Note: Descriptions are shown in the official language in which they were submitted.
The invention rela~es to mesophase pitch
and particularly to a feedstock for mesophase pitch.
Mesophase pitch is used for producing
carbon artifacts and particularly for producing
carbon fibers having excellent mechanical properties.
It is well known that mesophase pitch derived carbon
fibers are lightweight, strong, stiff, electrically
conductive, and both chemically and thermally inert.
The mesophase pitch derived carbon fibers perform
well in composites and have found use in aerospace
applications and quality sporting equipment.
As used herein, ~he term "mesophase" is
to be understood as used in the instant art and
generally is SyT1011ymOUS with liquid crystal. A
liquid crystal is a state of matter which is inter-
mediate between crystalline solid and a normal liquid.
Ordinarily, a material in the mesophase s~ate exhi-
bits both anisotropic and liquid properties.
As used herein, the term "mesophase pi~ch"
is a pitch containing more than about 40~ by weight
mesophase and is capable of forming a continuous
anisotropic phase when dispersed by agitation or the
like, in accordance with the prior art.
Generally, decant oil is converted to a
pitch by distillation. Sometimes the distillation
is preceded by a heat treatment step. The product
obtained from the distillation is an isotropic pitch
and this pitch must be subjected to additional pro-
cess steps to convert it to a mesophase pitch.
A conventional method for preparing meso-
phase pitch from an isotropic pitch feedstock
generally includes heat treating the feedstock at a
temperature from about 350C to 450~C to effeet
13311
thermal polymerization.
A typical conventional method is carried
out using reactors maintained at a temperature o
about 400C for about 20 hours. The properties o~
the mesophase pitch produced can be controlled by
the reaction temperature, heat ~reatment time, and
volatilization rate. The presence of the high molec-
ular weight fraction due to polymerization results in
a softening point of the mesophase pitch of at least
about 300~C for a mesophase content of about 807~ by
weight. The softening point increases as the meso-
phase content increases. Typically, the ~emperature
needed to spin the mesophase pitch into fibers i5
about 30C to about 50~C higher than ~he softening
point of the mesophase pitch. It is desirable to be
able to spin at relatively low temperatures to avoid
additional poly~erization which can clog the narrow
orifices used in spinning and ~o minimize the energy
eonsumption.
The mesophase conten~ of pitch can be
measured bY metnods described in the artlcle
"Quantitative Determination of Mesophase Content in
Pitch" by S. Chwastiak~ R. T. Lewis, and J. D.
Ruggiero, Fifteenth Biennial Conference on Carbon,
June 1981, pp. 148, 149.
Generally, the terms "softening point" and
"melting point" are used interchangeably in the art
to characterize a pitch broadly as to its molecular
weight composition and to provide an estimate oE the
spinning temperature needed.
There are several methods for determining
the softening temperature and the temperatures
measured by these differen~ methods vary somewhat
from each other.
13311
The Mettler softening point measurement
procedure is widely accep~ed as the standard for
evaluating pitches. This procedure can be adapted
for use on mesophase pitches.
The softening temperature of a mesophase
pitch can also be determined by hot stage microscopy.
In this method, the mesophase pitch is heated on a
microscope hot sta~e in an inert atmosphere under
polarized light. The ~emperature of the mesophase
pitch is raised under a controlled rate and the
temperature a~ which the mesophase pitch commences
to deorm is noted as the softening temperature.
As used `herein, softening point or soften-
ing temperature will be used interchangeably and will
refer to the temperature determined by the Mettler
measurement procedure for both precursor and meso-
phase pitches.
As used herein, the empirical formulas of
the decant oils prior and after the hydrotreatment
were obtained from molecular weight and elemental
analysis data in accordance with conventional methods.
Decant oils are widely used for producing
feedstocks in the form of isotropic pitches to be
converted into mesophase pitches. The methods for
producing a precursor pitch from a decant oil are
well known and usually include the the step of dis-
tilling the decant oil under a reduced pressure
while applying heat to the decant oil.
Decant oils are par~icularly desirable for
producing precursor pitches for mesophase pitches be-
cause decant oils have high aromaticity and the art
teaches that high aromaticity in the feedstock is
necessary to produce a good mesophase pitch. See
"Chemistry and Physics of Carbon", edited by P. L~
13311
Walker, Volume 4~ pp. 261, 262 (1960); "Carbon".
12, p. 332, (1974); and U. S. Pa~ent No. 4,005,183
to Singer.
The decant oil used in the art for malcing
a feedstock for mesophase pitch has a low sulfur
content in the raIIge of from about 1% to about 2.5%
by weight. The mesophase pitch produced from the
feeds~ock is capable of forming anisotropic domains
greater than about 200 microns under quiescent heat-
ing. The capability of forming such large domainsis important because it indicates that the mesophase
pitch is suitable for producing carbon fibers having
good mechanical properties, as well as good spinning
properties.
A mesophase pitch which is capable of
forming large anisotropic domains is known to be
highly deformable.
For spinnlng commercially, the mesophase
content of the mesophase pitch is at least 70% by
weight and preferably about 807~ in order to produce
good carbon fibers. This is a goal of the instant
invention.
The amount of sulfur in a decant oil could
be important for the production of commercial carbon
fibers. Carbon fi~ers which require process tempera-
tures of about 2500C or higher may have problems
because the elevated temperatures drive off the
sulfur and thereby result in a degradation in tensile
strength and a reduction in the denslty of the carbon
fiber produced.
According to the prior art, a high sulfur
decant oil would be unsuitable Eor the production of
a mesophase pitch for quality carbon fibers.
It would be desirable to subject the high
13311
sulfur decant oil to a hydrodesulfurization in ac-
cordance with known processes such as taught in U. S.
Paten~ No. 4,075,084 to Skripek et al or U. S.
Patent No. 4,166,026 to Fukui et al. Generally, the
hydrodesulfurization contacts a hydrocarbon oil with
hydrogen in the presence of a catalyst.
It is, however, well known that hydrotreat-
ing reduces the aromaticity of hydrocarbon oils so
that it would be expected from the art that a hydro-
greated decant oil would produce a mesophase pitchwhich has relatively poor quality for spinning and
the carbon fibers made from the mesophase pitch
would have poor mechanical properties. The refer-
ences, "Catalysis", Vol. V, edited by P. H. ~r~mett,
published by Rheinhold Publishing Corp., New York,
1957, and "Catalytic Processes and Proven Catalysts",
edited by C. L. Thomas, Academic Press (1970), point
out that hydrotreating reduces aromaticity.
As used herein, "hydrotreating" is any
process which contacts a decant oil with hydrogen in
the presence of a catalyst in accordance with the
art.
Contrary to the teachings in the art, it
has now been found that decant oil which has been
hydrotreated according to the invention can be pro-
cessed to produce mesophase pitch having improved
properties as compared to mesophase pitch produced
from decant oil which has not been hydrotreated.
Furthermore 7 the improved mesophase pitch
can be processed according to known rnethods into
carbon fibers which also possess improved properties.
A general explanation o these surprising
results is as follows and it is to be understood that
the explanation is not intended to be a limitation
13311
but only as a possible guideline in applying the in-
stant invention. The explanation is given with
respect to the thermal polymerization process for
converting a precursor pitch feedstock to a mesophase
pitch.
Typically, a precursor pitch has a rela-
tively broad molecular weight dis~ribution. The
pitch contains both less reactive and highly reactive
molecules. Rapid poly~erization of the highly reac-
tive molecules is undesirable because it leads to
very high molecular weight components in the meso-
phase pitch produced. These high molecular weight
components cause the viscosity of the mesophase pitch
to be relatively high and thereby reduce the relative
mesophase domain size. This phenomena is discussed
in U. S. Patent No. 3,976,729 to 1. C. Lewis et al.
Hydrogenation of a decant oil according to
the invention reduces the reaction rate of the highly
reactive molecules and makes it possible for these
molecules to undergo desirable structural rearrange-
ments prior to and during ~he polymerization reaction.
This effects a relatively low viscosity for the meso-
phase pitch as well as relatively large anisotropic
domain sizes.
A precursor pitch feedstock produced ac-
cording to the invention can also be converted to a
mesophase pitch by solvent extraction as described
in the article "Mesophase Transformation in a Solvent-
Extracted Pitch" by J. E. Zimmer, Fifteenth Biennial
Conference on Carbon, June 1981, pp. 146, 147 and
the references cited thereinO Surprisingly, the
mesophase pitch produced possesses excellent proper-
ties as to domain size and softening point.
The hydrogenated decant oil produces a
13311
3;~3
lower yield of mesophase pitch as compared to un-
treated decant oil, but the surprising improvement
in the quality of the mesophase pitch compensates
for the loss in yield as welL as the increased cost
for the hydrotreating step.
In its broadest embodiment, the invention
relates to a method for producing a feedstock for a
mesophase pitch, comprising the steps o~ hydrotreat-
ing a decant oil until there is from about 2 to about
3 hydrogen atoms per average molecule of the decant
oil, and distilling the hydrotreated decant oil to
form a pitch.
The invention also relates to mesophase
pitch fibers and carbon fibers formed from the meso-
phase pitch of the invention.
Another embodiment of the invention relates
to the improvement of subjecting the hydrotreated
decant oil to a thermal-pressure treatment to produce
a tar residue, and distilling the tar residue to
form a pitch.
The thermal-pressure treatment substantial-
ly increases the overall yield o~ the feeds-tock with
respect to the decant oil as compared to the instant
process without the thermal-treatment.
The severity of the heating under pressure
can be evaluated by the term "soaking volume factor"
which is a technical term widely used in the
petroleum industry for such a purpose. A soaking
volume factor of 1. O is e~uivalent to 4.28 hours
of heating at a temperature of about 427C under a
pressure of about 750 psig. The effect of tempera-
ture on polymerization or cracking rate of hydro-
carbons is known in the art. By way of example, the
cracking rate at 450~C is 3.68 times the cracking
rate at 427C. Most of the examples given herein
were carried out at a temperature near 450C so that
the thermal treatment severity was calculated on an
equivalent basis for that temperature.
For a batch ~hermal-pressure trea~ment, the
preferred temperature, pressure, and soaking volume
factor range depend upon the precursor materials.
For decant oils, the temperature range is from about
400C to about 475C, the pressure range is from
about 200 psig to about 1500 psig, and the scaking
volume actor range is from about 0.4 to about 8.6.
The soaking volume factor is equivalent to from
about 0.5 to about 10 hours at about 450C.
The batch thermal-pressure treatment is
discontinued when the Conradson carbon content is at
least about 20% and preferably greater than about
30% but no~ greater than about 65%. The mesophase
content is less than about 60% by weight and if in-
fusible solids are present 7 a high ~emperature fil-
tration is preferably carried out. For the filtra-
tion, an elevated temperature to liquify the produc~
is used so that the infusible solids can be separated
by the filtration. Preferably, stirring is used
during the thermal-pressure treatment in order to
maintain a homogeneous distribution.
The instant invention is more economical
if a continuous thermal-pressure treatment
13311
is carri~d out instead of the batch treatment. For
the continuous thermal-pressure treatment, the tem-
perature range is from about 420C to about 550C,
the pressure range is from about 200 psi~ to about
1500 psig, and the soaking volume factor is from
about 0.4 to about 2.6. The soaking volume factor
corresponds to from about 0.5 to about 3 hours at a
temperature of about 4S0C.
The continuous thermal-pressure treatment
is terminated when thc Conradson carbcn content of
the material is at least about 5% and preferably
greater than about 10~ but less than
about 65%. The mesophase content is less than about
60% by weight. If infusible solids are present, a
high temperature filtration is preferable.
The invention accordingly comprises the
several steps and the rela~îonship of one or more of
such steps with respect to each of the others, all as
exemplified in the following detailed disclosure, and
the scope of the application of which will be indi-
cated in the claims.
For a fuller understanding of the nature
and objects of the invention, reference should be
had ~o the following detailed description, taken in
connection with the accompanying drawings, in which:
Figure 1 shows a simplified flow diagram
for hydrotreating decant oil; and
Figure 2 is a simplified flow diagram for
carrying out the continuous thermal-pressure ~reat
ment of a hydrotreated decant oil.
Illustrative, non-limiting examples of the
practice of the invention are set out below. Numer-
ous other examples can readily be evolved in the
light of the guiding principles and teachings
13311
contained herein. The examples given herein are
intended merely to illustrate the invention and not
in any sense to limit the manner in which ~he inven-
tion can be practiced. The parts ~nd percentages
recited herein unless specifically provided otherwise
refer to parts by weight and percentages by weight.
Figure l hydrotreats decant oil as follows.
A reactor l comprises a stainless steel
tu~e having an inside diameter of 32 mm and is heated
with a resistance furnace (not shown). The reactor
l operates in a trickle~bed mode with the decant oil
from a decant oil feed 2 entering rom the top.
The hydrotrea~ing catalys~ in the reactor
is of the type commonly used for hydrodesulfurizing
petroleum feedstocks. Catalyst pellets amounting to
100 ml are mixed with 200 ml of quartæ chips (12/16
mesh) and loaded into the stainless steel tube. The
resulting catalyst bed is 370 mm longO
A fresh catalyst bed is activated with
hydrogen and hydrogen sulfide which are supplied
throu~h lines 3 and 4 and con~rolled by valves 6
and 7.
The nitrogen supplied by line 8 and con
trolled by valve 5 is used to purge the catalyst of
any dissolved hydrogen sulfide.
Gases from the reactor 1 are removed over
line 11 to a separator 12 and recovered hydrogen îs
removed over line 13 through valve 14. Hydrotreated
decant oil is removed from the reactor l over line
16 to storage 17.
The continuous thermal-pressure ~reatmen~
as shown in Figure 2 is as follows.
The hydrotreated decant oil is placed in
feed tank 18. The feed tank 18 can include heaters
13311
3~
if desired for heating thP decant oil to lower its
viscosity and thereby improve its flow. The feed
tank 18 is connected by line 19 to a pump 21 which
pumps the decant oil through line 22 and is monitored
by a pressure guage 23.
The decant oil moves through a furnace coil
in a fluidized sand bath 24. If a longer treatment
is desired, several fluidized sand baths can be used
in tandem.
The treated decant oil moves through line
26 to valve 27 which is controlled by a pressure con-
trol 29 and is collected through line 31 in a product
collection tanX 32 for subsequent steps of the inven-
tion.
EXAMPLE 1
A decant oil was subjected ~o a hydrotreat-
ment to the extent that an analysis showed that ~here
were about 3 atoms of hydrogen for each average mole-
cule of the decant oil. The hydrotreatment was
earried out using a oonventional process.
The hydrotreated decant oil was converted
to a pitch by distilling under a vacuum of about
2 mm Hg to a final pot temperature of about 260~C.
In order to evaluate the quality of the
precursor pitch as a feedstock for mesophase pitch,
a portion of the precursor pitch was converted to
mesophase pitch by subjecting it to a heat treatment
at about 400DC for about 24 hours. The domain size
of the mesophase pitch produced from the heat treat-
ment was measured and found to be about 500 microns.The mesophase pitch produced the same way from un-
treated decant oil had a domain size which is typl-
cally about 250 microns~ The larger domain size for
the mesophase pitch produced according to the
13311
13
invention is indicative of a better aualitv mesophase
pitch whict- can be expected to be well suited for
commercial spinning.
Furthermore, the relatively large domain
size indicates that the mesophase pitch produced
according to the invention is highly deformable and
the molecules can be expected to align relatively
easier when a fiber is spun. This will result in a
favorably low orientation parameter and excellen~
mechanical properties for the carbon fiber.
The precursor pitch obtained amounted to
about a 21% by weight yield with respect to the
decan~ oil. The precursor pitch was converted ~o
mesophase pitch by subjecting it to a conventional
heat treatment at about 390C for about 29 hours
while sparging with argon at the rate of about 5
scfh per pound of pitch and with agitation throughout
the reaction.
The resulting mesophase pitch contained
, about 100% mesophase by weight and amounted to a
14% yield with respect to the precursor pitch. The
Mettler softening point of the mesophase pitch was
about 289C. This softening point is surprisingly
low for a thermally produced mesophase having a 100%
~esophase content. Moreover, this mesophase pitch
can be spun at a temperature rom about 30C to about
40C lower than the conventional 100% mesophase pitch.
The overall yield of the mesophase pitch
with respect to the decant oil was about 3% on a
weight basis.
EXAMPLE 2
The hydrogreated decant oil of Example 1
was subjected to a batch thermal-pressure treatment
in a stirred autoclave under nitrogen at a pressure
13311
~3
14
from about 400 to about 500 psig a~d at a temperature
of about 430C for about 4 hours. A tar residue
amounting to about a 90% by weight yi~ld was obtained
and thereafter distilled to produce a precursor pitch
amounting to a yield of about 37% by weight with
respect to the hydrotreated decant oil.
The precursor pitch was then converted to
a mesophase pitch by heat treating i~ at about 390C
for about 30 hours. The mesophase pitch obtained
contained about 100% mesophase and had a Mettler
softening point o about 317~C. The mesophase pitch
yield was about 34~ by we;ght with respect ~o the
tar residue and the overall yield of the mesophase
pitch with respect to the hydrotreated decant oil
was about 11.3% by weight.
This overall yield was substantially higher
than the overall yield obtained for Example 1 and
shows the value of subjecting the hydrotreated decant
oil to a thermal-pressure treatment.
The mesophase p~tch obtained was spun into
monofilaments which were thermoset and thereafter
carbonized to a temperature of about ~700C in ac-
cordance with conventional practice. The filamen~s
had diameters of about 8 microns. Typically, the
filaments exhibited excellent mechanic~l properties.
The average Young's modulus was about ~8 x 1~6 psi
and the average tensile strength was about 560,000
psi. The ratio of these valùes shows ~hat the strain
to failure was about 2% and this i5 about twice the
value obtained for mesophase pitch derived carbon
fibers according to the prior art. A high strain
to failure value is considered advantageous for many
co mercial products.
13311
EXAMPLE 3
_
A second decant oil was hydrotreated until
there were about 2 atoms of hydrogen per average
molecule of decant oil.
In order to evaluate the hydrotrea~ed de-
eant oil, a portion was heat treated at a temperature
of about 400C for 24 hours to produce mesophase
pitch~ The domain size of the mesophase pitch was
about 300 microns.
In contrastS the un~reated decant oil pro-
duced a mesophase pitch having a domain size of about
200 microns for the same test.
The hydrotreated decant oil was subjected
to a batch thermal-pressure treatment in a stirred
pressure autoclave at a pressure of about 330 psig
and a temperature of about ~40C for about 4 hours.
The tar residue obtained amounted to about a 79% by
weight yield wi~h respect to the decant oil. The
tar residue was vacuum dis~illed at 2 mm pressure to
a pot temperature of about 262C. The feedstock ob-
~ained amounted to a 58% by weight yield with respect
to the tar residue and ~hereafter was converted to a
mesophase pitch by conventional thermal polymeriza-
tion using a reactor at a temperature of about 390C
for bout 24 hours while sparging with argon at a
rate of about 5 scfh per pound of pitch. The meso
phase pitch produced amounted to about 58% by weight
yield with respect to the feedstock and had a soft-
ening point of abou~ 332C. The mesophase content
was about 100% by weight.
The mesophase pitch was spun into mono-
filaments and the monofilaments were thermoset by
heating them in air at a temperature of a~out 375C.
The thermoset filaments were carbonized to a
1331~
3~
16
temperatur~ of about 1700C in accordance with the
art. The carbon fibers had diameters of about 18
microns.
The carbon fibers had an average Young's
modulus of about 22 x 106 psi and an average tensile
strength of about 200 x 103 psi. For comparison,
mesophase pi~ch derived carbon fibers made rom un
treated deca~t oil had an average Young's modulus of
about 22 x 106 psi and an average tensile strength
of about 165 x 103 psi.
EXAMPLE 4
Ano~her decant oil was hydrotreated to the
extent that there were about 2 hydrogen atoms per
average molecule of the decant oil. A portion of
the hydrotreated decant ~il was converted to meso-
phase pitch as in the foregoing examples and ~he
domain size of the mesophase pitch was measured to
be about 260 microns.
In con~rast, mesophase pitch produced from
~o the decant oil without hydrotreating had a measured
domain size of about 179 microns.
EXAMPLE 5
The decant oil of the Example 1 was hydro-
treated until there were about 3 hydrogen atoms per
average molecule of the decant oil. The hydrotreat-
ed deca~t oil was subjected to a conEinuous ~hermal-
pressure treatment at a pressure of about 1750 psig
at ~ temperature of about 525C for about 9 minutes.
A tar residue was obtained with a yield of about
97% by weight with respect to the decant oil. The
tar residue was distilled to produce a pitch feed-
stock having a softening point of about 104C and
constituting a yield of about 27% by weigh~ wi~h
respect to the tar residue. The feedstock was heat
13311
~2~
treated in a stirred reactor at a temperature of
about 400C for a period of about 18.5 hours while
being spar~ed with steam at the rate of about 1 scfh
per pound of pitch. The mesophase pitch ob~ained
5 amounted to a yield of about 52% by weight with
respect to the feedstock and had a softening point
of about 318~C. The mesophase content was about 957
by weight.
The mesophase pi~ch was spun into multi-
filaments and the multifilaments were thermoset byheating in air to about 375C and then carbonized in
an inert atmosphere to a temperature of about 2500C
in accordance with the art. The average properties
of the carbon fibers were a Young's modulus of about
100 x 106 psi and a tensile strength of about
390 ~ 103 psi.
For comparison 9 decant oil which had not
been hydrotreated was processed to make mesophase
pitch. The decant oil was converted to a tar resi-
due by subjecting the decant oil to a batch the~nal-
pressure treatment of a pressure of about 1000 psig
at a temperature of about 470C for about 8 minutes.
The tar residue obtained amounted to a 98.5% by
weight yield with respect to the decant oil and was
distilled to form a precursor pitch having a soften-
ing point of about 116C and amounting to a yield of
about 34% by weight with respect to the tar residue.
The pitch was converted to mesophase pitch by heat~
ing it at a temperature of about 400C for about
16.5 hours. This mesophase pitch amounted to a
yield of about 56% by weight with respect to the
precursor pitch and had a softening point of about
318C. The mesophase content was about 90% by
weight.
13311
1~
This mesophase pitch was processed into
carbon filaments as in the case of the mesophase
pitch derived from the hydrotreated decant oil. The
carbon fibers obtained had an average Young's modulus
of about 63 x 106 psi and a tensile strength of about
2~0 x 103 psi.
The carbon fibers which has been produced
from feedstock derived from hydrotreated decant oil
showed superior mechanical properties as compared to
carbon fibers derived from untreated decant oil.
EXAMPLE 6
The pitch feedstock derived from hydro-
treated decant oil of the Example 5 was solvent ex-
tracted to obtain mesophase pitch. The solvent ex-
traction was carried out by stirring solid feedstockwith toluene at room tempera~ure for one hour. The
feedstock to toluene ratio was 1 ~.:10 ml. The in-
soluble portion obtained in 8.3% by weigh~ yield was
mesophase pitch containing about 85% by weight meso-
phase. This mesophase pitch had a Mettler softeningpoint cf 272C and the anisotropic domain size was
about 500 micronsO
SUMMARY OF EXAMPLES
Table 1 is a summary of data oE the Exam-
ples 1 to 6. The hydrotreated decant oil is desul-
furized as indicated by the dataA
The aromatic hydrogen content was measured
by the conventional nuclear magnetic resonance (NMR).
13311
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13311
~ 3
It is to be understood that we do not wish
to be limited to the exact detalls shown and described
because obvious modifications will occur to a person
skilled in the art.
