Process for producing ceramic powders, especially titanium dioxide useful as a photocatalyst

• US 5,698,177 A
• Filed: 06/08/1995
• Issued: 12/16/1997
• Est. Priority Date: 08/31/1994
• Status: Expired due to Fees

• Current Assignee: One World Technologies (Techtronic Industries Company Limited)
• Original Assignee: Universitã¤T Karlsruhe (Th), University of Cincinnati
• Inventors: Gutsch, Andreas, Fotou, George P., Pratsinis, Sotiris Emmanuel, Vemury, Srinivas
• Primary Examiner(s): BOS, STEVEN J
• Application Number:
  US08/488,694
• Time in Patent Office: 922 Days
• Field of Search: 423/613, 106/437
• US Class Current: 423/613
• CPC Class Codes: C01B 13/28 using a plasma or an electric discharge
• CPC Class Codes: C01B 21/06 Binary compounds of nitrogen with metals, with silicon, or with boron, or with carbon, i.e. nitrides; Compounds of nitrogen with more than one metal, silicon or boronazides C01B21/08
• CPC Class Codes: C01B 33/183 by oxidation or hydrolysis in the vapour phase of silicon compounds such as halides, trichlorosilane, monosilane
• CPC Class Codes: C01G 19/02 Oxides
• CPC Class Codes: C01G 23/07 Producing by vapour phase processes, e.g. halide oxidation
• CPC Class Codes: C01P 2002/54 one element only
• CPC Class Codes: C01P 2004/82 two phases having the same anion, e.g. both oxidic phases
• CPC Class Codes: C01P 2006/12 Surface area

Abstract

A gas phase process for the production of titanium dioxide powders having well-controlled crystalline and surface area characteristics is disclosed. In this process, which is preferably carried out in a laminar diffusion flame reactor, vapor phase TiCl₄ and oxygen are mixed in a reaction area which is heated externally. The titanium dioxide powder formed is then collected. It is preferred that the heat source used be a hydrocarbon fueled (e.g., methane) flame. Optionally, a vapor phase dopant (such as SiCl₄) may be added to the reaction mixture to desirably affect the physical properties of the titanium dioxide produced. In a particularly preferred embodiment, a corona electric field is positioned across the area where the combustion reaction takes place (i.e., the reaction area). High anatase, high surface area titanium dioxide powders made by this process are excellent photocatalysts. The products of this process and the use of those products as photocatalysts are also disclosed. This process is also useful for producing other ceramic powders (such as silicon dioxide and tin oxide), as well as pure metallic or alloy powders.

Claims

1. A process carried out in a flame reactor for preparing titanium dioxide powder comprising the steps of:

(a) mixing vapor phase TiCl₄ and O₂ in a reaction area;

(b) heating said mixture in said reaction area by a flame which is formed by combustion of a hydrocarbon fuel and which is located external to said reaction area; and

(c) collecting the titanium dioxide powder formed;

wherein across said reaction area is a corona electric field formed between two needle electrodes.

2. A process according to claim 1 wherein the flame reactor is a laminar diffusion flame reactor.

3. A process according to claim 2 wherein said vapor phase TiCl₄ is fed into the center core of said diffusion flame reactor.

4. A process according to claim 3 wherein said vapor phase TiCl₄ is formed by bubbling an inert gas through TiCl₄ liquid.

5. A process according to claim 4 wherein said gas is selected from the group consisting of argon, nitrogen, krypton, helium, chlorine, and mixtures thereof.

6. A process according to claim 5 wherein the gas flow rate of the TiCl₄ vapor is from about 100 to about 300 cm³ /min and the concentration of TiCl₄ entering the reactor is from about 7×

10^-5 to about 1×

10^-2 mol/min.

7. A process according to claim 6 wherein the O₂ is fed into a sleeve of said diffusion flame reactor adjacent to the center core.

8. A process according to claim 7 wherein the O₂ is introduced as air having a flow rate is from about 0.3 to about 5.5 l/min.

9. A process according to claim 3 wherein the fuel is fed into said diffusion flame reactor in a sleeve which surrounds the sleeves carrying the vapor phase TiCl₄ and the O₂.

10. A process according to claim 9 wherein the flow rate of said fuel into the reactor is from about 125 to about 400 cm³ /min.

11. A process according to claim 10 wherein the fuel is selected from the group consisting of methane, acetylene, propane, ethane, ethylene, and mixtures thereof.

12. A process according to claim 11 wherein the flame has a temperature of from about 1100 K to about 2000 K and is blue indicating substantially complete combustion of the fuel.

13. A process according to claim 12 wherein the fuel is methane and the carrier gas for TiCl₄ is argon.

14. A process according to claim 13 which is carried out at a temperature of from about 1100 to about 1500 K and a residence time in the reaction area of from about 0.075 to about 0.1 seconds.

15. A process according to claim 14 wherein the argon flow rate is from about 150 to about 250 cm³ /min and the TiCl₄ concentration in the reaction area is from about 1×

10^-4 to about 5×

10^-3 mol/min.

16. A process according to claim 1 wherein said two needle electrodes are horizontally positioned on opposite sides of the flame at a height above the mouth of the burner which corresponds to the hottest area of the flame.

17. A process according to claim 16 wherein the distance between the opposing tips of the electrodes is from about 30 to about 60 mm.

18. A process according to claim 17 wherein the electrodes are placed from about 0.5 to about 30 mm above the mouth of the burner.

19. A process according to claim 18 wherein the voltage of the electric field is from about 4 to about 12 kV.

20. A process according to claim 19 wherein the electric field is unipolar.

21. A process for preparing titanium dioxide powder comprising the steps of:

(a) mixing in a reaction area vapor phase TiCl₄, O₂ and a dopant selected from the group consisting of compounds of silicon, phosphorus, germanium, boron, tin, aluminum, niobium, chromium, silver, gold, palladium, and mixtures thereof;

(b) heating said mixture in said reaction area by a flame which is formed by combustion of a hydrocarbon fuel and which is located external to said reaction area; and

(c) collecting the titanium dioxide powder formed;

wherein across said reaction area is a corona electric field formed between two needle electrodes.

22. A process according to claim 21, which is carried out in a laminar diffusion flame reactor and wherein said dopant is selected from the group consisting of chlorides of silicon, phosphorus, germanium, boron, tin, aluminum, niobium, chromium, silver, gold, palladium, and mixtures thereof.

23. A process according to claim 22 wherein the dopant is silicon tetrachloride.

24. A process according to claim 23 wherein the reaction mixture contains from about 5% to about 10% SiCl₄ on a molecular basis compared to the amount of TiCl₄.