Metal oxide reduction device and its use

Abstract

To provide a reductor capable of manufacturing a reduction body of a metal oxide with high productivity.SOLUTION: Using a reductor including a reaction unit having a reactor for reducing metal oxide particles with a hydrogen gas and circulation means for circulating a reduction gas containing the hydrogen gas to the reactor, the metal oxide particles are reduced with the reduction gas while being agitated and moved in a state where the reduction gas is circulated in a direction opposite to a movement direction of the metal oxide particles. The reactor has a cylindrical space as a reaction chamber, and an agitation movement means may be a screw housed in the cylindrical space. The metal oxide particles may be reduced at a temperature 853 to 1323K and a pressure 150 to 500kPa. An average particle diameter of the metal oxide particles may be 1 to 1000 μm. The reduction body may be an oxygen deficient type metal oxide particle.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a reduction apparatus capable of continuously producing a reduced metal oxide by reducing a metal oxide with hydrogen, and to uses thereof. [Background technology]

[0002] The construction of a lunar base is one of the important projects in space development, and water and oxygen are essential for manned activities on the lunar surface. Therefore, the development of a process for producing water and oxygen by hydrogen reduction of metal oxides such as ilmenite (iron ore), which is a lunar resource, has attracted attention. In addition, hydrogen reduction technology using a similar process can also be applied to the production of oxygen-deficient metal oxides by reducing metal oxides on Earth. Oxygen-deficient metal oxides have attracted attention as highly functional materials and are expected to be applied in a wide range of fields. A method for hydrogen reduction of metal oxides is known in which hydrogen molecules are brought into contact with metal oxides at temperatures of several hundred degrees Celsius. However, this method is prone to temperature unevenness in the metal oxide, which makes the reduction process uneven, making it difficult to efficiently produce the desired oxygen-deficient metal oxides with a high conversion rate.

[0003] Therefore, there is a need for a method for efficiently producing oxygen-deficient metal oxides by hydrogen reduction, and JP 2020-37491 A (Patent Document 1) discloses a method for producing oxygen-deficient metal oxides, which comprises filling a fluidized bed reactor with a metal oxide that has a Gibbs free energy change of 100 kJ / mol or less in the reduction temperature range, heating the fluidized bed reactor to a predetermined reduction temperature, continuously supplying a reducing gas containing a predetermined concentration of hydrogen gas to the fluidized bed reactor for a predetermined period of time, while discharging the generated water vapor from the fluidized bed reactor. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2020-37491 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, the production method using a fluidized bed reactor in Patent Document 1 does not allow continuous production of oxygen-deficient metal oxides, and is difficult to scale up, resulting in low industrial productivity. The uniformity of reduction is also insufficient, and it is difficult to produce a reduced product by reducing a metal oxide with a large Gibbs free energy change at a high conversion rate.

[0006] Therefore, an object of the present invention is to provide a reduction apparatus capable of producing a reduced metal oxide with high productivity, and uses thereof. [Means for solving the problem]

[0007] As a result of intensive research to achieve the above object, the present inventors have found that a reduced metal oxide can be produced with high productivity by moving the metal oxide particles while stirring them and reducing them with the reducing gas while circulating a reducing gas in a direction opposite to the direction of movement of the metal oxide particles, and have completed the present invention.

[0008] That is, the reduction apparatus of the present invention is a reduction apparatus including a reaction unit having a reactor for reducing metal oxide particles with hydrogen gas and a circulation means for circulating a reducing gas containing the hydrogen gas through the reactor, the reactor has a supply port for supplying the metal oxide particles; an outlet for recovering a reduced product obtained by reducing the metal oxide particles; a stirring and moving means for stirring and moving the metal oxide particles supplied from the supply port to the outlet in the presence of the reducing gas; an inlet for introducing the reducing gas; and an outlet for recovering or discharging exhaust gas after the reaction; The flow means is a flow means for flowing the reducing gas in a direction opposite to a moving direction of the metal oxide particles.

[0009] The reactor may have a cylindrical space as a reaction chamber, and the stirring and moving means may be a screw accommodated in the cylindrical space. The outer diameter of the screw may be 90% or more of the inner diameter of the reactor. The reaction unit may further include a heating means for heating the reactor. The inlet may be formed downstream of a region heated by the heating means in the moving direction of the metal oxide particles. The reducing gas may be hydrogen gas alone, or a mixed gas of hydrogen gas and an inert gas. The metal oxide particles may be reduced at a temperature of 853 to 1323 K and a pressure of 150 to 500 kPa. The metal oxide particles may have an average particle size of 1 to 1000 μm. The reduced body may be oxygen-deficient metal oxide particles. The reduction device may further include a circulation line for circulating the reducing gas contained in the exhaust gas to the reactor. The reduction device may further include an electrolysis unit for electrolyzing water contained in the exhaust gas into hydrogen gas and oxygen gas, and may circulate the hydrogen gas generated in the electrolysis unit to the reactor.

[0010] The present invention also includes a method for continuously producing a reduced product of a metal oxide by using the reduction device to move the metal oxide particles supplied from the supply port to the outlet while stirring, and recovering the reduced product from the outlet, in a state in which the reducing gas is circulated in a direction opposite to the direction of movement of the metal oxide particles. In this method, the reactor may be cylindrical, and the stirring and moving means may be a screw built into the cylinder, and the metal oxide particles may be moved while being stirred by rotation of the screw.

[0011] The present invention also includes a method for controlling the degree of oxygen deficiency in the metal oxide by adjusting at least one condition selected from the group consisting of a hydrogen gas concentration in the reducing gas, a flow rate of the reducing gas, a temperature, a pressure, a stirring speed, and a reduction time, in which the metal oxide particles supplied from the supply port are moved to the outlet while being stirred, and the reduced product is recovered from the outlet, using the reduction apparatus. Effect of the Invention

[0012] In the present invention, the metal oxide particles are stirred and moved while the reducing gas is circulated in the direction opposite to the movement direction of the metal oxide particles, and the metal oxide particles are reduced by the reducing gas. This allows the metal oxide reduction product to be continuously produced with a high conversion rate, and industrial productivity is high. In addition, the degree of oxygen deficiency in the metal oxide can be easily controlled by adjusting various conditions. Furthermore, the use of an electrolysis unit can generate not only water as a by-product but also oxygen, which is also effective for reducing metal oxides on the lunar surface. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic diagram illustrating an example of a reduction device of the present invention. [Diagram 2] FIG. 2 is an enlarged view for explaining a screw housed inside a reactor in the reduction apparatus of FIG. [Diagram 3] FIG. 3 is a graph showing the reduction state of tungsten oxide using the reduction device of Example 1. [Figure 4] FIG. 4 is a scanning electron microscope photograph of tungsten oxide particles, which are the raw material used in Example 1. [Diagram 5] FIG. 5 is a scanning electron microscope photograph of the oxygen-deficient tungsten oxide particles obtained in Example 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings as necessary.

[0015] 1, the metal oxide reduction device 1 includes a cylindrical reactor 4 for reducing metal oxide particles 2 with hydrogen gas. One end of this cylindrical reactor 4 is formed with a supply port 4a for supplying the metal oxide particles 2 to a reaction chamber, which is the internal space of the cylindrical reactor 4, and the metal oxide particles 2 are supplied from this supply port 4a to the reaction chamber by a hopper 3, which is a feeder of the metal oxide particles 2.

[0016] As shown in Fig. 2, the cylindrical reactor 4 has a screw 5 built in as an agitation and movement means inside the cylindrical interior. The screw 5 is in the shape of a propeller having blades 5b formed in a spiral shape around an axis 5a, and has a structure in which the blades 5b can be rotated around the axis 5a by a drive device 6. When the metal oxide particles 2 are supplied from the supply port 4a to the reaction chamber while being rotated by the drive device 6, the screw 5 moves the metal oxide particles 2 to the outlet 4b formed at the other end of the cylindrical reactor 4 while agitating the metal oxide particles 2 by the agitation force and propulsion force of the blades 5b.

[0017] Between the supply port 4a and the discharge port 4b, a heater 7 is disposed as a heating means for heating the cylindrical reactor 4. The reaction chamber of the cylindrical reactor 4 is heated by the heater 7, whereby the reduction of the metal oxide particles 2 can proceed. That is, in the reaction chamber of the cylindrical reactor 4, the region heated by the heating means becomes the main reaction chamber for causing the reduction reaction of the metal oxide particles 2, and the reduced product 2a reduced in the reaction chamber is recovered into a recovery container 8 from the discharge port 4b.

[0018] The reducing gas for reducing the metal oxide particles 2 is introduced from an inlet 4c formed downstream of the outlet 4b in the moving direction of the metal oxide particles 2, and is circulated in the reaction chamber of the reactor 4. The reducing gas introduced from the inlet 4c flows in a countercurrent manner with respect to the metal oxide particles 2 moving toward the outlet 4b by the screw 5. That is, the reducing gas flows in the reaction chamber of the cylindrical reactor 4 in a direction opposite to the moving direction of the metal oxide particles 2, and comes into contact with the metal oxide particles 2 moving while being stirred, thereby reducing the metal oxide particles 2. In the present invention, the reducing gas flows in a countercurrent manner with respect to the metal oxide particles 2 moving while being stirred by the screw 5, so that the reducing gas can be uniformly brought into contact with the metal oxide particles 2, and the metal oxide particles can be uniformly reduced at a high conversion rate.

[0019] The reducing gas is a mixed gas of hydrogen gas and argon gas, and is introduced into the inlet 4c through a reducing gas supply line 11. The reducing gas supply line 11 is a supply line formed by joining a hydrogen gas supply line 9a connected to a hydrogen cylinder 9 and an argon gas supply line 10a connected to an argon cylinder 10. The hydrogen gas supply line 9a and the argon gas supply line 10a are each equipped with flow control devices (mass flow controllers) 9b, 10b, and the ratio of hydrogen gas to argon gas can be controlled by adjusting the flow rates of the respective gases.

[0020] The reducing gas becomes exhaust gas after reducing the metal oxide particles 2 in the reaction chamber, and a part of the exhaust gas after the reaction is discharged through the discharge line 12 from the discharge port 4d formed between the region of the reaction chamber heated by the heating means (the region where the heating means is disposed) and the supply port 4a, but the remaining exhaust gas enters the supply device 3. For this reason, the upper part of the supply device 3 is also formed with the discharge port 3a for discharging the exhaust gas, and the exhaust gas remaining inside the supply device 3 is discharged through the discharge line 13 from the discharge port 3a. The exhaust gas that has passed through the discharge line 12 and the discharge line 13 join together in the discharge line 14 and is collected in the condenser 16. Furthermore, the discharge line 14 is equipped with a moisture meter 15, which can measure the amount of moisture in the exhaust gas. In the present invention, water (water vapor) generated by reduction is continuously discharged outside the reaction system and a non-equilibrium state is maintained within the reaction chamber system, making reduction possible even in systems where a reaction is thermodynamically difficult, and even difficult-to-reduc metal oxide particles can be easily reduced to the desired level of oxygen deficiency.

[0021] In the condenser 16, the recovered exhaust gas is cooled and separated into reducing gas and water. The separated water passes through a water supply line 17 and is recovered in an electrolysis unit 19, and the separated reducing gas passes through a reducing gas supply line 18 as a circulation line, merges with the reducing gas supply line 11, and is introduced into the cylindrical reactor 4 via an inlet 4c, where it is circulated.

[0022] In the electrolysis unit 19, the recovered water is electrolyzed into hydrogen gas and oxygen gas. The hydrogen gas generated by the electrolysis is circulated by joining the reducing gas supply line 11 through the hydrogen gas supply line 20 as a circulation line and being introduced into the cylindrical reactor 4 through the inlet 4c.

[0023] The reduction apparatus of the present invention is not limited to the reduction apparatus shown in Fig. 1. Details of each unit and raw material used in the reduction apparatus and reduction method of the present invention will be described below.

[0024] [Reaction unit] The reaction unit is not particularly limited as long as it includes a reactor for reducing metal oxide particles with hydrogen gas and a distribution means for circulating a reducing gas containing the hydrogen gas through the reactor, and the metal oxide particles can be moved while being stirred and reduced by the reducing gas while the reducing gas is circulated in a direction opposite to the direction of movement of the metal oxide particles.

[0025] (Reactor) The internal shape of the reactor (the internal space as the reaction chamber) may be selected according to the shape of the stirring and moving means as long as it can move the metal oxide particles while stirring them. In addition to a cylindrical shape, it may be a disk shape, a rectangular shape, or the like. However, a cylindrical shape is preferred from the viewpoint of efficiently and uniformly reducing the metal oxide particles.

[0026] The external shape of the reactor is not limited to a shape corresponding to the internal shape, and may be different from the internal shape, but the external shape is preferably the same as the internal shape from the viewpoint of productivity, etc. Therefore, the shape of the reactor is preferably cylindrical.

[0027] The locations of the supply port, outlet, introduction port and discharge port are not particularly limited as long as they are positions that allow the reducing gas to flow in a countercurrent manner relative to the moving metal oxide particles.

[0028] When the reactor is cylindrical, in FIG. 1 the inlet for the reducing gas is formed downstream of the outlet for the metal oxide particles in the direction of movement of the metal oxide particles, but this is not particularly limited and the inlet may be formed upstream. However, from the viewpoint of improving the efficiency and uniformity of the reduction, it is preferable to form the inlet downstream of the region where the heating means is disposed, it is even more preferable to form the inlet in the vicinity of the outlet, and it is even more preferable to form the inlet downstream of the outlet.

[0029] In addition, in FIG. 1, the exhaust gas outlet is formed between the region where the heating means is arranged and the supply port, but this is not particularly limited and may be formed upstream of the supply port in the direction of movement of the metal oxide particles. However, from the viewpoint of improving the efficiency and uniformity of the reduction, it is preferable to form it upstream of the region where the heating means is arranged, and from the viewpoint of efficiently recovering or discharging the exhaust gas, it is preferable to form it between the region where the heating means is arranged and the supply port.

[0030] (Agitating movement means) The stirring and moving means is not particularly limited as long as it can move the metal oxide particles from the supply port to the discharge port while stirring them, and is not limited to the screw shown in Fig. 1, but may be, for example, a vibrating conveyor, an eccentric rotary pump, a vibrating staircase (a step-like device capable of continuously moving the metal oxide particles to the lower step by vibration), etc. Among these, the screw is preferred because it can easily reduce the metal oxide particles uniformly.

[0031] The shape and size of the screw may be selected according to the properties of the target reduced product and are not particularly limited. From the viewpoint of uniformly reducing the metal oxide particles, the shape and size of the screw may be selected as follows.

[0032] The shape of the screw is not particularly limited as long as it is a propeller shape having helical blades centered on the axis, and the screw may have a different screw diameter on the upstream side from that on the downstream side. However, from the viewpoint of being able to uniformly stir the metal oxide particles, a shape in which the screw diameter on the upstream side is the same as that on the downstream side is preferable.

[0033] The groove depth of the screw (height of the blade relative to the shaft) (t) may be 5% or more of the outer diameter of the screw (screw diameter D), for example, 10 to 80%, preferably 20 to 60%, further preferably 30 to 50%, and further preferably 35 to 40%. If the groove depth is too shallow, there is a risk of reduced productivity decreasing.

[0034] The screw pitch P can be selected from the range of about 0.1 to 5 times the screw diameter D, and is, for example, 0.3 to 3 times, preferably 0.5 to 2 times, further preferably 0.8 to 1.5 times, more preferably 1 to 1.4 times, and most preferably 1.1 to 1.3 times. If the ratio of the pitch to the outer diameter is too small, the productivity of the reduced product may decrease, and if it is too large, it may become difficult to uniformly stir the metal oxide particles.

[0035] The inclination angle of the blade with respect to the axis of the screw may be 10° or more, for example, 20 to 80°, preferably 40 to 80°, and more preferably 60 to 70°. If the inclination angle is too small, the productivity of the reduced product may decrease, and it may become difficult to uniformly stir the metal oxide particles.

[0036] The screw diameter D may be 80% or more (particularly 90% or more) of the inner diameter of the reaction chamber (cylindrical space) in the cylindrical reactor, for example, 80 to 99%, preferably 90 to 98%, further preferably 92 to 97%, and further preferably 93 to 95%. If the ratio of the screw diameter D to the inner diameter of the reaction chamber is too small, there is a risk that the metal oxide particles cannot be uniformly stirred.

[0037] The screw rotation speed can be appropriately selected depending on the desired degree of oxygen deficiency and may be 0.1 rpm or more (particularly 0.4 rpm or more), for example, 0.1 to 11 rpm, preferably 0.3 to 3.0 rpm, and more preferably 0.4 to 1.1 rpm. If the rotation speed is too low, it may be difficult to uniformly stir the metal oxide particles.

[0038] In the present invention, the reduction time and the degree of oxygen deficiency can be adjusted by adjusting the size and shape of the screw and the rotation speed. In particular, since the rotation speed is inversely proportional to the reduction time, the reduction time can be easily adjusted by adjusting the rotation speed. Furthermore, since increasing the rotation speed also increases the stirring effect and makes it easier to reduce uniformly, the uniformity of reduction can be easily improved by increasing the rotation speed under conditions where the reaction time is short. Furthermore, when a long reaction time is required, it is also possible to adjust the stirring effect to a long time by selecting the shape of the screw.

[0039] The reduction time can be selected from the range of about 1 minute or more by adjusting the stirring and moving means as described above depending on the type of the target reduced product (e.g., the degree of difficulty of reduction). The specific reduction time may be, for example, 1 to 120 minutes, preferably 3 to 60 minutes, and more preferably 5 to 30 minutes.

[0040] (Heating means) The heating means is not particularly limited as long as it can heat the reaction chamber to the desired temperature, and may be a conventional heater such as an electric furnace or a combustion furnace.

[0041] The heating means is disposed in a predetermined region of the reactor and forms a main reaction chamber. The heating temperature by the heating means can be appropriately selected depending on the type of the target reductant, and can be selected, for example, from the range of about 753 to 1523 K, preferably 853 to 1323 K, and more preferably about 1023 to 1273 K.

[0042] In the present invention, the degree of oxygen deficiency of the resulting reduced product can be adjusted by adjusting the heating temperature with the heating means, and the degree of oxygen deficiency of the reduced product can be easily adjusted by combining this with other conditions such as the reduction time by the stirring and moving means.

[0043] (Means of distribution) The distribution means is not particularly limited as long as it can distribute the reducing gas countercurrently against the moving metal oxide particles, but from the viewpoint of simplicity, a means combining a cylinder filled with compressed reducing gas and a flow control device (mass flow controller) as shown in Fig. 1 is preferred. When the reducing gas is a mixed gas of hydrogen gas and an inert gas, the ratio of the mixed gas can be easily adjusted by controlling the flow rate of the gas supplied from each cylinder with a flow control device.

[0044] The pressure in the reactor may be adjusted by adjusting the circulation means. The pressure in the reactor can be appropriately selected depending on the type of the target reduced product, and can be selected, for example, from the range of about 100 to 1000 kPa, preferably 150 to 500 kPa, and more preferably 200 to 400 kPa.

[0045] The flow means may further include an automatic control means for automatically controlling the flow rate control device. The automatic control means may automatically control the flow rate control device to control the flow rate during the reaction or automatically control the flow rate according to the target reduced product. The automatic control means may be linked to the heater and / or the stirring and moving means, and by linking them, the heating temperature, pressure, stirring conditions, and reduction time in the reactor can be automatically controlled simultaneously.

[0046] [Supply unit and recovery unit] The reduction apparatus of the present invention may further include, in addition to the reaction unit, a supply unit for supplying metal oxide particles as a raw material and a recovery unit for recovering the reduced product. Both the supply unit and the recovery unit can use a conventional supply device and recovery container, and a hopper is generally used as the supply device because it can easily supply continuously.

[0047] [Condensing unit] The reduction apparatus of the present invention can continuously reduce metal oxide particles by providing the reaction unit with a stirring and moving means and a circulating means. Therefore, the reduction apparatus of the present invention is not limited to the reduction apparatus of Fig. 1 equipped with a condenser as a condensing unit, and may be a reduction apparatus that does not have a condensing unit. In other words, the exhaust gas generated by the reduction reaction in the reactor may be discharged or may be recovered in the condensing unit and reused for reduction.

[0048] In a reduction device equipped with a condensation unit, unreacted hydrogen gas can be reused, improving energy efficiency. That is, the exhaust gas generated in the reactor contains a reducing gas containing unreacted hydrogen gas and water vapor. Therefore, the condensation unit can separate the exhaust gas into reducing gas and water, and the separated reducing gas is returned to the reactor through a circulation line, so that the unreacted hydrogen gas can be reused and energy efficiency can be improved. A conventional condenser can be used as the condensation unit.

[0049] [Electrolysis unit] As described above, the reduction device of the present invention can continuously produce a reduced substance by the reaction unit, so the condensation unit is not an essential component. Therefore, the reduction device of the present invention is not limited to the reduction device of Fig. 1 equipped with a condensation unit and an electrolysis unit, and may be a reduction device not equipped with an electrolysis unit, for example, a reduction device not equipped with a condensation unit and an electrolysis unit, or a reduction device equipped with a condensation unit but not equipped with an electrolysis unit.

[0050] On the other hand, in a reduction device equipped with a condensation unit and an electrolytic decomposition unit, the water separated in the condensation unit can be decomposed into hydrogen gas and oxygen gas, so that the hydrogen gas separated in the electrolytic decomposition unit can be returned to the reactor via a circulation line, thereby making it possible to reuse the water vapor in the exhaust gas. A conventional electrolysis device can be used as the electrolysis unit. Furthermore, the electrolysis unit also generates oxygen gas, which is effective for reducing lunar soil on the lunar surface, where the supply of oxygen gas is important. Furthermore, since the supply of water is important as well as oxygen gas on the lunar surface, it is also possible to simultaneously generate water and oxygen gas by supplying a portion of the water generated in the condensation unit to the electrolysis unit.

[0051] [Raw materials] (metal oxide particles) In the reduction device of the present invention, even particles formed of difficult-to-reduc metal oxides can be uniformly reduced, so the type of metal oxide constituting the raw material metal oxide particles is not particularly limited. In terms of usefulness, for example, aluminum oxide (Al2O3, etc.), zirconium oxide (ZrO2, etc.), titanium oxide (TiO2, etc.), silica (SiO2, etc.), cerium oxide, zinc oxide (ZnO, etc.), vanadium oxide, iron oxide (FeO, Fe2O3, etc.), chromium oxide (Cr2O3, Cr3O4, etc.), molybdenum oxide (MoO3, etc.), niobium oxide (Nb2O5, etc.), tantalum oxide, tungsten oxide (WO3, WO2, etc.), manganese oxide, haumium oxide, etc. are commonly used as metal oxides. The metal oxide may be a composite metal oxide, for example, ilmenite (FeTiO3) contained in lunar soil. Particles formed of these metal oxides can be used alone or in combination of two or more.

[0052] Among these metal oxide particles, the reduction device of the present invention can uniformly reduce even difficult-to-reduc metal oxide particles, and is therefore suitable for difficult-to-reduc metal particles such as zirconium oxide, titanium oxide, niobium oxide, chromium oxide, tungsten oxide, etc. Furthermore, since it produces water and oxygen, it can also be used to reduce metal oxide particles on the lunar surface, and therefore iron oxide and ilmenite can also be suitably used.

[0053] The average particle size of the metal oxide particles can be appropriately selected depending on the reaction conditions and is not particularly limited, but is, for example, 1 to 1000 μm, preferably 2 to 100 μm, further preferably 3 to 70 μm, more preferably 5 to 50 μm, and most preferably 10 to 30 μm, from the viewpoint of production efficiency of the reduced product, etc. If the particle size is too small, there is a risk that the handling properties will decrease, and if it is too large, there is a risk that it will be difficult to reduce uniformly.

[0054] In this specification and claims, the average particle size of the metal oxide particles can be measured by a conventional method, for example, it means the median particle size (D50) measured on a volume basis using a laser diffraction particle size distribution analyzer.

[0055] The supply amount of the metal oxide particles is, for example, 1.0 to 58 g / min, preferably 1.0 to 20 g / min, more preferably 2.0 to 10 g / min, and even more preferably 2.5 to 5.8 g / min. If the supply amount is too small, the productivity of the reduced product may decrease, and if the supply amount is too large, it may become difficult to reduce uniformly.

[0056] (reducing gas) The reducing gas may contain hydrogen gas, and may be hydrogen gas alone or a mixture of hydrogen gas and an inert gas. When a mixture of hydrogen gas and an inert gas is used as the reducing gas, the degree of reduction of the metal oxide particles can be easily adjusted by adjusting the hydrogen gas concentration in the reducing gas. Examples of the inert gas include nitrogen gas, helium gas, and argon gas.

[0057] The concentration of hydrogen gas in the reducing gas can be selected from the range of 0.5 to 100% by volume, and is preferably 1 to 80% by volume, further preferably 1.5 to 50% by volume, further preferably 2 to 30% by volume, and most preferably 3 to 10% by volume. If the hydrogen gas concentration is too low, there is a risk of the productivity of the reduced product decreasing.

[0058] The flow rate of the reducing gas is, for example, 1 to 100 L / min, preferably 2 to 50 L / min, further preferably 3 to 30 L / min, more preferably 5 to 20 L / min, and most preferably 8 to 15 L / min. If the flow rate is too low, the productivity of the reduced product may decrease, whereas if the flow rate is too high, it may become difficult to adjust the degree of oxygen deficiency.

[0059] In this specification and claims, the hydrogen gas concentration in the reducing gas and the flow rate of the reducing gas refer to the volume ratio at atmospheric pressure and 0°C.

[0060] [Reduced form] In the reduction apparatus of the present invention, the metal oxide particles can be easily reduced with a high conversion rate, and the oxygen deficiency of the resulting reduced product can be easily controlled by adjusting reaction conditions such as the hydrogen gas concentration in the reduction gas, the flow rate of the reduction gas, the temperature, the pressure, the stirring speed, and the reduction time. Therefore, in the method for producing a reduced product using the reduction apparatus of the present invention, both metal particles and oxygen-deficient metal oxide particles can be produced as the reduced product. In addition, even if the reduced product is a difficult-to-reduc metal oxide particle such as oxygen-deficient tungsten oxide particles, a uniform reduced product can be easily produced. Furthermore, in the production method of the present invention, the reduced product can be continuously produced, and not only can the desired oxygen deficiency be easily adjusted by changing the flow conditions of the reduction gas and the shape of the stirring and moving means, but the process can also be easily scaled up by enlarging the shape of the reactor that houses the stirring and moving means. In particular, the conversion rate of the resulting reduced product is about 100%, so that the desired reduced product can be obtained efficiently. EXAMPLES

[0061] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0062] Example 1 In the reduction apparatus shown in FIG. 1, the metal oxide particles were reduced to produce a reduced material without supplying the produced exhaust gas to a condensation unit (without recycling hydrogen gas).

[0063] In detail, tungsten oxide WO3 particles (manufactured by A.L.M.T. Corp., average particle size 20 μm) were used as the raw material metal oxide particles and were supplied to the reactor at a rate of 2.5 g / min to 5.8 g / min. As the reducing gas, a mixed gas of hydrogen gas and argon gas with a hydrogen gas concentration of 3 vol% (0°C) was used and the flow rate of the mixed gas was adjusted to 10 L / min.

[0064] The reactor used was a cylindrical reactor (NCF600 tube) with an inner diameter of 32.9 mm and an outer diameter of 50 mm, in which a screw (outer diameter 31 mm, shaft outer diameter 7 mm, pitch 38 mm, blade inclination angle 65°, blade thickness 6.5 mm, S55C screw) was housed, and an electric furnace (Asahi Rika Seisakusho Co., Ltd., "ARF1110-300") was used as a heater. As reaction conditions, the screw was rotated at a rotation speed of 0.3 to 1.1 rpm, the reaction tube inlet pressure was fixed at 300 kPa, the reduction temperature was changed in the range of 1053 to 1123 K, and the reduction time was changed in the range of 7 to 26 minutes, and the influence of each operation condition on the reduction reaction was examined.

[0065] The mole fraction of the reduced product obtained at a reduction temperature of 1073 K was calculated from the XRD analysis results and is shown in Figure 3. As is clear from the results in Figure 3, at a reduction time of 7 minutes, the main components were WO3, WO 2.9 , WO 2.72 At a reduction time of 26 minutes, the generation of WO2 and W was also confirmed. In other words, the degree of reduction can be controlled by manipulating the reduction time, and at a reduction time of 10 minutes, oxygen-deficient WO 2.72 The mole fraction of reached 0.95. The reduction time was inversely proportional to the screw rotation speed, and under conditions of short reaction times, the stirring effect of the screw in the reaction tube was enhanced, enabling more uniform reduction.

[0066] The XRD analysis was performed using an X-ray diffraction device ("SmartLab" manufactured by Rigaku Corporation).

[0067] Figure 4 shows a cross-sectional SEM image of the raw material WO3 particle, and Figure 5 shows a cross-sectional SEM image of the reduced product at 1123K for 7 minutes. The molar fraction of WO3 after reduction was 1.01% by XRD. 2.72 The cross-section of the raw material particles showed cracks inside the particles, but no fine gaps were observed throughout the particles. On the other hand, the reduced material after reduction showed fibrous crystal growth throughout. WO 2.72 The anisotropic growth behavior of WO has been reported by Y. Sun, et al., Electrochim. Acta, 187, 329-339 (2016), and the results are consistent with this behavior. That is, the main component at a reduction time of 7 minutes was WO 2.72 It was confirmed that the reaction had progressed to the inside of the particles. [Industrial Applicability]

[0068] The reduction device of the present invention can be used to reduce metal oxides, and among the resulting reduced products, oxygen-deficient metal oxides can be used as various semiconductor materials such as photocatalysts and negative electrode materials for lithium-ion batteries. In addition, since the reduction device of the present invention produces water as a by-product in addition to the reduced products, it can also be used as a plant that generates water using lunar soil. [Explanation of symbols]

[0069] 1...Reducing device 2...Metal oxide particles 3... Feeder (hopper) 4. Reactor 4a…Supply port 4b...Outlet 4c...Inlet 4d…Discharge port 5...Moving stirring means (screw) 6. Drive unit 7...Heating machine 8. Collection container

Claims

1. A reduction apparatus including a reaction unit having a reactor for reducing metal oxide particles with hydrogen gas and a circulation means for circulating a reducing gas containing the hydrogen gas through the reactor, the reactor has a supply port for supplying the metal oxide particles; an outlet for recovering a reduced product obtained by reducing the metal oxide particles; a stirring and moving means for stirring and moving the metal oxide particles supplied from the supply port to the outlet in the presence of the reducing gas; an inlet for introducing the reducing gas; and an outlet for recovering exhaust gas after the reaction, Furthermore, the reactor has a cylindrical space as a reaction chamber, and the stirring and moving means is a screw housed in the cylindrical space, The outer diameter of the screw is 90% or more of the inner diameter of the reactor, The reduction device, wherein the circulating means is a circulating means for circulating the reducing gas in a direction opposite to a moving direction of the metal oxide particles.

2. 2. The reduction apparatus according to claim 1, wherein the outer diameter of the screw is 92 to 98% of the inner diameter of the reactor.

3. 3. The reduction apparatus according to claim 1, wherein the reaction unit further comprises a heating means for heating the reactor.

4. 4. The reduction apparatus according to claim 3, wherein the inlet is formed downstream of a region heated by the heating means in a moving direction of the metal oxide particles.

5. 5. The reduction apparatus according to claim 1, wherein the reducing gas is hydrogen gas alone or a mixed gas of hydrogen gas and an inert gas.

6. The reduction apparatus according to any one of claims 1 to 5, wherein the metal oxide particles are reduced at a temperature of 853 to 1323 K and a pressure of 150 to 500 kPa.

7. The reduction device according to any one of claims 1 to 6, wherein the metal oxide particles have an average particle size of 1 to 1000 µm.

8. The reduction device according to any one of claims 1 to 7, wherein the reductant is an oxygen-deficient metal oxide particle.

9. The reduction apparatus according to any one of claims 1 to 8, further comprising a circulation line for circulating the reducing gas contained in the exhaust gas to the reactor.

10. The reduction device according to any one of claims 1 to 9, further comprising an electrolysis unit that electrolyzes water contained in the exhaust gas into hydrogen gas and oxygen gas, and circulates the hydrogen gas generated in the electrolysis unit to the reactor.

11. 10. A method for continuously producing a reduced material of a metal oxide, using the reduction apparatus according to any one of claims 1 to 9, by moving the metal oxide particles supplied from the supply port to the outlet while stirring them, while circulating the reducing gas in a direction opposite to a direction of movement of the metal oxide particles, and recovering the reduced material from the outlet.

12. 10. A method for controlling a degree of oxygen deficiency in a metal oxide by adjusting at least one condition selected from the group consisting of a hydrogen gas concentration in the reducing gas, a flow rate of the reducing gas, a temperature, a pressure, a stirring speed, and a reduction time, the method comprising: moving the metal oxide particles supplied from the supply port to the outlet while stirring the metal oxide particles in the supply port and recovering the oxygen-deficient metal oxide particles as the reduced product from the outlet, using the reduction apparatus according to any one of claims 1 to 9;

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