Honeycomb structure, manufacturing method therefor, and carbon dioxide recovery device

Abstract

A honeycomb structure that contains 20-53 mass% of a solvent and is capable of adsorbing carbon dioxide.

Description

Honeycomb structure, its manufacturing method, and carbon dioxide recovery device

[0001] The present invention relates to a honeycomb structure, a method for manufacturing the same, and a carbon dioxide recovery device.

[0002] To realize a decarbonized society, there is a growing need for technologies that capture and utilize carbon dioxide (hereinafter sometimes referred to as "CO2") from the atmosphere and exhaust gases. A typical conventional CO2 capture technology has been developed, which is a technology that adsorbs CO2 in the atmosphere (DAC: Direct Air Capture). There are several types of DAC, such as liquid absorption, membrane separation, and solid adsorption. Among these, in the solid adsorption method, a CO2 adsorption (absorbing) material is generally supported on a substrate. As a substrate to be used in the solid adsorption method, honeycomb structures, which have a proven track record in purifying automobile exhaust gases, are expected to be used.

[0003] Conventional honeycomb structures have generally been manufactured by kneading raw materials containing ceramic raw materials, water, binders, etc. to form a clay, extruding the resulting clay to produce a honeycomb formed body, and then subjecting the honeycomb formed body to a heat treatment such as firing (Patent Document 1). However, heat treatments such as firing require a large amount of energy and often involve the combustion of hydrocarbon fuel, which generates CO2. Furthermore, when an organic binder is used as the binder, combustion during firing generates additional CO2.

[0004] Patent Document 2 describes a honeycomb ceramic substrate for CO2 capture. This honeycomb ceramic substrate for CO2 capture includes a honeycomb ceramic substrate having porous partition walls, a plurality of inorganic support particles in at least one pore of the porous partition walls, and an organic carbon dioxide sorbent supported by at least one of the inorganic support particles. This honeycomb ceramic substrate for CO2 capture is manufactured through a high-temperature heat treatment. Specifically, the honeycomb ceramic substrate obtained through the molding and firing processes is contacted with a support precursor slurry, followed by calcination at a temperature of about 100°C to about 600°C for about 1 hour to about 10 hours, further contacted with an organic CO2 sorbent, and then dried at about 50°C to about 100°C.

[0005] In light of this background, a technique for manufacturing a honeycomb structure without firing is also known. Patent Document 3 describes a honeycomb substrate having a plurality of partition walls extending axially from an inlet end to an outlet end, thereby forming a plurality of flow channels, the honeycomb substrate comprising a mixture of inorganic powder components and an organic binder, in which an amine polymer having functional structural unit groups capable of absorbing CO2 is dispersed in the inorganic powder components of the partition walls of the honeycomb substrate. This honeycomb substrate is formed by a method including the steps of dry-blending inorganic oxide powder components and the organic binder into a mixture, adding a solution of the amine polymer and a solvent to the mixture to form a precursor, kneading the precursor, extruding the kneaded precursor to form a connected monolith having a plurality of partition walls extending axially from the inlet end to the outlet end, thereby forming a plurality of flow channels, and drying the connected monolith to remove the solvent, thereby forming an absorbent structure for capturing CO2.

[0006] Japanese Patent Application Laid-Open No. 2020-019690 Special Publication No. 2018-538137 Special Publication No. 2015-508018

[0007] The honeycomb substrate described in Patent Document 3 is manufactured without a firing process requiring high heating temperatures, thereby reducing the amount of carbon dioxide generated during manufacturing. However, since the honeycomb substrate described in Patent Document 3 has most of the solvent (approximately 80 to 95%) removed during the drying process, the reduction in carbon dioxide generated during manufacturing is not sufficient. Furthermore, when a method is applied to desorb adsorbed carbon dioxide using a solvent (e.g., heated steam), the honeycomb substrate contains the solvent, resulting in wasted energy during drying. Furthermore, removing most of the solvent during the drying process makes defects such as cracks more likely to occur. On the other hand, if the honeycomb substrate is not dried sufficiently, the strength of the honeycomb substrate decreases.

[0008] The present invention has been made to solve the above-mentioned problems, and aims to provide a honeycomb structure that generates less carbon dioxide during manufacturing, suppresses defects such as cracks during drying, while maintaining strength, a manufacturing method for the same, and a carbon dioxide recovery device.

[0009] As a result of extensive research into honeycomb structures capable of adsorbing carbon dioxide, the inventors have found that the above-mentioned problems can be solved by controlling the ratio of solvent in the honeycomb structure within a specific range, and have thus completed the present invention. That is, the present invention is exemplified as follows.

[0010] [1] A honeycomb structure capable of adsorbing carbon dioxide, containing 20 to 53 mass % of a solvent.

[0011] [2] The honeycomb structure according to [1], wherein the solvent is water.

[0012] [3] The honeycomb structure according to [1] or [2], wherein the honeycomb structure has a plurality of cell channels passing through the interior and separated by partition walls, and the partition walls contain a carbon dioxide adsorbent, an organic binder, and an inorganic binder.

[0013] [4] The honeycomb structure according to [3], wherein the carbon dioxide adsorbent is dispersed in the partition walls.

[0014] [5] The honeycomb structure according to [3] or [4], wherein the carbon dioxide adsorbent is a solid organic compound having an amino group.

[0015] [6] The honeycomb structure according to any one of [1] to [5], wherein the carbon dioxide adsorption amount is 0.10 mol / kg or more.

[0016] [7] The honeycomb structure according to any one of [1] to [6], wherein the opening ratio is 60% or more.

[0017] [8] A method for manufacturing a honeycomb structure, comprising: a clay preparation step of kneading a forming raw material containing a solvent, a carbon dioxide adsorbent, an organic binder, and an inorganic binder to prepare a clay; a molding step of forming the clay into a honeycomb formed body, the honeycomb formed body having a plurality of cell channels that pass through the interior and are divided by partition walls; and a drying step of drying the honeycomb formed body so that the solvent in the honeycomb formed body becomes 20 to 53 mass %.

[0018] [9] The method for manufacturing a honeycomb structure according to [8], wherein the solvent is water.

[0019]

[10] The method for manufacturing a honeycomb structure according to [8] or [9], wherein the carbon dioxide adsorbent is a solid organic compound having an amino group.

[0020]

[11] The content of the carbon dioxide adsorbent in the forming raw material excluding the solvent is 40 to 94 mass%, the content of the inorganic binder in the forming raw material excluding the solvent is 3 to 50 mass%, and the content of the organic binder in the forming raw material excluding the solvent is 3 to 20 mass%. [8] to

[10] Any one of the manufacturing methods of the honeycomb structure described in

[10] .

[0021]

[12] The method for manufacturing a honeycomb structure according to any one of [8] to

[11] , wherein firing is not performed after the drying step.

[0022]

[13] A carbon dioxide recovery device comprising one or more honeycomb structures according to any one of [1] to [7].

[0023] According to the present invention, it is possible to provide a honeycomb structure that generates less carbon dioxide during manufacturing, suppresses defects such as cracks during drying, and ensures strength, as well as a manufacturing method for the honeycomb structure and a carbon dioxide recovery device.

[0024] Fig. 1 is a schematic perspective view of a honeycomb structure according to one embodiment of the present invention. Fig. 2 is a schematic view of a cross section parallel to the height direction (cell extension direction) of a honeycomb structure according to one embodiment of the present invention. Fig. 3 is a diagram for schematically explaining a method for measuring the hardness of a clay using a hardness meter. Fig. 4 is an enlarged view showing the shape and dimensions of the tip of a hardness meter. Fig. 5 is a graph showing the spring properties of a spring material used in a hardness meter.

[0025] The honeycomb structure of the present invention contains 20 to 53 mass% of solvent and is capable of adsorbing carbon dioxide. Because the honeycomb structure of the present invention having such a configuration contains a larger amount of solvent than conventional honeycomb structures, the load on the drying process can be reduced, and the effect of reducing carbon dioxide generated during manufacturing can be enhanced. Furthermore, because only a small amount of solvent is removed in the drying process, defects such as cracks during drying can be suppressed. Furthermore, because the solvent content is controlled within a predetermined range, the strength of the honeycomb structure can be ensured. The honeycomb structure of the present invention, which has these characteristics, is highly practical as a product that adsorbs carbon dioxide from the atmosphere and is believed to be able to make a significant contribution to realizing a decarbonized society.

[0026] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The present invention is not limited to the following embodiments, and it should be understood that modifications and improvements made to the following embodiments based on the ordinary knowledge of those skilled in the art without departing from the spirit of the present invention are also within the scope of the present invention.

[0027] (1. Honeycomb structure) Fig. 1 shows a schematic perspective view of a honeycomb structure according to an embodiment of the present invention. Fig. 2 shows a schematic view of a cross section parallel to the height direction (cell extension direction) of the honeycomb structure shown in Fig. 1.

[0028] As shown in FIGS. 1 and 2 , the honeycomb structure 100 has a plurality of cell channels that pass through the interior and are separated by partition walls 112. Specifically, the honeycomb structure 100 includes an outer peripheral wall 102 and partition walls 112 disposed on the inner circumferential side of the outer peripheral wall 102, extending from a first end face 104 to a second end face 106. The partition walls 112 separate a plurality of cells 108 that form fluid flow paths (cell channels). The plurality of cells 108 are arranged parallel to one another. The honeycomb structure 100 is a flow-through type in which both ends of each cell 108 are open to the first end face 104 and the second end face 106. When a CO2-containing gas such as the atmosphere flows in through the first end face 104 where the inlets of the plurality of cells 108 are located, CO2 is adsorbed as the gas passes through the plurality of cells 108, and a gas with a reduced CO2 concentration flows out from the second end face 106 where the outlets of the plurality of cells 108 are located.

[0029] The end face shape of the honeycomb structure 100 is not particularly limited, and may be, for example, a circular shape, an elliptical shape, a round shape such as a racetrack shape or an oval shape, a polygonal shape such as a triangular shape or a quadrangular shape, or any other irregular shape. The overall outer shape of the honeycomb structure 100 may typically be a columnar shape. The honeycomb structure 100 shown in FIG. 1 has a circular end face shape and is cylindrical as a whole.

[0030] When the honeycomb structure 100 is a columnar body, there is no particular limitation on its height (the length from the first end face 104 to the second end face 106) and it may be set appropriately depending on the application and required performance. There is also no particular limitation on the relationship between the height of the honeycomb structure 100 and the maximum diameter of each end face (referring to the maximum length of the diameters passing through the center of gravity of each end face of the honeycomb structure 100). Therefore, the height of the honeycomb structure 100 may be longer than the maximum diameter of each end face, or the height of the honeycomb structure 100 may be shorter than the maximum diameter of each end face.

[0031] There is no particular limitation on the length in the extension direction (height direction) of the cells 108 of the honeycomb structure 100. However, while a longer length can increase the amount of CO2 adsorption, if the length is too long, pressure loss increases, so the length is preferably 20 to 350 mm, more preferably 20 to 300 mm, and even more preferably 20 to 250 mm.

[0032] There is no particular limitation on the maximum diameter of each end face of the honeycomb structure 100. However, while a larger maximum diameter can increase the amount of CO adsorption, if the maximum diameter is too large, manufacturing becomes more difficult. Therefore, the maximum diameter is preferably 20 to 450 mm, more preferably 20 to 400 mm, and even more preferably 20 to 350 mm.

[0033] The honeycomb structure 100 contains a solvent. That is, the outer wall 102 and the partition walls 112 constituting the honeycomb structure 100 contain a solvent. The solvent is not particularly limited, and water or a mixed solvent of water and an organic solvent such as alcohol can be used. Among them, water is particularly preferably used.

[0034] The solvent content of the honeycomb structure 100, i.e., the peripheral wall 102 and partition walls 112 that constitute the honeycomb structure 100, is 20 to 53 mass %, preferably 23 to 50 mass %, and more preferably 27 to 40 mass %. By controlling the content to such a range, it is possible to reduce carbon dioxide generated during manufacturing, and ensure strength while suppressing cracks during drying. The solvent content of the honeycomb structure 100 can be measured as follows. First, a sample of an arbitrary size is prepared by cutting the honeycomb structure 100, and the sample is placed in a drying furnace set at 70 to 100°C for 20 minutes or more to completely dry the sample. The masses of the sample before and after drying are measured, and the solvent content of the honeycomb structure can be measured according to the following formula: Solvent content [mass %] = (mass [g] of sample before drying - mass [g] of sample after drying) / mass [g] of sample before drying × 100

[0035] The honeycomb structure 100 is capable of adsorbing carbon dioxide. There are no particular limitations on the method for making the honeycomb structure 100 capable of adsorbing carbon dioxide. For example, the honeycomb structure 100 may contain a carbon dioxide adsorbent or a coating film of a carbon dioxide adsorbent may be formed on the surface of the honeycomb structure 100. Among these, from the viewpoint of the amount of CO2 adsorption, it is preferable to contain a carbon dioxide adsorbent in the honeycomb structure 100.

[0036] The partition walls 112 constituting the honeycomb structure 100 can further contain a carbon dioxide adsorbent, an organic binder, and an inorganic binder. The outer peripheral wall 102 constituting the honeycomb structure 100 can also contain a carbon dioxide adsorbent, an organic binder, and an inorganic binder, similar to the partition walls 112. The carbon dioxide adsorbent, the organic binder, and the inorganic binder may each be contained alone or in combination of two or more.

[0037] The carbon dioxide adsorbent is preferably dispersed in the partition walls 112. Similarly, the carbon dioxide adsorbent is preferably dispersed in the outer peripheral wall 102. By dispersing the carbon dioxide adsorbent in the partition walls 112 and the outer peripheral wall 102 in this manner, the amount of CO2 adsorption can be increased.

[0038] The carbon dioxide adsorbent is not particularly limited, and known adsorbents can be used. Among them, the carbon dioxide adsorbent is preferably a solid organic compound having an amino group (one or more selected from -NH, -NHR, and -NRR' (R and R' represent organic groups)). Although the present invention is not intended to be limited by theory, a solid organic compound having an amino group can adsorb CO by reacting with CO to produce a carbamate or bicarbonate.

[0039] From the viewpoint of water resistance, it is desirable that the solid organic compound having an amino group be water-insoluble. Furthermore, the solid organic compound having an amino group may have any of -NH2, -NHR, and -NRR' (R and R' represent organic groups), or may have a combination of two or more of these. Among amino groups, it is particularly preferable that the solid organic compound have a primary amine (-NH2) as a functional group. It is also preferable that the solid organic compound having an amino group contain an aromatic ring.

[0040] A specific example of the solid organic compound having an amino group is a weakly basic anion exchange resin having an amino group. Thus, for example, the solid organic compound having an amino group may contain one or more selected from a styrene-based divinylbenzene polymer having an amino group (e.g., a copolymer of styrene and divinylbenzene) and an acrylic-based divinylbenzene polymer having an amino group (e.g., a copolymer of divinylbenzene with one or both of acrylic acid and methacrylic acid).

[0041] From the viewpoint of CO2 adsorption performance, the exchange capacity of the weakly basic anion exchange resin is preferably 0.6 meq / mL or more, more preferably 1.0 meq / mL or more, and even more preferably 1.4 meq / mL or more. The exchange capacity of the weakly basic anion exchange resin is measured by the tapping method, in which 10 mL of the ion exchange resin is treated with hydrochloric acid, the excess hydrochloric acid is washed off with ethanol, and ammonia water is passed through, and the amount of chloride ions that flow out is measured.

[0042] The content of the solid organic compound having an amino group in the partition wall 112 (and the outer peripheral wall 102 as necessary) is not particularly limited, but from the viewpoint of achieving a good balance between CO adsorption performance, crack suppression during drying, and water resistance, it is preferably 24 to 75 mass%, more preferably 25 to 70 mass%, and even more preferably 30 to 60 mass%.

[0043] Examples of organic binders include methyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, hydroxyethyl methyl cellulose, polyvinyl acetal, polyethylene oxide, polyvinyl butyral, polybutadiene, methacrylic acid esters, acrylic, ethyl cellulose, silicone, and polyolefin. These can be used alone or in combination of two or more. In particular, the use of water-soluble organic binders such as methyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, hydroxyethyl methyl cellulose, polyvinyl acetal, and polyethylene oxide can reduce environmental impact, the risk of organic solvent vapor during drying, and production costs.

[0044] The content of the organic binder in the partition walls 112 (and the outer peripheral wall 102 as necessary) is not particularly limited, but from the viewpoint of achieving a good balance between CO adsorption performance, crack suppression during drying, and water resistance, it is preferably 2 to 9 mass%, and more preferably 3 to 8 mass%.

[0045] Examples of inorganic binders include one or more inorganic binders selected from fibrous and granular binders. Among these, fibrous inorganic binders are preferred. Herein, "fibrous" inorganic binders refer to inorganic binders with an average aspect ratio of 3 or more. Furthermore, "granular" inorganic binders refer to inorganic binders with an average aspect ratio of less than 3. The average aspect ratio of the inorganic binder is determined by the following procedure. A test piece of the honeycomb structure 100 is cut to an appropriate size, placed in a crucible, and heated to 500°C in an electric furnace to remove organic matter. The remaining inorganic binder is then dispersed on a scanning electron microscope (SEM) stage, and the magnification is adjusted to fit the inorganic binder so that 20 inorganic binder particles fit in a single field of view. The longest and shortest diameters of any 20 inorganic binders are measured, and the average value of the longest diameter / shortest diameter is taken as the average aspect ratio of the inorganic binder. The longest diameter of an inorganic binder particle refers to the longest distance between two parallel lines sandwiching the inorganic binder on an SEM image. The shortest diameter of an inorganic binder particle refers to the shortest distance between two parallel lines sandwiching the inorganic binder on an SEM image.

[0046] Specific examples of inorganic binders include clay, diatomaceous earth, layered clay minerals, montmorillonite, hydrotalcite, activated clay, acid clay, hectorite, halloysite, attapulgite, silica, alumina, talc, chlorite, vermiculite, mica, illite, pyrophyllite, sericite, kaolin, sepiolite, boehmite, palygorskite, and bentonite. These can be used alone or in combination of two or more. Among these, the inorganic binder preferably contains one or more selected from sepiolite, boehmite, bentonite, silica, kaolin, and talc, and more preferably contains sepiolite.

[0047] The content of the inorganic binder in the partition walls 112 (and the outer peripheral wall 102 as necessary) is not particularly limited, but from the viewpoint of achieving a good balance between CO adsorption performance, crack suppression during drying, and water resistance, it is preferably 2 to 45 mass%, and more preferably 3 to 40 mass%.

[0048] In addition to the above components, the partition walls 112 (and the peripheral walls 102, if necessary) constituting the honeycomb structure 100 may further contain known additives such as surfactants and pore-forming materials within a range that does not impair the effects of the present invention.

[0049] The average thickness of the partition walls 112 (and the peripheral wall 102, if necessary) constituting the honeycomb structure 100 is not particularly limited, but is preferably 50 μm or more, more preferably 60 μm or more, and even more preferably 70 μm or more, from the viewpoint of ensuring strength. Furthermore, the average thickness of the partition walls 112 is preferably 600 μm or less, more preferably 550 μm or less, and even more preferably 500 μm or less, from the viewpoint of suppressing pressure loss. Therefore, the average thickness of the partition walls 112 is preferably, for example, 50 to 600 μm, more preferably 60 to 550 μm, and even more preferably 70 to 500 μm. In this specification, the thickness of the partition walls 112 is defined as the length of the portion of a line segment connecting the centers of gravity of adjacent cells 108 that passes through the partition wall 112 in a cross section perpendicular to the extension direction of the cells 108. Furthermore, the average thickness of the partition walls 112 refers to the average value of the thicknesses of all the partition walls 112 in the honeycomb structure 100.

[0050] The cell density (the number of cells per unit cross-sectional area) of the honeycomb structure 100 is not particularly limited, but from the viewpoint of improving the contact area between the carbon dioxide adsorbent contained in the partition walls 112 and the gas being passed through, it is set to 30 cells / cm. 2 Preferably, the number of cells is 40 or more. 2 More preferably, 50 cells / cm or more. 2 From the viewpoint of ensuring a gas flow path and reducing pressure loss, the cell density is more preferably 2000 cells / cm. 2 Preferably, the number of cells per square centimeter is 1200 or less.2 More preferably, it is 900 cells / cm or less. 2 Therefore, the cell density is, for example, 30 to 2000 cells / cm. 2 It is preferable that the density is 40 to 1200 cells / cm 2 More preferably, it is 50 to 900 cells / cm 2 In this specification, the cell density is calculated by dividing the number of cells 108 in the honeycomb structure 100 by the area of ​​one end face of the honeycomb structure 100 excluding the outer peripheral wall 102 .

[0051] The aperture ratio of the honeycomb structure 100 is not particularly limited, but is preferably 60% or more, more preferably 70% or more, and even more preferably 80% or more. Controlling the aperture ratio within such a range can improve CO adsorption performance while suppressing an increase in pressure loss. The upper limit of the aperture ratio of the honeycomb structure 100 is not particularly limited, but is preferably 90% or less, more preferably 89% or less, and even more preferably 88% or less, from the viewpoint of ensuring the strength of the honeycomb structure 100. The aperture ratio of the honeycomb structure 100 can be calculated by dividing the total area of ​​the cells 108 defined by the partition walls 112 at one end face (the first end face 104 or the second end face 106) by the area of ​​the one end face (the total area of ​​the outer peripheral wall 102, the partition walls 112, and the cells 108), and multiplying the result by 100.

[0052] There are no limitations on the shape of the cells 108 in a cross section perpendicular to the extension direction of the cells 108 (the height direction of the honeycomb structure 100), but a quadrangle, hexagon, octagon, circle, or a combination thereof is preferred. Among these, the shape of the cells 108 is preferably a square or hexagon. By configuring the cells 108 in this way, the pressure loss when a fluid is flowed through the honeycomb structure 100 is reduced.

[0053] The honeycomb structure 100 preferably has a carbon dioxide (CO2) adsorption capacity of 0.10 mol / kg or more, and more preferably greater than 0.50 mol / kg. Such a CO2 adsorption capacity indicates good CO2 adsorption performance. The CO2 adsorption capacity can be measured as follows. First, a cubic sample measuring 20 mm x 20 mm x 40 mm (length in the direction of extension of the cells 108) is cut from near the center of the honeycomb structure 100. Next, this sample is placed in a sealed container, and CO2 concentration sensors are installed on the inlet and outlet sides of the sample's cells. Next, as a pretreatment, nitrogen gas heated to 90-100°C is passed through the sample at a flow rate of 1.5 L / min until the CO2 concentration on the outlet side reaches 0 ppm. Then, heating is stopped while the nitrogen gas continues to flow until the sample reaches 25°C (room temperature). After reaching 25°C, 25°C air is passed through the sample at a flow rate of 15 L / min, and the CO2 adsorption capacity (mol) is measured until saturation is reached. The measured CO2 adsorption amount (mol) is divided by the mass (kg) of the sample to calculate the CO2 adsorption amount per mass of the sample (mol / kg).

[0054] (2. CO2 Capture and Desorption Method) According to an embodiment of the present invention, there is provided a CO2 capture and desorption method using a honeycomb structure 100. Specifically, the CO2 capture method according to the embodiment of the present invention includes flowing a gas to be treated (CO2-containing gas) containing CO2 through a plurality of cell channels of the honeycomb structure 100, adsorbing CO2 in the gas to be treated by a carbon dioxide adsorbent while the gas to be treated passes through the plurality of cell channels, and discharging the gas to be treated with a reduced CO2 concentration from the honeycomb structure 100. The gas to be treated is not particularly limited as long as it contains CO2, and examples thereof include environmental air (outdoor air as well as indoor or indoor air), factory exhaust gas, ship exhaust gas, and power plant exhaust gas.

[0055] Furthermore, a CO desorption method according to an embodiment of the present invention includes flowing a desorbed gas through a plurality of cell channels of the honeycomb structure 100 in which CO is adsorbed, and desorbing CO from the carbon dioxide adsorbent into the desorbed gas while the desorbed gas passes through the plurality of cell channels. The desorbed gas is not particularly limited as long as it is a gas capable of desorbing CO, and may be, for example, water vapor. The water vapor is preferably at a high temperature of 100°C or higher (e.g., 120°C).

[0056] (3. Manufacturing method of honeycomb structure) A suitable example of a manufacturing method of a honeycomb structure according to an embodiment of the present invention will be described below. The manufacturing method of a honeycomb structure according to an embodiment of the present invention includes a clay preparation step of kneading a forming raw material containing a solvent, a carbon dioxide adsorbent, an organic binder, and an inorganic binder to prepare a clay, a forming step of forming the clay into a honeycomb formed body (the honeycomb formed body has a plurality of cell channels that pass through the interior and are separated by partition walls), and a drying step of drying the honeycomb formed body so that the solvent in the honeycomb formed body is 20 to 53 mass %.

[0057] In the clay preparation step, a forming raw material including a solvent, a carbon dioxide adsorbent, an organic binder, and an inorganic binder is kneaded to prepare a clay. Examples of the solvent (dispersion medium) include water and a mixed solvent of water and an organic solvent such as alcohol, but water is particularly preferred.

[0058] From the viewpoint of achieving a good balance between CO2 adsorption performance, crack suppression during drying, and water resistance, the content of carbon dioxide adsorbent excluding the solvent in the forming raw material is preferably 40 to 94% by mass, the content of inorganic binder excluding the solvent in the forming raw material is 3 to 50% by mass, and the content of organic binder excluding the solvent in the forming raw material is preferably 3 to 20% by mass. Moreover, the content of carbon dioxide adsorbent excluding the solvent in the forming raw material is 40 to 90% by mass, the content of inorganic binder excluding the solvent in the forming raw material is 3 to 40% by mass, and the content of organic binder excluding the solvent in the forming raw material is more preferably 3 to 18% by mass. Furthermore, the content of carbon dioxide adsorbent excluding the solvent in the forming raw material is 40 to 80% by mass, the content of inorganic binder excluding the solvent in the forming raw material is 3 to 30% by mass, and the content of organic binder excluding the solvent in the forming raw material is even more preferably 5 to 15% by mass.

[0059] The solvent content in the molding raw material is determined to achieve a clay hardness suitable for extrusion. The clay hardness is preferably in the range of 14 to 26 mm, more preferably 15 to 25 mm, and even more preferably 16 to 24 mm. Here, clay hardness is measured as follows. Figure 3 is a diagram illustrating a method for measuring clay hardness using a hardness tester. (a) is an overall view of the hardness tester, (b) is the measurement state when the clay is soft, and (c) is the measurement state when the clay is hard. Figure 4 is an enlarged view showing the shape and dimensions of the tip of the hardness tester. The hardness tester 1 is configured by connecting a conical tip 4 and a support 3 via a spring material 2, which are housed in a cylindrical sheath 5 (Figure 3(a)). Figure 5 is a graph showing the spring properties of the spring material 2 used. To measure the hardness of the puddle, first, a 20 mm x 20 mm x 20 mm cubic sample is taken from the puddle. The sample is placed on a flat surface, and the tip 4 of the hardness meter 1 is inserted vertically from above into the puddle 6, 7 until the sheath 5 contacts it. The insertion is performed at a sheath speed of 1 mm / s. Next, the length (a1, a2) of the support 3 protruding above the sheath 5 is read 3 seconds after the sheath 5 contacts the puddle 6, 7, and this value (mm) is defined as the hardness of the puddle 6, 7. Therefore, the larger the value, the higher the hardness of the puddle. In this specification, the average value of measurements taken at two arbitrary locations is defined as the hardness measurement value of the puddle. Note that L0, L1, and L2 indicate the length of the spring material 2. Hardness testers employing such a hardness measurement method are commercially available, and for example, the NGK-type hardness tester (model number: NGK-01) manufactured by NGK Insulators, Ltd. can be used.

[0060] The preferred properties, types, and compounding ratios of the carbon dioxide adsorbent have already been described, but will be supplemented below. The carbon dioxide adsorbent used as a molding raw material is preferably porous. Furthermore, the carbon dioxide adsorbent has a median diameter (D50) based on a volume-based cumulative particle size distribution obtained by a laser diffraction / scattering method, which is preferably 200 μm or less, more preferably 100 μm or less, even more preferably 50 μm or less, even more preferably 30 μm or less, and even more preferably 15 μm or less, to prevent clogging during extrusion. The median diameter (D50) of the carbon dioxide adsorbent is preferably 0.1 μm or more, more preferably 0.5 μm or more, and even more preferably 1 μm or more, for reasons of easy availability. Therefore, the median diameter (D50) of the carbon dioxide adsorbent is, for example, preferably 0.1 to 100 μm, more preferably 0.5 to 50 μm, even more preferably 1 to 50 μm, still more preferably 1 to 30 μm, and particularly preferably 1 to 15 μm.

[0061] The preferred properties, types, and compounding ratios of the inorganic binder have already been described, but the following supplementary information is provided. The inorganic binder used as a molding raw material is preferably porous. Furthermore, the inorganic binder preferably has a median diameter (D50) determined from the volume-based cumulative particle size distribution obtained by a laser diffraction / scattering method of 200 μm or less, more preferably 100 μm or less, even more preferably 50 μm or less, even more preferably 30 μm or less, and particularly preferably 15 μm or less, to prevent clogging during extrusion molding. For reasons of availability, the median diameter (D50) of the inorganic binder is preferably 0.01 μm or more, more preferably 0.05 μm or more, and even more preferably 0.1 μm or more. Therefore, the median diameter (D50) of the inorganic binder is preferably 0.01 to 200 μm, more preferably 0.05 to 100 μm, and even more preferably 0.1 to 100 μm, for example.

[0062] The preferred properties, types, and compounding ratios of the organic binder have been described above. Water-soluble organic binders dissolve during kneading. Therefore, there are no particular limitations on the shape and size, and it is sufficient to use an organic binder in a generally available form. When a water-insoluble organic binder is used, it dissolves during kneading if an organic solvent is used. Therefore, there are no particular limitations on the shape and size, and it is sufficient to use an organic binder in a generally available form.

[0063] The molding raw materials containing the above-mentioned components can be kneaded using a known kneader, and it is desirable to carry out the kneading for a time required for each component to be uniformly distributed in the clay.

[0064] (Forming process) In the forming process, a honeycomb formed body having a plurality of cell channels that pass through the interior of the honeycomb formed body and are separated by partition walls is formed from a puddle. Typically, in the forming process, a honeycomb formed body having an outer peripheral wall and partition walls that are disposed on the inner peripheral side of the outer peripheral wall, extend from the first end face to the second end face, and separate a plurality of cells that form fluid flow paths (cell channels) is extrusion-formed. During extrusion molding, a die having a desired overall shape, cell shape, partition wall thickness, cell density, etc. can be used.

[0065] (Drying Process) In the drying process, the honeycomb formed body is dried so that the solvent content in the honeycomb formed body is 20 to 53 mass%. The solvent content in the honeycomb formed body can be controlled by appropriately adjusting the drying time and drying method. Conventional drying methods, such as hot air drying, microwave drying, dielectric drying, reduced pressure drying, vacuum drying, and freeze drying, can be used for drying. Among these, hot air drying, microwave drying, dielectric drying, or a combination thereof is preferred because it allows the entire honeycomb formed body to be dried quickly and uniformly. From the viewpoint of suppressing decomposition of the carbon dioxide adsorbent and organic binder during drying, the honeycomb formed body is preferably dried in an air atmosphere at 50 to 150°C, more preferably in an air atmosphere at 60 to 140°C, and even more preferably in an air atmosphere at 70 to 130°C. The drying time is not particularly limited and can be adjusted appropriately depending on the drying temperature.

[0066] In the method for manufacturing a honeycomb structure according to an embodiment of the present invention, it is preferable not to perform firing after the drying step. By not performing firing, decomposition of the carbon dioxide adsorbent and organic binder due to firing can be suppressed, and therefore CO2 adsorption performance and strength can be ensured.

[0067] (4. Carbon Dioxide Capture Apparatus) A carbon dioxide capture apparatus according to an embodiment of the present invention includes one or more of the above-described honeycomb structures 100. Because this carbon dioxide capture apparatus includes the above-described honeycomb structures 100, it has good CO2 adsorption performance and strength, and can enhance the CO2 capture effect.

[0068] The carbon dioxide capture device according to the embodiment of the present invention may further include a housing that accommodates the honeycomb structure 100. The housing is preferably connected to pipes that can supply and discharge the CO2-containing gas to be treated and the desorbed gas. A carbon dioxide capture device having such a structure can easily achieve CO2 capture and desorption.

[0069] The present invention will be described in detail below with reference to examples, but the present invention should not be construed as being limited thereto. (1. Raw Materials) A commercially available water-insoluble, weakly basic anion exchange resin (a styrene-based divinylbenzene polymer having a primary amine functional group with an exchange capacity of 2.0 meq / mL) was prepared as a carbon dioxide (CO2) adsorbent. This ion exchange resin was porous and granular. Furthermore, the median diameter (D50) of the volume-based cumulative particle size distribution measured by a laser diffraction / scattering method was 10 μm. Commercially available sepiolite, boehmite, colloidal silica, alumina sol, and kaolin were prepared as inorganic binders. Sepiolite was porous and fibrous, while boehmite, colloidal silica, and kaolin were solid and granular, and alumina sol was solid and fibrous. Furthermore, when the cumulative particle size distribution on a volume basis was measured by a laser diffraction / scattering method, the median diameter (D50) was 10 μm for sepiolite, 0.1 μm for boehmite, 0.05 μm for colloidal silica, 0.1 μm for alumina sol, and 10 μm for kaolin. Commercially available methyl cellulose was prepared as the organic binder. Industrial water was prepared as the solvent.

[0070] (2. Manufacturing of Honeycomb Structure) A raw material was prepared by blending the components and solvent shown in Table 1. The contents of the CO2 adsorbent, inorganic binder, and organic binder in Table 1 refer to the content when their total is taken as 100% by mass (i.e., when the total of the components excluding the solvent is taken as 100% by mass). The amount of solvent was adjusted so that the clay hardness measured with an NGK hardness tester (model number: NGK-01) manufactured by NGK Insulators, Ltd. was 17 mm. The raw material was then kneaded for 30 minutes in a vacuum kneader to prepare a cylindrical clay. While colloidal silica was provided as a dispersion with a solids concentration of 50% by mass and alumina sol was provided as a dispersion with a solids concentration of 5% by mass, only the solids were included in Table 1.

[0071]

[0072] Next, the obtained cylindrical clay was molded using an extrusion molding machine having a predetermined die structure to obtain a cylindrical honeycomb molded body in which each cell shape in a cross section perpendicular to the cell extension direction was square. For the honeycomb molded body, the honeycomb structure during extrusion molding was measured visually to evaluate its moldability. The moldability was evaluated according to the following criteria. The results of this evaluation are shown in the "Moldability" column of Table 3. ◯: A honeycomb structure was molded without any cracks occurring in the partition walls. △: A honeycomb structure was molded, although cracks were observed in the partition walls. ×: Shape retention was insufficient, and the honeycomb structure could not be maintained.

[0073] Next, the obtained honeycomb molded body was dried by microwave drying so that the solvent content reached a predetermined value, thereby obtaining a honeycomb structure. The solvent content in the honeycomb structure was adjusted by controlling the drying time. The honeycomb structure obtained by the above method had a circular end face with a diameter of 60 mm and a height (length in the cell extension direction) of 120 mm. The opening ratio was 73.3%, and the cell density was 300 cells / cm. 2 The average thickness of the partition walls was 200 μm. The honeycomb structure obtained above was evaluated as follows.

[0074] (3. Evaluation of honeycomb structure) <Defects> The honeycomb structure having each solvent content was visually evaluated for defects. The evaluation of defects was performed according to the following criteria. The results of this evaluation are shown in the "Defects" column of Table 2. ◯: No defects such as cracks Δ: Cracks are present ×: Defects such as cracks are present

[0075] <Strength> For the honeycomb structures with each solvent content, an attachment with a diameter of 13.3 mm was attached to the tip of a force gauge (IMADA Corporation, DST500N), and the strength was evaluated by applying pressure to the outer wall of the honeycomb structure so that the reading was 40 N or more. The strength was evaluated according to the following criteria. The results of this evaluation are shown in the "Strength" column of Table 2. ◯: No change in the shape of the outer wall of the honeycomb structure Δ: Cracks occurred in the outer wall of the honeycomb structure ×: The outer wall of the honeycomb structure cracked and caved in before reaching 40 N

[0076] <Water Resistance> A cube of 25 mm x 25 mm x 25 mm (length in the cell extension direction) was cut out from near the center of a honeycomb structure having a solvent content of 33 mass %. Moist air (humidity 96% or more) at 55°C was blown into the cells of the cut cube to a depth of 0.01 m. 3 / s for 1 hour. Thereafter, the state of the cube was checked visually and by dimensional measurement, and evaluated according to the following criteria. The results of this evaluation are shown in the "Water Resistance" column in Table 3. ◯: The cube was placed on a horizontal surface with its three perpendicular faces at the bottom, and the height (the maximum value from the horizontal plane was taken as the height) was measured, and the difference between the maximum and minimum heights measured in the three directions was less than 2 mm. △: The difference between the maximum and minimum heights measured in the three directions by the above method was 2 mm or more. ×: The honeycomb structure was not maintained during ventilation and collapsed.

[0077] <CO2 Adsorption Performance> CO2 adsorption performance was evaluated by the CO2 adsorption amount. A cubic sample of 20 mm x 20 mm x 40 mm (length in the extension direction of the cells 108) was taken from a honeycomb structure with a solvent content of 33% by mass. The CO2 adsorption amount (mol) was measured until saturation was reached according to the method described above, and the measured CO2 adsorption amount (mol) was then divided by the mass (kg) of the sample to calculate the CO2 adsorption amount. CO2 adsorption performance was evaluated according to the following criteria. The evaluation results are shown in the "CO2 Adsorption Performance" column in Table 3. ◯: CO2 adsorption amount greater than 0.50 mol / kg △: CO2 adsorption amount 0.10 to 0.50 mol / kg ×: CO2 adsorption amount less than 0.10 mol / kg

[0078]

[0079]

[0080] As shown in Table 2, the honeycomb structures of Examples 1 to 7, which had a solvent content of 20 to 53 mass%, were free of defects such as cracks and had good strength. Furthermore, the honeycomb structures of Examples 1 to 7 also had good formability, water resistance, and CO2 adsorption performance, as shown in Table 3. In contrast, Comparative Example 1 lacked shape retention and could not be formed into a honeycomb structure.

[0081] As can be seen from the above results, according to the present invention, it is possible to provide a honeycomb structure that generates less carbon dioxide during manufacturing, suppresses defects such as cracks during drying, while maintaining strength, and a manufacturing method therefor, as well as a carbon dioxide recovery device.

[0082] REFERENCE SIGNS LIST 1: Hardness tester 2: Spring material 3: Support portion 4: Tip portion 5: Sheath portion 6, 7: Clay a1, a2: Projecting length 100: Honeycomb structure 102: Peripheral wall 104: First end face 106: Second end face 108: Cell 112: Partition wall

Claims

1. A honeycomb structure capable of adsorbing carbon dioxide, containing 20 to 53 mass % of a solvent.

2. The honeycomb structure according to claim 1, wherein the solvent is water.

3. A honeycomb structure according to claim 1 or 2, wherein the honeycomb structure has a plurality of cell channels passing through the interior and separated by partition walls, and the partition walls contain a carbon dioxide adsorbent, an organic binder, and an inorganic binder.

4. The honeycomb structure according to claim 3, wherein the carbon dioxide adsorbent is dispersed in the partition walls.

5. The honeycomb structure according to claim 3, wherein the carbon dioxide adsorbent is a solid organic compound having an amino group.

6. A honeycomb structure according to claim 1 or 2, which has a carbon dioxide adsorption capacity of 0.10 mol / kg or more.

7. A honeycomb structure according to claim 1 or 2, having an opening ratio of 60% or more.

8. A method for manufacturing a honeycomb structure, comprising: a clay preparation step of kneading forming raw materials including a solvent, a carbon dioxide adsorbent, an organic binder, and an inorganic binder to prepare a clay; a molding step of forming the clay into a honeycomb formed body, the honeycomb formed body having a plurality of cell channels passing through the interior and separated by partition walls; and a drying step of drying the honeycomb formed body so that the solvent in the honeycomb formed body is 20 to 53 mass %.

9. The method for manufacturing a honeycomb structure according to claim 8, wherein the solvent is water.

10. A method for manufacturing a honeycomb structure according to claim 8 or 9, wherein the carbon dioxide adsorbent is a solid organic compound having an amino group.

11. A method for manufacturing a honeycomb structure as described in claim 8 or 9, wherein the content of the carbon dioxide adsorbent in the forming raw material excluding the solvent is 40 to 94 mass%, the content of the inorganic binder in the forming raw material excluding the solvent is 3 to 50 mass%, and the content of the organic binder in the forming raw material excluding the solvent is 3 to 20 mass%.

12. The method for manufacturing a honeycomb structure according to claim 8 or 9, wherein firing is not carried out after the drying step.

13. A carbon dioxide recovery device comprising one or more honeycomb structures according to claim 1 or 2.

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