US2043269A - Process for the treatment of hydrocarbon oil - Google Patents

Description

June .9, 1936- F. w. SULLIVAN. JR., El AL 2,043,269

PROCESS FOR THE TREATMENT OF HYDROCARBONOIL Filed Dec. 1, 1934 VISCOSITY BREAKING HEflTE/f HEATER HEATER CRACKING HEA TE I? .FUE TAR DST L INVENTORS BY M ' ATTORNEY Patented June 9, 1936 UNITED STATES PATENT OFFICE PROCESS FOR THE TBEATIVIENT F HYDROCABBON OIL Frederick W. Sullivan, Jr., and. Robert F.- Ruthruff, Hammond, 1nd,, assignors to Standard Oil Company, Chicago, EI a corporation of Indiana 1 Application December 1, 1934, Serial No. 755,538

110mm. (cries-49 s or the like, according to which the entire amount of cracking is carried out substantially one. oncethrough basis with only a small amount of re-' cycling, whereby the amount of oil pumped through the cracking zones is not greatly in excess of the amount of charging stock subjected to the process.

. 5 Processes are now known wherein crude charging oil or the like is subjected to distillation with the resulting formation of an intermediate condensate in the nature of gas oil suitable for use as clean cracking stock, and reduced crude, as well as a quantity of final desired light distillate,

if the charging stock contains constituents light enough to form such final desired distillate. Ihe intermediate condensate is then subjected to cracking to form additional quantities of final desired light products and intermediate condensate which is recycled to the cracking zone for further-"conversion. At the same time the reduced crude or other residual liquid is subjected.

to a cracking operation, such as to cause the formation of additional quantities of intermediate condensate stock suitable for mixture with the gas oil condensate derived from the initial charging stock, and this additional condensate is subjected to conversion in the cracking operation first-mentioned with the intermediate gas oil condensate from the initial charge. These processes are open to the objection that the cracking conditions in the zone in which the intermediate condensate is cracked, must be so- 40 le'cted with'a properregard for the presence in the oil undergoing cracking of constituents recycled from the cracking operation, which have a' greater coke-forming tendency than the initial condensate derived from the crude charging stock. It has been supposed heretofore that a cycle stock derived from a cracking operation always has greater coke-forming tendencies than the initial cracking stock from which is was formed, and cracking conditions have been ad-,

' justed accordingly.

We have now found that the cycle stock derived from the initial cracking of the intermediate distillate removed from crude oil charging stock, or the like, does not have such deleterious coke-forming tendencies as are associated with cycle stock from known cracking processes, but that, on the other hand, if the conditions; under which the initial cracking step is carried out are properly selected, cycle stock so obtained has substantially the same cracking characteristics p as the initial intermediate distillate charging stock and may be converted at relatively high percentages of cracking per pass, under substan-- tially the same conditions as the initial intermediate distillate charging stock. We have found my cycle stock derived by the cracking of cycle stock from the initial cracking operation conducted on said intermediate distillate stock is, on the other hand, of decidedly difierent character from the fresh distillate charging stock and has rather it marked coke-forming tendencies such as prevent it from being cracked successfuly under substantially the same conditions of temperature and pressure and conversion per pass as used in. connection Withthe fresh distillate charging stock. 20

In accordance with our invention fresh relatively heavy charging stock such as crude oil,

partially topped crude, or the like, is subjected to distillation after having been preheated in a suitable. fashion, as for example by indirect heat at exchange with hot products from the following cracking steps or by passage through-a directly fired coil in a heating zone, to form an intermediate condensate of a gas oil nature suitable for use as clean cracking stock, a reduced crude, 30 and also'a quantity of final desired light distillate, if the fresh charging stock contains constituents light enough to go into this distillate. There may likewise be formed an intermediate out such as kerosene, distillate fuel oil, or the 35 like, which may be withdrawn as a final desired product, as well as a heavy naphtha cut which it is desired to v.reform in order to produce relatively high anti-knock gasoline constituents.

The intermediate gas oil condensate is then 40 passed once through a first cracking zonewherein it is raised to a relatively high cracking temperature under relatively high super-atmospheric pressure, without recycling, and is subjected to conversion such as will result in the formation of it while the former are subjectedto fractionation to forma final desired light distillate, e, g., gasoline, and a reflux condensate of a gas oil nature. This reflux condensate is then passed once througha second cracking zon wherein it is subjected to conversion under substantially the 55 same conditions of temperature, pressure and conversion per pass as are used in the cracking zone first-mentioned, without recycling, the resulting cracked products are separated into vapors and liquid residue, and the residue is withdrawn from the process while the vapors are subjected to fractional condensation to form additional quantities of the desired light distillate, e. g. gasoline, and reflux condensate. The latter being of a refractory nature, is preferably diverted from the process as a distillate fuel oil, but may, if desired, be passed to a third cracking zone wherein it is cyclically cracked to completion in the vapor phase or otherwise, in accordance with known practices, to form additional quantities of final desired light distillate and residue.

Simultaneously the reduced crude or residual portion of the fresh charging stock is passed through a viscosity breaking cracking zone and is therein raised to a cracking temperature and subjected to conversion under relatively mild conditions, such as will result in the formation of only relatively small percentages of the final desired distillate such as gasoline, but will produce considerabie quantities of intermediate fractions suitable for use as a-cracking stock for the first-mentioned cracking step. The resulting mildly cracked products are separated into vapors and liquid residue and the latter is withdrawn from the process while the'former are subjected to fractional condensation to form more of the final desired light distillate such as gasoline, and quantities of intermediate condensate stock of a gas oil nature, and this latter condensate is combined with the intermediate condensate from the initial distillation stage for passage through the cracking zone first-mentioned. A heavier condensate than said intermediate condensate may likewise be formed and be returned to the said viscosity breakin cracking zone, if desired.

In conducting the operation as outlined hereinbefore the cracking temperature in the first and second-mentioned cracking zones is preferably in the range of 970 to 1100 F., while the pressure in each of these zones preferably falls in the range of 700 pounds to 1200 pounds per square from a few pounds to several hundred pounds per I square inch, for example, from pounds to 300 pounds per square inch. In case a cut of heavy naphtha is removed from the crude distilling zone, which it is desired to reform in order to raise the anti-knock value of the final desired distillate, this heavy naphtha is passed through a separate reforming zone wherein it is raised to a relatively high cracking temperature suitable to cause the conversion of the heavy naphtha into higher antiknock gasoline constituents, and the resulting highly heated reformed products are preferably introduced into the zone into which the cracked intermediate condensate or gas oil from the firstmentioned cracking zone is passed for separation into vapors and liquids. The temperature uriderin the range of 950 to 1150' F. more or less, while the pressure may vary considerably, being from a few pounds to several hundred pounds per square inch, for example about 700 pounds per square inch. I

Instead of separately cracking gas oil and reforming heavy naphtha to give the desired high anti-knock characteristics to the final light distillate, the heavy naphtha and gas oil may be passed together in a mixture through the initial once-through cracking zone and therein be subjected to conversion at the same time, the gas oil undergoin cracking and the heavy naphtha at the same time being subjected to reformation. Where the mixture is treated in a common cracking zone in this way the temperature to which the stock is elevated may be higher than where nection with the cracking of the cycle stock from the first stage cracking operation; the cycle stock or reflux condensate resulting from the fractionation of the cracked vapors then comprising not I only gas oil constituents but also heavy naphtha constituents, in which event additional reformation of the cracked heavy naphtha or heavy ends of gasoline would take place with an attendant increase in the anti-knock value of the desired light distillate.

In this case the fractionated vapors from the first crackingstage would consist essentially of light naphtha, while the end point gasoline distillate would beremoved from the fractionator of the second cracking stage and the final desired distillate could be formed by blending these two distiilates in desired proportions, while adding, if desired, light naphtha or virgin gasoline from the crude distilling zone.

The above-mentioned and further objects and advantages of our invention and the manner of attaining them will be more fully explained in the following description taken in conjunction with the accompanying drawing.

The single figure of the drawing represents diagrammatically an oil cracking system embodying our invention.

Referring more particularly to the drawing, reference numeral I indicates a crude flash tower or stripping tower, into which crude oil or the like is introduced through charging line 2, by aid of pump 3, after having been preheated in any desired manner, as by passage through indirect heat exchange coils in contact with highly heated products resulting from subsequent cracking steps, or by passage through a directly fired heating coil, or both.

In the tower I the introduced crude charging oil separates into vapors and liquids, the former passing upwardly through the tower past bubble trays, .baflie plates or other similar well known contacting means, while the liquid gravitates downwardly through the tower, over similar trays if desired, the vaporizing action being aided by the application of heat to the base of the tower through the agency of reboilercoil 4, or by the introduction of hot gases or steam in accordance with the known practice. In their passage upwardly through the tower the generated vapors undergo fractionation, the fractionated vapors passing from the top of the tower through vapor line 5 and condenser 6, resulting condensate being collected in receiver 1. This condensate may be light naphtha, gasoline, or other desired light distillate. At an intermediate point in the tower I a trap-out tray 8 is located, which serves to collect an intermediate condensate of a gas oil nature f suitable for use as clean cracking stock, this gas oil being removed through line 9 having pump l0,

' and forced through the heating coils of cracking heater I I, wherein the oil is raised to a relatively high cracking temperature, falling, for example,

in the range of 970 to 1100 F. under an outlet pressure of a relatively high value, falling most desirably in the range of 700 pounds to 1200 pounds per square inch, and being preferably about 1000 pounds per square inch, the time of contact being such that a conversion to products in the gasoline boiling range per pass, of at least 40%, is obtained although the value may exceed 40% being 45% or even more.

The resulting cracked products pass through the transfer line 92, having pressure control valve it, into separating chamber or evaporator M, wherein vapors separate from liquid residue. The vapors pass upwardly through the tower, undergoing partial fractionation if desired by passage through bubble trays or other suitable contacting elements It, any necessary cooling being provided by indirect heat exchange coil it, or by the introduction of a cooling oil in accordance with well known practices. The vapors travel through vapor line ll into. the fractionator l0 wherein fractionation thereof takes place in the usual way forming vapors of desired boiling characteristics and a reflux condensate. The fractionated vapors are conducted through pipe l0 into condenser 20, from which condensate flows into the receiver 2i, this condensate constituting a desired light distillate, e. g. gasoline.

While the preceding cracking operation is taking place the liquid reduced crude is withdrawn from the base of the crude flash tower l and forced by pump 22 through conduit 23 and the heating coils or furnace 24, wherein the oil is raised to a cracking temperature and subjected to only a moderate amount of conversion into products in the gasoline boiling range, with the attendant formation of additional quantities of gas oil constituents suitable for cracking in the heater II with the virgin stock withdrawn from trap-out tray 8. The oil during its passage through the heater 24 may be, for example, raised to a cracking temperature falling in the range of -840 to 900 F., the outlet pressure being, for

example, from a few pounds to several hundred pounds per square inch, preferably falling in the pass upwardly through the tower and are sub-v jected to partial fractionation by theagency of bafiie plates, bubble trays, or other contacting means, the fractionation being aided by cooling supplied to the top of the tower, for example by means of indirect heat exchange coil 28. In place of this-indirect heat exchange coil a cooling fluid might be introduced directly into the top of the.

tower. Additional cooling may be suppliedbelow the trap-out tray 29 if desired. This trap-out tray serves to collect a relatively heavy condensate of a heavy gas oil nature which is not suitable for passage through a cracking zone wherein Y fractionating column 34, which is equipped with the usual bubble trays or similar contacting means, and serves to fractionate the vapors in the well known manner, to separate undesirably heavy constituents, as reflux condensate, which collects in the base of the tower, from desirably light constituents, which pass from the top of travel through vapor line 3'5 into condenser 36,re-

sulting condensate being collected in receiver W,

as a desired light distillate, e. g. gasoline.

The reflux condensate from the bubble tower 30 is passed through conduit 30 into line 0 in which it mixes-with virgin stock from the tower l, for passage through the heating coils of cracking furnace ll, wherein it is subjected tothe cracking treatment as described already in connection with the intermediate gas oil condensate from the tower l. Or part or all of the reflux from bubble tower 34 may be commingled with the reflux from tower it, in conduit M,.for cracking therewith in heater 30, valved cross-over line 38' being provided for this purpose.

Reflux condensate from the base of fractionator i0 is withdrawn through pipe M and forced by pump 40 through the coils of cracking heater 39., In passage through the heater 39 the-oil is subjected to substantially the same cracking conditions of temperature, pressure, and time, as already described in connection with the cracking operation taking place in the heater II, the resulting cracked products passing through transfer line 44 having control valve 45, into the evaporator 46, wherein an action similar to that.

connection with evaporator H. In this tower partial fractionation occurs, the resulting 'iractioned vapors traveling through the connecting pipe 41 into the fractionator 48 wherein fractionation thereof takes place in the usual well known manner by aid of bubble plates or other contacting elements contained in the tower and an indirect cooling coil or other suitable cooling arrangement at the top of the tower. The fractionated vapors are removed from the tower and pass through the conduit 49 into condenser 50, from which the condensate emerges and is collected in receiver 5| as a desired light distillate, e. g. gasoline. Portions of the condensate formed in the tower 34 may be withdrawn from the process through pipe 42 and similarly portions of the condensate formed in the tower 18 may be withdrawn from the process through pipe 43, to establish balancedoperating conditions, or if desired, additional quantities of' similar oil may be supplied to the process through these same connections for a like purpose.

The distillates collected in receivers 1, 2'1, at

and 5|, or any combination of them, may be blended to producea final desired light distillate, the blending being accomplished by way of lines 52 and 53. Alternatively all or part of the dis tillate may be drawn off from the receivers mentioned by way of draw-on lines 54, 55, 56 and 51,

respectively. Reference numerals 58, 59 and 60 indicate draw-off lines by means of which liquid residue or tar may be withdrawn from the evaporators 21, I4 and 46, respectively, while reference numeral SI indicates a draw-off line by means of which reflux condensate formed in the fractionator 48 may be diverted from the process as a distillate fuel oil or for any other use. If desired, this condensate from line 6| may be passed to a separate cracking unit (not shown) wherein it is cracked to completion in any well known manner, preferably in a vapor phase low crack per pass recycling operation.

Simultaneous with the carrying out of the preceding cracking steps, where it is desired to raise the anti-knock value of the final distillate to a high value, a cut of heavy naphtha may be collected on trap-out tray 62' of the crude flash tower I, be withdrawn through pipe 62 and passed through the coils of reforming heater 63, by action of pump 64. ,In its passage through this heater the heavy naphtha israised to a relatively high cracking temperature sufficient to cause the reformation of the naphtha and the conversion thereof into relatively high anti-knock gasoline constituents. The resulting reformed products pass through transfer line 65, having pressure control valve 66, preferably into the evaporator I4 with the cracked products from the cracking heater H, and therein undergo separation into vapors and liquids, as already described in connection with the cracked products from the heater II. But if desired the hot reformed products may instead be introduced directly into evaporator 46. Or the heavy naphtha may be introduced directly into the coils of heater 39 for cracking in mixture with the gas oil.

As an alternative to carrying out a reforming action in the heater 63, the fractionation of the vapors in the crude flash tower I may be so regulatedthat a mixture of heavy naphtha and gas oil is collected on the trap-out tray 8 for passage through the cracking heater II. In this event the reformation of the heavy naphtha would be carried out in the heater mentioned, and to insure this the outlet temperature of the heater may be raised somewhat above the value used in connection with the cracking of gas oil alone.

Similarly the fractionation in the towers 34 and I8, or either of them, may be so controlled that the reflux condensate collected in the base thereof is a mixture of heavy naphtha and gas oil, the gas oil constituents being subjected to cracking and the heavy naphtha constituents being subjected to reforming in the following heaters. In this case the outlet temperature of the heater 39 may likewise be elevated somewhat in order to increase the reformation taking place therein. 7

Alternatively the gas oil and heavy naphtha constituents formed in the fractionators 34 and I8 might be separately collected in those towers and be passed through separate heating coils corresponding to heaters II and 39 respectively, so that the cracking of the gas oil and the reforming of the heavy naphtha would be carried out separately under the most advantageous conditions, the evaporators I4 and 46 being used to receive both the cracked and reformed products, or separate evaporators being used in cases where separate withdrawal of different cracked products is desired.

According to an alternative arrangement the method of operation would be to divide the charging stock introduced into the tower I into only an overhead fraction, including the desired light distillate and a liquid fraction collected in the base of the tower, this latter including constituents as light as gas oil or even heavy naphtha. This entire cut would then be subjected to a viscosity breaking cracking action in the heater 24, under preferably slightly more drastic conditions than used in carrying out the viscosity breaking action on the reduced crude alone as described hereinbefore. The cracked products obtained would then be treated just as described in connection with the preferred embodiment already hereinabove illustrated, except that the virgin gas oil and heavy naphtha would be absent.

A still further modification would be to carry out the cracking in the viscosity breaking heater 24, of the mixture of heavy constituents and lighter ones of a gas oil and even heavy naphtha nature, \as already mentioned, and then to form from the resulting cracked products two different reflux condensate stocks, one being a clean intermediate condensate of a relatively light gas oil nature, including even some heavy naphtha constituents, while the other would be a heavier gas oil condensate of less clean characteristics. These two stocks would then be subjected to cracking in separate furnaces and be introduced into a common evaporator corresponding to I4, or separate evaporators if desired, the resulting vapors being subjected to fractionation in a fractionator corresponding to I 8, or in separate fractionators, and the reflux condensate obtained might either be passed in its entirety to the cracking heater 39 and evaporator 45, as mentioned in the already described process, or the reflux condensate might be divided into a light and a heavy cut and these be passed through separate cracking furnaces and combined in the evaporator 46, or in separate evaporators if desired, to effect separate tar withdrawal.

In carrying out the modified form of operation wherein the reflux condensates from the several cracking steps are divided into two cuts, one an intermediate condensate and the other a somewhat heavier condensate; the cracking conditions used would be slightly less drastic for the heavy stock than for the lighter stock, on account of the greater coke-forming tendency of the heavier stock. The conditions under which the lighter of the constituents is cracked may be somewhat more drastic than those mentioned in connection with the cracking of the intermediate condensate in the preferred embodiment first described, in case the lighter of the two condensates of this modification is somewhat lighter than the intermediate condensate of the preferred embodiment.

Our invention as described hereinbefore permits the production from relatively heavy initial charging stock, which is itself not suitable for very drastic cracking, of relatively large quantities of high anti-knock gasoline, the preliminary viscosity breaking stage serving to produce a very clean cracking stock suitable for very high cracking per pass in the subsequent high-pressure cracking operation. Since this subsequent cracking operation is carried out under high pressure and high temperature conditions, gas production is min mized, while the production of tar is somewhat encouraged, both of these actions having a tendency to keep the hydrogen content in the cycle stock up to a satisfactory value, whereby this first cycle stock is suitable for subsequent cracking under substantially the same conditions as maintained in the tillate stock.

In the drawing various valves and other apparatus not specifically identified areior obvious control purposes. f

The cooling; coils not supplied directly with reference numerals perform their usual function. The fresh charging stock may be preheated prior to its introduction into the orudeflashing tower l by passage through some or all of the cooling coils shown on the drawing; 1

The heating coils for carrying out the several cracking operations may be located in separate furnaces as shown, or all or them may be placed in one furnace, or some may be placed in one cracking or the initial disiurnace and the others in one or more separate furnaces. If desired, enlarged reaction chambers may be placed in thepatli oi the oil from the cracking ,coils to the evaporators, in which case part of the cracking might be carried out in the coils and the remainder in the reaction chambers, but ordinarily it is preferable to efiect all of the cracking in the coils;

The pressures maintained in the several evaporators may vary considerably, but preferably fall in the range of pounds to 300 pounds per square inch, more or less. Undesirable coking in these evaporators may be inhibited by supplying cooling to the bases thereof in any well known manner.

In carrying out our invention on a charging stock such as. 36 A. P. I. gravity Mid-Continent crude oil, the constituents removed from thecrude flashing zone may be l0% to 30% light naphtha, 35% to 45% "gas oil, and 35% to 45% reduced crude, the exact percentages varying considerably in accordance with the specific operating conditions and the specific character of the final products desired. Obviously, if virgin heavy naphtha is to be included in the gas oil charging stock for passage through the initial cracking zone so as to be reformed therein,the percentage of naphtha removed from the top of the crude spirit of our invention as set forth in the ap- .pended claims.

We claim: 1. The process of treating hydrocarbon oil which. comprises. subjecting, fresh relatively heavy uncracked charging stock to non-cracking distillation toform an intermediate gas oil co'ndensate and an unvaporized fraction, passing said unvaporized traction throughv a first cracking zone wherein it is raised to a cracking temperature and subjected to conversion into products in the gasoline boiling range of not more than about 15% per pass separating the resulting cracked products into vapors and a liquid residue, iractionatingsaid vapors to form a final desiredlight distillate and a clean intermediate condensate of a gas oil nature, combining said (:ondensatelas'tmentioned with said intermediate condensate first-mentioned and passing the mixture once through a second cracking zone wherein the oil is raised to. a cracking temperature of at least 970 'F..under a superatmospheric pressure of at least 700 poundsper square inch and is subjected to conversion such as to formthe production of at least 40% of constituents in the gasoline boiling range, without recycling, introducing cracked products so obtained into a second separating zone wherein separation of vapors from liquid residue takes place, fractionating vapors so obtained to form a final desired light distillate and an intermediate condensate of a gas oil nature, passing gas oil condensate so obtained once through a third cracking zone wherein it is raised to a. cracking temperature of at least 970 F., under a superatrnospheric pressure of at least 700 pounds per square inch, and is subjected to conversion into products oi.- the gasoline boiling range of at least40% per pass, without recycling, introducing cracked products so obtained into a third separating zone wherein vapors separate from liquid residue, fractionating said vapors to form a final desired distillate and a reflux. condensat'e and diverting said reflux condensate from the process.

2. A process in accordance with claim 1 wherein the vapors from the cracked products firstmentioned are fractionally condensed to form a final desired'light distillate, a clean intermediate condensate of a gas oil'nature, and a heavier condensate; and said heavier condensate is returned ing. zone second-mentioned;

"4. The process of treating hydrocarbon oil which comprises passing relatively heavy fresh uncracked charging stock of a residual nature through a cracking zone wherein it is raised to a cracking temperature andsubjected to a moderate amount of conversion into lighter products in the gasoline boiling range, said conversionv not exceeding 15% per pass, introducing the re-' sulting cracked products into a first separating zone wherein vapors separate from liquid residue; passing said vapors to a fractionating zone and therein fractionally condensing them to form a final desired light distillate and a clean reflux condensate, passing said condensate once through in it is raised to a cracking temperature of at least 970 F., under a superatmospheric pressure of at least 700 pounds per square inch, and is subjected to at least 40% conversion into products in the gasoline boiling range per pass, introducing v a second cracking zone, without recycling, wherecracked products so obtained into a second separating zone wherein vapors separate from liquid "residue, passing liberated vapors into a second zone wherein vapors separate Irom liquid residue,

fractionating resulting vapors to form additional quantities of final desired light distillate and a reflux condensate, and diverting said reflux condensate from the process. I

5. A process in accordance with claim 4 wherein there is mixed with said condensate derived from said first-mentioned fractionating zone a quantity of virgin distillate stock of a boiling range similar to that of said condensate.

6. A process in accordance with claim 4 wherein said condensate derived from said first-mentioned fractionating zone includes heavy naphtha components which it .is desired to reform.

'7. The process of treating hydrocarbon oil which comprises fractionally distilling crude oil charging stock, without cracking the same, to form a clean intermediate condensate cracking stock including heavy naphtha constituents, and reduced crude, passing said reduced crude through a first cracking zone wherein it is'raised to a moderate cracking temperature and subjected to only mild cracking such as to form not over 15% of products in the gasoline boiling range per pass, introducing resulting cracked products into a first separating zone wherein vapors separate from liquid residue, passing said vapors to a first fractionating zone and therein fractionally condensing them to form a quantity of final desired light distillate and a clean intermediate condensate, combining clean intermediate condensate )so obtained with said intermediate condensate derived from said crude oil charging stock and passing the resulting mixture once through a second cracking zone wherein it is raised to a. cracking temperature of at least 970 F. under a'superatmospheric pressure of at least 700 pounds per square inch, and is subjected to conversion into products in the gasoline boiling range of at least per pass, without recycling, introducing resulting cracked products into a second separating zone wherein vapors separate from liquid residue, passing said vapors to a second fractionating zone and therein Iractionally condensing them to form additional quantities of final desired light distillate and a clean intermediate condensate, passing intermediate condensate so obtained once through a third cracking zone, without recycling, wherein it is raised to a cracking temperature of at least 970 F. under a high superatmospheric pressure and is subjected to conversion into products in the gasoline boiling range of at least 40% per pass, introducing resulting cracked products into a third separating zone wherein vapors separate from liquid residue, passing said vapors to a third fractionating zone and therein fractionally condensing them to form additional quantities of final desired light distillate and intermediate condensate.

8. A process in accordance with claim 7 wherein reflux condensate derived from said third-mentioned fractionating zone is withdrawn and cyclically cracked to completion in a separate recycling-cracking unit at only moderate rates of conversion per pass.

9. A process in accordance with claim 7 wherein light naphtha is separated from said crude oil charging stock and the final desired distillate is formed by blending said light naphtha with quantities of final desired light distillate obtainedfrom said fractionating zones.

10. The process of treating hydrocarbon oil which comprises subjecting fresh relatively heavy uncracked charging stock to non-cracking dis-' tillation to form an intermediate gas oil condensate and an unvaporized fraction, passing said unvaporized fraction through a first cracking zone wherein it is raised to a cracking temperature and subjected to not more than 15% of conversion into products in the gasoline boiling range, separating the resulting cracked products into vapors and a liquid residue, fractionating said vapors to form a final desired light distillate and a. clean intermediate condensate of a gas oil nature, passing said condensate first mentioned once through a second cracking zone wherein the oil is raised to a cracking temperature of at least 970 F. under a superatmospheric pressure of at'least 700 pounds per square inch and is subjected to conversion such as to form the production of at least 40% of constituents in the gasoline boiling range, without recycling, in-

troducing cracked products so obtained into a second separating zone wherein separation of vapors from liquid residue takes place, fractionating vapors so obtained to form a final desired light distillate and an intermediate condensate of av gas oil nature, passing gas oil condensate. so obtained once through a third cracking zone whereinit is raised to a'cracking temperature of at least 970 F., under a superatmospheric pressure of at least 700 pounds per square inch, and is subjected to conversion into products of the gasoline boiling range of at least 40% per pass,.without recycling, introducing cracked products so obtained into a third separating zone wherein vapors separate from liquid residue, fractionating said vapors to form a final desired distillate and a reflux condensate, diverting said reflux condensate from the process, and combining said intermediate condensate second-mentioned with one of said intermediate condensates first and third-mentioned, for cracking therewith.

11. A process in accordance with claim 10 wherein said intermediate condensate secondmentioned is combined with said intermediate condensate third-mentioned, for cracking therewith.

FREDERICK W. SULLIVAN, JR. ROBERT F. RUI'HRUFF.

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