Patent Application
20080217184
The present invention relates to a method and an apparatus for producing metallic Ti through reduction by Ca, in which titanium tetrachloride (TiCl4) is reduced by Ca to produce the metallic Ti.
The Kroll method for reducing TiCl4 by Mg is generally used as a method for industrially producing the metallic Ti. TiCl4 is obtained by chlorinating titanium oxide (TiO2). In the Kroll method, the metallic Ti is produced through a reduction step and a vacuum separation step. In the reduction step, TiCl4 is reduced by Mg in a reactor vessel. In the vacuum separation step, unreacted Mg and magnesium chloride (MgCl2) formed as a by-product are removed from the sponge metallic Ti produced in the reactor vessel.
In the reduction step, the reactor vessel is filled with molten Mg, and the TiCl4 liquid is supplied from above to a liquid surface of the molten Mg. This allows TiCl4 to be reduced by Mg near the liquid surface of the molten Mg to generate the granular metallic Ti. At the same time, molten MgCl2 which is of the by-product is generated near the liquid surface. The generated metallic Ti sequentially moves downward. Because a specific gravity of the molten MgCl2 is larger than that of the molten Mg, the molten MgCl2 also moves downward, and the molten Mg comes up to the liquid surface instead. The molten Mg is continuously supplied to the liquid surface by the specific-gravity difference substitution, and the reduction reaction of TiCl4 proceeds continuously.
In the metallic Ti production by the Kroll method, although a high-purity product is produced, production costs increase and products become remarkably expensive. One of factors of the increased production costs is some difficulty in enhancing a feed rate of TiCl4. The following items (a) to (c) can be cited as the reason why the feed rate of TiCl4is restricted.
(a) In order to improve productivity in the Kroll method, it is effective to enhance the feed rate of TiCl4, i.e., to enhance an amount of molten Mg supplied to the liquid surface per unit area or unit time. However, when the feed rate of TiCl4 is excessively enhanced, the rate of the specific-gravity difference substitution cannot respond to the reaction rate, MgCl2 remains on the liquid surface, and TiCl4 is supplied to the MgCl2, which reduces utilization efficiency of TiCl4. That is, the supplied TiCl4 becomes unreacted lower chloride gases (referred to as “unreacted gases”) such as an unreacted TiCl4 gas and an unreacted TiCl3 gas, and the unreacted gases are discharged outside the reactor vessel, which reduces utilization efficiency of TiCl4. It is necessary to avoid the generation of such unreacted gases, because a rapid increase in inner pressure of the reactor vessel is associated with the generation of the unreacted gases. Accordingly, there is a limit of the feed rate of TiCl4.
(b) When the feed rate of TiC4 is enhanced, Mg vapor generated from the liquid surface of the molten Mg reacts with TiCl4 vapor to increase the amount of deposited Ti in the inner surface of the reactor vessel above the liquid surface of the molten Mg. On the other hand, the liquid surface of the molten Mg rises as the reduction of TiCl4 proceeds. Therefore, the Ti deposited on the inner surface of the upper portion of the reactor vessel is immersed in the molten Mg at a later stage of the reduction step, which causes the effective area of the liquid surface to be reduced to decrease the reaction rate. In order to suppress the decrease in reaction rate, it is necessary that the feed rate of TiCl4 be restricted to prevent the Ti deposition on the inner surface of the upper portion of the reactor vessel as much as possible.
Japanese Patent Application Publication No. 0H8-295955 proposes a method in which the reaction efficiency is enhanced by supplying the liquid TiCl4 in a dispersive manner to the liquid surface where the molten Mg exists, and thereby the Ti deposition is suppressed on the inner surface of the upper portion of the reactor vessel. However, the method proposed in Japanese Patent Application Publication No. 08-295955 is not enough to suppress the Ti deposition.
(c) In the Kroll method, because the reaction is performed only near the liquid surface of the molten Mg in the reactor vessel, an exothermic area is narrowed and a temperature rises locally. Therefore, cooling is hardly performed, which causes the feed rate of TiCl4 to be restricted.
Although the feed rate of TiCl4 is not directly affected, in the Kroll method, Ti generated in the granular form near the liquid surface of the molten Mg is aggregated because of wetting properties (adhesion properties) of the molten Mg, the Ti granules moves downward while aggregated, and the Ti granules are sintered to generate grain growth of the Ti granules by the heat generated from the molten melt during the downward movement. Therefore, it makes difficult to take out the generated Ti as fine particles to the outside of the reactor vessel to recover the generated Ti. In the Kroll method, the continuous production is difficult to perform, and the improvement of the productivity is blocked. This is because that Ti is produced as a sponge titanium in a batch manner in the reactor vessel.
With reference to the Ti production methods except for the Kroll method, for example, U.S. Pat. No. 2,205,854 describes that, in addition to Mg, Ca can be used as the reducing agent of TiCl4. U.S. Pat. No. 4,820,339 describes a method for producing Ti through the reduction reaction by Ca, wherein the molten salt of calcium chloride (CaCl2) is held in a reactor vessel, metallic Ca powders are supplied into the molten salt from above, Ca is dissolved in the molten salt, and TiCl4 gas is supplied from below to react the dissolved Ca with TiCl4 in the molten salt of CaCl2.
In the reduction by Ca, the metallic Ti is generated from TiCl4 by the reaction of the following chemical formula (i), and CaCl2 which is of the by-product is also generated at the same time:
TiCl4+2CaTi+2CaCl2 (i)
Ca has an affinity for Cl stronger than Mg has, and Ca is suitable for a reducing agent of TiCl4 in principle. Particularly, in the method described in U.S. Pat. No. 4,820,339, Ca is used while dissolved in molten CaCl2. When the reduction reaction by Ca is utilized in the molten CaCl2, compared with the Kroll method in which TiCl4 is supplied to the liquid surface of the reducing agent in the reactor vessel, an area (reaction field) where the reaction is created is enlarged, and the exothermic area is also enlarged, which facilitates the cooling. Accordingly, the feed rate of TiCl4 can be largely enhanced, and the improvement of the productivity can be also expected.
However, the method described in U.S. Pat. No. 4,820,339 is hardly adopted as the industrial Ti production method. In the method, because highly expensive metallic Ca powders are used as the reducing agent, the production cost becomes higher than that of the Kroll method.
U.S. Pat. No. 2,845,386 describes another Ti production method (Olsen method) in which TiO2 is directly reduced by Ca not through TiCl4. The method is a kind of oxide direct-reduction method. Although the method is highly efficient, the oxide direct-reduction method is not suitable to produce a high-purity Ti because it is necessary to use expensive high-purity TiO2.
An object of the present invention is to provide a method and an apparatus for economically producing a high-purity metallic Ti with high efficiency without using an expensive reducing agent.
In order to achieve the above object, the inventors consider that the reduction of TiCl4 by Ca is indispensably required, and the inventors study the method for utilizing Ca dissolved in the molten salt of CaCl2 as described in U.S. Pat. No. 4,820,339.
In the method described in U.S. Pat. No. 4,820,339, Ca in the molten salt is consumed in the reduction reactor vessel as the reaction expressed by the chemical formula (i) proceeds, and it is necessary to continuously supply the metallic Ca powders to the reduction reactor vessel to replenish the consumed Ca.
However, in order to industrially establish the method for producing Ti through reduction by Ca, the inventors proposes a method for generating Ca by electrolysis of the molten CaCl2 liquid in an electrolytic cell to supply the CaCl2 liquid containing Ca to the reaction tank in consideration of the fact that it is necessary that Ca consumed by the reduction reaction is economically replenished into the molten salt, i.e., it is necessary that Ca is replenished at low costs.
That is, when the molten CaCl2 liquid is electrolyzed in the electrolytic cell, electrode reactions expressed by the following chemical formulas (ii) and (iii) proceed to generate a Cl2 gas near the surface of an anode while Ca is generated near the surface of a cathode, which allows the Ca concentration to be increased in the electrolytic bath salt (molten CaCl2 liquid) near the cathode. Therefore, the molten CaCl2 liquid containing the high-concentration Ca near the cathode is deposited on and adheres to a metal plate, net, or wire having a temperature lower than a bath temperature, and the molten CaCl2 liquid is transported into the reaction tank, which allows Ca consumed for the reduction of TiCl4 to be replenished as needed. Therefore, the replenishment of the metallic Ca from the outside or the extraction of the metallic Ca is not required, which allows the metallic Ti to be economically produced.
Anode: 2Cl−2e·+Cl2 (ii)
Cathode: Ca2++2e·Ca (iii)
The present invention is made based on the above consideration, and the summary of the present invention resides in (1) a Ti production method and (2) a production apparatus in which the Ti production method is implemented.
(1) A first aspect of the present invention provides a method for producing Ti through reduction by Ca, the method including: a Ti generation step wherein TiCl4 is supplied to a reaction tank to generate Ti in a molten salt while the molten salt is retained in the reaction tank, the molten salt containing CaCl2, the Ca being dissolved in the molten salt; an electrolytic step wherein a molten salt is electrolyzed in an electrolytic cell to generate Ca on an cathode side while the molten salt is retained in the electrolytic cell, the molten salt containing CaCl2; and a Ca transportation step wherein the Ca generated in the electrolytic step is transported to the reaction tank while the Ca is deposited on and adheres to a continuum body in the electrolytic cell, the continuum body being movably constructed while part of the continuum body is immersed in the molten salt either within the reaction tank or electrolytic cell, and the transported Ca is caused to dissolve in the molten salt retained in the reaction tank.
In the Ti production method of (1), preferably the continuum body is caused to function as a cathode. Therefore, Ca can directly, electrolytically be deposited on the surface of the continuum body.
In the Ti production method of (1), preferably a cathode is provided near part of the continuum body, the part of the continuum body being immersed in the molten salt.
In the Ti production method of (1), preferably the molten salt or the cathode in the electrolytic cell is kept at a temperature of a melting point of Ca or less. Therefore, Ca can surely electrolytically be deposited on the surface of the cathode.
In the Ti production method of (1), preferably Ti generated in the Ti generation step is extracted to the outside of the reaction tank along with the molten salt, Ti is separated, and the molten salt is transported to the electrolytic cell. Therefore, Ti can continuously be produced.
(2) A second aspect of the present invention provides an apparatus for producing Ti through reduction by Ca, the apparatus comprising: a reaction tank in which TiCl4 supplied to a molten salt is caused to react with Ca to generate Ti while the molten salt is retained, the molten salt containing CaCl2, the Ca being dissolved in the molten salt; an electrolytic cell which retains a molten salt containing CaCl2, the electrolytic cell including an anode and a cathode, the electrolytic cell performing electrolysis in the molten salt to generate Ca on the cathode side; and a continuum body which is movably constructed while part of the continuum body is immersed in the molten salt either in the reaction tank or electrolytic cell, the continuum body transporting the generated Ca to the reaction tank while Ca is deposited on and adheres to the part immersed in the electrolytic cell, the continuums body causing the transported Ca to dissolve in the molten salt retained in the reaction tank.
In the Ti production apparatus of (2), preferably the continuum body constitutes a cathode. Therefore, Ca can directly electrolytically be deposited on the surface of the continuum body.
In the Ti production apparatus of (2), preferably a cathode is provided near part of the continuum body, the part of the continuum body being immersed in the molten salt.
In the Ti production apparatus of (2), preferably the molten salt or the cathode in the electrolytic cell is kept at a temperature of a melting point of Ca or less. Therefore, Ca can surely electrolytically be deposited on the surface of the cathode.
In the Ti production apparatus of (2), preferably the Ti production apparatus includes means for separating Ti from the molten salt to transport the molten salt to the electrolytic cell after the Ti separation, the Ti being generated in the reaction tank and extracted to the outside of the reaction tank along with the molten salt. Therefore, Ti can continuously be produced.
The method for producing Ti through reduction by Ca according to the present invention is directed to a method for reducing TiCl4 in which the high purity material is easily obtained, so that the high-purity metallic Ti can be produced. Ca is used as a reducing agent, and TiCl4 is caused to react with Ca in the molten salt containing CaCl2, so that the feed rate of TiCl4 can be enhanced. Ca to be consumed in the reduction reaction can be replenished by the electrolysis of the molten CaCl2 liquid, so that the present invention has the economical advantage.
In addition, Ca is inferior to Mg in wetting properties (adhesion properties), and the Ti granules are generated in the molten CaCl2 liquid, so that the aggregation in the generated Ti granules and the grain growth by the sintering are significantly lessened. Therefore, the Ti granules can be taken out to the outside of the reactor vessel, and the Ti production can continuously be operated. The Ti production method of the present invention can preferably implemented with the Ti production apparatus of the present invention.
A method and an apparatus according to the present invention for producing Ti through reduction by Ca will be described below with reference to the drawings.
The continuum body 5 is a so-called endless belt, and the continuum body 5 is moved in an arrow direction of
In the example of
In order to implement the Ti production method of the present invention using the apparatus having the above configuration, at first the molten salt 3a in which CaCl2 is includes while Ca is dissolved is retained in the reaction tank 1, and TiCl4 is supplied into the reaction tank 1 to generate Ti in the molten salt 3a. That is, a “Ti generation step” is performed.
Usually the molten CaCl2 having a melting point of 780° C. is used as the molten salt 3a. However, preferably the temperature of the molten salt 3a is lowered because a lifetime of the reaction tank 1 is extended while the vaporization of Ca or the molten salt from the liquid surface is suppressed, when the temperature of the molten salt 3a is lowered. Therefore, desirably a mixed salt of CaCl2 and another salt is used as the molten salt 3a. For example, when the mixed salt of CaCl2 and NaCl is used as the molten salt 3a, the melting point of the molten salt 3a can be lowered to about 500° C. at the lowest temperature.
Desirably TiCl4 is supplied in a gas state to the molten salt 3a in the reaction tank 1 in consideration of contact efficiency between TiCl4 and Ca in the molten salt. However, the present invention is not limited to the gaseous TiCl4, but the liquid TiCl4 can be supplied on the liquid surface of the molten salt 3a or into the molten salt 3a. In the example of
The supply of TiCl4 into the reaction tank 1 causes the reaction of the chemical formula (i) to proceed to generate the metallic Ti. Although Ca in the molten salt 3a is consumed in association with the generation of Ti, Ca transported from the electrolytic cell 2 to the continuum body 5 is dissolved, and the molten salt whose Ca concentration is increased is supplied to the neighborhood of a front end of the TiCl4 supply pipe 7 through the opening in the lower portion of the partition wall 6a. Therefore, the reaction of the chemical formula (i) proceeds effectively.
Ti is generated in the form of granule or powder. The Ca is much inferior to Mg in wetting properties (adhesion properties), and Ca adhering to the deposited Ti granule is dissolved in CaCl2. Therefore, the aggregation of the generated Ti granules or the grain growth by sintering is hardly generated compared with the case of Mg.
Ti generated in the molten salt 3a can be separated from the molten salt 3a either inside the reaction tank 1 or outside the reaction tank 1. However, when Ti is separated from the molten salt 3a inside the reaction tank 1, the operation becomes a batch manner. In order to enhance the productivity, preferably Ti is extracted to the outside of the reaction tank 1 along with the molten salt 3a, and Ti is separated from the molten salt 3a outside the reaction tank 1. Although only the generated Ti can be extracted to the outside of the reaction tank 1, the operation becomes a batch manner because CaCl2 is continuously increased in the reaction tank 1.
The apparatus of
On the other hand, the molten salt 3b containing CaCl2 is also retained in the electrolytic cell 2, and the molten salt 3b is electrolyzed to generate Ca on the cathode side. That is, an “electrolytic step” is performed.
As described above, when the molten CaCl2 liquid is electrolyzed, Ca is generated near the surface of the cathode by the electrode reactions of the chemical formulas (ii) and (iii). The molten salt in which Ca is consumed by the reaction of the chemical formula (i) in the reaction tank 1 to lower the Ca concentration can also be used as the molten CaCl2 liquid.
The apparatus of
During the electrolysis of the molten CaCl2 liquid, there is a risk of generating a back reaction. In the back reaction, Ca generated on the cathode side is returned to CaCl2 by combining Ca and Cl2 generated on the side of the anode 4. However, in the apparatus of
As shown in
The continuum body 5 is slowly moved in the arrow direction by drive rollers 8a and 8b. Focusing attention on a portion of the continuum body 5 (or example, the portion designated by the letter A in
At this point, for example, when the mixed salt of CaCl2 and NaCl is used as the molten salt, the temperature of the molten salt is lowered to about 500° C. which is much lower than the melting point (839° C.) of Ca. As the result, Ca can be deposited efficiently and securely on the cathode.
Because the continuum body 5 (portion A) reaches the reaction tank 1 through the drive roller 8b while Ca and CaCl2 are deposited and adhere to the surface of the continuum body 5 (portion A), Ca is transported from the electrolytic cell 2 to the reaction tank 1 in association with the movement of the continuum body 5. When the deposited and adhered Ca comes into contact with the molten salt 3a in the reaction tank 1, Ca is gradually dissolved to increase the Ca concentration of the molten salt 3a in the reaction tank 1.
The metal plate, and the metal net or wire can be used as the continuum body 5. Molybdenum, tantalum, and titanium are suitable for the continuum body 5 because of excellent durability in the molten salts 3a and 3b. When the continuum body is made of metal, as shown in
The moving speed of the continuum body 5 can appropriately be adjusted as long as Ca generated in the electrolytic cell 2 is deposited on and adheres to the continuum body 5 without troubles, as long as Ca is transported into the reaction tank 1 without troubles, and as long as the transported Ca is dissolved in the molten salt 3a in the reaction tank 1 without trouble.
Desirably the molten salt 3a in the reaction tank 1 is kept at the temperature equal to or higher than the temperature of the molten salt 3b in the electrolytic cell 2. Therefore, solubility of Ca is enhanced to increase the Ca concentration of the molten salt 3a, and the TiCl4 reduction reaction of the chemical formula (i) can efficiently be performed. Additionally, Ca which is deposited on and adheres to the continuum body 5 can be dissolved in the molten salt 3a at a higher rate.
The apparatus of
When the operation (step) is incorporated into the Ti production method, CaCl2 which is of the by-product through the reduction of TiCl4 is introduced into the electrolytic cell 2 and electrolyzed in the electrolytic cell 2, Ca generated by the cathode is cyclically used as the reducing agent, and Cl2 generated by the anode is utilized in producing TiCl4. This enables the metallic Ti to be continuously produced only by replenishing TiO2 and C.
The temperature of the continuum body 5 immersed in the molten salt 3b in the electrolytic cell 2 is considerably lowered compared with the temperature of the molten salt 3b. Therefore, in the apparatus of
An electrode being made of a material and in a shape, which are commonly applied in the molten salt electrolysis such as CaCl2, can be used as the cathode 9. For example, an electrode made of a metal such as Fe and Ti can be used, and particularly a porous electrode is desirably used. Because a surface area per unit mass is increased, the electrolytic current can be enhanced to increase the amount of generated Ca.
Desirably the porous electrode is made of the metal such as Fe and Ti. The titanium oxide sintered material can also be used because the titanium oxide sintered material exhibits good conductivity at high temperatures.
When the cathode 9 is arranged near the continuum body 5 (i.e., near the portion where the continuum body 5 is immersed in the molten salt 3b), Ca generated near the surface of the cathode 9 is easily deposited on and adheres to the surface of the continuum body 5, which allows Ca to be transported from the electrolytic cell 2 to the reaction tank 1.
According to the method for producing Ti through reduction by Ca of the present invention, the feed rate of TiCl4 which is of the raw material can be enhanced, and the continuous production can be performed. Furthermore, the method of the present invention has an economical advantage because Ca consumed in a reduction reaction of TiCl4 can be replenished by the electrolysis of CaCl2. Therefore, the Ti production method of the present invention can efficiently be utilized as means for economically producing the high-purity metallic Ti, and the Ti production apparatus of the present invention can suitably be used for the Ti production method of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-317842 | Nov 2004 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP05/19655 | 10/26/2005 | WO | 00 | 3/28/2008 |
