Formation Example 4, carbon dioxide was concentrated under the conditions shown in Table 1. The results were excellent as shown in the table. Water vapor was not detected in the permeated gas.

(Example 14)
Carbon dioxide was concentrated under the conditions shown in Table 1 based on the method described above using the polyamide film produced in Film Formation Example 5. The results were excellent as shown in the table. Water vapor was not detected in the permeated gas.

(Example 15)
Carbon dioxide was concentrated under the conditions shown in Table 1 based on the method described above using the polyamide film produced in Film Formation Example 6. The results were excellent as shown in the table. Water vapor was not detected in the permeated gas.

(Examples 16 to 17)
Based on the method described above using the polyamide film produced in Film Formation Example 7, carbon dioxide was concentrated under the conditions as shown in Table 1. The results were excellent as shown in the table. Water vapor was not detected in the permeated gas.

(Examples 18 to 20)
Carbon dioxide was concentrated under the conditions shown in Table 1 based on the method described above using the polyamide film produced in Film Formation Example 8. The results were excellent as shown in the table. Water vapor was not detected in the permeated gas.

(Example 21)
Carbon dioxide was concentrated under the conditions shown in Table 1 based on the above-described method using the polyamide film produced in Film Formation Example 9. The results were excellent as shown in the table. Water vapor was not detected in the permeated gas.

(Comparative Example 1)
Based on the method described above using the polyamide film produced in Film Formation Example 10, carbon dioxide was concentrated under the conditions as shown in Table 1. As a result, the selectivity was low and sufficient concentration could not be achieved. Further, water vapor was not detected in the permeated gas.

(Comparative Example 2)
Based on the method described above using the polyamide film produced in Film Formation Example 2, carbon dioxide was concentrated under the conditions shown in Table 1. As a result, the selectivity was low and sufficient concentration could not be achieved. Further, water vapor was not detected in the permeated gas.

(Comparative Example 3)
Based on the above-described method, carbon dioxide was concentrated under the conditions shown in Table 1, using the polyethylene terephthalate film produced in Film Formation Example 11. As a result, the selectivity was low and sufficient concentration could not be achieved. Further, water vapor was not detected in the permeated gas.

(Comparative Example 4)
Based on the method described above, carbon dioxide was concentrated under the conditions shown in Table 1 using a Kapton (registered trademark) 500H film manufactured by Toray Du Pont Co., Ltd. As a result, the selectivity was low and sufficient concentration could not be achieved. Further, water vapor was not detected in the permeated gas.

  The present invention can be suitably used as a method for separating and recovering high-concentration carbon dioxide from a mixed gas such as natural gas or combustion gas.

DESCRIPTION OF SYMBOLS 1 Film 2 Gas permeable cell 3 Pressure gauge 4 Thermostatic bath 5 Humidifier 6 Back pressure valve 7 Gas chromatography 8 Gas chromatography 9 Pressure gauge 10 Permeate gas 11 Non-permeate gas

Claims (7)

Made of polyamide having a repeating unit represented by the following formula (I) and / or formula (II), the polyamide film oxygen permeability is 50 (cc / m ² /24hr/atm/0.1mm) below A method for concentrating carbon dioxide, wherein a mixed gas containing carbon dioxide at a partial pressure of 0.3 atm or more is permeated.
(Here, Ar ₁ , Ar ₂ , Ar ₃ are each selected from the group consisting of chemical formulas (III) and (IV).
Further, X, Y, Z _{is, -O -, - CH 2 -} , - CO -, - CO 2 -, - S -, - SO 2 -, - C (CH 3) 2 - is selected from. )   The method for concentrating carbon dioxide according to claim 1, wherein the polyamide film has a thickness of 7 μm or more. The carbon dioxide concentration method according to claim 1 or 2, wherein 10 mol% or more of the total number of Ar ₁ , Ar ₂ , and Ar ₃ constituting the polyamide film is selected from the group of the chemical formula (III).   The method for concentrating carbon dioxide according to any one of claims 1 to 3, wherein the polyamide film has a Young's modulus of 3 GPa or more in at least one direction.   The carbon dioxide concentration method according to any one of claims 1 to 4, wherein carbon dioxide is selectively permeated from a mixed gas of 60 ° C or higher.   6. The polyamide film according to claim 1, wherein the polyamide film is produced by a solution casting method, and is obtained after heat treatment at 160 ° C. or higher after forming the polyamide film into a film shape. The method for concentrating carbon dioxide according to any one of the above.   The method for concentrating carbon dioxide according to any one of claims 1 to 6, wherein the mixed gas contains hydrogen.