US2420534A

US2420534A - Catalytic cracking of hydrocarbon oils

Info

Publication number: US2420534A
Application number: US512426A
Authority: US
Inventors: Edwin J Gohr; Donald L Campbell; John M Graham; William I Thompson
Original assignee: Standard Oil Development Co
Current assignee: Standard Oil Development Co
Priority date: 1943-12-01
Filing date: 1943-12-01
Publication date: 1947-05-13
Anticipated expiration: 1964-05-13

Description

y 1947- E. J. GOHR ET AL 2,420,534-

CATALYTIC CRACKING OF HYDROCARBON OILS Original Filed Sept. 14, 1940 2 Sheets-Sheet l lnvenfow's y 13, 1947- E. -J. GOHR ET'AL 2,420,534

CATALYTIC CRACKING OF HYDROCARBON OILS Original Filed Sept. 14, 1940 L2 Sheets-Sheet 2 Patented May 13, 1947 2,420,534 CATALYTIC oascxggi or HYDROCARBON Edwin J. Gohr, Summit, Donald L. Campbell, Short Hills, John M. Graham, Plainfleld, and William I. Thompson, Westfield, N. J assignors to Standard Oil Development Company, a corporation of Delaware Continuation of application Serial No. 356,840,

September 14, 1940. This application December 1, 1943, Serial No. 512,426

3 Claims.

This invention relates to the conversion of hydrocarbon oils and particularly to a method of and apparatus for the conversion of such oils inthe presence of a powdered catalyst suspended in oils undergoing conversion.

While the invention in some of its broader phases has a more general application, it is particularly adapted to the cracking of higher boiling hydrocarbons into lower boiling motor fuel constituents. p

One of the broader objects of the present invention is to provide an improved method for cracking hydrocarbon oils in the presence of a finely-divided catalyst suspended therein.

A further object of the invention is to provide an improved continuous process for the catalytic cracking of hydrocarbon oils which is more simple and economical than processes heretofore employed.

A further object of the invention is to provide an improved apparatus for the continuous cracking of hydrocarbon oils in the presence of a powdered catalyst.

A further and more specific object of the invention is to provide an improved apparatus for catalytic cracking of oils which is more simple and compact than apparatus heretofore employed.

A further object of this invention is to provide an improved means for cooling of catalyst regeneration vapors by the controlled preheating of fresh feed oil. a

With the above-nature and objects in View, the invention will best be understood by reference to the accompanying drawing, wherein- Fig. I is a partly diagrammatic and 'partly schematic illustration of an apparatus forming a part of the present invention, and

Fig. II shows a modification of the type of reaction chamber shown in Fig. I.

Referring to the drawing, the reference character l designates a charge line having a feed pump ll through which the oil to be cracked, preferably preheated to from 300 to 625 F., is introduced into the system. The fresh oil to be cracked may be clean condensate stock such as a virgin or cycle gas oil or it may be a heavy stock containing residual constituents such as topped or reduced crude. The oil introduced through line i0 is further preheated by indirect heat exchange with cataly'st undergoing regeneration as later described. To this end the fresh oil is divided into two streams. One stream passes, through line l2 to a heat exchanger l3 and the second stream passes through line ll to a second heat exchanger I5.

Bothheat exchangers are located in the catalyst regenerating circuit to be later described and the oil is preheated by heat liberated during regeneration and the oil in turn is used to control the regenerating temperature.

The separate streams of fresh feed oil after passing through the heat exchangers l3 and I5 pass through lines [6 and il, respectively, which merge into line l8 leading to a fired coil I9 located in furnace 20 wherein the oil is heated to the desired vaporizing temperature. This tem perature is such that after the mixing of the vapors with regenerated catalyst, as hereinafter described, the suspension is at a temperature suitable for the catalytic reaction.

The-oil during passage through the heat exchangers l3 and I5 may be heated from the initial inlet temperature to a temperature of from 650 to 750 F. and the oil during passage through the fired coil l9 may be heated to from 800 to 1000 F., forexample. If desired, and particularly when high boiling feed stocks are employed, steam or other diluent gas may be introduced into the vaporizing coil I 9.-

The oil after passing through the vaporizing coil I! may be transferred through line 2| to a separator 22 wherein vaporsseparate from any unvaporized residue which may be present.

A by-pass line 23 is preferably provided around the vaporizing coil l-9 to insure more effective control of the coil outlet temperature. In some cases the oil may be heated to the desired vaporrizing temperature in heat exchangers l3 and 15. In such cases the vaporizing coil [0 may be omitted or the oil may be by-passed around the vaporizing coil through line 23. Additional steam may be introduced into theseparator 22 through line 24 to assist in the vaporization of volatile constituents in the feed. Any unvaporized residue segregated in the separator 22 may be removed through draw-off line 25 and rejected from the system.

Where the fresh feed is a clean condensate stock completely vaporizable at the desired tem perature, the separator '22 may be omitted or the oil vapors by-passed around it through line 26.

Vapors liberated in the separator 22 pass overhead through line 21 to a catalyst injector 28 wherein they are mixed with a finely-divided catalyst. In some cases it is desirable to further heat the vapors after passing through the separator 22. In such cases a coil'or other suitable heating means (not shown) may be placed in line 21.

The catalyst may comprise naturally active or activated clays, such as, for example, acid treated clays, or it may comprise synthetic adsorptive products, such as synthetic gels containing silica in combination with alumina or magnesia. The catalyst is in finely-divided form capable of passing through a hundred mesh screen.

The amount of catalyst introduced into the oil vapors in the injector 28 will depend upon various factors such as activity of the catalyst, temperature of the oil vapors, degree of conversion desired, characteristics of the oils undergoing cracking, and other factors. In most cases the amount will range from .5 to parts by weight of catalyst per part of oil treated, depending on the above factors.

The catalyst-oil suspension formed in the injector 28 passes through line 29 to a cracking zone 30, which, for illustrative purposes, has been shown in the form of a vertical tower.

' The velocity of the vapor stream passing through the column should be high enough to prevent the catalyst particles from settling out and the length of the cracking zone should be sufiicient to obtain the desired conversion. The

conversion of the feed to hydrocarbons boiling in the gasoline range should preferably be in excess of 30% by volume and may be as high as60%. In general, when using the powdered material of the type previously described, the velocity should be at least 1 feet pen second and preferably above 8 feet per second. Higher velocities of the order of 10.0 to 100.0 or more feet per second may be employed, but in such cases the length of the cracking zone must be correspondingly increased to give the required contact time. The resident time of the oil vapors within the cracking acne to obtain conversions of the order above mentioned may range from 2 seconds to 2 minutes, depending on catalyst activity, the temperature of cracking, the characteristics of the feed, the relative amount of catalyst used, and other factors. The resident time of the catalyst may be the same as the oil vapors or may be considerably longer.

The suspension of catalyst and cracked products after passing through the column 30 flows through line 3| to a primary separator 32 for the separation of catalyst from cracked vapors. As illustrated, this separator is shown in the form of a cyclone or centrifugal separator. It will be understood, however, that the invention is not restricted to any particular type of separator. The

separator 32 serves to remove the bulk of the powdered catalyst from the cracked products. The catalyst so separated drops through conduit 33 having a valve 34 to a steam injector 35 in which steam is introduced through line 36 to serve as a stripping and diluting agent for removing volatile oil from the catalyst and diluting the oil vapors associated therewith. The stream of stripping and diluting gas and catalyst after passing through the injector 35 is passed through conduit 31470 a secondary separator 38 wherein most of the steam and volatile hydrocarbons separate from the catalyst.

The catalyst powder separated in the separator '38 is passed through a second conduit 39 having a valve 40 through a second injector 4| in which additional steam or other stripping and diluting gas is introduced through line 42 to remove additional volatile hydrocarbons which may remain on or surrounding the catalyst.

The stream of stripping and diluting gas and 4 catalyst powder passes through conduit 43 to a final separator 44 wherein the catalyst powder is separated from the stripping gas and volatile hydrocarbons removed from the catalyst.

The provision of two injectors arranged in series as just described is a simple and rapid means of stripping or purging the catalyst of volatile hydrocarbons which would otherwise be burned during regeneration of the catalyst.

As illustrated, the bottom section 45 of the separator 44 forms a storage bin or hopper from which the catalyst is fed to a regenerating unit later described. To this end the bottom of hopper section 45 should be of sufficient size to provide a reserve supply of catalyst passing to the regenerating apparatus.

Returning now to the primary separator 32, the cracked products separated from the bulk of the catalyst but still containing entrained catalyst powder pass from separator 32 through line 46 to a secondary separator 41 for further removal of powdered catalyst entrained in the vapors.

Stripping gas and volatile hydrocarbons from separators 38 and 44 are passed through

lines

48 and 49 and combined with cracked vapors passing to the secondary separator 41.

Entrained catalyst powder-separated from the cracked vapors in the secondary separator 41 is discharged from the bottom thereof through a conduit 50 having a suitable gas sealing mechanism, such as a star feeder 5|, into the hopper section 45 of the cyclone separator 44 for passage through the regenerating apparatus.

The cracked vapors from the secondary separator 41 pass through line 52 to a further cyclone separator 53to further remove entrained catalyst powder from the cracked vapors. Catalyst powder separated in the third catalyst hopper 53 is passed to the hopper section 45 of the cyclone separator 44 through conduit 54 having a suitable valve such as a star feeder 55 providing a gas seal between the separator 53 and separator 44.

As previously described, the cracked vapors containing the powdered catalyst are caused to pass through three separate separators arranged in series to insure removal of the powdered material from the cracked vapors. It will be understood, however, that the invention is not limited to this particular number, since any desired number may be employed as necessary for recovery of catalyst from oil vapors. The number of separators necessary will depend upon the amount of catalyst present in the vapors, the efficiency of the separators, and other factors. Also, electrical precipitators or other separation means may be substituted for part or all of the cyclone separators.

The cracked vapors after passing through the final separator 53 are removed therefrom through line 56 and are passed to a, suitable fractionating and separating equipment for segregation of the desired distillate products from the normally gaseous products and higher boiling fractions. This fractionating equipment may be of any conventional construction and for purposes of simplicity has not been shown on the drawing. The cracked vapors from the final separato 53 may alternatively flow to a, further treating process or to a total condenser (not shown).

Returning to the hopper section 45 of the cyclone separator 44, the catalyst collected therein which has been through the catalytic cracking zone normally contains carbonaceous deposits which reduce the activity of the catalyst. In accordance with the present invention, this catalyst is subjected to regeneration as hereinafter described to remove the carbonaceous deposits before returning the same to the cracking circuit.

In order to provide an adequate supply of catalyst passing through the regenerating zone and to provide a further seal between the cracking circuit and the regenerating circuit, it is desirable to maintain a substantial level of catalyst within the hopper 45. To insure maintaining a proper level of catalyst within the hopper 45 a suitable level indicating mechanism i provided. One particularly efiective level indicator ls shown in the drawings. An inert gas such as steam from a common manifold 51 is introduced into the hopper at spaced points through lines 58 and 59 between which'it is desired to maintain the catalyst level. A suitable pressure indicator such as a manometer is connected in parallel with the inlet pipes 58 and 59. The difference of pressure recorded on the manometer indicates the hydrostatic head of catalyst between the lower and upper pipes 58' and 59. If the catalyst level drops below the lower inlet pipe 59, the pressure in the two lines 58 and 59 will be the same. In such case it may be desirable to discontinue the removal of catalyst from the hopper until the level has filled up to a point above the bottom of line 59.

The catalyst from the hopper 45 is discharged therefrom through a suitable feeding mechanism such as a rotary star feeder 60 into a suitable conveyor capable of maintaining a positive pressure seal between the cracking and regenerating circuit such as a compression screw 6|. The compression screw 6| feeds the catalyst'into a stream of regenerating gas as illustrated. High pressure steam may first be introduced into the catalyst to be regenerated through line 62. The mixture of catalyst and steam is then injected into a stream of oxidizing gas introduced through line 63. .This oxidizing or regenerating gas may be air or a mixture of air and diluent gas such as steam, nitrogen; carbon dioxide, spent combustion or regenerating gas, and the like. The catalyst introduced into the regenerating gas is preferably at the final cracking temperature which may be from 750 to 1000 F.

In order to' properly control the regenerating temperature to avoid deactivating the catalyst, the regenerating zone is divided, for example, into three sections separated by' the heat exchangers l3 and I5. As shown, each combustion avoided. In the case of synthetic gels of silica and alumina or silica and magnesia temperatures as high as 1400 F. may sometimes be tolerated.

The suspension during its passage through the initial combustion section 64 i heated from the initial temperature up to the maximum desired -iiemperature before passing to the heat exchanger The catalyst suspended in the regenerating gases during its passage through the initial heat exchanger i3 is cooled by indirect heat exchange with fresh oil for the process as previously described. a

section of the regenerating equipment is in the The heat exchanger I3 may be of any conventional design suitably modified to prevent catalyst settling out of its suspension. As illustrated, the suspension of catalyst and regenerating gases passes through a bank of tubes 61 located in the heat exchanger i3 around which the fresh oil is caused to circulate. The heat'exchanger may be provided with a plurality of staggered baflles 68 arranged to cause the cooling oil to take a circuitous path through the exchanger.

After the suspension of catalyst and regenerating gas has been cooled the desired amount in the heat exchanger i3, the suspension (still being at a high enough temperature to insure reasonably rapid oxidation of the carbonaceous deposits) is passed through line 69 to the second combustion section 65.. Additional air to oxidize the carbonaceous deposits is preferably added at spaced points in the second combustion section through line 10, II and 12 leading from a common manifold airline 13. As illustrated, it is desirable to increase the diameter of the combustion zone at the points of addition of the air so that the suspension will travel at comparatively uniform velocity during its passage through the combustion section. The suspension, during its course through the second combustion zone, is again heated from the exit temperature of the heat exchanger l3 to the maximum desired temperature.

The suspension after passing through the second combustion section 65 passes to a second heat exchanger l5 where it passes in heat exchange relation with fresh oil. The heat exchanger l5 may be of construction similar to that of I3. The products, during their passage through the'heat exchanger I5,are again cooled v to the minimum temperature which will effect rapid oxidation of the carbonaceous material obtained on the catalyst.

The suspension after passing through the 'second heat exchanger l5 continues through line 14 to the final combustion section 56 wherein the regeneration is completed. Additional air for oxidizing th carbonaceous deposits is introduced into the final combustion chamber 66 at spaced points through lines 15, I6 and 11 leading from a common manifold line I8. The final combustion section 66 i also enlarged with each addition of air to maintain a substantial uniform velocity of the suspension passing therethrough.

As previously set forth, the temperature during regeneration is controlled by successive stage cooling-in heat exchangers l3 and I5 by indirect heat exchange, with fresh oil passing through the circuit.

Provision is also made "for controlling temperature independently of the amount of preheat desired to be imparted to the oil passing through to the vaporizing coil I9. This control of tem- -the heat exchanger I 3, a part of the. oil .after being removedfrom the heat exchanger through Incipient cracking of the oil would be' cuits.

line l8 may be passed through line 19' and pump 80 to a supplemental heat exchanger 8| which for illustrative purposes has been shown in the form of a waste heat boiler through which water circulates in indirect contact with the oil. The oil from the heat exchanger 8| is returned to the heat exchanger I3 through line 82 which merges with line I2 entering the heat exchanger I3.

Water for cooling the oil is circulated to the heat exchanger 8| from a steam disengaging drum 83 through

lines

84 and 85. A by-pass line 86 around the Waste heat boiler 8| may be provided for more effectively controlling the tem-' perature of the oil returning to the heat exchanger through line 82.

In accordance with the construction Just described, the desired amount of excess heat liberated during regeneration of the catalyst over and above that necessary for preheating the oil is recovered in the form of steam in the waste heat boiler 8|. The steam generated is passed to a steam line 81 from which it may be utilized in any desired manner.

By regulating the relative amount of oil passing through the heat exchanger 8| as compared to that passing to the vaporizing coil l9 by varying the speed of the pump 80, the amount of cooling within the heat exchanger l3 can be controlled independently of the amount of final heat given to the oil. Also, by suitably controlling the volume of oil passing through the heat exchanger l3 in heat exchange relationship with the suspension of catalyst and regenerating gases, applicants are able to prevent the temperature of the oil from exceeding a predetermined maximum.

The heat exchanger I5 is also provided with a similar means for controlling the heat and for convenience similar parts are represented by prime numbers.

The suspension of catalyst and regenerating gases after passing through the final regeneration section 66 is transferred through line 88 to a primary cyclone separator 89 wherein the bulk of the regenerated catalyst is separated from the regeneration gases. As illustrated, the bottom section of this primary separator 89 forms a storage hopper for catalyst passing to the cracking circuit and should be of sufficient capacity to provicle an ample reserve supply of catalyst.

The catalyst separated in the primary separator 89 is continuously withdrawn from the bottom of the supply chamber attached thereto through conduit 90 having suitable feeding mechanism therein such as rotary star feeders 9| and 92 which are synchronized to insure a pressure seal between the cracking and regenerating cir- The lower star feeder 92 is preferably operated ata speed somewhat in excess of the speed of rotation of the feeder 9|.

The catalyst hopper forming the bottom section of the cyclone separator 89 is preferably provided with suitable level controllers arranged at spaced points longitudinal of the hopper. The upper level controller 94 is adapted to control the rotation of the upper star feeder 9| so that when the level of the catalyst in the hopper rises above the desired upper level control point the speed of the star feeder 9| is increased to reduce the level. The lower level controller 93 is adapted to conin)! the rotation of the lower star feeder 92 in such manner that when the level of the catalyst in the hopper drops below this level controller rotation of the star feeder 92 is stopped thereby insuring a head of atalyst material in the bottom section Of the hopper to help maintain a pressure seal between the catalyst hopper and the cracking circuit.

The regenerating circuit is preferably maintained under a pressure substantially in excess of that in the cracking circuit. This pressure differential may, for example, range from 2 to 10 atmospheres or more. It is therefore important to provide adequate seals-between the two circuits to avoid intermingling of the gases from the two circuits.

' Returning to the cyclone separator 89 in which the major portion of the regenerated catalyst is separated from the regenerating gases, the regenerating gases are removed therefrom through line and passed to a second cyclone separator 96 to further remove entrained powder retained in the gas. The entrained catalyst so removed is returned to the primary cyclone separator 89 through line 91 having a star feeder 98 or other suitable mechanism for preventing the gases from the cyclone separator 89 from passing upwardly through the discharge line 91.

Gases from second cyclone separator 96 are removed therefrom through line 99 and are passed to a third cyclone separator |00 wherein the gases are further cleaned of regenerated catalyst. Any catalyst separated in the third cyclone separator |00 is also discharged into the primary separator 89 through conduit |0| having a star feeder I02 or other suitable seal. Electrical precipitators or other suitable means may be employed for separating the catalyst material from the regeneration gases. The foregoing description is not intended to limit this separation to the use of cyclone separators. The regenerating gas after passing through the final cyclone separator I00 is removed therefrom through line I03 and may be rejected from the system through line I04. However, since these gases are normally under substantial pressure it is usually preferable to expand these gases to atmospheric pressure in a. suitable turbine to recover the energy therefrom. As illustrated, the regenerated gases from line I03 may be passed through line I05 to a turbine I06. This turbine may be employed for supplying a part of the power used for compressing the air introduced into the regenerating circuit. An additional turbine may be also provided for supplementing the regenerating gas turbine I06 for providing the necessary power requirements. As illustrated, the turbine I06 and the steam turbine I01 are connected with an air compressor I08 from which air is supplied through line I09 to the regenerating circuit.

The invention also contemplates in some instances the cooling of the cracked products after leaving the reaction zone and before entering the primary cyclone separator. To this end a clean condensate such as a cycle gas oil may be introduced into the transfer line 3| through line H3. In some cases it may be desirable to effect the further recovery of catalyst from the oil vapors by recycling a cycle gas oil stream containing catalyst from the bottom of the fractionating tower following the cyclone separators. Suitable means may be provided within the tower for concentrating the catalyst in this recycle stream.

As a guide for carrying out the invention, the following example may be helpful, it being understood that the conditions and values given therein are illustrative rather than limitative. In the example the unit will be assumed to have a capacity capable of cracking about 9500 barrels of oil per operating day.

Reduced crude at a temperature of 300 to 625 F. is introduced into the system through charge line Ill and is preheated to between 650 and. 700 F. in the heat exchangers l3 and It before passing to the vaporizing coil IS. The oil during its passage through the vaporizing coil is preferably heated to yield hydrocarbon vapors having a temperature from 750 to 920 F.

The oil'after passing through the vaporizing coil it passes into a vaporizer 22 where the vapors are separated from the liquid bottoms, preferably in the presence of steam.

The oil vapors from the vaporizer 22 at a temperature from 730 to 900 F. and under the necessary pressure to maintain the desired flow such as lbs. per sq. in. gauge are introduced into the injector 28 where the powdered catalyst is mixed with the oil vapors for the subsequent cracking operation. For illustrative purposes,

the catalyst will be assumed to be acid treated clay of the type commercially known as "Super Filtrol. The catalyst introduced into the oil stream in the injector 28 may amount to about 4 parts of catalyst by weight per part of oil. This catalyst as a result of regeneration may beat a temperature of from 950 to 1200" F. or more.

i As a result the equilibrium temperature of the catalyst-oil suspension may range from 840 to 1000" F.

The resulting suspension is then passed to the vertical reaction tower 30 where it may be main-' tained for a period of from 10 to 50 seconds, preferably about 25 seconds. example, have a diameter of from 6 to 10 feet and may have a length of 75 to 100 feet. The tower is also preferably provided with an insulating lining to protect the metal shell from high temperatures and from corrosion and/or erosion of the suspension passing through the reaction zone. When the inlet temperature of the suspension is between 900" and 950 F. the outlet temperature of the suspension from the reaction zone may be from 825 to 925 F. The initial cyclone separator 32 should be designed to handle from to 30 thousand cubic feet of gas per minute for the cracking unit of the size mentioned.

This gas may contain about .4 lb. of catalyst per cubic foot. The catalyst-oil suspension, during its passage through the initial cyclone separator 32, may have the catalyst concentration reduced to about 300 grains per cubic foot of vapors and the secondary and tertiary cyclone separators 41 and 53 may reduce the catalyst concentration from 300 grains per cubic foot to less than 2 grains per cubic foot.

.The catalyst separated in the cyclone separator 32 in passing through the' steam injector 35 ma be contacted with about 1800 lbs. of steam per hour and the catalyst in the second steam injector 4| may be treated with a similar quantity of steam before passing to the final cyclone separator 44 wherein the catalyst is separated from the stripping gas.

Under the above conditions from 30% to 50% by liquid volume of the oil'vapors passing to the reaction chamber is converted into gasoline.

The regenerating circuit may be operated as follows:

Catalyst from the spent'catalyst hopper at a temperature from 800 to 900 F. resulting from the cracking operation is discharged by means of star feeder 60 into a compression screw 6| which feeds the catalyst into the regenerating stream which may be under a pressure of from 2 to 10 or more atmospheres. Sufllcient air is added This tower may, for

' temperature of from 800 to 900 F.

through line 63 to raise the temperature of the catalyst from the initial temperature up to a temperature of about 1000" to 1100 F. during its passage through initial combustion zone 64. This combustion zone may, for example, comprise a tube having a diameter from 2 to 6 feet and the length of from 30 to 75 feet and may be provided with an internal insulating lining. The catalyst suspension after passing through the initial com,- bustion zone is cooled in heat exchanger l3 to a The catalyst suspension is cooled in heat exchanger It by indirect contact with the fresh feed oil to the unit which in time is preheated to a temperature of 650 to 750 F. 1

After cooling, the catalyst and regeneration gas mixture is passed through the second combustion zone where it is combined with additional air in sumcient quantities to further heat the catalyst to a temperature of from 1000 to 1100 F., for example. This combustion zone may, for example, comprise three sections of progressively increasing diameter, the first section being from 3 to 6 feet in diameter and from 30 to 40 feet in length, the second section being from 5 to 7 feet in diameter and 15 to 25 feet in length and the third section being from 6 to 7 feet in diameter.

cooled to a temperature of from 800 .to 900 F.

by heat exchange with fresh oil and is then passed through a third combustion zone where it is mixed with further quantities of air sufficient to. complete the regeneration. This third combustion zone may likewise be divided into three sections of progressively increasing diameter at the point of introduction of the air. The first section may, for example, be from 5 to 6 feet in diameter and from 40 to feet in length. the second section being from 6 to '7 feet in diameter and from 30 to 40 feet in length and the final section being from 6 to '7 feet in diameter and from 25 to 35 feet in lengt The suspension of regenerated catalyst and regenerating gas from the final combustion section then passes to the catalyst separators and may be returned to the cracking circuit.

In order to maintain the circulating catalyst within the system at an optimum cracking efllciency, it is desirable to withdraw periodically portions of the used catalyst. This material is then replaced with fresh unused catalyst. It is desirable to do this inasmuch as the effect of heat, oil vapors and/or regeneration gas causes the catalyst to become slightly deactivated with time and use.

This used catalyst may be withdrawn from either the spent or regenerated catalyst hoppers through draw-off lines 0 and II I. Fresh makeup catalyst may be supplied into the regenerated catallyiszt hopper through a fresh supp y hopper The reaction chamber has been shown in Fig. I in the form of an elongated tower. In many cases the height of the tower necessary to provide the required time of contact becomes excessive and it is desirable to pass the suspension of vapors and catalyst through a plurality of chambers arranged in series. Fig. II illustrates such a modification. Referring to Fig. II, the suspension of oil vapors to be cracked and powdered catalyst is introduced into a primary reaction chamber H5 from whence it passes through line llli to the bottom of a secondary tower ll'l,

wherein further reaction time is provided. It

H! is withdrawn It will be further understood that in lieu of passing the stream of regenerating gas and catalyst alternately upwardly and downwardly through the regenerating zone, the suspension may be passed upwardly through the individual regenerating zones. Also each regeneration zone may consist of several chambers in series.

This application is a continuation of application Serial No. 356,840, filed September 14, 1940. Having described the preferred embodiments of the invention, it will be understood that it embraces such other variations and modifications as come within the spirit and scope thereof.

What is desired to be protected byv Letters Patent is:

1. A process for cracking hydrocarbon oils which comprises vaporizing the oil to be cracked, mixing the resulting vapors with a finely-divided cracking catalyst to form a suspension, passing the resulting suspension through a'cracking zone maintained at an active cracking temperature between 800 and 1000 F., keeping said suspension within said cracking zone for a period suificient to convert at least 30% of said vapors into motor fuel constituents, thereafter separating cracked vapors from said catalyst, fractionally separating a motor fuel distillate from the resulting vapors, suspending the catalyst so separated in a stream of inert gas to remove volatile hydrocarbon constituents retained on or between said catalyst particles, thereafter separating the catalyst from the inert gas, suspending the catalyst in an oxidizing gas, passing the resulting suspension successively through a plurality of regenerating zones maintained at a temperature suificient to burn said carbonaceous deposits, passing fresh oil to be cracked in heat exchange v relation with the suspension of regenerating gas and catalyst between said successive regenerating zones to thereby preheat said oil and cool said regenerating stream to prevent the temperature thereof from exceeding 1200 F., thereafter segregating the regenerated catalyst from the regenerating gas, and returning the former to the cracking zone.

- 2. A process for cracking hydrocarbon oils which comprises vaporizing the oil to be cracked, mixing the resulting vapors with a finely-divided cracking catalyst to form a suspension, passing the resulting suspension through a cracking zone maintained at an active-cracking temperature between 800 and 1000 F., keeping said suspension within said cracking zone for a period sufficient to convert at least 30% of said vapors into motor fuel constituents, thereafter separating cracked vapors from said catalyst, fractionally separating a motor fuel distillate from the resulting vapors, suspending the catalyst so separated in a stream of inert gas to remove volatile hydrocarbon constituents retained on or between said catalyst particles, thereafter separating the catalyst from the inert gas, suspending the catalyst in an oxidizing gas, passing the resulting suspension successively through a plurality of regenerating zones maintained at a temperature sufficient to burn said carbonaceous deposits, passing fresh oil to be cracked in heat exchange relation with the suspension of regenerating gas and catalyst passing between the regenerating zones to preheat said oil and cool said regenerating stream to prevent the temperature thereof from exceeding 1200 F'., controlling the volume of oil passing in heat exchange relation with said regenerating stream to prevent the temperature of said oil from exceeding a predetermined maximum, and segregating regenerated catalyst from the regenerating gas and returning the former to the cracking zone.

3. A process for cracking hydrocarbon oils which comprises vaporizing the oil to be cracked, mixing the resulting vapors with a finely-divided cracking catalystto form a suspension, passing the resulting suspension through a cracking zone maintained at an active cracking temperature between 800" and 1000 F., keeping said suspension within said cracking zone for a period sumcient to convert at least 30% oil vapors into motor fuel constituents, thereafter separating cracked vapors from said catalyst, fractionally separating a motor fuel distillate from the resulting vapors, suspending the catalyst so separated in a stream of inert gas to remove volatile hydrocarbon constituents retained on vor between said catalyst particles, thereafter separating the catalyst from the inert gas, suspending the catalyst in an oxidizing gas, passing the resulting suspension successively through a plurality of regenerating zones maintained at a temperature suilicient to burn said carbonaceous deposits, passing fresh oil to be cracked in heat exchange relation with said suspension during passage between said suc cessive regenerating zones to thereby cool said stream of regenerating gas and preheat said oil, cooling a portion of the oil withdrawn from the heat exchange zone and recombining it with fresh oil passing to said heat exchange zone, regulating the amount of cool oil combined with said fresh oil to prevent the temperature in the heat exchange zone from exceeding incipient cracking temperature, cooling the catalyst between said regenerating zones by heat exchange with said fresh oil to prevent the temperature thereof from exceeding 1200 F., thereafter segregating regenerated catalyst from the regenerating gas and returning the former to the cracking zone.

EDWIN J. GOHR.

DONALD L. CAMPBELL.

JOHN M. GRAHAM. WILLIAM I. THOMPSON.

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

UNITED STATES PATENTS Gaylor Dec. 2, 1941