US2417527A

US2417527A - Conversion of hydrocarbon oils

Info

Publication number: US2417527A
Application number: US428995A
Authority: US
Inventors: William J Sweeney
Original assignee: Standard Oil Development Co
Current assignee: Standard Oil Development Co
Priority date: 1942-01-31
Filing date: 1942-01-31
Publication date: 1947-03-18
Anticipated expiration: 1964-03-18
Also published as: GB580087A; FR915584A

Description

March 18, 1947.

` Filed Jan. 31, 1942 HOL. (lobbvtlk lllow NN l Patented Mar. 18, 1947 CONVERSION or HYDRocARoN oILs I William J. Sweeney, Summit, N. J., assignor to Standard Oil Development Company, a corporation of Delaware Application January 31, 1942, serial No. 428,995

4 Claims.

This invention relates to the conversion of hydrocarbon oils and pertains more particularly to a catalytic conversion process which will produce not only an aviation base stock of required low acid heat, high aviation octane number and lead response but which will also produce a relatively high yield of olefinic hydrocarbons suitable as source material for alkylation and polymerization processes,l together with a relatively high concentration of aromatic hydrocarbons.

This application forms a continuation-impart of my earlier filed application Serial No. 349,434, filed August 21, 1940.

It has been known heretofore that aviation base stocks of required low acid heat and high octane number could be obtained by cracking petroleum oil in the presence of an active cracking catalyst under properly controlled conditions.

It has also been known that petroleum oils could be cracked under conditions which would also produce a produciI rich in olefinic and aromatic hydrocarbons. However, it has been generally recognized that conditions suitable for the production of aviation gasoline of required low acid heat and high octane number were not suitable for the production of products rich in olens and aromatic hydrocarbons.

For example, to produce aviation gasoline of required low acid heat and high octane number by a single catalytic cracking step, it has heretofore been necessary to carry out the cracking operation under one set of conditions, whereas-to produce a substantial yield of oleinic gases and I aromatic hydrocarbons it is necessary to crack under another set of conditions. V

It is unnecessary to mention that all of these products, namely, aviation gasoline, olenic hydrocarbons and particularly the lower boiling olefins, such as butenes and pentenes, and aromatic hydrocarbons, are of tremendous importance in view of present war conditions. The olenic hydrocarbons may, for example, form a source inaterial for the production of synthetic rubber and stock on the one hand and the olenic and aromatic hydro :arbons on the other.

One of the primary objects of the present invention is to provide a process for the conversion of hydrocarbon oils which will produce an aviation gasoline of good gum and octane stability and at the same time produce a relatively high yield of oleinic and aromatic hydrocarbons.

A further object of the invention is to provide a, process for the conversion of hydrocarbon oils lwhich will produce an aviation gasoline of low acid heat and a high aviation octane number and lead response.

Other objects and'advantages of the invention will be apparent from the detailed description hereinafter in which reference will be made to the accompanying drawing'which is a -diagrammatic rillustration of an apparatus suitable for carrying the invention into effect.

Referring to the drawing, the reference character Ill designates a charge line through which the oil to be processed is introduced into the system. This oil may comprise a totali or reduced crude or a condensate stock such as gas oil. The charge introduced through line Il! passes through a distilling and vaporizing furnace II in which the oil may be heated to a temperature `sufficient to va-v porize a substantial portion thereof. Products from the heating furnace II may be passed into a separator I2 in which unvaporized constituents are segregated from the vapors. Liquid collected in the separato;` I2 may be withdrawn from the system through line I3. The vapors liberatedin the separator I2 may pass overhead through line id to a cracking chamber I5 into which an active cracking-catalyst of the type later to be described may be introducedinto the reactor through line In many cases the preheating furnace II and separator l2 may be omitted and the oil may ne passed in relatively cold condition through lines lli, II and I 4 directly into the reactor I5. In the latter case, the heat necessary for carrying out the cracking operation may be supplied entirely by the hot catalyst introduced into the cracking chamber throughl line IB.

The catalyst introduced into the cracking chamber I5 through line I6 is preferably a synthetic gel having as its principal constituents silica and alumina. Such a catalyst may be prepared, for example, by first preparing a hydrous silica, such as a silica hydrosol, hydrogel or gelatinous precipitate, and thereafter mixing the hydrous silica with alumina or an aluminum salt which may be subsequently converted to alumina.

either by chemical or heat decomposition. Such a catalyst may also be prepared by adding alumina or an aluminum salt solution during formation of the hydrous oxide. One method of preparation which has been found particularly suitable is to impregnate a puried silica hydrogel prepared according to conventional procedure with an aluminum sulfate solution of a concentration suicient to produce a catalyst having the desired alumina content. This content may range from about 5% to 20% of the product, preferably from to 15%. Following impregnation the catalyst may be treated with ammonia to decompose the aluminum sulfate into alumina and the product then dried to remove the bulk of the water. The resulting catalyst may be activated by maintaining it at a temperature from 800 F. to 1000 F. for a period of several hours. The catalyst is preferably in a finely divided, powdered state having a particle size such that the bulk of the material may pass through a 400 mesh standard screen.

While synthetic silica-alumina gels constitute thepreferred catalysts, other highly active synthetic gel catalysts may be employed. Such catalysts may comprise silica-zirconia, boron oxidealumina, tungsten oxide-alumina, beryllia-silica, beryllia-alumina, silica-magnesia, or the like. Activated clays can be employed and still retain certain advantages but the more active catalysts are preferred.

It will be further understood that all of the I above catalysts should be substantially free of alkali metals, particularly sodium. in order that they may be regenerated repeatedly at high temperatures without loss in activity. It will also be understood that the catalyst may contain minor amounts of inert materials or materials which have an activating, promoting or stabilizing effect on the catalyst. The catalyst is also in llnely divided, powdered `form, having an average particle size below 400 mesh. y

The temperature of the cracking zone may be maintained between 850 F. and 1000 F. and pref- -erably between 875 F. and 975 F.

As illustrated, the cracking chamber I5 is in the form of a vertical upright vessel having an inverted conical base into which the oil to be treated is discharged. A perforated grid is preferably provided in the lower portion of the reaction chamber I5 forming a distributing plate to insure more uniform distribution of the oil vapors throughout the catalyst mass.

When this typel of cracking chamber is employed, it is preferable to regulate the velocity of the oil vapors passing upwardly through the cracking chamber I5 so as to maintain a relatively dense, turbulent, uidized mass of yoil vapors and catalyst therein. For example, by maintaining the velocity of the oil vapors passing up wardly through the cracking chamber I5 between 0.5 and 5 feet per second, a density of-from 5 to 30 pounds per cubic foot may be maintained within the cracking chamber. The amount of catalyst introduced into the crackingchamber I 5 in proportion to the amount of oil being treated may range from 0.5 to 20 or more parts, depending upon whether it is desired to supply all the heat of the cracking operation by hot catalyst introduced through line I6.

The time of residence of the oil vapors within the cracking zone in contact with the catalyst should be sufcient to obtain between and 80% or more conversion as determined by the yamount of feed oil converted to other constituents.

seconds and 1 minute or more, depending upon the activity of the catalyst, the temperature, and .the length of time the catalyst is retained within the cracking zone between regenerations, and other factors.

The pressure maintained within the cracking zone is preferably substantially atmospheric except for the pressure necessary to accc:A lish the required flow, but in some cases a mild superatmospheric pressure, such as from 1 to 10 atmospheres, may be employed.

It will be understood that, in accordance with the present invention, the cracking conditions in the cracking chamber I5 are controlled to obtain a maximum yield of oleilnic, isopara'lnic and aromatic hydrocarbons.

The upward flow of the oil vapors through the cracking chamber I5 at controlled velocity as -heretofore described will maintain the catalyst mass in a highly agitated, turbulent state so that a substantially uniform temperature will exist throughout the full length and breadth of the reaction chamber.

The cracked products after passing through the reaction chamber I5 discharge through line I8 into the bottom section of a fractionating tower I9 in which the temperature is controlled to segregate the products into a plurality of separate fractions. The condensate formed in the bottom fractionating tower I9 and which may contain a small amount of entrained catalyst powder carried overhead with the vapors may be withdrawn from the bottom section of the fractionating tower I9 through line 2| and may be removed from the system through line 22 or recycled to the cracking chamber through line 23 and pump 24 either to the vaporizing furnace II or through line I 'I directly into the cracking chamber I5. A portion of the condensate from the bottom of the tower I9 may be passed through line 2 I and cooler 20 for reducing the temperature of the cracked products entering the fraction-l ator to the dew point.

The fractionating tower I9 may also be provided with a trap-out tray 25 for segregating a cycle gas oil fraction. This fraction may be removed from trap-out tray 25 through line 26 and may be recirculated for further cracking or withdrawn from the system. The fractionating tower I 9 nv Ly also be provided with another trap-out tray 26' for segregating a separate lighter fraction. This fraction may, for example, comprise a heating oil or kerosene, or, in some cases, a heavy naphtha cut boiling between 300 F. and 400 F. The fraction collected in the trap-out tray 26 may be Withdrawn from the tower through line 21. The tower may also be provided with a trap-out tray 28 which may be used for segregating a fraction boiling between 200 F. and 300 P'. This productmay be withdrawn from trap-out tray 28 through line 28' and blended back with aviation gasoline distillate later to be described.

The top temperature of the tower may be controlled to take overhead both light and heavy naphtha or a light naphtha boiling up to 200' F. or 300 F. When operating to take overhead a total naphtha fraction, trap-out trays 26' and 21 may be omitted or used to collect light gas oil, kerosene, and the like.

Vapors remaining uncondensed in the frac tionating tower I9, together with normal hydrocarbon gases and hydrogen formed in the process, are passed overhead from the fractionating tower through line 29 to a condenser 3| in which the normally liquid constituents present in the vapors are condensed. Products from the condenser 3| then pass to a distillate receiver 32 in which the liquid condensed in the condenser 3| segregates from uncondensed vapors and gases. The uncondensed vapors and gases segregated in the receiver 32 are removed therefrom through line 33. These gases may he sent to suitable re`l covery equipment, such as an absorption tower, for removal of the higher molecularweight hydrocarbons, such as propane and uncondensed butane and butene. These higher boiling gaseous hydrocarbons may then be combined with the liquid distillate and treated las later described.

The raw liquid distillate collected in the receiver 32 is removed therefrom through line 3d. A portion of such distillate may be returned through line 35 and pump 3B to the top section of the fractionating tower i3 as a reflux therefor. The remainder of the raw distillate may then be passed through line 3l to a stabilizer and debutanizing tower 38, or it may be passed to a treating Zone for further treatment later to be described. When the products are passed to the debutanizing tower 38, the temperature and pressure conditions therein are preferably controlled to vaporize the butane-butene constituents and lower boiling hydrocarbons. In some cases it may also be desirable to regulate the top temperature of the tower`38 so that a portion or all 6 A relatively high percentage of toluene which may be segregated by simple distillation, solvent extraction, or by a suitable combination thereof.

The products withdrawn from the tower 38 through line 4| may be passed by means of pump 44 and line 45 into a treating chamber 46 which contains a nely divided treating catalyst in-V troduced through line 41.

The catalyst employed in the treating chamber 46 is preferably of the same general type 'as that used in cracking chamber l5 hereinbefore will contain a relatively high concentration of olenic material andisoparafns. These products may therefore constitute a source material for the production of synthetic rubber, or they may be passed to an alkylation process in which vthe isoparai'ns and oleflns are alkylated to form aviation alkylate.

In some cases it is desirable to control the cracking conditions within the reaction chamber- I5 so that the relative proportions of isoparafilns and oleflns in the gases removed from the debutanizing tower 38 through line 39 may be in the desired ratio for direct alkylation.

The liquid introduced into the debutanizing or rectifying tower 38 after being subjected to distillation and fractionation to remove the lower boiling constituents hereinbefore mentioned is removed from the bottom of the tower through line 4|. If desired, a portion of this product may be passed through line 42, heater 43 and back to the tower 38 to supply the desired heat for distillation and vaporization of the lower boiling constituents.

In accordance with the preferred embodiment of the invention, the product withdrawn from the bottom of the `debutanizing or rectifying described. 1t has been found that this type of catalyst is particularly suitable `for producing aviation gasoline of low acid heat, high aviation octane number andlead response. It has been found, for example, that an aviation gasoline treated as above described may have an octane number as determined by the l-C method of the order of from 95 to 100 with the addition' of 4 cc. of tetra-ethyl lead, so that little if any aviation alkylate is required to meet 100 octane specifications. This type of product is obtained from a high acid gasoline having an aviation octane number of from 85 to 92 with the same amount of lead.

The temperature maintained within the treating chamber 46 should be between 500 F. and 850 F., preferably between 700 F. and 750 F. However, the temperature of the second step with respect to that of the 'first will vary with the catalyst activity, the catalyst-to-oil ratio; the boiling range of the once-cracked distillate treated, and other variables.

The treating chamber. 4B is preferably of the same construction as the cracking chamber I 5j contained in the treating zone per hour may, in

tower 33 constitutes the initial feed for the production of the aviation base fuel later to be described. This product may be a 400 end point motor fuel fraction, a 300 end point aviation gasoline, or it may be a light naphtha boiling up to 200 F. or 225 F. It has been found, for example, that the fraction obtained by the oatalytic cracking process previously described, boiling between 200 F. and 300 F., is rich in aromatics and isoparaflins and only a relatively small amount of olellns so that in most cases it is not necessary or desirable to subject this fraction to further treatment. This product has a time of the oil vapors with the catalyst in the treating operation may be between 5 and 50 seconds, preferably between 15 and 30 seconds.

The velocity of the oil vapors passing upwardly through the treating zone 46 may be between 0.5 and 5 feet per second, preferably between 1 and 3 feet per second, and the density of the catalyst contained in the treatingzone may be between 5 and 30 pounds per cubic foot.

The treated vapors after passing` through the treating vessel 45 may be passed through line 48 to a fractionating column 49 in which the products are fractionated. l

The products introduced into the fractionating column 49 are subjected to fractionation to segregate an aviation gasoline. In addition to segregating an aviation gasoline, the heavier condensate boiling above aviation gasoline may be segregated into a heavy naphtha suitable as a blending stock for the production of motor fuel or solvent oil. A bottom fraction collected -in the fractionating tower 49 may be Withdrawn therefrom through line 5| and the' lower boiling fraction whichjmay consist of "a solvent oil or a heavy naphtha fraction may be withdrawn through line 52 from trap-out tray 53.

Vapors remaining uncondensed in the fractionating tower 49 and comprising the aviation gasoline constituents, together with lower boil; ing gaseous products formed in the process, are removed overhead from the tower through line 54 to a condenser 55. Products from the condenser 55 may then be passed to a distillate receiver 56 in which the liquid distillate formed. in the condenser 55 segregates from uncondensed gases and vapors. In cases where a low-boiling fraction, such.'as a 300 F. end point aviation fraction or a 200 F. end point naphtha fraction, is employed as a feed to the treating chamber, the secondary fractionating tower may be omitted and the products passed through line 48 directly through line 54 leading to condenser 55.

The uncondensed gases and vapors segregated in the receiver 56 are then passed from the receiver through line 51 and may' be further processed to recover the higher molecular Weight constituents contained therein. The raw aviation distillate collected in the receiver 56 may be withdrawn therefrom through line 58. If desired, a portion thereof may be returned to the top of the fractionating tower 49 through line 59 and pump 6I.

The raw aviation distillate collected in the receiver 56 forms one -of the final products of the process. This product may, however, be subjected to further nishing treatment for the production of an aviation gasoline of the desired vapor pressure, stability, and other properties, or if it is. a product of low end point feed (say 200 F.) from the treating step, it may be blended with a heavier cut (say 200 to 300 F.) previously separated from the fractionation carried out in tower I9. However, as previously described, this 200300 F. fraction from tower, I9 may be distilled or extracted to remove a portion of the 4toluene before blending back with the distillate fraction from the product receiver.

Returning now to the cracking c hamber I5, the catalyst contained therein in contact with the oil vapors accumulates carbonaceous deposits which reduce the activity of the catalyst. As a result, it is necessary to continuously withdraw catalyst from the reaction chamber and Subject it to regenerative treatment to remove such carbonaceous deposits. Referring to the drawing, the

catalyst after being held in the cracking chamber I5 until the activity has been dropped to the minimum level is withdrawn from the reaction 'chamber I5 through a conduit 62 which prefer ably has an extended portion 63 projecting upwardly into the reactor. A strippingand fluidthroughout the full length and breadth of the regenerating chamber. The regeneration of the catalyst material within the regenerator 88 re- Ysults in the liberation of a relatively large amount of heat. In many cases it may be desirable to control the temperature of the regenerator below a predetermined point which would tend to permanently impair the activity of the catalyst. This temperature control may be conveniently accomplished by circulating more or less of the Acatalyst through the cracking chamber I5. When may also be introduced at one or more spaced izing gas may be introduced into the conduit 62 at one or more spaced points by means of lines 64 and 65. reaction chamber I5 through conduit 62 discharges into a stream of air entering 'through line 66 and is passed upwardly through line 61 into a regenerating chamber 68 which may be of a construction similar to the cracking chamber I5. This regenerating chamber may, for example, comprise an upright vertical vessel throughwhich the stream of air for burning off the carbonaceous deposits passes in an upward direction at a controlled velocity to maintain a dense, agitated mixture of catalyst undergoing regeneration within the vessel 68. The st'ream of catalyst and air is introduced into the bottom .section of the regenerator 68 and a perforated grid is preferably provided above the point of entry of the catalyst-air suspension to obtain a. more uniform distribution of the suspension The catalyst withdrawn from the points into the conduit 69 through line 1I.

The regenerating gas after passing through the regenerator 68 may be withdrawn therefrom through line 12. These gases may be passed to a suitable separator such as a cyclone separator, electrical precipitator, or oil scrubber for removing the entrained catalyst powder contained therein.

Referring again to the treating chamber 46, this treatment also lays down a carbonaceous deposit on the treating catalyst which must be regenerated periodically to1 restore ,its activity. To this end, a stream of spent catalyst is continuously withdrawn from the treating chamber 46 through conduit 'I3 which discharges into an air line 14 leading to the regenerator 68. A fluidizing gas is also introduced at one or more spaced pointsv along the conduit 13 to maintain the circulating catalyst in a freelyvfiowing, iluidized state.

A portion of the regenerated catalyst withdrawn from the regenerator through conduits 69 may be returned through line 41. The catalyst return conduits I6 and 41 are provided with suitable valves for controlling the relative amounts of catalyst introduced into the cracking and treating chambers. To insure circulation of the catalyst through the cracking and treating chambers in the manner hereinbefore described, it is neecssary to maintain the catalyst particles in a freely flowing, fluidized state throughout the circulating system. It is also necessary to maintain the conduits 62, 13. 69, I6 and 41 at such height as to develop a fluistatic pressure suiicient to overcome the pressure drop through the circulating system.

While a common regenerator 68 has been shown for regenerating the catalyst from the treating chamber 46 and the cracking chamber I5, it will be understood that a separate regenerating lchamber may be provided, especially where different catalysts are used in the two Itreating stages or in cases where different pressures are employed in the cracking and treating chambers. The following example may be helpful to a better understanding of the invention, it being understood that the values and conditions given therein are illustrative rather than limitative.

An East Texas light gas oil having an A. P. I. gravity of about 33.8 was charged into a cracking chamber of the type shown -in the drawing containing a synthetic silica-alumina gel catcentration of butenes and isobutane.

alyst formed by impregnating a purifled silica hydrogel with aluminum sulfate solution of a concentration sufficient to form acatalyst having an alumina content of about 12%, determined on the dry basis. The temperature maintained within the cracking zone was 875 F. and the relative rate of feed of catalystiand oil was 8 parts of catalyst per part of oil by weight. The weight of oil treated per weight of catalyst per hour in the cracking chamber was 0.73 and the time of contact was about 30 seconds.

Under `the above conditions, 57% of the gas oil was converted to other constituents, of which 37.5% was a l-pound Reid vapor pressure 400 F. end point motor fuel and 18.7% comprised excess butane-butenes which contained a high con- A 300 F. end point aviation gasoline from this operation had an acid heat of about 110 F. and an aviation octane number of 91.7, determined by the 1-C method.

The 400 F. end point motor fuel fraction segre-l gated from the cracked products was subjected to various treating conditions. In each treating operation the same catalyst was employed as was employed in the cracking operation just mentioned. The conditions and the results obtained in the various treating operations are summarized brieiiy in the following table:

Table I Temp., F

Feed rate W./W.!hr.1. Cat/oil ratio 2 Fornaci time Products:

300 F. E. P.. vol per cent.- Cycle nil. 300 Fri- Cs excess LIT zozo

Ac cat Octane l-C-I-4 cc. Pb

l Weight of oil treated per hour per weight of catalyst in reactor. 2 Weight oi catalyst introduced into reactor per weight of oil.

The yields of the various products produced from the original feed are outlined in the following table:

The above results demonstrate that it is possible to produce an aviation gasoline of low acid l heat and high octane number and at the same time produce a substantial quantity of butane and butenes and pentane and pentenes which have a high concentration of olefins. For example, from 20% to 25% of the original gas oil can be converted into an aviation gasoline having an acid heat below 20 and an aviation octane number, with the addition of 4 cc. of lead, of between 98 and 100, while at the same time producing large quantities of butane and butenes which can be alkylated, if desired, to form aviation alkylate. If the excess butane-butene `fraction is alkylated for the production of aviation alkylate, a total yield of aviation gasoline of substantially 100 octane number with the addition of 4 cc. of lead may amount to from 30% to 50% of the original gas oil feed.

1f desired, the aviation fraction formed in the the C3 and C4 fractions.

present process maybe further treated to extract the aromatics, such as toluene, benzene and xylenefand these aromatics may be employed as starting material for other purposes. This extraction treatmentmay furthermore increase the octane number of the aviation gasoline but would, of course, reduce the total yield of aviation gasoline produced in the process.

Returning again to the product receiver 32, while it is preferred to reject the' gaseous hydrocarbons from the system before further processing of the liquid distillate fractions from the cracking operation, the total overhead from Ithe fractionating tower may be passed through lines 29 and 3i to the treating chamber 46. The products subjected to further treatment in treating chamber V lighter constituents formed in the cracking stage.

(6) The 300 F. end point fraction, together with the Ca and/ or C4 constituents.

(7) The debutanized and/0r depentanized 300 F. end point light naphtha.

(8) The 200 F. end point light naphtha fraction with the lighter constituents formed in the process.

(9) A 200 F. end point light naphtha, to-

- gether with the C3 and/or C4 constituents.

(10) A debutanized and/or depentanized 200 F. endpoint light naphtha fraction.

(11) A heavy naphtha fraction boiling above about 300 F. mixed with a light naphtha fraction boiling up to about 200 F. but without the 200 to 300 F. fraction and with or without lower boiling gaseous constituents.

In cases where the treating chamber 46 operates at a temperature materially below the regenerating temperature, it may be necessary or desirableto cool the catalyst passing from the regenerator to the treating chamber or to provide cooling means within the treating chamber.

While, for simplicity, I have shown the prod.- ucts passing directly from the cracking chamber l5 and treating chamber 4E directly to the fractionating towers I9 and 49, respectively, without `provision for separation of entrained powder, it

is desirable in most cases to provide suitable separating` devices, such as electrical precipitators, cyclone separators, and the like, for this purpose.

Also, it is preferred to recycle a portion of the condensate from the bottom of fractionator 49 through cooler 50 to reduce the temperature of the incoming products below the dew point.

The pressure in the treating zone 46 may be substantially the same as that in the cracking zone, or it may be at a higher level. However.

when operating at diierent pressuresy in the cracking and treating zones, separate regenerators should be provided.

Also, it is desirable in many cases to pass the catalyst from the treating zone through the cracking zone before subjecting the same toregeneration, as described in my earlier tiled apl plication referred to hereinbefore.

Having described the preferred embodiment of the invention, it will be understood that it em- 11 braces such other variations and modifications as come within the spirit and scope thereof. lWhat is desired to be protected by Letters Patent is:

1. A process for the conversion of higher boiling hydrocarbons into aviation gasoline of low acid heat which comprises cracking said oil at a l temperature of from 875 F. to 1000" F. in the presence of an active cracking catalyst, maintaining said oil in contact with saidl catalyst for a period sufficient to convert from 40% to 80% of said oil into other constituents, fractionating .the conversion products to segregate a light naphtha fraction comprising principally constituents boiling below 200 F. and a heavyv naphtha. fraction boiling within the range of the desired aviation gasoline, subjecting said light naphtha fraction to further treatment in the presence of said catalyst ataI temperature below the temperature employed in the cracking of said rstnamed oil, and thereafter combining the light fraction so treated with said heavy naphtha fraction to form an aviation gasoline.

2. A process for the conversion of higher boiling oils into aviation gasoline of low acid heat which comprises cracking said oil in the presence of anactive cracking catalyst While at a temperature of from 850 F. to 1000 F. and for a period suilicient to convert at least 40% of said oil into other constituents, thereafter fractionating the products to segregate a light naphtha fraction consisting principally of constituents boiling below 200 F., an intermediate naphtha fraction boiling between about 200 F. and 300 F., and a heavier naphtha fraction, combining said heavier naphtha fraction with said light naphtha fraction, subjecting the resulting mixture to further treatment in the presence of said catalyst while at a temperature below the temperature maintained during said cracking, maintaining said mixture in contact with said catalyst during said treatment for a period suilicient to materially reduce the acid heat thereof, and thereafter fractionatlng the treated product to segregate an aviation gasoline therefrom.

3. A process for the conversion of higher boiling hydrocarbons into aviation gasoline of low acid heat which comprises cracking said oil at a temperature of from 875 F. to 10005 F. in the presence of an active cracking catalyst, maintaining said oil in contact with said catalyst for a period sumcient to convert from 40% to 80% of said oil into other constituents, fractionating the conversion products to segregate a light naphtha fraction comprising, principally constituents boiling below 200 F. and a heavy naphtha fraction boiling within the range of the desired aviation gasoline, subjecting said light naphtha fraction to further treatment in the presence of said catalyst at a temperature below the temperature employed in the cracking oi said first-named oil, and thereafter combining the light fraction so treated with a heavy naphtha fraction relatively free of oleflnic constituents to form aviation gasoline.

4. The method of operating a catalytic conversion system employing finely divided solid catalyst particles in a regeneration zone and two conversion zones which method comprises maintaining a dense turbulent catalyst phase in the regeneration zone by passing regeneration gases upward in said zone at a low velocity, withdrawing hot catalyst directly from the dense turbulent catalyst phase `in the regeneration zone to a rst conversion zone, introducing a charging stock at a low point in said rst conversion zone at such a rate as to maintain a dense'turbulent catalyst phase therein, withdrawing catalyst directly from the dense turbulentcatalyst phase in the first conversion zone and returning it to the regeneration zone, removing conversion products from an upper part of the iirst conversion zone, withdrawing catalyst directly from the dense turbulent catalyst phase in the regeneration zone and introducing said catalyst into a second conversion zone, passing products produced in said rst conversion zone to a low point in the second conversion zone at such a rate as to maintain a dense turbulent catalyst phase there- 1n, withdrawing catalyst from the dense catalyst phase in the second conversion zone and returning it to said regeneration zone', 'removing products from an upper part of the second conversion zone and. fractionating the removed products.

WILLIAM J. SWEENEY.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,091,892 Stratford Aug. 31, 1937 2,267,766 Thomas et al Dec. 30, 1941 2,270,071 McGrew Jan. 13, 1942 2,270,072 McGrew Jan. 13, 1942 2,270,091 Thomas et al Jan. 13, 1942 2,271,148 Becker Jan. 27, 1942 2,276,081 McGreW Mar. 10, 1942 2,287,940 McGrew June 30, 1942 2,296,722 Marancik et al. Sept. 22, 1942 2,300,240 Thomas Oct. 27, 1942 2,328,756 Thomas Sept. 7, 1943 2,328,754 Thomas Sept. 7, 1943 2,311,498 Voorhies, Jr Feb. 16, 1943