JP7755331B2 - Metal manufacturing system and metal manufacturing method - Google Patents

Description

The present invention relates to a metal manufacturing system and a metal manufacturing method.

For example, when magnesium is produced using molten salt electrolysis, magnesium chloride is used as the material, but if this magnesium chloride contains moisture, it can cause deterioration of the electrodes used in molten salt electrolysis.

For this reason, anhydrous magnesium chloride is used in molten salt electrolysis, and Patent Document 1 discloses a method for producing anhydrous magnesium chloride in which solid magnesium carbonate is reacted with chlorine gas at a temperature of 1200°C or less in the presence of carbon monoxide gas, and the anhydrous magnesium chloride is extracted in a molten state to produce anhydrous magnesium chloride.

However, the method described in Patent Document 1 has the problem that carbon dioxide, a greenhouse gas, is generated as a by-product, which requires disposal methods such as atmospheric release.

Japanese Patent Application Publication No. 55-20296 International Publication No. 2018/221698 JP 2022-42280 A

The present invention was made in light of these circumstances, and aims to provide a metal production system and metal production method that suppresses the release of carbon dioxide gas into the atmosphere during operation and enables efficient metal production.

In order to achieve the above object, the present invention is realized by the following configuration.
(1) A metal production system according to an embodiment of the present invention includes a chlorination furnace that chlorinates a metal oxide to produce an anhydrous metal chloride, a molten salt electrolytic cell that electrolyzes the anhydrous metal chloride to produce a metal, a supply path that supplies the anhydrous metal chloride from the chlorination furnace to the molten salt electrolytic cell, and a supply path that supplies chlorine gas produced by the electrolysis from the molten salt electrolytic cell to the chlorination furnace.

(2) The configuration of (1) above may further include a gas reduction device that reduces carbon dioxide gas discharged from the chlorination furnace to produce carbon monoxide gas, a heating furnace that dehydrates metal hydroxides to produce the metal oxides that are to be supplied to the chlorination furnace, a supply path that supplies the carbon monoxide gas from the gas reduction device to the chlorination furnace, and a supply path that supplies the metal oxides from the heating furnace to the chlorination furnace.

(3) According to an embodiment of the present invention, a method for producing metals using the production system described in (1) above includes chlorinating metal oxides with a mixed gas of carbon monoxide gas and chlorine gas in the chlorination furnace to produce anhydrous metal chlorides, supplying the produced anhydrous metal chlorides to the molten salt electrolytic cell, electrolyzing the anhydrous metal chlorides in the molten salt electrolytic cell to produce metals and chlorine gas, and supplying the produced chlorine gas to the chlorination furnace.

The present invention provides a metal production system and a metal production method that can suppress atmospheric emissions of carbon dioxide gas during operation and efficiently produce metals.

FIG. 1 is a diagram illustrating the configuration of an apparatus for carrying out a chlorination step according to a first embodiment of the present invention. FIG. 1 is a diagram illustrating the configuration of an apparatus for carrying out a chlorination step according to a second embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, modes for carrying out the present invention (hereinafter referred to as embodiments) will be described in detail with reference to the accompanying drawings.
It should be noted that the same elements are denoted by the same reference numerals throughout the description of the embodiments.

The metal production system according to this embodiment includes a chlorination furnace that chlorinates metal oxides to produce anhydrous metal chlorides; a molten salt electrolytic cell that electrolyzes the anhydrous metal chlorides to produce metals; a supply path that supplies the anhydrous metal chlorides from the chlorination furnace to the molten salt electrolytic cell; and a supply path that supplies chlorine gas generated by electrolysis from the molten salt electrolytic cell to the chlorination furnace. By using this system, for example, chlorine generated at the anode of the molten salt electrolytic cell can be used in the chlorination furnace. Because chlorine gas is highly corrosive, it is preferable to be able to use the chlorine gas generated in the molten salt electrolytic cell in the chlorination furnace, as this shortens the storage time of the chlorine gas. From the perspective of shortening the storage time of the chlorine gas, the chlorine gas storage chamber may be omitted from the chlorine gas supply path.

The chlorination furnace may be a batch or flow reactor. When using a batch reactor, the anhydrous metal chloride is transferred from the chlorination furnace to the molten salt electrolytic cell after detecting that the chlorination reaction in the chlorination furnace has been completed. When using a flow reactor, the anhydrous metal chloride is continuously transferred from the chlorination furnace to the molten salt electrolytic cell.

The following describes an example in which magnesium oxide, carbon monoxide gas, and chlorine gas are added to a chlorination furnace to produce magnesium chloride, and then chlorine and magnesium are produced from the magnesium chloride in a molten salt electrolytic cell.

In the chlorination furnace, magnesium oxide, carbon monoxide gas, and chlorine gas are introduced, and the magnesium oxide is chlorinated. This reaction is preferably carried out in a molten salt of an alkali metal or alkaline earth metal chloride (e.g., sodium chloride, potassium chloride, calcium chloride, etc.). Because the solubility of magnesium oxide is low and the solubility of magnesium chloride is high in the molten salt, magnesium oxide exists as a solid, while magnesium chloride exists in the liquid phase. Furthermore, carbon dioxide is generated during the chlorination reaction of magnesium oxide. Therefore, when the chlorination furnace is a batch-type furnace, the solid components in the liquid phase can be monitored, and the contents of the chlorination furnace can be transported to a molten salt electrolytic cell when the decrease in the solid components falls below a certain level. Alternatively, the carbon dioxide concentration in the chlorination furnace can be measured, and the contents of the chlorination furnace can be transported to a molten salt electrolytic cell when the carbon dioxide concentration reaches or exceeds a predetermined value.

Therefore, the chlorination furnace may be equipped with a measuring device that measures the concentration of solid components in the liquid phase and/or a measuring device that measures the carbon dioxide concentration in the gas phase. Measuring devices that measure the concentration of solid components in the liquid phase include absorption meters that measure the absorbance or light transmittance of the suspension. Measuring devices that measure the carbon dioxide concentration in the gas phase include well-known carbon dioxide meters.

Furthermore, if the chlorination furnace is a flow type, it is preferable to install a filter at the exhaust port of the chlorination furnace to trap solid magnesium oxide so that unreacted magnesium oxide is not discharged from the chlorination furnace.

In addition, impurities may be removed from the liquid phase of the contents of the chlorination furnace before being transported to the molten salt electrolytic cell. Furthermore, if a filter to trap magnesium oxide is installed at the outlet of the chlorination furnace, the pore size of the filter may be large enough to allow particulate impurities to pass through. Particulate impurities may be collected separately using a filter with an even smaller pore size.

The anhydrous metal chloride produced in the chlorination furnace is transferred from the chlorination furnace to the molten salt electrolytic cell via a supply path. At this point, the anhydrous metal chloride may be supplied to the molten salt electrolytic cell along with a molten salt of an alkali metal or alkaline earth metal chloride without being separated. For example, if a molten salt of sodium chloride is used as the molten salt of an alkali metal or alkaline earth metal, a molten salt of sodium chloride with magnesium chloride dissolved therein may be supplied to the molten salt electrolytic cell.

In this way, the anhydrous metal chloride supplied from the chlorination furnace may differ from the operating temperature of the molten salt electrolytic cell. Therefore, the temperature of the liquid phase supplied to the molten salt electrolytic cell and the temperature of the molten salt electrolytic cell may be measured, and the temperature of the liquid phase supplied to the molten salt electrolytic cell may be adjusted based on these temperatures. Therefore, the molten salt electrolytic cell may be equipped with a thermometer that measures the temperature of the molten salt, and the supply path from the chlorination furnace to the molten salt electrolytic cell may be equipped with a thermometer that measures the temperature of the supply (liquid phase), as well as a cooler and/or heater that controls the temperature of the supply.

As an example of temperature control, if the molten salt electrolytic cell is at a temperature higher than the desired reaction temperature, the temperature of the molten salt electrolytic cell can be lowered by supplying a liquid phase from the chlorination furnace that is lower than the temperature of the molten salt in the molten salt electrolytic cell; if the molten salt electrolytic cell is within the desired reaction temperature, the temperature change caused by supplying the liquid phase can be suppressed by adjusting the temperature of the liquid phase supplied from the chlorination furnace to the desired reaction temperature.

In a molten salt electrolytic cell, inorganic chlorides are electrolyzed in molten salt to produce chlorine and magnesium. The chlorine produced at the anode is recovered and supplied to the chlorination furnace for reuse in the furnace. Magnesium may also liquefy in the molten salt and remain on the surface of the molten salt. In such cases, the liquefied magnesium can be recovered and cooled to obtain solid magnesium.

The chlorination process using a chlorination furnace and the preceding process are explained below.

(First embodiment)
The method for producing a metal according to a first embodiment of the present invention includes a chlorination step in which an anhydrous metal chloride is produced from a metal oxide using a mixed gas of carbon monoxide gas and chlorine gas. The method may further include a gas reduction step in which carbon dioxide gas ( _CO2 ) emitted in the chlorination step is reduced to produce carbon monoxide gas (CO). A specific example will be described below in which the metal oxide is magnesium oxide (MgO) and the anhydrous metal chloride is anhydrous magnesium chloride ( _MgCl2 ).

(Chlorination process)
Fig. 1 is a diagram illustrating the configuration of an apparatus (chlorination furnace) for carrying out the chlorination step of this embodiment. As shown in Fig. 1, the apparatus (chlorination furnace) for carrying out the chlorination step has a reactor, and the reactor is equipped with a reaction section 1 (e.g., a reaction vessel) and a heating section H (e.g., a heater) for heating the reaction section 1.

The reaction unit 1 comprises a cylindrical main body 11, an upper lid 12 that closes the upper opening of the main body 11, and a lower lid 13 that closes the lower opening of the main body 11.

For example, when adding magnesium oxide to the reaction chamber 1, open the top lid 12, add the magnesium oxide, and then close the top lid 12.

Conversely, after processing, when removing the produced anhydrous magnesium chloride, open the bottom lid 13, remove the anhydrous magnesium chloride, and then close the bottom lid 13.

The main body 11 of the reaction unit 1 is connected to a gas supply pipe IN that supplies gas to the lower side and a gas exhaust pipe OUT that exhausts gas to the upper side.

The gas supply pipe IN is connected to a line for mixed gas (process gas) supplied from a gas mixer M that mixes carbon monoxide gas and chlorine gas, and a line for general gas (inert gases such as nitrogen gas and argon gas). Valve B1 can be controlled to switch the line supplied to the gas supply pipe IN. For example, general gas may be used when replacing the gas in the reaction chamber 1 before opening the upper lid 12 and lower lid 13.

The gas exhaust pipe OUT branches into two lines, one of which may be connected to a vacuum pump (not shown), and the other may be connected to gas treatment equipment (not shown) for gas recovery. The exhaust from the vacuum pump (not shown) may be sent to a detoxification device (e.g., a scrubber, etc.) that detoxifies chlorine gas and other gases, although this is not shown.

The gas treatment facility may mainly comprise a chlorine gas recovery section (chlorine gas recovery device) that recovers chlorine gas from the exhaust gas, and a carbon dioxide gas recovery section (carbon dioxide gas recovery device) that recovers carbon dioxide gas from the exhaust gas.

In addition, the gas exhaust pipe OUT may also be configured so that the choice of sending the exhaust to one line side (vacuum pump side) or the other line side (gas processing equipment side) can be made by controlling valve B2.

Prior to the chlorination step, a drying process may be carried out on the magnesium oxide. The drying process may be carried out, for example, by placing magnesium oxide in the reaction unit 1, closing the top lid 12 to seal the reaction unit 1, and then, without supplying gas from the gas supply pipe IN, connecting the gas exhaust pipe OUT to the vacuum pump side. While drawing a vacuum inside the reaction unit 1, the heating unit H is driven to heat the reaction unit 1 to a temperature of 400°C or higher.

In this way, by vacuum heating the magnesium oxide as a pretreatment before supplying the mixed gas (treatment gas) of carbon monoxide gas and chlorine gas in the chlorination process, it is possible to remove adsorbed water that has adsorbed to the surface of the magnesium oxide.

Alternatively, the magnesium oxide can be heat-treated and dried using a similar process in a heating furnace connected to the chlorination furnace.

The temperature of the subsequent chlorination treatment should be below the melting point of anhydrous magnesium chloride (714°C), so that anhydrous magnesium chloride is produced in solid form. For example, it is best to treat it at a temperature in the range of 500°C to 700°C.

Alternatively, an alkali metal or alkaline earth metal chloride (e.g., sodium chloride, potassium chloride, calcium chloride, etc.) can be added to the reactor along with magnesium oxide, and the magnesium oxide can be chlorinated in the molten salt of the chloride. In such cases, it is preferable to heat the reactor to a temperature above the melting point of the metal chloride salt added.

The temperature for the chlorination treatment is preferably 300°C or higher, and considering the reaction rate, a temperature range of approximately 500°C to 700°C is more preferable.

Therefore, if the temperature during vacuum heating of this magnesium oxide is set to a range of 500°C to 700°C, chlorination can begin simply by starting the supply of treatment gas, so the temperature during vacuum heating may be set to a range of 500°C to 700°C.

After vacuum heating for a predetermined time, valve B2 on the vacuum side line is closed to seal the reaction unit 1, and then the supply of treatment gas (a mixture of carbon monoxide gas and chlorine gas) begins through the gas supply pipe IN.

After that, when the pressure inside reaction section 1 reaches atmospheric pressure, valve B2 is controlled so that exhaust gas can be supplied from gas exhaust pipe OUT to the gas treatment equipment side, allowing exhaust gas to flow to the other line side (gas treatment equipment side).

In other words, a flow of treatment gas is created within the reaction unit 1 from the gas supply pipe IN toward the gas exhaust pipe OUT. Note that performing treatment while the gas is still flowing in this manner is sometimes called streamer treatment.

When magnesium oxide (metal oxide) is heated in a mixed gas of carbon monoxide gas and chlorine gas, the reaction of the following formula (1) occurs, producing anhydrous magnesium chloride (anhydrous metal oxide).
MgO+CO+Cl ₂ → MgCl ₂ +CO ₂・・・・・・・・・・・・(1)

Then, carbon monoxide gas and chlorine gas that did not contribute to the reaction, and carbon dioxide gas produced by the reaction, are discharged from the gas exhaust pipe OUT. The exhaust gas may be sent to the gas treatment equipment (not shown) described above.

In the gas processing equipment (not shown), chlorine gas is recovered in the chlorine gas recovery section, and the recovered chlorine gas may be reused as chlorine gas to be sent to the gas mixer M.

In addition, carbon dioxide gas may be recovered in the carbon dioxide gas recovery section, and the recovered carbon dioxide gas may be sent to the gas reduction process, which will be described later.

Furthermore, the remaining carbon monoxide gas is reused as carbon monoxide gas to be sent to the gas mixer M.

Once the production of anhydrous magnesium chloride is complete, the supply of process gas to reaction unit 1 is stopped, valve B2 is controlled to stop the exhaust to the gas processing equipment (not shown), reaction unit 1 is sealed, heating of heating unit H is stopped, and valve B2 is then controlled to connect gas exhaust pipe OUT to the vacuum pump line, and reaction unit 1 is evacuated. Before evacuating, it is preferable to wait for the temperature inside reaction unit 1 to drop to at least 600°C or below. The reason for waiting for the temperature inside reaction unit 1 to drop to 600°C or below before evacuating is to prevent the produced anhydrous magnesium chloride from being discharged from reaction unit 1 due to the vacuum, as anhydrous magnesium chloride vaporizes at a temperature of around 650°C under vacuum.

Once the evacuation of reaction unit 1 is complete, valve B2 is again controlled to seal reaction unit 1, and then general gas (e.g., nitrogen gas) is supplied to reaction unit 1 through gas supply pipe IN. Once atmospheric pressure is reached, lower lid 13 is opened and anhydrous magnesium chloride is removed, completing the chlorination process.

The above is an example of a process when operating a chlorination furnace in batch mode. When operating a chlorination furnace in flow mode, it is preferable to charge an alkali metal or alkaline earth metal chloride (e.g., sodium chloride, potassium chloride, calcium chloride, etc.) along with magnesium oxide into the reactor and chlorinate the magnesium oxide in a molten salt of the chloride. In this case, as described above, magnesium oxide exists as a solid in the molten salt, and magnesium chloride exists in a liquid phase. Therefore, magnesium chloride can be supplied in liquid form by transferring the molten salt from the chlorination furnace to the molten salt electrolytic cell. It is preferable to install a filter immediately before the supply path from the chlorination furnace to the molten salt electrolytic cell to prevent the transport of solid magnesium oxide. Furthermore, in flow mode operation, the reaction gas can be supplied using a streamer or the like.

The metal production system according to this embodiment may further include a gas reduction device that reduces carbon dioxide gas discharged from a chlorination furnace to produce carbon monoxide gas; a heating furnace that dehydrates metal hydroxides to produce the metal oxides to be supplied to the chlorination furnace; a supply path that supplies the carbon monoxide gas from the gas reduction device to the chlorination furnace; and a supply path that supplies the metal oxides from the heating furnace to the chlorination furnace. By using such a system, carbon monoxide gas can be produced from carbon dioxide gas discharged from the chlorination furnace and reused in the chlorination process. Metal oxides can also be produced from metal hydroxides. Details of the heating furnace will be described later in the third embodiment.

(Gas reduction process)
Next, the gas reduction process using the gas reduction device will be described. The gas reduction process is a process in which carbon dioxide gas discharged in the chlorination process (i.e., carbon dioxide gas recovered in the carbon dioxide gas recovery section of the chlorination furnace) is reduced to produce carbon monoxide gas.

Note that various methods are known for reducing carbon dioxide gas to carbon monoxide gas, so here we will briefly explain the method that is preferred in this embodiment.

For example, as disclosed in Patent Document 2, there is a gas reduction process according to the reaction formula (2) below (so-called reverse shift reaction), that is, the gas reduction process is a process in which carbon dioxide gas is reduced using hydrogen gas as a reducing agent to produce carbon monoxide gas.
CO ₂ + H ₂ → CO + H ₂ O・・・・・・・・・・・・・・・・・・(2)

As shown in equation (1) above, in the chlorination process, an amount of carbon dioxide gas equivalent to the amount of carbon monoxide gas that contributed to the reaction is produced. Therefore, by producing an amount of carbon monoxide gas equivalent to the amount of carbon dioxide gas produced in the gas reduction process, a gas circulation loop with just the right amount of gas can be achieved between the chlorination process and the gas reduction process.

As a result, all carbon dioxide gas generated in the chlorination process can be converted into carbon monoxide gas in the gas reduction process and reused in the chlorination process, eliminating the need for disposal methods that release carbon dioxide gas into the atmosphere during the production operation of anhydrous metal chlorides.

Another method is to electrolyze carbon dioxide gas to produce carbon monoxide gas, as disclosed in Patent Document 3.

In this way, even when carbon dioxide gas is directly reduced by electrolysis, the amount of carbon dioxide gas input and the amount of carbon monoxide gas produced are roughly the same, so a gas circulation loop with no excess or deficiency between the chlorination process and the gas reduction process can be achieved.

On the other hand, as shown in Patent Document 1, when magnesium carbonate ore is chlorinated with carbon monoxide gas and chlorine gas, carbon dioxide gas is produced in an amount twice the amount of carbon monoxide gas used, as shown in the following formula (3).
MgCO ₃ +CO+Cl ₂ → MgCl ₂ +2CO ₂・・・・・・・・・(3)

For this reason, even if carbon dioxide gas were converted into carbon monoxide gas and reused, only half of the carbon dioxide gas produced could be used, with the remaining half having to be disposed of by means such as being released into the atmosphere.

Therefore, when magnesium oxide, a metal oxide, is treated with a mixed gas of carbon monoxide gas and chlorine gas, as in this embodiment, the amount of carbon monoxide gas used in the chlorination process and the amount of carbon monoxide gas produced in the gas reduction process are approximately the same, making it possible to create a gas circulation loop with just the right amount of carbon monoxide gas and carbon dioxide gas, and eliminating the need for disposal methods such as releasing carbon dioxide gas into the atmosphere.

Furthermore, in this embodiment, when magnesium oxide is converted into anhydrous magnesium chloride, only carbon monoxide gas is used as a reducing agent containing a carbon component. This has the advantage of preventing impurities resulting from the carbon-based solid reducing agent (e.g., carbon powder, impurities contained in coke) from being mixed into the produced anhydrous magnesium chloride, as occurs when a carbon-based solid reducing agent such as coke is used.

(Molten salt electrolysis process)
Next, the molten salt electrolysis process in the molten salt electrolytic cell will be described. The molten salt electrolysis process is a process for producing metals using the anhydrous metal chloride produced in the chlorination process as a raw material. Hereinafter, an example will be described in which magnesium is produced by electrolysis using the anhydrous magnesium chloride produced in the chlorination process as a raw material.

The molten salt electrolysis process may be, for example, a method used to produce magnesium. Briefly, in the molten salt electrolysis process, for example, magnesium chloride is heated to a temperature of around 700°C in a molten salt electrolysis tank (e.g., a brick furnace) to melt the magnesium chloride.

At least one pair of electrodes is installed inside the molten salt electrolysis cell. When a power source is connected between the electrodes and a voltage of 2.5 V or more is applied, chlorine gas is generated at the anode and magnesium is produced at the cathode.

The chlorine gas generated in the molten salt electrolysis process may be used in the chlorination process.

Second Embodiment
In the second embodiment, a method suitable for the case where the treatment temperature in the chlorination step is set to the melting point of anhydrous magnesium chloride or higher, or for the case where the chlorination step is carried out in molten salt will be described.

Figure 2 is a diagram illustrating the configuration of an apparatus for carrying out the chlorination step of the second embodiment. Note that the configuration of the apparatus shown in Figure 2 is similar in many respects to the configuration of the apparatus including the reactor described in the first embodiment, and therefore, a description of the same points as in the first embodiment may be omitted.

As shown in Figure 2, the reactor differs from the first embodiment in that the lower lid 13 (see Figure 1) is omitted and the main body 11 has a bottom, and is connected to a recovery section 2 that recovers anhydrous magnesium chloride via piping with valve B3, located slightly above the vertical middle of the main body 11.

The recovery section 2, which recovers anhydrous magnesium chloride, comprises a cylindrical main body 21 with a ceiling and an opening on the bottom, and a lower lid 22 that closes the opening on the bottom.

As mentioned above, the main body 21 of the recovery unit 2 is connected to the main body 11 of the reactor via a pipe having valve B3, and is also connected to a vacuum pump (not shown) via a pipe having valve B4. Although not shown, a gas pipe controlled by a valve may also be connected to the recovery unit 2 so that general gas can be supplied.

The chlorination treatment procedure is the same as in the first embodiment, except that valve B3 is closed to isolate reaction section 1 from recovery section 2, and the treatment temperature in the chlorination step is set to or above the melting point of anhydrous magnesium chloride, or the chlorination step is carried out in molten salt.

Specifically, after magnesium oxide is placed into reaction section 1, it is either vacuum heated to remove adsorbed water from the surface of the magnesium oxide, or heated in a separately provided heating furnace to remove adsorbed water from the surface of the magnesium oxide. After that, a mixed gas of carbon monoxide gas and chlorine gas (treatment gas) is supplied to reaction section 1 to produce anhydrous magnesium chloride.

It is preferable to add magnesium oxide in an amount that does not reach the position of the pipe with valve B3, which is connected to recovery section 2.

In this case, for example, it is preferable that the temperature from vacuum heating until the completion of the anhydrous magnesium chloride production reaction be set to a temperature above the melting point of the anhydrous magnesium chloride or above the melting point of the added alkali metal or alkaline earth metal chloride (e.g., sodium chloride, potassium chloride, calcium chloride, etc.). It is also preferable that the temperature be set to a temperature below 1200°C (e.g., around 1000°C).

In this case, the reaction equation itself is the same as that shown in Equation 1, but because the chlorination furnace is maintained under conditions that melt the anhydrous magnesium chloride, once the anhydrous magnesium chloride is produced, it becomes liquid. Since the boiling point of anhydrous magnesium chloride is 1412°C, it is preferable to maintain the temperature of the chlorination furnace at, for example, 1400°C or below, or 1200°C or below, to prevent the anhydrous magnesium chloride from boiling. The melting point of magnesium oxide is 2852°C.

Therefore, even if the treatment gas is supplied using a streamer as in the first embodiment, there is essentially no need to worry about anhydrous magnesium chloride being emitted as vapor.

In this way, the treatment gas is supplied so that it bubbles through the liquid of anhydrous magnesium chloride or the molten salt of the added alkali metal or alkaline earth metal chloride. This increases the probability of contact between the treatment gas and the pre-reacted magnesium oxide contained in the liquid, allowing the reaction to proceed efficiently.

After the chlorination treatment has been carried out for a predetermined time, the supply of treatment gas is stopped, heating by heating unit H is stopped, reaction unit 1 is left sealed, and it is waited for the temperature inside reaction unit 1 to drop, preferably to a temperature below 600°C.

While waiting for this temperature to drop, valve B4 is opened and the recovery unit 2 is evacuated using a vacuum pump until the internal pressure reaches, for example, 10 Pa or less. Once the evacuation is complete, valve B4 is closed, placing the recovery unit 2 in a vacuum-sealed state.

On the other hand, when the temperature inside reaction unit 1 drops below 600°C, a vacuum is also drawn inside reaction unit 1, for example, until the pressure reaches 10 Pa or less, and reaction unit 1 is once again sealed (vacuum sealed).

Then, valve B3 is opened to connect reaction section 1 and recovery section 2, and anhydrous magnesium chloride is supplied from reaction section 1 to recovery section 2. If no alkali metal or alkaline earth metal chloride has been added to reaction section 1, anhydrous magnesium chloride can be supplied to recovery section 2, for example, by operating heating section H and raising the temperature within reaction section 1 to a temperature at which the anhydrous magnesium chloride vaporizes. Note that if the anhydrous magnesium chloride is in a vacuum state, heating it to a temperature above 650°C, for example, around 700°C, will vaporize the anhydrous magnesium chloride.

In this case, the vaporized anhydrous magnesium chloride flows into recovery section 2, where it returns to a liquid or solid state within recovery section 2, which is at a temperature lower than the vaporization temperature. As a result, the anhydrous magnesium chloride is no longer in a gaseous state, the pressure in recovery section 2 decreases, and gaseous anhydrous magnesium chloride flows in succession from reaction section 1, and anhydrous magnesium chloride is recovered in recovery section 2.

Although not shown in the figure, the piping containing valve B3 is equipped with a heating mechanism that keeps the anhydrous magnesium chloride warm (heats it) inside to prevent it from solidifying.

Once the recovery of anhydrous magnesium chloride is complete, valve B3 is closed, heating unit H is stopped, and ordinary gas (e.g., nitrogen gas) is supplied into recovery unit 2 to restore atmospheric pressure within recovery unit 2. Lower lid 22 is then opened, and the anhydrous magnesium chloride is removed from recovery unit 2, completing the chlorination process.

In this embodiment, carbon dioxide gas is also generated during the chlorination process, but this generated carbon dioxide gas is recovered and converted back into carbon monoxide gas in a gas reduction process, and this carbon monoxide gas is then used again in the chlorination process. This is the same as in the first embodiment, so further explanation will be omitted.

Furthermore, as mentioned above, when the produced anhydrous magnesium chloride is recovered as vapor, even if there is magnesium oxide that did not react, magnesium oxide has a high boiling point and does not vaporize, so there is the advantage that anhydrous magnesium chloride can be recovered with almost no magnesium oxide contamination.

Although the above describes an example of a process for recovering anhydrous magnesium chloride as vapor, recovery of the anhydrous magnesium chloride from reaction section 1 to recovery section 2 may be carried out in liquid form. That is, recovery section 2 may be supplied with a molten salt of anhydrous magnesium chloride, or a mixture of a molten salt mixed with an alkali metal or alkaline earth metal chloride, in the liquid phase. Supplying the liquid phase to recovery section 2 in this way also makes it possible to perform flow-type operation.

(Third embodiment)
Although Japan is said to be poor in natural resources, magnesium resources are abundant in seawater. For example, when bittern water concentrated using the ion exchange membrane permeation method is treated with alkali, magnesium hydroxide (Mg(OH) ₂ ), a metal hydroxide, is obtained. Furthermore, when magnesium hydroxide is heated to several hundred degrees Celsius, a dehydration reaction occurs and it becomes magnesium oxide, a metal oxide.

Alkali treatment is a process in which, for example, calcium oxide (CaO), sodium hydroxide (NaOH), etc. are added to the bittern water to convert the magnesium chloride in the bittern water into magnesium hydroxide, which has low solubility, and precipitates it, which is then filtered and collected.

Therefore, by using magnesium oxide produced in this way, it is possible to secure a stable supply of raw materials that is not affected by global situations, etc.

For this reason, the magnesium oxide (metal oxide) used in the chlorination process of the previously described embodiments may be produced by a dehydration process in which magnesium hydroxide (metal hydroxide) is heated to dehydrate it. A case in which this dehydration process is included will be briefly described as a third embodiment. In the third embodiment, the metal production system according to this embodiment further includes a heating furnace that dehydrates the metal hydroxide and produces metal oxide to be supplied to the chlorination furnace. By using such a system, metal oxide can be produced from metal hydroxide.

The following describes a case where the metal production method of this embodiment includes a dehydration process in which a metal hydroxide is dehydrated to produce a metal oxide, and the metal oxide produced in the dehydration process is used in the chlorination process.

As explained earlier, magnesium oxide is not a material that forms hydrates, but water may adsorb to its surface.

For this reason, in the first embodiment, vacuum heating was described as a pretreatment for the chlorination process before the mixed gas (process gas) of carbon monoxide gas and chlorine gas was supplied. In this embodiment, metal oxide is produced from metal hydroxide, and this metal oxide is then dehydrated by this pretreatment in order to be used in the chlorination process.

In other words, if the dehydration process is carried out as a pretreatment before supplying the mixed gas (treated gas) for the chlorination process in the reactor where the chlorination process is carried out (for example, in reaction section 1) or in a heating furnace connected to the reactor, it will be possible to create an efficient production method that combines the dehydration process, chlorination process, and molten salt electrolysis in a single process. The reactor may also have a dehydration processing section that is capable of supplying dehydrated material to reaction section 1.

Therefore, the dehydration process in this embodiment can be carried out in the same manner as the vacuum heating process for removing adsorbed water from magnesium oxide in the first embodiment, and the subsequent chlorination process, gas reduction process, and molten salt electrolysis process can be carried out in the same manner as described in the first and second embodiments.

(Fourth embodiment)
In the third embodiment, a method was described in which magnesium hydroxide is obtained by alkaline treatment of bittern water, and then magnesium oxide is obtained by dehydrating the magnesium hydroxide. In the fourth embodiment, another method for obtaining magnesium hydroxide from seawater or bittern water will be described.

If seawater or bittern water is placed in an electrolysis furnace equipped with an anode and a cathode connected to a power source, and electricity is passed through to perform an electrolysis process in which direct electrolysis occurs, chlorine gas is generated from the anode and hydrogen gas is generated from the cathode, and this reaction reduces the hydrogen ions (H ⁺ ) and chlorine ions (Cl ^- ) in the seawater or bittern water. Note that a similar reaction occurs in a mixed water of seawater and bittern water, so a mixed water of seawater and bittern water may also be used.

As the hydrogen ions decrease, the proportion of hydroxide ions (OH ^- ) increases, making the solution alkaline, but as the chlorine ions decrease, the proportion of magnesium ions (Mg ²⁺ ), which are not electrically neutral, also increases, and these react to produce magnesium hydroxide. In other words, the hydroxyl groups react to compensate for the decrease in chlorine in magnesium chloride, producing magnesium hydroxide.

However, because magnesium hydroxide has low solubility in water, it precipitates in seawater or bittern water, making it easy to recover by filtration.

In this case, as mentioned above, chlorine gas is also generated from the anode, so if this chlorine gas is recovered using a chlorine gas recovery device, there is the advantage that the recovered chlorine gas can be used as chlorine gas in the chlorination process.

Therefore, the method for producing anhydrous metal chlorides includes an electrolysis step in which seawater, bittern water, or a mixture of seawater and bittern water is electrolyzed to produce magnesium hydroxide (metal hydroxide) and chlorine gas, and the magnesium hydroxide produced in the electrolysis step is used in the dehydration step described in the third embodiment. Furthermore, the chlorine gas produced in the electrolysis step is recovered in a chlorine gas recovery device, and the recovered chlorine gas is used in the chlorination step.

(Other forms)
As described in the fourth embodiment, in the electrolysis process in which seawater, bittern water, or a mixture of seawater and bittern water is electrolyzed, hydrogen gas (H ₂ ) is also produced in addition to magnesium hydroxide and chlorine gas (Cl ₂ ), and hydrogen chloride gas (HCl) can be produced by reacting the chlorine gas with the hydrogen gas (see formula (4)).
Cl ₂ +H ₂ → 2HCl・・・・・・・・・・・・・・・・・・・・・(4)

If the temperature is 300° C. or higher and 1200° C. or lower as shown in the chlorination step, the hydrogen chloride gas reacts quickly with magnesium oxide to produce magnesium chloride (see formula (5)).
MgO+2HCl → MgCl ₂ +H ₂ O・・・・・・・・・・・・(5)

Therefore, if hydrogen gas is recovered in a hydrogen gas recovery device in addition to the chlorine gas produced in the electrolysis process, and a gas production process is provided in which the chlorine gas and hydrogen gas are reacted to produce hydrogen chloride gas, magnesium chloride can be produced using hydrogen chloride gas instead of the mixed gas of carbon monoxide gas and chlorine gas used in the chlorination process described above.

As shown in formula (5), water ( _H2O ) is generated as a reaction by-product. However, as explained above, if the chlorination process is carried out using a gas blow-off process, that is, if hydrogen chloride gas is used, the generated water will continue to be exhausted from the reaction section 1, and anhydrous magnesium chloride can be obtained by continuing the process until the water runs out.

And because hydrogen chloride gas does not contain any carbon, no carbon dioxide is produced during this process.

For this reason, even if a method for producing anhydrous metal chloride includes an electrolysis process in which seawater, bittern water, or a mixture of seawater and bittern water is electrolyzed to produce magnesium hydroxide (metal hydroxide), chlorine gas, and hydrogen gas; a gas production process in which chlorine gas and hydrogen gas are reacted to produce hydrogen chloride gas; a dehydration process in which magnesium hydroxide (metal hydroxide) is dehydrated to produce magnesium oxide (metal oxide); and a chlorination process in which magnesium oxide (metal oxide) is heated to 300°C or higher and 1200°C or lower in hydrogen chloride gas to produce anhydrous magnesium chloride (anhydrous metal chloride), it is still possible to achieve a method for producing anhydrous magnesium chloride (anhydrous metal chloride) that does not require the release of carbon dioxide into the atmosphere.

Although the specific embodiment has been described above using an example in which the metal oxide is magnesium oxide and the anhydrous metal chloride is anhydrous magnesium chloride, the present invention is not limited to the specific embodiment. For example, the metal oxide may be titanium oxide (TiO) and the anhydrous metal chloride may be titanium tetrachloride ( _TiCl4 ).

In addition, in this embodiment, carbon monoxide gas and chlorine gas are mixed in a gas mixer M and supplied to the reaction section 1 in a uniformly dispersed state.

In this way, mixed gases that have been homogeneously dispersed and mixed by the Gas Mixer M do not separate due to differences in specific gravity. For example, oxygen gas and nitrogen gas are mainly present in air, but because these gases are homogeneously dispersed and mixed in air, gas separation due to specific gravity does not occur. As a result, just as people do not suffocate, the Gas Mixer M performs mixing that does not cause gas separation. The gas mixer itself is a device that is generally used when creating mixed gas cylinders to prevent gas separation within the cylinder.

For this reason, if carbon monoxide gas and chlorine gas are sent to the gas mixer M in a 1:1 ratio and the resulting homogeneously dispersed mixed gas is supplied to the reaction section 1, the mixed gas will come into contact with the magnesium oxide at a uniform reaction equivalence ratio (1:1), improving reaction efficiency.

However, the chlorination process itself can be carried out by combining carbon monoxide gas and chlorine gas and supplying them to the reaction section 1 without passing them through the gas mixer M, so it is not necessary to use the gas mixer M to create a mixed gas.

Furthermore, in the first embodiment, the anhydrous magnesium chloride was handled so as not to vaporize until it was extracted. However, the treatment temperature until the anhydrous magnesium chloride was produced may be set to a temperature below the melting point of the anhydrous magnesium chloride, and after the anhydrous magnesium chloride is produced, the anhydrous magnesium chloride may be recovered in the chlorination step as vapor recovery (sent in gaseous form from reaction section 1 to recovery section 2, where it is solidified and recovered) as in the second embodiment.

By doing this, as explained above, even if unreacted magnesium oxide is present, it is possible to obtain anhydrous magnesium chloride with reduced contamination by that magnesium oxide.

As such, appropriate modifications and improvements to the specific embodiments are also included within the technical scope of the present invention, and this will be clear to those skilled in the art from the claims.

1...Reaction section, 11...Main body section, 12...Top lid section, 13...Bottom lid section, 2...Recovery section, 21...Main body section, 22...Bottom lid section, B1, B2, B3, B4...Valves, H...Heating section, M...Gas mixer, IN...Gas supply pipe, OUT...Gas exhaust pipe.

Claims (4)

a chlorination furnace for chlorinating metal oxides at 300 to 700°C to produce anhydrous metal chlorides;
a molten salt electrolytic cell for electrolyzing the anhydrous metal chloride to produce a metal;
a supply path for supplying the anhydrous metal chloride from the chlorination furnace to the molten salt electrolytic cell;
a supply path for supplying chlorine gas generated by the electrolysis from the molten salt electrolytic cell to the chlorination furnace,
The anhydrous metal chloride is recovered from the chlorination furnace in a gaseous state ;
the metal oxide is magnesium oxide;
The anhydrous metal chloride is anhydrous magnesium chloride.
Metal manufacturing systems. a gas exhaust pipe for supplying exhaust gas from the chlorination furnace;
a gas treatment facility connected to the gas exhaust pipe, the gas treatment facility including: a carbon dioxide gas recovery unit that recovers carbon dioxide from the exhaust gas passing through the gas exhaust pipe; and a chlorine gas recovery unit that recovers chlorine gas from the exhaust gas;
a gas reduction device that reduces the carbon dioxide gas recovered from the exhaust gas to generate carbon monoxide gas,
The gas treatment facility supplies the chlorine gas recovered from the exhaust gas to the chlorination furnace.
The manufacturing system of claim 1 . a gas reduction device that reduces carbon dioxide gas discharged from the chlorination furnace to generate carbon monoxide gas;
a heating furnace for dehydrating the metal hydroxide to produce the metal oxide to be supplied to the chlorination furnace;
a supply path for supplying the carbon monoxide gas from the gas reduction device to the chlorination furnace;
a supply path for supplying the metal oxide from the heating furnace to the chlorination furnace;
The manufacturing system of claim 1 further comprising: chlorinating the metal oxide with a mixed gas of carbon monoxide gas and chlorine gas in the chlorination furnace to produce anhydrous metal chloride;
supplying the produced anhydrous metal chloride to the molten salt electrolytic cell;
electrolyzing the anhydrous metal chloride in the molten salt electrolytic cell to produce metal and chlorine gas;
supplying the produced chlorine gas to the chlorination furnace;
Including,
A method for manufacturing a metal using the manufacturing system according to claim 1.