Fine particulate titanium dioxide, and production process and uses thereof
View Patent ↗Titanium dioxide having a ratio D top /D 50 of 1 to 3, between the maximum particle diameter D top and the average particle diameter D 50 , as determined based on observing the primary particles by a field emission-type scanning electron microscope. A production process of the titanium dioxide comprises performing a vapor phase process of reacting a titanium tetrachloride-containing gas with an oxidative gas to produce titanium dioxide, wherein when the titanium tetrachloride-containing gas and the oxidative gas are reacted by introducing each gas into a reaction tube, the temperature in the reaction tube is from 1,050 to less than 1,300° C.
1. Titanium dioxide having a ratio D top /D 50 of 1 to 3 between the maximum particle diameter D top and the average particle diameter D 50 , wherein the D top and D 50 are determined based on observing the primary particles by a field emission-type scanning electron microscope, and wherein the D 50 is from 5 to 200 nm and the content of chlorine in the titanium dioxide is 0.001 mass % to 0.2 mass %.
2. The titanium dioxide according to claim 1 , wherein the D top /D 50 is from 1 to 2.
3. The titanium dioxide according to claim 1 , wherein in the particle size distribution of primary particles observed by a field emission-type scanning electron microscope, the distribution constant n according to the following Rosin-Rammler formula is 3 or more:
R= 100exp(− bD n )
wherein D is a particle diameter, R is a percentage of the number of particles larger than D (particle diameter) based on the number of all particles, and n is a distribution constant.
4. A process for producing the titanium dioxide as set forth in claim 1 , the process comprising performing a vapor phase process of reacting a titanium tetrachloride-containing gas with an oxidative gas to produce titanium dioxide, wherein when the titanium tetrachloride-containing gas and the oxidative gas are reacted by introducing each gas into a reaction tube, the temperature in the reaction tube being from 1,050 to less than 1,300° C., wherein in the synthesis of titanium dioxide by the vapor phase process, the titanium dioxide produced by the reaction of titanium tetrachloride with the oxidative gas stays in the reaction tube for an average residence time of 0.005 to 0.08 seconds, and wherein in the introduction of the titanium tetrachloride-containing gas and the oxidative gas into the reaction tube, the ratio (S 1 /S 2 ) of the cross-sectional area (S 1 ) of the reaction tube and the sum total (S 2 ) of cross-sectional areas of the inlet tubes for the titanium tetrachloride-containing gas and the oxidative gas is from 1 to 2.5.
5. The production process of titanium dioxide according to claim 4 , wherein the ratio S 1 /S 2 is from 1 to 1.5.
6. The production process of titanium dioxide according to claim 4 , wherein in the synthesis of titanium dioxide by the vapor phase process, the flow rate of each of the titanium tetrachloride-containing gas and the oxidative gas at the inlet part into the reaction tube is from 30 to 150 m/s.
7. The production process of titanium dioxide according to claim 4 , wherein the titanium tetrachloride-containing gas and the oxidative gas each is preheated at 600° C. to less than 1,200° C. and then introduced into the reaction tube.
8. The production process of titanium dioxide according to claim 4 , wherein a reaction is performed between a raw material gas prepared by mixing an inert gas at a ratio of 100 mol or less per mol of titanium tetrachloride and an oxidative gas in an amount of 1 to 150 equivalents per mol of titanium tetrachloride.
9. The production process of titanium dioxide according to claim 4 , wherein the oxidative gas is a water vapor-containing oxygen gas.
10. The production process of titanium dioxide according to claim 9 , wherein the oxidative gas contains 0.1 mol or more of water vapor per mol of oxygen gas.
11. The production process of titanium dioxide according to claim 4 , wherein the titanium dioxide is dechlorinated by a dry dechlorination method to obtain titanium dioxide having a chlorine content of 0.2 mass % or less.
12. The production process of titanium dioxide according to claim 11 , wherein the dry dechlorination method is a method of heating the titanium dioxide at 200 to 550° C.
13. The production process of titanium dioxide according to claim 11 , wherein the dry dechlorination method is a method of heating a water vapor-containing gas at 200 to 1,000° C. while contacting the gas with the titanium dioxide.
14. The production process of titanium dioxide according to claim 12 , wherein the dry dechlorination method is a method of heating a water vapor-containing gas and the amount of the water vapor is, in terms of mass ratio, 0.01 to 1 based on the titanium dioxide.
15. The production process of titanium dioxide according to claim 13 , wherein the water vapor-containing gas is an air containing 0.1 vol % or more of water vapor.
16. The production process of titanium dioxide according to claim 11 , wherein in the dry dechlorination method, the dechlorination of the titanium dioxide is performed in a vessel under reduced pressure.
17. The production process of titanium dioxide according to claim 16 , wherein the pressure reduction degree inside the vessel under reduced pressure is 0.5 kPa or more.