Radial secondary gas flow carbon black reactor

An apparatus is provided for producing a carbon black with a tint residual below -6. The apparatus entail introducing feedstock axially and generating a hot combustion gas vortex in a cylindrical precombustion section of a tubular carbon black reactor, producing a first mixture of feedstock and combustion gases, passing this mixture through an abruptly restricted passage axially connected to the precombustion section, abruptly expanding the first mixture into a frustoconical venturi converging section of the reactor with mixing of this first mixture with an additional flow of combustion gas at the exit of the converging section with the combustion gas entering the converging section in opposite, radial flow thereby forming a second mixture which is admitted into a reaction section of the carbon black reactor.

BACKGROUND OF THE INVENTION 
This invention relates to the production of carbon black. In one of its 
aspects this invention relates to the production of carbon black with a 
tint residual below -6. In another of its aspects this invention relates 
to carbon black reactors. 
It is important to reduce the heat buildup, also called hysteresis, or 
rubber/carbon black compositions. Hysteresis is a measurement of how much 
of the elastic deformation energy put into a carbon black/rubber 
composition remains in the composition as heat after the deformation 
forces have been released. Serious accidents have been attributed to the 
failure of tires made from high hysteresis rubber compositions. The higher 
the heat buildup in the rubber compositions the greater are the chances 
the tires made from such compositions can be destroyed in use. 
It has recently been set forth in copending application, Ser. No. 681,977, 
filed Apr. 30, 1976, incorporated herein by reference, that a rubber 
composition exhibiting low heat buildup along with satisfactory tread wear 
properties is provided in a composition comprising 100 parts by weight of 
rubber and 30 to 120 parts by weight of a carbon black having a tint 
residual of about -6 or less. Tint residual is a property of carbon black 
defined by the following formula: 
EQU TR = T - [56.0 + 1.057 (CTAB) - 0.002745 (CTAB).sup.2 - 0.2596 (DBP) - 
0.201 (N.sub.2 SA - CTAB)]. 
in this formula, the abbreviations used have the following meanings and the 
properties are measured as described: 
Tr: this is tint residual. 
Ctab: this is the surface area of the carbon black measured as described by 
J. Janzen and G. Kraus in Rubber Chemistry and Technology, 44, 1287 
(1971), m.sup.2 /gm. 
N.sub.2 sa: this is the surface area of the carbon black measured using 
nitrogen, in accordance with the ASTM method D-3037-71T, m.sup.2 /gm. 
Dbp: this is the structure of the carbon black in cc/100 g and is measured 
in accordance with U.S. Pat. No. 3,548,454 and, after crushing, by method 
B in accordance with ASTM D-2414-70. This property is also referred to as 
24M4 DBP. 
T: this is the tint or tinting strength of the carbon black measured by 
arbitrarily assigning the reference black IRB No. 3 the value of 100; the 
tint is measured in accordance with ASTM 3265-75. 
It is therefore an object of this invention to provide an apparatus 
suitable for preparing carbon black having a tint residual of -6 or less. 
It is another object of this invention to provide a method for producing 
carbon black having a tint residual of -6 or less. 
Other aspects, objects, and the various advantages of this invention will 
become apparent upon study of this specification, the drawings, and the 
appended claims. 
STATEMENT OF THE INVENTION 
According to this invention an apparatus is provided for the preparation of 
carbon black. In this apparatus, described as a tubular carbon black 
reactor, is a cylindrical precombustion section having axially aligned 
inlet for feedstock and means for generating a hot combustion gas vortex. 
The precombustion section is axially aligned and openly connected in 
operative communication with a passage of abruptly restricted dimensions, 
with this passage in further axial alignment and openly connected in 
operative communication with a frustoconical, venturi converging section 
which abruptly expands from the passage to a diameter equal to that of the 
precombustion section. The venturi converging section extends away from 
the passage at a converging angle of about 10.degree. to about 30.degree. 
between the frustoconical surface and the reactor axis and the converging 
section terminates openly connected in operative communication with an 
axially aligned reaction tube section which has a diameter equal to the 
least diameter of the converging section. In the converging section at the 
inlet to the reaction tube section are means for introducing radial and 
opposing streams of combustion gas into the reactor. The mixing action 
resulting from the placement of the entry of radially, opposing combustion 
gas streams into a reactor capable of producing a well mixed flow of 
combustion gas and carbon black feedstock will be shown herein to 
contribute to the production of carbon black having a low tint residual. 
In accordance with another embodiment of the invention a method is provided 
for producing carbon black having a tint residual of about -6 or less in 
which carbon black feedstock is axially passed into a cylindrical 
precombustion section of a carbon black reactor while a vortex of hot 
combustion gas is generated in the precombustion section thereby producing 
a first mixture of feedstock and combustion gases that is passed from the 
precombustion section axially through an abruptly restricted passage and 
abruptly expanded. The expanded mixture then is passed through a 
frustoconical venturi converging section thereby converging the axially 
flowing mixture and at the exit of the converging section mixing the first 
mixture with radial, opposite flow of combustion gas to form a second 
mixture. Carbon black is then produced from the second mixture in a 
confined reaction section of the carbon black reactor.

In the FIGURES the reactors are identical with the exception of the 
location of the entry for supplemental combustion gas in the 
frustoconical, venturi converging section. In FIG. 1 this supplemental 
combustion gas is supplied by opposing radial tubes preferably located 
near the outlet of the converging section and in FIG. 2, which depicts the 
prior art apparatus, the supplemental combustion gas is supplied 
tangentially into the converging section, preferably in the portion having 
the greatest diameter where a mixture of gases has been abruptly expanded 
into the venturi converging section of the reactor. 
Referring now to FIG. 1 or FIG. 2, like numbers will be used to designate 
portions of the apparatus that are duplicated in the two FIGURES. Feed 
enters with axial flow through inlet means 1 to be mixed in a cylindrical 
precombustion section 3 with combustion gases fed into precombustion 
section 3 through tangential inlet means 5 so that the axially flowing 
feedstock is mixed with a vortex of hot combustion gases to form a first 
mixture of feedstock and combustion gases. This first mixture then flows 
through a passage of abruptly restricted dimensions 7 which is axially 
aligned with both the feedstock inlet and the cylindrical precombustion 
section. The first mixture is discharged into a frustoconical, venturi 
converging section 9 which abruptly expands to a diameter equal to that of 
the precombustion section 3. The converging section 9 extends away from 
the restricted passage 7 at a converging angle of about 10.degree. to 
about 30.degree. between the frustoconical surface 11 and the axis of the 
reactor 13. The converging section 9 terminates in open communication with 
an axially aligned reaction tube section 15 which has a diameter equal the 
least diameter of the converging section. 
Apparatuses for the production of carbon black constructed as described 
above are well known in the art. Also known is the introduction of 
supplemental combustion gases through tangential flow means 17 located in 
the venturi converging section 9. In the present invention supplemental 
combustion gas is introduced into the venturi converging section 9 through 
opposed, radial flow means 19 preferably located near the termination of 
the converging section 9 into the reaction tube 15. 
The dimensions of the reaction apparatus according to this invention can 
range from a cylindrical precombustion section having a diameter about 4 
inches up to about 40 inches and an axial length from about 3 inches up to 
about 12 inches with the length shorter than the diameter. Depending upon 
the dimensions of the precombustion section the abruptly restricted 
dimensions of the outlet passage will range from about 1/2 inch up to 
about 16 inches in diameter. The converging section will generally have 
its greatest diameter equal to that of the precombustion secton and as it 
extends away from the restricted passage connecting it to the 
precombustion chamber will converge at an angle ranging from about 
10.degree. to about 30.degree. with the angle measured between the 
frustoconical surface of the converging section and the axis of the 
reactor. The reactor section will generally range from a diameter of about 
1/2 inch up to about 8 inches. The inlet lines for reactor feedstock and 
combustion gases can be sized according to the flow that these passages 
carry. 
In the following examples, reactor blocks were used in which the feed inlet 
1 was a 1/2 inch diameter 4-inch line, the cylindrical precombustion 
section 3 was 3 inches long and had a diameter of 4 inches, tangential 
combustion gas inlets 5 were 1/4 inch diameter, the abruptly restricted 
passage 4 was 1 inch long and of cross-section of an equilateral triangle 
circumscribed about a 1/2 inch diameter circle, the converging section 9 
was about 4 inches long with the converging angle of about 24.degree., the 
reaction tube 15 was about 1/2 inch diameter and both the opposed radial, 
supplemental combustion gas inlets 19 of this invention and the 
tangential, supplemental combustion gas inlets 17 of the prior art were 
about 1/4 inch in diameter. Flow rates and properties of the carbon black 
product produced in the various runs are described below in Table I. 
TABLE I 
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Invention Runs Control Runs 
Run Numbers: 1 2 3 4 5 6 7 8 
Axial Benzene.sup.(1), cc/min., 
5.75 8.0 15.5 17.2 17.2 19.2 14.5 13.0 
Cylindrical Zone: 
Tangential Air, SCF/min., 
3.96 for all eight runs 
Tangential Methane, SCF/min., 
0.314 for all eight runs 
Volume ratio Air to Fuel, 
12.6/1 for all eight runs 
Converging Zone: 
Equal Flow Opposing Jet Tangential 
Air, SCF/min., 0.30 2.27 2.27 2.27 2.27 2.27 2.27 2.27 
Methane, SCF/min., 
0 0.10 0.10 0.10 0.10 0.10 0.10 0.10 
Volume ratio Air to Fuel, 
-- 22.7 22.7 22.7 22.7 22.7 22.7 22.7 
Carbon Black Product: 
CTAB, m.sup.2 /gm., 
154 112 83 67 70 62 65 63 
N.sub.2 SA, m.sup.2 /gm., 
182 127 96 68 74 63 65 63 
I.sub.2 No., m.sup.2 /gm., 
159 120 89 64 69 55 61 62 
24M4 DBP, cc/100 gm., 
90 86 83 80 84 86 91 88 
Tint, 115 102 87 79 80 76 75 78 
Tint Residual, - 10 -13 -14 -14.5 -13.5 -12 +14 +11 
Photelometer Value, 
-- 96 95 90 93 88 86 92 
Grams Product/30 min., 
37.0 26 58 79 93 90 58 83 
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.sup.(1) Oil outlet at upstream face of first (cylindrical) zone. 
It will be noted that the tint residual of the carbon black product 
produced using the apparatus and method of this invention all fell in a 
range below -6 while the product of the control runs had a tint residual 
in a range well above -6.