US2385216A - Cracking of hydrocarbon oils - Google Patents

Description

Sept 38 3945- .L v. MARANCIK ETAL v 2,385,216

CRACKING OF HYDROCARBON OILS Filed March l, 1941 CAS OUTLET cYcLan/E SEPA RA T072 CYCLO/vf .SEPAPAToJz 2 MN5: rop.

SEPAuA com/Eyck Tuna caNvEYOR. coN vayan CEA QK/N G CHAMBER E D INLET Anz Patented Sept. 18, 1945 CRACKING F HYDROCARBON OILS Joseph V. Marancik, Roselle, and' Homer Z. Mar tin, Elizabeth, N. J., assiznors to Standard Oil Development Company, a corporation of Delaime Application March 1, 1941, Serial No. 381,234

6 Claims.

This invention relates to the cracking of hydrocarbon oils to form lower boiling motor fuel, and pertains more particularly to the cracking of such oils wherein a .powdered catalyst is suspended in the oil to be cracked and the suspension passed through the cracking zone.

This application is a continuation-in-part of our earlier led application Serial No. 292,002, illed August 26, 1939 now U. S. Patent 2,296,722.

It has heretofore been proposed to crack higher boiling oils into lower boiling products lsuitable for motor fuel in the presence of an adsorptive cracking catalyst such as activated clays, synthetic gels having similar chemical components, and the like.

According to one mode of operation, the oil to be cracked, preferably in vapor form, is passed through a cracking zone containing a bed, or

a plurality of beds, of catalytic material. During the cracking operation the catalyst mass rapidly becomes fouled with carbonaceous deposits which reduces the activity of the catalyst and necessitates frequent regenerations to restore the catalyst activity. In such operations, it is necessary to interrupt the cracking operation in order to attain the regeneration. This involves stopping the vcracking operation, purging the reaction chamber of volatile hydrocarbons, regenerating the resulting catalyst mass, purging the reaction chamber of regenerating gases and the return to the cracking cycle.

It has been observed that when operating such a process, an excessive amount of low-grade products such as coke and gas is formed at the very beginning of the cracking cycle, such as at the flrst minute or two of operation. In other words, during the early part ofthe cracking cycle a large portion of the oil treated is degraded to coke and gas with little if any formation of gasoline. While the explanation for this is not fully established, there is reason to believe that it is due to the fact that the initial oil vapors contact an excessive amount of catalyst and consequently become overcracked to gas and coke. As the cracking operation continues the deposition of coke tempers the activity of the catalyst so that the tendency of the oil to overcrack diminishes as the cracking operation continues. For example, assume that the operation is carried out with a feed rate in proportion to the amount of catalyst contained in the reaction chamber of 1.2 volumes of liquid oil per volume of catalyst per hour. During the first minute and for each minute thereafter .02 volume of oil is treated by the total volume of catalyst. This smal1 volume of oil treated in proportion to the amount of catalyst contained in the reaction chamber may explain why excessive overcracking occurs during the initial .part of the cycle when the catalyst is most active.

It has also been proposed to suspend the catalyst in the oil vapors to be cracked and to pass the suspension through a cracking zone. When operating in this manner the resident time of both the catalyst and the oil vapors within the cracking zone is substantially the same and any given quantity of oil vapors can be treated with a definite, fixed quantity of catalyst. In this case the tendency of the oil to overcrack can be controlled by regulating the amount of catalyst added to the oil stream and the resident time of the suspension within the cracking zone. I

While this method of operating makes it possible to more effectively control the tendency of the oil to overcrack with resulting excessive degradation of feed stock which is inherent in processes wherein the oil vapors pass through o. stationary mass of catalyst, such mode of operation, when carried out according to previous practices, is subject to other disadvantages.

For example, when operating in such manner it has been the practice to pass the suspension of powdered catalyst and cracked products issuing from the cracking zone through separators to remove the catalyst particles. According to previous practices, the powdered catalyst so removed was regenerated, and returned to the cracking zone. If the catalyst is regenerated each time it passes through the cracking zone a large amount of regenerating equipment is necessary for a cracking unit of commercial capacity due to the large number of regenerations to which the catalyst is subjected in a given time. Furthermore, there is a tendency for the catalyst to lose its activity at a faster rate as the number of regenerations to which it is subjected in a given time is increased.

Oneof the principal objects of the present invention is to provide a process of the type last mentioned which will not be subject to the disadvantages just mentioned.

A further'object of the invention is to provide a method of cracking oil with powdered catalyst wherein the number of regenerations of the catalyst can be reduced and controlled as desired.

Another main object of the invention is to provide a process for cracking hydrocarbon oil wherein the inherent activity of the catalyst can be utilized to better advantage.

Another object of the invention is to provide a process for cracking hydrocarbon oil which is more flexible in operation and more easily controlled. 1

Other objects and advantages of the invention will be apparent from the more detailed description hereinafter in which reference will be made to the accompanying drawing lwhich is a partly schematic and partly diagrammatic illustration of an apparatus capable of carrying the invention into effect.

Referring to the drawing, the reference character I designates a feed line having a pump Il through which the oil to be cracked is introduced into the system. The oil treated may be a clean, condensate stock such as virgin gas oil, or a residual stock such as topped or reduced crude. The oil introduced through the feed line I0 is forced by means of pump II through a preheating and vaporizing coil I2 located in furnace I3. 'I'he oil during its passage through heating coil I2 is preferably heated to a temperaturey suiiicient to vaporize a large percentage of such oil.

The outlet temperature of the heating coil may The oil vapor-catalyst suspension is passed through the cracking chamber I8 at a rate sufflcient to maintain the catalyst in suspension. For illustrative purposes, the cracking chamber I8 is shown in the form of a vertical tower having a conical bottom although it may take any other desired form such as, for example, an elongated coil, horizontal chamber, or the like. The reaction chamber may be heated, if desired, to offset radiation losses or to introduce heat into the suspension.

The suspension of cracked products and catalyst after passing through the reaction chamber I8 is passed through line 23 to a suitable solid gas separator such as a cyclone searator 24 in whichthe powdered material is separated from thecracked vapor. It is preferred to operate the separator at a temperature sufficient to avoid any substantial condensation of the cracked products therein so that the powdered catalyst so separated can be removed therefrom in a rela` tively dry form. While a single cyclone separator has been shown in the drawing for purposes of simplicity, it will be understood that additional ones may be provided for effecting substantially complete removal of the powdered material from r the cracked vapors. The cracked products, after in the separator I 5 may be withdrawn therefrom through line I6 and rejected from the system. Vapor liberated in the separator I5 is removed therefrom through line I1 and passed to a cracking chamber I8. In cases where clean condensate stock is employed, the separator I5 may be omitted or the product may be by-passed around the separator through line I9.

In accordance with the present invention, there is introduced into the vapor stream passing to the reaction chamber I8 a powdered cracking catalyst. According to one of the more specific phases of the invention the powdered catalyst so introduced is an unregenerated catalyst which has previously passed one or more times through the same ordiierent cracking unit. In the preferred embodiment of the invention, such unregenerated catalyst is that which has previously been employed for treating a more refractory oil or an oil which is more difficult to crack than the fresh feed charged to the unit through line III.

ASuch refractory oil may comprise, for example, a

cycle stock from the same or different cracking unit.

The catalyst may comprise, for example, natural or activated clays, synthetic compounds having similar chemical components, and the like.

Referring to the drawing, the powdered catalyst is injected into the oil vapor passing to the reaction chamber I8 by means of a suitable feeding mechanism such as through screw conveyor 2|, into which catalyst is fed from the hopper 22.

The relative amounts oi. powdered catalystand oil vapor passing to the reaction'chamber I8 may vary over a substantial-range depending upon the activity of the catalyst, the characteristics of the v feed stock, the time lof contact of the suspension within the reaction zone and other factors. In general, the ratio of catalyst to oil should bein the order of from 0.3 to 20 parts of catalyst per part of oil by weight, preferably between 0.5 and 3 parts of catalyst per part of oil.

separation of the solid catalyst therefrom, are passed overhead from the cyclone separator 24 through lines 25 and 26 to a fractionating tower 21 in which the vapors are subjected to fractionation to condense constituents boiling above the desired motor fuel. Vapors remaining uncondensed in the fractionating tower 21 are removed therefrom through line 28 and may be passed to a condenser 29 in which the desired liquid distillate is condensed. Products from the condenser 29 may be then passed to a receiver 30 wherein normally gaseous products formed in the cracking' operation may be segregated from liquid dstillates. The gases so separated may be released from the system through line 3I having a valve 32 for imposing the desired back pressure on the system. Liquid distillate collected in the receiver 30 may be withdrawn therefrom through line 32a as a nal product of the process.

Returning to the cyclone separator 24, the solid 'catalyst separated from the cracked product therein is withdrawnfrom the cyclone separator through conduit 33. If desired, a portion of the catalyst so withdrawn may be returned directly to the catalyst hopper 22 for return to the cracking zone through conduit 34, or a part or all of the catalyst .from the cyclone separator 24 may be passed through the line 33 to a purging zone 36 in which volatile hydrocarbons are removed from the catalyst in any suitable manner such as by steam stripping or by evacuation of the purging chamber. For example, steam may be introduced into the purging chamber 36 through line 31 for steam stripping the catalyst contained therein. The stripping gases may be released from the purging chamber 36 through line 38 and introduced into the cyclone separator 24. The catalyst, substantially free of volatile hydrocarbons, is then removed from strippingchamber 36 through conduit 39 leading to a suitable transfer mechanism such as screw conveyor 40 which feeds the catalyst into a stream of regenerating gasn containing oxygen introduced into the system through line 4I and blower 42. The suspension of catalyst and regenerating gas is then passed through a regenerating chamber 43 maincarbonaceous deposits on the catalyst formed during the cracking operation. It is ordinarily desirable to control the temperature during regeneration in order to avoid reducing the activity of the catalyst. l For example, in connection with naturally active or activated clays, the temperature of the regenerating zone should be maintained below 1200 F. and preferably below 1o00 F. Generally the temperature within the regenerating zone can be readily controlled due to the relatively low concentration of carbonaceous deposits on the catalyst.- In some cases, however, it may be desirable to regulate the oxygen concentration of the regenerating gas or to provide suitable cooling means, such as heat exchangers, within the regenerating chamber to control the temperature.

The catalyst is maintained in suspension in the regenerating gas within the regenerating chamber 43 for a period to remove the carbonaceous deposit formed on the catalyst from the cracking operation.

The suspension of regenerating gas and catalyst passes from the regenerating chamber 43 through line 44 to a suitable solid-gas separator such as cyclone separator 45 in which the regenerated catalysts are separated from the regenerating gases. The regenerating gas, after separation of the powdered catalyst therefrom, may be rejected from the system through line 46.

'I'he regenerated catalyst may be removed from the separator 45 through a conduit 41 leading to a purging chamber 48 in which the regenerated catalyst is stripped of oxygen. To

this end steam may be introduced into the purging chamber 48 through line 49 and the purge gases vented to the cyclone separator 45 through line 50.

According to one phase of the invention, the regenerated catalyst is utilized for cracking an oil which is more refractory and more difficult to crack than the oil charged to the heating coil I2. Such oil may comprise, for example, of cycle stock segregated in the fractionating tower 21 as hereinafter described. When operating in this manner, the regenerated catalyst is fed by means of a screw conveyor to a catalyst hopper 52 serving a separate cracking unit processing cycle stock as later described.

If desired, however, a part or al1 of the regenerated catalyst may be returned to the hopper 22 through valved conduit 53. It will be understood that it is also within the purview of the present invention to operate with a single cracking cir-cuit in which a part of the catalyst is recycled to the same circuit. For example, if

the recycle circuit is out of operation or not employed, all the regenerated catalyst can be passed to hopper 22 for return to the fresh oil circuit.

Returning to the fractionating tower 21 in which the cracked products are fractionated, the condensate formed in the fractionating tower 21 is withdrawn therefrom through line 54 and may be rejected from the system through line 55. According to one of the specific phases of the present invention, however, a part or all of the condensate formed in the fractionating tower 21 is passed through lines 54, 56 and pump 51 to the inlet side` of heating coil 58 located in furnace 59. The oil passing through the heating coil 58 is heated to a temperature sufficient to vaporize the oil. Vapors from the heating coil 58 may be then passed through transfer line 60 to a second cracking chamber 6I. In

` into gasoline.

case the oil passing to the heating coil 58 containes unvaporizable constituents, the products from the heating coil 58 may be passed to separator 62 wherein unvaporized residue may be dropped out of the oil stream and removed from the separator through line 63. In such case, the vapors liberated in the separator 62 pass overhead through line 64 which merges with line 60 leading to the cracking chamber 6I.

If desired, fresh oil from an extraneous source may be fed to the heating coil 58 through line 65 and pump 66.

Before passing to the cracking chamber 6I there is injected into the oil vapors to be cracked fresh or regenerated catalyst from hopper 52. Such catalyst may be introduced into the oil vapor through a suitable feeding mechanism such as a screw conveyor 61. The suspension of oil vapors and catalyst is passed through the cracking zone 6I at a velocity sum- `cient to maintain the catalyst in suspension within the vapors. The length of the cracking chamber and the velocity of the suspension should be controlled to give the required contact time to obtain the desired cracking of the oil The time required for the passage of the suspension through the cracking chamber 6I may range from one second up to a minute or two, depending upon the desired conversion, the characteristics of the feed stock, the temperature and other factors. The cracking zone should be maintained above active cracking temperature such as from 750 F. to 1000 F.

The suspension of the' cracked product and catalyst after passing through the cracking chamber 6i is transferred through line 68 to a suitable solid,gas separator such as cyclone separator 69 wherein the powdered catalyst is removed from the oil vapors. The separator 69 is also preferably maintained under a temperature which will avoid any. substantial condensation of cracked products. The cracked products after passing through the cyclone separator 59 are passed through line 10 which merges with line 26 leading to the fractionating tower 21.

While there is shown a common fractionating tower 21 for fractionation of cracked products from both cracking chambers I8 and 6l, it will be understood that the products from the two cracking zones may be subjected to independent fractionation if so desired. In such case, the products from theA two cracking operations may be kept separate from each other.

Returning to the cyclone separator 69, the catalyst separated therein is removed from the bottom thereof through conduit 1I. In accordance with the .preferred embodiment of the invention, the catalyst so separated is passed directly through conduit 1i to a catalyst hopper 22 and again used for cracking the fresh feed introduced through line Il) Without any intervening regeneration. If desired, however, a part or all of the catalyst separated in the cyclone separator 69 may be recycled to the catalyst hopper 52 feeding catalyst to the cracking chamber 5I, or a part or all of the catalyst removed from the cyclone separator 69 may be passed to the regenerating circuit through conduit 12.

With respect to the above, it is desired to emphasize that in accordance with the present invention it is not essential toregenerate the catalyst after each cracking operation but the catalyst after passing through a cracking chamber may be recycled to the same or different cracking units for a predetermined period beinvention, fresh or freshly regenerated catalyst is first utilized for cracking a relatively refractory stock such as a cycle gas oil from the cracking operation and the catalyst after passing through this'process is utilized directly without regeneration as catalyst for cracking a less refractory stock such as virgin oil introduced into the system through line Ill.

While there has been illustrated two separate cracking units operating more or lessr in successive stages, it will be understood that 1additional stages may be added to the system as desired.

For example, catalyst separated from the cracked products separated in the separator 24 or 69 may -be passed to a third cracking circuit without regeneration, or a part may be recycled to the same circuit.

'I'he invention also comprehends the further cracking treatment of cracked vapors before or after dry separation of powdered material therefrom and Without any intermediate condensation. For example, a part of the suspension of cracked vapors and catalyst removed from the recycle cracking chamber 6I may be returned through line 13 and injected into the stream of oil passing to the' heating coil 58. For illustrative puriposes there has been shown an injector 14 for introducing the suspension into the oil stream although a f-an or other suitable means may be substituted therefor. When operating in this way it is desirable to omit use of separator 62.

Likewise a partof the cracked vapors and catalyst suspension from the reaction chamber I8 operating on fresh feed may be returned through line 15 and injected into the fresh oil feed line Ill passing to the heating coil l2.

As a further alternative a part of the vapors from either the fresh oil or recycle circuit or both may be passed to either one of the two circuits for further cracking without intermediate condensation. For example, a part of the vapors from the vapor line leading from the cyclone separator 2l to the fractionating tower 21 may be passed through lines 16 and 11 and trans- 'cracking chambers I8 and 0I. For example. a part or all of the suspension being recycled through line 13 may be passed through a separate heating coil 8| and subjected to separate and independent heating. Products from heating coil 8| may then pass through line I2 to an injector 83 and there combine with vapors in line 64. Also a part of all of the suspension passing through line 15 may be pasesd through a separate coil 84 and then to imector 85 and combined with vapors passing through line l1.

By first separating the bulk of the catalyst in dry state and then independently recycling a portion of catalyst and vapors to the same or separate circuit, the relative proportions of catalyst and vapors can be controlled as desired. This is not possible when a portion of the suspension of cracked vapors and catalyst is recycled.

From the above description of the invention it should be evident that the present invention provides for recycling of a part of the products withdrawn from the cracking chamber back to the same or different cracking unit. Such products may consist of the catalyst powder or it may consist of a portion of the cracked vapors without intermediate condensation or it may comprise a portion of the suspension of cracked vapors and catalyst without intermediate separation or any combination thereof.

The recirculation'of one or more of the various fractions as above described permits a more effective control of the operating conditions, such as temperature, contact time, and catalyst activity, within the cracking chamber or chambers. For example, by controlling the amount of unregenerated catalyst recirculated back to the cracking chamber, the activity of the catalyst may be regulated within limits so as to avoid overcracking or insuflicient cracking. The tempera- 40 ture of the cracking zone may be controlled independently of the temperature of the fresh feed vapors by independently adjusting the temperature of the recycle stream. Furthermore, the

velocity and consequently the contact time of the ized overcracking which might otherwise occur ferred either through lines 18 and 15 to the inlet I of heating coil l2 or a .partor all may continue through line 19, to the inlet of heating coil 58 for further cracking.

Both methods of operating as just described have advantages.

By recycling a part of the suspension of cracked vapors and catalyst, the cracking time for a cracking unit of given size can be controlled and additional heat supplied to the recycled suspension to assist in maintaining temperature.

In lieu of recycling a portion of the suspension to the inlet of the heating coils l2 and IB as the case may be and there combining it with the feed stock, the suspensions may be passed through a separate heatingb coil and then combined dimuy with the vapors passing to the respective during initial contact of the oil vapors -with the highly heated, freshly regenerated catalyst.

Another advantage in combining unregenerated catalyst with freshly regenerated catalyst before mixing with oil vapors is that the cracking reaction takes place more uniformly throughout the reactor and the chamber is maintained at a more uniform temperature.

Having described the preferred embodiment 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 by Letters Patent is:

1. A process for the conversion of hydrocarbon oils which comprises vaporizing th'e oil to be K ing catalyst in the oil vapors passing through the cracking zone, withdrawing a suspension of cracked vapors and finely-divided catalyst from assaaio the cracking zone, continually recirculating a portion of the suspension so withdrawn to said cracking zone, separating the finely-divided oatalyst from the remaining portion of said suspension withdrawn from said cracking zone and fractionating the resulting oil vapors separated from said finely-divided catalyst to segregate a motor fuel product therefrom.

2. The process dei'lned in claim 1, wherein the suspension recirculated to the cracking 4zone is heated prior to returning the same to said cracking zone.

3. A process for the conversion of hydrocarbon oil. which comprises introducing a continuous stream of said oil, heated to cracking temperature, together with a nely divided catalyst to one end of an elongated reaction zone and therein effecting cracking of the oil, withdrawing a continuous stream of conversion products and catalyst from the opposite end oi said reaction zone. returning a portion of the last named stream to the reaction z'one along with the rst named stream and separating cracked vapors and catalyst containing residue from the remaining portion.

e. A process for the conversion of hydrocarbon oil, which comprises heating a owing stream of said oil, having dispersed therein iineiy divided catalyst particles, to a cracking temperature, introducing the resulting heated oil and dispersed catalyst as a continuous stream to one end of an elongated reaction zone and therein effecting cracking of the oil, withdrawing a continuous stream of conversion products and catalyst from the opposite end of said reactionzone, returning a portion of the last named stream to the reaction zone along with the heated oil, and sepa-'- rating cracked vapors and catalyst containing residue from the remaining portion.

5. A. process for the conversion of hydrocarbon oil, which comprises heating a iiowing stream of said oil, having dispersed therein nely divided catalyst particles, to a cracking temperature, introducing the resulting heated oil and dispersed catalyst as a continuous stream to one end of an elongated reaction zone and therein effecting cracking of the oil, withdrawing a continuous stream of conversion products and catalyst from the opposite end of said reaction zone, returning a portion of the last named stream to the reaction zone along with the heated oil. separating cracked vapors and catalyst containing residue from the remaining. portion, fractionating said vapors to form reflux condensate, recovering the fractionated vapors. and supplying said reilux condensate tothe heating step along with said hydrocarbon oil.

6. In the process of converting hydrocarbon oil into gasoline wherein the oil is vaporized in a restricted, conned stream in a heating coil and the vapors are thereafter contacted at conversion temperature with iinely divided suspended solid conversion catalyst in an enlarged conversion zone separate and independent of said heating coil, the improvement which comprises precontacting said hydrocarbon oil within said heating coil with a small amount of said flnely divided solid catalyst previously employed for treating said hydrocarbon vapors within said conversion zone and prior to any regenerative treatment thereof.

JOSEPH V. MARANCIK. HOMER Z. MARTES.

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