Catalytic cracking

Feb. 29, 1944. c. l. thomas 2,342,984

CATALYTIC CRACKING

Filed April 8, 1941

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Patented Feb. 29, 1944

2,342,984

UNITED STATES PATENT OFFICE

2,342,984

CATALYTIC CRACKING

Charles L. Thomas, Chicago, Ill., assignor to Universal OH Products Company, Chicago, Hl., a corporation of Delaware

Application April 8,

Claims.

This invention relates to a process for converting hydrocarbon oils to high yields of gasoline of high anti-knock proportion and is a contlnuatlon-ln-part of my co-pending application Serial No. 291,892, filed August 25, 1939, which in turn was a continuation-in-part of my application Serial No. 273,236, filed May 12, 1939, now Patent No. 2,286,447, dated June 16, 1942. More specifically the invention concerns a method of manufacturing motor fuels from petroleum sources although hydrocarbon oils from other sources may also be used.

Although the process may apply to the production of motor fuels for use in any type of internal combustion engine, it finds special application in the manufacture of fuels for use in airplane motors. This is true because of the highly stable character of the finished product as well as its great susceptibility to increase in octane number by the addition of tetraethyl lead.

Numerous processes have been developed for the production of increased yields of motor fuel from crude petroleum and other hydrocarbon sources. Among these is the non-catalytic thermal cracking process whereby heavy oils are converted to substantial yields of gasoline haying relatively high antiknock value. Straightrun gasoline and naptha which may have relatively poor antiknock properties are non-cataIytically reformed to produce gasoline of improved octane number. The reforming and cracking processes yield substantial quantities of gases containing polymerizable olefins, and various polymerization processes may be used in conjunction therewith to augment the yields of valuable motor fuel produced.

Among processes of more recent development are catalytic cracking processes wherein hydrocarbon fractions containing substantially no gasoline are converted to high yields of premium grade motor fuel.

The octane numbers obtainable by commercial non-catalytic cracking and reforming processes are relatively limited, since improved anti-knock properties beyond a certain point can be gained only at the expense of yield of gasoline, and eventually a point is reached wherein it is no longer economical to increase the octane rating in this manner. Catalytic cracking and polymerization processes may be used to produce motor fuel of higher octane rating than is economically feasible according to the noncatalytic method of operation.

The present invention relates to improvements

1941, Serial No. 387,470 (CL 196—52) in methods of manufacturing high anti-knock value gasoline from crude petroleum oils and especially to a combination of cooperative steps wherein substantial yields of gasoline are pro5 duced at relatively mild temperature conditions with a highly active catalyst, while further yields of gasoline are produced from the more refractory insufficiently converted fraction from this step in contact with the partially 10 spent catalyst which is still suitable for cracking at somewhat higher temperatures. Moreover, the process permits the use of so-called “dirty” oils rather than selected distillate fractions which are necessary for many existing 18 catalytic cracking processes. The overall result is increased yields of improved anti-knock gasoline.

In one specific embodiment the present invention comprises a method for producing high anti-knock motor fuel from hydrocarbon oil which consists in mixing a portion of said oil with a powdered cracking catalyst, heating the mixture to a temperature of 500-900° F. under a pressure of 50-1000 pounds per square inch, ²⁵ passing the mixture into a vertical reactor containing bubble trays, perforated pans or other type of contacting members which assist in contacting upwardly rising vapors with downwardly flowing llqulu-catalyst suspension, removing 30 gasoline and gas overhead from said contactor, withdrawing insufficiently converted oil contalntaining suspended catalyst from the base of said reactor, passing the mixture to a cracking zone comprising a tubular heater followed by a re85 action chamber at a temperature within the range of approximately 800-1200° F. and a pressure of approximately 100-1000 pounds per square inch, passing the reaction products containing suspended catalyst into a flashing zone, 40 withdrawing a portion of oil unsuitable for further conversion containing suspended catalyst, recovering and reactivating the catalyst, removing the vapors from said flashing zone and passing them with or without added heat to 45 the aforesaid catalytic reactor at a point below the point of introduction of the original hydrocarbon oil and catalyst mixture.

The charging stock which may be converted according to the present process is suitably 60 topped crude oil although crude oil Itself or various fractions thereof, such as gas, oil, kerosene distillate, etc., may also be used.

The vertical contactor .may be operated at a temperature of approximately 500-900° F. and a pressure sufficiently high to maintain the tern2,343,984 perature at the point of entry of the hydrocarboncataiyst mixture within the specified reaction range while removing a product of the desired end point overhead. Distillates of higher end point than gasoline may be removed from the reactor and separately fractionated to the desired end point in such cases as this procedure is most practical. The pressure in the contactor may be wjthln the range of 50-300 pounds per square inch and is normally of the order of 50-200 pounds per square inch. The point of entry is normally approximately midway in the tower. The upper section of the contactor is a conventional type of fractionator suitably consisting of a series of bubble trays. The lower section may be a series of bubble trays or other equivalent contacting members such as perforated pans, side-to-side baffles, etc.

The apparatus for the higher temperature cracking step may comprise any conventional type of non-catalytic cracking plant consisting essentially of a tubular heater followed by a reaction chamber and a flashing zone· and operated under conditions of temperature and pressure usual in such equipment, namely, 800-1000° F. and 100-1000 pounds per square inch.

The catalytic mixture after use at the relatively low temperature conditions existing in the vertical reactor loses some of its activity but is still sufficiently active at slightly higher temperatures to cause substantial conversion of heavier hydrocarbon oils into gasoline having a relatively high olefin content and a high antiknock value. This gasoline together with other readily vaporizable materials of higher than gasoline boiling range is returned to the vertical reactor wherein the olefin containing gasoline is converted into a substantially olefin-free product. If additional heat is needed in the vertical contactor, this can be supplied by heating the vapors from the flash chamber prior to their introduction, into the vertical contactor.

The spent catalytic mass is separated from the flashed residues by any suitable means such as filtering, settling, etc. The powdered catalyst may also be washed with a solvent such as cracked gasoline to remove the major portion of the residue remaining thereon. The catalyst is then reactivated by heating in the presence of an oxygen containing gas at a temperature in excess of approximately 1000° F.

As a further variation a liquid side cut of greater than gasoline boiling range may be withdrawn from the upper portion of the contactor, mixed with a portion of the powdered catalyst and returned to the contactor at a point above that at which the original charge is introduced. In this way additional contacting of the upwardly rising hydrocarbon vapors with the cracking catalyst can be obtained.

The catalysts which are useful in the present process may include cracking catalysts of various types, such as synthetic precipitated composites consisting essentially of a major portion of precipitated silica having added thereto relatively minor portions of precipitated refractory oxides to form masses consisting of silica-alumina, silica-zirconia, silica-aliimina-zirconia, etc., said composites being substantially free of alkali metal compounds.

In the following specification the terms “silicaalumina, silica-zirconia, and silica-alumina-zirconia” masses are used in a broad sense. Inasmuch as the chemical klfcwledge of the solid state has not been developed perfectly, it is not pos sible to give the «tractate of all solid substances. All that can be said definitely concerning these masses is that they contain silicon, oxygen, aluminum, and/or zirconium in combination. Gen5 erally speaking, however, all these components indicate more or less low catalytic activity individually but in the aggregate display high activity. This activity is not an additive function, it being relatively constant for a wide range of pro10 portions of the components, whether in molecular or fractions of molecular proportions. No one component can be determined as the one for which the remaining components may be considered as the promoters according to conventional 15 terminology, nor can any component be determined as the support and the others the catalyst proper.

According to the description of the preparation of the preferred catalysts given below, pre20 clpitated hydrated alumina and/or hydrated zirconia are composited with hydrated silica gel, otherwise known as silica hydrogel, and then the composite is washed, dried, and calcined, producing a catalytic mass. However, the different 25 catalysts which may be so produced therefrom do not necessarily give equivalent results.

A large number of catalysts which have been developed to assist in thermal cracking of hydrocarbon oils tend to accelerate the formation of gae SO rather than gasoline. Among these are the reduced metal catalysts, such as nickel or iron. A further characteristic of this type of catalyst is that poisoning by sulfur occurs and the catalytic surfaces are rendered inert by coatings of car35 bonaceous material.

The preferred catalysts of this invention are characterized by selectivity and by accelerating gasoline-forming reactions, rather than gas and carbon-forming reactions, by their refractory 40 character which enables them to retain their catalytic activity through many repeated periods of use and reactivation under severe conditions of temperature, and by the ease and simplicity of manufacture and their exact reproducibility.

The finished catalytic masses contain alumina and/or zirconia in amounts varying over a considerable range, for example, from 1 to 30 weight per cent and are preferably of the order of approximately 5 to 30 weight per cent of the com&lt;5° pound calculated as AliOa or ZrOi.

The present catalytic masses may be prepared according to a number of alternative methods which will be discussed in a general way in the following description. Briefly, the method in55 volves the precipitation of hydrogels of silica and the added compound, either simultaneously by co-precipitation methods, or by separate precipitation of the hydrogels, followed by mixing in such a manner as to produce a more or less uniC0 form mixture, or by the successive precipitation of silica hydrogel and the added alumina, and/or zirconia hydrogel constituent.

A preferred method of preparation is to precipitate a silica hydrogel by the addition of an 65 acid to a solution of water-soluble silicate. The precipitation of the silica gels should be carried out under controlled conditions in order to produce material which, when composited with alumina and/or zirconia as hereinafter described, 70 results in a catalytic mass of a high degree of activity. In general, when precipitating silica gel from solutions of sodium silicate, it is desirable to add sufficient acid to cause complete gel formation. If the excess of acid used exceeds approxi75 mately 20%, the precipitated hydrogel becomes

2,342,984 extremely difficult to filter, and its more desirable properties are lost.

After precipitation, the silica gel is preferably washed free of soluble salts. This may be done by washing the hydrogel with dilute solutions of a 5 mineral acid, such as hydrochloric acid, or with water containing small amounts of ammonium chloride or aluminum chloride.

The removal of the alkali-metal ions from the catalyst composites during preparation is of par- 10 ticular Importance, since the presence of these ions apparently causes certain undesirable side reactions to occur and also causes a substantial decrease in catalytic selectivity and activity. This may possibly be caused by reactions resulting in a 15 decrease, at elevated temperatures, in the active surface and porosity of the catalysts to an extent where the predominant reaction is no longer catalytic in character. It may also be possible that other reactions of an unknown character such as 20 the catalyzing of undesirable reactions by alkalimetal components may account for the observed detrimental effects. Whatever the explanation, we have observed that the removal of alkalimetal compounds is of primary importance and 25 our preferred catalysts are of this nature.

The accompanying drawing Illustrates diagrammatically one embodiment of the present invention. The drawing has not been made to scale nor has any attempt been made to propor- so L tion the equipment exactly. It should not be construed to limiting the invention to the exact equipment given therein.

Referring to the drawing the crude oil charged enters through line I, valve 2 and pump 3. A 35 portion of the oil is pumped through line 4 and valve S into slurring pot 6 wherein it is mixed by means of agitator T, with powdered catalyst from catalyst storage 8 which enters through line • and valve 10. The slurry passes through line II, valve 12 to line 15 where it meets and mixes with the remaining portion of charging stock from line 13 and valve 14. The mixture passes through valve 16, pump IT and valve 18, coil 19, which is disposed in heater 20, where it is heated to a 45 temperature within the range of 500-900° F. and a pressure of approximately 50 to 1000 pounds per square inch. The heated mixture passes through line 21 and valve 22 to reactor 23. The upper part of this reactor is a fractionating sec- 50 tion. Gas and gasoline are removed overhead through line 24 and valve 25 through suitable stabilizers, heat exchangers, condensers, etc., not shown. The insufficiently converted oil containing suspended catalyst passes downwardly 55 through the reactor through line 26, valve 27, pump 28, valve 29 to coil 30 which is disposed in heater 31. Line 32 and valve 33 serve as a means of removing a part or all of the mixture from the system. The heated mixture at a tern- eo perature of approximately 800 to 1200° F. and a pressure of 100 to 1000 pounds per square inch passes through line 34, valve 35 to reaction chamber 36, wherein additional conversion to gasoline and gas occurs. Reaction products leave through 65 line 37 and valve 38 entering flash chamber 39 wherein the pressure is substantially reduced. A fraction of residue unsuitable for further conversion passes through line 40 and valve 41 to separator 42. Spent catalyst is removed through 70 line 43 and valve 44 to reactivator 45 and thence by means of line 46 and valve 47 to catalyst storage 8. The cracked residue which may be used for fuel oil is removed through line 48 and valve ' 49. The vapors from flash chamber 39 pass 75 through line 69, valve 51 and line 52 to reactor 23, entering the reactor at a point below that at which the original oil is introduced. If additional heat is needed, a portion of the oil may be passed through line 53, valve 54, coil 55, which is disposed in heater 56 and through line 57 and valve 58 to line 52 and thence to reactor 23.

According to one alternative the vapors from flash chamber 39 pass through line 71 and valve 72 to separator 73, where the normally gaseous hydrocarbons with or without the gasoline fraction are separated and removed from the system through line 74 and valve 75. In this manner they are then taken to suitable stabilizers, heat exchangers, etc., and may be separated into a fraction which may be further treated by such methods as polymerization,' alkylation, etc., to produce valuable by-products. The higher boiling hydrocarbons with or without the gasoline are then removed from the bottom of separator 73, through line 76, valve 77, pump 78, line 53, valve 54 and coil 55 wherein the temperature is raised to a suitable point within the range of approximately 650°-900° F. The products then pass through line 57, valve 58 and line 52 to reactor 23.

According to another alternative method the reaction chamber 36 may be by-passed and the oil-catalyst mixture from line 34 may be passed through line 59 and valve 68 to flash chamber 39.

• Under certain conditions it is advantageous to introduce powdered catalyst into the upper section of the fractionating column in order to provide additional treatment of the upwardly flowing vapors. This may be done by withdrawing a portion of the oil through line 61, valve 62, heat exchanger 63, into slurry pot 64 where it is mixed with powdered catalyst from line 65 and valve 66, which is maintained in suspension by means of agitator 67. The slurry passes through line 68, valve 69 and heat exchanger 70 to reactor 23, entering at a point above that at which the original hydrocarbon charge is introduced.

According to another alternative, a portion of the hydrocarbon oil charging stock may be passed through line I, valve 2, pump 3, line 13, line 79, valve 80 to line 26 where it commingles with the suspension of cracking catalyst in insufficiently converted oil from line 26 and valve 27. The mixture passes by previously described routes to coil 30 and thence to reaction chamber 36, etc. This particular operation has the advantage that a part or all of the original charging stock may be passed to the high temperature cracking step without first being introduced into the low temperature catalytic reactor. When operating in this manner a portion of the charge may be used to form a slurry with the catalyst prior to introducing it into catalytic reactor 23. If all of the charge is passed through line 79, etc., the powdered catalyst may be introduced in the previously described manner from slurry pot 64.

The following example is given to illustrate the usefulness and practicability of the invention but should not be construed as limiting it to the exact conditions given therein,

A Mid-continent topped crude oil was made into a slurry with a powdered cracking catalyst. The catalyst was a composite of 100 parts precipitated silica having added thereto 8 parts of precipitated alumina and 4 parts precipitated zirconia under conditions such that the com9,849,984 poelte was substantially free of alkali-metal ions. The mixture of oil and suspended catalyst was heated to a temperature of 750’ F. under a pressure of 100 pounds per square inch and passed into the mid section of a vertical reactor the S top section of which was a conventional bubble tray fractionator and the lower section of which was a series of perforated pans over which the liquid-catalyst suspension flowed. Gasoline and gas were removed overhead and the insufficiently converted oil containing the catalyst in suspension was withdrawn from the bottom of the tower. The mixture was pumped through a heating coll at a pressure of 500 pounds per square inch and a temperature of 930° F. It 15 was then passed into the reaction chamber of', a conventional cracking unit where additional cracking took place. The conversion products were passed from the reaction chamber to a flash chamber wherein the pressure was reduced to 20 approximately 150 pounds per square inch. A cracked residue containing catalyst in suspension was withdrawn from the system and the catalyst was recovered by filtration. It was then reactivated by heating in the presence of oxygen 25 to burn off carbonaceous'deposits and returned for further use in the process. The vapors from the flash chamber were removed and returned tp the lower section of the catalytic reactor, the point of introduction being well below that at 30 which the original raw oil charge was introduced. In this manner gasoline vapors and gas passed upwardly through the descending oil-catalyst suspension and the gasoline was converted into a substantially olefln-free, high octane number 35 motor fuel. A total yield of 60% of 400° F. end point cracked gasoline having an octane number of 78 was produced in this manner. The octane number was increased by the addition of 6 cc. tetraethyl lead per gallon to 94.5. The ⁴⁰bromine number of the gasoline was 3, and the sulfur content was 0.03%.