US2632727A - Cracking of hydrocarbon oils - Google Patents

Description

March 24, 1953 K, P, LANNEAU ET L 2,632,727

cRAcKING oF HYnRocARBoN ons Filed Aug. s. 195o FLUID CATALY-rlc ai CEAClLrN@ UNIT CMS-fl LKGASQMNE l i `(Samsom. t

Clbborne Patented Mar. 24, 1953 CRACKING OF HYDROCARBON OILS Keith P. Lanneau and Elphege M. Charlet, Baton Rouge, La., assignors to Standard Oil Development Company, a corporation of Delaware Application August 3, 1950, Serial No. 177,366

4 Claims.

The present invention relates to the conversion of hydrocarbon oils to obtain valuable hydrocar- Y bonv products of lower molecular Weight. More particularly the invention pertains to an improved process of producing motor fuel range hydrocarbon oils from gas oil range feed stocks containing aromatic constituents, by catalytic cracking. In its broadest aspect, the invention .is directed to the catalytic cracking of gas oil 'range feed stocks of the type mentioned from which aromatic constituents have been removed by a treatment with silica gel.

It is well known in the art that aromatic hydrocarbons are less desirable feed stocks forV oils, for any given conversion. Excessive coke formation is objectionable in thermal cracking because it reduces the yield of gasoline and causes coking difficulties in the cracking unit. However,

such coke formation is particularly harmful in catalytic cracking since the coke formed collects `on the surface of the catalyst and reduces its activity. A hydrocarbon oil containing a high percentage of aromatics which are conducive to `a low ratio of gasoline to coke is therefore particularly undesirable as a feed stock to catalytic cracking processes.

Prior to the present invention it has been proposed, therefore, to remove the aromatic constituents from the feed stock before it is subjected to cracking. For this purpose, it has been `suggested to extract feed stocks containing aro- -matic constituents with solvents such as phenol, 802,- or various chlorinated, nitrated and/or loxygenated hydrocarbons which have a selective solvent power for aromatics, and to use only the rafnateof this fextraction as the cracking feed stock. While treatments of this kind afford asubstantial improvementV with respect to coke formation as well as to gasoline yield based on rainate it has been found to be necessary to limit the extent of extraction to a partial removal ofaromatics in order to prevent excessive amounts of non-aromatic constituents from going into the extract whereby the gasoline yield based on original feed stock would be severely curtailed. In addition the gasoline to coke ratios obtainable in this manner are far from optimum.

It has also been suggested to filter cracking feed stocks through various chars, alumina-containing adsorbents such as bauxite, alumina gel, activated alumina, natural and activated clays, such as fullers earth, Attapulgus clay, and the like'whereby aromatic constituents are removed in addition to other impurities of the feed stock. However, processes of this type likewise suffer from the serious disadvantage that aromatics cannot be'completelyf removed to establish desirable gasoline to coke ratios without greatly reducing the yield of gasoline based on original feed. The present Vinvention eliminates these difliculties.

It is thereforethe principal object of the in- Y vention to improve the gasoline yield and the gasoline to coke ratio of cracking processes, particularly catalytic cracking lprocesses which are based on feed stocks containing aromatic con- `stituents. Other objects and advantages will appear from the description of the invention given below wherein reference will be made to the accompanying drawing, the single figure of which illustrates schematically a system suitable to Jgarry out a preferred embodiment of the invenion. Y Y

It has now been found that in cracking and particularly in catalytically cracking feedstocks originally containing aromatic constituents gasoline yields and gasoline to coke ratio may be improved beyond anything attainable by the abovementioned known processes When aromatic constituents are completely removed from the feed stock by adsorption on silica gel prior to cracking. Actually it has been found that Vthe raffinate ob tained by removing the aromatic constituents in this manner gives upon cracking in the presence of catalysts not only a gasoline to cokeratio substantially higher than that obtainable by feed stock extraction With solvents or other solid adsorbents but in addition absolute gasoline yields substantially in excess of those obtainable from the quantity of the original feed from which the rainate Was obtained. The pretreatment of the feed stocks with silica gel may be carried out at temperatures oi about 50 to 150 F. and silica gel to feed stock ratios of about 3:1 to 12:1. Any desired pressure may be used.

The highly beneficial eiect of the process of the invention will rst be illustrated for catalytic cycle oils and partially hydrogenated cycle oils which are particularly undesirable cracking feed stocks as a result of their high aromatics concentrations.

Eample I Separate batches each of a catalytic cycle oil and a hydrogenated cycle oil were subjected to catalytic cracking one batcliaiter'pretreatinent with silica gel, the other Without such treatment.

time is required. Complete removal of nonaromatics was determined by the refractive index of the liquid dripping from the bottom of the vessel. The R. I. of n-heptane is reached when complete separation is effected. 'I'he aromatics remaining in the column were removed by desorption with approximately a 2500 cc. wash of acetone. This entire process required only 21A.; hours. Use of a cylindrical column properly dimensioned to accommodate this size sample will take 2 or 3 times as long. After the aromatics were desorbed, both the aromatics and non-aromatics were stripped to remove acetone and heptane. On the cycle oil sample the aromatic content was determined to be 44%? and this value was reproducible within 1% and it agreed V,'\`vitl`1in1% Withth'e value determined on`a small ASTM adsorption column.

vCracking was carried out in a 200 cc. fixed bed laboratory unit on fresh standard silica-alumina catalyst containing 13% alumina at 975 F. and a feed rate of 1 v./`v./hr. in single pass operation with 2hr. cycle time. The results of these experiments 'are 'tabulated below.

TABLE I v'cycle p11 Y nydregaseeacyue ou Aramaic Nmo' urbanisti@ N'oill'fomaticl Y.. .1 .mame Total Frgon, Fracton Total Frgtion, Frcfto' conversion- 4a. s 1'9. o y 86.5 51. s 29.14 82.11 Carbon, Wt. Percent 10.7 10.0 5., 1 9. 7 10. 3 5. 6 Dry Gas, Wt. Percent.. 15.9 5. 4 3l. 8 18.6 11.0 '28.9 Gas, C. F./B Q 734 326 '1048 l858 1 654 960 Gas Density-.. 0.85 0.65 1.19 0. 85 0.- 66 1.18 D |L 26 `6. 0 81 36 7.1i 77 Naphtha, Vol; Perce 19.18v 5.2' 58.0 `27.1 7.9 57.3 400 E. P Gasoline, Wt. erc t. 15. 5 1..8 48,;9 21.6 6.0 47.8 Wt. Percent of Total 100. 0 `4 56 10050 40.0

The ra stocks used had 'the fauowmg 'inspec- The treatment with silica gel was carried out as follovvs. The treating vessel was a glass laboratory bell jar of 2 liter Volume, '13 long, 5" top diameter tapering to 21/72" bottom diameter. This container was packed with a 28-200 mesh silica gel. The oil sample (175 cc. of cycle oil) Was diluted with 350 cc., of normal heptane and the mixture Was allowed` to drip rapidly through. a

piece of filter paper ontop of the silica gel into the vessel. When all the sample was in thegel the vnon-aromatics wereimmediately Washed from the'coluinh fw'ith approximately af2w500y cc.

ciiar's'eb'fnormal heptane. Ndextnded Contact 75 It will be `-seen `from the above data that an improvement in yield has been eiected by pre'- treating cycle stock with silica V'gelfor removal of aromatics. For instance, the non-aromatics separated from the feed (column 3') amount to 56% and give a naphtha Vyield of 48.9%. The naphtha yieldthen on the basis of the total oil amounts to 27.4% as .compared to -15.5% for the .actual yield obtained from the .total -oil. For 'the hydrogenated product .the results are 28.7% for the non-aromatic fraction gured on the basis of thetotal oil as, Comparedto the 21.6%Y yield actually obtained from thetotal oil.. In addition torpgreatly increased gasoline `yie1ds,.b oth loils showed marked reduction in carbon formation.

Example II fhf .l'esulfsfiptl il? .Eimple .I .are far superior Yto the Yoptimum resultsobtainable by extracting the feed tocatal'ytic crackingprocesses with selective solvents. The datareported in Table II belowvcoxnpaf ,the.. resultsshown in Table; with'those "outa 'able by sivht'xtaction at extractipnandv ackin'ghcondition's con". ducive 1n Veach-"ease 1x1-in ximum gasbli'e "15rda catalytic cracking cycle gas oil produced an optimum 50% rainate which yields upon catalytic cracking a gasoline to carbon ratio 2.7 times higher than the ratio for the unextracted cycle oil. A 2.3-fold improvement in gasoline to coke ratio is obtained on a 79% phenol extracted raffinate from heavy catalytic cycle gas oil and an increase by a factor of 3.2 in the gasoline to coke ratio on the phenol extracted raffinate (80%) from a somewhat heavier catalytic cracking clarified oil. These improvements in the cracking g characteristics of the cycle stock feeds by means of selective solvent extraction are not nearly as great as those'shown for complete removal of aromatics from cycle stocks by means of separation with silica gel adsorbent. The data above demonstrate that when treating a heavy cycle .oil plus clarified oil and entirely removing the aromatic portion, byadsorption on silica gel, a non-aromatic oil is obtained which yields a gasoline to carbon ratio 6.9 times higher than the j gasoline to carbon ratio obtained in fixed bed cracking tests on the total oil. This improvement of cycle stock feed resulting from removal of -aromatics by silica gel adsorption is more than twice as great as improvements effected lwith solvent treating.

Other solid adsorbents such as alumina gel, activated alumina, bauxite, 'fullers earth, At-

tapulgus clay, various chars, and natural clays which have been used in filter treatments to re- 'move from oils various undesirable constituents may somewhat reduce the aromatic content of an oil; but the complete selective removal of aromatics as a pretreat for catalytic cracking stocks without reducing gasoline yields based on original oil is not feasible with kthese other adsorbents.

The above data have dealt with results obtainable bythe treatment of such poo-r cracking stocks as cycle and yclarified oils, Where aromatic y content is high 'and there is present a large amount Aof condensed-ring yaromatics which are 'jknown to be particularly strong carbon formers. lVirgin' gas oils, the usual feeds to catalytic cracking units, are considerably better cracking stocks since their total as well as their condensed aromatics content is' lower. Ihoweventhfat cracking of virgin gas oils may -`likewise be substantially improved by complete selectivel 'aromatics removal with silica gel. This fis demonstrated in Example lII below.

TABLE II f Catalytic Cracking Results Method of Aromatics Removal ggitlig Wt. Pere Ratio E P cent Gasoline Gaolle Carbonto Carbon I. Extraction with Methyl Cellosolve: i -East Texas Catalytic Cracking Cycle Gas Oil,

untreated 34.0 4.2 Y V8.1 Methyl Cellosolve Rafiinate thereof 48. 8 2.2 22. 2 II. Extraction with Phenol:

Heavy Catalytic Cracking Cycle Gas Oil, un-

` treated 1 22. 2 3. l 7. 2 l 79% Phenol Raiinate thereof 133.4 2.0 16.8 Catalytic Cracking Clarified Oil, untreat 1 16. 5 7.9 V2.1 80% Phenol Railnate *l 31.2 4. 6 6. 8 III. Silica Gel Adsorption:` C (Data from Table I.)

Heavy Catalytic Cracking Cycle+C1arifled Oil, untreated 15. 5 10. 7 1. 4 Non-aromatic fraction thereof from Silica Gel Separation (56% of total oil) 48. 9 5. 2 9. 6

"Y 1 Volume percent gures. The above data show thatv solvent extraction of Eample III Extraction and cracking experiments were car- -ried out in the manner described in Example I using a heavy virgin gas oil as the feed stock having the following inspection:

This work has shown that complete removal of the aromatic portion from the virgin gas oil feed,

vby adsorbent lextraction on silica gel, yields a non-aromatic fraction of such improved cracking characteristics that equally as good yields of Y naphtha (rlguredon the basis of the total, un-

separated feed) and lower carbon make are obtained on the non-'aromatic fraction alone than from cracking `of the total unseparated feed.

Data to support this are tabulated below.

I-Iere, asin the case of the cycle oil. anV iml provement in the gasoline to carbon ratio may be observed when aromatics are extracted from the feed although the total virgin g-as oil'has beenV considered heretofore to bean excellent cracking stock las such.

- The great significance of this increase in gaso- V line yield and decrease of the carbon yield on It has been found,

the non-aromatic fraction from either the cycle Voil -or virgin gas oil (these two oils are conventional cracking feeds) lies in the fact that a silica gel pretreatment for aromatics extraction on either or both 'virgin gas oilor cyclestockfeeds v u W'mil will result in a tremendousincrease-in.gasoline @g2-asma production for the unit, particularly in fluid-type catalytic cracking, since process variables can be changed to permit this.

Most conventional uid catalytic cracking units are carbon balance units; i. e., the capa-city for Iburning carbon off the catalyst limit-s theiconversion permissible. With increased conversion of a given feed to gasoline there is of course ,an increase in carbon production.

The following is `an example of how, in conjunction With a silica gel pretreatmentmperating `process variables may be changed on la iluid catalytic cracking unit of a given coke-burning capacity to afford approximately a 100 %1increa se in gasoline output, using the heavy virginggasfoil feed mentioned above.

Example IV The data of Case I below were obtained in an exploratory 68 gm. catalyst, fluid-type catalytic cracking unit 'at standard test conditions. The data of Case II [below are cor-relations made on the basis of the data' f Easel.

` ""Thesigniicance 'otheabovecases fis affolzzlows. fJIhe:` carbon; burning'.` capacity i'of; thennit .iisffSll-bsxperiday. '.i'llieiefore;` the cvi-rgin-igasf'il f, is ffedA to -the unitLat the?rateewhichwill. give :this limiting maximum; amount,` of; carbon ,a which ins Gas-e I fis 100.- lbsperzday.; operatingxat 710% --conversion. Thisxitypefof foperation :yieldszz lbs:` of gasoline i In:l Case-211'; the virgin; gasv :cil ffeed,v zvvhich-. @is :311% faromatic, ris extracted 'with :silica: gel :and the nonraromaticfstream: is *fcdnintoi therjluid catalytic cracking unit. As in Case I, carbon burning capacity Jis*6v`-"lbs':/day, and the cracking Vunit `will be "operated" to` reach this maximum. Dataorrelations on the cracking of the nonarornatic feed showithat the cracking unit may now 'be operated atincreased feed rates and increasedV ratio of catalyst to oil feed rates. Specically in Case II, 248 lbs. per day of the virgin gas oil feed may" be charged to'the.: extraction unit, providing 77 'lbs. per day'of aromatic'exjtract and a feed rate of 171 lbs. perday intoithe cracking unit, Where conversion Ymayrbemaintained ratf'16% without yielding.moremhanlthe permissible .maximum...6 lbs... of carbon. For these new yoperating:conditions, fmadeepossible Y by .this invention, vthe fgasoline-v outputw-becomes 165 lbs. lper day. The increase in.,gasoline.ou-t put `perunit time-is thereforeapproximately .510079. Thefsigniiicance#ofthe-.data ofsCasesl and IIr lies in their relative values-whichf-will be substantially the same in operation= onfaf cpmmerci'al scale.

,In. conventional..fluid= 'cracking units :the total .feedis a.mixtureof.f1esh gasoil and :vcycleggas oil. Gas-loll .recycleis-Lnecessary- 'becauseF ofY the .largemake of .such. cycle oil. .As indicated above the Vcarlc'von vproduced in .catalytic..crackingj units y' "chiefly cornes from highly cbndensedfaromatics formed during'recycling'bperation- "VTheimf proved feed conditions resulting from silica gel treatment, permit singlevpass operation without ,gas Aoilrecycle, so that the production of highly condensed carbon forming aromatics may be eliminated. It should be pointe d.out,that even LkWhen f-eeding 100% non-aromatics, aromatics lvvill-.beformed in the cracking operation. Upon recycling, these -aromatics further condense and eventually go to coke or carbonon thecatalyst. 10 The gas oiliproducedlnsingle Dass operation, containing no or-very-lttle condensediaromatics may be'fed to thermal cracking unitsjforjfurther gasoline 'yields `-or used* forany .fo'ther desired;;purpose. ",The smaller .amountof cycle.` oil gel, renders such thermal crackngorrother disposal of catalyticgas.oilsto.cksiinplaceor recycling much more attractive than ,"(iheretofore and this type ofoperationisagpreferrediembodiment of the'invention.

In describing the silica gel ,extraction/.procedure ,used in Example I. it has been pointed out that` thetaperedbontacting vessel employed" af- "-fords" advantages as i coinparedto ,conventional 4contacting vessels-of V cylindrical shape. "'Itphas been ufound that af literfbell jar; 18"`l0r 1 g,`8" top dia-meter: and Vtapering toij 3 .'bottom. r diameter "wcrks equally as WellandA accommodates three times 'asrnuch oil. LBy comparison,'a2I diameter vcylindrical column holding liters of; adsorbent would have ,to-be 10ft. ilong, requiring: longer perpcolation times and'even application ofpressureto facilitate' percolationat'ja" feasible. rate. fIf the length ofthecylindni'cal column is reduced, to Vshorten the percolation times or iftheA diameter A'is'sincreasedi toV accommodate,largenamounts of silica n'gel iniarge ,scale operationl there isjga lstrong. tendencyV for. the oilsto 'f v'channel in the column, and" no cleancut A.separation ca nbe ef- 0- fected. vfIt is generally 'accepted' thatjthelength `to diameter ratio. .of a .silica gel .adsorption V'column shonldbe: abouti 30.21 and nevenless than 15:1. Thus, 'very high V,columns Awhiph :are in- 'convenient 'and 4slow Ain percolation have, been 4, required heretoforein conventional;V largegscale s vperation. 'lheicolunm.desianiused .incarrving 'out' the"exp.eriments describedhereiri ,Offers substantial'advantages inthisrespectas,pointed out above. vIn'generalfthese adyantages`4-may beisecuredby employing tapered s ilica ,g`el ,co1umns of Acircular cross sectionsihaving a ratio vof length: 'tgp-"diameter: bottom :diameter of theol-der, of "'13 5 :2.5. A suitable'mannerof applyinggsilica gel Lcolumns .of this .infileY inPTaQiCaLoperatiOn j 'isfillustrated' in' the' drawing.

Referring now lto the, drawinggthere, arev shown s vtl'rerei11."th ree tapered columns l," 2 -and 3V `of the typefspeciiied above. Columns I Land. 3 are usedin ajcyclic type ofpperation involving-three lcycles;-V namely (A) charging of the iced,r yand adsorption of the aromatics;Y (B) washing-out of the nonsaromatic raflnate Wthlovi/ ,boilingr4 parafiinv `hydrocarbons.v combined` withY stripping of the hydrocarbon .Solvent from the. rainate, Aand 651 PaS'SJgS 0f the Stripped .lafnatelo theicracking Junit; and (C) 'desorptionofftheromatics.from 4"thej gel .and'regeneration 'ofjthe latterby,.me ans 'of'steam :followed by 'dryinggoflthe gel 4Withhot air. f Each Yco1urnn isgused succcssivelyoicarry jout cycles Afland C in/ theorder namedicperation of the three columnsbeing properly vstagigered to provide a,continuonsllow.,ofgtreatedieed .'stoclnto the, cracking plant. Columns 2.,. and 3 are drawn so .that ,eachwill illustralenepf the three cycles, column" I 'illustrating cycle A, c olthrough a suitable distributing means Asuch as a 1 spray nozzle or a perforated grid'1 as shown in the drawing to assure even distribution of the feed over the cross-sectional area of 'the column. The charge may be allowed to flow into column I at atmospheric pressurev and tempera ture. This completes cycle A.

In the next cycle the column is operated as shown in connection with column 2. A low boiling normally liquid paraffinc hydrocarbon such as pentane, hexane, heptane, etc., may be supplied from tank 9 through line II and grid 1 to the silica gel at .atmosphericY temperature and pressure in an amount of about 3 to 16 lbs. per lb. of gas oil feed originally charged. The wash oil removes the non-aromatic fraction from the silica gel while the aromatics remain on the adsorbent. The wash oil extract may be withdrawn via line I3 and collected in a stripper I5 wherein the wash oil is stripped off the nonaromatic fraction with hot air or steam introduced through line I5 to be returned via line I1 to tank 9 for reuse. There is a continuous circulation of Wash oil until extraction is completed. The non-aromatic fraction may be passed via line I9 directly to a fluid type catalytic cracking unit schematically identified at 2I. This unit may be operated at conventional conditions except that in accordance with a preferred embodiment of this invention the feed rate may be increased by about 50 to 100% and no gas oil recycle is employed. When all of the non-aromatic fraction is removed from the silica gel as determined by continuous refractive index measurements on the stream in line I3 operation is switched to cycle C.

In cycle C, as illustrated by column 3, steam may be introduced through line 23 at a temperature of about 212 to 500 F. to desorb the aromatics and regenerate the silica gel. 'I'he desorbate withdrawn through line 25 may be stripped of residual wash oil in stripper 26 with hot air injected through line 21, cooled in cooler 28 and vpassed to settler 29 from which aromatic byproduct may be recovered via line 3| and water may be withdrawn via line 33. Wash oil is returned to tank 9 through line 35. After suicient steam to regenerate the gel has been so employed at the conditions specified the silica gel may be ydried by introducing air via line 23 at a temperature of about 100 to 300 F. until condensation of water in cooler 21 ceases. Thereafter the column is ready for a fresh charge of oil feed.

In place of the batch type operation of the I Fluid catalytic cracking hasbeenrepeatedly referred to in the above description as the preferred cracking operation for the purposes of the invention. While the design and operation of such uid catalytic cracking systems are widely known in the art it isnoted for the sake of completeness that they involve the use of nely divided catalysts such as various activated clays or composites of silica gel with alumina, magnesia and/or boria, having particle sizes of.' about 50,-400 mesh. The catalyst is maintained in separate cracking and regenerating vessels in a dense turbulent uidized state by gaseous media passing upwardly through the beds. at linear superficial velocities of about 0.3-5 ft.per sec'. The catalyst circulates continuously between the reactor andregeneraton'heat for cracking being generated by burning carbon from the catalyst in the regenerator. Conventional conditions include cracking temperatures of about SOO-1000 F., regenerator temperatures of about 950-1200 F. but higher than the cracking temperature employed, pressures of from subatmospheric to 500 p. s. i. g. or higher, total oil feed rates of about 4 to 5 w./hr./w. catalyst/oil ratios of about 6:1 to 10:1 and oil recycle to fresh feed ratios of about 0.5-5 on a weight basis. When employed in the present invention the oil feed rate may be increased to about 6 to 10 w./hr./w. at a recycle ratio of 0 and a catalyst/oil ratio of about 11:1 to 17:1, but otherwise conventional conditions. While operations of this type are preferred for the purposes of the invention, marked improvements may also be secured when fixed bed, moving bed or suspensoiol systems are used. The gasoline yields and the gasoline to carbon ratio may likewise be improved when employing thermal cracking in the cracking stage of the invention. The silica gel extraction of cracking stocks in accordance with the invention not only reduces carbon forming tendencies by aromatics removal, but it prevents catalyst contamination by removal of nitrogen, oxygen and sulfur compounds and removal. of ash contents such as metallic salts from the oil. Moreover, the aromatic extract is of unusual nature. This pure concentrate of high boiling aromatic oils is a valuable source of chemicals for such by-products of the oil industry as carbon black, plastioizers, detergents, weed killers, wood preservatives, solvents, and others.

The foregoing description and exemplary operations have served to illustrate specific embodiments of the invention but are not intended to be limiting in scope. v

What is claimed is:

l. The process of cracking hydrocarbon oils which comprises contacting in a contacting zone a gas oil range hydrocarbon oil boiling above the motor fuel range, having a final boiling point not exceeding 1045 F. at atmospheric pressure and containing aromatic constituents, with silica gel in proportions adequate to adsorb said aromatic constituents substantially completely on said silica gel, recovering an oil substantially free of aromatics from said contacting zone and catalytically cracking the oil so recovered in the absence of said aromatic constituents at conditions conducive to the formation of motor fuel range hydrocarbons.

2. The process of claim 1 in which said cracking is carried out in the presence of a dense turbulent fluidized mass of sub-divided cracking catalyst.

3. The process of cracking hydrocarbon oils which comprises contacting in a contacting zone a hydrocarbon oil boiling Within the gas. oil range, having a iinal boiling point not exceeding 1045 F. at atmospheric pressure and containing aromatic constituents with silica gel in proportions adequate to adsorb saidaromatic constituents substantially completely on said silica gel, recovering an oil substantially free of aromatics from said contacting zone, passingA the oil'so recovered to a system comprising a cracking zone and a product fractionation zone, cracking said recovered oil in saidV cracking zone at cracking conditions in the presence of a dense turbulent uidized mass of sub-divided cracking catalyst and in the absence of said aromatic constituents, withdrawing cracked products from said cracking zone, separating said products in said fractionation zone into motor fuel and heavier fractions and withdrawing all of said fractions from said system, so as to operate at a recycle ratio of zero.

l2 4. The process of claim 3 in which said cracking conditions include oil feed rates of about 6-10 lbs. of oil per hour per 1b. of catalyst in said cracking zone and catalyst. to oil feed ratios of 5 about 11:1 to 17:1 by Weight.

KEITH P. LANInr'AU. ELPHEGE M. CHARLET.

REFERENCES CITED The followingreierences are of record in the file of this patent:

UNITED STATES PATENTS 15 Number Name Date 74,698 Kirkpatrick Feb. 18, 1868 1,881,044 Cannon Oct. 4, 1932 2,281,257 Benedict et al Apr. 28, 1942 2,464,311 Hiat et al Mar. 15, 1949 20 2,525,812 Lien et el Oct. 17, 1950

Claims (1)

1. THE PROCESS OF CRACKING HYDROCARBON OILS WHICH COMPRISES CONTACTING IN A CONTACTING ZONE A GAS OIL RANGE HYDROCARBON OIL BOILING ABOVE THE MOTOR FUEL RANGE, HAVING A FINAL BOILING POINT NOT EXCEEDING 1045* F. AT A ATMOSPHERIC PRESSURE AND CONTAINING AROMATIC CONSTITUENTS, WITH SILICA GEL IN PROPORTIONS ADEQUATE TO ADSORB SAID AROMATIC CONSTITUENTS SUBSTANTIALLY COMPLETELY ON SAID SILICA GEL, RECOVERING AN OIL SUBSTANTIALLY FREE OF AROMATICS FROM SAID CONTACTING ZONE AND CATALYTICALLY CRACKING THE OIL SO RECOVERED IN THE ABSENCE OF SAID AROMATIC CONSTITUENTS AT CONDITIONS CONDUCTIVE TO THE FORMATION OF MOTOR FUEL RANGE HYDROCARBONS.

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