US2372018A - Conversion of hydrocarbons - Google Patents

Description

PERCENT OF PRODUC T March'zo, 1945. R. F; RUTHRUFF 2,372,018

CONVERS ION OF HYDROCARBONS Filed June 7, 1939 4 Sheets-Sheet 1 0 l I l l l 1 Z 4 6 8 I0 l2 l4 l6 I8 20 TIME MINUTES w F/GU/FE B ,5 50- k K 40- F2 R30- #1 a? Lu 20 0 I l I I l l TIME MINUTES ROBE/FT F HUT/{RUFF ill; INVENTOR @WW ATTORN EY March 20, 1945. RUTHRUFF 2,372,018

CONVERSION OF HYDROCARBONS Filed June 7, 1939 '4 Sheets-Sheet 2 F/G. LU

INVENTOR ROBERT F. RU-THRUFF Mun-.4,

ATTORNEY 4 Sheets-Sheet 4 Filed June 7, 1939 R Q Q INVENTOR RObERT F. RUTHRUFF BY uMB hlh? ATTORNEY Patented Mar. 20, 1945 uN TEo STATES PATENT OFFICE" CONVERSION OF HYDROCA RBONS Robert F. Rnthruil', Nutley, N. .L, assignor to The M. W. Kellogg Company, New York, N. Y., a' corporation of Delaware Application June 7, 1939, Serial No. 277,885

Claims.

perature, decomposition or cracking sets in with the production of various conversion products.

When, for example, a mixture of liquid hydrocarbons boiling in the temperature range 400-750 F., is thermally cracked or decomposed, the following conversion products are obtained; gas, gasoline, cycle stock having approximately the same boiling range as the hydrocarbon charge,

tar and coke. By returning the cycle stock to the conversion zone, gas, gasoline, tar and coke are obtained as ultimate conversion products. Usually, gasoline is the desired decomposition product while gas, tar and coke are, under most circumstances, undesirable.

Many advantages follow the use of contact materials or catalysts inthe decomposition or cracking of hydrocarbons. For example, the operating temperature required for a given amount of conversion may be considerably lowered in comparison with the temperatures required in operations conducted in the absence of catalysts. Additionally, the quality of the gasoline produced in the presence of catalysts is higher than that of thermally cracked gasoline and also the yield of this superior product is'enhanced. In catalytic cracking, gas, gasoline, cycle stock and coke are produced, so the ultimate products are gas, gasoline and coke. It will be observed that in catalytic cracking, no tar is usually produced although it is The coke produced during catalytic conversion "progressively increases throughout the conversion, and-finally reaches a stage at which it deactivates the catalyst to an extent necessitating its regeneration; Regeneration is usually efiected by passing air over the spent catalyst and burning oil the deposited coke at a suitable temperature. A great variety of catalytic materials, differing widely in physical structure and chemical composition have been suggested for use as cracking catalysts, and in each instance, these materials have been recognized as requiring periodic regeneration treatments for removal of deposited to be noted that generally the coke production in catalytic cracking is appreciably greater than in thermal cracking and this enhanced coke production may be considered equivalent to part of the tar produced in thermal cracking.

While the catalytic conversion of hydrocarbons is superior to thermal processes, the former operatibn is not perfect for here too, undesirable products (gas and coke) are formed. By the practice of this invention the production of these undeslrable products is decreased, while the production of gasoline is increased.

carbonaceous material in order to enable them to be employed for repeated conversion treatments.

The basis of this invention resides in the observation and discovery that, the alumina-silica type of cracking catalyst exhibits certain distinctive phenomena during the initial portion of the conversion cycle with respect to the products produced, and in the provision of a process arising from this observation whereby a more favorabledistribution and enhanced yield of the desired conversion products is obtained.

The catalytic material contemplated for use in the practice oi. the invention comprises. either. naturally occurring or synthetically prepared mixtures or compounds of silica and alumina,

suitably prepared so as to exhibit a high degree of catalytic cracking activity. A variety of difierent methods for the preparation of catalysts of this type have been described heretofore in the art. For example, a suitable type of aluminasilica cracking catalyst for use in accordance with my invention may be artificially prepared by im-' pregnating a hydrogel of silica with a heat-decomposable salt of alumina such aluminum nitrate, and then'heating the impregnated hydrogel to decompose the nitrate, thereby producing a suitable cracking catalyst consisting of a hard porous silica gel impregnated with alumina, this method of preparation being that described in U. S. Patent 1,782,857. Other materials containing alumina and silica such as naturally occurring, or activatedadsorbent clay materials such as for example i'ullers earth and bentonite, having the eflfect of catalytically converting the higher-boiling hydrocarbons into lower one, may

be employed. An activated bleaching clay sold under suitable conditions and thereafter removing the products or reaction by successive washings with large volumes of hot water. After dewatering, the pulp is dried under carefully controlled conditions followed by final grinding to desired mesh specification.

The term alumina-silica cracking catalyst as employed herein and in the appended claims, designates and is limited to a well recognized class of materials known for their capability of catalyzing the conversion of high boiling hydrocarbons to lower boiling hydrocarbons within the gasoline boiling range characterized by both high yield and quality of the gasoline product. This catalytic conversion is further characterized by the continuous conversion during the catalytic contact of a portion of the charge to produce a carbonaceous deposit on the catalyst. Activated clays such as Super-Filtrol and synthetic composites including silica-gel and alumina are well known examples of this class of catalyst material.

Other materials such as pumice, although including alumina. and silica in some form, are known to lack catalytic activity of the character referred to and are, therefore, expressly excluded from the term alumina-silica cracking catalyst.

The procedure employed in the practice of my invention, and its various features and advantages will be apparent from the following detailed description thereof, given in connection with the appended drawings, wherein:

Figures 1 and 2 are graphical representations of the per cent production, based on the hydrocarbon charged, of the various products of oncethrough catalytic cracking over alumina-silica type of cracking catalysts, asa function of the catalystexposure time; and

Figures 3, 4, and 5, each illustrates diagrammatically a suitable type of apparatus for the practice of specific embodiments'of the invention. Referring to Figures 1 and 2', the curves shown are graphical representations of the instantaneous yields of the per cent production, relative to feed stock, of the conversion products produced by passage of the feed in a once-through operation over alumina-silica type of cracking catalysts as a function of the catalyst exposure or contact time. Referring to the individual curves, curve A, represents coke yield; B, yield of gaseous material; C, yield of cycle stock; and D, yield of gaso-; line. It is to be noted that the yields shown are not cumulative, but rather represent the instantaneous yields obtained during any given period of catalyst life, For example, the yield data shown at ten minutes represent the production of conversion products obtaining at the instant when of itself the true cracking catalyst but that it is a, material capable of producing carbon or car-- the reactor containing the catalyst has been onstream ten minutes, and not the cumulative yield over the first ten minutes of the conversion cycle. The specific data shown in Figure 1 were obtained when passing West Texas gas oil over a catalyst consisting of an acid treated clay of the "Super-Filtrol type. A temperature of 850? F. was employed and the chargejwas passed at a rate of 0.3 liquid volume per volume of catalyst per hour.

The results in Figure 1 show that when using this catalyst, initially no gasoline or cycle stock is formed, only large amounts of coke and gas.

As time on-stream increases, the yields of gas and coke both decrease rapidly, the yield of cycle stock increases slowly while gasoline production rapidly increases to an optimum and then more slowly declines.

bonaceous residues of peculiar orientation and properties and that it is this carbon or these residues that form the true cracking catalyst. During the first few minutes on-stream the major product formed is this oriented carbon which is of course deposited on thecatalyst. As time goes on, production of gasoline increases rapidly, reaching a maximum in the present instance at an on-stream period of approximately ten minutes. At this time, coke production i practically nil while gas production is very low. When the on-stream period is increased beyond ten minutes, the proportion of gasoline in the reaction product decreases with increasing rapidity. It is believed that initially the contact material has little or no ability to make gasoline. As carbon is deposited on the surfaces of this contact material, this carbon, due to its peculiar orientation and properties which are due t the nature oi the surface of the contact material upon which it is deposited, has the ability to convert the charge to gasoline. Conversion to gasoline increases rapidly as the contact material becomes covered with carbon; likewise as the contact material becomes covered with carbon, less charge becomes converted to carbon. However, as cracking progresses, it is believed that tar or pitch forms as a byproduct and this material also is deposited on the contact agent, covering the active carbon already thereon. The tar or pitch or carbonaceous material derived therefrom does not, it is believed, possess the required orientation necessary for converting gas oil to gasoline and accordingly gasoline production decreases. As this occurs. the yield of cycle stock increases simultaneously since there is no fresh surface of contact material to convert it to coke and no orientated carbonaceous material to convert it to gasoline. Apparently the contact material during any one cycle acquires a double layer. When fresh, the contact material gives largely coke and gas; when covered with-oriented carbon it produces gasoline; and when the carbon is covered with tar or decomposition products thereof, the whole is inactive both as a carbon producer and as a gasoline producer.

Figure 2 is similar to Figure 1 except that Figure 2 represents conditions'wherein the gas oil charge was passed over the alumina-silica catalyst at a rate of 1.0 liquid volume-per volume of catalyst per hour. The time on-stream yield relationships in the two figures are quite similar, any differences being explainable on the basis of the difierent charging rates.- In Figure 1, maximum gasoline yield was 73%, attained when the catalyst was on-stream 10.5 minutes. In Figure 2, gasoline yield was maximum at 52.5% when the on-stream period was 2.7 minutes, approximately. The lower gasoline yield in this case refleets the shorter contact time. It will be noted that the increase in gasoline yield to the maximum is faster in Figure 2 than in Figure 1, while the decline from the maximum is slower. This last is due to the slower rate at which the oriented carbon surface is blanketed with tar or pitch and reflects in turn the lower extent of cracking at the higher charge rate. It appears, however, that the rate of depositing active, oriented carbon on the contact material is not so much a function of contact time. as it is of the total amount of charge passed. For example, in Figure 2, maximum activity was reached in 2.7 minutes. This multiplied by the charge rate, gives 2.7 volumes of charge passed to reach maximum activity. In Figure 1, maximum activity was reached in 10.5 minutes and this multiplied by the charge rate 0.3, gives 3.15 volumes of charge passed to reach maximum activity. Within the limit of experimental accuracy, these two values are substantially identical. I

It may be observed from Figures 1 and 2 that for any length of cycle X, the gasoline yield could be increased if the initial period could be, in effect, eliminated. In addition, not only is the gasoline yield increased but also thegasoilne to gas pluscoke ratio is very substantially increased. More specifically, in Figure 1, if the reaction is conducted over the period 6 to minutes shown, the gasoline'yield is higher than over the period, 0 to 9 minutes, and the gasoline to gas plus coke ratio is much higher. Likewise, in Figure 2, the yield of gasoline and the product distribution is much more favorable over the period, 2 to 6 minutes than the period, 0 to 4 minutes.

It may be further observed that when conducting a catalytic conversion operation in accordance with the operating conditions obtaining'ior Figure 1, if the products are sent to waste during the initial period, for example, the first five minutes of the reaction cycle after which the conversion products are collected for use in the production of distillate boiling within the usual gasoline boiling range, the product distribution in the finally collected products is much improved. However, under such conditions no useful result has been attained since the initial product showing poor distribution was sent to waste.

In accordance with my invention the initial period of the cycle characterized by undesirable product distribution and yield is, in eifect, eliminated by subjecting the catalyst to a preconditioning treatmentprior to the conversion reaction. In accordance with this treatment, a quantity of carbonaceous material is formed or deposited on the particular type of alumina-silica cracking catalyst employed approximating the quantity normally deposited during said initial period above described. The: quantity of carbon to be thus formed will, in general, range in quantity from about 0.5% to 2.0%, by weight, of the catalyst, and preferably resides in the somewhat narrower range of about 0.8% to 1.5%. Preconditioning of the catalyst, in accordance with my invention, may be effected by the decomposition of a hydrocarbon mixture which is readily broken down or decomposed to produce a mixture of carbon and other hydrocarbons by a suitable decomposition treatment, and contacting the decomposition products with the fresh or regenerated alumina-silica catalyst in such manner that carbon is deposited thereon to the required extent. Preferably, the conditioning treatment is effected by passing the hydrocarbons selected for the treatment, in contact with the fresh or regenerated catalyst under reacting conditions adapted deposit normally deposited during said initial period previously described, which is characterized by agradually increasing yield oi gasoline per unit of time up to an optimum value.

The invention may be practiced with a wide variety of types of catalytic reactors and regeneration equipment. One type involves the socalled "static bed type of operation wherein the catalyst is disposed in the reactorin the form of a stationary or static bed through which the hy drocarbons undergoing treatment are passed. Upon substantial deactivation of the catalyst, the flow of hydrocarbons thereover is discontinued, and ,a regenerating gas such as air is passed over the spent catalyst to burn ofl deposited carbon, Usually a plurality of such catalyst reactor chambers are arranged in parallel and suitably manifolded with respect to the incoming stream of treated hydrocarbons and regenerating gas, so that the operation is substantially continuous.

. one reactor being on-stream while another is being regenerated. Accordingly, a complete cycle in a given reactor involves both a conversion period and a regeneration period. In accordance with my inventiori the complete cycle includes an additional conditioning period. A suitable apparatus for the practice of this embodiment of the invention is shown in Fgure 3.

Referring to Figure 3, a single reactor I1 is shown, partly in elevation and partly in section. Charging stock, which may consist of reduced "crude or heavy gas oil is passed by line I and pump 2 to furnace 3. The preheatedcharge enters separator 4, through line 5, overhead prod ucts passing through line 6 and through opened valve 28 to a reactor or reactors (similar to II, hence not shown) which are exercising the cracking function, valve 1 in line 8 being closed. Heavy products in the preheated charge accumulate in the bottom of separator 4 from whence they may be eliminated from the system if desired through valve 3 in line l0.- Alternatively, these heavy products may be passed-through valve H in line 12, pump l3 and valve 21 to manifold l4, valve I5 in line l6 being closed. Line 16 leads to manifolds similar to It (not shown) serving to decompose it to a mixture of hydrocarbons the other reactor or reactors (not shown) exercising, at this stage, the cracking and/or regeneration operations.

Reactor l'l contains a suitable catalyst l8 disposed on a plurality of perforated trays l9. Manifold M is provided with a plurality of branched pipes 20, one or more for each tray. If desired, an atomizing fluid, suitably preheated, such as steam, gas made in the process or from another source, flue gas made in the regeneration process or from an outside source, may be passed through line 2! to manifold 22, said manifold having a plurality of branched pipes 23, each side pipe corresponding to a side pipe 20 from manifold M.

The heavy charge is distributed to a series oi atomizers or sprays 2t by means of the plurality of side pipes 20. Preferablythe atomizers or sprays 24 are disposed inthe layers of catalyst l8 on the perforated trays l9 although-they may also be disposed above the catalyst.- Also, itis not necessary to have atomizers or sprays .24 in or near each tray of catalyst. While this arrangement is preferable, satisfactory results can be obtained by atomizing, vaporizing or spraying all of the heavy charge in the bottom of reactor -reactor (not shown) which is on the cracking cycle. Passage of the heavy portion of the charge through line H and decomposition thereof is continued until the desired amount of carbon is deposited on the catalyst.

Vaporizable products derived by the decomposition of the heavy portion of the charge leave reactor I! through opened valve 25 in line 26, and may be disposed of as desired. After a short preconditioning treatment, valve 21 in manifold M, valve 25 in line 26, valve 31 in line 2|, and valve 28 in line 6, are closed while valve 1 in line 8 is opened, light product from the top of separator 4 then passing over the preconditioned catalyst in reactor H, the resulting product then being sent to conventional fractionating or condensirg means (not shown) through opened valve 29 in line 30. Also at this stage, valve i5 is opened and the conditioning stock passed through line to a reactor ready for the conditioning treatment, a continuous operation bein thus assured.

Because of the heavy nature of the conditioning stock it is readily decomposed into carbon and other hydrocarbons, and the time required 'for accomplishing the conditioning treatment is very short. For example, when operating under the conditions described in connection with Figure 1, a period of about 2 .5 minutes brings the catalyst to a condition similar to that shown by the catalyst after 5 minutes (Figure 1) where a relatively light gas oil was used as charge. In one series of experiments, satisfactory results have been obtained by passing preheated charge to the separator 4 at a rate of 100 volumes in unit .time, separating it into 80 volumes of overhead and of bottoms, pumping these bottoms at a rate of 20 volumes in unit time through line it for a time of 2.5 minutes which constitutes the conditioning period, and then passing the overhead from separator 4 to the reactor H at a rate of 80 volumes per unit of time for a time of 10 minutes which constitutes the conversion or cracking period of the cycle.

If desired, the product withdrawn through line 26 during the conditioning treatment may be recycled in the conditioning operation, for example by introducing this material through line 3| and valve 32. Alternatively, other conditioning materials may be added to the system through line 3| in addition to, or replacing in whole or part material from line l2. Suitable materials for such purposes include non-volatile hydrocarbons such as petroleum pitch, 'coal tar pitch, wax introduced as such or dissolved in a suitable volatile solvent such as naphtha. These materials may be suitably preheated if desired 'but it should be borne in mind that these are contacted with the catalyst in reactor ll immediately after the. regeneration step under which conditions the catalyst may be considerably above reaction temperature so that the addition of conditioning feed at relatively low temperatures may be necessary or desirable to aid in bringing-the catalyst temperature down to the required operating temperature before the conversion or cracking cycle begins. For this reason, in some cases it is necessary to cool the heavy bottoms from separator 4 before using them as a. conditioning means.

It is apparent that when using a light charging stock containing little or no bottoms suitable for conditioning, conditioning materials from outside sources must be used. For convenience, stocks suitable for use in the conditioning of catalysts may be termed carbogens.

At the conclusion of the cracking cycle in which the preconditioned catalyst, prepared as previously described, is employed the regeneration cycle begins. Valve '1 in line 6 is closed as is valve 29 in line 30. Reviviflcation gas enters through valve 33 in line 34 and leaves by valve 35 in line 36. It is apparent that one complete cycle is divided'into' three portions (:1) preconditioning (b) cracking and (c) regeneration.

My invention may be further employed in conjunction with the so-called moving-bed" type of catalytic cracking operation. In .this type of operation, the catalyst is moved through the conversion zone during the conversion period of the cycle, and regenerated in a zone external of the conversion zone. Figure 4 illustrates a suitable apparatus and flow procedure for use in the practice of this embodiment of the invention. Referring to Figure 4, the charge, such as reduced crude or heavy gas oil is introduced by line 4! and pump 42 to furnace 43. The preheated charge enters separator 44 by means of line 45. overhead from said separator 44 passing to reactor 46 through line 41. The contact material or catalyst in reactor 46 is constantly moving downward, contact material being added through conveyor 48 and leaving through conveyor 49. Converted or cracked hydrocarbons leave reactor 6 through line .50, passing to conventional of vapor therefrom.

Spent catalyst leaving reactor 46 through conveyor 49 is regenerated in any suitable manner, one' suitable form of regenerator being illustrated. This regenerator 52 contains a plurality of hearths 53, 54, 55, 56 and 51, each provided with one or more rakes 58 attached to rotatable shaft 59. Spent catalyst falls on the top hearth 53 and is distributed and agitated by means of the rake or rakes 58 which move over the surface of said hearth. The catalyst on hearth 53 is gradually moved down through the regenerator, resting in turn on hearths 54, 55, 56 and 51 and is finally discharged into conveyor 46 and moved to the top of reactor 46 to repeat the cycle.

Means are provided for contacting the catalyst in regenerator 52 with air or dilute air. For example, air or dilute air may pass through duct to to ducts 6|, over the hearths 53, 54 and 55 and out through ducts 52 and duct 63. The regenerating fluid may be suitably warmed or cooled before entering duct 60 and part or all of the flue gas leaving 63 may berecycled after eliminating a portion which is replaced by make-up air.

A separate duct 64 is shown supplying hearth 56. Inert material such as oxygen-free flue gas is supplied to duct 64 and may suitably be flue gas from duct 63. This inert flue gas is supplied at such a rate that it forms a seal, the inert material forming a partition between hearth 56 and hearth 65. While catalyst can fall irom the upper hearth in the last hearth.

.u onto hearth n and then hearth ll, gaseous products on the hearth "and on hearth II cannot difluse into the space occupied by-hearth ".1 7 Gaseous material ,irom hearth 50 may suitably leave by duct 02' opening into duct 80.

Heavy products from thebottom oi. separator oll where conversion into gasoline is elected in the presence of the catalyst, and the catalyst ls conditioned in accordance with my invention, for use in reactor 95,

' The conversion Products from reactors 00 and 00 are withdrawn through lines I00 and MI respectively and may be suitably fractionated into tail gas,.'gasoline, recycle stock and tar, in a conventional system of partial condensers. or fracmediate vicinity of hearth 01. The sp'rayers or atomizers may suitably form the teeth of the rakes passing over hearth 51. If desired, steam, flue gas, or gaseous hydrocarbons may be employed to aid in the-vaporization, spraying or atomization oi the heavy material from the'bottom of separator 44. This may be added through line H. The products from hearth 51 may be removed through line I2- and worked up as desired. By this process the catalyst is conditioned The conditioning treatment may be eilected, wholly or partly, at other points in the cycle if desired. For example, heavy oil may be vaporized, atomized or sprayed into conveyor 40 at one or-more points or it may be vaporized, sprayed or atomized into the upper portions of reactor 40. As in the embodiment previously described, the heavy oil used in conditioning may be supplemented or replaced by material from sources other than the charge and where the charge is comparatively light, such outside sources, preferably, are employed. Conditioning oil from said outside sources may enter the cycle through line I3 and valve II. It will be. noted that the reactor shown in Figure 4, differs from that shown in Figure 3 in that, with the former, operations are continuous. While the catalyst in reactor 46 difiers in activity from top to bottom of said reactor, the integrated activity of all the material in reactor 46 is always constant regardless of the length of time the reactor has been on stream.- Accordingly, the processed charge leaving reactor 46 by line 50 has constant characteristics which are highly advantageous.

A further modified embodiment, also, employinga "moving-bed" type of catalytic conversion operation is illustrated in Figure 5. In this embodiment, a suitable feed stock for the process such as a reduced crude oil is picked up from source 80 by pump BI and passed through heater 02 and line 83 into fractionating column 84- where fractional distillation of the oil is effected. The non-volatile portion, ii. any, is withdrawn as bottoms through line 85 while the remaining portion is divided into lightv and heavy fractions which are drawn off through lines 86 and 81 respectively. The light fraction passing overhead through line 86 as a vapor is cooled in exchanger 00; and condensed in condenser 08 and part of the condensate is pumped back from condenser 08 by pump 90 to serve as reflux to column 0|. Liquid from condenser 88 is pumped by pump III Through line 92 through a suitable heater 83 and the resultant vapors passed through line 94 to reactor 05. In reactor 95, conversion; to gasoline heated to the reaction temperature required in .reactor 90. The heavieriraction separated in column 04 is withdrawn by pump 00 and passed .through line 81 to heater I0. and thence to heavy tionators I02. 1

Hot regenerated catalyst is carried by a conveyor system I03 and discharged into reactor 99, travelling therethrough from top to bottom and droppin through a star-feeder or solids pump I00 into reactor 05. The catalyst continues downwardly through reactor 95' and drops through'a. I l

, star-feeder or solids pump I015 into regenerator ,I0I wherein the accumulated impurities are removed by burning with air or other suitable regenerating gas introduced through I08. The hot regenerated catalyst is returned to reactor 99 through conveyor system I03, and gaseous regeneration products are withdrawn through duct I09.

From the foregoing it will be apparent that the a process therein described. accomplishes the object of my invention of providing a process for the-catalytic conversion of hydrocarbons' whereby a more favorable distribution and enhanced yield of the desired conversion products is obtained. It will further be readily apparent to those skilled Y in the art that while the invention has been illustrated and described with respect toa preferred operation and examples, and with refertested, .in vapor form, with an alumina-silica cracking catalyst under reacting conditions adapted to produce the, required extent of conversion into low-boiling hydrocarbons distilling within the gasoline boiling range, and wherein said. catalyst in the absence of a conditioning treatment exhibits a catalytic activity characterized by an initial period of gradually increasing yleld'of gasoline per unit of time up to an optimum value and by the continuous formation of a carbonaceous deposit on the catalyst during said initial period, the steps, including, separating the hydrocarbon charged into a light fraction, and a heavy fraction relatively readily heatdecomposable to produce coke or carbon compared to said light fraction, passing the heavy normally deposited during said initial period, and

then passing the light fraction, in vapor form,

' in contact with said catalyst under reacting conditions adaptedto produce the required degree of conversion into low-boiling hydrocarbons distilling within the gasoline boiling range.

2. A process of converting high-boiling hydrocarbons to low-boiling hydrocarbons involving contacting said high-boiling hydrocarbons, in the vapor phase. with an alumina-silica cracking catalyst under reacting conditions adapted to' continuously produce a carbonaceous deposit on the catalyst with consequent relatively short onstream periods and a high yield and quality of hydrocarbons distilling within the gasoline boiling range, which comprises preconditionirfg said catalyst prior to the conversion treatment by passing a relatively readily heat-decomposable hydrocarbon in contactwith'said catalyst under reacting conditions adapted to decompose it to a mixture of hydrocarbons and solid carbonaceous material, and in quantity suflicient only to deposit a, coating of carbonaceous hydrocarbon terial on the catalyst in an amount of about 0.5% to 2.0% by weight of the catalyst, and then passing vaporized high boiling hydrocarbons relatively stable to decomposition by heat in contact with said preconditioned catalyst under reaction conditions adapted to produce a substantial conversion thereof to low boiling hydrocarbons with in the gasoline boiling range.

3. A process of catalytically cracking high boiling hydrocarbons to low boiling hydrocarbons within the gasoline boiling range and involving the concurrent production of a carbonaceous deposit on the catalyst with consequent relatively short on-stream periods, which comprises forming a relatively small amount of a carbonaceous hydrocarbon deposit on an aluminasilica cracking catalyst by passing a relatively readily heat decomposable hydrocarbon in contact with the catalyst under reaction conditions adapted to decompose the hydrocarbon to volatile hydrocarbons and carbonaceous material, thereby preconditioning the catalyst and eliminating its tendency to produce excessive coke and fixed gases at the initial portion of the conversion period, and then passing vaporized high" boiling hydrocarbons relatively stable to decomposition,

by heat in contact with said preconditioned catalyst under reaction conditions adapted to produce a. substantial conversion thereof to low boiling hydrocarbons within the gasoline boiling range.

4. A process asdefined in claim 3 wherein said readily heat decomposable hydrocarbon com prises a non-volatile fraction of a petroleum crude.

5; In a process of catalytically cracking high boiling hydrocarbons to low boiling hydrocarbons within the gasoline boiling range, the improvement which consists in passing a non-volatile readily heat decomposable fraction of a crude petroleum in contact with an alumina-silica cracking catalyst selected from the group consisting of synthetic composites of silica-gel and alumina, and activated clays, under reaction conditions adapted to decompose the hydrocarbon to volatile hydrocarbons and non-vo1atile carbonaceous hydrocarbon material with consequent relatively short on-stream periods, thereby preconditioning the catalyst with said non-volatile material and eliminating its tendency to produce excessive coke and fixed gases at the initial portion or a, subsequent conversion period wherein hydrocarbons are passed over the catalyst to con currently produce low boiling hydrocarbons within the gasoline boiling range and a carbonaceous deposit on the catalyst.

' ROBERT F. RU'I'HRUFF.

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