Synthetic Aromatic Pitch - American Chemical Society

8 Synthetic Aromatic Pitch Aromatic Pitches from the Distillate Fraction of Catalytic Cracker Bottoms and Residue Fractions

G. Dickakian

Downloaded by CORNELL UNIV on June 8, 2017 | http://pubs.acs.org Publication Date: April 14, 1986 | doi: 10.1021/bk-1986-0303.ch008

Specialties Technology Division, Exxon Chemical Company, Houston,TX77029

Catalytic cracking bottoms (CCB) is a widely used aro matic feedstock for carbon production, such as aro matic pitch, carbon black and carbon fibers. The d i s t i l l a t e and residue obtained by high vacuum-distillation of catalytic cracking bottoms were converted into highly aromatic and anisotropic pitches. We used a two-stage high temperature process at 400°C. The effect of various process parameters on pitch composition and rheology was investigated. Heavy a r o m a t i c f e e d s t o c k such as t h e b y - p r o d u c t s from t h e p e t r o l e u m and c o a l i n d u s t r i e s a r e used f o r t h e p r o d u c t i o n o f a r o m a t i c p i t c h e s . The c h a r a c t e r i s t i c s o f t h e p i t c h e s produced depend on t h e c h e m i s t r y of t h e f e e d s t o c k and t h e p r o c e s s type and c o n d i t i o n s . C a t a l y t i c C r a c k e r Bottoms (CCB) which i s t h e heavy r e s i d u e from the c a t a l y t i c c r a c k i n g of p e t r o l e u m d i s t i l l a t e i s a common a r o m a t i c f e e d s t o c k used f o r s y n t h e t i c carbons and p i t c h p r o d u c t i o n . CCB, l i k e o t h e r heavy a r o m a t i c f e e d s t o c k , i s composed of a l k y l - s u b s t i t u t e d polycondensed a r o m a t i c s w i t h a v e r y wide m o l e c u l a r w e i g h t d i s t r i b u tion. CCB was f r a c t i o n a t e d i n t o s i x a s p h a l t e n e - f r e e d i s t i l l a t e f r a c t i o n s o f v a r y i n g b o i l i n g ranges and an a s p h a l t e n e - r i c h n o n - d i s t i l l a b l e r e s i d u e . C h a r a c t e r i z a t i o n o f t h e d i s t i l l a t e and t h e n o n - d i s t i l l a b l e f r a c t i o n s i n d i c a t e s i g n i f i c a n t differences i n the a s p h a l t e n e , a s h , a r o m a t i c i t y , m o l e c u l a r w e i g h t and a r o m a t i c r i n g distributions. B o t h CCB f r a c t i o n s ( d i s t i l l a t e and r e s i d u e ) were transformed i n t o a r o m a t i c p i t c h e s by a h i g h temperature t h e r m a l p r o c e s s a t atmospheric p r e s s u r e f o l l o w e d by vacuum s t r i p p i n g . A number of r e a c t i o n parameters e f f e c t i n g p i t c h y i e l d and c h a r a c t e r i s t i c s were investigated. CCB was f r a c t i o n a t e d by h i g h vacuum d i s t i l l a t i o n (100-500 m i c rons and 1 5 / 5 column) i n t o s i x d i s t i l l a b l e f r a c t i o n s w i t h b o i l i n g p o i n t s r a n g i n g from 270°C t o 520°C a t 760 mm Hg and a n o n d i s t i l l a b l e r e s i d u e ( 5 1 0 ° C + ) . The b o i l i n g c h a r a c t e r i s t i c s of t h e CCB d i s t i l l a t e f r a c t i o n s a r e g i v e n i n Table I . The p h y s i c a l and c h e m i c a l 0097-6156/86/0303-0126$06.00/0 © 1986 American Chemical Society

Bacha et al.; Petroleum-Derived Carbons ACS Symposium Series; American Chemical Society: Washington, DC, 1986.


8.

DICKAKIAN

Aromatic Pitches from Residue Fractions

127

c h a r a c t e r i s t i c s of t h e d i s t i l l a t e and r e s i d u e f r a c t i o n s a r e g i v e n i n T a b l e I I . The NMR d a t a a r e g i v e n i n T a b l e I I I and the a r o m a t i c r i n g d i s t r i b u t i o n s (by Mass S p e c t r o s c o p y ) a r e g i v e n i n T a b l e I V . The CCB f r a c t i o n s were t h e r m a l l y - t r e a t e d a t 420°-450°C a t atmos p h e r i c p r e s s u r e i n a n i t r o g e n atmosphere and t h e n vacuum s t r i p p e d (0.5-1.Omm Hg) to remove t h e u n r e a c t e d f r a c t i o n s . The p i t c h c h e m i c a l s t r u c t u r e was determined by NMR, and t h e p i t c h c o m p o s i t i o n was d e t e r mined by s o l v e n t a n a l y s i s w i t h t o l u e n e ( a t r e f l u x ) and q u i n o l i n e (at 75°C). Toluene i n s o l u b l e s were determined because i t r e p r e s e n t s a f u s a b l e p i t c h f r a c t i o n w i t h a 100% o p t i c a l a n i s o t r o p y on m e l t i n g . Three d i s t i l l a b l e f r a c t i o n s (Numbers 4, 5, and 6, i n T a b l e I ) were t h e r m a l l y - t r e a t e d a t t h e same c o n d i t i o n s (430°C f o r 3 h o u r s ) to i n v e s t i g a t e t h e e f f e c t of t h e a r o m a t i c r i n g d i s t r i b u t i o n of the f r a c t i o n on t h e p i t c h y i e l d and c o m p o s i t i o n . We found t h a t i n c r e a s i n g t h e number of 4, 5, and 6 a r o m a t i c r i n g s r e s u l t s i n i n c r e a s i n g the p i t c h y i e l d and t h e r a t e of t o l u e n e i n s o l u b l e s f o r m a t i o n . The y i e l d and c o m p o s i t i o n of p i t c h e s prepared from d i s t i l l a t e f r a c t i o n s , Numbers 4, 5, and 6 a r e g i v e n i n T a b l e V . D i s t i l l a t e f r a c t i o n Number 4 (from T a b l e I ) was t r e a t e d a t 430°C f o r v a r y i n g time ( 3 , 4, and 5 h o u r s ) . Increasing reaction time l e d to i n c r e a s i n g p i t c h y i e l d and the r a t e of t o l u e n e i n s o l u b l e s f o r m a t i o n , but not q u i n o l i n e i n s o l u b l e s . Table VI gives the y i e l d and c o m p o s i t i o n of p i t c h e s prepared from d i s t i l l a t e f r a c t i o n Number 4 . The temperature used f o r t h e t h e r m a l t r e a t m e n t i s a v e r y i m p o r t a n t f a c t o r i n the d e a l k y l a t i o n , p o l y m e r i z a t i o n , and c o n d e n s a t i o n of the polycondensed a r o m a t i c m o l e c u l e s . The e f f e c t of t e m p e r a t u r e on t h e t o l u e n e and q u i n o l i n e i n s o l u b l e s f o r m a t i o n was i n v e s t i g a t e d u s i n g two of the h i g h e r b o i l i n g d i s t i l l a t e f r a c t i o n s (Numbers 5 and 6 from T a b l e I ) . We found t h a t i n c r e a s i n g t h e t h e r m a l t r e a t m e n t temperature l e d to I n c r e a s i n g t h e p i t c h y i e l d and the r a t e of t o l u e n e and q u i n o l i n e i n s o l u b l e s f o r m a t i o n . T a b l e V I I p r e s e n t s d e t a i l s of t h e t h e r m a l t r e a t m e n t of d i s t i l l a t e f r a c t i o n s Numbers 5 and 6, a t 420°C, 430°C, 440°C and 450°C. F i g u r e s 1, 2 and 3 i l l u s t r a t e g r a p h i c a l l y t h e e f f e c t of temperature on p i t c h y i e l d , and t o l u e n e and q u i n o l i n e i n s o l u b l e s f o r m a t i o n , r e s p e c t i v e l y . The u n d i s t i l l a b l e CCB r e s i d u e r e m a i n i n g a f t e r s e p a r a t i n g t h e d i s t i l l a b l e f r a c t i o n s from CCB has d i f f e r e n t c h a r a c t e r i s t i c s i n c o m p a r i s o n to the d i s t i l l a t e . The CCB r e s i d u e has a h i g h e r b o i l i n g p o i n t ( 5 1 0 ° C ) , h i g h a s h c o n t e n t , h i g h e r a s p h a l t e n e c o n t e n t (around 20 w e i g h t %), h i g h c o k i n g c h a r a c t e r i s t i c s (26-36% coke y i e l d a t 5 5 0 ° C ) , h i g h e r average m o l e c u l a r w e i g h t (339) and h i g h e r a r o m a t i c r i n g d i s t r i b u t i o n (6+ a r o m a t i c r i n g s ) . A c o m p a r i s o n of t h e c h a r a c t e r i s t i c s of a C C B - d i s t i l l a t e f r a c t i o n and C C B - r e s i d u e i s g i v e n i n Table V I I I . C C B - r e s i d u e was t h e r m a l l y - t r e a t e d a t 420°C f o r t h r e e hours a t a t m o s p h e r i c p r e s s u r e i n a n i t r o g e n atmosphere and t h e n vacuums t r i p p e d a t 1.0 mm Hg t o produce a p i t c h i n a v e r y h i g h y i e l d . We found t h a t u s i n g C C B - r e s i d u e as a feed f o r the t h e r m a l - t r e a t m e n t resulted i n : (a) p r o d u c i n g a p i t c h i n a v e r y h i g h y i e l d (63.2% v s . 2 4 . 5 % when using a d i s t i l l a t e feed). (b) C C B - r e s i d u e p i t c h has h i g h e r c o n t e n t o f t o l u e n e I n s o l u b l e s (32.0% v s 18.0% when u s i n g a d i s t i l l a t e f e e d ) .


128

PETROLEUM-DERIVED CARBONS

(c)

C C B - r e s i d u e p i t c h has h i g h e r q u i n o l i n e i n s o l u b l e s : toluene i n s o l u b l e s r a t i o t h a n C C B - d i s t i l l a t e p i t c h (about 10 times higher). A c o m p a r i s o n of the c o m p o s i t i o n of p i t c h e s produced from C C B - d i s t i l l a t e and r e s i d u e ( a t the same c o n d i t i o n s ) i s g i v e n i n T a b l e IX. I n c o n c l u s i o n , t h e a s h - f r e e and a s p h a l t e n e - f r e e CCB d i s t i l l a t e f r a c t i o n s provide a p o t e n t i a l aromatic feedstock f o r p r o d u c i n g h i g h l y a r o m a t i c and h i g h l y a n i s o t r o p i c p i t c h e s w i t h a h i g h t o l u e n e i n s o l u b l e s and low c o n t e n t of the h i g h m o l e c u l a r w e i g h t and infusible quinoline insolubles.


Table I .

D i s t i l l a t i o n C h a r a c t e r i s t i c s of C C B - F r a c t i o n s Boiling Point (°C/760mm Hg)

CCB-Fraction D i s t i l l a t e No. 1 D i s t i l l a t e No. 2 D i s t i l l a t e No. 3 D i s t i l l a t e No. 4 D i s t i l l a t e No. 5 D i s t i l l a t e No. 6 N o n - D i s t i l l a b l e Residue

Table I I .

271 400 427 454 471 488 510+

Wt.% of CCB Feed

400 427 454 471 488 510

10.0 23.8 13.3 11.7 13.4 10.0 17.5

C h a r a c t e r i s t i c s of C C B - F r a c t i o n s Distillates

No. 4 A s p h a l t e n e s (n-Heptane) n i l i n s o l u b l e s ) (Wt.%) A s h (Wt%) 0 .0004 Number Average M o l . Weight 269 Carbon/Hydrogen Atomic R a t i o 0.88 Coking Y i e l d at 550°C (Wt.%) nil Coking Y i e l d a t 1000°C(Wt.%) nil

No. 5 nil

No. 6 nil

Non-Distillable Residue 22.0

0.0005

0.0004

0.110

285

291

339

0.87

0.94

1.05

nil

nil

32.4

nil

nil

17.0


8.

DICKAKIAN

Table I I I .

Chemical S t r u c t u r e of C C B - F r a c t l o n s Diiï t i l l a t e s

NMR - D a t a


A r o m a t i c Carbon Aromatic Protons B e n z y l i c Protons

(%) (%) (%)

T o t a l A l i p h a t i c Protons

Table I V . Aromatic

129


(%)

Non-Distillate Residue

No. 4

No. 5

No. 6

62.5 26.4 27.6

62.8 25.7 28.5

65.8 26.7 28.8

68.8 35.4 31.6

46.0

45.8

45.3

32.9

A r o m a t i c R i n g D i s t r i b u t i o n s of C C B - F r a c t l o n s

Rings

2 rings 3 rings 4 rings 5 rings 6+ r i n g s 3+4 rings 4+5 rings 3 + 4 + 5 rings

Distillates Non-Distillable Residue No. 6 No. 4 No. 5 9.4 25.1 50.1 12.2 1.1 75.2 62.3 87.4

17.0 35.7 42.0 3.1 0.6 77.7 45.1 80.8

14.0 15.2 31.0 15.7 9.0 46.2 46.7 61.9

10.4 28.6 47.6 8.7 2.2 76.2 56.3 84.9

Table V . Aromatic P i t c h P r o d u c t i o n from C C B - F r a c t i o n s E f f e c t of D i s t i l l a t e F r a c t i o n B o i l i n g C h a r a c t e r i s t i c s

Distillate Fraction B o i l i n g Range No. (°C/760mm Hg) 4 5 6

454 - 471 471 - 488 488 - 510

Thermal Treatment Pitch Temp. Time Yield (°C) (Hrs.) (%) 430 430 430

3 3 3

19.0 25.0 31.5

P i t c h Composition Toluene Quinoline Insolubles Insolubles (%) (%) 38.0 42.0 45.8


0.4 0.5 0.7

130


Table V I .

A r o m a t i c P i t c h P r o d u c t i o n from Effect


Distillate Fraction No. 4 4 4

Pitch Yield (%)

430 430 430

18.0 21.0 27.6

3 4 5

Pitch Toluene Insolubles (%)

Composition Quinoline Insolubles (%)

41.5 51.0 63.5

A r o m a t i c P i t c h P r o d u c t i o n from Effect

Distillate Fraction No.

of R e a c t i o n Time

ThermalTreatment Temp Time TC) (Hrs.)

Table V I I .

CCB-Fractions

0.5 0.8 1.2

CCB-Fractions

of R e a c t i o n Temperature

ThermalTreatment Temp. Time (°C) (Hrs.)

Pitch Yield (%)

Pitch Toluene Insolubles (%)

Composition Quinoline Insolubles (%)

5 5 5 5

420 430 440 450

3 3 3 3

22.5 25.0 32.0 36.6

27.0 40.0 61.5 73.0

0.1 0.3 1.3 4.5

6 6 6

420 430 440

3 3 3

24.4 31.4 37.1

37.0 55.0 73.0

0.2 0.4 10.5


8.

DICKAKIAN

131


Table V I I I . Comparison of t h e C h a r a c t e r i s t i c s of CCB D i s t i l l a t e and Residue


CCB-Distillate B o i l i n g Range (°C/760mm Hg) A s p h a l t e n e s (Wt%) η-Heptane I n s o l u b l e s (Wt.%) C o k i n g Y i e l d @ 550°C (Wt%) C o k i n g Y i e l d @ 550°C (TGA) A r o m a t i c Carbon Atom (%) Carbon/Hydrogen Atomaic R a t i o Number Average M o l . Weight % M o l e c u l a r Weight (225 - 400) % Aromatic Rings ( 3 + 4 + 5 r i n g s )

Table I X .

CCB-Residue

471 - 488

510+

nil nil nil 65 0.87 285 94 87

18 - 22 26 - 32 12 - 17 69 1.05 339 77 10

A r o m a t i c P i t c h P r o d u c t i o n from CCB D i s t i l l a t e and Residue

Feed

Thermal Treatment Temp. Time (°C) ( H r s . )

Distillate Residue

420 420

3 3

Pitch Yield (%) 24.5 63.2

P i t c h Composition Toluene Quinoline Insolubles Insolubles (%) (%) 18.0 32.0


0.3 7.4



132

TEMPERATURE IN DEGREES CENTIGRADE

F i g u r e 1.

E f f e c t o f temperature on p i t c h y i e l d .

TEMPERATURE IN DEGREES CENTIGRADE

Figure 2.

E f f e c t o f temperature on t o l u e n e i n s o l u b l e s f o r m a t i o n .


8.

DICKAKIAN


133


DISTILLATE FRACTION #5

5 +

420

Figure

3.

430 440 TEMPERATURE IN DEGREES CENTIGRADE

E f f e c t o f temperature on q u i n o l i n e

450

insolubles

formation.

RECEIVED September 10, 1985


Synthetic Aromatic Pitch - American Chemical Society

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