Hydrocarbon Conversion With a Sulfided Acidic Multimetallic Catalytic Composite

The subject of the present invention is a novel sulfided acidic multimetallic catalytic composite which has exceptional activity and resistance to deactivation when employed in a hydrocarbon conversion process that requires a catalyst having both a hydrogenation-dehydrogenation function and a cracking function. More precisely, the present invention involves a novel dual-function sulfided acidic multimetallic catalytic composite which, quite surprisingly, enables substantial improvements in hydrocarbon conversion processes that have traditionally used a dual-function catalyst. In another aspect, the present invention comprehends the improved processes that are produced by the use of a sulfided acidic catalytic composite comprising a combination of catalytically effective amounts of a platinum or palladium component, a rhodium component, a lead component, a halogen component, and a sulfur component with a porous carrier material specifically, an improved reforming process which utilizes the subject catalyst to improve activity, selectivity and stability characteristics.

Composites having a hydrogenation-dehydrogenation function and a cracking function are widely used today as catalysts in many industries, such as the petroleum and petrochemical industry, to accelerate a wide spectrum of hydrocarbon conversion reactions. Generally, the cracking function is thought to be associated with an acid-acting material of the porous, adsorptive, refractory oxide type which is typically utilized as the support or carrier for a heavy metal component such as the metals or compounds of metals of Groups V through VIII of the Periodic Table to which are generally attributed the hydrogenation-dehydrogenation function.

These catalytic composites are used to accelerate a wide variety of hydrocarbon conversion reactions such as hydrocracking, isomerization, dehydrogenation, hydrogenation, desulfurization, cyclization, polymerization, alkylation, cracking, hydroisomerization, etc. In many cases, the commercial applications of these catalysts are in processes where more than one of the reactions are proceeding simultaneously. An example of this type of process is reforming wherein a hydrocarbon feed stream containing paraffins and naphthenes is subjected to conditions which promote dehydrogenation of naphthenes to aromatics, dehydrocyclization of paraffins to aromatics, isomerization of paraffins and naphthenes, hydrocracking of naphthenes and paraffins and the like reactions, to produce an octane-rich or aromatic-rich product stream. Another example is a hydrocracking process wherein catalysts of this type are utilized to effect selective hydrogenation and cracking of high molecular weight unsaturated materials, selective hydrocracking of high molecular weight materials, and other like reactions, to produce a generally lower boiling, more valuable output stream. Yet another example is an isomerization process wherein a hydrocarbon fraction which is relatively rich in straight-chain paraffin components is contacted with a dual-function catalyst to produce an output stream rich in isoparaffin compounds.

Regardless of the reaction involved or the particular process involved, it is of critical importance that the dual-function catalyst exhibit not only the capability to initially perform its specified functions, but also that it has the capability to perform them satisfactorily for prolonged periods of time. The analytical terms used in the art to measure how well a particular catalyst performs its intended functions in a particular hydrocarbon reaction environment are activity, selectivity, and stability. And for purposes of discussion here, these terms are conveniently defined for a given charge stock as follows: (1) activity is a measure of the catalyst's ability to convert hydrocarbon reactants into products at a specified severity level where severity level means the conditions used-- that is, the temperature, pressure, contact time and presence of diluents such as H.sub.2 ; (2) selectivity refers to the amount of desired product or products obtained relative to the amount of reactants charged or converted; (3) stability refers to the rate of change with time of the activity and selectivity parameters;13 obviously, the smaller rate implying the more stable catalyst. In a reforming process, for example, activity commonly refers to the amount of conversion that takes place for a given charge stock at a specified severity level and is typically measured by octane number of the C.sub.5 + product stream; selectivity refers to the amount of C.sub.5 + yield, relative to the amount of the charge, that is obtained at the particular activity or severity level; and stability is typically equated to the rate of change with time of activity, as measured by octane number of C.sub.5 + product, and of selectivity as measured by C.sub.5 + yield. Actually, the last statement is not strictly correct because generally a continuous reforming process is run to produce a constant octane C.sub.5 + product with severity level being continuously adjusted to attain this result; and furthermore, the severity level is for this process usually varied by adjusting the conversion temperature in the reaction zone so that, in point of fact, the rate of change of activity finds response in the rate of change of conversion temperatures and changes in this last parameter are customarily taken as indicative of activity stability.

As is well known to those skilled in the art, the principal cause of observed deactivation or instability of a dual-function catalyst when it is used in a hydrocarbon conversion reaction is associated with the fact that coke forms on the surface of the catalyst during the course of reaction. More specifically, in these hydrocarbon conversion processes, the conditions utilized typically result in the formation of heavy, high molecular weight, black, solid or semi-solid, carbonaceous material which is a hydrogen-deficient polymeric substance having properties akin to both polynuclear aromatics and graphite. This material coats the surface of the catalyst and thus reduces its activity by shielding its active sites from the reactants. In other words, the performance of this dual-function catalyst is sensitive to the presence of carbonaceous deposits or coke on the surface of the catalyst. Accordingly, the major problem facing workers in this area of the art is the development of more active and selective catalytic composites that are not as sensitive to the presence of these carbonaceous materials and/or have the capability to suppress the rate of the formation of these carbonaceous materials on the catalyst. Viewed in terms of performance parameters, the problem is to develop a dual-function catalyst having superior activity, selectivity and stability. In particular, for a reforming process the problem is typically expressed in terms of shifting and stabilizing the C.sub.5 + yield-octane relationship at the lowest possible severity level-- C.sub.5 + yield being representative of selectivity and octane being proportional to activity.

I have now found a dual-function sulfided acidic multimetallic catalytic composite which possesses improved activity, selectivity and stability characteristics when it is employed in a process for the conversion of hydrocarbons of the type which have heretofore utilized dual-function acidic catalytic composites such as processes for isomerization, hydroisomerization, dehydrogenation, desulfurization, denitrogenization, hydrogenation, alkylation, dealkylation, disproportionation, polymerization, hydrodealkylation, transalkylation, cyclization, dehydrocyclization, cracking, hydrocracking, halogenation, reforming and the like processes. In particular, I have ascertained that a sulfided acidic catalyst, comprising a combination of catalytically effective amounts of a platinum or palladium component, a rhodium component, a lead component, a halogen component and a sulfur component with a porous refractory carrier material, can enable the performance of hydrocarbon conversion processes utilizing dual-function catalysts to be substantially improved if the metallic components are uniformly dispersed throughout the carrier material, if their oxidation states are controlled to be in the states hereinafter specified, and if the catalyst is sulfided in the manner indicated herein before use in the conversion of hydrocarbons and after substantially all of the platinum or palladium and rhodium components contained therein are reduced to the elemental metallic state. Moreover, I have determined that a sulfided acidic catalytic composite, comprising a combination of catalytically effective amounts of a platinum or palladium component, a lead component, a rhodium component, a chloride component and a sulfur component with an alumina carrier material, can be utilized to substantially improve the performance of a reforming process which operates on a low-octane gasoline fraction to produce a high-octane reformate if the metallic components are uniformly dispersed throughout the alumina carrier material, if the oxidation states of the metallic components are fixed in the states hereinafter specified and if the catalyst is sulfided according to the procedure specified herein before use in the conversion of hydrocarbons. In the case of a reforming process, the principal advantage associated with the use of sulfided acidic multimetallic catalyst of the present invention involves the acquisition of the capability to operate in a stable manner in a high severity operation; for example, a low pressure reforming process designed to produce a C.sub.5 + reformate having an octane number of about 100 F-1 clear. As indicated, the present invention essentially involves the finding that the addition of a sulfur component to a dual-function acidic hydrocarbon conversion catalyst containing a platinum or palladium component, a rhodium component and a lead component can enable the performance characteristics of the catalyst to be sharply and materially improved, if the hereinafter specified limitations on amounts of ingredients, atomic ratio of lead to platinum or palladium, oxidation states of metals, distribution of metallic components in the support and sulfiding procedure are met.

It is accordingly one object of the present invention to provide an improvement in an acidic multimetallic hydrocarbon conversion catalyst having superior performance characteristics when utilized in a hydrocarbon conversion process. A second object is to provide a sulfided acidic catalyst having dual-function hydrocarbon conversion performance characteristics that are relatively insensitive to the deposition of hydrocarbonaceous material thereon. A third object is to provide preferred methods of preparation of this sulfided acidic multimetallic catalytic composite which insures the achievement and maintenance of its properties. Another object is to provide an improved reforming catalyst having superior activity, selectivity and stability. Yet another object is to provide a dual-function sulfided acidic hydrocarbon conversion catalyst which utilizes a combination of a lead component, a rhodium component and a sulfur component to promote and stabilize an acidic catalyst containing a platinum or palladium component.

In brief summary, the present invention is, in one embodiment, a sulfided acidic catalytic composite comprising a porous carrier material containing, on an elemental basis, about 0.01 to about 2 wt. % platinum or palladium metal, about 0.01 to about 2 wt. % rhodium metal, about 0.1 to about 3.5 wt. % halogen, about 0.01 to about 1 wt. % sulfur, and lead in an amount sufficient to result in an atomic ratio of lead to platinum or palladium of about 0.05:1 to about 0.9:1, wherein the platinum or palladium lead and rhodium are uniformly dispersed throughout the porous carrier material, wherein substantially all of the platinum or palladium and rhodium are present in a sulfided state or in a mixture of the sulfided state and the elemental metallic state, wherein substantially all of the lead is present in an oxidation state above that of the elemental metal and wherein the composite is sulfided, prior to contact with hydrocarbon and after substantially all of the platinum or palladium and rhodium contained therein have been reduced to the elemental metallic state, by treatment with a sulfiding gas at conditions selected to incorporate about 0.01 to about 1 wt. % sulfur.

A second embodiment relates to a sulfided acidic catalytic composite comprising a porous carrier material containing, on an elemental basis, about 0.05 to about 1 wt. % platinum or palladium metal, about 0.05 to about 1 wt. % rhodium metal, about 0.5 to about 1.5 wt. % halogen, about 0.05 to 0.5 wt. % sulfur and lead in an amount sufficient to result in an atomic ratio of lead to platinum or palladium of about 0.1:1 to about 0.75:1, wherein the platinum or palladium, lead and rhodium are uniformly dispersed throughout the porous carrier material, wherein substantially all of the platinum or palladium and rhodium are present in a sulfided state or in a mixture of the sulfided state and the elemental metallic state, wherein substantially all of the lead is present in an oxidation state above that of the elemental metal and wherein the composite is sulfided, prior to contact with hydrocarbon and after substantially all of the platinum or palladium and rhodium contained therein have been reduced to the elemental metallic state, by treatment with a sulfiding gas at conditions selected to incorporate about 0.05 to 0.5 wt. % sulfur.

Another embodiment relates to a process for the conversion of a hydrocarbon comprising contacting the hydrocarbon and hydrogen with the sulfided acidic catalytic composite described above in the first or second embodiment at hydrocarbon conversion conditions.

A preferred embodiment relates to a process for reforming a gasoline fraction which comprises contacting the gasoline fraction and hydrogen with the sulfided acidic catalytic composite described above in the first or second embodiment at reforming conditions selected to produce a high-octane reformate.

Other objects and embodiments of the present invention relate to additional details regarding preferred catalytic ingredients, preferred amounts of ingredients, suitable methods of composite preparation, operating conditions or use in the hydrocarbon conversion processes, and the like particulars, which are hereinafter given in the following detailed discussion of each of these facets of the present invention.

The sulfided multimetallic catalyst of the present invention comprises a porous carrier material or support having combined therewith catalytically effective amounts of a platinum or palladium component, a rhodium component, a lead component, a halogen component and a sulfur component.

Considering the porous carrier material utilized in the present invention, it is preferred that the material be a porous, adsorptive, high-surface area support having a surface area of about 25 to about 500 m.sup.2 /g. The porous carrier material should be relatively refractory to the conditions utilized in the hydrocarbon conversion process, and it is intended to include within the scope of the present invention carrier materials which have traditionally been utilized in dual-function hydrocarbon conversion catalysts such as: (1) activated carbon, coke or charcoal; (2) silica or silica gel, silicon carbide, clays and silicates including those synthetically prepared and naturally occurring, which may or may not be acid treated, for example, attapulgus clay, china clay, diatomaceous earth, fuller's earth, kaolin, kiesel-guhr, etc., (3) ceramics, porcelain, crushed firebrick, buaxite; (4) refractory inorganic oxides such as alumina, titanium dioxide, zirconium dioxide, chromium oxide, beryllium oxide, vanadium oxide, cesium oxide, hafnium oxide, zinc oxide, magnesia, boria, thoria, silica-alumina, silica-magnesia, chromia-alumina, alumina-boria, silica-zorconia, etc.; (5) crystalline zeolitic aluminosilicates such as naturally occurring or synthetically prepared mordenite and/or faujasite, either in the hydrogen form or in a form which has been treated with multivalent cations; (6) spinels such as MgAl.sub.2 O.sub.4, FeAl.sub.2 O.sub.4, ZnAl.sub.2 O.sub.4, MnAl.sub.2 O.sub.4, CaAl.sub.2 O.sub.4, and other like compounds having the formula MO.sup.. Al.sub.2 O.sub.3 where M is a metal having a valence of 2; and (7) combinations of elements from one or more of these groups. The preferred porous carrier materials for use in the present invention are refractory inorganic oxides, with best results obtained with an alumina carrier material. Suitable alumina materials are the crystalline aluminas known as gamma-, eta- and theta-alumina, with gamma- or eta-alumina giving best results. In addition, in some embodiments the alumina carrier material may contain minor proportions of other well-known refractory inorganic oxides such as silica, zirconia, magnesia, etc.; however, the preferred support is substantially pure gamma- or eta-alumina. Preferred carrier materials have an apparent bulk density of about 0.3 to about 0.7 g/cc and surface area characteristics such that the average pore diameter is about 20 to 300 Angstroms, the pore volume is about 0.1 to about 1 cc/g and the surface area is about 100 to about 500 m.sup.2 /g. In general, best results are typically obtained with a gamma-alumina carrier material which is used in the form of spherical particles having: a relatively small diameter (i.e. typically about 1/16 inch), an apparent bulk density of about 0.3 to about 0.8 g/cc, a pore volume of about 0.4 ml/g and a surface area of about 150 to about 200 m.sup.2 /g.

The preferred alumina carrier material may be prepared in any suitable manner and may be synthetically prepared or natural occurring. Whatever type of alumina is employed, it may be activated prior to use by one or more treatments including drying, calcination, steaming, etc., and it may be in a form known as activated alumina, activated alumina of commerce, porous alumina, alumina gel, etc. For example, the alumina carrier may be prepared by adding a suitable alkaline reagent, such as ammonium hydroxide, to a salt of aluminum such as aluminum chloride, aluminum nitrate, etc., in an amount to form an aluminum hydroxide gel which upon drying and calcining is converted to alumina. The alumina carrier may be formed in any desired shape such as spheres, pills, cakes, extrudates, powders, granules, tablets, etc., and utilized in any desired size. For the purpose of the present invention, a particularly preferred form of alumina is the sphere; and alumina spheres may be continuously manufactured by the well-known oil drop method which comprises: forming an alumina hydrosol by any of the techniques taught in the art and preferably by reacting aluminum metal with hydrochloric acid, combining the resultant hydrosol with a suitable gelling agent and dropping the resultant mixture into an oil bath maintained at elevated temperatures. The droplets of the mixture remain in the oil bath until they set and form hydrogel spheres. The spheres are then continuously withdrawn from the oil bath and typically subjected to specific aging treatments in oil and an ammoniacal solution to further improve their physical characteristics. The resulting aged and gelled particles are then washed and dried at a relatively low temperature of about 300.degree. to about 400.degree. F. and subjected to a calcination procedure at a temperature of about 850.degree. F. to about 1300.degree. F. for a period of about 1 to about 20 hours. This treatment effects conversion of the alumina hydrogel to the corresponding crystalline gamma-alumina. See the teachings of U.S. Pat. No. 2,620,314 for additional details.

One essential constituent of the sulfided acidic catalyst of the present invention is a lead component. An essential feature of the present invention is that substantially all of this component is present in the final catalyst in an oxidation state above that of the elemental metal. This component may be present in the catalytic composite in chemical combination with one or more of the other ingredients of the composite, or as a chemical compound such as the corresponding lead oxide, sulfide, halide, oxyhalide, aluminate, etc. Based on the evidence currently available, it is believed that best results are obtained when substantially all of the lead component is present in the composite in the form of lead oxide. That is, it is believed that particularly good results are obtained when the lead moiety exists in the final catalytic composite in the +2 or +4 oxidation state in the form of the corresponding oxide. The preferred method of preparation of the catalyst composite of the present invention which is specifically described in Example I is believed to result in the composite containing the lead component in the corresponding oxide state.

The lead component may be incorporated into the catalytic composite in any suitable manner known to effectively disperse this component uniformly throughout the carrier material or to result in this condition. Thus, this incorporation may be accomplished by coprecipitation or cogellation with the porous carrier material, ion exchange with the carrier material while it is in a gel state, or impregnation of the carrier material at any stage in its preparation. It is to be noted that it is intended to include within the scope of the present invention all conventional methods for incorporating a metallic component in a catalyst composite which results in a uniform distribution of the metallic component throughout the associated carrier material. One preferred method of incorporating the lead component to the catalytic composite involves coprecipitating the lead component during the preparation of the preferred refractory oxide carrier material. Typically, this involves the addition of a suitable soluble decomposable lead compound such as lead nitrate or lead chloride to the alumina hydrosol, mixing the resulting hydrosol until the lead moiety is uniformly dispersed therein, and then combining the thoroughly mixed hydrosol with a suitable gelling agent and dropping the resulting mixture into an oil bath as explained in detail hereinbefore. After drying and calcining the resulting gelled carrier material, there is obtained an intimate combination of alumina and lead oxide, which combination has the lead component uniformly dispersed throughout the alumina. Another preferred method of incorporating the lead component into the catalytic composite involves the utilization of a soluble, decomposable compound of lead to impregnate the porous carrier material. In general, the solvent used in this preferred impregnation step is selected on the basis of its capability to dissolve the desired lead compound and is typically an aqueous acidic solution. Hence, the lead component may be added to the carrier material by commingling the latter with an aqueous solution of a suitable lead salt or water-soluble compound of lead such as lead acetate, lead basic acetate, lead bromate, lead bromide, lead chlorate, lead perchlorate, lead chloride, lead citrate, lead ethylsulfate, lead formate, lead nitrate, lead basic nitrate, lead nitrite, and the like compounds. Best results are ordinarily obtained with an acidic aqueous solution of lead nitrate and nitric acid. In general the lead component can be impregnated either prior to, simultaneously with, or after the other metallic components are added to the carrier material. However, excellent results are obtained by impregnating the lead component simultaneously with the platinum or palladium and rhodium components. In fact, I have determined that a preferred impregnation solution contains chloroplatinic acid, rhodium trichloride hydrate, nitric acid, and lead nitrate.

Regardless of which lead compound is used in the preferred impregnation step, it is important that the lead component be uniformly distributed throughout the carrier material. That is, it is important that the concentration of lead in any reasonably divisible portion of the carrier material be approximately the same. In order to achieve this objective, it is necessary to maintain the pH of the impregnation solution in a range of about 7 to about 1 or less and to dilute the solution to a volume which is approximately the same or greater than the volume of the carrier material which is impregnated. Similarly, a relatively long contact time should be used during this impregnation step ranging from about 0.25 hours up to about 0.5 hours or more. The carrier material is likewise preferably constantly agitated during this impregnation step.

A second essential ingredient of the subject catalyst is the platinum or palladium component. That is, it is intended to cover the use of platinum or palladium or mixtures thereof as a second component of the present composite. It is an essential feature of the present invention that substantially all of this platinum or palladium component exists within the final catalytic composite in the sulfided state or in a mixture of the sulfided state and the elemental metallic state. Generally, the amount of this component present in the final catalytic composite is small compared to the quantities of the other components combined therewith. In fact, the platinum or palladium component generally will comprise about 0.01 to about 2 wt. % of the final catalytic composite, calculated on an elemental basis. Excellent results are obtained when the catalyst contains about 0.05 to about 1 wt. % of platinum or palladium metal.

This platinum or palladium component may be incorporated in the catalytic composite in any suitable manner known to result in a relatively uniform distribution of this component in the carrier material such as coprecipitation or cogellation, ion exchange or impregnation. The preferred method of preparing the catalyst involves the utilization of a soluble, decomposable compound of platinum or palladium to impregnate the carrier material in a relatively uniform manner. For example, this component may be added to the support by commingling the latter with an aqueous solution of chloroplatinic or chloropalladic acid. Other water-soluble compounds of platinum or palladium may be employed in impregnation solutions and include ammonium chloroplatinate, bromoplatinic acid, platinum trichloride, platinum tetrachloride hydrate, platinum dichlorocarbonyl dichloride, dinitrodiaminoplatinum, sodium tetranitroplatinate (II), palladium chloride, palladium nitrate, palladium sulfate, diammine palladium (II) hydroxide, tetrammine palladium (II) chloride, etc. The utilization of a platinum or palladium chloride compound, such as chloroplatinic or chloropalladic acid, is preferred since it facilitates the incorporation of both the platinum or palladium component and at least a minor quantity of the halogen component in a single step. Hydrogen chloride or the like acid is also generally added to the impregnation solution in order to further facilitate the incorporation of the halogen component and the uniform distribution of the metallic components throughout the carrier material. In addition, it is generally preferred to impregnate the carrier material after it has been calcined in order to minimize the risk of washing away the valuable platinum or palladium compounds; however, in some cases it may be advantageous to impregnate the carrier material when it is in a gelled state.

Yet another essential ingredient of the present catalytic composite is a rhodium component. It is of fundamental importance that substantially all of the rhodium component exists within the catalytic composite of the present invention in the sulfided state or in a mixture of the sulfided state and the elemental metallic state and the subsequently described reduction and sulfiding procedure is designed to accomplish this objective. The rhodium component may be utilized in the composite in any amount which is catalytically effective, with the preferred amount being about 0.01 to about 2 wt. % thereof, calculated on an elemental basis. Typically, best results are obtained with about 0.05 to about 1 wt. % rhodium. It is additionally preferred to select the specified amount of rhodium from within this broad weight range as a function of the amount of the platinum or palladium component, on an atomic basis, as is explained hereinafter.

This rodium component may be incorporated into the catalytic composite in any suitable manner known to those skilled in the catalyst formulation art which results in a relatively uniform distribution of rhodium in the carrier material. In addition, it may be added at any stage of the preparation of the composite-- either during preparation of the carrier material or thereafter-- and the precise method of incorporation used is not deemed to be critical. However, best results are obtained when the rhodium component is relatively uniformly distributed throughout the carrier material, and the preferred procedures are the ones known to result in a composite having this relatively uniform distribution. One acceptable procedure for incorporating this component into the composite involves cogelling or coprecipitating the rhodium component during the preparation of the preferred carrier material, alumina. This procedure usually comprehends the addition of a soluble, decomposable compound of rhodium such as rhodium trichloride hydrate to the alumina hydrosol before it is gelled. The resulting mixture is then finished by conventional gelling, aging, drying and calcination steps as explained hereinbefore. A preferred way of incorporating this component is an impregnation step wherein the porous carrier material is impregnated with a suitable rhodium-containing solution either before, during or after the carrier material is calcined. Preferred impregnation solutions are aqueous solutions of water soluble, decomposable rhodium compounds such as hexamminerhodium chloride, rhodium carbonylchloride, rhodium trichloride hydrate, rhodium nitrate, sodium hexachlororhodate (III), sodium hexanitrorhodate (III), rhodium sulfate and the like compounds. Best results are ordinarily obtained when the impregnation solution is an aqueous solution of rhodium trichloride hydrate or rhodium nitrate. This component can be added to the carrier material either prior to, simultaneously with, or after the other metallic components are combined therewith. Best results are usually achieved when this component is added simultaneously with the other metallic components. In fact, excellent results are obtained, as reported in the examples, with a one-step impregnation procedure using an aqueous solution comprising chloroplatinic or chloropalladic acid, rhodium trichloride hydrate, lead nitrate and nitric acid.

It is essential to incorporate a halogen component into the sulfided acidic catalytic composite of the present invention. Although the precise form of the chemistry of the association of the halogen component with the carrier material is not entirely known, it is customary in the art to refer to the halogen component as being combined with the carrier material, or with the other ingredients of the catalyst in the form of the halide (e.g. as the chloride). This combined halogen may be either fluorine, chlorine, iodine, bromine, or mixtures thereof. Of these, fluorine and particularly chlorine are preferred for the purposes of the present invention. The halogen may be added to the carrier material in any suitable manner, either during preparation of the support or before or after the addition of the other components. For example, the halogen may be added, at any stage of the preparation of the carrier material or to the calcined carrier material, as an aqueous solution of a suitable, decomposable halogen-containing compound such as hydrogen fluoride, hydrogen chloride, hydrogen bromide, ammonium chloride, etc. The halogen component or a portion thereof, may be combined with the carrier material during the impregnation of the latter with the platinum or palladium and rhodium components; for example, through the utilization of a mixture of chloroplatinic acid and hydrogen chloride. In another situation, the alumina hydrosol which is typically utilized to form the preferred alumina carrier material may contain halogen and thus contribute at least a portion of the halogen component to the final composite. For reforming, the halogen will be typically combined with the carrier material in an amount sufficient to result in a final composite that contains about 0.1 to about 3.5%, and preferably about 0.5 to about 1.5% by weight, of halogen, calculated on an elemental basis. In isomerization or hydrocracking embodiments, it is generally preferred to utilize relatively larger amounts of halogen in the catalyst-- typically ranging up to about 10 wt. % halogen calculated on an elemental basis, and more preferably, about 1 to about 5 wt. %. It is to be understood that the specified level of halogen component in the instant catalyst can be achieved or maintained during use in the conversion of hydrocarbons by continuously or periodically adding to the reaction zone a deomposable halogen-containing compound such as an organic chloride (e.g. ethylene dichloride, carbon tetrachloride, t-butyl chloride) in an amount of about 1 to 100 wt. ppm. of the hydrocarbon feed, and preferably about 1 to 10 wt. ppm.

Regarding the amount of the lead component contained in the catalyst, I have discerned that it is essential to fix the amount of the lead component as a function of the amount of the platinum or palladium component contained in the composite. More specifically, I have observed that the beneficial interaction of the lead component with the platinum or palladium component is only obtained when the lead component is present, or an atomic basis, in an amount substantially less then the platinum or palladium component. Quantitatively, the amount of the lead component is preferably sufficient to provide an atomic ratio of lead to platinum or palladium metal of about 0.05:1 to about 0.9:1 with best results obtained at an atomic ratio of about 0.1:1 to about 0.75:1. The criticalness associated with this atomic ratio limitation is apparent when an attempt is made to convert hydrocarbons with a catalyst having an atomic ratio of lead to platinum of 1:1. In this latter case, I observed substantial deactivation of the platinum component by the lead component. Accordingly, it is an essential feature of the present invention that the amount of the lead component is chosen as a function of the amount of the platinum or palladium component in order to insure that the atomic ratio of these components in the resulting catalyst is within the stated range. I have also found it to be a good practice to specify the amount of the rhodium component so that the atomic ratio of rhodium to platinum or palladium metal contained in the composite is about 0.1:1 to about 2:1, with the preferred range being about 0.25:1 to about 1.5:1.

Another significant parameter for the instant catalyst is the "total metals content" which is defined to be the sum of the platinum or palladium component, the rhodium component and the lead component, calculated on an elemental basis. Good results are ordinarily obtained with the subject catalyst when this parameter is fixed at a value of about 0.15 to about 3 wt. %, with best results ordinarily achieved at a metals loading of about 0.3 to about 2 wt. %.

In embodiments of the present invention wherein the instant multimetallic catalytic composite is used for the dehydrogenation of dehydrogenatable hydrocarbons or for the hydrogenation of hydrogenatable hydrocarbons, it is ordinarily a preferred practice to include an alkali or alkaline earth metal component in the composite and to minimize or eliminate the halogen component. More precisely, this optional ingredient is selected from the group consisting of the compounds of the alkali metals-- cesium, rubidium, potassium, sodium, and lithium-- and the compounds of the alkaline earth metals-- calcium, strontium, barium and magnesium. Generally, good results are obtained in these embodiments when this component constitutes about 0.1 to about 5 wt. % of the composite, calculated on an elemental basis. This optional alkali or alkaline earth metal component can be incorporated in the composite in any of the known ways, with impregnation with an aqueous solution of a suitable water-soluble, decomposable compound being preferred.

An optional ingredient for the multimetallic catalyst of the present invention is a Friedel-Crafts metal halide component. This ingredient is particularly useful in hydrocarbon conversion embodiments of the present invention wherein it is preferred that the catalyst utilized has a strong acid or cracking function associated therewith-- for example, an embodiment wherein hydrocarbons are to be hydrocracked or isomerized with the catalyst of the present invention. Suitable metal halides of the Friedel-Crafts type include aluminum chloride, aluminum bromide, ferric chloride, ferric bromide, zinc chloride and the like compounds, with the aluminum halides and particularly aluminum chloride ordinarily yielding best results. Generally, this optional ingredient can be incorporated into the composite of the present invention by any of the conventional methods for adding metallic halides of this type; however, best results are ordinarily obtained when the metallic halide is sublimed onto the surface of the carrier material according to the preferred method disclosed in U.S. Pat. No. 2,999,074. The component can generally be utilized in any amount which is catalytically effective, with a value selected from the range of about 1 to about 100 wt. % of the carrier material generally being preferred.

Regardless of the details of how the components of the catalyst are combined with the porous carrier material, the final catalyst generally will be dried at a temperature of about 200.degree. to about 600.degree. F. for a period of at least about 2 to about 24 hours or more, and finally calcined or oxidized at a temperature of about 700.degree. F. to about 1100.degree. F. in an air or oxygen atmosphere for a period of about 0.5 to about 10 hours in order to convert substantially all of the metallic components to the corresponding oxide form. Because a halogen component is utilized in the catalyst, best results are generally obtained when the halogen content of the catalyst is adjusted during this oxidation step by including a halogen or a halogen-containing compound such as HCl in the air or oxygen atmosphere utilized. In particular, when the halogen component of the catalyst is chlorine, it is preferred to use a mole ratio of H.sub.2 O to HCl of about 5:1 to about 100:1 during at least a portion of this oxidation step in order to adjust the final chlorine content of the catalyst to a range of about 0.1 to about 3.5 wt. %.

It is an essential feature of the present invention that the resultant oxidized catalytic composite is subjected to a substantially water-free and hydrocarbon-free reduction step prior to its use in the conversion of hydrocarbons. This step is designed to selectively reduce the platinum or palladium and rhodium components to the corresponding metals and to insure a uniform and finely divided dispersion of these metallic components throughout the carrier material, while maintaining the lead component in a positive oxidation state. Preferably substantially pure and dry hydrogen (i.e. less than 20 vol. ppm. H.sub.2 O) is used as the reducing agent in this step. The reducing agent is contacted with the oxidized catalyst at conditions including a temperature of about 800.degree. F. to about 1200.degree. F. and a period of time of about 0.5 to 2 hours effective to reduce substantially all of the platinum or palladium and rhodium components to their elemental metallic state while maintaining the lead component in an oxidation state above that of the elemental metal. This reduction treatment may be performed in situ as part of a start-up sequence if precautions are taken to predry the plant to a substantially water-free state and if substantially water-free and hydrocarbon-free hydrogen is used.

Another essential feature of the instant invention involves recognition that the resulting relatively reduced catalytic composite can be beneficially subjected to a presulfiding operation with a sulfiding reagent designed to incorporate in the catalytic composite from about 0.01 to about 1 and more preferably about 0.05 to about 0.5 wt. % sulfur calculated on an elemental basis. I have found that it is critical to perform this presulfiding procedure prior to use of the catalytic composite in the conversion of hydrocarbons and after substantially all of the platinum or palladium and rhodium components are reduced to the corresponding elemental metallic states. The principal reason for this requirement is that it ensures that the uniform distribution of the metallic components in the carrier material will not be adversely affected by the sulfur. Preferably, this presulfiding treatment takes place in the presence of hydrogen and a suitable sulfur-containing decomposable sulfiding reagent such as hydrogen sulfide, lower molecular weight mercaptans, organic sulfides, etc. Typically, this procedure comprises treating the selectively reduced catalyst with a sulfiding gas such as a mixture of hydrogen and hydrogen sulfide having about 10 moles of hydrogen per mole of hydrogen sulfide at conditions sufficient to effect the desired incorporation of sulfur, generally including a temperature ranging from about 50.degree. F. up to about 1100.degree. F. or more. It is generally a good practice to perform this presulfiding step under substantially water-free conditions. It is within the scope of the present invention to maintain the sulfided state of the instant catalyst during use in the conversion of hydrocarbons by continuously or periodically adding a decomposable sulfur-containing compound, such as the ones previously mentioned, to the reactor containing the catalyst in an amount sufficient to provide about 1 to 500 wt. ppm., preferably 1 to 20 wt. ppm. of sulfur based on hydrocarbon charge.

According to the present invention, a hydrocarbon charge stock and hydrogen are contacted with the sulfided acidic catalyst in a hydrocarbon conversion zone. This contacting may be accomplished by using the catalyst in a fixed bed system, a moving bed system, a fluidized bed system, or in a batch type operation; however, in view of the danger of attrition losses of the valuable catalyst and of well-known operational advantages, it is preferred to use a fixed bed system. In this system, a hydrogen-rich gas and the charge stock are preheated by any suitable heating means to the desired reaction temperature and then are passed into a conversion zone containing a fixed bed of the catalyst type previously characterized. It is, of course, understood that the conversion zone may be one or more separate reactors with suitable means therebetween to insure that the desired conversion temperature is maintained at the entrance to each reactor. It is also important to note that the reactants may be contacted with the catalyst bed in either upward, downward, or radial flow fashion with the latter being preferred. In addition, the reactants may be in the liquid phase, a mixed liquid-vapor phase, or a vapor phase when they contact the catalyst, with best results obtained in the vapor phase.

In the case where the sulfided acidic catalyst of the present invention is used in a reforming operation, the reforming system will comprise a reforming zone containing a fixed bed of the catalyst type previously characterized. This reforming zone may be one or more separate reactors with suitable heating means therebetween to compensate for the endothermic nature of the reactions that take place in each catalyst bed. The hydrocarbon feed stream that is charged to this reforming system will comprise hydrocarbon fractions containing naphthenes and paraffins that boil within the gasoline range. The preferred charge stocks are those consisting essentially of naphthenes and paraffins, although in some cases aromatics and/or olefins may also be present. This preferred class includes strain run gasolines, natural gasolines, synthetic gasolines, partially reformed gasolines and the like. On the other hand, it is frequently advantageous to charge thermally or catalytically cracked gasolines or higher boiling fractions thereof. Mixtures of straight run and cracked gasolines can also be used to advantage. The gasoline charge stock may be a full boiling gasoline having an initial boiling point of from about 50.degree. F. to about 150.degree. F. and an end boiling point within the range of from about 325.degree. F. to about 425.degree. F., or may be a selected fraction thereof which generally will be a higher boiling fraction commonly referred to as a heavy naphtha-- for example, a naphtha boiling in the range of C.sub.7 to 400.degree. F. In some cases, it is also advantageous to charge pure hydrocarbons or mixtures of hydrocarbons that have been extracted from hydrocarbon distillates-- for example, straight-chain paraffins-- which are to be converted to aromatics. It is preferred that these charge stocks be treated by conventional catalytic pretreatment methods such as hydrorefining, hydrotreating, hydrodesulfurization, etc., to remove substantially all sulfurous, nitrogenous and water-yielding contaminants therefrom and to saturate any olefins that may be contained therein.

In other hydrocarbon conversion embodiments, the charge stock will be of the conventional type customarily used for the particular kind of hydrocarbon conversion being effected. For example, in a typical isomerization embodiment the charge stock can be a paraffinic stock rich in C.sub.4 to C.sub.8 normal paraffins, or a normal butane-rich stock or an n-hexane-rich stock, or a mixture of xylene isomers, or an olefin-rich stock, etc. In a dehydrogenation embodiment, the charge stock can be any of the known dehydrogenatable hydrocarbons such as an aliphatic compound containing 2 to 30 carbon atoms per molecule, a C.sub.4 to C.sub.30 normal paraffin, a C.sub.8 to C.sub.12 alkylaromatic, a naphthene and the like. In hydrocracking embodiments, the charge stock will be typically a gas oil, heavy cracked cycle oil, etc. In addition, alkylaromatic, olefins and naphthenes can be conveniently isomerized by using the catalyst of the present invention. Likewise, pure hydrocarbons or substantially pure hydrocarbons can be converted to more valuable products by using the sulfided acidic catalyst of the present invention in any of the hydrocarbon conversion processes, known to the art, that use a dual-function catalyst.

In a reforming embodiment, it is generally preferred to utilize the sulfided acidic catalytic composite in a substantially water-free environment. Essential to the achievement of this condition in the reforming zone is the control of the water level present in the charge stock and the hydrogen stream which is being charged to the zone. Best results are ordinarily obtained when the total amount of water entering the conversion zone from any source is held to a level less than 50 ppm. and preferably less than 20 ppm. expressed as weight of equivalent water in the charge stock. In general, this can be accomplished by careful control of the water present in the charge stock and in the hydrogen stream. The charge stock can be dried by using any suitable drying means known to the art, such as a conventional solid adsorbent having a high selectivity for water, for instance, sodium or calcium crystalline aluminosilicates, silica gel, activated alumina, molecular sieves, anhydrous calcium sulfate, high surface area sodium and the like adsorbents. Similarly, the water content of the charge stock may be adjusted by suitable stripping operations in a fractionation column or like device. And in some cases, a combination of adsorbent drying and distillation drying may be used advantageously to effect almost complete removal of water from the charge stock. Preferably the charge stock is dried to a level corresponding to less than 20 ppm. of H.sub.2 O equivalent. In general, it is preferred to maintain the hydrogen stream entering the hydrocarbon conversion zone at a level of about 10 vol. ppm. of water or less. If the water level in the hydrogen stream is too high, drying of same can be conventionally accomplished by contacting the hydrogen stream with a suitable desiccant such as those mentioned above.

In the reforming embodiment, an effluent stream is withdrawn from the reforming zone and passed through a cooling means to a separation zone, typically maintained at about 25.degree. to 150.degree. F., wherein a hydrogen-rich gas is separated from a high octane liquid product, commonly called an unstabilized reformate. When a super-dry operation is desired, at least a portion of this hydrogen-rich gas is withdrawn from the separating zone and passed through an adsorption zone containing an adsorbent selective for water. The resultant substantially water-free hydrogen stream can then be recycled through suitable compressing means back to the reforming zone. The liquid phase from the separating zone is typically withdrawn and commonly treated in a fractionating system in order to adjust the butane concentration, thereby controlling front-end volatility of the resulting reformate.

The conditions utilized in the numerous hydrocarbon conversion embodiments of the present invention are those customarily used in the art for the particular reaction, or combination of reactions, that is to be effected. For instance, alkylaromatic, olefin, and paraffin isomerization conditions include: a temperature of about 32.degree. F. to about 1000.degree. F. and preferably from about 75.degree. to about 600.degree. F.; a pressure of atmospheric to about 100 atmospheres; a hydrogen to hydrocarbon mole ratio of about 0.5:1 to about 20:1 and an LHSV (calculated on the basis of equivalent liquid volume of the charge stock contacted with the catalyst per hour divided by the volume of conversion zone containing catalyst) of about 0.2 hr..sup..sup.-1 to 10 hr..sup..sup.-1. Dehydrogenation conditions include: a temperature of about 700.degree. to about 1250.degree. F., a pressure of about 0.1 to about 10 atmospheres, a liquid hourly space velocity of about 1 to 40 hr..sup..sup.-1 and a hydrogen to hydrocarbon mole ratio of about 1:1 to 20:1. Likewise, typically hydrocracking conditions include: a pressure of about 500 psig. to about 3000 psig., a temperature of about 400.degree. F. to about 900.degree. F., an LHSV of about 0.1 hr..sup..sup.-1 to about 10 hr..sup..sup.-1, and hydrogen circulation rates of about 1000 to 10,000 SCF per barrel of charge.

In the reforming embodiment of the present invention, the pressure utilized is selected from the range of about 0 psig. to about 1000 psig., with the preferred pressure being about 50 psig. to about 600 psig. Particularly good results are obtained at low pressure; namely, a pressure of about 50 to 350 psig. In fact, it is a singular advantage of the present invention that it allows stable operation at lower pressure than have heretofore been successfully utilized in so-called "continuous" reforming systems (i.e. reforming for periods of about 15 to about 200 or more barrels of charge per pound of catalyst without regeneration) with all platinum monometallic catalyst. In other words, the sulfided aidic catalyst of the present invention allows the operation of a continuous reforming system to be conducted at lower pressure (i.e. 100 to about 350 psig.) for about the same or better catalyst life before regeneration as has been heretofore realized with conventional monometallic catalysts at higher pressures (i.e. 400 to 600 psig.). On the other hand, the stability feature of the present invention enables reforming operations conducted at pressures of 400 to 600 psig. to achieve substantially increased catalyst life before regeneration.

Similarly, the temperature required for reforming is generally lower than that required for a similar reforming operation using a high quality catalyst of the prior art. This significant and desirable feature of the present invention is a consequence of the selectivity of the sulfided acidic catalyst of the present invention for the octane-upgrading reactions that are preferably induced in a typical reforming operation. Hence, the present invention requires a temperature in the range of from about 800.degree. F. to about 1100.degree. F. and preferably about 900.degree. F. to about 1050.degree. F. As is well known to those skilled in the continuous reforming art, the initial selection of the temperature within this broad range is made primarily as a function of the desired octane of the product reformate considering the characteristics of the charge stock and of the catalyst. Ordinarily, the temperature then is thereafter slowly increased during the run to compensate for the inevitable deactivation that occurs to provide a constant octane product. Therefore, it is a feature of the present invention that the rate at which the temperature is increased in order to maintain a constant octane product is substantially lower for the catalyst of the present invention than for a high quality reforming catalyst which is manufactured in exactly the same manner as the catalyst of the present invention except for the inclusion of the rhodium and lead components. Moreover, for the catalyst of the present invention, the C.sub.5 + yield loss for a given temperature increase is substantially lower than for a high quality reforming catalyst of the prior art.

The reforming embodiment of the present invention also typically utilizes sufficient hydrogen to provide an amount of about 1 to about 20 moles of hydrogen per mole of hydrocarbon entering the reforming zone, with excellent results being obtained when about 5 to about 10 moles of hydrogen are used per mole of hydrocarbon. Likewise, the liquid hourly space velocity (LHSV) used in reforming is selected from the range of about 0.1 to about 10 hr..sup..sup.-1, with a value in the range of about 1 to about 5 hr..sup..sup.-1 being preferred. In fact, it is a feature of the present invention that it allows operations to be conducted at higher LHSV than normally can be stably achieved in a continuous reforming process with a high quality reforming catalyst of the prior art. This last feature is of immense economic significance because it allows a continuous reforming process to operate at the same throughput level with less catalyst inventory than that heretofore used with conventional reforming catalysts at no sacrifice in catalyst life before regeneration.

The following working examples are given to illustrate further the preparation of the sulfided acidic composite of the present invention and the use thereof in the conversion of hydrocarbons. It is understood that the examples are intended to be illustrative rather than restrictive.

An alumina carrier material comprising 1/16 inch spheres is prepared by: forming an aluminum hydroxyl chloride sol by dissolving substantially pure aluminum pellets in a hydrochloric acid solution, adding hexamethylenetetramine to the resulting alumina sol, gelling the resulting solution by dropping it into a hot oil bath to form spherical particles of an aluminum hydrogel aging and washing the resulting particles and finally drying and calcining the aged and washed particles to form spherical particles of gamma-alumina containing about 0.3 wt. % combined chloride. Additional details as to this method of preparing the preferred carrier material are given in the teachings of U.S. Pat. No. 2,620,314.

An acidic aqueous impregnation solution containing chloroplatinic acid, rhodium trichloride hydrate, lead nitrate and nitric acid is then prepared. This solution is then intimately admixed with the gamma-alumina particles. The amounts of the reagents contained in this impregnation solution are calculated to result in a final composite containing on an elemental basis 0.375 wt. % platinum, 0.25 wt. % rhodium and 0.1 wt. % lead. In order to insure uniform distribution of the metallic components throughout the carrier material, the amount of nitric acid corresponds to about 3 wt. % of the alumina particles. This impregnation step is performed by adding the carrier material particles to the impregnation mixture with constant agitation. In addition, the volume of the solution is approximately the same as the void volume of the carrier material particles. The impregnation mixture is maintained in contact with the carrier material particles for a period of about 1/2 hour at a temperature of about 70.degree. F. Thereafter, the temperature of the impregnation mixture is raised to about 225.degree. F. and the excess solution is evaporated in a period of about 1 hour. The resulting dried particles are then subjected to an oxidation treatment in an air atmosphere at a temperature of about 925.degree. F. for about 1 hour. The oxidized spheres are then contacted with an air stream containing H.sub.2 O and HCl in a mole ratio of about 40:1 for about 2 hours at 975.degree. F. in order to adjust the halogen content of the catalyst particles to a value of about 0.90.

The resulting catalyst particles are analyzed and found to contain, on an elemental basis, about 0.375 wt. % platinum, about 0.25 wt. % rhodium, about 0.1 wt. % lead and about 0.9 wt. % chloride. For this catalyst, the atomic ratio of lead to platinum is 0.25:1 and the atomic ratio of rhodium to platinum is 1.26:1.

Thereafter the catalyst particles are subjected to a dry prereduction treatment designed to reduce substantially all of the platinum and rhodium components to the elemental metallic state while maintaining the lead component in a positive oxidation state by contacting them for 1 hour with a substantially pure hydrogen stream containing less than 5 vol. ppm. H.sub.2 O at a temperature of about 1050.degree. F., a pressure slightly above atmospheric and a flow rate of the hydrogen stream through the catalyst particles corresponding to a gas hourly space velocity of about 720 hr..sup..sup.-1.

The resulting selectively reduced catalyst particles are then contacted with a sulfiding gas comprising a mixture of H.sub.2 S and H.sub.2 in a mole ratio of about 0.1:1 moles of H.sub.2 S per mole of H.sub.2 at a temperature of about 1050.degree. F., atmospheric pressure and a GHSV of about 800 hr..sup..sup.-1 for a period of about 1/2 hour effective to incorporate about 0.2 wt. % sulfur which is present in the form of platinum sulfide and rhodium sulfide.

A portion of the spherical sulfided catalyst particles produced by the method described in Example I is loaded into a scale model of a continuous, fixed bed reforming plant of conventional design. In this plant a heavy Kuwait naphtha and hydrogen are continuously contacted at reforming conditions: a liquid hourly space velocity of 1.5 hr..sup..sup.-1, a pressure of 100 psig., a hydrogen to hydrocarbon mole ratio of 8:1, and a temperature sufficient to continuously produce a C.sub.5 + reformate having an octane number of 102 F-1 clear. It is to be noted that these are exceptionally severe conditions.

The heavy Kuwait naphtha has an API gravity at 60.degree. F. of 60.4, an initial boiling point of 184.degree. F., a 50% boiling point of 256.degree. F., and an end boiling point of 360.degree. F. In addition, it contains about 8 vol. % aromatics, 71 vol. % paraffins, 21 vol. % naphthenes, 0.5 wt. parts per million sulfur, and 5 to 8 wt. parts per million water. The F-1 clear octane number of the raw stock is 40.0.

The fixed bed reforming plant is made up of a reactor containing the sulfided acidic catalyst, a hydrogen separation zone, a debutanizer column, and suitable heating, pumping, cooling and controlling means. In this plant, a hydrogen recycle stream and the charge stock are commingled and heated to the desired temperature. The resultant mixture is then passed downflow into a reactor containing the catalyst as a fixed bed. An effluent stream is then withdrawn from the bottom of the reactor, cooled to about 55.degree. F. and passed to a separating zone wherein a hydrogen-rich gaseous phase separates from a liquid hydrocarbon phase. A portion of the gaseous phase is continuously passed through a high surface area sodium scrubber and the resulting water-free hydrogen stream recycled to the reactor in order to supply hydrogen thereto, and the excess hydrogen over that needed for plant pressure is recovered as excess separator gas. The liquid hydrocarbon phase from the hydrogen separating zone is withdrawn therefrom and passed to a debutanizer column of conventional design wherein light ends are taken overhead as debutanizer gas and a C.sub.5 + reformate stream recovered as bottoms.

The test run is continued for a catalyst life of about 20 barrels of charge per pound of catalyst utilized, and it is determined that the activity, selectivity and stability of the present sulfided acidic multimetallic catalyst are vastly superior to those observed in a similar type test with a conventional commercial reforming catalyst. More specifically, the results obtained from the subject catalyst are superior to the platinum metal-containing catalyst of the prior art in the areas of temperature required to make octane, C.sub.5 + yield at octane, average rate of temperature increase necessary to maintain octane, and C.sub.5 + yield decline rate. Also it is noted that the principal effect of the sulfiding step of the present invention on the performance of the instant catalyst involves diminished undesired exothermic demethylation and other hydrogenolysis activity during the initial portion of the test run and markedly increased over-all stability.

It is intended to cover by the following claims all changes and modifications of the above disclosure of the present invention which would be self-evident to a man of ordinary skill in the catalyst formulation art or the hydrocarbon conversion art.