Rubber for CO2 separation and capture and CO2 separation and capture method using the same

Abstract

A rubber having a glass transition temperature of -150°C to -10°C, an SP value of 7(cal / cm3)0.5 to 10.5(cal / cm3)0.5, and an elastic modulus at 25°C of 0.03 to 5 MPa.

Description

[Technical Field]

[0001] The present invention relates to a CO2 adsorbent and a method for separating and capturing CO2 using the same. [Background technology]

[0002] Separating and capturing carbon dioxide (CO2) has become an extremely important issue in preventing global warming, but the methods and conditions for separating and capturing CO2 vary greatly depending on the source and CO2 concentration, as described below.

[0003] In exhaust gas after air combustion, such as boiler exhaust gas, the CO2 concentration is usually 15 wt% or less, and in such cases, CO2 is generally captured using a strong adsorbent such as an amine adsorbent. For example, such adsorbents are disclosed in Patent Documents 1-4, and CO2 capture is disclosed in Patent Document 5.

[0004] Strong adsorbents generally require a large amount of heat energy to desorb CO2, but this energy problem is less if the CO2 concentration in the mixed gas is low and CO2 can be separated with a small amount of adsorbent. In other words, when the CO2 concentration is low, it is effective to separate CO2 using a small amount of strong adsorbent. For example, strong adsorbents are effective when removing CO2 from a mixed gas to produce gas products. On the other hand, from the perspective of greenhouse gas separation, the separation and capture of low-concentration CO2 is not very efficient because the desorption energy is large relative to the amount of CO2 separated.

[0005] From the perspective of reducing greenhouse gas emissions, taking into account the energy efficiency of desorption, there is a strong demand for low-energy separation and recovery from high-concentration CO2 sources, such as natural gas and associated gas separation processes.

[0006] The natural gas and associated gas separation processes can be classified as follows based on the CO2 concentration: (1) When the CO2 concentration is 2% or less In this case, it is not necessary to separate the CO2, as if the CO2 concentration is 2% or less, there is no risk of it clogging pipelines, even in polar regions. However, when producing liquefied natural gas (LNG), the Acid Gas Removal (AGR) process is applied before applying the cryogenic method. (2) When the CO2 concentration is around 30% Older facilities used molten potassium carbonate, but this is being replaced by the AGR process using an amine solvent. Amine solvents allow the adsorbent to be regenerated by heat, making equipment maintenance easy. On the other hand, corrosion of steel is often a problem with molten potassium carbonate. (3) When the CO2 concentration is 30-60% An organic solvent such as propylene carbonate (PC) is used as the adsorbent. High CO2 concentrations require a large amount of heat energy to regenerate the amine solvent, making the AGR process unusable. (4) When the CO2 concentration is 70% or higher Currently, there are difficulties in developing the separation process, and there are high hopes for new CO2 separation technology. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent Publication No. 2021-3664 [Patent Document 2] Japanese Patent Application Publication No. 2020-58967 [Patent Document 3] Japanese Patent Publication No. 2020-69417 [Patent Document 4] Japanese Patent Application Publication No. 2019-147099 [Patent Document 5] Patent Publication No. 2021-171744 Summary of the Invention [Problem to be solved by the invention]

[0008] Under these circumstances, there is a need to separate the high concentration of CO2 in natural gas, which is over 30%, and reduce it to 2% or less.In addition to natural gas, mixed gases containing high concentrations of CO2 are also generated in thermal power plants and biogas production, and low-cost capture technology is desired. However, the method of capturing CO2 using organic solvents as adsorbents (absorbents) requires dissolving the mixed gas in high-pressure microbubbles, which results in a large energy loss. In addition, some of the organic solvent evaporates, which incurs recovery costs.

[0009] In view of the above background, an object of the present invention is to provide a CO2 adsorbent suitable for capturing CO2 from a mixed gas containing a high concentration of CO2, and a CO2 separation and capture method using the same. [Means for solving the problem]

[0010] The configuration of the present invention to solve the problems is shown below. (Configuration 1) Glass transition temperature is between -150℃ and -10℃, and SP value is 7 (cal / cm 3 ) 0.5 More than 10.5(cal / cm 3 ) 0.5 The following refers to a CO2 adsorbent made of rubber with an elastic modulus of 0.03 MPa or more and 5 MPa or less at 25°C. (Configuration 2) 2. The CO2 adsorbent according to claim 1, wherein the rubber has a glass transition temperature of -125°C or higher and -20°C or lower. (Configuration 3) The SP value of the rubber is 7.3 (cal / cm 3 ) 0.5 More than 7.6(cal / cm 3 ) 0.5 3. A CO2 adsorbent according to claim 1 or 2, wherein: (Configuration 4) 4. The CO2 adsorbent material according to any one of configurations 1 to 3, wherein the elastic modulus of the rubber at 25°C is 0.1 MPa or more and 4.5 MPa or less. (Configuration 5) 5. The CO2 adsorbent according to any one of claims 1 to 4, wherein the rubber is made of PDMS. (Configuration 6) 6. The CO2 adsorbent material according to any one of configurations 1 to 5, wherein the thickness of the rubber is 0.1 mm or more and 5 mm or less. (Configuration 7) 6. The CO2 adsorbent according to any one of claims 1 to 5, wherein the rubber is in a powder form having a sphere-equivalent diameter of 0.002 mm or more and 0.1 mm or less. (Configuration 8) 1. A method for separating and capturing CO2 from a gas mixture, comprising: A mixed gas containing CO2 and having a pressure of 1 MPa or more and 10 MPa or less at a temperature below freezing is brought into contact with the rubber according to any one of Configurations 1 to 7 (mixed gas contact step); and A CO2 separation and recovery method comprising: after contacting the rubber with the mixed gas (after the mixed gas contacting step), isolating the rubber from the mixed gas; and desorbing CO2 from the rubber in an environment where the pressure is lower than the pressure at which the mixed gas was contacted with the rubber (the pressure in the mixed gas contacting step) and is 0.1 MPa or more and 5 MPa or less. [Effects of the Invention]

[0011] According to the present invention, there are provided a CO2 adsorbent suitable for recovering CO2 from a mixed gas containing a high concentration of CO2, and a CO2 separation and recovery method using the same. As a result, the present invention reduces the energy costs required for CO2 capture, and in particular the cost of regenerating the adsorbent, making it possible to contribute to reducing greenhouse gas emissions. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a flow chart showing a CO2 separation and recovery method of the present invention. [Figure 2] FIG. 1 is a characteristic diagram showing the CO2 adsorption characteristics of PDMS rubber. [Figure 3] FIG. 1 is a characteristic diagram showing the temperature and pressure dependence of the CO2 adsorption amount of fluororubber. [Figure 4]FIG. 1 is a characteristic diagram showing the temperature and pressure dependence (adsorption isotherm) of the amount of CO2 adsorbed by PDMS rubber. [Figure 5] FIG. 1 is a characteristic diagram showing the temperature and pressure dependence (adsorption isotherm) of the amount of CO2 adsorbed by PDMS rubber. [Figure 6] FIG. 1 is a characteristic diagram showing the CO2 adsorption isotherm of rubber at -78°C. [Figure 7] FIG. 1 is a characteristic diagram showing a CO2 adsorption isotherm of NBR at -78°C. [Figure 8] FIG. 1 is a characteristic diagram showing the CO2 adsorption isotherm of activated carbon (WH5C) at -78°C. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the description, the expression "A to B" means "A or more and B or less."

[0014] (Embodiment 1) In the first embodiment, a CO2 adsorbent made of rubber with numerically defined glass transition temperature, SP value (Solubility Parameter), and elastic modulus will be described. Here, rubber refers to a polymer that exhibits entropy elasticity at room temperature.

[0015] Generally, rubber does not have a particularly high CO2 absorption capacity, and high pressure is required to absorb CO2 at room temperature. However, the inventors of the present invention have found through extensive experiments that rubber with a low glass transition temperature is capable of adsorbing and desorbing CO2 at sub-zero temperatures, where the vapor pressure of CO2 is low, and that it can adsorb more than 20 wt% of CO2 at relatively low pressures. We also found that the SP value and elastic modulus must be within a certain range in order to efficiently adsorb large amounts of CO2.

[0016] The rubber of the first embodiment has a glass transition temperature of -150°C or higher and -10°C or lower, and an SP value of 7.0 (cal / cm 3 ) 0.5More than 10.5(cal / cm 3 ) 0.5 and the modulus of elasticity at 25°C is 0.03 MPa or more and 5 MPa or less.

[0017] If the glass transition temperature of rubber is between -150°C and -10°C, and more preferably between -125°C and -20°C, the bulk modulus when absorbing CO2 is small, allowing the rubber to absorb large amounts of CO2 even at temperatures below freezing. Note that the bulk modulus of rubber is proportional to its elastic modulus (usually the tensile modulus) as long as the Poisson's ratio remains constant. The glass transition temperature of rubber is the phenomenon in which the elastic modulus increases rapidly as the temperature decreases. At temperatures above the glass transition temperature, rubber is soft and easily absorbs CO2. If the glass transition temperature is below -20°C, the partial pressure of CO2 is appropriately reduced, making it more suitable for absorbing large amounts of CO2. However, regardless of the rubber, the elastic modulus increases at very low temperatures, so a temperature above -125°C is preferable.

[0018] The SP value of the rubber is 7.0 (cal / cm 3 ) 0.5 More than 10.5(cal / cm 3 ) 0.5 Less than or equal to 7.3 (cal / cm 3 ) 0.5 More than 7.6(cal / cm 3 ) 0.5 If the SP value is within the following range, the affinity of the rubber with CO2 increases, making it possible to adsorb a large amount of CO2 into the rubber. A more preferable condition is an SP value of 7.3 (cal / cm 3 ) 0.5 More than 7.6(cal / cm 3 ) 0.5 The reason for this is as follows: The SP value near the critical point of CO2 is 3.9 (cal / cm 3 ) 0.5 However, at 0°C and around 5 atmospheres, it is 7.3 (cal / cm 3 ) 0.5 At -10°C and around 3 atmospheres, it is 7.6 (cal / cm 3 ) 0.5The SP value of CO2 at -40°C is 8.8 (cal / cm 3 ) 0.5 At temperatures below this, it is 9.4 (cal / cm 3 ) 0.5 To the vicinity increase However, below -56.6°C, the SP value cannot be defined because it loses its liquid properties. The SP value of CO2 increases as the temperature decreases, but also increases with increasing pressure. For example, even at -30°C and 50 atmospheres, the SP value is 8.5 (cal / cm 3 ) 0.5 In the CO2 separation and capture method of the present invention, it is necessary to adsorb CO2 at sub-zero temperatures and high pressures, and it is desirable that the SP value of the rubber be close to the SP value of CO2 under these conditions. However, in the present invention, a range of values ​​at 25°C is shown as the preferred SP value range. This is because there is not necessarily a sufficient amount of data on the SP value of rubber at sub-zero temperatures. Note that, like CO2, the SP value of rubber also increases as the temperature decreases.

[0019] If the rubber has a relatively soft elastic modulus at 25°C, in the range of 0.03 MPa to 5 MPa, and more preferably 0.1 MPa to 4.5 MPa, then volume expansion occurs easily when CO2 is adsorbed, making it possible to adsorb large amounts of CO2 within the rubber. This flexibility at room temperature of 25°C makes it highly useful as a CO2 adsorbent.

[0020] Due to the above characteristics, the rubber of the first embodiment is a suitable CO2 adsorbent for recovering CO2 from a mixed gas containing a high concentration of CO2. The rubber of the first embodiment is a CO2 adsorbent suitable for capturing CO2 by adsorbing CO2 from a high-pressure mixed gas and desorbing it by reducing the pressure.Furthermore, it is a CO2 adsorbent suitable for capturing CO2 by adsorbing CO2 from a low-temperature mixed gas and desorbing it by reducing the pressure, thereby improving the capture efficiency.

[0021] Rubbers that satisfy the above conditions include one or more types of rubber selected from fluorine-based rubbers, polysiloxane-based rubbers, butyl rubber, natural rubber, silicone, etc. Among these rubbers, polysiloxane-based rubbers are particularly preferred. Examples of polysiloxanes that are used include dimethylpolysiloxane (PDMS) and diethylpolysiloxane. As shown in the examples, soft PDMS rubbers with a particularly low elastic modulus can achieve extremely high CO2 adsorption at low temperatures around -80°C, where the vapor pressure of CO2 approaches atmospheric pressure.

[0022] Dimethylpolysiloxanes in which some of the methyl groups have been substituted with other reactive groups (e.g., phenyl, ethyl, or vinyl groups) may be used. Similarly, diethylpolysiloxanes in which some of the ethyl groups have been substituted with other reactive groups (e.g., phenyl, methyl, or vinyl groups) may be used. One type of polysiloxane may be used, or multiple types may be used in combination.

[0023] To further improve CO2 adsorption at low temperatures, it is preferable for the rubber to contain a certain amount of diethyl. For example, this can be achieved by using PDMS (dimethylpolysiloxane) in which some of the reactive groups have been substituted with ethyl, or by using PDMS in combination with diethylpolysiloxane.

[0024] SP value is 10.5 (cal / cm 3 ) 0.5 The rubbers listed below are generally hydrophobic, but some are prone to adsorbing water. In such cases, making the rubber hydrophobic makes it possible to adsorb large amounts of CO2 below freezing. At temperatures below freezing, water tends to adsorb into the rubber's interfaces and voids, and even a small amount of water can easily reduce adsorption performance. However, by adsorbing hydrophobic molecules such as decane onto the rubber, water adsorption is suppressed, making it easier to maintain high adsorption power for CO2. The water contact angle of the rubber adsorbent surface should be between 80° and 150°.

[0025] Furthermore, by turning the rubber into powder, the surface area increases, allowing it to quickly adsorb CO2. When the rubber is in powder form, the average particle size (sphere-equivalent diameter) of the rubber is, for example, 0.5 mm or less, preferably 0.1 mm or less, from the viewpoint of CO2 adsorption and desorption rates. The lower limit of the average particle size of the rubber is, for example, 0.002 mm or more, preferably 0.01 mm or more. In particular, polysiloxane-based rubbers such as PDMS, powdered to the above average particle size, are preferred. The average particle size of the rubber is the average of the sphere-equivalent diameters observed under a microscope using a TEM or SEM. Handling of the powdered rubber as an adsorbent can be facilitated by placing it in an appropriate cloth bag (e.g., a nylon cloth bag). In this case, rubber with a sphere-equivalent diameter of 0.001 mm or more can be used. For example, when powdered rubber is used in a cloth bag woven with twisted fibers with a fiber diameter of approximately 0.03 mm, even rubber with an average particle size of approximately 0.002 mm can be used as an adsorbent without any problems.

[0026] The shape of the rubber is not limited to powder, but may be, for example, a thick plate, square, or pellet. CO2 adsorbed by the rubber desorbs from the rubber surface at a diffusion-limited rate. In this rubber, CO2 desorbs rapidly from a depth of 2.5 mm or less from the surface (i.e., within 2.5 mm from the surface). Therefore, from the perspective of rapid CO2 desorption, a rubber thickness of 5 mm or less is preferred. While there is no particular lower limit for the rubber thickness, a thickness of 0.1 mm or more is preferred for ease of handling and quality stability. The thickness of the rubber is defined as the length of the thinnest part of the rubber. For example, if the rubber is square and can be conceived in the vertical, horizontal, and height directions, the thickness of the rubber is defined as the shortest length among the vertical length, horizontal length, and height length.

[0027] In CO2 separation technology that uses organic solvents such as propylene carbonate (PC) as adsorbents (absorbents), the mixed gas must be converted into high-pressure microbubbles and dissolved, resulting in a large energy loss.In addition, part of the organic solvent volatilizes, which requires recovery costs. In contrast, the separation of CO2 using rubber according to the first embodiment of the present invention has the advantages that rubber is solid and easy to handle, the loss of adsorbent is small, the adsorption capacity is large, and the device can be made smaller.Furthermore, when rubber is powdered, the specific surface area is large, and the CO2 adsorption and desorption rate is increased.

[0028] (Embodiment 2) In the second embodiment, a method for separating and capturing CO2 using the rubber of the first embodiment will be described with reference to Fig. 1. Fig. 1 shows a flow chart of an example of the method for separating and capturing CO2.

[0029] The CO2 separation and capture method of embodiment 2 is a method for separating and capturing CO2 by performing a mixed gas contact step (step S02) in which the rubber of embodiment 1 is placed in a mixed gas containing CO2, the pressure of which is 1 MPa or more and 10 MPa or less, and the temperature of which is below freezing, a mixed gas isolation step (step S03) in which the rubber is isolated from the mixed gas after the mixed gas contact step, and a desorption step (step S04) in which CO2 is desorbed from the rubber in an environment where the pressure is lower than the pressure in the mixed gas contact step and is 0.1 MPa or more and 5 MPa or less,

[0030] The mixed gas contact step is, for example, a step of supplying the mixed gas to rubber placed in a container (e.g., an adsorption tower) and bringing the mixed gas into contact with the rubber. The mixed gas is supplied to the container after adjusting the pressure to 1 MPa or more and 10 MPa or less and the temperature to below freezing. In the gas contact step, CO2 is adsorbed into the rubber. The temperature of the mixed gas is, for example, -50 to -0°C, preferably -40 to -30°C. The mixed gas contact step is carried out for a time (e.g., 5 minutes to 2 hours) sufficient for CO2 to be sufficiently adsorbed into the rubber.

[0031] In the mixed gas shutoff step, the supply of the mixed gas to the container is stopped.

[0032] In the desorption step, for example, the pressure inside the container is lowered to 0.1 MPa or more and 5 MPa or less, lower than the pressure in the mixed gas contact step, by opening a pressure reducing valve. As the pressure inside the container decreases, CO2 is desorbed from the rubber. The mixed gas contact step is carried out for a time (for example, 1 minute to 1 hour) sufficient for CO2 to be desorbed from the rubber.

[0033] The CO2 concentration in the mixed gas used in the CO2 separation and capture method of the present invention is, for example, 20 to 70 vol %.

[0034] The CO2 separation and capture method using the solid rubber adsorbent of the present invention has a high adsorption rate, a large adsorption capacity, and no evaporation of the adsorbent during desorption, making it unnecessary to recover the adsorbent. Therefore, it is significantly more advantageous than the method of removing CO2 from natural gas containing high concentrations of CO2 using organic solvents such as PC. When removing CO2 from natural gas, the primary pressure of the produced gas is extremely high, so it can be easily cooled by heat exchange and decompression. The CO2 adsorbent of the present invention can separate CO2 by supplying such a low-temperature mixed gas to a container (adsorption tower). In addition, the separated CO2 can be easily recovered.

[0035] Currently, in biogas production, mixed gases are pressurized to around 8 atmospheres, but the resulting methane contains 40 wt% CO2, which is similar to natural gas, which contains high concentrations of CO2. To reduce equipment costs, water is used as an adsorbent to separate CO2 from methane. However, even at a pressure of 10 atmospheres, the partial pressure of CO2 is only 4 atmospheres, and the solubility of CO2 at room temperature is less than 4%. The dissolution of CO2 produces carbon dioxide, which lowers the pH and increases the risk of corrosion. On the other hand, according to the present invention, CO2 can be efficiently recovered by performing pressurization, heat exchange, and cooling. Furthermore, since the adsorbent of the present invention has a large adsorption capacity, the adsorption tower can be made smaller, and the capital investment required to remove a large amount of CO2 is small.

[0036] As can be understood from the above explanation, the CO2 separation and capture method according to the present invention is a method comprising a mixed gas contacting step in which a sub-zero mixed gas containing CO2 and having a pressure of 1 MPa to 10 MPa is brought into contact with rubber, and a desorption step in which, after the mixed gas contacting step, the rubber is isolated from the mixed gas and CO2 is desorbed from the rubber in an environment where the pressure is lower than that in the mixed gas contacting step and is 0.1 MPa to 5 MPa. [Example]

[0037] Example 1 In Example 1, the PDMS rubber prepared using the PDMS rubber preparation kit was used to evaluate the properties of CO2 adsorption and desorption.

[0038] The PDMS rubber preparation kit used was SYLGARD manufactured by DOW Inc. TM The PDMS rubber was cut into 5 mm square pieces. The glass transition temperature of the PDMS rubber was -125°C, and the SP value was 7.6 (cal / cm 3 ) 0.5 and the elastic modulus at 25°C is 2.0 MPa. CO2 was adsorbed onto a 5 mm square PDMS rubber at 25°C under 30 atmospheres of CO2, and then the sample was isolated from the high-pressure CO2 gas. Note that in the following experiments, including Example 1, adsorption was performed using a gas with a 100% CO2 concentration. The CO2 adsorbed onto the PDMS rubber was then leaked into a vacuum chamber. Figure 2 shows the pressure change in the sample chamber at this time. This pressure change includes all of the CO2 in the sample chamber. That is, it includes the CO2 adsorbed onto the PDMS rubber and the CO2 present in the gaps between the PDMS rubber. However, the pressure change several seconds after the leak is due to the increase in pressure caused by the CO2 being released from the PDMS rubber. These results show that desorption at around 10 atmospheres achieves 80% or more desorption in approximately 5 minutes.

[0039] For PDMS rubber with a sphere-equivalent diameter of 500 μm, CO2 desorption occurs within a few seconds. Even with a 5mm square PDMS rubber (5mm thick adsorbent), the desorption rate of CO2 from the surface is fast. CO2 adsorbed inside desorbs slightly slower than CO2 from the surface. The results in Figure 2 show that if the adsorbent thickness is 5mm or less, a sufficient speed (within 5 minutes) can be achieved for regeneration of the CO2 adsorbent.

[0040] Example 2 In Example 2, the CO2 adsorption amounts of various rubbers at -40°C were evaluated. The samples used were three types: KMP-598 (PDMS rubber powder manufactured by Shin-Etsu Silicones, particle size: 2-30 μm), NBR (NBR powder manufactured by JSR (PN30A), sphere equivalent diameter: 400 μm), and PDMS-h8 (homemade PDMS rubber powder, average particle size: 130 μm). Here, PDMS-h8 is a two-component mixed PDMS rubber preparation kit (SYLGARD TM This is a sample of PDMS-h8 (184 Silicone Elastomer) cured and dried by adding 8g of hexane to 2g of PDMS macromer. The modulus of elasticity at room temperature (25°C) is 0.04MPa. This is about 100 times smaller than that of regular PDMS rubber, making PDMS-h8 a soft rubber. The moduli of elasticity at room temperature (25°C) for KMP-598 and NBR are about 4MPa and 1MPa, respectively. The glass transition temperatures of KMP-598, PDMS-h8, and NBR are around -125°C, -110°C, and -25°C, respectively, and the SP value is 7.3 (cal / cm 3 ) 0.5 , 7.3(cal / cm 3 ) 0.5 and 10.3 (cal / cm 3 ) 0.5 is.

[0041] CO2 was adsorbed onto 10 g of each rubber at -40°C. The amount of CO2 adsorbed onto the rubber was calculated from the increased pressure inside a buffer container (1 L) under vacuum when CO2 was desorbed at room temperature. The results are shown in Table 1. The pressures in Table 1 are the absolute pressure of CO2 during adsorption.

[0042] KPM-598 adsorbs 10.9 wt% of CO2 at 8 atmospheres, while the softer PDMS-h8 adsorbs a larger amount, 12.38 wt%. Furthermore, when the pressure is increased to 8.8 atmospheres and 10.0 atmospheres, the CO2 adsorption amount for PDMS-h8 increases significantly to 16.15 wt% and 25.20 wt%. NBR also shows adsorption of 21.20 wt% at 10 atmospheres. The results show that the glass transition temperature is below -40°C and the SP value is 7.0 to 10.5 (cal / cm 3 ) 0.5 This indicates that rubber with an elastic modulus of 0.03 MPa or more and 5 MPa or less at 25°C can adsorb 10 wt% or more of CO2 at low temperatures.

[0043] [Table 1]

[0044] (Comparative Example 1) As Comparative Example 1, the amount of CO2 adsorption at -40°C into NR (rubber powder #2500, sphere equivalent diameter: 400 μm, manufactured by Toyo Rubber Chip Co., Ltd.), a natural rubber powder derived from waste tires, was investigated. The results are shown in Table 2. The glass transition temperature of the rubber component of this powder sample was near -70°C, and the SP value was approximately 8.2 (cal / cm 3 ) 0.5 The elastic modulus of the NR of Comparative Example 1 at 25°C is about 20 MPa.

[0045] [Table 2]

[0046] In Comparative Example 1, the CO2 adsorption amount at an absolute pressure of 9.5 atmospheres was 4.09 wt%. Natural rubber is thought to easily adsorb CO2, but rubber that has been vulcanized or hardened with carbon additives has a lower CO2 adsorption amount.

[0047] The PDMS rubber used in Example 1 has a modulus of elasticity of 42 MPa at -90°C, but its modulus decreases to 27 MPa, 18 MPa, 13 MPa, and 10 MPa at -80°C, -70°C, -60°C, and -50°C, respectively, and its modulus at 25°C is 4.4 MPa. When CO2 is adsorbed, the rubber undergoes volumetric swelling. Therefore, using a rubber with a high modulus of elasticity and at a temperature range where the modulus is high is more likely to adsorb CO2.

[0048] Example 3 In Example 3, the change in the amount of CO2 adsorbed by the fluorine rubber with respect to temperature was evaluated. The sample was a fluorine rubber powder with an average particle size of 130 μm (G-701BP manufactured by Daikin Corporation, crushed to a size of 500 μm or less using a freeze crusher). The experimental method was the same as in Example 2, and the amount of CO2 adsorbed was measured by changing the adsorption temperature to -40° C., -35° C., -30° C., and -20° C. The results are shown in Figure 3 and Table 3. At -40°C, the CO2 adsorption capacity exceeds 13.5 wt% at an absolute pressure of 8 atmospheres. On the other hand, at -35°C, the adsorption capacity is 11.1 wt% even at 9.5 atmospheres. At -30°C and -20°C, the adsorption capacity does not exceed 10 wt% at pressures below 10 atmospheres. These results show that the lower the temperature, the greater the CO2 adsorption capacity, which is desirable for CO2 separation and capture.

[0049] [Table 3]

[0050] (Reference example 1) In Reference Example 1, the CO2 adsorption isotherm of PDMS-h8 used in Example 2 was measured. Here, the measurement device used was a Belsorp max manufactured by Microtrac-Bell. The results are shown in Figure 4.

[0051] When CO2 temperatures are raised to 4°C, 6°C, or 8°C, which are relatively high for CO2 adsorption, and the absolute CO2 pressure is raised to above 30 atmospheres, high adsorption of over 30 wt% is achieved. However, under these conditions, the partial pressure of unadsorbed CO2 in the mixed gas becomes high, making it impossible to efficiently capture CO2 in the gas phase. This is because, for example, if a 70% CO2 mixed gas is to be reduced to a 10% CO2 concentration (10% partial pressure) using an adsorbent, the total gas pressure must be increased to 300 atmospheres, and adsorption operations at such high pressures are impractical. It is desirable for adsorbents to achieve high adsorption capacities at low CO2 partial pressures, and low-temperature operation is preferable.

[0052] Example 4 In Example 4, the CO2 adsorption isotherm of PDMS-h8 below the freezing point, i.e., below 0° C., is shown. Here, the measurement method conforms to that of Reference Example 1. As is clear from the results shown in Figure 5, below freezing temperatures a large amount of adsorption was observed even at low CO2 pressures, indicating that below freezing temperatures are desirable for efficient CO2 capture. For example, at -38°C, CO2 can be adsorbed at approximately half the pressure compared to 0°C, which means that the amount of CO2 remaining in the gas phase during CO2 separation and capture is halved.

[0053] Example 5 In Example 5, the CO2 adsorption isotherm at -78°C was evaluated.

[0054] The triple point of CO2 is 0.52 MPa and -56.6°C. Therefore, even though it is generally referred to as below freezing, it exhibits different physical properties above and below -56.6°C. At around -40°C, CO2 liquefies under pressure, at a pressure of approximately 10 atmospheres. On the other hand, at around -80°C, the sublimation pressure is about 1 atmosphere, and when a high-concentration CO2 mixed gas is pressurized, the CO2 solidifies. As a result, the adsorption operation is carried out at a pressure about one-tenth that of around -40°C, but because the vapor pressure of CO2 is also reduced, the concentration of CO2 remaining in the gas phase can also be reduced.

[0055] The samples used in Example 5 were KMP-598 used in Example 2 and a homemade PDMS rubber powder (PDMS_Ph_DIPE). PDMS_Ph_DIPE was prepared by mixing PDMS (molecular weight: 57,000) with vinyl groups at both ends and polyphenylmethylpolysiloxane (viscosity: 500 cSt) in a 1:1 ratio, and a diluent equivalent to 10 wt% of the 1:1 mixture was used. Kumi The sample was prepared by adding methyl peroxide, heating at 150°C for 12 hours, and pulverizing it in a freeze pulverizer (average particle size: 130 μm). PDMS_Ph_DIPE has a glass transition temperature of -120°C and an SP value of 7.6 (cal / cm 3 ) 0.5 and the modulus of elasticity at 25°C is 2 MPa. The measurements were carried out using a Belsorp Mini manufactured by Microtrac-Bell, and the experimental results are shown in Figure 6.

[0056] The CO2 adsorption capacity of KMP-598 was 32 wt% at an absolute pressure of 97 kPa, and PDMS_Ph_DIPE also showed an adsorption capacity of over 30 wt%. Both adsorption capacities exceeded 10 wt% at a pressure of 35 kPa, indicating that the CO2 partial pressure can be reduced to 0.35 atmospheres or less. This result indicates that when adsorption is performed at 35 atmospheres, the partial pressure of CO2 can be reduced to 1% or less. In addition, since the amount of adsorption changes according to Henry's law, it indicates that desorption can be easily achieved by reducing the pressure.

[0057] Example 6 In Example 6, the CO2 adsorption isotherm at -78°C for the NBR used in Example 2 was evaluated. The measurement method was the same as in Example 4. The results are shown in FIG. The adsorption to NBR at a temperature of -78°C is about half that of Example 5. This is because the glass transition temperature of NBR is around -35°C and it hardens at low temperatures.

[0058] (Comparative Example 2) As Comparative Example 2, the CO2 adsorption isotherm onto activated carbon at -78°C was evaluated. The sample used was vacuum-dried activated carbon (Granular Shirasagi WH5C) manufactured by Osaka Gas Chemicals Co., Ltd. The measurement conditions were the same as those in Example 4. The results are shown in Figure 8. Activated carbon shows a large CO2 adsorption capacity, but as is clear from the adsorption isotherm, the adsorption pressure is large at low pressures, and even under a reduced pressure of -70 kPa (approximately 30 kPa absolute pressure), 40 wt% of CO2 is adsorbed to the activated carbon. Further pressure reduction is required to desorb this. Also, the activated carbon experiments used vacuum-dried carbon, but because water is strongly adsorbed into the micropores of activated carbon, even the inclusion of even a small amount of water reduces the adsorption performance. On the other hand, this type of deterioration does not occur with hydrophobic rubber.

[0059] Example 7 In Example 7, the CO2 adsorption isotherm at -96°C was evaluated. The measurement method was the same as in Example 4, and the following four types of samples were used. All four types had an average particle size of 130 μm. (1) PDMS_h15: Two-component mixed PDMS rubber preparation kit (SYLGARD TM 184 Silicone Elastomer), 15g of hexane was added to 2g of PDMS macromer during curing, and the mixture was dried and freeze-pulverized. (2)PDMS_PDE: PDMS (molecular weight: 57,000) with vinyl groups at both ends was mixed with 10 wt% of the vinyl group. Kumi A sample was prepared by adding hydroxypropyl peroxide, heating at 150°C for 12 hours, and then pulverizing it in a freeze pulverizer. (3)PDMS_Ph_DIPE: Samples described in Example 5. (4) PDMS_d8: Two-component mixed PDMS rubber preparation kit (SYLGARD TM184 Silicone Elastomer), 8 g of decane was added to 2 g of PDMS macromer during curing, and the resulting sample was washed with hexane, dried, and freeze-ground.

[0060] The measurement results are summarized in Table 4. The SP value of the sample used in Example 7 was 7.3 (cal / cm 3 ) 0.5 More than 7.6(cal / cm 3 ) 0.5 The modulus of elasticity at 25°C is 0.034 MPa for PDMS_h15, 3.0 MPa for PDMS_PDE and PDMS_Ph_DIPE, and 0.04 MPa for PDMS_d8. The modulus of elasticity at -96°C is in the range of 5 MPa to 45 MPa.

[0061] [Table 4]

[0062] From the results in Table 4, it can be seen that only PDMS_d8 has an adsorption amount exceeding 10 wt% at -96°C, and only in this case can the CO2 partial pressure be reduced to approximately 20 kPa. The elastic modulus of PDMS_d8 is 9 MPa at -90°C and approximately 15 MPa at -96°C. In other words, the elastic modulus is 20 MPa or less, and it is still soft enough to adsorb a large amount of CO2. On the other hand, the PDMS rubber used in Example 1 has an elastic modulus of over 40 MPa at -96°C, resulting in a small amount of CO2 adsorption. Even PDMS_DIPE and PDMS_Ph_DIPE, which are expected to have a high degree of cross-linking, show a small amount of CO2 adsorption. In addition, PDMS_h15 was prepared by adding 15g of hexane during cross-linking of the PDMS, but the cross-linking was barely progressed, making it more of a liquid than a rubber. In fact, the elastic modulus at -96°C was 5MPa. Even in this case, the amount of CO2 adsorption was small at low temperatures. In summary, from the viewpoint of increasing the CO2 adsorption efficiency, it is desirable for the CO2 adsorbent of the present invention to have an elastic modulus of 40 MPa or less at the adsorption temperature, although it is not essential for the CO2 adsorbent to have an elastic modulus of 40 MPa or less at the adsorption temperature. [Industrial Applicability]

[0063] As described above, the present invention provides a CO2 adsorbent suitable for capturing CO2 from mixed gases containing high concentrations of CO2, and a CO2 separation and capture method using the same. CO2 separation and capture is important for reducing greenhouse gas emissions, and the present invention contributes to preventing global warming. The present invention reduces the energy costs required for CO2 capture, and in particular the cost of regenerating the adsorbent, and is therefore believed to greatly contribute to the development of the industry.

Claims

1. Glass transition temperature is -150°C or higher and -10°C or lower, and SP value is 7 (cal / cm ３ ) ０．５ More than 10.5 (cal / cm ３ ) ０．５ The rubber for CO 2 separation and recovery has an elastic modulus at 25°C of 0.03 MPa or more and 5 MPa or less.

2. 2. The rubber for CO 2 separation and capture according to claim 1, wherein the glass transition temperature of the rubber for CO 2 separation and capture is -125°C or higher and -20°C or lower.

3. The SP value of the rubber for CO 2 separation and capture is 7.3 (cal / cm ３ ) ０．５ More than 7.6 (cal / cm ３ ) ０．５ The rubber for CO 2 separation and capture according to claim 1 or 2, wherein:

4. The rubber for CO 2 separation and capture according to claim 1 , wherein the rubber for CO 2 separation and capture has an elastic modulus at 25° C. of 0.1 MPa or more and 4.5 MPa or less.

5. The rubber for CO 2 separation and capture according to claim 1 , wherein the rubber for CO 2 separation and capture is made of PDMS.

6. The rubber for CO 2 separation and capture according to claim 1 , wherein the rubber for CO 2 separation and capture has a thickness of 0.1 mm or more and 5 mm or less.

7. The rubber for separating and capturing CO 2 according to claim 1 , wherein the rubber for separating and capturing CO 2 is in the form of powder having a sphere-equivalent diameter of 0.002 mm or more and 0.1 mm or less.

8. CO from mixed gas ２ 1. A method for separating and recovering CO ２ and contacting the rubber according to claim 1 with a subzero mixed gas containing the compound and having a pressure of 1 MPa or more and 10 MPa or less; After the mixed gas is brought into contact with the rubber for CO 2 separation and capture, the rubber for CO 2 separation and capture is isolated from the mixed gas, and CO is released from the rubber for CO 2 separation and capture in an environment where the pressure is lower than the pressure at which the mixed gas was brought into contact with the rubber for CO 2 separation and capture and is in the range of 0.1 MPa to 5 MPa. ２ Desorbing CO ２ Separation and recovery method.

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