Carbon dioxide separation membrane

Abstract

To provide a carbon dioxide separation membrane which can efficiently recover carbon dioxide from mixed gas containing carbon dioxide in a low concentration.SOLUTION: A carbon dioxide separation membrane 1 includes a porous base material 11, a protective layer 12 provided on a surface of the base material 11 and having a higher density than the base material 11, and a separation layer 13 provided on a surface of the protective layer 12 and containing a substance having high affinity with carbon dioxide. The thickness of the protective layer 12 is 15 nm or less, and the thickness of the separation layer 13 is 300 nm or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a carbon dioxide separation membrane. [Background technology]

[0002] A method for separating and recovering carbon dioxide from a mixed gas using a separation membrane is known. Patent Document 1 discloses a carbon dioxide separation membrane including a polymer resin and a separation layer in which an organic liquid having a high affinity for carbon dioxide is immobilized in the polymer resin. The carbon dioxide separation membrane disclosed in Patent Document 1 has a separation layer having a high affinity for carbon dioxide, and therefore can selectively separate carbon dioxide from a mixed gas. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2013 / 180218 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, there has been a demand for selective and highly efficient recovery of carbon dioxide from mixed gases containing low concentrations of carbon dioxide, such as a few percent or less. However, when a separation layer is provided as in Patent Document 1, it becomes physically difficult for gas molecules to pass through the membrane, which reduces the carbon dioxide permeation flux and makes it difficult to efficiently recover carbon dioxide.

[0005] The present invention has been made in view of the above circumstances, and provides a carbon dioxide separation membrane that can efficiently recover carbon dioxide from a mixed gas containing a low concentration of carbon dioxide. [Means for solving the problem]

[0006] The carbon dioxide separation membrane of the present invention comprises a porous substrate, a protective layer provided on the surface of the substrate and having a higher density than the substrate, and a separation layer provided on the surface of the protective layer and containing a substance with a high affinity for carbon dioxide, wherein the thickness of the protective layer is 15 nm or less and the thickness of the separation layer is 300 nm or less. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a carbon dioxide separation membrane that can efficiently recover carbon dioxide from a mixed gas containing a low concentration of carbon dioxide. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a cross-sectional view of a carbon dioxide separation membrane according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0009] Specific embodiments to which the present invention is applied will be described in detail below with reference to the drawings. However, the present invention is not limited to the following embodiments. Furthermore, for clarity of explanation, the following description and drawings have been simplified as appropriate. Furthermore, the multiple configuration examples described below can be implemented independently or in appropriate combination. These multiple configuration examples have novel features that are different from each other. Therefore, these multiple configuration examples contribute to solving different purposes or problems and achieving different effects from each other.

[0010] 1 is a cross-sectional view of a carbon dioxide separation membrane 1 according to this embodiment. The carbon dioxide separation membrane 1 includes a porous substrate 11, a protective layer 12 provided on the surface of the substrate 11, and a separation layer 13 provided on the surface of the protective layer 12.

[0011] The structure of the substrate 11 is not particularly limited as long as it is porous, and for example, hollow fibers or other filtration membranes can be used. In this case, from the viewpoint of highly selectively permeating carbon dioxide at a high flow rate, it is preferable to use an UF membrane (ultrafiltration membrane) or an MF membrane (microfiltration membrane) for the substrate 11. The material of the substrate 11 can be, for example, polyethersulfone, polysulfone, polyacrylonitrile, cellulose acetate, polyvinylidene fluoride, tetrafluoroethylene, polyethylene, polypropylene, polyvinyl alcohol, etc.

[0012] The protective layer 12 is a layer with a higher density than the substrate 11. The thickness of the protective layer 12 is 15 nm or less, and preferably 10 nm or less. The lower limit of the thickness of the protective layer 12 may be within a range that does not impair the effects of the present invention, and can be, for example, 1 nm or more. The material of the protective layer 12 is not particularly limited as long as it is a substance that can be fixed to the substrate 11, but it is preferably hydrophilic from the viewpoint of increasing affinity with the separation layer 13.

[0013] The protective layer 12 can be provided on the surface of the substrate 11 by a known film formation method. Alternatively, the vicinity of the surface of the substrate 11 may be deformed by applying pressure or heat to densify that portion and form it into the protective layer 12. From the viewpoint of ease of production, it is preferable that the substrate 11 and the protective layer 12 are formed in the same piece in this manner.

[0014] Separation layer 13 is a layer containing a substance that has a high affinity for carbon dioxide. Examples of such substances that can be used include polyvinyl alcohol, polyacrylic acid, polyethyleneimine, polyallylamine, and copolymers thereof. From the viewpoint of excellent supportability for the amine compound described below, separation layer 13 preferably contains polyacrylic acid, polyethyleneimine, polyallylamine, or a copolymer containing these.

[0015] Separation layer 13 can be provided on the surface of protective layer 12 by a known film-forming method. For example, separation layer 13 can be formed by applying a liquid containing a substance with high affinity for carbon dioxide onto protective layer 12 and drying it. In this case, protective layer 12 serves to prevent the components of separation layer 13 from penetrating into substrate 11. Therefore, separation layer 13 can be formed thinly.

[0016] The thickness of the separation layer 13 is 300 nm or less, preferably 210 nm or less, and more preferably 100 nm or less. A thinner separation layer 13 is preferable because it increases the carbon dioxide permeation flux. The lower limit of the thickness of the separation layer 13 may be any thickness within a range that does not impair the effects of the present invention, but from the viewpoint of selectively separating carbon dioxide, it is preferably 10 times or more the thickness of the protective layer 12.

[0017] In the carbon dioxide separation membrane 1 having the above configuration, carbon dioxide is selectively captured into the separation layer 13 from a mixed gas that is in contact with the surface of the separation layer 13, and moves to the substrate 11 via the protective layer 12. In this way, carbon dioxide can be selectively separated. Furthermore, because the thickness of the separation layer 13 is as thin as 300 nm, the carbon dioxide permeation flux can be maintained at a sufficiently high level. Therefore, carbon dioxide can be efficiently recovered from a mixed gas that contains a low concentration of carbon dioxide.

[0018] Preferably, separation layer 13 further contains an amine compound. When separation layer 13 contains an amine compound, carbon dioxide is adsorbed to the amine compound and transported, thereby improving the separation selectivity of carbon dioxide. From the viewpoint of improving the transport efficiency of carbon dioxide, the amine compound is preferably an amine compound other than a polymer, more preferably an alkanolamine or diethylenetriamine, and particularly preferably diethylenetriamine. [Example]

[0019] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0020] The following materials were used in the production of the Examples and Comparative Examples. [material] (Support) Support A: Among the hollow fiber membrane modules "SLP-0053" manufactured by Asahi Kasei Corporation, one in which the area from the surface to a depth of 10 nm was formed at a higher density than the interior was designated as Support A. In other words, Support A was a hollow fiber substrate and a high-density protective layer integrally formed on the surface of the hollow fiber substrate. Support B: A hollow fiber membrane module of the same type but different production lot as Support A, in which the density near the surface and the inside was approximately the same, was designated Support B. In other words, Support B was a hollow fiber substrate without a protective layer formed on the surface. (Coating liquid) Coating liquid a: An aqueous solution containing polyvinyl alcohol at a concentration of 2% by mass was used as coating liquid a. Coating liquid b: An aqueous solution containing polyvinyl alcohol at a concentration of 2% by mass and diethylenetriamine at a concentration of 20% by mass was used as coating liquid b.

[0021] The manufacturing methods of the examples and comparative examples are as follows. [Manufacturing method] Example 1: The carbon dioxide separation membrane of Example 1 was produced by applying the coating liquid a to a module of the support A. Example 2: The carbon dioxide separation membrane of Example 2 was produced by applying the coating liquid b to a module of the support A. Comparative Example 1: Support B was used as the carbon dioxide separation membrane of Comparative Example 1 as it was. Comparative Example 2: The coating solution a was applied to a module of the support B to prepare a carbon dioxide separation membrane of Comparative Example 2. Comparative Example 3: The coating solution b was applied to a module of the support B to prepare a carbon dioxide separation membrane of Comparative Example 3. The coating solution was applied according to the method described in the literature (DUAN, Shuhong, et al. Development of PAMAM dendrimer composite membranes for CO2 separation. Journal of membrane science, 2006, 283.1-2: 2-6.).

[0022] [evaluation] For structural evaluation, the thickness of the protective layer and separation layer in each example was measured from cross-sectional SEM (Scanning Electron Microscope) images. For performance evaluation, a mixed gas containing a low concentration of carbon dioxide was brought into contact with the separation membrane under the same conditions, and the CO2 permeation flux and CO2 / N2 selectivity were measured. The results are shown in Table 1. The unit GPU for permeation flux in Table 1 is 1 [GPU] = 3.35 × 10 -7 [mol / m 2 ·s·kPa].

[0023] [Table 1]

[0024] As shown in Table 1, Examples 1 and 2, which had a separation layer, had higher CO2 / N2 selectivity than Comparative Example 1, which did not have a separation layer. In addition, in Comparative Examples 2 and 3, the components of the coating solution penetrated to a depth of 1000 nm from the substrate surface, forming a thick separation layer, whereas in Examples 1 and 2, a relatively thin separation layer could be formed. As a result, Examples 1 and 2 had a higher CO2 permeation flux than Comparative Examples 2 and 3. The above results demonstrate that the carbon dioxide separation membrane of the present invention can efficiently recover carbon dioxide from a mixed gas containing a low concentration of carbon dioxide.

[0025] The present invention is not limited to the above-described embodiment, and can be modified as appropriate within the scope of the invention. [Explanation of symbols]

[0026] 1 Carbon dioxide separation membrane 11 Base material 12 Protective layer 13 Separation layer

Claims

1. a porous substrate; a protective layer provided on a surface of the substrate and having a density higher than that of the substrate; a separation layer provided on the surface of the protective layer and containing a substance having a high affinity for carbon dioxide; the thickness of the protective layer is 15 nm or less; The thickness of the separation layer is 300 nm or less. Carbon dioxide separation membrane.

2. The carbon dioxide separation membrane according to claim 1 , wherein the separation layer contains an amine compound other than the polymer.

3. The carbon dioxide separation membrane according to claim 2 , wherein the amine compound is diethylenetriamine.

4. The carbon dioxide separation membrane according to claim 1 , wherein the thickness of the protective layer is one-tenth or less of the thickness of the separation layer.

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