US2417867A - Cracking hydrocarbon oils - Google Patents

Description

Mam? 25, W47 s. c. FULTON ET AL,

CRACKING HYDROCARBON OILS Filed 001'.. 24, 1939 co Mailman ech/VER Toa? SEPARA TOE EGENEZEATJNG Patented Mar. 25, 1947 CRACKING HYDROCARBON OILS Stewart C. Fulton, Elizabeth, Carl O. Tongberg, Westfield, and Edward D. Reeves, Cranford, N. J., assignors to Standard Oil Development Company, a corporation of Delaware Application October 24, 1939, Serial No. 300,920

2 Claims. (Cl. 196-52) 'I'his invention relates to the' cracking of hydrocarbon oils and pertains more particularly to a method of cracking such oils in the presence of a powdered catalyst carried in suspension within the oil undergoing cracking.

It has heretofore been proposed to crack hydrocarbon oil in the presence of solid adsorbent materials such as fullers earth, iron oxide supported on silica gel, acid-treated clays, synthetic gels consisting principally of silica and alumina, and the like. During the cracking operation the catalyst mass more or less gradually becomes contaminated with carbonaceous deposits which reduces the activity of the catalyst. As a result it is necessary to periodically regenerate the catalyst.

According to one method of catalytic cracking, the oil to be cracked is passed in vapor form at the desired reaction temperature through a cracking zone containing a stationary mass of catalyst. The cracking operation is continued until the activity of the catalyst has been reduced, by formation of such deposits, to a point where it becomes desirable to regenerate the catalyst. The cracking cycle is then interrupted and, alter purging the cracking chamber of volatile hydrocarbons, the catalyst is regenerated by burning such carbonaceous deposits in an oxidizing atmosphere. Upon completion of the regeneration,

the chamber is again purged of regenerating gases and the cracking cycle is repeated. The length of each cracking cycle may be of the order of 5 minutes to an hour or more depending on the type of catalyst, nature of feed stock, the degree of conversion desired and other factors. The time required for accomplishing the regeneration and purging between each cracking cycle in most cases exceeds and may even double the length of the cracking period.

In order to operate such a process in a more or less continuous manner, a bank of reaction chambers is usually provided so that the cracking operation can be transferred from one reaction chamber to another as regeneration is required.

Such a method of operation has a number of inherent disadvantages. First, as the activity of the catalyst decreases during each cracking cycle due to the building up of carbonaceous deposits, the conversion of the oil to gasoline tends to decrease unless compensating action is taken. To maintain an average conversion over the length of the cycle of a given amount, such as for example 30%, the conversion during the initial part of the cycle must be materially higher with correspondingly greater gas and coke loss. During the final stages of the cracking cycle the conversion is below the average for the complete cycle.

Furthermore, continuous variation in the composition of the cracked products passing to the fractionating equipment during the cracking cycle makes it difcult to obtain uniform fractionation since continuous and uniform frac` tionation requires that the products fractionated be of uniform composition.

It has been proposed to compensate for the drop in activity ofthe catalyst during each cracking cycle by increasing temperature and/or decreasing feed rate but these corrective measures introduce other complications dilcult to control in commercial operation.

A further inherent disadvantage of such a method of operation is the necessity of carrying out both cracking and regeneration in the same reaction chamber. This necessitates a relatively complicated structure, since the conditions best suited for carrying out the catalytic cracking operation are not suitable for carrying out regeneration. For example, the cracking cycle is an endothermic reaction which makes it desirable to superheat the feed or to supply some heat to the reaction chamber or at least avoid removing heat during this cycle. On the other hand, the regenerating cycle is a strong exothermic reaction and, to` avoid deactivating the catalyst, it is necessary to remove a considerable quantity of heat during this cycle. Furthermore the velocity of the gases passing the reaction chamber during the cracking cycle is of an entirely different order than during the regenerating cycle. During the cracking cycle the velocity of the vapors is controlled to obtain the required time of contact whereas during the regenerating period it is desirable to pass the regenerating gas through the catalyst at much higher velocities in order to reduce the length of theregenerating period. It is also usually desirable to employ pressure during regeneration of higher order than that employed during the cracking cycle.

In View of these and other factors it is impossible to design a reaction chamber which can be utilized to full advantage in both the cracking and regenerating cycles.

Furthermore, such a process requires a high initial investment in lequipment due to the fact that the individual reaction chambers are not on the 4cracking. cycle at all times but usually less than half the time.

It has also been attempted to carry out catalytic cracking by suspending the catalyst in the oil vapors to be cracked and passing the suspension through the reaction zone. However, early attempts to operate in this manner were not commercially successful for one reason or another. In some cases, the wrong type of catalyst was employed. In other cases an lnsuflicient amount of catalyst was employed or the temperature, pressure and other conditions were not suited to realize the maximum advantages from such an operation.

One of the principal objects of the present invention is to provide a continuous process for the cracking of hydrocarbon oils which will not be subject to the inherent objections heretofore discussed.

A further important object of the invention is to provide an improved process for the catalyticcracking of hydrocarbon oils which will result in the production of a higher yield of motor fuel and other valuable products than is obtained by processes of the nature heretofore used.

A further object of the present invention is to provide a more economical process for the catalytic cracking of hydrocarbon oil.

Other objects and advantages of the invention will be apparent from the more detailed description hereinafter.

It has been discovered that by suspending the catalyst, of the nature hereinafter described, in powdered form and in the proper proportions into the oil to be cracked and passing the suspension through the reaction zone under the conditions later set forth, a materially higher ratio of motor fuel and cycle oil to low grade products such as coke and low molecular weight gases is obtained.

It is well known that when cracking oils, either with or Without a catalyst, other side reactions normally occur which result in the formation of low-grade products such as low molecular weight gas and coke. It is a. more or less commonly accepted belief that the relative amounts of motor fuel and such low-grade products formed during cracking is substantially a constant which is independent of any particular method of operation. Contrary to such belief, however, it has been found that, when operating in accordance with `the present invention under conditions hereinafter described, there is less degradation of feed stock into low-grade products such as coke and gas for a given conversion to gasoline.

While the exact reason for this has not been fully established, there are fundamental differences in operation between cracking with a catalyst suspended in the oil vapors under the conditions forming the subject matter of the present invention and wherein the oil vapors are passed in contact with a bed of catalytic material. In the latter' case, for example, the catalyst is exposed to a passing stream of oil vapors throughout the length of the operating cycle, whereas in. the case where the catalyst is suspended in the oil vapors, the catalyst is carried along with the oil Vapor at more or less the same velocity. As a result each catalyst particle contacts substantially the same vapor atmosphere within the cracking zone during its travel therethrough whereas when a stationary bed of catalyst is employed each particle contacts a stream of passing vapors so that it is continuously exposed to a new atmosphere of vapors. Another distinction is that, in the case of stationary bed catalyst, the oil vapors initially contacting the catalyst at the start of the cracking cycle contact the total volume of fresh catalyst contained in the reaction zone and become greatly overcracked with formation of excessive coke whereas in the case of the suspended catalyst each unit portion of oil vapors is contacted with a definite and optimum quantity of catalyst.

It has been found, for example, in the case of the stationary catalyst mass, that during the very beginning of the cracking cycle the oil is cracked almost completely to coke and gas with the formation of little if any gasoline. When cracking with the catalyst in suspension under the present invention the overcracking at the beginning of the cycle is avoided.

Having described the general nature and objects, the invention will be better understood from the more detailed description hereinafter in which reference will be made to the accompanying drawing which is a diagrammatic illustration of' an apparatus suitable for carrying the invention into effect.

Referring now to the drawings, the reference character I0 designates a charge line through which the oil to be cracked is introduced to the system. The charging stock may comprise a clean condensate stock, such as gas oil, or it may be a residual stock such as topped or reduced crude.

The oil introduced through charge line I0 is forced by means of pump I I through a preheating and vaporizing coil I2 located in furnace I3. The oil, during its passage through the heating coil I2, is heated to a temperature sufdcient to vaporize all or a substantial part of the oil. The oil after being preheated to the required temperature within the heating coil I2, is passed through transfer line I4 to a separator I5 in which vapors formed in the heating coil I2, are separated from unvaporized residue. The unvaporized residue collecting in the bottom of the separator I5 may be withdrawn therefrom through the line I6 and rejected from the system.

Vapors liberated in the separator I5 are removed therefrom through line I'I which communicates with a reaction chamber I8. In cases where a clean condensate stock is employed as charge to the unit, the separator I5 can be omitted or the product from the heating coil I2 by-passed around the separator I5 through line Illa.

According to the present invention, there is injected into the vapor stream passing to the reaction chamber I8, a powdered catalytic material of adsorbent nature, said catalytic material is preferably a bentonitic clay which has been purified to remove alkali and iron compounds therefrom, such as by acid treatment or the like. In lieu of the treated clay, a synthetic gel containing silica and alumina but substantially free of iron oxide or oxides of the iron group may be employed. It has been found that to obtain the objects of the present invention, particularly the production of a high ratio of gasoline to coke, the catalyst agent must -be substantially free of iron compounds.

As illustrated, a hopper I9 is provided for supplying catalyst to the cracking circuit. The catalyst may be fed by means of suitable feeding mechanism such as a star feeder 20 to a screw conveyor 2I which discharges the catalyst in the oil vapors to be cracked.

The catalyst, introduced into the vapor stream should be in a finely divided state capableof passing a 400 mesh screen of a standard series.

The relative proportions of catalyst and oil vapors may vary over a considerable range depending upon the nature of the feed stock, the activity of the catalyst, the desired degree of conversion, the temperature of the cracking zones and other factors. This ratio, however, in general, should be from .3 to 20 parts of catalyst per part of oil by weight and preferably between 1 and 6 parts of catalyst per part of oil by weight in order to fully realize all of the advantages of lthe invention.

The suspension of oil vapors and catalyst is passed through the reaction chamber I3 at a velocity suciently high to cause the catalyst particles to travel through the reaction zone at substantially the same rate as the oil vapors. This velocity may be, for example, between 8 and 50 feet per second depending upon the size of the catalyst particle, the density of the catalyst, the gravity of the vapors, and other factors.

The time of passage of the suspension through the cracking zone may range from 2 seconds up to 2 minutes and preferably between 5 and 50 seconds depending upon the degree of conversion desired, the temperature of the reaction zone, the nature of the feed and other factors.

The temperature of the cracking zone should be maintained between 750 F. and 1000 F.,

preferably between 800 F. and 950 F.

The reaction zone may be maintained at the desired reaction temperature either by supplying heat to the reaction zone, by preheating the oil to the required temperature, by preheating catalyst to the required temperature before introduction into the oil vapors, or by any combination of such methods. The suspension of cracked products and catalysts after passage through the reaction zone, is passed through line 22 to a v suitable separating equipment, such as, for example, a cyclone separator 23, wherein the powdered catalyst material is removed from the oil vapors.

To reduce the cost of recovering the catalyst from the cracked products, it is important to remove, as much as possible of the powdered material from the oil vapors before condensing the latter. To this end a plurality of cyclone separators may be arranged in series or other suitable dust collectors may be employed before passing the oil vapors to the fractionating equipment.

The powdered catalyst removed from the oil vapors in the cyclone separator 23 or other equivalent equipment, is withdrawn through line 24. The vapors separated from the powdered catalyst in the cyclone separator 23 are removed therefrom through line 25 and are passed to a suitable fractionating equipment such as a bubble tower 26, wherein the vapors are subjected to fractionation to condense insufficiently cracked constituents. A trap-out tray 21 may be provided in the lower section of the fractionating tower 26, so that a heavy condensate fraction may be segregated from the remainder of the condensate formed in the tower. By providing such a trap-out tray any catalyst remaining in the vapors entering the fractionating tower will appear in the heavy condensate fraction formed below the trap-out tray. The bottom temperature of the tower may be controlled to segregate from 5% to 10% of the total condensate formed in the tower.

The heavy condensate stock collecting in the bottom of the fractionating tower 26, is withdrawn therefrom through line 28. This product may, if desired, be recycled through line 29 and pump 30 to the inlet side of the heating coil I2 and subjected to further cracking treatment without segregation of any catalyst which may be contained therein. As an` alternative however, such heavy fraction may be ltered or otherwise treated to rst remove any catalyst contained therein before recycling the same to the heating furnace. The clean condensate stock formed in the fractionating tower 26 and substantially free of catalyst particles, is withdrawn from the trapout tray 21 through line 3 I. This product may be withdrawn from the system or recycled for further cracking treatment as desired. y

Vapors remaining uncondensed in the fractionating tower 26 are removed overhead through line 32 and passed to a condenser 33 in which the desired motor fuel distillate is condensed. Products from the condenser 33 pass to a receiver 34 wherein liquid distillate separates from normally gaseous products. The gaseous products are removed from the receiver 34 through line 35 having a pressure release valve 36 which may be utilized to maintain the desired back pressure on the system.

The pressure in the cracking zone may be substantially atmospheric except for sufficient positive pressure to overcome frictional losses through the unit or a mild superatmospheric pressure up to 300 lbs. per square inch. The gases removed from the receiver 34 through line 35 may be passed to a suitable adsorption system for removal of uncondensed gasoline constituents therefrom. The adsorption system has not been illustrated on the drawings since it does not come within the purview of the invention. Liquid distillates collected are withdrawn therefrom through line 31 and may be subjected to any further finishing treatment desired for the production of the nal marketable product.

Returning to the cyclone separator 23, the catalyst removed therefrom through line 24 and which contains carbonaceous deposits is preferably regenerated and returned to the hopper I9 for further cracking treatment.

As a guide to a fuller understanding of the invention, the following examples may be of assistance. It will be understood however, that the values and conditions given in the examples are illustrative rather than limitive.

Example 1 A suspension of oil vapor from an East Texas gas oil having an A. P. I. gravity of 33.4 and a catalyst comprising an acid treated bentonite clay of the type commercially known as Super Filtro having a ratio of catalyst to oil vapors of 1.5 parts of catalyst to 1 part of oil by weight was passed through a reaction zone maintained at 850 F. and under atmospheric pressure. The time of contact of the suspension within the reaction zone was 25 seconds. |After separation of the powdered catalyst the cracked products were segregated into dry gas, excess C4, 400 F. end point gasoline 10 R. V. P., cycle gas oil, and amount of coke remaining on the catalyst was determined. The relative amounts of the various fractions together with the coke determination is given in the table hereinafter.

Example '2 The same feed was passed through a stationary bed of the same type of catalyst as in Example 1. The temperature of the reaction'zone was maintained at 850 F. and the rate of feed, contact time, and length of the cracking cycle was controlled to produce the same amount of gasoline as in Example 1.

The distribution of the cracked products when operating according to Examples 1 and 2 are shown in the following table.

From the above table it will be seen that when operating under the same conditions with respect to catalyst used, temperature, feed stock and gasoline conversion. materially lower gas and coke is formed when using the suspended catalyst than when using a stationary bed. This reduction in yield of low grade products is reflected in increased yield of cycle gas oil.

It will further be evident that when operating to produce a predetermined maximum gas or coke loss a higher yield of gasoline can be obtained.

Having thus described our invention it will be understood that it embraces such other variations and modifications as come within the spirit and scope thereof.

It is claimed:

1. The process for the conversion of hydrocarbon oils which comprises preheating said oil to vaporize a substantial portion thereof, forming a suspension of oil vapors and nely divided conversion catalyst, passing said suspension through a, conversion zone maintained at conversion temperature, removing vaporous conversion products containing said nely divided conversion catalyst from said conversion zone, separating the major portion of the catalyst from said vaporous conversion products at a temperature above the dew point of said vaporous products to thereby effect dry separation of the major portion of said catalyst from the conversion products, thereafter cooling the vaporous conversion products to form an initial oil condensate containing the remainder of said finely divided conversion catalyst, and combining said initial condensate with said rstnamed oil prior to passing the same to said conversion zone.

.f 8 2. The process for converting hydrocarbon oil into motor fuel which comprises passing the oli Ito be converted through a heating and vaporizing zone, contacting the resulting vapors in a conversion zone with nely divided solid conversion catalyst while at conversion temperature, malntaining the catalyst in suspension in said oil vapors within the conversion zone for a period sudcient to obtain a substantial conversion of said oil, thereafter separating iinely divided con- Version catalyst from the\conversion products, subjecting the major portionof the catalyst so separated to regeneration to remove combustible deposits therefrom, and thereafter returning the regenerated catalyst tothe reaction zone. combining a, minor portion of the catalyst separated from said vaporous conversion products with the oil passing through said heating zone wherein said conversion catalyst is heated with said oil and dispersed in the resulting hydrocarbon vapors before introduction into said conversion zone.

STEWART C. FULTON. CARL O. TONGBERG. EDWARD D. REEVES.

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

UNITED lSTATES PATENTS Number Name Date 1,799,858 Miller Apr. 7, 1931 1,860,199 Osterstrom May 24,- 1932 1,893,804 Mittasch Jan. 10, 1933 2,086,287 Towne July 6, 1937 2,128,220 Cooke Aug. 30, 1938 2,231,231 Subkow Feb. 11, 1941 2,247,097 Menshih June 24, 1941 2,253,486 Belchetz Aug. 19, 1941 2,259,486 Carpenter Oct. 21, 1941 2,259,487 Payne Oct. 21, 1941 2,268,094 Russell Dec. 30, 1941 2,289,329 Prickett July 7, 1942 1,887,047 Smith et al Nov. 8, 1932 FOREIGN PATENTS Number Country Date 328,649 British May 1, 1930 416,976 British Sept. 19, 1934

Images