US3929619A - Hydrocracking process with tri-metallic catalyst - Google Patents

Abstract

The instant invention relates to a novel hydrocracking process wherein carbon-carbon bonds are ruptured and carbon-hydrogen bonds are formed in the presence of hydrogen and a catalyst comprising platinum, iridium and rhodium supported on an inorganic refractory oxide. This process relates to the dealkylation of alkyl aromatics to form lower molecular weight aromatics, for example, alkylbenzenes such as ethylbenzene, xylene, toluene, etc. may be converted to benzene in the process of the instant invention. The process can also be used to convert a gas-oil fraction to gasoline by converting the higher molecular weight constituents of the gas-oil fraction to lower molecular weight products.

Description

United States Patent Sinfelt et al.

HYDROCRACKING PROCESS WITH TRl-METALLIC CATALYST lnventors: John H. Sinfelt, Berkeley Heights;

Allan E. Barnett; James L. Carter, both of Westfield, all of NJ.

Exxon Research & Engineering Co., Linden, NJ,

Filed: Jan. 30, 1975 Appl. N0.: 545,371

Related US. Application Data Continuation-impart of Ser. No. 380,833, July 19, 1973, Pat. No. 3,871,996.

Assignee:

US. Cl 208/111; 208/112; 252/455 R; 252/460; 252/463; 252/472; 260/672 R Int. Cl. C10G 13/06; CO7C 3/58 Field of Search 208/111, 112; 260/672 R; 252/460, 463, 472

References Cited UNlTED STATES PATENTS 2/1916 Mittasch 252/466 PT 2/1954 Strecker 4/1954 Rosenblatt... 252/466 PT Primary ExaminerDelbert E. Gantz Assistant ExaminerG. E. Schmitkons Attorney, Agent, or FirmRobert J. Baran [57] ABSTRACT The instant invention relates to a novel hydrocracking process wherein carbon-carbon bonds are ruptured and carbon-hydrogen bonds are formed in the presence of hydrogen and a catalyst comprising platinum, iridium and rhodium supported on an inorganic refractory oxide. This process relates to the dealkylation of alkyl aromatics to form lower molecular weight aromatics, for example, alkylbenzenes such as ethylbenzene, xylene, toluene, etc. may be converted to benzene in the process of the instant invention. The process can also be used to convert a gas-oil fraction to gasoline by converting the higher molecular weight constituents of the gas-oil fraction to lower molecular weight products.

12 Claims, No Drawings HYDROCRACKING PROCESS WITH TRI-METALLIC CATALYST H. Sinfelt, A. E. Barnett, and]. L. Carter, now US. Pat. No. 3,871,996 issued Mar. 18, 1975.

FIELD OF THE INVENTlON The instant invention relates to a novel hydrocracking process wherein carbon-carbon bonds are ruptured and carbon-hydrogen bonds are formed in the presence of hydrogen and a catalyst comprising platinum, iridium and rhodium supported on an inorganic refractory oxide. This process relates to the dealkylation of alkyl aromatics to form lower molecular weight aromatics, for example, alkylbenzenes such" as ethylbenzene, xylene, toluene, etc. may be converted to benzene in the process of the instant invention.The process can also be used to convert a gas-oil fraction to gasoline by converting the higher molecular weight constituents of the gas-oil fraction to lower molecular weight products.

BACKGROUND OF THE PRIOR ART Hydro processes are catalytic processes carried out in the presence of hydrogen, wherein hydrocarbon feed streams undergo hydrocracking, hydrogenolysis, hydrogenation, hydroisomerization and hydrodealkylation reactions. In these processes the main reactions which take place are the cracking of hydrocarbons, that is, carbon-carbon bonds are ruptured with a net formation of carbon-hydrogen bonds. These processes also include removal of sulfur and nitrogen impurities as H 8 and NH Other reactions which take place in the hydrocarbon feed streams during hydro processing include isomerization of paraffinic hydrocarbons and removal of alkyl groups from alkyl aromatic hydrocarbons. Some specific examples of deak-ylation reactions include dealkylation of alkylbenzenes and alkylnaphthalenes to form lower molecular weight aromatics. For example, methyl and ethylnaphthalene can be converted to naphthalene and ethylbenzene and xylene may be converted to benzene and toluene. Thus, it is evident that the dealkylation of alkyl aromatics is a specie of the general hydrocracking processes known in the art.

In hydro processes the presence of hydrogen is necessary to yield saturated products and suppress formation of deactivating carbonaceous residues as well as to allow removal of sulfur and nitrogen impurities as H 5 and NH Materials which may be hydro processed include petroleum, coal, shale oil and tar. The process of the instant invention is concerned mainly with hydro processes wherein there is no net removal of hydrogen, that is, the process of the instant invention does not include catalytic reforming.

The instant invention is mainly concerned with the hydrocracking of hydrocarbon feed streams. Catalysts which are useful in hydrocracking processes are bifunctional catalysts that contain sites for bothcracking and hydrogenation. The two sites are preferably in close proximity .to minimize fouling of the-catalyst by deposition of sulfur, nitrogen and coke.

The hydrogenation activity is usually supplied'by a metal which is deposited .on a support which will have acidic sites to provide the cracking activity. Supports which'may be used include acidic refractory oxides such as alumina, silica alumina, etc. Silica aluminas include zeolite supports, i.e., crystalline alumino silicates. In these bifunctional catalysts, a principal role of themetal hydrogenation site is to keep the acid sites clean and effective by hydrogenating the coke precursors which block the acid sites. The metal must be highly dispersed to support this hydrogenation activity.

' The prior art hydrocracking catalysts include cobaltmolybdate catalysts, and tungsten sulfide on clay. These catalysts have been substantially replaced by the palladium on zeolite catalyst which has higher activity. This catalyst can be operated at a lower temperature thereby reducing the deactivation rate. This catalyst also has a higher activity maintenance in the presence of nitrogen and sulfur compounds in the feed.

The supported platinum-iridium-rhodium catalyst of the instant invention, which is further described below, shows an even lower rate of deactivation by coke, as well as at least similar activity maintenance in the presence of nitrogen and sulfur impurities. It is found that this trimetallic combination of active metals provides an effective hydrogenation site, in a manner similar to palladium, but, unlike palladium, contributes a great degree of hydrocracking activity. Thus, this very active trimetallic combination may be supported on materials that are less acidic than zeolites, such as alumina, and still function as an effective hydrocracking catalyst.

Prior art hydro processes for the dealkylation of aromatics to form benzene and naphthalene from their alkylated precursors employ catalyst such as chromiaalumina, cobalt-molybdenum-alumina, nickel-alumina, silica-alumina, nickel-chromia-alumina and cobaltchromium-molybdenum-alumina. These catalysts have been replaced in some of the more recent processes by noble metal catalysts which have higher activity and activity maintenance and also provide improved selectivity to the desired aromatic product. In the dealkylation of alkylbenzenes and alkylnaphthalenes the trimetallic catalysts of the instant invention show improved activity and activity maintenance over the prior art noble metal catalysts SUMMARY OF THE INSTANT INVENTION The instant invention relates to a process for the hydrocracking of petroleum feed streams. In this process, the petroleum feed stream is contacted with a catalyst comprising platinum, iridium and rhodium supported on an inorganic refractory oxide in the presence of hydrogen to yield a petroleum fraction characterized as having a lower average molecular weight than the starting feed stream. In this process, carboncarbon bonds are ruptured and there is a net formation of carbon-hydrogen bonds.

The petroleum feed stream may range from heavy naphtha to a deasphalted residuum and may contain sulfur and nitrogen impurities. in a preferred embodiment of the instant invention, an alkylbenzene or an alkylnaphthalene-containing feed stream is contacted with the platinum-iridium-rhodium catalyst of the instant invention under conditions whereby the alkyl aromatics are converted to benzene and naphthalene respectively in the presence of hydrogen.

The catalyst compositions used in the process of the present invention comprise platinum, iridium and rhodium in a highly dispersedrnetallic state on a refractory support. The catalysts will comprise at least 0.05 wt.

rhodium, at least 0.1 wt. platinum, and'at lea'st 0.1 wt. iridium based on total catalyst weight. Preferably, the catalyst compositions of the instant invention will comprise from 0.1 to 1.0 wt platinum, from 0.1 to 1.0 wt. iridium, and from 0.05- to 0.5 wt.v% rhodium. The total metal surface area 'of the catalyst pref,- erably is at least 200 square meters'per gram of said total metaL'as-determined bythe gas chemisorption method described by Sinfelt and Yates, J. Catalysis, 8, 82-90 (1967). The catalyst support is preferably substantially free of alkali or alkaline earth metal compounds and, as further described below, will give most effective performance when prepared in a manner avoiding exposure'of the catalyst to air or oxygen at temperatures above about 425C. When'the catalysts are prepared in this manner, highly dispersed multimetallic clusters are formed, which are preferred to the compositions prepared by the general. techniques known in the art for preparing reforming catalysts, i.e., calcination in air at temperatures of 500C. or higher.

The catalyst of theinstant invention is preferably prepared by coimpregnation of the supports using a solution of the catalyst metal precursors. However, in the case where a zeolite is used as the support material ion exchange of the metals into the zeolite is an alternate preferred method of depositing the metals onto the support. [on exchange of metals into zeolites is well known in the art. coimpregnation or in the case of zeolite supports ion exchange using a single solution comprising the precursors for all three metals dissolved therein is generally favored over sequential techniques to enhance the formation of trimetallic clusters. It should especially be noted that such cluster formation is desirable in preparing the instant trimetallic catalysts. Thus, the preparation of the catalystsof the instant invention comprises contacting a solution of soluble metallic precursors with the support at suitable impregnating or ion exchange conditions. The catalyst metal precursor-solution is preferably aqueous and precursor compounds may beselected from the group consisting of chloroplatinic acid, chloroiridic acid, rhodium trichloride, iridium trib romide, ammonium chloroiridate, ammonium chloroplatinate, platinum amine salts, rhodiumnitrate, etc. In general, anyprecursor salt which is water soluble may be used. The impregnated or ion exchanged catalyst is then dried. During drying, it is important that the catalyst not be contacted withoxygen if the temperature of drying exceeds about 425C. The catalyst may be driedby contacting with an inert gas or by applying a vacuum to said impregnated or io'n exchanged catalyst. The catalyst, when sufficiently dried, is contacted with a reducing atmosphere to reduce the metallic precursors to the desired metallic form. Preferably,'the catalyst is reduced in hydrogen. The catalyst is then a dispersed p'olymetallic cluster. The metallic atoms which constitute the cluster will Refractory inorganic oxide materials such as alumina, silica'alum in'a, and alumino silicates are the preferred catalyst support materials. In general, superior results 'are ,obtained when acidic supports are employed. Aluminasandsi lica-aluminas, including zeolites, are the preferred support materials. The support materials mentioned above are'known articles of commerce 'andcan beprepared'for use as catalyst constituents by many varied techniques. Typically, the support materials are used in the form of spheres, granules, powders, extrudates or pellets, etc. Theprecise size or shape of the'support material used isdependent upon many engineering factors not within the purview of the instant invention. 1

The platinum, iridium, and rhodium exist as components of a polymetallic clusteron the surface of the refractory support. Improved catalyst performance is l obtained 'when'the catalyst is prepared inv the manner [described above, which favors formation of dispersed multimetallic' clusters rather than separate crystallites of the individual metalsz As disclosed hereinabove, at

least'0.05 wt'. rhodium, 0.1 wt. platinum, and 0.1 wt. iridium must be present. Total metal-concentra- 'tion of the catalyst should be from 0.25 to 2.5 wt; As

is known to those familiar with the hydroprocessing of petroleum feed streams the metals utilizedinthe instant catalyst are costly, and thus minimum amounts must be utilized as long as said minimum amount does be separated by distances of about 2.5 to 4 Angstroms,

and the average distance between the polymetallic cluster centers is at least 10 times the average distance between the atoms within a cluster.

The support or carrier component of the catalysts of .the present invention is preferably a porous, adsorptive material having a surface area, as determined by the Brunauer-Emmett-Teller (BET) metho'chof about20 to 800, preferably 100 to 300, square meters/gram, The support material should be substantiallyrefractory at the temperature and pressure conditionsutilized in any given hydrocarbon conversion process.

As is taught in U.S. Ser. No. 194,461, filed in the names of J. H. Sinfelt and A. E. Barnett, on November 1, 1971, herein incorporated by reference, iridiumcontaining catalysts mustbe treated carefully to obtain maximum surface area. Thus, itis critical to the instant invention that prior to reduction to the metal the iridium does not exist in the form of large crystallites of iridium oxide, since iridium crystallites of low surface area will be obtained on reduction of said large'crystallites. Agglomerated iridium, however, can be redispersed' by contacting with halogen-containing gases, e.g., chlorine, in a substantial absence of oxygen as disclosed in-'U.S. Ser. No. 343,304, filed on Mar. 21, 1973, in the name of D. J .C. Yates, and herein incorporated by-tefere'nce. The'techniques which are-disclosed in U.S. 'Ser. No. 343,304 may be conveniently used with the catalyst of the instant-invention.

The catalyst used in the process of the instant invention is effective in the presence 'of feedsulfur levels of from 0.1 to 3 percent by weight, i .e., those levels which may be encountered in hydrocracking heavier-petroleum fractions. However, the performance. of the catalyst system of the present invention may be affected by the presence of sulfur or sulfur-containing materials arising from the feed stock or other sources, as when used in the'dealkylation of alkyl aromatics. Accordingly when the catalyst is employed for dealkylation of alkyl aromatics, the sulfur content of the catalyst is preferably maintained at a level less than about: two

atoms of sulfur, preferably less than one atom of sulfur, perfatom of iridium and additional catalyst metals. The desired low-"catalyst sulfur levels-are advantageously maintained during the predominant portion of any dealkylation cycle. Higher catalyst sulfurlevels may be encountered'd'uring some portions-of a run in which case thesulfur' maybe at least partially removed from '5 the catalyst by contacting the same with sulfurfree feed stock. Finally, the catalyst 'should be substantially free of alkali metal (Group vlA-);or alkaline earth metal (Group llA') constituents; (less' t han 0.1: wt: since the presence of basic components on the catalyst serves to inhibithydrocracking activity. w .1

Following the impregnation of the support with the catalyst metal precusors, the catalystmay be dried at a temperature varying from about 100 to 125C. The catalyst may simply be dried in air at the above-stated temperatures or may be dried by treating the catalyst in a flowing stream of inert gas or hydrogen. The drying step may be followed by an additional calcination step at a temperature of about 260to 370C. Care must be taken to avoid contacting the catalyst at temperatures in excess of about 370 to 425C. with air .or other gas of high oxygen concentration. Otherwise the iridium will be oxidized, with loss of surface area, to crystallites of iridium oxide, and the polymetallic cluster structure will not be obtained on reduction.

Additional materials may be present in the catalyst to promote the desired reactions. For example, ifalumina is the support, halogens such as chlorine or fluorine may be incorporated in the catalyst to enhance the acidity. The halogen may be incorporated during the catalyst preparation using, for example, HCl or HP. Alternatively, it may be incorporated after the catalyst is charged to a reactor in a manner analogous to the chlorine treating of reforming catalysts.

The catalyst compositions of the present invention have uses in processes other than hydrocracking. For example, the catalysts can be employed in the formation of aromatic compounds by contacting the catalyst with suitable paraffins or naphthenes at a temperature varyi ng between about 370 and 540C. and a pressure of less than about atmospheres in the presence of hydrogen. The catalysts of this invention can also be employed to promote the isomerization of ethylbenzene to xylenes by contacting ethylbenzene with the catalyst at a temperature varying from about 200 to 600C. at elevated pressures in the presence of hydrogen. The catalysts are also useful for promoting hydrogenation, oxidation, polymerization, condensation and other reactions known to the art.

In a typical hydrocracking process, a petroleum feed stream which contains various high molecular weight hydrocarbons known in the art to undergo hydrocracking reactions, such as alkyl aromatics, is contacted with the above-described catalysts in the presence of hydrogen. The petroleum feed stream typically contains components boiling in the range of 100 to 600C. and as will be known by those skilled in the art, may be any cut from a deasphalted residua to a heavy naphtha. The temperature of contacting is typically from 200 to 600C., more preferably from 300 to 500C. The pressure of contacting is typically from 100 to 10,000 psi, more preferably from 200 to 3,000 psi. The petroleum feed stream is passed over the catalyst at space velocities varying from about 0.2 to 5.0 parts by weight of feed stream per hour per part by weight of catalyst (W/Hr/W The mole ratio of hydrogen to hydrocarbon maintained within the reaction zone is between about 1 and 20.

The catalyst is typically used as a fixed bed in a single reactor or in a series of reactors. Alternatively, the catalyst could be employed in a fluidized bed or ebulliating bed reactor or in a slurry reactor, depending on the particular application.

The hydrocracking process generally involves the ruptureof carbon-carbon bonds and the net formation of carbon-hydrogenbonds, with a resulting decease in the average molecular weight of the petroleum feed stream. Thus, typically, alkyl aromatics are converted to lower molecular weight aromatics. For example, alkylnaphthalenes and alkylbenzenes are converted to naphthalene-and benzene respectively. Thus, the process is useful for converting low value feed streams into higher value aromatic fractions. 1

An outstanding feature of the instant platinum-iridium-rhodium catalyst is its ability to maintain its catalytic activity at commercially desirable levels for protracted periods of time. In a typical commercial hydrocracking process, the reaction temperature is increased during the course of the run to maintain conversion at a given leveL Raisin g the reaction temperature is necessary because thecatalyst is continuously deactivated as coke is deposited on the surface. Unfortunately, the reaction temperature cannot be raised much beyond about 525C. before rapid catalyst deactivation commences. Therefore, as the reaction temperature approaches about 525C., it is necessary to regenerate or replace the catalyst. Typically, a regeneration operation consists of burning the coke deposits from the catalyst and may also include treating the catalyst with a gas containing chlorine, HCl, organic chlorides or mixtures thereof to incorporate halogen in the catalyst.

It is desirable to increase the duration of the periods between process start-up and catalyst regeneration and/or between catalyst regenerations since valuable production time is lost when the catalyst is being regenerated. As noted above, the present platinum-iridiumrhodium catalyst needs to be regenerated very infre quently.

EXAMPLE 1 A feed stream of vacuum gas oil with a boiling range of 300 to 490C, A.P.l. Gr. 21.7, aniline point of 69C., 0.6 wt. sulfur and 2,400 wt ppm nitrogen is passed over a catalyst consisting of 0.3% Pt, 0.15% Rh, 0.15% Ir and 0.6% Cl on alumina. The pressure is 2,500 psig, the H rate is 8,000 SCF/BBl of feed, the temperature is 425C and the space velocity is adjusted to obtain the desired conversion level. The product has a much lower average molecular weight and 50 vol. of the product boils in the gasoline range.

EXAMPLE 2 Meta xylene and hydrogen are passed over a catalyst consisting of 0.3% Pt, 0.15% lr, 0.15% Rh, and 0.6-1.5% Cl on alumina at a pressure of 150-250 psig and at temperatures of 500550C. The mole ratio of hydrogen to meta xylene is 3-5. The extent of conversion of m-xylene to benzene and toluene is 50-75 percent, depending on the liquid hourly space velocity and the length of time on stream.

What is claimed is:

l. A process for hydrocracking a petroleum feed stream which comprises contacting said feed stream with a catalyst comprising platinum, iridium and rhodium supported on an inorganic refractory oxide in the presence of hydrogen at reaction conditions whereby a petroleum fraction characterized as having a lower average molecular weight than the starting feed stream is obtained.

2. The process of claim 1 wherein said petroleum feed stream has a boiling point of from about to 7 about 600C.

3. The process of claim 1 wherein 'said support is selected from the group consisting of alumina, silicaaluminas and aluminosilicates. I

4. The process of claim 3 wherein said support is selected from the group consisting of alumina and silica aluminas.

5. The process of claim 4 wherein said catalyst comprises from 0.1 to 1.0 wt. platinum, from 0.1 to 1.0 wt. iridium, and from 0.05 to 0.5 wt. rhodium.

6. The process of claim 5 wherein said reaction conditions comprise contacting said petroleum feed stream with said catalyst at a temperature of from 200 to 600C and a pressure of from 100 to 10,000 psi.

7. The process of claim 6 wherein said petroleum feed stream is passed over the catalyst at a space velocity varying from about 0.2 to 5.0 parts by weight of feed stream per hour per part by weight of catalyst.

1 8. The process of claim 7 wherein the mole ratio of hydrogen to hydrocarbon maintained within the reaction zone is between about 1 and 20.

9. The process of claim 2 wherein said petroleum feed stream comprises an alkyl aromatic and said reaction product comprises a lower molecular weight aromatic.

10. The process of claim 9 wherein said alkyl aromatic is an alkyl naphthalene, which is converted into naphthalene.

11. The process of claim 9 wherein said alkyl aromatic is an alkyl benzene which is converted to a mixture of lower molecular weight alkyl aromatics and benzene.

12. The process of claim 9 wherein said alkyl aromatic is an alkyl benzene which is converted into benzene.

Claims (12)

1. A PROCESS FOR HYDROCRACKING A PETROLEUM FEED STREAM WHICH COMPRISES CONTACTING SAID FEED STREAM WITH A CATALYST COMPRISING PLATINUM, IRIDIUM AND RHODIUM SUPPORTED ON AN INORGANIC REFRACTORY OXIDE IN THE PRESENCE OF HYDROGEN AT REACTION CONDITIONS WHEREBY A PETROLEUM FRACTION CHARACTERIZED AS HAVING A LOWER AVERAGE MOLECULAR WEIGHT THAN THE STARTING FEED STREAM IS OBTAINED.

2. The process of claim 1 wherein said petroleum feed stream has a boiling point of from about 100* to about 600*C.

3. The process of claim 1 wherein said support is selected from the group consisting of alumina, silica-aluminas and aluminosilicates.

4. The process of claim 3 wherein said support is selected from the group consisting of alumina and silica aluminas.

5. The process of claim 4 wherein said catalyst comprises from 0.1 to 1.0 wt. % platinum, from 0.1 to 1.0 wt. % iridium, and from 0.05 to 0.5 wt. % rhodium.

6. The process of claim 5 wherein said reaction conditions comprise contacting said petroleum feed stream with said catalyst at a temperature of from 200* to 600*C and a pressure of from 100 to 10,000 psi.

7. The process of claim 6 wherein said petroleum feed stream is passed over the catalyst at a space velocity varying from about 0.2 to 5.0 parts by weiGht of feed stream per hour per part by weight of catalyst.

8. The process of claim 7 wherein the mole ratio of hydrogen to hydrocarbon maintained within the reaction zone is between about 1 and 20.

9. The process of claim 2 wherein said petroleum feed stream comprises an alkyl aromatic and said reaction product comprises a lower molecular weight aromatic.

10. The process of claim 9 wherein said alkyl aromatic is an alkyl naphthalene, which is converted into naphthalene.

11. The process of claim 9 wherein said alkyl aromatic is an alkyl benzene which is converted to a mixture of lower molecular weight alkyl aromatics and benzene.

12. The process of claim 9 wherein said alkyl aromatic is an alkyl benzene which is converted into benzene.