Note: Descriptions are shown in the official language in which they were submitted.
.~2~37~64
-- 1 --
FIELD OF THE INVENTION:
2 This invention pertains to an aromatic pitch
3 containing a high liquid crystal (optically active)
4 fraction, and more particularly to a pitch which can be
directly spun into carbon fibers.
6 BACKGROUND OF THE INVENTION:
.
7 As is well-known, the catalytic conversion of
8 virgin gas oils containing aromatic, naphthenic and
9 paraffinic molecules results in the fGrmation of a
variety of distillates that have ever-increasing utility
ll and importance in the petrochemical industry. The
12 economic and utilitarian value, however, of the residual
13 fractions of the cat cracking processes (also known as
14 cat cracker bottoms) has not increased to the same
lS extent as have the light overhead fractions. One
16 potential use for such cat cracker bottoms is in the
17 manufacture of carbon artifacts. As is well-known,
18 carbon artifacts have been made by pyrolyzing a wide
19 variety of organic materials. Indeed, one carbon
artifact of particularly important commercial interest
21 is carbon fiber. Hence, particular reference is made
22 herein to carbon fiber technology. Nevertheless, it
23 should be appreciated that this invention has applica-
24 bility to carbon artifacts in a general sense, with
amphasis upon the production on shaped carbon articles
26 in the form of filaments, yarns, films, ribbons,
27 sheets, etc.
28 The use of carbon fibers for reinforcing
29 plastic and metal matrices has gained considerable
commercial acceptance. The exceptional properties of
31 these reinforcing composite materials, such as their
32 high strength to weight ratio, clearly offset their high
33 preparation costs. It is generally accepted that large
.
7~6~
1 scale use of carbon fibers as reinforcing materîal would
2 gain even greater acceptance in the marketplace, if the
3 costs of the fibers could be substantially reduced.
4 Thus, the formation of carbon fibers from relatively
inexpensive carbonaceous pitches has received consider-
6 able attention in recent years.
7 Many materials containing polycondensed
8 aromatics can be converted at early stages of carboni-
9 zation to a structurally ordered optically anisotropic
spherical liquid crystal called mesophase. The presence
11 of this order d structure prior to carbonization is
12 considered to be fundamental in obtaining a high ~ua:Lity
13 carbon fiber. Thus, one of the first requirements of a
14 feedstock material suitable for carbon fiber prcduction,
is its ability to be converted to a highly optically
16 ani50tro~ic material.
17 In addition, suitable feedstocks for carbon
18 artifact manufacture, and in particular carbon fiber
19 manufacture, should have relatively low softening points
and sufficient viscosity suitable for chaping and
21 spinning into desirable articles and fibers.
22 Unfortunately, many carbonaceous pitches have
23 relatively high softening points. Indeed, incipient
24 coking frequently occurs in such materials at temper-
atures where they have sufficient viscosity for spinning
26 The presence of coke, infusible materials, and/or high
27 softening point components, are detrimental to the
28 fiber-making process. Thus, for example, U.S. Patent
29 3,919,376 discloses the difficulty in deforming pitches
which undergo coking and/or polymerization at the
31 softening temperature of the pitch.
32 Another important characteristic of the
33 feedstock for carbon artifact manufacture is its rate of
-- 3 --
1 conversion to a suitable optically anisotropic material.
2 For example, in ye above-mentioned U.S. patent, i* is
3 disclosed that 350C is the minimum temperature gener-
4 ally required to produce mesophase from a carbonaceous
pitch. More importantly, however, is the fact that at
6 least one week of heating is necessary to produce a
7 mesophase content of about 40%, at that minimum temper-
8 ature. Mesophase, of course, can be generated in
9 shorter times by heating at higher temperatures.
However, as indicated above, incipient coking and other
11 undesirable side reactions take place at temperatures in
12 excess of about 440C.
13 In U.S. Patent 4,208,267, it has been
14 disclosed that typical graphitized carbonaceous pitches
contain a separable fraction which has important physi-
16 cal and chemical properties. Indeed, this separable
17 fraction exhibits a softening range and viscosity suit-
18 able for spinning. It also has the ability to be
19 converted rapidly (at temperatures in the range gener-
ally of about 230C to about 400C) to an optically
21 anisotropic, deformable, liquid crystalline material
22 structure Unfortunately, the amount of separable
23 fraction present in well-known commercially available
24 petroleum pitches, such as Ashland 240* and Ashland
260*, to mention a few, is exceedingly low. For example,
26 with Ashland 240, no more than about 10% of the pitch
27 constitutes a separable fraction capable of being
28 thermally converted to a deformable anisotropic phase.
29 In U.S. Patent 4,184,942, it has been
disclosed that the amount of the aforementioned fraction
31 yielding an optical anisotropic pitch can be increased
32 by heat soaking the feedstock at temperatures in the
33 range of 350C to 450C, until spherules visible under
34 polarized light begin to appearO
* denotes trade mark
..~,
- ~2~726~L
1 In U.S. Patent 4,219,404, it has been dis-
2 closed that the polycondensed aromatic oils present in
3 isotropic graphitizable pitches are generally detrimen-
4 tal to the rate of formation of highly anisotropic
material in such feedstocks when they are heatad at
6 elevated temperatures and that, in preparing a feedstock
7 for carbon artifact manufacture, it is particularly
8 advantageous to remove at least a portion of the poly-
9 condensed aromatic oils normally present in the pitch
simultaneously with, or prior to, heat soaking of the
11 pitch for converting it into a feedstock suitable in
12 carbon artifact manufacture.
13 More recently, in U.S. Patent 4,271,006 (June
l 2,. 1981), a process has been disclosed for converting
cat cracker bottoms to a feedstock suitable in carbon
16 artl~act manufacture. Basically, the process requires
17 stripping cat cracker bottoms of fractions toiling below
18 400C and thereafter heat soaking the residue followed
lg by vacuum stripping to provide a carbonaceous aromatic
pitch
21 Cat cracker bottoms like all other heavy
22 aromatic residues obtained from steam cracking, fluid
23 cracking or coal processing are composed of two compo-
24 nents: (1) a low molecular weight oil fraction which
can be distilled; and (2) an undistillable fraction of
26 high molecular weight. This high molecular weight
27 fraction is insoluble in paraffinic solvents such as
28 n-heptane; iso-octane, pet ether, etc. This fraction is
>9 generally called "asphaltene~.
- It is preferred to use an asphaltene-free feed
31 for the production of pitches. These asphaltenes have a
32 very high molecular weight (up to 10,000), a very high
33 coking characteristic (coking value as high as 67.5 wt~
~'7~
-- 5 --
1 coke yield at 550C)~ and a very high melting point
2 (200-~50C).
3 It is desired to use an asphaltene-free cat
4 cracker bottom. The asphaltene-free cat cracker bottom
is free of ash, coke particles and other impurities
6 The absence of asphaltene, ash, coke particles and other
7 organic and inorganic impurities make the cat cracker
8 bottom distillate an ideal feed for the production o
g an aromatic pitch with a very high content of liquid
crystals. This asphaltene-free cat cracker bottom can
11 be prepared by two methods: (a) by a distillation
12 process; ego, vacuum or steam distillation; and (b)
13 by deasphaltenation of the cat cracker bottom. The
14 deasphaltenation can be made readily by solvent extrac-
tion with a paraffinic solvent.
16 In U.S. Patent No. 4,363,715 a process is
17 de5cribed for obtaining a feedstock with a low liquid
18 crystal fraction by heat soaking a distillate derived
19 from a cat cracker bottom. The pitch produced in the
above patent No. 4,363,715 cannot be used directly for
21 carbon fiber production. The liquid crystal fraction
22 has to be extracted from the pitch and used for fiber
23 production.
24 Whereas, U.S. Patent No. 4,363,715 teaches
that all of the cat cracker bottoms can be used to
26 obtain a pitch having low toluene insolubles (Ti), the
27 present invention teaches the opposite, i.e. obtaining
28 a pitch from fractions of the cat cracker bottoms
29 which has a high Ti content (a high content of liquid
crystals).
31 The present invention uses deasphaltenated
32 feedstock fractions to provide a pitch having a high Ti
- .
~2~172~4
-- 6 --
content, and one which does not require Ti solvent
2 extraction prior to spinning into fibers.
3 The deasphaltenated fractions of a feedstock
4 in accordance with this invention is generally free of
ash and impurities and has the proper rheological
6 properties to allow direct spinning into carbon fibers.
7 The pitch obtained from this fraction produces fibers
8 which have high strength and performance. For example,
9 a deasphaltenated cat cracker bottom fraction obtained
in accordance with the present invention, has virtually
11 no coking value at 550C compared with a 56% standard
12 coking value for Ashland 2~0. The deasphaltenated cat
13 cracker bottom fraction is composed of 4, 5, and 6
14 polycondensed aromatic rings. This provides a uniform
weed material which can be carefully controlled to
16 produca a uniform product with a narrow molecular weight
17 distrihution,
18 SUMMARY OF THE INVENTION:
19 The present invention pertains to a high Ti
pitch for direct spinning into carbon fibers. An
21 aromatic pitch with a very high liquid crystal fraction
22 (80-100%) can be prepared by thermally reacting a
23 deasphaltenated fraction of either a cat cracker bottom,
24 steam cracker tar or a coal distillate, that are respec-
tively rich in (4, 5 and 6); (2, 3, 4 and 5); and (3, 4,
26 5 and 6) aromatic rings. The various feedstocks frac-
27 tion are heat soaked in a temperature range from 420C
28 to 450C at atmospheric pressure, and then vacuum
29 stripped to remove at least a portion of the unreacted
oils at a temperature in the approximate range of from
31 320C to 440C at 0.1 to 100 mmHg, and preferably at
32 greater than 400C at 1.0 - 5.0 mmHg of pressure.
'7~64
-- 7 --
1 More specifically, in the case of cat cracker
2 bottoms the fraction is heat soaked at approximately
3 440C for 2-4 hours at atmospheric pressure. In the
4 case of steam cracker tars, the fraction is heat soaked
at 430C for approximately 4~0 hours; and in the case
6 ox coal distillate, the fraction is heat soaked at
7 approximately 440C for l/4 to l/2 hour. All the heat
8 soaked materials are then vacuum stripped and spun
9 directly into carbon fibers. The pitch of this inven-
tion is definable only in terms of deasphaltenated
ll fractions of a feedstock and containing 4, 5 and 6
12 aromatic rings.
13 For the purposes of definition the terms
lo "deasphaltenated feedstock~' and/or "deasphaltenated
middle traction of a feedstock" shall mean: a deas-
16 phaltenated material obtained from a middle cut of a
17 feedstock, and/or one caused to be relatively free ox
18 asphaltenes by means of obtaining a distillate portion
l9 of said feedstock which when further treated will form a
precursor which can be spun into a carbon fiber and
21 which has the following general characteristics:
22 (l) a relatively low coking value;
23 (2) a relatively low content of ash and
24 impurities; and
~3) a relatively narrow averaga molecular
26 weight range.
27 (4) consisting of 3, 4, 5 and 6 alkyl-substi-
28 tuted polycondensed aromatics.
29 A typical weight percentage of asphaltenes
in a deasphaltenated cat cracker bottom feedstock being
31 in the range of approximately 0.0 to 1.0%.
JL2~7Z64
1 A directly spinnable pitch of this invention
2 has the proper rheological properties characterized as a
3 glass transition temperature (Tg) in the approximate
4 range of 180C to 250C at atmospheric pressure, and/
or a viscosity of less than approximately 2,500 cps
6 ;n a temperature of approximately 360C at atmospheric
7 pressure.
8 It is an object of this invention to provide
g an improved pitch which can be directly spun into carbon
fibers
11 It is another object of the invention to
12 provide a pitch for manufacturing carbon fibers which is
13 more uniform, and which is relatively free of ash and
14 impurities
It is a further object of this invention to
16 provide a pitch having high toluene insolubles, and
17 which does not require Ti solvent extraction prior to
18 spinning into fibers.
19 These and other objects of this invention will
be better understood and will become more apparent with
21 reference to the following detailed description con-
22 sidered in conjunction with the accompanying drawings.
23 BRIEF DESCRIPTION OF THE DRAWINGS:
24 Figure 1 is a graphical representation of
deasphaltenated fractions of various feedstocks used to
26 provide the inventive pitches for direct spinning into
27 carbon fibers, including the deasphaltenated cat cracker
28 bottom of this invention.
1~726'~
1 Figure 2 shows a graph of viscosity vs.
2 temperature for a number of pitches made from deasphal-
3 tena~ed cat cracker bottom distillates; and
4 Figure 3 depicts a graph of a glass transition
temperature scan for one of the pitches shown in Figure
6 2.
7 DETAILED DESCRIPTION OF THE INVENTION:
8 The term catalytic cracking refers to a ther-
9 mal and catalytic conversion of gas oils, particularly
virgin gas oils, boiling generally between 316C and
11 566C, into lighter, more valuable products.
12 Cat cracker bottoms refer to that fraction of
13 the product of the cat cracking process which boils in
14 the range of from about 200C to about 550C.
Cat cracker bottoms typically have relatively
16 low aromaticity as compared with graphitizable isotropic
17 carbonaceous pitches suitable in carbon artifact manu-
18 facture.
l9 Specifications for a typical cat cracker
bottom that is suitable in the present invention are
21 given in Table 1:
~2~7264
-- 10
1 TABLE 1
2 Physical Characteristics Range
3 Viscosity cst @ 210F 1.0-10.0
4 Ash content, wt% 0.010-02.0
5 Coking value (wt%.@ 550C) 6.0-18.0
6 Asphaltene (n-heptane insoluble), 1.1-12.0
7 Toluene insolubles (0.35 ), % 0.010-1.0
8 Number average mol. wt. 220-290
9 Elemental Analysis
10 Carbon, % ~8.0-90.32
11 Hydrogen, % 7.74-7.40
12 Oxygen, % 0.10-0.30
13 Sulfur, % 1.0-4.5
14 Ch cal Analysis (proton NMR)
15 Aromatic carbon (atom%) 54-7~
16 Carbon/hydrogen atomic ratio0.90-1.0
17 Asp~ltene Analysis - .
18 Number average mol. wt. 550-750
19 Coking value, wt% at 550C 3.5-6.5
20 Aromatic carbon (atom%) 55-70
21 Bureau of Mines Correlation Index 120-140
22 Tables 2 and 3 below, illustrate the various
23 fractions and characteristics of fractions 3 through 6 for
24 a typical cat cracker bottom:
12~ 6~
1 TABLE 2
2 Boiling ~ointt
3Frac~ions C/760 mm Mercury wt%
4Distillate Fraction 1 271-400 10.0
5Distillate Fraction 2 ~00-427 23.8
6Distillate Fraction 3 454 13.3
7Distillate Fraction 4 454-471 11.7
8Distillate Fraction 5 471-488 13.4
9Distillate Fraction 6 488 10.0
10 (Residue) 5~ 17.5
11 The boiling point corrected to atmospheric
12 pressure and weight percent breakdown of fractions 3-6 is
13 given in Table 3 below:
14 TABLE 3
15 Chemical and Physical Characteristics of
16 Distillate Fractions 3-6 (427-510C)
17 of Cat Cracker Bottoms
.
18 Ash (wt~) 0.0001
19 Asphaltene (n~heptane insolubles), % nil
20 Coking value (coke yield at 550C) nil
21 Average mol wt% (MS-method) 260
22 Carbon/hydrogen atomic ratio 0.89
23 Aromaticity (aromatic carbon atom% by NMR) 66
24 Aromatic Rin Distribution (MS-method)
25 1 ring (%) 1.5
26 2 ring (%) 13.0
27 3 ring (%) 31.0
28 4 ring (%)
29 5 ring (~) 6.4
30 6+ ring(%) 1.0
64
- 12 -
1 TABL_ 3 (CONTINUED3
2 Aromatic Rink Composition (by MS-method)
3 Rings with carbon and hydrogen (%) 63
4 Rings with carbon, hydrogen and oxygen (~) 2
5 Rings with carbon, hydrogen and sulfur (~j 33
6Mass Spectrometric Analysis o the Distillate
7Fractions 3-6 (427-510C) of Cay Cracker
8Residue Indicated the Presence of the
gFollowin~ Main Polycondensed Aromatics
10Weight (%)
Molecular Typical(Average Molecular
12 Formula Name Weight)
13 Cn~2n-16 Acenophthenesl.S4 (218
14 CnH2n-18 Phenantbrenes8.95 (243)
CnH2n-20 Naphtheno-9.78 (254)
16 Phenanthrene
17 CnH2n~22 Pyrenes 15.4 (253)
18 CnH2n-24 Chrysenes8.70 (265)
19 CnH2n-26 Cholanthrenes2.9 (283)
CnH2n-14S Benzopyrene1.0 (295)
21 CnH2n-16S Indothiophenes 1.45 (280)
22 CnH2n-18S Naphthotiophene 4.7 (249)
23 CnH2n-20S Acenophthylene 4.0 (273)
24 Thiophenes
CnH2n-22S Anthraceno- 3.8 (261)
26 Thiophenes
27 CnH2n-24S Naphteno- 9.9 (271)
28 Phenanthreno
29 Thiophenes
CnH2n-26s Pyrenothiophenes 1.20 (295)
31 CnH2n-28s Chryseno- 0.82 (295)
32 Thiophenes
33 CnH2n_30S
~Z~7Z6~
1 In the process of the present invention, the
2 cat cracker bottoms are fractionally distilled by
3 heating the cat cracker bottom to elevated temperatures
4 and reduced pressures, for example, by heating to
temperatures in the range of 200C to 300~C at pres-
6 sures ranging from about 250 to 500 millimeters of
7 mercury. Basically, the cat cracker bottom is separated
8 into at least a single distillake having a boiling point
g at 760 mm mercury in the range of from about ~50C to
about 530C, and the residue being the raction not
11 distillable at temperatures up to 530C, at a pressure
12 of about 350 to 450 millimeters of mercury. In a par-
13 ticularly preferred embodiment of the present invention,
14 the distillate fraction of the cat cracking bottom which
is employed in forming a suitable carbonaceous pitch for
16 carbon artiEact manufacture is that fraction boiling in
1~7 the approximate range of about 450C to about 510C
13 at 760 mm of mercury. The desired cat cracker bottom
19 fraction can also be obtained by other commercially
known separation methQds such as steam distillation,
21 flash stripping or by using a thin film evaporator.
22 To produce a pitch with a high fraction of
23 anisotropic liquid crystal, the cat cracker bottom
24 fraction is heat soaked at temperatures in the approxi-
mate range of 420C to 450C at atmospheric pressure.
26 In general, heat soaking is conducted for times ranging
27 from 2 hours to about 4 hours. In the practice of the
28 present invention, it is particularly preferred that
29 heat soaking be done in an atmosphere such as nitrogen,
30 or alternatively in a hydrogen atmosphere.
31 When the heat soaking is completed, the
32 reaction mixture is then subjected Jo a reduced pressure
33 at a liquid temperature between 320-440C, and most
34 preferably at 400-430C, Jo remove from the mixture at
35 least part of the distillable unreacted oils. Prefer-
~l2C)726~
- 14 -
1 ably, all of the unreacted oils are removed in order to
2 concentrate and increase the anisotropic liquid crystal
3 fraction in the final pitch product. The use of a high
liquid temperature, e.g., 400-430C, is very desirableO
The high liquid temperature helps to remove the dis-
6 tillable unreacted oils, which if left in the final
7 pitch product tend to dilute and reduce the liquid
8 crystal content of the pitch. Optionally, the heat
g soaked mixture can be purged with a gas such as nitrogen
in order to accelerate the removal of the unreacted oils.
11 The resultant pitch produced by the above-
12 described method has a low melting point (as defined by
13 our DSC method) (190-230C), has very high aromaticity
14 (85-90% of aromatic carbon atoms by carbon NMR method)
15 and contains a high anisotropic liquid crystal fraction
l (80-100~ by polarizad light microscopy). The pitch
17 composition is defined readily by using solvent analysis,
l8 wherein the content insolubles in toluene at room
19 temperature and the content insolubles in guinoline
at 75C are determined. The toluene insoluble (Ti)
21 fraction in the pitch can be used to give a measure of
22 the liquid crystal content in the pitch. One of the
23 objectives of this invention is to transform the cat
24 cracker bottom distillate fraction into a pitch with a
very high content of toleune insolubles (80-100%), and
26 which can be spun directly into carbon fibers, as shown
27 in Figure 1.
28 The present invention distinguishes over the
29 invention of this referenced application most partic-
ularly in the heat soaking step of the process.
31 The pitches of all these inventions are
32 definable only in terms of deasphaltenated fractions of
33 a feedstock (Figure 1).
- 15 -
1 Table 4 below, summarizes the heat soaking
2 conditions for a variety of deasphaltenated feedstocks,
3 and the resultant characteristics of each pitch:
,
-`" lZ~)7~
En Lrl
O .. I ,. .....
or
O
O En
H OD O N O O to O OD t`
a
Ul O _I
0
L3
En I` o o --I OD
`
En co
o
s
O _, Us o o
er I a
o or ~9 o
a
a
.
o or o r-
' en o or I I I I I
or N Us N
.rl I) ~9
~U~
Us
:~. t0 O N a _I a or a. or
I, O . Ln . . . ox _l
v I> En er Ox f a
O U N eP N en
a
~4 o
~1
En 1: us En o f a ct) er ox
a) us I ' N elm O
l H `1 N ' l l I
o a or er
,~ l a
c ,~ m
O r~
Jo O O a o a
0 rl er ~9 11'~ G N N
:~ Cl CD I L-')
O E --I o M In _I IJ~ N
l 0~ _I N
a
o
.
C o
Q~ _
U)
ul us C pa
o E o C ,s: to
.L) O t)
.,, ,1 _ _
UP dP
cr _ L9 _ l I- _
C _ us O _ dP Us I: dP dP
) UP-- f C `~ C
a o s -- _ as t~5 0 _1 Q) Q~
_ 5~ C: h
O us O or O O I) O
Q~ O u3 a) us v E-) ,~
l 1 E E Q~ us
a x a .,, 4~ l :) x ,~
EL) En v E~01~; O o 5tnoz
Z~7264
-- 17 --
O
I
I:; H
O En cry
n us
H 00 1 I I I I I
t l l
En II IIIII
S ~J
.~ on
So O I I I I t I I
to O
,~ r
8
Ox
C Er U') I I I I N N 0~
a) > Us ED
Us
Us
I Do
C l U O
O I I I l 1
U f
or 1.1 0 1¢
IU _1 O N 0~
~0 En f
O
o .rl
.,, m
V Us
Q
O
O h
o f o
S CO OD O
En f I
IQ
0
I` do
a o
--It.> JJ E v J- O o c\ O o
Q~rl C OOOOO
E V En v
a e o 2 I) I)
o 0 oe, q2~ a
~3 h
~21)7264
- 18 -
1 The rehology of pitches used for direct
2 spinning is of great importance to obtain good spinn-
3 ability. It is desired to have pitches with low vis-
4 cosity at the spinning temperature which is preferrably
below around 400C, in order to avoid pitch cracking
6 and volatilization which could lead t:o serious foaming
7 of the fiber and substantial reduction in the fiber
8 strength. The pitch for direct spinning is also desired
9 to be less sensitive to heat, i.e. does not change its
viscosity too much when changing temperature. The
ll sensitivity of the pitch to temperature variation can be
12 determined from viscosity - temperature curves. This
13 relationship for several pitches designated A, B, C, and
14 D is shown in Figure 20
Differential Scanning Calorimetry (DSC) is
16 used to obtain information on glass transition and
~7 sotening characteristics of pitches. xn OMINITHERM
18 Corp. DSC Model (QC25) is used to obtain the glass
l9 transition (Tg) data. The method comprises heating a
small sample of the pitch in the DSC pan, allowsd to
21 cool and the DSC trace was then obtained by heating at
22 the rate of 10C/min under nitrogen (30cc/min). From
23 the DSC trace three DSC data points are determined; the
24 onset of Tg (Ti), the termination of Tg (Tf) and the Tg
point which is at the midway between the Ti and Tf
26 point. It has been reported what there is a relation-
27 ship between the Tg of the pitch and its softening point
28 as determined by the traditional method such as the ring
29 and ball method. The softening point is higher by
around 60C than the Tg.
31 The DSC data of CCB-distillate pitches is
32 presented in table 5 below:
. . .
~IL2~Z6~
-- 19 --
1 TABLE 5
2 Pitch _ _ A _ E_C B D
3 D5C data
4 Ti (onset of Tg) 166 185 193 179 166
5 Tg (glass transition) 194 219 228 214 207
6 Tf (termination of Tg) 228 258 269 253 251
7 The DSC scan of CCB-distillate pitch D is shown
8 in Figure 3.
