A History of Early Catalytic Cracking Research at Universal Oil

20 Downloaded by NANYANG TECHNOLOGICAL UNIV on September 20, 2017 | http://pubs.acs.org Publication Date: June 3, 1983 | doi: 10.1021/bk-1983-0222.ch020

A History of Early Catalytic Cracking Research at Universal Oil Products Company CHARLES L. THOMAS Tempe,AZ85282

Catalytic cracking research at UOP began in the early 1930's under the supervision of Dr. Hans Tropsch (of the Fischer-Tropsch Process) with the research work being done by Dr. Julian M. Mavity. The thrust of the research was to develop a catalyst that could be produced from an economical natural clay or mineral. It should be noted that certain clays were, at that time, well known in the refining of petroleum products. Most commonly, clays were used for decolorizing lubricating oils either alone or in conjunction with sulfuric acid treating and for stabilizing gasolines produced by thermal cracking. It was assumed that unstable hydrocarbons ("gum" formers), presumably dienes, were polymerized by the clay treating. Certainly higher boiling substances were formed so that that product had to be redistilled and the distillation curve of the gasoline (Engler or A.S.T.M) was altered. Some of the clays were "natural" clays as mined, e.g., Florida or Georgia clays. Others were natural clays that had been acid treated, e.g., the clays then supplied by the Filtrol Corporation. These clays, and others, were explored for the catalytic cracking of gas o i l . Quite a few had some activity but the most active was Superfiltrol from the Filtrol Corporation. This was thought to be a sulfuric acid treated montmorillonite or halloysite. This led to exploratory attempts to enhance the activity of Superfiltrol by adding small amonts of other substances as "promotors". Certain metal phosphates, especially acid phosphates and even phosphoric acid were mildly effective. It was known that Superfiltrol already had acidic properties but this was presumed to be residual traces of sulfuric acid remaining from the sulfuric acid treatment of the original clay. Dr. Tropsch proposed to "open up" feldspar, an alkali aluminum silicate, to produce an alumino-silicate catalyst. He had a reference saying feldspars could be "opened" by heating the feldspar with lime and calcium chloride followed by acid leaching. This gave encouraging results and evolved into 0097-6156/83/0222-0241$06.00/0 © 1983 American Chemical Society Davis and Hettinger; Heterogeneous Catalysis ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

Downloaded by NANYANG TECHNOLOGICAL UNIV on September 20, 2017 | http://pubs.acs.org Publication Date: June 3, 1983 | doi: 10.1021/bk-1983-0222.ch020

242

HETEROGENEOUS

CATALYSIS

"replaced feldspar" c a t a l y s t s that were more active than Superfiltrol. Since S u p e r f i l t r o l was an a l u m i n o s i l i c a t e , i t was thought that other metal s i l i c a t e s , n a t u r a l or s y n t h e t i c , might also be a c t i v e cracking catalysts. I was added to the catalytic cracking research team and was assigned t h i s part of the problem. I prepared some c o - p r e c i p i t a t e d c a t a l y s t s from water glass (sodium s i l i c a t e ) and aluminum s a l t s and U. S. Patent 2,282,922 proposing the use of these c a t a l y s t s was f i l e d March 20, 1937. At that time there were synthetic " z e o l i t e s " used for softening water by base exchange. These were amorphous sodium a l u m i n o s i l i c a t e s . Active cracking c a t a l y s t s were made from them by exchanging the sodium ions with other ions. In 1935, when Dr. Tropsch learned he was a f f l i c t e d with a terminal i l l n e s s , he gave up the work and returned to h i s native Germany. The research was i n t e r r u p t e d . I was assigned to work on the a l k y l a t i o n of isobutance under the supervision of Dr. A. von Grosse. This r e a c t i o n took place in the presence of strong acid c a t a l y s t s and the work l a t e r had an influence on my t h i n k i n g about c a t a l y t i c cracking. A l i t t l e l a t e r , a cracking research group was formed with me as supervisor and Drs. Gustav E g l o f f and J . C. M o r r e l l as directors. The group included, in i t s e a r l y years, Drs. J . E l s t o n Ahlberg, Herman S. Bloch, Edward C. Lee and Mr. George Tobiasson. We did research on both thermal and catalytic cracking. We started the c a t a l y t i c cracking work with the "replaced f e l d s p a r " as the c a t a l y s t . The feldspars have the composition MAIS13O3 i n which M i s K, Na, or Ca. It was assumed that the heating with lime and calcium c h l o r i d e "opened up" the f e l d s p a r . Acid leaching then removed the lime, calcium c h l o r i d e and a l k a l i metal ions and l e f t an a l u m i n o - s i l i c a t e of some kind. Dr. Ahlberg analyzed the c a t a l y s t to put our thinking on a more q u a n t i t a t i v e basis and found that the c a t a l y s t was mostly s i l i c a with only small amounts of alumina; far less than the A l : 3 S i of f e l d s p a r . From t h i s we concluded that the "replaced feldspar" preparation was mostly a method for preparing hydrous s i l i c a containing a l i t t l e alumina but s u b s t a n t i a l l y free of other m e t a l l i c ions due to the extensive a c i d treatment to remove the a l k a l i and calcium ions. We also concluded that p u r i f i e d s i l i c a hydrogel could be made less expensively from water glass (sodium silicate). S t a r t i n g with a large batch of undried, c a r e f u l l y p u r i f i e d s i l i c a hydrogel, h i g h l y active cracking c a t a l y s t s were prepared by p r e c i p i t a t i n g hydrous alumina on the s i l i c a . U. S. Patent 2,285,314 d e s c r i b i n g t h i s method of preparation was filed October 22, 1938. Since there was no obvious stoichiometry involved, we c a l l e d the products " s i l i c a - a l u m i n a s " . Besides s i l i c a - a l u m i n a , we found silica-magnesia and silica-zirconia were also h i g h l y a c t i v e cracking c a t a l y s t s .

Davis and Hettinger; Heterogeneous Catalysis ACS Symposium Series; American Chemical Society: Washington, DC, 1983.


20.

THOMAS

Early Catalytic Cracking

243

Similarly, we prepared a large batch of purified p r e c i p i t a t e d hydrous alumina and p r e c i p i t a t e d other m a t e r i a l s on it. We found that alumina-boria was an a c t i v e c a t a l y s t . Moving down the P e r i o d i c Table from s i l i c o n to titanium, we were not able to prepare an a c t i v e c a t a l y s t from t i t a n i a - a l u m i n a but t i t a n i a - b o r i a was a c t i v e . Besides c a t a l y s t e x p l o r a t i o n , we were also e x p l o r i n g other feed stocks besides our standard t e s t gas o i l and a l s o doing some catalytic cracking of pure hydrocarbons with silica-alumina. This l e d to the conclusion that the s i l i c a - a l u m i n a must be a high temperature a c i d ; a concept that came g r a d u a l l y rather than a " f l a s h of genius". For one thing, we saw that gas o i l s containing n a t u r a l n i t r o g e n compounds were more r e f r a c t o r y than the standard gas o i l , and deposited more coke on the c a t a l y s t during cracking even though the depth of cracking was l e s s . We removed a few percent of the gas o i l by a c i d t r e a t i n g (nitrogen bases removed) and the gas o i l cracked readily. The nitrogen bases were poisoning the high temperature acid catalyst. This was confirmed by adding a l i t t l e q u i n o l i n e to our standard gas o i l . In the c a t a l y t i c cracking of the pure hydrocarbons, the s u s c e p t i b i l i t y and r e a c t i o n products were compared with thermal cracking of the same hydrocarbons (1-5). The c a t a l y t i c cracking of cumene was amazingly easy and s e l e c t i v e compared to the thermal cracking. The c a t a l y t i c cracking was e s s e n t i a l l y pure d e a l k y l a t i o n to benzene and propylene. According to c a t a l y s i s theory, i f the c a t a l y s t dealkylates i t should a l s o a l k y l a t e . But alky l a t ion c a t a l y s t s are w e l l known to be acids so the cracking c a t a l y s t must also be an a c i d . More or less concurrently with our work, Dr. Louis Schmerling i n the same UOP Research Laboratories was studying the mechanism of the a l k y l a t i o n of isobutane with o l e f i n s . He showed c o n c l u s i v e l y that t h i s was a carbonium ion mechanism i n the presence of strong a c i d c a t a l y s t s , and that one of the key steps i n the mechanism was the t r a n s f e r of a hydride ion from a donor hydrocarbon to a t e r t i a r y carbonium i o n . There were enough s i m i l a r i t i e s with hydrocarbon reactions i n the presence of cracking c a t a l y s t s to j u s t i f y concluding that these are also carbonium ion r e a c t i o n s . We even showed that hydride t r a n s f e r r e a c t i o n s occurred i n the presence of cracking c a t a l y s t s at temperatures s l i g h t l y below normal cracking temperatures, and that at such lower temperatures cracked gasoline of very low o l e f i n content could be obtained from gas o i l . I n c i d e n t a l l y , there are c a t a l y s t s that accelerate cracking that are not a c i d i c , e.g., a c t i v a t e d carbons. They produce reactions that are quite s i m i l a r to thermal cracking and seem to be free radical reactions. There remained the question: How can s i l i c a - a l u m i n a be a high temperature acid? Minerology described many minerals i n


HETEROGENEOUS CATALYSIS


244

which an a l u m i n o - s i l i c a t e complex acts as an anion with various strong cations, e.g., Na, K, Mg, e t c . It i s i n t e r e s t i n g that at l e a s t a part of the aluminum i n these s i l i c a t e s i s thought to be in tetrahedral coordination with oxygen. Although our s i l i c a - a l u m i n a c a t a l y s t s were amorphous, i t seemed to us that a t r i v a l e n t aluminum in a matrix of t e t r a h e d r a l l y coordinated s i l i c o n with oxygen would also be t e t r a h e d r a l l y coordinated with the oxygen consistent with one of Pauling's r u l e s . This would leave un saturât ion i n the 4 oxygen atoms attached to the aluminum, i . e . I

Ο I

( - 0 - Α Ι - 0 - ) " ι Ο ι

This could be associated with a hydrogen ion to form a protonic acid or could lead to a Lewis a c i d . The fact that the c a t a l y s t was a high temperature a c i d was the important point to us. It confirmed our s p e c i f i c a t i o n s that, i n the commercial manufacture of the c a t a l y s t , sodium ions had to be reduced to very low levels to prevent them from migrating at high temperatures and n e u t r a l i z i n g the a c i d i t y . There remained the s u s p i c i o n that the a c i d i t y of the c a t a l y s t might be due to a c i d remaining from the preparation of the s i l i c a hydrogel from water glass by acid t r e a t i n g . This suspicion led to a s e r i e s of c a t a l y s t s made from e t h y l s i l i c a t e and aluminium isopropoxide i n which no acids were used. These were also a c i d i c and the a c i d i t y could be t i t r a t e d with a l k a l i as was the case with the s i l i c a - a l u m i n a from water g l a s s . I n t e r e s t i n g l y , both a c i d i t y and cracking a c t i v i t y of the e t h y l s i l i c a t e c a t a l y s t s came to a maximum at a S i : A l r a t i o of 1, i . e . , as the c a t a l y s t composition approached the h y p o t h e t i c a l H A l S i 0 (6). It may be worth noting here that the Petroleum Administrator f o r War during World War I I had an industry group, PAW 41, coordinate t h e i r e f f o r t s on c a t a l y t i c cracking. This group included Kellogg, S h e l l , Standard O i l Co. (Indiana), Standard O i l Co. of New Jersey (Exxon), Texaco and U n i v e r s a l O i l Products Co. I gave a report "What Makes the Cracking C a t a l y s t Crack" at one of t h e i r meetings, d e s c r i b i n g the s i l i c a - a l u m i n a c a t a l y s t as a high temperature a c i d and g i v i n g evidence r e l a t i n g to the s t r u c t u r e of the c a t a l y s t i t s e l f plus d e s c r i b i n g the cracking as carbonium ion r e a c t i o n s . The report was then classified. After the War and after the report was d e c l a s s i f i e d , i t was published (6). This summary was w r i t t e n 40 to 50 years a f t e r the f a c t s without access to the primary documents. While the f a c t s are b e l i e v e d to be as stated, a f a u l t y memory may have a l t e r e d something u n i n t e n t i o n a l l y . 4


20.

THOMAS

Literature 1. 2. 3.


4. 5. 6.

Early Catalytic Cracking

245

Cited

Egloff, G . ; Morrell, J. C.; Thomas, C. L.; Bloch, H. S. J. Amer. Chem. Soc., (1939), 61, 3571. Thomas, C. L . J . Amer. Chem. Soc., (1944), 66, 1586. Bloch, H. S., Thomas, C. L. J . Amer. Chem. Soc., (1944), 66, 1589. Thomas, C. L., Hoekstra, J.; Pinkston, J. J. Amer. Chem. Soc., (1944), 66, 1694. Thomas, C. L., Hoekstra, J.; Pinkston, J. J. Amer. Chem. Soc., (1944) 66, 1694. Thomas, C. L. Ind. Eng. Chem., (1949), 41, 2564.

RECEIVED November 17,

1982


A History of Early Catalytic Cracking Research at Universal Oil

Recommend Documents