JP2018131351A - Method for recovering co2 in air to separate carbon - Google Patents

Abstract

An object of the present invention is to provide a method for industrially easily recovering and decomposing CO2 in the atmosphere, which is said to cause global warming, industrially. In addition, only one kind of general chemical substance that is not harmful is used, and this chemical substance is also reused. A step of preparing an alkali silicate, a step of causing the alkali silicate to absorb CO2 in the air in the presence of H2O, and an alkali silicate having absorbed the CO2 and H2O in a non-oxidizing atmosphere. A method for separating carbon by recovering CO2 in the atmosphere, comprising a step of separating the carbon by heating to 700 ° C. or more and 1600 ° C. or less. [Selection figure] None

Description

The present invention relates to a method for separating CO by recovering CO ₂ in the atmosphere.

In recent years, CO ₂ in the atmosphere has been steadily increasing, and this is said to contribute to global warming. However, CO ₂ in the atmosphere is recovered by a simple method and decomposed into C. The method to do was not established. For example, there was no method that could easily absorb and decompose CO _{2 in} the atmosphere using a single chemical substance and decompose CO ₂ into C.

As described above, there is almost no attempt to recover and decompose atmospheric CO ₂ with the same chemical substance. However, in Patent Documents 1 and 2 that were previously filed by the present inventors, alkali silicate is used. Thus, a method for separating carbon from carbonate is shown. It has also been mentioned for the degradation of atmospheric CO _2.

  In Patent Document 1, an alkali element carbonate and / or an alkaline earth element carbonate compound is mixed with water glass or alkali silicate and heated to 700 ° C. or higher and 1600 ° C. or lower in a non-oxidizing atmosphere. A method for producing free carbon is described which separates carbon from carbonates.

  In Patent Document 2, a mixture of water glass and an alkali element carbonate and / or an alkaline earth element carbonate is applied to the surface of a silica-alumina ceramic sintered body, and in a non-oxidizing atmosphere, A method for producing film-like free carbon by heating to 700 ° C. or more and 1600 ° C. or less to separate carbon from carbonate is described.

The methods for producing free carbon described in Patent Document 1 and Patent Document 2 require alkali element carbonates and / or alkaline earth element oxides as a carbon source.
However, alkaline earth and alkali metal oxides represented by CaO and Na ₂ O are strong alkali compounds. In addition, alkali metal oxides typified by Na ₂ O are very unstable and easily react with various materials constituting the apparatus. It would be highly desirable if atmospheric CO ₂ could be recovered and decomposed into C without using these strongly alkaline oxides. Of course, it is economically advantageous to use fewer chemical substances.

Further, when CO ₂ is absorbed by Na ₂ O, as described in paragraph 0025 in the specification of Patent Document 1, “carbon dioxide is released from the carbonate, and the remaining part is alkali silicate. The reaction to form a compound and a compound proceeds simultaneously with the reaction of the present invention. That is, when Na ₂ O is used, the composition of Na ₂ O · nSiO ₂ gradually shifts in the direction of increasing the Na ₂ O ratio as the number of reactions is repeated, and Na ₂ O · nSiO ₂ can be reused. There was a problem of disappearing.
Also in Patent Document 2, since the reaction mechanism is the same as that of Patent Document 1, when Na ₂ O is used, the composition of Na ₂ O · nSiO ₂ increases in the direction of increasing the Na ₂ O ratio when the number of reactions is repeated. Gradually deviated and eventually Na ₂ O · nSiO ₂ could not be reused.

Patent Document 3 discloses a method of adsorbing CO ₂ on a conductive mayenite compound and heating it to reduce it to CO.
Patent Document 4 discloses a method in which zirconium-containing cerium oxide and CO ₂ are brought into contact under heating and reduced to CO by a stoichiometric reaction. However, in the production methods described in Patent Document 3 and Patent Document 4, the product obtained by decomposing CO ₂ is CO. In order to obtain carbon itself, a further reduction step is required. Of course, CO is useful as a raw material for various synthesis reactions, but if the product is C, it can be said that it is more preferable because it can be directly used as a heat energy source.

Japanese Patent Laying-Open No. 2015-187059 Japanese Patent Application No. 2006-000542 JP 2012-025636 A Japanese Patent No. 5858926

In view of the above circumstances, the present invention has no harmful properties without using a strong alkali compound such as CaO as a carbonate source and without using a strong alkaline and unstable compound such as Na ₂ O. The object is to provide a method for the capture of atmospheric CO ₂ and separation of carbon using a single available chemical that does not have any of the above. Another object of the present invention is to make this common chemical substance reusable any number of times for the recovery of atmospheric CO ₂ and decomposition into C.

  The present inventors have found a technique for mixing carbon from water glass or alkali silicate and carbonate, heating in a non-oxidizing atmosphere to 700 ° C. or more and 1600 ° C. or less to separate carbon from the carbonate, This is reported in Patent Document 1. Therefore, the present inventors diligently studied a method for solving the above problem in the research process of this technology.

As a result, it was found that the alkali silicate itself can absorb CO _{2, and} after absorbing atmospheric CO ₂ and H ₂ O at room temperature, in a non-oxidizing atmosphere, 700 ° C. or more and 1600 ° C. or less. As a result, a technique for efficiently producing free carbon from absorbed CO ₂ was found, and the present invention was completed.

The gist of the present invention is as follows.
(1) preparing an alkali silicate;
Allowing the alkali silicate to absorb atmospheric CO ₂ in the presence of H ₂ O;
The alkali silicate product that has absorbed the CO ₂ and with H _{2 O,} in a non-oxidizing atmosphere, heated to 700 ° C. or higher 1600 ° C. or less, characterized in that it comprises a step of separating the carbon, the atmosphere CO ₂ A method to recover and separate carbon.
(2) The method according to (1), wherein the alkali silicate is sodium silicate.
(3) The method according to (1), wherein the alkali silicate after separating the carbon is reused in the step of preparing the alkali silicate.

According to the present invention, atmospheric CO ₂ can be recovered and decomposed into C by a simple method. The carbon can be used as a carbon source for ordinary industrial materials or fuel, it is possible to manufacture efficiently from CO ₂ in the atmosphere, it is possible to both effective use and recovery of atmospheric CO _2. Moreover, carbon can be directly generated from CO ₂ without using a strong alkali compound or a compound having a high unstable reactivity as a carbonate source.
Furthermore, in the method of the present invention, the alkali silicate after carbon separation can be reused any number of times for the recovery of atmospheric CO ₂ and decomposition into C.

Hereinafter, the method for separating carbon by recovering atmospheric CO _{2 according} to the present invention will be sequentially described.
First, the alkali silicate used in the step of preparing the alkali silicate will be described.

As an alkali silicate used as a starting material, for example, sodium silicate is a typical compound, and is described by a molecular formula of Na ₂ O · nSiO ₂ . Here, the coefficient n represents the ratio of SiO _{2 to} Na ₂ O and can be varied continuously. In the present invention, n is not particularly limited. In general, n = 0.3 to 4 in many cases, but in the present invention, n is not particularly limited. The compound represented by Na ₂ O · nSiO ₂ is anhydrous sodium silicate, but in addition, it is represented by solid Na ₂ O · nSiO ₂ · mH ₂ O having coordination water or crystal water. Sodium silicate can also be used. In addition, these alkali silicates, for example, sodium silicate mentioned as an example are all solids, and are distinguished from water glass which is a highly viscous aqueous solution of sodium silicate, and have different chemical properties such as CO ₂ absorption characteristics. Moreover, as a method for producing water glass, a method of producing by mixing solid sodium silicate and water, pressurizing near 10 atm using an autoclave or the like, and further heating to 100 ° C. or more is common. Water glass is not easily obtained just by mixing sodium silicate and water at atmospheric pressure, particularly at room temperature.

Na ₂ O.nSiO ₂ that can be used in the present invention has completely different properties from Na ₂ O described in Patent Document 1 and Patent Document 2 as being capable of becoming a carbonate source. By way of example the Na ₂ O · 2SiO ₂ is n = 2 of the alkali silicate compound i.e. Na ₂ O · nSiO _2, often inherently This is described as _Na 2 _Si 2 _{O 5,} very stable compound And is generally commercially available. On the other hand, Na ₂ O is a very unstable compound and is hardly commercially available as a reagent as well as an industrial product. Slightly commercially available Na ₂ O is also low in purity and is at most about 90% pure. In this way, Na ₂ O is hardly noticed unless it is specially synthesized, but Na ₂ O · nSiO ₂ is a generally available stable compound, and it is widely used as an industrial product. It is in circulation.

In the present invention, CO ₂ and H ₂ O in the atmosphere are absorbed by the alkali silicate, and then heated to convert CO ₂ to carbon. Therefore, it is preferable that the gas absorption of the alkali silicate is excellent. For this reason, about the shape of an alkali silicate, a powder form or a granular form is preferable rather than a lump form. The individual particle size is preferably 0.1 μm to several mm, more preferably 1 μm to 1 mm. If the particle size is too small, there is a concern that impurities are mixed into the alkali silicate during the pulverization process. Therefore, even if pulverized, it is preferably about 1 μm. However, in the present invention, the particle diameter and shape of the alkali silicate are not particularly limited.

As a method for absorbing CO ₂ and H ₂ O into alkali silicate, for example, powdery or granular alkali silicate as described above may be allowed to stand at room temperature for a certain period of time. In this case, it is difficult to measure the absorption amounts of CO ₂ and H ₂ O in the air independently, but the total absorption amount of CO ₂ and H ₂ O can be measured from the increase in mass of the alkali silicate. it can.

In the present invention, the CO ₂ absorption amount of the sum of _{H 2} O is not particularly limited to the alkali silicate compound, for example, the combined CO ₂ and _{H 2} O, 0.01 to alkali silicate product 70% by mass can be absorbed. Preferably, CO ₂ and H ₂ O may be combined to absorb 1 to 50% by mass of the alkali silicate. If it is less than 1% by mass, the CO ₂ recovery / decomposition efficiency is low from an industrial point of view. If it is more than 50% by mass, general weather conditions, for example, temperature 5 to 35 ° C., humidity 20 to 80% This is because it takes a long time to absorb and is industrially inefficient.

The time for which the above amounts of atmospheric CO ₂ and H ₂ O are absorbed into the alkali silicate depends on the surrounding conditions, the particle size of the alkali silicate, etc., and cannot be specified unconditionally. In general, it is often from half a day to several days, but it is only a guideline, and when the mass increase rate of alkali silicate is measured, when the appropriate absorption amount is reached, the next step is heating. To do.

In addition, for example, as a method of absorbing CO ₂ and H ₂ O into sodium silicate, in addition to the above-described natural absorption, a method of leaving it in the atmosphere in the vicinity where water is disposed, or a method of circulating an atmosphere in which water is bubbled is circulated. There is a method of forced absorption, such as a method of leaving it in a container.
In the former case, for example, by placing a small open container with water and a small container with alkali silicate in the upper open container at the same time, the humidity around the alkali silicate is higher than that of the general atmosphere. High humidity can be maintained, and atmospheric CO ₂ and H ₂ O can be efficiently absorbed into the alkali silicate.
In the latter case, the closed vessel having inlet and outlet of the gas, through the water reserved in the tank was circulated feeding the atmosphere was bubbled at room temperature, allowed to stand an alkali silicate compound in the sealed container, the atmosphere CO ₂ And H ₂ O may be absorbed. In this case, as a result of bubbling the atmosphere into water, the introduced atmosphere is considered to contain water vapor in an amount close to the saturated vapor pressure.

As another method of absorbing CO ₂ and H ₂ O into sodium silicate, an atmosphere in which H ₂ O is forcibly introduced and the amount of H ₂ O is controlled can be used. In this method, the amount of H ₂ O to be forcibly introduced is preferably close to the saturated vapor pressure in the atmosphere brought into contact with sodium silicate.

The anhydrous sodium silicate absorbs CO ₂ is not generally known. Although this mechanism is unknown, it is thought that sodium silicate absorbs CO ₂ and H ₂ O together to form a so-called deliquescent state. The product at this time is not exactly known. However, when an anhydrous sodium silicate granule was allowed to stand in the presence of CO ₂ and water vapor and an infrared spectrum was obtained by infrared spectroscopy, formation of Na ₂ CO ₃ .10H ₂ O was observed on the particle surface. . From this, it is considered that a hydrate of Na ₂ CO ₃ is formed on the surface of sodium silicate from CO ₂ and H ₂ O in the atmosphere.
When CO ₂ and H ₂ O are absorbed into sodium silicate, considering that Na ₂ CO ₃ · 10H ₂ O is generated, the atmospheric CO ₂ concentration is approximately 500 ppm. _{The 2} O content is preferably 10 times or more, that is, 0.5% or more. If this concentration is considered to be able to absorb atmospheric CO ₂ efficiently sodium silicate.

Next, the heating process will be described.
Various heating furnaces and heating devices can be used as the heating method. In addition, exhaust heat exhausted from various high-temperature processes can be used if the temperature is suitable, and a heating device using exhaust heat can also be used. Moreover, the heating apparatus which condenses sunlight can also be used. In general, a heating device that collects sunlight is difficult to use because the temperature control is rough, but in the present invention, it can be used because the temperature window of the reaction is wide, and this point is a feature of the present invention. is there.

For example, these heating apparatuses can be charged with a crucible containing alkali silicate that has absorbed CO ₂ and H ₂ O in the atmosphere and heated in a non-oxidizing atmosphere. The crucible material is not particularly limited, but a material having heat resistance to the heating temperature is preferably selected. For example, a crucible made of silica alumina, alumina, quartz or the like can be used.

  A non-oxidizing atmosphere is selected as the atmosphere during heating. This is to prevent the generated carbon from being oxidized. For example, an inert gas atmosphere such as an argon atmosphere or a nitrogen atmosphere can be selected as the non-oxidizing atmosphere. As the purity of the non-oxidizing gas to be used, the purity of a general gas cylinder, for example, 99.99% is sufficient. With such a purity, it can be substantially ignored that the generated carbon is oxidized in a general reaction apparatus as a heating apparatus. There is no restriction | limiting in particular as a flow volume of non-oxidizing gas, and a small amount may be sufficient from an economical viewpoint. When the present invention is carried out in a gas flow system for the purpose of preventing an increase or breakage of the pressure in the reaction vessel due to heating, the flow rate may be such that the non-oxidizing gas does not flow backward from the exhaust pipe. Examples of the flow rate include a flow rate of several tens of mL to several tens of L / min, preferably 100 mL to 2 L / min.

The heating temperature is preferably 700 ° C. or higher and 1600 ° C. or lower, more preferably 850 ° C. or higher and 1300 ° C. or lower. As can be seen from the examples, 700 ° C. or higher is necessary in order to produce carbon according to the present invention. Furthermore, when heating at 700 ° C. or more and about 850 ° C. or less, the alkali silicate that has absorbed the CO ₂ is often not brought into a molten state by heating, and the generated carbon is often widely distributed as a solid. When heated to about 850 ° C. or more, the alkali silicate is often in a molten state by heating, and the generated carbon is likely to collect on the crucible wall surface or the upper surface of the melt, which is convenient for carbon recovery.

  Further, when the heating temperature is higher than 1600 ° C., only a little carbon is recognized, so the heating temperature is preferably 1600 ° C. or less. The reason for this is presumed that at a temperature higher than 1600 ° C., once generated carbon is oxidized by the alkali silicate, it decreases, but the details are unknown. Furthermore, considering the heat resistance of a general crucible, 1300 ° C. or lower is more preferable.

  There is no restriction | limiting in particular in the temperature increase rate at the time of a heating, For example, 1-40 degrees C / min which is the temperature increase rate of a normal heating furnace can be selected, Preferably, 10-20 degrees C / min can be selected. The holding time after reaching the maximum temperature is not particularly limited. A short holding time may be selected from an economical point of view, for example, 1 to 180 minutes, preferably 10 to 60 minutes is sufficient. The cooling rate is not particularly limited, and immediately after the holding time after reaching the maximum temperature, heating may be terminated immediately and left to natural cooling of the device. If the cooling rate is limited due to the structure of the device, Good according to it.

By these manufacturing methods, the produced carbon is crushed and separated if the carbon is segregated in the apparatus after the temperature is lowered, and if the carbon is widely distributed in solids, hot water or water is used. What is necessary is just to melt | dissolve a solid substance with hydrofluoric acid and isolate | separate the remaining carbon.
The carbon obtained as described above can then be used as a normal carbon source such as fuel.

Although little is known about the reaction mechanism by which carbon is produced by the method of the present invention, the following mechanism is presumed.
Alkali silicates have the maximum amount of oxygen atoms and cannot act as reducing substances. Therefore, the reducing substance is not involved in the progress of the reaction, and the alkali silicate is considered to act as a catalyst. Further, as described above, when an alkali silicate compound absorbs CO ₂ and _{H 2} O, the surface of the alkali silicate compound, for example, hydrates of _Na 2 CO ₃ from the CO ₂ and of _{H 2} O in the atmosphere generated I think that. From this, the presumed mechanism during heating is that oxygen atoms of the produced Na ₂ CO ₃ hydrate diffuse in the sodium silicate, and as a result carbon is left behind. In this mechanism, oxygen atoms must be detached from the molten alkali silicate as oxygen molecules, but this phenomenon has not been confirmed so far, but is estimated.

  However, if estimated from this mechanism, the oxygen diffusion rate in the alkali silicate is not sufficient at 700 ° C. or lower, and therefore it is considered that 700 ° C. or higher is necessary in the present invention. In addition, as described above, it is assumed that once generated carbon is oxidized by alkali silicate at a temperature higher than 1600 ° C.

The carbon production efficiency from the absorbed CO _{2 according} to the present invention is about 50% as described in Invention Example 1 described later. The lower reasons than 100% carbon generation efficiency, when an alkali silicate product heating, since the absorbed CO ₂ is released as CO ₂ again without the carbon, the 100% carbon efficiency of generation of the absorbing CO ₂ It is thought that it does not reach. The alkali silicate after separating the carbon, such as sodium silicate, can be reused as the starting sodium silicate.

  Differences between the present invention and Patent Documents 1 and 2 previously disclosed by the present inventors and the present invention will be described by reaction equations.

In Patent Literature 1 and Patent Literature 2, when Na ₂ O is used, the following reaction formula is obtained.
(1) In advance, in another apparatus, Na ₂ O absorbs CO ₂ to generate Na ₂ CO ₃ .
Na ₂ O + CO ₂ → Na ₂ CO ₃
(2) The produced Na ₂ CO ₃ and Na ₂ O.nSiO ₂ are mixed. Let the mixing ratio be x: y.
(3) When the mixture is heated to decompose Na ₂ CO ₃ , it is presumed that the following reaction proceeds.
x · Na ₂ CO ₃ + y (Na ₂ O · nSiO ₂ )
→ x · Na ₂ O + x · C + x · O ₂ + y (Na ₂ O · nSiO ₂ )
→ x · C + x · O ₂ + (x + y) Na ₂ O · nSiO ₂

As can be seen from the above (3), when Na ₂ O is used, the composition of Na ₂ O · nSiO ₂ to be produced gradually shifts in the direction of increasing the Na ₂ O ratio when the number of reactions is repeated. Eventually, Na ₂ O · nSiO ₂ cannot be reused.

In contrast to the above, the reaction formula of the present invention is as follows.
(1) Absorb CO ₂ and H ₂ O in Na ₂ O.nSiO ₂ .
Thereby, it is presumed that Na ₂ CO ₃ decahydrate is formed on the surface of Na ₂ O · nSiO ₂ .
(The absorption ratio of CO ₂ to Na ₂ O · nSiO ₂ is x: y, x <y.)
x (CO ₂ + 10H ₂ O) + y (Na ₂ O · nSiO ₂ )
→ x (Na ₂ CO ₃ · 10H ₂ O) + (y−x) Na ₂ O · ynSiO ₂
(2) Then, when Na ₂ O · nSiO _{2 in} which Na ₂ CO ₃ decahydrate is formed is heated on this surface, the following reaction occurs.
_{x (Na 2 CO 3 · 10H} 2 O) + (y-x) Na 2 O · ynSiO 2
→ x · Na ₂ O + x · C + x · O ₂ + 10x · H ₂ O + (y−x) Na ₂ O · ynSiO ₂
→ x · C + x · O ₂ + 10 x · H ₂ O + y (Na ₂ O · nSiO ₂ )
Thus, since x (Na ₂ CO ₃ .10H ₂ O) is derived from y (Na ₂ O.nSiO ₂ ), there is no change in the composition of Na ₂ O.nSiO ₂ as a result.

That is, in the present invention, even if the number of reactions is repeated, the composition of Na ₂ O · nSiO ₂ does not change, and Na ₂ O · nSiO ₂ can be reused any number of times.

(Example 1: Invention Example)
Commercially available sodium hydroxide (granular special grade reagent) and silica sand (SiO ₂ ) (200-300 mesh) have a Na ₂ O: SiO ₂ ratio of 2: 1, and sodium hydroxide and silica sand react to form Na _2. When O.0.5SiO ₂ was formed, the amount of about 20 g was weighed and charged into a nickel crucible having 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. The quartz crucible was covered with an alumina lid, heated to 1200 ° C. at 10 ° C./min in a heating furnace in an Ar atmosphere, 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, the sodium hydroxide was completely dehydrated and reacted with silica sand to form Na ₂ O · 0.5SiO _{2, which} was consistent with the mass loss, Na ₂ O · 0.5SiO _2. Turned out to be generated.

The nickel crucible has a taper, but when the nickel crucible was turned down and the bottom was tapped, the generated glassy Na ₂ O · 0.5SiO ₂ could be taken out. The parts of the Na ₂ O · 0.5SiO ₂ contacted with the nickel crucible were slightly light yellow in some places, so this part was scraped off with a stainless steel scraper to obtain a colorless Na ₂ O · 0.5SiO ₂ lump. Obtained. This lump was pulverized to 1 mm or less in an alumina mortar, and about 5 g of the mass was charged into a silica alumina crucible.

The silica alumina crucible was placed in a heating furnace, heated at 10 ° C./min while flowing dry air at 2 L / min, held at 700 ° C. for 12 hours, and then naturally cooled to room temperature. By this oxidation treatment, organic substances and carbon in the Na ₂ O · 0.5SiO ₂ powder were completely removed. _Further, Na ₂ O · 0.5SiO 2 powder is totally considered to have become an anhydride. After cooling, the silica alumina crucible was taken out from the heating furnace, immediately weighed, and left in the atmosphere.

When the silica alumina crucible containing the Na ₂ O · 0.5SiO ₂ powder was left in the atmosphere for about 30 hours, it was about 15% of the mass of the Na ₂ O · 0.5SiO ₂ powder immediately after the 700 ° C. oxidation treatment. There was an increase in mass. The silica alumina crucible was heated to a temperature of 800 ° C., 1000 ° C., 1200 ° C., 1500 ° C. at 10 ° C./min in a heating furnace in an Ar atmosphere, held for 30 minutes, and then naturally cooled to room temperature. After cooling, the inner wall of the silica alumina crucible turned black and a black product was deposited. The above experimental conditions and results are shown in Table 1.

  When the crucible wall was roughly crushed and washed with hot water, a powdery black product separated and floated on the surface of the hot water, which was separated by filtration, further washed with heated pure water, and then dried. About all the experiments (No. 1-4) of Table 1, when the carbon analysis was carried out for the dried powdery black thing by the combustion infrared absorption method, it was almost 100% carbon. Furthermore, No. 1 in Table 1 When the black precipitate of No. 4 was analyzed by XPS (X-ray photoelectron spectroscopy), it was graphite type carbon.

Since there is only atmospheric CO ₂ is the carbon source in the experimental system, atmospheric CO ₂ is absorbed in sodium silicate was found to be produced carbon upon heating. Moreover, since the produced | generated carbon was carbon of about 100% purity, it can be used as carbon sources, such as a fuel. Assuming that Na ₂ CO ₂ · 10H ₂ O was generated as a result of the absorption of CO ₂ and H ₂ O in the atmosphere by Na ₂ O · 0.5SiO ₂ , that is, the molar amount of CO ₂ and H ₂ O absorbed. When the ratio is assumed to have been 1:10 recovered carbon was an amount corresponding to about 50% absorption CO _2.

In addition, since the sodium compound is used only when Na ₂ O · 0.5SiO ₂ is first synthesized, the composition of sodium silicate dissolved in hot water remains Na ₂ O · 0.5SiO ₂ When the filtrate was dried and Na ₂ O · 0.5SiO ₂ was recovered, this Na ₂ O · 0.5SiO ₂ could be reused for the recovery and decomposition of CO _{2 in} the atmosphere.
Thus, in the present invention, the alkali silicate can be reused any number of times.

(Comparative Example 1)
In Comparative Example 1, the same experiment as in Example 1 was performed except that the temperature rising temperature of the Ar atmosphere furnace was changed. In Comparative Example 1, no black matter was visible after the experiment. The experimental conditions and results are shown in Table 2.

(Example 2: Invention example)
In Example 2, sodium hydroxide and silica sand were weighed and charged so that the Na ₂ O: SiO ₂ ratio was 1: 2, and the standing time in the atmosphere after 700 ° C. oxidation treatment was about 60 hours. Except for this point, the same experiment as in Example 1 of the present invention was performed. Incidentally, the left in the air, there was about 10% of the mass increases to the mass of 700 ℃ _{Na 2} O · 2SiO 2 powder after the oxidation treatment. Table 3 shows the experimental conditions and results.

About all the experiments (No. 7-10) of Table 3, when the carbon analysis was performed for the dried powdery black thing by the combustion infrared absorption method, it was about 100% carbon. Further, in Table 3, No. 10 black precipitates were analyzed by XPS (X-ray photoelectron spectroscopy) and found to be graphite-type carbon.
Since there is only atmospheric CO ₂ is the carbon source in the experimental system, atmospheric CO ₂ is absorbed in sodium silicate was found to be produced carbon upon heating. Moreover, since the produced | generated carbon was carbon of about 100% purity, it can be used as carbon sources, such as a fuel.

In addition, since the sodium compound is used only when Na ₂ O · 2SiO ₂ is first synthesized, the composition of sodium silicate dissolved in hot water remains Na ₂ O · 2SiO ₂ and the filtrate is not changed. When Na ₂ O · 2SiO ₂ was recovered, this Na ₂ O · 2SiO ₂ could be reused for the recovery and decomposition of CO _{2 in} the atmosphere.
Thus, in the present invention, the alkali silicate can be reused any number of times.

(Comparative Example 2)
In Comparative Example 2, the same experiment as in Example 2 was performed except that the temperature rising temperature of the Ar atmosphere furnace was changed. In Comparative Example 2, no black matter was visible after the experiment. Table 4 shows the experimental conditions and results.

(Example 3: Invention example)
Example 3 of the present invention proceeds in the same manner as Example 1 until heating at 700 ° C. for 12 hours and natural cooling, and the silica alumina crucible containing anhydrous Na ₂ O.0.5SiO ₂ powder of Example 1 is left in the atmosphere. The operation was changed from where it was done, and the following operation was performed after this. This silica alumina crucible is placed in a sealed container having a gas inlet / outlet, and the air stored in the tank is bubbled into the sealed container at room temperature (20 ° C.) at a flow rate of 2 L / min. CO ₂ and H ₂ O were absorbed into the Na ₂ O · 0.5SiO ₂ powder in the alumina crucible. As a result of bubbling the atmosphere into water, it is considered that the introduced atmosphere contained H ₂ O having a water vapor amount of about 3 vol% close to the saturated vapor pressure.

When the silica alumina crucible was weighed after about 10 hours, there was a mass increase of about 20% with respect to the mass of 2Na ₂ O · SiO ₂ powder after 700 ° C. oxidation treatment. After this, the experiment was advanced by the same operation as in Example 1. Table 5 shows the experimental conditions and results.

  When the crucible wall was roughly crushed and washed with hot water, a powdery black product separated and floated on the surface of the hot water, which was separated by filtration, further washed with heated pure water, and then dried. About all the experiments (No. 13-16) of Table 5, when the carbon analysis was performed for the dried powdery black thing by the combustion infrared absorption method, it was almost 100% carbon. Further, in Table 5, No. The 16 black precipitates were analyzed by XPS (X-ray photoelectron spectroscopy) and found to be graphite-type carbon.

Since there is only atmospheric CO ₂ is the carbon source in the experimental system, atmospheric CO ₂ is absorbed in sodium silicate was found to be produced carbon upon heating. Moreover, since the produced | generated carbon was carbon of about 100% purity, it can be used as carbon sources, such as a fuel. Assuming that Na ₂ CO ₂ .10H ₂ O was produced as a result of absorption of CO ₂ and H ₂ O, that is, the molar ratio of the absorption amount of CO ₂ and H ₂ O was 1:10. Then, the recovered carbon was an amount corresponding to about 60% of the absorbed CO ₂ .

In addition, since the sodium compound is used only when Na ₂ O · 0.5SiO ₂ is first synthesized, the composition of sodium silicate dissolved in hot water remains Na ₂ O · 0.5SiO ₂ When the filtrate was dried and Na ₂ O · 0.5SiO ₂ was recovered, this Na ₂ O · 0.5SiO ₂ could be reused for the recovery and decomposition of CO _{2 in} the atmosphere.
Thus, in the present invention, the alkali silicate can be reused any number of times.

(Comparative Example 3)
In Comparative Example 3, the same experiment as in Example 1 was performed except that air dried using a hygroscopic agent was introduced into a sealed container. There was an increase in mass of about 3% with respect to the mass of Na ₂ O · 0.5SiO ₂ powder immediately after the 700 ° C. oxidation treatment by introduction of dry air. The experimental conditions and results are shown in Table 6.

About all the experiments (No. 17-20) of Table 6, when the carbon analysis was performed for the dried powdery black thing by the combustion infrared absorption method, it was almost 100% carbon. Furthermore, in Table 6, No. About 20 black deposits, when it analyzed by XPS (X-ray photoelectron spectroscopy), it was graphite type carbon.
Since there is only atmospheric CO ₂ is the carbon source in the experimental system, atmospheric CO ₂ is absorbed in sodium silicate was found to be produced carbon upon heating. Moreover, since the produced carbon was carbon of almost 100% purity, it can be used as a carbon source for fuel and the like.
Further, the amount of recovered carbon was small and could not be quantified, and it was not possible to measure what amount of absorbed CO ₂ corresponds to.

When Example 3 was compared with Example 1 and Comparative Example 3, Example 3 had the advantages as summarized in Table 7 as a result of positively introducing H ₂ O into the atmosphere.
That is, in Embodiment 3, CO ₂ and _{H 2} 1/3 and absorption of very short even though CO ₂ and of _{H 2} O absorption time Example 1 and Comparative Example 3 O is large, and, The carbon recovery rate from the absorbed CO ₂ was also excellent.
In Example 3, the absorption amount is about 1.33 times (= 20/15) and the carbon recovery rate is about 1.2 times (= 60/50) compared to Example 1. As a result, the absorption time 1 / However, the carbon recovery amount was about 1.6 times (= 1.33 × 1.2).
Further, in Comparative Example 3 using dry air, the amount of carbon recovered was very small, and Example 3 of the present invention was much more advantageous.

Claims (3)

Preparing an alkali silicate,
Allowing the alkali silicate to absorb atmospheric CO ₂ in the presence of H ₂ O;
The alkali silicate product that has absorbed the CO ₂ and with H _{2 O,} in a non-oxidizing atmosphere, heated to 700 ° C. or higher 1600 ° C. or less, characterized in that it comprises a step of separating the carbon, the atmosphere CO ₂ A method to recover and separate carbon.   The method according to claim 1, wherein the alkali silicate is sodium silicate.   The method according to claim 1, wherein the alkali silicate after separating the carbon is reused in the step of preparing the sodium silicate.