CA1197206A

CA1197206A - Aromatic pitch from asphaltene-free steam cracker tar fractions

Info

Publication number: CA1197206A
Application number: CA000421066A
Authority: CA
Inventors: Ghazi Dickakian
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1982-02-08
Filing date: 1983-02-07
Publication date: 1985-11-26
Also published as: US4431512A; JPS58147490A; AU1120483A; AU549983B2; EP0086607A1; DE3371534D1; EP0086607B1

Abstract

ABSTRACT OF THE DISCLOSURE

A process and a product of the process for preparing a pitch suitable for carbon artifact manufac-ture 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 steam cracker tar feedstock. The middle fraction is rich in 2, 3, 4, and 5 polycondensed aromatic rings.
The pitch is characterized as being relatively free of impurities and ash.

Description

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1 Field of the Invention

2 The present invention relates to the process

3 for preparing a pitch used in carbon artifact manufac-

4 ture such as carbon fiber production. More particularly, the present invention relates to a process for preparing 6 a pitch with high li~uid crystal fraction from a steam 7 cracker tar distillate or a deasphaltenated steam 8 cracker tar.

g Background of the Invention As is well-known, carbon artifacts have been 11 made by pyrolyzing a wide variety of organic materials.
12 Indeed, one carbon artifact of particularly important 13 commercial interest today is carbon fiber. Hence, 14 specific reference is made herein to carbon fiber technology. Nevertheless, it should be appreciated that 16 this invention has applicability to carbon artifact 17 manufacturing generally, and most particularly, to the 18 production of shaped carbon articles in the form of 19 filaments, yarns, films, ribbons, sheets and the like.

The use of carbon fibers for reinforcing 21 plastic and metal matrices has gained considerable 22 commercial acceptance. The exceptional properties of 23 these reinforcing composite materials, such as their 24 high strength to weight ratio, clearly offset their high preparation costs. It is generally accepted that large 26 scale use of carbon fibers as a reinforcing material 27 would gain even greater acceptance in the marketplace, 28 if the costs of the fibers could he substantially 29 reduced. Thus, formation of carbon fibers for rela-tively inexpensive carbonaceous pitches has received 31 considerable attention in recent years.

115~7~'()6 1 Many materials containing polycondensed 2 aromatics can be converted at early stages of car-3 bonization to a structurally ordered optically aniso-4 tropic spherical liquid crystal called mesophase. The presence of this ordered structure prior to carboniza-6 tion is considered to be fundamental in obtaining a 7 high quality carbon artifact. Thus, one of the first 8 requirements of a feedstock material suitable for carbon g artifact manufacture, and particularly for carbon fiber production, is its ability to be converted to a highly 11 optically anisotropic material.

12 In addition, suitable feedstocks for carbon 13 artifacts manufacture, and in particular carbon fiber 14 manufacture, should have relatively low softening points and sufficient viscosity suitable for shaping and 16 spinning into desirable articles and fibers.

17 Unfortunately, many carbonaceous pitches have 18 relatively high softening points. Indeed, incipient 19 coking frequently occurs in such materials at tempera-tures where they have sufficient viscosity for spinning.
21 The presence of coke, infusible materials, and~or high 22 softening point components are detrimental to the fiber 23 making process.

24 As is well-known, pitches have been prepared from the total tars obtained from steam cracking of gas 26 oil or naphtha. In this regard, see, for example, U.S.
27 Patent Nos. 3,721,658 and 4,086,156.

28 Steam cracker tar, like other heavy aromatics, 29 is composed of a complex mixture of alkyl-substituted polycondensed aromatics. The chemical structure, 31 molecular weight and aromatic ring distribution can be 32 determined quantitatively using advanced analytical 11~7;~(~6 1 methods such as carbon and proton nuclear resonance 2 spectroscopy or mass spectrometry.

3 Steam cracker tar, like other heavy aromatics 4 such as coal tars and tars from catalytic or fluid cracking, is composed of two major parts: (1) a low 6 molecular oil; and (2) a high molecular weight fraction 7 called asphaltene, which is insoluble in a paraffinic 8 solvent. The asphaltene in steam cracker tar varies g from 10-30 wt~ depending on the type of feedstock being introduced into the cracker, the design of the cracker ll and the severity of the cracking.

12 Asphaltenes can be determined quantitatively 13 in steam cracker tar using n-heptane.

14 The two aforementioned parts of steam cracker tar, i.e., the oil and the asphaltene, vary significant-16 ly in their chemical composition, molecular weight,17 melting characteristics and most importantly their 18 coking characteristics.

19 The asphaltene presence in the steam cracker tar tends to be detrimental to carbon artifact manufac-21 ture, because it produces coke in the pitch and more 22 importantly it does not provide a pitch with a high 23 liquid crys~al content; i.e., it severely limits the 24 composition o~ the pitch.

Summary of the Invention 26 This invention features an optically aniso-27 tropic pitch which is prepared from an asphaltene-free 28 steam cracker tar middle distillate fraction by heat 29 soaking the middle distillate fraction at 420-440C
between 2-6 hours at atmospheric pressure and then 31 vacuum stripping the heat soaked mixture at temperatures , .

il9~V6 1 from 370-420C. The pitch comprises approximately 80 2 to 100~ toluene insolubles by weight and is further 3 characterized as being relatively free of impurities and 4 ash.

It is an object of this invention to provide 6 an improved pitch for manufacturing a carbon artifact.

7 It is another object of the invention to 8 provide a pitch for manufacturing carbon fibers which is g more uniform, and which is free of ash and impurities.

It is a further object of this invention to 11 provide a pitch having high toluene insolubles, and 12 which does not necessarily require Ti solvent extraction 13 prior to spinning into fibers.

14 The5e and other objects of this invention will be better understood and will become more apparent 16 with reference to the following detailed description 17 considered in conjunction with the accompanying drawings 18 Brief Description of the Drawings 19 A figure shows a graphical representation of various feedstocks including the deasphaltenated steam 21 cracker tar bottom fraction of this invention, and 22 corresponding Ti content materials derived from heat 23 soaking these feed stocksO

24 Detailed Description of the Invention Generally speaking, the steam cracker tar 26 which is used as a starting material in the process of 27 the present invention is defined as the bottoms product 28 obtained by cracking gas oils, particularly virgin gas 29 oils, such as naphtha, at temperatures of from about ~972U6 1 700C to about 1000C. A typical process steam cracks 2 gas oil and naphtha, at temperatures of 800C to 900C, 3 with 50% to 70~ conversion to C3 olefin and lighter 4 hydrocarbons, by stripping at temperatures of about 200C to 250C for several seconds. The tar is obtained 6 as a bottoms product. A gas oil is, of course, a liquid 7 petroleum distillate with a viscosity and boiling range 8 between kerosene and lubricating oil, and having a g boiling range between about 200C and 400C. Naphtha is a generic term for a refined, partly refined or 11 unrefined liquid petroleum product of natural gas 12 wherein not less than 10% distills below 175C and not 13 less than 95% distills below 240C, as determined by 14 ASTM Method D-86. Steam cracker tars typically consist of alkyl substituted polycondensed aromatic compounds.

16 Obviously, the characteristics of a steam 17 cracker tar vary according to the feed in the steam 18 cracking plant.

19 Characteristics of typical steam cracker tars obtained from the steam cracking of naphtha, gas oil and 21 desulfurized gas oil are respectively given in Table 1, 22 below:

1 Table 1 2 Physical and Chemical Characteristics of Steam Cracker 3 Tars from Naphtha, Gas Oil and Desulfurized Gas Oil Cracking 4SCT from SCT from Gas SCT from Desulfurized 5Naphtha Cracking Oil Cracking Gas Oil Cracking 6 Ex(l) Ex(2) 7 1. Physical Characteristics 8 Viscosity cst Q 210F 13.9 . 19.3 12.4 25.0 9 Coking Value at 550F (%) 12 16 24 25 Toluene Insolubles t~) 0.200 0.200 0.250 0.100 11 n-~eptane Insolubles (~) 3.5 16 20 15 12 Pour Point (C) ~5 +5 -6 +6 13 Ash (%) 0.003 0.003 0.003 0.003 14 2. Chemical Structure (by carbon and proton NMR) 16 Aromatic Carbon (ato~ %) - 65 72 71 74 17 Aromatic Protons (%) 34 42 42 38 18 Benzylic Protons (%) 40 44 46 47 C~
19 Paraffinic Protons (%) 25 14 12 15 Carbon/Hydrogen Atomic Ratio 0.942 1.011 1.079 1.144 21 3. Elemental Analysis 22 Carbon (wt%) 91.60 90.31 88.10 90.61 23 Fydrogen ~wt%) 8.10 7.57 6.80 6.60 24 Nitrogen (wt~) 0.15 0.10 0.15 0.18 Oxygen twt%) 0.20 0.22 0.18 0.19 26 Sulfur (wt%) 0.06 1.5 4.0 1.5 27 Iron (ppm) 0,003 0,003 28 Vanadium ~ppm) o.ooo 0.001 29 Silicon ~ppm) 0.001 0.00 1Table 1 ContinJed 2Phys~cal and Chemical Characteristics of Steam Cracker 3Tars from Naphtha, Gas Oil and Desulfurlzed Gas Oil Cracking 4 SCT from SCT from GasSCT from Desulfurized Naphtha Cracking Oil CrackingGas Oil Cracking 6 Ex(l) Ex(2) 7 4.Number Average Molecular Wt 295 300 3û5 315 8 5. Distillation Characteristics 9 5~ Vol 203 283 245 10% Vol 233 296 260 11 20% Vol 245 330 296 12 30% Vol 266 373 358 13 40% Vol 308 421 371 14 5û% Vol 356 470 401 60% Vol - 540 - - ~, 16 7û~ Vol - 601 - -17 77% Vol - 610 - -. ~

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

16 An ASTM D1160 distillation of a typical steam 17 cracker tar is given in Table 2, below:

18 Table 2 19Vol%Vapor Temperature Vapor Temperature 20Distillate@ 10 mm~g G @ 760 mmHg G

31 The middle fraction taken at distillate 32 370-490C @ 760 mmHg has high aromaticity and narrow ~9'72~

g 1 molecular weight. It contains no ash or solid par-2 ticulate and does not contain high coking asphaltene.
3 Chemically it is composed of polycondensed 2, 3, 4 and 5 4 aromatic rings. Table 3 below gives the physical and chemical characteristics of a typical middle distillate 6 fraction of a steam cracker tar:

7 Table 3 8 Characteristics of Steam Cracker Tar Distillate (370-490C) 9 1. Physical Characteristics Ash Content (%) = Nil 11 Asphaltene (n-heptane insolubles) (%) = Nil 12 Viscosity cps @ 99C = 4.5 13 Toluene Insolubles (%) = Nil 14 Coking Value ~ 550C (%) = 2.0 2. Chemcial Structure (CMR and PMR) 16 Aromatic Carbon (atom ~) 17 Paraffinic Protons (%?
18 Benzylic Protons (%) 19 3. Elemental Analysis Carbon (wt%) = 90.7 21 Hydrogen (wt%) = 7.3 22 Oxygen (wt%) = 0.20 23 Nitrogen (wt%) = 0.10 24 Sulfur (wt%) = 1.6 25 4. Number Average Mol. Wt (GPC) = 245 ~1~7~

l Table 3 Continued 2 Characteristics of Steam Cracker Tar Distillate (370-490C) 3 5. Aromatic Ring Distribution (MS) 4 l Ring = 3.7 2 Rings = 43.6 6 3 Rings = 39.2 7 4 Rings = ll.l 8 5 Rings = 1.5 9 6 Rings = 0.8 7 Rings = 0.1 ll Aromatics with Carbon and Hydrogen = 84.3 12 Aromatics with Carbon, Hydrogen and Oxygen = 3.7 13 Aromatics with Carbon, Hydrogen and Sulfur = ll.9 14 6. Average Carbon Atom in Side Chain = 3.0 The molecular structure of a typical steam 16 cracker tar middle distillate fraction as determined by 17 high resolution Mass Spectrometer, is given below in 18 Table 4:

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1Table 4 2Molecular Structure of a Typical 3Steam Cracker Tar Distillate 4 Compound Type Typical Name CnH2n-8 Indanes 0.6 6 CnH2n-lo Indenes 1.3 7 CnH2n-12 Naphthalenes 5.0 8 CnH2n-14 Naphthenonaphthalene 9.1 9 CnH2n-16 Acenaphthalenes 17.2 CnH2n-18 Penanthrenes 29.0 11 CnH2n-2o Naphthenophenanthrenes 8.8 12 CnH2n-22 Pyrenes 7.3 13 CnH2n-24 Chyrsenes 2.3 14 CnH2n-26 Cholanthrenes o.g CnH2n-12S Naphthenobenzothiophenes 0.4 16 CnH2n-14S Indenothiophenes 0.6 17 CnH2n-16S Naphtnothiophenes 8.5 18 CnH2n-l8s Naphthenonaphthothiophenes 0.6 19 CnH2n-20S 0.5 CnH2n-loo Benzofurans 21 CnH2n-16 Naphthenofurans 2.8 22 CnH2n-18O Naphthenonaphthofurans 0.44 23 CnH2n-20 Acenaphthyenofurans 0.2 24 Another method to prepare an asphaltene-free steam cracker tar fraction is by removing the asphaltene 26 from steam cracker tar by a solvent extraction of the 27 asphaltene with a paraffinic solvent such as n-heptane, 28 iso-octane, n-pentene, or pet-ether. Table 5, below, 29 gives the characteristics of a deasphaltenated oil obtained from a steam cracker tar using n-heptane as a 31 solvent (Feed:solvent ratio = 1:30):

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1Table 5 2The Preparation of Deasphaltenated 3Steam Cracker Tar 4Deasphaltenated 5Steam Cracker Tar Steam Cracker Tar 7 Weight t%) 100 100 80 82 8 Sp. Gr. @ 15C1.112 1.1171.0841.073 9 Coking Value @ 550C 18.1 18.8 7.8 7.3 11 viscosity ~cps) 12 @ 100F 779 925 33.0 22.2 13 Ash Content (%) 0.003 0.004 Nil Nil 14 Asphaltene (%)20.0 18.0 1.0 1.2 (n-heptane 16 insolubles) 17 Carbon (%) 87.2 86.6 86.7 87.22 18 ~ydrogen (~) 6.7 6.6 6.91 7.22 19 Oxygen (%) 0.32 0.310.46 0.21 20 Sulfur (%) 3.7 5.3 4.5 4.5 21 Aromatic Carbon 22 (atom ~) 73 72 70 71 23 C/H Atomic Ratio 1.07 1.10 1.04 1.00 24 After separating the steam cracker tar middle fraction distillate, the middle fraction distillate 26 is heat soaked at temperatures in the range of about 27 400C to 500C. Optionally and preferably, the heat 28 soaking is conducted at temperatures in the range of 29 about 390C to about 450C, and most preferably at temperatures in the range of about 410C to about 31 440C. In general, heat soaking is conducted for 32 times ranging from one minute to about twenty hours, and 33 preferably from about two to six hours. In the practice 34 of the present invention, it is particularly preferred that heat soaking be done in an atmosphere such as 119~2~

1 nitrogen, or alternatively in hydrogen atmosphere. Heat 2 soaking also may be conducted at reduced pressures in 3 the range of from about 50 to 100 m~ of mercury.

~ After heat soaking the distillate, the heat soaked distillate is then heated in a vacuum at tempera-6 tures generally about 400C and typically in the range 7 of about 370C to 420C, at pressures below atmospheric 8 pressure, generally in the range of about 1.0 to 100 mm g mercury. This additional heating removes at least part of the oil present in the heat soaked distillate.
11 Typically, from about 90 to 100% of the oil which is 12 present in the heat soaked distillate is removed.

13 As can be readily appreciated, the severity of 14 the heat soaking conditions outlined above, will affect the nature of the pitch produced. The higher the 16 temperature chosen for heat soaking, and the longer the 17 duration of the heat soaking process, the greater the 18 amount of toluene insoluble components that will be 19 generated in the pitch.

Aromatic pitch can be characterized by various 21 instrumental techniques. The aromaticity of pitch 22 prepared from steam cracker tar distillate is very high, 23 around 87~ (measured by carbon NMR). These pitches have 24 high C/H atomic ratio and contain little or no oil.

Solvent analysis is widely used to define or 26 characterize the pitch composition and/or the liquid 27 crystal fraction in the pitch. We define the pitch of 28 this invention by the toluene insolubles content (by 29 weight percent). The quinoline insolubles in the pitch is also a useful guide in defining the pitch charac-31 teristicS.

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1 The inventive process can prepare pitches with 2 a very high toluene insolubles content (80-100% by 3 weight) and low quinoline insolubles content (0.1-15% by 4 weight). This pitch content can only be produced because of the use of a middle distillate fraction which 6 has a low molecular weight and contains 2, 3, 4, and 5 7 polycondensed aromatic rings.

8 As is disclosed in U.S. Patent 4,208,267, in 9 carbon fiber manufacture, it i~ particularly beneficial to use a fraction of the pitch which is readily conver-11 tible into a deformable optically anisotropic phase.
12 Consequently, in the process of the present invention, 13 it is particularly preferred to isolate that fraction of 14 the heat soaked and vacuum stripped steam cracker distillate which is readily convertible into a deform-16 able optically anisotropic phase. The preferred 17 technique for isolating that fraction of the pitch is 18 set forth in U.S. Patent 4,208,267. Basically, that 19 process requires treatment of the pitch with the solvent system which consists of a solvent or mixture of 21 solvents that has a solubility parameter of between 8.0 22 and 9.5 and preferably between 8.7 and 9.2 at 25~C.

23 Also and more preferably when extracting a 24 fraction of a completely de-oiled pitch prepared from steam cracker tar distillate, it is preferred to use a 26 single solvent, such as toluene. The crushed or molten 27 pitch is mixed with toluene at 1:2 to 1:16 pitch/toluene 28 ratio, and the mixture is agitated for 3-20 hours at 29 room temperature. The toluene insoluble fraction is then filtered, washed and dried.

31 Examples 1-4 32 The following experimental method was used:

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1 About 600 grams of a steam cracker tar middle 2 distillate fraction was charged to an electrically 3 heated reactor equipped with nitrogen injection and 4 mechanical agitation. The feed is then heated to the desired temperature, 420-440C, under a blanket of 6 nitrogen and allowed to react at that temperature for 7 the desired time, 15 to 90 minutes, with good agitation 8 under nitrogen.

g The heat soaked mixture was then vacuum stripped at reduced pressure, 0.2-1.0 mmHg, at a liquid 11 temperature of 400-420C to remove most, if not all, 12 of the distillable oils. The vacuum stripped pitch is 13 allowed to cool under reduced pressure and discharged.
14 Results for these Examples 1-4, are listed in Table 6.

The percent quinoline insolubles in the 16 product pitch was determined by the standard technique 17 of quinoline extraction at 75C (ASTM Test Method 18 D2318/76).

19 The toluene insoluble fraction of the pitch was determined by the following method:

21 About 40 grams of the crushed pitch product 22 were mixed for 18 hours at room temperature with 320 ml 23 of toluene. The mixture was thereafter filtered using a 24 10-15 micron fritted glass filter.

The filter cake was washed with 80 ml of 26 toluene, reslurried and mixed for about four hours at 27 room temperature with 120 ml of toluene, and then 28 filtered using a 10-15 micron glass filter.

29 The filter cake was washed with 80 ml of toluene followed by a wash with 80 ml of heptane, and 1197~

1 finally the solid was dried at 120C in a vacuum for 2 24 hours 3 The above method for determining toluene 4 insolubles is hereinafter referred to as the SEP method (an achronym for the standard extraction procedure).

6 The toluene insolubles in the pitch can also 7 be determined by a one stage extraction method, by 8 simply agitating the pitch and toluene (pitch:toluene g ratio = 1:8) at room temperature for 4 hours and then filtering, washing and drying the extract.

11 The optical anisotropicity of the pitch was 12 determined by first heating the pitch to 375C and 13 then cooling the pitch. A sample of the pitch was then 14 placed on a slide with Permount, a histological mounting medium sold by the Fisher Scientific Company, Fairlawn, 16 New Jersey. A slip cover was placed over the slide by 17 rotating the cover under hand pressure. The mounted 18 sample was crushed to a powder and evenly dispersed on 19 the slide. Thereafter, the crushed sample was viewed under polarized light at a magnification of 200X, and 21 the percent optical anisotropicity was estimated.

1 Table 6 2 Preparation of Steam Cracker Tar ~ic~ A~ Pitch 3 Heat Soaking Vacuum Stripplng Pitch Composition Toluene Insoluble (SEP) C~Ld~LeListics 4 Tbluene Insolubles 6 Llquid Toluene Quinoline (One-Stage Viscosity (~) 7 n aLu~ Time Pressure 'h aLu~ % Oil Insolubles Tnco~ es Method) Cps Q Optical 8 Example (C) (hrsJ (mmHg) (CJ Removed (SEP) ~%) ~%) (%) Iq(l) C/H 360C Activity 9 1 420 4 1.0 370 11.2 50.4 1.9 256 1.8S
10 2 430 3 1.0 370 14.8 54.0 1.3 255 1.80 - -11 3 430 4. 0.2 360 12.3 80.0 8.0 95 249 1.831,393 75+
12 4 430 4 0.5 400 10.3 86.0 0.4 100 249 1.801,210 ~ 6 13 (1) Tg = Glass Transition r aLuie 1~7~

1 Referring to the illustrative Figure, various 2 feedstocks are shown including the deasphaltenated 3 steam cracker tar bottom fraction of this invention.
4 These feedstocks are shown divided into their corre-sponding percentages of useable (precursor) pitch 6 materials, and non-useable (non-precursor) pitch mate-7 rials. It is observed that when all the cat cracker 8 bottom fractions are used to obtain precursor materials, 9 only a small percentage of liquid crystal rich materials are obtained. For example, heat soaked Ashland Pitch is 11 observed to contain only approximately 25 percent Ti 12 precursor.

13 Such a pitch material must be further treated 14 to extract the useable Ti fraction. However, the problem with extracting the Ti content from such a pitch 16 material is that it is very difficult to do this without 17 also including the so-called "bad actors". In other 18 words, the impurities and ash are also carried along.
19 In addition, heat treating these low Ti materials will very often produce coke, which is detrimental to the 21 spinning process.

22 Therefore, the elimination of the "bad actors"
23 and the coke producing substances in advance of further 24 processing would not only be desirable in producing a trouble-free precursor material, but also should usually 26 eliminate the need to perform an additional extraction 27 step.

28 Thus, it is observed that a feedstock material 29 which uses only a middle fraction, i.e. distillate fractions (370-490C), of a steam cracker tar bottom, 31 will be virtually free of the "bad actors", and will 32 contain between 80 and 100% Ti after heat soaking and 33 vacuum stripping. Such precursor materials will be very 34 uniform, relatively free of ash and impurities as 1~97Z(~6 1 further defined by a low quinoline insoluble content 2 (less than 15~ by weight), and will easily lend them-3 selves to further controlled processing.

4 As aforementioned, such precursors may not require an additional extraction step for the Ti.

6 The Figure also represents similar results 7 obtained from other feedstock materials such as Steam 8 Cracker Tars (SCT~ and Cat Cracker Bottoms tCCB). When g the middle fractions of these feedstocks are separated, heat soaked, and vacuum stripped, it is observed that 11 high content Ti substances are also produced.

12 Thus, the invention is not necessarily limited 13 to the starting materials, but rather to the realization 14 of the need to prefractionate and separate the middle fractions from these materials, and to vacuum strip 16 these fractions after heat soaking at temperatures 17 generally in excess of 400C.

18 A pitch of this invention can be generally 19 defined by the following solvent analysis:

Solvent Analysis 21 Toluene insolubles wt%80-100 22 (SEP method) 23 Quinoline insolubles wt% 1.0-15 24 (ASTM D2318-66) (preferably less than 5%) Aromaticity 80-90 26 (% Aromatic carbon atom) 27 Melting point (C) 150-250 28 Glass Transition Temperature 170-220 29 (C) (Tg) Ash wt% nil-0.1 31 optical Activity 70-100 32 (% by polarized light 33 microscopy)

Claims

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

1. A pitch suitable for carbon artifact manufacture, comprising by weight content between 80 and 100 percent toluene insolubles, said pitch having been derived, by heat soaking followed by vacuum stripping, from a deasphaltenated middle fraction of a steam cracker tar feedstock which is rich in 2, 3, 4 and 5 polycondensed aromatic rings, and wherein said pitch is further characterized as being relatively free of impurities and ash.

2. The pitch of claim 1, wherein said middle fraction is a distillate fraction boiling off at temper-atures approximately between 370° and 490°C at 760 mm of mercury.

3. A pitch suitable for carbon artifact manufacture, such as the manufacture of carbon fibers, comprising by weight content between 80 and 100 percent toluene insolubles, and derived, by heat soaking followed by vacuum stripping, from a deasphaltenated middle fraction of a steam cracker tar bottom, said middle fraction being a distillate fraction boiling off at a temperature approximately between 370° and 490°C at 760 mm mercury, said pitch being further characterized as being relatively free of impurities and ash.

4. The pitch of claim 3, wherein said middle fraction is rich in 2, 3, 4, and 5 polycondensed aromatic rings.

5. A pitch suitable for carbon artifact manufacture, comprising by weight content between 80 and 100 percent toluene insolubles, said pitch having been derived, by heat soaking followed by vacuum stripping, from a deasphaltenated middle fraction of a steam cracker tar feedstock which is rich in 2, 3, 4, and 5 polycondensed aromatic rings, and wherein said pitch is further characterized as having approximately less than 15 percent quinoline insolubles by weight.

6. The pitch of claim 5, wherein said middle fraction is a distillate fraction boiling off at temper-atures approximately between 370° and 490°C at 760 mm of mercury.

7. A process for preparing a pitch suitable for carbon artifact manufacture, comprising the steps of:

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

(b) subjecting said middle fraction to heat soaking to produce a pitch intermediate;
and (c) stripping oils from said pitch intermediate to produce a pitch comprising between 80 and 100 percent by weight of toluene insolubles, and which is further characterized as being relatively free of impurities and ash.

8. The process of claim 7, wherein said heat soaking of said middle fraction is accomplished at a temperature in an approximate range of between 390° and 450°C for a duration of from 1 minute to 20 hours at 760 mm of merucry.

9. The process of claim 8, wherein said middle fraction is heat soaked at approximately 430°C
for 2 to 6 hours at 760 mm of mercury.

10. The process of claim 7, wherein said middle fraction is obtained by distilling said feedstock at a temperature in an approximate range of between 370°
and 490°C at 760 mm of mercury.

11. The process of claim 10, wherein said oils are removed by vacuum stripping said intermediate at a temperature in an approximate range of between 370° to 420°C at approximately 1 to 100 mm of mercury.

12. A process for preparing a pitch suitable for carbon artifact manufacture, comprising the steps of:

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

(b) heating soaking said middle fraction; and (c) vacuum stripping said heat soaked middle fraction to remove oils therefrom, resulting in a pitch comprising 80 to 100 percent by weight of toluene insolubles and further characterized as being relatively free of impurities and ash.

13. The process of claim 12, wherein said heat soaking step (b) includes heat soaking said middle frac-tion at a temperature in an approximate range of between 390° and 450°C for a duration of from 1 minute to 20 hours at 760 mm of mercury.

14. The process of claim 13, wherein said middle fraction is heat soaked at approximately 430°C
for 2 to 6 hours at 760 mm of mercury.

15. The process of claim 12, wherein said distilling step (a) includes distilling said feedstock at a temperature in an approximate range of 370° and 490°C at 760 mm of mercury.

16. The process of claim 12, wherein said vacuum stripping step (c) includes vacuum stripping said heat soaked middle fraction at a temperature in an approximate range of between 370° and 420°C at approximately 1 to 100 mm of mercury.

17. A process for preparing a pitch suitable for carbon artifact manufacture, comprising the steps of:

(a) distilling a steam cracker tar bottom to obtain a deasphaltenated middle fraction rich in 2, 3, 4, and 5 polycondensed aromatic rings;

(b) heat soaking said middle fraction; and (c) vacuum stripping said heat soaked middle fraction to remove oils therefrom, resulting in a pitch comprising 80 to 100 percent by weight of toluene insolubles and further characterized as being relatively free of impurities and ash.

18. A pitch suitable for carbon artifact manufacture made by the process including the steps of:

(a) distilling a steam cracker tar to obtain a deasphaltenated middle fraction rich in 2, 3, 4, and 5 polycondensed aromatic rings;

(b) heat soaking said middle fraction; and (c) vacuum stripping said heat soaked middle fraction to remove oils therefrom, resulting in a pitch comprising 80 to 100 percent by weight of toluene insolubles and further charactarized as being relatively free of impurities and ash.

19. A process for preparing a pitch suitable for carbon artifact manufacture, comprising the steps of:

(a) distilling a steam cracker tar bottom to obtain a deasphaltenated middle fraction rich in 2, 3, 4, and 5 polycondensed aromatic rings;

(b) heat soaking said middle fraction; and (c) vacuum stripping said heat soaked middle fraction to remove oils therefrom, resulting in a pitch comprising 80 to 100 percent by weight of toluene insolubles and further characterized as having approximately less than 15% by weight quinoline insolubles.

20. A pitch suitable for carbon artifact manufacture made by the process including the steps of:

(a) distilling a steam cracker tar to obtain a deasphaltenated middle fraction rich in 2, 3, 4, and 5 polycondensed aromatic rings;

(b) heat soaking said middle fraction; and (c) vacuum stripping said heat soaked middle fraction to remove oils therefrom, resulting in a pitch comprising 80 to 100 percent by weight of toluene insolubles and further characterized as having approximately less than 15% by weight quinoline insolubles.