Titanium oxide production process

Details Titanium oxide production process Titanium oxide production process

2001-03-29

2004-04-27

Bos, Steven (Department: 1754)

Chemistry of inorganic compounds

Oxygen or compound thereof

Metal containing

C423S610000

Reexamination Certificate

active

06726891

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a process for producing titanium oxide. Specifically, the present invention relates to a process for producing titanium oxide suitable for use for a photocatalyst.
BACKGROUND OF THE INVENTION
It has been investigated that malodorous substances in air are removed and that window glass and driveway walls are cleaned by a photocatalytic activity shown by titanium oxide. Recently, a decomposition and removal method using visible light as a light source has been drawing attention owing to the wide usability and the convenience and, therefore, titanium oxide exhibiting a high photocatalytic activity by irradiation of visible light has been developed.
Although a variety of processes as a method for producing such a titanium oxide have been proposed, there are problems for the production such that a specific apparatus equipped with a vacuum container is required and that the obtained titanium oxide is insufficient in the photocatalytic activity. The above-described problems especially become obstacles when a titanium oxide having a small particle size is needed, for example, when the titanium oxide is used by being uniformly applied to automotive materials or construction materials such as window glass and driveway walls.
SUMMARY AND OBJECTS OF THE INVENTION
One of the purposes in the present invention is to provide a process for easily producing a titanium oxide showing a high photocatalytic activity by visible light radiation without using a specific apparatus equipped with a vacuum container. Preferably, the purpose of the present invention is to provide a process for easily producing a titanium oxide having a small particle size.
Inventors of the present invention have investigated the process for producing titanium oxide and completed the present invention.
That is, the present invention provides a process for producing a titanium oxide which comprises the steps of (i) reacting a titanium compound with ammonia in an amount exceeding the stoichiometric amount necessary to convert the titanium compound to a titanium hydroxide or reacting a titanium compound with a base at pH of from about 2 to about 7, to obtain a reaction product and (ii) calcining the obtained product.
DETAILED DESCRIPTION OF THE INVENTION
A titanium oxide in the present invention is produced by a process which comprises the steps of (i) reacting a titanium compound with ammonia in an amount exceeding the stoichiometric amount necessary to convert the titanium compound to a titanium hydroxide or reacting a titanium compound with a base at pH of from about 2 to about 7, to obtain a reaction product and (ii) calcining the obtained product.
A titanium compound to be used for the present invention may be any titanium compound capable of producing a titanium hydroxide by reaction with a base and examples thereof are titanium trichloride (TiCl
3
), titanium tetrachloride (TiCl
4
), titanium sulfate [Ti(SO
4
)
2
mH
2
O, 0≦m≦20], titanium oxysulfate [TiOSO
4
.nH
2
O, 0≦n<20], titanium oxychloride (TiOCl
2
) and the like. Among them, titanium oxysulfate is preferably used. A titanium compound having a high purity is preferably used and a titanium compound having a purity of 99% by weight or higher is more preferably used. By using a titanium compound with a high purity, a minute particulate titanium oxide exhibiting a high photocatalytic activity may be obtained. The purity of the titanium compound may be measured by JIS K8401-1992 method in the case of titanium trichloride and by JIS K8460-1992 method in the case of titanium tetrachloride. In the case of titanium oxysulfate, the purity thereof may be calculated by measuring the contents of TiO
2
and SO
3
as main components and the contents of impurities such as SiO
2
, P
2
O
5
and Nb
2
O
5
to obtain the purity in accordance with the following equation:
Purity(%)=[(
A
1
+A
2
)/(
A
1
+A
2
+A
3
+A
4
+A
5
+ . . . )]×100,
wherein A
1
and A
2
respectively represent the contents (% by weight) of TiO
2
and SO
3
and A
3
, A
4
, A
5
, . . . respectively represent the contents (% by weight) of impurities such as SiO
2
, P
2
O
5
and Nb
2
O
5
.
One (the first production process) of the production processes in the present invention comprises a step of reacting a titanium compound with ammonia in an amount exceeding the stoichiometric amount necessary to convert the titanium compound to a titanium hydroxide prior to the calcining step.
In the case that the titanium compound is reacted with ammonia in an amount exceeding the stoichiometric amount necessary to convert the titanium compound to a titanium hydroxide, the stoichiometric amount is practically equivalent to the amount (by mole) of (B×C) times as much as the molar amount of titanium compound to be converted, the (B×C) being calculated by multiplying the number B of the acid radicals contained in one molecule of the titanium compound by the valence C of the acid radicals. The stoichiometric amount necessary to convert the titanium compound to a titanium hydroxide is the amount of, for example, 3 times (by mole) in the case of using titanium trichloride, 4 times (by mole) in the case of using titanium tetrachloride, 4 times (by mole) in the case of using titanium sulfate, 2 times (by mole) in the case of using titanium oxysulfate, and 2 times (by mole) in the case of titanium oxychloride as much as the molar amount of titanium compound to be converted. In the first production process, a titanium compound is reacted with ammonia in an amount exceeding the stoichiometric amount and the amount of ammonia may be that of about 1.2 times or more, preferably about 2 times or more as much as the stoichiometric amount, and abut 20 times or less, preferably about 10 times or less as much as the stoichiometric amount.
The reaction of a titanium compound with ammonia may be carried out at about 70° C. or lower. The temperature is preferably about 40° C. or lower and more preferably about −5° C. or lower. The reaction may be carried out in a process comprising the steps of placing a titanium compound in a reaction container, adding ammonia, e.g. ammonia solution (ammonia water) while stirring them and mixing them, in a process comprising the steps of placing ammonia in a reaction container, adding a titanium compound while stirring them and mixing them, or in a process comprising the steps of simultaneously placing a titanium compound and ammonia in a reaction container and mixing them.
Another one (the second production process) of the production processes in the present invention comprises a step of reacting a titanium compound with a base at pH of from about 2 to about 7 prior to the calcining step. In this process, the pH is the pH value of the mixed solution or slurry of the titanium compound and the base. The reaction may be carried out thoroughly (from the starting to the finishing) at pH of from about 2 to about 7.
For this reaction, any process of converting a titanium compound to a titanium hydroxide may be employed. The rection may be conducted in a process comprising the steps of placing an aqueous medium in a reaction container and then supplying an aqueous solution of a titanium compound and a base to the reaction container while stirring them or in a process comprising a step of continuously supplying an aqueous medium, a titanium compound and a base to a reaction tube. The yield of titanium hydroxide may be about 90% or higher and preferably about 95% or higher. The reaction may be carried out at pH of about 2 or higher and at pH of about 7 or lower. When the pH of the reaction is higher than about 7, the particle size of the resulting titanium oxide, which is obtained by calcining the reaction product of titanium compound with base, tends to be large. The pH of the reaction is preferably about 2.5 or higher, more preferably about 3 or higher and is preferably about 5.5 or lower, more preferably about 5 or lower.
Examples of the base to be reacted with the tit

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