Production of carbon artifact precursors

A low coking pitch suitable for carbon artifact manufacture, especially carbon fiber manufacture, is obtained by heat soaking and vacuum stripping the distillate recovered from cat cracker bottoms. Preferably a cat cracker bottom distillate boiling in the range of about 450.degree. C. to 510.degree. C. at 760 mm Hg is heat soaked at about 350.degree. C. to about 500.degree. C. for up to about 20 hours and then vacuum stripped at below 400.degree. C.

FIELD OF THE INVENTION 
This invention is concerned generally with the preparation of a feedstock 
for carbon artifact manufacture from cat cracker residues. 
BACKGROUND OF THE INVENTION 
As is well known, the catalytic conversion of virgin gas oils containing 
aromatic, naphthenic and paraffinic molecules results in the formation of 
a variety of distillates that have ever-increasing utility and importance 
in the petrochemical industry. The economic and utilitarian value, 
however, of the residual fraction of the cat cracking processes has not 
increased to the same extent as the light overhead fractions has. One 
potential use for such cat cracker bottoms is in the manufacture of carbon 
artifacts. As is well known, carbon artifacts have been made by pyrolyzing 
a wide variety of organic materials. Indeed, one carbon artifact of 
particularly important commercial interest today is carbon fiber. Hence, 
particular reference is made herein to carbon fiber technology. 
Nevertheless, it should be appreciated that this invention has 
applicability to carbon artifact formation generally and, most 
particularly, to the production of shaped carbon articles in the form of 
filaments, yarns, films, ribbons, sheets, and the like. 
Referring now in particular to carbon fibers, suffice it to say that the 
use of carbon fibers in reinforcing plastic and metal matrices has gained 
considerable commercial acceptance where the exceptional properties of the 
reinforcing composite materials, such as their higher strength to weight 
ratio, clearly offset the generally higher costs associated with preparing 
them. It is generally accepted that large scale use of carbon fibers as a 
reinforcing material would gain even greater acceptance in the marketplace 
if the costs associated with the formation of the fibers could be 
substantially reduced. Thus, the formation of carbon fibers from 
relatively inexpensive carbonaceous pitches has received considerable 
attention in recent years. 
Many carbonaceous pitches are known to be converted at the early stages of 
carbonization to a structurally ordered optically anisotropic spherical 
liquid crystal called mesophase. The presence of this ordered structure 
prior to carbonization is considered to be a significant determinant of 
the fundamental properties of any carbon artifact made from such a 
carbonaceous pitch. Indeed, the ability to generate high optical 
anisotropicity during processing is accepted, particularly in carbon fiber 
production, as a prerequisite to the formation of high quality products. 
Thus, one of the first requirements of a feedstock material suitable for 
carbon artifact manufacture, and particularly carbon fiber production, is 
its ability to be converted to a highly optically anisotropic material. 
In addition to being able to develop a highly ordered structure, suitable 
feedstocks for carbon artifact manufacture, and in particular carbon fiber 
manufacture, should have relatively low softening points rendering them 
suitable for being deformed and shaped into desired articles. Thus, in 
carbon fiber manufacture, a suitable pitch which is capable of generating 
the requisite highly ordered structure also must exhibit sufficient 
viscosity for spinning. Unfortunately, many carbonaceous pitches have 
relatively high softening points. Indeed, incipient coking frequently 
occurs in such materials at temperatures where they have sufficient 
viscosity for spinning. The presence of coke, however, or other infusible 
materials and/or undesirably high softening point components generated 
prior to or at the spinning temperatures are detrimental to processability 
and are believed to be detrimental to product quality. Thus, for example, 
U.S. Pat. No. 3,919,376 discloses the difficulty in deforming pitches 
which undergo coking and/or polymerization at the softening temperature of 
the pitch. 
Another important characteristic of the feedstock for carbon artifact 
manufacture is its rate of conversion to a suitable optically anisotropic 
material. For example, in the above-mentioned U.S. patent, it is disclosed 
that 350.degree. C. is the minimum temperature generally required to 
produce mesophase from a carbonaceous pitch. More importantly, however, is 
the fact that at least one week of heating is necessary to produce a 
mesophase content of about 40% at that minimum temperature. Mesophase, of 
course, can be generated in shorter times by heating at higher 
temperatures. However, as indicated above, at temperatures in excess of 
about 425.degree. C., incipient coking and other undesirable side 
reactions do take place which can be detrimental to the ultimate product 
quality. 
In U.S. Pat. No. 4,208,267, it has been disclosed that typical 
graphitizable carbonaceous pitches contain a separable fraction which 
possesses very important physical and chemical properties insofar as 
carbon fiber processing is concerned. Indeed, the separable fraction of 
typical graphitizable carbonaceous pitches exhibits a softening range and 
viscosity suitable for spinning and has the ability to be converted 
rapidly at temperatures in the range generally of about 230.degree. C. to 
about 400.degree. C. to an optically anisotropic deformable pitch 
containing greater than 75% of a liquid crystalline type structure. 
Unfortunately, the amount of separable fraction present in well known 
commercially available petroleum pitches, such as Ashland 240 and Ashland 
260, to mention a few, is exceedingly low. For example, with Ashland 240, 
no more than about 10% of the pitch constitutes a separable fraction 
capable of being thermally converted to a deformable anisotropic phase. 
In U.S. Pat. No. 4,184,942, it has been disclosed that the amount of that 
fraction of typical graphitizable carbonaceous pitches that exhibits a 
softening point and viscosity which is suitable for spinning and which has 
the ability to be rapidly converted at low temperatures to highly 
optically anisotropic deformable pitch can be increased by heat soaking 
the pitch, for example at temperatures in the range of 350.degree. C. to 
450.degree. C., until spherules visible under polarized light begin to 
appear in the pitch. The heat soaking of such pitch results in an increase 
in the amount of the fraction of the pitch capable of being converted to 
an optically anisotropic phase. 
In U.S. Pat. No. 4,219,404, it has been disclosed that the polycondensed 
aromatic oils present in isotropic graphitizable pitches are generally 
detrimental to the rate of formation of highly optically anisotropic 
material in such feedstocks when they are heated at elevated temperatures 
and that, in preparing a feedstock for carbon artifact manufacture, it is 
particularly advantageous to remove at least a portion of the 
polycondensed aromatic oils normally present in the pitch simultaneously 
with, or prior to, heat soaking of the pitch for converting it into a 
feedstock suitable in carbon artifact manufacture. 
More recently, in copending application Ser. No. 143,136, filed Apr. 23, 
1980 now U.S. Pat. No. 4,271,006, a process has been disclosed for 
converting cat cracker bottoms to a feed stock suitable in carbon artifact 
manufacture. Basically, the process requires stripping cat cracker bottoms 
of fractions boiling below 400.degree. C. and thereafter heat soaking the 
residue followed by vacuum stripping to provide a carbonaceous pitch. 
SUMMARY OF THE INVENTION 
It has now been discovered that the distillates recovered from the residual 
materials generated in cat cracking processes can be readily converted 
into a low coking pitch which is eminently suitable for carbon artifact 
manufacture. Basically, the distillate is converted into the pitch by heat 
soaking the distillate fraction at elevated temperatures, for example, 
temperatures ranging from about 350.degree. C. to 500.degree. C. and for 
times ranging up to about twenty hours and thereafter subjecting the heat 
treated material to a vacuum stripping step to remove at least a portion 
of the oil present in the heat treated distillate, thereby providing a 
pitch suitable for carbon artifact manufacture. 
Full appreciation of all the ramifications of the present invention will be 
more readily understood upon a reading of the detailed description which 
follows:

DETAILED DESCRIPTION OF THE INVENTION 
The term catalytic cracking refers to a thermal and catalytic conversion of 
gas oils, particularly virgin gas oils, boiling generally between about 
316.degree. C. and 566.degree. C., into lighter, more valuable products. 
Cat cracker bottoms refer to that fraction of the product of the cat 
cracking process which boils in the range of from about 200.degree. C. to 
about 550.degree. C. 
Cat cracker bottoms typically have relatively low aromaticity as compared 
with graphitizable isotropic carbonaceous pitches suitable in carbon 
artifact manufacture. 
Specifications for a typical cat cracker bottom that is suitable in the 
present invention are given in Table I. 
TABLE I 
______________________________________ 
Range 
______________________________________ 
Physical Characteristics 
Viscosity cst at 210.degree. F. 
1.0-10.0 
Ash content, wt. % 0.010-2.0 
Coking value (wt. % at 550.degree. C.) 
6.0-18.0 
Asphaltene (n-heptane insoluble), % 
0.1-12.0 
Toluene insolubles (0.35.mu.), % 
0.010-1.0 
Number average mol. wt. 220-290 
Elemental Analysis 
Carbon, % 88.0-90.32 
Hydrogen, % 7.74-7.40 
Oxygen, % 0.10-0.30 
Sulfur, % 1.0-4.5 
Chemical Analysis (proton NMR) 
Aromatic carbon (atom %) 54-64 
Carbon/hydrogen atomic ratio 
0.90-1.0 
Asphaltene Analysis 
Number average mol. wt. 550-750 
Coking value, wt. % at 550.degree. C. 
3.5-6.5 
Aromatic carbon (atom %) 55-70 
Bureau of Mines Correlation Index 
120-140 
______________________________________ 
In the process of the present invention, the cat cracker bottoms are 
fractionally distilled by heating the cat cracker bottom to elevated 
temperatures and reduced pressures, for example, by heating to 
temperatures in the range of 200.degree. C. to 300.degree. C. at pressures 
ranging from about 250 to 500 microns of mercury. Basically, the cat 
cracker bottom is separated into at least a single distillate having a 
boiling point at 760 mm mercury in the range of from about 250.degree. C. 
to about 310.degree. C., and the residue being the fraction not 
distillable at temperatures up to 530.degree. C. at a pressure of about 
350 to 450 microns of mercury. In a particularly preferred embodiment of 
the present invention, the distillate fraction of the cat cracking bottom 
which is employed in forming a suitable carbonaceous pitch for carbon 
artifact manufacture is that fraction boiling in the range of about 
450.degree. C. to about 510.degree. C. at 760 mm of mercury. After 
separating the distillate from the cat cracking bottom, the distillate is 
heat soaked at temperatures in the range of about 350.degree. C. to 
500.degree. C. Optionally and preferably, the heat soaking is conducted at 
temperatures in the range of about 390.degree. C. to about 450.degree. C., 
and most preferably at temperatures in the range of about 410.degree. C. 
to about 440.degree. C. In general, heat soaking is conducted for times 
ranging from one minute to about twently hours, and preferably from about 
two to five hours. In the practice of the present invention, it is 
particularly preferred that heat soaking be done in an atmosphere such as 
nitrogen, or alternatively in hydrogen atmosphere. Optionally, however, 
heat soaking may be conducted at reduced pressures, for example, pressures 
in the range of from about 50 to 100 mm of mercury. 
After heat soaking the distillate, the heat soaked distillate is then 
heated in a vacuum at temperatures generally below about 400.degree. C., 
and typically in the range of about 320.degree. C. to 380.degree. C. at 
pressures below atmospheric pressure generally in the range of about 1.0 
to 100 mm mercury to remove at least a portion of the oil present in the 
heat soaked distillate. Typically from about 20% to about 60% of the oil 
present in the heat soaked distillate is removed. 
As can be readily appreciated, the severity of the heat soaking conditions 
outlined above will affect the nature of the pitch produced. The higher 
the temperature chosen for heat soaking and the longer the time chosen, 
the greater the amount of high softening point components that will be 
generated in the pitch. Consequently, the precise conditions selected for 
carrying out the heat soaking depend, to an extent, on the use to which 
the pitch is to be put. Thus, where low softening point is a desirable 
property of the product pitch, less severe heat soaking conditions will be 
chosen within the parameters outlined above. 
As indicated in copending application Ser. No. 143,136, filed Apr. 23, 
1980, the heat soaking of cat cracker bottoms and subsequent vacuum 
stripping can lead to a pitch which may contain as low as 0.5% and as high 
as 60%, for example, of materials which are insoluble in quinoline at 
75.degree. C. The quinoline insoluble material present in such heat soaked 
cat cracker bottom typically consist of coke, ash, catalyst fines, and the 
like, including high softening point materials generated during heat 
soaking and carbon fiber manufacture these high softening point materials 
are detrimental to processability of the pitch into fibers. Consequently, 
when the heat soaked cat cracker bottom is to be used in carbon fiber 
production, it is important to remove the undesirable high softening 
components present in the pitch. In employing a distillate from a cat 
cracker bottom, which has been treated in accordance with the present 
invention, it is not necessary to remove the quinoline insoluble 
materials, since heat soaking conditions can be chosen which do not 
generate large amounts of quinoline insoluble material, especially 
coke-like material. Moreover, since a distillate is used, the resultant 
pitch material is free from the ash and catalyst fines normally present in 
other petroleum pitches and residues. Additionally, it has been discovered 
that a distillate from a cat cracker bottom does not have a significant 
coking value. Consequently, coke is not generated during heat soaking of 
the distillate. 
In Table II below the coking value (SMTTP Test Method No. PT-10-67) for a 
commercially available petroleum pitch Ashland 240 is given along with the 
coking value for a cat cracker bottom, a cat cracker bottom distillate 
obtained in accordance with the present invention, and the residue of the 
distilled cat cracker bottom. 
TABLE II 
______________________________________ 
Standard Coking 
Material Used Value at 550.degree., % 
______________________________________ 
Ashland 240 56.0% 
Cat cracker bottom 6.5% 
Cat cracker bottom distillates 
nil 
Cat cracker bottom residue 
26.1% 
______________________________________ 
As is disclosed in U.S. Pat. No. 4,208,267, in carbon fiber manufacture, it 
is particularly beneficial to use a fraction of the pitch which is readily 
convertible into a deformable optically anisotropic phase. Consequently, 
in the process of the present invention, it is particularly preferred to 
isolate that fraction of the heat soaked and vacuum stripped cat cracker 
distillate which is readily convertible into a deformable optically 
anisotropic phase. The preferred technique for isolating that fraction of 
the pitch is set forth in U.S. Pat. No. 4,208,267, which patent is 
incorporated herein by reference. Basically, that process requires 
treatment of the pitch with the solvent system which consists of a solvent 
or mixture of solvents that has a solubility parameter of between 8.0 and 
9.5 and preferably between about 8.7 and 9.2 at 25.degree. C. The 
solubility parameter .gamma. of a solvent or mixture of solvents is given 
by the expression 
##EQU1## 
where H.sub.v is the heat of vaporization of material, R is the molar gas 
constant, T is the temperature in degrees K., and V is the molar volume. 
In this regard, see, for example, J. Hildebrand and R. Scott, "Solubility 
of Non-Electrolytes," 3rd edition, Reinhold Publishing Company, New York 
(1949), and "Regular Solutions," Prentice Hall, New Jersey (1962). 
Solubility parameters at 25.degree. C. for hydrocarbons and commercial 
C.sub.6 to C.sub.8 solvents are as follows: benzene, 8.2; toluene, 8.9; 
xylene, 8.8; n-hexane, 7.3; n-heptane, 7.4; methylcyclohexane, 7.8; 
bis-cyclohexane, 8.2. Among the foregoing solvents, toluene is preferred. 
Also, as is well known, solvent mixtures can be prepared to provide a 
solvent system with the desired solubility parameter. Among mixed solvent 
systems, a mixture of toluene and heptane is preferred having greater than 
about 60 volume % toluene, such as 60% toluene/40% heptane and 85% 
toluene/15% heptane. 
The amount of solvent employed will be sufficient to provide a solvent 
insoluble fraction capable of being thermally converted to greater than 
75% of an optically anisotropic material in less than 10 minutes. 
Typically the ratio of solvent to pitch will be in the range of about 5 
milliliters to about 150 milliliters of solvent to a gram of pitch. After 
heating the solvent, the solvent insoluble fraction can be readily 
separated by techniques such as sedimentation, centrifugation, filtration 
and the like. Any of the solvent insoluble fraction of the pitch prepared 
in accordance with the process of the present invention is eminently 
suitable for carbon fiber production. 
In Table III below a comparison is made between the two different pitches, 
one obtained by vacuum stripping and heat soaking of cat cracker bottom, 
the other obtained in accordance with the practice of the present 
invention. As can be seen in Table III below, the pitch that was obtained 
by the heat soaking and vacuum stripping a cat cracker bottom contained 
considerably more quinoline insoluble material as determined by the ASTM 
Test Method No. D2318/76. Thus, although high yields were obtained of 
desirable material insoluble in toluene in each instance, a material 
prepared in accordance with the present invention did not necessitate 
treatment to remove the quinoline insoluble materials because of their 
relatively low content. 
TABLE III 
______________________________________ 
Heat Soak Conditions 
Qi(ASTM) in 
Feed Temp .degree.C. 
Time Hrs. Pitch, % 
______________________________________ 
Vacuum Stripped - 
430 3 9.9 
Cat Cracker Bottom 
Distillate of Cat 
430 3 0.8 
Cracker Bottom 
______________________________________ 
As should be appreciated, however, in the practice of the present 
invention, the severity of the heat soaking conditions can lead to higher 
levels of quinoline insoluble material than might be desirable in the feed 
stock. Although the total amount of toluene insoluble material of that 
fraction of the pitch suitable in carbon artifact manufacture may be 
increased, it may be necessary to treat the pitch prepared from the cat 
cracker bottom in such a manner as to remove the quinoline insoluble 
components generated during the heat soaking. A particularly preferred 
technique for removing these components is disclosed in copending 
application Ser. No. 29,760 filed Apr. 13, 1979 now U.S. Pat. No. 
4,277,324, which aplication is incorporated herein by reference. 
Basically, the heat soaked pitch is fluxed, i.e., it is treated with an 
organic liquid in the range, for example, of from about 0.5 parts by 
weight of organic liquid per weight of pitch to about 3 parts of fluxing 
liquid per weight of pitch, thereby providing a fluid pitch having 
substantially all quinoline insoluble material suspended in the fluid in 
the form of a readily separable solid. The suspended solid is then 
separated by filtration of the like and the fluid pitch is then treated 
with the antisolvent compound so as to precipitate at least a substantial 
portion of the pitch free of quinoline insoluble solids. 
The fluxing compounds suitable in the practice of the present invention 
include tetrahydrofuran toluene, light aromatic gas oil, heavy aromatic 
gas oil, tetralin and the like. The antisolvent preferably will be one of 
the solvents or mixture of solvents which have the solubility parameter 
between 8.0 and 9.5, preferably between about 8.7 and 9.2 at 25.degree. C. 
as discussed hereinabove. 
A more complete understanding of the process of this invention can be 
obtained by reference to the following examples which are illustrative 
only and are not meant to limit the scope thereof which is fully disclosed 
in the hereafter appended claims. 
EXAMPLES 1-12 
In each of the following examples, 12 kilograms, of a cat cracker bottom 
having the following physical inspections was used: 
______________________________________ 
Physical Characteristics 
Viscosity cst at 210.degree. F. 
9.0 
Ash content, wt. % 0.015 
Coking value (wt. % at 550.degree. C.) 
6.9 
Asphaltene (n-heptane insolubles), % 
1.0 
Toluene insolubles (0.35.mu.), % 
0.150 
Number average mol. wt. 280 
Elemental Analysis 
Carbon, % 89.29 
Hydrogen, % 7.92 
Oxygen, % 0.15 
Sulfur, % 2.90 
Chemical Analysis (by proton NMR) 
Aromatic carbon (atom %) 56 
Carbon/hydrogen atomic ratio 
0.94 
Asphaltene Analysis 
Number average mol. wt. 660 
Coking value (at 550.degree. C.), % 
5.0 
Bureau of Mines Correlation Index 
125 
______________________________________ 
The cat cracker bottom was charged into a 20 kilogram stainless steel 
reactor which was electrically heated and equipped with a mechanical 
agitator. A vacuum was applied during the heating and the pitch was 
distilled into seven fractions, the boiling point corrected to atmospheric 
pressure and weight percent of each fraction is given in Table IV below. 
TABLE IV 
______________________________________ 
Boiling Point .degree.C./ 
Fractions 760 mm mercury 
Wt. % 
______________________________________ 
(Distillate) 271-400 10.0 
(Distillate) 400-427 23.8 
(Distillate) 427-454 13.3 
(Distillate) 454-471 11.7 
(Distillate) 471-488 13.4 
(Distillate) 488-510 10.0 
(Residue) 510 + 17.5 
______________________________________ 
600 grams of samples of each of the fractions were charged into a 1000 ml 
glass reactor which was electrically heated and equipped with a mechanical 
agitator. The material charged into the reactor was heat soaked at 
atmospheric pressure and in a nitrogen atmosphere for the times and 
temperatures given in Table V below. Subsequently, the heat soaked 
material was cooled to about 300.degree. C. and the pressure in the vessel 
is reduced to generally in the range from about 0.5 to 5.0 mm Hg and 
effectively vacuum stripping the heat soaked pitch of the oil contained 
therein. 
The percent quinoline insolubles in the product pitch was determined by the 
standard technique of quinoline extraction at 75.degree. C. (ASTM Test 
Method No. D2318/76). 
The toluene insoluble fraction of the pitch was determined by the following 
process: 
(1) 40 grams of crushed sample were mixed for 18 hours at room temperature 
with 320 ml of toluene. The mixture was thereafter filtered using a 10-15 
micron fritted glass filter; 
(2) the filter cake was washed with 80 ml of toluene, reslurried and mixed 
for four hours at room temperature with 120 ml of toluene, filtered using 
a 10-15 micron glass filter; 
(3) the filter cake was washed with 80 ml of toluene followed by a wash 
with 80 ml of heptane, and finally the solid was dried at 120.degree. C. 
in the vacuum for 24 hours. 
The above method for determining toluene insolubles is hereinafter referred 
to as the SEP technique, which is an achronym for the standard extraction 
procedure. 
The optical anisotropicity of the pitch was determined by first heating the 
pitch to 375.degree. C. and then after cooling, placing a sample of the 
pitch on a slide with Permount, a histological mounting medium sold by the 
Fisher Scientific Company, Fairlawn, N.J. A slip cover was placed over the 
slide by rotating the cover under hand pressure, the mounted sample was 
crushed to a powder and evenly dispersed on the slide. Thereafter the 
crushed sample was viewed under polarized light at a magnification factor 
of 200.times. and the percent optical anisotropicity was estimated. 
The text results for some samples are given in Table V below. 
TABLE V 
__________________________________________________________________________ 
Heat Soaking 
Pitch Composition 
Feed Distillate, 
Condition 
Toluene Optical 
Example 
Boiling Point 
Temp 
Time 
Insoluble 
Anisotropicity 
No. Range .degree.C./760 mm Hg 
(.degree.C.) 
(hrs) 
% Qi % 
% 
__________________________________________________________________________ 
1 427-454 420 3 21.0 0.1 ND 
2 454-471 430 3 41.5 0.5 ND 
3 471-488 420 3 27.0 0.3 100 
4 471-488 430 3 40.0 0.8 ND 
5 471-488 440 3 63.5 1.3 ND 
6 488-510 420 3 37.0 0.1 ND 
7 488-510 430 3 45.0 1.4 100 
8 Middle Distil- 
430 3 45.0 0.4 ND 
late (1) 
9 Middle Distil- 
430 5 64.0 2.7 ND 
late (1) 
10 Middle Distil- 
430 51/2 
74.0 3.4 100 
late (1) 
11 Middle Distil- 
430 53/4 
77.0 5.1 100 
late (1) 
12 510 + (Residue) 
420 3 43.5 17.0 
ND 
__________________________________________________________________________ 
(1) boiling point range = 450.degree.-510.degree. C./760 mm Hg 
ND not determined