US3254019A - Catalytic cracking of residual oils and pitch - Google Patents

Description

CATALYTIC CRACKING OF RESIDUAL OILS AND PITCH Filed May 27, 1963 TO FRACTIONATOR s FLUIDIZING 29 GAS 2| ,|7

-|8 INVENTOR. N.W. MITCHELL BY 0. E. MERRYFIELD A TTO/PNEYS Uniteci States Patent 3,254,019 CATALYTHC (IRACKING 0F RESIDUAL OILS AND PITCH Norris W. Mitchell, Borger, Tex., and George E. Merryfield, Bartlesville, Okla, assignors to Phillips Petroleum Company, a corporation of Delaware Filed May 27, 1963, Ser. No. 283,433 8 Claims. (Cl. 20887) This invention relates to catalytic cracking wherein hydrocarbons are catalytically converted into more valuable products. In one aspect this invention relates to a method and means for catalytically cracking petroleum pitch along with a normal feed such as topped crude in a catalytic cracking operation. In another aspect this invention relates to a method and means for catalytically cracking a combination of petroleum pitch and topped crude in a catalytic cracking operationso that the production of coke is minimized and the production of liquid hydrocarbons is increased.

It is known to crack hydrocarbon fluids catalytically to increase the quantity and quality of the gasoline or motor fuel product. It is also known to employ two or more separate cracking zones wherein feed stocks containing differing concentrations of contaminating metals are separately cracked. It has been proposed to crack pitch, obtained as a residuum in the vacuum distillation of topped crude along with the charge of topped crude to a catalytic cracking zone utilized for cracking feed stocks containing high concentrations of contaminating metals. A method for dissolving the solid pitch in the aromatic extract oil obtained by solvent extraction of a cycle oil obtained from the same cracking step to which the pitch is fed, and a method for feeding the resulting solution, along with the topped crude, are described in copending application Ser. No. 191,161, filed Apr. 30, 1962, by G. W. Britton, now U.S. Patent No. 3,200,062.

We have now discovered that the yield of valuable liquid hydrocarbons in the gasoline range is increased and the yield of coke and light gases is reduced if the solution of pitch in an aromatic oil, along with a diluting amount of liquid parafiinic hydrocarbon stream and a small amount of water, is contacted with the catalyst and introduced to the cracking zone separately from the topped crude rather than being mixed with the topped crude prior to being introduced to the cracking operation.

A principal object of the invention is to provide a method and means for increasing the yield of liquid hydrocarbons and decreasing the yield of coke and light gases in a catalytic cracking operation wherein petroleum pitch and topped crude are being catalytically cracked. It is also an object of this invention to provide a feed stream for a catalytic cracking operation containing petroleum pitch, paraflinic hydrocarbon and water so as to obtain the maximum amount of liquid hydrocarbons and the minimum amount of coke and light gas when the stream is catalytically cracked. Other objects and advantages of the present invention will be apparent to one skilled in the art upon study of the disclosure of the invention including the detailed description of the invention and the appended drawing wherein:

FIGURE 1 is a sectional elevation of a catalytic cracking apparatus illustrating schematically the invention; and

FIGURE 2 is a cross-sectional view along lines 22 of FIGURE 1.

Various items of equipment not necessary for an understanding of the invention have been omitted from the drawing in order to simplify the description of the invention. Such items are conventional and those skilled in the art will know where inclusion of same will be advantageous.

Referring now specifically to FIGURE 1, a catalytic cracking apparatus is illustrated having an upper reactordisengaging chamber 10, an intermediate stripping chamber 11 and a lower regeneration chamber 12. Risers 13, 14 and 15 are provided for conveying regenerated, finely-divided, catalytic material from the lower portion of the regeneration chamber 12 up and into the reactordisengaging chamber 10 along with the hydrocarbon charge stock. A standpipe 16 conveys stripped catalyst from the stripping chamber 11 to the lower portion of the regeneration chamber 12 and the rate of supplying stripped catalyst to the regeneration chamber 12 is controlled by vertically movable plug valve 17 which is aligned with the lower outlet end of standpipe 16. According to the invention, the conventional feed stream to the catalytic cracking apparatus, such as topped crude and recycle streams, is introduced via conduits 18 and 19 to the bottom inlets of risers 13 and 14- through vertically movable hollow stem plug valves such as 20. The valve inlet to riser 14 is similar to plug valve 20 but is not shown because it is directly behind valve 17.

A feed stream comprising a solution of petroleum pitch in aromatic extract oil, raffinate obtained from the solvent extraction of a cycle oil obtained from cracking a hydrocarbon feed stock, and liquid water is passed to the bottom inlet of riser 15 via conduit 21 and a vertically movable, hollow stem plug valve 22. The vaporized hydrocarbon products are removed from reactor-disengaging chamber 10 via cyclone separator 23 and conduit 24. Solids removed in the cyclone separator 23 are returned to the reactor-disengaging chamber 10 via conduit 25. Steam is admitted via conduit 26 and sparge ring 27 to the stripping chamber 11 to strip residual hydrocarbons from the catalyst descending through the stripper chamber 11. A fluidizing gas, such as steam or other inert gas, is passed via conduit 28 and sparge ring 29 into the lower portion of regeneration chamber 12 to maintain the finely divided catalyst in a fluidized state. Air or other oxidizing gas is passed via conduit 31 and sparge ring 32 into the lower portion of regeneration chamber 12 to provide the oxygen required to burn the coke from the surface of the catalyst particles and thereby to regenerate the catalyst. Combustion products and fluidizing gas are removed from regeneration chamber 12 via cyclone separator 33 and conduit 34. Solid catalyst removed in cyclone separator 33 is returned to regeneration chamber 12 via conduit 35.

Pitch applicable for use in the present invention includes petroleum pitch, coal tar pitch, and any of the naturally-occurring asphaltic compounds which are normally solid, soluble in aromatic hydrocarbons and display limited solubility in conventional catalytic cracking feed stocks such as topped crude and other liquid residual hydrocarbons. Petroleum pitch is the preferred feed stock for the present invention because of its availability as a by-product in certain refinery operations such as the vacuum distillation of topped crude. Petroleum pitch obtained as a residuum from vacuum reduction of West Texas topped crude has a specific gravity, 60 F./ 60 F. in the range of 1.002 to 1.135, a penetration, 5 seconds,

gm., 77 F., in the range of 010', and a ring and ball softening point in the range of to 260 F.

The aromatic extra-ct oilwhich is normally utilized as the solvent for dissolving the pitch is obtained by solvent extraction of a cycle oil obtained from the same cracking step to which the pitch is fed and will normally have the following characteristics: API gravity, 60 F./

60 F., in the range of about 7 to 20-; BMCI in the range of about 60 to 99 and 50 percent boiling point, in the range of about 550 to 750 F. A particularly preferred solvent is an extract oil resulting from the S0 extraction of light cycle oil, heavy cycle oil or decant oil, or a combination of these oils and having an API gravity, 60 F./60 F., in the range of about 8 to 15; BMCI in therange of about 78 to 99; and a 50 percent boiling point in the range of about 630 to 680 F. The extract oil and pitch are blended in a ratio of about 1 to volumes of extract oil per 1 volume of pitch. When thepitch is being treated separately from the topped crude but in the same apparatus along with the topped crude, the volume of topped crude will be in the range of to 50 volumes per volume of pitch-extract oil solution.

The paraflinic hydrocarbon will usually be the raffinate obtained from the solvent extraction of cycle oils obtained from the same catalytic cracking step to which the pitch-containing mixture is charged. The paraffinic hydrocarbon can, however, be any liquid hydrocarbon having a hydrogen-to-carbon ratio about as high as that of hydrocarbons'such as virgin gas oil, catalytic cycle oils, Tetralin, Decalin, isobutane, and the like. The paraffinic hydrocarbon is believed to serve as a hydrogen donor which operates to reduce the yield of coke and dry gas (C and lighter) which would normally result from cracking the hydrogen-deficient solution of pitch in aromatic hydrocarbon.

The paraflinic hydrocarbon will be added to the solution of pitch in aromatic hydrocarbon in an amount of about 0.5 to 6 volumes of paraffinic hydrocarbon per volume of solution. A more preferred range is about 1 to 3 volumes of paraflinic hydrocarbon per volume of solution. In any event, the amount of paraflinic hydrocarbon should be sufiicient to provide an excess of hydrogen in the reaction fluids over that required by the hydrogendeficient pitch and aromatic hydrocarbon.

The catalyst-to-oil ratio for the pitch-containing stream will be in the range of about 5 :1 to :1 and will usually be about the same as that normally used with conventional liquid residual hydrocarbon fraction feed stocks wherein liquid water is added to the oil and will usually be above about 8:1.

The amount of liquid water added to the pitch-containing solution will be in the range of about 0.5 to pounds of liquid water per barrel of combined pitch solution and paraflinic hydrocarbon. The invention can the practiced Without the addition of liquid water; however, the use of liquid water instead of steam or other diluent contributes to the increase in liquid hydrocarbon product.

The amount of liquid water and the catalyst-to-oil ratio will be adjusted to provide the desired reaction temperature in the confined stream of catalyst and pitch-containing fluids. The reaction temperature can be in the range of about 800 to 1050" F. and will usually be in the range of about 870 to 930 F. and also will usually be up to about 10 F. lower than for conventional liquid residual hydrocarbon charge stocks.

The invention is herein described and illustrated as applied to a fluid catalytic cracking apparatus commonly referred to as orthoflow fluid catalytic cracking apparatus. It is believed that the reaction occurs, or at least is initiated, in the riser wherein the catalyst and fluids are conveyed to the reaction-disengaging zone. The invention can, however, be practiced in any fluid cracking apparatus wherein the mixture of pitch solution, water and paraflinic hydrocarbon can be contacted with the hot catalyst in a confined zone which is separate from the topped crude or other liquid residual hydrocarbon charge so that the hydrogen-deficient pitch and paraffinic hydrogen donor are in intimate contact when the reaction is initiated. 4

An understanding of the invention may be facilitated by reference to the following example wherein results obtained according to the invention are compared to results of the prior art.

EXAMPLE The results of a run made prior to the invention are shown in the following table as Run 1 and the results of a run made according to the process of the invention are shown as Run 2.

Table 1 Run 1 Run 2 Process of Process of invention prior art- Risers 1, 2

and 3 Risers 1 and 2 Riser 3 Charge:

Topped crude (21.8"

P 20, 300 20, 300 Q Pitch solution (9.4

vAPI), B/D 410 0 410 Rafiinate (39.5 API), B D 3, 500 3,090 410 v Liquid water, lb./hr 5, 600 5, 400- 200 Catalyst-to-oil, wt. ratio 11:1 11:1 11:1 Outlet temperature, F 934 934 932 Products, wt. percent of feed:

Butane and lighter- 8. 8 7. 5 Butane-free gasoline 28.1 29. 2 Cycle oils 53. 1 53. 7 Coke 10. 0 9.l6

' reduction in the amounts of butane and normally gaseous materials and coke and an increase in liquid hydrocarbons such as gasoline and cycle oil fractions. The increase in gasoline is of particular importance, being an increas of about 350 barrels per day in gasoline production, assuming the API gravity of the gasoline to be 68. It should also be noted that the amount of coke produced according to the practice of the invention is about 31,000 pounds per day less than is produced according to the process of the prior art. The production of cycle oil is increased about barrels per day by the practice of the process of the invention.

That which is claimed is:

1. In the catalytic conversion of liquid residual hydrocarbons wherein said residual hydrocarbons in a fluidized catalyst system are admixed with a finely divided catalyst which has been heated to a cracking temperature of said hydrocarbon and conveyed as a confined stream to a reaction-disengaging zone from whencehydrocarbon products are recovered in vapor form, the improvement comprising admixing a solution of pitch, dissolved in an aromatic hydrocarbon, with a liquid paraflinic hydrocarbon as a hydrogen donor; admixing liquid water with the mixture of pitch, aromatic hydrocarbon and paraflinic hydrocarbon; passing the resulting admixture of water, pitch, aromatic hydrocarbon and paraflinic hydrocarbon into contact With heated catalyst in a-confined zone; passing the resulting suspension of catalyst in vaporized water, pitch, aromatic hydrocarbon and paraflinic hydrocarbon in said confined. zone and separate from the said residual hydrocarbons to said reaction-disengaging zone.

2. The process of claim 1 wherein the aromatic hydrocarbon is an aromatic extract oil obtained from the solvent extraction of a cycle oil from the same conversion step to which the pitch solution 'is charged; and wherein the paraflinic hydrocarbon is a raflinate obtained from said solvent extraction.

3. In the catalytic conversion of a charge stock comprising liquid residual hydrocarbons and pitch dissolved in an aromatic hydrocarbon in a fluidized catalyst system wherein the charge stock is admixed with a finely divided catalyst which has been heated to cracking temperature of said charge and conveyed as a confined stream to a reaction-disengaging zone from whence hydrocarbon products are obtained in vapor form, the improvement comprising admixing a liquid parafliuic hydrocarbon With said pitch dissolved in said aromatic hydrocarbon; contacting in a confined stream the resulting mixture of pitch solution and paraflinic hydrocarbon with a finely divided cracking catalyst which has been heated to a cracking temperature of the hydrocarbons; and passing the confined stream, separately from the liquid residual hydrocarbon, to said reaction-disengaging zone.

4. The method of converting hydrocarbons in a fluidized catalyst system which comprises admixing a solution of pitch in the extract aromatic obtained from the solvent extraction of a cycle oil, with a liquid paraffinic hydrocarbon as a hydrogen donor; admixing liquid water with the admixture of pitch solution and parafiin; passing a stream consisting essentially of the resulting mixture into contact with a finely divided, solid cracking catalyst which has been heated to a temperature of about 1050 to 1175 F.; passing the resulting suspension of solid catalyst in vapors as a confined stream to a combined reaction-disengaging zone of said fluidized catalyst system. 5. The process of claim 1 wherein the amount of liquid paraflinic hydrocarbon is about 0.5 to 6 volumes per volume of the solution of pitch in aromatic hydrocarbon.

6. The process of claim 1 wherein the amount of liquid parafiinic hydrocarbon is about 1 to 3 volumes per volume of the solution of pitch in aromatic hydrocarbon.

7. In the catalytic cracking of liquid residual'hydrocarbons wherein said residual hydrocarbons are admixed with a finely divided catalyst which has been heated to a cracking temperature of said residual hydrocarbon and conveyed as a confined stream to a reaction-disengaging zone from whence hydrocarbon products are recovered in vapor form and cycle oils are separated and returned to the reaction with the residual hydrocarbon, the improvement comprising solvent extracting a cycle oil to produce an aromatic extract and a parafiinic rafiinate; dissolving 1 volume of pitch in about 1 to 5v volumes of said extract; admixing one volume of the solution of pitch in extract with 0.5 to 6 volumes of said parafiinic raffinate; admixing about 0.5 to 25 pounds of liquid water with each barrel of combined pitch solution and parafiinic hydrocarbon; passing the resulting admixture of water, pitch, aromatic hydrocarbon and paraflinic hydrocarbon into contact with heated catalyst in a confined zone; passing the resulting suspension of catalyst in vaporized water, pitch, aromatic hydrocarbon and paraifinic hydrocarbon in said confined zone and separate from said residual hydrocarbons to said reaction-disengaging zone.

8. The process of claim 7 wherein the solution of pitch in extract is added to the catalytic cracking step in an amount of 1 volume per 10 to volumes of liquid residual hydrocarbon.

References Cited by the Examiner UNITED STATES PATENTS 2,937,135 5/1960 Middleton 20887 2,982,718 5/1961 Constantikes 2081l3 3,152,064 10/1964 Osborne 208ll3 DELBERT E. GANTZ, Primary Examiner.

ALPHONSO D. SULLIVAN, Examiner.

A. RIMENS, Assistant Examiner.

Claims (1)

1. 7. IN THE CATALYTIC CRACKING OF LIQUID RESIDUAL HYDROCARBONS WHEREIN SAID RESIDUAL HYDROCARBONS ARE ADMIXED WITH A FINELY DIVIDED CATALYST WHICH HAS BEEN HEATED TO A CRACKING TEMPERATURE OF SAID RESIDUAL HYDROCARBON AND CONVEYED AS A CONFINED STREAM TO A REACTION-DISENGAGING ZONE FROM WHENCE HYDROCARBON PRODUCTS ARE RECOVERED IN VAPOR FORM AND CYCLE OILS ARE SEPARATED AND RETURNED TO THE REACTION WITH THE RESIDUAL HYDROCARBON, THE IMPROVEMENT COMPRISING SOLVENT EXTRACTING A CYCLE OIL TO PRODUCE AN AROMATIC EXTRACT AND A PARAFFINIC RAFFINATE; DISSOLVING 1 VOLUME OF PITCH IN ABOUT 1 TO 5 VOLUMES OF SAID EXTRACT; ADMIXING ONE VOLUME OF THE SOLUTION OF PITCH IN EXTRACT WITH 0.5 TO 6 VOLUMES OF SAID PARAFFINIC RAFFINATE; ADMIXING ABOUT 0.5 TO 25 POUNDS OF LIQUID WATER WITH EACH BARREL OF COMBINED PITCH SOLUTION AND PARAFFINIC HYDROCARBON; PASSING THE RESULTING ADMIXTURE OF WATER, PITCH, AROMATIC HYDROCARBON AND PARAFFINIC HYDROCARBON INTO CONTACT WITH HEATED CATALYST IN A CONFINED ZONE; PASSING THE RESULTING SUSPENSION OF CATALYST IN VAPORIZED WATER, PITCH, AROMATIC HYDROCARBON AND PARAFFINIC HYDROCARBON IN SAID CONFINED ZONE AND SEPARATE FROM SAID RESIDUAL HYDROCARBONS TO SAID REACTION-DISENGAGING ZONE.

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