Method for concentrating carbon dioxide and apparatus for concentrating carbon dioxide

Abstract

This invention provides a method for concentrating CO2 using a CO2 separation membrane, which allows the separation performance of the CO2 separation membrane to be maintained for a long period of time. [Solution] A method for concentrating carbon dioxide, comprising concentrating carbon dioxide from a gas mixture containing carbon dioxide using a CO2 separation membrane including a separation functional layer, A method for concentrating carbon dioxide, wherein the gas mixture contains ammonia.

Description

[Technical Field]

[0001] This invention relates to a method for concentrating carbon dioxide and a carbon dioxide concentration apparatus. [Background technology]

[0002] From the perspective of preventing global warming, development is underway to remove greenhouse gases containing carbon dioxide (CO2), such as exhaust gases. Furthermore, development is also underway to concentrate the removed CO2 so that it can be utilized in other fields such as agriculture.

[0003] Among the methods for removing and concentrating CO2 from the aforementioned gas mixture, a membrane separation method using a CO2 separation membrane is known as a method that is excellent in terms of energy consumption and cost, and can efficiently remove and concentrate CO2 (Patent Documents 1 and 2, Non-Patent Document 1).

[0004] Furthermore, Patent Document 2 states that the gas mixture derived from exhaust gas contains nitrogen oxides (NOx). x ) is included, and the NO x It is stated that the CO2 separation membrane deteriorates as a result, and the separation performance decreases. Here, the NO x As a method to prevent deterioration caused by NO, Patent Document 2 describes a method of pre-treating the gas mixture by, for example, an SCR treatment using a denitrification apparatus such as a selective catalytic reduction denitrification (SCR) apparatus before applying it to a CO2 separation membrane. x A method for removing it is disclosed. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] International Publication No. 2024 / 014285 Brochure [Patent Document 2] Japanese Patent Publication No. 2023-122497 [Non-patent literature]

[0006] [Non-Patent Document 1] Tanaka, Manabu, "Gas Separation Using Polymer Membranes": Chemistry and Education, Vol. 65, No. 12 (2017), pp. 630-631. [Overview of the project] [Problems that the invention aims to solve]

[0007] However, the NO described in Patent Document 2 x Conventional CO2 concentration methods, including methods for removing NO, x There was a problem in that the removal of the substance was insufficient, which could not prevent the aforementioned deterioration and potentially prevent the CO2 separation performance from being maintained for a long period of time.

[0008] The object of the present invention is to prevent the aforementioned deterioration while avoiding the aforementioned problems. In other words, the object of the present invention is to provide a method for concentrating CO2 using a CO2 separation membrane that can maintain the separation performance of the CO2 separation membrane for a long period of time by preventing the aforementioned deterioration. [Means for solving the problem]

[0009] As a result of diligent research, the inventors have discovered, surprisingly, that the aforementioned problem can be solved when ammonia (NH3) is included in the gas mixture fed to the CO2 separation membrane in a method for concentrating CO2 using a CO2 separation membrane, and have completed the present invention.

[0010] To solve the aforementioned problems, a carbon dioxide concentration method according to one aspect of the present invention is a carbon dioxide concentration method that concentrates carbon dioxide from a gas mixture containing carbon dioxide using a CO2 separation membrane including a separation functional layer, wherein the gas mixture contains ammonia. [Effects of the Invention]

[0011] According to an embodiment of the present invention, the separation performance of the CO2 separation membrane can be maintained for a long time. Therefore, according to an embodiment of the present invention, CO2 can be concentrated from a gas mixture containing CO2 over a long period of time.

Brief Description of the Drawings

[0012] [Figure 1] It is a schematic diagram showing the configuration of a carbon dioxide concentration device used in Examples and Comparative Examples.

Embodiments for Carrying Out the Invention

[0013] An embodiment of the present invention will be described below, but the present invention is not limited to the following embodiments. The present invention can be variously modified within the scope shown in the claims, and embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

[0014] [Embodiment 1: Carbon Dioxide Concentration Method] A carbon dioxide concentration method according to an embodiment of the present invention is a carbon dioxide concentration method for concentrating carbon dioxide from a gas mixture containing carbon dioxide using a CO2 separation membrane including a separation functional layer, wherein the gas mixture contains ammonia. Hereinafter, the carbon dioxide concentration method according to an embodiment of the present invention will also be referred to as "this concentration method".

[0015] Here, the gas mixture that is the target of the carbon dioxide concentration method is usually a gas mixture derived from exhaust gas or the like, and in addition to carbon dioxide (CO2), nitrogen oxides (NO x ) such as nitrogen dioxide (NO2), water (water vapor) (H2O), oxygen (O2), etc. are included.

[0016] In addition, in a method for concentrating carbon dioxide using a conventional carbon dioxide separation membrane, the presumed mechanism of deterioration of the carbon dioxide separation membrane will be described below. In the above method, when nitrogen dioxide in the gas mixture comes into contact with the carbon dioxide separation membrane, the carbon dioxide separation membrane exhibits a function like a catalyst, and the nitrogen dioxide changes into activated nitrogen dioxide. Subsequently, the activated nitrogen dioxide reacts with water to generate nitric acid (HNO3). Due to the presence of the nitric acid, for example, reactions such as acid hydrolysis occur to alter or decompose the constituent substances of the carbon dioxide separation membrane, and it is presumed that the carbon dioxide separation membrane deteriorates. Furthermore, it is also conceivable that the activated nitrogen dioxide radicalizes the constituent substances of the carbon dioxide separation membrane. In this case, when the radicalized constituent substances react with components in the gas mixture such as O2, reactions occur to alter or decompose the constituent substances, and it is also presumed that the carbon dioxide separation membrane deteriorates.

[0017] On the other hand, the presumed mechanism for preventing the deterioration of the carbon dioxide separation membrane by this concentration method will be described below. In this concentration method, since ammonia is contained in the gas mixture, nitrogen dioxide in contact with the carbon dioxide separation membrane reacts with the ammonia. Or the nitrogen dioxide reacts with water and ammonia. In this case, the nitrogen dioxide is reduced or neutralized to produce ammonium nitrate (NH4NO3). As a result, since the nitrogen dioxide is deactivated, nitric acid is not generated, and the constituent substances are not radicalized either. According to this concentration method, it is presumed that the above deterioration is prevented by such a mechanism. In this concentration method, nitrogen dioxide that is not in contact with the carbon dioxide separation membrane has low reactivity and thus does not react with other gases such as ammonia contained in the gas mixture.

[0018] From the above matters, according to this concentration method, since the deterioration of the carbon dioxide separation membrane can be prevented, the separation performance of the carbon dioxide separation membrane can be maintained for a long time, and it is considered that carbon dioxide can be concentrated from a gas mixture containing carbon dioxide over a long period. Note that this concentration method is different from the method for removing NO described in Patent Document 2. x Without removing NO x Without removing NO xThis method is unique in that it prevents the aforementioned deterioration by reducing its reactivity, and therefore differs from conventional methods for preventing deterioration.

[0019] (CO2 separation membrane) The CO2 separation membrane in one embodiment of the present invention is not particularly limited as long as it includes a separation functional layer and is a membrane capable of selectively separating CO2. As the CO2 separation membrane, for example, a CO2 separation membrane commonly used to concentrate carbon dioxide from a gas mixture containing carbon dioxide can be used.

[0020] <Separation functional layer> In one embodiment of the present invention, the CO2 separation membrane includes a separation functional layer. The separation functional layer is a layer that can preferentially permeate carbon dioxide, which is the gas to be concentrated and contained in the gas mixture targeted by this concentration method. Typically, the separation functional layer may be a dense layer in which no holes can be observed using an electron microscope (SEM) at a magnification of 5000x; in other words, it may be a non-porous layer.

[0021] In one embodiment of the present invention, a thin separation functional layer is preferable from the viewpoint of improving the permeability of the CO2 separation membrane and concentrating carbon dioxide more efficiently. From this viewpoint, the thickness of the separation functional layer is preferably 300 nm or less, more preferably 150 nm or less, and even more preferably 100 nm or less. On the other hand, a thicker separation functional layer is preferable from the viewpoint of further preventing the deterioration of the CO2 separation membrane, maintaining separation performance for a longer period of time, and concentrating carbon dioxide from a gas mixture containing carbon dioxide for a longer period of time. From this viewpoint, the thickness of the separation functional layer is preferably 10 nm or more, and more preferably 100 nm or more.

[0022] In this specification, the thickness of the separation functional layer can be measured, for example, by the following method. First, a method is to observe a cross-section of the CO2 separation membrane with a scanning electron microscope. Using the obtained electron microscope image, the distance between a pair of opposing main surfaces of the separation functional layer is measured at a plurality of arbitrary points. Specifically, these arbitrary points may be at least two points. The average value of the distance between the pair of main surfaces at the obtained plurality of points is calculated, and this average value is taken as the thickness of the separation functional layer.

[0023] In one embodiment of the present invention, the separation functional layer may be a dissolution diffusion membrane. A dissolution diffusion membrane is a membrane that allows gas molecules to permeate through a mechanism in which gas molecules dissolve on the membrane surface on the side to which the gas mixture is supplied, diffuse through the inside of the membrane, and then desorb from the membrane surface on the side from which the gas molecules permeate. Dissolution diffusion membranes are usually membranes made of polymers. Dissolution diffusion membranes can generally selectively and efficiently permeate only the target gas molecules. Therefore, it is preferable for the separation functional layer to be a dissolution diffusion membrane from the viewpoint of more efficiently concentrating carbon dioxide by this concentration method.

[0024] It is known that dissolved diffusion membranes are prone to deterioration because nitrogen oxides come into contact with them and diffuse through their interior, making the nitrogen oxides more likely to react with the membrane's constituent materials. However, according to this concentration method, as shown in the estimated mechanism for preventing deterioration of the CO2 separation membrane described above, the nitrogen oxides that come into contact with the dissolved diffusion membrane and diffuse through its interior are deactivated, making it difficult for the nitrogen oxides to react with the membrane's constituent materials. Therefore, even when a dissolved diffusion membrane is used as the separation functional layer, this deterioration can be prevented.

[0025] In one embodiment of the present invention, the substance contained in the separation functional layer, that is, the substance constituting the separation functional layer, is not particularly limited, and a general substance constituting the separation functional layer can be used. In one embodiment of the present invention, the separation functional layer may contain an organic substance, preferably an organic substance having an amide bond, and more preferably a polyether block amide copolymer. The inclusion of an organic substance having an amide bond, particularly a polyether block amide copolymer, in the separation functional layer is preferable from the viewpoint of achieving both CO2 selectivity and strength in the separation functional layer. When selectivity and strength are achieved together, CO2 can be concentrated more efficiently by this concentration method, and the CO2 separation membrane is less likely to be damaged.

[0026] In one embodiment of the present invention, if the separation functional layer contains organic matter, the content of the organic matter may be, for example, 50% or more by weight, 60% or more by weight, 70% or more by weight, 80% or more by weight, 90% or more by weight, and 95% or more by weight, relative to the total weight of the separation functional layer. Furthermore, if the separation functional layer contains organic matter, the separation functional layer may be substantially composed solely of the organic matter.

[0027] If the separation functional layer contains an organic substance having an amide bond, the content thereof may be the same as the content of the organic substance. If the separation functional layer contains a polyether block amide copolymer, the content thereof may be the same as the content of the organic substance.

[0028] <Base material> In one embodiment of the present invention, the CO2 separation membrane may include a substrate that supports the separation functional layer. From the viewpoint of improving the permeability of the CO2 separation membrane, the substrate is preferably a porous substrate, and more preferably has continuous pores formed in a three-dimensional manner. The porous support may have independent pores, or may have both continuous pores and independent pores. The porous support may also have through pores that penetrate the porous support.

[0029] In one embodiment of the present invention, the substance constituting the base material is not particularly limited. The substance may be an organic substance. Examples of the substance include polyethylene, polypropylene, polyamide, polysulfone, polyacrylonitrile, and the like.

[0030] In one embodiment of the present invention, the thickness of the substrate is not particularly limited. For example, the lower limit of the substrate thickness may be, for example, 1 μm or more, 10 μm or more, 20 μm or more, 30 μm or more, 40 μm or more, and even 50 μm or more. The upper limit of the substrate thickness may be, for example, 300 μm or 100 μm. It is preferable for the substrate thickness to be greater than or equal to the lower limit from the viewpoint of improving the strength of the CO2 separation membrane. It is also preferable for the substrate thickness to be less than or equal to the upper limit from the viewpoint of improving the permeability of the CO2 separation membrane. The thickness of the substrate can be measured by the same method as the method for measuring the thickness of the separation functional layer described above.

[0031] <Support layer> In one embodiment of the present invention, the CO2 separation membrane may include a support layer that is in direct contact with the separation functional layer or the substrate and reinforces the strength of the CO2 separation membrane. The support layer is not particularly limited as long as it is a layer that can reinforce the strength of the CO2 separation membrane, and may be, for example, a nonwoven fabric.

[0032] The material constituting the support layer is not particularly limited. The material may be an organic substance. Examples of such materials include polyethylene terephthalate (PET), polyethylene, polypropylene, and the like.

[0033] In one embodiment of the present invention, the thickness of the support layer is not particularly limited. The lower limit of the thickness of the support layer is, for example, 1 μm or more, and may be 10 μm or more, 20 μm or more, 30 μm or more, 40 μm or more, or even 50 μm or more. The upper limit of the thickness of the support layer may be, for example, 300 μm or 100 μm. That the thickness of the support layer is not less than the lower limit value is preferable from the viewpoint of improving the strength of the CO2 separation membrane. Also, that the thickness of the support layer is not more than the upper limit value is preferable from the viewpoint of improving the permeability of the CO2 separation membrane. The thickness of the support layer can be measured by the same method as the method for measuring the thickness of the separation functional layer described above.

[0034] <Properties of CO2 separation membrane> In one embodiment of the present invention, from the viewpoint of improving strength, the thickness of the entire CO2 separation membrane is preferably 1 μm or more, more preferably 10 μm or more, 20 μm or more, 30 μm or more, or 40 μm or more, and even more preferably 50 μm or more. From the viewpoint of improving permeability, the thickness of the entire CO2 separation membrane is preferably 300 μm or less, and more preferably 100 μm or less. The thickness of the entire CO2 separation membrane can be measured by the same method as the method for measuring the thickness of the separation functional layer described above. Also, for example, by previously measuring the thicknesses of the members constituting the CO2 separation membrane, such as the separation functional layer, the base material, and the support layer, and summing the respective thicknesses of the members, the thickness of the entire CO2 separation membrane can also be measured.

[0035] <Method for manufacturing CO2 separation membrane> In one embodiment of the present invention, the method for manufacturing the CO2 separation membrane is not particularly limited, and examples thereof include a method of using the separation functional layer itself as the CO2 separation membrane, and a method of laminating the separation functional layer, the base material, and / or the support layer. Here, the separation functional layer, the base material, and the support layer can be prepared by known methods. Also, commercially available products having predetermined properties such as a predetermined thickness can be used as the separation functional layer, the base material, and the support layer.

[0036] (Gaseous mixture) In one embodiment of the present invention, the gas mixture includes carbon dioxide. In one embodiment of the present invention, the gas mixture means the gas mixture immediately before being subjected to the CO2 separation membrane. In other words, it is sufficient that the gas mixture subjected to and passing through the CO2 separation membrane contains carbon dioxide, and this concentration method may include a step of preparing the gas mixture before it is subjected to the CO2 separation membrane.

[0037] In this concentration method, the gas mixture contains ammonia. Therefore, the gas mixture further contains ammonia in addition to carbon dioxide. This concentration method, with its configuration, prevents the deterioration of the CO2 separation membrane as shown in the estimated mechanism for preventing the deterioration of the CO2 separation membrane described above. Therefore, this concentration method can maintain the separation performance of the CO2 separation membrane for a long period of time and concentrate CO2 from the gas mixture containing CO2 for a longer period of time. From the viewpoint of concentrating CO2 for a longer period of time, a higher concentration of ammonia in the gas mixture is preferable. From this viewpoint, the concentration is preferably 0.1 ppm by volume or more, more preferably 0.5 ppm by volume or more, and even more preferably 1 ppm by volume or more.

[0038] In this concentration method, from the viewpoint of improving the efficiency of carbon dioxide concentration, it is preferable that the concentration of ammonia in the gas mixture be below a predetermined value. From this viewpoint, the concentration of ammonia is preferably 100 ppm by volume or less, more preferably 50 ppm by volume or less, even more preferably 20 ppm by volume or less, even more preferably 10 ppm by volume or less, and particularly preferably 4 ppm by volume or less.

[0039] In one embodiment of the present invention, the gas mixture may use a gas derived from exhaust gas as the raw material gas for the gas mixture. Here, the exhaust gas and the gas derived from the exhaust gas generally include, in addition to carbon dioxide, nitrogen oxides such as NO2 (NO2). x), may contain O2 and H2O, etc. Therefore, the gas mixture is NO x It may further include the following. The gas mixture may further include O2 or H2O.

[0040] Furthermore, in this concentration method, the gas mixture is NO x Furthermore, if O2 and / or H2O are optionally included, the deterioration of the CO2 separation membrane can be prevented as shown in the estimated mechanism for preventing the deterioration of the CO2 separation membrane described above. Therefore, this concentration method can solve the problem of maintaining the separation performance of the CO2 separation membrane for a long period of time. In addition, in this concentration method, if the gas mixture is NO x If O2 and H2O are not present, the CO2 separation membrane does not deteriorate because the reaction that alters or decomposes the components of the CO2 separation membrane, as shown in the estimated mechanism for deterioration of the CO2 separation membrane described above, does not occur. Therefore, in this concentration method, the gas mixture is NO x The aforementioned problems can be solved even if O2 and H2O are not included.

[0041] In one embodiment of the present invention, the concentration method may include an ammonia concentration adjustment step of adjusting the ammonia concentration in the gas mixture to 0.1 ppm by volume or more and 100 ppm by volume or less. By including the ammonia concentration adjustment step, the concentration of ammonia in the gas mixture can be adjusted to the preferred range described above.

[0042] The ammonia concentration adjustment step may be a step of adjusting the ammonia concentration in the gas mixture to preferably 0.5 ppm by volume or more, more preferably 1 ppm by volume or more. By adjusting the ammonia concentration to above these lower limits, CO2 can be concentrated from the gas mixture containing CO2 over a longer period of time.

[0043] Furthermore, the ammonia concentration adjustment step may be a step of adjusting the ammonia concentration in the gas mixture to preferably 50 ppm by volume or less, more preferably 20 ppm by volume or less, even more preferably 10 ppm by volume or less, and particularly preferably 4 ppm by volume or less. By adjusting the ammonia concentration to be below these upper limits, the efficiency of carbon dioxide concentration can be further improved.

[0044] The process includes, for example, a step of regulating the supply amount of ammonia or urea by providing a member in a conduit that connects a conduit for supplying a gas mixture to a supply source of ammonia or urea, and adjusting the ammonia concentration in the gas mixture with the member. Examples of such members include a mass flow controller (MFC) and a control valve.

[0045] In one embodiment of the present invention, the ammonia concentration adjustment step may include an SCR treatment. That is, the concentration method may include, as the ammonia concentration adjustment step, a step of performing an SCR treatment on the raw material gas before providing the gas mixture to the CO2 separation membrane, in order to prepare a gas mixture in which the ammonia concentration is adjusted to a range of 0.1 volume ppm or more and 100 volume ppm or less. Since the SCR treatment may include a step of introducing ammonia into the raw material gas, the gas obtained by performing an SCR treatment on the raw material gas may be the gas mixture in which ammonia remains.

[0046] The concentration method may include a step of introducing ammonia or urea into the gas mixture in the ammonia concentration adjustment step.

[0047] Here, "introducing ammonia or urea into the gas mixture" means preparing the gas mixture by introducing ammonia or urea into the raw material gas. The raw material gas into which ammonia or urea is introduced may be the raw material gas after pretreatment such as SCR treatment.

[0048] If the ammonia concentration adjustment step includes a step of introducing urea into the raw material gas, this concentration method may also include a step of performing a treatment to produce ammonia from the urea. For example, this treatment may involve heating the urea at a temperature in the range of 100°C to 300°C.

[0049] [Embodiment 2: Carbon dioxide concentration device] A carbon dioxide concentration apparatus according to one embodiment of the present invention is a carbon dioxide concentration apparatus for carrying out the concentration method, comprising: a CO2 separation membrane including a separation functional layer; a member for supplying a gas mixture containing carbon dioxide to the CO2 separation membrane; a member for recovering the gas that has permeated the CO2 separation membrane and in which carbon dioxide has been concentrated; and an ammonia concentration adjustment member for controlling the concentration of ammonia in the gas mixture. Hereinafter, the carbon dioxide concentration apparatus according to one embodiment of the present invention will also be referred to as "the present concentration apparatus".

[0050] This concentration apparatus enables the implementation of this concentration method. Therefore, this concentration apparatus allows for the concentration of CO2 from a gaseous mixture containing CO2 over a long period of time.

[0051] (CO2 separation membrane) Regarding the "CO2 separation membrane" provided in this concentration device, the description of the "CO2 separation membrane" in the section [Embodiment 1: Method for concentrating carbon dioxide] above can be applied.

[0052] This concentration apparatus may include an evaluation cell that sandwiches the CO2 separation membrane. Here, the evaluation cell consists of a supply-side cell and a permeate-side cell, and the CO2 separation membrane is sandwiched between these two cells.

[0053] Furthermore, the evaluation cell is typically provided with a supply port, a supply outlet, and a permeate outlet. The supply port is an inlet for supplying the gas mixture. The supply outlet is an outlet for discharging the residual gas from which CO2 has been removed without passing through the CO2 separation membrane. The permeate outlet is an outlet for discharging the gas that has permeated the CO2 separation membrane, specifically the gas derived from the gas mixture and in which CO2 has been concentrated.

[0054] Furthermore, the concentration apparatus may include a member for adjusting the pressure difference between the pressure on the supply side of the CO2 separation membrane and the pressure on the permeate side of the CO2 separation membrane. Here, the pressure on the supply side of the CO2 separation membrane is, for example, the internal pressure of the supply-side cell constituting the evaluation cell. The pressure on the permeate side of the CO2 separation membrane is, for example, the internal pressure of the permeate-side cell constituting the evaluation cell. The member for adjusting the pressure difference is not particularly limited and may include, for example, a back pressure valve provided on the supply outlet side and / or a vacuum pump and control valve provided on the permeate outlet side. More specifically, the back pressure valve is a conduit connected to the supply outlet and equipped with a back pressure valve. More specifically, the vacuum pump and control valve are a conduit connected to a tank described later and equipped with a vacuum pump and a control valve.

[0055] (Component for supplying gas mixture) Regarding the "gas mixture" in this concentration apparatus, the description of the "gas mixture" in the section [Embodiment 1: Method for Concentrating Carbon Dioxide] above can be applied.

[0056] The concentration apparatus includes a component that supplies a gas mixture containing carbon dioxide to the CO2 separation membrane. The component that supplies the gas mixture is not particularly limited as long as it is a component that can supply the gas mixture to the CO2 separation membrane. Examples of the component that supplies the gas mixture include conduits. The conduit can be connected to the supply port. In other words, in the concentration method using the concentration apparatus, the gas mixture can be passed through the conduit and supplied to the CO2 separation membrane via the supply port. In addition, in the concentration method using the concentration apparatus, each component of the gas mixture may be introduced separately into the conduit, and the components may be mixed in the conduit to prepare the gas mixture.

[0057] The concentration apparatus may include components for controlling the flow rate when supplying the gas mixture and its constituent elements into the conduit. The components for controlling the flow rate are not particularly limited and include, for example, a mass flow controller (MFC) and a pump.

[0058] (A component for recovering concentrated carbon dioxide gas) The concentration apparatus includes a component for recovering the gas in which carbon dioxide has been concentrated after permeating the CO2 separation membrane. The component for recovering the gas in which carbon dioxide has been concentrated is not particularly limited as long as it can recover the gas in which carbon dioxide has been concentrated, and may be, for example, a conduit and a tank connected to the conduit. The conduit may be connected to the permeation outlet. For example, in the concentration method using the concentration apparatus, the gas in which carbon dioxide has been concentrated can be discharged from the permeation outlet into the conduit, pass through the conduit, and be recovered in the tank.

[0059] (Ammonia concentration adjusting component) This concentration apparatus includes an ammonia concentration adjusting member that controls the concentration of ammonia in the gas mixture. The ammonia concentration adjusting member, similar to the ammonia concentration adjustment step described above, is a member that adjusts the concentration of ammonia in the raw gas of the gas mixture to prepare a gas mixture in which the ammonia concentration is adjusted to a predetermined range. The predetermined range may be a preferred range for the ammonia concentration in the gas mixture described above.

[0060] The ammonia concentration adjusting member is not particularly limited as long as it can adjust the concentration of ammonia in the gas mixture, and may include, for example, a member for introducing ammonia or urea into the gas mixture. The member may be, for example, another conduit connecting the member supplying the gas mixture to a source of ammonia or urea when the member supplying the gas mixture is a conduit. The other conduit may be equipped with a member for adjusting the amount of ammonia or urea supplied from the source. Examples of such members include a mass flow controller (MFC) and a control valve. The source of ammonia or urea may be, for example, a tank for storing ammonia or urea. Here, "introducing ammonia or urea into the gas mixture" means preparing the gas mixture by introducing ammonia or urea into the raw material gas, as described in this concentration method. Here, as described in this concentration method, the raw material gas into which ammonia or urea is introduced may be raw material gas that has undergone pretreatment such as SCR treatment.

[0061] If the ammonia concentration adjustment member of this concentration apparatus includes a member for introducing urea into the raw material gas, it may also include, if necessary, a member for performing a process to generate ammonia from the urea. Examples of such a member for performing the process include a member for heating the gas containing urea, more specifically, a member for heating the gas containing urea at a temperature in the range of 100°C to 300°C. For example, a heater can be used as such a member.

[0062] (SCR device) The concentration apparatus may include an SCR apparatus. In this case, in the concentration method using the concentration apparatus, an SCR-treated gas mixture can be used as the gas mixture further containing ammonia in addition to carbon dioxide. The SCR-treated gas mixture may be a gas mixture in which the ammonia concentration is adjusted to a preferred range of the ammonia concentration in the aforementioned gas mixture, for example, 0.1 ppm by volume or more and 100 ppm by volume or less. The SCR apparatus may also be included in the ammonia concentration adjustment member. That is, the ammonia concentration adjustment member may include the SCR apparatus.

[0063] One embodiment of the present invention may be the inventions shown in [1] to

[14] below. [1] A method for concentrating carbon dioxide from a gas mixture containing carbon dioxide using a CO2 separation membrane that includes a separation functional layer, A method for concentrating carbon dioxide, wherein the gas mixture contains ammonia. [2] The method for concentrating carbon dioxide according to [1], wherein the concentration of ammonia in the gas mixture is 0.1 ppm by volume or more. [3] The method for concentrating carbon dioxide according to [2], wherein the concentration of ammonia in the gas mixture is 0.1 ppm by volume or more and 100 ppm by volume or less. [4] A method for concentrating carbon dioxide according to any one of [1] to [3], wherein the thickness of the separation functional layer is 10 nm or more and 300 nm or less. [5] The gas mixture is NO x A method for concentrating carbon dioxide as described in any one of [1] to [4], including the above. [6] A method for concentrating carbon dioxide according to any one of [1] to [5], wherein the gas mixture comprises O2 or H2O. [7] A method for concentrating carbon dioxide according to any one of [1] to [6], comprising an ammonia concentration adjustment step of adjusting the concentration of ammonia in the gas mixture to 0.1 ppm by volume or more and 100 ppm by volume or less. [8] The method for concentrating carbon dioxide according to [7], wherein the ammonia concentration adjustment step includes a step of introducing ammonia or urea into the gas mixture. [9] The method for concentrating carbon dioxide according to [7] or [8], wherein the ammonia concentration adjustment step includes an SCR treatment.

[10] A method for concentrating carbon dioxide according to any one of [1] to [9], wherein the separation functional layer is a dissolution diffusion membrane.

[11] The method for concentrating carbon dioxide according to any one of [1] to

[10] , wherein the separation functional layer contains organic matter. A carbon dioxide concentration apparatus for carrying out the carbon dioxide concentration method described in any one of

[12] [1] to

[11] , A CO2 separation membrane including a separation functional layer, A component that supplies a gas mixture containing carbon dioxide to the CO2 separation membrane, A component for recovering the gas that has permeated the CO2 separation membrane and is concentrated with carbon dioxide, An ammonia concentration adjusting member for controlling the ammonia concentration in the gas mixture, A carbon dioxide concentration device equipped with [a specific feature].

[13] The carbon dioxide concentration apparatus according to

[12] , wherein the ammonia concentration adjusting member is a member for introducing ammonia or urea into the gas mixture.

[14] The carbon dioxide concentration apparatus according to

[10] ,

[12] , or

[13] , wherein the thickness of the separation functional layer is 10 nm or more and 300 nm or less. [Examples]

[0064] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0065] [Measurement methods and evaluation methods] The methods for measuring the properties of the CO2 separation membranes used in the examples and comparative examples, and the methods for evaluating the carbon dioxide concentration methods in the examples and comparative examples are shown below.

[0066] (Thickness of the separation layer) The cross-sections in the thickness direction of the CO2 separation membranes used in the examples and comparative examples were observed at a magnification of 50,000x using a scanning electron microscope (manufacturer: Hitachi High-Tech Corporation, product name: S-4800), and electron microscope images of the cross-sections were obtained. Using the obtained electron microscope images, the distance between a pair of opposing main surfaces of the separation functional layer was measured at two points separated by 1 μm. The average of the two obtained measurement values ​​was calculated and defined as the thickness of the separation functional layer.

[0067] (transmission rate) The carbon dioxide permeation rate of the CO2 separation membranes used in the examples and comparative examples was measured by the method described below.

[0068] A circular CO2 separation membrane with a diameter (membrane diameter) of 35 mm was punched out to obtain a circular CO2 separation membrane '. The CO2 separation membrane ' was sandwiched between two cells, one serving as the supply cell and the other as the permeate cell, to create a measuring device consisting of the CO2 separation membrane ' and an evaluation cell sandwiching the CO2 separation membrane '. A supply port and a supply port were provided in the supply cell of the evaluation cell, and a permeate port was provided in the permeate cell of the evaluation cell. The CO2 supply source (supply tank) and the supply port were connected by a conduit. A mass flow controller (MFC) was installed in the conduit between the CO2 supply source and the confluence point, with a back pressure valve at the supply port and a flow meter at the permeate port.

[0069] Next, CO2 gas was supplied to the evaluation cell using the aforementioned measuring device. Furthermore, the pressure inside the supply cell, i.e., the supply pressure, was adjusted to 100 kPaG using a back pressure valve, and the permeation flow rate of the CO2 gas was measured using a flow meter to calculate the permeation velocity [GPU].

[0070] A transmission speed [GPU] of less than 500 GPU was rated as "poor," a speed between 500 GPU and 2000 GPU was rated as "acceptable," and a speed of 2000 GPU or more was rated as "good."

[0071] (Duration of separation performance) The duration of the separation performance of the CO2 separation membranes used in the examples and comparative examples was evaluated by the method described below.

[0072] In the examples described later, the permeation rates [GPU] for CO2 and N2, and the CO2 / N2 selectivity were calculated. The CO2 / N2 selectivity at the start of the evaluation was set as the baseline (100%), and the time until the CO2 / N2 selectivity decreased to 50% was evaluated as the maintenance time of separation performance.

[0073] [Manufacturing Example 1: Fabrication of CO2 Separation Membrane] A CO2 separation membrane was fabricated by laminating a separation functional layer (Pebax® polyether block amide copolymer, 50 nm thick), a porous substrate (polyacrylonitrile), and a PET nonwoven fabric as a reinforcing support layer in this order.

[0074] [Manufacturing Example 2: Fabrication of CO2 Separation Membrane] A CO2 separation membrane was fabricated using the same method as in Manufacturing Example 1, except that a separation functional layer with a thickness of 130 nm was prepared. This CO2 separation membrane is referred to as CO2 separation membrane B.

[0075] [Manufacturing Example 3: Fabrication of CO2 Separation Membranes] A CO2 separation membrane was fabricated using the same method as in Manufacturing Example 1, except that a separation functional layer with a thickness of 310 nm was prepared. This CO2 separation membrane is referred to as CO2 separation membrane C.

[0076] [Example 1] A carbon dioxide concentration apparatus was fabricated using CO2 separation membrane A, with the configuration shown in Figure 1. Figure 1 is a schematic diagram showing the configuration of the carbon dioxide concentration apparatus used in the examples and comparative examples. Specifically, CO2 separation membrane A was punched out into a circle with a diameter (membrane diameter) of 35 mm to obtain a circular CO2 separation membrane 11. The CO2 separation membrane 11 was sandwiched between two cells, one serving as the supply cell and the other as the permeate cell, to fabricate a separation apparatus consisting of the CO2 separation membrane 11 and an evaluation cell 12 sandwiching the CO2 separation membrane 11. A supply port 13 and a supply outlet 14 were provided in the supply cell of the evaluation cell 12, and a permeate outlet 15 was provided in the permeate cell of the evaluation cell 12. The evaluation cell 12 was placed in a constant temperature bath. The supply sources (supply tanks) for CO2, N2, N2+NO2, N2+NH3, and H2O (water vapor) were connected to the supply port 13 by conduits. At that time, each of the aforementioned conduits merged in front of the supply port 13 to form a single conduit, and this single conduit was connected to the supply port 13. In addition, a mass flow controller (MFC) was installed in each conduit between the respective supply sources of CO2, N2, N2+NO2, and N2+NH3 and the confluence point, and a pump 16 was installed in the conduit between the supply source of H2O (water vapor) and the confluence point. A back pressure valve 19 was installed at the supply outlet 14, and a conduit connected to a tank was connected to it. A conduit connected to a tank was connected to the permeate outlet 15, and this tank was connected to a conduit that was equipped with a control valve 18 and a vacuum pump 17 and connected to a GC (gas chromatography) system. Note that the vacuum pump 17 is closer to the GC than the control valve 18. A carbon dioxide concentration apparatus was manufactured using the above method. This carbon dioxide concentration apparatus is referred to as concentration apparatus A.

[0077] Next, the carbon dioxide concentration method was carried out by supplying gases O2, N2, N2+NO2, N2+NH3, and H2O (water vapor) using the concentration device A. The gases were mixed at the confluence point to prepare the gas mixture. The total flow rate of the gas mixture was 500 Nml / min (dry state). The flow rates of CO2, N2, N2+NO2, and N2+NH3 were adjusted by the MFC to ensure that the composition of each component of the gas mixture was as shown in Table 1 below. Furthermore, H2O (water vapor) was supplied using pump 16 so that the humidity of the gas mixture was 85%RH. In addition, the pressure in the supply-side cell, i.e., the supply pressure, was adjusted to 20 kPaG using the back pressure valve 19, and the pressure in the permeate-side cell, i.e., the permeate pressure, was adjusted to 10 kPaA using the control valve 18 and vacuum pump 17. Furthermore, the temperature inside the constant temperature bath was adjusted to 40°C. [Table 1] [Example 2] Concentrator B was prepared in the same manner as in Example 1, except that CO2 separation membrane B was used instead of CO2 separation membrane A. The carbon dioxide concentration method was carried out in the same manner as in Example 1, except that concentrateator B was used instead of concentrateator A.

[0078] [Comparative Example 1] Concentrator A was prepared using the same method as in Example 1. Using concentrateator A, the carbon dioxide concentration method was carried out using the same method as in Example 1, except for the points described below. - Instead of supplying N2+NH3 gas, the flow rates of CO2, N2, and N2+NO2 were adjusted by an MFC (Microfiltration Converter) to ensure that the composition of the CO2, N2, and NO2 components of the gas mixture was as shown in Table 2 below. [Table 2] [Comparative Example 2] Concentrator C was prepared in the same manner as in Example 1, except that CO2 separation membrane C was used instead of CO2 separation membrane A. The carbon dioxide concentration method was carried out in the same manner as in Comparative Example 1, except that concentrator C was used instead of concentrator A.

[0079] [result] Table 3 below shows the thickness of the separation functional layer and the concentration of ammonia in the gas mixture used in Examples 1 and 2 and Comparative Examples 1 and 2, as well as the permeation rate of the CO2 separation membrane and the maintenance time of separation performance, which were measured and evaluated using the method described above. In Table 3, the concentration of ammonia in the gas mixture is simply written as "ammonia concentration". Also, "None" in Table 3 means that no ammonia is contained in the gas mixture and its concentration is 0 ppm by volume. [Table 3] As described in Examples 1 and 2, and as shown in Tables 1 and 3, the carbon dioxide concentration methods of Examples 1 and 2 satisfy the following requirements (i) and (ii), and therefore qualify as the present concentration method. (i) Carbon dioxide is concentrated from a gas mixture containing carbon dioxide using a CO2 separation membrane that includes a separation function layer. (ii) The process includes a step of adjusting the concentration of ammonia in the gas mixture to 0.1 ppm by volume or more and 100 ppm by volume or less.

[0080] On the other hand, as described in Comparative Examples 1 and 2, and as shown in Tables 2 and 3, the carbon dioxide concentration methods of Comparative Examples 1 and 2 do not satisfy the requirements of (ii) above, and therefore do not fall under the category of this concentration method.

[0081] As shown in Table 3, the carbon dioxide concentration methods of Examples 1 and 2 maintain the separation performance of the CO2 separation membrane for a longer period compared to the carbon dioxide concentration methods of Comparative Examples 1 and 2.

[0082] Therefore, it was found that this concentration method can maintain the separation performance of the CO2 separation membrane for a long period of time by preventing the aforementioned deterioration of the CO2 separation membrane, and as a result, carbon dioxide can be concentrated from a gas mixture containing carbon dioxide over a long period of time. Furthermore, since this concentration apparatus can implement this concentration method, carbon dioxide can be concentrated from a gas mixture containing carbon dioxide over a long period of time. [Industrial applicability]

[0083] According to one embodiment of the present invention, carbon dioxide can be concentrated from a gas mixture containing carbon dioxide over a long period of time. Therefore, one embodiment of the present invention can be applied to a method for removing carbon dioxide from a gas mixture containing carbon dioxide, such as exhaust gas, and a method for utilizing the removed carbon dioxide in other fields such as agriculture. [Explanation of Symbols]

[0084] 11 CO2 separation membrane 12 evaluation cells 13 Supply port 14 Supply outlet 15 Transmission outlet 16 pumps 17 Vacuum pump 18 Control valve 19 Back pressure valve

Claims

1. CO2 containing the separation function layer ２ A method for concentrating carbon dioxide, comprising concentrating carbon dioxide from a gas mixture containing carbon dioxide using a separation membrane, A method for concentrating carbon dioxide, wherein the gas mixture contains ammonia.

2. The method for concentrating carbon dioxide according to claim 1, wherein the concentration of ammonia in the gas mixture is 0.1 ppm by volume or more.

3. The method for concentrating carbon dioxide according to claim 2, wherein the concentration of ammonia in the gas mixture is 0.1 ppm by volume or more and 100 ppm by volume or less.

4. The method for concentrating carbon dioxide according to claim 1, wherein the thickness of the separation functional layer is 10 nm or more and 300 nm or less.

5. The aforementioned gas mixture is NO ｘ A method for concentrating carbon dioxide according to claim 1, comprising:

6. The aforementioned gas mixture is O ２ or H ２ A method for concentrating carbon dioxide according to claim 1, comprising O.

7. The method for concentrating carbon dioxide according to claim 1, comprising an ammonia concentration adjustment step of adjusting the concentration of ammonia in the gas mixture to 0.1 volume ppm or more and 100 volume ppm or less.

8. The method for concentrating carbon dioxide according to claim 7, wherein the ammonia concentration adjustment step includes a step of introducing ammonia or urea into the gas mixture.

9. The method for concentrating carbon dioxide according to claim 7, wherein the ammonia concentration adjustment step includes SCR treatment.

10. The method for concentrating carbon dioxide according to claim 1, wherein the separation functional layer is a dissolution diffusion membrane.

11. The method for concentrating carbon dioxide according to claim 1, wherein the separation functional layer contains organic matter.

12. A carbon dioxide concentration apparatus for carrying out the carbon dioxide concentration method according to any one of claims 1 to 11, CO2 containing the separation function layer ２ Separation membrane and The aforementioned CO ２ A component that supplies a gas mixture containing carbon dioxide to the separation membrane, The aforementioned CO ２ A component that recovers the gas that has permeated the separation membrane and in which carbon dioxide has been concentrated, An ammonia concentration adjusting member for controlling the ammonia concentration in the gas mixture, A carbon dioxide concentration device equipped with [a specific feature].

13. The carbon dioxide concentration apparatus according to claim 12, wherein the ammonia concentration adjusting member includes a member for introducing ammonia or urea into the gas mixture.

14. The carbon dioxide concentration apparatus according to claim 12, wherein the thickness of the separation functional layer is 10 nm or more and 300 nm or less.

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