Chemistry of inorganic compounds – Treating mixture to obtain metal containing compound – Group ivb metal
Reexamination Certificate
1995-11-03
2002-06-04
Nguyen, Ngoc-Yen (Department: 1754)
Chemistry of inorganic compounds
Treating mixture to obtain metal containing compound
Group ivb metal
C423S076000, C423S077000, C423S492000, C423S610000
Reexamination Certificate
active
06399033
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application is a United States counterpart patent application to originating German Patent Application No. P4442783.2 filed Dec. 1, 1994, the disclosure of which is hereby incorporated by reference.
FIELD OF THE INVENTION
The process of the present invention relates to an improved process for the manufacture by the chloride process of titanium dioxide useable for pigments and other purposes. In such process, titanium dioxide—containing ore is reacted with chlorine to produce gaseous titanium tetrachloride. Then the titanium tetrachloride, after purification, is reacted or combusted with oxygen in a burner reactor unit or zone to produce highly pure titanium dioxide.
SUMMARY OF THE INVENTION
The present invention relates specifically to a process for the continuous production of titanium tetrachloride by chlorination of titanium-containing raw materials in the presence of coke at temperatures around 1000° C. in a reactor, which is normally in actual operation a fluidized-bed reactor. Discharged from the reactor are gaseous volatile metal chlorides and, in addition, finely divided bed material, in particular unreacted titanium dioxide (TiO
2
) and silica or quartz (SiO
2
) from the ore, and coke or carbon (C) which are entrained in the discharge gases. Cooling or quenching of the gas-solid mixture then occurs to approximately 150°-200° C., and the solid mixture is separated. This separated material has been long termed “cyclone dust”; for example a cyclone separator used with halide containing gases is shown in U.S. Pat. No. 4,125,385. This cyclone dust comprises condensed metal chlorides and the other solids including TiO
2
, C, and SiO
2
. The dust is then suspended in a liquid, and solid particles are classified in a single separation apparatus. Separate fractions are created and after drying and grinding, the titanium dioxide-rich fraction is returned to the reactor.
DESCRIPTION OF THE PRIOR ART
Titanium dioxide pigment is widely used in industry as an opacifying pigment for paints and paper coatings, and as a pigmentary agent for a wide variety of fibers and textiles. To create or enhance specially desired pigmentary properties for particular end uses, the pigment is conventionally coated or mixed with other substances, and subjected to a wide variety of treatments.
The production of titanium dioxide by vapor phase oxidation of titanium tetrachloride with oxygen, or an oxygen-containing gas, has been growing in importance compared with older processes in which titaniferous raw materials such as ores and/or slag were digested with mineral acids, preferably sulfuric acid.
The chemical stoichiometry of the chlorinating titanium dioxide process can be simply exemplified by the following equations wherein titanium dioxide is reacted with chlorine gas and carbon:
TiO
2
+2Cl
2
+C→TiCl
4
+CO
2
TiO
2
+2Cl
2
+2C→TiCl
4
+2CO
Among the reasons for growing acceptance of the chloride process is that in vapor phase titanium tetrachloride oxidation only solid and gaseous reaction products are generated. Thus, little or none dilute liquid waste acid is created, as in the sulfate process, requiring additional process steps and higher operating costs for re-concentration and treatment. Furthermore, the chloride process is more cost-efficient, and produces, in the view of many customers of titanium dioxide pigments, better quality titanium dioxide.
Titanium tetrachloride is the important initial raw material for the manufacture of titanium dioxide. As shown above, titanium tetrachloride is produced by the chlorination of titanium-containing raw materials in the presence of a carbon-containing compound. Suitable titanium-containing raw materials referred to as “ores” include natural and synthetic rutile, titanium-containing slags or other titanium-containing minerals, for example ilmenite. Carbon-containing compounds include anthracite coal and coke, for example petroleum coke.
The ore materials are chlorinated in a dispersed form at elevated temperatures. In the process, the metal oxides contained in the ore raw material are converted into the corresponding metal chlorides. Following the precipitation of low volatility metal chlorides and other impurities, as discussed below, from the exhaust gases of the chlorination, the highly volatile titanium tetrachloride is liquified by cooling in a condensation stage to approximately −20° C. and then reacted with oxygen at very elevated temperatures to produce pure titanium dioxide.
Titanium dioxide ore raw materials also contain silica compounds. Ilmenite, for example, contains on the average up to 3% by weight SiO
2
. The exhaust gas in addition to SiO
2
also can contain small amounts of silicon tetrachloride.
As a consequence of the increasing severity of regulations concerning purity of air and water and in view of the necessity to operate chemical processes as economically as possible, efforts in all chemical businesses throughout the world are being made to reduce the volume of industrial wastes and to recycle any reusable waste material as secondary raw material. It has become particularly important to the success of the chloride process of making titanium dioxide that both maximum use of the starting ore be achieved and that the amount and type of waste disposed is minimized. The use of as much as possible of the titanium dioxide contained in the ore has long been a goal, and environmental and other concerns have put increasing pressure on the economics of waste disposal. The present invention in fact satisfies both these important concerns.
U.S. Pat. No. 5,073,355 describes how the chlorination of titaniferous and ferriferous ore material generates not only titanium tetrachloride but other solids and gases as well as non-reacted constituents of the ore feedstock. The patent further describes how an aqueous solution containing such materials in suspension is produced from these solids including non-reacted feedstock material, reducing agents, and insolubles formed during the dissolving process. U.S. Pat. No. 3,906,077 discloses a process for purifying ferric chloride involving the withdrawal of a liquid containing non-volatile impurities and introducing this along with ferric chloride, into the chlorinator effluent gases.
U.S. Pat. No. 4,435,365 shows the reuse and processing of titanium-containing material in a three separation zone process involving a hydrocyclone (see second separation zone 44) and requiring a digestion step, where after digestion and drying, the recycled titanium dioxide is transported to the reaction zone which preferably comprises a chlorination reactor. The recycled titanium dioxide is transported in a different path than the chlorine to the reaction zone of the chlorination reactor where it is combined with a carbonaceous reducing agent and mixed with chlorine at elevated temperature.
U.S. Pat. No. 4,183,899 shows the separation of titanium dioxide and coke in a vapor process in an unreacted feedstock-coke separator zone. U.S. Pat. No. 4,442,076 shows a process for separating carbon and titaninferous solids from the effluent of the reaction zone with a solids separator and recycling these as powder into the reaction zone. Another prior art titanium dioxide process patent showing recycling steps for ferric chloride is U.S. Pat. No. 4,144,316.
In European Patent No. 318 231 A1, which has no United States counterpart, the considerable expenditure for processing waste material is described where finely divided bed material (especially TiO
2
and coke) discharged from a reactor is separated from the metal chlorides and land-filled. Hydrocyclones and concentrating tables are used for the separation. Such concentrating tables react very critically to the ore composition, because of which, constant monitoring and change of the process parameters must be carried out if the composition of the ore used changes in even the slightest degree. In this process the coke is separated off from the titanium dioxide relatively sharply but with great
Kronos Inc.
Nguyen Ngoc-Yen
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