The Influence of Chain Length in Hydrocracking ... - ACS Publications

1 T h e Influence o f C h a i n Length in H y d r o c r a c k i n g and Hydroisomerization o f n-Alkanes

Downloaded by 117.255.212.18 on March 1, 2016 | http://pubs.acs.org Publication Date: June 1, 1975 | doi: 10.1021/bk-1975-0020.ch001

JENS WEITKAMP Engler-Bunte-Institute, Division of Gas, Oil, and Coal, University of Karlsruhe, D-75 Karlsruhe, West Germany Since 1960 catalytic hydrocracking has received considerable importance in petroleum refining where it is used mainly for the production of gasoline, jet fuel, middle distillates and lubricants. Its outstanding advantages are flexibility as well as high quality of the products. In the course of its commercial growth the chemistry of hydrocracking over various types of bifunctional catalysts has been scrutinized with model hydrocarbons, most commonly with alkanes. Several reviews on this subject are now available (1-3) showing that the product distributions are markedly influenced by the relative strength of hydrogenation activity versus acidity of the catalyst. A unique type of hydrocracking associated with an utmost degree of product flexibility may be attained with bifunctional catalysts of both high acidity and especially high hydrogenation activity which have been counterbalanced carefully. The term "ideal" hydrocracking has been introduced (2) to characterize the reactions of n-alkanes with hydrogen on such catalysts. Typical features of ideal hydrocracking of long chain alkanes include: 1. low reaction temperatures 2. the possibility of high selectivities for isomerization 3. the possibility of pure primary cracking all being in contrast to catalytic cracking over monofunctional catalysts. Actually, both reactions may be looked upon as pure mechanisms of cracking with many intermediate mechanisms between them. Such a concept has been shown to be fruitful for classifying the numerous types of product distributions observable in hydrocracking of pure compounds over bifunctional catalysts with a hydrogénation activity ranging from very weak to very strong (2, 3). The validity of this concept for hydrocracking real feedstocks has also been confirmed, e. g., by Coonradt and Garwood (4) or by Sullivan and Meyer (5). 1 In Hydrocracking and Hydrotreating; Ward, John W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.


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HYDROCRACKING AND HYDROTREATING

O t h e r p u r e m e c h a n i s m s of c r a c k i n g a r e t h e r m a l c r a c k i n g and hydrogenolysis over metals. V e r y detailed investigations on p l a t i n u m c a t a l y z e d h y d r o g e n o l y s i s of v a r i o u s a l k a n e s , e. g . , the i s o m e r i c h e x a n e s , have b e e n p u b l i s h e d r e c e n t l y (6-8). I d e a l h y d r o c r a c k i n g and h y d r o i s o m e r i z a t i o n of n - d o d e c a n e f u r n i s h e d m u c h i n s i g h t into the p r i m a r y r e a r r a n g e m e n t and c l e a v a g e r e a c t i o n s of a l k y l c a r b e n i u m i o n s (9). T h e s y s t e m s e e m s to be s t r o n g l y g o v e r n e d b y c o m p e t i t i v e c h e m i s o r p t i o n at the a c i d i c s i t e s and, to a l e s s e r d e g r e e , at the h y d r o g e n a t i v e s i t e s (10). It i s the i n t e n t i o n o f the p r e s e n t p a p e r to extend t h e s e data that s e e m to be of p r i n c i p l e s i g n i f i c a n c e f o r the c h e m i s t r y of c a t a l y t i c c o n v e r s i o n of h y d r o c a r b o n s , to the l o w e r m o l e c u l a r weight n - a l k a n e s . In l i t e r a t u r e o n h y d r o c r a c k i n g s o m e r e s u l t s have b e e n r e p o r t e d c o n c e r n i n g r e a c t i v i t i e s of and p r o d u c t d i s t r i b u t i o n s f r o m n - a l k a n e s of d i f f e r e n t c h a i n l e n g t h (11, 12). H o w e v e r , as a c o n s e q u e n c e of the c a t a l y s t s u s e d , h y d r o c r a c k i n g i n t h e s e cases was far f r o m being i d e a l . Experimental T h e e x p e r i m e n t s w e r e c a r r i e d out i n a s m a l l flow type f i x e d b e d r e a c t o r w h i c h has been d e s c r i b e d i n a r e c e n t p u b l i c a t i o n (9) a l o n g w i t h the m e t h o d s of a n a l y s i s by c a p i l l a r y g a s - l i q u i d c h r o m a t o g r a p h y . R e s u l t s a r e r e p o r t e d that w e r e g a i n e d w i t h a l l p u r e n - a l k a n e s r a n g i n g f r o m n - h e x a n e to n - d o d e c a n e . F e e d h y d r o c a r bons w e r e d e l i v e r e d f r o m F l u k a , B u c h s , S w i t z e r l a n d (purum). P u r i t y e x c e e d e d 99. 5 wt. - % i n any c a s e . T h e P t / C a - Y - z e o l i t e c a t a l y s t (0. 5 wt. - % P t , S K 200, U n i o n C a r b i d e , L i n d e D i v i s i o n ; v o l u m e of c a t a l y s t b e d : 2 c m ; p a r t i c l e s i z e : 0. 2 - 0 . 3 m m ) w a s c a l c i n e d i n a d r i e d s t r e a m of N and a c t i v a t e d i n a d r i e d s t r e a m of at a t m o s p h e r i c p r e s s u r e p r i o r to u s e . T h e m a s s of d r y c a t a l y s t was 1. 0 g. T h e t o t a l p r e s s u r e and m o l a r r a t i o h y d r o g e n : n - a l k a n e w e r e kept c o n s t a n t at 39 b a r and 1 7 : 1 , r e s p e c t i v e l y , w h e r e a s the r e a c t i o n t e m p e r a t u r e s and s p a c e v e l o cities were varied. 3

2

C o n v e r s i o n o f n - A l k a n e s , H y d r o i s o m e r i z a t i o n and H y d r o c r a c k i n g It was found that h y d r o i s o m e r i z a t i o n and h y d r o c r a c k i n g of n - d o d e c a n e o v e r the P t / C a - Y - z e o l i t e r e q u i r e l o w r e a c t i o n t e m p e r a t u r e s , a t y p i c a l v a l u e b e i n g 275 °C (9). T h i s t e m p e r a t u r e was c h o s e n i n the p r e s e n t w o r k to i n v e s t i g a t e the i n f l u e n c e of c h a i n l e n g t h o n the r e a c t i v i t y of the n - a l k a n e s . In F i g u r e 1 the d e g r e e of o v e r a l l c o n v e r s i o n has b e e n p l o t t e d v e r s u s the s u p e r f i c i a l

In Hydrocracking and Hydrotreating; Ward, John W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

1.

3

Influence of Chain Length

WEiTKAMP

h o l d i n g t i m e . A s e x p e c t e d r e a c t i v i t y of the h y d r o c a r b o n s i n c r e a s e s with i n c r e a s i n g chain length. F o r a quantitative c o m p a r i s o n appro x i m a t e v a l u e s of the i n i t i a l r e a c t i o n r a t e s m a y be d e r i v e d f r o m the i n i t i a l s l o p e s i n F i g u r e 1 u s i n g the equation


- ra

1 100

dX m , d(ysL) a

In T a b l e I t h e s e v a l u e s a r e r e p o r t e d , t h o s e f o r n-nonane and n - u n d e c a n e b e i n g l e s s a c c u r a t e on account of the r e l a t i v e l y h i g h d e g r e e s of c o n v e r s i o n even at l o w h o l d i n g t i m e s . F r o m n - h e x a n e to n - u n d e c a n e a t e n f o l d i n c r e a s e i n the i n i t i a l r e a c t i o n r a t e i s observed. T a b l e I.

Influence of c h a i n l e n g t h o n i n i t i a l r e a c t i o n r a t e s (T = 275 °C) ^2 Feed n

C

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H

" 6 14

n

-S

H

n

- 8 18

n

- 9 20

n

- ll

16

r

) ["raole n - a l k a n e l a Ig catalyst · h J 0.13 0. 38

C

H

0. 53

C

H

1.1

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24

1. 3

H y d r o g e n a t i v e c o n v e r s i o n of n - a l k a n e s on the P t / C a - Y - z e p l i t e r e s u l t s i n two p r i n c i p l e r e a c t i o n s , h y d r o i s o m e r i z a t i o n o r h y d r o c r a c k i n g , the r e l a t i v e i m p o r t a n c e of e a c h d e p e n d i n g o n the r e a c t i o n c o n d i t i o n s . A t l o w s e v e r i t i e s and c o r r e s p o n d i n g l y l o w d e g r e e s of o v e r a l l c o n v e r s i o n h y d r o i s o m e r i z a t i o n p r e d o m i n a t e s . W i t h η - o c t a n e at 275 ° C , f o r e x a m p l e , the r a t e of h y d r o i s o m e r i z a t i o n i s h a r d l y affected b y h y d r o c r a c k i n g at l o w h o l d i n g t i m e s ( F i g u r e 2). A t h i g h h o l d i n g t i m e s , h o w e v e r , w h e r e the d e g r e e of h y d r o i s o m e r i z a t i o n c o n v e r s i o n goes t h r o u g h a m a x i m u m the r a t e of h y d r o c r a c k i n g i n c r e a s e s . It m i g h t be s u g g e s t e d f r o m the shape of the c u r v e s i n F i g u r e 2 that h y d r o i s o m e r i z a t i o n and h y d r o c r a c k i n g are reactions in series. A w i d e r i n s i g h t into the i n f l u e n c e of c h a i n l e n g t h o n r e a c t i v i t i e s o f n - a l k a n e s m a y be g a i n e d by p l o t t i n g the d e g r e e s of h y d r o -


HYDROCRACKING AND HYDROTREATING


4

20

40

60

80

SUPERFICIAL HOLDING TIME

100

[s]

Figure 1. Hydroisomerization and hydrocracking of n-alkanes with different chain length (T - 275°C)



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5

i s o m e r i z a t i o n c o n v e r s i o n and h y d r o c r a c k i n g c o n v e r s i o n v e r s u s r e a c t i o n t e m p e r a t u r e (cf. F i g u r e s 3 and 4, r e s p e c t i v e l y ) . S i m i l a r c u r v e s a r e o b s e r v e d f o r a l l n - a l k a n e s u s e d . It w i l l be noted that lower reaction temperatures are required for hydroisomerization than f o r h y d r o c r a c k i n g . T h e d e g r e e s of h y d r o i s o m e r i z a t i o n c o n v e r s i o n , h o w e v e r , a r e p a s s i n g t h r o u g h a m a x i m u m w h i c h i s due to the c o n s u m p t i o n of b r a n c h e d i s o m e r s b y h y d r o c r a c k i n g . W i t h d e c r e a s i n g c h a i n l e n g t h the p o s i t i o n of the m a x i m a s h i f t s t o w a r d s higher reaction temperatures reflecting decreasing reactivities. It s h o u l d be m e n t i o n e d that v e r y h i g h m a x i m u m v a l u e s e x c e e d i n g 60 % a r e a t t a i n a b l e e v e n f o r l o n g c h a i n n - a l k a n e s l i k e n - d e c a n e . T h i s r e s u l t has to be a t t r i b u t e d to the h i g h h y d r o g é n a t i o n a c t i v i t y of the P t / C a - Y - z e o l i t e and i s i n c o n t r a s t to h y d r o c r a c k i n g o v e r c a t a l y s t s of l o w h y d r o g é n a t i o n a c t i v i t y (9, 11,12) o r c a t a l y t i c c r a c k i n g (13), w h e r e l i t t l e o r no i s o m e r i z a t i o n of the feed t a k e s p l a c e . W i t h d e c r e a s i n g c h a i n l e n g t h the height of the m a x i m a i n c r e a s e s , indicating a d e c r e a s i n g tendency for cleavage. A n a c t i v a t i o n e n e r g y of 45 k c a l / m o l e i s c a l c u l a t e d f o r the h y d r o i s o m e r i z a t i o n of, e. g . , n - d e c a n e . A n e v e n m o r e m a r k e d i n f l u e n c e of c h a i n l e n g t h e x i s t s f o r the h y d r o c r a c k i n g r e a c t i o n ( F i g u r e 4). T h e d e g r e e s of h y d r o c r a c k i n g c o n v e r s i o n r a p i d l y i n c r e a s e w i t h t e m p e r a t u r e i n the c a s e of n - d e c a n e , n - n o n a n e and η - o c t a n e . W i t h t h e s e h y d r o c a r b o n s h y d r o c r a c k i n g i s c o m p l e t e at c a . 300 - 320 ° C . In s h a r p c o n t r a s t to t h i s the d e g r e e of h y d r o c r a c k i n g c o n v e r s i o n i n c r e a s e s v e r y s l o w l y w i t h r e a c t i o n t e m p e r a t u r e i n the c a s e of n - h e x a n e , whereas a somewhat intermediate behaviour is o b s e r v e d for η - h e p t a n e . It w i l l be s h o w n l a t e r i n c o n n e c t i o n w i t h p r o d u c t d i s t r i b u t i o n s that o n the P t / C a - Y - z e o l i t e h y d r o c r a c k i n g of h e x a n e p r o c e e d s v i a a d i f f e r e n t m e c h a n i s m as c o m p a r e d w i t h i d e a l h y d r o c r a c k i n g of the l o n g e r c h a i n h o m o l o g u e s . F r o m a p r a c t i c a l viewpoint catalysts with high h y d r o g é n a t i o n a c t i v i t y l i k e the P t / C a - Y - z e o l i t e p r o v i d e a h i g h d e g r e e of p r o d u c t f l e x i b i l i t y . L o n g c h a i n feed h y d r o c a r b o n s i n the b o i l i n g r a n g e o f k e r o s e n e m a y be i s o m e r i z e d w i t h e x c e l l e n t y i e l d s w h i c h i s of i n t e r e s t f o r p o u r p o i n t l o w e r i n g . If, o n the o t h e r h a n d , c o m p l e t e h y d r o c r a c k i n g i s d e s i r e d , t h i s m a y be a c h i e v e d s i m p l y b y a p p l i c a tion of somewhat higher r e a c t i o n t e m p e r a t u r e s . In P ' i g u r e 5 the g e n e r a l l y a c c e p t e d r e a c t i o n path (14) f o r h y d r o i s o m e r i z a t i o n of n - a l k a n e s has b e e n r e p r e s e n t e d a l o n g w i t h d i f f e r e n t p o s s i b i l i t i e s f o r the c r a c k i n g s t e p . T h e n - a l k a n e m o l e c u l e s a r e a d s o r b e d at a d e h y d r o g e n a t i o n / h y d r o g e n a t i o n s i t e w h e r e n - a l k e n e s a r e f o r m e d . A f t e r d e s o r p t i o n and d i f f u s i o n to an a c i d i c s i t e c h e m i s o r p t i o n y i e l d s s e c o n d a r y c a r b e n i u m i o n s that r e a r r a n g e



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240

260

280

300

A N D

HYDROTREATING

320

340

TEMPERATURE

[ C] e

Figure 3. Influence of reaction temperature on hydroisomerization conversion of n-alkanes with different chain length (F = 12 · 10~ mole · h' ) 3

1

a

TEMPERATURE

[ Cj e

Figure 4. Influence of reaction temperature on hydrocracking conversion of n-alkanes with different chain length (F = 12 · 10~ mole · h' ) 3

a


1


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into t e r t i a r y c a r b e n i u m i o n s w i t h a b r a n c h e d c a r b o n s k e l e t o n . D e s o r p t i o n of i - a l k e n e s and h y d r o g é n a t i o n at a m e t a l l i c s i t e f i n a l l y y i e l d s i - a l k a n e s . A l l s t e p s of the o v e r a l l h y d r o i s o m e r i z a t i o n r e a c tion are r e v e r s i b l e . F o u r p r i n c i p l e c r a c k i n g r e a c t i o n s , a l l of t h e m b e i n g i r r e v e r s i b l e , have to be t a k e n into account: h y d r o g e n o l y s i s of the n - a l k a n e feed; / 3 - s c i s s i o n of s t r a i g h t c h a i n c a r b e n i u m i o n s ; β - s c i s s i o n of b r a n c h e d c a r b e n i u m i o n s ; h y d r o g e n o l y s i s of i - a l k a n e s f o r m e d b y h y d r o i s o m e r i z a t i o n . It w i l l be s h o w n that the t h i r d step (full a r r o w i n F i g u r e 5) r e p r e s e n t s the m a i n r e a c t i o n path of i d e a l h y d r o c r a c k i n g . C a r b e n i u m i o n s w i t h a b r a n c h e d c a r b o n s k e l e t o n then p l a y the r o l e of k e y i n t e r m e d i a t e s i n that t h e y m a y e i t h e r d e s o r b o r c l e a v e thus d e t e r m i n i n g the d i r e c t i o n of the o v e r a l l r e a c t i o n . W h i l e the r a t e of c l e a v a g e i s g i v e n b y t e m p e r a t u r e , a c i d i t y of the c a t a l y s t and c o n c e n t r a t i o n of i - a l k y l c a t i o n s , the r a t e of d e s o r p t i o n i s a s s u m e d to be enhanced b y the s t e a d y s t a t e c o n c e n t r a t i o n s of n - a l k e n e s , i . e . , a h i g h d e h y d r o g e n a t i o n a c t i v i t y of the c a t a l y s t f a v o r s h y d r o i s o m e r i z a t i o n . T h i s i s the concept of competitive chemisorption which in ideal bifunctional catalysis k e e p s the r e s i d e n c e t i m e s of the a l k y l c a r b e n i u m i o n s l o w . H e n c e , p r i m a r y p r o d u c t s m a y be o b t a i n e d w h i c h i s not the c a s e in catalytic c r a c k i n g over monofunctional catalysts where f o r m a t i o n of c a r b e n i u m i o n s o c c u r s b y h y d r i d e a b s t r a c t i o n f r o m the n-alkane r a t h e r than v i a n - a l k e n e s . A c c o r d i n g to F i g u r e 5 a s e r i e s of e l e m e n t a r y r e a c t i o n s a r e i n v o l v e d i n h y d r o i s o m e r i z a t i o n and h y d r o c r a c k i n g o f n - a l k a n e s . A t the t i m e b e i n g , the r a t e c o n t r o l l i n g step of the o v e r a l l r e a c t i o n i s unknown b e c a u s e of the l a c k of a d e t a i l e d k i n e t i c a n a l y s i s of the s y s t e m . P o s s i b l e i n t e r p r e t a t i o n s of the i n f l u e n c e of c h a i n l e n g t h upon r e a c t i v i t y a r e s p e c u l a t i v e . M a x i m u m c o n c e n t r a t i o n s of n alkenes, l i m i t e d by thermodynamics, increase with i n c r e a s i n g c h a i n l e n g t h of the feed. T h e s a m e w i l l be t r u e f o r r a t e s of a d s o r p t i o n b o t h of the feed and the o l e f i n i c i n t e r m e d i a t e s . R a t e s of s u r face r e a c t i o n s too m a y depend on the c h a i n l e n g t h of the c h e m i s o r b e d s p e c i e s . T h e c h e m i s t r y of i d e a l h y d r o c r a c k i n g w i l l be d i s c u s s e d i n t e r m s of d e t a i l e d p r o d u c t d i s t r i b u t i o n s , p r o v i d i n g i n s i g h t into the p r i m a r y p r o d u c t s of b i f u n c t i o n a l c a t a l y s i s . Hydroisomerization L i t e r a t u r e o n h y d r o i s o m e r i z a t i o n of l o n g c h a i n a l k a n e s > C^ i s v e r y l i m i t e d (2, 9 , 1 5 , 1 6 ) due to both a n a l y t i c a l d i f f i c u l t i e s and the fact that h y d r o c r a c k i n g p r e d o m i n a t e s u n l e s s the b i f u n c t i o n a l



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A N D

HYDROTREATING

c a t a l y s t has b e e n s u i t a b l y s e l e c t e d . In F i g u r e 6 the c o m p o s i t i o n of the o c t a n e and undecane f r a c t i o n have b e e n p l o t t e d v e r s u s h o l d i n g t i m e at a r e a c t i o n t e m p e r a t u r e of 275 ° C . T h e f o l l o w i n g g e n e r a l f e a t u r e s of h y d r o i s o m e r i z a t i o n m a y be r e c o g n i z e d : M o n o branched i s o m e r s are p r i m a r y products from which multiple branched i s o m e r s are formed in a consecutive reaction. The c h a i n l e n g t h o f the feed has a m a r k e d i n f l u e n c e both on r a t e of h y d r o i s o m e r i z a t i o n and the amount of m u l t i p l e b r a n c h e d i s o m e r s , which increases considerably with i n c r e a s i n g chain length. Q u a l i t a t i v e l y , t h i s i s i n a g r e e m e n t w i t h t h e r m o d y n a m i c s and m a y be a t t r i b u t e d to the n u m b e r of m u l t i p l e b r a n c h e d i s o m e r s w h i c h r a p i d l y grows with increasing chain length. A m o r e d e t a i l e d p i c t u r e of h y d r o i s o m e r i z a t i o n of n - o c t a n e and n - n o n a n e i s g i v e n i n T a b l e II i n w h i c h p r o d u c t d i s t r i b u t i o n s a r e l i s t e d f o r d i f f e r e n t d e g r e e s of c o n v e r s i o n a l o n g w i t h t h e r m o d y n a m i c e q u i l i b r i u m v a l u e s . T h e l a t t e r have b e e n c a l c u l a t e d f r o m G i b b s f r e e e n e r g y data a v a i l a b l e i n l i t e r a t u r e (17) the a c c u r a c y of w h i c h , h o w e v e r , i s not k n o w n . F r o m T a b l e II the f o l l o w i n g c o n c l u s i o n s m a y be d r a w n : H y d r o i s o m e r i z a t i o n proceeds towards thermodynamic equili b r i u m w h i c h i s a p p r o x i m a t e l y r e a c h e d b e t w e e n the n o r m a l , m o n o b r a n c h e d and d i - b r a n c h e d s t r u c t u r e s at h i g h d e g r e e s of o v e r a l l conversion. H y d r o c r a c k i n g , however, i s severe under these c o n d i t i o n s . It i s evident f r o m T a b l e II that m o n o m e t h y l i s o m e r s a r e p r i m a r y p r o d u c t s ; the s a m e i s a p p a r e n t l y t r u e f o r m o n o e t h y l i s o m e r s a l t h o u g h due to t h e r m o d y n a m i c r e a s o n s l o w e r c o n c e n t r a tions are obtained. D i m e t h y l i s o m e r s including those containing a q u a r t e r n a r y c a r b o n a t o m a r e f o r m e d as s e c o n d a r y p r o d u c t s . H o w e v e r , t r i m e t h y l i s o m e r s a r e f o r m e d v e r y s l o w l y so that t h e i r c o n c e n t r a t i o n s do not r e a c h e q u i l i b r i u m v a l u e s . It f o l l o w s f r o m t h i s that the n u m b e r of r a m i f i c a t i o n s i s d e c i d i n g as to w h e t h e r a branched i s o m e r is a p r i m a r y , secondary or t e r t i a r y product i n h y d r o i s o m e r i z a t i o n of η - o c t a n e and n - n o n a n e . T h o u g h m o n o m e t h y l i s o m e r s , as a w h o l e , a r e p r i m a r y p r o d u c t s , the r a t e s of f o r m a t i o n of i n d i v i d u a l m e m b e r s m a y d i f f e r s u b s t a n t i a l l y f r o m e a c h o t h e r . F u r t h e r m o r e t h e y depend o n the d e g r e e of c o n v e r s i o n . W i t h , e. g . , n - d e c a n e ( T a b l e III) at l o w d e g r e e s of c o n v e r s i o n r e l a t i v e r a t e s of f o r m a t i o n f o r 2 - m e t h y l nonane : 3 - m e t h y l n o n a n e : 4 - m e t h y l n o n a n e : 5 - m e t h y l n o n a n e a r e 1 : 2 : 2 : 1 and shift to 2 : 2 : 2 : 1 at h i g h d e g r e e s of c o n version. T h e l a t t e r r e p r e s e n t the t h e r m o d y n a m i c e q u i l i b r i u m d i s t r i b u t i o n w h i c h m a y e a s i l y be u n d e r s t o o d i n t e r m s of s t a t i s t i c s : L e t m r e p r e s e n t the c a r b o n n u m b e r of the n - a l k a n e feed. If i t i s e v e n


1.

WEiTKAMP

Influence of Chain Length HYDROGENOLYSIS

n-ALKANE

— CRACKED PRODUCTS

-21

1

SEC. n-ALKYL CATIONS — f * C R A C K E D PRODUCTS

n-ALKENES

REARRANGEMENT


i-ALKENES

ι

•

2H1"Î"

/?-SCISSION

- H ®

1

/Î-SCISSION 7 / CRACKED PRODUCTS

TERT. i-ALKYL CATIONS HYDROGENOLYSIS

i-ALKANES

CRACKED PRODUCTS

Figure 5. Reaction scheme for hydroisomerization of n-alkanes on bifunctional catalysts and possible modes of cleavage

FEED: n-OCTANE

SUPERFICIAL HOLDING TIME [s]

F E E D : n-UNDECANE

SUPERFICIAL HOLDING TIME [s]

Figure 6. Course of hydroisomerization of η-octane and n-undecane (T — 275°C)


10

HYDROCRACKING

Table II.

n- O C T A N E

[ c]

275

e

F -ΙΟ" a

3

[mole

h" ] 1

X ,so ['/·]


Xcr

HYDROTREATING

Mole-% of Isomers Formed in Hydroisomerization of «-Octane and w-Nonane

F E E D τ

A N D

W

n-Octane 2-Methylheptane 3-Methylheptane 4-Methylheptane 3-Ethylhexane 2,3-Dimethylhexane 2,4-Dimethylhexane 2,5-Dimethylhexane 3,4-Dimethylhexane 2-Methyl-3-ethylpentane 2,2- Dimethylhexane 3,3- Dimethylhexane Trimethylpentanes n-Nonane 2-Methyloctane 3-Methyloctane 4-Methyloctane 3-Ethylheptane 4-Ethylheptane (b) 2,3-Dimethylheptane 2,4-Dimethylheptane 2,5*3,5-Dimethylheptane 2,6 *4,4- Dimethylheptane 2,2- Dimethylheptane 3,3- Dimethylheptane Others (c)

1 7

n-NONANE

275

310

275

275

3

13

43

7

12

67.1

24.3

9.3

72.6

29.6

67.0

26.5

25.8

The Influence of Chain Length in Hydrocracking ... - ACS Publications

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