Gas separation method, purified fluid, and gas separation device

Abstract

To provide a gas separation method that is capable of separating a highly permeable gas from a separation target gas containing steam at a high throughput.MEANS FOR ACHIEVING THE PURPOSE: A gas separation method comprises: supplying a separation target gas containing steam, a highly permeable gas, and a low-permeable gas to a gas separation membrane module; and separating the separation target gas into a permeate gas enriched in the steam and the highly permeable gas, and a non-permeate gas enriched in the low-permeable gas, wherein the partial pressure of steam in the separation target gas is from 20 kPa to 1 MPa inclusive.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a gas separation method, a purified fluid, and a gas separation apparatus. [Background technology]

[0002] Membrane separation is known as a method for selectively separating and purifying a specific gas component from a mixture containing multiple gas components. Because membrane separation utilizes pressure differences, it has the advantage of consuming less energy than other separation and purification methods.

[0003] The gas separation membrane used in the membrane separation method is a separation membrane that has a higher gas permeability for a specific gas component (permeable gas) than for other gas components (non-permeable gas), and separates the permeable gas from the non-permeable gas based on the difference in size or the difference in interaction with the separation membrane. Polymer membranes and inorganic membranes are known as gas separation membranes, and inorganic membranes are preferably used in applications requiring heat resistance and chemical resistance.

[0004] Water vapor is a gas molecule with a small kinetic diameter, and can be removed using a gas separation membrane. As a method for purifying biogas, a mixed gas containing water vapor, a method is known in which water vapor is removed using a separation membrane dehumidifier, and then carbon dioxide is removed using a carbon dioxide removal device to obtain methane (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2014-91766 A Summary of the Invention [Problem to be solved by the invention]

[0006] Patent Document 1 discloses a biogas utilization system including a compression means for pressurizing biogas, a separation membrane type dehumidifier for dehumidifying the pressurized biogas, and at least one gas utilization means for utilizing the dried biogas generated by the separation membrane type dehumidifier, characterized in that (a) the biogas pressurized by the compression means is supplied to the gas utilization means without pressure increase or decrease operations, and (b) the separation membrane type dehumidifier reduces the dew point (compression dew point) of the biogas by 5° C. or more. However, in the method of Patent Document 1, the pressurized biogas is supplied to the separation membrane type dehumidifier via a cooler and a drain separator for generating and removing drain (condensed water), so that the water vapor in the gas to be separated cannot be utilized for gas separation, and there is a problem in that the throughput of highly permeable gas cannot be improved.

[0007] Therefore, an object of the present invention is to provide a gas separation method capable of separating a highly permeable gas from a gas to be separated that contains water vapor with a high throughput. [Means for solving the problem]

[0008] In order to solve the above problems, the present invention has the following configuration. [1] A gas separation method in which a gas to be separated, which contains water vapor, a highly permeable gas, and a low permeable gas, is supplied to a gas separation membrane module and separated into water vapor, a permeable gas in which the highly permeable gas is concentrated, and a non-permeable gas in which the low permeable gas is concentrated, wherein the partial pressure of water vapor in the gas to be separated is 20 kPa or more and 1 MPa or less. [2] The gas separation method according to [1], wherein the gas to be separated contains a highly permeable gas having a kinetic diameter of 0.25 nm or more and 0.35 nm or less. [3] The gas separation method according to [2], wherein the highly permeable gas is carbon dioxide. [4] The gas separation method according to [1], characterized in that the gas to be separated and the permeable gas flow in parallel. [5] The gas separation method according to [1], characterized in that the water vapor partial pressure relative to the high permeability gas partial pressure in the gas to be separated is 5% or more and 50% or less. [6] The gas separation method according to [1], characterized in that the total pressure on the permeation side of the gas separation membrane module is 0.01 MPa or more and 0.15 MPa or less. [7] The gas separation method according to [1], further comprising a step of humidifying the gas to be separated prior to being supplied to the gas separation membrane module. [8] The gas separation system according to [1], further comprising a step of pressurizing the gas to be separated prior to being supplied to the gas separation membrane module. [9] The gas separation method according to [8], characterized in that the compression ratio of the fluid to be separated before and after the pressure increase is 1.5 times or more and 100 times or less.

[10] The gas separation method according to [8], characterized in that the humidity of the gas to be separated after the pressurization is 50 RH% or more and 95 RH% or less.

[11] The gas separation method according to any one of [1] to

[10] , wherein the gas separation membrane housed in the gas separation membrane module is an inorganic membrane.

[12] The gas separation method according to

[11] , wherein the inorganic membrane is a carbon membrane.

[13] The gas separation method according to

[12] , wherein the gas to be separated further contains 100 ppm or more and 30% or less of hydrocarbons having a carbon number of 2 to 8.

[14] The gas separation method according to

[12] , characterized in that the gas to be separated is selected from the group consisting of natural gas, biogas, and exhaust gas.

[15] The gas separation method according to

[14] , characterized in that the temperature of the natural gas from when it is ejected until when it is supplied to the gas separation membrane module is 60°C or higher and 200°C or lower.

[16] A purified fluid, characterized by being purified by the gas separation method described in

[12] .

[17] A gas separation apparatus including a humidification mechanism and a gas separation membrane module, A gas separation apparatus comprising a means for supplying the gas to be separated humidified by the humidification mechanism to a gas separation membrane.

[18] The gas separation device according to

[17] , wherein the gas separation membrane contained in the gas separation membrane module is a carbon membrane. Effect of the Invention

[0009] In the gas separation method of the present invention, the gas to be separated contains a large amount of highly permeable water vapor, so that the water vapor partial pressure on the permeation side increases, promoting the permeation of the highly permeable gas and improving the permeation amount of the highly permeable gas. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram showing one embodiment of a gas separation method of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The present invention will be described below by way of examples with reference to the drawings, but the present invention should not be construed as being limited to these examples.

[0012] The gas separation method of the present invention is a gas separation method in which a gas to be separated, which contains water vapor, a high permeability gas, and a low permeability gas, is supplied to a gas separation membrane module and separated into water vapor, a permeability gas in which the high permeability gas is concentrated, and a non-permeability gas in which the low permeability gas is concentrated, and is characterized in that the water vapor partial pressure in the gas to be separated is 20 kPa or more and 1 MPa or less.

[0013] As described above, in the conventional technology, the gas to be separated was supplied to the gas separation membrane in a state where the water vapor partial pressure of the gas to be separated was reduced, and therefore the amount of water vapor that could be utilized for separating the gas to be separated was insufficient. In the separation method of the present invention, the gas to be separated having a high water vapor partial pressure is supplied to the gas separation membrane, thereby improving the amount of water vapor that permeates the gas separation membrane and promoting the permeation of the highly permeable gas.

[0014] The gas to be separated in the present invention refers to a mixed gas supplied to a gas separation membrane module. The gas to be separated contains at least three components: water vapor, a high permeability gas, and a low permeability gas. The gas to be separated is supplied to the gas separation membrane module and separated into a permeable gas in which water vapor and the high permeability gas are concentrated, and a non-permeable gas in which the low permeability gas is concentrated.

[0015] A schematic diagram of one embodiment of the gas separation method of the present invention is shown in Figure 1. Figure 1 is a schematic diagram showing an embodiment in which a gas to be separated that has passed through a pressure increasing mechanism and a humidifying mechanism is supplied to a gas separation membrane module and separated into a permeate gas and a non-permeate gas.

[0016] The gas separation membrane method 1 of the present invention is a gas separation method in which a gas 10 to be separated is supplied to a gas separation membrane module 2 and separated into a permeable gas 11 that has permeated the gas separation membrane 3 and a non-permeable gas 12 that has not permeated the gas separation membrane 3. A pressurization mechanism 5 and a humidification mechanism 4 are disposed upstream of the gas separation membrane module 2. By adopting the configuration of Figure 1, even if the gas to be separated has a small amount of water vapor at or below atmospheric pressure, the pressure can be increased through the pressurization mechanism 5 and the amount of water vapor can be increased through the humidification mechanism 4, making it possible to separate highly permeable gases with high efficiency.

[0017] The gas to be separated in the present invention contains water vapor having a partial pressure of 20 kPa or more and 1 MPa or less. When the gas to be separated contains water vapor having a partial pressure of 20 kPa or more, the amount of water vapor in the gas to be separated is ensured, and therefore the amount of water vapor in the permeable gas increases, and the permeation of the highly permeable gas can be promoted. The water vapor partial pressure contained in the gas to be separated is more preferably 30 kPa or more, and even more preferably 50 kPa or more. On the other hand, when the gas to be separated contains water vapor having a partial pressure of 1 MPa or less, the ratio of the highly permeable gas and the low permeable gas in the gas to be separated can be increased. The water vapor partial pressure contained in the gas to be separated is preferably 0.5 MPa or less, and even more preferably 0.1 MPa or less.

[0018] The water vapor partial pressure of the gas to be separated can be calculated from a vapor pressure table by measuring the temperature and humidity of the gas to be separated at a temperature equal to or higher than the dew point of the gas to be separated. If the total pressure of the gas to be separated is high, the total pressure of the gas to be separated may be lowered to prevent condensation of water vapor, and the temperature and humidity may be measured, and the water vapor partial pressure relative to the original total pressure may be calculated.

[0019] The gas to be separated in the present invention is preferably supplied to the gas separation membrane module at a temperature of 65°C or higher and 200°C or lower. When the temperature of the gas to be separated is 65°C or higher, the saturated vapor pressure increases, the amount of water vapor in the gas to be separated increases, and the amount of water vapor permeating the gas separation membrane can be improved. The temperature of the gas to be separated is more preferably higher than a temperature that is 0°C or higher and 10°C or lower than the dew point, depending on the water vapor partial pressure. In this way, condensation of water vapor in the gas separation membrane module can be suppressed. On the other hand, when the temperature of the gas to be separated is 200°C or lower, the energy required for heating can be suppressed. The temperature of the gas to be separated is more preferably 180°C or lower, and even more preferably 150°C or lower.

[0020] The highly permeable gas is preferably a gas molecule with a kinetic diameter of 0.25 nm or more and 0.35 nm or less. Gases with a kinetic diameter of 0.25 nm or more and 0.35 nm or less have a kinetic diameter close to that of water vapor, and therefore easily permeate the gas separation membrane. That is, the highly permeable gas is preferably He with a kinetic diameter of 2.6 nm, H2 with a kinetic diameter of 2.89 nm, CO2 with a kinetic diameter of 3.3 nm, or O2 with a kinetic diameter of 3.46 nm. From the viewpoint of high interaction with the gas separation membrane and easy permeation, polar CO2 is more preferable.

[0021] The low permeation gas is not particularly limited as long as it does not permeate the gas separation membrane as much as the high permeation gas, and includes gases with a larger kinetic diameter than the high permeation gas and gases with low solubility in the gas separation membrane. Examples of low permeation gases include nitrogen, methane, ethane, ethylene, propane, propylene, sulfur hexafluoride, and nitrogen trifluoride.

[0022] In the gas separation method of the present invention, it is preferable that the flow of the gas to be separated and the permeating gas are arranged in parallel flow, whereby water vapor that permeates the gas separation membrane near the inlet of the gas separation membrane module becomes a sweep gas of the highly permeable gas until it reaches the outlet of the gas separation membrane module, thereby improving the permeation amount of the highly permeable gas.

[0023] In the gas separation method of the present invention, the water vapor partial pressure relative to the high permeable gas partial pressure in the gas to be separated is preferably 5% or more and 50% or less. When the water vapor partial pressure relative to the high permeable gas partial pressure in the gas to be separated is 5% or more, the water vapor partial pressure of the permeable gas becomes high, and the permeated water vapor becomes a sweep gas for the high permeable gas, thereby promoting the permeation of the high permeable gas. It is more preferable that the water vapor partial pressure relative to the high permeable gas partial pressure in the gas to be separated is 10% or more. On the other hand, when the water vapor partial pressure relative to the high permeable gas partial pressure in the gas to be separated is 50% or less, the ratio of the high permeable gas in the gas to be separated increases, and the pressure difference between the gas separation membrane and the permeation side can be secured. In addition, the energy required for heating, humidification, etc. required to increase the water vapor partial pressure in the gas to be separated can be reduced. It is more preferable that the water vapor partial pressure relative to the high permeable gas partial pressure in the gas to be separated is 30% or less.

[0024] In the gas separation method of the present invention, the total pressure of the gas to be separated supplied to the gas separation membrane module is preferably 1 atmosphere or more and 10 MPa or less. When the total pressure of the gas to be separated is 1 atmosphere or more, the pressure reduction load on the permeation side of the gas separation membrane module can be reduced. The total pressure of the gas to be separated is more preferably 0.4 MPa or more, and even more preferably 0.8 MPa or more. On the other hand, when the total pressure of the gas to be separated is 10 MPa or less, the pressure increase load of the gas to be separated can be reduced. The total pressure of the gas to be separated is more preferably 8 MPa or less, and even more preferably 2 MPa or less.

[0025] In the gas separation method of the present invention, the total pressure on the permeate side of the gas separation membrane module is preferably 0.01 MPa or more and 0.15 MPa or less. By having a total pressure on the permeate side of 0.01 MPa or more, the pressure reduction load on the permeate side can be reduced. On the other hand, the total pressure on the permeate side is preferably 0.15 MPa or less, since it can reduce the pressure increase load of the gas to be separated. In the gas separation method of the present invention, since the water vapor partial pressure of the gas to be separated is high, the water vapor partial pressure on the permeate side can be ensured even in an embodiment in which the total pressure on the permeate side is high, and the permeation of the highly permeable gas can be promoted.

[0026] In one embodiment of the present invention, the gas separation method preferably includes a step of humidifying the gas to be separated before it is supplied to the gas separation membrane module. This makes it possible to supply any gas to be separated to the gas separation membrane module with the water vapor partial pressure controlled to 20 kPa or more and 1 MPa or less. Examples of the humidification mechanism include bubbler-type, injection-type, shower-type, and split-flow-type humidifiers.

[0027] In another aspect of the present invention, the gas separation method preferably includes a step of pressurizing the gas to be separated before being supplied to the gas separation membrane module. In this way, the water vapor partial pressure can be increased according to the compression ratio before and after the pressurization (pressure after pressurization / pressure before pressurization). At the same time, even with a low-pressure gas to be separated, it becomes easier to ensure the pressure difference between the permeate side and the non-permeate side of the gas separation membrane, improving the driving force for gas separation. Examples of the pressurization mechanism include a compressor.

[0028] In an embodiment in which the gas separation method includes a step of pressurizing the gas to be separated, the compression ratio before and after pressurization (pressure after pressurization / pressure before pressurization) is preferably 1.5 times or more and 100 times or less. A compression ratio of 1.5 times or more increases the pressure of the gas to be separated, making it easier to ensure a pressure difference between the permeate side and the non-permeate side of the gas separation membrane, thereby improving the driving force for gas separation. The compression ratio is more preferably 3 times or more and 5 times or more. On the other hand, a compression ratio of 100 times or less can suppress the energy required for compression. The compression ratio is preferably 50 times or less, and more preferably 20 times or less. In addition, when the compression ratio is large, it is preferable to reduce the pressure increase load by multi-stage pressure increase.

[0029] In an embodiment in which the gas separation method includes a step of pressurizing the gas to be separated, the humidity of the gas to be separated after pressurization is preferably 50 RH% or more and 95 RH% or less. By making the humidity of the gas to be separated after pressurization 50 RH% or more, the energy required for heating the gas to be separated can be reduced. On the other hand, by making the humidity of the gas to be separated after pressurization 95 RH% or less, it is possible to prevent the partial pressure of water vapor from being reduced due to condensation of water vapor and the clogging of piping due to condensed water. It is more preferable that the humidity of the gas to be separated after pressurization is 90 RH% or less.

[0030] A gas separation membrane module (hereinafter, simply referred to as a "module") is a module in which a gas separation membrane is housed in a vessel, and a permeate side and a non-permeate side of the gas separation membrane are partitioned. The shape of the gas separation membrane can be a hollow fiber membrane or a flat membrane. From the viewpoint of improving the membrane area per unit volume, the gas separation membrane is preferably a hollow fiber membrane.

[0031] Examples of gas separation membranes used in the gas separation membrane module include inorganic membranes such as zeolite membranes, metal-organic framework (MOF) membranes, and carbon membranes, as well as polymer membranes. From the viewpoint of being able to increase the supply temperature of the gas to be separated, inorganic membranes with high heat resistance are preferred, and carbon membranes are more preferred from the viewpoint of being less interactive with water vapor and being expected to have long-term durability.

[0032] Zeolite membranes suitable for use as gas separation membranes include membranes made of aluminosilicates, such as NaX type (FAU), ZSM-5, MOR, silicalite, and A type. Two or more of these may be used. It is preferable to use a zeolite species with a small Si / Al ratio, since this reduces the interaction with water vapor.

[0033] Examples of MOF membranes suitable as gas separation membranes include membranes made of Cu-BTC, MOF-5, IRMOF-3, MIL-47, MIL-53, MIL-96, MMOF, SIM-1, ZIF-7, ZIF-8, ZIF-22, ZIF-69, ZIF-90, etc. Two or more of these may be used.

[0034] Examples of carbon membranes suitable as gas separation membranes include membranes obtained by carbonizing polyphenylene oxide, polyvinyl alcohol, polyacrylonitrile, phenol resin, wholly aromatic polyester, unsaturated polyester resin, alkyd resin, melamine resin, urea resin, polyimide resin, diallyl phthalate resin, lignin resin, urethane resin, etc. Two or more of these may be used.

[0035] The gas separation membrane used in the present invention may contain a support. When the gas separation membrane used in the present invention contains a support, it is more preferable that the support is disposed on only one surface of the gas separation membrane.

[0036] Examples of the support include a porous inorganic support and a porous organic support, but since the amount of water vapor in the gas to be separated is large, a porous inorganic support is preferable, and a porous carbon support is even more preferable. That is, it is more preferable to use a composite membrane consisting of a porous carbon support and a carbon membrane as the gas separation membrane, and such an embodiment can be produced by a method of coating a precursor of a separation functional carbon layer on a porous carbon support and carbonizing it again, or a method of carbonizing a porous organic support having a layer of a precursor of a separation functional carbon layer on its surface and carbonizing the support and the separation functional layer at the same time.

[0037] Since the carbon membrane does not easily dissolve hydrocarbons in the gas to be separated, separation performance can be maintained and suitable separation is possible even in the gas to be separated that contains 100 ppm to 30% of hydrocarbons having a carbon number of 2 to 8. Examples of hydrocarbons having a carbon number of 2 to 8 include linear and branched alkanes, alkenes, alkynes, and aromatic hydrocarbons.

[0038] In the gas separation membrane module used in the present invention, the cross-sectional shape of the vessel is preferably elliptical or circular, more preferably circular, from the viewpoint of improving the pressure resistance of the vessel. Here, the cross section of the vessel refers to a cross section of the vessel perpendicular to the longitudinal direction of the gas separation membrane. Examples of the material of the vessel include metal, resin, fiber reinforced plastic (FRP), etc., and can be appropriately selected depending on the environment of the installation location and the situation in which it is used. In applications requiring pressure resistance and heat resistance, metals that combine strength and moldability are preferred, and stainless steel and the like are more preferred.

[0039] The inlet and outlet for the gas to be separated arranged in the vessel has the function of directing the gas to be separated to the gas separation membrane. When the gas separation membrane is used in a dead-end filtration method, it is sufficient to have one inlet and outlet for the gas to be separated, and when used in a cross-flow filtration method, it is preferable to have two or more inlets and outlets for the gas to be separated in total. The vessel may have multiple inlets and outlets for the gas to be separated as long as the mechanical strength of the vessel is maintained. In this case, it is preferable to place a fabric such as a mesh or felt between the inlet and the gas separation membrane to the extent that it does not hinder the passage of the fluid, which has the effect of diffusing the gas and protecting the gas separation membrane.

[0040] Methods for fixing the gas separation membrane to the vessel include a method in which the gas separation membrane is directly fixed to the inner surface of the vessel with a potting material, and a method in which a separation membrane element having a plurality of gas separation membranes fixed with a potting material is fixed to the vessel via an adapter or the like that can ensure liquid-tightness or airtightness (one example is an O-ring, etc.) Fixing to the vessel via an adapter or the like is preferable because it allows only the separation membrane element to be replaced when the performance of the separation membrane element deteriorates over time.

[0041] The separation membrane element used in the present invention may further have a casing (hereinafter referred to as "element casing") to be housed in the vessel. The element casing preferably has an inlet and outlet for the gas to be separated. The shape of the element casing is not particularly limited as long as it does not prevent the element casing from being housed in the vessel. Examples of materials for the element casing include metal, resin, fiber reinforced plastic (FRP), etc., and can be appropriately selected depending on the situation in which the element casing is used. Resins are preferred because they have high compliance with the hardening shrinkage of the potting material, and polyphenylene sulfide, polytetrafluoroethylene, polyethylene, polypropylene, polyether ether ketone, polyphenylene ether, polyetherimide, polyamideimide, and polysulfone are more preferred because they have both moldability and chemical resistance.

[0042] The potting material may be, for example, a thermoplastic resin, a thermosetting resin, etc. Furthermore, other additives may be contained.

[0043] Examples of thermoplastic resins used as potting materials include polyethylene, polyethersulfone, polystyrene, polyphenylene sulfide, polyarylate, polyester, liquid crystal polyester, polyamide, polymethyl methacrylate, etc. Examples of thermosetting resins include epoxy resins, unsaturated polyester resins, urethane resins, urea resins, phenolic resins, melamine resins, silicone resins, etc. Two or more of these may be used. Among these, epoxy resins and urethane resins are preferred from the viewpoint of the balance of moldability, curing time, adhesion, hardness, etc.

[0044] The gas separation apparatus of the present invention is a gas separation apparatus including a humidification mechanism and a gas separation membrane module, and is characterized in having a means for supplying the gas to be separated that has been humidified by the humidification mechanism to the gas separation membrane.

[0045] The gas separation apparatus of the present invention preferably includes a plurality of gas separation membrane modules depending on the gas processing amount of the gas to be separated. The plurality of gas separation membrane modules may be connected in series or in parallel to the gas to be separated. From the viewpoint of being able to shorten the longitudinal length of the gas separation membrane module and improve the production efficiency, it is preferable that the gas separation membrane modules are connected in series, and from the viewpoint of being able to partially replace the gas separation membrane module, it is preferable that the gas separation membrane modules are connected in parallel. As a preferred embodiment of the gas separation apparatus of the present invention, the modules are connected in series, and the modules connected in series are further connected in parallel. In this way, it is possible to achieve both the advantages of connecting modules in series and the advantages of connecting modules in parallel.

[0046] The gas to be separated in the gas separation method of the present invention is not particularly limited, but is preferably a fluid to be separated that contains water vapor. The gas separation method of the present invention can be suitably used in, for example, a carbon dioxide separation and storage system from exhaust gases of power plants, blast furnaces, etc., purification of biogas and natural gas, purification of purified gas after steam methane reforming, etc.

[0047] The natural gas to be separated by the gas separation method of the present invention preferably has a temperature of 60°C or higher and 200°C or lower from the time of jetting until being supplied to the gas separation membrane module. By having a temperature of 60°C or higher from the time of jetting until being supplied to the gas separation membrane module, the water vapor partial pressure in the natural gas can be maintained, and the permeation of highly permeable gas can be promoted without a humidification process. The temperature of 70°C or higher from the time of jetting until being supplied to the gas separation membrane module is more preferably 70°C or higher, and even more preferably 80°C or higher. On the other hand, by having a temperature of 200°C or lower from the time of jetting until being supplied to the gas separation membrane module, the load on piping and the like can be reduced. The temperature of 150°C or lower from the time of jetting until being supplied to the gas separation membrane module is more preferably 150°C or lower.

[0048] The gas separation apparatus of the present invention preferably includes a pretreatment facility, a purified fluid recovery facility, a by-product fluid recovery facility, and the like, before and after the gas separation membrane module. The pretreatment facility is a facility for removing impurities from the fluid to be separated before separation and adjusting the composition of the fluid to be separated before separation, and includes the above-mentioned humidification mechanism and pressure boosting mechanism. The purified fluid recovery facility is a facility for recovering a purified fluid obtained by removing unnecessary components from the fluid to be separated before separation, and for further refining the purified fluid as necessary or supplying it to a pipeline or the like. The by-product fluid recovery facility is a facility for recovering a by-product fluid removed from the fluid to be separated before separation, and for example, for rendering the by-product fluid harmless after additional purification and discharging the by-product fluid. In the gas separation apparatus of the present invention, the gas separation membrane module and the pretreatment facility, the purified fluid recovery facility, and the by-product fluid recovery facility are preferably connected by piping or the like, and the fluid to be separated before separation is continuously separated into a purified fluid and a by-product fluid.

[0049] The purified fluid of the present invention is characterized in that it is purified by a method in which the gas separation membrane housed in the gas separation membrane module is an inorganic membrane, and the inorganic membrane is a carbon membrane, in the gas separation method of the present invention. The purified fluid of the present invention may be purified by an additional process for the permeate gas or non-permeate gas separated by the gas separation method of the present invention, or may be used by mixing with a purified fluid purified by a different purification process. Examples of the additional or different purification process include distillation, adsorption, and absorption. Examples of the additional process include component adjustment for mixing with another fluid.

[0050] Next, an example of a method for manufacturing the module used in the present invention will be described. The module used in the present invention can be manufactured by inserting a plurality of gas separation membranes into an element casing or vessel and potting both ends of the gas separation membranes with a potting material. Potting methods include, for example, a centrifugal potting method in which centrifugal force is used to permeate between the gas separation membranes, and a static potting method in which a fluidized potting material is delivered by a metering pump or head and permeated into the gas separation membranes.

[0051] It is preferable to cut the potted gas separation membrane at the potting site to open the gas separation membrane. It is preferable to attach a cap as a pipe joint member to the cut surface of the gas separation membrane module so that it can be connected to an external flow path (such as a flow path for recovering a fluid that has permeated the gas separation membrane). EXAMPLES

[0052] The present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited thereto. Evaluations in each of the examples and comparative examples were carried out by the following methods.

[0053] (Ratio of water vapor partial pressure to the high permeability gas partial pressure in the gas to be separated) In the gas separation methods of the Examples and Comparative Examples, the ratio of the water vapor partial pressure to the CO2 partial pressure in the gas to be separated was calculated from the pressure and composition of the gas to be separated before it was supplied to the gas separation membrane.

[0054] (Permeation rate and gas separation performance of high and low permeation gases) In the gas separation methods of the examples and comparative examples, the permeable gas of the gas separation membrane module was connected to a soap film flowmeter via a gas chromatograph. The CO2 permeation rate and CH4 permeation rate per unit time were calculated from the CO2 fraction and CH4 fraction in the permeable gas obtained from the gas chromatograph and the flow rate of the permeable gas obtained from the soap film flowmeter. Gas separation performance was evaluated as "excellent" when the CH4 permeation rate relative to the CO2 permeation rate was 5% or less, "good" when it was 5% to 10%, "fair" when it was 10% to 30%, and "poor" when it was 30% or more.

[0055] (Production Example 1) A spinning dope was prepared by mixing 10 parts by weight of polyacrylonitrile (PAN) (MW 150,000) manufactured by Polysciences, 10 parts by weight of polyvinylpyrrolidone (PVP) (MW 40,000) manufactured by Sigma-Aldrich, and 80 parts by weight of dimethyl sulfoxide (DMSO) manufactured by Wako Pure Chemical Industries, Ltd., and stirring at 100°C.

[0056] After the obtained spinning solution was cooled to 25°C, a concentric triple spinneret was used to simultaneously discharge an 80 wt% DMSO aqueous solution from the inner tube, the spinning solution from the middle tube, and a 90 wt% DMSO aqueous solution from the outer tube, and then the spinning solution was introduced into a coagulation bath of pure water at 25°C and wound up on a roller to obtain a raw fiber. The obtained raw fiber was washed with water and then dried in a circulating dryer at 25°C for 24 hours to produce a precursor of a porous carbon support for hollow fibers.

[0057] The precursor of the porous carbon support was then passed through an electric furnace at 250° C. and heated in an air atmosphere for 1 hour to perform infusibility treatment. The infusible yarn was then carbonized in an inert atmosphere at 500° C. to produce a hollow fiber-shaped porous carbon support having an outer diameter of 280 μm and an inner diameter of 90 μm.

[0058] Aromatic polyimide "Matrimid" (registered trademark) 5218 was dissolved in N-methylpyrrolidone (NMP) to prepare a 10.0 wt% aromatic polyimide solution (hereinafter referred to as "aromatic PI solution"). Here, "Matrimid" (registered trademark) 5218 is a condensation product of 3,3',4,4'-benzophenonetetracarboxylic dianhydride and 5(6)-amino-1-(4'-aminophenyl)-1,3,3'-trimethylindane.

[0059] The porous carbon support was immersed in the aromatic PI solution, then pulled up at a speed of 10 mm / min, and then immersed in water to remove the solvent, and dried in a circulating hot air dryer to obtain a coated yarn in which the aromatic PI was coated on the surface of the porous carbon support. The coated yarn was then carbonized at 550°C in an inert atmosphere to produce a gas separation carbon membrane.

[0060] One hundred of the above gas separation carbon membranes were bundled and housed in an acrylic pipe (inner diameter 5 mm) with an inlet and outlet for the gas to be separated, and one end of the acrylic pipe was statically potted with epoxy resin. After the epoxy resin hardened, the potted portion at one end was cut with a rotary saw to open the fluid separation membrane, and a gas separation carbon membrane module of Production Example 1 was obtained.

[0061] (Production Example 2) Twenty polymer membranes sampled from a polymer membrane module (UBE Corporation, NM-B01) were bundled and housed in an acrylic pipe (inner diameter 5 mm) with an inlet and outlet for the gas to be separated, and one end of the acrylic pipe was statically potted with epoxy resin. After the epoxy resin hardened, the potted portion at one end was cut with a rotary saw to open the fluid separation membrane, and a gas separation carbon membrane module of Production Example 2 was obtained.

[0062] Example 1 Pipes were connected so that the mixed gas could be supplied to the inlet of the fluid to be separated of the gas separation membrane module of Production Example 1 from the gas cylinders of CH4, which is a low permeable gas, and CO2, which is a high permeable gas, via a mass flow controller and a humidity control mechanism, and the gas separation membrane module and the pipes that required heat retention were placed in a thermostatic chamber. The set temperature of the thermostatic chamber was 70°C, the non-permeation side pressure of the gas separation membrane module was 0.5 MPa, the permeation side pressure was 1 atm, and the partial pressures of the gas to be separated flowing into the gas separation membrane were controlled to CH4: 0.3 MPa, CO2: 0.2 MPa, and water vapor (H2O): 20 kPa (total pressure 0.5 MPa conversion), respectively, to separate gases by the gas separation method of Example 1. As a result of evaluation by the above-mentioned method, the ratio of water vapor partial pressure to the high permeation gas partial pressure of the gas separation method of Example 1 was 10%, the CO2 permeation amount was 18.0 mL / min, and the gas separation property was "excellent".

[0063] Example 2 Gas was separated by the gas separation method of Example 2 in the same manner as in Example 1, except that the set temperature of the thermostatic chamber was changed from 70°C to 90°C, and the water vapor partial pressure of the gas to be separated flowing into the gas separation membrane was changed from 20 kPa (converted to a total pressure of 0.5 MPa) to 60 kPa (converted to a total pressure of 0.5 MPa). As a result of evaluation by the above-mentioned method, the ratio of the water vapor partial pressure to the high permeable gas partial pressure of the gas separation method of Example 2 was 30%, the CO2 permeation amount was 26.9 mL / min, and the gas separation property was "excellent."

[0064] Example 3 Gas was separated by the gas separation method of Example 3 in the same manner as in Example 1, except that the set temperature of the thermostatic chamber was changed from 70°C to 120°C, and the water vapor partial pressure of the gas to be separated flowing into the gas separation membrane was changed from 20 kPa (converted to a total pressure of 0.5 MPa) to 60 kPa (converted to a total pressure of 0.5 MPa). As a result of evaluation by the above-mentioned method, the ratio of the water vapor partial pressure to the high permeable gas partial pressure in the gas separation method of Example 3 was 30%, the CO2 permeation amount was 40.5 mL / min, and the gas separation property was "good".

[0065] Example 4 Gas was separated by the gas separation method of Example 4 in the same manner as in Example 1, except that the gas separation membrane module of Production Example 2 was used instead of the gas separation membrane module of Production Example 1. As a result of evaluation by the above-mentioned method, the ratio of water vapor partial pressure to the high permeable gas partial pressure in the gas separation method of Example 4 was 10%, the CO2 permeation rate was 21.8 mL / min, and the gas separation property was "good."

[0066] Example 5 Gas was separated by the gas separation method of Example 5 in the same manner as in Example 3, except that the gas separation membrane module of Production Example 2 was used instead of the gas separation membrane module of Production Example 1. As a result of evaluation by the above-mentioned method, the ratio of water vapor partial pressure to the high permeable gas partial pressure in the gas separation method of Example 5 was 30%, the CO2 permeation rate was 31.3 mL / min, and the gas separation performance was "fair."

[0067] Example 6 The temperature of the thermostatic bath was changed from 70°C to 150°C, the non-permeation side pressure of the gas separation membrane module was changed from 0.5MPa to 5MPa, and the partial pressures of the gases to be separated flowing into the gas separation membrane were changed from 0.3MPa to 3MPa for CH4, 0.2MPa to 2MPa for CO2, and 20kPa (total pressure of 0.5MPa equivalent) to 20kPa (total pressure of 5MPa equivalent) for water vapor (H2O). The gas was separated in the same manner as in Example 1 by the gas separation method of Example 6. As a result of evaluation by the above-mentioned method, the ratio of water vapor partial pressure to the high permeation gas partial pressure of the gas separation method of Example 6 was 1%, the CO2 permeation amount was 690mL / min, and the gas separation property was "fair".

[0068] Example 7 Gas was separated by the gas separation method of Example 7 in the same manner as in Example 6, except that the water vapor partial pressure of the gas to be separated flowing into the gas separation membrane was changed from 20 kPa (equivalent to a total pressure of 5 MPa) to 200 kPa (equivalent to a total pressure of 5 MPa). As a result of evaluation by the above-mentioned method, the ratio of the water vapor partial pressure to the high permeable gas partial pressure of the gas separation method of Example 7 was 10%, the CO2 permeation amount was 780 mL / min, and the gas separation property was "good".

[0069] Comparative Example 1 Gas was separated by the gas separation method of Comparative Example 1 in the same manner as in Example 1, except that the water vapor partial pressure of the gas to be separated flowing into the gas separation membrane was changed from 20 kPa (equivalent to a total pressure of 0.5 MPa) to 5 kPa (equivalent to a total pressure of 0.5 MPa). As a result of evaluation by the above-mentioned method, the ratio of the water vapor partial pressure to the high permeable gas partial pressure of the gas separation method of Comparative Example 1 was 2.5%, the CO2 permeation amount was 15.2 mL / min, and the gas separation property was "excellent."

[0070] Comparative Example 2 Gas was separated by the gas separation method of Comparative Example 2 in the same manner as in Example 1, except that the set temperature of the thermostatic chamber was changed from 70°C to 90°C, and the water vapor partial pressure of the gas to be separated flowing into the gas separation membrane was changed from 20 kPa (converted to a total pressure of 0.5 MPa) to 5 kPa (converted to a total pressure of 0.5 MPa). As a result of evaluation by the above-mentioned method, the ratio of the water vapor partial pressure to the high permeable gas partial pressure in the gas separation method of Comparative Example 2 was 2.5%, the CO2 permeation amount was 23.1 mL / min, and the gas separation property was "good."

[0071] Comparative Example 3 Gas was separated by the gas separation method of Comparative Example 3 in the same manner as in Example 1, except that the set temperature of the thermostatic chamber was changed from 70°C to 120°C, and the water vapor partial pressure of the gas to be separated flowing into the gas separation membrane was changed from 20 kPa (converted to a total pressure of 0.5 MPa) to 5 kPa (converted to a total pressure of 0.5 MPa). As a result of evaluation by the above-mentioned method, the ratio of water vapor partial pressure to the high permeable gas partial pressure of the gas separation method of Comparative Example 3 was 2.5%, the CO2 permeation amount was 33.6 mL / min, and the gas separation ability was "fair."

[0072] Comparative Example 4 Gas was separated by the gas separation method of Comparative Example 4 in the same manner as in Comparative Example 1, except that the gas separation membrane module of Production Example 2 was used instead of the gas separation membrane module of Production Example 1. As a result of evaluation by the above-mentioned method, the ratio of water vapor partial pressure to the high permeable gas partial pressure in the gas separation method of Comparative Example 4 was 2.5%, the CO2 permeation amount was 18.3 mL / min, and the gas separation property was "good."

[0073] Comparative Example 5 Gas was separated by the gas separation method of Comparative Example 5 in the same manner as in Comparative Example 3, except that the gas separation membrane module of Production Example 2 was used instead of the gas separation membrane module of Production Example 1. As a result of evaluation by the above-mentioned method, the ratio of water vapor partial pressure to the high permeable gas partial pressure in the gas separation method of Comparative Example 5 was 2.5%, the CO2 permeation rate was 29.9 mL / min, and the gas separation performance was "unacceptable."

[0074] Comparative Example 6 The temperature of the thermostatic bath was changed from 70°C to 150°C, the non-permeation side pressure of the gas separation membrane module was changed from 0.5MPa to 5MPa, and the partial pressures of the gases to be separated flowing into the gas separation membrane were changed from 0.3MPa to 3MPa for CH4, 0.2MPa to 2MPa for CO2, and 20kPa (total pressure of 0.5MPa equivalent) to 5kPa (total pressure of 5MPa equivalent) for water vapor (H2O). The gas was separated in the same manner as in Example 1 by the gas separation method of Comparative Example 6. As a result of evaluation by the above-mentioned method, the ratio of water vapor partial pressure to the high permeation gas partial pressure of the gas separation method of Comparative Example 6 was 0.25%, the CO2 permeation amount was 630mL / min, and the gas separation property was "fair".

[0075] [Table 1] [Explanation of symbols]

[0076] 1: Gas separation system 2: Gas separation membrane module 3: Gas separation membrane 4: Humidification mechanism 5: Boost mechanism 10: Gas to be separated 11: Permeable gas 12: Non-permeable gas [Industrial Applicability]

[0077] INDUSTRIAL APPLICABILITY The gas separation method and gas separation apparatus of the present invention can be suitably used in carbon dioxide separation and storage systems for exhaust gases from power plants, blast furnaces, etc., purification of biogas and natural gas, purification of purified gas after steam methane reforming, etc.

Claims

1. A gas separation method in which a gas to be separated, which contains water vapor, a high permeability gas, and a low permeability gas, is supplied to a gas separation membrane module and separated into water vapor, a permeability gas in which the high permeability gas is concentrated, and a non-permeability gas in which the low permeability gas is concentrated, wherein the partial pressure of water vapor in the gas to be separated is 20 kPa or more and 1 MPa or less.

2. 2. The gas separation method according to claim 1, wherein the gas to be separated contains a highly permeable gas having a kinetic diameter of 0.25 nm or more and 0.35 nm or less.

3. 3. The gas separation method according to claim 2, wherein the highly permeable gas is carbon dioxide.

4. 2. The gas separation method according to claim 1, wherein the gas to be separated and the permeate gas flow in parallel.

5. 2. The gas separation method according to claim 1, wherein the partial pressure of water vapor relative to the partial pressure of the highly permeable gas in the gas to be separated is 5% or more and 50% or less.

6. 2. The gas separation method according to claim 1, wherein the total pressure on the permeation side of the gas separation membrane module is 0.01 MPa or more and 0.15 MPa or less.

7. 2. The gas separation method according to claim 1, further comprising a step of humidifying the gas to be separated before being supplied to the gas separation membrane module.

8. 2. The gas separation system according to claim 1, further comprising a step of pressurizing the gas to be separated before being supplied to the gas separation membrane module.

9. 9. The gas separation method according to claim 8, wherein the compression ratio of the fluid to be separated before and after the pressure increase is 1.5 times or more and 100 times or less.

10. 9. The gas separation method according to claim 8, wherein the humidity of the gas to be separated after the pressure increase is 50 RH % or more and 95 RH % or less.

11. The gas separation method according to any one of claims 1 to 10, wherein the gas separation membrane housed in the gas separation membrane module is an inorganic membrane.

12. 12. The gas separation method according to claim 11, wherein the inorganic membrane is a carbon membrane.

13. 13. The gas separation method according to claim 12, wherein the gas to be separated further contains 100 ppm to 30% of hydrocarbons having a carbon number of 2 to 8.

14. 13. The gas separation method according to claim 12, wherein the gas to be separated is selected from the group consisting of natural gas, biogas, and exhaust gas.

15. 15. The gas separation method according to claim 14, wherein the temperature of the natural gas from when it is ejected until when it is supplied to the gas separation membrane module is 60° C. or higher and 200° C. or lower.

16. A purified fluid, characterized in that it is purified by the gas separation method according to claim 12.

17. A gas separation apparatus including a humidification mechanism and a gas separation membrane module, A gas separation apparatus comprising a means for supplying the gas to be separated humidified by the humidification mechanism to a gas separation membrane.

18. 18. The gas separation apparatus according to claim 17, wherein the gas separation membrane housed in the gas separation membrane module is a carbon membrane.

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