US3352639A

US3352639A - Process for the oxidation of ticl4 to produce tio2

Info

Publication number: US3352639A
Application number: US433491A
Authority: US
Inventors: Wikswo John Peter
Original assignee: American Cyanamid Co
Current assignee: Wyeth Holdings LLC
Priority date: 1965-02-17
Filing date: 1965-02-17
Publication date: 1967-11-14
Anticipated expiration: 1984-11-14

Description

United States Patent 3,352,639 PROCESS FOR THE OXIDATION OF TiCl T0 PRODUCE TiO John Peter Wikswo, Ridge Drive, Va., assignor to American Cyanamid Company, Stamford, Conn., a corporation of Maine No Drawing. Filed Feb. 17, 1965, Ser. No. 433,491 10 Claims. (Cl. 23-202) ABSTRACT OF THE DISCLOSURE The present invention relates to an improved method of preparing TiO by the reaction of titanium tetrachloride and relatively pure carbon monoxide with oxygen in the presence of a small amount of hydrogen sulfide. This invention is based upon the discovery that hydrogen sulfide in relatively small amounts, not only exerts a catalytic effect upon the reaction, but also produces an additional beneficial effect beyond that produced by water alone and that it does this without the undesirable hydrolysis of the feed materials occurring when water alone is used.

This invention relates to an improved method of burning TiCl, to produce TiO pigment.

In the manufacture of TiO pigment by the combus tion of TiCl it is known that a small amount of water will serve to nucleate the formation of TiO pigment particles. As to such systems, it was found by previous workers that at least .05% by volume of water, based on the total combustion mixture, shall be used in order to obtain a beneficial nucleating effect. However, these findings have been discovered in connection with what is com monly referred to as a turbulent-type burner. Contrary to what might be expected, it was found that a beneficial effect could result from using water in amounts less than 0.05% in a combustion system involving a laminar flame burner of the type described in U.S. Patent No. 3,121,641. One significant difference between the two systems is that in the laminar flame burner, CO is one of the ingredients of the combustion feed mixture which serves to furnish additional heat to that generated by the combustion of TiCl to TiO Further, in a laminar flame burner, the relatively smaller beneficial amounts of water, viz., from .005% to .06% by volume, based on the total feed mixture, appear to catalyze the combustion of CO to CO and the heat thus evolved appears to have a beneficial effect on pigment formation. From these considerations, it is apparent that the nature of the reactions occurring in a turbulent-type burner is different from that taking place in a laminar-flow burner.

In a laminar-flame burner, it is customary to use screens in the feed inlets to create a laminar-flow condition. The presence of water in the feed may tend to hydrolyze the TiCl to produce a hydrolytic product that may tend to deposit on the screens of the feed tubes. The deposition of the hydrolytic product tends to interfere with the flow of the feed material, thus leading towards an undesirable condition. To avoid this tendency, additional materials were examined from the standpoint of determining how the combustion reaction could be benefited without the possibility of depositing hydrolytic product in the feed inlet. Quite unexpectedly, we have discovered that hydrogen sulfide in relatively small amounts not only exerts a catalytic efiect but also produces .an additional beneficial effect on the combustion reaction beyond that produced by water only and that it does this without the undesirable hydrolysis of the feed materials occurring in the burner inlet. Also, quite surprisingly, it was found from a series of experiments which led to the present discovery that propane and HCl gave no beneficial effect in the laminar flame system, which illustrates that the benefit resulting from the use of H 3 involves a phenomenon other than merely forming H O in situ during the combustion reaction.

Accordingly, an object of this invention is to provide an improved method for the production of TiO pigment.

Another object of this invention is to provide a method of producing pigmentary TiO of an exceptionally high tint tone and tinting strength.

Other objects and advantages of this invention will become apparent from the following description and explanation thereof.

By means of the present invention, the feed mixture of TiCl oxygen, aluminum chloride, H 5 and CO is fed to a laminar-flow burner under conditions suitable for the production of pigmentary TiO The combustion reaction is conducted at a temperature of about 1400" to 1850 C., and more usually about 1450 to 1600 C. The amount of CO present in the feed mixture is measured as a volumetric ratio of CO to TiC1 and in general, this ratio is about 0.1 to 3.0: 1, more usually about 0.3 to 1.0:1. The total feed mixture being fed to the combustion zone is determined as a volumetric space velocity, i.e., the cubic feet per minute of feed mixture, measured at 25 C. at 1 atmosphere of pressure, per square foot of flow area in the feed mixture inlets leading to the burning zone. Generally, the volumetric space velocity is about 15 to 45, and more usually about 20 to 40. The combustion reaction takes place satisfactorily under essentially atmospheric pressure, however, a higher or lower pressure may be employed. The oxygencontaining gas, measured as the excess over the stoichiometric amount needed to react with all the TiCl (and assuming that a stoichiometric amount of oxygen is present to act with all the CO), is about 5 to excess, on a volumetric basis, and more usually about 40 to 80% on the same basis. Aluminum chloride may also be present in the feed mixture in an amount of about 1 to 5% by weight, more usually about 2 to 3% by weight, measured as A1 0 in the TiO finished product. The amount of H 8 present in the feed mixture may vary from about ,002 to .06% by volume, based on the total feed, and more usually .01 to .04% by volume on the same basis. Water may also be present in the feed mixture in an amount ranging from about .005 to .06% by volume, based on the total feed mixture, and more usually to .02 to .04% by volume on the same basis. The conditions described above for the reaction involving production of pi-gmentary TiO may be varied outside the ranges specified above without departing from the spirit of the invention.

In a laminar-flame burner of the type described in U.S. Patent No. 3,121,641, the feed material is divided into two main streams which are introduced into the burning zone from diametrically opposed directions. The combustion flames resulting from the burning of each stream oppose each other to form two adjacent continuous flame fronts which contact each other without significant intermixing between the materials of the undivided flames. The introduction of the feed mixture into the combustion zone may be accomplished in a variety of ways, however, in a commercial operation, it is preferred that dampening screens be present in the feed tubes of the burner system. The dampening screens reduce any tendency towards flow turbulence which may tend to occur from the passage of the gas within the confined area of the feed conduits. The feed mixture may be preheated to a temperature of about to 300 C., more usually about 200 to 250 C. The oxygen-containing gas which is used in the combustion reaction may be either pure oxygen, .air or enriched air. For reasons of efiiciency of operation it is preferred thatpure oxygen be used as the source of oxygen for the reaction.

We have also discovered that large excesses of oxygen have a beneficial effect on the quality of the pigmentary TiO The greatest benefit is obtained when using from about 80120% excess oxygen. The excess oxygen appears to behave as a promoter of the Ti product, and coning brick, which replaced the cooling jacket shown in the patent. The experiments were made using the reaction conditions shown in Table I below, including a reaction pressure of essentially one atmosphere. The apparatus and method of operation described in the patent are hereby incorporated by reference and made a part of the present specification.

TABLE I Run No 1 2 3 4 5 i 6 l 7 8 9 TiCh, lb. mol/hr 3.2 3.2 3.2 3-2 3-2 3.2 3.2 3.2 3,2 Oxygen, molar excess. 80 S0 80 80 8O 80 80 8O 80 CO/TiCh, molar excess. .55 .55 .55 55 .55 .55 55 .55 ,55 Vol. space velocity 31 3 31 3 d1 31 31 31 31 E20, Vol. percent (total feed) 0 O 0 0 0 .0185 0185 0063 .0063 HgS, Vol. percent (total feed) 0 0061 .0122 0184 .0243 .0063 0 0 .0061 Combustion Ternp., C t 1, 505 1. 505 1, 505 1, 505 1,505 1, 505 1,505 1, 505 1, 505 Pigment quality, Tint Tone V Br Br 2 B1'1 3 Br 1 Br .3 B1 1. 5 Br 2. 6 Br-7 B1-7 Tinting Strength 1, 200 1, 650 1, 6 0 705 670 1, 675 1, 650 1, 470 1, 630 Pi ment ualit round): 3

g Tint %0ne, V Bl Bll 1310.5 B11 B11 1311 B1 2.2 Brfi B1 1 Tinting Strength 1, 310 7 0 7 775 7 0 l, 740 1, 740 1, 575 1, 770

1 TiCll contains 3 mol percent A101 sequently it is possible to reduce the amount of aluminum chloride and/or water for the reaction by the use of such large excesses of oxygen. Without being bound by any theory, it appears that the large excess of oxygen creates a beneficial mass-action effect which makes possible reducing the amount of H 0 and H 5 which may be needed to obtain beneficial effects.

The H S may be added by a variety of methods to the total feed mixture. It can be added directly to the CO stream, which is later combined with the other ingredients of the feed mixture. Alternatively, it may he added to the vaporous mixture of aluminum chloride and TiCl Generally, however, the H 8 is added to the CO stream in an amount of about 200 to 4000 ppm, and more usually about 600 to 1800 ppm. In any case, the amount of H 8 in the CO stream will be sufficient to provide the desired final concentration of H 8 in the total feed material.

When water is added to the reaction, it may be injected directly into the feed mixture or along with any one or more of the ingredients thereof. In commercial practice it is preferred that the CO stream be humidified in order to have an intimate association of the two materials. This can be accomplishedby drying a wet stream of CO to the desired water concentration, or in the case of dry CO, the water can be added by passing the CO through a water tower. By whatever method is employed, generally the water content of the CO stream may be from about 400 to 4000 p.p.m., and more usually about 1200 to 1800 ppm. In any case, the amount of water present in the CO stream will provide the desired final water concentration in the total feed stream.

Aluminum chloride may also be added to the feed mixture containing TiC1 The aluminum chloride promotes theformation of rutile pigmentary TiO and therefore is desirable for commercial practice. The aluminum chloride is first combined with TiCl This may be done by vaporizing a mixture or solution of aluminum chloride and TiCL, by heating the same to a temperature of about 140 C. to 250 C., more usually about 175 to 200 C., at a pressure of about 1 to 120 p.s.i.g., more usually about to 45 p.s.i.g. The vaporous mixture of TiCl and AlCl may be readily combined with the other ingredients of the total feed mixture, such as CO and H S prior to entering the burner To provide a better understanding of the present in vention, experiments were made in a burner of the type described in U.S. Patent No. 3,121,641, except that the burner tubes employed in the experiments reported below were 15 inches in diameter and the feed gases were introduced into the burner tubes without the tangential swirl. The hood of the burner was aluminum lined with insulat- What is claimed is:

1. A process for producing titanium dioxide which comprises reacting titanium tetrachloride with an oxygen containing gas in the presence of a gaseous mixture consisting essentially of carbon monoxide and hydrogen sulfide, the hydrogen sulfide being present in an amount of about .002 to .06% by volume of the total gas, the volumetric ratio of carbon monoxide to titanium tetrachloride being about 0.1 to 3.0: l, at a temperature of about 1400 C. to 1850 C., the oxygen being employed in a stoichiometric excess of about 5 to 120% by volume, and a volumetric space velocity of the total gas being about 15 to 45.

2. A process for producing titanium dioxide which comprises reacting titanium tetrachloride with oxygen in the presence of a gaseous mixture consisting essentially of carbon monoxide and hydrogen sulfide, the hydrogen sulfide being present in an amount of about .01 to .04% by volume of the total gas, the volumetric ratio of carbon monoxide to titanium tetrachloride being about .3 to 1.0:1, ata temperature of about 1450 to 1600 C., the oxygen being. employed at a stoichiometric excess of 40 to by volume, and a volumetric space velocity of the total gas being about 20 to 40.

3. The process of claim 1 being further characterized by the additional presence of water in an amount of about .005 to .06% by volume of the total gas.

4. The process of claim 2 being further characterized by the additional presence of Water in an amount of about .01 to .04% by volume of the total gas.

5. The process of claim 1 wherein the oxygen containing gas is oxygen.

6. The process of claim 2 being further characterized by the additional presence of about 1 to 5% aluminum chloride measured as A1 0 in the final pigment.

7. In a process of producing titanium dioxide by reacting titanium tetrachloride with an oxygen containing gas by means of diametrically opposed reactant streams to form two parallel laminar flames, the improvement which comprises reacting said materials in the presence of a gaseous mixtnreconsisting essentially of carbon monoxide and hydrogen sulfide, the hydrogen sulfide being present in an amount of about .002 to .06% by volume of the total gas, the volumetric ratio of carbon monoxide to titanium tetrachloride being about .01 to 3.0:1, at a temperature of about 1400 to 1850 C., the oxygen being employed in a stoichiometric excess of about 5 to by volume and a volumetric space velocity of the total gas being about 15 to 45.

8. In a process of producing titanium dioxide by reacting titanium tetrachloride with oxygen by means of diametrically opposed reactant streams to form two parallel laminar flames, the improvement which comprises reacting said materials in the presence of a gaseous mixture consisting essentially of carbon monoxide and a small amount of hydrogen sulfide, the hydrogen sulfide being present in an amount of about .01 to .04% by volume of the total gas, the volumetric ratio of carbon monoxide to titanium tetrachloride being about 0.3 to 1.021, at a temperature of about 1450 to 1600 C., the oxygen being employed in a stoichiometric excess of about 40 to 80% by volume, and a volumetric space velocity of the total gas being about 20 to 40.

9. The process of claim 8 being further characterized by the additional presence of about .01 to .04% by volume of water.

10. The process of claim 8 being further characterized by the additional presence of Water in an amount of .01 to .04% by volume of the total gas and about 1 to 5% by Weight aluminum chloride measured as A1 0 in the finished pigment.

References Cited UNITED STATES PATENTS 911,494 2/1909 Hall 233.1 1,678,630 7/1928 Bahr 23--3.1 1,807,528 5/1931 Hiatt 233.1 2,635,946 4/ 1953 Weber et al. 23202 2,689,781 9/1954 Schaumann 23202 2,823,982 2/1958 Saladin et al. 23-202 2,957,753 10/1960 Nelson et a1 23202 3,069,282 12/1962 Allen 23202 3,121,641 2/1964 Wiksmo et al. 23202 3,224,836 12/1965 Allen et al. 23202 OSCAR R. VERTIZ, Primary Examiner.

EDWARD STERN, Assistant Examiner.

Claims

1. A PROCESS FOR PRODUCING TITANIUM DIOXIDE WHICH COMPRISES REACTING TITANIUM TETRACHLORIDE WITH AN OXYGEN CONTAINING GAS IN THE PRESENCE OF A GASEOUS MIXTURE CONSISTING ESSENTIALLY OF CARBON MONOXIDE AND HYDROGEN SULFIDE, THE HYDROGEN SULFIDE BEING PRESENT IN AN AMOUNT OF ABOUT .002 TO .06% BY VOLUME OF THE TOTAL GAS, THE VOLUMETRIC RATIO OF CARBON MONOXIDE TO TITRANIUM TETRACHLORIDE BEING ABOUT 0.1 TO 3.0:1, AT A TEMPERATURE OF ABOUT 1400*C. TO 1850*C., THE OXYGEN BEING EMPLOYED IN A STOICHIOMETRIC EXCESS OF ABOUT 5 TO 120% BY VOLUME, AND A VOLUMETRIC SPACE VELOCITY OF THE TOTAL GAS BEING ABOUT 15 TO 45.