CA1173772A - Aromatic pitch - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A novel process is described for preparing an aromatic pitch having a high liquid crystal fraction and being suitable for the manufacture of carbon articles such as for the manufacture of pitch carbon fiber.

Description

~737~

Aromatic pi'cches such as coal ~ar pitch or petrol-

2 eum pitch are made of a comlplex mixture of al3cvl-substituted

3 polycondensed axomatics having a high desree of aromatic

4 ring condensation (as e~tidenced by the carbon/hydrogen

5 atomic ratio). C~ne simple method to charac~erize these

6 pitches is by the use of solvent analysis, for example,

7 the degree o~ insolubility in benzene, toluene, pvridine, ~ ~uinoline, or anthracene. For the pur~oses of the present 9 in~ention, aromatic pitches are characterized by t.'leir 1~ insolubilities in toluene and c~uinoline.
11 The solubility analysis for determining quinoline 12 insolubles is conducted according to ASTM D 2318-66; the 13 solubility analysis for determining toluene insolubilities 1~ is conducted by mixing 40 grams of a sample in 320 ml of 15 toluene over an 18-hour time period, filtering, washing 16 the insolubles in additional toluene, drying, and calculat-17 ing the yield of insolubles as a percentage of initial 1~ sample.
lS The production of a highly aromatic pitch which ~0 will yield a non-ordered, isotroPic carbon has previously 21 been described in my United States Patent No. 3,721,658.
22 ~ore particularly, this patent describes a process for 23 prepari~g an aromatic pitch by the catalytic air oxidation 24 of an aromatic feedstock such as st~ cracked tar, at a 25 temperatura of 240-260C. This pitch has low toluene in-26 solubles (about 15%) and ~ery low quinoline insolubles.
27 ~3ecause of the chemical structure o~ the pitch, and not 28 because of the toluene or quinoline insolubles content, 29 ~his pitch on melting or carbonizing will yield a highly 30 isotro~ic carbon.
31 A~other exam~le of aromatic pitch l~roduction may 32 be found in United States Patent No. 4,086,156. This pat-33 ent describes a method for preparing an a-omatic ~itch by 34 the ~hermal treat.nent o~ steam crac~ser tar in the absence 35 of oxvgen a~d at a t~nperature of 380-390C. The pitch 36 obtained by this method contains a low concentration of ~73~Z

1 toluene and quinoline insolubles and will produce an iso-2 tropic carbon on melting or carbonizing.
3 In addition, my U.S. patent 4,271,006 discloses 4 the production of an aromatic, low Ti pitch. However, this 5 pitch requires a two-stage extraction process in order to 6 prepare carbon precursor.
7 Accordingly, the process of the present invention

8 describes a method of preparing a highly polycondensed aro-

9 matic hydrocar~on pitch.w~t~ a defined composition ~y ~h~
0 catalytic or ~on-catalyt;c thermal trea~ment of a low molecular weight feed comprised of alkyl-substîtuted poly-condensed hydrocar~on aroma~ic fraction obtained from cata-3 lytic cracking resid~e (cat crac~er bottoms or CC~l having 4 a spec~ic c~emical and molecuIar structure~
The important feature of t~e pitc~ produced ~y the method according to the present invention is t~at it proauces carbon on melting or car~onization with anisotrop-ic structure, that is,an ordered or crystalline structure, as determined ~y meas~ ing t~e optical activity~ of the car-21 ~on via polarized light micros~opy. T~is type of pitch is 22 use~ul ~or the production of car~on products wi ~ aniso-23 tropic structure such as pitcE~ carE~on fiBer or needle co~se.
24 ~ore particularly, the process of ~e present 25 in~ention specifically descri~es a me ~od to prepare a low 26 softening point C200-300CL aromatic pitc~i wit~i a de'inite 27 composition. T~e p~tc~ maae in accordance with the pres-28 ent invention contains a ~i:g~ toluene insolu~Sle content 29 C5Q-~Q weight ~ercent~ and a high quinoline insolu~}e con-30 ~ent ua-6Q weight pe~cent~ The high content s:f toluene 31 and quinoline insoluEles is desired in this pitcEi (~IQ
32 pitch~ as thi~ fraction is essential for development o~ an-33 isotropic st~ucture wnen melting or car~onizing ~e pitch ~377~.

1 in an inert atmosphere.
2 Not all aromatic compounds containing polycon-3 densed aromatic rings are suitable for the production of 4 ~T~Q pitch with the desired composition and characteris-S tics. For example, coal tars from the high temperature 6 car~onization o~ coal, steam cracker ~ar from the steam 7 cracking of ~as oil or naphtha, or coal tar from coal gas-8 ification or liquefaction are highly aromatic and composed 9 of polyconde~sed aromatics but are not suitable for the production of ~T~Q pitch because they do not have the de~
11 sired chemical and moleculzr structure needed. According-12 ly, the prodllction of an aromatic pitch which will yield a 13 highly ordered anisotropic structured carbon requires a 14 specific polycondensed aromatic feed with a definite chem-ical and molecular structure.
16 U.S. Patent No. 4,005,183, for example, describes 17 the produc~ion of pitch with hi~h guinoline insolubles by 18 the atmospheric heat soaking of a high softening point 19 (110-115C) petrole~m pitch. The procPss described in U.S.
Patent No. 4,005,183 requires a feed which is physically, 21 chemically, and thermally diffexent from CCB or fractions 22 which are mainly low molecular weight polycondensed aro-23 matics. The present invention's three-stage process is 24 also di~feren~ from the process desc_ibed in U.5. Patent No. 4,005,183, which is done by heating a petroleum pitch 26 at 400C for 32 hours at atmospheric pressure until the 2~ high quinoline insolubles content is formed in the pitch.
28 Table I illustrates the chemical and physical differences 29 between petroleum pitch and cat cracker bottom feedstock.

~ 7 ~72 1 ~BLE I
2 PetroleumCCB Vacuum 3 PitchDistillate Strip~ed CCB
4 Toluene Insolu~les (%) 10 0 0 5 Softening Point, C 122 Liquid 20-4a 6 Arom2tic Car~on 7 (atom %) 84 55-65 55-65 8 Coking Value at 9 5;0C (wt.%) 56 0 14

10 Asphaltene Content,

11 wt.% ~n-heptane

12 insolubles) 70 0 4

13 Car~on/~ydrogen

14 Atomlc Ratio 1.5 0.g5 1.0 A suita~le aromat~c feea for ~e production of 16 RT~Q pitc~, as noted a~ove, ~s t~e aromatic residu~ o~tained 17 from the cracking of refinery distillates. This residual 18 feedstcck, called cat cracker ~ottoms CCCBI, reers to 19 that fraction of the product of t~e cat cracking proce~s which boils in t~e range o~ fro~ a~out 20a to a~out SQQC, 21 and i5 presently a by-~roduct residue. Its chemical struc-22 ture can be defined ~y quantitatively measuring its car~on 23 and proton nuclear magnetic resonance spectroscopy (CMR and 24 NMR); a typical distribution is given in Ta~le II.
.

Ta~L~ II
26 Ca~o~ and P~oton Distri~t~on of 3 27 Aromatic car~on (atom %1 55-65 28 Aromatic protons (~1 24-35 29 Ben~ylic protons ~%j 27-31 Para~f~ic protons ~ 47~33 31 ~ore particularly, t~e specifications ~or a ty~i~
32 cal cat crac~er ~ottomsthat is 2 suita~le eedstoc~ ror the 33 present in~ention are given in Table III.

~ 3 f ~
- s -TABLE III
2 ~tlarac~eristics of Cat Crac~ce~ 3Ot~oms .__ 3 ~hysical C~a~ ac,eris~ics 4 Viscosity cst at 210C 1. 0-10 0 As'n Con'cent, ~t % O . 010-2 . O
6 Coking Value (wt ~ at 550C) 6.U-18.0 7 Asphaltene l(n-heptane i~solubles), % 0.1-12.0 8 Toluene In~ les (0 - 35~ Q . 010-1. 0 9 Num~er ~verage Mol. wt:. 220-2~0 Ele:mental ~nalysis 11 Carbon, ~ 88 . 0-90 . 32 12 ~ydrogen, ~6 7. 74-7. 4C
13 Oxygen, % 0.10-0.30 14 Sulfur, ~ - 1.0-~.5

15 Car~on/Hydrogen Atomic Rat~o ~90-l.Q

16 Chemic21 Analysis by Proton NM~

17 ~romatic Carbcn ~atom %) 5;-65

18 Aro~2tic R~n~ Distribution (by Mass Spectroscopy)

19 ~ g (96) 102

20 2 Rin~s ~96) 23. 6

21 3 ~i~ss ( % ) 3 7 . 5

22 4 Rinss (~) 31. 8

23 5 ~ings (%) 3. 8

24 6 ~ings ~)

25 Molecular ~ight Dis'~ri~ution (bv Mass S~ectrosco~y)

26 175 200 ~%) 2 D 9

27 200-225 (~) 13.4

28 225-2~0 (%) 29.

29 ~50-275 (~) 23.

30 27~-300 ~) 15.5

31 300-325 (%) ~-

32 32~-350 (%)

33 Composition by Clay-Silica G21 Chromatography

34 Aromatic, ~ 62 . 2

35 Saturat~, % 17. O

36 Polar, % 18. 3 ~73~

~lthough the total cat cracker bottoms fraction can be used as feedstock Eor the manufacture of the aromatic pitch according to my invention, this would require the thermal treatment of the feedstock -to be carried out under pressure; this requires the cost of equipment capable of operating under pressure.

One method of performing the required thermal treatment under atmospheric pressure is by first removing the low boiling point fraction, that is, the fraction which boils below the desired thermal treatment temperature. This can be carried out using various methods, such as (1~ by the vacuum stripping of cat cracker bottoms at - elevated temperatures and reduced (1~100 mm Hg) pressures or (2~ by the fractional distillation of cat cracker bottoms at elevated temperatures, for example, between 200 and 300C, and reduced pressures, for example, between 200-500 microns of mercury. Fractional distillation results in either a single or several distillate fractions and a residue referred to as CCB
residue which is that fraction not distillable at temperatures of up to 530C and at a pressure of about 350 to 450 microns of mercury. The distillate fraction has a boiling point in the range of from about 500F to about 1000 F.

The CCB distillate and CCB residue obtained by fractionation are highly aromatic, being composed of poly-condensed aromatics, but vary in their molecular weight, aromatic ring distribution~
and coking characteristics. The following Table 4 graphically summarizes some of these differences.

~l7~77~2 1 T~B~ rv 2 Charac~eris-ics of CCB Distiliate and ~esidue 4 Distillate Residue Aromatic Car~ons (a~om~
6 ~y NMR) 62 68 7 ~olecular Weight 270 329 8 Aromatic Ring Distribution 9 2 rings ~%) 12 0 3 rings (~) 29 0 11 4 ring~ 46 0 12 5 rings (%) 8 0 13 6 rings+(~) 1 10 14 The CCB distillate is composed o aromaticshaving 3, 4, and 5 aromatic rings polycondensed with hydrogen and 16 carbon as the main component, and also containing (but to 17 a lesser extent) polycondensed aromatics with polar atoms 18 such as sulfur or oxygen. Typical of thë polycondensed 19 aromatic compounds found în CCB feed or distillate are napthenonaphthalene,acenap~h nes, phenanthrene, naphtheno~
21 phenanthrene, pyrenes, chrysenes, cholanthrenes, benzopyr-22 enes, indothiophenes, naphthothiophenes, naphthano-naphthothio-23 phenes, acenaphthylene-thiophenes, and anthracenothiophenes 24 I have discovered tnat there are several process variations which can ~e used to transform CCB or its frac-26 tions into a ~T~Q pitch with tie desired composition. For 27 example, ~THQ pitch may ~a made by a thermal treatment at 28 high temperatures o~ CCB feedstoc~ under atmospheric, 2~ or Eigh pressure, and ~urthermore such treabment m~
30 be in the presence or absence of a catalyst (sucn as a 31 Priedel-Crafts catalyst), and in the presence of an inert 32 or hyd~ogen atmosphere. Because of the economic savings 33 invol~ed, my preferred process is to carry out the process 34 o~ this invention at atmospheric pressure in an inert at-mosphere such as ~itrocen.
36 . In general, my~invention can be considered to be

37 composed of a three-stage process for the production of a 3~7Z

HTHQ pitch. This process requires high temperatures in the range of about 380 to about 450C. The required temperature is, of course, dependent upon the CCB fraction used as a feedstock, and whether or not a catalyst is presenk. When CCB distillate is used as the feedstock, for example, temperature in the range of about 420 to about 450C is required; when CCB residue is used as a feedstock, temperature in the range of about 380 to about 440C is required. The treatment of the CCB distillate fraction can be carried out in a temperature range of from about 400C to about 450C and for a period of time ranging from 30 minutes to 1200 minutes.

The first stage of my process comprises the vacuum stripping or fractional distillation of CCB at elevated temperatures. The second stage comprises the thermal treatment of the vacuum stripped CCB or CCB distillate at a high temperature of about 380 to about 450C. This treatment may be carried out under atmos-pheric pressure, high pressure, or low pressure. In addition, the treatment may be carried out in the absence or presence of a suitable aromatic condensation catalyst. Such catalysts are well known in the art as being Friedel-Crafts catalysts such as anhydrous aluminum chloride or anhydrous ferric chloride. The treating can be conducted in the presence of a catalyst and in a temperature range of about 370C to 400C. The third and last stage of my inVention comprises the vacuum stripping of the thermally treated mixture from stage two at a low temperature of about 300 to about 360C, and at a pressure of about l to about 5 mm of mercury. The objective of this stage is to remove all un-desirable oils thus concentrating and increasing the liquid crystal fraction, that is,Ti and Qi in the pitch. To accomplish this, the u~e of the low temperature is critical at this stage.

To be more specific, in the laboratory experimental pro-cedure to prepare HTHQ pitch, the total CCB is vacuum stripped ~L~73~

or fractionally distilled at elevated temperatures to prepare the desired fraction of CCB. The desired frackion is then thermally treated under atmospheric pressure conditions, and in the presence or absence of a catalyst (continuous agitation of the fraction at this time will avoid coke formation). After treatment, the temperature of the mixture is rapidly lowered to around 300C and the pressure is reduced to about 1 to about 10 mm Hg, after which the temperature is increased slowly, with agitation, to about 360 to about 370C to remove at least 1% of the distillable oil from the mixture, preferably more than 10~. The mixture is then cooled to room temperature under reduced pressure or under nitrogen atmosphere.
Alternatively, the thermal treatment stage can also be carried out under reduced (10-200 mm Hg) pressure. The treating can be carried out in a temperature range of about 400C to about 450C, and 10-200 mm Hg for a period of time ranging from about 30 minutes to about 600 minutes. In this instance, when the thermal treatment is completed, the mixture is cooled to room temperature under reduced pressure or a nitrogen atmosphere.
The time required to produce HTHQ pitch is dependent on the temperature used during the thermal treatment of the CCB fraction.
Generally, the higher the temperature of the thermal treatment, the shorter is the time required to produce a HTHQ pitch. The desired time and temperature required to produce a HTHQ pitch depends on the CCB fraction. When using a CCB residue which has a higher molecular weight and aromatic ring distribution than the CCB distillate, less time and lower temperature will be required to produce a HTHQ pitch.
It is believed that one of ordinary skill in the art can, using the preceding description, utilize the present invention to its fullest extent. The following specific embodiments are, therefore, to be construed as merely illustrative of this invention, and are not meant to limit the remainder of the speci-fication and claims in any way whatsoever.

~73~2 - 9a -Examples 1-4 illustrate the production of HTHQ pitch, according to the present invention by the atmospheric thermal treatment of vacuum stripped CCB;
Examples 5-8 illustrate the production of HTHQ pitch, according to the present invention, by the atmospheric heat soaking of a CCB distillate fraction;
Example 9 illustrates the production of HTHQ pitch, according to the present invention, by the vacuum heat soaking of vacuum stripped CCB; and Example 10 illustrates the production of ~THQ pitch, accord-ing to the present invention, by the catalytic heat soaking of a vacuum stripped CCB fraction.

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1 From the foregoing descri~tion one s~illed in 2 the art can easily ascertain the essential characteristics 3 of this invention and wi~hout departinq from the spirit and 4 scope ~heraof can make various changes and/or modifications to the invention for adaDting it to various usages and con-6 ditions. Accordingly, such changes and modifications are 7 properly intended to be within the full range of equiva-8 lents of the following claims.
9 ~aving thus described my invention and .he manner and process of making and using it in such full, clear, 11 concise and exact terms as to enable any ~erson skilled in 12 the art to which it pertains, or with which it is most near-13 ly connected, to make and use the same, and having setforth 14 the best modes for carrying out my invention:

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Claims (11)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for the preparation of an aromatic pitch suitable for manufacturing a carbon product with an anisotropic structure comprising:
providing a cat cracker bottom;
distilling said cat cracker bottom to obtain a distillate fraction, said distillate fraction having a boiling point in the range of from about 500°F to about 1000°F;
treating said fraction at a temperature within the range of about 380°C to about 450°C for a period of time effective to produce an aromatic pitch containing a toluene insoluble content of 50 to 90 weight percent and a quinoline insoluble content of 10 to 60 weight percent; and stripping said treated fraction to remove a portion of the distillable oil from the treated mixture.

2. The process of claim 1 wherein said treating is carried out in a temperature range of about 400°C to 450°C and for a period of time ranging from 30 minutes to about 1200 minutes.

3. The process of claim 1 wherein said treating is conducted in the presence of a catalyst and in a temperature range of about 370°C to 400°C.

4. The process of claim 1 wherein said thermal treatment is carried out in an inert atmosphere.

5. The process of claim 1 wherein said thermal treatment is carried out in a hydrogen atmosphere.

6. The process of claim 3 wherein the catalyst is a Friedel-Crafts catalyst.

7. The process of claim 1 wherein said treating is carried out in a temperature range of about 400°C to about 450°C, and 10-200 mm Hg for a period of time ranging from about 30 minutes to about 600 minutes.

8. The process of claim 1 wherein the stripping is vacuum strip-ping at a temperature range of about 300°C to about 370°C, and at about 1 to about 10 mm of mercury, said stripping removing at least 1% of distillable oil up to about 10% or more.

9. A polycondensed aromatic hydrocarbon pitch having a toluene insoluble content of 50 to 90 weight percent, a quinoline in-soluble content of 10 to 60 weight percent, and further characterized in that said pitch develops an anisotropic carbon structure upon melting or carbonization.

10. The process of claim 11 wherein more than 10% of the distillable oil is removed by vacuum stripping.

11. The process of claim 1 wherein treatment is carried out at atmospheric pressure.