Patent Application
20090286154
THIS invention relates to a process for the preparation of a crystalline vanadyl sulphate/vanadous sulphate material. It also extends to a process for preparing an electrolyte from such a crystalline vanadyl sulphate/vanadous sulphate material.
Vanadyl/vanadous sulphate solutions or electrolytes are becoming more and more important in various applications, including in the battery industry. A problem with the solutions, however, is that they are highly acidic and hazardous. Accordingly, there may be serious problems in transporting these products around the world.
U.S. Pat. No. 6,764,663 addresses this problem by providing a process in terms of which a vanadyl sulphate/vanadous sulphate solution is evaporated to produce vanadyl sulphate/vanadous sulphate crystals that are suitable for transport. These crystals can then be re-dissolved to form a reconstituted vanadyl sulphate/vanadous sulphate solution having substantially the same chemical composition as the starting material. The starting material is produced by forming a vanadous sulphate solution from a vanadyl sulphate solution electrolysed with sulphuric acid, and combining it with a further portion of vanadyl sulphate solution.
The present invention provides an alternative method of producing a crystalline vanadyl sulphate/vanadous sulphate material, and a method of producing an electrolyte from such vanadyl/vanadous sulphate material.
According to the invention a process for preparing a crystalline vanadyl sulphate/vanadous sulphate material includes the steps of—
The vanadium trioxide is preferably a commercial grade V2O3 powder having an equivalent V2O5 content of 110% to 125%, more preferably 115% to 122%, and most preferably 119% to 120%.
The sulphuric acid solution is preferably greater than 98% pure sulphuric acid.
The relative amounts of V2O3 and V2O5 are dependent on the required molar concentration in the vanadyl sulphate/vanadous sulphate material, but are generally in the order of 3 V2O3:1 V2O5 w/w. Thus, for a 2 molar final product, the ratio of V2O3 to V2O5 is about 13:4, and for a 1.6 molar product it is about 11:3.7.
The amount of sulphuric acid is also dependent on the molarity of the final product. Thus, for instance, for a 2 molar final product utilising 13 grams V2O3 and 4 grams V2O5, 26 ml of sulphuric acid (>98%) are required. Likewise, for a 1.6 molar final product utilising 11 grams of V2O3 and 3.7 grams of V2O5, 22.6 ml of sulphuric acid (>98%) are required.
A stabilising agent, preferably in the form of chemically pure phosphoric acid, is preferably used to stabilise the electrolyte produced from the crystalline vanadyl sulphate/vanadous sulphate material. The electrolyte can be produced by dissolving the crystalline material in boiling water, preferably in a 50:50 w/w ratio.
In one embodiment of the invention, the phosphoric acid is added to the sulphuric acid and slurried with the powder mixture prior to the slurry being heated to form the crystalline material. In this embodiment, an electrolyte can be produced simply by dissolving the crystalline material in boiling water, preferably in a 50:50 w/w ratio.
In an alternative embodiment, the crystalline material is first dissolved in boiling water to which the phosphoric acid is added to produce the electrolyte.
The reaction of the starting material and sulphuric acid, and where appropriate the stabilising agent, is carried out for a period of 30 to 240 minutes, preferably for about 45 to 60 minutes, and at a temperature of about 25° C. to 230° C., preferably a temperature of 200° C. to 220° C.
The crystalline material is typically cooled, crushed and then vacuum packed for delivery.
The process preferably takes place in an inert atmosphere, typically a sealed reaction chamber that is flooded with nitrogen, argon or other appropriate inert gas.
The mixing step of the starting mixture and sulphuric acid is preferably a homogenous mixing step, preferably using a high intensity mixer.
The crux of the invention is a process for the preparation of a crystalline vanadyl sulphate/vanadous sulphate material with a specified molar concentration, from a first starting material containing V2O5 and a second starting material containing V2O3, and a sulphuric acid solution.
The reaction proceeds according to the following formula:
V2O3+V2O5+4H2SO4→4VOSO4+4H2O
The reaction between the V2O5, V2O3 and sulphuric acid solution is highly exothermic, and requires careful control. In addition, it is very important that a homogenous mixture of V2O3 and V2O5 is provided, and that the whole of the homogenous mixture is contacted by the sulphuric acid, to avoid localised reactions taking place. The mixture of V2O3 and V2O5 is produced in a high intensity mixer, to which the sulphuric acid is added.
Regarding the reaction chamber, an inert atmosphere is required. The reaction chamber therefore needs to be sealed and is flushed with nitrogen, argon or other inert gas to maintain the inert atmosphere.
Once the V2O3/V2O5 mixture and sulphuric acid have been thoroughly mixed, the reaction mixture is heated at a temperature of no less than 25° C. and no more than 230° C. A temperature of 200 to 220° C. is preferred.
The heating step is continued for a period of 30 to 240 minutes, 45 to 60 minutes being preferred. The matured crystalline material is cooled, crushed and vacuum processed. It can then be reconstituted with water to produce the electrolyte.
It is also important that the electrolyte is stabilised. This is done by adding a stabilising agent, typically phosphoric acid, to the mixture prior to the maturing step or to the reconstituted vanadyl sulphate/vanadous sulphate solution. In the former case the electrolyte is simply produced by adding the crystalline material to boiling water in a ratio of about 50:50 w/w. In the latter case, the crystalline material is dissolved in boiling water and then the phosphoric acid is added to the electrolyte.
The advantages of the process of the invention include less environmental risk during transport, 75% less material to handle, hence lowering transport costs, and no electrolysis is required for polishing the crystalline material, hence reducing production time and costs.
Except for sodium and potassium, all other impurities can be reduced by filtration to conform to the required specification.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2005/08606 | Oct 2005 | ZA | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IB2006/002984 | 10/24/2006 | WO | 00 | 8/13/2008 |
