CA1199758A - Pitch for direct spinning into carbon fibers derived from a steam cracker tar feedstock - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A pitch suitable for carbon fiber manufacture features a pitch having a weight content of between 80 and 100 percent toluene insolubles. The pitch is derived from a deasphaltenated middle fraction of a feedstock. The pitch is characterized as being rela-tively free of impurities and ash. The pitch can be spun directly into carbon fibers.

Description

~., FIELD OF THE INVENTION:
---- ., .. .... _ _

2 This invention pertains to an aromatic pitch

3 containing a high li~uid crystal (optically active)

4 fraction, and more particularly to a pitch which can be directly spun into carbon fibers.

6 BACKGROUND OF THE INVENTI ON:

7 As is well-known, the catalytic conv~rsion of 8 virgin gas oils containing aromatic, naphthenic and 9 paraffinic molecules results in the for~ation o~ a variety of distillates that have ever-increasing utility 11 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 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-kno~n, 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 applic-24 ability to carbon artifacts in a general sense, with emphasis upon the production on shaped carbon articles ~6 in the form of filaments, yarns, films, ribbons, ~heets, 27 etc.

28 The use of carbon fibers or reinforcing 29 plastic and metal matrices has gained considerable commercial acceptanceO The exceptional properties of 31 these reinforcing composite materials, such as their 32 high strength to weight ratio, clearly offset their high 75~

1 preparation costs. It is generally accepted that large 2 scale use of carbon fibers as reinforcing material would 3 gain even greater acceptance in the marketplace, if the 4 costs of the fibers could be substantially reduced.
Thus, the formation of carbon fibers from relatively 6 inexpensive carbonaceous pitches has received consider-7 able attention in recent years.

8 Many m~terials containing polycondensed 9 aromatics can be converted at early stages of carboniza-tion to a structurally ordered optically anisotropic 11 spherical liquid crystal called mesophase. The presence 12 of this ordered structure prior to carboni~ation is 13 considered to be fundamental in obtaining a high quality 14 carbon fiber. Thus, one of the first requirements of a feedstock material suitable for carbon fiber production, 16 is its ability to be converted to a highly optically 17 anisotropic material.

18 In addition, suitable feedstocks for carbon 19 artifact manufacturer and in particular carbon fiber manufacture, should have relatively low softening points 21 and sufficient viscosity suitable for shaping and 22 spinning into desirable articles and fibers.

23 Unfortunately, many carbonaceous pitches have 24 relatively high softening points. Indeed, incipient coking frequently occurs in such materials at tempera-26 tures where they have sufficient viscosity for spinning.
27 The presence of coke, infusible materials, and/or high 28 softening point components, are detrimental to the 29 fibermaking process. Thus, for example, U.S. Patent 3,919,376 discloses ~he difficulty in deforming pitches 31 which undergo coking and/or polymerization at the 32 softening tempera~ure of the pitch.

7~

1 Another important characteristic of the 2 feedstock for carbon artifact manufacture is its rate of 3 conversion to a suitable optically anisotropic ma-terial.
4 For example, in the above-mentioned U.S. patent, it is disclosed that 350C is the minimum temperature gener-6 ally required to produce mesophase from a carbonaceous 7 pitch. More importantly, however, is the fact that at 8 least one week of heating is necessary to produce a 9 mesophase content of about 40~, at that minimum tempera~
ture. Mesophase, of course, can be generated in shorter 11 times by heating at higher temperatures. However, as 12 indicated above, incipient coking and other undesirable 13 side reactions take place at temperatures in excess of 14 about 425C.

In U.S. Patent 4,208,267, it has been dis-16 closed that typical graphitized carbonaceous pitches 17 contain a separable fraction which has important phy-18 sical and chemical propertiesO Indeed, this separablP
19 rac~ion exhibits a softening range and viscosity suitable for spinning. It also has the ability to be 21 converted rapidly (at temperatures in the range gener-22 ally of about 230C to about 400QC) to an optically 23 anisotropic, deformable~ liquid crystalline material 24 structure~ Unfortunatsly, the amount of separable 2S fraction present in well-known commercially available 26 petroleum pitches, such as Ashland 240 and Ashland 260, 27 to mention a few, is exceedingly low. For example, with 28 Ashland 240, no more than about 10% of the pitch consti-29 tutes a separable fraction capable of being thermally converted tD a deformable anisotropic phase 31 In U.S. Patent 4,184,942, it has been dis-32 closed that ~he amount of the aforementioned fraction 33 yielding an optical anisotropic pitch can be increased 34 by heat soaking the feedstock a~ temperatures in the a97~;~

1 range of 350C to 450C, until spherules visible 2 under polarized light begin to appear.

3 In U.S. Patent 4,219,404, it has been dis-4 closed that the polycondensed aromatic oils present in isotropic graphitizable pitches are generally detri-6 mental to the rate of formation of highly anisotropic 7 material in such feedstocks when they are heated at 8 elevated temperatures and that, in preparing a feedstock g for carbon artifact manuacture, it is particularly advantageous to remove at least a portion of ~he poly~
11 condensed aromatic oils normally present in the pitch 12 simultaneously with, or prior to, heat soaking of the 13 pitch for converting it into a feedstock suitable in 14 carbon artifact manufacture.

More r~cently, in U~S. Patent 4,271,006 ~June 16 2, 1981), a process has been disclosed for converting 17 cat cracker bottoms to a feedstock suitable in carbon 18 artifact manufacture. Basically, the process requires 19 stripping cat cracker bottoms of fractions boiling below 400C and thereafter heat soaking the residue followed 21 by vacuum stripping to provide a carbonaceous pitch.

22 Cat cracker bottoms liks all other heavy 23 aromatic residues obtained from steam cracking, fluid 24 cracking or coal processing are composed of two compo-nents: (1) a low molecular weight oil fraction which 26 can be distilled; and ~2) an undistillable fraction of 27 high molecular weight. This high molecular weight 28 fraction is insoluble in paraffinic solvents such as 29 n-heptane, iso-octane, pet ether, etc. This fraction is generally called nasphaltenen.

31 It is preferred to use an asphaltene free feed 32 for the production of pitches. These asphaltenes have a 1 very high molecular weight (up to 10,000), a very high 2 coking characteristic (coking value as high as 67.5 wt%
3 coke yield at 550C), and a very high melting point 4 (200-250C).

It is desired to use an asphaltene-free cat 6 cracker bottom~ The asphaltene-free cat cracker bottorn 7 is free of ash, coke particles and other impuritiesO
8 The absence of asphaltene, ash, coke particles and other 9 organic and inoryanic impurities make the cat cracker bottcm distillate an ideal feed for the production of an 11 aromatic pitch with a very high content of liquid 12 crystals~ This asphaltene-free cat cracker bottom can 13 be prepared by two methods: (a) by a distillation 14 process; e.g., vacuum or steam distillation; and ~b) by deasphaltenation of the cat cracker bottomO The 16 deasphaltenation can be made readily by solvent extrac-17 tion with a paraffinic solvent.

18 In U.S. Patent 4,363,715 a process is des-19 cribed for obtaining a feedstock with a low liquid crystal fraction by heat soaking a distillate derived 21 from a cat cracker bottomO The pitch produced in 22 the above Patent No. 4~363,715 cannot be used directly 23 for carbon fiber production. The liquid crystal 24 fraction has to be extracted from the pitch and used for fiber production.

26 Whereas, U.S. Patent No. 4,363,715 teaches 27 that all of the cat cracker bottoms can be used to 28 obtain a pitch having low toluene insolubles (Ti), 29 the present invention teaches the opposite, i.e. obtain-ing a pitch from fractions of the cat cracker bottoms 31 which has a high Ti content (a high content of liquid 32 crystals)~

75~

1 The present invention uses deasphaltenated 2 feedstock fractions to provide a pitch having a high Ti 3 content, and one which does not require Ti solvent ~ extraction prior to spinning into fibers.

The deasphaltenated fractions of a feedstock 6 in accordance with this invention is generally free of 7 ash and impurities~ and has the proper rheological 8 properties to allow direct spinning into carbon fibers.
9 The pitch obtained ~rom this fraction produces fibers which have high strength and performance. For example, 11 a deasphaltenated cat cracker bottom fraction obtained 12 in accordance with the present invention, has virtually 13 no coking value at 550C compared with a 56~ standard 14 coking value for Ashland 240. The deasphaltenated cat cracker bottom fraction is composed of 4, 5, and 6 16 polycondensed aromatic rings. This provides a uniform 17 feed material which can be carefully controlled to 18 produce a uniform product with a narrow molecular weight 19 distribution.

SUMMARY OF THE INVENTION:

21 The present invention pertains to a high Ti 22 pitch for direct spinning into carbon fibers. An 23 aromatic pitch with a very high liquid crystal fraction 24 (80-100%) can be prepared by thermally reacting a deasphaltenated fraction of either a cat cracker bottom, 26 steam cracker tar or a coal distillate, that are respec-27 tively rich in (4, 5 and 6~; (2, 3, 4 and 5); and (3, 4~
28 5 and 6) aromatic rings. The various feedstocks are 29 heat soaked in a temperature range from 420C to 450C at atmospheric pressure, and t~en vacuum stripped 31 ~o remove at least a portion of the unreacted oils at a 32 temperature in the approxima~e range of from 320C to 33 420C at 0.1 to 100 mmHg, and preferably at greater 34 than 400C a~ 5.0 mmHg of pressure.

9751~

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 case of steam cracker tars, the fraction is heat soaked at 430C for approximately 40 hours; and in the case 6 of coal distillate, the fraction is heat soaked at 7 approximately 440C for 1/4 t-o 1/2 hour. All the heat 8 soaked materials are then vacuum stripped and spun g directly into carbon fibers~ The pitch of this inven-tion is definable only in terms of deasphaltenated 11 fractions of a feedstock.

12 For the purposes of definition the terms 13 'Ideasphaltenated feedstock" and/or "deasphaltenated 14 middle fraction of a feedstock" shall mean: a deas-phaltenated material obtained from a middle cut of a16 feedstock, and/or one caused to be relatively free of 17 asphaltenes by means of obtaining a distillate portion 18 Of said feedstock which when further treated will form a 19 precursor which can be spun into a carbon fiber and which has the following general characteristics:

21 (1) a relatively low coking value;

22 (2) a relatively low content of ash and 23 impurities; and 24 (3) a relatively narrow average molecular weight range.

26 (4) consisting of 3, 4, S and 6 polycondensed 27 aromatics~

28 A typical weight percentage of asphaltenes 29 in a deasphaltenated stream cracker tar being in a range f approximately 0.5 to 2.0~D

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1 ~ directly spinnable pitch of this invention 2 has the proper rheological properties characterized by a 3 glass transition temperature (Tg) in the approximate ~ range of 180C to 250C at atmospheric pressure, and/or a viscosity of less than approximately 2,500 cps 6 in a temperature range of approximately 300C, to 7 360C, at atmospheric pressure.

8 It is an object of this invention to provide 9 an improved pitch which can be directly spun into carbon ~ibers.

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 T~E DRAWINGS:

24 Figure 1 is a graphical representation of deasphaltenated fractions of ~arious feedstocks used to 26 provide the inventive pitches for direct spinning into 27 carbon fibers, including the deasphaltenated steam 28 cracker tar bottom of this invention;

29 Figure 2 depicts a graph of a glass transition temperature scan for the pitch of Figure 1.

751~
g DETAILED DESCRIPTION OF THE INVENTION

2 Generally speaking, the steam cracker tar 3 which is used as a starting material in the process of 4 the present invention is defined as the bottoms product obtained by cracking gas oils, particularly virgin gas 6 oils, such as naphtha, at temperatures of from about 7 700C to about 1000C. A typical process steam cracks 8 gas oil and naphtha, at temperatures o~ 800C to 9 900C, with 50% to 70~ conversion to C3 olefin and lighter hydrocarbons, by strippin~ at temperatures 11 o~ about 200C to 250C for several seconds. The 12 tar is obtained as a bottoms product. A gas oil is, of 13 course, a liquid petroleum distillate with a viscosity 14 and boiling range between kerosene and lubricating oil, and having a boiling range between about 200C and 16 400Co Naphtha is a generic term for a refined, 17 partly refined or unrefined liquid petroleum product of 18 natural gas wherein not less than 10% distills below 19 175C and not less than 95% distills below 24UC, as determined by ASTM Method D-86. Steam cracker tars 21 typically consist of alkyl substituted polycondensed 22 aromatic compounds.

23 Obviously, the characteristics of a stea~
24 cracl~er tar vary according to the ~eed in the steam cracking plant.

26 Characteristics of typical steam cracker tars 27 obtained from the steam cracking of naphtha, gas oil and 28 desulfurized gas oil are respectively given in Table 1, 29 below:

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~ In 1 In the process of the present invention, the 2 steam cracker tars are distilled by heating to elevated 3 temperatures at reduced pressures. For example, the 4 stream cracker tar is heated to temperatures in the range of 130C to 320C at an approximate pressure 6 of 10 mm of mercury. Basically, the steam cracker tar 7 is separated into a middle distillate fraction having a 8 boiling .point at 760 mm mercury in the range of from g about 270C to about 490C. In a particularly pre-ferred embodiment of the present invention, the distil-11 late fraction of the steam cracker tar which is employed 12 in forming a suitable carbonaceous pitch for carbon 13 artifact manufacture, is that fraction boiling in the 14 range of about 370 to 3bout 490C at 760 ~n of mercury.

An ASTM D1160 distillation of a typical steam 16 cracker tar is given in Table 2, below:

17 Ta ble 2 1~Vol% Vapor Temperature Vapor Temperature 19Distillate@ 10 mmH~ G ~ 760 mmH~ G

2~10 147 285 27~0 282 444 2870 316 ~3 3Q The middle fraction distillate taken at 370-, 975~g 1 490C @ 760 mmHg has high aromaticity and narrow molec-2 ular weight. It contains no ash or solid particulate and 3 does not contain high coking asphaltene. Chemically 4 it is composed of polycon~ensed 2, 3, g and 5 arornatic rings. Table 3 below gives the physical and chemical 6 characteristics of a typical middle distillate fraction 7 of a steam cracker tar:

8 Table 3 g haracteristics of Steam Cracker Tar Distillate (370-490C) 1. Physical Characteristics 11 Ash Content (%) = Nil 12 Asphaltene (n~heptane insolubles) (%) = Nil 13 Viscosity cps @ 99C = 4.5 14 Toluene Insolubles (%) = Nil Coking Value @ 550C (%) = 2.0 16 20 Chemical_Structure (CMR and PMR) 17 Aromatic Carbon (ato~ %) - 71 18 Paraffinic Protons (%) = 22 19 Benzylic Protons (~) ~ 41 3. Elemental Anal~sis 21 Carbon (wt~) = 90.7 22 Hydrogen (wt%) = 7O3 23 Oxygen (wt%) ~ 0.20 24 Nitrogen (wt%) = 0.10 Sulfur (wt%) = 1~6 26 4. Number Average Mol. Wt (GPC) c 245 1 Table 3 _Continued 2 5. Aromatic Rin~_Distribution (MS) 3 1 Ring ~ 3-7 2 Rings = 43.6 3 Rings = 39.2 6 4 Rings = 11 1 7 5 Rings = 1.5 8 6 Rings = 0.8 9 7 Rings = 0.1 Aro~atics with Carbon and Hydrogen = ~4.3 11 Aromatics with Carbon, Hydrogen and Oxygen = 3 7 12 Aromatics with Carbon, Hydrogen and Sulfur = 11.9 13 Characteristics of Steam Cracker Tar Di5tillate (370--490C) . _ . _ . . ..

14 6. Avera~e Carbon Atom in Side Chaln = 3 0 The molecular structure of a typical steam 16 cracker tar middle distillate fraction as determined ~y 17 high resolution Mass Spectrometer, is ~iven below in 18 Table 4:

19 Table 4 Molecular Structure o a Typical 21 Steam Cracker Tar Distilla~e 22 i~ ye~ _ Ty~ical Name W %_ 23 cnH2n-8 Indanes 0.6 24 CnH2n-10 Indenes 1.3 ~5 CnH2n-12 Naphthalenes 5.0 26 CnH2n-14 Naphthenonaphthalene 9.1 -27 CnH2n-l6 Acenaphthalenes 17.2 28 - CnH2n~18 Penanthrenes 29.0 751~

1 Table 4 Continued 2 Compound Type T~ical Name Wt %

3 Cn~2n-2o Naphthenophenanthrenes 8.8 4 CnH2n-22 Pyrenes 7.3 CnH2n-24 Chyrsenes 2.3 6 C~2n~26 Cholanthrenes 0.9 7 CnH2n-12S Naphthenobenzothiophenes 0~4 8 Cn~2n-14S Indenothiophenes. 0.6 9 CnH2n-16S Naphtnothiophenes 8.5 CnH2n~18S Naphthenonaphthothiophenes 0O6 11 CnH2n-20S 0.5 12 ~nH2n-10 Benzofurans 13 CnH2n-16 Naphthenofurans 2.8 14 CnH2n-18O Naphthenonaphthofurans 0.44 Cn~2n-20O Acenaphthyenofurans 0~2 16 Another method to prepare an asphaltene-free 17 steam cracker tar fraction is by removing the asphaltene 18 from steam cracker tar by a solvent extraction of the 19 asphaltene with a paraffinic solvent such as n-heptane, iso-octane, n-pentene, or pet-ether. Table 5, below 21 gives the characteristics of a deasphaltenated oil 22 obtained from a steam cracker tar using n-heptane as a 23 solvent (Feed: solvent ratio = 1:30):

7~ !3 1 Table 5 2 The Preparation of Deasphaltenated 3 Stea~ Cracker Tar 4 Deasphal-enated Steam 6 Steam Cracker Tar Cracker Tar . . ~
7 1 2 1 _ 2 8 Weight (%~ 100 100 B0 32 9 Sp. Gr. @ 15C 1.112 1.117 1.0~4 1.073 10 Coklng Value @ 550C 18.1 18.8 7.8 7.3 11 Viscosity (cps) ~ 100F 779 925 33.0 22.2 12 Ash Content (%~ 0.003 0.004 Nil Nil 13 Asphaltene (~) 20.0 18.0 1~0 1.2 14 (n-heptane insolubles) 15 Carbon (%) 87.2 86.686.7 87.22 16 ~ydrogen (~) 6.7 6.66.91 7.22 17 Oxygen (%) 0.32 0.310.46 0.21 18 Sulfur (%) 3.7 5.3 4.5 4.5 19 Aromatic Carbon (atom %) 73 72 70 71 20 C/H Atomic ~atio 1 07 1~101.04 1.00 21 After separating the steam cracker tar middle 22 fraction distillate, the ~iddle fraction distillate is 23 heat soaked at temperatures of about 430C at atmospheric 24 pressure. In general, heat soaking is conducted ~or 25 about forty (40) hours. In the practice of the present 26 invention, it is particularly preferred that heat 27 soaking be done in an atmosphere such as nitrogen, or 28 alternatively in hydrogen atmosphere.

9 After heat soaking the distillate, the heat 30 soaked distillate is then heated in a vacuum at tempera-31 tures generally about 400C and ~ypically in ~he range 32 of about 370C to 420C, at pressures below atmospherîc 7~

1 pressure, generally in the range of about 1.0 to 100 mm 2 mercury. This additional heating removes at least part 3 of the oil present in the heat soaked distillate.
4 Typically, from about 90 to 100% of the oil which is present in the heat soaked distillate is removed.

6 As can be readily appreciated, the severity of 7 the heat soaking conditions outlined above, will affect 8 the nature of the pitch produced. The higher the 9 temperature chosen for heat soaking, and the longer the duration of the heat soaking process, the greater the 11 amount of toluene insoluble components that will be 12 generated in the pitch.

13 The inventive process can prepa~e pitches with 14 a very high toluene insolubles content (80-100% by weight), and one which can be spun directly into carbon 16 fibers, as shown in Figure 1.

17 The present invention dis~inguishes over the 18 invention of this referenced application most partic-19 ularly in the heat soaking step of the process.

The pitches of all these inventions are 21 definable only in ter~s of deasphaltenated fractions of 22 a feedstock (Figure l)o 23 Table 6 below, summarizes the heat soaking 2~ conditions for a variety of deasphaltenated feedstocks, and the resultant characteristics of each pitch , ~ H
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~975~

1 The following Table 7, presents data derived 2 from additional examples of steam cracker tar pitches A, 3 B, C and D in accordance with this invention:

4 Table 7 PRODUCTION OF SCT - DISTILLATE PITCHES

6 Example A B C

7 Heat S aking Condition Temperature (C) 430 430 430 440 g Time (hrs.) 2.0 2 1/2 3 1/2 3.0 10 Vacuum-Stripping Condition 11 Max. Temperature (C) 400 400 400 400 12 Pressure [mmHg] 1-2 1-2 1-2 1-2 13 Pitch Composition 14 Toluene Insoluble [SEP]% 86.5 91.7 ~9.3 98.2 15 Quinoline Insolubles % (ASTM) 30.4 34.7 37.6 87.9 16 Pyridine Insolubles (%)51.5 60.0 58.6 17 Chemical Characteristics 18 Aromatic Carbon (atom %) ~ 86.0 19 Carbon/hydrogen atomic ratio 1~78 1.85 1.84 20 Glass Transition Temp~ (C) 21 of pitch 197 234 240 249 22 of toluene insolubles ~ 240 247 - 252 23 Viscosity 2~ 310 9400 28 350 ~ 2350 7~8 1 The rehology of pitches used for direct 2 spinning is of great importance to obtain good spin-3 nability. It is desired to have pitches with low 4 viscosity at the spinning temperature which is prefer-rably below around 400C, in order to avoid pi~ch 6 cracking and volatilization which could lead to serious 7 foaming of the iber and substantial reduction in th~-8 fiber strength. The pitch for direct spinning is also g desired to be less sensitive to heat, i.e. does not change its viscosity too much when changing temperature.
11 The sensitivity of the pitch to temperature variation 12 can be determined from viscosity - temperature curves.

13 Differential Scanning Calorimetry (DSC) is 14 used to obtain information on glass transition and softenin9 characteristics of pitches. An OMINITHERM
16 Corp. DSC Model (QC25) is used to obtain the glass 17 transition (Tg) data. The method comprises heating a 18 s~all sample of the pitch in the DSC pan, allowed to 19 cool and the DSC trace was then obtained by heating at the rate of 10C/min under nitrogen (30cc/min~. From 21 the DSC trace three DSC data points are determined; the 22 onset of Tg (Ti), the termination of Tg (Tf), and the Tg 23 point which is at the midway hetween the Ti and Tf 24 point. It has been reported that there is a relation-ship betw~en the Tg of the pitch and its softening point 26 as determined by the traditional method such as the ring 27 and ball method. The softening point is higher by 28 around 60C than the Tg~

29 Figure 2 depicts a glass transition tempera-ture scan for Example B in Table 7 above, 31 Table 8, below, illustrates glass transition 32 temperatures for the previous examples A-D (Table 7):

97~i~

2DSC - Data of SCT - Distillate Pitches 3 DSC - Data 4 Example Tg onset Tg point Tg Termination

5 10 177 197 220

6 11 ' 200 23~ 283

7 12 2~1 240 260

8 13 219 249 288

Claims (10)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A pitch suitable for carbon fiber manu-facture which can be spun directly into carbon fibers, comprising approximately by weight content between 80 and 100 percent toluene insolubles and approximately greater than 15 percent quinoline insolubles, said pitch having been derived from a substantially deasphaltenated fraction of a steam cracker tar, and wherein said pitch is further characterized as being relatively free of impurities and ash.

2. A pitch suitable for carbon fiber manufac-ture which can be spun directly into carbon fibers, comprising approximately by weight content between 80 and 100 percent toluene insolubles and approximately between 1 and 60 percent pyridine insolubles, and derived from a substantially deasphaltenated fraction of a steam cracker tar, said pitch being further character-ized as being relatively free of impurities and ash.

3. A process for spinning pitch directly into carbon fibers, comprising the steps of:

(a) obtaining a substantially deasphaltenated middle fraction of a feedstock which is rich in 2, 3, 4, and 5 polycondensed aromatic rings;

(b) subjecting said middle fraction to a thermal reaction in a temperature range from 420°C to 450°C to produce a pitch intermediate;

(c) removing under vacuum of 0.1 to 100 mm Hg at least a portion of said pitch inter-mediate to produce a pitch comprising approximately between 80 and 100 percent by weight of toluene insolubles; and (d) spinning said pitch directly into carbon fibers.

4. The process of claim 3, wherein said thermal reaction includes heat soaking said fraction at a temperature in an approximate range of between 420 and 450°C for a duration of approximately 4 hours at atmospheric pressure.

5. A process for spinning a pitch, directly into carbon fibers, comprising the steps of:

(a) distilling a feedstock to obtain a sub-stantially deasphaltenated middle fraction rich in 2, 3, 4, and 5 polycondensed aromatic rings;

(b) heat soaking in a temperature range of from 420° to 450°C said middle fraction;

(c) vacuum stripping under vacuum of 0.1 to 100 mm Hg said heat soaked middle fraction to remove oils therefrom, resulting in a pitch comprising 80 to 100 percent by weight of toluene insolubles; and (d) spinning said pitch directly into carbon fibers.

6. A pitch fiber made by the process including the steps of:

(a) distilling a feedstock to obtain a substantially deasphaltenated middle frac-tion rich in 2, 3, 4, and 5 polycondensed aromatic rings;

(b) heat soaking in a temperature range from 420°C to 450°C said middle fraction;

(c) vacuum stripping under vacuum of 0.1 to 100 mm Hg said heat soaked middle fraction to remove oils therefrom, resulting in a pitch comprising 80 to 100 percent by weight of toluene insolubles; and (d) spinning said pitch directly into carbon fibers.

7. A pitch for spinning directly into carbon fibers that has been derived from a substantially de-asphaltenated fraction of a steam cracker tar feedstock and having the proper rheological properties for direct spinning into carbon fibers characterized by a glass transition temperature in the approximate range of 180°C
to 250°C at atmospheric pressure.

8. The pitch of claim 7, wherein said pitch is derived from a middle fraction of a steam cracker tar rich in 2, 3, 4, and 5 polycondensed aromatic rings.

9. A pitch for spinning directly into carbon fibers that has been derived from a substantially deasphaltenated fraction of a steam cracker tar feedstock and having the proper rheological properties for direct spinning into carbon fibers characterized by a glass transition temperature in the approximate range of 180°C to 250°C, and a viscosity of less than approxi-mately 2,500 cps in a temperature range of approximately 360°C, at atmospheric pressure.

10. The pitch of claim 9, wherein said pitch is derived from a middle fraction of a steam cracker tar rich in 2, 3, 4, and 5 polycondensed aromatic rings.