US3340178A - Process for catalytically cracking pyrolysis condensates - Google Patents

Description

Sept. 5, 1967 G. F. HORNADAY ETAL 3,340,178

PROCESS FOR CATALYTICALLY CRACKING PYROLYSIS CONDENSATES Filed Aug. 25, 1964 I N VE N TORJ' fieargeflfiforlzaddy BY 17001 D. No]! United States Patent Office 3,349,173 Patented Sept. 5, 1967 3,340,178 PROCESS FGR CATALYTICALLY CRACKING PYROLYSIS CONDENSATES George F. Hornaday, Wallingford, and Henry D. Noll,

Philadelphia, Pa., assignors to Air Products and Chemicals, Inc., Philadelphia, Pa., a corporation of Delaware Filed Aug. 25, 1964, Ser. No. 391,887 4 Claims. (Cl. 20-S89) This invention relates to the catalytic cracking of pyrolysis condensates and more particularly to a process for the preparation of gasoline from a cracking stock comprising steam-cracked naphtha and gas oils obtained from crude petroleum.

Steam-cracked naphtha having a boiling range, for eX- ample, of 30-250" C. is obtained as a by-product when petroleum naphtha is cracked in the presence of steam at elevated temperatures for the production of ethylene and propylene. Although steam-cracked naphtha has a good octane rating, its potential as a blending stock for gasolines has not been reailzable. A high unsaturates content (particularly olefins and diolefins which tend to form gum-like polymers, espectially when heated) has materially restricted the quantity of steam-cracked naphtha blended into motor fuels.

It has now been discovered that a blended cracking stock can be prepared from steam-cracked naphtha and gas oils obtained from crude petroleum without requiring pretreatment of the steam-cracked naphtha. This discovery permits the utilization of an otherwise unsaleable by-product by a noved method without affecting product quality of the gasolines produced which typically have F-1 octane values in the range of 88 to 94, F-l clear and 95 to 99 F1 plus 3 cc. TEL. Moreover, use of the blended cracking stock does not materially alter the rate of coking or catalyst deactivation in the catalytic cracker.

In accordance with the present invention crude petroleum, which may contain substantial amounts of sulfurous materials such as West Texas Crude, Kuwait Crude, Baxterville Crude, Wafra Crude, etc., is subjected to crude distillation and hydrodesulfurization. Gas oils (i.e., liquid hydrocarbons boiling about the gasoline boiling range) thereby obtained are then blended with up to 30 Weight percent and preferably 5 to 30 weight percent steam-cracked naphtha and catalytically cracked in a moving bed unit without further treatment.

The invention is clarified by reference to the following description read in connection with the drawing. In this description all percentages are by weight and are based on the crude petroleum charge stock unless otherwise noted.

Referring tothe drawings, wherein the general layout of a refinery is diagrammatically illustrated with omission of various pieces of apparatus not considered necessary to an understanding of the invention, crude petroleum charge stock consisting of 40% Khafji and 60% Gach-Saran is introduced along line to distillation Column 11. Several fractions are obtained from the distillation column, including (1) a 3% gas fraction in line 14 obtained from line 12 and separator 13, (2) a 7.4% light naphtha fraction in line 15 obtained from line 12 and separator 13, (3) a 12.2% heavy naphtha fraction in line 16, (4) a 7.5 kerosene fraction in line 17, (5) a 19.9% diesel oil fraction in line 18 and (6) a 50% bottoms fraction comprising heavy gas oil in line 19. The kerosene and diesel oil fractions are combined and passed through line 20 into hydrodesulfurizer 21. The thus-treated material is then passed through line 22 into fractionator 23 where it is separated into a 0.075%

gasoline fraction in line 24, a 7.5% kerosene fraction in line 25, a 16% diesel oil fraction in line 26 and a gas oil fraction in line 27.

The bottoms fraction in line 19 containing about 3.28% sulfur is passed in whole or in part through line 28 into vacuum tower 29. In the illustrated embodiment, approximately 56% of the bottoms fraction is passed into vacuum tower 29 and the remaining portion in line 53 is utilized as fuel oil.

Asphalt having a 3.9% sulfur content is removed from vacuum tower 29 by line 30. Vacuum gas oil, on the other hand, is recovered from vacuum tower 29 and passed through line 31 into hydrodesulfurization unit 32. Vacuum gas oil from line 31 is circulated through line 35 to efiect a heat exchange with the desulfurized vacuum gas oil in line 33. Hydrogen is then removed in line 38 from the gas oil following its transmission from hydrodesulfurization unit 32 via lines 33 and 36 to high pressure separator 37.

The combined effect of heat exchanger 34 and separator 37 eliminates the necessity of fractionating the gas oil in line 39 which is combined with the gas oil from line 27. The combined gas oil stream (line 40) is finally blended with steam-cracked naphtha from line 4-1 in an amount of 5 to 30 weight percent steam-cracked naphtha based on the weight of the gas oils in line 40. Characteristics of the steam-cracked naphtha are shown in the following table:

In the illustrated embodiment about 27.6% steamcracked naphtha is added to the gas oil and this blended cracking stock is passed through line 42 into a Houdritlow moving bed catalytic cracking unit 43. Houdriflow catalytic cracking is well known in the art and has been widely disclosed in the literature. For example, see Hoge, Houdriflow, the Petroleum Engineer, April 1954.

The resulting products from the catalytic cracking of the blended stock (line 44) is then fractionated in fractionator 45 to obtain an overhead fraction in line 46, a 11.8% light recycle fraction in line 51 and a 23.5% heavy recycle fraction in line 52, based on the blended cracking stock in line 42 at 55% conversion. The overhead fraction is separated in separator 47 into a 5.9% fraction containing C and lighter materials (line 48), a 10% C fraction (line 49) and 54% C gasoline fraction (line based on the blended cracking stock in line 42 at 55% conversion.

It is to be understood that the foregoing is illustrative of a single preferred operation in accordance with the invention which makes possible the recovery of gasoline of low sulfur content and relatively high octane value.

In addition to gasoline, the C and C light products are rich in unsaturates and may be further processed for the production of alkylate, polymer gasoline or used in the petroleum industry.

A substantial investment saving in processing equipment is realized by the present invention. Not only does the present procedure eliminate the necessity of a fractionator for treating the desulfurized vacuum gas oil but the presence of two hydrodesulfurization units (21 and 2) further eliminates the necessity for separate desulfurizer units in each of the product lines, e.g., in lines 24 to 26and 48 to 52. This latter feature is of particular importance with'respect to gasoline fractions which are extremely difficult to desulfurize without loss of octane rating through the hydrogenation of unsaturates.

Typically, desulfurization is accomplished by treating an oil in vapor phase with a hydrogenation catalyst under moderate conditions of temperature and pressure in the presence of a large excess of hydrogen. Although the vapor phase process is theoretically applicable to the desulfurization of any hydrocarbon oil, from a practical standpoint vapor phase operation is limited tov the desulfurization of light hydrocarbon oils such as gasoline, kerosene, diesel oils, etc., which are easily vaporized without decomposition.

Desulfurization of the vacuum gas oil in the described process is accomplished in the liquid phase over a 0.8 to 2.4 mm. cobalt-molybdenum-alumina catalyst. Operating conditions are maintained between 355 to 430 C., a pressure of 500 to 800 p.s.i.g., a space rate of 0.5 to 2.5 LHSV and a hydrogen recycle rate of 4000 to 6000 s.c.f./bbl. For a vacuum gas oil having the properties set forth in the following table, it has been calculated that essentially none of the oil would be vaporized at the operating conditions present in hydrodesulfurizer 32.

Vacuum assay, (1.:

The effect of hydrodesulfurization on the catalytic cracking of vacuum gas oil is shown in the following table. Operating conditions for the catalytic cracking were 480 C., p.s.i.g., 10 weight percent steam and a 4 catalyst/ oil ratio.

Desulfu- Gas Oil rized Gas Oil Coke Yield, Wt. Percent 3. 9 3. 9 Conversion, V01. Percent (to fuel oil, gasoline,

gas and coke) 56. 7 69. 6 Gasoline, Vol. Percent (385 F. at 90%) 31.5 40. 5 04's Vol. Percent 7. 6 12.9 Sulfur, Wt. Percent (after removing H 5 and free sulfur):

Charge Stock 2. 55 0.36 Gasoline 0. 34 0. 05 Octane of Gasoline:

F-l Clear 90.5 92.0 F1 -|3 cc. T.E.L 95.6 97. 5

Thus at a fixed coke yield of 3.9 weight percent, conversion (to fuel oil, gasoline, gas and coke) was 13 volume percent greater for the desulfurized gas oil. This increased conversion resulted in an increased gasoline yield from 31.5 to 40.5 volume percent. Moreover, the gasoline from the desulfurized gas oil had a significantly lower sulfur only such limitations should be imposed as are indicated in the appended claims.

What is claimed is:

1. A process for the production of gasoline which comprises distilling a crude petroleum to obtain heavy gas oil, a kerosene fraction and a diesel oil fraction; subjecting the kerosene and diesel oilfractions to vapor phase hydro-desulfurization; fractionating the desulfurized kerosene and diesel oil fractions to obtain a light desulfurized gas oil; 'desulfurizing said heavy gas oil in the liquid phase preparing a steam-cracked naphtha containing troublesome amounts of diolefins as a by-product of the steamcracking of naphtha to produce gaseous olefins; preparing a steam-cracked naphtha containing troublesome amounts of diolefins as a by-product of the steam-cracking of naphtha to produce gaseous olefins; blending said steamcracked naphtha in an amount from about 5 to about30 weight percent with the combined desulfurized gas oil obtained by mixing the light desulfurized gas oil from the vapor phase desulfurization and the heavy desulfurized gas oil from the liquid phase desulfurization operations; catalytically cracking the blended steam-cracked naphtha-gas oil material in a continuous moving bed catalytic cracker at about atmospheric pressure and fractionating the product from the catalytic cracker to obtain gasoline.

2. The process for the preparation of gasoline which comprises subjecting gas oil to hydrodesulfurization prior to catalytic cracking; preparing a steam-cracked naphtha containing troublesome amounts of diolefins as a byproduct of the steam-cracking of naphtha to produce gaseous olefins; blending 5 to 30 weightpercent said steam-cracked naphtha with the desulfurized gas oil, catalytically cracking the steam-cracked naphthaand desulfurized gas oil in a moving bed catalytic cracker at about atmospheric pressure and fractionating the resulting cracked product to obtain gasoline. V

3. The process of claim 2 wherein the gasoline has an F-1 clear octane value of at least 88.

4. In the process in which a gas oil is subjected to hydrodesulfurization and the hydrodesulfurized gas oil is catalytically cracked to provide gasoline, the improvement 7 gas oil from the product of vapor-phase desulfurization;

subjecting the heavy gas oil fraction to liquid-phase hydrodesulfurization at a temperature from about 355 to about 430 C., at a pressure from about 500 to about 800 p.s.i.g., at a space rate from about 0.5 to about 2.5 liquid volumes per volume of catalyst per hour in the presence of hydrogen rich recycle gas at a rate of about 4000 to about 6000 standard cubic feet of gas per barrel of heavy gas oil to provide a heavy desulfurized gas oil; mixing the light desulfurized gas oil and heavy desulfurized gas oil to provide a blended gas oil; subjecting naphtha to steam cracking for the preparation of gaseous olefins and a by-product diolefin-containing naphtha; preparing a mixture of said blended gas oil and from 5% to 30% of said diolefin-containing steam-cracked naphtha; subjecting said mixture to a catalytic cracking zone at about atmospheric pressure; and separating by distillation from the products from the catalytic cracking zone a stable naphtha having no troublesome amounts of diolefins.

References Cited UNITED STATES PATENTS 2,914,459 11/1959 Mills et a1 208-130 6 3,147,210 9/1964 Hass et a1. 208210 3,155,608 11/1964 Hopper et a]. 20889 3,240,695 3/1966 Hamner et a1. 208-130 5 DELBERT E. GANTZ, Primary Examiner.

SAMUEL P. JONES, Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3 ,340 ,178 September 5 1967 George F. Hornaday et al.

rror appears in the above numbered pat- It is hereby certified that e Patent should read as ent requiring correction and that the said Letters corrected below.

Column 1, line 22, for "reailzable" read realizable line 32, for "noved" read novel line 53, for "drawings" read drawing column 2, after line 34, insert 5%--3E column 4, line 20, beginning wlth "preparing" Strike out all to and including "olefins;" in line 22, same column 4.

Signed and sealed this 30th day of Jul 1968.

(SEAL) Attest:

EDWARD J. BRENNER Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer

Claims (1)

1. 4. IN THE PROCESS IN WHICH A GAS OIL IS SUBJECTED TO HYDRODESULFURIZATION AND THE HYDRODESULFURIZED GAS OIL IS CATALYTICALLY CRACKED TO PROVIDE GASOLINE, THE IMPROVEMENT WHICH INCLUDES THE COMBINATION OF; DISTILLING CRUDE PETROLEUM TO PROVIDE A NAPTHIA FRACTION, KEROSENE AND DIESEL OIL FRACTIONS AND A HEAVY GAS OIL FRACTION; SUBJECTING SAID KEROSENE AND DIESEL OIL FRACTIONS TO VAPOR-PHASE HYDRODESULFURIZATION; DISTILLING TO SEPARATE A LIGHT DESULFURIZED GAS OIL FROM THE PRODUCT OF VAPOR-PHASE DESULFURIZATION; SUBJECTING THE HEAVY GAS OIL FRACTION TO LIQUID-PHASE-HYDRODESULFURIZATION AT A TEMPERATURE FROM ABOUT 355 TO ABOUT 430*C., AT A PRESSURE FROM ABOUT 500 TO ABOUT 800 P.S.I.G., AT A SPACE RATE FROM ABOUT 0.5 TO ABOUT 2.5 LIQUID VOLUMES PER VOLUME OF CATALYST PER HOUR IN THE PRESENCE OF HYDROGEN RICH RECYCLES GAS AT A RATE OF ABOUT 4000 TO 6000 STANDARD CUBIC FEET OF GAS PER BARREL

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