The Development of Hydrocracking - ACS Publications - American

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The Development of Hydrocracking RICHARD F. SULLIVAN and JOHN W. SCOTT Chevron Research Company, Richmond, CA 94802

In 1959 Chevron Research announced the "world's f i r s t commercially proven low temperature hydrocracking process" called Isocracking. Among its attractive features was the a b i l i t y to efficiently crack aromatics and to produce paraffins that were far on the "iso" side of thermodynamic equilibrium. Although hydrocracking had been practiced previously at high temperatures and pressures, the invention of superior catalysts permitted operation at moderate temperatures (200-400°C) and lower pressures (35-140 atm.). Isocracking was developed as a response to major changes in the domestic petroleum market during the 1950's. The trend toward automobile engines with high compression ratios resulted in an increased demand for high octane gasoline. The shift by the railroads from steam to diesel locomotives caused corresponding downward shifts in fuel o i l demand. The overall consequence was a need to convert excess refractory cutter stocks to high octane gasoline, and Isocracking addressed this problem. In the intervening years, further catalyst improvements made both at Chevron and in the petroleum industry generally have extended the range of modern hydrocracking feedstocks to high boiling distillates and residua; and hydrocracking has become one of the most useful and flexible refining processes. Catalysts can be tailored to f i t spec i f i c needs of a refiner by careful control of

0097-6156/83/0222-0293$06.00/0 © 1983 American Chemical Society In Heterogeneous Catalysis; Davis, Burtron H., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

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t h e i r chemical and p h y s i c a l p r o p e r t i e s . Depending upon the c a t a l y s t and processing c o n d i t i o n s , the major product can be l i q u e f i e d petroleum gas (LPG), gasoline, j e t f u e l , middle distillates, l u b r i c a n t s , petrochemicals, or a combination of products. In a broad sense, hydrocracking can be defined as any cracking of molecules i n the presence of hydrogen, whether i t takes place i n the presence or absence of a c a t a l y s t . Because some cracking occurs i n many h y d r o r e f i n i n g processes, the O i l and Gas Journal a r b i t r a r i l y defines "hydrocracking" as a convers i o n process u t i l i z i n g hydrogen i n which at l e a s t 50% of the reactant molecules are reduced i n molecular s i z e (1). This rough d e f i n i t i o n i s s u i t a b l e f o r the purposes of t h i s paper. Most modern hydrocracking processes are c a t a l y t i c , and the c a t a l y s t employed i s u s u a l l y dual f u n c t i o n a l with both a hydrogénation component and an a c i d i c component. T y p i c a l a c i d i c components include amorphous s i l i c a - a l u m i n a , alumina, and a l a r g e family of z e o l i t e s . T y p i c a l hydrogénation components are noble metals such as palladium and platinum and nonnoble metals such as n i c k e l , c o b a l t , tungsten, and molybdenum. The l a t t e r metals are u s u a l l y i n s u l f i d e d form. Modern c a t a l y t i c hydrocracking i s probably the most versat i l e and c e r t a i n l y one of the most important conversion processes i n modern r e f i n i n g technology. Research i n the 1950 s l e d to the large commercial development of hydrocracking i n the 1960 s, and modern commercial hydrocracking processes are cont i n u i n g to evolve. However, hydrocracking i n an e a r l i e r form i s one of the oldest hydrocarbon conversion processes. I t was the f i r s t c a t a l y t i c cracking process to a t t a i n appreciable commerc i a l importance. An extensive hydrocracking technology f o r c o a l conversion was b u i l t up i n Germany between 1915 and 1945 (21-5). The d r i v i n g force that l e d to t h i s productive e f f o r t was s t r a t e g i c rather than economic. Germany needed a secure supply of l i q u i d f u e l s derived from a domestic energy source; namely, coal. In 1943, 12 plants were operating which provided Germany with 98% of the a v i a t i o n gasoline and 47% of the t o t a l hydrocarbon products consumed i n Germany during the l a t t e r years of World War I I (6). S i m i l a r , though l e s s extensive, e f f o r t s took place i n Great B r i t a i n , France, Manchuria, and Korea (6_, 7_, JB). A p a r a l l e l development i n the United States was d i r e c t e d toward the conversion of heavier petroleum f r a c t i o n s (9, 10). In general, the conversion of coal was accomplished i n two or 1

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In Heterogeneous Catalysis; Davis, Burtron H., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.


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three separate c a t a l y t i c steps. Reaction conditions were t y p i c a l l y 200-700 atm. (3,000-10,000 psig) and 375-525°C (700-975°F). Although somewhat less severe c o n d i t i o n s were appropriate f o r petroleum hydrocracking, design pressures were 200-300 atm. (3,000-4,500 p s i g ) ; and temperatures g e n e r a l l y exceeded 375°C (700°F). Both t e c h n i c a l and economic changes reduced the importance of hydrocracking a f t e r the end of World War I I . The general a v a i l a b i l i t y of Middle Eastern crude o i l s removed the i n c e n t i v e for conversion of coal to l i q u i d f u e l s . New c a t a l y t i c cracking processes, which subtract carbon rather than add hydrogen, proved more economic f o r converting heavy petroleum gas o i l s to g a s o l i n e . Construction of new hydrocracking plants stopped. Although a few of the e x i s t i n g plants were adapted to petroleum hydrocracking (11, 12), most were shut down or converted to other s e r v i c e (13, 14). A modest c o a l conversion i n d u s t r y was continued i n East Germany, Czechoslovakia, and the U.S.S.R., countries i n which the government c o n t r o l l e d the industry and no competitive market existed (6). The f i e l d lay dormant u n t i l 1959 when Chevron Research Company, then known as C a l i f o r n i a Research Corporation, announced that a new hydrocracking process, "Isocracking," was i n commercial operation i n the Richmond Refinery of the Standard O i l Company of C a l i f o r n i a (15). The f o l l o w i n g year, the U n i v e r s a l O i l Products Company announced a hydrocracking process c a l l e d "Lomax" (16) and Union O i l Company announced the "Unicracking" process (17). P u b l i c a t i o n s i n the e a r l y 1960 s showed that most of the other major petroleum companies a l s o had a s i g n i f i c a n t research e f f o r t i n hydrocracking. The rapid acceptance of hydrocracking i n the I960's as a major r e f i n i n g process i n d i c a t e d the t i m e l i n e s s of the development. By 1966, seven d i f f e r e n t hydrocracking processes were o f f e r e d f o r l i c e n s e T

(18)· In t h i s paper, we w i l l review the considerations that led to the development of modern hydrocracking and some aspects of the chemistry of hydrocracking. A l s o , we w i l l b r i e f l y discuss some of the advances i n hydrocracking during the 23 years s i n c e the Isocracking process was announced. Need of a New

Conversion Process

A s e r i e s of r e l a t e d events i n the l a t e 1940's and e a r l y 1950 s led to the need f o r a new hydrocarbon conversion process. Reduced overseas shipments as a r e s u l t of the end of f



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World War I I , the conversion of r a i l r o a d s from steam to d i e s e l power, and the a v a i l a b i l i t y of a large supply of cheap n a t u r a l gas a l l c o n t r i b u t e d to reduced f u e l o i l demand. The rapid growth of c a t a l y t i c cracking led to an excess of r e f r a c t o r y c y c l e stocks. The trend i n the automobile industry was to make higher compression r a t i o , high performance cars with high octane requirements. R e l a t i v e l y inexpensive gasoline was a v a i l a b l e and there was l i t t l e emphasis on f u e l economy. There was a p r e s s i n g need to convert r e f r a c t o r y stocks to g a s o l i n e . A g o a l - o r i e n t e d research program was s t a r t e d by Chevron i n 1952 with the exploratory research of Scott et a l . (19). The object was to f i n d a processing route to convert excess gas o i l s to high octane gasoline components. The papers of M. P i e r d e s c r i b i n g the German hydrocracking process had given an i n d i c a t i o n that hydrocracking had the p o t e n t i a l to f i l l t h i s need (3, 4_, 11). I t was c l e a r , however, that both s e l e c t i v i t y and product character needed to be modified i n order to s a t i s f y gasoline q u a l i t y requirements economically. New p i l o t plant c a p a b i l i t y and m u l t i p l e screening u n i t s permitted a wide v a r i e t y of test c o n d i t i o n s , and d i r e c t comparisons of c a t a l y s t s could be made r a p i d l y . What was needed was a c a t a l y s t that could: (1) produce p a r a f f i n s on the i s o side of e q u i l i b r i u m , (2) crack aromatics and c y c l o p a r a f f i n s without loss of r i n g s t r u c t u r e , (3) c o n t r o l demethanation r e a c t i o n s , (4) minimize hydrogen consumption, (5) operate at lower pressures than the e a r l i e r hydrocracking processes, and (6) operate with a v a r i e t y of feedstocks. Furthermore, such a process should be s u f f i c i e n t l y f l e x i b l e that product d i s t r i b u t i o n s could be changed as product demand s h i f t e d . For example, when commercial j e t a i r c r a f t s were introduced i n the 1950 s, low freeze point kerosene j e t f u e l became another important petroleum product. Branched p a r a f f i n s ( c o l l e c t i v e l y r e f e r r e d to as " i s o p a r a f f i n s " ) g e n e r a l l y have high octane numbers; normal p a r a f f i n s have low octane numbers. Normal p a r a f f i n s of carbon numbers of seven or fewer are p a r t i c u l a r l y hard to reform to aromatics and r e l a t i v e l y hard to isomerize. Therefore, the target s e l e c t i v i t y was a maximum production of i s o p a r a f f i n s and a minimum production of normal p a r a f f i n s , p a r t i c u l a r l y i n the lower carbon number range (c4-c7). The thermodynamic e q u i l i b r i u m f o r i s o p a r a f f i n s compared to normal p a r a f f i n s improves as the temperature decreases; however, a r e l a t i v e l y large amount of normal p a r a f f i n s are present at e q u i l i b r i u m even at low temperatures. Therefore, the d e s i r e d f



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i s o p a r a f f i n to normal p a r a f f i n s e l e c t i v i t y was on the " i s o " s i d of e q u i l i b r i u m . Aromatic compounds g e n e r a l l y have very high octane numbers. With the i n t r o d u c t i o n of c a t a l y t i c reforming i n the 1950's, p a r a f f i n s and c y c l o p a r a f f i n s could be c a t a l y t i c a l l y reformed to high octane aromatic components. However, dehydroc y c l i z a t i o n of p a r a f f i n s i s much harder to accomplish than dehydrogenation of r i n g - c o n t a i n i n g compounds and i s accompanied by the unwanted side r e a c t i o n of cracking to l i g h t gases. Therefore, a maximum conservation of c y c l i c s t r u c t u r e s was a target s e l e c t i v i t y . L i q u i d products are u s u a l l y more valuable than methane and ethane. At the high temperatures of the e a r l i e r hydrocracking processes, a considerable amount of demethanation took place. Therefore, the goal was to f i n d c a t a l y s t s that operated at low temperatures where demethanation r e a c t i o n s could be avoided. Then, as now, hydrogen was r e l a t i v e l y expensive. By m i n i mizing aromatics s a t u r a t i o n and cracking to l i g h t gases, hydrogen consumption could be minimized. The e a r l y high pressure hydrocracking processes were very c o s t l y . For a hydrocracking process to be cost e f f e c t i v e , lowe pressures were necessary. Hydrocracking Reactions As promising new c a t a l y s t s were developed, a research program was designed to study the chemistry of hydrocracking by t e s t i n g pure compounds and simple mixtures to determine the mechanism of hydrocracking r e a c t i o n s . The i n t r o d u c t i o n of gas chromotography i n the middle 1950 s, i n combination with mass spectrometry, provided a powerful new a n a l y t i c a l t o o l f o r i d e n t i f y i n g i n d i v i d u a l compounds i n complex mixtures of product hydrocarbons. A fortunate combination of t h e o r e t i c a l c o n s i d e r a t i o n s and experimental circumstances d i r e c t e d a t t e n t i o n to some unusual r e a c t i o n paths. This l e d to d e t a i l e d studies of r e a c t i o n s of t y p i c a l hydrocarbon c l a s s e s . New and h i g h l y s p e c i f i c nonequil i b r i u m r e a c t i o n s were i d e n t i f i e d . Techniques and c a t a l y s t s were discovered which permitted d e s i r a b l e ' r e a c t i o n s of the i n d i v i d u a l hydrocarbon classes to dominate the conversion of mixtures. These studies became the basis f o r the commercial hydrocracking process c a l l e d Isocracking and the c a t a l y s t s developed f o r t h i s s e r v i c e . The t e c h n i c a l o b j e c t i v e s of a low pressure, low temperature process were achieved as demonstrated f


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i n many long p i l o t plant t e s t s p r i o r to the f i r s t commercial test. The chemistry of hydrocracking i s discussed i n d e t a i l i n other review papers (20 21). In t h i s paper, we w i l l b r i e f l y discuss some of the reactions of the unusual reactions of a l k y l benzenes, alkylcyclohexanes, and p a r a f f i n s . Aromatics. One of the e a r l i e s t reactions to gain a t t e n t i o n i n screening t e s t s was an unexpected type of hydrodealkylation observed when hydrocracking p o l y s u b s t i t u t e d alkylbenzenes. This r e a c t i o n produced lower b o i l i n g aromatics as d e s i r e d . The conc e n t r a t i o n of aromatics i n the product was, however, higher than would be explained by any known r e a c t i o n mechanism, and the missing methyl substituents appeared i n the product mainly as i s o p a r a f f i n s rather than as methane. The importance of alkylbenzene d i s p r o p o r t i o n a t i o n to the course of t h i s r e a c t i o n was r e a d i l y apparent; but the f a t e of one important intermediate, hexamethylbenzene, was obscure. Our research (22) showed hexamethylbenzene cracked over such simple c a t a l y s t s as NiSs i l i c a - a l u m i n a to give, mainly, lower b o i l i n g aromatics, i s o butane, and isopentane. F i g u r e 1 i l l u s t r a t e s the unusual product d i s t r i b u t i o n observed. This r e a c t i o n , i n i t s apparent e f f e c t , peels or pares methyl groups from the r i n g and, theref o r e , was named the paring r e a c t i o n . A r e a c t i o n mechanism was proposed which involves repeated c o n t r a c t i o n and expansion of aromatic r i n g s adsorbed on a c i d s i t e s on the c a t a l y t i c surface. This probably proceeds by way of an i s o m e r i z a t i o n between an aromatic C^ r i n g and a r e l a t i v e l y stable cyclopentadienyl c a t i o n i c intermediate. Isomerization proceeds u n t i l a branched side chain i s formed that can crack o f f to form an i s o p a r r a f i n . The remainder of the molecule desorbs as a lower molecular weight aromatic. The p l a u s i b i l i t y of the cyclopentadienyl cations postulated as intermediates i s s t r o n g l y supported by the work on DeVries (23) and Winstein and co-workers (24, 25). These workers propose that such intermediates have a n o n c l a s s i c a l form. Further research showed that the paring r e a c t i o n occurs on s i l i c a - a l u m i n a i n the absence of hydrogen or the hydrogénation component. C y c l o p a r a f f i n s are not formed at the r e a c t i o n condit i o n s ; therefore, they are not e s s e n t i a l intermediates i n the r e a c t i o n . Under these conditions, the s i l i c a - a l u m i n a i s d e a c t i vated r a p i d l y , and the observed reactions rates are much lower. An important f u n c t i o n of the metal s u l f i d e and hydrogen



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Number

of

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in

Product

Figure 1 - Hydrocracking of hexamethylbenzene at 349°C and 14 atm.


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i s to maintain c a t a l y s t a c t i v i t y by preventing buildup of c a r bonaceous deposits on the c a t a l y s t . Cycloparaffins* A s i m i l a r , even more rapid paring r e a c t i o n occurs with c y c l o p a r a f f i n s (26). For example, F i g u r e 2 shows that hexamethylcyclohexane r e a c t s to form isobutane and a mixture of Cg c y c l o p a r a f f i n s (mainly cyclopentanes) as the most important products. S i m i l a r l y , diisopropylcyclohexane reacts to form isobutane and Cg c y c l o p a r a f f i n s instead of forming (as one might expect) l a r g e q u a n t i t i e s of propane. As with aromatics, e s s e n t i a l l y a l l of the r i n g s t r u c t u r e s are preserved i n the paring r e a c t i o n of c y c l o p a r a f f i n s . The c y c l o p a r a f f i n s tend to form isobutane and a c y c l o p a r a f f i n of four carbon numbers lower than the reactant molecule. Therefore, the dominant products from C^Q c y c l o p a r a f f i n s are isobutane and methylcyclopentane. A sequence of r e a c t i o n s to produce these compounds from tetramethylcyclohexane i s given i n F i g u r e 3. The product d i s t r i b u t i o n s from d i f f e r e n t c y c l o p a r a f f i n s of any given carbon number are very s i m i l a r to each o t h e r — a strong i n d i c a t i o n that s i m i l a r intermediates are i n v o l v e d i n each case. Paraffins* The r e a c t i o n s of p a r a f f i n s , while somewhat l e s s unexpected than the paring r e a c t i o n of c y c l i c compounds, gave us an important key as to how to t a i l o r c a t a l y s t s to f i t s p e c i f i c r e f i n i n g needs and to y i e l d d i f f e r e n t product s l a t e s . We found a profound d i f f e r e n c e between the behavior of normal p a r a f f i n s i n hydrocracking with a c a t a l y s t c o n t a i n i n g a strong hydrogénat i o n component such as n i c k e l metal or a noble metal and a r e l a t i v e l y weak hydrogénation component such as n i c k e l s u l f i d e . Mechanisms of hydrocracking of p a r a f f i n s have been studied e x t e n s i v e l y (27-33). A carbonium ion mechanism i s u s u a l l y proposed s i m i l a r to the mechanisms p r e v i o u s l y proposed f o r c a t a l y t i c c r a c k i n g except that hydrogénation and hydroisomerization are superimposed. The p a r a f f i n s are f i r s t dehydrogenated to an o l e f i n , then are adsorbed as a c a t i o n on an a c i d i c s i t e , isomeri z e d to the p r e f e r r e d t e r t i a r y c o n f i g u r a t i o n , and undergoes beta s c i s s i o n . V i r t u a l l y no methane and ethane are formed. The r e a c t i o n becomes more s e l e c t i v e f o r i s o p a r a f f i n production as the temperature i s decreased. F i g u r e 4 shows the iso-to-normal r a t i o of the combined pentanes and hexanes f o r the r e a c t i o n of pure normal decane over c a t a l y s t s with a s t r o n g l y a c i d i c component and i l l u s t r a t e s the advantage of operating at low temperatures f o r maximum


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HETEROGENEOUS

(Ή —C—(Ή 3 3

I

Η

Figure 3 - Proposed mechanism f o r the hydrocracking of tetramethylcyclohexane.


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i s o p a r a f f i n y i e l d s . The high iso-to-normal r a t i o s i n the product gave Isocracking i t s name. By i n c r e a s i n g the hydrogénation a c t i v i t y of the c a t a l y s t r e l a t i v e to i t s a c i d i t y , the product d i s t r i b u t i o n from normal p a r a f f i n reactants can be d r a m a t i c a l l y changed. For example, f o r the hydrocracking of normal decane at comparable c o n d i t i o n s , the f o l l o w i n g iso-to-normal r a t i o s f o r the combined pentanes and hexanes were obtained with three d i f f e r e n t metal compositions on a s i n g l e , a c i d i c s i l i c a - a l u m i n a support: Iso/Normal N i c k e l Metal Platinum Nickel Sulfide

0.1 1 8

The c a t a l y s t s with the high hydrogénation a c t i v i t y give product with low iso-to-normal r a t i o s . Apparently, o l e f i n i c intermediates are quenched and l e s s hydroisomerization occurs. With n i c k e l metal, appreciable hydrogenolysis occurs without isomerization. F i g u r e 5 compares the r e a c t i o n s of n-hexadecane on a c a t a l y s t with strong hydrogénation a c t i v i t y (platinum on s i l i c a alumina) to one with strong a c i d i t y and weaker hydrogénation a c t i v i t y ( n i c k e l s u l f i d e on the same s i l i c a - a l u m i n a support). I s o p a r a f f i n s of carbon numbers of four, f i v e , and s i x are the p r e f e r r e d products with the s t r o n g l y a c i d i c c a t a l y s t . The c a t a l y s t with the stronger hydrogénation a c t i v i t y makes much less isobutane, and the product d i s t r i b u t i o n i s spread more evenly over a wide molecular weight range. Therefore, the C^+ l i q u i d y i e l d i s higher f o r the c a t a l y s t with strong hydrogénation a c t i v i t y , although iso-to-normal r a t i o s are much lower. Commercial Feeds* The same e f f e c t shown f o r pure compounds i s here i l l u s t r a t e d i n Figure 6 with a commercial feed, a C a l i f o r n i a vacuum gas o i l . A l l of the feed b o i l i n g above the r e c y c l e cut point of 288°C (550°F) was r e c y c l e d to e x t i n c t i o n . The c a t a l y s t with the higher h y d r o g e n a t i o n - t o - a c i d i t y r a t i o gives the higher l i q u i d y i e l d . The increased l i q u i d y i e l d i s l a r g e l y due to more p a r a f f i n s i n the higher b o i l i n g product and l e s s isobutane formation (34). F i g u r e 7 shows r e s u l t s f o r the same feed with a v a r i e t y of c a t a l y s t s with varying hydrogenation-to-acidity r a t i o . The C + 5



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3 No.

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7 in

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Figure 5 - Products from hydrocracking of n-hexadecane with two different catalysts.

100 Low Acidity, High Hydrogénation Catalyst

»•

95 >- SZ Ό

oo

CD

•

•

+»

•

High Acidity, Low Hydrogénation Catalyst

-82_

90H

85

300 Average

325 Catalyst

350 Temperature,

375 °C

+

Figure 6 - E f f e c t of temperature on C^ l i q u i d y i e l d i n the hydrocracking of C a l i f o r n i a gas o i l .



Figure 7 - R e l a t i o n between f o r hydrocracking (symbols i n d i c a t e l e v e l s of a c i d i t y

l i q u i d y i e l d and isohexanes/n-hexane of C a l i f o r n i a gas o i l a t 315°C various c a t a l y s t s with d i f f e r e n t and hydrogénation a c t i v i t y ) .

Isohexanes/n-Hexane


>

s

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M

χ Η p g

ο


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y i e l d v a r i e s as the r a t i o changes, and t h i s can be c o r r e l a t e d with the iso-to-normal hexane r a t i o i n the product. As the i s o to-normal r a t i o increases, the octane number of the naphtha product i n c r e a s e s . This i s p a r t i c u l a r l y important f o r the l i g h t naphtha (C^-C^) which i s an important l i g h t gasoline blending component. In the previous paragraphs, we have shown how to change product d i s t r i b u t i o n and iso-to-normal r a t i o s by a l t e r i n g the catalyst hydrogenation-to-acidity r a t i o . Another way to do t h i s i s by p r e f e r e n t i a l l y poisoning one or the other c a t a l y t i c site. Nitrogen (as ammonia) i s a t y p i c a l poison f o r an a c i d s i t e ; s u l f u r (as hydrogen s u l f i d e ) i s a t y p i c a l poison f o r a metal hydrogénation s i t e . Table I shows that the same e f f e c t s just discussed can be achieved i n the presence of heteroatoms.

Table I Product

from Pd on S ^ - A ^ O ^ with C a l i f o r n i a Gas O i l E f f e c t s of S u l f u r and Nitrogen

C -82°C 138-288°C c5+ (280-550°F) (C -180°F) Octane, Isohexanes/ Y i e l d , Yield, F - l Clear n-Hexane LV % Wt % 5

5

Before A d d i t i o n of S u l f u r or Nitrogen

5

95

65

80

8 ppm Nitrogen Added to Feed ( C a t a l y s t Equilibrated)

3

96

71

78

13

93

58

84

100 ppm to Feed Volumes taining

S u l f u r Added ( A f t e r 170 of Feed ConSulfur)

With these p r i n c i p l e s , we found i t p o s s i b l e to make s p e c i f i c c a t a l y s t s to achieve desired product d i s t r i b u t i o n s . In



308

HETEROGENEOUS CATALYSIS

1959, at the time Isocracking was introduced, the strong a c i d c a t a l y s t s were the p r e f e r r e d hydrocracking c a t a l y s t to produce high octane g a s o l i n e . For maximum production of kerosene j e t f u e l , c a t a l y s t s with more hydrogénation a c t i v i t y could be employed. The f i r s t Chevron Isocrackers operated as two-stage processes. The f i r s t stage involved h y d r o t r e a t i n g to remove heteroatoms; the cracking r e a c t i o n s occurred i n the second stage over c a t a l y s t s with strong a c i d i t y and moderate hydrogénation activity. The

1

I960 s - Growth of Hydrocracking 1

The I960 s were years of rapid growth of hydrocracking. By the end of the decade, nine d i f f e r e n t processes were operating commercially or had plants under c o n s t r u c t i o n . New c a t a l y s t s were developed, both more a c t i v e and more s t a b l e than the earl i e r c a t a l y s t s . Of p a r t i c u l a r note, molecular sieve c a t a l y s t s were introduced (35, 36). Because of t h e i r high surface area and large number of c a t a l y t i c s i t e s , they were more t o l e r a n t of heteroatom i m p u r i t i e s , such as nitrogen, than the previous c a t a lysts. In general, the r e a c t i o n mechanisms f o r sieve c a t a l y s t s were b e l i e v e d to be s i m i l a r to those f o r amorphous c a t a l y s t s . However, i n some s p e c i a l i z e d cases, the shape s e l e c t i v e p r o p e r t i e s of z e o l i t e s could be used to permit l i m i t e d access to the c a t a l y s t s i t e s , thus allowing c e r t a i n molecules to react while excluding others. (The more recent c a t a l y t i c hydrodewaxing developments are an example of such an a p p l i c a t i o n . However, because t y p i c a l l y fewer than 50% of the molecules are cracked, they f a l l outside of our working d e f i n i t i o n of hydrocracking.) Another development of the I960's was that of stable, large-pored c a t a l y s t s which could crack very heavy feeds (37). For example, i n Richmond, Chevron has had a hydrocracker processing deasphalted o i l (DAO) since the middle I960*s. The H - o i l process was commercialized by Hydrocarbon Research, Inc., also i n the 1960's as a residuum hydrocracking process (38). The v e r s a t i l i t y of hydrocracking was demonstrated i n the I960's as the demands f o r a v a r i e t y of products increased. In a d d i t i o n to gasoline and j e t f u e l , the product range included d i e s e l f u e l , l u b r i c a t i n g o i l s , low s u l f u r f u e l o i l s , LPG, and chemicals. A wide v a r i e t y of flow schemes, both s i n g l e - s t a g e and twostage, were p r a c t i c e d commercially. In p a r t i c u l a r , s i n g l e - s t a g e processes were used advantageously to produce middle


24.

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d i s t i l l a t e s (37). The tolerance of sieve containing c a t a l y s t s f o r hetoatoms permitted operation of two-catalyst systems i n s e r i e s without intermediate removal of ammonia and hydrogen s u l f i d e i n the Unicracking process (39). Most f i x e d bed processes operated i n a downflow c o n f i g u r a t i o n . In contrast, the Η-Oil process employed an e b u l l a t e d c a t a l y s t bed and operated i n an upflow mode (38). The

1970*s

Figure 8 shows the rapid growth of hydrocracking i n the United States during the I960 s and e a r l y 1970's. However, i n the l a t e r 1970's, the rate of growth of the hydrocracking was more moderate. Among the reasons f o r t h i s l e v e l i n g o f f were major improvements i n c a t a l y t i c cracking due to the widespread use of z e o l i t e c a t a l y s t s . The high cost of hydrogen g e n e r a l l y made hydrocracking a more expensive process than c a t a l y t i c cracking f o r gasoline production. By the 1970*s, hydrocracking was a mature process. Although there was l i m i t e d growth of hydrocracking i t s e l f , there was a large growth i n r e l a t e d hydrotreating processes such as hydrodesulfurization. The 1970*s were years i n which a d d i t i o n a l use of new cata l y s t s permitted better u t i l i z a t i o n of e x i s t i n g f a c i l i t i e s . The trends toward heavier feeds continued. Development of superior a n a l y t i c a l t o o l s permitted more d e t a i l e d studies of the mechanisms of hydrocracking r e a c t i o n s . In p a r t i c u l a r , the work of Weitkamp and coworkers should be noted (40, 41). 1

The

Future

At present, the United States' hydrocracking c a p a c i t y i s over 900,000 b a r r e l s per stream day (BPSD); worldwide c a p a c i t y i s approaching 1.5 m i l l i o n BPSD (42). Despite a l l of the u n c e r t a i n t i e s of the present economic climate, some trends can be predicted f o r the 1980*s. Because of t h e i r v e r s a t i l i t y , hydrocrackers o f f e r the r e f i n e r the a b i l i t y to meet these changing demands. In the e a r l y 1980 s, the demand f o r gasoline decreased due to more energy conservation measures, smaller and more e f f i c i e n t automobile engines, higher p r i c e s , and reduced economic growth. It i s g e n e r a l l y b e l i e v e d that the demand f o r gasoline w i l l continue to decrease. How ever, we expect an increased demand f o r middle d i s t i l l a t e s . Hydrocracking i s a p a r t i c u l a r l y e f f e c t i v e route f o r production f




310



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of incremental j e t and d i e s e l f u e l s . With modern hydrocracking c a t a l y s t s , y i e l d s of at l e a s t 95 LV % of s p e c i f i c a t i o n d i e s e l f u e l s (based on feed) can be obtained from heavy gas o i l s by hydrocracking. The demand f o r f u e l o i l i s expected to decrease. As i t decreases, r e f i n e r s w i l l consider using hydrotreaters that were o r i g i n a l l y b u i l t to make low s u l f u r f u e l o i l f o r p o s s i b l e con v e r s i o n to hydrocracking u n i t s . Bottom of the b a r r e l conversion continues to be a top r e f i n i n g p r i o r i t y . Hydrocracking i s expected to f i n d an impor tant place i n residuum conversion technology. For example, the German Veba processes are modern versions of the e a r l y German hydrocracking processes adapted to residuum (43). Because some of the pressures on world petroleum s u p p l i e s have been r e l i e v e d , i t i s now expected that, at most, s y n t h e t i c f u e l s w i l l have only a minor impact i n the 1980 s. However, a t l e a s t some s y n t h e t i c crudes from o i l shale are expected to be a v a i l a b l e i n the l a t t e r part of the decade. Hydrocracking remains the l o g i c a l choice f o r conversion of shale o i l to j e t f u e l (44). S i m i l a r l y , when c o a l l i q u i d s become a v a i l a b l e , they too w i l l be l i k e l y candidates f o r hydrocracking (45). We are continuing our research on the upgrading of s y n t h e t i c crudes by h y d r o t r e a t i n g and hydrocracking. In conclusion, we expect hydrocracking to play an important r o l e i n the r e f i n e r y of the f u t u r e . f

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RECEIVED October 29, 1982


The Development of Hydrocracking - ACS Publications - American

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