JP2012250224A - Hybrid adsorbent and recovery method of carbon dioxide in gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a recovery method of carbon dioxide in a gas, with which the energy consumption can be reduced more than a conventional method upon the desorption of carbon dioxide from an adsorbent in a physical adsorption method.SOLUTION: After the carbon dioxide in the carbon dioxide-containing gas is adsorbed by a hybrid adsorbent in which the adsorbent and an activated carbon are mixed, a microwave is irradiated to the hybrid adsorbent so that the adsorbed carbon dioxide is desorbed and recovered.

Description

  The present invention relates to a hybrid adsorbent and a method for separating and recovering carbon dioxide from a carbon dioxide-containing gas such as blast furnace gas or combustion exhaust gas using the hybrid adsorbent.

  In recent years, early implementation of effective measures for preventing global warming is desired. Carbon dioxide in the atmosphere is the main component of greenhouse gases that cause global warming. Therefore, it is thought that global warming can be greatly suppressed if carbon dioxide in combustion exhaust gas discharged from thermal power plants, etc. and carbon dioxide in blast furnace gas of steelworks are separated and recovered, and this carbon dioxide can be fixed or effectively used. .

As a method for separating and recovering carbon dioxide from a carbon dioxide-containing gas, a chemical absorption method using an amine-based absorbent and a physical adsorption method using an adsorbent have been put into practical use.
A chemical absorption method using an amine was developed in the 1930s and put into practical use at a urea synthesis plant. However, as disclosed in Patent Document 1, when an aqueous solution of an alkanolamine such as monoethanolamine is used as the absorbing solution, this aqueous solution is likely to corrode the apparatus, and therefore it is necessary to use an expensive corrosion-resistant steel apparatus. Moreover, the physical adsorption method described in Patent Document 1 requires high energy to desorb carbon dioxide from the absorbing solution.

  As an adsorption method using activated carbon or zeolite as an adsorbent, a pressure swing (PSA) method in which carbon dioxide is desorbed from the adsorbent by depressurization using a vacuum pump is widely used for small-scale apparatuses. As shown in Non-Patent Document 1, this PSA method has a merit that it is a dry method, and therefore does not require a countermeasure against corrosion that is required in the chemical absorption method. However, the PSA method has a drawback of requiring high energy when desorbing carbon dioxide using a vacuum pump. Further, as shown in Non-Patent Document 2, when a large-scale apparatus is used, the layer thickness of the packed bed in the apparatus increases, and the pressure loss ΔP increases when carbon dioxide is desorbed. For this reason, the required ultimate vacuum (several kPa level) cannot be ensured in the upper part of the layer, and the amount of carbon dioxide recovered decreases. In addition, a high-performance vacuum pump is required to ensure the necessary ultimate vacuum above the layer. In this case, there arises a problem that the energy required for desorbing carbon dioxide further increases.

  In Patent Document 2, when regenerated activated carbon used for water treatment such as industrial wastewater treatment, domestic wastewater treatment, and water treatment, solvent recovery or air purification, waste carbon is treated under microwave heating. A method of contacting with an activated carbon utilization gas such as water vapor is disclosed. However, the contents relating to the desorption of carbon dioxide are not disclosed, and the detailed contents relating to the microwave irradiation method are not disclosed.

As shown in Patent Document 3, the present inventors have so far applied a microwave when desorbing carbon dioxide from an adsorbent used in a physical adsorption method as a technique for separating and recovering carbon dioxide in a gas. By doing so, the present inventors have found a method that makes it possible to reduce energy consumption more than the conventional method. Patent Document 3 discloses that zeolite and activated carbon are effective as the adsorbent.
As an example in which microwaves are used for heating, Patent Document 4 discloses that in an applicator, microwaves are applied to generate magnetite to generate heat, and CFCs are decomposed by bringing CFCs into contact with the magnetite in the heat generation state. Is disclosed.

JP 2006-240966 A JP 51-43394 A JP 2008-238221 A JP-A-6-293501

Toshicho Kawai, Kenichiro Suzuki, Chemical Equipment, Vol.31 (8), p.54 (1989) Osamu Wakamura, Kentaro Shibamura, Kiyoshi Uenoyama, Nippon Steel Technical Report, No.345, p.55 (1992)

  As described above, in the separation and recovery method by physical adsorption using a carbon dioxide adsorbent, the method of desorbing the adsorbed carbon dioxide from the adsorbent is to reduce the pressure in the system (packed bed) and remove the carbon dioxide from the adsorbent. A pressure swing (PSA) method for desorbing carbon is generally used. However, since this PSA method has the above-mentioned problems, it is not suitable for large-scale operation. Further, as a method for desorbing carbon dioxide from the adsorbent, a thermal swing (TSA) method for raising the temperature in the system (packed bed) is also conceivable. In this TSA method, the adsorbent is heated using heated carbon dioxide, the adsorbed carbon dioxide is desorbed from the adsorbent, and the adsorbent is cooled using a gas such as low-temperature nitrogen or air. The contained gas is circulated to adsorb carbon dioxide. The temperature increase and temperature decrease in the TSA method basically depends on heat transfer between the gas and the solid (adsorbent). Therefore, the TSA method has a problem that it takes time to desorb carbon dioxide as compared with the PSA method.

  Therefore, in view of the above-described problems of the prior art, the present inventors have been able to carry out the carbon dioxide from the adsorbent more efficiently than the PSA method if the temperature increase and decrease can be performed in a short time in the TSA method. We thought that it could be desorbed. Therefore, as a result of intensive studies, the present inventors have found that carbon dioxide can be efficiently desorbed by irradiating microwaves during desorption of carbon dioxide (see Patent Document 3). However, in order to further reduce the carbon dioxide recovery cost, it is necessary to further reduce the energy required for desorption of carbon dioxide and further increase the amount of carbon dioxide recovered.

  Accordingly, an object of the present invention is to provide a method for recovering carbon dioxide in a gas that can reduce energy consumption as compared with conventional methods when desorbing carbon dioxide from an adsorbent by a physical adsorption method. .

The present inventors believe that the above problem can be solved by using a hybrid adsorbent in which a substance that easily absorbs microwaves is mixed with the adsorbent as an adsorbent that can further reduce the carbon dioxide recovery energy intensity. It was. Therefore, as a result of intensive studies on this substance, the present inventors have found that activated carbon is effective. That is, the present inventors have found that carbon dioxide can be desorbed with lower energy and the amount of carbon dioxide recovered can be increased by using a hybrid adsorbent obtained by mixing activated carbon in an adsorbent such as zeolite.
As used herein, the term “carbon dioxide recovery energy intensity” refers to the amount of energy required to recover unit mass (eg, 1 kg) of carbon dioxide. That is, the carbon dioxide recovery energy intensity is calculated by converting the amount of power of the irradiation microwave into the amount of power used and dividing this amount of power used by the mass of carbon dioxide desorbed.

The gist of the invention is as follows.
(1) The hybrid adsorbent according to an aspect of the present invention includes an adsorbent that adsorbs carbon dioxide and activated carbon that absorbs microwaves, and a mixing amount of the activated carbon is 0.1 mass% or more and 50 mass% or less. is there. The mixing amount of the activated carbon is preferably 15 mass% or more and 30 mass% or less.

(2) In the hybrid adsorbent described in (1) above, the adsorbent may include at least one of crystalline zeolite and mesoporous silica.

(3) In the hybrid adsorbent described in (2) above, the adsorbent may be a crystalline zeolite represented by the chemical formula Na ₈₆ [(AlO ₂ ) ₈₆ (SiO ₂ ) ₁₀₆ ] · 276H ₂ O. .

(4) The hybrid adsorbent described in (1) above may be used after being molded with a binder.

(5) In the method for recovering carbon dioxide in a gas according to one aspect of the present invention, the hybrid adsorbent according to any one of (1) to (4) described above is caused to adsorb carbon dioxide in the gas; The hybrid adsorbent that has adsorbed carbon dioxide is irradiated with microwaves to desorb the carbon dioxide adsorbed on the hybrid adsorbent from the hybrid adsorbent; the carbon dioxide desorbed from the hybrid adsorbent Recover.

  By using the method for recovering carbon dioxide from the carbon dioxide-containing gas of the present invention, it is possible to efficiently separate and recover carbon dioxide from the carbon dioxide-containing gas at a lower cost than before.

FIG. 1 is an explanatory diagram showing an example of a recovery apparatus for carrying out the carbon dioxide recovery method of the present invention. FIG. 2 is an explanatory diagram of the cycle time when the two towers of the present invention are used.

Hereinafter, preferred embodiments of the present invention will be described.
The adsorbent used in the present invention is applicable as long as it has a carbon dioxide adsorption ability.

For example, activated carbon, activated coke, and clay compounds such as zeolite, mesoporous silica, activated alumina, and montmorillonite can be used as the adsorbent. In particular, crystalline zeolite (A type, X type, Y type, mordenite (MOR) type, etc.) and mesoporous silica excellent in carbon dioxide adsorption ability are preferable. Among these, crystalline zeolite (molecular sieve 13X (MS-13X)) represented by the chemical formula Na ₈₆ [(AlO ₂ ) ₈₆ (SiO ₂ ) ₁₀₆ ] · 276H ₂ O is more preferable. This crystalline zeolite is effective as an adsorbent because of its large amount of carbon dioxide adsorption.

  In the present invention, a hybrid adsorbent obtained by mixing the adsorbent and activated carbon is used. The adsorbent itself can absorb microwaves, and the crystalline zeolite used as the adsorbent (molecular sieve 13X (MS-13X)) is a substance that easily absorbs microwaves. The activated carbon to be mixed is more easily absorbed by microwaves, and is therefore efficiently heated by microwave irradiation. On the other hand, activated carbon itself is an adsorbent for carbon dioxide, but its adsorbability is inferior to that of the adsorbent. Heating by microwave irradiation is due to the conductive loss effect of activated carbon.

  The term “hybrid adsorbent” used in the present specification is an adsorbent obtained by mixing an adsorbent such as the above-mentioned zeolite and the above-mentioned activated carbon.

  The mixing amount (blending amount) of activated carbon in the hybrid adsorbent is preferably 0.1 mass% to 50 mass%. If the mixing amount of the activated carbon is 0.1 mass% or more, the activated carbon generates heat by microwave irradiation, and heat transfer from the activated carbon to the adsorbent can be sufficiently performed. Moreover, if the mixing amount of activated carbon is 50 mass% or less, the mixing amount of an adsorbent will be 50 mass% or more, and the adsorption amount of the carbon dioxide by an adsorbent can fully be ensured. More preferably, the mixing amount of the activated carbon is 2 mass% to 30 mass%. Most preferably, the mixing amount of activated carbon is 15 mass% to 30 mass%. In this case, the balance between the heat generation / heat transfer amount and the adsorption amount of carbon dioxide is optimized, and carbon dioxide can be recovered more efficiently. In order to ensure a sufficient amount of carbon dioxide adsorption, the adsorbent mixing amount in the hybrid adsorbent is preferably 50 mass% to 99.9 mass%. The hybrid adsorbent can also be used in powder form. However, as with a general adsorbent, a hybrid adsorbent is granulated into a spherical or pellet shape having a diameter of about 2 mm to 5 mm using a binder such as clay according to the gas flow rate in order to suppress pressure loss. Forming). Note that the amount of the binder is evaluated as an external number of the amount of the hybrid adsorbent.

Hereinafter, preferred embodiments of a carbon dioxide recovery method using the hybrid adsorbent of the present invention will be described in detail with reference to the accompanying drawings.
In the embodiment of the present invention, for example, using a recovery device as shown in FIG. 1, the adsorption process, the cleaning process, the desorption process, and the cooling process are repeated to recover carbon dioxide.
In the adsorption step, the switching valve _{V 1} and _{V 2} are opened and the switching valve _V 3 ~V ₅ is in the closed state. In this adsorption step, a gas containing dehumidified carbon dioxide is introduced through a flow path 1 into a packed bed (not shown) filled with a hybrid adsorbent in the adsorption tower 2. In the adsorption tower 2, carbon dioxide is preferentially adsorbed compared to other gases, and the gas that has not been adsorbed is discharged through the flow path 9. In this adsorption process, the flow path 6 is closed.

In the washing step, when the hybrid adsorbent in the adsorption tower 2 has adsorbed a sufficient amount of carbon dioxide, the switching valve V ₁ is closed and the switching valve V ₄ is opened to switch the flow path 1 to the flow path 3. Furthermore, a part of the carbon dioxide already recovered is flowed from the product tank 7 into the adsorption tower 2 as a carrier gas, and impurity components such as nitrogen remaining in the adsorption tower 2 are discharged from the flow path 9.

In the desorption process, the switching valve V ₂ is closed and the switching valve V ₃ is opened, and the flow path 9 is switched to the flow path 6. In a state where the flow path 3 and the flow path 6 are open, the microwave adsorbed from the microwave oscillator 5 is irradiated to the hybrid adsorbent in the adsorption tower 2 through the waveguide 4 connected to the adsorption tower 2. The hybrid adsorbent irradiated with microwaves is heated rapidly and uniformly because microwaves are absorbed by activated carbon and heat is generated by the conductive loss effect, generating heat from inside the hybrid adsorbent and transferring it to the adsorbent. . As a result, carbon dioxide adsorbed on the adsorbent is efficiently desorbed from the adsorbent. The carbon dioxide after desorption passes through the flow path 6 (at this time, the flow path 9 is closed) and is collected in the product tank 7.

In the cooling step, the switching valve V ₂ is opened again, the switching valve V ₃ is closed, and the flow path 6 is switched to the flow path 9. Further, the switching valve V ₄ is closed and the switching valve V ₅ is opened to switch the flow path 3 to the flow path 8. Furthermore, a cooling gas such as dried nitrogen or air is introduced from the flow path 8 to cool the hybrid adsorbent after desorption of carbon dioxide.
After the cooling step, the switching valve V ₅ is closed and the switching valve V ₁ is opened, so that the flow path 8 is switched to the flow path 1. Again, a gas containing carbon dioxide is introduced into the adsorption tower 2 through the flow path 1 to perform adsorption of carbon dioxide (adsorption process). In this way, the adsorption process, the cleaning process, the desorption process, and the cooling process are repeated.

  In the above, an example in which there is one adsorption tower 2 has been described in order to easily explain the process of separating and recovering carbon dioxide. However, normally, carbon dioxide is continuously separated and recovered by providing two to four adsorption towers in parallel and adjusting the timing of adsorption and desorption.

  FIG. 2 shows an example of a time schedule when two adsorption towers are used. In this schedule example, the desorption step (microwave irradiation) is performed in the B tower while the cooling step, the adsorption step, or the cleaning step (discharge of impurity components) is performed in the A column. Further, while the desorption process (microwave irradiation) is performed in the A tower, the cooling process, the adsorption process, and the cleaning process (discharge of impurity components) are performed in the B tower. In this way, carbon dioxide can be continuously separated and recovered (desorption step). In general, because adsorption time is shorter than desorption time, and it is necessary to take both washing time and cooling time, in the case of a two-column adsorption tower, carbon dioxide is recovered from continuously discharged gas such as combustion exhaust gas. When this occurs, a time period during which carbon dioxide cannot be adsorbed occurs. In this case, a gas holder is provided in front of the adsorption tower (upstream of the gas flow) to adjust the gas introduction time.

  In addition, it is possible to more smoothly and continuously separate and recover carbon dioxide by providing three or more adsorption towers in parallel and switching the piping of each process (for example, an adsorption process or a desorption process).

  The method of the present invention can be applied to any gas that contains carbon dioxide. In particular, coal combustion power plant combustion exhaust gas (carbon dioxide concentration: about 15 vol.%), Blast furnace gas (BFG) (carbon dioxide concentration: about 20 vol.%), Hot blast furnace exhaust gas (carbon dioxide concentration: about 25 vol.%) It can be suitably applied to such a gas containing a relatively high concentration of carbon dioxide.

  In the physical adsorption method, since the amount of carbon dioxide adsorbed by the adsorbent increases as the carbon dioxide concentration in the gas increases, the carbon dioxide recovery energy intensity can be kept low. Therefore, the carbon dioxide concentration in the gas is 10 vol. % Or more is desirable. For example, BFG having a high carbon dioxide concentration (about 20 vol.%) Or blast furnace hot-blast furnace exhaust gas (about 25 vol.%) Is optimal. Carbon dioxide concentration is 10 vol. If it is less than%, the amount of carbon dioxide adsorbed per unit mass of the adsorbent decreases rapidly, and a large amount of adsorbent is required. Therefore, 10 vol. It is economically undesirable to recover carbon dioxide from a gas having a carbon dioxide concentration of less than%.

  In addition, since water vapor has a strong polarity and inhibits the adsorption of carbon dioxide to the adsorbent, the carbon dioxide-containing gas contains water vapor at a high concentration (for example, several vol.% To several tens vol.%). It is preferable to dehumidify in advance. Since the affinity between the adsorbent and water vapor varies depending on the type of adsorbent, it is necessary to change the degree of dehumidification according to the type of adsorbent. For example, zeolitic adsorbent (zeolite) has a strong affinity for water vapor, and therefore needs to be dehumidified to a dew point of about −40 ° C. to −60 ° C. In addition, to adsorb more carbon dioxide to the hybrid adsorbent and increase the microwave absorption efficiency to the hybrid adsorbent, pre-dry the hybrid adsorbent before introducing the gas into the adsorption tower. Is preferred. For example, moisture can be removed by irradiating and heating microwaves while flowing dehumidified gas through the adsorbent. A hygrometer is provided at the outlet of the adsorption tower (downstream of the gas flow), and it can be determined by the hygrometer that the humidity of the outlet gas has decreased and stabilized, and that it has been sufficiently dried beforehand.

  A wide range of frequencies from 300 MHz to 300 GHz can be used as the microwave frequency. However, when microwaves are actually used, the frequency band is limited by communication-related laws and regulations. That is, in Japan, a frequency of 2,450 MHz or 915 MHz is used. Furthermore, in the United States, a frequency of 5,800 MHz is also available.

  The number of waveguides 4 is one in the above description (FIG. 1). However, it is preferable to arrange a plurality of waveguides 4 in the adsorption tower according to the shape and dimensions of the packed bed. When the width of the filling layer is wide (in the case of a cylinder, the diameter of the filling layer is large), a plurality of waveguides 4 are arranged in the circumferential direction of the filling layer. It is preferable to arrange a plurality of waveguides 4 in the length direction.

  The packed bed may have any shape. When the shape of the packed bed is rectangular and cylindrical, the inner circumference of the adsorption tower is preferably 31.4 cm or less (when the packed bed is cylindrical, the inner diameter of the adsorption tower is 10 cm or less). Furthermore, the inner circumference of the adsorption tower is more preferably 15.7 cm or less (when the packed bed has a cylindrical shape, the inner diameter of the adsorption tower is 5 cm or less). When the inner circumference of the adsorption tower is more than 31.4 cm, it is a problem in that microwaves do not easily reach the center of the packed bed, and heating in the packed bed tends to be uneven.

  When the inner circumference of the adsorption tower is small, the heat removal area of the packed bed per unit packed amount is small, so that sufficient heat removal (radiation) is not performed during microwave irradiation, and cooling takes time. Therefore, the lower limit of the inner periphery of the adsorption tower is determined from the dimensions of the hybrid adsorbent. For example, when using a hybrid adsorbent formed into a spherical shape with a diameter of 0.2 cm, the cylindrical packed bed needs to have a diameter (1 cm) that is about five times the diameter of the adsorbent, so The minimum inner circumference is 3.14 cm. The smaller the inner circumference of the adsorption tower, the smaller the packed amount per unit length of the packed bed. Therefore, it is necessary to increase the length of the packed bed. However, since the pressure loss increases as the packed bed becomes longer, it is preferable to arrange a plurality of short packed beds. The lower limit of the inner periphery of the adsorption tower is not determined from the efficiency of microwave irradiation and the heat removal efficiency.

Since adsorption is an exothermic reaction, the lower the adsorption temperature at the adsorption tower, the higher the adsorption rate and amount of carbon dioxide. However, in consideration of economy, the adsorption temperature is preferably room temperature. The adsorption time is comprehensively determined from the performance of the hybrid adsorbent and the number of adsorption towers. Unlike adsorption, the higher the desorption temperature, the higher the desorption rate and desorption amount. However, at a high temperature of 500 ° C. or higher, particularly 600 ° C. or higher, the hybrid adsorbent containing the zeolite adsorbent is liable to cause the structural collapse of the zeolite and requires a long time for cooling. Therefore, it is desirable to perform efficient desorption at the lowest possible temperature.
An optical fiber thermometer that is not affected by an electromagnetic field caused by microwave irradiation can be used for temperature measurement.

  When the microwave is continuously irradiated, the temperature of the packed bed rapidly rises, so that it is difficult to control the heating rate. For this reason, the hybrid adsorbent is directly heated while intermittently irradiating microwaves and controlling the rate of temperature increase. In this method, desorption can be performed at a relatively low temperature without increasing the ambient temperature. In intermittent microwave irradiation, microwave irradiation and microwave pause are alternately performed. Specifically, for example, microwave irradiation for 30 seconds and microwave irradiation pause for 30 seconds are alternately repeated five times. The desorption time, the microwave irradiation time, and the irradiation interval are comprehensively determined from the performance of the adsorbent, the microwave output, the arrangement of the waveguide, and the like.

Further, the outer wall of the adsorption tower holding the hybrid adsorbent is made of any one of SiO ₂ , MgO, Si ₃ N ₄ , AlN, and BN. The above substance alone does not absorb microwaves (the temperature does not rise due to microwave irradiation) and has relatively good thermal conductivity (easy to be cooled even when heated). Therefore, the microwave can be efficiently absorbed by the hybrid adsorbent by using the substance in the absorption tower. For example, quartz glass can be used for SiO ₂ . Further, for example, refractories manufactured by firing each material after molding each material can be used as MgO, Si ₃ N ₄ , AlN, and BN.

  Furthermore, for example, by providing protrusions on the outer wall of the adsorption tower, heat dissipation is promoted, and carbon dioxide can be desorbed while suppressing an increase in the temperature of the packed bed. In order to increase the outer surface area, it is preferable that the protrusion has a fin shape, a columnar shape, or a weight shape.

In the present invention, carbon dioxide in the gas is adsorbed on a hybrid adsorbent obtained by mixing adsorbent and activated carbon. Furthermore, the hybrid adsorbent is irradiated with microwaves to desorb the adsorbed carbon dioxide from the hybrid adsorbent, and the desorbed carbon dioxide is recovered.
In conventional technologies such as indirect external heating from the outside of the outer wall and internal heating with heated flow gas, the adsorbent is heated by convective heat transfer from the atmospheric gas to the adsorbent, so heat is released from the adsorbent during heating. I can't. In the case of microwave heating, since the hybrid adsorbent itself generates heat, heat can be radiated from the adsorbent surface to the atmosphere gas to the outside. In the present invention, since the activated carbon in the hybrid adsorbent absorbs more microwaves, the efficiency is further improved as compared with the case where the adsorbent is used alone.

[Comparative Example 1]
As a model gas for blast furnace gas and hot blast furnace exhaust gas, 20 vol. % Carbon dioxide and 80 vol. A mixed gas with% nitrogen was used. Moreover, in order to collect | recover carbon dioxide from this mixed gas, molecular sieve 13X (MS-13X) which is a commercial zeolite was used as an adsorbent. In order to clarify the effect of mixing activated carbon and adsorbent, which will be described later, this adsorbent is pressure-molded without using a binder such as clay, pulverized, sized, and adsorbent sample. Produced. 40 g of this adsorbent sample was filled in a quartz pipe, and a mixed gas was allowed to flow through the quartz pipe at a flow rate of 2 L / min, and carbon dioxide in the mixed gas was saturatedly adsorbed on the adsorbent at about 40 ° C. While carbon dioxide is adsorbed on the adsorbent, the concentration of carbon dioxide in the exhaust gas from the quartz tube is 20 vol. %. When carbon dioxide is saturated and adsorbed on the adsorbent, the concentration of carbon dioxide in the exhaust gas is again 20 vol. Return to%. Therefore, the carbon dioxide concentration in the exhaust gas was measured, and saturated adsorption was confirmed from the change in the carbon dioxide concentration described above. The amount of carbon dioxide adsorbed is such that the carbon dioxide concentration is 20 vol. It is obtained by integrating the measured decrease in carbon dioxide concentration until it stabilizes to%. The carbon dioxide adsorption amount (CO ₂ adsorption amount) was evaluated as the carbon dioxide adsorption rate (mass%). That is, the adsorption rate of carbon dioxide is calculated by dividing the mass of adsorbed carbon dioxide by the mass of the adsorbent filled. Thereafter, while the mixed gas was allowed to flow through the quartz pipe as it was, the adsorbent was irradiated with microwaves of 2,450 MHz and 200 W for 2 minutes to desorb the adsorbed carbon dioxide from the adsorbent. While measuring the carbon dioxide concentration in the exhaust gas, the carbon dioxide concentration was 20 vol. % Measured value of carbon dioxide and 20 vol. % Difference (increase in carbon dioxide concentration) was integrated to determine the amount of desorbed carbon dioxide. The amount of carbon dioxide desorbed (CO ₂ desorption rate) was evaluated as the desorption rate (%). This desorption rate is calculated by dividing the mass of desorbed carbon dioxide by the mass of adsorbed carbon dioxide. Further, the energy intensity E is calculated by the following equation (1).
E = P × t / 60 / k _P / Nx (1)
Here, the microwave irradiation power P is 200 W, and the microwave irradiation time t is 2 min. The coefficient k _P for converting the irradiated microwave power to the power consumption is 0.7. Nx is the mass (g) of desorbed carbon dioxide. The temperature of the adsorbent was measured with a thermocouple.

In Comparative Example 1, carbon dioxide is adsorbed only by MS-13X, MS-13X is heated by microwaves, and carbon dioxide is desorbed from MS-13X. As a result, as shown in Table 1, the carbon dioxide desorption rate was 21.5%, and the energy intensity was 8.7 kWh / kg-CO ₂ .

[Example 1]
Next, carbon dioxide was adsorbed and desorbed under the same conditions as in Comparative Example 1 except that a hybrid adsorbent obtained by mixing 5 mass% of activated carbon with MS-13X was used as the adsorbent. As a result, as shown in Table 1, the carbon dioxide desorption rate in Example 1 was 28.2%, which was higher than the desorption rate in Comparative Example 1. Moreover, the energy basic unit of Example 1 was 6.5 kWh / kg-CO ₂ , which was lower than the energy basic units of Comparative Examples 1 and 2.

[Example 2]
Adsorption and desorption of carbon dioxide were performed under the same conditions as in Example 1 except that the mixing amount of activated carbon in the hybrid adsorbent was 10 mass%. As a result, as shown in Table 1, the maximum temperature reached by the hybrid adsorbent of Example 2 increased from 64 ° C. in Example 1 to 71 ° C. Therefore, the desorption rate of carbon dioxide in Example 2 was 35.1%, which could be further improved than the desorption rate in Example 1. Moreover, energy consumption of Example 2 is 5.8kWh / kg-CO _2, it could be further reduced than the energy intensity of Example 1.

Example 3
Carbon dioxide was adsorbed and desorbed under the same conditions as in Example 1 except that the mixing amount of activated carbon in the hybrid adsorbent was 15 mass%. As a result, as shown in Table 1, the maximum reached temperature of the hybrid adsorbent of Example 3 increased from 64 ° C. to 74 ° C. in Example 1. Therefore, the desorption rate of carbon dioxide in Example 3 was 46.7%, which could be further improved than the desorption rate in Example 2. Moreover, energy consumption of Example 3 is 4.4kWh / kg-CO _2, it could be further reduced than the energy intensity of the second embodiment.

Example 4
Carbon dioxide was adsorbed and desorbed under the same conditions as in Example 1 except that the mixing amount of the activated carbon in the hybrid adsorbent was 20 mass%. As a result, as shown in Table 1, the maximum attainable temperature of the hybrid adsorbent of Example 4 increased from 64 ° C. to 77 ° C. in Example 1. Therefore, the desorption rate of carbon dioxide in Example 4 was 55.3%, which was further improved than the desorption rate in Example 3. Moreover, the energy basic unit of Example 4 was 4.0 kWh / kg-CO ₂ , which could be further reduced from the energy basic unit of Example 3.

Example 5
Carbon dioxide was adsorbed and desorbed under the same conditions as in Example 1 except that the mixing amount of the activated carbon in the hybrid adsorbent was 30 mass%. As a result, as shown in Table 1, the maximum reached temperature of the hybrid adsorbent of Example 5 increased from 64 ° C. in Example 1 to 80 ° C. Therefore, the carbon dioxide desorption rate of Example 5 was 53.6%, which could be further improved than the desorption rates of Examples 1 to 3, but was lower than that of Example 4. Moreover, energy consumption of Example 5 is 4.4kWh / kg-CO _2, here was the same as the energy per unit of Example 3.

Example 6
Carbon dioxide was adsorbed and desorbed under the same conditions as in Example 1 except that the amount of activated carbon in the hybrid adsorbent was 40 mass%. As a result, as shown in Table 1, the maximum attainable temperature of the hybrid adsorbent of Example 6 increased from 64 ° C. in Example 1 to 82 ° C. Therefore, the desorption rate of carbon dioxide in Example 6 was 48.6%, which was higher than the desorption rate in Examples 1 to 3, but was lower than that in Example 4 or 5. Moreover, the energy basic unit of Example 6 was 4.9 kWh / kg-CO ₂ , which was lower than that of Comparative Example 1, but higher than that of Examples 3 to 5.

Example 7
Carbon dioxide was adsorbed and desorbed under the same conditions as in Example 1 except that the amount of activated carbon in the hybrid adsorbent was 50 mass%. As a result, as shown in Table 1, the maximum temperature reached by the hybrid adsorbent of Example 7 increased from 64 ° C. to 86 ° C. in Example 1. Therefore, the carbon dioxide desorption rate of Example 7 was 38.6%, which was higher than the desorption rate of Comparative Example 1 and Examples 1-2, but from Examples 3-6 Declined. Moreover, energy consumption of Example 7 is 7.5kWh / kg-CO _2, but can be lowered than Comparative Example 1 was higher than Examples 1-6.

Example 8
Carbon dioxide was adsorbed and desorbed under the same conditions as in Example 1 except that the mixing amount of the activated carbon in the hybrid adsorbent was 60 mass%. As a result, as shown in Table 1, the maximum temperature reached by the hybrid adsorbent of Example 8 increased from 64 ° C. to 90 ° C. in Example 1. Therefore, the carbon dioxide desorption rate in Example 8 was 37.9%, which was higher than the desorption rates in Comparative Example 1 and Examples 1-2, but from Examples 3-7. Declined. Moreover, energy consumption of Example 8 is 8.5kWh / kg-CO _2, but can be lowered than Comparative Example 1 was higher than Examples 1-7.

[Comparative Example 2]
In Comparative Example 2, carbon dioxide was adsorbed and desorbed under the same conditions as in Comparative Example 1, except that only mesoporous silica was used as the adsorbent. As a result, as shown in Table 2, the carbon dioxide desorption rate was 19.2%, and the energy intensity was 13.5 kWh / kg-CO ₂ .

Example 9
Carbon dioxide was adsorbed and desorbed under the same conditions as in Example 1 except that a hybrid adsorbent in which 20 mass% of activated carbon was mixed with mesoporous silica was used as the adsorbent. As a result, as shown in Table 2, the carbon dioxide desorption rate of Example 9 was 45.6%, which was higher than the desorption rate of Comparative Example 2. Moreover, the energy basic unit of Example 9 was 5.9 kWh / kg-CO ₂ , which was lower than that of Comparative Example 2.

[Comparative Example 3]
In Comparative Example 3, carbon dioxide is adsorbed only on activated carbon, activated carbon is heated by microwaves, and carbon dioxide is desorbed from the activated carbon. As a result, as shown in Table 2, the carbon dioxide desorption rate was 42.6%, and the energy intensity was 14.6 kWh / kg-CO ₂ . The reason why the energy intensity is small although the carbon dioxide desorption rate is about twice that of MS-13X is that the amount of carbon dioxide adsorbed on the activated carbon is about 1/3 that of MS-13X. Although the CO ₂ desorption rate is good, the energy intensity is significantly inferior to Examples 1-9.

[Comparative Example 4]
Carbon dioxide was adsorbed and desorbed under the same conditions as in Comparative Example 1 except that the microwave irradiation time was increased so that the maximum temperature of the adsorbent reached 64 ° C., which was the same as in Example 1. It was. Under the conditions of Comparative Example 4, only MS-13X was used as the adsorbent. As a result, as shown in Table 2, the maximum temperature reached in Comparative Example 4 was higher than the maximum temperature reached in Comparative Example 1, and the desorption rate of carbon dioxide was improved from the desorption rate of Comparative Example 1. However, it is inferior compared with Examples 1-9. However, since the increase rate of the input energy with respect to the increase in the desorption rate is large, the energy intensity of Comparative Example 4 is larger than that of Comparative Example 1 and Examples 1-9. Therefore, it can be seen that a hybrid adsorbent mixed with 15% to 30% activated carbon is most effective for desorption of carbon dioxide by microwave heating.

1 Channel 2 Adsorption Tower 3 Channel 4 Waveguide 5 Microwave Oscillator 6 Channel 7 Product Tank 8 Channel 9 Channel

Claims (6)

  A hybrid adsorbent comprising an adsorbent that adsorbs carbon dioxide and activated carbon that absorbs microwaves, and a mixing amount of the activated carbon is 0.1 mass% or more and 50 mass% or less.   2. The hybrid adsorbent according to claim 1, wherein a mixing amount of the activated carbon is 15 mass% or more and 30 mass% or less.   The hybrid adsorbent according to claim 1 or 2, wherein the adsorbent contains at least one of crystalline zeolite and mesoporous silica. 3. The hybrid adsorbent according to claim 1, wherein the adsorbent is a crystalline zeolite represented by a chemical formula Na ₈₆ [(AlO ₂ ) ₈₆ (SiO ₂ ) ₁₀₆ ] · 276H ₂ O. 4.   A hybrid adsorbent obtained by molding the hybrid adsorbent according to any one of claims 1 to 4 with a binder.   The hybrid adsorbent according to any one of claims 1 to 5 is adsorbed to the hybrid adsorbent by adsorbing carbon dioxide in a gas, irradiating the hybrid adsorbent adsorbing the carbon dioxide with microwaves. A method for recovering carbon dioxide in a gas, comprising desorbing the carbon dioxide that has been released from the hybrid adsorbent and recovering the carbon dioxide desorbed from the hybrid adsorbent.

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