System for increasing the capacity of a titanium dioxide producing process

A system for increasing the capacity of a process for producing titanium dioxide by reacting titanium tetrachloride vapors with oxygen wherein the process includes an oxygen preheat assembly for preheating oxygen to a predetermined temperature level and a first titanium tetrachloride preheat assembly for preheating titanium tetrachloride to a first, relatively high, temperature level, a portion of the oxygen and the titanium tetrachloride vapors at the first temperature level being reacted in a first reaction zone to produce a mixture of titanium dioxide reaction product, oxygen and unreacted titanium tetrachloride vapors at the first temperature level. The system comprises adding a second titanium tetrachloride preheat assembly for preheating titanium tetrachloride to a second temperature level, substantially below the first temperature level, and adding a second reaction zone adapted for receiving the mixture from the first reaction zone, the titanium tetrachloride vapors at the first temperature level in said mixture and the titanium tetrachloride vapors at the second temperature level being reacted with the oxygen in the mixture from the first reaction zone to produce titanium dioxide. The present invention also contemplates an improved reactor for use in the system for increasing the capacity of the titanium dioxide producing process.

BACKGROUND OF THE INVENTION 
Field of the Invention 
The present invention relates generally to a system for producing titanium 
dioxide by reacting titanium tetrachloride vapors with oxygen and, more 
particularly, but not by way of limitation, to a system for increasing the 
capacity of a titanium dioxide producing process and to an improved 
reactor for use in such a system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Titanium dioxide, which is useful as a pigment, has been produced on a 
commercial scale by reacting titanium tetrachloride vapor with oxygen. In 
one type of titanium tetrachloride-oxygen reactor, a preheated oxidizing 
gas was passed into a reaction zone and preheated titanium tetrachloride 
vapor was passed into the same reaction zone where the titanium 
tetrachloride vapor was reacted with the oxygen contained in the oxidizing 
gas according to the following reaction: 
EQU TiCl.sub.4 +O.sub.2 .fwdarw.TiO.sub.2 +2Cl.sub.2 
The combined temperature of the reactants (titanium tetrachloride and 
oxygen), before reaction, had to be at least 1600.degree. F. in order to 
sustain the oxidation reaction and, preferably, the combined temperature 
of the reactants was between about 1650.degree. F. and about 1800.degree. 
F. In one operable embodiment, the oxidizing gas was preheated for 
introduction into the reaction zone to a temperature of about 1800.degree. 
F. and the titanium tetrachloride vapor was preheated for introduction 
into the reaction zone to a temperature of about 1750.degree. F. 
Titanium tetrachloride vapors at relatively high temperatures of about 
1750.degree. F., for example, are highly corrosive and, thus, the 
preheating equipment utilized for preheating such titanium tetrachloride 
vapors has been extremely expensive. It is highly desirable to develop a 
system for producing titanium dioxide by reacting titanium tetrachloride 
vapor with oxygen utilizing titanium tetrachloride vapors preheated to 
minimum temperature levels, such as below 400.degree. F., for example, 
since this would permit the utilization of less expensive equipment for 
preheating the titanium tetrachloride. The present invention provides a 
system for increasing the capacity of a titanium dioxide producing process 
in a more efficient and more economical manner. 
A reactor of the type which has been utilized in the process for producing 
titanium dioxide by reacting titanium tetrachloride vapor with oxygen in 
the manner just generally described was disclosed in U.S. Pat. No. 
3,512,219, issued to Stern, et al. and the disclosure of the Stern, et al. 
patent specifically hereby is incorporated herein by reference. 
In this prior process, pure oxygen was heated in a radiant tube furnace. In 
one operable embodiment, the oxygen only could be heated to a maximum 
temperature of about 1800.degree. F. due primarily to the thermal 
efficiency and the materials of construction of the particular oxygen 
preheating apparatus. Thus, in this process, the titanium tetrachloride 
vapors also had to be heated to a temperature of about 1800.degree. F. in 
the titanium tetrachloride vapor preheating apparatus. In the alternative, 
additional oxygen preheating equipment might be added to the existing 
oxygen preheating equipment in an effort to elevate the oxygen temperature 
to a level above 1800.degree. F., thereby permitting the utilization of 
titanium tetrachloride vapors which have been preheated to lower 
temperature levels, below 1800.degree. F. However, the additional oxygen 
preheating equipment represents a substantial expense and such expense 
might not be offset by any savings in the titanium tetrachloride vapor 
preheating apparatus resulting from the lower temperature requirements for 
the titanium tetrachloride vapors. 
In the operable process referred to before, the titanium tetrachloride 
vapor preheating equipment utilized silica pipe for the containment of the 
highly corrosive titanium tetrachloride vapors. The size of the silica 
pipe has been limited to a maximum of about six inches, because current 
manufacturing techniques suitable for producing relatively flawless silica 
pipe apparently are limited to a maximum of about six inches. Also, the 
strength and integrity of the welded silica pipe joints decreases with 
increasing diameters and breakage has been more probable with higher 
diameter silica pipes. The maximum permissible pressures within the silica 
pipe decreases with increasing diameters and above six inch diameter 
silica pipes might result in working pressures insufficient to efficiently 
drive the titanium tetrachloride vapors downstream from the titanium 
tetrachloride vapor preheating equipment. 
Also, the injection of auxiliary fuels, such as carbon monoxide and 
methane, for example, directly into the reactor to stabilize the flame in 
the reactor has been suggested as a means for lowering the temperature 
level requirements for the titanium tetrachloride vapors, thereby 
increasing the capacity of existing titanium tetrachloride vapor 
preheating equipment, the silica pipe preheaters. However, this approach 
leads only to minor reduction in the temperature required for the titanium 
tetrachloride vapors, such reduction being in the range of about 
200.degree. F. to about 500.degree. F. Thus, the titanium tetrachloride 
vapors still would have to be preheated to significantly high temperatures 
where titanium tetrachloride corrosion problems still would exist. In 
addition, the combustion products from the reactor utilizing this approach 
diluted the chlorine recycle gas and resulted in larger capacity 
downstream equipment being required to process the increased gas load. 
Shown in FIGS. 1 and 2 is a reactor 10 which is constructed in accordance 
with the present invention for use in a process for producing titanium 
dioxide by vapor-phase oxidation of titanium tetrachloride. In general, 
the reactor 10 comprises: an oxidizing gas introduction assembly 12 which 
is adapted to receive oxygen from oxygen preheat equipment 14 by way of a 
flowline 16 and pass the oxygen into a first reaction zone 18 formed in 
the reactor 10; a first titanium tetrachloride vapor introduction assembly 
20 which is adapted to receive titanium tetrachloride vapor at an elevated 
first temperature level from first titanium tetrachloride preheat 
equipment 22 by way of a flowline 24 and to pass the titanium 
tetrachloride vapor at the first temperature level into the first reaction 
zone 18; and a second titanium tetrachloride vapor introduction assembly 
26 which is adapted to receive titanium tetrachloride vapor at a second 
temperature level, substantially less than the first temperature level, 
from second titanium tetrachloride preheat equipment 28 by way of a 
flowline 30 and to pass the titanium tetrachloride vapor at the second 
temperature level into a second reaction zone 32, the mixture from the 
first reaction zone 18 being passed into the second reaction zone 32 for 
reacting with the titanium tetrachloride vapors at the second temperature 
level which simultaneously are being passed into the second reaction zone 
32. 
The oxidizing gas introduction assembly 12 includes a tubular conduit 34 
having a downstream end 36, an upstream end 38 and an opening 39 extending 
axially therethrough. The conduit 34 generally is cylindrically shaped and 
has a length 40 extending generally between the downstream and the 
upstream ends 36 and 38. The conduit 34 has an internal diameter 41. 
The oxidizing gas introduction assembly 12 also includes a cylindrically 
shaped case 42 having a downstream end 44, an opposite upstream end 46 and 
an opening 47 extending axially therethrough. A downstream end wall 48 is 
secured to the downstream end 44 and an upstream end wall 50 is secured to 
the upstream end 46 of the case 42. 
The inner diameter of the case 42 formed by the opening 47 is larger than 
the outer diameter of the conduit 34 and the upstream end 38 of the 
conduit 34 extends through a central portion of the downstream end wall 48 
so that a portion of the conduit 34, generally near the upstream end 38 is 
disposed within a portion of the opening 47 in the case 42, the upstream 
end 38 being spaced a distance from the upstream end wall 50. The space 
between the inner wall formed by the opening 47 extending through the case 
42 and the outer peripheral surface of the conduit 34 cooperate to form a 
gas chamber 52 and the space between the upstream end 38 of the conduit 34 
and the upstream end wall 50 cooperate to form a slot 54 for providing 
fluidic communication between the gas chamber 52 and the opening 39 in the 
conduit 34. 
As shown in FIGS. 1 and 2, one end of the flowline 16, opposite the end of 
the flowline 16 which is connected to the oxygen preheat equipment 14, is 
connected to the case 42, so the flowline 16 provides fluidic 
communication between the oxygen preheat equipment 14 and the gas chamber 
52. 
In one embodiment, as shown in FIGS. 1 and 2, an injection tube 56 is 
disposed through a central portion of the upstream end wall 50 and the 
injection tube 56 extends a distance axially through a central portion of 
the opening 39 in the conduit 34. As mentioned in U.S. Pat. No. 3,512,219, 
issued to Stern, et al., it sometimes is advantageous in the operation of 
a reactor of the reactor 10 type to introduce an inert, particulate 
material into the flow of gases through such a reactor and the injection 
tube 56 provides a means for injecting such material. 
The first titanium tetrachloride introduction assembly 20 includes a 
cylindrically shaped case 58 having an upstream end 60, a downstream end 
62 and an opening 64 extending axially therethrough. An upstream end wall 
66 is secured to the upstream end 60 and a downstream end wall 68 is 
secured to the downstream end 62 of the case 58. 
The inner diameter of the case 58 formed by the opening 64 is larger than 
the outer diameter of the conduit 34, and the downstream end 36 of the 
conduit 34 extends through a central portion of the upstream end wall 66 
so that a portion of the conduit 34, generally near the downstream end 36, 
is disposed within a portion of the opening 64 in the case 58. The space 
between the inner wall formed by the opening 64 extending through the case 
58 and the outer peripheral surface of the conduit 34 cooperate to form a 
first titanium tetrachloride chamber 70. 
As shown in FIG. 2, one end of the flowline 24, opposite the end of the 
flowline 24 which is connected to the first titanium tetrachloride preheat 
equipment 22, is connected to the case 58, so the flowline 24 provides 
fluidic communication between the first titanium tetrachloride preheat 
equipment 22 and the first titanium tetrachloride chamber 70. In one 
embodiment, the flowline 24 is connected to the case 58 in an offset 
manner so that titanium tetrachloride vapor is passed from the flowline 24 
and tangentially injected into the first titanium tetrachloride chamber 70 
to introduce a circular or swirling motion to such titanium tetrachloride 
vapors. For similar reasons, the flowline 16 is connected to the case 42 
of the oxidizing gas introduction assembly 12 in a similar manner so the 
oxidizing gas is passed into the oxygen chamber 52 tangentially to 
introduce a circular or swirling motion to the oxidizing gas in the 
embodiment of the reactor 10 shown in FIGS. 1 and 2. 
The reactor 10 includes a frusto-conical section 72 having a downstream end 
74, an upstream end 76 and an opening 78 extending axially therethrough 
intersecting the downstream and upstream ends 74 and 76. The section 72 
has an inner diameter 80 formed by the opening 78, generally at the 
upstream end 76, an inner diameter 82 formed by the opening 78, generally 
at the downstream end 74, and the opening 78 in the section 72 diverges 
generally outwardly at an angle 84. The section 72 has a length 86 
extending generally between the downstream and the upstream ends 74 and 
76. 
The upstream end 76 of the section 72 extends through a central portion of 
the downstream end wall 68. The upstream end 76 of the section 72 is 
spaced a distance 88 axially from the downstream end 38 of the conduit 34, 
thereby forming a slot 89 in the first titanium tetrachloride chamber 70 
providing fluidic communication between the chamber 70 and the opening 78 
in the section 72. The opening 78 in the section 72 is axially aligned 
with the opening 39 in the conduit 34. 
The second titanium tetrachloride introduction assembly 26 spaced a 
distance in a downstream direction from the first titanium tetrachloride 
assembly 20, and the second titanium tetrachloride introduction assembly 
26 includes a cylindrically shaped case 90 having a downstream end 92, an 
upstream end 94 and an opening 96 extending axially therethrough. An 
upstream end wall 98 is secured to the upstream end 94 and a downstream 
end wall 100 is secured to the downstream end 92 of the case 90. 
The inner diameter of the case 90 formed by the opening 96 is larger than 
the outer diameter of the section 72, and the downstream end 74 of the 
section 72 extends through a central portion of the upstream end wall 98, 
so that a portion of the section 72, generally near the downstream end 74, 
is disposed within a portion of the case 90. The space between the inner 
wall formed by the opening 96 extending through the case 90 and the outer 
peripheral surface of the section 72, generally near the downstream end 74 
of the section 72, cooperate to form a second titanium tetrachloride 
chamber 102. 
The flowline 30, opposite the end of the flowline 30 which is connected to 
the second titanium tetrachloride preheat equipment 28, is connected to 
the case 90, so the flowline 30 provides fluidic communication between the 
second titanium tetrachloride preheat equipment 28 and the second titanium 
tetrachloride chamber 102. In one embodiment, the flowline 30 is connected 
to the case 90 in an offset manner similar to that described before with 
respect to the flowlines 16 and 24, so the titanium tetrachloride vapor is 
passed from the flowline 30 and tangentially injected into the second 
titanium tetrachloride chamber 102 to introduce a circular motion or 
swirling action to such titanium tetrachloride. 
The reactor 10 includes another frusto-conical section 104 having a 
downstream end 106, an upstream end 108 and an opening 110 extending 
axially therethrough intersecting the downstream and the upstream ends 106 
and 108. The section 104 has an inner diameter 112 formed by the opening 
110 generally at the upstream end 108, an inner diameter 114 formed by the 
opening 110, generally at the downstream end 106, and the opening 110 in 
the section 104 diverges generally outwardly at an angle 116. The section 
104 has a length 118 extending generally between the downstream and the 
upstream ends 106 and 108. 
The upstream end 108 of the section 104 extends through a central portion 
of the downstream end wall 100. The upstream end 108 of the section 104 is 
spaced a distance 120 axially from the downstream end 74 of the section 
72, thereby forming a slot 122 in the second titanium tetrachloride 
chamber 102 providing fluidic communication between the chamber 102 and 
the opening 110 in the section 104. The opening 110 in the section 104 is 
axially aligned with the opening 78 in the section 72. 
The reactor 10 includes a cooling tube 124 having an upstream end 126 and 
an opening 128 extending therethrough intersecting the upstream end 126 
and the downstream end (not shown in the drawings). The cooling tube 124 
has an internal diameter formed by the opening 128. 
The oxygen preheat equipment 14 is contructed to heat the oxygen gas to a 
temperature level of about 1800.degree. F., in one example preferred 
embodiment. Oxygen preheat equipment which is constructed to preheat 
oxygen gas to a temperature level of about 1800.degree. F. for use in a 
process for producing titanium dioxide by vapor-phase oxidation of 
titanium tetrachloride is commercially available and such equipment is 
well known in the art. 
In this example embodiment, the first titanium tetrachloride preheat 
equipment 22 is constructed to heat titanium tetrachloride vapors to a 
first temperature level of about 1800.degree. F. Titanium tetrachloride 
preheat equipment which is constructed to heat titanium tetrachloride 
vapors to the first temperature level of about 1800.degree. F. for use in 
a process for producing titanium dioxide by vapor-phase oxidation of 
titanium tetrachloride is commercially available and such equipment is 
well known in the art. In one embodiment, for example, the titanium 
tetrachloride first is heated and vaporized in a shell-and-tube type heat 
exchanger operating at a temperature level of about 350.degree. F. and, 
then, the titanium tetrachloride is superheated to the first temperature 
level of above 1600.degree. F. in the silica pipe type of heater. One type 
of heater which is useful in heating and vaporizing the titanium 
tetrachloride at temperature levels of about 400.degree. F. is a 
shell-and-tube heat exchanger with a u-shaped tube bundle of nickel and 
glass-lined carbon steel sheel manufactured by The Pfaudler Company, for 
example. The tube-side heating medium is steam, but may, at temperatures 
approaching 400.degree. F., be some other heat transfer fluid such as 
Dowtherm, available from Dow Chemical Co., for example, should suitable 
steam pressure be unavailable. One silica pipe heater which is useful for 
receiving the titanium tetrachloride at about 400.degree. F. and for 
superheating the titanium tetrachloride to the first temperature level of 
above 1600.degree. F. is a tubular radiant-heat furnace with vertical 
silica pipe, manufactured by Selas Corporation of America, for example. 
In this example embodiment, the second titanium tetrachloride preheat 
equipment 28 is constructed to preheat and vaporize titanium tetrachloride 
vapor at the second temperature level of about 350.degree. F. This 
titanium tetrachloride can be heated and vaporized in the same type of 
heat exchanger employed in the first preheat step described above, and 
which is not subject to the capacity limitations presently existing with 
respect to the silica pipe heaters utilized in heating titanium 
tetrachloride to the elevated, relatively high temperature levels, such as 
the 1800.degree. F. temperature level, for example. 
In this example embodiment, a suitable reactor 10 would have the following 
approximate dimension values by way of example and for the purpose of 
illustrating the present invention. 
______________________________________ 
the inner diameter of the 
3 inches 
flowline 16 entering the 
first oxidizing gas intro- 
duction assembly 
the inner diameter 41 of 
4 inches 
the conduit 34 
the outer diameter of the 
1 inch 
injection tube 56 
the inner diameter of the 
4 inches 
flowline 24 entering the 
first titanium tetra- 
chloride introduction 
assembly 20 
the length 40 24 inches 
the distance 88 with re- 
0.6 inches 
spect to slot 89 
the diameter 80 of 4 inches 
section 72 
the diameter 82 of 6 inches 
section 72 
the length 86 24 inches 
the angle 84 2.5 degrees 
the inner diameter of 3 inches 
the flowline 30 entering 
the second titanium 
tetrachloride introduction 
assembly 26 
the distance 120 with re- 
0.3 inches 
spect to slot 122 
the diameter 112 of section 
6 inches 
104 
the diameter 114 of section 
8 inches 
104 
the distance 118 of section 
24 inches 
104 
the angle 116 2.5 degrees 
______________________________________ 
In this example embodiment and assuming a capacity of 100 tons per 
twenty-four hour period of titanium dioxide produced utilizing the reactor 
10, the flow of oxygen gas into the oxidizing gas introduction assembly 12 
and through the reactor 10 is about 120 pound mole per hour, the flow of 
titanium tetrachloride at the first temperature level into the first 
titanium tetrachloride introduction assembly 20 and through the reactor 10 
is about 52 pound mole per hour and the flow of titanium tetrachloride at 
the second temperature level into the second titanium tetrachloride 
introduction assembly 26 and through the reactor 10 is about 52 pound mole 
per hour. In this example embodiment, about one pound mole per hour of 
oxygen together with two hundred pounds per hour of sand is passed through 
the injection tube 56. 
In operation, oxygen is preheated in the oxygen preheat equipment 14 to the 
predetermined temperature level and the preheated oxygen is passed at a 
controlled, predetermined rate through the flowline 16 to the oxidizing 
gas introduction assembly 12. The oxidizing gas introduction assembly 12 
receives the preheated oxygen and the preheated oxygen is passed into the 
oxygen chamber 52, through the slot 54 and through the opening 39 in the 
conduit 34 downstream into the first reaction zone 18. 
Titanium tetrachloride is preheated in the first titanium tetrachloride 
preheat equipment 22 to the first predetermined temperature level and the 
preheated titanium tetrachloride vapors are passed through the flowline 24 
at a controlled rate into the first titanium tetrachloride introduction 
assembly 20. The first titanium tetrachloride introduction assembly 20 
receives the preheated titanium tetrachloride vapors and the preheated 
titanium tetrachloride vapors are passed in the first titanium 
tetrachloride chamber 70, through the slot 89 and into the first reaction 
zone 18, where the oxygen and the titanium tetrachloride at the first 
temperature level react to produce a mixture including particles of 
titanium dioxide, this mixture being passed downstream into the second 
reaction zone 32. 
Titanium tetrachloride is preheated in the second titanium tetrachloride 
preheat equipment 28 to the predetermined second temperature level and the 
titanium tetrachloride vapors are passed at a controlled rate through the 
flowline 30 into the second titanium tetrachloride introduction assembly 
26. The second titanium tetrachloride introduction assembly 26 receives 
the preheated titanium tetrachloride vapors and the titanium tetrachloride 
vapors are passed into the second titanium tetrachloride chamber 102, 
through the slot 122 and into the second reaction zone 32, where the 
titanium tetrachloride vapors at the second temperature level react with 
the oxygen in the mixture passed from the first reaction zone 18 to 
produce a mixture including additional titanium dioxide, the mixture from 
the second reaction zone 32 being passed downstream for further processing 
in a manner well known in the art of producing titanium dioxide by 
vaporphase oxidation of titanium tetrachloride. 
In order to react the oxygen and the titanium tetrachloride vapors in a 
manner which ensures rutile as the dominant phase in the titanium dioxide 
product, the temperature in the reaction zones 18 and 32 must be above a 
minimum temperature level of about 2200.degree. F. 
The combined temperature of the reactants, prior to reaction, to produce 
the required reactions, must be at least 1600.degree. F. to sustain the 
oxidation reaction and, preferrably, the combined temperature of the 
reactants, before reaction, should be in the range of about 1650.degree. 
F. to about 1800.degree. F. In practice and in one operational process for 
producing titanium dioxide by vapor-phase oxidation of titanium 
tetrachloride, the oxygen is preheated to a temperature level of 
1800.degree. F. and the titanium tetrachloride is preheated to a 
temperature level of above 1750.degree. F. or about 1800.degree. F. In 
this operational process, the oxygen and the titanium tetrachloride vapors 
are reacted in a reaction zone utilizing a reactor like that disclosed in 
Stern, et al., U.S. Pat. No. 3,512,219 to produce a mixture including 
titanium dioxide, and the mixture (product of reaction) is passed 
downstream for further processing. 
The reaction of the titanium tetrachloride vapors with the oxygen to form 
the titanium dioxide is exothermic. In a completely adiabatic system, a 
reaction temperature of about 2400.degree. F. is attainable, starting with 
350.degree. F. TiCl.sub.4 vapor and 77.degree. F. oxygen, which is above 
the minimum temperature of 2200.degree. F. required to insure rutile as 
the dominate phase in the titanium dioxide product of reaction. The system 
of the present invention utilizes this heat of reaction to reduce the 
preheat requirement for a portion of the titanium tetrachloride vapors 
utilized. 
Utilizing only the first reaction zone and assuming a flow of oxygen from 
the oxygen preheat assembly 14 of 60 pound moles per hour at a temperature 
level of about 1800.degree. F. and assuming a flow of titanium 
tetrachloride from the first titanium tetrachloride preheat assembly 28 of 
52 pound moles per hour at a temperature level of about 1800.degree. F., 
about 4150 pounds per hour of titanium dioxide are produced and the heat 
of reaction in the first reaction zone, assuming a completely adiabatic 
system, will generate a temperature of above 2400.degree. F., which is 
well above the minimum temperature level required to ensure rutile as the 
dominant phase in the titanium dioxide product. 
Assuming a plant existed operating with a single reaction zone reactor as 
mentioned above, the equipment associated with the first titanium preheat 
assembly 28 already is in existence and the silica pipe heater portion of 
this equipment is relatively expensive equipment due to the corrosive 
nature of the titanium tetrachloride at the first temperature level of 
about 1800.degree. F. In this situation, the reactor 10 can be substituted 
for the single reaction zone reactor, additional equipment can be added to 
the oxygen preheat assembly 14 to increase the capacity of such oxygen 
preheat assembly 14 so that about 120 pound moles per hour are preheated 
by the oxygen preheat assembly 14, and the second titanium tetrachloride 
preheat assembly 28 can be added for preheating titanium tetrachloride to 
the second temperature level of about 350.degree. F. and for passing about 
52 pound moles per hour into the second reaction zone 32. Under these 
conditions, about one-half of the oxygen will react with the titanium 
tetrachloride in the first reaction zone 18 and the mixture including the 
excess oxygen will reach a temperature level of above 2400.degree. F. due 
to the heat of reaction and assuming a completely adiabatic system. This 
mixture is passed from the first reaction zone into the second reaction 
zone 32 wherein the excess oxygen in the mixture will combine with the 
titanium tetrachloride vapors at the second temperature level which are 
being passed into the second reaction zone 32 from the second titanium 
tetrachloride preheat assembly 28 and the temperature level of this 
combined mixture will be above 1800.degree. F. which is sufficient to 
sustain the oxidation reaction. Thus, the excess oxygen in the mixture 
passed from the first reaction zone 18 will react with the titanium 
tetrachloride vapors at the second temperature level in the second 
reaction zone to produce additional titanium dioxide product. Under these 
assumed conditions, the reactor 10 will produce about 8300 pounds per hour 
of the titanium dioxide product. Thus, utilizing the reactor 10 of the 
present invention with two reaction zones 18 and 32, about twice the 
amount of titanium dioxide product is produced without the necessity of 
adding any additional titanium tetrachloride preheat equipment capable of 
heating the titanium tetrachloride to the first temperature level of about 
1800.degree. F. and in a manner wherein it only was necessary to add the 
second titanium tetrachloride preheat assembly 28 which is capable of 
heating the titanium tetrachloride to the lower temperature level of about 
350.degree. F. Utilizing the system of the present invention, the capacity 
of a plant almost can be doubled without a corresponding doubling of the 
costs of equipment. Of course, a new plant also can be constructed for 
substantially less investment in equipment per pound of titanium dioxide 
produced. 
It should be noted that, in some embodiments, it may be desirable to 
utilize a shell-and-tube heat exchanger to heat and vaporize the titanium 
tetrachloride at the second temperature level of about 350.degree. F. and 
a portion of the titanium tetrachloride at the second temperature level of 
about 350.degree. F. can be fed or passed into the second reaction zone 
32, while the remaining portion of the titanium tetrachloride at the 
second temperature level can be fed or passed to the silica pipe type of 
heaters wherein the titanium tetrachloride is heated to the first 
temperature level of about 1750.degree. F. In other applications, it may 
be desirable to utilize two, separate shell-and-tube heat exchangers in 
the first and second titanium tetrachloride preheat assemblies 22 and 28. 
It should be noted that, in a preferred embodiment, the walls of the 
reactor 10 are cooled (fluid cooling) to protect the walls and to reduce 
titanium dioxide deposition on the walls. Also, other reagents, such as 
aluminum chloride and water vapor, are added through the conduit 34 for 
controlling or modifying pigment (titanium dioxide) properties in an 
operational embodiment of the reactor 10. 
Embodiment of FIG. 3 
Shown in FIG. 3 is a modified reactor 10a which is constructed exactly like 
the reactor 10 shown in FIGS. 1 and 2 and described in detail above, 
except the conduits 16, 24 and 30 are not offset at the connections to the 
respective cases 42, 58 and 90. Rather, the conduits 16, 24 and 30 each 
are connected to the respective case 42, 58 and 90 at and along the 
vertical centerlines of the cases 42, 58 and 90. In FIG. 3, only the 
conduit 24 specifically is shown; however, the conduits 16 and 30 each are 
connected to the respective cases 58 and 90 in a manner exactly like that 
shown in FIG. 3 with respect to the conduit 24 and described above. 
Embodiment of FIG. 4 
Shown in FIG. 4 is one embodiment of the system of the present invention. 
The first titanium tetrachloride preheat assembly 22 is a silica pipe type 
of preheater and the second titanium tetrachloride preheat assembly 28 is 
a shell-and-tube type of heat exchanger. In this embodiment, titanium 
tetrachloride is added to the shell-and-tube heat exchanger 28 through a 
conduit 150 and a heat exchange medium, such as steam, for example, is 
passed through a conduit 152 into and through the tubes within the 
shell-and-tube heat exchanger 28, the heat exchange medium being passed 
from the tubes in the shell-and-tube heat exchanger 28 through a conduit 
154. The shell-and-tube heat exchanger 28 heats the titanium tetrachloride 
to the predetermined second temperature level and the titanium 
tetrachloride heated to the second temperature level is passed from the 
shell-and-tube heat exchanger 28 through a conduit 156. 
A portion of the titanium tetrachloride heated to the predetermined second 
temperature level is passed from the shell-and-tube heat exchanger 28 
through the conduit 156 and through a conduit 158 into the first titanium 
tetrachloride preheat assembly 22 (the silica pipe preheater 22). The 
silica pipe preheater first titanium tetrachloride assembly 22 heats the 
titanium tetrachloride to the predetermined first temperature level and 
passes the heated titanium tetrachloride from the silica pipe preheater 
first titanium tetrachloride assembly 22 into the first titanium 
tetrachloride introduction assembly 20 in the reactor 10. 
Another predetermined portion of the titanium tetrachloride heated to the 
predetermined second temperature level by the shell-and-tube heat 
exchanger second titanium tetrachloride preheat assembly 28 is passed 
through the conduit 156 into the conduit 30. The titanium tetrachloride 
heated to the predetermined second temperature level is passed through the 
conduit 30 into the second titanium tetrachloride introduction assembly 
26. 
In this embodiment, preferably aluminum chloride is mixed with the titanium 
tetrachloride and the mixture of titanium tetrachloride and aluminum 
chloride are passed through the conduit 150 into the shell-and-tube heat 
exchanger second titanium tetrachloride preheat assembly 28. Thus, with 
this arrangement, the mixture of titanium tetrachloride and aluminum 
chloride is passed into both of the first and the second titanium 
tetrachloride introduction assemblies 20 and 26 in the reaction 10. Also, 
in this embodiment, the shell-and-tube heat exchanger second titanium 
tetrachloride preheat assembly 28 actually functions as a portion of the 
first titanium tetrachloride preheat assembly 22, since the shell-and-tube 
heat exchanger second titanium tetrachloride preheat assembly 28 heats the 
titanium tetrachloride to the predetermined second temperature level and a 
portion of this preheated titanium tetrachloride is passed into the silica 
pipe preheater first titanium tetrachloride preheat assembly 22. 
Embodiment of FIG. 5 
The system shown in FIG. 5 is similar to the system shown in FIG. 4. 
The second titanium tetrachloride preheat assembly 28 comprises a 
shell-and-tube heat exchanger wherein titanium tetrachloride is passed 
into the shell-and-tube heat exchanger second titanium tetrachloride 
preheat assembly 28 through a conduit 160 and a heat exchange medium, such 
as steam, for example, is passed into the tubes within the shell-and-tube 
heat exchanger second titanium tetrachloride preheat assembly 28 through a 
conduit 162, the heat exchange medium being passed from the shell-and-tube 
heat exchanger second titanium tetrachloride preheat assembly 28 through a 
conduit 164. The shell-and-tube heat exchanger second titanium 
tetrachloride preheat assembly 28 preheats the titanium tetrachloride to 
the predetermined second temperature level and passes the heated titanium 
tetrachloride through the conduit 30 into the second titanium 
tetrachloride introduction assembly. 
The first titanium tetrachloride preheat assembly 22 includes a 
shell-and-tube heat exchanger 166 which receives titanium tetrachloride 
through a conduit 168 and which receives a heat exchange medium through a 
conduit 170, the heat exchange medium being passed from the shell-and-tube 
heat exchanger 166 through a conduit 172. The shell-and-tube heat 
exchanger 166 preheats the titanium tetrachloride to a predetermined 
temperature level and passes the preheated titanium tetrachloride through 
a conduit 174 into a silica pipe preheater 176. The silica pipe preheater 
176 preheats the received titanium tetrachloride to the predetermined 
first temperature level and passes the preheated titanium tetrachloride 
through the conduit 24 into the first titanium tetrachloride introduction 
assembly 20. 
In some applications, it may be desirable to pass a mixture of aluminum 
chloride and titanium tetrachloride only into the second titanium 
tetrachloride introduction assembly 26. In those applications, a single 
shell-and-tube heat exchanger cannot function to preheat the titanium 
tetrachloride both for passing the preheated titanium tetrachloride into 
the second titanium tetrachloride introduction assembly and for passing 
the preheated titanium tetrachloride to a silica pipe preheater, as shown 
in the embodiment of the present invention shown in FIG. 4. In those 
applications, the mixture of titanium tetrachloride and aluminum chloride 
are passed into the second titanium tetrachloride preheat assembly 28 
through the conduit 160 and titanium tetrachloride alone is passed into 
the shell-and-tube heat exchanger 166 of the titanium tetrachloride 
preheat assembly 22 through the conduit 168. 
Embodiment of FIG. 6 
Shown in FIG. 6 is a modified construction of an introduction assembly 200 
which preferably is utilized in lieu of the construction of the titanium 
tetrachloride introduction assemblies 26, shown in FIG. 1. Also, the 
introduction assembly 200 may be utilized in lieu of the titanium 
tetrachloride introduction assembly 20 and the oxidizing gas introduction 
assembly 12. 
The introduction assembly 200 includes a cylindrical inner case 202 having 
an upstream end 204, a downstream end 206 and an opening 208 extending 
axially therethrough intersecting the upstream and downstream ends 204 and 
206 thereof. A flange 210 is formed on the downstream end 206, the flange 
210 extending radially a distance from the outer peripheral surface of the 
inner case 202. The inner case 202 has an inner diameter 212 and an outer 
diameter 214 which is provided by the outer peripheral surface of the 
inner case 202. 
The introduction assembly 200 also includes an outer case 216 which has an 
upstream end 218, a downstream end 220 and an opening 222 which extends 
axially therethrough. The opening 222 forms an inner diameter 224 and the 
outer peripheral surface forms an outer diameter 226 of the outer case 
216. The inner diameter 224 of the outer case 216 is larger than the outer 
diameter 214 of the inner case 202. A flange 228 is formed on the upstream 
end 218 of the outer case 216 and the flange 228 extends a distance 
radially from the outer peripheral surface of the outer case 216. 
In an assembled position of the introduction assembly 200, the inner case 
202 is disposed in the opening 222 in the outer case 216. The downstream 
end 220 of the outer case 216 is secured to the downstream end 206 of the 
inner case 202 or, more particularly, the downstream end 220 is secured to 
the flange 210 formed on the downstream end 206 of the inner case 202. 
In the connected position of the outer and inner cases 216 and 202, the 
outer peripheral surface of the inner case 202 is spaced a distance 230 
from the inner surface formed by the opening 222 in the outer case 216, 
the space between the inner and outer cases 202 and 216 forming a chamber 
232. A plurality of spaced apart rods 234 are connected to the inner and 
the outer cases 202 and 216, generally near the respective upstream ends 
204 and 218 for the purpose of providing additional structural integrity 
to the connection between the inner and the outer cases 202 and 216. 
A downstream end 236 of a first tube 238 is connected to the upstream end 
218 of the outer case 216. The first tube 238 has an opening 240 extending 
therethrough which, in the assembled position, is axially aligned with the 
opening 208 in the inner case 202. The downstream end 236 is spaced a 
distance 242 axially from the upstream end 204 of the inner case 202 
thereby forming a slot 250 which is in fluidic communication with the 
chamber 232 and the opening 208 in the inner case 202. 
An upstream end 252 of a second tube 254 is connected to the downsteam end 
206 of the inner case 202. The second tube 254 has an opening 256 which 
extends axially therethrough and the opening 256 is axially aligned with 
the opening 208 in the inner case 202 and the opening 240 in the first 
tube 238. 
When the introduction assembly 200 is utilized in the reactor 10, the first 
tube 238 would be either the conduit 34 or the first section 72 depending 
on whether the introduction assembly 200 is replacing the first or the 
second titanium tetrachloride introduction assembly 20 or 26, as shown in 
FIG. 1. The second tube 254 would be either the section 72 or the section 
104 depending on whether the introduction assembly 200 is replacing the 
first or the second titanium tetrachloride introduction assembly 20 or 26, 
as shown in FIG. 1. 
A flowline 260 is connected to the outer case 216 for passing preheated 
titanium tetrachloride vapors from a titanium tetrachloride preheat 
assembly (not shown in FIG. 6) into the titanium tetrachloride chamber 
232. The flowline 260 would be the flowline 24 or 30 depending on whether 
the introduction assembly 200 is replacing the first or the second 
titanium tetrachloride introduction assemblies 20 or 26, as shown in FIG. 
1. The titanium tetrachloride vapors pass from the chamber 232 through the 
slot 188 and into the openings 208 and 256 in the inner case 202 and the 
second tube 254, respectively. 
Changes may be made in the construction and operation of the various 
assemblies and elements disclosed herein or in the steps or the sequence 
of the steps disclosed herein without departing from the spirit and the 
scope of the invention as defined in the following claims.