Chemistry of inorganic compounds – Treating mixture to obtain metal containing compound – Group vb metal
Reexamination Certificate
2001-07-02
2003-09-02
Bos, Steven (Department: 1754)
Chemistry of inorganic compounds
Treating mixture to obtain metal containing compound
Group vb metal
C423S544000, C429S105000, C429S205000
Reexamination Certificate
active
06613298
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method of producing trivalent and tetravalent mixed vanadium compounds to be used as a redox flowbattery-use electrolyte and a method of producing a vanadium electrolyte.
2. Description of the Related Art
Demand for electric power in Japan increases continuously year after year, but a fluctuation in the demand for electric power also tends to become remarkable according to heightening of the industrial structure and an improvement in national living standard. For example, when an amount of the daytime demand for the electric power in summer is assumed to be 100, it is not more than 30 at dawn under the present conditions. Meanwhile, from the viewpoint of the supply of electric power, percentages of nuclear plants and new thermal power stations whose fluctuations in outputs are not desirable tend to increase, and thus the necessity of facilities for storing electric power is heightened. The current storage of electric power is executed by pumping power generation, but their site conditions become gradually severe. Because of these circumstances, various secondary batteries are being studied as a method of storing electric power as energy which does not cause environmental pollution and has high versatility. But in them, attention is paid to a redox flow secondary battery which is constituted so that two kinds of redox agents are brought into contact via a diaphragm.
The redox flow secondary battery is such that two kinds of aqueous solutions (electrolyte) of metallic ions whose oxidation number changes are prepared and they are stored as a positive electrode solution and a negative electrode solution in separate tanks, and the positive electrode solution and the negative electrode solution are supplied to a circulation type electrolytic cell having electrolytic cells of a structure such that the two kinds of electrolytes contact via a diaphragm by a pump, and the oxidation number of the metallic ions increases in one electrolytic cell and the oxidation number of the metallic ions decreases in the other electrolytic cell so that charging and discharging take place.
As the technique relating to such a redox flow battery, conventionally there are typically suggested techniques using an iron-chromium hydrochloric acid solution as an electrolyte (for example, Japanese Patent Application Laid-Open No. 60-148068 (1985), Japanese Patent Application Laid-Open No. 63-76268(1988)), and techniques using vanadium sulfate solution as an electrolyte (for example, Japanese Patent Application Laid-Open No. 4-286871 (1992), Japanese Patent Application Laid-Open No. 6-188005(1994)). However, as for an iron-chromium redox flow battery, preparation of an electrolyte is restricted from the viewpoint of mixing and solubility of electrolyte, and an output voltage is about 1 V, namely, an energy density is low. Further, there arise problems that a charging state between the positive electrode solution and the negative electrode solution becomes imbalanced, that chlorine gas is possibly generated from the positive electrode at the time of charging and the like.
On the contrary, as for the vanadium redox flow battery, its output voltage is 1.4 V, namely, high, and thus this battery has high efficiency and high energy density. For this reason, in recent years, development of a vanadium redox flow battery is particularly desired. The electrolyte of the redox flow battery is prepared in such a manner that tetravalent vanadium electrolyte is put into the positive electrode solution cell and trivalent vanadium electrolyte is put into the negative electrode solution cell. As for the state of the electrolyte at the time of charging and discharging, in charging, the tetravalent vanadium in the positive electrode solution is changed into pentavalent vanadium and the trivalent vanadium in the negative electrode solution is changed into bivalent vanadium. At the time when the electrolytes in the positive electrode and negative electrode solution cells are changed respectively into the pentavalent vanadium and the bivalent vanadium electrolytes, discharging starts to take place. Normally, as for the electrolyte, the tetravalent vanadium electrolyte is used for the positive electrode solution and the trivalent vanadium electrolyte is used for the negative electrode solution, but the positive electrode solution and the negative electrode solution may be mixed solution of tetravalent vanadium and trivalent vanadium in which their amounts are equal. Further, it is known that the positive electrode solution may be a mixed solution of tetravalent vanadium and trivalent vanadium in 2:1 proportion, and the negative electrode solution may be a mixed liquid of tetravalent vanadium and trivalent vanadium in 1:2 proportion.
In these solutions, since the solution of tetravalent vanadium and trivalent vanadium in 1:1 proportion can be directly used for the positive electrode solution and the negative electrode solution simultaneously, if the mixed vanadium containing tetravalent vanadium and trivalent vanadium in 1:1 proportion can be produced industrially and advantageously, industrial utility value is heightened. As such a method of producing a trivalent and tetravalent mixed vanadium compound, there suggest a method of producing a tetravalent and trivalent mixed electrolyte in such a manner that a vanadium compound is dissolved in a solvent under a condition of alkali or neutrality, vanadium ions are heated and polymerized under a condition of acidity so that polyvanadium oxide compound is separated, a part of the polyvanadium oxide compound is calcined in an atmosphere of inert gas or oxidation so that ammonium is removed, at least another part of the polyvanadium oxide compound is processed in an atmosphere of a reducing gas so that a trivalent vanadium compound is generated, vanadium pentoxide from the ammonia removing step is mixed and made to react with one part of the trivalent vanadium solution (Japanese Patent Application Laid-Open No. 08-148177 (1996)), a method of producing a trivalent and tetravalent vanadium electrolyte in such a manner that a reducing operation is performed on a compound containing pentavalent vanadium so that a vanadium compound with valence lower than pentavalent in which a heating peak of reoxidation is not more than 600° C. when this peak is measured by differential thermogravimetric analysis under airflow is generated, and an obtained reductant is mixed with the compound containing pentavalent vanadium so that the mixture is dissolved in a sulfuric acid solution (Japanese Patent Application Laid-Open No. 11-67257(1999)), and the like.
However, the above methods of producing the trivalent and tetravalent mixed vanadium are a method of producing vanadium pentoxide and trivalent vanadium separately from a starting material, mixing them in desired proportion, and obtaining trivalent and tetravalent mixed vanadium. Furthermore, since the vanadium compound which is dissolved in sulfuric acid is vanadium oxide, solubility with sulfuric acid tends to be deteriorated.
Therefore, it is an object of the present invention to provide a method of producing trivalent and tetravalent mixed vanadium compound having excellent solubility with sulfuric acid directly from tetravalent or pentavalent vanadium compound by using a reducing agent, and a method of producing a vanadium electrolyte.
SUMMARY OF THE INVENTION
In the above circumstances, as a result of enthusiastic examination by the inventors, it was found that a tetravalent or pentavalent vanadium compound, sulfur and concentrated sulfuric acid were kneaded in specified molar ratio into paste form, and the paste-form mixture was heated to a predetermined temperature so that a trivalent and tetravalent mixed vanadium compound could be produced directly from the tetravalent or pentavalent vanadium compound. In such a manner, the present invention was completed.
Namely, the present invention provides a trivalent and tetravalent mixed vanadium compound producing method of knead
Horikawa Ken
Kubata Michiru
Mita Muneo
Tanaka Yasuyuki
Tokuda Nobuyuki
Armstrong Westerman & Hattori, LLP
Bos Steven
Kansai Electric Power Co., Inc.
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