US2010370A - Conversion of hydrocarbon oils - Google Patents

Description

3 J. c. MORRELL 2,010,370

CONVERSION OF HYDROCARBON OILS Filed 00k 24, 1933 VAPORIZING AND FRACTIONATING CONDENSER FURNACE 42 TOPPING AND FRACTIONATING CONDENSER FURNACE 28 I F RO M EATER RECEIVER INVENT R JACQUE C. RRELL ATTO Patented Aug. 6, 1935 UNITED STATES PATENT OFFlC CONVERSION OF HYDROCARBON OILS Jacque C. Morrell, Chicago, Ill., assignor to Universal Oil Products Company, Chicago, 111., a corporation of Delaware Application October 24, 1933, Serial No. 694,971

13 Claims. (Cl. 196-60) This invention relates to an improved process what higher boiling components of the vapors. and apparatus for the fractional distillation of I have found that, by careful selection of the hydrocarbon oils of relatively wide boiling range, intermediate fractions of the charging stock and such as crude petroleum, for example, for the the low-boiling components of the intermediate recovery of their desirablelow-boiling fractions conversion products of the process, which are to 5 and separation of the intermediate and highbe subjected to more severe conversion conditions boiling fractions accompanied by pyrolytic conthan those employed for conversion of the higher version of the intermediate and high-boiling boiling components of the charging stock and fractions under independently controlled condiintermediate conversion products, they may be tions of elevated temperature and superatmossubjected to further conversion for the produc- 19 pheric pressure, together with various selected tion of additional high yields of motor fuel of intermediate conversion products of the process. high anti-knock value under conditions which The advantages of separating oils of relatively are also suitable for the further conversion of wide boiling range, which are to be subjected to the vaporous products resulting from the relapyrolytic conversion for the production of high tively mild conversion of said higher boiling oils yields of good quality motor fuel, into selected for the purpose of improving the quality of the low-boiling and high-boiling fractions and sepamotor fuel components of the vapors, particurately subjecting each fraction to independently larly with respect to their anti-knock value, and controlled conversion conditions are now well to produce additional yields of good quality motor 20 recognized. The best conditions for obtaining fuel from the higher boiling components of the 20 high yields of motor fuel of high anti-knock value vapors. However, the nature of the low-boiling from low-boiling oils are ordinarily more severe oils selected for conversion withthe vaporous than those to which higher boiling oils may be conversion products will vary considerably with subjected without the danger of high losses, due different types of charging stocks, as will also the to the excessive formation of coke and/or gas. conversion conditions to which the commingled 25 It is also fairly well established that while high low-boiling oils and vaporous conversion products yields of motor fuel are obtainable from relaare subjected, and it is therefore not intended tively high-boiling oils at fairly low temperatures, to limit the present invention to the treatment the anti-knock value of the motor fuel produced of low-boiling oils of specific characteristics nor is ordinarily inferior to that obtainable from to the use of specific conversion conditions for 30 lower boiling oils under more severe conversion the treatment of the commingled vaporous concondltions. version products and low-boiling oils, except In the present invention the advantages of sewithin the range of relatively wide limits, herelective cracking are obtained by separating the inafter defined.

components of the charging stock which are not One specific embodiment of the present inven- 35 of satisfactory motor fuel characteristics, partion comprises subjecting hydrocarbon oil of relticularly withrespect to their. anti-knock value, atively wide boiling rangeto fractional distillaas well as intermediate conversion products of tion whereby any desirable low-boiling compothe process boiling above the range of the denents of satisfactory motor fuel characteristics 40 sired final motor fuel product, into selected loware recovered and the remaining components 40 boiling and high-boiling fractions and subjectseparated/into high-boiling fractions and relaing the low-boiling fractions to independently tively low-boiling intermediate fractions, subcontrolled more severe conversion conditions than jecting the high-boiling fractions to conversion those employed for the conversion of the hightemperature at superatmospheric pressure in a boiling fractions and, as a further step in the heating coil, introducing the hot conversion 45 process, the vaporous products resulting from the products into a reaction chamber wherein the relatively mild conversion of said high-boiling liquid and vaporous conversion products are sepfractions are subjected to further conversion, toarated, introducing the liquid conversion prodgether with said low-boiling fractions, whereby ucts-from said reaction chamber into a reduced the anti-knock value of the motor fuel compopressure vaporizing chamber, supplying the va- 50 nents of the vapors resulting from said relatively porous conversion products from the reaction mild conversion of the high-boiling fractions is chamber to a separate heating coil wherein they materially improved without excessively altering are subjected to continued conversion under intheir boiling range and additional yields of good dependently controlled more severe conversion quality motor fuel are obtained from the some-, conditions than those to which said high-boiling 55 fractions are subjected, introducing the resulting products into said reduced pressure vaporizing chamber wherein a final separation is obtained between vaporous and non-vaporous conversion products, subjecting vaporous conversion products from said reduced pressure vaporizing chamber to fractionation, whereby their components boiling above the range of the desired motor fuel conversion product of the process are condensed as reflux condensate and separated into selected low-boiling and high-boiling fractions, subjecting fractionated vapors of the desired end-boiling point to condensation, collecting the resulting products, returning highboiling fractions of the reflux condensate to the first mentioned heating coil for further conversion, together with the high-boiling fractions of the charging stock, and returning the low-boiling fractions of the reflux condensate, together with said intermediate fractions of the charging stock, to conversion, together with said vaporous conversion products from the reaction chamber.

The accompanying diagrammatic drawing illustrates one specific form of apparatus which may be'utilized in carrying out my invention.

Referring to the drawing, charging stock for the process, preferably comprising an oil of relatively wide boiling range such as crude petroleum, for example, is supplied in heated state through line I and valve 2 to topping and fractionating column 3. The charging stock may be heated in any desired manner, not illustrated in the drawing, for example, by means of heat recovered from within the system by the use of heat exchangers or the like or by means of heat from any desired external source, prior to its introduction into column 3 and the temperature to which it is heated is sufiicient to effect its ,substantial vaporization and fractionation in column 3, whereby it may be separated into desired low-boiling fractions, intermediate fractions and high-boiling fractions.

Any components of the charging stock boiling within the range of gasoline and of satisfactory motor fuel characteristics, particularly with respect to their anti-knock value, are withdrawn from the upper portion of column 3 through line 4 and may pass through line 5 and valve 6 to be subjected to condensation and cooling in con-- denser 1, from which the resultingdistillate and gas pass through line 8 and valve 9 to collection and separation in receiver ID, or if desired, the low-boiling fractionated vapors from column 3 may pass through valve II, in line 4, into line 49 to, commingle therein with fractionated vaporous conversion products of the process and subjected to condensation and collection therewith, as will be later more fully described. Any uncondensable gas produced by the topping operation may be withdrawn from receiver l0 through line l2 and valve l3. The distillate recovered may be withdrawn from receiver Ill through 'line M and valve l5 to storage or to 'vapors in this zone and to maintain the desired vapor outlet temperature, thus regulating the end-boiling point of the light distillate product recovered from column 3.

Intermediate fractions of the charging stock, including any components of the charging stock version of the products from this zone.

boiling within the range of gasoline but of inferior motor fuel characteristics, particularly with respect to their anti-knock value, as well as, if desired, somewhat higher boiling components of the charging stock such as naphtha, kerosene or kerosene distillate, light gas oil and the like or suitable fractions or combinations of such materials, are withdrawn from any suitable intermediate point or points in column 3. for example, through line It and valve H to pump H! by means of which they are supplied through line i9, valve 20 and lines 62 and 31 to conversion in heating coil 39, as will be later more fully described.

High-boiling fractions of the charging stock, including its components boiling above the range of the selected intermediate fractions supplied,

as already described, to heating coil 39, are withdrawn from the lower portion of column 3 through line 22 and valve 23 to pump 24 by means of which they are supplied through line 25 and valve 26 to conversion in heating coil 21.

Heating coil 21 is located within a furnace 28 of any suitable form, by means of which the oil supplied to this zone is heated to the desired conversion temperature, preferably at a substantial superatmospheric pressure, and the heated materials are discharged from the heating coil through line 29 and valve 30 into reaction chamber 3|.

Chamber 3| is also preferably maintained at a substantial superatmospheric pressure, which may be substantially the same or somewhat lower than the pressure employed at the outlet from heating coil 21, depending upon the degree of vaporization desired in this zone. Liquid conversion products which remain unvaporized in chamber 3| are withdrawn therefrom through line 32 and valve 33 and are introduced into vaporizing chamber 45, which is preferably operated at a substantially reduced pressure relative to that employed in chamber 3|. Vaporous conversion products are separately withdrawn from the upper portion of chamber 3| through line 34 and may pass through valve 35, in this line, to pump or compressor 36 by means of which they are supplied through line 31 and'valve 38 to further conversion in heating coil 39 or, in case a relatively high superatmospheric pressure is employed in chamber 3|, suitable for further conversion of the vapors in heating coil 39, as is preferably the case, pump 36 may be bypassed by'means of line 40 and valve 4|.

A furnace 42 of any suitable form supplies the required heat to the oils passing through heating coil 39 to bring them to the desired conversion temperature, preferably at a substantialsuper: atmospheric pressure, although if desired, pressures down to substantially atmospheric may be employed at the outlet from heating coil 39.

lntovaporizin'g chamber 45. Preferably, when a substantial superatmospheric pressure is employed in heating coil 39 the pressure employed in vaporizing chamber 45 is substantially reduced relative to the outlet temperature from the heating coil in order to cool and retard further con- Introduction of the liquid conversion products from chamber 3| into line 43, as illustrated, will also serve as a means of partially cooling and retarding conversion of the heated products from heating coil 39 and as a means of heating the liquid conversion products from chamber 3| to assist their further vaporization in chamber 45. It is also within the scope, of the invention, although not illustrated in the drawing, to separately introduce the conversion products from heating coil 39 and the liquid conversion products from chamber 3| into vaporizing chamber 45, particularly in case appreciable further conversion of the latter in this zone is not desired.

vaporizing chamber 45, in the case hereillustrated, comprises the lowr portion of vaporizing and fractionating column 2 l, although it is specifically within the scope of the present invention to employ one or a plurality of separate vaporizing chamberswherein the desired degree of further vaporization of the liquid conversion products from both chamber 3 l, and heating'coil 39 may be accomplished. In the case here illustrated, residual liquid conversion products remaining unvaporized in chamber may be withdrawn from the lower portion thereof through line 46 and valve 41 to cooling and storage or to any desired further treatment. It is, however, specifically Within the scope of the present invention to produce substantially dry coke as the only residual conversion product of the process, in which case' a plurality of coking chambers, not illustrated,

are preferably employed instead of chamber 45 and may be simultaneously operated or, preferably'are alternately operated, cleaned and prepared for further operation.

Vaporous conversion products pass from chamber 45, in the case here illustrated, through a riser 48 to the upper portion of column 2|, wherein they are subjected to fractionation for the formation of reflux condensate comprising the components of the vapors boiling above the range of the desired motor fuel conversion product of the process.

Fractionated vapors of the desired end-boiling point are withdrawn from the upper portion of column 2! through line 49 and valve 50 and are subjected to condensation and cooling in condenser 5!, either alone or together with the lowboiling Vaporous components of the charging stock, supplied to line 49 as previously described. The resulting distillate and uncondensable gas passes through line 52 and valve 53 to collection and separation in receiver 54. Uncondensable gas may be released from the receiver through line 55 and valve 58. The distillate may be withdrawn from receiver 54 through line 51 and valve 58 to storage or to any desired further treatment. When desired, a regulated portion of the distillate collected in receiver 54 may be recirculated by well known means, not shown in the drawing, to the upper portion of column 2! to serve as refluxing and cooling medium to assist fractionation of the vapors in this zone and to maintain the desired vapor outlet temperature from the fractionator, thus controlling the end-boiling point of the final motor fuel conversion product of the process.

The reflux condensate formed, as previously described, in fractionator 2| is separated into selectccl low-boiling and high-boiling fractions. The low-boiling fractions comprise materials boiling above the range of the desired motor fuel conversion products removed as the overhead streamof fractionated vapors from column 21, the endboiling point of which motor fuel product may 650 F., for example.

more or less.

range, for example, from 350 to 437 F., or thereabouts, and the low-boiling fractions may, if desired, include materials boiling as high as 500 to The selected; low-boiling fractions are withdrawn as one or a plurality of suitable side streams from column 2|, for example, through line 59 and valve 60, to pump SI by means of which they are returned through line 62, valve 63 and line 31 to further conversion in heating coil 39, together with the Vaporous conversion products from chamber 3|.

Components of the reflux condensate formed in fractionator 2|, boiling above the range of the selected low-boiling fractions supplied to heating coil 39, as hereinbefore described, may be withdrawn from the lower portion of the fractionating section of the column through line 64 and valve 65 to pump 66 by means of which they are returned through line 61, valve 68 and line 25 to further conversion in heating coil 21, together with high-boiling fractions of the charging stock from column 3.

In an apparatus such as illustrated and above described, the preferred operating conditions maybe approximately as follows: any desired pressure from substantially atmospheric or subatmospheric to a superatmospheric pressure of 200 pounds, or more, per square inch may be employed in the topping and fractionating stage of the process and the temperature to which the charging stock is subjected, to accomplish its fractional distillation, may range, depending upon the character of the charging stock, the pressure conditions employed and the desired separation, for example, from 400 to 600 F., The temperature employed for conversion of the high-boiling fractions of the charging stock and high-boiling fractions of the reflux condensate, measured at the outlet from the heating coil to which they are supplied, may range, for example, from 800 to 950 F.,.or thereabouts, and preferably a superatmospheric pres-.

sure is employed at this point in the system of the order of to 500 pounds per square inch. Substantially the same or somewhat reduced pressure may be employed in the succeeding reaction chamber and a substantially reduced pressure relative to that employed in the reaction chamber is preferred in the succeeding vaporizing chamber to which liquid conversion products from the reaction chamber are supplied. The heating coil to which Vaporous products from the reaction chamber, intermediate fractions of the charging stock and low-boiling fractions of the reflux condensate are supplied may utilize an outlet conversion temperature ranging, for example, from 900 to 1050 F., and any desired pressure ranging from substantially atmospheric to 1000 pounds, or thereabouts, per square inch may be employed at the outlet from this heating coil, a substantial superatmospheric pressure being preferred. The fractionating, condensing and collecting portions of the cracking system may employ pressures either substantially equalized with or somewhat reduced relative to the pressure employed in the vaporizing chamber.

As a specific example of one ofthe many possible operations of the process as it may be practiced in an apparatus such as illustrated and above described: The charging stock is a Mid- Continent crude of about 38 "R -P. I. gravity, containing approximately 35% of 437 end-point gasoline. The crude oil is subjected to fractional distillation whereby its components, boiling up to about 250 R, which comprise approximately 12% of the crude and are of satisfactory antiknock value, are recovered. Intermediate fractions of the charging stock, boiling between approximately 250 to 550 F., and comprising about 38% of the charging stock are subjected to a conversion temperature of approximately 980 F., at a superatmospheric pressure of about 800 pounds per square inch together with low-boiling fractions of the reflux condensate from the fractionator of the cracking system and vaporous products from the reaction chamber, and the resulting products are introduced into a reduced pressure vaporizing chamber, the remaining. higher boiling fractions of the charging stock are subjected, together with high-boiling fractions of the reflux condensate, in a separate heat-- ing coil, to an outlet conversion temperature of approximately 920 F., at a superatmospheric pressure of about 300 pounds per square inch and the-heated products are introduced into, a reaction chamber maintained at substantially the same pressure, wherein the resulting vapor- 011s and liquid conversion products separate.

The liquid conversion products from the reaction chamber are supplied to the reduced pressure vaporizing chamber and the vaporous conversion products, as already mentioned, are subjected to conversion together with the intermediate fractions of the charging stock. vaporous products from the vaporizing chamber are subjected to fractionation whereby low-boiling and high-boiling fractions of reflux condensate are recovered, the low-boiling fractions being returned, as already mentioned, to further conversion together with the vaporous products from the reaction chamber and the intermediate fractions of the charging stock, while the high-boiling fractions are subjected to further conversion, together with the high-boiling fractions of the charging stock. A motor fuel product of about 400 F., end-boiling point is recovered as the overhead stream from the fractionator of the cracking system and is blended with the low-boiling fractions of the straight-run gasoline, recovered from the fractional distillation of the charging stock, as the total motor fuel product of the process.

An operation such as above described, may yield per barrel of crude oil charging stock, about 74% of motor fuel having an anti-knock value equivalent to an octane number of approximately 70 and 12% of heavy residual liquid, the remaining 14% or thereabouts, based on the crude, being chargeable principally to uncondensable gas and loss.

I claim as my invention:

1. In a process for the conversion of hydrocarbon oils wherein raw oil charging stock for the process is subjected to fractional distillation whereby it is separated into desirable low-boiling components, which are condensed and collected, intermediate fractions and high-boiling components, the latter subjected to pyrolytic conversion, the resulting vaporous and liquid conversion products separated and said intermediate fractions of the charging stock separately subjected to pyrolytic conversion, the improvement which comprises subjecting the vaporous products resulting from the first mentioned conversion stage of the process to further conversion together with said intermediate fractions of the charging stock, separating the resulting vadensed as reflux condensate and separated into selected low-boiling and higher boiling fractions, subjecting fractionated vapors of the desired end-boiling point to condensation, collecting the resulting products and returning the selected low-boiling fractions of the reflux condensate to the last mentioned cracking stage of the process for further conversion.

2. In a process for the conversion of hydrocarbon oils wherein raw oil charging stock for the process is subjected to fractional distillation whereby it is separated into desirable low-boiling components, which are condensed and collected, intermediate fractions and high-boiling components, the latter subjected to pyrolytic conversion, the resulting vaporous and liquid conversion products separated and said intermediate fractions of the charging stock separately subjected to pyrolytic conversion, the improvement-which comprises subjecting the vaporous products resulting from the first mentioned conversion stage of the process to further conversion together with said intermediate-fractions of the charging stock, separating the resulting vaporous and non-vaporous products from the last mentioned conversion stage, subjecting the vapors to fractionation, whereby their insufficiently converted components are condensed as reflux condensate and separated into selected low-boiling and higher boiling fractions, subjecting fractionated vapors of the desired end-boiling point to condensation, collecting the resulting products, returning the selected low-boiling fractions of the reflux condensate to the last mentioned cracking stage of the process for further conversion and returning the higher boiling fractions of the reflux condensate to further conversion in the first mentioned cracking stage of the process.

3. In a process for the conversion of hydrocarbon oils wherein raw oil charging stock for the process is subjected to fractional distillation whereby it is separated into desirable low-boiling components, which are condensed and collected, intermediate fractions and high-boiling components, the latter subjected to pyrolytic conversion, the resulting vaporous and liquid conversion products separated and said intermediate fractions of the charging stock separately subjected to pyrolytic conversion, the improvement which comprises subjecting the vaporous'products resulting from the first mentioned conversion stage of the process to further conversion together with said intermediate fractions of the charging stock, separating the resulting vaporous and non-vaporous products from the last mentioned conversion stage, subjecting the Vapors to fractionation, whereby their insufiiciently converted components are condensed as reflux condensate and separated into selected low-boiling and higher boiling fractions, subjecting fractionatedvapors of the desired end-boiling point to condensation, collecting the resulting products, returning the selected low-boiling fractions of the reflux condensate to the last mentioned cracking stage of the process for further conversion, returning the higher boiling fractions of the reflux condensate to further conversion in the first mentioned cracking stage of the process and commingling the liquid conversion products from the first mentioned cracking stage with the products from the, last mentioned cracking stage, prior to their fractionation.

4, In a process for the conversion of hydrocarbon oils wherein high-boiling fractions of the raw oil charging stock for the process, separated from its lower boiling components by fractional distillation, are subjected to pyrolytic conversion and the resulting vaporous and liquid conversion products separated, the improvement which comprises subjecting the vaporous conversion prodnets to independently controlled more severe conversion conditions, separating the resulting vaporous and non-vaporous conversion products, subjecting the vapors to fractionation, whereby their insufi'iciently converted components are condensed as reflux condensate and separated into low-boiling and high-boiling fractions, subjecting fractionated vapors of the desired end-boiling point to condensation, collecting the resulting products, returning the high boiling fractions of the reflux condensate to further conversion, together with said high-boiling fractions of the charging stock, and returning the low-boiling fractions of the reflux c'onden-- sate to further conversion, together with said vaporous conversion products from the first de scribed cracking stage of the process.

' 5. A process of the character defined in claim 4 wherein selected low-boiling fractions of the charging stock, separated from its higher boiling fractions by said fractional distillation, aresubjected to conversion together with the low-boiling fractions of the reflux condensate and the vaporous conversion products from the first described cracking stage of the process.

6. A process of the character defined in claim 4 wherein the liquid conversion products from the first described cracking stage of the process are commingled with theconversion products from the last described cracking stage of the process, prior to their fractionation.

7. In a process for the conversion of hydrocarbon oils wherein raw oil charging stock for the process is subjected to fractional distillation whereby it is separated into desirable low-boiling components, which are condensed and collected, intermediate fractions and high-boiling components, the high-boiling components subjected to relatively mild conversion conditions of elevated temperature and superatmospheric pressure in a heating coil, the heated materials introduced into a reaction chamber, wherein vaporous and liquid conversion products separate, and the intermediate fractions of the charging stock subjected to more severe conversion conditions in a separate heating coil, the improvement which comprises supplying the vaporous products from the reaction chamber to the last-mentioned heating co-il for further conversion, together with the intermediate fractions of the charging stock, introducing the products from the last mentioned heating coil into a vaporizing chamber, wherein their vaporous and non-vaporous conversion products separate, supplying the liquid conversion products from the reaction chamber to said vaporizing chamber, whereby they are subjected to further vaporization, subjecting vaporous products from the vaporizing chamber to fractionation, whereby their insufficiently converted components are condensed as reflux condensate and separated into selected low-boiling and higherboiling fractions, subjecting fractionated vapors of the desired end-boiling point to'condensation, collecting the resulting products, returning the selected low-boiling fractions of the reflux condensate to the last mentioned heating coil for further conversion, together with the intermediate fractions of the charging stock and the vaporous products from the reaction chamber, and returning the higher boiling fractions of the reflux condensate to the first mentioned heating coil for further conversion, together with highboiling fractions of the charging stock.

8. In a process for the conversion of hydrocarbon oils wherein raw oil charging stock for the process is subjected to fractional distillation whereby it is separated into desirable low-boiling components, which are condensed and collected, intermediate fractions and high-boiling components, the high-boiling components subjected to relatively mild conversion conditions of elevated temperature and superatmospheric pressure in a heating coil, the heated materials introduced into a reaction chamber, also maintained at substantial superatmospheric pressure, wherein vaporous and liquid conversion products separate, and the intermediate fractions of the charging stock subjected to more severe conversion conditions of elevated temperature and superatmospheric pressure in a separate heating coil, the improvement which comprises supplying the vaporous products from the reaction chamber to the last mentioned heating coil for further conversion, together with the intermediate fractions of the charging stock, introducing the products from the last mentioned heating coil into a reduced pressure vaporizing chamber, wherein their vaporous and non-vaporous conversion products separate, supplying the liquid conversion products from the reactionchamber to said vaporizing chamber, whereby they are subjected to further vaporization, subjecting vaporous products from the vaporizing chamber to fractionation, whereby their insuffioiently converted components are condensed as reflux condensate and separated into selected low-boiling and higher-boiling fractions, subjectingfractionated vapors of the desired endboiling point to condensation, collecting the resulting products, returning the selected low-boiling fractions of the reflux condensate to the last,

mentioned heating coil for further conversion, together with the intermediate fractions of the charging stock and the vaporous products from the reaction chamber, and returning the higher boiling fractions of the reflux condensate to the first mentioned heating coil for further conversion, together with high-boiling fractions of the charging stock.

9. A hydrocarbon oil conversion process which comprises fractionating the charging oil and separating therefrom a relatively light fraction and a heavier fraction, heating the latter to cracking temperature under pressure in a first heating zone and separating volatiles from residue, combining such volatilized hydrocarbons with said light fraction and heating the mixture in a second heating zone to higher cracking temperature than said heavier fraction in said first zone, fractionating the vapors produced by the cracking of said mixture to form relatively light and heavy reflux condensates, supplying the heavy reflux condensate to the first heating zone for heating therein in admixture with said heavier fraction of the charging oil, supplying the light reflux condensate to the second heating zone for retreatment with said mixture, and finally condensing the fractionated vapors.

10. A hydrocarbon oil conversion process which comprises partially distilling the charging oil to form a light distillate fraction and a heavier residual fraction, heating the latter to relatively mild cracking temperature and combining resultant vapors with said light fraction, heating the mixture to highercracking temperature than said residual fraction, fractionating the cracked vapors ofsaid mixture to form relatively light and 'heavy reflux condensates, supplying such light reflux condensate to the last mentioned heating step for retreatment with said mixture, and finally condensing the fractionated vapors.

11. A hydrocarbon oil conversion process which comprises partially distilling the charging oil to form a light distillate fraction and a heavier residual fraction, heating the latter to relatively mild cracking temperature and combining resultant vapors with said light fraction, heating the mixture to higher cracking temperature than said residual fraction, fractionating the cracked vapors of said mixture to form relatively light and heavy reflux condensates, supplying such light reflux condensate to the last named heating step for retreatment with said mixture, combining the heavy reflux condensate with said residual fraction to be heated therewith to the relatively mild cracking temperature, and finally condensing the fractionated vapors.

12. A hydrocarbon oil conversion process which comprises fractionating the charging oil and separating therefrom a relatively light fraction and a. heavier fraction, heating the latter to relatively mild cracking temperature and separating resultant volatiles from unvaporized oil, combining such vclatilized hydrocarbons with said light fraction and heating the mixture to higher cracking temperature than said heavier fraction, combining the heated mixture with said unvaporized oil and separating the thus conmiingled materials into vapors and residue, fractionating the former to form relatively light and heavy reflux condensates, returning such light reflux condensate to the last named heating step for retreatment at the higher cracking temperature with said mixture, and finally condensing the fractionated vapors. V

13. A hydrocarbon oil conversion process which comprises fractionating the charging oil and separating therefrom a relatively light fraction and a heavier fraction, heating the latter to relatively mild cracking temperature and separating resultant volatiles from unvaporized oil, combining such volatilized hydrocarbons with said light fraction and heating the mixture to higher cracking temperature than said heavier fractionjcombining the heated mixture with said unvaporized oil and separating the thus commingled materials into vapors and residue, fractionating the former to form relatively light and heavy reflux condensates, returning such light reflux condensate to the last named heating step for retreatment at the higher cracking temperature with said mixture, combining the heavy reflux condensate with said heavier fraction of the charging oil for heating therewith to the milder cracking temperature, and finally condensing the fractionated vapors.

'JACQUE C. MORRELL.

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