Method for sealing defective membranes in a gas separation membrane module, gas separation membrane module, and purified gas

Abstract

To provide a gas separation membrane module that ensures gas separation performance even when multiple defective membranes are present in adjacent areas. [Solution] A method for sealing a defective membrane in a gas separation membrane module filled with hollow fiber membranes, comprising: step 1 filling the hollow portion of the hollow fiber membrane with powder at one end of the gas separation membrane module; step 2 supplying a test gas from the outer surface of the hollow fiber membrane; step 3 determining a defective membrane at one end of the gas separation membrane module; and step 4 sealing the end of the defective membrane.

Description

Technical Field

[0001] The present invention relates to a method for sealing a defective membrane of a gas separation membrane module, a gas separation membrane module, and a purified gas.

Background Art

[0002] As a method for selectively separating and purifying a specific gas component from a mixture containing a plurality of gas components, a membrane separation method is known. Since the membrane separation method utilizes a pressure difference, it has an advantage of low energy consumption compared to other separation and purification methods.

[0003] The gas separation membrane used in the membrane separation method separates the permeating gas and the non-permeating gas by having a higher gas permeability for a specific gas component (permeating gas) than for other gas components (non-permeating gas). A bundle of gas separation membranes is housed in a partitioned space and used as a gas separation membrane module with an increased gas processing amount per unit volume. When a defective membrane with breaks or cracks is mixed into the gas separation membrane module, a relatively large amount of non-permeating gas leaks from the defective membrane to the permeating side of the gas separation membrane module, significantly degrading the gas separation performance. Therefore, it is necessary to identify and seal the defective membrane. As methods for detecting a defective membrane, a method of visualizing the leak from the defective membrane as bubbles at the end of the gas separation membrane module and a method of directly visualizing with a thermal camera are known (see, for example, Patent Document 1 and Patent Document 2).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] Patent Document 1 discloses a method for detecting leaks in hollow fiber mass transfer devices, characterized in that at least one end of a number of hollow fibers is filled and supported within a tube sheet made of synthetic resin, the hollow fibers open to the outer wall surface of the tube sheet, the inside and outside of the hollow fibers are separated to form separate flow channels, liquid is filled onto the outer wall of the tube sheet of the hollow fiber mass transfer device, and gas is injected under pressure into the external flow channels of the hollow fibers to generate gas columns in the liquid on the outer wall of the tube sheet, thereby individually detecting leaking hollow fibers. However, in the method of Patent Document 1, if multiple leaking hollow fibers are present in adjacent areas, the gas columns interfere with or merge with each other, requiring a very long time to identify all leaking hollow fibers. In addition, because liquid is used to detect leaking hollow fibers, the liquid must be removed and dried before sealing the leaking hollow fibers, resulting in a large amount of work time when the detection and sealing of leaking hollow fibers is repeated.

[0006] On the other hand, Patent Document 2 discloses a method for detecting leaks in a hollow fiber membrane module, in which a group of hollow fiber membranes consisting of multiple fibers is fixed with at least one end face of each fiber open. This method involves supplying gas heated to 60°C or higher or cooled to 5°C or lower to the outer surface of the hollow fiber membranes from a gas supply port on the side of a cylindrical module, and measuring the temperature difference of the gas that passes through the hollow fiber membranes and is emitted from the end face openings using an infrared camera to detect whether or not there is a leak in the hollow fiber membrane module. However, in the method disclosed in Patent Document 2, if there are multiple leaking hollow fiber membranes in adjacent areas, the leaks interfere with each other, requiring complex image processing to detect all leaking hollow fiber membranes, which presents a challenge in ensuring accuracy.

[0007] Therefore, the present invention aims to provide a gas separation membrane module that ensures gas separation performance even when multiple defective membranes exist in adjacent regions. [Means for solving the problem]

[0008] To solve the above problems, the present invention is as follows.

[0009] A method for sealing a defective membrane in a gas separation membrane module filled with hollow fiber membranes, comprising: step 1 filling the hollow portion of the hollow fiber membrane with powder at one end of the gas separation membrane module; step 2 supplying a test gas from the outer surface of the hollow fiber membrane; step 3 determining a defective membrane at one end of the gas separation membrane module; and step 4 sealing the end of the defective membrane. [Effects of the Invention]

[0010] The defect membrane sealing method of the present invention allows for the determination of whether an individual hollow fiber membrane is a defect membrane based on the change in the state of the powder packed at the end of the hollow fiber membrane. Therefore, even if multiple defect membranes exist in adjacent areas, all defect membranes can be identified, and a gas separation membrane module can be provided in which gas separation performance is guaranteed by sealing the defect membranes. [Modes for carrying out the invention]

[0011] The present invention relates to a method for sealing a defective membrane in a gas separation membrane module filled with hollow fiber membranes, and is characterized by comprising: step 1 of filling the hollow portion of the hollow fiber membrane with powder at one end of the gas separation membrane module; step 2 of supplying a test gas from the outer surface of the hollow fiber membrane; step 3 of determining a defective membrane at one end of the gas separation membrane module; and step 4 of sealing the end of the defective membrane.

[0012] A gas separation membrane module is a module in which gas separation membrane elements, each consisting of hollow fiber membranes bundled in a nearly straight line and with at least one end fixed by a potting material, are fixed to the inner surface of a vessel.

[0013] A defective membrane is a gas separation membrane that cannot perform its intended gas separation performance due to defects such as rupture, cracks, or pinholes. The defective membrane sealing method of the present invention is a method that ensures the gas separation performance of the gas separation membrane module by sealing the edges of the defective membrane.

[0014] The present invention describes a method for sealing defective membranes. In step 1, powder is filled into the hollow portion of the hollow fiber membrane at one end of the gas separation membrane module. In this way, at one end of the gas separation membrane module, all the hollow portions of the hollow fiber membrane are filled with powder. The powder filled into the hollow portion of the hollow fiber membrane can be removed by passing a test gas at a certain flow rate or higher through it. In step 2, the test gas is supplied from the outer surface of the hollow fiber membrane. Compared to a hollow fiber membrane without defects (hereinafter referred to as a "defect-free membrane"), the test gas can easily reach the hollow portion of a defective membrane, causing a change in the state of the powder filled at the end of the defective membrane. In step 3, a defective membrane is identified at one end of the gas separation membrane module, and in step 4, the end of the defective membrane is sealed. Powder remaining at the end of the defect-free membrane may be removed between steps 3 and 4. As mentioned above, in conventional technology, leaks from defective membranes were detected in the three-dimensional space at the end of the gas separation membrane module. Therefore, when multiple defective membranes existed in close proximity, the leaks interfered with each other, making it difficult to identify individual defective membranes. The defective membrane sealing method of the present invention can determine whether an individual hollow fiber membrane is a defective membrane by the change in the state of the powder packed at the end of the hollow fiber membrane. Therefore, even when multiple defective membranes exist in close proximity, it becomes possible to easily identify all defective membranes. In step 2, the pressure at which the test gas is supplied is preferably 0.11 MPa or higher and less than 1 MPa in absolute pressure. A test gas supply pressure of 0.11 MPa or higher allows a change in the state of the powder filling the hollow portion at the end of the defective film. On the other hand, a test gas supply pressure of less than 1 MPa allows for the suppression of test gas usage.

[0015] Changes in the state of the powder that occur in step 2 include, for example, scattering and changes in color. In other words, a defective film that has gone through step 2 can be distinguished from a defect-free film in which the powder remains filled in the hollow space without any changes in color, because the powder may scatter and expose the hollow space, or the filled powder may change in color.

[0016] Methods for determining defective films in step 3 include, for example, a combination of visual inspection and binarization using image processing.

[0017] Examples of sealing materials used to seal the defective film in step 4 include epoxy resin, urethane resin, and acrylic resin. The sealing material may contain additives to ensure strength.

[0018] Examples of powders include particles made of minerals, metal oxides, carbon materials, and resin compounds. It is more preferable that the powder consists of particles made of minerals, metal oxides, and carbon materials because they are less susceptible to static electricity. Examples of minerals include talc. Examples of metal oxides include silica and alumina. Examples of carbon materials include activated carbon and carbon nanotubes. Examples of resin compounds include polyethylene and polypropylene. From the viewpoint of ease of dispersion, the powder is preferably flat, hollow, or bulky, and it is more preferable to use particles made of talc, hollow silica, and activated carbon. The powder may also be a mixture of particles of multiple materials.

[0019] In one embodiment of the present invention, the powder is preferably a gas detection agent that changes color upon contact with a test gas. This makes it possible to identify defective films even if the defect size is on the order of micrometers, and improves the gas separation performance of the gas separation membrane module after sealing.

[0020] Examples of combinations of detection agents and test gases include hexavalent chromium compounds and alkanes, molybdates and alkenes, permanganates or dichromates and ethanol, and iodine pentoxide and aromatic compounds. Combinations of hexavalent chromium compounds and propane, or molybdates and propylene are more preferable due to the ease of gasification of the test gas. Furthermore, when using the reaction gas of the gas detection agent as the test gas, it may be diluted with air or nitrogen.

[0021] The particle size of the powder is preferably 0.1 μm or more and 100 μm or less. When the particle size of the powder is 0.1 μm or more, even if the powder remains in the hollow portion of the hollow fiber membrane, it is possible to secure a gas flow path passing through the hollow portion. The particle size of the powder is more preferably 0.5 μm or more, and even more preferably 1 μm or more. On the other hand, when the particle size of the powder is 100 μm or less, it becomes easier to fill the hollow portion of the hollow fiber membrane. The particle size of the powder is more preferably 50 μm or less, and even more preferably 20 μm or less.

[0022] The particle size of the powder can be represented by the diameter of the minimum circumscribed circle when the powder sampled from the hollow portion of the hollow fiber is observed with a transmission electron microscope. At the same time, it is possible to evaluate the material of the powder by elemental analysis.

[0023] Examples of the hollow fiber membrane include inorganic membranes such as zeolite, MOF, and carbon membranes, and polymer membranes. From the viewpoint of being able to supply a high-pressure test gas in Step 2, it is preferably an inorganic membrane with high pressure resistance, and more preferably a carbon membrane.

[0024] The inner diameter of the hollow fiber membrane is preferably 10 μm or more and 1,000 μm or less. By setting the inner diameter of the hollow fiber membrane to 10 μm or more, it becomes easier to fill the powder into the hollow portion. The inner diameter of the hollow fiber membrane is more preferably 20 μm or more, and even more preferably 50 μm or more. On the other hand, by setting the inner diameter of the hollow fiber membrane to 1,000 μm or less, it becomes easier to hold the powder in the hollow portion only at the end of the hollow fiber membrane. The inner diameter of the hollow fiber membrane is more preferably 500 μm or less, and even more preferably 300 μm or less. Since the defective membrane sealing method of the present invention can determine whether each hollow fiber membrane is a defective membrane, it can be suitably used even in a gas separation membrane module in which thin-diameter hollow fiber membranes are stored at a high filling rate.

[0025] In one aspect of the present invention, the hollow fiber membrane may have a porous support. Examples of the porous support include porous inorganic materials such as alumina, silica, cordierite, zirconia, titania, bicol glass, zeolite, magnesia, and sintered metal; porous organic materials containing at least one polymer selected from the group consisting of homopolymers and copolymers such as polysulfone, polyethersulfone, polyamide, polyester, cellulose polymer, vinyl polymer, polyphenylene sulfide, polyphenylene sulfide sulfone, polyphenylene sulfone, and polyphenylene oxide; and porous carbon materials obtained by carbonizing porous organic materials made of carburable resins. Examples of carburable resins include polyphenylene oxide, polyvinyl alcohol, polyacrylonitrile, phenolic resin, fully aromatic polyester, unsaturated polyester resin, alkyd resin, melamine resin, urea resin, polyimide resin, diallyl phthalate resin, lignin resin, and urethane resin. Two or more of these may be used.

[0026] The gas separation membrane module of the present invention is a gas separation membrane module in which a defective membrane is sealed by the defective membrane sealing method of the present invention. The gas separation membrane module of the present invention is characterized in that, because it goes through a process of filling the hollow portion of the hollow fiber membrane with powder at one end of the gas separation membrane module, the powder remains in the hollow portion of the hollow fiber membrane or between the hollow fiber membrane and the sealing material. In the gas separation membrane module of the present invention, methods for fixing the gas separation membrane element to the inner surface of the vessel include, for example, directly fixing it to the inner surface of the vessel using the potting material itself, or fixing it inside the vessel via an adapter (for example, an O-ring) that can ensure liquid-tightness or airtightness. It is preferable to fix it inside the vessel via an adapter or the like, as this allows only the gas separation membrane element to be replaced when the performance of the gas separation membrane deteriorates over time.

[0027] Furthermore, in one aspect of the present invention, the gas separation membrane element may have a casing separate from the vessel (hereinafter referred to as "element casing"). Examples of materials for the element casing include metal, resin, fiber-reinforced plastic (FRP), etc., which can be appropriately selected depending on the situation in which it is used. Resin is preferred because it has high adaptability to the curing shrinkage of the potting material, and polyphenylene sulfide, polytetrafluoroethylene, polyethylene, polypropylene, polyetheretherketone, polyphenylene ether, polyetherimide, polyamideimide, and polysulfone are more preferred because they combine moldability and chemical resistance.

[0028] The potting portion of the gas separation membrane element may be one or multiple locations, but from the viewpoint of sufficiently fixing the position of the gas separation membrane and ensuring the effective surface area of ​​the gas separation membrane, it is preferable to fix both ends of multiple gas separation membranes bundled in a substantially straight line with potting material. Alternatively, the bundled multiple gas separation membranes may be bent into a U-shape and both ends of the gas separation membrane may be fixed at one location with potting material, or only one end of the gas separation membrane may be fixed with potting material and the other end sealed by means other than potting material.

[0029] Potting materials include, for example, thermoplastic resins and thermosetting resins. Furthermore, other additives may also be included.

[0030] The mixed gases to be separated by the module of the present invention are not particularly limited, but examples include carbon dioxide separation and storage systems from exhaust gases of power plants and blast furnaces, removal of sulfur components from gasified fuel gas in coal gasification combined cycle power generation, purification of biogas and natural gas, and hydrogen purification from organic hydrides.

[0031] The purified gas of the present invention is a gas purified using the gas separation membrane module of the present invention. Since the purified gas of the present invention is purified using a gas separation membrane module that ensures gas separation performance, energy-saving production is possible. The purified gas may be purified by including additional steps before and after the purification process in the gas separation membrane module of the present invention. Examples of additional steps include purification such as distillation, adsorption, and absorption, or component adjustment for mixing with other gases. [Examples]

[0032] The present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited to these. Evaluations in each example and comparative example were carried out by the following methods.

[0033] (powder particle size) At the end of the gas separation membrane module in the example, powder was sampled from the hollow portion of the hollow fiber membrane and observed with a transmission electron microscope (Hitachi High-Tech Corporation, S-5500). The radius of the smallest circumscribed circle of 10 or more powder particles was measured, and the average value was taken as the particle size of the powder.

[0034] (Defect film sealing time) For the gas separation membrane modules of the examples and comparative examples, the time required for detecting and sealing defective membranes was measured, and the sealing time per defective membrane (hereinafter referred to as "defective membrane sealing time") was calculated by dividing this by the number of sealed membranes. The defective membrane sealing time of the gas separation membrane of the examples was compared with the defective membrane sealing time of the gas separation membrane module of Comparative Example 1. A result of less than 0.1 times was classified as "excellent," a result of 0.1 times or more but less than 0.5 times was classified as "good," a result of 0.5 times or more but less than 1 time was classified as "acceptable," and a result of 1 time or more was classified as "unacceptable."

[0035] (Gas separation performance of gas separation membrane module) A single gas (carbon dioxide or nitrogen-) at an absolute pressure of 0.2 MPa was supplied to the gas separation membrane modules of the examples and comparative examples, and the amount of atmospheric pressure permeate to the permeate side was measured using a soap membrane flow meter (HORIBA, SF-U). The gas separation performance of the gas separation membrane modules was rated as "Excellent" if the carbon dioxide permeate rate was 50 times or more compared to the nitrogen permeate rate, "Good" if it was 20 times or more but less than 50 times, "Good" if it was 5 times or more but less than 20 times, and "Poor" if it was less than 5 times.

[0036] (Manufacturing Example 1) Ten parts by weight of polyacrylonitrile (PAN) (MW 150,000) manufactured by Polyscience, ten parts by weight of polyvinylpyrrolidone (PVP) (MW 40,000) manufactured by Sigma-Aldrich, and eighty parts by weight of dimethyl sulfoxide (DMSO) manufactured by Fujifilm Wako Pure Chemical Industries were mixed and stirred at 100°C to prepare a spinning stock. After cooling the obtained spinning stock to 25°C, an 80 wt% aqueous solution of DMSO was simultaneously discharged from the inner tube, the spinning stock from the middle tube, and a 90 wt% aqueous solution of DMSO from the outer tube using a concentric triple-nozzle. The mixture was then guided into a coagulation bath consisting of pure water at 25°C and wound onto a roller to obtain yarn. The obtained yarn was washed with water and dried to prepare a precursor for a hollow fiber-like carbon film.

[0037] The obtained carbon film precursor was passed through an electric furnace at 250°C and heated in an air atmosphere for 1 hour to perform an infusibility treatment, thereby obtaining infusible fibers. Subsequently, the infusible fibers were carbonized at 650°C to obtain a carbon film with an outer diameter of 300 μm and an inner diameter of 100 μm. The obtained carbon film is a hollow fiber film having a porous carbon support.

[0038] 700 carbon films were bundled together and housed inside an acrylic pipe (12 mm inner diameter) with an inlet. Both ends of the acrylic pipe were then potted one at a time using epoxy resin. After the epoxy resin cured, the potted portion at one end was cut with a rotary saw to open the carbon film, obtaining the gas separation membrane module of Manufacturing Example 1.

[0039] (Example 1) In one end of the gas separation membrane module of Manufacturing Example 1, talc (manufactured by Nippon Talc Co., Ltd., SG-2000) was filled into the hollow portion of the carbon membrane, and then nitrogen at an absolute pressure of 0.2 MPa was supplied to the outer surface of the carbon membrane. The opening of the carbon membrane at one end of the gas separation membrane module was observed, and the opening of the carbon membrane where the talc had scattered was sealed with Quick Mender (manufactured by Konishi Co., Ltd.). As a result of evaluation using the above method, the powder particle size was 1.5 μm, the defect membrane sealing time was "excellent", and the gas separation performance was "excellent".

[0040] (Example 2) At one end of the gas separation membrane module of Manufacturing Example 1, the hollow portion of the carbon membrane was filled with powder obtained by crushing a gas detection agent extracted from a propane detection tube (manufactured by Komei Rikagaku Kogyo Co., Ltd., 125SA). Then, propane at an absolute pressure of 0.2 MPa was supplied to the outer surface of the carbon membrane. The opening of the carbon membrane at one end of the gas separation membrane module was observed, and the openings of the carbon membrane where the gas detection agent had scattered and the carbon membrane where the gas detection agent had discolored were sealed with a QuickMender (manufactured by Konishi Co., Ltd.). As a result of evaluation using the above method, the particle size of the powder was 5.3 μm, the defect membrane sealing time was "excellent", and the gas separation performance was "outstanding".

[0041] (Comparative Example 1) At one end of the gas separation membrane module in Manufacturing Example 1, nitrogen at an absolute pressure of 0.2 MPa was supplied to the outer surface of the carbon membrane with water filling the openings in the carbon membrane. The openings in the carbon membrane at one end of the gas separation membrane module were observed, and the openings of the carbon membrane with a large amount of bubble generation were sealed with QuickMender (manufactured by Konishi Co., Ltd.). As evaluated using the method described above, the repair effect was "good". [Industrial applicability]

[0042] The defect membrane sealing method and gas separation membrane module of the present invention can be suitably used in carbon dioxide separation and storage systems from exhaust gases of power plants and blast furnaces, removal of sulfur components from gasified fuel gas in coal gasification combined cycle power generation, purification of biogas and natural gas, and hydrogen purification from organic hydrides.

Claims

1. A method for sealing a defect in a gas separation membrane module filled with hollow fiber membranes, Step 1 involves filling the hollow portion of the hollow fiber membrane with powder at one end of the gas separation membrane module, Step 2 involves supplying a test gas from the outer surface of the hollow fiber membrane, Step 3 involves determining a defective film at one end of the gas separation membrane module, A method for sealing a defective film, comprising step 4 of sealing the end of the defective film.

2. The defect film repair method according to claim 1, wherein the particle size of the powder is 1 μm or more and 100 μm or less.

3. The defect film repair method according to claim 1, wherein the powder is selected from the group consisting of talc, hollow silica, and activated carbon.

4. The method for repairing a defective film according to claim 1, wherein the powder is a gas detection agent that changes color upon contact with the test gas.

5. The method for repairing a defective film according to claim 1, wherein the inner diameter of the hollow fiber membrane is 10 μm or more and 1,000 μm or less.

6. The method for repairing a defective film according to claim 1, wherein the gas separation membrane is a carbon membrane.

7. A gas separation membrane module in which a defective membrane is sealed by the defective membrane sealing method according to any one of claims 1 to 6.

8. Purified gas purified by the gas separation membrane module described in claim 7.