US2854401A

US2854401A - Hydrocracking with a physical mixture of catalyst particles containing platinum

Info

Publication number: US2854401A
Application number: US455765A
Authority: US
Inventors: Paul B Weisz
Original assignee: Socony Mobil Oil Co Inc
Current assignee: ExxonMobil Oil Corp
Priority date: 1954-09-13
Filing date: 1954-09-13
Publication date: 1958-09-30
Anticipated expiration: 1975-09-30

Description

HYDROCRACKING WHH A kHYSlCAL MIXTURE gig/:{ATALYST PARTICLES CONTAINING PLATI- Paul B. Weisz, Pitman, N. 3., assignor to Socony Mobil Oil Company, Inc, a corporation of New York No Drawing. Application September 13, 1954 Serial No. 455,765

12 Claims. (Cl. 208-111) This invention relates to an improved catalytic cracking process. More particularly, the present invention is directed to a process wherein a high boiling hydrocarbon or hydrocarbon mixture, for example, a petroleum fraction, is subjected to cracking in the presence of hydrogen and a catalyst consisting essentially of a particularly defined mechanical mixture of (1) particles of a porous inert carrier impregnated with a small amount of a metal of the platinum series and (2) particles of an acidic cracking component. The invention is further directed to the aforesaid catalyst.

As is well known, cracking refers generally to opera tions wherein a long chain hydrocarbon or a mixture of high molecular weight hydrocarbons is converted into a shorter chain hydrocarbon or into a mixture of lower molecular weight hydrocarbons. Cracking accomplished solely as a result of the high operational temperature employed is known as thermal cracking while cracking effected in the presence of catalysts is ordinarily known as catalytic cracking. Cracking carried out in the presence of hydrogen is referr d to as hydrocracking.

Catalytic cracking of petroleum hydrocarbons has heretofore been carried out at temperatures in the range of 800 F. to 1100 F. Such high temperatures have been ineflicient from an economics standpoint and undesirable from an operational standpoint, resulting in the production of unwanted coke, relatively large amounts of dry gas, and excess quantities of C hydrocarbons. The production of coke and dry gas represents a loss, thereby bringing about an overall decrease in the yield of useful cracked product.

As is Well known, charge stocks heretofore employed in catalytic cracking operations have been selected petroleum stocks. Thus, heavy residual stocks, as well as cycle stocks obtained from the catalytic cracking of non-refractorypetroleum cracking stocks, have not been suitable for catalytic cracking processes because of their inherent coke-forming characteristics and the excessive amounts of dry gas produced. Accordingly, the supply of available cracking stocks has been somewhat restricted.

Cracking operations carried out in the presence of hydrogen at relatively high temperatures and under high pressures, i. e., hydrocracking, do not impose the aforesaid limitations on the type of utilizable charge stock. Thus, cycle stocks, heavy residuals, etc., can be cracked in hydrocracking operations. Conventional operations of this type, however, have many disadvantages. Thus, in order to maintain catalyst activity at a desired level and to avoid a heavy deposition of coke on thecatalyst, it has been found necessary to employ exclusively high hydrogen pressures of the order of at least about 3000 pounds per square inch and preferably much higher. Such pressures have necessitated the use of expensive high-pressure equipment. Hydrocracking processes of the prior art have necessarily employed special sulfur-resistant catalysts for cracking of a sulfur-containing stock since the catalysts heretofore conventionally employed in hydrocracking are poisoned by sulfur.

" .iinite States Patent In accordance with the present invention, it has beendiscovered that cracking of hydrocarbons in the presence of hydrogen and a particular catalyst permits the useof appreciably lower reaction temperatures and pressures. Thus, it has been found that cracking of hydrocarbons can be effected in the presence of hydrogen and in the presence of two chemically distinct catalytic substances which, although chemically not combined, are simultaneously present as mechanical mixtures in the reaction zone and thereby produce a new catalytic activity different from and beyond that obtainable from the simple addition of separate reactions on the two components. For example, a mechanical mixture of two types of particles, one containing a platinum metal deposited on an inert carrier and one of the family of cracking catalysts, has been found to effect cracking of hydrocarbons in the presence of hydrogen although this reaction proceeds to a negligible charge stocks.

Without being limited by any theory, it is believed that the optimum results achieved herein with a mechanical mixture of finely divided particles of catalyst are due to the accomplishment of two reactions, namely, dehydrogenation and cracking, by way of olefinic intermediates.

Thus, it is believed that the cracking reaction occurringin the present process proceeds in accordance with a two-- step cracking mechanism as follows:

(A) High molecular weight hydrocarbons are dehydrogenated to high molecular weight olefins on the platinum metal catalyst sites.

(B) High molecular weight olefins readily crack on acid cracking centers to low molecular weight olefins, which are thereafter hydrogenated on the platinum metal catalyst sites. 7

It is believed that the two components comprising the instant catalyst mixture, i. e., particles of the platinum metal deposited on an inert carrier and particles ofthe acid-cracking catalyst, should present sufficient; reaction surface and be sufiiciently proximate to one another that the olefinic intermediates formed during the reaction proceed to the desired cracked end products during the li fe-. time of such intermediates. In accordance with the pres:

ent invention, it has been discovered'that optimum cra'cking is obtained when the particle size of the components making up the instant catalyst is fairly small and specifically less than about microns in diameter.

Broadly, the present invention aifords a cracking catalyst consisting essentially of a mechanical mixture of finely divided particles of a porous inert carrier having deposited thereon a small amount of one or more of the platinum metals, i. e., platinum, palladium, rhodium, osmium, iridium, and ruthenium, and finely divided particles of an acidic cracking component, the relationship between the components making up said mixture being governed by the following expressions:

nXO. C. I.=5 to 100 mXC Xd :m to .s

Patented Sept. 30, 1958 the density of inert carrier particles in grams per cubic centimeter.

The instant invention also provides a process for cracking hydrocarbons and particularly petroleum hydrocarbon fractions having an initial boiling. point of at least about 400 F., a 50 percent point of at least about 500 F., and an end boiling point of at least about 600 F., and boiling substantially continuously between said initial boiling point and said end boiling point by contacting said fractions with the above catalyst in the presence of hydrogen at a pressure between about 100 and about 2500 pounds per square inch gage at a liquid hourly space velocity of between about 0.1 and about at a temperature between about 400 F. and about 825 F., employing a molarratio of hydrogen to hydrocarbon charge between about 2 and about 80.

It has heretofore been proposed to convert hydrocarbon fractions to products of increased octane number by subjecting them to reforming operations. These operations' employ hydrogen and catalysts which in some cases comprise'a'platinum metal component. The cracking process described herein is distinct from the reforming processes of the prior art that involve use of a platinum metal-containing catalyst. Thus, there are at least four differences between the cracking process of this inventionand the aforesaid reforming operations. First of all, it may be noted that the processes are carried out for two different purposes. Cracking is used to-convert high boiling hydrocarbon fractions into low boiling hydrocarbon fractions, while reforming is carried out for the sole purpose of increasing the octane number of low boiling hydrocarbon fractions with little or no cracking. Secondly, the charge stocks employed in cracking and in reforming are not the same. A reforming charge stock, i. e., gasolines, kerosenes, or naphthas, ordinarily has an initial boiling point well below about 400 F. and usually a's'low as 60 F. to 150 F. Regardless of the initial boiling point, however, the reforming charge stocks have 50 percent points well below 500 F. and end boiling points far below 600 F. Cracking charge stocks employed in the instant process, on the other hand, have initial boiling points of at least about 400 F., 50 percent points of at least about 500 F., and end boiling points of at least about 600 F. A third difference relates to the chemical reactions involved in the processes. In reforming, it is desired to produce gasolines having substantial aromatic hydrocarbon contents from highly aliphatic reforming charge stocks. Accordingly, reforming involves aromati'zation reactions resulting in the production of large amounts of hydrogen during the reforming operation. Cracking, on the other hand, does not involve these aromatization reactions since the purpose of cracking is to convert high boiling hydrocarbons by selective breakage of carbon to carbon bonds. In contrast to reforming, such operation consumes hydrogen. A still further distinction resides in the fact that the cracking process of this invention is operable at temperatures that are lower than the temperatures at which reforming processes are operable. It will accordingly be appreciated that the 4 aforementioned reforming processes of the prior art which utilized platinum metal-containing catalysts and'the cracking process of this invention are clearly distinct.

The conventional cracking activity of a catalyst is generally expressed in terms of the percent by volume of a standard hydrocarbon charge which is cracked under specific conditions in the CAT-A test. The method of this test is described in National Petroleum News 36, page P. R. 537 (August 2, 1944) and the cracking activity so determined is referred to as the Activity Index (A. 1.). Accordingly, it will be understood that the term activity index when employed herein shall refer to' the cracking activity of the material under consideration, determined in accordance with the CAT-A method. The term oletinic cracking index as employed herein shall refer to the percent by volume of dodecene-l converted to 350 F.

4 end point liquid cracked products when charged at substantially atmospheric pressure, a liquid hourly space velocity of 1, and a temperature of 630 F. The apparatus employed for determining the olefinic cracking index is similar to that used in the aforementioned CAT-A test.

It has previously beensuggested to convert hydrocarbon fractions by subjecting the same under conversion conditions with a catalyst comprising a platinum metal supported on an active cracking component. Thus, it has been taught that a platinum metal deposited on a carrier or support which is inert as regards cracking activity is not an effective cracking catalyst. In accordance with the process described herein, it has been found that,

contrary to the teachings of the prior art, excellent erack-' ing of hydrocarbons can be achieved in the presence of hydrogen and a catalyst consisting essentially of a mechanical mixture of finely divided particles of components having the characteristics defined hereinabovc. It has been discovered that hydrocarbons, and particularly hydrocarbon fractions having the aforementioned boiling point characteristics, can be converted into hydrocarbon fractions boiling in the gasoline and/ or fuel oil range by subjecting such fractions to cracking in the presence of hydrogen and the aforesaid catalyst.

The mechanical mixture comprising the present catalyst allows a wide choice for the carriers supporting the plati num metal component. Thus, it is contemplated that the carrier employed herein may be any porous inert material which is not adversely affected by the temperature conditions of the instant process. The carrier desirably has a surface area greater than about 10 square meters per gram and preferably in excess of 30 square meters-per gram, and may extend upto 500 square meters per gram or more to achieve efficient surface spreading of the platinum metal. The term surface area as used herein designates the surface area of the carrier as determined by the adsorption of nitrogen according to the method of Brunnauer et al., Journal American Chemical Society, 60, 309 et. seq. (1938). The carrier is inert, that is, it is devoid of or exerts negligible catalytic activity under the reaction conditions at which the present process is carried out. Suitable carriers include single oxides of the metals of group IIA, IIIB, IVA, and IVB of the periodic table. Non-limiting examples thereof include alumina, zirconia, titania, silica, magnesia, etc. Other suitable inert materials include charcoal, kieselguhr, porous glass, porcelain, pumice, coke, activated carbon, bauxite, etc. The density of the carrier employed, i. e., the bulk density thereof, will usually be within the range of .2 to 2.0 grams/ cc. and more particularly between about .4 and about 1.2 grams/ cc.

The porous inert carrier serves as a support for a catalytically effective amount of a platinum metal, i. e., platinum, palladium, rhodium, osmium, iridium, and ruthenium, as well as alloys or mixtures of these metals. Of the foregoing, platinum and palladium, and in particular platinum, are accorded preference. The amount of the platinum metal contained in the instant catalyst is generally between about 0.05 and about 10 percent by weight of the carrier and more particularly between about 0.1 and about 5 percent byweight of the carrier.

In accordance with the present invention, the weight fraction of inert carrier supporting the platinum metal component may vary widely, thereby affording desirable flexibility in the catalyst composition, which may be varied with the specific charge stock undergoing trcatment and with the particular reaction conditions under which the cracking operation is effected. In general, however, the weight fraction of carrier supporting the platinum metal component of the instant catalyst is between about .1 and about .9.

It is to be understood that following the teachings of this invention, the weight fraction of carrier supporting the platinum metal component, the density of said carrier, and the concentration of said metal are so related that the product thereof lies within the range of .01 to .8, thereby fulfilling the condition:

where m, C and d have the above-designated significance.

The nature and amount of the acidic cracking component contained in the instant catalyst may, in accordance with the present invention, vary widely. Typical acidic cracking components include synthetic composites of two or more refractory oxides. Generally, this group includes oxides of elements of groups HA, IIIB, IVA, and IVB of the periodic table. Non-limiting examples of suitable synthetic composites include silica-alumina, silicazirconia, silica-alumina-zirconia, silica-alumania-thoria, silica-magnesia, silica-alumina-magnesia, alumina-boria, and the like. The above composites may also contain halogens and/or other materials which are known in the art as promoters for cracking catalysts. Also, halogenpromoted aluminas may be employed as the acidic cracking component. The preferred cracking component is a synthetic composite of silica and alumina containing from about 0.25 percent up to about 20 percent by weight of alumina. The activity index of such silica-alumina cracking component is preferably within the range of 25 to 50.

The amount and activity of the acidic cracking components employed herein are such that the conditions of the expression:

n O. C. I.=5 to 100 are fulfilled where O. C. I. is the olefinic cracking index of the cracking component and n represents the weight fraction of this component in the catalyst mixture. The latter weight fraction may also vary widely, depending on the particular stock undergoing cracking and the specific conditions under which such operation is efiected. In general, however, the weight fraction of the acidic cracking component of the instant catalyst is between about .1 and about .9. It is particularly preferred that the acidic cracking component of the present catalyst be characterized by the expression:

n O. C. 1.:25 to 100 The particle size of the components comprising the catalyst mixture of this invention has been found to be a critical feature thereof. It has been established, as will be evident from data hereinafter set forth, that, for optimum cracking under the specified reaction conditions and with the described catalyst, the average particle size of each of the components making up such catalyst should be less than about 100 mesh. Excellent results have been obtained with a catalyst having a particle size in the range of about 100 to about 400 mesh (Tyler). It is accordingly contemplated that the catalysts of this invention will in general comprise particles having a diam eter below 100 microns and particularly a diameter in the approximate range of l to 100 microns.

The catalyst of this invention may be used in the form of discrete particles having the aforesaid requisite diameter, or the components having such particle size may be admixed and pelleted, cast, molded, or otherwise formed into pieces of desired size and shape, such as rods, spheres, pellets, etc., it being essential, however, for optimum results that each of said pieces is composed of particles of both components having a particle diameter of less than about 100 microns.

The process of this invention may be carried out in any equipment suitable for catalytic operations. The process may be operated batchwise. It is preferable, however, and generally more feasible to operate continuously. Accordingly, the process is adapted to operations using a fixed bed of catalyst. Also, the process can be operated using a moving bed of catalyst wherein the hydrocarbon fiow may be concurrent or countercurrent to the catalyst flow. A fluid type of operation wherein the catalyst is carried in suspension in the hydrocarbon charge is well adapted for use with the instant catalyst since pelleting or otherwise shaping of the catalyst components is thus rendered unnecessary.

The carriers for the platinum metal component of the instant catalyst as indicated hereinabove are inert with respect to cracking of hydrocarbons, i. e., they are not effective in catalytic cracking operations carried out under the conditions of the process of this invention. A number of platinum-containing hydrocarbon conversions catalysts have heretofore been proposed wherein the platinum metal is impregnated on an alumina base. Such base has been known to impart stability to the platinum in subsequent aging, thereby permitting use of the catalyst over an extended period of time in conversion operations without necessitating regeneration. However, inasmuch as the alumina base itself is not acidic, it has heretofore been the practice to combine the alumina with promoting agents, such as halogen, boria, and the like. It is well known that such promoters are not permanent but may be lost upon contact with water vapor which is inherently or accidently contained in the hydrocarbon feed stock.

Utilizing one embodiment of this invention, it is now possible to combine the advantages of employing alumina as a support or carrier for the platinum component without the attendant disadvantages of the prior art catalysts, since, in accordance with the present invention, the acid centers desired for accomplishing cracking under the conditions described herein are located on separate particles distinct from those employed as a carrier for the platinum metal component. It is accordingly a preferred embodiment of this invention to employ as the platinum metal bearing component a carrier consisting of alumina having impregnated thereon between about 0.05 and about 10 percent by weight and more particularly between about 0.1 and about 5 percent by weight of platinum.

The platinum metal may be deposited on the carrier in any suitable manner. One feasible method is to admix particles of the carrier with an aqueous solution of an acid of the metal, for example, chloroplatinic or chloropalladic acid or of the ammonium salt of the acid, of suitable concentration. The impregnated particles are then dried and treated with hydrogen at elevated temperatures to reduce the chloride to the metal and to activate the catalyst.

it is contemplated that the cracking component of the present catalyst may be produced by any of the usual methods, well-known in the art, employing cogellation or impregnation techniques. Thus, taking the preparation of silica-alumina composites as a typical example, cogels of silica and alumina may be prepared by intimately admixing an acidic solution of an aluminum salt with sodium silicate to yield a silica-alumina hydrosol which sets after lapse of a suitable period of time to a hydrogel. The resulting hydrogel is thereafter water washed, base-exchanged to remove zeolitic sodium, dried, preferably in superheated steam and finally calcined at 900 F. to 1400 F. in air. Alternately, a silica-alumina. composite may be produced by separately forming a hydrogel or gelatinous precipitate of silica and a hydrogel or gelatinous precipitate of alumina and ballmilling or otherwise intimately admixing the silica and alumina together to yield a resultant silica-alumina composite. In such instances, the silica is suitably prepared by mixing an acid solution, for example, aqueous sulfuric acid solution, with sodium silicate. If it is desired to prepare silica initially free of alkali metal ions, such may be accomplished by effecting hydrolysis of alkyl silicates,

i. e., ethyl silicate. Alumina is readily prepared by the addition of ammonium or alkali metal hydroxide to an aqueous aluminum salt solution, for example, an aluminum salt of a mineral acid, such as aluminum nitrate, aluminum chloride or aluminum sulfate. As another alternate procedure for preparing the silicaalumina composite, a synthetic silica gel or precipitate may be prepared in accordance with oneof the foregoing processes and alumina may be deposited thereon by contacting the silica gel or precipitate with an aqueous aluminum salt solution, followed by the addition of a suflicient amount of ammonium hydroxide to eifect precipitation of alumina on the silica. The composite of silica and alumina can further be prepared by contacting a preformed silica gel with an aqueous aluminum salt solution, thereafter removing the impregnated silica gel from the solution and heating to a sufiiciently elevated temperature to decompose the aluminum' salt laid down by impregnation to alumina so that the resulting product is silica impregnated with the requisite amount of alumina. All of the foregoing methods for preparing composites of alumina and silica are well known in the art and are referred to herein merely as exemplary of suitable preparation procedures. It will be realized that composites of other oxides than silica and alumina and composites of more than two oxides may with suitable modification likewise be prepared in-accordance with the general procedures above outlined.

It is also feasible to produce the cracking component in the form of spheroidal particles such as beads, following the teachings of Marisic set forth in U. S. 2,384,946, or in the form of uniformly shaped pellets prepared by casting or extrusion methods. The cracking component may also be prepared as a mass which is thereafter broken up into irregularly shaped pieces. In all of the foregoing procedures, the particles or pieces of produced cracking component are ground to finely divided particles having a requisite particle diameter of less than 100 microns. It is also feasible to initially produce the cracking component in the form of finely divided particles of requisite particle size by employing techniques used in the preparation of fluid catalyst particles, for example, by spraying or rapid agitation of a hydrosol to form minute particles of hydrosol that set to particles of hydrogel which, upon drying, yield discrete gel particles having a diameter of less than 100 microns.

A preferred catalyst, as indicated above, is one consisting essentially of a mechanical mixture of finely divided particles of alumina having platinum deposited thereon and finely divided particles of silica-alumina cracking component. This catalyst may be used in the form of a powdered mixture in a fluidized type reactor. Alternatively, the composite powder may be pelleted for use in static reactors. It has been conventional practice in obtaining hard pellets to initially mix the material undergoing pelleting with a binder, such as stearic acid, etc., and to subsequently remove such binder from the formed pellets by burning. Since the high temperatures necessarily employed to effect substantially completeremoval of the binder from the pelleted product by combustion may adversely affect the platinum metal, it is preferred to prepare the platinum-containing catalyst pellets of this invention by initially admixing alumina carrier particles having a particle diameter of less than 100 microns with silica-alumina particles having a particle diameter of less than-100 microns and pelleting the resulting composite with a binder of the conventional type, i. 0., one which is capable of being'subsequently removed from the pelleted product by combustion. The pellets of alumina and silica-alumina so obtained are then heated in an oxygen-containing atmosphere to a temperature sufiicient to burn out the binder. The pellets, after cooling, are than brought into contact with a solu- 8 7 tion containing platinum as ananio'n, the time of such contact being sufficient to fill the pores of the pelleted composite with impregnating solution. The impregnated pellets are thereafter removed from the solution and permitted to remain under non-drying conditions for a period of time sufficient to allow the platinum from the solution to reach an adsorption equilibrium between the alumina and silica-alumina surfaces. Such time may extend from about 15 minutes to 30 hours, depending on the size of the particles. The pelleted composite is thereafter dried and the deposited platinum compound is reduced to elemental platinum by treating with hydrogen. By following the foregoing procedure, substantially all of the platinurn is deposited on the alumina particles of the composite and very little is deposited on the silica-alumina component of the catalyst. The above procedure takes advantage of the relatively high adsorption constant of alumina for the platinum anion and the comparatively low adsorption constant of the silica-alumina component. Thus, it is estimated that, ,under the above-outlined conditions of impregnation, less than ,5 of the platinum deposited is laid down on the silica-alumina particles. Other of the inert carriers employed herein having a high adsorption constant for the platinum anion, such as activated carbon, may likewise be used in place of the alumina in the above method. It may be noted that silica, due to its relatively low adsorption constant for the platinum anion cannot be employed in the above procedure since the differential between the adsorption characteristics of silica and silica-alumina components is not sufficiently great to afford the desired selective adsorption of platinum on the inert carrier.

Cracking, in accordance with the present process, is generally carried out at a temperature between about 400 F. and about 825 F. and preferably between about 500 F. and about 800 F. The hydrogen pressure in such operation is generally within the range of about 100 and about 2500 pounds per square inch gage and preferably about 350 and 2000 pounds per square inch gage; The liquid hourly space velocity, i. e., the liquid volume of hydrocarbon per hour per volume of catalyst is between about 0.1 and about 10 and preferably between about 0.1 and about 4. In general, the molar ratio of hydrogen to hydrocarbon charge employed is between about 2 and about and preferably between about 5 and about 50.

Hydrocarbon charge stocks undergoing cracking in accordance with this invention comprise hydrocarbons, mixtures of hydrocarbons, and particularly hydrocarbon fractions having an initial boiling point of at least about 400 F., a 50 percent point of at least about 500 F., and an end boiling point of at least about 600 F., and boiling substantially continuously between said initial boiling point and said end boiling point. Such hydrocarbon fractions include gas oils, residual stocks, cycle stocks, whole topped crudes, and heavy hydrocarbon fractions derived by the destructive hydrogenation of coal, tars, pitches, asphalts, and the like. As will be recognized, the distillation of higher boiling petroleum fractions (above about 750 F. must be carried out under vacuum in order to avoidthermal cracking. The boiling temperatures utilized herein, however, are expressed for convenience in terms of the boiling point corrected to atmospheric pressure.

The term gas oil as employed in the art includes a variety of petroleum stocks. As utilized herein, this term, unless further modified, includes any fraction distilled from petroleum which has an initial boiling point of at least about 400 F., a 50 percent point of at least about 500 F. and an end boiling point of at least about 600 F. and boiling substantially continuously between the initial boiling point and the end boiling point. The exact boiling range of a gas oil accordingly will be determined by the initial boiling point, the 50 percent point, and by the end boiling point; In practice,pe'trole1im distillations have been eflected under vacuum at temperatures as high as 1200 F. (corrected to atmospheric pressure). Accordingly, in the broad sense, a gas oil is a petroleum fraction which boils substantially continuously within an approximate range of 400 F. to 1200 F., the 50 percent point being at least about 500 F. Thus, a gas oil may boil over the entire approximate range of 400 F. to 1200 F. or over an intermediate range such as 500 F. to 900 F.

A residual stock is any fraction which is not distilled. Accordingly, any fraction, regardless of its initial boiling point, which includes heavy bottoms, such as tars, asphalts, etc., is a residual fraction. A residual stock may be the portion of the crude remaining undistilled at about 1200 F. or it may be made up of a gas oil fraction plus the portion undistilled at about 1200 F.

A Whole topped crude is the entire portion of the crude remaining after the light ends; i. e., the portion boiling up to about 400 F. has been removed by distillation. Accordingly, such a fraction includes the entire gas oil fraction and the undistilled portion of the crude petroleum boiling above about 1200 F. If desired, the residual fractions and the whole topped crude may be deasphalted by any suitable well-known means. Such deasphalting treatment, however, is not considered necessary for charge stocks utilizable in the process of this invention.

The refractory cycle stocks are cuts of cracked stocks which boil above the gasoline boiling range usually between about 400 F. and about 850 F. The refractory cycle stocks can be charged to the process of this invention, together with a fresh petroleum charge stock or the refractory cycle stocks may be charged to the process alone. If desired, sulfur-containing charge stocks may be employed in the present process since the catalysts of this invention are not deactivated by sulfur compounds under the conditions of the process.

The collaborative but independent action of the metal and acid sites in cracking under conditions specified herein has been established by data set forth in Table I below. Thus, neither particles of an acid silica-alumina cogelled cracking catalyst of 14-20 mesh size containing 10 percent A1 and having an activity index (CAT A method) of 42 nor particles of 1420 mesh size containing 0.9 percent by weight of platinum supported on activated carbon alone accomplish cracking of a saturated hydrocarbon charge at 700 F. while the mechanical mixture of equal volumes of these two types of particles converted approximately 36% of the charge to products boiling in the gasoline range. The hydrocarbon charge employed was cetane. The reaction conditions involved a liquid hourly space velocity of 1, a H /HC ratio of 4:1, a temperature of 700 F., and atmospheric pressure. The results are shown below:

TABLE I Percent Vol. Example Catalyst Gasoline (525 F. E. P.)

Sim-A1203 1. 5 Pt on Activated Carbon 1.5 Mixture of above two 36. 0

Further evidence of the collaborative but independent action of the metal and acid sites of the present catalyst, as well as an illustration of the selective cracking achieved -by the instant process, is shown by the data contained i0 platinum supported on activated carbon, and an e ual volume mechanical mixture of these two are as follows:

The product distribution of the liquid cracked product obtained in Example 6 was as follows:

TABLE III Percent Carbon Chain Volume of Collected Liquid It will be noted from the above that the C7 fraction predominates, demonstrating that the reactions occurring under the conditions of the present process are selective forcenter cracking.

The independent action of the two catalyst components shown by the data of Tables I and II establishes that choice of support for the platinum metal component is not restricted to an acid cracking base such as heretofore conventionally employed. It is further evident that the ability to choose the amount of acid cracking component to be incorporated in the instant catalyst mixture allows the use of a cracking component having a wide range of surface area.

It is further evident from the data of Table III that the process of this invention is very selective. It is well known that, in cracking processes of the prior art; splitting of the carbon-carbon bond is random and uncontrolled so that cracking occurs at the end of the hydrocarbon chains, as well as near the center. As a result, large amounts of methane, ethane, etc., are produced. Consequently, large amounts of hydrogen are consumed in the production of undesirable products. The process of this invention, on the other hand, is selective for center cracking, i. e., breakage of the hydrocarbon chain near its middle. Both cracked fragments, therefore, have suflicient chain length to produce hydrocarbons useful in gasoline. As a result, the hydrogen consumed in the production of undesirable products is minimized.

The effect of particle size of the components making up the present catalyst mixture is shown by the comparative data set forth in Table IV below. The catalyst of Example 7 was composed of an equal volume mixture of particles of a cogelled silica-alumina component containing 10 percent A1 0 and having an activity index (CAT-A method) of 42 and particles of activated carbon having .9 percent by weight of platinum deposited thereon. The particle size of each of the above components was 1420 mesh. The catalyst of Example 8 was identical with that of Example 7 except that the particle size of each of the components was -200 mesh. The hydrocarbon charge employed was dodecane. The reaction conditions involved a liquid hourly space velocity of 0.5, a H /HC ratio of 4:1, a temperature of 700 F.,

' 11 and atmospheric pressure. The duration of the run was 1% hours. The results are shown below:

TABLE IV Percent Particle Vol. Gaso- Size line, 350 F. E. P.

Example Catalyst 7 Mixture of SiOr-AIZO: and Pt on 8 Apitivated Carbon 0......

Example 9 Silica gel particles of less than 200 mesh size having 0.71 percent by weight of platinum deposited thereon were mixed in the amount of 31.1 grams with 37.5 grams of silica-alumina gel particles of less than 200 mesh, containing 10 percent by weight of A1 and having an activity index of 46. The resulting mechanical mixture was pelleted without a binder under high pressure to M pellets.

The above catalyst was tested for cracking activity by contacting with a charge of dodecane, using a liquid hourly space velocity of 1, a H /HC ratio of 4:1, a temperature of 675 F., and atmospheric pressure. Under such conditions, the percent volume conversion to 350 F. E. P. products was 47.

Example Activated carbon particles of less than 200 mesh size having 2.1 percent by weight of platinum deposited thereon were mixed in the amount of 34 grams with 1010 grams of silica-alumina hydrogel having a dry solids content of about 9 percent by weight and in which about 10 percent by weight of the solids content was A1 0 After thorough admixture by ball milling, the resulting composite was pelleted under high pressure to pellets.

The above catalyst was tested for cracking activity by contacting with a charge of dodecane, using a liquid hourly space velocity of 1, a H /HC ratio of 4:1, a temperature of 675 F., and atmospheric pressure. Under such conditions, the percent volume conversion to 350 F. E. P. products was 30.

One of the advantages of the mixed catalyst system of this invention resides in the ability to use a variety of available starting materials. For example, spent cracking catalysts deactivated by age, having surface areas of bout 150 square meters per gram could be employed directly as a cracking component of the instant catalyst. in addition, since small amounts of metals which accumulate in catalytic cracking operations have no deletericus effect in the present operation, it is feasible to use metal-poisoned cracking catalyst, which would otherwise be discarded as useless, for the cracking component of the instant mechanical catalyst mixture.

The process of this invention accordingly affords complete and immediate flexibility in catalyst composition within the limits set forth hereinabove. Thus, in changing types of charge stocks, a catalyst compositioncan be adjusted immediately inaccordance with this invention by the adding or withdrawing one or the other catalyst component. The present process further affords considi2 erable flexibility in the nature of the product obtained. Thus, using a petroleum hydrocarbon fraction having the preferred boiling point characteristics set forth hereinabove, it is possible to provide substantially gasoline and fuel oil in any ratios depending upon the temperature of operation, other conditions being maintained constant. Thus, when operating at lower temperatures, substantially all of the charge can be converted into fuel oil. When operating at higher temperatures, on the other hand, substantially all the charge stock can be converted into substantially gasoline. When operating at intermediate temperatures, any ratio of fuel oil to substantially gasoline can be achieved. As will be appreciated, the ability to adjust catalyst composition, together with the flexibility in the nature of desired product upon change in temperature, is highly advantageous in a cracking operation.

The fact that the platinum metal and cracking catalyst components utilized in the present mechanical catalyst mixtures have generally different properties on the one hand but are seen to be operable as physically independent or separable entities. on the other hand, atfords a basis for improved cracking processes with regard to catalyst regeneration and methods for the recovery of the valuable platinum metal constituent of the catalyst after the same has become catalytically spent.

Thus, platinum-containing hydrocarbon conversion catalysts of the type heretofore employed, in which platinum is impregnated on a cracking base, have been regenerated by contacting the spent catalyst with air or other oxygen-containing gas at an elevated temperature sufiicient to burn carbonaceous deposits from the catalysts. Careful control of the rate of burning and temperature during regeneration of such catalysts has been necessary in order not to impair the catalytic activity of the platinum component. The usual procedure in effecting such regeneration has involved initial contact of the spent catalyst at a temperature in the range of 900 F. to 950 F. with a gas of low oxygen content (about 2 volume percent) and gradual increase of the oxygen concentration during the regeneration period until pure air or oxygen is being used. It is important in such procedures that the regeneration temperature be maintained below about 1000 F.

By utilizing the mechanical catalyst mixture of this invention, it is possible to provide means for ready regeneration of the cracking component without subjecting the platinum metal to the severity of such regeneration. Thus, the catalyst of the present invention, after becoming spent, may be separated into its components of platinum-containing particles and cracking catalyst particles by providing such components with a suitable different physical characteristic which permits their ready separation, such as a diiference in particle size. Thereafter,

the cracking component may be directly recycled to the reactor, discarded, or regenerated by contacting with an oxygen-containing gas, i. e., air for a sufficient time and at a sufficiently elevated temperature to burn carbonaceous material therefrom but under conditions such that sintering of the cracking component is not encountered. Generally these conditions are fulfilled by regenerating in air for a period in the range of 10 minutes to about 1 hour and at a temperature in the approximate range of 1000 F. to 1400 F. The separated platinum-containing component may likewise be directly recycled to the reactor, discarded, or regenerated by undergoing extraction with a suitable acid solution, such as aqua regia. The resulting acid solution of platinum may then be used in impregnation of fresh particles of inert carrier, which particles are subsequently recycled to the reactor. In those instances wherein a pelleted composite of cracking component and platinum-containing component is employed, the catalyst mixture may be separated into its components by initially crushing to a particle size comparable to or below the magnitude of the small constituent particles, and thereafter separating the component particles by flotation, air-blowing, sifting, or by any of the various other known means for separating physically and/ or chemically different materials. The separated cracking and platinumcontaining components may then be separately regenerated. The above methods applicable for regeneration of hydrocarbon conversion catalysts, consisting essentially of mechanical mixtures of a cracking component and a platinum-containing component, have been described in greater detail in my copending application Serial No. 442,975, filed July 13, 1954.

It is accordingly to be understood that the above description is merely illustrative of preferred embodiments of the invention, of which many variations may be made within the scope of the following claims by those skilled in the art without departing from the spirit thereof.

What is claimed:

1. A process for cracking a hydrocarbon charge which comprises contacting the same in the presence of hydrogen with a catalyst consisting essentially of a mechanical mixture of particles of less than 100 microns in diameter of (l) a porous inert carrier having deposited thereon between about 0.05 and about 10% by weight of a platinum metal and (2) an acidic cracking component, the relationship between the components making up said mixture being governed by the following expressions:

where O. C. I. is the olefinic cracking index of the acid cracking component, it is the weight fraction of acid crack ing component in the mixture, m is the weight fraction of inert carrier impregnated with platinum metal in the mixture, C is the platinum metal content expressed in Weight percent of the inert carrier and d is the density of the inert carrier in grams per cubic centimeter.

2. A process for cracking hydrocarbon fractions which comprises contacting a hydrocarbon fraction having an initial boiling point of at least about 400 F., a 50%- point of at least about 500 F. and an end point of at least about 600 F. and boiling substantially continuously between said initial boiling point and said end point, with a catalyst consisting essentially of a mechanical mixture of particles of less than 100 microns in diameter of (l) a porous inert carrier having deposited thereon between about 0.05 and about by weight of a platinum metal and (2) an acidic cracking component, the relationship between the components making up said mixture being governed by the following expressions:

where O. C. I. is the olefinic cracking index of the acid cracking component, n is the weight fraction of acid cracking component in the mixture, m is the weight fraction of inert carrier impregnated with platinum metal in the mixture, C is the platinum metal content expressed in weight percent of the inert carrier and d is the density of the inert carrier in grams per cubic centimeter, at a temperature between about 400 F. and about 825 F., a liquid hourly space velocity between about 0.1 and about 10 in the presence of hydrogen and with a net consumption of hydrogen, under a pressure between about 100 and about 2500 pounds per square inch gauge, employing a molar ratio of hydrogen to hydrocarbon charge between about 2 and about 80.

3. A process for cracking a hydrocarbon mixture which comprises contacting the same in the presence of hydrogen with a catalyst consisting essentially of a mechanical mixture of particles of less than about 100 microns in diameter of (1) a porous inert carrier having deposited thereon between about 0.1 and about 5% by weight of a metal selected from the group consisting of platinum and palladium and (2) an acidic cracking component consisting of the oxides of at least two elements selected from the groups consisting of groups 11A, 111B,

IVA and IVB of the periodic table, the relationship bewhere O. C. I. is the olefinic cracking index of the acid cracking component, n is the weight fraction of acid cracking component in the mixture, In is the weight fraction of inert carrier impregnated with a metal selected from the group consisting of platinum and palladium, C is the concentration of a metal selected from the group consisting of platinum and palladium expressed in weight percent of the inert carrier and d is the density of inert carrier in grams per cubic centimeter.

4. A process for cracking petroleum hydrocarbon stocks which comprises contacting a petroleum hydrocarbon stock having an initial boiling point of at least about 400 F., a 50%-point of at least about 500 F. and an end point of at least about 600 F. and boiling substantially continuously between said initial boiling point and said end point with a catalyst consisting essentially of a mechanical mixture of particles having a size in the approximate range of to 400 mesh and composed of (l) a porous inert carrier having deposited thereon between about 0.1 and about 5% by weight of platinum and (2) an acidic cracking component consisting essentially of at least two elements selected from the groups consisting of groups IIA, IIIB, IVA and IVB of the periodic table, the relationship between the components making up said mixture being governed by the following expressions:

where O. C. I. is the olefinic cracking index of the acid cracking component, 11 is the weight fraction of acid cracking component in the mixture, in is the weight fraction of inert carrier impregnated with platinum metal in the mixture, C is the platinum metal content expressed in weight percent of the inert carrier and d is the density of the inert carrier in grams per cubic centimeter, at a temperature between about 500 F. and about 800 F., a liquid hourly space velocity between about 0.1 and about 4 in the presence of hydrogen and with a net consumption of hydrogen, under a pressure between about 350 and about 2000 pounds per square inch gauge,

employing a molar ratio of hydrogen to hydrocarbon where O. C. I. is the olefinic cracking index of the silicaalumina cracking component, it is the weight fraction of silica-alumina cracking component in the mixture, m is the weight fraction of inert carrier impregnated with platinum in the mixture, C is the platinum content expressed in weight percent of the inert carrier and a is the density of the inert carrier in grams per cubic centimeter.

6. A process for cracking hydrocarbon fractions which comprises contacting a hydrocarbon fraction having an initial boiling point of at least about 400 F., a 50%- point of at least about 500 F. and an end point of at least about 600 F. and boiling substantially continuously between said initial boiling point and said end point with a catalyst consisting essentially of a mechanical mixture of particles of less than100'microns in diameter of'(l) a porous inert carrier having deposited thereon between about 0.05 andzibout by weight;

metal (m)-, the platinum metal content expressed in weight percent of the inert carrier-(C and the' density of the inert carrier in grams per cubic centimeter. ((1,)

being related in accordance with the expression:-

m C,,, d,=.01 to .8

said contact taking place at a temperature between about 400 F. and about 825'F., a liquid hourly space'velo'eity between about 0.1 and about 10 in the presence of hydrogen and with a net consumption of hydrogen, under a pressure between about 100 and about 2500 pounds per square inch gauge, employing a molarratio of hydrogen to hydrocarbon charge between about 2 and about 80.

7. A process for cracking petroleum hydrocarbon stocks which comprises'contacting a petroleum hydrocarbon-stock having an initial boiling point ofat least about 400 F., a 50%-point of at least about 500 and an end point of at least about 600 F. and boiling substantially continuously between said initial boiling point and said end point with a catalyst consisting essentially of a mechanical mixture made up of particles having a size in the approximate range of 100 to 400 mesh and composed of (1) 'a porousinert carrier of alumina having deposited thereon between about 0.05 and about 10% by weight of platinum and (2) a silica-alumina cracking component having 'an activityindex of between about 25 and about 50 and consisting between about .1 and'about .9 weight fraction of said mixture, the weight combining the regenerated componentsand recycling the fraction of said inert carrier impregnated :with platinum metal (m), the platinum metal content expressed in weight percent of the inert carrier (C and the density of the inert carrier in grams per cubic centimeter ((1 being related in accordance with the expression:

mxC Xd =.01 to .8

said contact taking place at a temperaturebetween about 500 F. and about 800 F., a liquid hourly space velocity between about 0.1 and about 4 in the presence of hydrogen and with a net consumption of hydrogen, under a pressure between about 350 and 2000 pounds per square inch gauge, employing a molar ratio of hydrogen to hydrocarbon charge between about 5 and about 50.

8. A process for cracking a hydrocarbon charge which comprises contacting the same in the presence of hydrogen with a catalyst consisting essentially of a mechanical mixture of particles of less than 100 microns indiameter of (1) a porous inert carrier vhaving deposited thereon between about 0.05 and about 10% by weight of a platinum metal and (2) an acidic cracking component, the relationship between'the components making up said mixture being governed'by the following expressions:'

n O. C. I.-=5 to 100 mXC Xd =.01' to .8

where O. C. I. is the olefinic cracking index'of the-acid" cracking component, ,n is theweight fraction of acid cracking component in the mixture, m is the weight fractionof inert carrier impregnated with-platinum 'metal per cubic centimeter, separating the aforesaid-mixture after cracking therewith into its components,'separately regenerating each of said components, combining 'the regenerated components and recycling the resulting eatalyst-mixture-to further contact with said hydrocarbon 16 9. 'A process for cracking hydrocarbon fractions which comprises contacting 'a hydrocarbon fraction having an initial boiling point of at least about 400 F., a 50%- point of at least about 500 F.and an end point of at least about 600 F. and boiling substantially continuously between said initial boiling point and said end point, with a catalyst consisting essentially of a mechanical mixture of particles of less than microns in diameter of (1)'a porous inert carrier having deposited thereon between about 0.05 and'about 10% by weight of a platinum metal and (2) an acidic cracking component, the relationship between the components making up said mixture being governed by the following exwhere O. C. I. is the olefinic cracking index of the acid cracking component, n is the weight fraction of acid cracking component in the mixture, In is the weight fraction of inert carrier impregnated with platinum metal in the mixture, C is the platinum metal content expressed in weight percent of the inert carrier and d is the density of the inert carrier in grams per cubic centimeter, at a temperature between about 400 F. and about 825 F., a liquid hourly space velocity between about 0.1 and about 10 in the presence'of hydrogen and with a net consumption of hydrogen, under a pressure. between about 100 and about 2500' pounds per square inch gauge, employing a molar ratio of hydrogen to hydrocarbon charge between about 2 and about 80, separating the aforesaid mixture after cracking therewith into its components, separately regenerating each of said components,

resulting catalyst mixture to further contact with said hydrocarbon fraction.

10. A catalyst consisting essentially of a mechanical mixture of particles of less than 100 microns in diameter of (1) a porous inert carrier having deposited thereon between about 0.05 and about 10% by weight of a platinum metal and (2) an acidic cracking component, the relationship between the components making up said mixture being governed by the following expressions:

where O. C. I. is the olefinic cracking index of the acid cracking component, n is the weight fraction of acid cracking component in the'mixtureym is the weight fraction of inert carrier impregnated with platinum metal in the mixture, C is the platinum metal content expressed diameter of (1) a porous inert carrier having deposited 1 thereon between about 0.1 and about 5% by weight of a metal selected from the group consisting of platinum. and palladium and (2) an acidic cracking component consisting of the oxides of at least two elements selected from the groups consisting of groups IIA, IIIB, IVA and IVB of the periodic table, the" relationship between the components making up said'mixture being governed by the following expressions:

nXO.C.I.=25 to 100 v mXC Xd =.01 to .8

inert carrier impregnated with a metal'selected from the group consisting of platinum and palladium, C is the concentration of a metal selected from'thegroup eon- "-sisting of platinum. andrpalladium expressed :in weight 17 percent of the inert carrier and d, is the density of inert carrier in grams per cubic centimeter.

12. A catalyst consisting essentially of a mechanical mixture of particles of less than 100 microns in diameter of (l) a porous inert carrier of alumina having deposited thereon between about 0.05 and about 10% by weight of platinum and (2) a silica-alumina cracking component having an activity index of between about 25 and about 50 and constituting between about .1 and about .9 weight fraction of said mixture, the weight fraction of said inert carrier impregnated with platinum metal (In), the platinum metal content expressed in Weight percent of the inert carrier (C and the density of the inert carrier in grams per cubic centimeter (d,,) being related in accordance with the expression:

mXC Xd =.01 to .8.

References Cited in the file of this patent UNITED STATES PATENTS UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,854,401 September 30, 1958 Paul B, Weisz It is herebfl certified that error appears in the-printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 5, line 16, for 'silicaalumania thoria" read silicaalumina -thoria column 6, lines 14 and 15, for "conversions" read conversion column-14, line 53, for "insert" read w inert i-'-; column 15, line 35, for "consisting" read we constituting Signed and sealed this 10th day of March 1959,

I (SEAL) Attest:

KARL H. AXLINE ROBERT C. WATSON Commissioner of Patents Attesting Oflicer

Claims

1. A PROCESS FOR CRACKING A HYDROCARBON CHARGE WHICH COMPRISES CONTACTING THE SAME IN THE PRESENCE OF HYDROGEN WITH A CATALYST CONSISTING ESSENTIALLY OF A MECHANICAL MIXTURE OF PARTICLES OF LESS THAN 100 MICRONS IN DIAMETER OF (1) A POROUS INERT CARRIER HAVING DEPOSITED THEREON BETWEEN ABOUT 0.05 AND ABOUT 10% BY WEIGHT OF A PLATINUM METAL AND (2) AND ACIDIC CRACKING COMPONENT, THE RELATIONSHIP BETWEEN THE COMPONENTS MAKING UP SAID MIXTURE BEING GOVERNED BY THE FOLLOWING EXPRESSIONS: