Carbon dioxide adsorbent and its evaluation method

Abstract

This allows for the selection of materials that can be regenerated under low vacuum conditions while maintaining their performance. [Solution] A method for evaluating a carbon dioxide adsorbent, comprising: (a) heating or depressurizing the carbon dioxide adsorbent, supplying a gas containing carbon dioxide to the carbon dioxide adsorbent, and measuring the amount of carbon dioxide adsorbed Q0 at a predetermined time from the start of supply; and (b) distributing the carbon dioxide adsorbent to 10 2 ~10 4 An evaluation method comprising (c) a step of regenerating the carbon dioxide adsorbent under low vacuum conditions of Pa, and (d) a step of supplying a gas containing carbon dioxide to the carbon dioxide adsorbent again and measuring the amount of carbon dioxide adsorbed QLow over a predetermined time, wherein the ratio RLow of QLow to Q0 is 70% or more.

Description

[Technical Field]

[0001] The present invention relates to a carbon dioxide adsorbent and a method for evaluating the same. [Background technology]

[0002] In recent years, technologies for directly capturing carbon dioxide from the atmosphere (hereinafter referred to as DAC technology) have attracted attention. In DAC technology, it is important that the carbon dioxide adsorbent repeatedly adsorbs and regenerates carbon dioxide efficiently and at low cost.

[0003] For example, Patent Document 1 discloses a technique for improving carbon dioxide adsorption performance using Y-type zeolite. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2017-77541 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] However, in many DAC technologies, including the technology described in Patent Document 1, high-temperature processing and high-vacuum processing have been widely used for the regeneration of adsorbents. While these methods offer excellent regeneration efficiency, they require a great deal of energy for the regeneration process itself, resulting in increased operating costs.

[0006] In view of the above problems, the present invention aims to provide an evaluation method capable of evaluating the adsorption performance of a carbon dioxide adsorbent after regeneration under low vacuum conditions, and to provide a carbon dioxide adsorbent whose effectiveness has been confirmed by this evaluation method, thereby enabling the selection of a material that can be regenerated under low vacuum conditions and maintain its performance. [Means for solving the problem]

[0007] To solve the above problems, according to a first aspect of the present invention, the following evaluation method is provided. This evaluation method is a method for evaluating a carbon dioxide adsorbent, (a) A step of heating or depressurizing the carbon dioxide adsorbent, supplying a gas containing carbon dioxide to the carbon dioxide adsorbent, and measuring the amount of carbon dioxide adsorbed Q0 at a predetermined time from the start of supply, (b) The carbon dioxide adsorbent is divided into 10 2 ~10 4 A process of regeneration under low vacuum conditions of Pa, (c) A step of supplying a gas containing carbon dioxide to the carbon dioxide adsorbent again and measuring the amount of carbon dioxide adsorbed QLow over the predetermined time, An evaluation method that includes and evaluates whether the ratio RLow of QLow to Q0 is 70% or more. [Effects of the Invention]

[0008] According to the present invention, it is possible to select materials that can be regenerated under low vacuum conditions and maintain their performance. [Brief explanation of the drawing]

[0009] [Figure 1] This figure schematically shows an example of the configuration of an evaluation apparatus for a carbon dioxide adsorbent according to an embodiment of the present invention. [Figure 2] This graph schematically illustrates the breakthrough test results showing the evaluation method according to an embodiment of the present invention. [Figure 3] This graph shows the evaluation results using a zeolite-based carbon dioxide adsorbent according to an embodiment of the present invention. [Modes for carrying out the invention]

[0010] Embodiments of the present invention will be described below with reference to the attached drawings.

[0011] Figure 1 is a schematic diagram showing an example of the configuration of an evaluation apparatus 1 for carbon dioxide adsorbent according to an embodiment of the present invention.

[0012] The evaluation device 1 is composed of an air pump 10 that supplies gas, a dehumidification tower 20 that removes moisture in the supplied gas, an adsorption tower 30 filled with a carbon dioxide adsorbent, a flow meter 40 that controls the gas flow rate to be constant, and a carbon dioxide concentration meter 50 that measures the carbon dioxide concentration.

[0013] During operation, a gas adjusted to a predetermined carbon dioxide concentration is supplied to the air pump 10 and sent into the device from here. Note that the gas supplied to the air pump 10 is not necessarily limited to a gas with an adjusted carbon dioxide concentration, and unadjusted air may also be used.

[0014] Next, the supplied gas is introduced into the dehumidification tower 20, and after the dew point is adjusted to about -40°C to 20°C, it is sent to the adsorption tower 30. The carbon dioxide contained in the supplied gas is adsorbed by the adsorbent filled in the adsorption tower 30.

[0015] Next, the flow meter 40 measures the gas flow rate, and the carbon dioxide concentration meter 50 measures the carbon dioxide concentration of the gas at the outlet of the adsorption tower. When adjusting the gas flow rate, a flow rate adjustment valve or the like may be provided separately as necessary.

[0016] In addition, the adsorption tower 30 is configured to be removable from the device main body, and the removed adsorption tower 30 can be connected to an external heating device or decompression device for regeneration treatment.

[0017] With this configuration, the adsorption behavior of carbon dioxide in the adsorption tower 30 can be quantitatively grasped, and the adsorption performance after regeneration under low vacuum conditions can be evaluated. Note that the components of this device are not limited to those described above, and design changes can be made as appropriate. For example, the flow meter 40 may be omitted, or other measuring instruments may be used.

[0018] For example, in the evaluation method of the present invention, the carbon dioxide concentration of the supplied gas is preferably adjusted to a range of 300 to 1000 ppm. This range approximates the actual carbon dioxide concentration in the atmosphere and is suitable for evaluations that are appropriate for DAC applications. On the other hand, the evaluation conditions are not limited to this, and may be set to a wider range, such as 200 to 1200 ppm. Furthermore, depending on the specific application or simulation conditions, it is also possible to adjust to a narrower range, for example, 350 to 450 ppm. In this way, the carbon dioxide concentration can be arbitrarily set according to the target environmental conditions and evaluation objectives.

[0019] Furthermore, the dew point of the supplied gas is preferably adjusted to -40°C to 0°C. Setting it within this range reduces the effect of moisture on the adsorbent (especially zeolite). Generally, zeolites tend to preferentially adsorb moisture over carbon dioxide, and it is known that the carbon dioxide adsorption capacity decreases in the presence of moisture (so-called competitive adsorption at adsorption sites occurs). Therefore, by lowering the dew point and using dry air, the carbon dioxide adsorption characteristics can be evaluated stably. However, depending on the application and test conditions, the dew point may be reduced to, for example, -50°C to increase the degree of dryness, or raised to +10°C to simulate relatively high humidity conditions. The present invention is not limited to a specific dew point range and can be adjusted according to the purpose.

[0020] The evaluation method of the present invention will be described in detail below, using the evaluation apparatus 1 shown in Figure 1 as an example.

[0021] First, the adsorption tower 30 is removed from the evaluation device 1 and connected to a heating device for regeneration. Specifically, the adsorbent inside the adsorption tower 30 is subjected to a heat treatment to substantially remove the adsorbent held on the surface and in the pores of the adsorbent. Here, "substantially removed" means that no adsorbent remains at a level that would affect subsequent measurements.

[0022] Next, the adsorption tower 30 is reconnected to the evaluation device 1, and gas supplied from the air pump 10 is introduced. The supplied gas passes through the dehumidification tower 20 to remove moisture and reduce the dew point to approximately -20°C to 0°C. After that, the gas is introduced into the adsorption tower 30, where carbon dioxide is adsorbed by the adsorbent inside the adsorption tower 30. At the outlet side, the gas flow rate is measured by the flow meter 40, and the carbon dioxide concentration in the exhaust gas is continuously measured by the carbon dioxide concentration meter 50. At this time, the amount of adsorption at a predetermined time t1 after the start of supply is defined as the adsorption amount Q0. Here, Q0 represents the ratio of carbon dioxide that was not reached to the outlet side by the predetermined time t1 and was captured by the adsorbent inside the adsorption tower 30. "Determined time t1" means the time range in which substantially most of the adsorption has progressed. Specifically, for example, it is 90 seconds, but it may be arbitrarily set in the range of 30 to 180 seconds. If necessary, the saturated adsorption capacity may be measured separately. Supply conditions such as temperature, dew point, carbon dioxide concentration, and flow rate are also recorded.

[0023] After the adsorption described above, the adsorption tower 30 is removed from the main body of the device again, and the adsorption tower 30 is placed 10 2 ~10 4 Low vacuum regeneration is performed by reducing the pressure to the Pa low vacuum pressure range and holding it for 30 minutes.

[0024] After the regeneration process, the adsorption tower 30 is connected to the evaluation device 1 again, and a adjusted gas containing carbon dioxide is supplied to measure the change in carbon dioxide concentration at the outlet. At this time, the amount of adsorption at the same predetermined time t1 as when Q0 was measured is defined as the adsorption amount QLow after regeneration. Here, QLow represents the ratio of carbon dioxide that, of the carbon dioxide supplied in the same way as Q0, did not reach the outlet side by the predetermined time t1 and was captured by the adsorbent in the adsorption tower 30.

[0025] Finally, the ratio RLow = (QLow / Q0) × 100 [%] is calculated by dividing QLow by Q0. If this RLow is 70% or higher, it can be determined that the adsorbent maintains a certain level of performance even under low vacuum regeneration conditions. Furthermore, an RLow of 80% or higher is even more preferable, and 90% or higher is even more preferable. Note that a similar comparison can be made using the saturated adsorption capacity to evaluate the adsorption performance (regeneration performance) of the adsorbent after low vacuum regeneration.

[0026] The evaluation method described above allows for objective and reproducible assessment of the regeneration performance of adsorbents, which previously required processing at high temperatures or high vacuums, even under low vacuum conditions.

[0027] In this specification, "carbon dioxide adsorbent" or "adsorbent" is a general term for a material or molded article thereof that has the function of physically adsorbing carbon dioxide. That is, a carbon dioxide adsorbent contains porous structures such as zeolites, metal-organic frameworks (MOFs), activated carbon, and mesoporous silica, and may also contain binders, carriers, auxiliary materials, etc., to impart mechanical strength and moldability as needed. Alternatively, for example, a "carbon dioxide adsorbent" may be formed solely from a porous structure.

[0028] Here, "porous structure" is a general term for materials having regularly or irregularly arranged pores, and includes, for example, zeolites (natural or synthetic zeolites, Y-type, MFI-type, BEA-type, etc.), MOFs (metal-organic frameworks, e.g., ZIF), carbon-based porous materials such as activated carbon and mesoporous carbon, mesoporous silica, and oxide-based porous materials such as alumina and titania. These materials can be used individually or in combination.

[0029] Furthermore, the evaluation method of the present invention is also applicable to regeneration treatment under medium vacuum conditions. That is, after substantially removing adsorbent material from the adsorbent by heat treatment, 10 ‐1 ~10 2The adsorbent is regenerated by reducing the pressure to a medium vacuum (Pa) and holding it for 30 minutes. Then, a gas containing carbon dioxide is supplied again, and the amount of adsorption at a predetermined time t1 from the start of supply is measured to determine the adsorption amount Qmiddle after regeneration. By comparing Qmiddle with the adsorption amount QLow after regeneration under low vacuum conditions, the effect of different regeneration conditions on adsorption performance can be evaluated. This allows for understanding the regeneration characteristics of the adsorbent under both low and medium vacuum conditions, enabling the selection of the optimal adsorbent according to the application and design requirements.

[0030] Furthermore, the evaluation method of the present invention allows for the selection of carbon dioxide adsorbents that have been evaluated to have an RLow of 70% or higher after regeneration treatment under low vacuum conditions. By incorporating these selected adsorbents into a DAC device, a DAC device that can operate efficiently based on regeneration under low vacuum conditions can be manufactured. A DAC device with such a configuration can reduce energy consumption and efficiently recover carbon dioxide from the atmosphere compared to conventional devices that require high-vacuum regeneration.

[0031] Figure 2 is a schematic graph showing the results of a breakthrough test related to the evaluation method of the present invention. The horizontal axis represents time (seconds), and the vertical axis represents the carbon dioxide concentration (ppm) at the outlet of the adsorption tower.

[0032] After the start of supply, the carbon dioxide concentration at the outlet of the adsorption tower 30 gradually increases and exhibits a breakthrough behavior toward equilibrium. In this evaluation method, as shown in Figure 2, the amount of carbon dioxide adsorbed at a predetermined time t1 from the start of supply is measured.

[0033] After the start of supply, the outlet concentration gradually increases as adsorption progresses, eventually becoming equal to the inlet concentration. This behavior is known as the breakthrough curve, and by analyzing the change in outlet concentration over time, the performance of the adsorbent can be quantitatively evaluated.

[0034] Figure 2 shows how the shape of the breakthrough curve tends to change depending on the regeneration conditions. If the regeneration conditions are sufficient, the amount of adsorption immediately after the start of supply is large, and the initial adsorption rate is high. On the other hand, if the regeneration is insufficient, the initial adsorption capacity is low. In Figure 2, the adsorption capacity is highest under heated regeneration conditions, and it gradually decreases under medium vacuum regeneration conditions and low vacuum regeneration conditions.

[0035] For example, if there is little difference in the breakthrough curve between low-vacuum or medium-vacuum regeneration conditions and heating regeneration conditions, it means that the adsorbent is sufficiently regenerated even under low-vacuum or medium-vacuum conditions, and there is no need to perform the more costly high-vacuum or heating regeneration. [Examples]

[0036] The following describes examples in which adsorbents containing various zeolites were evaluated using the evaluation method of the present invention. However, the present invention is not limited to these examples.

[0037] In this example, several types of adsorbents were evaluated. The adsorbents were evaluated using the evaluation apparatus 1 shown in Figure 1. The carbon dioxide concentration of the supplied gas was set to 500 ppm, and the humidity was adjusted to a dew point of -25°C by the dehumidification tower 20. The gas flow rate introduced into the evaluation apparatus 1 was maintained at 50 L / min. The adsorption amounts Q0, QLow, and QMiddle represent the adsorption amounts during the first 90 seconds after the start of carbon dioxide supply.

[0038] Table 1 shows the properties of adsorbents containing various zeolites evaluated in this embodiment and the amount of carbon dioxide adsorbed under various regeneration conditions. Table 1 shows the adsorption amount Q0 when carbon dioxide is adsorbed after substantially removing adsorbent material by heating at 200°C for 3 hours, the adsorption amount Qmiddle when the adsorbent is regenerated under medium vacuum conditions (pump: Kashiyama Industries Co., Ltd., NeoDry15G, ultimate pressure 1 Pa), and low vacuum conditions (pump: ULVAC KIKO, Inc., DA-20D, ultimate pressure 5.33 × 10⁻⁶). 3The amount of adsorption when the adsorbent is regenerated at Pa) is shown, and an overall evaluation of the adsorbent's performance is provided in the right column. The ranking of the adsorbent's performance was mainly based on the following indicators. (i) RLow must be 70% or higher. (ii) The adsorption amount Q0 is maintained at 50% or more. (iii) However, depending on the application, it may be considered practically usable if Q0 remains above 30%. In other words, adsorbents that satisfy both (i) and (ii) were designated as S, adsorbents that satisfy (i) and (iii) but not (ii) were designated as A, adsorbents that satisfy (i) but not (iii) were designated as B, and adsorbents that do not satisfy (i) were designated as C.

[0039] [Table 1]

[0040] Figure 3 is a graph showing the adsorption amounts of various adsorbents listed in Table 1, arranged under different regeneration conditions. The vertical axis represents the amount of carbon dioxide adsorbed, and the horizontal axis represents the regeneration conditions. In the figure, each adsorbent is indicated by the following colors and marker shapes. ZCl MFI-S: Black, thick line, × HSZ-642NAD1C: White, square HSZ-320NAD1W: Black, Triangular HSZ-500KODAC: Black, square HSZ-720KOD1C: Black, diamond shape HSZ-822HOD1A: Black, × HSZ-931HOD1A: White, triangular

[0041] As is clear from FIG. 3, both HSZ-320NAD1W and HSZ-500KODAC maintained a high adsorption amount under any regeneration conditions, and particularly maintained an adsorption amount of around 70% even under regeneration conditions of low vacuum and medium vacuum. On the other hand, HSZ-822HOD1A had low adsorption performance and showed a rapid performance decline under low vacuum conditions. In addition, HSZ-720KOD1C showed large fluctuations in the adsorption amount for each regeneration condition, indicating that its adsorption performance strongly depends on the regeneration conditions.

[0042] As described above, the carbon dioxide adsorbent according to the present embodiment is a carbon dioxide adsorbent used for recovering carbon dioxide in the atmosphere, and includes: (a) a step of heating or depressurizing the carbon dioxide adsorbent, and then supplying a gas containing carbon dioxide to the carbon dioxide adsorbent and measuring the adsorption amount Q0 of carbon dioxide at a predetermined time from the start of supply; and (b) a step of subjecting the carbon dioxide adsorbent to regeneration treatment under a low vacuum condition of 10 2 ~10 4 Pa; and (c) a step of supplying a gas containing carbon dioxide to the carbon dioxide adsorbent again and measuring the adsorption amount QLow of carbon dioxide at the predetermined time. When evaluated by the evaluation method including these steps, it is a carbon dioxide adsorbent in which the ratio RLow of QLow to Q0 is 70% or more.

[0043] According to this configuration, the carbon dioxide adsorbent can maintain high adsorption performance even after regeneration treatment under low vacuum conditions. As a result, it contributes to cost reduction in practical use and efficient DAC operation. Furthermore, according to the present invention, by applying a carbon dioxide adsorbent having regeneration performance under low vacuum conditions to a DAC device, a DAC device capable of efficiently recovering carbon dioxide in the atmosphere while reducing energy consumption can be realized.

[0044] In addition, the evaluation method according to the present embodiment is a method for evaluating a carbon dioxide adsorbent, and includes: (a) a step of heating or depressurizing the carbon dioxide adsorbent, and then supplying a gas containing carbon dioxide to the carbon dioxide adsorbent and measuring the adsorption amount Q0 of carbon dioxide at a predetermined time from the start of supply; and (b) a step of subjecting the carbon dioxide adsorbent to regeneration treatment under a low vacuum condition of 10 2 ~10 4(c) a step of regenerating the carbon dioxide adsorbent under low vacuum conditions of Pa, and (c) a step of supplying a gas containing carbon dioxide to the carbon dioxide adsorbent again and measuring the amount of carbon dioxide adsorbed QLow over a predetermined time. The system includes and evaluates whether the ratio RLow of QLow to Q0 is 70% or more.

[0045] This configuration allows for quantitative determination of the regeneration performance of adsorbents even under low vacuum conditions, which can be effectively utilized in material selection and development.

[0046] Furthermore, in the evaluation method according to this embodiment, the carbon dioxide adsorbent includes zeolite.

[0047] This configuration makes it easier to select an adsorbent suitable for DAC applications.

[0048] Furthermore, in the evaluation method according to this embodiment, the dew point of the gas is -40°C or higher and 0°C or lower.

[0049] This configuration reduces the influence of adsorption of moisture in the supplied gas, enabling stable evaluation of carbon dioxide adsorption characteristics.

[0050] Furthermore, in the evaluation method according to this embodiment, the carbon dioxide concentration when supplying the gas containing carbon dioxide is 200 ppm or more and 1000 ppm or less.

[0051] This configuration allows for adsorption evaluation that is in line with actual concentration conditions in the atmosphere.

[0052] Furthermore, in the evaluation method according to this embodiment, the regeneration processing time in step (b) is 10 minutes or more and 60 minutes or less.

[0053] This configuration allows for the evaluation of regeneration performance in a short time and with low energy consumption.

[0054] Furthermore, the evaluation method according to this embodiment involves (d) substantially removing the adsorbent in step (a), and then adding a carbon dioxide adsorbent to 10 ‐1 ~102 The process further includes a step of regenerating the carbon dioxide adsorbent under Pa vacuum conditions, and a step of supplying a gas containing carbon dioxide to the carbon dioxide adsorbent regenerated in step (d), and measuring the amount of carbon dioxide adsorbed Qmiddle at a predetermined time from the start of supply, and comparing Qmiddle and QLow, and evaluating based on the comparison result.

[0055] This configuration allows for the evaluation of the adsorbent's applicability range and optimal conditions by comparing low vacuum and medium vacuum conditions.

[0056] Furthermore, the manufacturing method of the DAC device according to this embodiment involves incorporating a carbon dioxide adsorbent with an RLow of 70% or more, as evaluated by the aforementioned evaluation method, into the DAC device.

[0057] This configuration provides a DAC device (low-vacuum regenerative DAC device) capable of regenerating the adsorbent at low vacuum. Such a low-vacuum regenerative DAC device offers the following remarkable advantages: (i) Air ingress from joints, which is prone to occur under high vacuum conditions, is reduced, and the carbon dioxide concentration in the recovered gas is stably maintained at a high concentration. (ii) Under low vacuum conditions, the time required to reach the target pressure is shorter, thus accelerating the desorption process of the adsorption tower and reducing unnecessary adsorption stop time. (iii) Energy consumption can be suppressed, and carbon dioxide emissions associated with the regeneration process can be reduced. As a result, the DAC device according to the present invention enables carbon dioxide recovery that is superior in efficiency and environmental compatibility compared to conventional high-vacuum methods.

[0058] Furthermore, the DAC device according to this embodiment incorporates a carbon dioxide adsorbent in which the RLow is 70% or more.

[0059] This configuration provides the aforementioned low-vacuum regenerative DAC device.

[0060] Furthermore, the carbon dioxide adsorbent according to this embodiment has a Q0 of 50% or more.

[0061] This configuration ensures sufficient initial adsorption capacity, allowing for efficient carbon dioxide recovery even with small amounts of carbon dioxide adsorbent, contributing to miniaturization and energy savings of the equipment.

[0062] <Variation> The present invention is not limited to the embodiments described above, and various modifications are possible. Specific examples are shown below.

[0063] For example, instead of the amount of adsorption in a predetermined time, the saturated adsorption capacity may be used as an evaluation index. That is, the carbon dioxide adsorbent is a carbon dioxide adsorbent containing zeolite, and (a) after substantially removing adsorbent material from the adsorbent by heating or depressurizing treatment, carbon dioxide is adsorbed and the saturated adsorption capacity Qs_0 is measured, and (b) the adsorbent is 10 2 ~10 4 When evaluated by an evaluation method that includes (c) a step of regenerating under low vacuum conditions of Pa, and (c) a step of adsorbing carbon dioxide again and measuring the saturated adsorption capacity Qs_Low after regeneration, the ratio Rs_Low of Qs_Low to Qs_0 may be above a certain ratio. With the above configuration, the performance of the adsorbent can be evaluated from a more multifaceted perspective.

[0064] Furthermore, the evaluation criteria for the adsorbent are merely examples, and the evaluation range can be changed as appropriate. For example, in this embodiment, a criterion of RLow of 70% or higher was adopted, but RLow may be set to 80% or higher, 85% or higher, or 90% or higher depending on the application and required performance. Similarly, while a criterion of 50% or higher was adopted for the adsorption amount Q0, it can be set to 60% or higher, 70% or higher, or 40% or higher depending on the application. The present invention is not limited to these examples and can be broadly applied depending on corrections and application conditions.

[0065] Furthermore, the regeneration time is not limited to 30 minutes; for example, it may be set to any time between 10 and 60 minutes. The regeneration conditions can be selected according to the type of adsorbent. In addition, the process of substantially removing the adsorbed material is not limited to heat treatment; it may also be performed under high vacuum conditions with reduced pressure.

[0066] Furthermore, in addition to the adsorption amount Q0 and QLow, the gradient of concentration decrease may also be used as an indicator. This allows the adsorption rate to be incorporated into the evaluation index. Moreover, it is not limited to a single measurement, but multiple adsorption and regeneration cycles may be repeated. This allows for the evaluation of long-term durability.

[0067] Furthermore, the dehumidification tower is not limited to a single unit; multiple dehumidification towers filled with different desiccant materials may be arranged in series. This configuration allows for more stable and precise control of the dew point of the supplied gas.

[0068] Furthermore, a temperature control unit, such as a constant temperature bath, may be installed around the adsorption tower. This allows the temperature of the adsorption tower to be kept constant, making it possible to compare the carbon dioxide adsorption performance under conditions that eliminate temperature dependence.

[0069] Furthermore, the DAC device of the present invention may employ a pressure swing method (PSA method). In conventional PSA methods using high vacuum conditions, the time required to complete desorption is longer than the time required to complete adsorption, resulting in unnecessary gas discharge during switching and potentially reducing recovery efficiency. In contrast, by using an adsorbent that can be regenerated under low vacuum conditions as used in the present invention, the time required to reach the target pressure is shortened, thereby significantly reducing the desorption time. As a result, the time during which adsorption processing must be stopped in one tower while desorption processing is being performed in the other tower is reduced, resulting in an improvement in the amount of carbon dioxide recovered per day. Moreover, because it can be regenerated under low vacuum conditions, air contamination from joints, which is a problem under high vacuum conditions, is suppressed, and the carbon dioxide concentration in the recovered gas is maintained at a high level. In addition, since energy consumption can be reduced compared to high vacuum, the environmental burden of the entire carbon dioxide recovery process can be reduced. [Explanation of Symbols]

[0070] 1: Evaluation device, 10: Air pump, 20: Dehumidification tower, 30: Adsorption tower, 40: Flow meter, 50: Carbon dioxide concentration meter, Q0, QLow, QMiddle: Adsorption amount

Claims

1. A method for evaluating carbon dioxide adsorbents, (a) A step of heating or depressurizing the carbon dioxide adsorbent, supplying a gas with a carbon dioxide concentration of 200 ppm or more and 1000 ppm or less to the carbon dioxide adsorbent, and measuring the amount of carbon dioxide adsorbed Q0 during a predetermined time of 30 to 180 seconds from the start of supply, (b) The carbon dioxide adsorbent is divided into 10 ２ ~10 ４ A process of regeneration under low vacuum conditions of Pa for 10 minutes to 60 minutes, (c) A step of supplying a gas containing carbon dioxide to the carbon dioxide adsorbent again and measuring the amount of carbon dioxide adsorbed QLow over the predetermined time, An evaluation method that includes and evaluates whether the ratio RLow of QLow to Q0 is 70% or more.

2. The evaluation method according to claim 1, wherein the carbon dioxide adsorbent comprises zeolite.

3. The evaluation method according to claim 1, wherein the dew point of the gas is -40°C or higher and 0°C or lower.

4. (d) After step (a), the carbon dioxide adsorbent is 10 -１ ~10 ２ A process of regeneration under Pa medium vacuum conditions, (e) A step of supplying a gas containing carbon dioxide to the carbon dioxide adsorbent that has been regenerated in step (d), and measuring the amount of carbon dioxide adsorbed Qmiddle at a predetermined time from the start of supply, The evaluation method according to any one of claims 1 to 3, further comprising comparing the Qmiddle and the QLow and evaluating based on the comparison result.

5. A method for manufacturing a low-vacuum regenerative DAC that allows for the regeneration of adsorbents at low vacuum, comprising incorporating a carbon dioxide adsorbent, which has an RLow of 70% or more, among the carbon dioxide adsorbents evaluated by the evaluation method described in any one of claims 1 to 3, into a DAC device.

6. A low-vacuum regenerative DAC device that incorporates a carbon dioxide adsorbent, which has been evaluated by the evaluation method described in any one of claims 1 to 3, and in which the RLow is 70% or more, and which allows for the regeneration of the adsorbent at a low vacuum.

7. A carbon dioxide adsorbent used in a low-vacuum regenerative DAC device capable of regenerating the adsorbent at a low vacuum, (a) A step of heating or depressurizing the carbon dioxide adsorbent, supplying a gas with a carbon dioxide concentration of 200 ppm or more and 1000 ppm or less to the carbon dioxide adsorbent, and measuring the amount of carbon dioxide adsorbed Q0 during a predetermined time of 30 to 180 seconds from the start of supply, (b) The carbon dioxide adsorbent is divided into 10 ２ ~10 ４ A process of regeneration under low vacuum conditions of Pa for 10 minutes to 60 minutes, (c) A step of supplying the carbon dioxide adsorbent with a gas having a carbon dioxide concentration of 200 ppm or more and 1000 ppm or less, and measuring the amount of carbon dioxide adsorbed QLow over the predetermined time, A carbon dioxide adsorbent in which, when evaluated by an evaluation method including the above, the ratio RLow of QLow to Q0 is 70% or more.

8. The carbon dioxide adsorbent according to claim 7, wherein the aforementioned Q0 is 50% or more.

9. The carbon dioxide adsorbent according to claim 7, wherein the carbon dioxide adsorbent comprises zeolite.

10. (d) After step (a), a step of regenerating the carbon dioxide adsorbent under medium vacuum conditions of 10⁻¹ to 10² Pa, (e) A step of supplying a gas with a carbon dioxide concentration of 200 ppm to 1000 ppm to the carbon dioxide adsorbent that has been regenerated in step (d), and measuring the amount of carbon dioxide adsorbed Qmiddle at a predetermined time from the start of supply, The carbon dioxide adsorbent according to claim 7, further comprising the ratio Rmiddle of QLow to Qmiddle, wherein the ratio Rmiddle of QLow is 90% or more.

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