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Патент USA US3025314

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March 13, 1962
Filed March '7, 1960
//v l/E/V r05’
ire States atent
Patented Mar. 13, 1962
taining starting material, such as anthracene oil, is intro
duced in the liquid phase to a ?ash still 1 through line 7.
In still 1, the oil is vaporized and the vapor is then passed
Gerald Gilbert, Pittsburgh, Pa., assignor to United States
Steel Corporation, a corporation of New Jersey
Filed Mar. 7, 1960, Ser. No. 13,269
3 Claims. ((31. 260—318)
of a loosely packed absorbent medium, prepared by mix
through line 8 into a reaction bed 2. Bed 2 is composed
iiug asbestos with a concentrated solution of potassium
hydroxide and allowing the water to evaporate. As the
vapors pass through bed 2, the carbazole is selectively
absorbed and the other components of anthracene oil
This invention relates to a method of recovering from
anthracene oil certain useful compounds present therein 10 pass out by line 12, are condensed and carried out of the
system through line 18 for use in other processes or as
in low concentration. Carbazole is typical of such com
In the second step, the vapor is diverted through line 10
No satisfactory process has heretofore been available,
so far as I am aware, for recovering certain components
to bed 3, which is similar to bed 2. In bed 3, the car
of anthracene oil which are present in low concentrations.
Carbazole is an example. While it is used commercially
for a variety of purposes, it is present in anthracene oil
bazole is again selectively absorbed and the remaining
components are discharged through line 14. Concur
rently, steam is passed through bed 2, entering through
line 9 to regenerate the carbazole by hydrolysis. The
vapor thereof arising from bed 2 ?ows through line 13
The unstable character of many of the components of
anthracene oil and the low concentration of carbazole 20 as a mixture with steam. This mixture is condensed in
condenser 5, the water is separated and the carbazole is
largely explain the dif?culties encountered in separating
discharged through line 16 to crystallizer v6 in which it is
the latter in good yield and high purity. Even more im
upgraded to commercial purity and discharged through
portant, the complexity of the mixture and the numerous
line 17. The upgrading process generally consists of one
interactions that can occur between components cause
ditliculty in predicting the effectiveness of any given proc 25 crystallization from xylene. After bed 2 has been regen
erated with steam, the carbazole vapor from the ?ash still
ess. Many processes for the isolation of carbazole from
in concentrations of only about 5%.
coal tar or a fraction thereof have been reported.
1 is again passed through it, and bed 3 is then regenerated
by passing steam through line 11. The carbazole-water
most of these, the yield or purity of the product is low
or the process is too complex for efficient operation. Ex
amples of the methods used are (1) multiple distilla
tions or crystallizations; (2) sublimation; (3) acid or
mixture emerges from bed 3 through line 15 and is con
densed in condenser 5. The water is then decanted, and
the carbazole is discharged through line 16, crystallized
in crystallizer 6, and discharged through line 17. This
solvent extraction; and (4) reaction of the anthracene-oil
fraction with an alkali. It is therefore the object of this
invention to provide a method for recovering carbazole
which is inexpensive, ef?cient and easy to practice.
In general terms, my method comprises, as a ?rst stage,
system permits the continuous treatment of a coal-tar
vaporizing anthracene oil at reduced pressure and bring
illustrated by the following examples.
stream and the continuous production of carbazole from
a starting material of low carbazole concentration.
The process of the present invention can be further
ing the vapor into contact with a base deposited on a
Example I
porous medium, thereby causing the formation and depo
sition of a salt (carbazolate) thereon. In a second stage, 40
I pass steam through the porous medium, thereby hy
drolyzing the salt and carrying off the carbazole vapor
with the steam.
Condensation of the vapor and steam
permit ready separation of the resulting water and car
A glass tube 2 feet long and 1/2 inch in diameter was
attached at its upper end to a standard distilling ?ask and
at its lower end to a distillation receiver ?tted for reduced
pressure. The apparatus was similar to the normal la
boratory equipment ‘for reduced-pressure distillation, with
45 the glass tube replacing a condenser. The glass tube was
The absorbent medium is prepared by impregnating a
carrier such as asbestos with a base such as potassium
placed in a column wound ‘with nichrome wire for effi
cient heating. Thermocouples were introduced at proper
intervals to record the temperature of the column during
operation. The distilling ?ask and distilling head were
carbazoleecontaining material passed through in the gas
phase. At the temperature of operation, the c-arbazole 50 wrapped with heating tape for greater efficiency in va
porizing the sample into the tube. In order to raise the
remains in the vapor phase, but the potassium carbazolate
hydroxide. This material is packed into a tube and the
formed is a solid and remains on the absorbent.
Water formed in this reaction is vaporized rapidly under
the conditions of operation and leaves the tube in the
vapor stream to the desired reaction temperature, the
first part of the tube was wrapped for greater heating ca
pacity than the latter part.
The column packing was prepared by mixing 100 grams
gas stream. Since most other materials associated with 55
of potassium hydroxide, 80 grams of asbestos and 250
carbazole in coal tar and other mixtures are not acidic,
grams of water, and evaporating the water under reduced
they do not form salts but remain in the gas stream to
pressure. This mixture was packed into the reaction tube,
pass out of the end of the tube with the water formed
except for the topmost several inches of the tube, which
in the above reaction. Thus, in the ?rst cycle of this
were packed with untreated asbestos to act as an intro
process, potassium carbazolate is formed in high con‘
ductory section for preheating the vapor to the desired
centration in the reactor tube, but other associated ma
reaction temperature before contacting it with the potas
terials remain in the gas stream and may be condensed
sium hydroxide. A 31.6 gram sample of anthracene oil
and separated at the end of the tube. In the second step
boiling between 315 and 355° C. and containing 15%
of the process, steam is passed through the bed contain
ing the potassium carbazclate. The carbazole thus formed 65 carbazole, was placed in the distillation ?ask and the
system exacuated to 50 millimeters pressure.
will vaporize under the conditions of operation and be
The distilling flask was then heated to vaporize the
carried from the end of the tube to be separated from
carbazole charge and pass it into the absorbent, which
the water and upgraded to the desired commercial purity.
was kept at 300° C. 82% of the material charged dis
The process of the present invention can be further
illustrated by reference to the drawing which represents 70 tilled through the absorbent bed apparently unchanged.
The remainder of the material was trapped in the bed.
diagrammatically a commercial unit for the production
In the second step, the distillation ?ask and head were
of carbazole. In operating this unit, the carbazole-con
removed and steam was passed through the bed at atmos
pheric pressure.
The steam-carbazole mixture issuing
from the bed was condensed and the water separated by
decantation or ?ltration.
The carbazole obtained was
92% pure. Of the carbazole in the starting material, 81%
was recovered as product.
Example I]
The same crude carbazole used in Example I was again
of course, affect the utility of the present process for their
isolation. My process, furthermore, is not limited to the
use of potassium hydroxide, although this alkali has been
found preferable for isolation of carbazole. Any base
can be used that forms a readily hydrolyzable salt at
elevated temperatures with the substance to be isolated.
It will be evident from the foregoing that the invention
affords a simple effective method for recovering carbazole
anthracene oil. It thus makes the product available
The charge amounted 10 from
at a lower cost than heretofore.
Although I have disclosed herein the preferred practice
pressure and the charge was distilled through the packed
charged to the distillation ?ask.
to 36.8 grams. The system was reduced to 50 millimeters
bed prepared as in Example I. In this run, the bed was
of my invention, I intend to cover as well any change or
modi?cation therein which may be made Without depart--.
kept at 280° C. during the passage of the impure car
from the spirit and scope of the invention.
bazole. Of the charged material, 75.7% distilled in the 15 ingI claim:
?rst phase of the process. The regeneration process was
1. A method of recovering carbazole from anthracene
repeated as in Example I, and it yielded a product con
which comprises forming a gas-permeable bed of ?
taining 88.2% carbazole and representing 61% of the
brous material, depositing a layer of an alkali on the ma
carbazole in the impure fraction. The initial distillate
contained only 0.3% carbazole or approximately 1.4% 20 terial of said bed from an aqueous solution thereof, va
porizing anthracene oil under a partial vacuum, passing
of the original carbazole present.
the resulting vapor through said bed until a deposit of
Example 111
carbazolate builds up thereon, then passing steam through
said bed to hydrolyze and vaporize the carbazolate, con
The process of Example I was repeated with the bed at
320° C. The amount of distillate obtained in the ?rst 25 densing the resulting vapor and separating the carbazole
from the aqueous condensate.
step was 78.2% of the total charge. The product con
2. A method as de?ned by claim 1, characterized by
tained 87% carbazole and represented 74% of the car
said vacuum being about 50 millimeters of mercury.
bazole in the impure fraction.
3. A method as de?ned by claim 1, characterized by
Operation at pressures ‘lower than 50 millimeters ma
said bed being heated to a temperature of about 300° C.
terially reduces the yield of carbazole. It is, of course,
necessary to keep the reaction pressure at such a point
References Cited in the ?le of this patent
that the carbazole will boil below the reaction tempera
ture and may be vaporized into the reactor.
Since my process is based on the hydrolytic reversal
Weil _________________ __ Oct. 5, 1926
of the salt formation of very weak acids, it is not limited
Jaeger _______________ __ Oct. 30, 1934
to carbazole but may ‘be applied to any weak acid that
O’Brochta et a1 ________ __ Sept. 17, 1946
may be regenerated or hydrolyzed readily at elevated
lnsinger _____________ __ Mar. 22, 1949
temperatures. Thus, other substances that may be sepa
rated by this method are pyrrole, indole, diphenylamine,
and such acidic hydrocarbons as indene, ?uorene, tri 40
phenylmethane, xanthenes, and acetylenes. The stability
of these compounds at the temperatures of operation will,
Swietoslawski _________ __ Mar. 22, 1949
Great Britain _________ __ Sept. 25, 1924
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