Field of the invention
[0001] The present invention relates to a method of modifying 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
[0002] Coal-tar is usually obtained as a by-product of the distillation of coal in coke
ovens, e.g. in the manufacture 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 viscous
material which softens and flows when heated. Pitches are conventionally 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 characteristic.
[0003] Much of the Q.I. formation takes place at the high temperature to which the tar is
subjected during coke formation, and stays in the pitch residue following distillation.
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 material. The particulate
nature of the Q.I. renders difficult virtually any process which requires the passage
of the pitch through small orifices; e.g. 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 carbonizing) the pitch will
be significantly increased.
[0004] In orderto reduce the quinoline-insolubles ("QI") content of pitches, various separating
methods have been developed. For example, mechanical separation by filter, centrifugal
or distillative methods have been put forward (see, for example, German Patent Specification
No 1189517, particularly at column 1, line 49 onwards). According to the mechanical
separation process, the pitch is preferably treated at an elevated temperature with
a tar solvent and the residue mechanically separated.
[0005] It is an object of this invention to provide a process for decreasing and modifying
the quinoline-insoluble content in coal-tar material.
[0006] It is also an object of this invention to provide a process for obtaining pitch material
with a diminished content of quinoline-insoluble material.
Brief description of the invention
[0007] According to one aspect of the present invention in a process for obtaining a pitch
material from an undistilled coal-tar material, the improvement essentially consists
in decreasing the content of quinoline-insolubles (Q.I.) of said pitch material prior
to distilling said coal-tar material by mixing said undistilled coal-tar material
with a solvent which consists of at least one of the following: n-methyl-2-pyrrolidone
and the fraction of a coal-tar distillate which boils between 100 and 350°C, said
mixing being carried out at a temperature such as to form a solvent-dissolved fraction
and a solvent-undissolved fraction, separating and removing said solvent-undissolved
fraction of said undistilled coal-tar material, said undissolved fraction containing
Q.I. having a high content of ash-forming impurities and using said solvent-dissolved
fraction to produce coal-tar material with a decreased Q.I. and lower impurities by
distilling said solvent-dissolved fraction of said undistilled coal-tar material so
as to obtain from said solvent-dissolved product a pitch material having a lower Q.I.
and lower impurities than pitch material typically, obtained by the conventional distillation
of said coal-tar material. Preferably, the process comprises the additional step of
recovering the solvent.
[0008] 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
[0009]
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.
Detailed description of the invention
[0010] 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 material 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.1. 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.
[0011] Broadly, the process of the present invention comprises 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 contains at least one of n-methyl-2-pyrrolidone
and the fraction of the coal-tar distillate which boils between 100 and 350°C, preferably
between 200 and 350°C. 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 material
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, centrifugation, decantation and the
like. The solvent-dissolved fraction 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 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 boiling 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 for use in the extraction
of more coal-tar material.
[0012] The amount of solvent employed for this extraction will be partially determined by
the viscosity of the resultant 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 substantially all the quinoline soluble material.
Typically, the proportion of the solvent in the mixture will usually range from about
20 to 80% of the mixture, ie. the solvent: tar ratio will be in the range 1:4 to 4:1.
[0013] 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 additionally
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
04, at a temperature high enough to facilitate its handling and further processing.
The mixture then passes via line 06 to the separation step 20 where the solvent-dissolved
fraction and the fraction insoluble in the solvent are separated, 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 us the earlier fractions
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 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.
[0014] The advantages accruing to the user of this process 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 process viz. the n-methyl-2-pyrrolidone and/or the light
boiling 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.
[0015] A surprising outcome of this process is the manner in which the viscosity of the
pitch and the size distribution 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 often characterized by a greater degree of
particulate agglomeration. The pitch material thus obtained is characterized 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.
[0016] The following examples will serve to illustrate the invention.
Example 1
[0017] This example illustrates how the Q.I. of a conventional coal tar material can be
decreased by the present invention using the light boilers of coal tar distillation
(wash oil) as the solvent.
[0018] 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. 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 atmospheric pressure, and the Q.I. content of
the pitch residue determined in accordance with ASTM D2318. The experimental results
are summarized in Table 1 below. The above procedure was repeated with two other commercially
available coal tar samples having Q.I. values of 7.0 and 23.7% respectively. In each
of the cases, the Q.I. in the treated tar was a small fraction of that in the original
sample.
[0019] A possibly more remarkable outcome which was indicative of the degree to which the
process resulted in the Q.I. removal was the low Q.I. content in the pitch residue
as compared to the original tar. This is surprising because Q.L is normally concentrated
in the pitch, partly due to a large decrease in the volume, and partly due to some
cracking 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.
[0020] The above procedure was repeated with the same three tar samples, but with a tar:solvent
ratio of 1:4. The experimental results which are qualitatively substantially the same
as the preceding set; are also summarized in Table 1 below.
Example 2
[0021] This example illustrates the use of n-methyl-2-pyrrolidone as the solvent in the
extraction of the Q.I. from the tar.
[0022] 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 preceding 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.
Example 3
[0023] 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 pitch after an extraction of the precursor tar according
to the present invention.
[0024] Figure 2(a) is a scanning electron microscope (S.E.M.) photograph of residual tar
Q.I. following an extraction using quinoline. Figure 2(b) is a S.E.M. photograph of
the insolubles in a pitch prepared from an identical tar after extraction with n-methyl-2-pyrrolidone.
[0025] It is evident that typical particle sizes in the former photograph are greater than
about 1 micrometer, with sizes of the agglomerated particles ranging up to about 4
micrometers. The particle sizes in the latter photograph (Figure 2(b)) range from
less than about 0.1 micrometer to about 0.5 micrometer, with the larger agglomerates
being about 1 micrometer in size.
[0026] The difference in the particle size distribution is all the more substantial when
we note that the particles in the latter photograph include not only the insolubles
following 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.
1. In a process to obtain a pitch material from an undistilled coal-tar material,
the improvement which consists essentially in decreasing the content of quinoline-insolubles
(Q.I) of said pitch material prior to distilling said coal-tar material by mixing
said undistilled coal-tar material with a solvent which consists of at least one of
the following: n-methyl-2-pyrrolidone and the fraction of a coal-tar distillate which
boils between 100 and 350°C, said mixing being carried out at a temperature such as
to form a solvent-dissolved fraction and a solvent-undissolved fraction, separating
and removing said solvent-undissolved fraction of said undistilled coal-tar material,
said undissolved fraction containing Q.I. having a high content of ash-forming impurities
and using said solvent-dissolved fraction to produce coal-tar material with a decreased
Q.I. and lower impurities by distilling said solvent-dissolved fraction of said undistilled
coal-tar material so as to obtain from said solvent-dissolved product a pitch material,
having a lower Q.I. and low impurities than pitch material typically obtained by the
conventional distillation of said coal-tar material.
2. The process as defined in Claim 1, wherein said separated solvent is used in the
extraction of additional coal-tar material.
3. The process as defined in Claim 1, wherein the ratio of said solvent to said coal-tar
material ranges from about 4:1 to about 1:4.
4. The process as defined in Claim 1, wherein said mixing and separation steps are
carried out at a temperature in the temperature range of 75-95°C.
5. The process as defined in Claim 1, wherein said separation is carried out by filtration
of said mixture.
6. The process as defined in Claim 1, wherein said separation is carried out by centrifugation
of said mixture.
7. The process as defined in Claim 1, wherein said separation is a gravity separation.
8. A product derived from coal-tar material by the process defined in Claim 1.
1. Verfahren zum Gewinnung eines pechartigen Stoffes aus undestilliertem Steinkohlenteer,
dadurch gekennzeichnet, daß man den Gehalt an Chinolin-unlöslichen Bestandteilen (Q.I.)
des pechartigen Stoffes vor der Destillation des Steinkohlenteers verringert, indem
man den undestillierten Steinkohlenteer mit einem Lösungsmittel mischt, welches mindestens
aus einem der Bestandteile N-Methyl-2-pyrrolidon und einer zwischen 100 und 350°C
siedenden Fraktion eines Steinkohlenteer-Destillates besteht, wobei das Mischen bei
einer solchen Temperatur durchgeführt wird, daß eine im Lösungsmittel gelöste Fraktion
und eine im Lösungsmittel ungelöste Fraktion entsteht, und man die im Lösungsmittel
ungelöste Fraktion des undestillierten Steinkohlenteers abtrennt und entfernt, wobei
die das Q.I. enthaltende ungelöste Fraktion einen hohen Gehalt an aschebildenden Verunreinigungen
hat, und man die im Lösungsmittel gelöste Fraktion zur Gewinnung eines Steinkohlenteers
mit verringertem Q.I. und geringeren Verunreinigungen verwendet, wobei man die im
Lösungsmittel gelöste Fraktion des undestillierten Steinkohlenteers destilliert und
dabei aus dem in Lösungsmittel gelösten Produkt einen pechartigen Stoff erhält, der
einen niedrigen Gehalt an Q.I. und weniger Verunreinigungen enthält als ein pechartiger
Stoff, wie er typischerweise erhalten wird durch übliche Destillation des Steinkohlenteers.
2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß das abgetrennte Lösungsmittel
zur Extraktion zusätzlichen Steinkohlenteers verwendet wird.
3. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß das Verhältnis des Lösungsmittel
zum Steinkohlenteermaterial im Bereich von etwa 4:1 bis etwa 1:4 liegt.
4. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß die Misch- und Abtrennungsschritte
bei einer Temperatur im Bereich von 75 bis 95°C durchgeführt werden.
5. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß der Abtrennungsschritt in
einer Filtration des Gemisches besteht.
6. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß der Abtrennungsschritt in
einer Zentrifugierung des Gemisches besteht.
7. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß die Trennung durch Gravitation
erfolgt.
8. Von Steinkohlenteer abgeleitetes Produkt, erhalten nach dem Verfahren gemäß Anspruch
1.
1. Dans un procédé pour obtenir un brai à partir d'un goudron de houille non distillé,
l'amélioration qui consiste essentiellement à réduire la teneur en matières insolubles
dans la quinoléine (Q.I.) de ce brai avant de distiller ce goudron de houille en mélangeant
ce goudron de houille non distillé avec un solvent qui consiste en au moins un des
suivants: la n-méthyl-2-pyrrolidone et la fraction d'un distillat de goudron de houille
qui bout entre 100 et 350°C, ce mélange étant effectué à une température telle que
l'on forme une fraction dissoute dans le solvant et une fraction non dissoute dans
le solvant, à séparer et à éliminer cette fraction non dissoute dans le solvant de
ce goudron de houille non distillé, cette fraction non dissoute contenant des matières
insolubles dans la quinoléine ayant une teneur élevée en impuretés formant des cendres,
et à utiliser cette fraction dissoute dans le solvant pour produire un goudron de
houille ayant une teneur en Q.I. réduite et moins d'impuretés en éliminant par distillation
cette fraction dissoute dans le solvant de ce goudron de houille non distillé de façon
à obtenir à partir de ce produit dissous dans le solvant un brai ayant une teneur
en Q.I. plus faible et moins d'impuretés que le brai généralement obtenu par la distillation
classique de ce goudron de houille.
2. Procédé suivant la revendication 1, dans lequel ce solvant séparé est utilisé dans
l'extraction d'un supplément de goudron de houille.
3. Procédé suivant la revendication 1, dans lequel le rapport de ce solvant à ce goudron
de houille va d'environ 4:1 à environ 1:4.
4. Procédé suivant la revendication 1, dans lequel ces stades de mélange et de séparation
sont effectués à une température dans l'intervalle de 75 à 95°C.
5. Procédé suivant la revendication 1, dans lequel cette séparation est effectuée
par filtration de ce mélange.
6. Procédé suivant la revendication 1, dans lequel cette séparation est effectuée
par centrifugation de ce mélange.
7. Procédé suivant la revendication 1, dans lequel cette séparation est une séparation
par gravité.
8. Produit obtenu à partir d'un goudron de houille par le procédé défini dans la revendication
1.