US2859172A - Combination catalytic cracking process - Google Patents

Description

Nov. 4- 1958 w. G. REYMOND I 2,859,172 COMBINATION CATALYTIC CRACKING PROCESS Filed Oct. 26. 1954 1 5 DISTILLATION Y ZONE 2 CATALYTIC 3 r 6 }f: "CRACKING a ZONE T 4 FRACTIONATING 32 ZONER 2 3h. I

GAS OIL LUBE RAFFINATE CYCLE o "5 F 28 RAFFINATE |5 RAFFINATE PHENOL HEAVY GAS -J Z QIL 53cm IO OIL CYCLE OIL AROMATIC EXTR CT EXTRACT 1 INVENTOR.

WILLIAM G.REYMOND ATTO NEY United States Patent COMBINATION CATALYTIC CRACKING PROCESS William G. Reymond, Baton Rouge, La., assignor to Esso Research and Engineering Company, a corporation of Delaware Application October 26, 1954, Serial No. 464,768

6 Claims. (Cl. 208-87) This invention relates to the refining of petroleum oils aromatic hydrocarbon types which are refractory to cracking. In another aspect, the invention includes a method for improving the value of a virgin gas oil fraction of a petroleum oil for catalytic cracking by substantially reducing or eliminating organic compounds containing metals that normally are present in the gas oil. Furthermore, the invention includes provision for improving the quality of the extract hydrocarbons obtained from extraction of a lubricating oil distillate, making these bydrocarbons more suitable for catalytic cracking.

The basic feature of this invention concerns the solvent extraction of virginor cracked fractions of petroleum boiling in the gas oil boiling range so as to upgrade these fractions for use as catalytic cracking feed. The invention entails the use of selective solvents for aromatic hydrocarbons, employing these solvents to efliciently remove metal contaminants and refractory hydrocarbons from catalytic cracking feed stocks with substantially no loss of hydrocarbon constituents suitable for cracking. This is achieved by employing at least two extraction stages, in one of which cracked fractions of petroleum are treated and in the other of which virgin fractions of petroleum are treated. The heart of this invention entails the use of the total extract phase from one of these extraction stages for the treating or extraction agentin the other of the extraction stages. This innovation not only materially simplifies solvent recovery facilities but greatly improves the efliciency with which constituents are removed which are undesirable for catalytic cracking.

In its most specific and :preferred form, the present invention accomplishes these objectives by integrating a lubricating oil extraction process with a catalytic cracking operation. In one embodiment of the invention, a lubricating oil is treated in an extraction operation with a selective solvent for aromatic hydrocarbons. The total extract phase formed in this extraction step is then used to contact catalytic cycle oil providing a first rafiinate product. The total extract phase from this extraction of.

catalytic cycle oil is then employed to contact a gas oil which has undesired organic compounds containing metal contaminants providing a second rafiinate product. The

I combined rafiinate products resulting from these treatments include substantially all of the desirable constituents of the lubricating oil extract, cycle oil, and gas oil which are suitable for catalytic cracking while minimizing inclusion of detrimental metal contaminants and refractory aromatic hydrocarbons. In another embodiment of this invention, the extract phase from extraction of a' lubricating oil is used to contact gas oil. The extract phase resulting is then used to contact catalytic cycle 7 tivity and life of this catalyst.

. at an economically prohibitive cost.

the fact that the phenol acts as a selective solvent to re' 2 3 oil. The cycle oil and gas oil rafiinate products are particularly suitable for cracking.

In these and other specific embodiments of the invention high molecular weight aromatic hydrocarbons present in the solvent extract phase of -a prior contacting step, serve to alter the nature of the gas oil and cycle oil ex traction so as to provide rafiinate products of improved characteristics forcatalytic cracking feed.

As indicated, the present invention comprises arla tively complicated. combination of a variety of treating steps and refining processes. In order to lay a basis for fully understanding the nature and features of this invention, attention will be directed to several aspects. of the field involved.

At the present time, the process of catalytic cracking is extensively employed for converting high boiling portions of a petroleum crude oil to lighter boiling, commercially valuable products including gasoline and heating oils. The feed stock to a catalytic cracking unit ordinarily constitutes portions of 'a petroleum crude oil boiling above the gasoline boiling range or boiling above about 430 F. It is economically desirable to include the highest boiling fraction of a petroleum crude oil attainable by the vacuum distillation of atmospheric reduced crude, and for this purpose, the feed to a catalytic cracking unit preferably includes constituents of the crude oil boiling up to about 1100 F., or higher. As used herein, the term gas oil is used to identify this portion of a crude oil boiling in the range of about 430 to 1l00' F. or somewhat higher.

For some time it has been appreciated that inclusion organic compounds which contain certain metal contaminants. Among the organic metallic contaminants present in heavy gas oil compounds of nickel, vanadium and iron are particularly objectionable in poisoning the catalyst used during catalytic cracking so as to decrease the selec- Recognizing this problem, there have been many suggestions aimed at minimizing metal contamination of gas oils to catalytic cracking feed. In this connection, one possibility is that organic metal contaminants can be reduced by contacting the gas oil with a solvent such as phenol. The contacting of phenol and gas oil reduces these contaminants, but

move aromatic constituents of the gas oil as well as the undesired compounds containing metal contaminants. 'As a result, phenol contacting of gas oil conducted to eliminate organic metal contaminants of the gas oil provides a raflinate product in undesirably low yields. mainder of the gas oil is present in the extract phase from this contact together with the organic metal contaminants removed from the raflinate. From the standpoint of hydrocarbon types, it is desirable to use the extract portion of the gas oil for catalytic cracking feed as well as the raflinate portion. It is apparent therefore that this process does not provide the desired objective of selectively separating the organic metal contaminants from the gas oil usable as catalyticcracking feed.

A basic feature involved in the present invention is thev discovery that a selective solvent for aromatic hydrocarbons can be used to selectively extract organic metal feed. This is made possible by inclusion of high molecular weight aromatic hydrocarbonsin the selective solventgas oil extraction system. The included high molecular,

weight aromatic hydrocarbons serve to displace compo- This results from.

The renents of the gas oil normally extracted by fresh solvent alone. Another-feature of this invention is the discovery that these high molecular weight, aromatic hydrocarbons actually serve as a solvent for these organic metal .constituents. Consequently, larger reduction of these contaminant-sis realized.

' It-hasbeen' found that the high molecular weight aromatic compounds present'in the extract phase of a catalytic cycle oil extraction process or alubricating oil extraction process are uniquely adapted to provide the above function. Consequently, ,one aspect of the present invention entails the contact of a'heavy gas oil with a selective solvent in the presence of aromatic hydrocarbons obtained from heavy cycle oil derived from a catalytic cracking process or in the presence of aromatic hydrocarbons derived from a lubricating oil. It is a particular feature of this invention that the desired-aromatic hydrocarbons are derived from cycle oil or lubricating oil by solvent extraction, using the extract phase resulting from this contact as a selective solvent-for gas oil extraction with use of the resulting extract phase in subsequent extraction steps, if desired.

'The principles of this invention are illustrated in the accompanying drawing, which illustrates in diagrammatical form a flow plan embodying a specific embodiment of the invention.

Referring to the drawing, the processing steps involved in the practice of this invention are illustrated. The numeral 1 designates a catalytic cracking zone. The operation conducted in zone 1 may constitute any desired type of catalytic cracking operation. Thus, the catalytic cracking may constitute the fixed bed type of cracking, moving bed type of cracking, or fluidized catalytic cracking. In each of these types of operation, any of the various Well known cracking catalysts may be employed. Generally, such catalysts are'the metal oxide types and preferably include silica-alumina, silica-magnesia, or silica-gel promoted with metal oxides" which are adsorbed thereon. Typical cracking conditions are at temperatures in the range of about 750 to 1050 F., and pressures ranging from atmospheric to somewhat above atmospheric pressure. The catalytic agent employed is regenerated intermittently or continuously in order to restore or maintain the activity of the catalyst.

Inv accordance with this invention, a particular catalytic cracking feed stock as derived in the manner described hereinafter is introduced to catalytic cracking zone 1 through line 2. For the present, it is sufficient to note that the feed to catalytic crackingzone 1 generally includes the fraction of a crude oil boiling within the range of about 430 to 1100 F. or higher. For typical operation, catalytic cracking of this feed stock would result in con- 800 F. may be removed from the lower sidestream with-,

drawal 7. Heavy residual. fractions of the vcatalytically cracked products are removed from the bottom of the fractionator through line 8. Bottoms withdrawal stream 8 wil include the highest boiling constituents of the cracked products including hydrocarbons boiling up to about 1100 F. or somewhat higher. In the event that powdered catalyst is employed in the catalytic cracking zone 1, some catalyst will be entrained in the bottoms Withdrawal. In this casethe product of line 8 may be device. A raflinate phase may then he recovered from subjected to a clarification or settling operation in order to segregate the hydrocarbons 'from cracking catalysts. The product of this operation is commonly called clanfied oil and the stream of line 8 wil be so designated 1 preferably employs both of these products as combined,

in line 9 of the drawings and designated by the term cycle oil.

It is well known that cycle oil of the character identified is more refractory than virgin catalytic cracking feed stocks of the same boiling range and consequently constitutes relatively poor catalyti cracking feed stock.

Cycle oil particularly includes refractory, high .molecthv lar weight, aromatic hydrocarbons which, if recycled to a catalytic cracking operation, cause excessive .forma-.

tion of undesirable gas, .coke and .tar during-catalytic; cracking. The constituents of cycle oil whichare ,par-

ticularly objectionable for cracking are high molecular.

weight, aromatic hydrocarbons. The aromatic ,hydrocarbons present in cycle oil include polynuclear aromatic hydrocarbons and condensed ringaromatic hydrocarbons.

The condensed ring aromatic hydrocarbons are particularly undesirable for inclusion in catalytic crackingfeed stock. As will be seen, the process .of this invention.

provides a means for improving cycle oil for catalytic cracking by elimination of these undesirable aromatic hydrocarbon types. 4 1

In accordance with the illustrated embodiment of .the

.invention, the cycle 'oil is contacted with the :extract l phase of a lubricating oil extractionprocess. This-:ex-

tract phase may be obtained from the process illustrated at the left of the drawing occurring in the extractionzzone In zone 12, a lubricatingoildistillat'e constituting the fraction of a crude oil boiling in'the range..of:about* 500 to 1100 F. is contacted with a selective solvent adapted to selectively extract aromatic constituents of"- the lubricating oil. Phenol is oneof the selective solvents which may be employed, although other solvents maybe employed such as furfural,nitrobenzene, aniline,

cresol, etc. Anti-solvents or solventmodifiers may he used and conventionally are used in conjunction with these solvents for the extraction of a lubricating oil. For

example, in the case of phenol, about 1 to 15% or some? what higher percentages of water are preferably mixed" with the phenol or separately injected during extraction, to provide .the best extraction results. stood therefore, thatthe lubricatingoil extraction process conducted in zone 12 may constitute any desired type i As diagram- I of selective solvent extraction operation. matically illustrated, extraction can be conducted-byin troducing lubricating oil at'the lower portion ofthe'extraction zone through line 13. The selective solvent; such as phenol, is introduced into the top of the illustrated extraction zone through line 1'4. The phenol will i move downwardly through the extractionzone countercurrent to an upwardly moving stream offlubricatin'g' oil; permitting extraction of constituents of the lubricating oil by the phenol during this contact. Perforated" plates, pack1ng,fetc., may be usedin the tower to aid this con- Alternatively, the extraction zone may be a' tac'ting. tank mixer-settler combinationor a centrifugal extraction the uppermost portion of the tower and withdrawn through line 15, the product of which upon dewaxing.

The extractphase re-.. moved from the bottom ofthe tower through line.1'6'-L Will include the spent phenol solvent together with the, extracted Virgin aromatic constituentsof the lubricating constitutes a finished lubricant.

It isl to be under- In this extraction process, the solvent to oil ratio will ordinarily be between about 0.5 to 1 and 3 to 1. When employed phenol, or phenoLwater mixtures as the selective solvent, a solvent to oil ratio of about 1 to 1 to 2 to 1 is particularly suitable. In the case of phenol extraction, the extract phase of line 16 will primarily constitute spent phenol including aromatichydrocarbons extracted from the lubricating oil. In general, the extract phase, will constitute about 60 to 95% (preferably 75 to 85%) phenol and about 40 to 5% of hydrocarbons extracted from the lubricating oil. enton the amount of water injection, about 0 to of water'will be included in the extract phase.

This extract phase resulting from selective extraction of a gas oil to produce high quality lubricating oil is usually of value as a catalytic cracking feed stock. The extracted hydrocarbons for the most part constitute single nucleus aromatic hydrocarbons with substituted alkyl radicals which make the compounds sufficiently parafiinic so that they can be attractively subjected to cracking. In the past, after solvent removal, the extract hydrocarbons from a lubricating oil extraction process have been used as catalytic cracking feed. The 'solventrecovery operation is a processing step which requires extensive and expensive recovery facilities. It is one of the features of this invention to permit extraction of catalytic cycle oils without the addition of such expensive equip-' ment by making use of the lubricating oil extraction process in a novel and inexpensive manner.: This is achieved in accordance with this invention by employing the lubricating oil extract phase as the extraction agent for catalytic cycle, oil. Incidental quality improvement is realized for lubricating oil extract as a catalytic cracking-feed.

For this purpose, the totalextract phase from the lubricating oil extraction is contacted with the cycle oil of line 9. This' may be carried out in any kind of extraction zone which may be an extraction tower 24 similar in:

Thus, the cycle oil will nature to extraction tower 12. be introduced to a lowermost portion of tower 24 through line 9 while lubricating oil extract phase will be introduced to the top'of'tower 24 through line 16. Cycle oil will flow upwardly through the tower countercurrent to downwardly moving portions of the lubricating oil extract phase. l l 1 This contacting results in displacement of lubricating oil constituents from the phenol solvent by cycle oil consti'tuents. In particular, it appears that condensedring aromatic hydrocarbons present in the cycle oil are more soluble in the solvent than the extracted lube constituents in the lubricating oil extract phase. Therefore, these extract hydrocarbons are displaced from the phenol phase. It has been found that substantially all of the lubricating oil constituents can be recovered from the lube extract phase so as to be removable as a rafiinate product from the top of tower 24 through line 25. This raffinate product will also include constituents of the cycle 'oil suitable for catalytic cracking.

The extra t phase formed in tower 24 is removed as a bottoms product through line 26. This extract phase. will-include most of the phenol originally introduced to In addition, dependtower 27 Preferably'the cycle oil extract phase is used in amounts of about 125 to 225% based on the-gasoil.

feed. The virgin gas oil of line 10 may constitute, the gas oil fractions of a crude oil boiling above about 430 F. The present invention is of particular application to gas oils in the higher boiling range up to 1150 F., or somewhat higher in which higher concentrationsof or-- ganic metal compounds exist. As indicated, such gas oils are characterized by inclusion of organic compounds containing metal contaminants such as nickel, vanadium I and iron. These metallic compounds may be present in amounts of about 0.00002 to a 0.001% or somewhat higher. The process of this invention is of application to such gas oils in permitting removal of the metalcontaminants referred to.

In tower 27, contact of gas oil with the cycle oil extract phase results in the selective removal of metallic contaminants from the gas oil. Since the solvent present in the cycle oil extract is essentially saturated with high molecular weight, condensed ring aromatic hydrocarbons, extracted from cycle oil, substantially none of the gas oil is taken up by solvent in extraction tower 27." As a result, the rafiinate product withdrawn from tower 27 through line 28 comprises the hydrocarbon composition of the heavy gas oil introduced to the tower through line 10, with the substantial exclusion of the inants originally present in the gas oil.

The extract phase removed from tower 27 through line 29 will constitute spent phenol solvent together with highly aromatic hydrocarbons extracted from cycle oil and metal contaminants removed from gas oil. Solvent tower 12 through line 14 and will include aromatic hydrocarbons' extracted primarily from the cycle oil. In

general, the cycle oil extract will include about 40 to 90% (more narrowly, to phenol, and about 0 to 15% water, assuming that water is mixed with the phenol solvent during extraction, This cycle oil extract is em-- ployed to contact a heavy gas oil in extraction zone 27' which may ,be'a tower, a tank mixer-settler combination, or a centrifugal extraction device. In the illustration, a tower is depicted.

In accordance with this invention, the cycle oil extract phase of' line 26 is contacted with a virgin gas oil introduced to thesystem through line 10 for treatment in may be recovered from this extract phase and the purified solvent can be recycled to line 14 constituting the phenol fed to tower 12. The concentrated aromatic hydrocarbons segregated in the extract phase are valuable for many purposes.

The raffinate products of line 25 and 28 are combined in line 30 and passed to distillation zone 31. Fractionation zone ,31 is operated to permit removal of phenol through line 32 and to permit removal of hydrocarbon constitutents' of the combined rafiinates through line 33. The phenol recovered through line 32 may be recycled to the system through line 14 of extraction tower 12. The hydrocarbon products of line 33 are then employed as the feed to catalytic cracking zone 1 supplied through line 2. In order to establish the novel and advantageous features of this invention, reference will be made to exemplary data showing the particular advantages of the multi-stage contacting described.

In order to demonstrate the operation of the first two stages of the process described, conducted in extraction zones 12 and 24, two phenol extraction units of a lubricating oil refining plant were converted to the processing principles of this invention. In one of the phenol extrac- Gravity, API 26.5-27.5

Viscosity, SSU/210" F. 39-42 Aniline point, F. 185-195 Diesel index -1 49-54 This distillate was treated with phenol in a counter.- current extraction tower providing about 5 theoretical stages. The feed rates were about 12,300 B./S. D. of phenol and about 7,450 B./S. D. of lube distillate to pro vide a phenol treat of Water injection was main tained during extraction to "provide a total injection metal contam- A typical 7 amount of about 2.5%, based on the phenol. The extractiontemperature was about-145 F.

Theextract phase obtained from this operation, constituted 84% penol; 2% water, and 14% hydrocarbons extractedfrom the lubricating oil feed. Thehydrocarbon constituents of the extract phase were primarily mono-nuclear aromatic compounds having substantial alkyl side chain substitution. Phenol'was separated from a portionof this extract phase and it was found that the 8 treat expressed as the ratio of extract phase-to cycle oil. About 5 vol. percent water, based on the extract-phase; was injected during extraction. The temperature mainvol. percent based on total oil feed. The rafiinateprod hydrocarbon constituents of the extract phase had the 1; uct had the following inspections: following inspections: Gravity API 303 Gravity, .API 16.8- Viscosity, SSU/210 F. 41.3 Viscosity, SSU/2'10 F. 48.5 Silica gel analysis: 7 Silica gel analysis: v Aromatics, wt. percent 25.8 Aromatics, wt. percent 69.9 Paraifins, wt. perceent 74.2 Parafiins,.wt. percent 30.1 Conradson carbon, wt. percent 0. 11 Conradson carbon, wt. percent 0.3 Aniline point, F. 205.7. Aniline point, F. 130 Diesel index 62.3 Diesel index 22 no Distillation, mm. Engler: Distillation, 10 mm. Engler: I. B. P., F 321 I. B. P.', 'F.' 366 5% 390 5% 411v 50% 483. 50% 490 90% 576 n 584 For comparative purposes significant data including The economical disposition for these hydrocarbons is to that of the foregoing tests are collected'and reproduced catalytic cracking feed. Consequently, .in normal operas Table I below:

Table 1 Column 1 Column 2 C0lumn3 Column 4 Column 5 Column'fi" Raflinate from V Blend of Blendoi' Fresh Phenol Hydrocar- Extract and Extract and Cycle Oil Extraction of hen Extract Cycle Oil Cycle Oil Raffinate- Feed Cycle Oil at from Lube InFeed Raffinate 90%treat, 6% Oil Prop. In Prod.

1120 Prop.

PI 19.1 :5 16.8 18.8 30,8 30. SSU/210 F 41. 8 39.1 48.5 42.6 40. 6 41. Aromatics, Wt. percent" 46. 4 11. 2 69.9 49. 7 25. 9 25. Paraifins, Wt perce t 53.6 88.8 30.1 50.3 74.1 74. Aniline F 159 220 130 Conradson Carbon content,

Wt. percent; 2. 5 0.3 0. 1. Diesel Index 30 7s 22 2e 66 62. 3

ation, after removal of the phenol in phenol recovery facilities, extract is sent to catalytic cracking feed In accordance with one feature of this invention, the desirable portion of the hydrocarbon extract is recovered as rai-finate from the extract phase when the extract phase is contacted with cycle oil. Thequality of the hydrocarbon extract as catalytic cracking feed is accordingly improved. This operation was conducted in the second of the phenol extraction units employing a catalytic cycle oil having the following inspections:

This cycle oil was. contacted with the lubricating oil extract phase in a countercurrent treating tower having about 5 theoretical contacting stages. A cycle oil feed In this table, column 1 shows the inspectiousof the catalytic cycle oil used in these tests. Column 2 shows the nature of a rafiinate product obtained by extract-' ing this cycle oil with fresh, or in other words, pur'e phenol for comparative purposes with the process. of this invention. Column 3 shows the inspections of the hydrocarbon portion of the lubricating oil extract phase referred to in the foregoing tests. inspections of a blend of the extract ofcolumn 3 and the. cycle oil of column 1 in the proportions used as feed in the foregoing tests of this phase of this invention; 85.9% cycle oil and 14.1% extract. Column 5 shows a blend of the cycle oil raffinate of column 2.and the lubricating oil extract of column 3 in the proportions resulting from the tests exemplifying this phase of' the invention; 77.1% raffinateand 22.9% extract. Finally, column 6 shows the inspections of the raflfinate product resulting from the foregoing tests in accordance with the principles of this I invention.

of 6000 B./S. D: was maintained while introducing 7,020 B. /S, D. of the extract phase equivalent to 117%- The inspections given above must be considered in.

connection with the initial'characteristics ofboth the cycle oil feed to treating tower 17 (column 1) and the hydrocarbon extract feed to tower 17 (column 3). Thus, as mentioned above, the raflinate product shown in column 6 includes constituents from each of these streams so that in eifect the raifinate product constitutes the seg-" regated portion of both the cycle oil and the lube' ex tract suitable for catalytic cracking feed. Comparing the inspections of therafiinate product to either those. of the cycle oil feed or the hydrocarbon extract, it

Column 4 shows the 9 be observed that this product has substantially better characteristics for catalytic cracking feed than either the untreated cycle oil or the hydrocarbon extract. For

example, it will be observed that the untreated cycle oil had a Conradson carbon content of 2.5 wt. percent and the hydrocarbon extract, 0.3 wt. percent, while the raflinate product from tower 17 had a Conradson carbon contentv of 0.1 wt. percent. Again the paraflin content of the raffinate product was raised to 74.2 wt. percent as against a value of 56.3 wt. percent for the untreated cycle oil and 30.1 wt. percent for the hydrocarbon extract. It is therefore shown that operation of the first two stages of the process illustrated in the drawing results in substantially upgrading a cycle oil and a hydrocarbon lube extract, serving to materially improve their value as catalytic cracking feedstocks.

By a similar comparison of the inspections of column 6 with the inspections of column 5, it is shown that the rafiinate product of the extraction described is fully equivalent as a feed stock for catalytic cracking in comparison to a blend of lube oil extract and extracted cycle oil. This data, in combination with material balances, establishes that a ratfinate product is obtained which segregates the hydrocarbon constituents of the extract phase from lubricating oil together with the less aromatic portion of cycle oil much as though these were separately prepared and blended. In other words, the volume of lubricating oil extract hydrocarbons present in spent phenol from a lubricating oil extraction process is directly added to the volume of cycle oil rafiinate which would normally be obtained by the extraction of cycle oil with pure (or fresh) phenol at the same extraction conditions. Yet this is achieved without necessity for distilling phenol from the lubricating oil extract phase, avoiding the expensive solvent recovery facilities ordinarily required for this at this step of the process. Again, this is achieved without any loss in quality of the product as catalytic cracking feed.

These steps of the process illustrated in the drawing have additional features above and beyond those brought out heretofore. It is a particular feature that lubricating oil constituents, normally contaminated with metal compounds, are upgraded for catalytic cracking by substantial elimination of the metal contaminants. The metal contaminants referred to include compounds of nickel, vanadium, and iron which result in poisoning of the cracking catalyst so as to seriously decrease the selectivity and life of the catalyst. As indicative of the problem that exists, a typical lubricating oil fraction of a petroleum oil contained 0.58 p. p. m. of nickel. This lubricating oil was extracted with phenol at a temperature of about 215 F. using a 200% treat of phenol and 2% of water. Separation of solvent from the extract phase provided segregated hydrocarbon constituents suitable forcatalytic cracking feed stock. However, extraction of lubricating oil ordinarily results in concentrating metal contaminants in .the hydrocarbon extract so that in this case the extract contained 1.16 p. p. m. of nickel. Heretofore the use of lube extract for catalytic cracking has been severely debited because of this metal contamination.

In the practice of this invention, however, a catalytic cracking feed is obtained, including the hydrocarbons present in a lubricating oil extract phase, which is substantially free of metal contaminants. Referring to the drawing, for example, the lube extract present in line 16 is freed of metal contaminants in treating tower 24.

Metal contaminants are removed from tower 24 through line 26 together with the extract phase of tower 24. The raflinate product of line 25, including the hydrocarbons originally present in the lube extract stream of line 16, is recovered for catalytic cracking free of metal contaminants. In a typical case 90% removal of nickel was obtained by this technique, providing a rafiinate product for catalytic cracking containing the extremely low nickel content of 0.02 p. p. m.

The data presented heretofore has concerned the preparation of a cycle oil extract phase as obtained in treating tower 24 illustrated in the drawing. It has been shown that extract and raflinate phases of cycle oil, useful in the process of this invention, can be obtained by treating cycle oil with a selective solvent by itself. It has also been shown that particular advantages are secured if this is achieved by treating cycle oil with the total extract phase of a lubricating oil extraction process. As pointed out, in either case a cycle oil extract phase is obtained constituting a major portion of spent solvent and a minor portion of aromatic hydrocarbons extracted from the cycle oil. It is a particular feature of this inven-- tion that the total cycle oil extract phase be employed as an extraction agent for the treatment of a virgin gas oil 1 as conducted in tower 27 of the drawing.

in order to demonstrate the portion of the process conducted in tower 27, experiments were conducted in which a cycle stock extract phase derived by contact of cycle oilwith lube oil extract phase as indicated in the foregoing experimental results was contacted with a heavy gas oil. phenol and 30% oil. extract phase had the following inspections:

This cycle oil extract phase was employed to contact a gas oil having the following inspections:

Gravity, API

Viscosity, SSU/2l0 F 116 Conradson carbon, wt. percent 2.29 Sulfur, wt. percent 0.39 Nickel, p. p. m 2.1 Percent aromatics, wt. percent 39.9 Percent paraffins, wt. percent 60.1

The cycle oil extract phase and gas oil were contacted in an extraction unit providing about 5 stages of theoretical contacting. The extraction was carried out at a temperature of about 160 F. providing a phenol treat of 114 volume percent based on the cycle stock extract phase. The hydrocarbons present in the raifinate resulting from this contact had the following inspections:

Volume percent Yield of cracking feed 113 Gravity, APi 18.5 Viscosity, SSU/210 F 77.5 Conradson carbon, wt. percent 1.60 Nickel, p. p. m 0.3 Percent aromatics, wt. percent 45.5 Percent paraffins, wt. percent 54.5

It will be noted from this data that contact of the gas oil with the cycle stock extract resulted in substantial elimination 'of metal contaminants from the gas oil (87.0% removal) while permitting substantially complete recovery of all constituents of the gas oil suitable for use as catalytic cracking feed., In fact, as indicated by the 113% yield based on gas oil feed, the process was operative to recover the more paraffinic type hydrocarbons originally present in the cycle oil extract phase. This is The cycle stock extract phase constituted 70% The hydrocarbon portion of this .borne out bythe fact-that the cycle oil extract phase used to contact the gas oil had an aromatic content of 84.6% while'th'e resulting extract phase had an aromatic content of about 94.5%.

A critical feature of this invention is the.use of separate contacting stages for the extraction of cycle stock and gas oil. border to show the benefits of staged contact, reference is made to the following exemplary data:

Ina first series of experiments; cycle stock and gas oil were mixed'together and contacted with a lubricating oil extract phase in a single stage contacting operation. In a second, comparative series of experiments, the same catalytic cycle stock and the same gas oil were separately extracted in a two-stage operation. In this case, the cycle oil was first contacted with thelubricating oil extract phase'to form a cycle oil extract phase. This'cycle oil extract phase was then contacted with the gas oil in a second stage contacting operation. These experiments established that substantially better extraction results could be obtained by the two stage contacting as comparedto the single stage contacting. The unique advantage of plural stage contacting resides in the recovery of greater yields of raifinate product suitable for cracking while securing equivalent or superior removal of metal contaminants. To clearly show this, the tabulated data following was chosen for comparative single and double stage contacting adjusted to secure the same amount of raflinate product. It will be noted that substantially better nickel removal was obtained in the two stage process.

This data brings out the substantial advantages obtained from the staged extraction process of this invention. The data shows that by employing two contacting stages as described in place of a single contacting stage, substantially better removal of nickel contaminants from gas oil is secured.

' Additional benefits also exist for this two stage process. In order to appreciate their significance, reference may be made to a typical plant situation. Assuming the availability of lube oil spent solvent to be 20,000 B./D. with a solvent content of 85 vol. percent, it can be seen that a maximum of 19,666 B./D. of combined cycle stocksgas oils can be extracted in a single stage operation at a 75% solvent treat (defined as volume of solvent per volume of total oil). In a two stage process, a maximum of 29,799 B./D. of cycle stocks-gas oils can be extracted at the same 75% solvent treat. In this example, maximum permissible feed rate at constant treat is increased by about'l0,133 B.'/D. or 51%.

As described, this invention concerns extraction operations in which virgin and cracked gas oil fractions of a petroleum oil are separately extracted with a selective solvent for aromatic hydrocarbons wherein thetotal extract phase resulting from one extraction step is used in the second extraction step. Two of the most important applications of this invention have been brought out in the foregoing description and data. bone of these, fresh selective solvent is employed to'extract cycle oil and the'extract'phase from this extraction step is then used to extract virgin gas oil. As established, the aromatic constituents'of the gas oil present in the cycle oil extract phase serve to improve removal of metal contaminantsfrom the gas oil. The full advantages of this technique are also achieved in the preferred embodiment of the invention illustrated. In this case, fresh solvent; is first-used to extract the lubricating oil fraction'ofai virgin gas oil. The extractphase from this operation'is" then employed to extract" cycle'oil; Finally, the cycle oil extract phase is used 'to'extract gas oil: It'is apparent that the advantages of this invention can be achieved toa lesser extent by use of additional contacting stages with the total extract phase of each stagebeingused as the For example, in

extraction agent in successive stages. the case just described, the gas oil extract phase could be used in a subsequent extraction of virgin gas oil in order to-secure greater removal of metal contaminants 7 tract phase of a lubricating oil extraction step; and about 95% of the nickel can be removed by using cycle oil extract phase. While this data establishes that the embodiment of the invention described is best. adapted for metal removal, it must be recalled that the invention is also of utility for minimizing aromaticity of catalytic cracking feed stock.

Thus, for example, it is within the scope of this invention to employ fresh solvent to extract lubricating, oil, using the lube extract phase to extract virgin gas oil, andusing the gas oil extract phase to extract cycle oil Removal of metal contaminants fromthe gas oil in this sequence of steps is somewhat inferior but the combination process does serve to provide the objective of minirnizing the aromatic hydrocarbons in cracking feed.

Again, if desired, fresh solvent can be used to extractgasoil with the gas oil extract phase being used to extract cycle oil in order to recover gas oil extract constituents suitable for cracking.

Among these variations of the invention, a preferred process entails use of the solvent extract phase from a lubricating oil'extraction process to extract gas oil at treats of about IOU-250% providing a first rafiinate product and an aromatic extract phase.

extract phase is then used to extract cycle oil at treats of This aromatic about 50300% to provide a second raffinate product. The combined rafiinate products are of high quality for catalytic cracking feed; Tests which have been carried' out show that this sequence of treating steps serves to provide an over-all removal of nickel contaminants of about 60-75% based on gas oil input. In this treating combination, it is particularly contemplated touse a portion of the lubricatingoil extract phase as a Wash for cycle oil raffinate, thereby further reducing the metal content of this stream. Volumetrically, the paratfinic part of catalytic cycle stock and essentially all of the recycle gas oil are recovered as catalytic cracking feed;

What is claimed is:

'1. An improved extraction process for the'preparation. of catalytic cracking feed stocks including in combin'a tion the steps of: contacting a lubricating oil distillate .with a selective solvent for aromatic hydrocarbons, seg-- regating a lubricating oil extract phase, contacting. a

catalytic cycle oil with said lubricating oil extract phase,,

segregating a cycle oil extract phase, contacting a virgin gas oil including constituents boiling up to at least about process in which catalytically cracked products-boiling above about 430 F. are segregated and contacted with a selective solvent for aromatic hydrocarbons forming a extract and raffinate phases, recycling hydrocarbons in said ratfinate phase to catalytic cracking and contacting a virgin gas oil fraction including constituents boiling up to at least about 1100 F. and containing metallic contaminan'ts with said extract phase, forming a gas oil extract phase and a gas oil raflinate phase substantially free of metallic contaminants, and passing hydrocarbons in said gas oil raflinate phase to catalytic cracking.

3. In the extraction of metal contaminants from a gas oil fraction including constituents boiling up to at least about 1100 F. by contact with a selective solvent for aromatic hydrocarbons, the improvement which comprises contacting said gas oil fraction with spent selective solvent constituting the extract phase resulting from prior contact of the said selective solvent with hydrocarbons boiling above 430 F. selected from the group consisting of lubricating oil distillates and cycle oil, and recovering a gas oil raflinate phase substantially free of metallic contaminants.

4. A method of extracting the metal contaminants from a straight run heavy gas oil fraction including constituents boiling up to at least about 1100 P. which comprises in combination contacting a lubricating oil fraction with a selective solvent for aromatic hydrocarbons to form lube oil rafiinate and extract phases, segregating the lube oil extract phase and contacting the same with a cycle oil to form cycle oil rafiinate and extract phases, segregating the cycle oil extract phase and contacting the same with said straight run heavy gas oil to form separate gas oil raflinate and extract phases, said gas oil raflinate phase being substantially free of metallic contaminants and said gas oil extract phase containing metal contaminants from the heavy gas oil.

5. A combination catalytic cracking and extraction 14 process wherein a straight run heavy gas oil including constituents boiling up to at least about 1100 F. and containing metallic contaminants is employed as the catalytic cracking feed stock which comprises in combination the steps of contacting a lube oil fraction boiling above about 500 F. with a selective solvent for aromatic hydrocarbons to form lube oil extract and rafiinate phases, segregating the lube oil extract phase and contacting the same with a cycle oil boiling above 430 F. from a catalytic cracking operation to form separate cycle oil raflinate and extract phases, contacting the cycle oil extract phase with said straight run heavy gas oil to form separate gas oil raflinate and extract phases, said gas oil raflinate phase being substantially free of metallic contaminants and said gas oil extract phase containing metallic contaminants from said straight run gas oil, segregating the gas oil component of the gas oil raflinate phase and subjecting said component to catalyticcrack- 6. A process as defined in claim 5 in which the cycle oil component of the cycle oil raflinate phase is segregated from rafiinate phase and is catalytically cracked.

References Cited in the file of this patent UNITED STATES PATENTS' 2,228,510 Dearbom et a1. Ian. 14, 1941' r 2,270,827 Tijmstra Jan. 20, 1942 2,279,550 Benedict et a1 Apr. 14, 1942 2,342,888 I Nysewander et a1 Feb. 29, 1944 2,374,102 Jahn' et al. Apr. 17, 1945 2,748,055 Payne May 29, 1956

Claims (1)

1. AN IMPROVED EXTRACTION PROCESS FOR THE PREPARATION OF CATALYST CRACKING FEED STOCKS INCLUDING IN COMBINATION THE STEPS OF: CONTACTING A LUBRICATING OIL DISTILLATE WITH A SELECTIVE SOLVENT FOR AROMATIC HYDROCARBONS, SEGREGATING A LUBRICATING OIL EXTRACT PHASE, CONTACTING A CATALYTIC CYCLIC OIL WITH SAID LUBRICATING OIL EXTRACT PHASE, SEGREGATING A CYCLE OIL EXTRACT PHASE, CONTACTING A VIRGIN GAS OIL INCLUDING CONSTITUENTS BOILING UP TO AT LEAST ABOUT 1100*F. AND CONTAINING METALLIC CONTAMINANTS WITH SAID CYCLE OIL EXTRACT PHASE, AND SEGREGATING A GAS OIL RAFFINATE PHASE SUBSTANTIALLY FREE OF METALLIC CONTAMINANTS.

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