The present invention relates to process of production of 95% pure anthracene
from coal tar. The pure anthracene of the invention is useful for various purposes
including production of anthraquinone, a key chemical for synthesis of wide range
of vat dyes, plasticizer for thermo-setting resins as a raw material for making
artificial diamonds, scintillator to detect light energy radiation's and synthetic
perfumes.
Anthracene is a valuable chemical obtained from coal tar produced during high
temperature carbonization of coal in coke oven of integrated steel plants.
Anthracene oil fraction of coal tar is a rich resource of anthracene.
Anthracene oil fraction (boiling range 300-360°C) obtained during coal tar
distillation constitutes about 15-20% of tar. Crude anthracene is obtained as a
cake by indirect stirred cooling and centrifuging of anthracene oil and it has a
typical composition as follows :
Anthracene 20-35%
Phenanthrene 20-40%
Carbazole 12-20%
Remainder Ace-Napthene, Fluorene etc.
It is well known that the separation of anthracene and carbazole from the
anthracene mud is effected by employing separation techniques such as :
i) simple distillation
ii) selective use of solvents
iii) azeotropic distillation
iv) selective reactivity
v) fractional crystallization
However, the above process had limitation/drawbacks in yield/purity of
anthracene and the same affected the recovery of the other valuable constitution
of anthracene oil fraction i.e. carbazole.
Most of these techniques further involve multiple stages for separating each
component in commercially pure state and thus are cumbersome and cost
intensive.
It is thus the basic objective of the present invention to provide a process for
producing technical grade anthracene in good yield from anthracene oil fraction
(anthracene mud) which would not affect isolation of carbazole from the same oil
fraction.
Another object is to provide a process for manufacture of pure anthracene from
anthracene oil fraction which would be simple and cost-effective.
Yet further object is to provide a process for manufacture of technical pure
anthracene from anthracene oil fraction having inherent flexibility to adopt to wide
variations in the raw material composition.
Yet another object is to provide a process for manufacture of anthracene
technical pure wherein the reagents used in the process are readily available at
comparative low cost.
Yet further object is to provide a process of manufacture of technical pure
anthracene in high yields (60 to 70%) compared to other known processes of its
recovery from anthracene oil fractions.
Yet further object of the invention is to provide a process for the manufacture of
technical pure anthracene from anthracene mud which would also enable
possible recovery of high purity carbazole/phenantherene.
Thus according to the present invention there is provided a process for the
manufacture of technical pure anthracene from anthracene mud of coal tar
distillation comprising :
providing the said anthracene mud (anthracene oil fraction) from coal tar
distillation ;
subjecting the anthracene oil fraction to vacuum distillation to obtain therefrom a
heart cut rich in anthracene and carbazole ;
subjecting the heart cut fraction to benzene digestion and filtration to obtain filter
cake containing the concentrated anthracene and carbazole ;
washing the anthracene-carbazole (AC) concentrate with benzene to thereby
dissolve out the soluble phenanthrene ;
subjecting the washed and dried filter cake to formalin treatment to thereby obtain
enriched anthracene as residue and carbazole-formaldehyde complex as filtrate ;
purifying the enriched anthracene to thereby obtain the pure anthracene.
The step of vacuum distillation of anthracene mud is carried out by distilling
anthracene mud under 5 to 15mm Hg. preferably 10mm Hg., absolute pressure
with partial reflex to obtain the following cuts :
First fraction upto 160°C
Second fraction (Heart cut) 160°C - 245°C
Residue > 245°C
The first fraction was discarded. The second fraction, a heart cut, rich in
anthracene and carbazole, is taken as feedstock for further processing.
In the step of benzene digestion of second fraction (heart cut), the second
fraction is digested in benzene in proportions of 1.5 to 2.5 lit/kg preferably 2
lit./kg. which is carried out under total reflux for 0.5 to 1.5 hr, preferably 1 hr at
about 80 to 85°C, preferably 80°C. After digestion, the contents were cooled to
room temperature and vacuum filtered. The filter cake, mostly containing
anthracene and carbazole (AC concentrate) was washed with benzene (sufficient
amount to thoroughly wet the cake). Phenanthrene being soluble in benzene
goes into the filtrate.
The AC concentrate was next subjected to formalin treatment. In the above
process of manufacture of pure anthracene, the step of formalin treatment of the
dried filter cake comprise treatment with formalin solution, methanol and Na2CC>3,
heating the mix and maintaining under total reflux, cooling the solution and
vacuum filtering. In particular, washed filter cake was dried and formalin solution
in amounts of 1.0 to 1.2 times cake weight preferably equal to cake weight,
methanol in amount of 4 to 5 times preferably 5 times cake weight and Na2C03 in
amount of 8 to 10% cake weight, preferably 10% cake weight were added to it.
The mixture was heated and kept under total reflux for 1.0 to 1.5 hrs. preferably 1
hr. The solution was then cooled and vacuum filtered to obtain enriched
anthracene as residue and carbazole formaldehyde complex in methanol medium
as filtrate, feedstock for carbazole recovery.
The step of purification of the enriched anthracene comprise washing enriched
anthracene with dilute HCI followed by distilled water to remove traces of
Na2C03. Hot acetone wash was given to remove traces of carbazole to obtain
anthracene of >95% purity.
The process of the invention is further illustrated by way of a flow diagram as per
the figure 1 of the accompanying drawings:
The details of the invention, its objects and advantages are explained hereunder
in greater detail in relation to non-limiting exemplary embodiments :
EXAMPLE
Under this exemplary process anthracene mud in 18.2 kg amount and containing
anthracene, carbazole, phenanthrene and other minor constituents was used for
producing the purified anthracene as discussed hereunder:
Vacuum distillation of Anthracene mud
The anthracene mud was distilled under 10 mm Hg, absolute pressure with
partial reflex to obtain the following cuts :
First fraction upto 160°C
Second fraction (Heart cut) 160°C - 245°C
Residue > 245°C
The first fraction was discarded. The second fraction, a heart cut, rich in
anthracene and carbazole, is taken feedstock for further processing. The quality
of the cuts achieved are indicated in TABLE 1 hereunder:
TABLE -1
ANALYSIS OF FRACTIONS OBTAINED BY VACUUM DISTILLATION OF
ANTHRACENE MUD

Benzene digestion of second fraction (Heart cut)
The second fraction was digested in benzene (2 lit./kg.). digestion was carried out
under total reflux for 1 hr. at about 80°C. After digestion, the contents were
cooled to room temperature and vacuum filtered. The filter cake, mostly
containing anthracene and carbazole (AC concentrate) was washed with
benzene (sufficient amount to thoroughly wet the cake). Phenanthrene being
soluble in benzene goes into the filtrate.
Formalin treatment of AC concentrate
The washed filter cake was dried and formalin solution (equal to the cake wt),
methanol (5 times of the wt. of cake) and Na2C03 (10% of the wt. of cake) were
added to it. The mixture was heated and kept under total reflux for 1 hr. The
solution was then cooled and vacuum filtered to obtain enriched anthracene as
residue and carbazole formaldehyde complex in methanol medium as filtrate,
feedstock for carbazole recovery.
Purification of products
Enriched anthracene was washed with dilute HCI followed by distilled water to
remove traces of Na2C03. Hot acetone wash was given to remove traces of
carbazole to obtain anthracene of >95% purity.
The yield and purity of anthracene obtained following the above process is
detailed hereunder in TABLE 2.

As would be evident from the above results the process of the invention achieved
producing substantially pure anthracene in good yield.
In the above process of the invention vacuum distillation of anthracene mud
enriches anthracene, phenanthere and carbazole in the heart cut, without any
possible decomposition due to relatively low temperature used in distillation due
to vacuum application.
Benzene digestion of heart cut is directed to eliminate phenanthrene and most of
the other components which are soluble in benzene.
Formaldehyde treatment provides for necessary separation of anthracene from
carbazole almost completely.
It is thus possible by way of the present invention to provide technical pure
anthracene (95%) in good yield from anthracene mud of coal tar distillation.
WE CLAIM'
1. A process for the manufacture of 75% pwte anthracene
from anthracene mud of coal tar distillation comprising :
providing the said anthracene mud (anthracene oil fraction) from coal tar
distillation;
subjecting the anthracene oil fraction to nitration grade vacuum distillation to
obtain therefrom a heart cut rich in anthracene and carbazole ;
subjecting the heart cut fraction to benzene nitration grade digestion and
filtration to obtain filter cake containing the concentrated anthracene and
carbazole;
washing the anthracene-carbazole concentrate with benzene to thereby
dissolve out the soluble phenanthrene ;
subjecting the washed and dried filter cake to formalin treatment in a formalin
solution to thereby obtain enriched anthracene as residue and carbazoie-
formaldehyde complex as filtrate ;
purifying the enriched anthracene to thereby obtain the anthracene having
purity of at ;»aot 95%.
2. A process as claimed in claim 1 wherein the step of formalin treatment of the
dried filter cake comprise treatment with formalin solution, methanol and
Na2C03, heating the mix and maintaining under total reflux, cooling the
solution and vacuum filtering.
3. A process as claimed in anyone of claims 1 or 2 wherein the step of vacuum
distillation of anthracene mud is carried out by distilling anthracene mud under
5 to 15mm Hg, preferably 10 mm Hg., absolute pressure with partial reflux to
obtain the following cuts :
First fraction upto 160°C
Second fraction (Heart cut) 160°C - 245°C
Residue > 245°C
4. A process as claimed in anyone of claims 1 to 3 wherein the step of benzene
digestion of second fraction (heart cut) comprise digesting the said fraction in
benzene in proportions of 1.5 to 2.5 lit/kg preferably 2 lit./kg. under total reflux
for 0.5 to 1.5 hrs, preferably 1 hr at about 80 to 85°C preferably 80°C, after
digestion, cooling the contents to room temperature and vacuum filtering to
provide the filter cake, containing substantially anthracene and carbazole (AC
concentrate).
5. A process as claimed in anyone of claims 1 to 4 wherein the step of
subjecting the AC concentrate to said formalin treatment comprise drying the
filter cake and adding formalin solution in amounts of 1.0 to 1.2 times cake
weight preferably equal to cake weight, methanol in amount of 4 to 5 times
cake weight preferably 5 times cake weight and Na2C03 in amount of 8 to
10% cake weight preferably 10% cake weight heating the mix and maintaining
under total reflux for 1.0 to 1.5 hrs. preferably 1 hr, cooling the solution and
vacuum filtering to obtain enriched anthracene as residue and carbazole
formaldehyde complex in methanol medium as filtrate.
6. A process as claimed in anyone of claims 1 to 5 wherein the step of
purification of the enriched anthracene comprise washing enriched
anthracene with dilute HCI followed by distilled water to remove traces of
Na2C03 followed by hot acetone wash remove traces of carbazole to obtain
said pure anthracene.
7. A process for manufacture of tochnicQl grade anthracene having purity of-at
leaot 05% from anthracene mud obtained from coal tar distillation substantially
as hereindescribed and illustrated with reference to the accompanying
examples.

A process of production of 95% pure anthracene from coal tar. Anthracene mud
(obtained from anthracene oil fraction) of coal tar is a rich resource of anthracene
containing about 20 to 25% of anthracene. The process of isolation of anthracene
involves vacuum distillation of the mud to obtain a fraction rich in anthracene and
carbazole which is next digested in benzene to provide an anthracene-carbazole
(AC) residue, subjecting the said AC residue to formaline treatment to obtain
enriched anthracene and finally purifying the enriched anthracene. The process
produces substantially pure anthracene in good yield from anthracene oil fraction
(anthracene mud) not affecting isolation of carbazole from the same oil fraction.
The process is simple and cost-effective having inherent flexibility to adopt to
wide variations in the raw material composition. The pure anthracene of the
invention is useful for various purposes including production of anthraquinone, a
key chemical for synthesis of wide range of vat dyes, plasticizer for thermo-
setting resins as a raw material for making artificial diamonds, scintillator te
detect light energy radiation's and synthetic perfumes.