US2777802A

US2777802A - Extractive distillation operation for preparation of catalytic cracking feed stocks

Info

Publication number: US2777802A
Application number: US474477A
Authority: US
Inventors: Nick P Peet
Original assignee: Exxon Research and Engineering Co
Current assignee: ExxonMobil Technology and Engineering Co
Priority date: 1954-12-10
Filing date: 1954-12-10
Publication date: 1957-01-15
Anticipated expiration: 1974-01-15
Also published as: DE1035296B; GB782791A; BE543301A; NL100147C; FR1138469A; NL202701A

Description

Jan. 15, 1957 N. P. PEET 2,7 EXTRACTIVE DISTILLATION OPERATION FOR PREPARATION OF CATALYTIC CRACKING FEED STOCKS Filed Dec. 10, 1954 FIG. 2. 25 7532? g 3: i

' FIG- 1.

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EXTRACTIVE DISTILLATION OPERATION FOR PREPARATION OF CATALYTIC CRACKING FEED STOCKS Nick P. Peet, Baytown, Tex., assignor, by mesne assignments, to Esso Research and Engineering Company, Elizabeth, N. 3., a corporation of Delaware Application December 10, 1954, Serial No. 474,477 14 Claims. (Cl. 196-49) This invention concerns a novel erative to reduce the content present in catalytic cracking charge stocks. The invention concerns the use of a novel refluxing agent in a distillation operation in a manner to cause removal of metal contaminants by the principles of extractive distillation. The novel refluxing agent employed in accordance with this invention is a high molecular weight asphaltic material.

In recent times, a great deal of efiort has been applied in the petroleum refining field to increase the recovery of catalytic cracking feed stock from residual fractions of petroleum oil. Conventionally, the feed stock to a catalytic cracking operation constitutes a so-called gas oil fraction of crude oil which boils in the range of about 400 to 800 F. or somewhat higher. Portions of the gas oil boiling distillation process opof metal contaminants petroleum crude oil boiling above the range may be considered residual petroleum fractions. Such residual fractions may be used as sources of asphalt, fuel, and other products which are of relatively low economic value. It, therefore, becomes attractive to develop means for successfully utilizing portions of the residual fractions of crude oil as catalytic cracking feed stock.

Attempts to employ heavier fractions of crude oil for catalytic cracking have been limited heretofore due to the presence of certain metal contaminants in such heavy fractions. Thus the highest boiling fractions of a crude oil contain substantial portions of metal contaminants, particularly including nickel, vanadium and iron compounds. The residual fractions of typical crude oils generally contain these metal contaminants in quantities of about 10 to 500 pounds per 1000 barrels of residual fraction. When an attempt is made to segregate higher boiling distillate fractions of a crude oil, some portion of these metal contaminants are inherently and unavoidably carried over into the distillate products. For example, in a vacuum distillation operation where a heavy boiling gas .oil fraction is segregated from a crude oil, about 0.5 to 10 pounds per 1000 barrels of metal contaminants Will be obtained in the gas oil distillate in a typical situation. In this example, the gas oil distillate referred to would have a boiling range of about 700 to 1100 F.

The problem of metal contaminant carry over in the segregation of heavy distillate fractions is apparently due to two phenomena. First of all, it appears that the metal contaminants occur or are converted during distillation to the form of metal complexes. These complexes may generally be identified as large condensed ring substances. Some of these metal complexes and particularly nickel porphyrins are sufliciently volatile so as to be carried overhead at a temperature of about 1050 F. Consequently, when attempting to segregate heavy boiling gas oil fractions including components boiling above about 900 F., volatile metal contaminants are unavoidably obtained in the distillate product. It

" nited States Patent 0 appears that a second phenomenon is also involved which may be referred to as mechanical entrainment. To generally indicate the mechanism of this effect, it can be considered that a small portion of high boiling liquid hydrocarbons from the residual fraction are normally entrained overhead in a distillation operation. Since such liquid hydrocarbons contain concentrated amounts of metal contaminants, such entrainment in distillate products accounts for a portion of the metal contamination of such distillates.

By virtue of the fact that catalytic cracking operations are adversely affected by the presence of such metal contaminants, it is apparent that the need exists for some means to recover high boiling fractions of a crude oil while eliminating contamination in the manner described. The presence of metal contaminants and particularly nickel in a catalytic cracking operation results in direct contamination of the catalyst by the metal compound. Metal continues to accumulate on the catalyst during the life of the catalyst having the result of seriously altering the catalytic properties of the catalyst. In general, it is considered essential to reduce the metal contaminant content of the catalytic cracking feed stock to a value of less than about 3 pounds per 1000 barrels. It is the principal object of this invention to provide this objective in a novel and practically attractive manner.

The present invention is based on the discovery that certain high molecular weight condensed ring aromatic compounds are effective as solvents for the objectionable metal complexes present in crude oil. Consequently, by introducing these particular solvents into a distillation zone, by virtue of their high boiling character, metal contaminants can be removed from distillate fractions by the principles of extractive distillation. The present invention, therefore, concerns a technique by which certain high molecular weight condensed ring aromatic compounds are employed as an extractive distillation refluxing agent in the segregation of heavy oil fractions.

The extractive distillation refluxing agent to be employed may be defined as a high molecular Weight asphaltic material containing a low concentration of nickel compounds and particularly characterized by substantially no volatilization of nickel components at temperatures of about 1050 to 1300" F. at atmospheric pressure. The high molecular weight asphaltic material referred to contains a large portion of condensed ring aromatic compounds believed to have more than about 15 rings in the molecule. The asphaltic materials boil from about 1050" F. up to about 1400 F. and higher. For the purpose of this invention it is apparent that such refluxing agents must contain a low concentration of metal contaminants, although some high boiling metal contaminants can be tolerated. In this connection, it is essential that the concentration of metal contaminants capable of volatilizing at temperatures below about 1300 F. should be less than about 2 to 5 pounds per 1000 barrels. In some cases, somewhat greater concentrations of higher boiling metal contaminants can be tolerated, the limitation relating to the possibility of entrainment in the particular distillation facilities available.

The extractive distillation refluxing agent can be derived from two potential sources. First of all, in the case of those petroleum crude oils having remarkably low content of total metal contaminants or remarkably low content of volatile metal contaminants, it is possible to segregate suitably high molecular weight asphaltic material for the purposes of t 's invention. This, however, is the exceptional case since the asphaltic materials of the character required when derived from the average or typical crude oil contain prohibitively high concentrations of metal contaminants.

This does not prevent using heavy virgin stocks as refluxing agents. For example, very high molecular weight fractions obtained by solvent precipitation such as with a low molecular weight hydrocarbon, even though'containingappreciably amounts of metal contaminants are suitable agents because the initial boiling point of such fractions will usually be high enough to prevent volatilization of contaminants-at normal vacuum distillation temperatures up to about 1050 F.

The refluxing agent can also be a synthetic, high molecular weight asphaltic material derived from cracking operations. A desirable source of the refluxing agent free from metal contaminants is secured from thermal tar obtained in conventional refinery operations, particularly when cracking distillate stocks. Such a tar may be obtained by distilling the products from a thermal cracking unit. The objective is to remove the greatest possible portion of constituents boiling below about I050 F. This is best conducted by carrying out the distillation as a vacuum flashing process although alternatively a deasphalting process may be used to segregate the desired asphaltic fraction.

While, as indicated, the refluxing agent to be employed can be derived from virgin or thermally cracked stocks by distillation or deasphalting, the preferred source of the refluxing agent is from :catalytically cracked products. The highest boiling fractions of catalytically cracked feed stocks are conventionally designated as cycle oil and/ or clarified oil. Such fractions include high molecular weight condensed ring aromatic compounds which may be designated as synthetic asphalts formed during the catalytic cracking operation. These materials are particularly effective in the practice of this invention and can be recovered from cycle oil or a clarified oil by vacuum flashing or deasphalting processes. It is also attractive to obtain the refluxing agent from thermal tars derived from catalytically cracked stock.

As used hereinafter the term synthetic asphaltic material will be used to identify these extractive distillation refluxing agents of this invention.

In the practice of this invention, synthetic asphaltic materials are injected into the distillation zone for segregating heavy boiling gas oil fractions in proportions of about 1% to 50% based on the hydrocarbon vapor rate at the portion of the distillation zone at which the refluxing agent is injected. The lower limit of the amount of refluxing agent to be used is determined by the concentration of metal contaminants in the stock distilled coupled with a consideration of the degree of contaminant removal required in the distillate product. In general, however, it is preferred to employ amounts of refluxing agent in the range of about 2% to about 20% and particularly about 5% based on the hydrocarbon vapor rate in the distillation operation. In order to secure the desired contaminant removal from heavy distillate products, it is essential that the refluxing agent be brought into the distillation tower at a point somewhat below the side stream withdrawalpoint of the highest boiling distillate product. The refluxing agent must be brought into intimate contact with upflowing hydrocarbon vapors in the distillation tower. For this purpose, the refluxing agent must be deposited over at least one plate in the distillation tower and preferably a greater number of plates ideally providing at least one theoretical stage of contacting of the vapors. If desired, the refluxing agent together with extracted metal contaminants can be removed from the distillation tower at a lower side stream withdrawal point or, alternatively, the refluxing agent can be withdrawn together With the bottoms product of the distillation tower.

Referring now to the accompanying drawings, preferred embodiments of this invention are diagrammatically illustrated in which:

Fig. 1 diagrammatically illustrates application of the present invention to a vacuum distillation operation;

Fig. 2 shows the application ofthe invention in a coking process;

Fig. 3 shows the application of the invention to a combination distillation and cracking operation;

Fig. 4 illustrates the invention when employed in a combination coking and cracking operation; and

Fig. 5 shows the invention when used in a combination distillation coking and cracking operation.

Referring first to Fig. l, the invention is illustrated in its basic application to a distillation tower. In Fig. l the numeral I identifiies a distillation tower for the segre gation of oil fractions of a petroleum crude oil. Tower 1 can particularly constitute a vacuum still operated at pressures of about 25 mm. to 250 mm. of mercury. Thus in conventional refinery operations a petroleum oil is generally subjected to preliminary fractionation in an atmospheric distillation tower providing a bottoms fraction constituting reduced crude oil boiling above about 600 F. Such a reduced crude oil can be brought into tower 1 through line 2 at temperatures of about 600 to 850 F. The reduced crude oil undergoes a flashing operation in the lowest portion of the vacuum distillation tower so that light portions of the reduced crude are carried overhead in vaporform and the heaviest boiling fractions are carried downwardly toward the bottom of the tower. The lightest boiling fractions can be removed from line 3 but successively higher boiling fractions can be removed from side stream withdrawals 4, 5 and 6. Ordinarily the heaviest fractions of the reduced crude are'subjected to a steam stripping operation in the bottom of the distillation tower utilizing steam injected through line 7. The stripped products constituting residual crude oil are then withdrawn through bottoms withdrawal 8.

It is an object of this invention to eliminate or substantially reduce the content of metal contaminants carried overhead in the higher boiling distillate fractions such as those withdrawn through lines 5 and 6. In this connection, data are presented in Table I illustrating the amount of metal contaminants typically present in reduced crude derived from a variety of sources. In this table columns 1, 2, 3, 4 and 5, respectively, show the characteristics of residua derived from a mixture of Gulf Coast and West Texas crudes, a West Texas crude, a Panhandle crude, a Hawkins crude and a Lagunillas crude.

TABLE I T yptical feed stock inspections Percent on Crude 9.8 12.8 15. 6 29. 0 44.0 Gravity, API 8. 7 8. 7 20. 1 4. 7 (i. 5 Viscosity, SSU at 210 F 679 Conradson Carbon, Wt. Perce 8. 17.3 8 40 19.8 24. 0 Bomb Sulfur, Wt. Percent 3.05 3. 67 t. 6 3.1 Contaminants, #/l,000 Bbls:

Ni l3. 0 9. 0 5. 0 10. 2 24. 3

In accordance with this invention, a synthetic asphaltic material of the character identified is brought into distillation tower 1 through line 9 at an introduction point somewhat below the lowest side stream withdrawal point. The synthetic asphalt is introduced in quantities of about 1% to 50% by weight based on the volume of hydro carbon gases flowing upwardly through the portion of the distillation tower at which the synthetic asphalt is introduced. Since the synthetic asphalt, as identified, is a high boiling'material, it is present in liquid phase in distillation tower 1. Contact with upflowing hydrocarbon vapors results in selective extraction of metal contaminants and, in addition, the'synthetic asphalt serves to prevent entrainment of liquid portions "of the residual oil present in tower 1. By both of these mechanisms contact of the -asphaltic materials with upflowing vapors in the distillationtower serves-to eliminate metal contamination of distillate products withdrawn from the tower. The synthetic asphaltic material can be withdrawn from distillation tower 1 through lower side stream Withdrawal or, alternatively, the asphaltic material may be allowed to pass downwardly through the tower for removal with residuum through line 8. Preferably the synthetic asphaltic material containing extracted metallic contaminants is then discarded from the system and finds use as a fuel. Optionally, however, on withdrawal from the tower the synthetic asphaltic material may be subjected to severe flashing conditions, permitting removal of high boiling gas oil rich in metal contaminants as overhead product and withdrawal of a purified synthetic asphaltic material as a bottoms product which can be recycled to tower 1.

The remaining figures of the drawings diagrammatically illustrate application of the principles of Fig. 1 in a variety of refining operations. These will be briefly identified with the understanding that the basic individual processes involved are conventional and well known to the art.

With reference to Fig. 2, for example, the invention is illustrated as applied to the distillation of products subjected to a coking operation in order to obtain heavy boiling products suitable for catalytic cracking. In the drawing, the numeral designates a coking reactor in which residual portions of petroleum oil are contacted with coke particles at temperatures of about 800 to 1000 F. in order to secure conversion to lighter boiling constituents. The coking operation conducted in zone 2% may be of any desired type and can constitue, for example, a fluidized operation in which coke particles are maintained as a fluid bed in accordance with the principles of fluidized solids contacting. Residual oil introduced into coking zone 20 through line 21 undergoes conversion permitting removal of a product stream through line 22 including gases, intermediate liquid fractions, and unconverted residual fractions. Coke can be withdrawn periodically from zone 20 through line 23. The products of the coking process removed through line 22 are then introduced to a distillation zone 24. The distillation may be either atmospheric or vacuum distillation but preferably constitutes vacuum distillation of the character referred to in connection with Fig. 1. successively higher boiling portions of the feed are removed from still 24 through

lines

25, 26,. 27 and 28. Uncoverted portions of the residual stock originally fed to the coking process can be removed as a bottoms product through line 29 and can be recycled to the process.

In accordance with this invention, a synthetic asphaltic material is introduced to distillation zone 24 through line 30 at a point somewhat below the side stream withdrawal of the highest boiling distillate product. This distillate product will include heavy gas oil suitable for catalytic cracking. As indicated in connection with Fig. 1, the injected synthetic asphaltic material can be removed from the tower 24 through a lower side stream Withdrawal 31 or, alternatively, the asphaltic material may be permitted to remain in the bottoms product of the fractionator.

The process of Fig. 2 is a particularly valuable process for upgrading residual stocks to catalytic cracking feed material. The coking step of the process serves to remove a-substantial portion of metal contaminants the coking feed stock. These metal contaminants are deposited on the coke solids employed and/or produced in the process; consequently, by using the process of this invention in combination with this effect, heavy gas oil feed stocks having extremely low content of metal contaminants can be obtained for catalytic cracking feed stoc Fig. 3 fllustrates the application of this invention to a fractionator of the character employed in the so-called combination distillation cracking operation. As illustrated by Fig. 3, fractionation of catalytically cracked products can be carried out in the same distillation tower in which a crude oil is fractionated. Thus the terial can be removed from a lower total product from catalytic reactor "18 may bepassed through line 32 for introduction near the bottom portion of the fractionator 33. Crude oil is brought into fractionator 33 at an intermediate portion of the tower through line 34. Light boiling fractions of the catalytic cracking products rise upwardly in vapor form through the distillation zone, serving as an effective stripping agent for heavy portions of the crude oil. In addition, other stripping gases may be brought into tower 33 through other side stream introduction points. Such stripping agents can constitute light naphtha fractions derived from other refining processes, such as a reforming process. The necessary heat input for the distillation operation is supplied by a reboiler circuit indicated by numeral 36. Distillate products including fractions of both the crude oil and the catalytically cracked products are withdrawn from the tower through

lines

37, 28, 39 and 49. Operation of still 33 can be adjusted so that the product withdrawn through line 40 will constitute a gas oil suitable for catalytic cracking. In accordauce with this invention the distillate products are processed to minimize the presence of metal contaminants by introduction of a synthetic asphaltic material of the character described through line 41. This mapoint in the tower through line 42 after contact with upflowing vapors or, alternatively, the synthetic asphaltic material may be permitted to pass downwardly through the tower for re moval with residual oil through line 43.

The process of Fig. 3 is particularly attractive in providing a distillation process for segregating a heavy gas oil for catalytic cracking which can be conducted at atmospheric pressures. The use of this invention as described in this figure is particularly attractive in providing heavy boiling gas oils of low metal content suitable for catalytic cracking.

With reference to Fig. 4, this figure diagrammatically illustratesapplication of the invention to the distillation of the products of a coking operation when con-. ducted in combination with a cracking reaction. In this drawing a high boiling residual fraction of crude oil containing metal contaminants is introduced to a coking reactor 45 through line 46. The coking process may be of the character identified in connection with Fig. 2. The hydrocarbon products. of the coking process are removed through line 47 for introduction to a sembbing tower 48 which is essentially a distillation zone in which the total coke products which have been converted during coking are removed overhead through line 49. These products are then subjected to catalytic cracking reactor 50. The products of catalytic cracking are then passed through line 5-1 to distillation tower 52. Still 52 is preferably a vacuum distillation tower permitting segregation of light boiling products through

lines

53, 54, 55 and 56 and segregation of a heavy catalytic tar through line 57. This tar will constitute a synthetic asphaltic material which can be recycled through line 57 to scrubbing tower 48 for contact with the coke products. Portions of the residual stock originally fed to the coking zone together with the synthetic asphaltic material are removed from scrubbing tower 48 through line 58 for recycle to the coking operation.

As described, therefore, Fig. 4 illustrates a process having the advantages of Fig. 2 by employing a combination of coking, catalytic cracking and fractionation. The process of Fig. 4 provides an integrated process for production of a suitable extractive distillation refluxing agent and use of this agent to effectively upgrade residual stock for catalytic cracking.

Fig. 5 illustrates a somewhat different combination of distillation, coking and cracking. Fractionation zone 66 of Fig. 5 is similar to fractionation zone 33 of Fig. 3: and constitutes a combination fractionator in which both crude oil and products of catalytic cracking are subjected to fractionation. in the samedietillationzone.

illustrated in Fig. 5, a crude oil isintroduced' into distillation zone 60 through line 61 together with the total products of a catalytic cracking zone brought into the tower through line 62. Distillate products of varying boiling ranges are withdrawn from tower 60 through

Withdrawal lines

31, 82, 83, 84 and 85. As described in connection with Fig. 3 the product of line 85 may constitute a gas oil fraction adaptable for catalytic cracking. In order that this gas oil fraction be freed of metallic contaminants present in the crude oil brought into distillation zone 60, synthetic asphaltic material is brought into tower 60 through line 66. Residual fractions are removed from distillation zone 60 through line 67 together'with the synthetic asphaltic material introduced to the tower. These are subjected to a coking operation in the coking reactor 68. Products of the coking reaction are @passedthrough line 69 to a scrubber 7 3' of thecharacter described in connection with Fig. 4. in scrubbing tower 70, the coking products are contacted with a synthetic asphaltic material introduced through line 71. The lighter boiling products are removed from tower 70 through line 72for introduction to the catalytic cracking zone 73 together with the gas oil in line 85 derived from still 60. Residual products of scrubbing tower 70 are returned to the coking reactor through line 75.

It will be observed that the process of Fig. 5 provides a combination of the processes of Figs. 2, 3 and 4 which provides an attractive application for the present invention. A particular feature of the process of Fig. 5 is the manner in which a high molecular weight asphaltic material is essentially used in a two-stage contacting operation to eliminate metal contaminant content of a catalytic cracking feed. This occurs in combination with the elimination of metal contaminants achieved in a coking operation so the process is well adapted for providing the highest quality catalytic cracking feed stock.

It will be observed from the description of this invention, as brought out in connection with the drawings, that the present invention is of broad application to the recovery of high boiling. distillate fractions intended for catalytic cracking. The process of this invention may be adapted to virtually any type of distillation operation including the atmospheric, vacuum, and stripping type distillation operations particularly described. Included within the scope of this invention is the new combination of coking and catalytic cracking processes with fractionation so as to employ the full advantages of this invention.

What is claimed is:

1. In a distillation process wherein a metals contaminated petroleum hydrocarbon feed stock containing a substantial portion of hydrocarbon constituents boiling above 900 F. is charged to a distillation tower and fractionated therein to segregate at least a heavy gas oil distillate fraction including said constituents boiling above 900 F., the improvement which comprises countercurrently contacting said constituents boiling above 906 F. in vapor phase in said tower prior to withdrawal of the same under extractive distillation conditions with a refluxing agent introduced into said tower below the point of withdrawal of the heaviest distillate fraction, said refluxing agent comprising an extraneously derived high molecular weight asphaltic material substantially free from metal contaminants, whereby a heavy gas oil fraction having a significantly reduced content of metal contaminants is obtained.

2. The process defined by claim 1 in which the said feed stock constitutes a residual portion of petroleum oil characterized by inclusion of metal contaminants in amounts greater than at least 3 pounds per 1000 barrels.

3. The process defined by claim 1 in which the said high molecular weight asphaltic material is introduced in amounts of about 1% to 50% by weight based onvaporous hydrocarbons present in the,- distillation process for contact with the asphaltic material.

4. The process defined by'claiml in which the said asphaltic material is synthetically derived from a cracking operation.

5. The process defined by claim l in which the said asphaltic material constitutes a tar derived from catalytic cycle stock and characterized by inclusion of less than about 5 pounds per 1000 barrels of metal contaminants.

6. In a distillation process wherein a metals con taminated reduced crude oil boiling above about 600 F. and containing a substantial portion of hydrocarbon constituents boiling above 900 F. is charged to a distillation tower and fractionated therein to segregate a heavy gas oil distillate fraction including said constituents boiling above 900 F, the improvement which comprises couutercurrently contacting said constituents boiling above 900 F. in vapor phase in said tower prior to withdrawal of the same under extractive distillation conditions with a refluxing agent introduced into said tower below the point of withdrawal of the heaviest distillate fraction, said refluxing agent comprising an extraneously derived high molecular weight asphaltic material substantially free from metal contaminants, whereby a heavy gas oil fraction having a significantly reduced content of metal contaminants is obtained.

7. A process as in claim 6 wherein the distillation process is a vacuum distillation process.

-8. A process as in claim 6 wherein the distillation process is an atmospheric distillation process.

9. A process as in claim 6 wherein the distillation process is a high pressure distillation-stripping process.

10. In a distillation process wherein the products of a coking process are charged to a distillation tower and fractionated therein to segregate a heavy gas oil distillate fraction, the improvement which comprises countercurrently contacting the constituents of said heavy gas oil fraction in vapor phase in said tower prior to withdrawal of the same under extractive distillation conditions with a refluxing agent introduced into said tower below the point of withdrawal of the heaviest distillate fraction, said refluxing agent comprising an extraneously derived high molecular weight asphaltic material substantially free from metal contaminants, whereby a heavy gas oil fraction having a significantly reduced content of metal contaminants is obtained.

11. In a distillate process wherein a feed stock comprising catalytic cracking products and a petroleum crude oil is charged to a distillation tower and fractionated therein to segregate a heavy gas oil distillate fraction including constituents boiling above 900 F., the improvement which comprises countercurrently contacting the constituents of said heavy gas oil fraction in vapor phase in said tower prior to withdrawal of the same under extractive distillation conditions with a refluxing agent introduced into said tower below the point of withdrawal of the heaviest distillate fraction, said refluxing agent comprising an extraneously derived high molecular weight asphaltic material substantially free from metal contaminants, whereby a heavy gas oil fraction having a significantly reduced content of metal contaminants is obtained.

12. In a process wherein a product obtained from the coking of a residual petroleum hydrocarbon fraction is passed upwardly through a scrubbing tower and thence to a catalytic cracking process as the feed stock therefor, and wherein the products from the catalytic cracking process are fractionally distilled to provide a residue containing a synthetic high molecular weight asphaltic material substantially free from metal contaminants, the improvement which comprises countercurrently contacting said coking product with said residue in said scrubbing towe'r'prior to removal of said coking product from said scrubbing tower.

13. In a combination process wherein the products of a catalytic cracking operation and a petroleum crude oil are charged to a distillation tower andfraction'ated therein to provide a heavy gas oil distillate fraction and a residual fraction, wherein the said heavy gas oil distillate fraction is charged to the said catalytic cracking operation as a portion of the feed therefor, wherein the said residual fraction is subjected to a coking reaction and wherein the products of the said coking reaction are passed upwardly through a scrubbing tower and are then charged to the said catalytic cracking operation as another portion of the feed therefor, the improvement which comprises couutercurrently scrubbing said coking products with an extraneously derived high molecular weight asphaltic material substantially free from metal contaminants prior to removal of said coking products from said scrubbing tower, and also countercurrently contacting said heavy gas oil distillate fraction in said tower in vapor phase prior to removal of the same under extractive distillation conditions with a refluxing agent introduced into said tower below the point of withdrawal of the heaviest distillate fraction, said refluxing agent comprising an extraneously derived high molecular weight asphaltic material substantially free from metal contaminants.

14. In a distillation process wherein a petroleum hydrocarbon residual fraction containing from about to 500 pounds per 1000 barrels of metal contaminants is charged to a distillation tower and fractionated therein to i provide at least a between about 700 gas oil distillate boiling in the range and about 1100 F., the improvement which comprises countercurrently contacting said distillate fraction in ascending vapors phase in said tower prior to withdrawal of the same under extractive distillation conditions with about 1 to about based on the ascending vapors of tion, of a refluxing agent introduced weight percent, said distillate fraclow the point of withdrawal of the heaviest distillate fraction, said refluxing agent boiling in the'range between about 1050 and about 1400 F. and comprising an extraneously derived high molecular weight asphaltic material substantially free from metal contaminants.

References Cited in the file of this patent UNITED STATES PATENTS into said tower be- I

Claims

1. IN A DISTILLATION PROCESS WHEREIN A METALS CONTAMINATED PETROLIEUM HYDROCARBON FEED STOCK CONTAINING A SUBSTANTIAL PORTION OF HYDROCARBON CONSTITUENTS BOILING ABOVE 900*F. IS CHARGED TO A DISTILLATION TOWER AND FRACTIONATED THEREIN TO SEGREGATE AT LEAST A HEAVY GAS OIL DISTILLATE FRACTION INCLUDING SAID CONSTITUENTS BOILING ABOVE 900*F., THE IMPROVEMENT WHICH COMPRISES COUNTERCURRENTLY CONTACTING SAID CONSTITUENTS BOILING ABOVE 900* F. IN VAPOR PHASE IN SAID TOWER PRIOR TO WITHDRAWAL OF THE SAME UNDER EXTRACTIVE DISTILLATION CONDITIONS WITH A REFLUXING AGENT INTRODUCED INTO SAID TOWER BELOW THE POINT OF WITHDRAWAL OF THE HEAVIEST DISTILLATE FRACTION, SAID REFLUXING AGENT COMPRISING AN EXTRANEOUSLY DERIVED HIGH MOLECULAR WEIGHT ASPHALTIC MATERIAL SUBSTANTIALLY FREE FROM METAL CONTAMINMANTS, WHEREBY A HEAVY GAS OIL FRACTION HAVING A SIGNIFICANTLY REDUCED CONTENT OF METAL CONTAMINANTS IS OBTAINED.