JP2020196654A - Method for absorbing co2 and decomposing into carbon - Google Patents

Abstract

To provide a method for absorbing CO2 and decomposing into C in which, when absorbing CO2 by using an alkali silicoxide and decomposing into C, the decomposition temperature of C can further be lowered.SOLUTION: Provided is a method for absorbing CO2 and decomposing into carbon characterized by having a step of having an alkali silicoxide and a quartz wool be at a ratio of 1:40 to 1: 6000 in mass ratio and having them be present in a reaction system in a state in which they are in contact with each other at least in a part, and bringing a CO2-containing gas containing CO2 into contact with the materials in the reaction system to absorb CO2, and a step of decomposing the absorbed CO2 into carbon by making the atmosphere non-oxidative and heating to 350°C or more and 700°C or less, for recovery.SELECTED DRAWING: Figure 5

Description

The present invention relates to a method of absorbing CO ₂ and decomposing it into carbon, and more particularly, to a method of absorbing CO ₂ using an alkaline silicic oxide and decomposing it into carbon.

In recent years, carbon dioxide (CO ₂ ) in the atmosphere has been increasing steadily, and it has long been said that this is one of the causes of global warming. If CO ₂ in the atmosphere can be decomposed (reduced) into carbon (C), it will help solve this problem, and the decomposed C can be used as a carbon source for industrial materials and fuels. It is extremely advantageous. However, no promising method has been found so far that can easily perform both absorption of CO ₂ and decomposition into C.

For example, in Patent Document 1, a carbonic acid oxide of an alkaline element and / or a carbonic acid oxide of an alkaline earth element is mixed with water glass or an alkaline siliceous oxide, and this mixture is brought to 700 ° C. or higher and 1600 ° C. or lower in a non-oxidizing atmosphere. A method for producing free carbon from carbonic acid oxide by heating is disclosed.

Regarding this method, for example, CaO (quick lime) and Na ₂ O efficiently absorb CO ₂ to generate carbon oxide. Therefore, by using such carbon oxide, CO ₂ is converted to C as a result. Will be done. That is, in this method, carbon is separated from the carbon oxide obtained by absorbing CO ₂ using water glass or an alkaline silicic oxide.

However, CaO and Na ₂ O are strong alkaline compounds, and among them, Na ₂ O is very unstable, so that it easily reacts with various materials constituting the apparatus. Further, when heated in a non-oxidizing atmosphere, alkaline silicic acid oxide, carbonic acid oxide and the like are melted and integrated, so that repeated use is difficult. Furthermore, the precipitated carbon (C) may adhere to the melt and act as a catalytic poison, making repeated use difficult.

Like above, Patent Document 2, and Patent Document 3, it generates a carbonate of lithium orthosilicate of lithium silicate compound (Li ₄ SiO ₄₎ and lithium metasilicate (Li ₂ SiO ₃₎ absorbs the CO ₂ It is disclosed to do. Even if these techniques are combined with the method for producing free carbon from the carbon oxide of Patent Document 1, CO ₂ can be converted to C as a result. However, it is difficult to use it repeatedly because alkali silicic acid oxide, carbonic acid oxide and the like grow into grains during heating and sintering progresses to integrate them. Further, the precipitated carbon (C) may adhere to the alkali silicic acid oxide or the carbon oxide and act as a catalytic poison, which makes it difficult to use repeatedly.

Further, Patent Document 4, to absorb CO ₂ in the atmosphere of sodium silicate (Na ₂ O · nSiO ₂₎ in the presence of H 2 _O, a non-oxidizing sodium silicate having absorbed CO ₂ and H _{2 O} A method for separating carbon by heating to 700 ° C. or higher and 1600 ° C. or lower in an atmosphere is disclosed. According to this, it is possible without the use of strong alkaline compound such as CaO and Na 2 _O, to absorb the CO ₂ is decomposed into C as carbonates source.

However, in order to separate C from sodium silicate that has absorbed CO ₂ , it must be heated to at least 700 ° C. in a non-oxidizing atmosphere, which is an improvement in that a large amount of energy is required for the separation of C. There is room.

JP 2015-187059 Japanese Unexamined Patent Publication No. 2008-105006 Japanese Unexamined Patent Publication No. 2011-161332 Japanese Unexamined Patent Publication No. 2018-131351

Therefore, the present inventors are surprised as a result of diligent studies on a means capable of lowering the decomposition temperature of C in a method of absorbing CO ₂ using an alkaline silicic oxide and decomposing it into C. In particular, they have found that the above problems can be achieved by allowing quartz wool to exist in the reaction system together with the alkali silicic oxide, and have completed the present invention.

Therefore, an object of the present invention is to provide a method capable of lowering the decomposition temperature of C when absorbing CO ₂ using an alkaline silicic oxide and decomposing it into C.

That is, the gist of the present invention is as follows.
(1) Alkali silicic oxide and quartz wool are allowed to exist in the reaction system in a mass ratio of 1:40 to 1: 6000 and at least partially in contact with each other, and these materials in the reaction system. a step a of absorbing by contacting the CO ₂ containing gas containing CO _2, the CO ₂ in the CO ₂ containing gas to the reaction system in the material,
The reaction system by heating to the 350 ° C. or higher 700 ° C. or less in a non-oxidizing atmosphere, characterized by having a decomposing step B of CO ₂ to the reaction system the material has absorbed carbon, CO ₂ A method of absorbing carbon dioxide and decomposing it into carbon dioxide.
(2) In the step A, the method of absorbing CO ₂ and decomposing it into carbon according to (1), wherein the material in the reaction system is brought into contact with a CO _2- containing gas at a temperature of room temperature or higher and 650 ° C. or lower.
(3) The alkali silicic acid oxide has nNa ₂ O · SiO _{2 having} n of 2.6 to 4.6, nK ₂ O · SiO _{2 having} n of 3.4 to 5.4, and n having 2.4 to 2.4 to n. The method for absorbing CO _{2 according} to (1) or (2) and decomposing it into carbon, which comprises any one or more selected from the group consisting of nLi ₂ O · SiO _{2 of} 5.
(4) The method according to any one of (1) to (3), wherein after the step B, the step A and the step B are performed again to repeat the absorption of CO ₂ and the decomposition into carbon. A method of absorbing CO ₂ and decomposing it into carbon.

According to the present invention, when CO ₂ is absorbed by using an alkaline silicic oxide and decomposed into C, the decomposition temperature of C can be made lower than that of the conventional method. Moreover, in the method of decomposing the carbon absorbs CO ₂ in the present invention, since it is possible to repeat the decomposition to absorb carbon of CO _2, by effective use of CO ₂ of carbon that can be used as a carbon source It will be possible to manufacture efficiently.

FIG. 1 is a two-component phase equilibrium diagram of Na ₂ O—SiO ₂ . FIG. 2 is a two-component phase equilibrium diagram of K ₂ O-SiO ₂ . FIG. 3 is a two-component phase equilibrium diagram of Li ₂ O—SiO ₂ . FIG. 4 is an explanatory diagram for explaining the tendency of the CO ₂ absorption property and the CO ₂ decomposition property of the alkali metal. FIG. 5 is a schematic diagram for explaining the reaction device (CO ₂ absorption / decomposition device) used in the examples.

Hereinafter, the present invention will be described in detail.
In the method of absorbing CO ₂ and decomposing it into carbon in the present invention, the alkali siliceous oxide and the quartz wool are made to have a mass ratio of 1:40 to 1: 6000, and at least some of them are in contact with each other. and it is present in the reaction system in a state, by contacting the CO ₂ containing gas containing CO ₂ in these reaction system material, a step a of absorbing CO ₂ in the CO ₂ containing gas to the reaction system in the material Step B of decomposing CO ₂ absorbed by the material in the reaction system into C by heating the inside of the reaction system containing alkali siliceous oxide and quartz wool to a non-oxidizing atmosphere and heating it to 350 ° C. or higher and 700 ° C. or lower. have.

In the present invention, the presence of quartz wool in the reaction system makes it possible to lower the decomposition temperature of CO ₂ to carbon (C) in step B to a lower temperature than in the case where quartz wool is not present. The reason for this has not been fully elucidated at this time, but it is considered that the presence of quartz wool assists the decomposition of CO ₂ absorbed by the material in the reaction system into C. That is, although the mechanism is unknown, it is speculated that the presence of quartz wool may provide a field for CO ₂ decomposition reaction at the contact interface between the alkali silicic oxide and quartz wool. .. It is also possible that the presence of quartz wool creates gaps between the alkali silicic oxides, making it easier for this gas-related reaction to proceed at low temperatures.

With respect to the blending amount of the quartz wool, the alkali silicic oxide and the quartz wool are allowed to be present in the reaction system at a ratio of 1:40 to 1: 6000, preferably at a ratio of 1:50 to 1: 5000. It should be present in the reaction system. When the alkali silicic oxide is present in a mass ratio of more than 1/40 with respect to quartz wool, the decomposition does not proceed at 350 ° C. when the absorbed CO ₂ is decomposed into C by the heat treatment in step B, and the object of the present invention is It becomes impossible to reduce the decomposition temperature. On the other hand, if the mass ratio of alkaline silicic acid to quartz wool is less than 1/6000, the amount of C produced (free carbon amount) that absorbs and decomposes CO ₂ is small, so it is industrially effective. It cannot be said that.

The alkali silicic acid oxide used in the present invention preferably contains an alkali metal which is a Group 1 element, and more preferably contains any of Li, Na, and K. Regarding these, in the present invention, an alkali silicic acid oxide containing any one kind of alkali metal may be used, and a mixture thereof is used by combining two or more kinds of alkali silicic acid oxides in which different alkali metals are selected. However, since the relative ratio of the alkaline silicic oxide is small, it is sufficient to use a single type of alkaline silicic oxide. When two or more kinds of alkaline silicic oxides are used, the total amount thereof should satisfy the mass ratio to the quartz wool described above.

Specifically, as the alkali siliceous oxide, nNa ₂ O · SiO _{2 having} n of 2.6 to 4.6, nK ₂ O · SiO ₂ having n of 3.4 to 5.4, and n being 2. It is preferably 4 to 5 nLi ₂ O · SiO ₂ , and one or a combination of two or more of these can be used.

Of these, for nNa ₂ O · SiO ₂ having n of 2.6 to 4.6, FIG. 1 shows a two-component phase equilibrium state diagram of Na ₂ O-SiO ₂ . As can be seen from this, nNa ₂ O · SiO ₂ in which n is in the above range is advantageous from the viewpoint of CO ₂ absorption because it has a high alkali ratio in which the ratio of the Na component is large. Further, if n is in the above range, the melting point is low, which is advantageous from the viewpoint that the reaction of absorption and decomposition of CO ₂ as in the present invention is likely to occur. More preferably, it is nNa ₂ O · SiO ₂ in which n is 3.2 to 4.0, and most preferably 3.6 Na ₂ O · SiO ₂ .

Further, for nK ₂ O · SiO ₂ having n of 3.4 to 5.4, FIG. 2 shows a two-component phase equilibrium state diagram of K ₂ O-SiO ₂ . As can be seen from this, nK ₂ O · SiO ₂ in which n is in the above range is advantageous from the viewpoint of CO ₂ absorption because it has a high alkali ratio in which the ratio of the K component is large. Further, if n is in the above range, the melting point is low, which is advantageous from the viewpoint that the reaction of absorption and decomposition of CO ₂ as in the present invention is likely to occur. More preferably, it is nK ₂ O · SiO ₂ in which n is 4 to 4.8, and most preferably 4.4K ₂ O · SiO ₂ .

Further, for nLi ₂ O · SiO ₂ having n of 2.4 to 5, FIG. 3 shows a two-component phase equilibrium diagram of Li ₂ O-SiO ₂ , and nNa ₂ O · SiO ₂ and The same reason as in the case of nK ₂ O · SiO ₂ can be mentioned, more preferably nLi ₂ O · SiO ₂ having n of 3.0 to 4.6, and most preferably 3.4 Li ₂ O · SiO. It is ₂ . In FIGS. 1 to 3, the horizontal axis showing the composition of the compound represents the mole fraction of the alkali metal (Group 1 element). Further, including the above-mentioned nNa ₂ O · SiO ₂ and nK ₂ O · SiO ₂ , these coefficients n are positive numbers representing the ratio of Li ₂ O, Na ₂ O, and K ₂ O to SiO ₂ . .. Further, since these alkaline silicic oxides are hardly commercially available as reagents as well as industrial products, the main acquisition method is by synthesis.

Of these, the reason for the low melting point is still speculative, but if the alkali silicic oxide is in a molten state during the reaction, or if the temperature is close to the melting point, oxygen ions ( ^O2- ) It is considered that the movement is facilitated, the reaction is facilitated, and the conductivity is also increased, so that the electrons (e ⁻ ) are diffused after the O ₂ is released, and the formation of carbon (C) is likely to occur. Therefore, if the reaction is carried out at the same reaction temperature, a compound having a lower melting point is more advantageous.

By the way, among the alkaline silicic oxides, those having high and low CO ₂ absorption characteristics and those having high and low CO ₂ decomposition characteristics into C have different characteristics. In particular, the tendency in the types of alkali metals (Group 1 elements) is as shown in FIG. 4, and the absorption characteristics of CO ₂ are Li, Na, and K in descending order, and the decomposition characteristics of CO ₂ into C. On the contrary, (CO ₂ decomposition characteristics) are K, Na, and Li in order from the highest. Regarding the absorption of CO ₂ , it can be understood that O is sucked at the time of CO ₂ absorption, in descending order of the effective nuclear charge of the alkaline element. Regarding the decomposition characteristics of CO ₂ , the order of ease of decomposition of alkaline carbon oxide is considered from the viewpoint of Gibbs energy.

Further, in the present invention, since it is desirable that the alkali silicic acid oxide has excellent gas absorption, the shape thereof is preferably powdery or granular rather than lumpy. Although not particularly limited, the particle size of each particle is preferably about 0.1 μm to 5 mm, preferably 1 μm to 0.1 mm. If the particle size is too small, there is a concern that impurities may be mixed in during the pulverization process, so even if the pulverization is performed, the particle size should be limited to about 0.1 μm.

On the other hand, the quartz wool used in the present invention is not particularly limited, and a general commercially available product can be used as it is. In addition to air, CO _2- containing gas is emitted from, for example, thermal power plants that use coal, heavy oil, natural gas, etc. as fuel, boilers at factories, and blast furnaces at steelworks that reduce iron oxide with coke. It is also possible to use exhaust gas as such.

In the method of the present invention, first, the alkali silicic acid oxide and the quartz wool are allowed to exist in the reaction system in a state where at least a part of them are in contact with each other while having a predetermined mass ratio, and the material in the reaction system contains CO ₂ . The CO ₂ containing gas is brought into contact with each other to absorb CO ₂ (step A). Here, the alkali silicic acid oxide and the quartz wool may exist in a state of being mixed with each other, and even if they are not mixed, for example, a fine powder of the alkali silicic acid oxide is applied to the inner surface of the quartz tube, and then the quartz. Quartz wool is inserted into the tube, or alkali silicic acid oxide is sprinkled on the quartz wool so that the alkali silicic acid oxide and the quartz wool are in contact with each other at least in part. That is, considering the possibility that the contact interface between the alkali silicic acid oxide and the quartz wool contributes to the reaction, it is necessary that the two are in contact with each other. At that time, by absorbing CO ₂ in a state where the alkaline silicic acid oxide and the quartz wool are present in the reaction system, for example, a part of K ₂ O in nK ₂ O · SiO ₂ or nLi ₂ O · SiO _It is considered that a part of Li ₂ O in ₂ is changed to a compound having a structure similar to K ₂ CO ₃ or a structure similar to Li ₂ CO ₃ . At present, it is unknown what kind of change occurs at the contact interface between the alkaline silicic acid oxide and the quartz wool due to the absorption of CO ₂ .

Here, the presence of the alkaline silicic acid oxide and the quartz wool in the reaction system means that the CO _2- containing gas is simultaneously present in the alkaline silicic acid oxide and the quartz wool in a state where the materials in the reaction system are heated to a predetermined temperature. It represents a form in which CO ₂ is absorbed by the alkali silicic oxide by contacting substantially at the same time, so that at least a part of the materials in the reaction system has a contact interface in which the alkaline silicic oxide and the quartz wool are in contact with each other. To do. In such a situation, for example, the atmosphere is such that the alkali silicic oxide and quartz wool mixed with each other are placed in a container with an open top, and the materials in the reaction system are heated to a predetermined temperature. A reactor may be configured in which the CO ₂ inside can be contacted. Further, the alkali siliceous oxide and the quartz wool are mixed and arranged in a closed container having a gas inlet / outlet for flowing the gas, or the alkaline siliceous oxide and the quartz wool are partially mixed with each other even if they are not mixed. The materials in the reaction system are arranged in contact with each other so that the CO _2- containing gas flows in the container in a state where the materials in the reaction system are heated to a predetermined temperature to form a reaction device capable of contacting CO _2. May be good.

In the present invention, the CO ₂ containing gas into contact with the reaction system in the material when to absorb CO _2, which may be also to absorb CO ₂ at a temperature from room temperature state of the reaction system within the material, the CO ₂ From the viewpoint of enhancing absorption, it is preferable to heat the material in the reaction system to room temperature or higher and 650 ° C. or lower. If the temperature of the material in the reaction system exceeds 650 ° C., the amount of CO ₂ absorbed by the material in the reaction system decreases, which is not preferable.

Next, the reaction system in the material imbibed with CO _2, the reaction system by heating to the 350 ° C. or higher 700 ° C. or less in a non-oxidizing atmosphere, the CO ₂ which is absorbed into the reaction system in the material C Disassemble (step B). At the time of this heating, it is necessary to create a non-oxidizing atmosphere in order to prevent the generated C (carbon) from being oxidized. Examples of the non-oxidizing atmosphere include an atmosphere of an inert gas such as argon and helium, a nitrogen atmosphere, and the like. By the way, as the purity of the non-oxidizing gas used, the purity of a general gas cylinder, for example, about 99.99% is sufficient. With such purity, it is possible to substantially ignore the oxidation of the produced carbon in the reaction apparatus housed in a general heating apparatus such as a heating furnace used for heating. The flow rate of the non-oxidizing gas is not particularly limited, and a small amount may be used from an economical point of view. For example, when the present invention is carried out in a gas flow system for the purpose of preventing an increase or breakage of pressure in the reactor due to heating, the flow rate may be such that the non-oxidizing gas does not flow back from the exhaust pipe. As a result, a flow rate of about several tens of mL to several tens of L / min, preferably about 100 mL to 2 L / min can be shown.

When the CO ₂ absorbed by the material in the reaction system is decomposed into C, the material in the reaction system is heated to 350 ° C. or higher and 700 ° C. or lower, preferably 350 ° C. or higher and 650 ° C. or lower. In the present invention, decomposition into C can be performed at a much lower temperature than in the case of Patent Document 2 (700 ° C. or higher).

The heating rate when heating the material in the reaction system when absorbing CO ₂ in step A and the heating rate when heating CO ₂ into C in step B are not particularly limited, but for example. , 1 to 40 ° C./min, which is the heating rate of a commonly used ordinary heating furnace, can be selected, and preferably 10 to 20 ° C./min. Further, there is no particular limitation on the holding time after reaching the maximum temperature in each heating. From an economical point of view, a short holding time is selected, and for example, 1 to 180 minutes, preferably 10 to 60 minutes is sufficient. Furthermore, the cooling rate after reaching the maximum temperature is also not limited, and the heating may be stopped immediately after the holding time at the maximum temperature is completed and left to the natural cooling of the device, if the structure of the device. If there is a restriction on the cooling rate from above, it may be followed. As described above, it is also possible to absorb CO ₂ at room temperature without heating.

The reaction mechanism by which C is produced from the alkali silicic oxide that has absorbed CO ₂ by the method of the present invention has not yet been clarified, but it is speculated as follows so far.
For example, nNa ₂ O · SiO ₂ which is a Na ₂ O · SiO ₂ system compound, nK ₂ O · SiO ₂ which is a K ₂ O · SiO ₂ system compound, and nLi ₂ O which is a Li ₂ O · SiO ₂ system compound. -Silica _{2 and the} like have a maximum amount of oxygen atoms, and cannot act as a reducing substance. Therefore, reducing substances are not involved in the progress of the reaction, and it is considered that these alkaline silicic oxides act as catalysts. Further, as described above, when these alkali silicic oxides absorb CO ₂ , it is presumed that, for example, a part of K ₂ O of nK ₂ O · SiO ₂ changes to a compound having a structure similar to K ₂ CO _3. doing.

From this, as a presumed mechanism during heating, for example, oxygen atoms in a compound similar to K ₂ CO ₃ diffuse in nK ₂ O · SiO ₂ , and as a result, carbon (C) is left behind. Is. The same applies to the case where nLi ₂ O · SiO ₂ and nNa ₂ O · SiO ₂ absorb CO ₂ .

Further, in the present invention, when an alkaline silicic acid oxide that has absorbed CO ₂ is heated in a non-oxidizing atmosphere, the decomposed carbon does not adhere to the alkaline silicic acid oxide or quartz wool, but can be separated from the materials in the reaction system. Can be collected in a good condition. In addition, the alkaline silicic oxide is not completely melted by heating for absorption and decomposition of CO ₂ , but is suppressed to the extent that powdery particles are bonded to each other at most.

Further, as described above, in the method of the present invention, carbon (C) is not fixed to the alkali siliceous oxide or quartz wool, but can be recovered in a separable state from the materials in the reaction system. Since the shape change of alkaline siliceous oxide and quartz wool can be suppressed by heating for absorption and decomposition of CO ₂ , after carbon is once recovered in step B, CO ₂ is absorbed again in the material in the reaction system. The step A for causing the carbon dioxide and the step B for decomposing the carbon dioxide may be repeated. At that time, since carbon does not adhere to the alkali silicic oxide, there is no problem of so-called catalyst poisoning, and it is possible to repeat the absorption of CO ₂ and the decomposition into C multiple times without lowering the reaction efficiency. Silicic acid can be used efficiently.

In the present invention, CaO, an oxide of an oxide or alkaline earth element of the alkali elements Na 2 _O or the like may be used together with the alkali silicate compound. That does not preclude the combination of CaO and Na ₂ O or the like. Even when used in combination with CaO or Na 2 _O, etc., according to the present invention, the carbon is recovered in a state of being separated from the alkali silicate compound, also alkali silicate product by heating for the absorption and decomposition of CO ₂ CaO Melt integration with Na ₂ O and the like hardly progresses, and shape change is almost suppressed especially when CaO is used in combination.

The carbon obtained by the method of the present invention can be used as a normal carbon source used as an industrial material, fuel or the like. In particular, according to the present invention, it is possible to repeatedly absorb CO ₂ and decompose it into carbon by a simple method, which is significant in that effective utilization of CO ₂ and countermeasures against global warming can be achieved at the same time. It can be said that there is.

Hereinafter, the present invention will be specifically described based on Examples and the like, but the present invention is not limited to these contents.

(Example 1)
3.6Na ₂ O · SiO ₂ is not generally commercially available and was synthesized by the following steps.
First, commercially available sodium hydroxide (granular special grade reagent) and silica sand (SiO ₂ ) (200 to 300 mesh) are mixed with Na ₂ O: SiO ₂ ratio of 3.6: 1, and sodium hydroxide and silica sand are formed. When 3.6 Na ₂ O · SiO ₂ was produced by the reaction, the amount of about 20 g was weighed and charged into a nickel rut with an upper inner diameter of about 36 mm and a depth of about 36 mm. This was put into a quartz crucible having an inner diameter of about 41 mm and a depth of about 115 mm together with the nickel crucible. The quartz crucible was covered with an alumina lid, and the temperature was raised to 1100 ° C. at 10 ° C./min in an Ar atmosphere heating furnace, held for 30 minutes, and then naturally cooled to room temperature. After cooling, an almost colorless and transparent uniform glassy substance was formed in the nickel crucible. When the mass loss of this product was measured, it was consistent with the mass loss when sodium hydroxide was completely dehydrated and reacted with silica sand to produce 3.6Na ₂ O · SiO ₂ , and 3.6Na ₂ O · It was confirmed that SiO ₂ was generated.

Nickel crucible tapers, but it could be taken glassy 3.6Na ₂ O _· SiO 2 produced a tapping bottom face down nickel crucible. The contact part of 3.6Na ₂ O · SiO _{2 with} the nickel crucible was slightly yellowish in some places, so this part was scraped off with a stainless steel scraper, and _two colorless 3.6 Na ₂ O · SiO ₂ lumps. Got

The 3.6 Na ₂ O · SiO ₂ lumps obtained above were pulverized to 1 mm or less in an alumina mortar, and about 15 g of them was charged into a silica alumina crucible. Next, the silica alumina crucible was placed in a heating furnace, and the temperature was raised to 700 ° C. at 10 ° C./min while flowing dry air at 2 L / min. The temperature was maintained at that temperature for 12 hours, and then naturally cooled to room temperature. By this oxidation treatment, organic substances and carbon in the 3.6 Na ₂ O · SiO ₂ powder were completely removed. Further, it is considered that the 3.6 Na ₂ O · SiO ₂ powder became completely anhydrous by this.

0.4 g of 3.6 Na ₂ O · SiO ₂ synthesized in this manner, pulverized and oxidized was weighed and applied to the inner surface of the quartz reaction dish 2 shown in FIG. Then, 3.6Na ₂ the O · SiO ₂ was charged with quartz wool 20g to the reaction tray 2 coated, coated 3.6Na ₂ O · to SiO ₂ as a part of the quartz wool is contacted in the reaction system The material 3 was used, and the reaction dish 2 was placed in a reaction vessel 1 made of a quartz tube. Here, as the quartz wool, a commercially available product (quartz wool manufactured by Tosoh Corporation, Fine) is used, and the diameter is 2 to 6 μm and the length is several tens of mm, but when inserted as the material 3 in the reaction system, a part of the quartz wool is used. It breaks to a length of several to several tens of mm.

For the reaction vessel 1 in which the material 3 in the reaction system is charged, a gas introduction pipe 4 for gas supply is connected to one end, and a gas discharge pipe 5 for gas discharge is connected to the other end. ing. Among them, the upstream side of the gas introduction pipe 4 is divided into two, CO ₂ and the CO ₂ supply pipe 6 for supplying a gas containing helium (the He) the He supply pipe 7 for supplying the gas, respectively valves 8,9 It is connected via. On the other hand, a mass spectrometer (quadrupole mass spectrometer) (not shown) is connected to the tip of the gas discharge pipe 5 so that the gas discharged from the reaction vessel 1 can be analyzed. Then, the reaction vessel 1 is placed in the heating furnace 10 so that the material 3 in the reaction system in the reaction vessel 2 charged in the reaction vessel 1 can be heated to a predetermined temperature. The reactor (CO ₂ absorption / decomposition device) is configured.

In such a reaction apparatus, first, 10 mL of 100% concentrated CO ₂ gas is added from the CO ₂ supply pipe 5 to the reaction vessel 1 having the reaction vessel 2 in which the material 3 in the reaction system is charged at room temperature. after circulating for 2 hours at a flow rate of / min, and stopping the supply of CO ₂ gas from the CO ₂ supply pipe 6. Next, when the reaction dish 2 was removed from the reaction vessel 1 and weighed, it was found that about 0.04 g of CO ₂ was absorbed by the material 3 in the reaction system. The above is step A.

Next, the reaction vessel 2 is quickly charged into the reaction vessel 1, and the reaction vessel 1 is heated to 350 ° C. while flowing He gas from the He supply pipe 7 at a flow rate of 20 mL / min, and at that temperature. Heat treatment B (step B) of holding for 60 minutes was performed. During that time, it was confirmed that black matter was deposited on the inner surface of the reaction dish 2.

After the completion of the heat treatment B, the reaction dish 2 containing the material 3 in the reaction system was taken out from the naturally cooled reaction vessel 1, and the quartz wool was taken out from the reaction dish 2. Next, with a small spatula, about 0.001 g of a considerable portion of the black matter deposited on the surface of 3.6 Na ₂ O · SiO ₂ on the inner surface of the reaction dish 2 was scraped out. When the black matter recovered in this manner was carbon-analyzed by the combustion infrared absorption method, 90% or more was carbon. Carbon source in the reaction vessel 1 is only CO ₂ in contact with the reaction system in the material 3 in the preceding step A, is considered to have been CO ₂ absorption in the reaction system in the material 3 is reduced to C by heat treatment B .. From the above analysis, it was found that the conversion efficiency of CO ₂ absorbed by the material 3 in the reaction system to C was about 8%. Here, the conversion efficiency of the CO ₂ C is considered to C content in the absorbed CO ₂ is a 12/44 absorption CO _2, was calculated from the ratio of this value and the amount of C obtained by analysis ..

On the other hand, the material 3 in the reaction system recovered from the reaction vessel 1 is in a state where it can be reused because no bonds of alkali silicic acid (3.6 Na ₂ O · SiO ₂ ) particles or quartz wool are observed. Met.

(Example 2)
Except that the 3.6Na ₂ O · SiO ₂ applied to the inner surface of the reaction tray 2 was 0.1 g, was subjected to the experiment in the same manner as Experimental Example 1, approximately 0.011g of CO ₂ reaction It was absorbed by the material 3 in the system, and a black substance was produced by the heat treatment B. Then the reaction tray 2 is taken out from the reaction vessel 1, about taking out the quartz wool, which corresponds to a substantial portion of 3.6Na ₂ O _· SiO 2 black product deposited on the surface that is applied to the inner surface of the reaction tray 2 0.0006 g was scraped out with a small spatula. When the black matter recovered in this manner was carbon-analyzed by the combustion infrared absorption method, 90% or more was carbon. Carbon source in the reaction vessel 1 is only CO ₂ in contact with the reaction system in the material 3 in the preceding step A, is considered to have been CO ₂ absorption in the reaction system in the material 3 is reduced to C by heat treatment B .. From the above analysis, it was found that the conversion efficiency of CO ₂ absorbed by the material 3 in the reaction system to C was about 18%.

(Example 3)
The 3.6Na ₂ O · SiO ₂ applied to the inner surface of the reaction tray 2 and 0.005 g, also, except followed by the charging quartz wool was 25g in the experiment in the same manner as Experimental Example 1 As a result, approximately 0.0007 g of CO ₂ was absorbed by the material 3 in the reaction system, and a black substance was produced by the heat treatment B. Then the reaction tray 2 is taken out from the reaction vessel 1, about taking out the quartz wool, which corresponds to a substantial portion of 3.6Na ₂ O _· SiO 2 black product deposited on the surface that is applied to the inner surface of the reaction tray 2 0.00002 g was scraped out with a small spatula. When the black matter recovered in this manner was carbon-analyzed by the combustion infrared absorption method, 90% or more was carbon. Carbon source in the reaction vessel 1 is only CO ₂ in contact with the reaction system in the material 3 in the preceding step A, is considered to have been CO ₂ absorption in the reaction system in the material 3 is reduced to C by heat treatment B .. From the above analysis, it was found that the conversion efficiency of CO ₂ absorbed by the material 3 in the reaction system to C was about 9%.

(Comparative Example 1)
The 3.6Na ₂ O · SiO ₂ applied to the inner surface of the reaction tray 2 and 0.5g, also, except followed by the quartz was charged wool was 15g in the experiment in the same manner as in Example 1 As a result, approximately 0.04 g of CO ₂ was absorbed by the material 3 in the reaction system. Next, heat treatment B was performed, but the formation of black matter was not confirmed, and only a trace amount of gray part was formed. To be on the safe side, carbon analysis was performed on all of this part by the combustion infrared absorption method, but no carbon was detected. The lower limit of carbon analysis in the combustion infrared absorption method is 5 μg, and even if carbon is produced, the amount of carbon produced is less than 5 μg. From this, the conversion of CO ₂ absorbed by the material 2 in the reaction system to C did not proceed, or even if it did, the efficiency was less than 0.05%, which was an impractical value.

(Comparative Example 2)
The 3.6Na ₂ O · SiO ₂ applied to the inner surface of the reaction tray 2 and 0.003 g, also, except followed by the charging quartz wool was 24g in the experiment in the same manner as in Example 1 As a result, approximately 0.004 g of CO ₂ was absorbed by the material 3 in the reaction system. Next, heat treatment B was performed, but the formation of black matter was not confirmed, and only a trace amount of gray part was formed. To be on the safe side, carbon analysis was performed on all of this part by the combustion infrared absorption method, but no carbon was detected. The lower limit of carbon analysis in the combustion infrared absorption method is 5 μg, and even if carbon is produced, the amount of carbon produced is less than 5 μg. From this, the conversion of CO ₂ absorbed by the material 2 in the reaction system to C did not proceed, or even if it did, the efficiency was less than 0.5%, which was an impractical value.

(Comparative Example 3)
When the experiment was carried out in exactly the same manner as in Example 1 above except that quartz wool was not used, approximately 0.037 g of CO ₂ was absorbed by the material 3 in the reaction system. Next, heat treatment B was performed, but the formation of black matter was not confirmed, and only a trace amount of gray part was formed. To be on the safe side, carbon analysis was performed on all of this part by the combustion infrared absorption method, but no carbon was detected. The lower limit of carbon analysis in the combustion infrared absorption method is 5 μg, and even if carbon is produced, the amount of carbon produced is less than 5 μg. From this, the conversion of CO ₂ absorbed by the material 2 in the reaction system to C did not proceed, or even if it did, the efficiency was less than 0.05%, which was an impractical value.

(Comparative Example 4)
The amount of each reaction system material 2 are the same as in Example 1, without contacting the 3.6Na ₂ O _· SiO 2 and quartz wool, a state or more away 15 mm, other than the above Example 1 The experiment was performed in exactly the same way. That is, in Comparative Example 4, 3.6Na instead _{of 2} O · SiO ₂ is charged quartz wool in a reaction tray 2 which has been applied to distribution at a position apart more than 15mm from the reaction tray 2 in the reaction vessel 1 I did it. Then, by step A, approximately 0.038 g of CO ₂ was absorbed by the material 2 in the reaction system.
Next, heat treatment B was performed, but the formation of black matter was not confirmed, and only a trace amount of gray part was formed. To be on the safe side, carbon analysis was performed on all of this part by the combustion infrared absorption method, but no carbon was detected. The lower limit of carbon analysis in the combustion infrared absorption method is 5 μg, and even if carbon is produced, the amount of carbon produced is less than 5 μg. From this, the conversion of CO ₂ absorbed by the material 2 in the reaction system to C did not proceed, or even if it did, the efficiency was less than 0.05%, which was an impractical value. From this Comparative Example 4 and Example 1, it can be seen that in order to decompose CO ₂ into carbon, contact between the alkali silicic oxide and quartz wool is necessary.

(Comparative Example 5)
The experiment was carried out in exactly the same manner as in Example 1 above, except that the temperature of the heat treatment B was set to 750 ° C. By step A, approximately 0.039 g of CO ₂ was absorbed by the material 2 in the reaction system. Next, heat treatment B was performed, but only a very small amount of gray substance was produced. This gray substance was stuck to 3.6 Na ₂ O · SiO ₂ and could not be recovered. In Comparative Example 5, since the temperature of the heat treatment B was too high, some carbon that may have been generated during the temperature rise of the heat treatment B reacted with 3.6 Na ₂ O · SiO ₂ and scattered as a gas. Imagine. As described above, it can be seen that 750 ° C. is too high as the temperature of the heat treatment B, and in the present invention, the carbon generated from CO ₂ can be recovered at a relatively low temperature.

1: Reaction vessel 2: Reaction dish 3: Reaction system internal material 4: Gas introduction pipe 5: Gas discharge pipe, 6: CO ₂ supply pipe, 7: He supply pipe, 8, 9: Valve, 10: heating furnace.

Claims (4)

Alkali siliceous oxide and quartz wool are allowed to exist in the reaction system in a mass ratio of 1:40 to 1: 6000, and at least partly in contact with each other, and CO _{2 is} added to the materials in the reaction system. by contacting the CO ₂ containing gas containing a step a of absorbing CO ₂ in the CO ₂ containing gas to the reaction system in the material,
The reaction system by heating to the 350 ° C. or higher 700 ° C. or less in a non-oxidizing atmosphere, characterized by having a decomposing step B of CO ₂ to the reaction system the material has absorbed carbon, CO ₂ A method of absorbing carbon dioxide and decomposing it into carbon dioxide. The method for absorbing CO ₂ and decomposing it into carbon according to claim 1, wherein in the step A, the material in the reaction system is brought into contact with a CO _2- containing gas at a temperature of room temperature or higher and 650 ° C. or lower. The alkali silicic acid oxides are nNa ₂ O · SiO _{2 having} n of 2.6 to 4.6, nK ₂ O · SiO _{2 having} n of 3.4 to 5.4, and nLi of n of 2.4 to 5. _{2 The method according} to claim 1 or 2, which comprises any one or more selected from the group consisting of O · SiO _2, and absorbs CO ₂ and decomposes it into carbon. The CO _{2 according} to any one of claims 1 to 3, wherein after the step B, the step A and the step B are performed again to repeat the absorption of CO ₂ and the decomposition into carbon. And how to decompose it into carbon.

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