US3403001A - Process and apparatus for the production of metal oxides - Google Patents

Description

Sept. 24, 1968 R..J. MAS ET Al.

PROCESS AND APPARATUS FOR THE PRODUCTION OF METAL OXIDES 4 4 Sheets-Sheet 1 Filed July 16, 1963 INVENTORS ROBERT JEAN MAS ANDRE L'OUIS MICHAUD A2ORNEY Sept. 24, 1968 Q R. J. MAS Ef AL 3,403,001

PROCESS AND APPARATUS FOR THE PRODUCTION OF METAL OXIDES Filed July 16, 1963 4 Sheets-Sheet 2 INVENTORS ROBERT JEAN MAS A D E LOUIS MICHAUD A ORNEY Sept. 24, 1968 R. J. MAS ET AL 3,403,001

PROCESS AND APPARATUS FOR THE PRODUCTION OF METAL OXIDES Filed July 16, 1963 4 Sheets-Sheet 3 0 N N 8 co b010 0) OQ'NOIO A INVENTORS (D N N N ,C ROBERT JEAN MAS ANDRE LOUIS MICHAUD AT ORNEY Sept. 24, 1968 R. J. MAS ET AL 3,403,001

PROCESS AND APPARATUS FOR THE PRODUCTION OF METAL OXIDES Filed July 16, 1963 4 Sheets-Sheet i g n INVENTO S R0 RT JEAN MAS ANDR LOUIS MICHAUD v ATT NEY United States Patent 3,403,001 PROCESS AND APPARATUS FOR THE PRO- DUCTION 0F METAL OXIDES Robert Jean Mas and Andr L. Michaud, Thann, France, assignors to Fabriques de Produits Chimiques de Thann et de Mulhouse, Thann, France, a French body corporate Filed July 16, 1963, Ser. No. 295,489 Claims priority, application Great Britain, July 17, 1962, 27,499/62; Feb. 8, 1963, 5,317/63 23 Claims. (Cl. 23202) This invention relates to the production of finely-divided metal oxides by the high temperature, vapour phase oxidation of metal chlorides. The invention is primarily concerned with the production of titanium dioxide from titanium tetrachloride, but the process and apparatus of the invention may also be used for the oxidation of other volatile metal chlorides into the oxides of the corresponding metals. Examples of chlorides which can be used include those of zirconium, aluminum, tin, chrominum, iron and silicon (which for the purpose of this invention is considered to be a metal).

Metal chlorides in the vapour phase may be burnt in oxygen at high temperatures, e.g. above 1000 C., to give a suspension of metal oxide particles in a chlorine-containing gas. The finely-divided oxide particles thus produced make the oxide very suitable for many commercial applications, e.g. as a pigment.

Many modifications of this general type of process are known. For example, the chloride vapour may be mixed, prior to combustion, with an inert diluent gas or with various substances said to improve the quality of the oxide produced. Various burner arrangements have been used to ensure adequate mixing of the metal chloride vapour and oxygen, and the period the oxide remains in the combustion zone has been closely controlled.

Three main categories of process may be specifically referred to: processes involving an auxiliary flame, i.e. a flame of a combustible gas, usually carbon monoxide, into which the metal chloride and oxygen are introduced to induce combustion; processes in which no auxiliary flame is used; and processes in which the combustion of the metal chloride takes place in a fluidized bed of the oxide produced by the combustion. These types of process have certain disadvantages.

Thus, in processes in which an auxiliary flame is not used, it is necessary to preheat the gaseous reactants, and this makes necessary large and complicated installations outside the reaction furnace.

Processes involving the use of a fluidized bed have the same disadvantages and it is also necessary to keep the fluidized bed at a high, constant temperature.

In the processes in which an auxiliary flame is used, there is no problem of heating the reactants, but the ditficulty of maintaining a homogeneous and stable flame still exists. In known processes, this difliculty has not, so far, been completely overcome.

Thus, in one such process titanium tetrachloride, oxygen and nitrogen are introduced through a number of inlets arranged in a circle into the interior of the auxiliary carbon monoxide flame which heats the reactants to combustion temperature. The carbon monoxide flame is formed of a relatively large number of individual flames which burn round the inlets through which the reactants are introduced. This arrangement gives a complex flame structure which is difficult to control closely, and the lack of control results in a non-uniform metal oxide product.

In another process a stream of hot burnt gases from an auxiliary flame is introduced into a cylindrical combustion chamber in a direction tangential to the walls of 3,403,001 Patented Sept. 24, 1968 "ice the said chamber and a mixture of metal chloride and oxygen is injected into the spiralling stream of hot, burnt gases in a direction parallel with the axis of the combustion chamber. In this process the flame produced by the combustion of the metal chloride (hereinafter referred to as the chloride flame) is separated from the auxiliary flame and control of the chloride combustion is, to some extent, facilitated, but the mixture of metal chloride and oxygen is not sufficiently rapidly mixed with hot, burnt gases for adequate control of the chloride flame to be possible, and the walls of the combustion chamber are corroded by the spiralling gases.

The process of the present invention comprises injecting into rectilinearly moving hot burnt gases passing at a high velocity from an auxiliary flame a mixture of metal chloride vapour and oxygen entering the hot gases in a direction which intersects the axis of the direction of motion of the said burnt gases. The mixture of chloride vapour and oxygen advantageously is injected in a plurality of separate streams thereof spaced apart about the periphery of the stream of hot burnt gases. The precise angle at which the mixture of metal chloride and oxygen is injected into the hot burnt gases may be selected as desired but is preferably from about 45 to about In the new flame processes, as in the process previously mentioned, the temperature of the mixture of reactants (chloride and oxygen) is raised very suddenly from a relatively low temperature, above the dew point of the halide, to a very much higher temperature above the minimum temperature of reaction. Thus, the initial temperature of the mixture of chloride vapour and oxygen, with or without inert gas, may be between and C. while the burnt gases into which the mixture is injected may have a temperature of 1900 C., and the consequent sudden heating of the reactants promotes homogeneity and constancy in the properties of the metal oxide obtained. However, in the process of the present invention the burnt gases and the chloride flame are kept away from the walls of the combustion chamber and this prevents contamination of the metal oxide formed and corrosion of the walls. Moreover, the mixture of metal chloride and oxygen is more rapidly mixed with the burnt gases from the auxiliary flame than in the prior processes and the chloride flame is consequently much better controlled, and a more uniform product is obtained.

It has also been found that in the process of this in-. vention it is unnecessary to add to the feed streams, the activators and nuclei formers, such as silicon and aluminum chloride, which are generally used in known processes to control the combustion of the metal chloride, especially titanium tetrachloride. In the process of the invention, nitrogen-containing products, which have favourable influences on the reaction, are formed in the auxiliary flame (because the gases fed to the flame ordinarily contain nitrogen) and are subsequently mixed with the reactants and improve the stability and homogeneity of the chloride flame. It is thus unnecessary to add other activators or nuclei formers. The maximum number of nuclei is produced by the nuclei formers, which include, for example, nitrogen oxides and ozone formed in the auixiliary flame, when the initial temperature difference between the reactants and the burnt gases is greatest.

The auxiliary flame is preferably, as in known processes, a carbon monoxide flame. At its hottest part it may reach 2400 C. but the gases leaving it are rather cooler, e.g. about 1900 C. The injection of the mixture of metal chloride and oxygen causes a further lowering of the temperature, e.g. to about 1400 C. The latter temperature may be reduced still further by cooling the walls of the zone in which the chloride flame burns, and it is often advantageous to effect such cooling.

The maximum temperature of the auxiliary flame can be reduced by supplying excess oxygen over and above that required to convert all the carbon monoxide to carbon dioxide, since this excess absorbs heat in being brought to flame temperature. Similarly, if oxygen is supplied to the auxiliary flame in the form of air (as is normally the case) the nitrogen will absorb part of the heat of combustion of the carbon monoxide.

The precise composition of the burnt gases from the auxiliary flame naturally depends on the chemical composition of the combustible gas mixture supplied to the flame. At high temperatures, in the presence of nitrogen and Water vapour, carbon monoxide burns to give a mixture containing carbon dioxide, water, hydrogen, carbon monoxide, oxygen, nitric oxide, and the H, O, and OH radicals. As the mixture cools ozone and nitrogen peroxide may be produced. As already mentioned, some of the products of combustion of carbon monoxide in air, i.e. the products of the auxiliary flame, exert a beneficial effect on the combustion of metal chlorides by acting as nuclei formers for the formation of oxide particles.

The invention is most advantageously applied to the production of titanium dioxide, in a form suitable for use, inter alia, as a pigment, by the combustion of titanium tetrachloride. The titanium dioxide produced has a very uniform grain size, the average maximum dimension being less than 0.5a. The actual grain size may be varied somewhat by varying the conditions of the process and thus the grain size of the product can be adapted for its intended use. As already explained, the oxide may be obtained without the use of activators or nuclei formers other than those produced by the auxiliary flame.

The invention includes within its scope a burner device for use in the new process. This burner comprises a precombustion chamber, openings in the said chamber for feeding oxygen and an inflammable gas thereto, a tubular mixing chamber in open communication, and having a common axis, with the precombustion chamber, a plurality of conduits of small diameter opening into the said mixing chamber, the axis of each of which intersects the axis of the mixing chamber, for feeding a mixture of metal chloride vapour and oxygen to the said mixing chamber, and means for cooling the walls of the said precombustion and mixing chambers. The means for cooling the walls of the precombustion and mixing chambers are provided to lower the temperature of the chloride flame which, as mentioned above, is advantageous, especially in reducing corrosion of the mixing chamber.

The combustion of the chloride is, in general, not completed in the mixing chamber but continues as the mixture of burnt gases, metal chloride and oxygen leaves the burner device and passes into the containg furnace. The metal forms a thick smoke in the furnace. The burner may, of course, be provided with means for fixing it to the furnace.

The volume of the precombustion chamber is preferably enough to ensure that complete combustion of the carbon monoxide or other fuel in the auxiliary flame takes place in it but not so great that any appreciable cooling of the burnt gases takes place before they leave the chamber. The residence time of the gases in this chamber may be from some tenths of seconds to as little as one or two hundredths of a second. The precise time will depend on the rapidity of combustion of the inflammable gas supplied, being, of course, least for gases of the highest chemical reactivity with oxygen.

The actual size of the precombustion chamber and the mixing chamber will depend on the consideration discussed in the last paragraph, the disposition and number of the nozzles through which the chloride and oxygen are injected and the total output required of the burner device.

The invention includes within its scope installations for carrying out the process of the invention comprising a furnace containing one or more burner devices of the above type, means for discharging metal oxide-containing gases from the furnace, means for cooling and separating the oxide, and means for recycling unspent gases. Such a construction ensures etficient use of the reactants and heat of reaction, and thus leads to an improved yield of oxide and a reduction in overall size of the installation.

Suitable forms of burner device for use in the invention are shown, by way of example, in the accompanying drawings, wherein:

FIGURE 1 is a front section of a burner device with a cooled mixing chamber comprising pipes for the injection of the chloride at right-angles to the axis of the burnt FIGURE 2 is a front section of a burner device, the mixing chamber of which has been reduced in size, and in which the injection pipes are at an acute angle of about 45 to the burnt gas stream;

FIGURE 3 is a horizontal section along A-A of the burner device of FIGURE 2 and shows the symmetrically disposed chloride injection pipes; and

FIGURE 4 is a front section of a burner device with a precombustion chamber and mixing chamber forming a Venturi tube.

Referring to FIGURE 1, A indicates a burner head with concentric pipes, B the refrigerating jacket of the body cooled by circulation of cold water entering at inlet 11, and leaving at outlet :1 C the precombustion chamber in which the carbon monoxide or other auxiliary gas is burnt, and D is the chamber, formed as an axial extension of the combustion chamber and receiving hot burnt gases from the latter through a constriction E increasing their velocity, for mixing the hot burnt gases and the metal chloride and oxygen.

The oxygen is introduced into the burner head A by way of inlet g and enters the combustion chamber C through inlet g passing the fins I1 and h Carbon monoxide or other inflammable gas is introduced through inlet k and burns in the chamber C after having passed the fins k and k which are provided to increase the turbulence of the gas.

Nitrogen can be introduced through inlet l and can be mixed with the combustible gas, while the auxiliary flame and the combustion can be observed through Window The mixture of, e.g., titanium tetrachloride with an excess of oxygen enters the burner head A through inlet m The mixture reaches the mixing chamber by way of inlets m and 111 which lead into conduits discharging through openings m and 111 as Well as through other peripheral openings in symmetrical position, as shown in FIGURE 3. These openings may have various shapes, e.g. rectangular.

This burner device may be operated as follows: the auxiliary flame, usually of carbon monoxide, is set in operation and the rate of flow of the gas is regulated in an appropriate manner. The combustion of carbon monoxide gives a very hot flame which may have a temperature higher than 2000 C. (e.g. up to 2400 C.), and the burnt gases obtained are also very hot. These gases are violently directed into the mixing chamber D, at the entrance of which they meet the jets of chloride, which gives a mixture which burns in the oxidation furnace proper, not shown in the figure.

In burnt gases derived from carbon monoxide, carbon dioxide predominates, but there are naturally other gaseous products which are formed at the various temperatures inside the flame. The formation of these other products leads to heat adsorption, thus causing a temperature drop in the burnt gases, which are cooled thereby usually to about 1350 C. This temperature is suitable for obtaining rutile by the combustion of titanium tetrachloride.

FIGURES 2, 3 and 4 also show improved burner devices in accordance with the invention. These devices permit the introduction of chloride vapours diluted with oxygen into the hot burnt gases formed by the combustion of carbon monoxide. These burners are preferably of metal construction and may, for example, be made of,

aluminum protected against corrosion and a too high temperature by a cooling jacket through which flows a current of water or another appropriate fluid, such as an oil with a low vapour tension, e.g. Dowtherm (a eutectic mixture of diphenyl and diphenyl oxide). The oxygen stream entraining the chloride vapour passes through this iacket by a metal conduit, which is thermally insulated from the fluid in the main jacket, thus avoiding excessive cooling of the vapours. The combustion of the auxiliary flame is practically complete when the gases reach the point at which the evaporized chloride is introduced. To avoid loss of heat, the interior of the precombustion chamber is preferably lined with ceramic material.

An especially advantageous burner arrangement according to the invention is that shown in FIGURE 4, which represents a special burner device inside which the mixing chamber D forms, with the precombustion chamber C a Venturi tube having a constricted throat E; into which the halide is introduced. The Venturi form makes it possible to obtain partial vacuum and a high velocity at the throat between the precombustion chamber and the mixing chamber, and this facilitates mixing. The advantages of this arrangement (when used for the combustion of titanium tetrachloride with an auxiliary flame of carbon monoxide) are:

(a) more rapid and efficient mixing of the gases;

(b) a substantial increase in the number of nuclei formers produced with better utilization thereof;

(c) increase in yield quantity of titanium dioxide per hour while permitting an economy in carbon monoxide; and

(d) the white pigments obtained have improved characteristics.

A flame produced, for example, by burning a mixture of oxygen and carbon monoxide usually comprises two portions; a brilliant internal cone and a less brilliant external envelope. Although the combustion occurs mainly at the internal surface of the internal cone, the combustion of the carbon monoxide begins in the internal cone and the partially oxidised products pass into the external envelope. A considerable quantity of oxidised products or elements in the atomic or molecular state are formed at the external surface of the internal cone.

As the products pass into the progressively colder regions of the external envelope the combustion giving carbon dioxide continues until the reaction is complete. The heat liberated in the combustion depends on the degree of completion of the reaction and also on the local temperature. The heat given off by the combustion exists in the form of sensible heat in the gaseous combustion products and, as they are eliminated, the temperature of the combustion products is lowered.

The following examples illustrate the invention.

Example I An aluminum burner, such as that shown in FIGURE 1, is arranged in a cylindrical furnace.

The total height of-the apparatus is 150 cm. and its diameter is 45 cm. It is cooled by water at a rate of 2.5 cubic metres per hour and is fed with 50 cubic metres per hour of oxygen, 80 cubic metres per hour of carbon monoxide, and 155 cubic metres per hour of a mixture of titanium tetrachloride and oxygen, containing 33% by volume of the tetrachloride and 67% by volume of oxygen.

It is possible to add to the reacting gases modifiers which have been recommended for modifying the structure of the product in a desirable manner; for example, steam may be added to the oxidising gas or to the carbon monoxide, or chlorides, such as aluminum chloride or silicon chloride, may be added to the stream of volatilised chloride. Nevertheless, as stated above, such additions are not essential and the necessary nuclei formers appear to be formed in situ.

Example 11 In order to obtain titanium dioxide of pigmentary quality as rutile or anatase, an oxidising furnace of any desired type is used, but preferably one which comprises a discharge device for the hot gases containing titanium dioxide, as described in French Patent No. 1,307,280.

The burner shown in FIGURE 4 is arranged in this fur-.

nace.

Oxygen, at a rate of 45 cubic metres per hour, and carbon monoxide containing gas, at a rate of 70 cubic metres per hour, are introduced into the burner. The combustible gas is made up of 75% by volume of carbon monoxide, 5% of carbon dioxide, and 20% of nitrogen. It is introduced through a single pipe; that is to say, the pipe for introducing nitrogen is not used. A mixture of titanium tetrachloride and oxygen comprising 39% to 40% by volume of titanium tetrachloride is introduced at a rate of 215 cubic metres per hour.

The reaction forming the titanium dioxide is entirely carried out inside the oxidation furnace. 304 kg./hour of titanium dioxide are recovered, the satistical distribution of which from the granulometric point of view is very interesting. The particle size distribution by weight and by number of different samples gives a very valuable indication of the pigmentary quality of different kinds of titanium dioxide. This is illustrated in FIGURES 5 and 6 of the accompanying drawings. FIGURE 5 represents the statistical distribution, in percentages by weight as a function of particle size in Angstrom units, of the particles in three samples of pigment. The dotted curves represent two extreme types of pigment having different pigmentary properties resulting from the differences in particle size distribution. The percentages by weight are calculated from the formula:

statistical volume of all particles corresponding to a given size statistical volume of all the particles examined FIGURE 6 shows the particle size distribution of the same three samples as in FIGURE 5 with the difference that the percentage distribution by number of the particles examined is plotted as a function of particle size. Each point plotted on the curve represents the percentage of particles having a diameter within a given range of sizes. This range is obtained by grouping together the mean values of the dimensions of the particles in order to simplify the method of calculation and the representation of the results. The main diameter of the particles, 1922 angstroms (solid curve in FIGURE 5), is obtained from the formula:

Example III A burner having precombustion and mixing chambers of the kind shown in FIGURE 1 is arranged in an oxidation furnace as described in French Patent No. 1,307,280, from which titanium dioxide can be removed continuously. The burner has the following principal characteristics. The precombustion chamber C is in the form of an elongated drum having a height of 530 mm. and a greatest diameter of mm. The mixing chamber D is cylindrical, with a diameter of 130 mm. and a height of 390 mm. The injection orifices m and 111 have a diameter of 25 mm. There are eight such orifices in all and they are disposed symmetrically in the upper part of the mixing chamber. Their diameter is less than that of the orifice m through which the mixture of metallic chlorine and oxygen is introduced into the head of the burner. The latter also includes the separate orifices on entry k and g for carbon monoxide and oxygen, respectively. The head of the burner is fed with the reacting gases at rates which can be varied at will. The conditions of operation are as follows:

The auxiliary flame is first produced as follows. Oxygen gas at a rate of 60 cubic metres per hour is introduced through orifice g and carbon monoxide at a rate of 100 cubic metres per hour through orifice k and the mixture is lit. A powerful, hot flame is thus produced. When the gases leaving the precombustion chamber C have heated the internal Walls of the burner, a mixture of titanium tetrachloride and oxygen is introduced through the orifice m at a rate of 55 cubic metres per hour of titanium tetrachloride and 72 cubic metres per hour of oxygen so that the mixed gases contain 44.5% by volume of titanium tetrachloride.

The chloride flame is thus produced and burns at the exit of the burner. If desired the walls of the burner can be cooled and the rate of introduction of the various gases varied. Titanium dioxide is produced continuously at a rate of 195 kg. per hour. At this rate of production it is necessary to add 5 to 6 kg. of titanium dioxide to the furnace to form a store which can be recovered subsequently without interruption of the operation of the furnace. All the samples of product analysed are of pigmentary quality and show excellent properties and particle size distribution.

Example IV The process of Example III is repeated with the same burner arrangement, except that the injection orifices are four in number and have a rectangular cross-section x 20 mm., permitting even distribution of the reaction gas. The auxiliary flame is obtained using cubic metres of oxygen per hour, introduced through orifice g and 90 cubic metres per hour of a gas containing by volume of carbon monoxide, introduced through orifice k The flame of metallic chloride is obtained by introducing into the head of the burner 55 cubic metres per hour of titanium tetrachloride and 82 cubic metres per hour of oxygen. The proportion of titanium tetrachloride in the mixture is 40% by volume and the mixture is introduced at an angle of to the burnt gases from the auxiliary flame. The chloride flame obtained in the furnace is long and stable. As in Example 111, titanium dioxide is produced very regularly and the examination of samples shows it to be of fine pigment quality.

Example V Into an oxidation furnace permitting the recycling of all the combustion gases to cool the titanium dioxide produced, as described in British specification No. 673,725,

a carbon monoxide burner having a mixing chamber of reduced size, as shown in FIGURE 2, is introduced. This burner includes the entry orifices necessary for the reaction gases. The diameters of the orifices for admission of carbon monoxide and oxygen are respectively 65 mm. and 40 mm. The tube for admitting the mixture of titanium tetrachloride and oxygen is mm. across. The total height of the head of the burner is 550 mm., and the height of the precombustion chamber is 725 mm. There are eight orifices, each 18 mm. in diameter, for injecting the reaction gases at an angle of 45 to the gases from the auxiliary flame.

The burner is fed under the following conditions. The auxiliary flame is formed from 60 cubic metres per hour of oxygen and 100 cubic metres per hour of a gas containing 67% by volume of carbon monoxide. The chloride flame is obtained by injecting a gaseous mixture of titanium tetrachloride and oxygen through the aforesaid eight injection orifices. The mixture is formed from 67 cubic metres per hour of titanium tetrachloride and 90 cubic metres per hour of oxygen and contains 42.5% by volume of titanium tetrachloride. The flame obtained in the furnace is stable and homogeneous. It is sharply separated from the auxiliary flame, as in other burners in accordance with the invention, although the mixing chamber is much reduced in size. Titanium dioxide is produced at a rate of 236 kg. per hour, with 7 kg. of a recoverable residue, and is of pigmentary quality.

Example VI An oxidation apparatus is used which permits the recycling through the burner of part of the oxidation gases, containing chloride but from which titanium dioxide has been removed, as described in French Patent No. 1,260,- 110. The burner of this apparatus is replaced by a burner of the type shown in FIGURE 4. The precombustion chamber C, has a height of 530 mm. and a largest diameter of mm. The mixing chamber D has a height of 330 mm. It tapers to form a Venturi towards the precombustion chamber, the aperture of which has a diameter of 130 mm. The throat E of the Venturi contains eight holes, each having a diameter of 15 mm.

The reaction is carried out as in the preceding example. The auxiliary flame is formed from 50 cubic metres per hour of oxygen and 80 cubic metres per hour of a gas containing 70% by volume of carbon monoxide. A mixture of titanium tetrachloride and oxygen containing 25% by volume of titanium tetrachloride is introduced at a rate of kg. per hour.

A large excess of oxygen does not vitiate the process of the invention because it contributes to the formation of ozone, which acts as an activator in the oxidation. As has already been mentioned, the temperature of the carbon monoxide flame in the precombustion chamber is about 2400 C. while the temperature of the gases leaving the combustion chamber is about 1900 C. In the mixing chamber the combustion gases mix with the reaction gases (metal chloride plus oxygen) and the temperature falls to about 850 to 1350 C. The chloride flame burns in the furnace with a long, stable flame and the temperature of the reaction is, on average, greater than 1150" C. These conditions of temperature and reaction enable titanium dioxide pigment to be obtained in the rutile form in the absence of any agent for promoting the formation of the rutile allotrope.

The process of the invention can be applied not only to the oxidation of titanium tetrachloride in the vapour phase but also to the oxidation in the vapour phase of other metallic chlorides, such as those of aluminum, iron, zirconium, hafnium and niobium, all of which can he vaporized at below 500 C. at atmospheric pressure. Essentially the same technique and apparatus are used as that described above.

It can be shown that the titanium dioxide pigments which are obtained in accordance with the invention are fine and regular, and it is thus possible for them to be used, for example, in the pigmentation of plastic materials.

We claim:

1. A process for the production of finely divided metal oxide, which comprises continuously forming hot burned gases in a combustion chamber by substantially completely burning a flammable fuel gas with oxygen-containing gas therein, continuously passing said hot burned gases from said chamber in a stream thereof directed rectilinearly through a constriction substantially increasing its velocity, and continuously injecting into said stream, in a region thereof of increased velocity produced by said constriction, a gasous mixture of metal chloride vapor and oxygen containing at least the amount of oxygen theoretically required for complete oxidation of said vapor, thereby continuously obtaining at the downstream side of said constriction a reaction mixture composed of said burned gases and said gaseous mixture, in which said metal oxide is produced "by a steady flaming reaction.

2. A process according to claim 1, said gaseous mixture being injected in a plurality of streams thereof separately entering said stream of hot Iburned gases, each in a direction toward its axis, from locations spaced apart about its periphery.

3. A process according to claim 1, said mixture being injected in a plurality of streams thereof separately entering said stream of hot burned gases, each at an angle of 45 to 90 to its axis, from locations spaced apart about its periphery.

4. A process according to claim 1, said oxygen-com taining gas comprising air.

5. A process according to claim 1, said mixture of metal chloride vapor and oxygen being maintained, until injected into said hot burned gases, at a temperature insufficient to induce oxidation of said vapor.

6. A process according to claim 1, said gaseous mixture containing oxygen in excess of the amount theoretically required for complete oxidation of the metal chloride content.

7. A process for the production of a finely divided metal oxide, which comprises continuously forming in a combustion chamber burned gases having a temperature of at least about 1900 C. by substantially completely burning carbon monoxide with oxygen-containing gas in said chamber, continuously passing said gases from said chamber in a stream thereof directed rectilinearly through a constriction substantially increasing its velocity, and continuously injecting into said stream of increased velocity at the location of said constriction a gaseous mixture, directed toward the axis of said stream, of metal chloride vapor and oxygen for the oxidation of said vapor, thereby continuously obtaining at the downstream side of said constriction a homogeneous reaction mixture composed of said burned gases and said gaseous mixture, in which said metal oxide is produced by a steady flaming reaction.

8. A process according to claim 7, said constriction being the throat of a Venturi tube and said gaseous mixture being injected in a plurality of separate streams thereof entering through openings in the throat of said tube.

9. A process according to claim 7, said oxygen-containing gas comprising air, and said gaseous mixture containing oxygen in excess of the amount theoretically required for complete oxidation of the metal chloride content.

10. A process for the production of finely divided titanium dioxide, which comprises continuously forming hot burned gases at a temperature of at least about 1900 C. in a combustion chamber by substantially completely burning carbon monoxide with oxygen in the presence of nitrogen in said chamber, continuously passing said burned gases from said chamber in a stream thereof directed rectilinearly through a constriction substantially increasing its velocity, and continuously injecting into said stream, in a region thereof of increased velocity produced by said constriction, a plurality of separate streams of a gaseous mixture of titanium tetrachloride vapor and oxygen directed from the periphery of said stream toward its axis and containing an amount of oxygen exceeding that theoretically required to oxidize said vapor to titanium dioxide, thereby continuously obtaining at the downstream side of said constriction a reaction mixture composed of said burned gases and said gaseous mixture, in which said titanium dioxide is produced continuously by a steady flaming reaction.

11. A process according to claim 10, said gaseous mixture being at a temperature between 120 and 150 C. and being injected into said stream of burned gases in a quantity forming with the latter a reaction mixture having a selected temperature in the range of 850 to 1400 C.

12. A process according to claim said gaseous mixture being at a temperature between 120 and 150 C. and :being injected into said stream of burned gases in a quantity forming with the latter a flaming reaction mixture having a temperature of at least about 1150 0, whereby said titanium dioxide is produced in the rutile form.

13. An apparatus for the production of finely divided metal oxide, comprising an elongated combustion chamber, means for continuously feeding flammable gas and oxygen-containing gas into one end of said chamber for combustion in said chamber to form hot substantially completely burned gases continuously therein, an axially open tubular extension at the other end of said chamber for passing said burned gases continuously from said chamber to a reaction zone in a rectilinearly directed stream, said extension comprising a constriction at said other end for substantially increasing the velocity of said stream, and means for continuously injecting into said extension in a region thereof of increased velocity produced by said constriction, a gaseous mixture of metal chloride vapor and oxygen to oxidize said vapor, whereby a homogeneous reaction mixture composed of said burned gases and said gaseous mixture, for producing said metal oxide by a steady flaming reaction, is obtained in said extention at the downstream side of said constriction.

14. An apparatus according to claim 13, said injecting means including a plurality of conduits spaced apart about said tubular extension and each opening thereinto in a direction toward the axis thereof, for delivering a plurality of separate streams of said gaseous mixture into said stream of hot burned gases.

15. An apparatus according to claim 13, said tubular extension having the form of a Venturi tube.

16. An apparatus according to claim 13, said tubular extension having the form of a Venturi tube, and said injecting means including a plurality of conduits spaced apart about the throat of said tube and each opening into said throat in a direction toward the axis thereof.

17. An apparatus according to claim 13, and means for cooling the walls of said combustion chamber and said tubular extension.

18. An apparatus according to claim 13, and means including a jacket surrounding said combustion chamber and said tubular extension for holding a cooling liquid in contact with their walls.

19. An apparatus according to claim 13, and means including a jacket surrounding said combustion chamber and said tubular extension for holding a cooling liquid in contact with their walls, said injecting means including a head chamber surrounding a part of said feeding means, for receiving said gaseous mixture, and a plurality of heat-insulated conduits extending from said head chamber through the liquid containing space of said jacket to said tubular extension, each of said conduits opening into said tubular extension in a direction toward the axis thereof.

20. An apparatus for the production of divided metal oxide, comprising an elongated combustion chamber, means for continuously feeding fuel gas and oxygen-containing gas into one end of said chamber for combustion in said chamber to form hot substantially completely burned gases continuously therein, an axially open tubular extension at the other end of said chamber for passing said burned gases continuously from said chamber to a reaction zone in a rectilinearly directed stream, said extension comprising a constriction at said other end for substantially increasing the velocity of said stream, and means for continuously injecting into said extension, in a region thereof of increased velocity produced by said constriction, a gaseous mixture of metal chloride vapor and oxygen to oxidize said vapor, whereby a homogeneous reaction mixture composed of said burned gases and said gaseous mixture, for producing said metal oxide bya steady flaming reaction, is obtained in said extension downstream of said constriction, and means including a jacket surrounding said combustion chamber and said tubular extension for holding a cooling liquid in contact with their walls, said injecting means including a head chamber for receiving said gaseous mixture, said head chamber surrounding a part of said feeding means, and a plurality of conduits spaced apart about said combustion chamber and 1 1 extending from said head chamber through the liquid containing space of said jacket to said tubular extension, each of said conduits opening into said extension in a direction toward the axis thereof.

21. An apparatus according to claim 20, said tubular extension and said other end of said combustion chamber forming a Venturi tube the throat of which constitutes said constriction, said conduits opening radially into said throat.

22. An apparatus according to claim 20, said combustion chamber comprising successively in the direction away from said burner means, an entrance portion of progressively increasing diameter, an intermediate portion of largest diameter and an exit portion progressively decreasing in diameter to said constriction.

23. An apparatus according to claim 20, said feeding means comprising concentric pipes for conducting separate streams of said fuel gas and said oxygen-containing gas coaxially into said combustion chamber.

References Cited UNITED STATES PATENTS Kinnaird 23--277 Weber et a1 23202 X Frey 23202 Schrader 23277 X Burden 23277 Burt et al. 23277 Allen et a1. 106300 Leistritz 23277 Ebner 231 Hellwig 23277 Nelson et a1. 23202 Wagner 23277 Canada.

OSCAR R. VERTIZ, Primary Examiner.

E. STERN, Assistant Examiner.

Claims (1)

1. A PROCESS FOR THE PRODUCTION OF FINELY DIVIDED METAL OXIDE, WHICH COMPRISES CONTINUOUSLY FORMING HOT FURNED GASES IN A COMBINATION CHAMBER BY SUBSTANTIALLY COMPLETELY BURNING A FLAMMABLE FUEL GAS WITH OXYGEN-CONTAINING GAS THEREIN, CONTINUOUSLY PASSING SAID HOT BURNED GASES FROM SAID CHAMBER IN A STREAM THEREOF DIRECTED RECTILINEARLY THROUGH A CONSTRICTION SUBSTANTIALLY INCREASING IN VELOCITY, AND CONTINUOUSLY INJECTING INTO SAID STREAM, IN A REGION THEREOF OF INCREASED VELOCITY PRODUCED BY SAID CONSTRICTION, A GASOUS MIXTURE OF METAL CHLORIDE VAPOR AND OXYGEN CONTAINING AT LEAST THE AMOUNT OF OXYGEN THEORETICALLY REQUIRED FOR COMPLETE OXIDATION OF SAID VAPOR, THEREBY CONTINUOUSLY OBTAINING AT THE DOWNSTREAM SIDE OF SAID CONSTRICTION A REACTION MIXTURE COMPOSED OF SAID BURNED GASES AND SAID GASEOUS MIXTURE, IN WHICH SAID METAL OXIDE IS PRODUCED BY A STEADY FLAMING REACTION.

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