US2833834A - Alkylation of high boiling catalytically cracked products - Google Patents

Description

y 958 J. REHNER. JR.. EIAL ALKYLATION OF HIGH BOILING CATALYTICALLY CRACKED PRODUCTS Filed July 16, 1953 FRACTl-QNATOR REGENERATOR |2 I Q 4 3 CRACKING a ZONE 9 4 2 r 1 GRID |6 I I l--- I IS ,7 GRID '0 l l SETTLING 6 ONE l9 1 AIR 7 SETTLER 2o 24 4 IF on. PRoDuc'r' AL I YLATION ZONE JOHN I-LREHNER JR.

LAWRENCE T EBY IIVEIITOR United States Patent ALKYLATION OF HIGH BOILING CATALYTI- CALLY CRACKED PRODUCTS John Rehner, Jr., Westfield, and Lawrence T. Eby,

Linden, N. J., assignors to Esso Research and Engineering Company, a corporation of Delaware Application July 16, 1953, Serial No. 368,376

3 (Ilaims. (Cl. 260-671) leum molecules are broken down into small molecules providing products such as gasoline, kerosene, home heating oils and diesel oils. However, in the catalytic cracking process there is a residual material which contains higher boiling constituents including a substantial concentration of high boiling polycyclic aromatic hydrocarbons. Higher boiling residual material of this character is frequently used for industrial fuels.

Because the residual fractions of catalytic cracking referred to contain polycyclic aromatic hydrocarbons, it was suspected that this material might be carcinogenic in character. At this date it has been established that this is the fact, at least as applied to lower animals. Furthermore, this has been borne out by a limited amount of information indicating that direct contact with certain higher boiling petroleum fractions has caused occupational cancer in man. As a result of this discovery, it has become important to provide all possible safeguards to prevent any possibility for the occurrence of cancer due to contact with high boiling catalytically cracked products.

The problem has heretofore been met by economically expensive expedients. For example, it has been recommended that the high boiling catalytically cracked residues which are suspected of being carcinogenic must be blended with noncarcinogenic products so as to include no more than of the carcinogenic fraction; such blends have been shown to be safe. This has created some problem in the disposal of the heavy residues from catalytic cracking and has caused a considerable loss in the economic value of the residual cracked products.

Since this problem was first recognized, it has been ap preciated that some technique should be found for minimizing the carcinogenicity of heavy catalytically cracked residues. Such methods should be employed in order to further minimize the occupational hazard of handling or processing such stocks and in order to eliminate need for the more expensive safety expedients heretofore used, The present invention is directed to this purpose and for the first time provides a practical and eflicient process for reducing the carcinogenicity of heavy catalytically cracked residues.

The process of this invention is a relatively simple process providing for the alkylation of carcinogenic petroleum fractions.

This process is based on fundamental work which has been carried out to determine the carcinogenic compo ncnts of heavy, catalytically cracked stocks. In an early phase of this work, a wide variety of hydrocarbon com-- pounds of the nature which have been identified in such stocks were tested for their carcinogenic properties. This work established that carcinogens present in high boiling catalytic stocks are generally polynuclear aromatic hydrocarbons which are either devoid of alkylgroups attached to the aromatic nuclei or alternatively have a few low molecular weight, alkyl groups attached to the nuclei. It was found that the introduction of alkyl groups having about 8 carbon atoms into carcinogenic polynu= clear aromatic hydrocarbons renders such compounds inactive. The process of this invention is therefore based on the discovery that carcinogenic oils can be rendered inactive by introduction of alkyl groups having about 8 carbon atoms into the molecules.

In the work on which this invention is based, it was discovered that what may be called a selective alkylatio'n' could readily be obtained. By employing an olefin having about 8' carbon atoms, it was found that such olefins could be reacted selectively with the carcinogens present in heavy catalytically cracked stocks. This presumably follows from the statement formerly made that carcinogens have few or no alkyl groups attached to the molecule. Apparently, under alkylation conditions, it there fore becomes possible to alkylate these compounds without substantially changing the properties of the other constituents of catalytically cracked stocks. This selective alkylation is a particular feature of this invention. It becomes possible to eliminate the carcinogenicity of cata lytically cracked stocks without appreciably changing the character of the stocks.

Conventional alkylation catalysts and alkylation conditions may be employed. Thus, if desired, thermal al-' kylation carried out at high pressures and high tempera tures can be used to secure the reaction of the indicated olefins with the carcinogens. Preferably, however, alkylation catalysts are to be employed making possible the use of lower temperatures and lower pressures. The alkylation catalysts can constitute aluminum chloride, concentrated sulfuric acid, hydrofluoric acid, boron lluoride or others of the compounds known to promote the alkylation reaction. With a suitable catalyst of this character, the alkylation can proceed readily at temperatures of about 0 to 200 degrees centigrade, and pressures of about 0 to p. s. i. Since the stocks to which this invention have application are relatively difiicult to al-' kylate, the reaction period to be used is relatively long and in the range of about 0.5 to 10 hours. In general, about 1 to 10% of an alkylation catalyst is to be employed, and from 5 to 100% of the alkylating olefin, depending on the nature of the stock, the amount of catalyst employed, and the temperature and pressure of the process.

As described therefore, the process of this invention entails the contact of an olefin having about 8 carbon atoms with carcinogenic high boiling catalytically cracked products under alkylation conditions.

The accompanying drawing diagrammatically illustrates an embodiment of the invention showing the overall processing of petroleum fractions resulting in the formation of carcinogenic products and permitting the destruction of the carcinogenic components in accordance with this invention.

A conventional catalytic cracking system is illustrated in the drawing including the cracking zone 1, the catalyst regenerator 2 and the product fractionator 3. While it' will be understood that this invention is of application to catalytically cracked products however obtained, the process illustrated is a fluidized catalytic cracking operation. In this process conventional and well-known cracking catalysts may be used such as silica-alumina mixtures,

like. In the particular process illustrated, a gas oil feed stock may be introduced to the cracking zone through line 4. This is brought into the reaction zone 1 through a suitable distributing grid so as to be brought in contact with a mass of cracking catalyst maintained in fluidized condition in the cracking zone 1. For this purpose, particles of cracking catalyst of suitable size are employed and the ratio of oil to catalyst is maintained so as to permit the establishment and maintenance of a fluidized condition. In this condition, upfiowing oil vapors passing through the catalyst particles cause the catalyst to have the general characteristics of a liquid. Thus, the catalyst bed is characterized by an upper surface and the bed has the general hydraulic properties of a liquid. During passage through the cracking zone at a temperature of about 800 to 1000 F., the oil feed stock undergoes the cracking reaction and the cracked products may be removed overhead through line 5. As will be described, these cracked products are subjected to fractionation in the fractionation zone 3.

Cracking catalyst is continuously withdrawn from the fluidized bed of catalyst in zone 1 through line 6. Air is introduced to intersecting conduit 7 so as to force the catalyst upwardly into the regeneration zone 2. In the presence of the air, carbonaceous impurities are oxidized in zone 2 so as to regenerate the catalyst. The products of this oxidation are removed overhead through lines 8 and 9, while the regenerated catalyst is withdrawn from the regenerator through line 10 for recycle to the cracking zone through line 4.

It is not considered necessary to further describe the catalytic cracking operation identified since this is not a part of the present invention. As indicated, however, regardless of the manner of carrying out the catalytic cracking reaction, a cracked product stream is obtained which is fractionated in a distillation tower such as fractionator 3 illustrated. In fractionationzone 3 the catalytically cracked products are separated so as to permit a withdrawal of gaseous products from the uppermost portion of the fractionator through line 11. Light boiling, liquid products such as gasoline may be withdrawn from suitable side stream withdrawals such as line 12. Higher boiling products are withdrawn from other withdrawals positioned at lower portions of the fractionator and from the bottom withdrawal of the fractionator. For example, fractionator 3 may be operated to permit withdrawal of a side stream through line 13 boiling above 700 F. Such a side stream is commonly identified as cycle oil. Still heavier boiling residual products of cracking are then withdrawn from the lowest portion of the fractionator through bottom withdrawal 14. The bottoms product will contain small proportions of catalyst particles carried over from the cracking zone. Consequently, this fraction is passed to a settling zone 15 permitting withdrawal of a clear or clarified slurry oil through line 16.

As described, fractionator 3 is operated to permit segregation of the portion of the cracked products boiling above 700 F. This particular fraction of the cracked products is specified since it has been established that the portion of the cracked products boiling below 700 F. is noncarcinogenic. For this reason, the process of this invention is applied to the products withdrawn from the fractionator through lines 13 and 14 boiling above 700 F. Sharp fractionation is not required however, and lower boiling constituents may be included.

Either or both of the product streams of lines 13 and 14 may be processed. As illustrated, these product streams may be combined and passed together to the alkylation zone 17.

The temperature of the product streams of lines 13 and 16 may be adjusted to the alkylation temperature by passage through the heat exchanger 19. Alkylation catalysts and the olefin to be used for alkylation may be admixed with the stream of lines 13 and 16 by introduction of the catalysts through line 18. The high boiling 4 catalytically cracked materials together with alkylation catalysts are then brought into the alkylation zone 17.

Alkylation zone 17 may be of conventional character providing for the thorough and intimate contact of the catalytically cracked materials, the olefins and the alkylation catalyst. Thus, alkylation zone 17 may be of the character providing for the jetting of olefins into the stream of catalytically cracked products, or mechanical agitators may be provided in zone 17. Suitable heat exchange equipment may be provided in or about zone 17 so as to suitably control the alkylation temperature. In the drawing, zone 17 is illustrated as having a reaction product withdrawal line 20 together with a recycle line 21. Recycle line 21 may be used for the recycle of alkylation product so as to maintain a high ratio of product to olefins in the conventional manner.

The alkylation product withdrawn from the system is passed to a settling zone 22 wherein the product may be separated from the alkylation catalyst employed. For example, in the case in which aluminum chloride is employed as the catalyst, the aluminum chloride may be separated in settler 22 by a phase separation. In general, sulfuric acid and the other alkylation catalysts which can be employed, are separated in a similar manner permitting the withdrawal of spent catalyst through line 23 and the alkylated oil product through line 24. The oil product may be subjected to caustic washing, water washing, and the like, to eliminate residual portions of the alkylation catalyst.

The alkylated oil product withdrawn from line 24, is substantially identical in character to the product withdrawn from the catalytic cracking fractionator. However, the alkylated product will be characterized by the addition of alkyl groups of about 8 carbon atoms to the carcinogens of the alkylation feed. This renders the final product of line 24 substantially inactive as regards carcinogenicity. As a result, the product of line 24 may safely be employed as a fuel oil or for any other desired use as an end product. However, it is a particular feature of this invention that the alkylated catalytically cracked oil of line 24 may, if desired, be recycled to the catalytic cracking zone 1. In this connection it has been found that recycle catalytic cracking of the entire high boiling fraction of catalytically cracked products has heretofore been undesirable or uneconomical. Recycle cracking is not successful in breaking down the objectionable carcinogens present in the heaviest portion of the catalytically cracked products. As a result, conventional recycling of such materials does not serve to reduce the carcinogenic nature of the final product. However, by reducing the carcinogenicity of the heaviest catalytically cracked products prior to recycle in accordance with this invention, recycle catalytic cracking becomes attractive. It is thereby possible to effectively upgrade the heaviest catalytically cracked products by repeated cracking to more valuable light fuel products.

In order to fully demonstrate the nature and advantages of this invention, reference will be made to typical experiments conducted to evaluate the invention. In a first experiment the fraction of catalytically cracked products boiling above 700 F. was segregated from a commercial cracking operation. This fraction was tested for carcinogenicity according to the procedure identified in the paper Properties of high boiling petroleum products by Dietz, King, Priestley and Rehner, published in Industrial and Engineering Chemistry, vol. 44, page 1818. This procedure permits an identification of the carcinogenicity of a sample by determination of the tumor potency of the sample in carefully controlled tests with mice. In the scale employed, tumor potency values of 50 or 60 or more are considered high. Potency values of about 30 or less are low or marginal and commonly indicate that only benign tumors would result. When the identified sample was tested in this general manner, it was found to have a tumor potency of about 61.

In order to evaluate the process of this invention, the fraction of catalytically cracked products identified, was subjected to contact with diisobutylene unde'r alkylation conditions. In the experiment conducted 8.25% aluminum chloride was mixed with the catalytically cracked products as an alkylation catalyst. 40 weight percent of diisobutylene was then intimately contacted with the heavy catalytic oil and the aluminum chloride for a period of 2 /2 hours at 100 C. After this alkylation .period the catalyst was separated from the product by washing With aqueous acid and with water. Excess diisobutylene was stripped from the product.

The properties of the catalytic oil feed and the alkylated product are shown in Table I. In this table, the cafieine number is an indication of the carcinogenicity of the material as described in the publication properties of high boiling petroleum products, physical and chemical properties as related to carcinogenic activity, by Fischer, Priestley, Eby, Wanless, and Rehner, published in Archives of Industrial Hygiene and Occupational Medicine, vol. 4, page 315 (1951). The portion of aromatics and non-aromatics was determined by a characterization procedure employing silica gel in an elutriation technique found satisfactory to separate these constituents.- The refractive index of the different fractions is given as an indication of the substantial identity of the molecular composition of the aromatic and non-aromatic portions of the feed and product.

It will be observed from these data that the alkylated product showed relatively little change in character from the catalytic oil employed as feed. The only outstanding difference as shown in the table is the calfeine number of the two samples. The caffeine number, as established in the publication referred to, indicates that the alkylation was successful in materially reducing the carcinogenicity of the catalytic oils.

This was borne out by the determination of the tumor potency values of these samples. As indicated, the original catalytic oil employed as a feed was found to have 'a tumor potency of about 61. However, after alkylation it was found that the alkylated product had a tumor potency of only 35. It was therefore established that the alkylation process of this invention is effective in substantially inactivating objectionable catalytically cracked oils.

In order to verify this result to'establish that alkylation was responsible for this improvement, in a control test, the catalytic oil feed was contacted with the same proportion of aluminum chloride for the same period of time and at the same temperature, but without the addition of diisobutylene. It was found that this was not successful in changing the tumor potency value of the catalytic oil. This indicates that aluminum chloride does not effectively isomerize the catalytic oil under the conditions employed, and establishes that the essential mechanism depends upon alkylation of the catalytic oil.

What is claimed is:

1. A process for reducing the carcinogenicity of a catalytically cracked petroleum fraction boiling above about 700 F. which comprises intimately contacting said fraction under alkylation conditions with an olefin having about 8 carbon atoms per molecule and selectively alkylating carcinogenic constituents of said fraction.

2. A process as defined by claim 1 wherein said fraction is contacted with diisobutylene in the presence of an aluminum chloride catalyst.

3. A process as defined by claim 1 wherein said fraction is recycled to a catalytic cracking process following said selective alkylation.

References Cited in the file of this patent UNITED STATES PATENTS Wadsworth et a1 Feb. 22, 1949 Loane et al Dec. 13, 1949 OTHER REFERENCES

Claims (1)

1. A PROCESS FOR REDUCING THE CARCINOGENICITY OF A CATALYTICALLY CRACKED PETEOLEUM FRACTION BOILING ABOVE ABOUT 700*F. WHICH COMPRISES INTIMATELY CONTACTING SAID FRACTION UNDER ALKYLATION CONDITIONS WITH AN OLEFIN HAVING ABOUT 8 CARBON ATOMS PER MOLECULE AND SELECTIVELY ALKYLATING CARCINGENIC CONSTITUENTS OF SAID FRACTION.

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