-
The present invention relates in general to a tar or
oil pitch with a low content of polycyclic aromatic
substances.
-
In particular, the present invention relates to a
pitch of the aforementioned type which is substantially
free of benzo[a]pyrene.
-
The terms "tar pitch" and "oil pitch" are intended
to define residues which can be produced, respectively,
by the distillation of coal tar and of petroleum
fractions and/or residues thereof resulting from
processes such as thermal or catalytic cracking.
-
The present invention also relates to a method of
producing tar and/or oil pitches which are substantially
free of benzo [a] pyrene.
-
It is known that an isotropic pitch based on
aromatic compounds and having a low softening point,
normally below 150°C, can be produced by the primary
distillation of tar or of petroleum.
-
It is also possible to remove a certain quantity of
oils from pitch with a low softening point (soft pitch)
by subsequent distillation, generally under vacuum and
possibly in the presence of a stripping agent, and thus
to produce a residue with a higher softening point (hard
pitch).
-
The aforementioned pitches are widely used in
various industrial applications but they have the serious
disadvantage of containing various aromatic compounds
which are suspected of having or which have carcinogenic
properties, and the presence of which leads to
considerable problems due to environmental impact and
constitutes a potential hazard to workers' health.
-
Of these aromatic compounds, the one which has been
investigated most is benzo[a]pyrene; this compound,
which has been confirmed to be carcinogenic, is found in
concentrations of about 0.5-1.5% by weight in soft
pitches derived from tar and about 0.1-1% by weight in
soft pitches derived from petroleum.
-
In hard pitches, on the other hand, the
concentration of benzo[a]pyrene is reduced as a result of
the second distillation and is generally within the range
of 4,000-12,000 ppm.
-
The presence of benzo[a]pyrene in pitches is in any
case not desirable and, moreover, the current regulations
classify pitches having a benzo[a]pyrene content greater
than 50 ppm as carcinogenic products and provide for
particular care and attention during their handling.
-
For this reason, special methods of distilling
residues from the primary distillation of tar or of
petroleum have been devised and sometimes adopted in
order to reduce as far as possible the benzo[a]pyrene
content in the final pitches.
-
European patent EP 0 510 315 describes a method of
producing pitches having a benzo[a]pyrene content of less
than 50 ppm in which a residue of the primary
distillation of tar is distilled at a temperature of 300-380°C
and at a pressure of less than 1 mbar in an
evaporator having a heat-exchange area:volume ratio of
between 330 and 10,000 m2/m3, with the residue spending a
period of 2-10 minutes in the evaporator.
-
In Examples 1, 2 and 3 of this patent, it is
reported that, by distilling the aforementioned residue
in a thin-layer evaporator operating at a temperature of
300°C, 320°C, and 340°C and at a pressure of 1 mbar, with
an average period of about 5 minutes spent in the
evaporator, pitches containing 35 ppm, 20 ppm and 20 ppm
of benzo[a]pyrene, respectively, were produced.
-
However, it is clear from a comparison of Examples 2
and 3 of EP 0 510 315 that even a considerable increase
in the distillation temperature (20°C) does not permit a
further reduction of the benzo[a]pyrene content in the
final pitches which, in fact, is never less than 20 ppm
in the examples given in the above-mentioned document.
-
In EP 0 510 315, the German patent DE 3702720, which
relates to a method of preparing a tar pitch with a high
softening point and a low content of substances insoluble
in quinoline, is cited as prior art.
-
In this method, a filtered tar pitch having a low
softening point is distilled in a thin-layer evaporator
at a temperature of 300-425°C and at a pressure no
greater than 10 mbars.
-
In DE 3702720 it is taught that, in order to have a
low content of substances insoluble in quinoline in the
final pitches, the average time spent by the filtered
pitch in the evaporator should be very short and in fact,
in Examples 1 and 2, with distillation carried out at a
pressure of 1 mbar and at a temperature within the range
of 300-380°C, it is always less than 1 minute.
-
However, in EP 0 510 315, Example 2 of the
aforementioned German application is cited, and it is
stated that the pitch obtained in accordance with this
example still contains 140 ppm of benzo[a]pyrene and the
method described in DE 3702720 is therefore not suitable
for producing a pitch with a low benzo[a]pyrene content
in the sense indicated by the current regulations.
-
In fact, it is clear from the above-mentioned
examples of EP 0 510 315 and DE 3702720 that, in order to
eliminate the benzo[a]pyrene from the primary residues,
it is important to extend the time spent by these
residues in the evaporator rather than to increase the
distillation temperature.
-
However, it is well known that the subjection of
residues of the primary distillation of tar or oil to
temperature conditions of 350-450°C for a prolonged
period results in the progressive formation therein of an
optically anisotropic ordered structure which is known as
a mesophase and is quantifiable by suitable microscopic
techniques in polarized light, and the presence of which
is undesirable for some industrial uses of the final
pitches as binding and impregnation agents.
-
For this reason, in the prior art, the subsequent
distillation of residues resulting from the primary
distillation of tar or petroleum is performed in
evaporators which have a large heat-exchange area, such
as thin-layer or thin-film evaporators which allow the
residues to have short contact times with the exchange
surface, generally less than 10 minutes, so as to reduce
the mesophase content of the final pitches as far as
possible.
-
Both in the method of EP 0 510 315 and in that of DE
3702720, pitches having optical anistropy of less than 2%
are thus produced by distillation in thin-layer
evaporators.
-
However, thin-layer or thin-film evaporators have
the disadvantage that it is extremely difficult to
achieve a uniform layer of pitch on their exchange
surfaces so that exchange efficiency is not particularly
high.
-
The technical problem upon which the present
invention is based is that of providing tar and/or oil
pitches which are substantially free of benzo[a]pyrene
and which, at the same time, also have low optical
anisotropy so that they can be used in all industrial
applications which require substantially isotropic
pitches.
-
This problem is solved by a tar and/or oil pitch,
characterized in that it has a benzo[a]pyrene content
less than or equal to 5 ppm and optical anisotropy of
less than 1%.
-
As well as having optical anisotropy of less than
1%, the pitches of the invention are preferably
characterized in that they are free of benzo[a]pyrene.
-
According to one embodiment, the pitches of the
invention are further characterized in that they have a
content of less than 50 ppm, preferably less than 5 ppm,
of each of the following polycyclic aromatic compounds:
benzo[a]anthracene, chrysene, benzo[a]fluoranthene,
benzo[k]fluoranthene, benzo[b]fluoranthene,
benzo[e]pyrene, indeno[1,2,3-c,d]pyrene,
dibenzo[a,h]anthracene and benzo[g,h,i]perylene.
-
According to another embodiment, the pitches of the
invention are further characterized in that they are free
of the above-mentioned polycyclic aromatic compounds.
-
The present invention also relates to a method of
preparing tar and/or oil pitches substantially free of
benzo[a]pyrene, the method comprising the steps of:
- performing a first distillation of tar and/or
petroleum so as to produce a residue with a low softening
point;
- supplying the residue or a mixture of the residue
with tar and/or petroleum into an evaporator having a
heat-exchange area:volume ratio of between 1 m2/m3 and
200 m2/m3, the residue or mixture being kept in a state
of continuous mixing;
- distilling the residue or the mixture with
continuous mixing, in the evaporator, at a pressure less
than or equal to 10 mbars and at a temperature of between
250°C and 360°C, for a period of at least 20 minutes;
- discharging the pitch from the evaporator and, at
the same time, recovering a distillate.
-
Preferably, the period for which the residue or the
mixture is distilled in the evaporator is between 20
minutes and 10 hours.
-
Surprisingly, it has been found that, as well as
being free of benzo[a]pyrene or having a content of this
compound less than or equal to 5 ppm, the pitch produced
in the manner described above also has optical anisotropy
of less than 1%.
-
Thus, in contrast with the teachings of the prior
art, in the method of the invention, the removal of the
benzo[a]pyrene from the above-mentioned residue or from
the above-mentioned mixture by distillation for long
periods is not accompanied by the formation of
unacceptable quantities of mesophase in the final pitch.
Naturally, the operative temperature and vacuum
conditions of the evaporator and the distillation time
can be selected within the above-mentioned ranges
according to the chemico-physical characteristics and the
benzo[a]pyrene content of the residue or of the mixture
to be distilled so as to produce a final pitch
substantially free of this compound.
-
It has also been found that the pitches produced by
the method of the invention can be produced free of the
following polycyclic aromatic compounds:
benzo[a]anthracene, chrysene, benzo[a]fluoranthene,
benzo[k]fluoranthene, benzo[b]fluoranthene,
benzo[e]pyrene, indeno[1,2,3-c,d]pyrene,
dibenzo[a,h]anthracene and benzo[g,h,i]perylene, or,
alternatively, have a content of less than 50 ppm,
preferably less than 5 ppm, of the above-mentioned
compounds.
-
This renders the method of the invention
particularly advantageous, since some of the above-mentioned
polycyclic aromatic compounds, that is:
benzo[a]anthracene, benzo[a]fluoranthene,
benzo[k]fluoranthene, benzo[b]fluoranthene and
dibenzo[a,h]anthracene, are possibly or probably
carcinogenic to man, whilst the other compounds mentioned
above are suspected of having this property.
-
In the method of the invention, the apparatus used
for the distillation of the residue from the primary
distillation of tar and/or petroleum or of the mixture of
this residue with tar and/or petroleum is of particular
importance and should have a heat-exchange area:volume
ratio of between 1 m2/m3 and 200 m2/m3, preferably between
5 m2/m3 and 60 m2/m3, and should enable the residue or the
mixture to be mixed continuously during distillation.
-
According to a preferred embodiment of the method of
the invention, the distillation of the above-mentioned
residue or of the above-mentioned mixture is performed in
an evaporator which at the same time acts as a mixer and
which comprises a cylindrical body provided with a jacket
for heating its internal wall, at least one inlet opening
for the residue or the mixture, at least one outlet
opening for the final pitch, at least one distillate-recovery
opening connected to a system for applying a
reduced pressure to the interior of the cylindrical body,
and a rotary shaft which can be heated and is supported
for rotating in the cylindrical body, and along the axis
of which radial mixing elements, which may also be
capable of being heated, are disposed.
-
According to one embodiment of the method of the
invention, the evaporator further comprises opposed
mixing elements fixed radially to the internal wall of
the cylindrical body and interposed between the radial
elements in order to facilitate the removal of the
residue or of the mixture from the peripheral surface of
the shaft and from the surfaces of the mixing elements.
-
Preferably, the radial mixing elements comprise disc
sectors to which mixing bars are fixed and the opposed
mixing elements are substantially hook-shaped with at
least one portion skimming the disc sectors and at least
one portion skimming the peripheral surface of the shaft.
-
The rotary shaft of the evaporator is heated by
means of a diathermic fluid which flows through an
internal circuit thereof and the mixing elements (the
disc sectors and the bars) may also be heated by the same
fluid; in this case, ducts through which the fluid can
flow and which are in communication with the heating
circuit of the rotary shaft are formed in the mixing
element.
-
With the use of an evaporator of this type, the
distillation of the residue of the primary distillation
of tar and/or petroleum or of the mixture of the residue
with tar and/or petroleum according to the method of the
invention comprises the steps of:
- supplying the residue or the mixture into the
evaporator in which the internal wall, the rotary shaft,
and possibly the mixing elements, are kept at a
temperature of 250-360°C, the rotary shaft is rotated at
a speed of 1-150 revolutions/minute, and the pressure is
equal to or less than 10 mbars, the mixer having a heat-exchange
area:volume ratio between 1 m2/m3 and 200 m2/m3;
- mixing the residue or the mixture for a period of
at least 20 minutes by means of the mixing elements in a
relationship permitting thermal exchange with the
internal wall of the evaporator, the rotary shaft and,
possibly, the mixing elements;
- discharging from the evaporator a pitch
substantially free of benzo[a]pyrene and having optical
anisotropy of less than 1% and, at the same time,
recovering a distillate.
-
During the mixing step of the method of the
invention, if the evaporator comprises the above-mentioned
opposed fixed mixing elements, these facilitate
the removal of the residue or of the mixture from the
peripheral surface of the rotary shaft and from the
surfaces of the mixing elements.
-
The above-described evaporator-mixers, which may be
used continuously, semi-continuously or for batch
operation, have the advantage of highly efficient heat
exchange and mass transfer since the product treated
therein is mixed continuously in conditions permitting
thermal exchange with contact surfaces all of which can
be heated and which at the same time are cleaned of the
product by any opposed mixing elements.
-
These evaporators are known per se and are used for
performing various processes such as drying,
evaporation, sublimation, etc., by the thermal and
mechanical treatment of products in liquid, paste or
powder form.
-
However, they are particularly advantageous in the
treatment of residues of the primary distillation of tar
and/or petroleum in order to produce pitches
substantially free of benzo[a]pyrene and with low optical
anisotropy.
-
The pitches produced by the method of the invention
can be used in various industrial applications for which
an isotropic pitch is required.
-
They can be used, for example, as binding agents in
the production of electrodes, refractory materials or
special graphitized materials, as impregnating agents, or
as a raw material for the production of paints, pitch
coke and rechargeable batteries.
-
In these applications, at least one viscosity-modifying
agent is generally added to the pitches of the
invention before use.
-
In fact, with the method of the invention, in
addition to the substantial removal of benzo[a]pyrene and
a large number of polycyclic aromatic compounds from the
residues subjected to distillation, most of the volatile
oily component of these residues is also removed, so that
the pitches of the invention are produced with a
viscosity too high for them to be usable directly in most
cases.
-
For some applications, however, the pitch thus
produced is advantageously used directly without the aid
of viscosity-modifying agents.
-
Viscosity-modifying agents which may be used are,
for example, aromatic oils, resins, bituminous products
miscible with pitches, etc., selected in dependence on
the final use of the pitches.
-
In any case, the at least one viscosity-modifying
agent added to the pitches of the invention is
advantageously substantially free of benzo[a]pyrene so
that compositions comprising the pitches of the invention
and at least one such agent can be used in the various
applications without problems of environmental impact or
risk to workers' health.
-
The characteristics and advantages of the present
invention will become clear from the following
description of some examples of the implementation of the
method of the invention, given with reference to the
drawing appended by way of non-limiting example.
-
The drawing is a schematic side view of an
evaporator, partially open, which is usable for
implementing the method of the invention, and is of the
type described, for example, in US patent 5,121,992, the
text of which should be referred to for a detailed
description.
-
With reference to the drawing, an evaporator,
generally indicated R, comprises a cylindrical body 1
arranged with its longitudinal axis horizontal,
surrounded by a heating jacket 2 through which a
diathermic fluid is intended to flow, and having an inlet
opening 3 for a residue or a mixture to be distilled, an
outlet opening 4 for the final pitch, and a distillate-recovery
opening 5 connected to a system (not shown) for
applying a reduced pressure to the interior of the
cylindrical body 1.
-
A shaft 6 supported for rotating in the cylindrical
body 1 about a rotation axis A is heated by a diathermic
fluid which is admitted to its interior through an
opening 7 and emerges therefrom through an opening 8.
A motor M is provided for driving the shaft 6 at a speed
of between 1 and 150 revolutions/minute.
-
Arranged along the longitudinal axis of the shaft 6
are radial mixing elements 9 between which opposed mixing
elements 10, arranged radially on the internal wall 13 of
the cylindrical body 1, are interposed.
-
The mixing elements 9 comprise disc sectors 11 to
which mixing bars 12 are fixed. The disc sectors 11
rotate together with the shaft 6 and the bars 12 pass a
small distance from the internal wall 13 of the
cylindrical body 1.
-
The internal wall 13 is thus cleaned of the product
subjected to distillation in the evaporator R.
-
Between adjacent disc sectors 11 there is an empty
space 14 for the mixing of the product to be treated and
between adjacent bars 12 there is an empty space 15
through which a support 17 of an opposed mixing element
10 fixed to the internal wall 13 of the cylindrical body
1 can pass.
-
The opposed mixing elements 10 are substantially
hook-shaped and each comprises a support 17 and portions
18, 20 and 21.
-
The support 17 is arranged radially relative to the
shaft 6 and is joined to the portion 18 which is parallel
to the axis of rotation A.
-
The portion 18 forms, together with the respective
portion of the mixing bar 12, a slot 19 through which the
bar 12 can move.
-
The product to be treated is thus also forced
between the portion 18 and the internal wall 13 of the
cylindrical body 1 and is mixed continuously.
-
The portion 18 in turn is joined, in the region of
the disc sector 11, to a radial portion 20 which extends
as far as the vicinity of the shaft 6.
-
The purpose of this portion 20 is to remove the
product from the disc sectors 11, preventing the
formation of deposits on these sectors and, at the same
time, to mix the product between the portion 20 and the
disc sectors 11, thus improving the mixing action.
-
The portion 20 in turn is joined to a portion 21
parallel to the peripheral surface of the shaft 6 and
inclined away from the section 20 in the direction of
rotation of the shaft 6.
-
The purpose of this portion 21 is to remove the
product from the peripheral surface of the shaft 6.
-
The drawing shows opposed mixing elements 10 which
skim the surface of the disc sectors 11 on one side.
-
Similar opposed mixing elements (not shown) may be
provided in the cylindrical body 1 in an opposite
arrangement so as to remove the product from the other
surface of the disc sectors 11 with a corresponding
radial portion, and from the peripheral surface of the
shaft 6 which is not cleaned by the portion 21.
-
According to the method of the invention, a residue
from the primary distillation of tar and/or petroleum or
a mixture of this residue with tar and/or petroleum is
supplied to the mixer R through the inlet opening 3 and
is taken from this inlet and worked mechanically by the
mixing elements 9 of the shaft 6 which are kept rotating
at a suitable speed.
-
The residue or mixture is then mixed continuously by
the mixing elements 9 in a relationship permitting
thermal exchange with the internal wall 13 of the
cylindrical body 1 and with the shaft 6 which are kept at
a predetermined temperature and in conditions of reduced
pressure in the cylindrical body 1, applied through the
opening 5 thereof, through which the distillate is also
recovered.
-
The mixing of the residue or of the mixture takes
place substantially in the space 14, in the slot 19 and
between the radial portion 20 and the disc sectors 11
and, at the same time, it is removed from the surfaces of
the disc sectors 11 by means of the radial portions 20
and from the peripheral surface of the shaft 6 by means
of the portions 21 of the opposed mixing elements 10.
-
After a suitable distillation time, a pitch
substantially free of benzo[a]pyrene is then discharged
from the outlet opening 4.
-
Naturally, for technical and contingent reasons,
many modifications may be applied to the above-described
evaporator for example, to its shape, its size and the
arrangement of its component parts, or it may have one or
more inlet and outlet openings and one or more heating
and cooling jackets, for example, in order to achieve a
temperature gradient and thus to implement an exchange of
heat for the purposes of particular working requirements.
-
Moreover, the method of the invention may also be
implemented with the use of other evaporators based on
the same operating principle as the evaporator described
above, for example, evaporators of the type described in
US patent 5,407,266 comprising two or more rotary shafts
which carry radial mixing elements mating with one
another in a manner such that the surfaces of the mixing
elements of one shaft are continuously cleaned by the
mixing elements of another shaft and vice versa during
the processing of the product.
EXAMPLE 1
-
5.4 kg of a residue produced by the primary
distillation of coal tar and having the characteristics
given in Table 1A was supplied to an evaporator exactly
the same, in its basic elements, as the apparatus
described above, produced by the firm LIST AG and sold
under the name DT-B.
| Parameters | Analytical method | Value |
| Mettler softening temperature (°C) | ASTM D 3104 | 107.5 |
| Insoluble in quinoline Q.I. (% by weight) | ISO 6791 | 12.4 |
| Insoluble in toluene T.I. (% by weight) | ISO 6376 | 36.1 |
| Alcan coke yield (% by weight) | ASTM D 4715 | 59.3 |
| Benzo[a]anthracene (ppm) | GLC | 9060 |
| Benzo[e]pyrene (ppm) | GLC | 9170 |
| Benzo[a]pyrene (ppm) | GLC | 10920 |
| Indeno[1,2,3-c,d]pyrene (ppm) | GLC | 11510 |
| Dibenzo[a,h]anthracene(ppm) | GLC | 10300 |
| Benzo[g,h,i]perylene (ppm) | GLC | 5080 |
| Chrysene (ppm) | GLC | 9750 |
| Benzo[a]fluoranthene + Benzo[k]fluoranthene (ppm) | GLC | 13850 |
| Benzo[b]fluoranthene (ppm) | GLC | 6210 |
| Optical anisotropy (% by volume) | ASTM D 4616 | 0 |
-
This evaporator had a heat-exchange area:volume
ratio of about 50 m2/m3.
-
The internal wall of the evaporator was heated to a
temperature of about 320°C, the pressure inside the
evaporator was brought to about 0.4 mbars, and the rotary
shaft was rotated at a constant speed of 60
revolutions/minute.
-
After a period of about 45 minutes spent by the
residue in the evaporator in the conditions given above,
3.1 kg of a tar pitch was discharged and the distillate
was recovered separately and condensed.
-
A series of analytical determinations was performed
on the pitch thus obtained, the results of which are
given in Table 1B:
| Parameters | Analytical method | Value |
| Insoluble in quinoline Q.I. (% by weight) | ISO 6791 | 24.3 |
| Insoluble in toluene, T.I. (% by weight) | ISO 6376 | 67.2 |
| Alcan coke yield (% by weight) | ASTM D 4715 | 89.6 |
| Benzo[a]anthracene (ppm) | GLC and HPLC | 0 |
| Benzo[e]pyrene (ppm) | GLC and HPLC | 0 |
| Benzo[a]pyrene (ppm) | GLC and HPLC | 0 |
| Indeno[1,2,3-c,d]pyrene (ppm) | GLC and HPLC | 0 |
| Dibenzo[a,h]anthracene (ppm) | GLC and HPLC | 0 |
| Benzo[g,h,i]perylene (ppm) | GLC and HPLC | 0 |
| Chrysene (ppm) | GLC and HPLC | 0 |
| Benzo[a]fluoranthene + Benzo[k]fluoranthene (ppm) | GLC and HPLC | 0 |
| Benzo[b]fluoranthene (ppm) | GLC and HPLC | 0 |
| Optical anisotropy (% by volume) | ASTM D 4616 | 0 |
-
The above-mentioned pitch showed no trace of
benzo{a]pyrene or of the other polycyclic aromatic
compounds given in Tables 1A and 1B, determined by gas-liquid
chromatography (GLC) and liquid-liquid
chromatography (HPLC) and also had zero optical
anisotropy.
EXAMPLE 2
-
6 kg of a residue produced by the primary
distillation of residues of the cracking of petroliferous
fractions and having the characteristics given in Table
2A were supplied to the evaporator of Example 1.
| Parameters | Analytical method | Value |
| Mettler softening temperature (°c) | ASTM D 3104 | 109.0 |
| Insoluble in quinoline Q.I. (% by weight) | ISO 6791 | 0.8 |
| Insoluble in toluene, T.I. (% by weight) | ISO 6376 | 9.1 |
| Alcan coke yield (% by weight) | ASTM D 4715 | 48.3 |
| Benzo[a]anthracene (ppm) | GLC | 3770 |
| Benzo[e]pyrene (ppm) | GLC | 2920 |
| Benzo[a]pyrene (ppm) | GLC | 3240 |
| Indeno[1,2,3-c,d]pyrene (ppm) | GLC | 1040 |
| Dibenzo[a,h]anthracene (ppm) | GLC | 1150 |
| Benzo[g,h,i]perylene (ppm) | GLC | 650 |
| Chrysene (ppm) | GLC | 4940 |
| Benzo[a]fluoranthene + Benzo[k]fluoranthene (ppm) | GLC | 2230 |
| Benzo[b]fluoranthene (ppm) | GLC | 2180 |
| Optical anisotropy (% by volume) | ASTM D 4616 | 0 |
-
The internal wall of the evaporator was heated to a
temperature of about 320°C, the pressure inside the
evaporator was brought to about 0.4 mbars, and the rotary
shaft was rotated at a constant speed of 30
revolutions/minute.
-
After a period of about 30 minutes spent by the
residue in the evaporator in the conditions given above,
3.5 kg of an oil pitch was discharged and the distillate
was recovered separately and condensed.
-
A series of analytical determinations was performed
on the pitch thus produced, the results of which are
given in Table 2B:
| Parameters | Analytical method | Value |
| Insoluble in quinoline Q.I. (% by weight) | ISO 6791 | 1.1 |
| Insoluble in toluene T.I. (% by weight) | ISO 6376 | 17.4 |
| Alcan coke yield (% by weight) | ASTM D 4715 | 71.8 |
| Benzo[a]anthracene (ppm) | GLC and HPLC | 0 |
| Benzo[e]pyrene (ppm) | GLC and HPLC | 0 |
| Benzo[a]pyrene (ppm) | GLC and HPLC | 0 |
| Indeno[1,2,3-c,d]pyrene (ppm) | GLC and HPLC | 0 |
| Dibenzo[a,h]anthracene (ppm) | GLC and HPLC | 0 |
| Benzo[g,h,i]perylene (ppm) | GLC and HPLC | 0 |
| Chrysene (ppm) | GLC and HPLC | 0 |
| Benzo[a]fluoranthene + Benzo[k]fluoranthene (ppm) | GLC and HPLC | 0 |
| Benzo[b]fluoranthene (ppm) | GLC and HPLC | 0 |
| Optical anisotropy (% by volume) | ASTM D 4616 | 0 |
-
The above-mentioned pitch showed no trace of
benzo[a]pyrene or of the other polycyclic aromatic
compounds given in Tables 2A and 2B, determined by gas-liquid
chromatography (GLC) and liquid-liquid
chromatography (HPLC), and also had zero optical
anisotropy.
EXAMPLE 3
-
5.6 kg of a mixture constituted by 80 parts by
weight of the residue of Example 1 having the
characteristics given in Table 1A and 20 parts by weight
of the residue of Example 2 having the characteristics
given in table 2B was supplied to the evaporator of
Example 1.
-
The internal wall of the evaporator was heated to a
temperature of about 320°C, the pressure inside the
evaporator was brought to about 0.4 mbars, and the rotary
shaft was rotated at a constant speed of 60
revolutions/minute.
-
After a period of about 30 minutes spent by the
residue in the evaporator in the conditions given above,
3.3 kg of a pitch was discharged and the distillate was
recovered separately and condensed.
-
The pitch showed no trace of benzo[a]pyrene or of
the other polycyclic aromatic compounds given in the
tables of the previous examples, determined by gas-liquid
chromatography (GLC) and liquid-liquid chromatography
(HPLC), and also had zero optical anisotropy.
EXAMPLE 4
-
5.5 kg of a residue produced by the primary
distillation of coal tar and having the characteristics
given in Table 1A was supplied into an evaporator with
two rotary shafts both having mixing elements coupled
with one another, produced by the firm LIST AG and sold
with the name CRP.
-
This evaporator had a heat-exchange area:volume
ratio of about 50 m2/m3.
-
The internal wall of the evaporator was heated to a
temperature of about 320°C, the pressure inside the
evaporator was brought to about 0.4 mbars, and the rotary
shaft was rotated at a constant speed of 60
revolutions/minute.
-
After a period of about 90 minutes spent by the
residue in the evaporator in the conditions given above,
3.2 kg of a tar pitch was discharged and the distillate
was recovered separately and condensed.
-
A series of analytical determinations was performed
on the pitch thus produced, the results of which are
given in Table 4B:
| Parameters | Analytical method | Value |
| Insoluble in quinoline Q.I. (% by weight) | ISO 6791 | 25.3 |
| Insoluble in toluene T.I. (% by weight) | ISO 6376 | 68.0 |
| Alcan coke yield (% by weight) | ASTM D 4715 | 90.6 |
| Benzo[a]anthracene (ppm) | GLC and HPLC | 0 |
| Benzo[e]pyrene (ppm) | GLC and HPLC | 0 |
| Benzo[a]pyrene (ppm) | GLC and HPLC | 0 |
| Indeno[1,2,3-c,d]pyrene (ppm) | GLC and HPLC | 0 |
| Dibenzo[a,h]anthracene (ppm) | GLC and HPLC | 0 |
| Benzo[g,h,i]perylene (ppm) | GLC and HPLC | 0 |
| Chrysene (ppm) | GLC and HPLC | 0 |
| Benzo[a]fluoranthene + Benzo[k]fluoranthene (ppm) | GLC and HPLC | 0 |
| Benzo[b]fluoranthene (ppm) | GLC and HPLC | 0 |
| Optical anisotropy (% by volume) | ASTM D 4616 | 0 |
-
The above-mentioned pitch showed no trace of
benzo[a]pyrene or of the other aromatic compounds given
in Tables 1A and 4B, determined by gas-liquid
chromatography (GLC) and liquid-liquid chromatography
(HPLC), and also had zero optical anisotropy.
-
Naturally, in order to produce pitches with specific
QI, TI and coke characteristics, an expert in the art
will be able to use, in the method of the invention,
residues of the distillation of tar and/or petroleum with
QI, TI and coke characteristics and contents of
polycyclic aromatic compounds other than those mentioned
in the foregoing examples.
-
These pitches will in any case always be produced
substantially free of benzo[a]pyrene and will have
optical anisotropy of less than 1%.
EXAMPLE 5
-
100 parts by weight of the pitch produced in
accordance with the method of Example 1, and having the
characteristics given in Table 1B were mixed with 25.5
parts by weight of an aromatic oil completely free of
benzo[a]pyrene and having, in accordance with the ASTM-D86
method, an initial distillation point of 245°C and a
final distillation point of 300°C.
-
A pitch having the following characteristics given
in Table 5A was thus produced:
| Parameters | Analytical method | Value |
| Mettler softening temperature (°C) | ASTM D 3104 | 107.0 |
| Insoluble in quinoline Q.I. (% by weight) | ISO 6791 | 19.4 |
| Insoluble in toluene, T.I. (% by weight) | ISO 6376 | 53.5 |
| Benzo[a]anthracene (ppm) | GLC + HPLC | 0 |
| Benzo[e]pyrene (ppm) | GLC + HPLC | 0 |
| Benzo[a]pyrene (ppm) | GLC + HPLC | 0 |
| Indeno[1,2,3-c,d]pyrene (ppm) | GLC + HPLC | 0 |
| Dibenzo[a,h]anthracene (ppm) | GLC + HPLC | 0 |
| Benzo[g,h,i]perylene (ppm) | GLC + HPLC | 0 |
| Chrysene (ppm) | GLC + HPLC | 0 |
| Benzo[a]fluoranthene + Benzo[k]fluoranthene (ppm) | GLC + HPLC | 0 |
| Benzo[b]fluoranthene (ppm) | GLC + HPLC | 0 |
| Optical anisotropy(% by volume) | ASTM D 4616 | 0 |
-
This pitch can advantageously be used as a binding
agent for the production of electrodes, for example, for
the steel industry, the aluminium industry, etc.
EXAMPLE 6
-
100 parts by weight of the pitch produced in
accordance with the method of Example 2 and having the
characteristics given in Table 2B were mixed with 30
parts by weight of an aromatic oil completely free of
benzo[a]pyrene and having, in accordance with the ASTM-D86
method, an initial distillation point of 245°C and a
final distillation point of 300°C.
-
A pitch which had the following characteristics
given in Table 6A was thus produced:
| Parameters | Analytical method | Value |
| Mettler softening temperature (°C) | ASTM D 3104 | 92.0 |
| Insoluble in quinoline Q.I. (% by weight) | ISO 6791 | 0.8 |
| Insoluble in toluene T.I. (% by weight) | ISO 6376 | 13.4 |
| Alcan coke yield (% by weight) | ASTM D 4715 | 55.2 |
| Benzo[a]anthracene (ppm) | GLC + HPLC | 0 |
| Benzo[e]pyrene (ppm) | GLC + HPLC | 0 |
| Benzo[a]pyrene (ppm) | GLC + HPLC | 0 |
| Indeno[1,2,3-c,d]pyrene (ppm) | GLC + HPLC | 0 |
| Dibenzo[a,h]anthracene (ppm) | GLC + HPLC | 0 |
| Benzo[g,h,i]perylene (ppm) | GLC + HPLC | 0 |
| Chrysene (ppm) | GLC + HPLC | 0 |
| Benzo[a]fluoranthene + Benzo[k]fluoranthene (ppm) | GLC + HPLC | 0 |
| Benzo[b]fluoranthene (ppm) | GLC + HPLC | 0 |
| Optical anisotropy (% by volume) | ASTM D 4616 | 0 |
-
This pitch can advantageously be used as an
impregnation agent for electrodes and also as an
impregnation and/or binding agent for aluminium anodes
and for refractory materials.
-
Naturally, an expert in the art will be able to mix
pitches produced in accordance with the method of the
invention with different viscosity-modifying agents free
of benzo[a]pyrene, having different characteristics from
those of the oils mentioned in Examples 5 and 6, and/or
will be able to use different mixing ratios so as to
produce pitches more specifically suitable for individual
uses/users' various requirements for characteristics/workability.
