Control of carbon black production

Carbon black is produced by heating a carbonaceous feed material to an elevated temperature to decompose the feed material to produce carbon black. A sample of the effluent from the reactor is passed as a suspension of carbon black particles in a gas into an optical cell. A beam of light is directed into the cell, and scattered light is measured at two different locations. A signal representative of the ratio of the two measured scattered light intensities is employed to control the introduction into the reactor of an alkali metal which controls the structure of the carbon black produced.

It is common practice to produce carbon black by introducing a carbonaceous 
feed material, such as an aromatic oil, into a carbon black reactor. This 
feed material is heated to an elevated temperature to form carbon black. 
Hot combustion gases are normally employed for this purpose. The reactor 
effluent is a smoke which contains carbon black particles. It is common 
practic to control the structure of the produced carbon black by 
introducing an alkali metal, particularly potassium, into the reactor. 
This is usually accomplished by injecting a salt of the metal into the 
feed oil. The amount of alkali metal introduced is selected to provide a 
black having the desired structure. Heretofore, a laboratory measurement 
of the structure of the black has been made to determine the amount of 
alkali metal to be introduced. Unfortunately, this procedure requires a 
substantial amount of time. 
In accordance with the present invention, a method is provided for 
controlling the structure of carbon black in response to a measurement of 
the structure of the black which is substantially instantaneous. A sample 
of the produced black is withdrawn from the reactor and passed as a 
suspension into a photometer. A beam of light is passed through the 
suspended black, and light scattered at two different angles is measured. 
A signal is established which is representative of the ratio of the two 
scattered light intensities. It has been found that this signal is 
representative of the structure of the carbon black. The ratio signal can 
be employed to control the rate at which an alkali metal is introduced 
into the carbon black reactor so as to produce a carbon black having a 
desired structure.

Referring now to the drawing in detail and to FIG. 1 in particular, there 
is shown a schematic view of a typical furnace carbon black reactor 10. 
This reactor comprises a cylindrical precombustion section 11 and a 
cylindrical reaction section 12. Both sections are surrounded by a mass of 
insulating material 13. A feed oil is introduced through a conduit 14 
which terminates in a nozzle 15 adjacent the upstream wall of 
precombustion section 11. Air, which is employed to assist in atomizing 
the oil, is introduced through a conduit 16. A mixture of fuel and air, or 
the combustion products resulting from the burning of such fuel, is 
introduced through a conduit 17 which communicates with one or more inlet 
ports 18 in precombustion section 11. The gases introduced through conduit 
17 generally enter the precombustion section in a direction tangential to 
the side wall thereof. A quench material, such as water, is introduced 
through a conduit 19 which terminates in one or more nozzles 20. The 
reactor effluent smoke is withdrawn through a conduit 21 and passed to 
suitable recovery equipment 22. Carbon black is withdrawn through a 
conveyor 23, and gases are removed through a conduit 24. 
The apparatus thus far described is typical of conventional carbon 
black-producing apparatus. Such apparatus is described in detail in U.S. 
Pat. No. 2,564,700, for example. However, the invention is not limited to 
any specific configuration of the carbon black reactor. 
It is common practice to introduce an alkali metal, preferably potassium, 
into the reactor in order to regulate the structure of the produced carbon 
black. This can be accomplished by introducing the alkali metal through a 
conduit 26 which communicates with oil conduit 14. The use of an alkali 
metal for this purpose is well known, and is described in U.S. Pat. No. 
3,010,794, for example. In accordance with the present invention, the rate 
at which the alkali metal is introduced is controlled by a recorder-flow 
controller 27 which adjusts a valve 28 in conduit 26. The setpoint of 
controller 27 is ajusted in response to a signal which is representative 
of the structure of the produced carbon black. This signal is obtained by 
withdrawing a sample of the smoke from reactor 10 through a probe 29 and 
passing the sample through a conduit 30 to an analyzer and controller 31. 
The output signal from analyzer and controller 31 is employed to adjust 
the setpoint of controller 27. 
Probe 29 is illustrated in FIG. 2. A central conduit 32 is positioned to 
terminate adjacent, but spaced from, an end plate which is formed of two 
rings 33 and 33a, the latter having a central opening 34 therein. This 
plate is positioned so as to be substantially flush with the wall of 
reactor section 12 of reactor 10. This permits a sample of the smoke to be 
withdrawn through opening 34 into conduit 32. Conduit 32 is surrounded by 
a jacket 35 which engages ring 33a. Jacket 35 is provided with an inlet 36 
through which an inert gas, such as nitrogen, is introduced from a conduit 
37. This inert gas is supplied at a preselected rate, which preferably is 
adjustable. The inert gas flows to the right through jacket 35 and then to 
the left conduit 32. The flow of inert gas serves to transport the sample 
withdrawn from the reactor out through conduit 32 into conduit 30. A tube 
38, which engages plate 33, surrounds jacket 35 and is free to slide on 
the jacket. A jacket 39 surrounds tube 38 and terminates adjacent plate 
33. Jacket 39 is provided with an inlet 40. A jacket 41 surrounds jacket 
39 and engages plate 33. Jacket 41 is provided with an outlet 42. A 
coolant is introduced into inlet 40 from a conduit 43. This coolant flows 
through jackets 39 and 41 and is removed through outlet 42. A plurality of 
spacers 44 and 45 can be employed to retain the jackets in proper 
alignment. 
Referring now to FIG. 3, the cooled sample withdrawn through conduit 30 is 
passed to a nozzle 46 which extends into a chamber 47. Nozzle 46 
preferably is adjustable to permit the flow to be varied. A stream of 
nitrogen, or other inert carrier gas, is passed from a conduit 48 to a 
port 49 in chamber 47. This chamber is provided with two outlet ports 50 
and 51. Port 50 is connected by a conduit 52 to a photometer 53, and port 
51 is connected by a conduit 54 to a reference or dummy cell 55. The 
outlets of 53 and 55 are connected by respective conduits 57 and 58 to a 
conduit 59. Conduit 59 is connected to a vacuum source, not shown. Control 
valves 60, 61, 62, 63 and 64 are disposed in respective conduits 37, 48, 
52, 54 and 30. These valves are operated by a timer 65 in the sequence to 
be described hereinafter. Timer 65 can be any conventional timing device 
which provides output signals to operate the valves. For example, the 
valves can be solenoid-operated, and the timer can include a plurality of 
cam-operated switches. During the time that an analysis is being made, a 
sample of the smoke withdrawn from reactor 10 is passed through photometer 
53. 
Photometer 53 is illustrated in FIGS. 4 and 5. A housing 66 is provided 
with an inlet conduit 67 which is connected to conduit 52 of FIG. 3. An 
outlet conduit 68, which is connected to conduit 57, is positioned in 
spaced relationship with inlet conduit 67 so that a sample of the smoke 
passes through the space between these ports. A cap 69, which is provided 
with a plurality of openings 70, extends across the top of housing 66 and 
surrounds conduit 68. A tube 71 surrounds a portion of conduit 68 and is 
spaced therefrom. When conduit 57 is connected to the vacuum source, air 
flows into housing 66 through openings 70, downwardly through tube 71, and 
is withdrawn through outlet conduit 68. This flow of air assists in 
removing carbon black from the interior of housing 66. 
Light from a source 72 passes through a tube 73 and enters housing 66 
through a lens 74 which serves to direct a beam of light through a tube 76 
into a light trap tube 77. This beam of light passes immediately above 
inlet port 67 so as to impinge on carbon black introduced through port 67. 
Two light detectors 80 and 81, which can be photomultiplier tubes, are 
positioned within housing 66 so as to detect light scattered from the 
carbon black at two different angles. In the illustrated embodiment, 
detector 81 is positioned to detect light scattered at an angle of 
approximately 45.degree. with respect to the transmitted radiation. 
Detector 80 is positioned to measure light which is scattered at an angle 
of approximately 135.degree.. Detectors 80 and 81 are connected to the 
inputs of respective amplifiers 82 and 83. The outputs of the two 
amplifiers are connected to the inputs of a divider circuit 84 which 
establishes a signal which is representative of the quotient of the output 
signal rom amplifier 83 divided by the output signal from amplifier 82. 
This signal is applied to a recorder 85 and is also transmitted as the 
setpoint signal 86 to controller 27 of FIG. 1. The signal detecting and 
control apparatus of FIG. 4 can be of the type described in U.S. Pat. No. 
2,897,247, for example. 
In order to obtain reliable measurements of the scattered radiation, it is 
necessary to have a steady smoke jet in the optical cell. This is somewhat 
difficult to achieve because of the natural tendency of carbon black 
particles to clog flow lines in and leading to the cell. The equipment 
illustrated in FIG. 3 is provided to clean the lines periodically. At the 
end of an analysis cycle and the beginning of a cleaning cycle, valves 60, 
62 and 63 are closed and valves 61 and 64 are open. The results in a flow 
of purge gas from conduit 48 through chamber 47, conduit 30 and probe 29. 
This serves to backflush the probe and sample conduit. The next step of 
the cleaning cycle is accomplished by closing valve 64 and opening valves 
62 and 63. The results in purge gas passing through photometer 53 and cell 
55. At the end of the cleaning cycle, valve 60 is opened, valve 63 remains 
open, and valves 61 and 62 are closed. After a few seconds, valve 63 is 
closed and valve 62 is opened to initiate the analysis cycle. The short 
delay in opening valve 63 permits stable flow conditions to be established 
before the analysis is started. Timer 65 also establishes a signal which 
deactivated the analysis and control equipment during the cleaning cycle. 
The setpoint of controller 27 thus remains unchanged during the cleaning 
cycle. Reference cell 55 can be of the same configuration as photometer 53 
except that the optical components are not included. Instead, the cell is 
provided with a window to permit visual observation of the smoke 
introduced through conduit 54. This enables an operator to adjust flow 
rates to obtain a stable jet of smoke in the cell and to determine that 
the cleaning cycle is adequate. 
Light source 72 can be a mercury lamp, such as a Type AH-4, for example. 
Filter 78 can advantageously be selected to transmit radiation in the blue 
or green region of the visible spectrum. The exact wavelength to be 
employed is not critical, but this wavelength preferably is of the order 
of the size of the carbon black particles. Cells 80 and 81 should be 
spaced to measure scattered light in directions such that there is a 
substantial angular difference. This is 90.degree. in the illustrated 
embodiment employing angles of 45.degree. and 135.degree.. It is generally 
desirable that cell 81 measure light scattered in a "forward" direction 
and that cell 80 measure light scattered in a "backward" direction. Filter 
79 is a neutral filter which is employed merely to adjust the intensity of 
the transmitted radiation to a desired value. 
A number of runs have been carried out to demonstrate this invention. 
Carbon black was produced in a reactor of the configuration of FIG. 1. 
Precombustion chamber 11 had a diameter of 15 inches and a length of 4-3/4 
inches. Reactor section 15 had a diameter of 4 inches. Probe 29 was 
located 30 inches downstream from the inlet end of section 15. Two inlet 
ports 18 were employed. The feed oil was a decant oil having a BMCI of 
120. This feed oil was preheated to 310.degree. F. (154.4.degree. C.) and 
charged through an air-atomized bifluid nozzle having a spray of about 
20.degree.. The reactor was operated under two sets of conditions, and 
carbon black was produced having the following properties: 
______________________________________ 
Condition I 
Condition II 
______________________________________ 
Combustion air, scfh 
6000 6000 
Fuel (natural gas), scfh 
400 400 
Atomizing air, scfh 
250 250 
Feed oil, lb./hr. 
70 50.4 
N.sub.2 SA.sup.(1), m.sup.2 /g 
80 130 
CTAB.sup.(2), m.sup.2 /g 
79 112 
24M4.sup.(3), g/100 cc 
95 93 
Tint.sup.(4) 99 119 
Smoke concentration, at 2500.degree. F., g/m.sup.3 
13 7.5 
at 80.degree. F., g/m.sup.3 
70 41 
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.sup.(1) ASTM D 3037-71T, Method A. 
.sup.(2) Janzen, J. and Kraus, G., Rubber Chemistry and Technology, 44, 
1287 (1971). 
.sup.(3) U.S. 3,548,454, as measured after crushing, by Method B, ASTM 
2414-70. 
.sup.(4) ASTM D 3265-75. 
The smoke removed through probe 29 was cooled to about 80.degree. F. 
(26.7.degree. C.). 
The measuring apparatus was of the configuration shown in FIG. 4. The light 
transmitted into the cell had a wavelength of 546.1 nm. 
A series of runs was conducted wherein carbon black was produced both with 
and without the addition of potassium (as potassium nitrate solution with 
distilled water) to the feed oil. The results were as follows: 
______________________________________ 
Oil Rate K 
lb./hr. ppm.sup.(1) 
CTAB 24M4 Z.sup.(3) 
______________________________________ 
70 0 80 94 4.61 
70 0 79 95 4.68 
70 0 82 92 4.69 
70 10 84 85 4.04 
70 0 -- -- 4.66 
70 5 82 88 4.24 
70 0 79 95 4.53 
70 5 81 89 4.00 
70 0 79 95 4.53 
70 1 81 92 4.29 
70 0 80 95 4.63 
70 1 -- -- 4.43 
50 0 112 93 4.31 
50 1 113 94.sup.(2) 
4.06 
50 0 -- -- 4.20 
______________________________________ 
.sup.(1) Parts per million, by weight, of oil. 
.sup.(2) Value may have been erroneous. 
.sup.(3) Ratio of intensities detected by cells 81/80. 
A blank in the table indicates that samples were not taken. 
It can be seen from the foregoing data that changes in the structure of the 
carbon black, as evidenced by the 24M4 values, due to changes in the 
amount of potassium added are measured by changes in the light ratio Z. 
The foregoing runs were conducted over a period of several days so that 
there are small deviations of Z for the several control runs. However, the 
runs demonstrated that the measured Z ratio is reduced as the structure is 
reduced. 
While this invention has been described in conjunction with a presently 
preferred embodiment, it obviously is not limited thereto.