WO2018151175A1

WO2018151175A1 - Gas separation membrane

Info

Publication number: WO2018151175A1
Application number: PCT/JP2018/005134
Authority: WO
Inventors: 泰孝栗下; 美河　正人; 諒黒木; ひとみ大橋
Original assignee: 旭化成株式会社
Priority date: 2017-02-15
Filing date: 2018-02-14
Publication date: 2018-08-23
Also published as: JP6806809B2; TWI643663B; JPWO2018151175A1; TW201831228A

Abstract

A gas separation membrane that comprises a porous support and a gas separation active layer formed on the porous support, wherein: the gas separation active layer contains a gas separation polymer; the gas separation polymer is a polysaccharide containing at least one kind of functional group selected from among an amino group, a pyridyl group, a group having an imidazole skeleton, a group having an indole skeleton, an amide group and a sulfonamide group; and the crystallinity of the gas separation polymer, said crystallinity being represented by the formula: crystallinity(%)=[Ic/(Ic+Ia)]×100 {wherein Ic stands for the sum of the integrals of the scattering intensities of crystalline peaks obtained from X-ray diffraction analysis of the gas separation membrane, and Ia stands for the sum of the integrals of the scattering intensities of the amorphous halo}, is 18-46% inclusive.

Description

Gas separation membrane

The present invention relates to a gas separation membrane that exhibits excellent practicality in the long term. The gas separation membrane of the present invention exhibits particularly excellent performance for olefin separation.

Gas separation / concentration using a gas separation membrane is superior in energy efficiency, energy saving, and high safety compared to distillation, high pressure adsorption, and the like. Examples of pioneering practical applications in this field include separation and concentration of gas using a gas separation membrane, hydrogen separation in an ammonia production process, and the like. Recently, studies on gas separation membranes targeting hydrocarbon gases such as separation of olefin gas and paraffin gas have been actively conducted.

The gas separation membrane generally has a form in which a gas separation active layer is formed on the surface of a porous support (Patent Documents 1 and 2). This configuration is effective for increasing the amount of gas permeation while giving a certain degree of strength to the membrane. In this case, the gas separation active layer is, for example, a layer composed only of a gas separation polymer.
In general, the performance of a gas separation membrane is expressed using a permeation rate and a separation coefficient as indices. The transmission speed is expressed by the following formula:
(Permeability coefficient of gas separating polymer) / (Thickness of separation layer)
Represented by The separation factor is expressed as a ratio of the permeation speeds of the two gases to be separated, and is an amount depending on the material of the gas separating polymer. In order to obtain practical performance as a gas separation membrane, it is necessary to have high gas separation performance and high gas permeability, and to maintain these performances during the use period of the gas separation membrane.

The gas separation membrane module for separating hydrocarbon-based gas includes, for example, a porous support, a gas separation active layer, a housing, and an adhesive. The gas separation active layer may optionally contain a metal species (for example, a metal salt) (Patent Documents 3 and 4).

In order to increase the practicality of the membrane module for gas separation, it is necessary to make each component of the module have chemical resistance. When a gas separation active layer with low chemical resistance is used, the separation target gas causes the gas separation active layer to swell, deteriorate, etc., and the gas separation active layer has defects, peeling from the porous support, etc. There may be a problem that the long-term stability is not good.

International Publication No. 2015/141686 US Patent Application Publication No. 2015/0025293 International Publication No. 2009/093666 JP 2005-246222 A

There are various materials having chemical resistance as the porous support, gas separation active layer, housing, and adhesive of the membrane module for gas separation, and these can be used.

As the gas separation active layer used in the membrane module for gas separation, many materials having excellent gas separation performance, that is, permeation performance and separation performance have been reported so far. However, they all exhibit excellent performance in the initial or short term, but may not be practical when considered for long term use.
For example, polysaccharides such as cellulose and chitosan are frequently used as a gas separation active layer because of excellent gas separation performance derived from their structural characteristics and availability. However, it is pointed out that polysaccharides are easily decomposed by hydrolysis or the like, and there is a potential danger for carrying out stable long-term operation.

Therefore, an object of the present invention is to provide a gas separation membrane having a gas separation membrane active layer having high gas separation performance and high gas permeability and capable of performing stable long-term operation.

The present inventors have intensively studied in order to achieve the above object. As a result, it has been found that the above object can be achieved by adjusting at least one of the crystallinity and crystallite size of the gas separation active layer provided in the produced gas separation membrane, preferably both in an optimum range. It was.

That is, the present invention is summarized as follows.
[1] A gas separation membrane having a porous support and a gas separation active layer formed on the porous support,
The gas separation active layer contains a gas separation polymer, and the gas separation polymer is selected from an amino group, a pyridyl group, a group having an imidazole skeleton, a group having an indole skeleton, an amide group, and a sulfonamide group. A polysaccharide containing at least one functional group, and
The gas separating polymer has the following conditions (A) and (B):
(A) The following mathematical formula (1):
Crystallinity (%) = [Ic / (Ic + Ia)] × 100 (1)
{Wherein Ic is the sum of integral values of the scattering intensity of the crystalline peak when X-ray diffraction analysis is performed on the gas separation membrane, and Ia is the sum of the integral values of the scattering intensity of the amorphous halo. . } The degree of crystallinity of the gas-separable polymer represented by the formula (18) is from 46% to 46%, and (B)

{Where K is the Scherrer constant, λ is the X-ray wavelength, β is the half-width of the X-ray diffraction peak, b is the half-width of the spread of the incident beam, θ is the Bragg angle, However, the Scherrer constant K is set to 0.9. }, The crystallite size on either side of the gas-separable polymer is 3.3 nm or more and 4.0 nm or less,
A gas separation membrane satisfying at least one of the above.
[2] The gas separation membrane according to [1], wherein the degree of crystallinity of the gas-separable polymer in the condition (A) is 18% or more and 31% or less.
[3] The gas separation membrane according to [1], wherein the degree of crystallinity of the gas-separable polymer in the condition (B) is 3.3 nm or more and 3.8 nm or less.
[4] The gas separation membrane according to any one of [1] to [3], which satisfies both the condition (A) and the condition (B).
[5] The gas separation membrane according to any one of [1] to [4], wherein the gas separation membrane contains silver ions or copper ions.
[6] The gas separation membrane according to any one of [1] to [5], wherein the functional group is an amino group.
[7] The gas separation membrane according to [6], wherein the gas separating polymer is chitosan.
[8] The gas separation membrane according to any one of [1] to [7], wherein a surface average pore diameter of the porous support is from 0.05 μm to 0.5 μm.
[9] The gas separation membrane according to any one of [1] to [8], wherein the porous support contains a fluororesin.
[10] The gas separation membrane according to [9], wherein the fluororesin is polyvinylidene fluoride.
[11] The gas separation membrane according to any one of [1] to [10], wherein the porous support is in the form of a hollow fiber.
[12] Using a mixed gas composed of 40% by mass of propane and 60% by mass of propylene,
The supply side gas flow rate per membrane area 2 cm ² is 190 cc / min, the permeation side gas flow rate is 50 cc / min,
Propylene gas permeation rate measured at 30 ° C. in a humidified isobaric formula is 10 GPU or more and 3,000 GPU or less, and
The separation factor of propylene / propane is 50 or more and 3,000 or less,
The gas separation membrane according to any one of [1] to [11].
[13] A method for producing a gas separation membrane according to any one of [1] to [12],
The following steps:
A step of producing a coating liquid by dissolving a polymer in a solvent,
A step of applying the obtained coating liquid to the surface of the porous support,
A step of drying the coated surface at a temperature below the melting point of the porous support to form a gas separation active layer; and
The manufacturing method of a gas separation membrane including the process immersed in the water of 40 to 100 degreeC.

According to the present invention, there is provided a gas separation membrane that exhibits excellent practicality in the long term, particularly in the separation of hydrocarbon gases such as olefins.

Hereinafter, the present invention will be described in detail with a focus on preferred forms (hereinafter referred to as “this embodiment”). The gas separation membrane in this embodiment has a porous support body and the polysaccharide layer arrange | positioned on the said porous support body as a more preferable form.

<Gas separation membrane>
[Porous support]
The porous support of the gas separation membrane in the present embodiment is a membrane having a large number of fine holes penetrating the front and back of the membrane.
In the porous support, the surface average pore diameter measured with a scanning electron microscope (SEM) is preferably 0.05 μm or more and 0.5 μm or less.

The material of the porous support is not limited. From the viewpoint of chemical resistance and solvent resistance, polysulfone, polyethersulfone, fluorine-based resin, etc. are preferable, and from the viewpoint of heat resistance, homopolymers or copolymers such as polyimide, polybenzoxazole, polybenzimidazole, etc. Preferably, any of these alone or a mixture thereof is preferable. Examples of the fluororesin include polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE).
Among the above, in particular, the fluorine-based resin has high durability in a hydrocarbon atmosphere, and PVDF is most preferable from the viewpoint of workability of the porous support.

The shape of the porous support can be, for example, a hollow fiber shape, a flat membrane shape, or a pleated shape.
The film thickness of the porous support having a flat membrane shape or a pleated shape is preferably 1 μm or more and 1,000 μm or less from the viewpoint of ensuring sufficiently high gas separation ability and sufficiently high gas permeability. .
In the case of a porous support having a hollow fiber shape, the outer diameter is preferably 0.1 mm or more and 20 mm or less;
The inner diameter is preferably 0.1 mm or more and 20 mm or less.
The film thickness of the hollow fiber-like porous support is preferably 0.1 mm or more and 20 mm or less from the viewpoint of ensuring sufficiently high gas separation performance and sufficiently high gas permeability.

[Gas separation active layer]
In the gas separation membrane of this embodiment, the gas separation active layer is disposed on the above porous support in order to improve the gas separation performance. The gas separation active layer contains at least a gas separation polymer. The gas-separable polymer is a polysaccharide containing at least one functional group selected from an amino group, a pyridyl group, a group having an imidazole skeleton, a group having an indole skeleton, an amide group, and a sulfonamide group, and ,
The following conditions (A) and (B)
(A) The following mathematical formula (1):
Crystallinity (%) = [I _c / (I _c + I _a )] × 100 (1)
In {formula (1), I _c is the sum of the integral value of scattering intensity of the crystalline peaks when subjected to X-ray diffraction analysis of the gas separation membrane, I _a is the integral of the scattering intensity of the amorphous halo It is the sum of values. } Is 18% or more and 46% or less, and (B) the following formula (2):

{Where K is the Scherrer constant, λ is the X-ray wavelength, β is the half-width of the X-ray diffraction peak, b is the half-width of the spread of the incident beam, θ is the Bragg angle, However, the Scherrer constant K is set to 0.9. }, The crystallite size on either side of the gas-separable polymer represented by is not less than 3.3 nm and not more than 4.0 nm.
Satisfying at least one of the following.

When the degree of crystallinity (%) represented by the formula (1) is 18% or more, the degree of crystallinity is considered to be sufficiently high, and the crystallite size represented by the formula (2) is 3.3 nm or more. The crystal size is considered sufficiently large. In any of these cases, it is presumed that the effect of suppressing swelling and deterioration due to the separation target gas, metal salt, and the like is exhibited by increasing the cohesive force between the polymer chains of the gas-separable polymer. Further, gas does not pass through the crystal part of the gas separating polymer. Therefore, by reducing the crystallinity (%) represented by the formula (1) to 46% or less, or limiting the crystallite size represented by the formula (2) to 4.0 nm or less, It is presumed that the effect of preventing the reduction is manifested.
The degree of crystallinity (%) represented by the mathematical formula (1) is 18% or more and 46% or less, preferably 18% or more and 34% or less, more preferably 18% or more and 31% or less, and 20 It is more preferable that it is not less than 30% and not more than 30%. The crystallite size on either surface represented by the formula (2) is 3.3 nm to 4.0 nm, preferably 3.3 nm to 3.8 nm, and preferably 3.4 nm to 3.8 nm. It is more preferable that

The degree of crystallinity (%) and crystallite size (nm) are respectively divided into XRD profiles in the range of 2θ = 5 to 40 ° into crystal peaks and amorphous peaks, and all peak shapes are assumed to be Gaussian functions. Is calculated. A specific method for obtaining a scattering profile for performing peak separation is shown below.

(When measuring using a gas separation membrane with a porous support)
1) When a metal salt is contained in the gas separation membrane, the gas separation membrane is washed with distilled water. Washing is performed until the metal salt does not elute in the distilled water after washing. The presence or absence of elution can be confirmed by, for example, high frequency inductively coupled plasma (ICP) emission.
2) A section having a cross section perpendicular to the fiber axis is cut out from the gas separation active layer disposed on the porous support.
3) The X-ray having a beam diameter of 1 μm is incident on the gas separation active layer in the cut section from the normal direction of the section of the section, and the transmission method XRD measurement is performed using a two-dimensional detector to perform two-dimensional XRD. A scattering pattern is obtained as a pattern. At this time, only the gas separation active layer is included in the X-ray beam, and the porous support is not included. In addition, measurement is performed under a condition that a sufficient S / N ratio is obtained, and empty cell scattering correction is performed on the obtained scattering pattern. When the porous support is included in the X-ray beam, the scattering from the porous support is subtracted from the obtained scattering pattern to obtain only the gas separation active layer.
4) When diffraction derived from an inorganic compound is observed in the two-dimensional XRD pattern, the diffraction profile of only the gas separation active layer is obtained by performing annular averaging after removing the diffraction by masking or the like.
5) The background derived from thermal diffuse scattering or the like is removed from the obtained scattering profile assuming a straight line. The background is determined as a tangent line connecting the skirt on the small-angle side and the skirt on the wide-angle side of the combined scattering of the crystal peak and the amorphous peak existing at 2θ = 5 to 40 °. Avoid unreasonable occurrences such as negative scattering after background removal.

(When the gas separation active layer is isolated and measured)
1) The gas separation membrane is immersed in a solvent to dissolve the porous support to obtain only the gas separation active layer. Examples of the solvent include alcohols such as methanol, ethanol and propanol; polar solvents such as acetonitrile, acetone, dioxane, tetrahydrofuran, chloroform, dichloromethane, dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone and toluene. Specifically, for example, when the porous support is polyethersulfone, chloroform is preferably used, and when the porous support is PVDF, N-methylpyrrolidone is preferably used.
2) Using the gas separation active layer obtained by the operation of 1) as a sample, the same operation as 3) to 5) in the above (when measuring using a gas separation membrane having a porous support) is performed.

The gas separating polymer in this embodiment is a polysaccharide containing at least one functional group selected from an amino group, a pyridyl group, a group having an imidazole skeleton, a group having an indole skeleton, an amide group, and a sulfonamide group. is there. This is because the excellent gas separation performance derived from the structural characteristics of such a polymer and the availability are considered.
A polysaccharide means a polymer having a structure in which monosaccharides are linked by glycosidic bonds, and is a concept including oligosaccharides. The number of repeating units of the polysaccharide is preferably 100 to 10,000, more preferably 300 to 7,000, and still more preferably 500 to 4,000.
As the polysaccharide in the present embodiment, preferably, chitosan, chondroitin, hyaluronic acid, cellulose, chitin, oligoglucosamine and the like, and derivatives thereof are exemplified. These polysaccharides may be used alone or as a mixture. Among these, chitosan is preferably used because of its excellent gas separation performance. Here, chitosan is composed of β-1,4-N-glucosamine alone or β-1,4-N-glucosamine and β-1,4-N-acetylglucosamine as a repeating unit. The ratio of β-1,4-N-glucosamine in the repeating unit is 70 mol% or more. The ratio of β-1,4-N-glucosamine in this repeating unit is referred to as the deacetylation rate of the polysaccharide.

The gas-separable polymer in the present embodiment has at least one of an amino group, a pyridyl group, a group having an imidazole skeleton, a group having an indole skeleton, an amide group, and a sulfonamide group as repeating units in the molecule. It consists of a gas-separable polymer containing the functional groups of It can be assumed that the gas separation active layer has a repeating unit containing such a group, so that the metal species (particularly metal salt) optionally contained in the gas separation active layer can be highly dispersed and contained. The gas separation membrane can be suitably applied to, for example, separation of olefin and paraffin. Among these, a gas-separable polymer containing an amino group is preferable. This is because the amino group has a relatively weak interaction with the metal species (especially metal salts) optionally contained in the gas separation active layer, and thus the mutual interaction between the metal species and the gas to be separated (especially olefins). This is because it is expected that the decrease in action can be suppressed.

The presence or absence of the polysaccharide and the presence or absence of a functional group are, for example, elemental analysis, time-of-flight secondary ion mass spectrometry (TOF-SIMS), solid nuclear magnetic resonance analysis (solid NMR), X-ray photoelectron spectroscopy (XPS), argon It can be confirmed by X-ray photoelectron spectroscopy (GCIB-XPS) mounted on a gas cluster ion gun.

The gas separation active layer in the gas separation membrane of the present embodiment may contain a substance having affinity for the separation target gas (particularly olefin). In that case, the obtained gas separation membrane can be applied to, for example, separation of olefin and paraffin. A substance having affinity for the separation target gas may also be included in the porous support.
Examples of the substance having affinity for olefins include metal salts. The metal salt is preferably a metal ion selected from the group consisting of monovalent silver ions (Ag ⁺ ) and monovalent copper ions (Cu ⁺ ), or metal salts containing complex ions thereof. More preferably, Ag ⁺ or Cu ⁺ or a complex ion thereof and F ⁻ , Cl ⁻ , Br ⁻ , I ⁻ , CN ⁻ , NO ₃ ⁻ , SCN ⁻ , ClO ₄ ⁻ , CF ₃ SO ₃ ⁻ , BF ₄ ⁻ , and PF ₆ ^- is comprised metal salt and an anion selected from the group consisting of.
The concentration of the metal salt in the gas separation active layer is preferably 10% by mass to 70% by mass, more preferably 30% by mass to 70% by mass, and still more preferably 50% by mass to 70% by mass. This is because the gas separation performance with high practicality cannot be obtained if the concentration of the metal salt is too low, and the manufacturing cost of the membrane module for gas separation becomes high if the concentration of the metal salt is too high. This is because the balance between the two is taken into consideration.

The gas separation active layer may be on both sides of the porous support or only on one side.
When the gas separation membrane is in the form of a hollow fiber, the gas separation active layer may be only on the outer surface of the hollow fiber, may be only on the inner surface, or both the outer surface and the inner surface. It may be on the surface.

<Performance of gas separation membrane>
The gas separation membrane of this embodiment as described above can be suitably used for separation of olefin and paraffin, for example. Specifically, for example, film to the gas separation membrane of area 2 cm ^2, propane 40% by weight and using a mixed gas consisting of propylene 60 wt%, film feed side gas flow area 2 cm ² per 190 cc / min, transparent The side gas flow rate is 50 cc / min, the permeation rate of propylene gas measured at 30 ° C. by a constant pressure system in a humidified atmosphere is 10 GPU to 3,000 GPU, and the propylene / propane separation factor is 50 to 3,000. be able to. The permeation rate of propylene gas is preferably 50 GPU to 2,000 GPU, more preferably 100 GPU to 2,000 GPU. The separation factor of propylene / propane is preferably 100 or more and 1,000 or less, and more preferably 150 or more and 1,000 or less.
These values should be measured under conditions of a propylene partial pressure of 1 atm or less, specifically 0.6 atm.

<Method for producing gas separation membrane>
Next, the manufacturing method of the gas separation membrane of this embodiment is demonstrated.
The gas separation membrane of the present embodiment has at least the following steps:
A process of producing a coating liquid by dissolving the polymer in a solvent (coating liquid manufacturing process),
A step of applying the obtained coating solution to the surface of the porous support (application step),
A step of drying the coating surface at a temperature lower than the melting point of the porous support to form a gas separation active layer (drying step), and a step of immersing in water of 40 ° C. or more and 100 ° C. or less (dipping step),
It is characterized by including.

[Coating liquid manufacturing process]
The coating liquid of this embodiment can be produced by dissolving or dispersing a desired gas separating polymer in an aqueous solvent.
The concentration of the gas separating polymer in the coating liquid is preferably 0.2% by mass or more and 10% by mass or less, and more preferably 0.5% by mass or more and 5% by mass or less. When the gas separation polymer concentration is less than 0.2% by mass, a highly practical gas separation membrane may not be obtained.
The coating solution may contain an organic solvent in a range of 80% by mass or less with respect to the total amount of the solvent. Examples of the organic solvent used here include alcohols such as methanol, ethanol and propanol; polar solvents such as acetonitrile, acetone, dioxane and tetrahydrofuran; These organic solvents may be used alone or in combination of two or more.

The coating liquid may contain a surfactant. The surfactant should be a nonionic surfactant from the standpoint of not electrostatically repelling with the gas-separable polymer and being uniformly dissolved in any of acidic, neutral, and basic aqueous solutions. Is preferred.
Examples of the nonionic surfactant include a long-chain fatty acid ester of polyoxyethylene, a fluorine surfactant having a perfluoro group, and the like. Specific examples thereof include polyoxyethylene long-chain fatty acid esters such as Tween 20 (polyoxyethylene sorbitan monolaurate), Tween 40 (polyoxyethylene sorbitan monopalmitate), Tween 60 (polyoxyethylene sorbitan monostearate). , Tween 80 (polyoxyethylene sorbitan monooleate) (manufactured by Tokyo Chemical Industry Co., Ltd.), Triton-X100, Pluronic-F68, Pluronic-F127, etc .; Examples of fluorine surfactants having a perfluoro group include fluorine-based compounds Surfactants FC-4430, FC-4432 (above 3M), S-241, S-242, S-243 (above AGC Seimi Chemical), F-444, F-477 (above, DIC) Etc.); It can be mentioned are.

The concentration of the surfactant in the coating liquid is preferably 0.001% by mass or more and 1% by mass or less, and 0.01% by mass or more and 0.5% by mass or less with respect to the total amount of the coating liquid. More preferably. This may cause problems such as difficulty in dissolving the surfactant in the coating solution if the concentration of the surfactant is too high; conversely, if the concentration of the surfactant is too low, it is obtained. This is because problems such as a decrease in gas separation performance may occur in the gas separation membrane.

[Coating process]
In the coating step, the porous support is brought into contact with the coating liquid as described above. Examples of the contact method at this time include coating by a dip coating method (dipping method), gravure coating method, die coating method, spray coating method, etc., or coating by a method of depositing on a porous support by filtration Is preferred.
The temperature of the coating liquid in contact with the porous support is preferably 0 ° C. or higher and 100 ° C. or lower, and more preferably 20 ° C. or higher and 80 ° C. or lower. If the contact temperature is too low, the coating solution may not be applied uniformly on the porous support; conversely, if the contact temperature is too high, the solvent of the coating solution during contact ( For example, water) may volatilize excessively.
The contact time (immersion time) in the case of contact by the immersion method is preferably 15 minutes or more and 5 hours or less, and more preferably 30 minutes or more and 3 hours or less. If the contact time is too short, it may cause problems such as insufficient coating on the porous support; conversely, if the contact time is too long, the production efficiency of the gas separation membrane will decrease. May occur.

[Drying process]
After the application step, a drying step (solvent removal step) is performed. In this drying process, the porous support after the coating process is heated at a temperature lower than the melting point of the porous support to dry the coating film, thereby forming a gas separation active layer on the porous support. It is a process to do.
The drying step is preferably performed in an environment of 40 ° C. or more and 160 ° C. or less, more preferably 40 ° C. or more and 120 ° C. or less, preferably 5 minutes or more and 5 hours or less, more preferably 10 minutes or more and 3 hours or less, for example, standing. It can be done by a method. This may cause problems such as inability to sufficiently remove the solvent if the drying temperature is too low or if the drying time is too short or both; This is because when the drying temperature is excessively high, the drying time is excessively long, or both of them, problems such as an increase in manufacturing cost and a decrease in manufacturing efficiency may occur.

[Immersion process]
After the coating step or the drying step, the obtained gas separation membrane is immersed in water at 40 ° C. or higher and 100 ° C. or lower. This step is performed for the purpose of increasing the crystallinity of the gas separating polymer constituting the gas separation membrane and increasing the chemical resistance of the gas separation membrane. This process is presumed to improve the crystallinity of the gas-separable polymer and increase the chemical resistance.
The water used for the immersion may contain an organic solvent in a range of 80% by mass or less with respect to the total amount. Examples of the organic solvent used here include alcohols such as methanol, ethanol and propanol; polar solvents such as acetonitrile, acetone, dioxane and tetrahydrofuran; These organic solvents may be used alone or in combination of two or more.

The temperature of the water contacted with the gas separation membrane is 40 ° C. or higher and 100 ° C. or lower, preferably 40 ° C. or higher and 80 ° C. or lower, and more preferably 40 ° C. or higher and 60 ° C. or lower. If the temperature is too low, the degree of crystallinity does not increase and the desired chemical resistance cannot be imparted, so that there is a possibility that stable gas separation performance cannot be maintained over a long period of time. On the other hand, if the temperature is too high, peeling of the porous support and the gas separation active layer may occur, which may cause defects in the gas separation membrane.
The pressure when immersing the gas separation membrane in water is preferably 0 to 10 atm. If the pressure is too high, the porous support and the gas separation active layer may be peeled off, which may cause defects in the gas separation membrane.
The time for immersing the gas separation membrane in water is preferably 1 minute or more and 5 hours or less, and more preferably 1 minute or more and 3 hours or less. When the contact time is too short, the degree of crystallinity does not increase, and the desired chemical resistance cannot be imparted. Therefore, there is a possibility that stable gas separation performance cannot be maintained for a long time. Conversely, if the contact time is too long, there is a possibility that problems such as a decrease in the production efficiency of the gas separation membrane may occur.

[Metal salt impregnation process]
The gas separation membrane in which the gas separating polymer layer contains a metal salt is further subjected to a metal salt impregnation step in which the gas separation membrane obtained as described above is brought into contact with a metal salt aqueous solution containing a desired metal salt. Can be manufactured. Thereafter, a drying step may optionally be performed.

The concentration of the metal salt in the metal salt aqueous solution is preferably 0.1 M or more and 50 M or less. When the concentration of the metal salt in the aqueous metal salt solution is 0.1 M or less, when the obtained gas separation membrane is used for separation of olefin and paraffin, separation performance with high practicality may not be exhibited. When this concentration exceeds 50M, inconveniences such as an increase in raw material cost occur.
The contact treatment of the gas separation membrane with the aqueous metal salt solution is preferably performed by an immersion method. The aqueous solution temperature during immersion is preferably 10 ° C. or higher and 90 ° C. or lower, and more preferably 20 ° C. or higher and 80 ° C. or lower. If this immersion temperature is too low, problems such as insufficient impregnation of the metal salt into the gas-separable polymer layer may occur; conversely, if the immersion temperature is too high, an aqueous solution of metal salt during the immersion may occur. May cause problems such as excessive volatilization of the solvent (water).

Hereinafter, the present invention will be described more specifically using examples and the like. However, the present invention is not limited to these examples.

<XRD measurement of gas-separable polymer>
[Analysis Example 1]
(1) Production of gas-separable polymer film To a plastic bottle containing 2 g of acetic acid and 94 g of distilled water, 4 g of chitosan having a deacetylation rate of 100% was added as a raw material chitosan and dissolved by stirring overnight. After dissolution, the resulting aqueous solution was filtered under pressure with a filter having a pore size of 5 μm to remove insoluble impurities. The aqueous solution after filtration was left to stand for 24 hours for degassing. The defoamed aqueous solution is spread on a glass plate, and after adjusting the coating film thickness using a doctor blade whose coating thickness is controlled to 1,250 μm, the drying process is performed by heating at 80 ° C. for 3 hours. A coating film was formed. Then, after being immersed in a 0.8 M sodium hydroxide solution (the solvent is a mixed solvent of ethanol: water = 80: 20 (volume ratio)) for 24 hours, it was immersed in distilled water for 24 hours. Subsequently, using water (H ₂ O) as a solvent, a film of a gas separating polymer was obtained by performing a dipping process for 60 minutes under the conditions of a temperature of 40 ° C. and a pressure of 1 atm.

(2) Evaluation of crystallinity and crystallite size About the obtained film, the crystallinity and crystallite size were computed with the following method.
The film was left in the atmosphere for 24 hours and dried. Then, XRD measurement was performed using the following apparatus and conditions. X-rays were incident perpendicular to the film.
X-ray diffractometer: “NanoViewer” manufactured by Rigaku Corporation
X-ray wavelength λ: 0.154 nm
Optical system: Point collimation (1st slit: 0.4 mmφ, 2nd slit: 0.2 mmφ, and guard slit: 0.8 mmφ)
Detector: Imaging plate (IP)
Sample-detector distance: 75.3 mm
Environment around the sample: Vacuum Exposure time: 12 hours

After the XRD measurement, the detector background correction and empty cell scattering correction were performed on the X-ray diffraction pattern obtained from the imaging plate, and an XRD profile was obtained by annular averaging. Subsequently, a straight line connecting 2θ = 5 ° and 2θ = 40 ° of the XRD profile was drawn and removed as a background.
Subsequently, the multi-peak fit function of Wave Metrics software Igor Pro 6.36 was used to approximate both the crystalline peak and the amorphous peak with a Gaussian function, and the XRD profile was separated into peaks.

The degree of crystallinity was calculated as follows.
Considering four peaks as crystal peaks, the initial values of the four peak positions are 2θ = 11.0 °, 15.6 °, 20.7 °, and 21.5 °, and the full width at half maximum is a small-angle peak. In order from 2.3 °, 0.9 °, 1.2 °, and 3.7 °. Considering one peak as an amorphous peak, the peak position was 2θ = 19.0 °, and the full width at half maximum of the peak was 14.5 °. As for the crystal peak, only the peak position of the crystal peak having a peak position of 2θ = 21.5 ° was fixed, and the other crystal peaks were subjected to peak separation without giving constraint conditions. Further, the peak separation and the full width at half maximum of the amorphous peak were fixed to the above values, and the peak separation was performed. If there is a peak whose peak position is significantly different from the initial value as a result of peak separation, or there is a peak with a negative peak value, the peak separation is performed again without considering that peak. did.
The degree of crystallinity was calculated by substituting the area of each peak obtained as a result of peak separation into the above formula (1).

As the crystallite size, the full width at half maximum of the crystal peak located at 2θ = 10 ° to 12 °, or the full width at half maximum of the crystal peak located at 2θ = 15.4 °, obtained as a result of the above peak separation, is the above formula. Substituting into (2), the crystallite size was calculated. Note that K = 0.9 was used as the Scherrer constant.

[Analysis Examples 2 to 7 and 12]
A gas-separable polymer film was prepared in the same manner as in Analysis Example 1 except that the deacetylation rate of the raw material chitosan and the conditions of the drying step and the dipping step were changed as shown in Table 1, respectively. Crystallinity and crystallite size were evaluated.
The results are shown in Table 1.

[Analysis Example 8]
A gas-separable polymer film obtained by the same method as in Analysis Example 2 was immersed in a 7M aqueous silver nitrate solution for 72 hours to introduce silver atoms into the film. The obtained film was washed with distilled water until the aqueous silver solution was not eluted to obtain a gas-separable polymer film containing silver atoms.
About the obtained film, the crystallinity and the crystallite size were evaluated in the same manner as in Analysis Example 1.
The results are shown in Table 1.

[Analysis Example 9]
A film of a gas-separable polymer containing silver atoms was prepared in the same manner as in Analysis Example 8 except that the conditions of the immersion process were changed as shown in Table 1, and the crystallinity and crystallite size were changed. evaluated.
The results are shown in Table 1.

[Analysis Examples 10 and 11]
The conditions of the drying process were as shown in Table 1, and a gas-separable polymer film was prepared in the same manner as in Analysis Example 1 except that the immersion process was not performed, and the crystallinity and crystallite size were evaluated. did.
The results are shown in Table 1.

[Analysis Example 13]
(1) Synthesis of isobutyl modified chitosan 4.00 g of chitosan (number average molecular weight of about 100,000), 0.358 g of isobutyraldehyde, 4.50 g of acetic acid, and 392 g of water were mixed and stirred at 25 ° C. for 24 hours. Thereafter, the pH was adjusted to about 10 with a 1N aqueous sodium hydroxide solution, and the produced precipitate was separated by filtration. The obtained precipitate was washed with distilled water and ethanol, and dried overnight to obtain 3.10 g of isobutyl modified chitosan. The isobutyl modification rate was calculated by proton nuclear magnetic resonance spectroscopy ( ¹ H-NMR) measurement. ^{The 1} H-NMR measurement was performed by dissolving the obtained isobutyl-modified chitosan in a mixed solvent of heavy water: heavy trifluoroacetic acid (10: 1) so as to be 10 mg / mL, and using deuterated chloroform as a standard substance. The isobutyl modification rate was 4.2 mol%.
¹ H-NMR measurement was performed under the following conditions.
Device name: JEOL Ltd., model “JNM-GSX400G” (400 MHz)
Measurement temperature: 25 ° C
Integration count: 16 times

(2) Preparation of gas-separable polymer film and evaluation of crystallinity and crystallite size As in analysis example 1 except that the isobutyl-modified chitosan prepared by the above method was used as the raw material chitosan and the immersion process was not performed. Thus, a gas-separable polymer film was prepared, and its crystallinity and crystallite size were evaluated.
The results are shown in Table 1.

<Performance test of gas separation membrane>
[Example 1]
(1) Production of gas separation membrane As the porous support, a hollow fiber membrane made of polyvinylidene fluoride (PVDF) having an inner diameter of 0.7 mm, an outer diameter of 1.2 mm, and a length of 7.1 cm was used.
A gas separation active layer made of chitosan was formed on the outer surface of the hollow fiber membrane-shaped porous support as described below.
To a plastic bottle containing 2 g of acetic acid and 94 g of distilled water, 4 g of chitosan having a deacetylation rate of 100% as raw material chitosan was added and stirred overnight to dissolve. After dissolution, the resulting aqueous solution was filtered under pressure with a filter having a pore size of 5 μm to remove insoluble impurities. The aqueous solution after filtration was left to stand for 24 hours for degassing.
Thereafter, the porous support in the form of a hollow fiber membrane was immersed in the above aqueous solution and then heated at 100 ° C. for 3 hours to perform a drying step, thereby forming a coating film on the outer surface of the hollow fiber. Thereafter, the hollow fiber having the coating film was immersed in a 0.8 M sodium hydroxide solution (the solvent is a mixed solvent of ethanol: water = 80: 20 (volume ratio)) for 24 hours, and then distilled water. For 24 hours. Further, water (H ₂ O) is used as a solvent, and an immersion process is performed for 60 minutes under the conditions of a temperature of 40 ° C. and a pressure of 1 atm, so that gas separation property is provided on the surface of the hollow fiber membrane porous support. A gas separation membrane was obtained by forming a gas separation active layer made of a polymer. The thickness of the gas separation active layer in the obtained gas separation membrane was 0.5 μm.
For evaluation of the performance of the gas separation membrane, ten hollow fiber-like gas separation membranes were bundled and used.
The method for forming a gas separation active layer in Example 1 is substantially the same as the method for forming a film of a gas separation polymer in Analysis Example 1 above, except that the drying temperature in the drying step is different.

(2) Performance Evaluation of Gas Separation Membrane The propane and propylene permeation rates were measured using the gas separation membrane. In the measurement, a mixed gas composed of propane and propylene (propane: propylene = 40: 60 (mass ratio)) is supplied to the outside of the hollow fiber membrane as the supply gas, and helium is supplied to the inside of the hollow fiber membrane as the permeation gas, and the supply gas The flow rate was 190 cc / min and the permeate gas flow rate was 50 cc / min.
The result calculated from the composition of the permeated gas 3 hours after the start of the supply of the mixed gas consisting of propane and propylene is taken as the result of the first day of measurement, and one month and three months after the start of the supply. The results obtained later were taken as the results of the first month of measurement and the third month of measurement, respectively.
The analysis of the separation gas was performed using gas chromatography (GC).
The results are shown in Table 2.

[Examples 2 to 5 and Comparative Example 3]
A gas separation membrane was prepared in the same manner as in Example 1 except that the conditions of the dipping process were changed as shown in Table 1, and the performance was evaluated. The film thicknesses of the gas separation active layers in the gas separation membranes obtained in these examples and comparative examples were both 0.5 μm.
The results are shown in Tables 2 and 3.

[Example 6]
(1) Production of gas separation membrane A flat membrane made of polyvinylidene fluoride (PVDF) is used as a porous support, and a gas separation active layer made of a gas separation polymer is formed on one side in the same manner as in Analysis Example 3. As a result, a gas separation membrane was obtained. The film thickness of the gas separation active layer in the obtained gas separation membrane was 50 μm.
(2) Performance Evaluation of Gas Separation Membrane Using the gas separation membrane, the supply gas is circulated on the gas separation active layer forming surface side, and the permeated gas is circulated on the surface opposite to the gas separation active layer formation surface. The measurement was carried out by the same method as in Example 1 except that the measurement was performed. The results are shown in Table 2.

[Comparative Examples 1, 2, and 4]
A gas separation membrane was prepared in the same manner as in Example 1 except that the type of raw material chitosan and the conditions of the drying step were as shown in Table 3 and the immersion step was not performed, and the performance was evaluated. The thicknesses of the gas separation active layers in the gas separation membranes obtained in these comparative examples were all 0.5 μm.
The results are shown in Table 3.

In Tables 2 and 3, the numbers of analysis examples in which a gas-separable polymer film was formed by a method substantially the same as the method for forming a gas-separation active layer in each of Examples and Comparative Examples were added. In Examples 1 to 6 and Comparative Examples 2 to 4, the drying temperature in the drying process is different from the corresponding analysis examples.

From the above examples, on the porous support, the gas separation weight was controlled such that the crystallinity was controlled to 18% to 46% and / or the crystallite size was controlled to 3.3 nm to 4.0 nm. When a gas separation membrane having a gas separation active layer formed of a coalescence was used, it was verified that it had excellent separation performance stably over the long term. When the crystallinity is 18% or more and / or the crystallite size is 3.3 nm or more, it is considered that the crystallinity is sufficiently high and / or the crystal size is sufficiently large. Therefore, it is surmised that the cohesive force between the polymer chains of the gas-separable polymer is increased, so that the swelling and deterioration due to the gas to be separated, the metal salt, and the like are suppressed, and a suitable result is shown. On the other hand, gas does not pass through the crystal part. Therefore, by reducing the crystallinity to 46% or less and / or limiting the crystallite size to 4.0 nm or less, an effect of preventing a decrease in gas permeation performance was exhibited, and a favorable result was shown. Inferred.

When the gas separation membrane of the present embodiment is used, a method for separating olefin gas or the like that exhibits excellent practicality over the long term is provided.

Claims

A gas separation membrane having a porous support and a gas separation active layer formed on the porous support,
The gas separation active layer contains a gas separation polymer, and the gas separation polymer is selected from an amino group, a pyridyl group, a group having an imidazole skeleton, a group having an indole skeleton, an amide group, and a sulfonamide group. A polysaccharide containing at least one functional group, and
The gas separating polymer has the following conditions (A) and (B):
(A) The following mathematical formula (1):
Crystallinity (%) = [Ic / (Ic + Ia)] × 100 (1)
{Wherein Ic is the sum of integral values of the scattering intensity of the crystalline peak when X-ray diffraction analysis is performed on the gas separation membrane, and Ia is the sum of the integral values of the scattering intensity of the amorphous halo. . } The degree of crystallinity of the gas-separable polymer represented by the formula: 18% or more and 46% or less, and (B) the following formula (2):

{Where K is the Scherrer constant, λ is the X-ray wavelength, β is the half-width of the X-ray diffraction peak, b is the half-width of the spread of the incident beam, θ is the Bragg angle, However, the Scherrer constant K is set to 0.9. }, The crystallite size on either side of the gas-separable polymer is 3.3 nm or more and 4.0 nm or less,
A gas separation membrane satisfying at least one of the above.
The gas separation membrane according to claim 1, wherein the degree of crystallinity of the gas-separable polymer in the condition (A) is 18% or more and 31% or less.
The gas separation membrane according to claim 1, wherein a crystallite size of the gas separating polymer in the condition (B) is 3.3 nm or more and 3.8 nm or less.
The gas separation membrane according to any one of claims 1 to 3, which satisfies both the condition (A) and the condition (B).
The gas separation membrane according to any one of claims 1 to 4, wherein the gas separation membrane contains monovalent silver ions or monovalent copper ions.
The gas separation membrane according to any one of claims 1 to 5, wherein the functional group is an amino group.
The gas separation membrane according to claim 6, wherein the gas separating polymer is chitosan.
The gas separation membrane according to any one of claims 1 to 7, wherein the porous support has an average surface pore size of 0.05 to 0.5 µm.
The gas separation membrane according to any one of claims 1 to 8, wherein the porous support contains a fluororesin.
The gas separation membrane according to claim 9, wherein the fluororesin is polyvinylidene fluoride.
The gas separation membrane according to any one of claims 1 to 10, wherein the porous support is in the form of a hollow fiber.
Using a mixed gas composed of 40% by mass of propane and 60% by mass of propylene,
The supply side gas flow rate per membrane area 2 cm 2 is 190 cc / min, the permeation side gas flow rate is 50 cc / min,
Propylene gas permeation rate measured at 30 ° C. in a humidified isobaric formula is 10 GPU or more and 3,000 GPU or less, and
The separation factor of propylene / propane is 50 or more and 3,000 or less,
The gas separation membrane according to any one of claims 1 to 11.
A method for producing a gas separation membrane according to any one of claims 1 to 12,
The following steps:
A step of producing a coating liquid by dissolving a polymer in a solvent,
A step of applying the obtained coating liquid to the surface of the porous support,
A step of drying the coated surface at a temperature below the melting point of the porous support to form a gas separation active layer; and
The manufacturing method of a gas separation membrane including the process immersed in the water of 40 to 100 degreeC.