JPH01261202A - Production of oxygen from gaseous carbon dioxide - Google Patents

Abstract

PURPOSE:To enable simplification of a production apparatus, by providing a catalyst combustor for hydrogen on the downstream side of a methane forming reactor in electrolyzing formed water and producing oxygen utilizing reaction for forming methane and the water from gaseous carbon dioxide and hydrogen and reaction for decomposing the methane into a carbon and hydrogen. CONSTITUTION:Oxygen is produced from gaseous carbon dioxide by the following steps (a)-(f). (a) Gaseous carbon dioxide is reacted with hydrogen in a methane forming reactor 2 to produce a methane-containing gas; (b) water contained in the methane-containing gas is removed in a water condensing separator 4; (c) the methane-containing gas is passed through a catalyst combustor 5 to selectively convert hydrogen into water; (d) the methane-rich gas passed through the step (c) is converted into carbon and hydrogen in a methane decomposition reactor 6 to capture the carbon; (e) water obtained in the step (b) for removing the water is electrolyzed in a water electrolyzer 7 and converted into oxygen and hydrogen to produce the oxygen and (f) the hydrogen obtained in the steps (d) and (e) is recycled to the step (a) for producing the methane- containing gas.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is a method for producing breathing oxygen used in manned space bases, manned spacecraft, nuclear submarines, nuclear shelters, etc. The present invention relates to a method for producing oxygen.

[Conventional technology]

Is the chemical reaction formula for reducing carbon dioxide gas as shown in the following formula? The Tsusch reaction and the Sabatier reaction are known.

(a) Gerash reaction CO2+2H2→C+2H20
(b) Sabatier 1st reaction (methane production reaction) CO2+4
H2→CH4+2H20 (c) Sabatier second reaction (methane decomposition reaction) CH-+C
+2H2 The apparatusization of these reactions has rarely been revisited from an economic standpoint. Regarding carbon dioxide gas reduction and oxygen gas recovery, practical research is being carried out mainly by the US Space Agency, but only the methane production reaction of equation (0) above is carried out, and the methane gas after water recovery is Consideration has been given to releasing hydrogen outside the spacecraft, but this method would not only result in a shortage of hydrogen for carbon dioxide reduction within the spacecraft, but would also require hydrogen replenishment from the ground, as well as releasing it outside the spacecraft. Methane and other substances can cling to spacecraft and cause problems such as reduced visibility when observing space from inside the ship.

[Problem to be solved by the invention]

Conventionally, the Sabatier two-stage reaction method has been frequently used, but it has the following problems.

(1) In order to completely reduce C02 in the first reactor (methane production), an excess of hydrogen, i.e. 1 mole of carbon 1! !
4 moles or more of hydrogen is required for a gas.

(See Figure 2) Therefore, excess hydrogen always remains in the outlet gas.

On the other hand, in the @2 reactor (methane decomposition), the presence of hydrogen in the inlet gas will inhibit the reaction. (See Figure 4) Therefore, the second reactor becomes large.

(2) Since the optimum reaction temperature for the first reactor is approximately 300-400°C and that for the second reactor is 700-1300°C, a large heat exchanger is required between these reactors, which increases costs. It becomes.

Furthermore, the Sabatier two-stage method using a hydrogen separation membrane has the following problems.

(1) Even if a hydrogen separation membrane is used, hydrogen separation is insufficient, and due to the presence of this hydrogen, methane decomposition in the Sapatie second reaction is not completed completely, and the second reactor becomes larger.
Unreacted methane is recycled.

(2) There is still a large heat exchanger to raise the reaction gas temperature (approximately 600-1300°C) in the building.

Since the gas is a heat exchanger, the equipment is quite large.

(3) Hydrogen separation using a membrane uses the pressure difference as the driving force, so a compressor is required before the membrane.

An object of the present invention is to provide a method for producing oxygen from carbon dioxide gas that can solve the above conventional problems.

[Means to solve the problem]

The method for producing oxygen from carbon dioxide gas according to the present invention includes a step of reacting carbon dioxide and hydrogen to generate a methane-containing gas, a step of removing water contained in the methane-containing gas, and a step of removing the water contained in the methane-containing gas. A step of selectively converting hydrogen into water by passing it through a combustion catalyst layer, a step of decomposing the methane-rich gas that has passed through this step to convert it into carbon and hydrogen, and capturing the carbon, and a step of removing the water. The method comprises a step of electrolyzing the obtained water to convert it into oxygen and hydrogen to produce oxygen, and a step of circulating the hydrogen obtained in the step to the step of producing the methane-containing gas. Features.

[Effect]

The effects of the present invention are as follows.

(1) By selectively reacting hydrogen with high reaction activity using a combustion catalyst in the rear seed of the methane production reactor (see Figure 3), the reaction heat raises the methane-rich gas to the reaction temperature, and at the same time, Converts hydrogen, which is negative to the reaction, into water. Therefore, a hydrogen removal device is not required, and a large heat exchanger for heating the methane-rich gas is not required or is extremely small.

(2) The reaction temperature can be easily controlled by adjusting the hydrogen content in the process gas at the inlet of the catalytic combustor, that is, the amount of hydrogen circulated in the recycled gas, or the amount of oxygen supplied to the catalytic combustor. can.

(3) Since there is virtually no hydrogen in the gas at the inlet of the second reactor, the second reaction can be ideally carried out, and the second reactor can be used as a con- i'? It will be made into an ICT.

〔Example〕

FIG. 1 is a diagram showing an example of equipment used to carry out the method of the present invention, in which 1 is a heat exchanger and 2 is a methane production reactor.
36-1 is a heat exchanger, 4 is a water condensation separator, 5 is a catalytic combustor, 6 is a methane decomposition reactor, 7 is a water electrolyzer, 8 is a heat exchanger, and 9 is a compressor.

In Figure 1, carbon dioxide gas, which is the raw material gas, and circulating gas (mainly hydrogen) separated and recovered in the post-process are mixed into a gas mixer (
(not shown), preheated in a heat exchanger 1, and supplied to a methane production reactor 2.

In the methane production reactor 2, the following reaction takes place.

CO2+4■I2→CH4+2■■20 Methane production reactor 2 is filled with a ruthenium catalyst, etc. In the presence of the ruthenium catalyst, the mixed gas of carbon dioxide gas and hydrogen gas undergoes methanation through an exothermic reaction, and the reaction temperature is preferably set at 300 to 400°C. By maintaining this, a CO2 conversion rate of nearly 100% can be obtained. Therefore, a cooling device is installed in the methane production reactor 2 to remove heat. The molar ratio of hydrogen to carbon dioxide is preferably 4.5 or more as shown in FIG. This hydrogen excess condition can be fully achieved by circulating hydrogen from each step. However, it is dangerous to use too much hydrogen! This is undesirable from the viewpoint of gas compression and subsequent hydrogen treatment.

The reactor outlet gas preheats the raw material gas in a heat exchanger 1, and is cooled in a heat exchanger 3 to near room temperature in a ridge.

In the water condensation separator 4, water is condensed and separated, and the water is stored in a water tank (not shown). It is sent to the It analyzer 7. On the other hand, the uncondensed gas component in the water condensation separator 4 contains unreacted hydrogen gas in addition to the generated methane. They are mixed (in FIG. 1, a portion of the product oxygen obtained in the water electrolyzer 7 is used) and introduced into the catalytic combustor 5, where the hydrogen is selectively combusted and converted into water.

As shown in Figure 3, we take advantage of the fact that hydrogen is much easier to burn than methane.

Hydrogen is supplied from outside the system to the circulation line, the amount of circulating gas is set, and the amount of oxygen supplied is adjusted so that the outlet gas from the catalytic combustor 5, which is essentially methane and water vapor, has the optimum temperature for the methane decomposition reaction. will be held.

This outlet gas is further introduced into the methane decomposition reactor 6, where the next reaction occurs.

CH → 2H2 + C The methane decomposition reactor 6 contains silica wool or a catalyst containing a group III element (particularly a nickel-containing catalyst), etc., which functions as a heat medium and a carbon deposition substrate, or a medium that promotes methane decomposition through a catalytic reaction. Filled and heated to approximately 1300℃
Hydrogen gas is produced along with carbon precipitation at the following temperatures: The entrained carbon is separated by a carbon separator (not shown), and the hydrogen gas is mixed with hydrogen gas from the water electrolyzer 7 and returned to the gas mixer (not shown) by the compressor.

As shown in Figure 4, this methane decomposition reaction is influenced by the molar composition ratio of hydrogen and methane at the inlet of the reactor, and the higher the methane partial pressure, the higher the methane decomposition conversion rate. (approximately 600 to 1
300°C), methane generation reactor 2 and methane decomposition reactor 6
It is extremely significant that by installing a catalytic combustor 5, which is a hydrogen conversion device, between the two, the temperature can be inevitably raised to a predetermined temperature.

Further, the hydrogen gas generated in the water electrolyzer 7 is also returned to the gas mixer (not shown) and reused.

The generated oxygen is also released as a product.

According to the process flow shown in FIG. 1, the temperature, pressure, and material balance at major locations are shown in Table 1.

Carbon dioxide gas 1. O
Omo4/H is supplied, the inside of the methane production reactor 2 is filled with a catalyst in which ruthenium is supported on alumina R-let, and the gas conditions at the inlet of the methane production reactor 2 are such that the temperature is 30.
0℃, pressure 2 kg/m2A, GT (sv670hr
= Closed. The catalytic combustor 5 is filled with a catalyst in which 0.5% by weight of platinum is supported on porous alumina fibers.
V 1000hr-'.

The inside of the methane decomposition reactor 6 is filled with a nickel-based catalyst, and the supplied gas condition is a temperature of 800°C.

Conversion of hydrogen by some catalytic combustors and high temperature (800° C.) of the feed gas to the methane cracking reactor has been achieved effectively and easily.

〔Effect of the invention〕

(1) By using a hydrogen combustion catalyst, hydrogen separation becomes unnecessary, and hydrogen in the process fluid (methane-rich gas) can be virtually eliminated.

(2) Because the process fluid is heated by the combustion heat of hydrogen,
A heat exchanger for heating is not required.

(3) The second reactor is extremely simplified since there is no hydrogen to inhibit methane decomposition.

(4) Since there is no need to increase the pressure of the process fluid before hydrogen removal, a compressor is not required compared to the membrane separation method, and since methane is almost completely decomposed, the only circulating gas is H2, making the equipment simpler.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an example of the apparatus used to carry out the method of the present invention, Fig. 2 is a diagram showing the relationship between H2/C02 (molar ratio) and CO2 conversion rate, and Fig. 3 is a diagram showing the oxidation of fiber catalyst. FIG. 4 is a diagram showing reactivity and shows H2/CFI4 (molar ratio) and methane decomposition rate in methane decomposition. 1... Heat exchanger, 2... Methane production reactor, 3...
・Heat exchanger, 4...Water condensation separator, 5...Catalytic combustor, 6...Methane decomposition reactor, 7...Water electrolyzer, 8
...Heat exchanger, 9...Compressor. 5iO agent Patent attorney Takehiko Suzue 7' 1. Heat exchanger? ... Methane production reactor 3 ... Heat exchanger 4 ... Water condensation separator 5 ... Catalytic combustor 6 ... Methane decomposition reactor 7 ... Water electrolyzer 8 ... Heat exchanger 9 - Compression Machine diagram 1

Claims (1)

[Claims] A step of reacting carbon dioxide and hydrogen to generate a methane-containing gas, a step of removing water contained in the methane-containing gas, and a step of selectively converting hydrogen into water by passing the methane-containing gas through a combustion catalyst layer. a step of decomposing the methane-rich gas that has passed through this step to convert it into carbon and hydrogen, and a step of capturing carbon; and a step of electrolyzing the water obtained in the step of removing the water and converting it into oxygen and hydrogen. A method for producing oxygen from carbon dioxide gas, comprising: a step of producing oxygen; and a step of circulating hydrogen obtained in the step to the step of producing the methane-containing gas.