Note: Descriptions are shown in the official language in which they were submitted.
3~73
Field of the Invention
The present invention relates to a method of modi-
fying coal-tars. More particularly it relates to a method
of decreasing and/or modifying the quinoline insoluble
content therein.
Background of the Invention/Prior Art
Coal-tar is usually obtained as a by-product of
the distillation of coal in coke ovens, e.g. in the manu-
facture of metallurgical coke. It comprises a mixture of a
number of hydrocarbon compounds which can be separated by
distillation of the tar. Pitch, which is the residue in the
still following such a distillation is a viscuous material
which softens and flows when heated. Pitches are conven-
tionally classified according to their softening points and
their solubility in various solvents eg. quinoline, benzene
and dimethylformamide~ The latter characteristic is usually
indicated by the proportion of the pitch which is insoluble
in the solvent eg. the proportion of the pitch which is
quinoline-insoluble (Q.I.) is a widely-used pitch character-
istic.
Much of the Q.I. formation takes place at the hightemperature to which the tar is subjected during coke forma-
tion, and stays in the pitch residue following distilla-
tion. The presence of the Q.I. in the tar or pitch can be
tolerated for a limited number of applications; however, in
most of the uses, the presence of significant amounts of
Q.I. is viewed as an undesirable characteristic of the mate-
rial. The particulate nature of the Q.I. renders difficult
virtually any process which requires the passage of the
pitch through small orifices; eg. penetration of pitch is
rendered difficult. Additionally, should the Q.I. have a
high content of ash-forming impurities, the combustion rate
of the carbon body produced by coking (or otherwise
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~ 73~73carbonizing~ the pitch will be significantly increased.
Accordingly, it is an object of this invention to
provide a process for decreasing and modifying the
quinoline-insoluble content in coal-tar material.
It is also an object of this invention to provide
a process for obtaining pitch material with a diminished
content of quinoline-insoluble materialO
Brief Description of the Invention
In one aspect, the present invention relates to a
process for decreasing and modifying the quinoline-insoluble
content (Q.I.) of coal-tar material comprising: mixing the
coal-tar material with a solvent which contains at least one
of n-methyl-2-pyrrolidone and the fraction of a coal-tar
distillate which boils between 100 and 350C, thereby to
form a solvent-dissolved fraction and a solvent-undissolved
fraction of the coal-tar material, separating the two
fractions, where the Q~Io of the coal-tar material is
concentrated in the latter fraction; and the solvent-
dissolved fraction comprises coal-tar material with a
decreased and modified Q.I. Preferably, the process
comprises the additional step of recovering the solvent.
In another aspect, the present invention relates
to the production of pitch material by the distillation of
the aforesaid solvent-dissolved fraction where the pitch has
a reduced and modified Q.I.
Brief Description of the Drawings
: Figure 1 is a schematic flow diagram which
illustrates the steps which an embodiment of this invention
entails.
Figure 2 (Figures 2(a) and 2(b)) are scanning
electron microscope photographs of the insoluble particulate
matter in the tar and pitch respectively.
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~'7~7~3
Detailed Description of the Invention
-
Accordingly, the present invention relates to a
process whereby the content of quinoline-insolubles (Q.I.)
in coal-tar material can be decreased. The coal-tar materi-
al which has been thus treated can be distilled in order to
obtain a pitch having a diminished Q.I. Additionally, the
Q.I. contained in the pitch so obtained will usually have a
size distribution different from a conventionally obtained
pitch having the same Q.I. This latter attribute of the
present invention is referred to as the "modification" of
the Q.I..The present invention additionally relates to a
novel coal tar pitch material having a significantly reduced
viscosity and a lower average particle size.
Broadly, the process of the present invention com-
prises a solvent extraction of coal-tar material in order to
separate the quinoline-soluble from the quinoline-insoluble
components; where the solvent chosen for this procedure con~
tains at least one of n-methyl-2-pyrrolidone and the frac-
tion of the coal-tar distillate which boils between 100 and
350C, preferably between 200 and 350C~ In the following,
the latter solvent will be referred to as wash oil, a term
which is widely used in the art. The mixing of coal-tar ma-
terial with the solvent results in the formation of two
fractions which can be subsequently separated, viz. the
solvent-dissolved and that undissolved in the solvent, with
most of the Q.I. being localized in the latter fraction,
while the former fraction comprising the coal-tar material
has a greatly reduced Q.I. These fractions may be separated
by conventional techniques such as filtration, centrifuga-
tion, decantation and the like. The solvent-dissolved frac-
tion of the coal-tar material so treated can be distilled to
separate the various fractions with different boiling points
and obtain a pitch material with a significantly diminished
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73~3
Q.I. The pitch material, thus produced has a number of
characteristics and uses that are associated with a low
Q.I., a substantially reduced viscosity, and a relatively
low average size of particulate matter. The distillation,
which serves to separate the higher boiling components from
the pitch residue, also serves to separate the n-methyl-2-
pyrrolidone from the higher boiling components with which it
distils over. The n-methyl-2-pyrrolidone has a lower boil-
ing point than the light boilers contained in the distillate
and can be separated therefrom. The wash oil fraction of
the distillate can be permitted to distil over with the
n-methyl-2-pyrrolidone and can equivalently (individually,
or in combination with the n-methyl-2-pyrrolidone) be used
as a solvent in this solvent extraction process. This will
permit some flexibility in the distillation procedure. The
n-methyl-2-pyrrolidone and/or the wash oil fraction which
will be contained in the distillate can then be recycled ~or
use in the extraction of more coal-tar material.
The amount of solvent employed for this extraction
will be partiall~ determined by the viscosity of the resul-
tant coal-tar-solvent mixture required for the separation
technique (and which is also dependent upon the temperature
of this process) and by the amount required to dissolve sub-
stantially all th2 quinoline soluble material. Typically,
the proportion of the solvent in the mixture will usually
range ~rom about 20 to 80% of the mixture, ie. the solvent:
tar ratio will be in the range 1:4 to 4:1.
Turning now to the single figure (Figure 1), we
note that n~methyl-2-pyrrolidone which is introduced via
line 01, can be mixed with recycled solvent which can addi-
tionally contain some light boilers and is introduced to the
mixing tank 10, via line 02 where it is mixed with the
untreated tar which has been introduced to the tank via line
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~.~73773
04, at a temperature high enough to facilitate its handling
and further processing. The mixture then passes via ].ine 06
to the separation step 20 where the solvent-dissolved frac-
tion and the fraction insoluble in the solvent are sep~rat-
ed, possibly by differences in specific gravity or by
filtration, as a result of which the former fraction leaves
this step via line 08 and the latter fraction via line 07.
The former fraction which contains a tar with a depleted
Q.I. can be distilled in the distillation step 30 from which
the n-methyl 2-pyrrolidone and the light boilers come over
as the earlier fr~ctions of the distillate and can be
separated from each other, at separation step 40, if so
desired or recycled via lines 13 and 15 for use as a solvent
in the extraction of subsequent batches of coal-tar
material. The pitch residue obtained from this distillation
via line 09 will have a substantially reduced viscosity, a
lower average particle size of insolubles, in addition to a
reduced Q.I. content.
The advantages accruing to the user of this pro-
cess are many, not the least of which is the extent of the
Q.I. removal from the coal-tar which results from the use of
this process. Some of the other advantageous features of
this process stem from the solvent system used in this pro-
cess viz. the n-methyl-2-pyrrolidone and/or the light boil-
ing cut of the tar distillate; in particular, the ease with
which the solvent can be used, recovered, reused; and the
facility with which these operations can be integrated into
a conventional pitch production process.
A surprising outcome of this process is the manner
in which the viscosity of the pitch and the size distribu~
tion of the Q.I~ is affected. The size distribution of a
pitch derived from an unextracted tar, or one extracted with
a solvent different from that of the present invention, is
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" ~73773
often characterized by a greater degree of particulate
agglomeration. The pitch material thus obtained is charac-
terized by a viscosity lower than that of pitches obtained
by the distillation of the untreated coal tar. This is
particularly important where the particulate size of the
pitch is important e.g. in applications such as the
impregnation of prebaked electrodes.
The following examples will serve to illustrate
the invention.
Example 1
This example illustrates how the Q.I. of a conven-
tional coal tar material can be decreased by the present
invention using the light boilers of coal tar distillation
(wash oil) as the solvent.
A sample of coal-tar having a Q.I. of 6.5~, and
representative of the output obtained from steel mills was
mixed with wash oil in a tar to wash oil ratio of 3:2. The
mixture was filtered using a Buchner funnel and No. 1
analytical filter paper with a moderate vacuum being applied
to accelerate the process. The Q.I. of the treated tar
was measured. The filtrate was then distilled under atmo-
spheric pressure, and the Q.I. content of the pitch residue
determined in accordance with ASTM D2318. The experimental
: recults are summarized in Table 1 below. The above proce-
dure was repeated with two other commercially available coal
tar samples having Q.I values of 7.0 and 23.7% respective-
ly. In each of the cases, the Q.I. in the treated tar was a
small fraction of that in the original sample.
A possibly more remarkable outcome which was in-
dicative of the degree to which the process resulted in theQ.I. removal was the low Q.I. content in the pitch residue
as compared to the original tar. This is surprising because
Q.I. is hormally concentrated in the pitch, partly due to a
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3~7~3
large decrease in the volume, and partly due to some crack-
ing which occurs during the distillation. Nonetheless, in
all the cases the Q.I. in the pitch was a small fraction of
that in the tar prior to filtration.
i The above procedure was repeated with the same
three tar samples, but with a tar:solvent ratio of 104. The
experimental results which are qualitatively substantially
the same as the preceding set; are also summarized in Table
1 below.
Table 1
_.~,. . .
, .,
,Q.I. (%)
'Coal Tar.Tar: Solvent'Untreated~ QoI~ (%) 'Q.I.(%)
Sample ' Ratio . Tar ' (Treated Tar) '(Pitch)
1 , 3:2 '6.5 . 0.02 , 0.3
2 J 3:2 '7.0 ' 0.5 . 1.0
1 3 ' 3:2 '23.7 0.7 ~.5
` ' 1 , 1:4 '6.5 ' 0.5 . 0.5
' 2 ' 104 .7.0 ' 0.03 ' O.S g
i 3 i 1:4 j23.7 ~ 0 3 i 3 0
Exam21e 2
This example illustrates the use of n-methyl-2-
pyrrolidone as the solvent in the extraction of the Q.I.
from the tar,
Tar samples identical to those in example 1 were
subjected to essentially the same procedure and tests as~
described above in the preceding Example. The results of
these experimental runs which are summarized in Table 2
below follow essentially the same pattern as in the preced
ing Example. The treated tar has a greatly reduced Q.I.
which is also manifested in the low Q.I. content of the
pitch residue remaining after the distillation of the tar.
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3~7i73
Table 2
,
Q.I. (%) l '
Coal Tar'Tar: Solvent'Untreated' Q.I. (%) 'Q.I.(%).
Sample ' Ratio ' Tar . (Treated Tar) '(Pitch)'
1 : 3:2 . 5.0 0.1 0.7
' 2 ' 3:2 ' 4.2 ' 0.1 . 3.4
. 3 , 3:2 '18.2 ' 0.3 . 4.5
,_ ., .. ._ , . ., . . , ~
1 , 1:4 , 5.0 0~2 , 1.3
2 ' 1:4 , 4.2 ' 0.1 ' 1.8
i 3 i 1:4 j18.2 , 0-03 i 5.1
. . . .
Example 3
This example presents a qualitative comparison of
particle sizes of insolubles in tar which has been extracted
using a conventional solvent (in this case quinoline), and
that which is residual in E~ after an extraction of the
precursor tar according to the present invention.
Figure 2(a) is a scanning electron microscope
(S.B.M.) photograph of residual tar Q.I. following an
extraction using quinoline. Figure 2(b) is a S.E.M. photo-
graph of the insolubles in a pitch prepared from an
identical tar after extraction with n-methyl-2-pyrrolidone.
It will readily moved that typical particle sizes
in the former photograph are greater than about 1 micron,
with sizes of the agglomerated particles ranging up to about
4 microns. The particle sizes in the latter photograph
~Fiyure 2(b)) range from less than about 0.~ microns to
about 0.5 micron, with the larger agglomerates being about 1
micron in size.
The difference in the particle size distribution
is all the more substantial when we note that the particles
in latter photograph include not only the insolubles follow-
ing the extraction of the tar, but additionally include the
"secondary" Q.I. produced during the tar distillation to
produce the pitch, where the original Q.I. is concentrated
and function as nuclei for the growth of Q.I. particles.
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~73~73
The above described procedure can be subjected to
a great variety of modifications which will be evident to
those skilled in the art and which fall within the scope of
the appended claims.
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