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) supplying a gas containing water vapor to the carbon dioxide adsorbent and allowing water to be adsorbed onto the carbon dioxide adsorbent for a predetermined time from the start of supply; (b) supplying an inert gas to the carbon dioxide adsorbent; and (c) raising the temperature of the carbon dioxide adsorbent and measuring the water desorbed from the carbon dioxide adsorbent, wherein the evaluation method evaluates whether the desorption peak temperature, which is the temperature at which the detection signal corresponding to the water desorbed from the carbon dioxide adsorbent is maximized, is 130°C or less in step (c).

Description

[Technical Field]

[0001] This 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 project] [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.

[0007] The inventors of this application conducted intensive studies on the regeneration behavior of carbon dioxide adsorbents under low vacuum conditions and found that the desorption behavior of carbon dioxide under low vacuum conditions may be related to the desorption behavior of water adsorbed on the carbon dioxide adsorbent. Specifically, they found that if the water adsorbed on the carbon dioxide adsorbent has the characteristic of desorbing at relatively low temperatures, the carbon dioxide adsorbent tends to desorb carbon dioxide easily even under low vacuum conditions. [Means for solving the problem]

[0008] 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, and includes the steps of (a) supplying a gas containing water vapor to the carbon dioxide adsorbent and adsorbing water onto the carbon dioxide adsorbent for a predetermined time from the start of supply, (b) supplying an inert gas to the carbon dioxide adsorbent, and (c) raising the temperature of the carbon dioxide adsorbent and measuring the water desorbed from the carbon dioxide adsorbent, wherein in step (c), it is evaluated whether the desorption peak temperature, which is the temperature at which the detection signal corresponding to the water desorbed from the carbon dioxide adsorbent is maximum, is 130°C or less. [Effects of the Invention]

[0009] 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]

[0010] [Figure 1] This figure schematically shows an example of the configuration of an evaluation apparatus for a carbon dioxide adsorbent according to the first embodiment of the present invention. [Figure 2] This graph schematically illustrates the breakthrough test results showing the evaluation method according to the first embodiment of the present invention. [Figure 3] Table 1 is a graph showing the amount of CO2 adsorbed by various adsorbents under different regeneration conditions. [Figure 4] This graph schematically illustrates the evaluation method according to the second embodiment of the present invention.

Mode for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. The evaluation method of the present invention includes a first embodiment for evaluating the carbon dioxide adsorption performance after regeneration under low vacuum conditions and a second embodiment for evaluating the water desorption performance.

[0012] <First Embodiment> FIG. 1 is a diagram schematically showing a configuration example of an evaluation apparatus 1 for a carbon dioxide adsorbent according to the first embodiment of the present invention.

[0013] The evaluation apparatus 1 includes an air pump 10 for supplying gas, a dehumidification tower 20 for removing water in the supplied gas, an adsorption tower 30 filled with a carbon dioxide adsorbent, a flow meter 40 for controlling the gas flow rate at a constant value, and a carbon dioxide concentration meter 50 for measuring the carbon dioxide concentration.

[0014] In operation, a gas adjusted to a predetermined carbon dioxide concentration is supplied to the air pump 10 and sent into the apparatus 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 may be unadjusted air.

[0015] 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. Carbon dioxide contained in the supplied gas is adsorbed by the adsorbent filled in the adsorption tower 30.

[0016] Next, the gas flow rate is measured by the flow meter 40, and the carbon dioxide concentration of the gas at the outlet of the adsorption tower is measured by the carbon dioxide concentration meter 50. When adjusting the gas flow rate, a flow rate adjustment valve or the like may be provided separately as necessary.

[0017] In addition, the adsorption tower 30 is configured to be removable from the apparatus main body, and the removed adsorption tower 30 can be connected to an external heating device or decompression device to perform a regeneration process.

[0018] This configuration allows for quantitative understanding of the carbon dioxide adsorption behavior in the adsorption tower 30 and evaluation of the adsorption performance after regeneration under low vacuum conditions. The components of this apparatus are not limited to those described above and can be modified as appropriate. For example, the flow meter 40 may be omitted, or other measuring instruments may be used.

[0019] 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.

[0020] 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 water on the adsorbent (especially zeolite). Generally, zeolites tend to adsorb water preferentially over carbon dioxide, and it is known that the adsorption capacity for carbon dioxide decreases in the presence of water (so-called competitive adsorption at adsorption sites occurs). Therefore, by lowering the dew point and using dry air, the adsorption characteristics of carbon dioxide 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.

[0021] 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.

[0022] 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 adsorbed material held on the surface and within the pores of the adsorbent. Here, "substantially removed" means that no adsorbed material remains at a level that would affect subsequent measurements.

[0023] 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 water 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 CO2 adsorbed 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.

[0024] 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.

[0025] 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 CO2 adsorbed at the same predetermined time t1 as when measuring Q0 is defined as the regenerated CO2 adsorption amount QLow. 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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 CO2 adsorbed at a predetermined time t1 from the start of supply is measured to determine the regenerated CO2 adsorption amount Qmiddle. By comparing Qmiddle with the regenerated CO2 adsorption amount QLow 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] Figure 2 shows how the shape of the breakthrough curve changes depending on the regeneration conditions. If the regeneration conditions are sufficient, the amount of CO2 adsorbed 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 and low vacuum regeneration conditions.

[0036] 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.

[0037] <Second Embodiment> The second embodiment is an evaluation method for evaluating the properties of a carbon dioxide adsorbent by focusing on the behavior of water adsorbed on the carbon dioxide adsorbent. The evaluation method according to the first or second embodiment may be used in combination with the other evaluation method, or it may be used independently.

[0038] In the evaluation method according to the second embodiment, the carbon dioxide adsorbent is first regenerated. Specifically, the carbon dioxide adsorbent can be heated. The heating conditions are set appropriately according to the type and purpose of the carbon dioxide adsorbent to be evaluated. For example, the conditions can be such that the adsorbent is heated at approximately 300°C for 1 hour under normal pressure, but are not limited to this.

[0039] Next, a process is carried out in which water vapor is supplied to the carbon dioxide adsorbent to adsorb water onto it. The supply of water vapor is carried out under predetermined conditions, thereby creating a state in which water is adsorbed onto the carbon dioxide adsorbent to be evaluated.

[0040] Next, after supplying a gas containing water vapor, an inert gas is supplied to the carbon dioxide adsorbent. This process removes any remaining water vapor in the apparatus and any water vapor weakly adsorbed on the outer surface of the pores. Examples of inert gases that can be used include helium and nitrogen, but are not limited to these.

[0041] Subsequently, a process of heating the carbon dioxide adsorbent is carried out. The heating is performed according to predetermined heating conditions, and the desorption behavior of water from the carbon dioxide adsorbent can be evaluated as the temperature rises. Based on the behavior of water observed during the heating process, the properties of the carbon dioxide adsorbent are evaluated.

[0042] The shape and quantity of the carbon dioxide adsorbent described above are not particularly limited, but for example, pellet-shaped carbon dioxide adsorbent can be used. The sample quantity is set appropriately according to the evaluation device and measurement conditions, and can be, for example, about 0.1 g, but is not limited to this.

[0043] The water vapor-containing gas is configured as a water vapor-containing carrier gas. For example, helium can be used as the carrier gas, and the gas can be adjusted to have a water vapor concentration of several percent. The supply of the water vapor-containing gas is carried out under predetermined flow rate and temperature conditions, for example, at room temperature (15°C to 25°C).

[0044] The supply time of the water vapor-containing gas is set to be sufficient time for the carbon dioxide adsorbent to adsorb water, for example, about 30 minutes. This process creates a state in which water is adsorbed onto the carbon dioxide adsorbent.

[0045] In the process of supplying an inert gas, the supply of gas containing water vapor is stopped, and then an inert gas is supplied to the carbon dioxide adsorbent. For example, helium can be used as the inert gas. The supply flow rate is set appropriately according to the evaluation device, and is supplied at a constant flow rate, for example.

[0046] The supply time for the step of supplying the inert gas can be, for example, 30 minutes or more, preferably about 60 minutes. This step removes the water that is weakly held by the adsorbent, leaving a state where the water is adsorbed by the adsorbent.

[0047] During the heating process, the desorption behavior of water is observed by detecting the water released from the carbon dioxide adsorbent into the gas phase as the temperature rises, along with an inert carrier gas. Detection is performed by mass spectrometry or the like. In mass spectrometry, the gas phase components introduced with the carrier gas are ionized, and these ions are separated and detected based on their mass-to-charge ratio (m / z). The detection signal is obtained as a signal intensity corresponding to the amount of water released during the heating process, and the change in this signal intensity with increasing temperature is measured.

[0048] The heating conditions in the heating process can be appropriately set to allow observation of the desorption behavior of water adsorbed on the carbon dioxide adsorbent. For example, heating may be carried out continuously at a constant heating rate, or the temperature may be increased in stages.

[0049] The desorption behavior of water observed during the heating process can be expressed as the temperature at which the signal intensity is maximum as the temperature rises, i.e., the water desorption peak temperature. The desorption peak temperature is an indicator of the temperature range in which water held in the carbon dioxide adsorbent is mainly released into the gas phase as the temperature rises. If the desorption peak temperature is located on the relatively low temperature side, it indicates that the water held in the carbon dioxide adsorbent is released at a relatively low temperature range.

[0050] Furthermore, in the heating process, evaluation may be performed using the temperature distribution of signal intensity during the heating process, in addition to the desorption peak temperature. For example, by integrating the signal intensity for each temperature range, the proportion of the total amount of water desorbed during the heating process that is released in a temperature range below a predetermined temperature can be calculated. Specifically, by calculating the ratio of the integrated signal intensity in the temperature range below a predetermined temperature to the integrated signal intensity for the entire heating process, the proportion of the amount of water desorbed that is released in that temperature range below a predetermined temperature can be determined.

[0051] The predetermined temperature can be, for example, 150°C, and the properties of the carbon dioxide adsorbent can be evaluated based on whether a predetermined proportion of the desorption amount is released within a temperature range of 150°C or below. The predetermined proportion can be appropriately set according to the application and operating conditions of the carbon dioxide adsorbent to be evaluated, and can be, for example, 40% or more, 50% or more, or 60% or more, but is not limited to these.

[0052] Figure 4 is a schematic graph showing the water desorption behavior in the heating process according to the second embodiment of the present invention. The horizontal axis represents temperature, and the vertical axis represents the amount of water desorbed.

[0053] In the heating process, increasing the temperature of the carbon dioxide adsorbent causes the water adsorbed on the carbon dioxide adsorbent to gradually desorb into the gas phase. The curves shown in Figure 4 exemplify the changes in the amount of water desorbed with increasing temperature for several carbon dioxide adsorbents with different water desorption behaviors. Each curve shows an example where the water desorption peak temperature is different, illustrating that the water desorption behavior differs when the desorption peak temperature is located on the low-temperature side compared to when it is located on the high-temperature side.

[0054] As the temperature rises, water desorption progresses, increasing to a maximum amount, and then decreasing as desorption continues. The temperature at which this maximum desorption amount occurs corresponds to the H2O desorption peak temperature mentioned earlier. The difference in water desorption peak temperatures indicates that at what temperature range H2O adsorbed on the carbon dioxide adsorbent is primarily desorbed. For example, a curve where the desorption peak temperature is located on the relatively low temperature side indicates that H2O is desorbed at relatively low temperatures. On the other hand, a curve where the desorption peak temperature is located on the high temperature side indicates that H2O continues to be adsorbed up to higher temperatures.

[0055] In this way, by analyzing the desorption behavior of H2O during the heating process, the water desorption capacity of the carbon dioxide adsorbent can be evaluated.

[0056] Incidentally, in conventional carbon dioxide adsorbent regeneration methods, one of the main challenges has been the removal of water adsorbed on the adsorbent during repeated adsorption and regeneration operations. In particular, when water is strongly retained by the adsorbent, 10 2 ~10 4 Under low vacuum conditions of around Pa, it is difficult to adequately remove water, and repeated regeneration can lead to water accumulation in the adsorbent, potentially reducing its carbon dioxide adsorption performance. Therefore, conventional DAC devices have generally incorporated heating means, such as heaters, to reliably remove water from the adsorbent. On the other hand, as mentioned above, by using a carbon dioxide adsorbent with a water desorption peak temperature located on the lower side and capable of water desorption in a relatively low temperature range, it becomes possible to remove water even under low vacuum conditions. By configuring a DAC device using a carbon dioxide adsorbent with such characteristics, a regeneration method that does not require high-temperature heating can be adopted, making it possible to realize a DAC device with a simplified heating means or a reduced heating load.

[0057] As described above, according to the evaluation method of the second embodiment, the water desorption capacity of a carbon dioxide adsorbent can be evaluated by an evaluation method that includes the steps of supplying a gas containing water vapor, supplying an inert gas, and raising the temperature. Furthermore, it is possible to evaluate the properties of the carbon dioxide adsorbent based on the desorption behavior of water adsorbed on the carbon dioxide adsorbent. For example, it can be used to evaluate whether a carbon dioxide adsorbent regenerated under low vacuum conditions is suitable for direct air recovery (DAC) applications. Specifically, a carbon dioxide adsorbent with a relatively low water desorption peak temperature observed in the second embodiment can be evaluated as having high carbon dioxide adsorption performance after regeneration under low vacuum conditions in the first embodiment.

[0058] Furthermore, the evaluation method according to the second embodiment can be used in combination with the evaluation method according to the first embodiment. By evaluating the carbon dioxide adsorption performance after regeneration under low vacuum conditions and the desorption behavior of water together, the characteristics of the carbon dioxide adsorbent can be understood from multiple perspectives. [Examples]

[0059] 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.

[0060] <Example 1> In Example 1, 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 supply 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 CO2 adsorption amounts Q0, QLow, and QMiddle represent the amount of CO2 adsorbed during the first 90 seconds after the start of carbon dioxide supply.

[0061] Table 1 shows the properties of adsorbents containing various zeolites evaluated in Example 1 and the amount of carbon dioxide adsorbed under various regeneration conditions. Table 1 shows the amount of CO2 adsorbed Q0 when carbon dioxide was adsorbed after substantially removing adsorbent material by heating at 200°C for 3 hours, the amount of CO2 adsorbed Qmiddle when the adsorbent was regenerated under medium vacuum conditions (pump: Kashiyama Industries Co., Ltd., NeoDry15G, ultimate pressure 1 Pa), and under low vacuum conditions (pump: ULVAC KIKO, Inc., DA-20D, ultimate pressure 5.33 × 10⁻⁶). 3 The amount of CO2 adsorbed 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 CO2 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.

[0062] TIFF0007876927000002.tif48170

[0063] Figure 3 is a graph showing the CO2 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. HSZ-320NAD1W: Black, Triangular HSZ-500KODAC: Black, square HSZ-720KOD1C: Black, diamond shape HSZ-822HOD1A: Black, ×

[0064] As is clear from Figure 3, the HSZ-320NAD1W and HSZ-500KODAC maintained high CO2 adsorption under all regeneration conditions, and in particular maintained around 70% CO2 adsorption even under low and medium vacuum conditions. On the other hand, the HSZ-822HOD1A had low adsorption performance and showed a rapid decline in performance under low vacuum conditions. Furthermore, the HSZ-720KOD1C showed large fluctuations in CO2 adsorption for each regeneration condition, indicating that its adsorption performance is strongly dependent on the regeneration conditions.

[0065] <Example 2> In Example 2, the water desorption behavior was evaluated for several types of adsorbents. The water desorption behavior was evaluated by purging with an inert gas and measuring desorption at a higher temperature (H2O-TPD measurement) after adsorbing water vapor.

[0066] The adsorbents used for evaluation are shown in Table 2. All adsorbents used for measurement were in pellet form, and the sample amount was 0.1 g. As a pretreatment, each adsorbent was heated at 300°C for 1 hour under normal pressure to substantially remove the adsorbed material.

[0067] Water was adsorbed onto the pre-treated adsorbent by supplying a carrier gas (helium) containing water vapor. The water vapor was supplied by bubbling, and the concentrator temperature was set to 21.3°C to adjust the water vapor concentration in the carrier gas to 2.5%. The carrier gas flow rate was 50 sccm and the temperature was 25°C. The water vapor adsorption test time was 30 minutes.

[0068] After water vapor adsorption, a gas purge treatment was performed with an inert gas (100% helium). The flow rate of the inert gas was 50 sccm, and the treatment time was 60 minutes.

[0069] Subsequently, H2O-TPD measurements were performed. For TPD measurements, 100% helium was used as the carrier gas, with a flow rate of 50 sccm. The temperature was increased at a rate of 10°C / min, with an upper temperature limit of 400°C. Desorbed water was detected by mass spectrometry, and the desorption behavior of water was evaluated from the temperature dependence of the obtained signal intensity.

[0070] Table 2 shows the water desorption peak temperatures for each adsorbent evaluated in Example 2.

[0071] TIFF0007876927000003.tif74170

[0072] As shown in Table 2, the water desorption peak temperature was 125°C for both the HSZ-320NAD1W and HSZ-500KODAC.

[0073] On the other hand, for other adsorbents, the peak water desorption temperature was higher (above 130°C). This suggests that water is relatively strongly retained by the adsorbent, and that removing water may be difficult under low vacuum conditions.

[0074] From the above, among the adsorbents measured in this example, it was confirmed that HSZ-320NAD1W and HSZ-500KODAC have the property that water desorbs in the low temperature range. Considering such adsorbents in combination with the evaluation results of the carbon dioxide adsorption performance shown in Example 1, they are considered to be adsorbents suitable for regeneration under low vacuum conditions.

[0075] As described above, the carbon dioxide adsorbent according to the first embodiment is a carbon dioxide adsorbent used for recovering carbon dioxide in the atmosphere, and includes: (a) after heating or depressurizing the carbon dioxide adsorbent, supplying a gas containing carbon dioxide to the carbon dioxide adsorbent, and measuring the carbon dioxide adsorption amount Q0 at a predetermined time from the start of supply; and (b) subjecting the carbon dioxide adsorbent to a regeneration treatment under a low vacuum condition of 10 2 ~10 4 Pa; and (c) supplying a gas containing carbon dioxide to the carbon dioxide adsorbent again, and measuring the carbon dioxide adsorption amount QLow 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.

[0076] 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 operation of DAC. 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.

[0077] In addition, the evaluation method according to the first embodiment is a method for evaluating a carbon dioxide adsorbent, and includes: (a) after heating or depressurizing the carbon dioxide adsorbent, supplying a gas containing carbon dioxide to the carbon dioxide adsorbent, and measuring the carbon dioxide adsorption amount Q0 at a predetermined time from the start of supply; and (b) subjecting the carbon dioxide adsorbent to a 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.

[0078] 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.

[0079] Furthermore, in the evaluation method according to the first embodiment, the carbon dioxide adsorbent includes zeolite.

[0080] This configuration makes it easier to select an adsorbent suitable for DAC applications.

[0081] Furthermore, in the evaluation method according to the first embodiment, the dew point of the gas is -40°C or higher and 0°C or lower.

[0082] This configuration reduces the influence of water adsorption in the supplied gas, enabling stable evaluation of carbon dioxide adsorption characteristics.

[0083] Furthermore, in the evaluation method according to the first embodiment, the carbon dioxide concentration when supplying the gas containing carbon dioxide is 200 ppm or more and 1000 ppm or less.

[0084] This configuration allows for adsorption evaluation that is in line with actual concentration conditions in the atmosphere.

[0085] Furthermore, in the evaluation method according to the first embodiment, the regeneration processing time in step (b) is 10 minutes or more and 60 minutes or less.

[0086] This configuration allows for the evaluation of regeneration performance in a short time and with low energy consumption.

[0087] Furthermore, the evaluation method according to the first 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.

[0088] This configuration allows for the evaluation of the adsorbent's applicability range and optimal conditions by comparing low vacuum and medium vacuum conditions.

[0089] Furthermore, the manufacturing method of the DAC device according to the first embodiment involves incorporating a carbon dioxide adsorbent with an RLow of 70% or more, selected from the carbon dioxide adsorbents evaluated by the aforementioned evaluation method, into the DAC device.

[0090] 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.

[0091] Furthermore, the DAC device according to the first embodiment incorporates a carbon dioxide adsorbent in which the RLow is 70% or more.

[0092] This configuration provides the aforementioned low-vacuum regenerative DAC device.

[0093] Furthermore, the carbon dioxide adsorbent according to the first embodiment has a Q0 of 50% or more.

[0094] 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.

[0095] Furthermore, the method for evaluating the carbon dioxide adsorbent according to the second embodiment includes the steps of supplying a gas containing water vapor to adsorb water onto the carbon dioxide adsorbent, supplying an inert gas, and heating the carbon dioxide adsorbent and measuring the water desorbed from the adsorbent, and in the heating step, it is evaluated whether the desorption peak temperature, which is the temperature at which the detection signal corresponding to the water desorbed from the carbon dioxide adsorbent is maximum, is 130°C or lower.

[0096] With this configuration, the regeneration suitability under low vacuum conditions can be evaluated based on another indicator, the water desorption peak temperature. That is, when the water desorption peak temperature is 130°C or lower, the carbon dioxide adsorbent is 10 2 ~10 4 This allows for evaluation to determine suitability for DAC applications under low vacuum conditions of Pa. This enables efficient selection of adsorbents that easily remove water under low vacuum conditions and maintain carbon dioxide adsorption performance after regeneration, thus facilitating the selection of adsorbent materials suitable for DAC applications.

[0097] Furthermore, in the method for evaluating the carbon dioxide adsorbent according to the second embodiment, the step of supplying an inert gas is carried out continuously for 30 minutes or more.

[0098] This configuration allows the heating process to be carried out with sufficient removal of water weakly held by the adsorbent, enabling a more accurate evaluation of the water desorption behavior.

[0099] The manufacturing method of the DAC device according to the second embodiment involves incorporating a carbon dioxide adsorbent, among the evaluated carbon dioxide adsorbents, in which the water desorption peak temperature is 130°C or lower, into the DAC device.

[0100] This configuration allows for the application of a carbon dioxide adsorbent with regenerative properties under low vacuum conditions to the DAC device. As a result, it is possible to manufacture a DAC device that can efficiently recover carbon dioxide from the atmosphere while reducing energy consumption compared to conventional configurations that require high-vacuum regeneration.

[0101] The manufacturing method of the DAC device according to the second embodiment involves incorporating a carbon dioxide adsorbent, among the evaluated carbon dioxide adsorbents, in which the water desorption peak temperature is 130°C or lower, into a low-vacuum regenerative DAC device capable of regenerating the adsorbent under low vacuum.

[0102] This configuration allows for the application of a carbon dioxide adsorbent with regenerative properties under low vacuum conditions to the DAC device. As a result, it is possible to manufacture a DAC device that can efficiently recover carbon dioxide from the atmosphere while reducing energy consumption compared to conventional configurations that require high-vacuum regeneration.

[0103] The low-vacuum regenerative DAC device capable of regenerating adsorbent at a low vacuum according to the second embodiment is 10 2 ~10 4 The system is equipped with a low-vacuum regeneration mechanism that regenerates the carbon dioxide adsorbent under low vacuum conditions of Pa, and the low-vacuum regeneration mechanism regenerates the carbon dioxide adsorbent under temperature conditions of less than 100°C.

[0104] With this configuration, the regeneration of the carbon dioxide adsorbent can be completed by a low-vacuum regeneration mechanism that operates under low-vacuum conditions. Therefore, even in repeated regeneration operations, stable regeneration can be achieved while suppressing water accumulation.

[0105] The carbon dioxide adsorbent according to the second embodiment is a carbon dioxide adsorbent used in a low-vacuum regenerative DAC device capable of regenerating the adsorbent at a low vacuum, and is a carbon dioxide adsorbent in which, when evaluated by an evaluation method including (a) supplying a gas containing water vapor to the carbon dioxide adsorbent and adsorbing water onto the carbon dioxide adsorbent for a predetermined time from the start of supply, (b) supplying an inert gas to the carbon dioxide adsorbent, and (c) raising the temperature of the carbon dioxide adsorbent and measuring the water desorbed from the carbon dioxide adsorbent, the desorption peak temperature, which is the temperature at which the detection signal corresponding to the water desorbed from the carbon dioxide adsorbent is maximized, is 130°C or lower.

[0106] This configuration makes it possible to provide a carbon dioxide adsorbent that allows water to be easily desorbed at relatively low temperatures even under low vacuum conditions, and that suppresses water accumulation during repeated regeneration operations. As a result, it is possible to realize an adsorbent that can stably maintain carbon dioxide adsorption performance in DAC applications that assume regeneration under low vacuum conditions.

[0107] <Variation> The present invention is not limited to the embodiments described above, and various modifications are possible. Specific examples are shown below.

[0108] For example, instead of the amount of CO2 adsorbed 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.

[0109] Furthermore, the evaluation criteria for the adsorbent are merely examples, and the evaluation range can be changed as appropriate. For example, in the first 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, for CO2 adsorption amount Q0, a criterion of 50% or higher was adopted, but 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.

[0110] 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.

[0111] Furthermore, in addition to the CO2 adsorption amount Q0 and CO2 adsorption amount 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.

[0112] 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.

[0113] 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.

[0114] 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.

[0115] Furthermore, the temperature condition used as the water desorption peak temperature is not limited to 150°C, but may be set appropriately depending on the application and regeneration conditions of the carbon dioxide adsorbent being evaluated. For example, the suitability for regeneration under low vacuum conditions may be evaluated based on whether the water desorption peak temperature is 140°C or lower, 135°C or lower, or 130°C or lower.

[0116] Furthermore, carbon dioxide adsorbents may be evaluated in stages according to the water desorption peak temperature. For example, adsorbents with a water desorption peak temperature of 130°C or lower may be classified as highly suitable, those with a water desorption peak temperature between 130°C and 150°C as moderately suitable, and those with a water desorption peak temperature above 150°C as poorly suitable.

[0117] Furthermore, the evaluation of water desorption behavior during the heating process is not limited to the desorption peak temperature, but may also be performed using the distribution of the amount of desorption. For example, the properties of the carbon dioxide adsorbent may be evaluated based on whether the proportion of water desorbed at a temperature below a predetermined temperature, for example, below 150°C, is above a predetermined proportion of the total amount of water desorbed.

[0118] Furthermore, the heat treatment performed as a pretreatment before evaluation is not limited to 300°C for 1 hour, but may be performed at a temperature of 200°C to 400°C for 30 minutes to 3 hours, for example. Also, the water vapor concentration in the water vapor-containing gas is not limited to 2.5%, but may be set in a range of 1% to 5%, for example. Also, the processing time for the inert gas supply process is not limited to 60 minutes, but may be set in a range of 30 minutes to 90 minutes, for example. Also, the inert gas is not limited to helium, but may be argon, for example. Also, the flow rate of the carrier gas in each process may be set in a range of 10 sccm to 100 sccm, for example. Also, the heating rate in the heating process is not limited to 10°C / min, but may be set in a range of 5°C / min to 20°C / min, for example. Also, the heating process is not limited to continuous heating, but may be carried out as a stepwise heating method with holding time set at predetermined temperatures.

[0119] Furthermore, in evaluating the desorption behavior of water, it is possible to distinguish between water desorbed by the inert gas supply process and water desorbed by the heating process. For example, the proportion of water weakly retained by the adsorbent can be evaluated based on the ratio of the amount of water desorbed in the inert gas supply process to the amount of water desorbed in the heating process.

[0120] Furthermore, evaluation based on the desorption behavior of water may be performed in combination with the evaluation results of carbon dioxide adsorption performance in the first embodiment. For example, an adsorbent in which the peak temperature of water desorption is below a predetermined temperature and the adsorption amount ratio RLow after low-vacuum regeneration is above a predetermined value may be selected as an adsorbent suitable for regeneration under low-vacuum conditions. With this configuration, it is possible to reliably select an adsorbent that can be regenerated under low-vacuum conditions and can actually maintain high carbon dioxide adsorption performance. [Explanation of symbols]

[0121] 1: Evaluation device, 10: Air pump, 20: Dehumidification tower, 30: Adsorption tower, 40: Flow meter, 50: Carbon dioxide concentration meter, Q0, QLow, QMiddle: CO2 adsorption amount

Claims

1. A method for evaluating a carbon dioxide adsorbent containing zeolite, (a) A step of supplying a gas containing water vapor to the carbon dioxide adsorbent and allowing water to be adsorbed by the carbon dioxide adsorbent for a predetermined time from the start of supply, (b) A step of supplying an inert gas to the carbon dioxide adsorbent, (c) A step of raising the temperature of the carbon dioxide adsorbent and measuring the water released from the carbon dioxide adsorbent, Includes, An evaluation method for evaluating whether the desorption peak temperature, which is the temperature at which the detection signal corresponding to the water desorbed from the carbon dioxide adsorbent is at its maximum in step (c), is 25°C or higher and 130°C or lower.

2. The evaluation method according to claim 1, wherein step (b) is carried out continuously for 30 minutes or more.

3. Furthermore, (x) A step of heating or depressurizing the carbon dioxide adsorbent, then 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 Q0 at a predetermined time from the start of supply, (y) The carbon dioxide adsorbent is 10 ２ ~10 ４ A process of regeneration under low vacuum conditions of Pa, (z) 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, Includes, The evaluation method according to claim 1, which evaluates the desorption behavior of water and whether the ratio RLow of QLow to Q0 is 70% or more.

4. A method for manufacturing a DAC, comprising incorporating a carbon dioxide adsorbent, which has been evaluated by the evaluation method described in any one of claims 1 to 3, and which has a desorption peak temperature of 25°C or more and 130°C or less, into a low-vacuum regenerative DAC capable of regenerating the adsorbent at a low vacuum.

5. 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 whose desorption peak temperature is 25°C or higher and 130°C or lower, and which allows for the regeneration of the adsorbent at a low vacuum.

6. A carbon dioxide adsorbent containing zeolite, used in a low-vacuum regenerative DAC device capable of regenerating the adsorbent at low vacuum, (a) A step of supplying a gas containing water vapor to the carbon dioxide adsorbent and allowing water to be adsorbed by the carbon dioxide adsorbent for a predetermined time from the start of supply, (b) A step of supplying an inert gas to the carbon dioxide adsorbent, (c) A step of raising the temperature of the carbon dioxide adsorbent and measuring the water released from the carbon dioxide adsorbent, A carbon dioxide adsorbent having a desorption peak temperature of 25°C or higher and 130°C or lower, which is the temperature at which the detection signal corresponding to the water desorbed from the carbon dioxide adsorbent is maximized when evaluated by an evaluation method including the above.

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