GB2037266A

GB2037266A - Vapour phase oxidation of titanium tetrachloride

Info

Publication number: GB2037266A
Application number: GB7941763A
Authority: GB
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1978-12-04
Filing date: 1979-12-04
Publication date: 1980-07-09
Also published as: JPS5580721A; BR7907852A; FR2443423B1; GB2037266B; KR830001136A; KR830001367B1; IN152047B; FR2443423A1

Abstract

In the conventional process for production of TiO2 by oxidation of TiCl4 in the vapour phase a reduction in reaction initiation temperature, the avoidance of excessive reactor temperatures, a uniform reactor temperature profile and savings in energy are achieved by introducing at least 1% (but not all) of the titanium tetrachloride into a first reactor zone and adding the remainder to at least one further zone.

Description

SPECIFICATION Process for the oxidation of titanium tetrachloride This invention relates to an improved process for the vapor phase oxidation of TiCI4 to pigmentary TiO2. The processes in current use are wasteful of engergy and result in higher temperatures than are desirable in the reactor because of the exothermic nature of the reaction. Such processes are single step reactions including processes such as are taught in UK Patent 907,211 which attempt to utilize the exothermic nature of this reaction through the recirculation of combustion products.Further, it is well-known that both the oxygen and TiCI4 containing reactant streams must be preheated and well mixed to achieve efficient oxidation into pigmentary TiO2, see for example, US Patents 3,414,379; 3,632,313 and 3,650,694. The instant process is an improvement over prior processes in that it reduces the energy required to initiate amd maintain the reaction and also provides for a more uniform and lower temperature profile during the reaction through the use of sequential addition of TICI4 to the oxygen-containing stream.

This invention is an improvement in the vapor phase oxidation of TiCI4 which comprises introducing the at least 1% of the titanium tetrachloride based upon the total TiCI4 to be oxidized into the oxygen-containing gas stream, allowing the reaction between the titanium tetrachloride and oxygen to be initiated and then introducing the remainder of the titanium tetrachloride into the reaction stream. Such addition may, if desired, also be carried out incrementally. In general, the addition of the second, and further increments of TiCI4 will ideally be added to the reaction stream at the point where the previously added TiCI4 has released its heat of reaction.These addition points can be experimentally determined and will, of course, depend upon the TiCI4 to 2 ratio, the relative volumes of the reactant streams, the flow rate of the reaction streams, the amont of preheat of the reaction gases involved and the heat loss of the reactor itself.Specifically, the process of this invention involves preheating the oxidizing gas stream to a temperature of from 800"C to 1 600 C; preferably from 900"C to 1 300"C; preheating the titanium tetrachloride to a temperature of from 250into 500"C and injecting from 1% to 75% of the TiC14 to be reacted, preferably 10% to 40% and most preferably 15% to 35% of the TiC14 to be reacted, into the oxidizing gas stream; allowing oxidation to occur and adding from, in one or more increments, 99 to 25% of the TiC14 to be reacted into the reaction stream.As indicated above, the amount of TiCI4 introduced into the oxygen-containing stream is expressed as the amount of TiCI4 to be reacted since the oxygen in the stream will always be in excess of that required to form TiO2. It will also be understood that the term "oxidizing gas stream" refers to a reactant stream containing oxygen. The composition of the oxidizing gas stream may range from low concentrations of oxygen such as air to pure oxygen and may, for example, be oxygen-enriched air. In addition, the oxidizing gas stream may, if desired, contain other substances beneficial to the reaction such as water vapor, chlorine, alkali and/or alkaline earth metal halides. Likewise, the TiCI4 reactant stream may contain substances beneficial to the reaction such as a halide (preferably the chlorides) of aluminium, silicon and/or phosphorous (e.g.

aluminium trichloride).

As indicated above, both the oxidizing gas stream and the TiCI4-containing gas stream are preheated to some extent. The amount of preheat of each of the streams will depend upon the reiative amounts of each gas present in the streams at the point when the TiCI4 is first introduced into the oxidizing gas stream. The bulk temperature of the reaction stream, i.e., the combined oxidizing gas stream and TiCI4-containing stream, at the point limiting combustion should be between 700"C and 1 2000C and preferably between 750"C and 950"C to assure that rapid oxidation will occur and that the reaction will not be extinguished.The subsequent additions of the TiCI4 stream will also have to be adjusted so that at no time does the bulk temperature of the reaction stream fall to the point where the reaction would be extinguished.

In order to assure production of uniform high quality pigmentaryTiO2, rapid efficient mixing of the TiC14 into the oxidizing gas stream must be accomplished upon its introduction into the oxidizing gas stream. This proper mixing, to assure rapid contact of the reactants, can be accomplished such as taught in US Patent 2,791,490 by means of, for example, an annular ring of holes, side tee mixing or annular flow from a center pipe. The reactor itself will in general be tubular to provide for good pigment properties and thoughput with minimum maintenance problems.Typically, when 25% of the TiC4 to be reacted is introduced into the first stage of a two stage reaction process, the oxidizing gas stream is conveniently preheated to a temperature of about 1000"C. The TiCI4 preheated, for example, to a temperature of 400 C, is injected into the oxidizing stream, for example, through circumferential ring jet nozzles. The reaction stream thus formed passes through the reactor to a second TiC14 addition point. It will also be understood the Cl2 or other inert purge gas may also be introduced into the reactor, for example to help control temperature, to reduce pigment wall scale formation and to reduce back mixing.The procedure for introducing the TiCl4-containing stream is repeated as often as desired to achieve the reaction profile desired. It is believed that a sequential, multistep oxidation of TiC14 wll be especially suited to the production of anatase TiO2, which hitherto has been difficult to obtain in a vapor phase oxidation of TiCI4, the process yielding a less agglomerated and, therefore, more desirable pigment.

The following examples are intended to illustrate the invention by way of particular example.

Examples 1-7 A two-stage reaction would be accomplished as follows: A stream of oxygen preheated to a temperature of A C is introduced into a 10-inch, inside diameter, tubular, chlorine purged reactor operated at 25 psig pressure at a rate of 9,800 pounds (4,445 kg) per hour.

The reactor is divided into oxidation zones at the beginning of which are circumferential rings of holes through which the titanium tetrachloride gas stream is introduced into the reactor. The titanium tetrachloride stream contains aluminium trichloride sufficient to provide 1% by weight A1203 in the titanium dioxide pigment produced. The titanium tetrachloride stream is preheated to 400"C and is fed to the reactor at a rate of 47,200 pounds (21,410 kg) pounds per hour. In the first oxidation zone, B% of the titanium tetrachloride to be oxidized is introduced into the reactor through circumferential holes in a manner which will insure complete and uniform mixing with the preheated oxygen.The temperature of the reaction gas stream after the titanium tetrachloride has been oxidized is C"C. The remaining D% of the titanium tetrachloride to be oxidized into titanium dioxide is introduced into the reaction gas stream in a second reaction zone through a circumferential ring of holes. The temperature of the reaction gas stream is E"C after the addition of the titanium tetrachloride is complete, whereupon TiO2 scrub solids are introduced into the reactor and the reaction stream exits the reactor into cooling ducts. The reaction product is pigmentary size rutile TiO2.

The amount of titanium tetrachloride, oxygen preheat temperature and reaction stream temperature for each example is presented in the table below: TABLE Example A B C D E 02 Wet air %TiCl4 C % TiC14 C Temp. C 1 1600 1.0 1415 99 1382 2 1375 10.0 1317 90 1309 3 1100 20 1250 80 1316 4 965 25 1255 75 1323 5 1000 30 1313 70 1335 6 1070 40 1370 60 1341 7 1300 75 1439 25 1362 Example 8 Athree-stage reaction is accomplished as follows: A stream of oxygen preheated to a temperature of 900"C is introduced into a 10-inch inside diameter tubular, chlorine purged, reactor operated at 25 psig pressure at a rate of 12,250 pounds (5,557 kg) per hour.

The reaction is divided into oxidation zones at the beginning of which are circumferential rings of holes through which the titanium tetrachloride gas stream is introduced into the reactor. The titanium tetrachloride stream contains aluminium trichloride sufficient to provide 1% A1203 in the titanium dioxide pigment produced. The titanium tetrachloride stream is preheated to 400 C. In the first oxidation zone, 5% of the titanium tetrachloride to be oxidized is introduced into the reactor through circumferential holes in a manner which will insure complete and uniform mixing with the preheated oxygen.The temperature of the reaction gas stream after the titanium tetrachloride has been oxidized is 980"C. In the second oxidation zone, 20% of the titanium tetrachloride to be oxidized is introduced into the reactor through circumferential holes in a manner which will insure complete and uniform mixing with the oxygen-containing reaction gas stream. The temperature of the reaction gas stream after the second addition of titanium tetrachloride is 1220"C. The remaining 75% of the titanium tetrachloride to be oxidized is introduced into the oxygen-containing reaction gas stream in a third reaction zone through a circumferential ring of holes.The temperature of the reaction gas stream is 1 280"C after the addition of the titanium tetrachloride is complete, whereupon TiO2 scrub solids are introduced into the reactor and the reaction stream exits the reactor into cooling ducts. The reaction product is pigmentary size anatase TiO2.

Example 9 A 10-inch inside diameter, tubular, chlorine purged reactor was charged with 12,000 pounds (5,443.2 kg) per hour of oxygen preheated to a temperature of 1406"C. Into this oxygen-containing stream was charged, through a circumferential ring of holes, 10,440 pounds (4,735.6 kg) per hour of TiCI4 containing about 29 pounds (13.2 kg) per hour of PC13 and 84 pounds (38.1 kg) per hour of SiC4. Approximately 4.6 feet down-stream of the first zone of addition, 36,740 pounds (16,665.3 kg) per hour of TiCI4, 101 pounds (45.8 kg) per hour of PCI3 and 296 pounds (134.3 kg) per hour of SiCI4 is added to the reaction stream through a circumferential ring of holes. The TiCI4 stream containing the PCl3 and SiCI4 was preheated to a temperature of 468"C prior to injection into the reaction stream. The reaction was allowed to proceed and the product was conventionally cooled, coilected in water, calcined and ground. The product was of pigmentary size and was composed of about 67% anatase and about 33% rutile TiO2.

Claims

1. A process for producing titanium dioxide which process comprises oxidizing titanium tetrachloride, at least 1% of the titanium tetrachloride being introduced into a first oxidation zone of an oxidation reactor and the remainder of the titanium tetrachloride being introduced into a second and optionally one or more further oxidation zones of said reactor.

2. A process as claimed in Claim 1 wherein the titanium tetrachloride is oxidized by contact with an oxidizing gas stream having a temperature upon contact of from 800"C to 1 6000C.

3. A process as claimed in Claim 1 wherein the titanium tetrachloride is oxidized by contact with an oxidizing gas stream having a temperature upon contact of from 900"C to 1300 C.

4. A process as claimed in any one of Claims 1 to 3 wherein the titanium tetrachloride has a temperature of from 250"C to 500or.

5. A process or producing titanium dioxide by reacting preheated oxygen in an oxidizing gas stream and a preheated titanium tetrachloride-containing stream, the process comprising: (a) preheating the oxidizing gas stream to a temperature of from 800"C to 1600"C; (b) preheating the titanium tetrachloride containing-stream to a temperature of from 250"C to 5000C; (c) adding from 1 to 75% of the titanium tetrachloride to be oxidized to the oxidizing gas stream; (d) allowing oxidation reaction to occur; (e) adding to the reaction stream in one or more feed zones, from 99% to 25% of the titanium tetrachloride to be oxidized; (f) allowing oxidation reaction to occur; and (g) cooling and collecting the TiO2 produced.

6. A process as claimed in Claim 5 wherein from 10% to 40% of the titanium tetrachloride to be oxidized is introduced into a first reaction zone and the remainder of the titanium tetrachloride to be oxidized is added in one or more feed zones.

7. A process as claimed in Claim 6 in which from 15% to 35% of the titanium tetrachloride to be oxidized is introduced into the first reaction zone.

8. A process of producing titanium dioxide by reacting preheated oxygen in an oxidizing gas stream and a preheated titanium tetrachloride-containing stream, the process comprising: (a) preheating the oxidizing gas stream to a temperature of from 900"C to 1300"C; (b) preheating the titanium tetrachloride-containing stream to a temperature of from 250"C to 5000C; (c) adding from 15% to 35% of the titanium tetrachloride to be oxidized to the oxidizing gas stream; (d) allowing the oxidation reaction to occur; (e) adding from 65% to 85% of the titanium tetrachloride to be oxidized to the reaction stream; (f) allowing oxidation reaction to occur; and (g) cooling and collecting the TiO2 produced.

9. A process as claimed in any preceding claim wherein the oxidation of the titanium tetrachloride is effected by contact thereof with oxygen, air or oxygen-enriched air, optionally containing water vapour, chlorine, an alkali metal halide and/or an alkaline earth metal halide.

10. A process as claimed in any preceding claim wherein the oxidation is effected in the presence of one or more of the following materials present in the titanium tetrachloride, namely a halide of aluminium, a halide of silicon and a halide of phosphorus.

11. A process as claimed in Claim 1 and substantially as hereinbefore described in any one of the foregoing specific examples.

12. Titanium dioxide whenever obtained buy a process as claimed in any preceding claim.