JP7368845B2 - How to decompose sodium oxide - Google Patents

Description

The present invention relates to a method for decomposing sodium oxide.

Global energy demand is increasing, but currently most energy sources rely on fossil fuels such as oil, coal, and natural gas. There is much talk about the future depletion of fossil fuels and global warming caused by greenhouse gases. Under these circumstances, hydrogen is attracting attention as a clean energy source, and various methods for producing hydrogen have been proposed.

As a method for producing hydrogen, a method for producing hydrogen that focuses on the redox reaction of sodium and utilizes the following reaction cycles (1) to (3) is known (for example, Patent Documents 1 and 2).
(1) Sodium hydroxide and sodium are reacted to generate sodium oxide and hydrogen.
2NaOH (s) + 2Na (l) → 2Na ₂ O (s) + H ₂ (g)
(2) Generate sodium peroxide and sodium from sodium oxide.
2Na ₂ O (s) → Na ₂ O ₂ (s) + 2Na (g)
(3) React sodium peroxide and water to generate sodium hydroxide and hydrogen.
Na ₂ O ₂ (s) + H ₂ O → 2NaOH (s) + 1/2O ₂ (g)

Japanese Patent Application Publication No. 2014-166931 JP2015-231920A

In the reaction cycle described above, the decomposition reaction of sodium oxide (2) requires thermodynamically high thermal energy. When sodium oxide is placed in a reaction vessel and heated, there is a problem in that the reaction vessel tends to corrode due to the high reactivity of sodium.

The present invention has been made in view of the above-mentioned matters, and its purpose is to provide sodium oxide that can suppress corrosion of a reaction vessel when sodium oxide is heated and decomposed into sodium peroxide and sodium. The purpose is to provide a decomposition method.

The method for decomposing sodium oxide according to the present invention includes:
A method for decomposing sodium oxide in which sodium oxide is heated to generate sodium peroxide and sodium, the method comprising:
A corrosive reaction vessel is filled with sodium oxide,
A portion of the sodium oxide is heated to form a temperature gradient such that the temperature decreases from the sodium oxide at the heating point to the sodium oxide near the inner surface of the reaction vessel, suppressing the temperature rise in the reaction vessel and increasing the temperature of the reaction vessel. Decomposes sodium oxide into sodium peroxide and sodium while suppressing corrosion.
It is characterized by

Furthermore, using the reaction vessel having a cylindrical shape with a bottom,
The surface of the filled sodium oxide and the center of the reaction vessel in plan view may be heated.

Alternatively, the reaction may be carried out while cooling the reaction vessel.

Further, the reaction container may include a light-transmitting member, and the reaction vessel may be heated by a condensing heating device through the light-transmitting member.

Alternatively, heating may be performed by blowing a high temperature inert gas.

Further, the reaction container may include a translucent member, and the reaction vessel may be heated by reflecting sunlight through the translucent member.

According to the method for decomposing sodium oxide of the present invention, it is possible to suppress corrosion of a reaction vessel when sodium oxide is heated and decomposed into sodium peroxide and sodium.

FIG. 3 is a plan view showing an example of a heated portion of sodium oxide. FIG. 3 is a plan view showing an example of a heated portion of sodium oxide. It is a figure which shows an example of the method of heating sodium oxide with a condensing type heating device. FIG. 3 is a diagram showing an example of a method of heating sodium oxide with high-temperature gas. FIG. 5(A) shows an example of a trough-type method, and FIG. 5(B) shows an example of a tower-type method of concentrating sunlight to heat sodium oxide. 2 is a graph showing temperature changes at the top and bottom of sodium oxide and the body of a reaction vessel when powdered sodium oxide is filled and heated with a halogen point heater in an example. 2 is a graph showing temperature changes at the top and bottom of sodium oxide and the body of a reaction vessel when granular sodium oxide is filled and heated with a halogen point heater in an example.

A method for decomposing sodium oxide according to this embodiment will be explained. A method for decomposing sodium oxide is to fill a corrosive reaction vessel with sodium oxide and heat the sodium oxide to generate sodium peroxide and sodium. Heating is carried out by locally heating a part of the interior of the reaction vessel to form a temperature gradient such that the temperature decreases from the sodium oxide at the heating point to the sodium oxide close to the inner surface of the reaction vessel.

Since the decomposition reaction of sodium oxide requires high-temperature thermal energy, sodium produced during decomposition and oxygen coexist at high temperatures. These substances then cause a chemical reaction with the reaction vessel, corroding the reaction vessel.

In this embodiment, by heating sodium oxide by forming a temperature gradient inside the reaction vessel, some of the heated sodium oxide is decomposed into sodium peroxide and sodium, but the sodium oxide near the reaction vessel is temperature rise is suppressed. Therefore, a situation in which sodium and oxygen coexist near the reaction vessel at high temperatures is suppressed, and corrosion of the reaction vessel is suppressed.

By suppressing corrosion of the reaction vessel, sodium oxide can be decomposed stably with high yield, and running costs can also be suppressed by reducing the cost of replacing the reaction vessel.

Here, the corrosive reaction vessel is a commonly used metal reaction vessel, such as a stainless steel reaction vessel, a reaction vessel made of pure metal such as nickel, tungsten, or molybdenum, a nickel alloy, etc. These include reaction vessels made of alloys, and reaction vessels coated with surface treatment materials such as copper plating. Corrosion of metals refers to the chemical reaction that occurs with the surrounding environment, such as adjacent metals or gases, causing them to melt or produce corrosion products. It also includes opening.

In order to locally heat a portion of the sodium oxide in the reaction vessel and create a temperature gradient where the temperature decreases from the heating point toward the inner surface of the reaction vessel, for example, as shown in Figure 1, a bottomed When a cylindrical reaction vessel is used and the longitudinal axis of the reaction vessel is placed in the vertical direction, heating is performed by heating the surface of the sodium oxide filled in the reaction vessel and the central portion in plan view. obtain. The range of the heated area may be appropriately set depending on the size of the reaction vessel, and may be within a circle having a diameter of 30% or less, preferably 10% or less of the inner diameter of the reaction vessel.

Further, as shown in FIG. 2, when the reaction container is placed so that its longitudinal axis faces in the horizontal direction, heating may be performed linearly.

Heating can be carried out in such a way that the sodium oxide can be decomposed at the heating point and that no corrosion reaction occurs near the inner surface of the reaction vessel. It is sufficient that a temperature gradient is formed so that the surface temperature of the substrate does not exceed 400°C.

The heating method is not limited as long as it can be heated while forming a temperature gradient as described above, but some heating methods are illustrated below.

First, as a heating method, as shown in FIG. An example of this method is to heat sodium oxide by irradiating concentrated heating light.

In the case of this heating method, a reaction vessel 10 is used which partially includes a light-transmitting member 11 having heat resistance and light-transmitting properties such as quartz glass so that the sodium oxide is irradiated with heating light. The sodium oxide filled in the reaction container 10 can be heated through the light-transmitting member 11.

Here, the reaction container 10 has a cylindrical shape with a bottom, and a point-concentrating infrared condensing heating device 20 is used, and in a plan view inside the reaction container 10, near the center of the reaction container 10, and The area near the surface of the filled sodium oxide is heated. By locally heating the vicinity of the center, a temperature gradient is formed in which the temperature decreases from the sodium oxide in the heated area to the sodium oxide in the vicinity of the inner surface of the reaction vessel 10, and a rise in temperature near the inner surface of the reaction vessel 10 is suppressed. Thereby, sodium peroxide and sodium can be generated by thermally decomposing sodium oxide while suppressing corrosion of the reaction vessel 10.

Note that the infrared condensing heating device 20 is preferably one that can reach a heating temperature of 600° C. or higher, preferably 700° C. or higher so that sodium oxide can be decomposed. Further, the focal length and focal diameter of the infrared condensing heating device 20 are appropriately set depending on the size of the reaction vessel used. Further, depending on the shape of the reaction vessel, etc., a line condensing infrared condensing heating device 20 may be used.

Further, sodium is generated as vapor, and in order to discharge the sodium vapor from the reaction vessel 10, it is preferable to carry out the reaction while supplying and discharging an inert gas such as nitrogen or argon. It is preferable that an inert gas is introduced through the gas introduction path 12, and sodium vapor generated by the flow of the inert gas is discharged from the gas exhaust path 13 to recover sodium.

Further, as a heating method, as shown in FIG. 4, a method using high temperature gas can be mentioned. Here, an inert gas such as nitrogen or argon is heated to a high temperature of 600° C. or higher by a heat exchanger 40 and supplied into the reaction vessel 10 from a high temperature gas supply path 30. The tip of the high-temperature gas supply path 30 extends to near the surface of the filled sodium oxide, and a high-temperature inert gas is blown onto a portion of the sodium oxide, thereby heating the sodium oxide. As a heat source for the heat exchanger 40, exhaust heat from a factory or the like may be used.

Further, as a heating method, a method of heating by concentrating sunlight can be mentioned. For example, a method of concentrating sunlight using a reflective member 50, such as a trough type shown in FIG. 5(A) or a tower type shown in FIG. 5(B), can be used. This is done by changing the design of the reaction vessel 10 as appropriate so that the concentrated sunlight is locally irradiated onto the sodium oxide inside the reaction vessel 10.

Moreover, when heating, the reaction container 10 may be cooled. The cooling method is not limited, and for example, a method of cooling the reaction container 10 by blowing air onto the outer surface of the reaction container 10 using an air blower may be mentioned. Alternatively, a method in which a flow path such as a tube is placed along the outer surface of the reaction vessel 10 and cooling is performed by passing a cooling medium such as water through the tube, or a method in which a cooling medium such as water or the like is passed through the tube, or by using a reaction vessel 10 in which a cooling flow path is formed, water or the like is placed in the cooling flow path. Examples include a method of cooling through a cooling medium.

An apparatus was constructed in the same manner as the apparatus configuration shown in FIG. 3, and a sodium oxide decomposition experiment was conducted.
A bottomed cylindrical reaction vessel made of SUS316 was used as the reaction vessel. The upper surface of the reaction vessel is made of light-transmitting heat-resistant glass.
A halogen point heater (manufactured by HEATTECH Co., Ltd., HPH-60/f60/36V-450W) was used as an infrared condensing heating device. This halogen point heater has a focal length of 60 mm and a focal diameter of 14 mm. The irradiation surface of the halogen point heater was placed opposite the glass on the top surface of the reaction vessel.

(Experiment 1)
A reaction vessel was filled with powdered sodium oxide. The amount of sodium oxide filled was φ60×85 mm, and the focal point of the halogen point heater was placed on the upper surface of the filled sodium oxide and at the center in plan view.

A halogen point heater was operated and the sodium oxide was heated while changing the voltage. In addition, argon gas is introduced (0.5 slm) as an inert gas from the gas introduction path and discharged from the gas exhaust path, and a filter is installed in the gas exhaust path to capture sodium. The process was continued until the supply flow rate and discharge flow rate were reduced by half. In addition, the temperature at the top (space) of the reaction vessel, the temperature at the bottom of the filled sodium oxide, and the temperature at the body of the reaction vessel were measured.

FIG. 6 shows changes in the temperature at the top of the reaction vessel, the temperature at the bottom of the sodium oxide, and the temperature at the body of the reaction vessel. The temperature at the top of the reaction vessel (temperature in the space above the sodium oxide heated by a halogen point heater) has risen to about 550°C, but the temperature at the bottom of the sodium oxide and the temperature at the body of the reaction vessel are each 25°C. The temperature was approximately 110° C., and a temperature gradient was formed in which the temperature decreased from the sodium oxide at the heating point to the sodium oxide near the reaction vessel.

The sodium oxide in the heated area turned pale yellow, suggesting the formation of sodium peroxide. In addition, deposits were found on the filter installed in the gas exhaust channel, and when the deposits were analyzed using SEM-EDS, it was confirmed that sodium was produced.

No change was observed in the sodium oxide near the inner wall surface of the reaction vessel, and it was confirmed that there was no change in the inner wall of the reaction vessel.

(Experiment 2)
Subsequently, using granular sodium oxide, the sodium oxide was heated and decomposed in the same manner as above.
FIG. 7 shows temperature changes at the top and bottom of the filled sodium oxide and at the body of the reaction vessel. The temperature at the top of the sodium oxide heated by a halogen point heater rose to about 500°C, but the temperature at the bottom of the sodium oxide and the temperature at the body of the reaction vessel were about 30°C and 150°C, respectively. .

The sodium oxide in the heated area turned pale yellow, suggesting the formation of sodium peroxide. In addition, deposits were found on the filter installed in the gas exhaust channel, and when the deposits were analyzed using SEM-EDS, it was confirmed that sodium was produced.

No change was observed in the sodium oxide near the inner wall surface of the reaction vessel, and it was confirmed that there was no change in the inner wall of the reaction vessel.

As described above, by heating a portion of sodium oxide locally and forming a temperature gradient such that the temperature decreases from the heated area to the vicinity of the reaction vessel, sodium oxide can be heated while suppressing corrosion of the reaction vessel. It was confirmed that it was possible to disassemble the

INDUSTRIAL APPLICATION This invention can be utilized for the decomposition reaction of sodium oxide in the hydrogen production method which utilizes the redox reaction of sodium.

10 Reaction container 11 Transparent member 12 Gas introduction path 13 Gas discharge path 20 Infrared condensing heating device 30 High temperature gas supply path 40 Heat exchanger 50 Reflection member

Claims (6)

A method for decomposing sodium oxide in which sodium oxide is heated to generate sodium peroxide and sodium, the method comprising:
A corrosive reaction vessel is filled with sodium oxide,
A portion of the sodium oxide is heated to form a temperature gradient such that the temperature decreases from the sodium oxide at the heating point to the sodium oxide near the inner surface of the reaction vessel, suppressing the temperature rise in the reaction vessel and increasing the temperature of the reaction vessel. Decomposes sodium oxide into sodium peroxide and sodium while suppressing corrosion.
A method for decomposing sodium oxide, which is characterized by: Using the reaction vessel having a cylindrical shape with a bottom,
heating the surface of the filled sodium oxide and the center of the reaction vessel in plan view;
The method for decomposing sodium oxide according to claim 1, characterized in that: carried out while cooling the reaction vessel,
The method for decomposing sodium oxide according to claim 1 or 2, characterized in that: The reaction container has a translucent member, and is heated with a condensing heating device via the translucent member.
The method for decomposing sodium oxide according to any one of claims 1 to 3. Heating by blowing high temperature inert gas,
The method for decomposing sodium oxide according to any one of claims 1 to 3. The reaction container has a translucent member, and the reaction vessel is heated by reflecting sunlight through the translucent member.
The method for decomposing sodium oxide according to any one of claims 1 to 3.

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