CO2 capture method

Abstract

To provide a CO2 capture method that can capture CO2 efficiently and at low cost. [Solution] The CO2 recovery method according to the present disclosure is a CO2 recovery method which alternately repeats the adsorption and desorption of CO2, wherein the shortest time at which the adsorption rate of CO2 to the CO2 adsorbent becomes 80% by volume or more is t1, and the time of one cycle consisting of the adsorption and desorption of CO2 is t2.

Description

Technical Field

[0001] The present disclosure relates to a CO2 recovery method.

Background Art

[0002] Development of CO2 recovery methods for recovering CO2 (carbon dioxide) from the atmosphere is in progress. For example, a known CO2 recovery method involves passing air through a direct air capture device at normal temperature to adsorb CO2, then heating the device to about 100°C to desorb the CO2 (Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, the method disclosed in Patent Document 1 has a high cost when recovering CO2 from the atmosphere, and improvements in cost performance have been desired.

[0005] The present disclosure has been made in view of the above background, and an object thereof is to provide a CO2 recovery method capable of efficiently recovering CO2 at low cost.

Means for Solving the Problems

[0006] The CO2 recovery method according to the present disclosure alternately repeats CO2 adsorption and desorption, in which CO2 contained in a supplied gas is adsorbed onto a CO2 adsorbent, and the CO2 adsorbent is adjusted to a temperature higher than that during CO2 adsorption, thereby desorbing and recovering the CO2 adsorbed on the CO2 adsorbent from the CO2 adsorbent. When the shortest time for the CO2 adsorption rate to the CO2 adsorbent to reach 80% by volume or more is defined as t1, and the time for one cycle consisting of the CO2 adsorption and desorption is defined as t2, the relationship t1<t2<4×t1 is satisfied. As described above, the CO2 recovery method according to the present disclosure performs CO2 recovery in a shorter cycle time compared to a conventional CO2 recovery method in which the CO2 adsorption rate to the CO2 adsorbent is set to 100% by volume, that is, the adsorption capacity of the CO2 adsorbent is fully utilized. As described above, in the method according to the present disclosure that performs CO2 recovery in a shorter cycle time than usual, when the CO2 recovery amount and various costs related to CO2 recovery are comprehensively evaluated, the CO2 recovery cost can be reduced and CO2 can be recovered efficiently compared to the conventional recovery method.

[0007] The CO2 adsorbent may include a CO2 adsorbing agent and a plurality of porous carriers supporting the CO2 adsorbing agent, and the CO2 adsorbing agent may contain polyethyleneimine having an isopropyl group.

[0008] The porous carrier may have a honeycomb structure.

[0009] The supply speed of the gas to the CO2 adsorbent may be 11 m / s or more.

[0010] The porous carrier may be coated with silica gel, and the thickness of the silica gel may be 250 μm or less. [Effects of the Invention]

[0011] According to the present disclosure, it is possible to provide a CO2 recovery method capable of efficiently recovering CO2 at low cost. [Brief Description of the Drawings]

[0012] [Figure 1] This is a diagram showing a configuration example of a CO2 recovery apparatus that can be used in the CO2 recovery method according to the present disclosure. [Figure 2] This is a diagram for explaining the operation of the CO2 recovery apparatus in the CO2 recovery method according to the present disclosure. [Figure 3] This is a graph showing an example of the relationship between the adsorption rate of a CO2 adsorbent (CO2 adsorbing agent) and the thickness of silica gel that coats a porous carrier. [Figure 4] This is a graph showing an example of the relationship between cycle time and cost ratio in the CO2 recovery method according to the present disclosure. [Modes for Carrying Out the Invention]

[0013] Hereinafter, the present invention will be described through embodiments of the invention, but the invention according to the claims is not limited to the following embodiments. In addition, not all of the configurations described in the embodiments are necessarily essential as means for solving the problems. For clarity of explanation, the following descriptions and drawings are appropriately omitted and simplified.

[0014] In the CO2 recovery method according to the present disclosure (hereinafter also referred to as the present method), CO2 contained in a gas supplied from the outside is adsorbed onto a CO2 adsorbent. Then, by adjusting the adsorbent to a temperature higher than that during CO2 adsorption, the CO2 adsorbed on the adsorbent is desorbed from the adsorbent and recovered, and the adsorption and desorption of CO2 are alternately and repeatedly performed. At that time, when the shortest time for the CO2 adsorption rate on the CO2 adsorbent to reach 80% by volume or more is defined as t1, and the time for one cycle consisting of the CO2 adsorption and desorption is defined as t2, the specific relationship of Formula 1: t1 < t2 < 4 × t1 is satisfied. When the one-cycle time t2 satisfies the relationship of the Formula 1, costs such as electricity charges can be further reduced. Here, FIG. 1 shows a configuration example of a CO2 recovery apparatus that can be used in the CO2 recovery method according to the present disclosure. In addition, FIG. 2 shows a diagram for explaining the operation of the CO2 recovery apparatus.

[0015] The CO2 recovery device shown in Figure 1 is a device that recovers CO2 by alternately repeating CO2 adsorption and CO2 desorption processes. The CO2 recovery device comprises a blower 1, a first valve 2, a desorption gas feeder 3, an adsorbent 4 equipped with a heating / cooling mechanism, a vacuum pump 5, and a second valve 6. More specifically, as shown in Figure 2, the gas (exhaust gas or atmosphere) supplied from an external source before CO2 recovery is sent to the adsorber 4, which is equipped with a heating / cooling mechanism, through the opened first valve 2 by turning on the blower 1. This gas may be exhaust gas from a factory or power plant, etc., with a relatively high CO2 concentration, or it may be atmosphere with a relatively low CO2 concentration. Then, the CO2 (carbon dioxide) contained in the gas is adsorbed onto the CO2 adsorbent in the adsorber 4 at room temperature (for example, 25°C). After some of the CO2 has been recovered by the CO2 adsorbent, the gas is discharged to the outside through the opened second valve 6. Then, after performing an adsorption treatment for, for example, 5 minutes or less, a CO2 desorption treatment is performed. Specifically, first, the adsorber 4 is evacuated using a vacuum pump 5, purged with oxygen, and heated by a heating mechanism. As a result, the temperature of the adsorber 4 (CO2 adsorbent) is adjusted to a higher temperature (gas desorption temperature) compared to the CO2 adsorption treatment. In addition, in the CO2 desorption treatment, the adsorber 4 may be adjusted to a lower pressure compared to the CO2 adsorption treatment, or the partial pressure of CO2 may be adjusted to a lower CO2 by circulating a gas such as water vapor. As a result, the CO2 adsorbed on the CO2 adsorbent begins to desorb. At that time, with the desorption gas feeder 3 and vacuum pump 5 turned on, the CO2 adsorbed on the CO2 adsorbent is desorbed from the CO2 adsorbent and recovered. If the CO2 recovery treatment is to be continued, the adsorber 4 is cooled by a cooling mechanism, and the gas before CO2 recovery is adsorbed onto the adsorber 4 again, and the CO2 recovery treatment is continued. The CO2 recovery device may also be configured as multiple units, each sharing a blower 1, a desorption gas feeder 3, and a vacuum pump 5, and having multiple or more first valves 2, adsorbers 4, and second valves 6. In such a CO2 recovery device, since the blower 1, desorption gas feeder 3, and vacuum pump 5 are shared, it is preferable to control the operation of each unit, consisting of the first valve 2, adsorber 4, and second valve 6, so that the operations shown in Figure 2 do not overlap. Furthermore, the CO2 recovery device may include a temperature regulator for adjusting the temperature of the adsorber 4, a pressure regulator for adjusting the pressure of the adsorber, a humidity regulator for adjusting the humidity of the adsorber 4, and the like. Furthermore, the CO2 recovery device may have a control unit that controls the alternating repetition of CO2 adsorption and CO2 desorption processes. The control unit can also set the processing conditions (temperature, pressure, humidity, etc.) for each of the CO2 adsorption and CO2 desorption processes. Furthermore, since this method allows for a configuration that repeats shorter cycles at a higher speed than conventional CO2 capture methods, the equipment can be made smaller than conventional CO2 capture devices. Furthermore, this method allows for CO2 desorption at lower temperatures (e.g., below 60°C) than conventional CO2 recovery methods. For example, by performing adsorption for 5 minutes and desorption for 5 minutes in a 10-minute cycle, and setting the desorption temperature to 60°C, it is possible to obtain the same amount of recovered CO2 as when CO2 recovery is performed under conventional high-temperature conditions (e.g., above 80°C) in a similar 10-minute cycle. Thus, low-temperature desorption and high-speed cycles can further reduce costs.

[0016] In this method, as described above, the CO2 recovery device is operated repeatedly with four operations of adsorption, heating, desorption and cooling in the adsorber as one cycle, and CO2 can be recovered by alternately repeating the CO2 adsorption process (cooling and adsorption operations) and the CO2 desorption process (heating and desorption operations. At that time, as described above, the operation time of the four operations is set such that the time t2 of one cycle is within a time period satisfying Formula 1: t1 < t2 < 4 × t1 with respect to the shortest time t1 at which the CO2 adsorption rate for the used CO2 adsorbent is 80% by volume or more. As long as the above formula 1 is satisfied, the operation time of each operation is not particularly limited, and for example, the CO2 adsorption process (cooling and adsorption operations) may be set to a time of t1 / 2 or more and less than 2 × t1, and the CO2 desorption process (heating and desorption operations) may be set to a time of t1 / 2 or more and less than 2 × t1.

[0017] The temperature during desorption can be appropriately set by heating, and can be, for example, 90°C or lower, 85°C or lower, 80°C or lower, 75°C or lower, or 70°C or lower. In addition, the temperature during adsorption can be appropriately set by cooling, and can be 20°C or higher, 25°C or higher, 30°C or higher, 35°C or higher, or 40°C or higher.

[0018] Here, t1 means the shortest time in which the adsorption capacity becomes 80% by volume or more, assuming that the adsorption capacity when CO2 is adsorbed to the adsorber 4 to be used (more specifically, the CO2 adsorbent) for a sufficiently long time (for example, 1 hour or more) (when the adsorption power of the adsorber is utilized to the maximum) is 100% by volume. In other words, t1 can be said to be the adsorption time at which the CO2 adsorption capacity of the adsorber 4 to be used reaches 80% by volume.

[0019] t1 can be appropriately set according to the CO2 recovery device to be used (more specifically, the CO2 adsorbent to be used), and can be, for example, 5 minutes or less, 4 minutes and 30 seconds or less, 4 minutes or less, 3 minutes and 30 seconds or less, 3 minutes or less, 2 minutes and 30 seconds or less, or 2 minutes or less. When t1 is 5 minutes or less, cost reduction can be easily achieved.

[0020] From a cost perspective, t1 is set to the shortest time at which the CO2 adsorption rate on the CO2 adsorbent used is 80% by volume or more. However, the CO2 adsorption rate at t1 can also be set to, for example, 75% by volume or more, 81% by volume or more, 82% by volume or more, 83% by volume or more, 84% by volume or more, or 85% by volume or more. However, from the viewpoint of keeping costs as low as possible, it is preferable that the CO2 adsorption rate at t1 be 80% by volume or more.

[0021] t2 is the time for one cycle consisting of CO2 adsorption and desorption, and can be set appropriately depending on the adsorbent used, within the range that satisfies Equation 1 above. For example, t2 can be less than 60 minutes, 55 minutes or less, 50 minutes or less, 45 minutes or less, 40 minutes or less, 35 minutes or less, 30 minutes or less, 25 minutes or less, or 20 minutes or less. Furthermore, the lower limit of t2 can be appropriately set according to the adsorbent used, within the range that satisfies Equation 1 above. For example, t2 ≥ 1.1 × t1, t2 ≥ 1.2 × t1, t2 ≥ 1.3 × t1, t2 ≥ 1.4 × t1, and t2 ≥ 1.5 × t1 can be used. By satisfying Equation 1 above, the lower limit of t2 can be sufficient for CO2 desorption and adsorption. For example, t2 can be set to 4 minutes or more, 4.5 minutes or more, or 5 minutes or more.

[0022] Furthermore, in this method, it is preferable that the supply rate of gas from the outside to the adsorber 4 (CO2 adsorbent) is 11 m / s or higher. In other words, it is preferable that the wind speed of the blower 1 in the CO2 recovery device is 11 m / s or higher. By setting the supply rate to the adsorber to 11 m / s or higher and improving the adsorption rate, t1 can be made shorter, and cost reduction becomes easier. The upper limit of the supply rate can be set appropriately within the range in which the effects of this disclosure can be obtained, and is not particularly limited. Note that the supply rate may be less than 11 m / s.

[0023] Furthermore, the components of the CO2 capture device are not particularly limited and can be any conventionally known equipment as long as the effects of this disclosure are achieved. Therefore, in the following description, only the parts of this method that are of particular interest will be described, and other components will not be explained.

[0024] The CO2 adsorbent may include a CO2 adsorbent capable of adsorbing CO2 and a plurality of porous carriers supporting the CO2 adsorbent. It is preferable that the adsorber 4 used in this method, which includes the CO2 adsorbent, is capable of achieving an adsorption rate of 80% by volume or more of the CO2 adsorbent even in short cycles (for example, one cycle being 4 minutes or more but less than 60 minutes).

[0025] The porous carrier preferably has a honeycomb structure. Having a honeycomb structure in the porous carrier makes it easier to suppress pressure loss and air velocity reduction during CO2 recovery, allowing for a shorter t1 time and easily achieving cost reductions. The porous support can be, for example, a honeycomb-shaped substrate (honeycomb substrate) coated with a porous material mainly composed of either silica gel or alumina, with multiple pores having an average pore diameter of 2 nm to 200 nm. Thus, it is preferable that the porous support is coated with silica gel or alumina (especially silica gel).

[0026] Figure 3 shows a graph illustrating an example of the relationship between the adsorption rate of a CO2 adsorbent and the thickness of the silica gel coating the porous support. The adsorption rate of the CO2 adsorbent refers to the adsorption capacity (adsorption capacity) when the CO2 adsorbent is allowed to adsorb CO2 for a sufficiently long time (e.g., 1 hour or more), with 100 volume% being the adsorption capacity. Figure 3 also shows the relationship between the silica gel thickness and the adsorption rate of the CO2 adsorbent (the same in each pattern) for four patterns where the CO2 adsorption time on the CO2 adsorbent is 200 seconds, 300 seconds, 500 seconds, and 900 seconds.

[0027] As shown in Figure 3, the thinner the coating layer, the shorter the time it takes for CO2 to penetrate from the surface of the adsorbent into the interior, resulting in faster CO2 adsorption to the adsorbent and improved adsorption rate. The thickness of the silica gel coating layer can be, for example, 250 μm or less, 220 μm or less, 200 μm or less, 180 μm or less, 150 μm or less, 120 μm or less, or 100 μm or less. For example, in the example shown in Figure 3, if the adsorption time is 200 seconds, the adsorption rate of the CO2 adsorbent can be 80 volume% or more when the thickness of the silica gel (coating layer) is 120 μm or less.

[0028] The CO2 adsorbent is not particularly limited, but examples include polyamines containing any of polyethyleneimine, methylated polyethyleneimine, isopropylated polyethyleneimine, polyallylamine, pentaethylenehexamine, methylated pentaethylenehexamine, isopropylated pentaethylenehexamine, tetraethylenepentamine, methylated tetraethylenepentamine, and isopropylated tetraethylenepentamine, or amino group-containing compounds containing polyamines. Among these, the CO2 adsorbent is preferably polyethyleneimine having an isopropyl group, due to its superior cycle durability.

[0029] The various costs associated with CO2 capture (CO2 capture cost: the cost required to capture 1 kg of CO2) can be considered in two parts, for example. A comprehensive assessment of these costs and the amount of CO2 captured is required to determine whether cost reduction has been achieved (see JST (Japan Science and Technology Agency) Proposal for Innovation Policy Planning Based on Quantitative Scenarios for Technology, Economy, and Society Towards the Realization of a Low-Carbon Society LCS-FY2020-PP-06). The amount of CO2 captured per unit time by a CO2 capture device is the product of the number of cycles per unit time and the amount of CO2 that can be captured in one cycle. • CAPEX: The sum of equipment costs, depreciation period, construction costs, and labor costs, divided by the total amount of CO2 recovered by the equipment. OPEX: Operating costs required to capture 1 kg of CO2, including energy costs and replacement costs for degraded adsorbents. This method, for example, uses a low-pressure-drop honeycomb adsorbent to increase the rate of CO2 adsorption and desorption (the number of adsorption / desorption cycles per unit of time) compared to conventional methods, thereby reducing the proportion of equipment costs (CAPEX) in the CO2 recovery cost. As a result, CO2 can be recovered at a lower cost than before.

[0030] For example, this method can recover CO2 using a CO2 recovery device having the following adsorbent (and other configurations shown in Figure 1). ·Adsorber: This product consists of a porous support (a honeycomb substrate coated with silica gel) with a silica gel portion (120 μm thick) on which a CO2 absorbent (polyamine such as polyethyleneimine with an isopropyl group) is impregnated and supported. The honeycomb substrate used is made of cordierite with a cell density of 400 cpsi and a wall thickness of 4.5 mil, and the amount of CO2 absorbent supported on the coating material (silica gel) is 50 to 150 g / L. Thickness in the direction of wind speed: 0.1 meters Pressure loss: 0.0218 × (wind speed (m / s) squared): Approximate formula based on the measured data below. Actual measurement data: In a honeycomb substrate with L=0.05m, 400cpsi-4.5mil, and a 100g / L silica gel coating, At a wind speed of 11.8 m / s, the pressure is 1.7 kPa; at a wind speed of 23.6 m / s, it is 6 kPa. • Operating conditions The total time for one cycle of adsorption and desorption treatment is less than 60 minutes (t1: 15 minutes, t2 < 60 minutes).

[0031] For comparison, a conventional CO2 recovery method using a CO2 recovery apparatus equipped with the following amine / nanofiber adsorbent will be used. ·Adsorber: A fiber filter formed by impregnating the following amine, used as a CO2 adsorbent, with the following substrate, used as a support. Amine:N-(2-aminoethyl)-3-aminopropyl-methyldimethoxysilane:AEAPDMS Base material: Nanofiber (Fibrillated cellulose suspension) Thickness in the direction of wind speed: 1.2 meters Pressure loss: 5.53 kPa (wind speed 0.573 m / s) • Operating conditions Adsorption treatment: Room temperature (25°C), 1 atm, 30 minutes Desorption process: 90°C, 0.03 atm, 30 minutes per cycle, for a total of 60 minutes.

[0032] Figure 4 shows a graph illustrating the relationship between cycle time (minutes) and cost ratio for this method and the conventional CO2 capture method used for comparison. This graph shows the cost when using the conventional CO2 capture method and the relative cost ratio when the baseline S is set to 1. The cost is determined comprehensively using the CAPEX and OPEX mentioned above. Since electricity rates (yen / kWh) also significantly impact CO2 capture costs, three scenarios are shown: 4 yen / kWh, 6 yen / kWh, and 12 yen / kWh. In this process, we estimated the cost ratio of CO2 capture costs to baseline S based on the following five assumptions, and the results are shown in Figure 4. 1) Assuming the CAPEX value remains constant, the ratio of CAPEX to 1 kg of CO2 captured decreases as the cycle time shortens, i.e., as the amount of CO2 captured per hour increases. 2) The amount of air supplied to the adsorbent during one cycle is kept constant. 3) As the cycle time decreases, the wind speed increases, and the energy required for airflow increases due to pressure loss, which in turn increases the cost per kilogram of CO2 captured. 4) The energy required to blow air is proportional to the square of the wind speed. 5) CO2 capture costs are a trade-off with points 1) and 3) above.

[0033] Referring to the graph, this method using the CO2 capture device described above can achieve lower costs than the standard reference S using a normal CO2 capture method, regardless of electricity rates, when t2 is less than 60 minutes. The lower limit of the cycle time at which low cost can be achieved can be appropriately set depending on the adsorbent used, but in the CO2 recovery device shown in Figure 4, the cost ratio becomes less than 1 when t2 is 4 minutes or longer. Therefore, the range of cycle times indicated by the symbol X is the range in which cost reduction can be achieved compared to conventional methods. Furthermore, referring to Figure 4, even greater cost reduction can be achieved when the cycle time is, for example, between 4 minutes and 20 minutes.

[0034] The present invention is not limited to the embodiments described above, and can be modified as appropriate without departing from the spirit of the invention. The present invention contributes to carbon neutrality, decarbonization, and the Sustainable Development Goals (SDGs). [Explanation of symbols]

[0035] 1. Blower 2. First valve 3. Desorption gas feeder 4 Adsorber 5. Vacuum pump 6. Second valve S standard X The extent to which cost reduction is achieved

Claims

1. A CO2 recovery method that alternately repeats the adsorption and desorption of CO2, wherein CO2 contained in a supplied gas is adsorbed onto a CO2 adsorbent, and the CO2 adsorbed onto the CO2 adsorbent is desorbed and recovered by adjusting the temperature of the CO2 adsorbent to a higher temperature than that at the time of CO2 adsorption, A CO2 recovery method that satisfies t1 < t2 < 4 × t1, where t1 is the shortest time at which the CO2 adsorption rate on the CO2 adsorbent becomes 80% by volume or more, and t2 is the time of one cycle consisting of CO2 adsorption and desorption.

2. The CO2 adsorbent comprises a CO2 adsorbent and a plurality of porous carriers supporting the CO2 adsorbent. The CO2 recovery method according to claim 1, wherein the CO2 adsorbent comprises polyethyleneimine having an isopropyl group.

3. The CO2 recovery method according to claim 2, wherein the porous carrier has a honeycomb structure.

4. The CO2 recovery method according to claim 1 or 2, wherein the supply rate of the gas to the CO2 adsorbent is 11 m / s or more.

5. The CO2 recovery method according to claim 2 or 3, wherein the porous carrier is coated with silica gel, and the thickness of the silica gel is 250 μm or less.

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