EP1838433A1

EP1838433A1 - Reforming catalyst with chelated promoter

Info

Publication number: EP1838433A1
Application number: EP05711584A
Authority: EP
Inventors: Frank S. UOP LLC MODICA; Thomas K. UOP LLC MCBRIDE; Irina Z. Galperin
Original assignee: UOP LLC
Current assignee: Honeywell UOP LLC
Priority date: 2005-01-18
Filing date: 2005-01-18
Publication date: 2007-10-03
Also published as: NO20074221L; CA2594803C; EP1838433A4; JP2008526503A; WO2006078240A1; CA2594803A1

Abstract

A process for preparing a naphtha reforming catalyst has been developed. The process involves the use of a chelating ligand such as ethylenediaminetetraacetic acid (EDTA). The aqueous solution of the chelating ligand and a tin compound is used to impregnate a support, e.g., alumina extrudates. A platinum-group metal is also an essential component of the catalyst. Rhenium may also be a component. A reforming process using the catalyst has enhanced yield, activity, and stability for conversion of naphtha into valuable gasoline and aromatic products.

Description

(

REFORMING CATALYST WITH CHELATED PROMOTER

BACKGROUND OF THE INVENTION

[0001] This invention relates to a process for preparing a catalyst. The process involves the use of a chelating ligand to form a tin chelate complex. The invention also relates to a reforming process using the catalyst which provides increased selectivity to gasoline components and aromatic products.

[0002] Catalytic reforming involves a number of competing processes or reaction sequences. These include dehydrogenation of cyclohexanes to aromatics, dehydroisomerization of alky Icy clopentanes to aromatics, dehydrocyclization of an acyclic hydrocarbon to aromatics, hydrocracking of paraffins to light products boiling outside the gasoline range, dealkylation of alkylbenzenes and isomerization of paraffins. Some of the reactions occurring during reforming, such as hydrocracking which produces light paraffin gases, have a deleterious effect on the yield of products boiling in the gasoline range. Process improvements in catalytic reforming thus are targeted toward enhancing those reactions effecting a higher yield of the gasoline fraction at a given octane number.

[0003] It is of critical importance that a catalyst exhibits the capability both to initially perform its specified functions efficiently and to perform them satisfactorily for prolonged periods of time. The parameters used in the art to measure how well a particular catalyst performs its intended function in a particular hydrocarbon reaction environment are activity, selectivity and stability. In a reforming environment, these parameters are defined as follows: [0004] (1) Activity is a measure of the ability of the catalyst to convert hydrocarbon reactants to products at a designated severity level, with severity level representing a combination of reaction conditions: temperature, pressure, contact time, and hydrogen partial pressure. Activity typically is characterized as the octane number of the pentanes and heavier ("C5⁺") product stream from a given feedstock at a given severity level, or conversely as the temperature required to achieve a given octane number.

[0005] (2) Selectivity refers to the percentage yield of petrochemical aromatics or C5⁺ gasoline product from a given feedstock at a particular activity level. [0006] (3) Stability refers to the rate of change of activity or selectivity per unit of time or of feedstock processed. Activity stability generally is measured as the rate of change of operating temperature per unit of time or of feedstock to achieve a given C5⁺ product octane, with a lower rate of temperature change corresponding to better activity stability, since catalytic reforming units typically operate at relatively constant product octane Selectivity stability is measured as the rate of decrease of Cζ⁺ product or aromatics yield per unit of time or of feedstock.

[0007] Programs to improve performance of reforming catalysts are being stimulated by the reformulation of gasoline, following upon widespread removal of lead antiknock additive, in order to reduce harmful vehicle emissions. Gasoline-upgrading processes such as catalytic reforming must operate at higher efficiency with greater flexibility in order to meet these changing requirements. Catalyst selectivity is becoming ever more important to tailor gasoline components to these needs while avoiding losses to lower- value products. The major problem facing workers in this area of the art, therefore, is to develop more selective catalysts while maintaining effective catalyst activity and stability. [0008] Reforming catalysts containing tin as platinum-group (or Group VIII) modifiers, along with optional third metal promoters such as rhenium, indium, gallium, iridium, etc., are well known in the art. US 6,153,090 discloses a process for catalytic reforming using a catalyst comprising at least one group VIII metal, at least one additional element selected from the group consisting of germanium, tin, lead, rhenium, gallium, indium, thallium, where the promoter element is added in the form of an organometallic carboxylate compound containing at least one organometallic bond such as tributyl tin acetate.

[0009] It is also known that chelating ligands can be used to impregnate metals onto a support. For example, US 4,719,196 discloses preparing a catalyst using a solution containing ethylene diaminetetraacetic acid (EDTA), a noble metal and ammonia. US 5,482,910 discloses a process for preparing a catalyst using a mixed solution comprising EDTA, a noble metal, and a promoter metal, such as an alkali earth metal. US 6,015,485 and US 6,291,394 disclose a process for treating an existing catalyst with EDTA in order to create a bimodal mesopore structure with alumina at two different crystallite sizes.

[0010] Accordingly, applicants have developed a process for preparing catalysts which involves the use of a stannous tin chelate complex to impregnate the tin component. The process involves preparing a tin solution containing a chelating ligand such as EDTA. This solution is heated and then used to impregnate a refractory oxide support such as alumina.

Before, during, or after the chelated impregnation, another solution can be used to impregnate platinum-group metals and any other desired promoter metals such as rhenium. Preferably, the impregnation with the tin chelate is performed at basic conditions, while the impregnation of the other components is performed at acidic conditions. After impregnation, calcination and reduction provide the desired catalyst.

SUMMARY OF THE INVENTION

[0011] This invention relates to an improved naphtha reforming process, a catalyst for carrying out the naphtha reforming process, and a process for preparing a naphtha reforming catalyst. Accordingly, one aspect of the invention is a process for preparing a naphtha reforming catalyst comprising: a) preparing a first aqueous solution containing a chelating agent and a stannous tin compound; b) heating said first solution for a time of 5 minutes to 5 hours at a temperature of 40°C to 100⁰C; c) preparing a second aqueous solution containing a platinum-group compound and a rhenium compound; e) impregnating a solid refractory oxide support with said first solution to give a first impregnated solid support; g) impregnating said first impregnated solid support with said second solution to give a second impregnated solid support; h) calcining the second impregnated solid support at a temperature of 300⁰C to 850°C for a time of 10 minutes to 18 hours to give a calcined catalyst; and i) reducing the calcined catalyst at a temperature of 300° to 850⁰C for a time of 30 minutes to 18 hours under a reducing atmosphere, thereby providing said catalyst suitable for naphtha reforming. [0012] The invention also relates to a process for the catalytic reforming of a naphtha feedstock which comprises contacting the feedstock at reforming conditions with a catalyst comprising a particulate inorganic oxide support having dispersed thereon a stannous tin component, a platinum-group metal component, and a rhenium component; the catalyst characterized in that the tin component is deposited on the support by impregnation using a tin chelate complex and is uniformly distributed throughout the support. [0013] Furthermore, the invention relates to a catalyst effective for naphtha reforming comprising a particulate refractory inorganic oxide support having dispersed thereon a stannous tin component in an amount of 0.01 to 5 mass-% on an elemental basis, a platinum component in an amount of 0.01 to 2 mass-% on an elemental basis, and a rhenium component in an amount of 0.05 to 5 mass-% on an elemental basis. The catalyst is characterized in that the tin is uniformly distributed and the platinum-group metal is uniformly distributed; the tin being dispersed on the support with an impregnation using a tin chelate complex.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG. 1 presents plots of C5⁺ liquid yields as a function of catalyst life for various catalysts incorporating tin by different methods.

[0015] FIG. 2 presents plots of average reactor block temperatures corresponding to catalyst activity as a function of catalyst life for various tin incorporation methods.

DETAILED DESCRIPTION OF THE INVENTION

[0016] The catalyst of the present invention has particular utility as a hydrocarbon conversion catalyst. The catalyst is particularly suitable for catalytic reforming of gasoline- range feedstocks, and also may be used for, inter alia, dehydrocyclization, isomerization of aliphatics and aromatics, dehydrogenation, hydro-cracking, disproportionation, dealkylation, alkylation, transalkylation, and oligomerization. In the preferred catalytic reforming process, hydrocarbon feedstock and a hydrogen-rich gas are preheated and charged to a reforming zone containing typically two to five reactors in series. Suitable heating means are provided between reactors to compensate for the net endothermic heat of reaction in each of the reactors. Reactants may contact the catalyst in individual reactors in either upflow, downflow, or radial flow fashion, with the radial flow mode being preferred. The catalyst is contained in a fixed-bed system or, preferably, in a moving-bed system with associated continuous catalyst regeneration. Alternative approaches to reactivation of deactivated catalyst are well known to those skilled in the art, and include semi-regenerative operation in which the entire unit is shut down for catalyst regeneration and reactivation or swing-reactor operation in which an individual reactor is isolated from the system, regenerated and reactivated while the other reactors remain on-stream. [0017] Reforming conditions applied in the reforming process of the present invention include a pressure selected within the range of 100 kPa to 7 MPa (abs). Particularly good results are obtained at low pressure, namely a pressure of 350 to 2500 kPa (abs). Reforming temperature is in the range from 315° to 600°C, and preferably from 425° to 565°C. As is well known to those skilled in the 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. Sufficient hydrogen is supplied to provide an amount of 1 to 20 moles of hydrogen per mole of hydrocarbon feed entering the reforming zone, with excellent results being obtained when 2 to 10 moles of hydrogen are used per mole of hydrocarbon feed. Likewise, the liquid hourly space velocity (LHSV) used in reforming is selected from the range of 0.1 to 20 hr" 1, with a value in the range of 1 to 5 hr 1 being preferred. [0018] The hydrocarbon feedstock that is charged to this reforming system preferably is a naphtha feedstock comprising naphthenes and paraffins that boil within the gasoline range. The preferred feedstocks are naphthas consisting principally of naphthenes and paraffins, although, in many cases, aromatics also will be present. This preferred class includes straight- run gasolines, natural gasolines, synthetic gasolines, and the like. The gasoline-range naphtha charge stock may be a full-boiling gasoline having an initial ASTM D-86 boiling point of from 40° to 80⁰C and an end boiling point within the range of from 160° to 220°C, 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 100° to 200°C. If the reforming is directed to production of one or more of benzene, toluene and xylenes, the boiling range may be principally or substantially within the range of 60° to 150⁰C.

[0019] As stated, the present invention relates to a process for preparing a catalyst. The catalyst comprises a solid refractory oxide support having dispersed thereon a tin component, at least one platinum group metal component and optionally a modifier metal such as rhenium. The support can be any of a number of well-known supports in the art including aluminas, silica/alumina, silica, titania, zirconia, and zeolites. The aluminas which can be used as support include gamma alumina, theta alumina, delta alumina, and alpha alumina with gamma and theta alumina being preferred. Included among the aluminas are aluminas which contain modifiers such as tin, zirconium, titanium and phosphate. The zeolites which can be used include: faujasites, zeolite beta, L-zeolite, ZSM-5, ZSM-8, ZSM-11, ZSM-12 and ZSM-35. The supports can be formed in any desired shape such as spheres, pills, cakes, extrudates, powders, granules, etc. and they may be utilized in any particular size. [0020] One way of preparing a spherical alumina support is by the well known oil drop method which is described in US 2,620,314. The oil drop method comprises forming an aluminum hydrosol by any of the techniques taught in the art and preferably by reacting aluminum metal with hydrochloric acid; combining the 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 and drying treatments in oil and ammoniacal solutions to further improve their physical characteristics. The resulting aged and gelled spheres are then washed and dried at a relatively low temperature of 80° to 260°C and then calcined at a temperature of 455° to 705°C for a period of 1 to 20 hours. This treatment effects conversion of the hydrogel to the corresponding crystalline gamma alumina If theta alumina is desired, then the hydrogel spheres are calcined at a temperature of 950° to 1100°C.

[0021] An alternative form of carrier material is a cylindrical extrudate, preferably pre- pared by mixing the alumina powder with water and suitable peptizing agents such as HCl until an extrudable dough is formed. The amount of water added to form the dough is typically sufficient to give a loss on ignition (LOI) at 500⁰C of 45 to 65 mass-%, with a value of 55 mass-% being preferred. The acid addition rate is generally sufficient to provide 2 to 7 mass-% of the volatile-free alumina powder used in the mix, with a value of 3 to 4 mass-% being preferred. The resulting dough is extruded through a suitably sized die to form extrudate particles. These particles are then dried at a temperature of 260° to 427°C for a period of 0.1 to 5 hours to form the extrudate particles. It is preferred that the refractory inorganic oxide comprises substantially pure alumina having an apparent bulk density of 0.6 to 1 g/cc and a surface area of 150 to 280 m^/g (preferably 185 to 235 m^/g, at a pore volume of 0.3 to 0.8 cc/g).

[0022] A Group IVA(IUPAC 14) metal component is an essential ingredient of the catalyst of the present invention. Of the Group IVA(IUPAC 14) metals, germanium and tin are preferred and tin is especially preferred. This component may be present as an elemental metal, as a chemical compound such as the oxide, sulfide, halide, oxychloride, etc., or as a physical or chemical combination with the porous carrier material and/or other components of the catalytic composite. Preferably, a substantial portion of the Group IVA(IUPAC 14) metal exists in the finished catalyst in an oxidation state above that of the elemental metal. The Group IVA(IUPAC 14) metal component optimally is utilized in an amount sufficient to result in a final catalytic composite containing 0.01 to 5 mass-% metal, calculated on an elemental basis, with best results obtained at a level of 0.1 to 0.5 mass-% metal. [0023] The Group IVA(IUPAC 14) metal or metals are dispersed onto the desired support as follows. First, an aqueous solution of a chelating ligand and at least one soluble, decomposable metal promoter compound is prepared to give a promoter metal chelate complex. Preferably, the metal compound is a tin compound. More preferably, the tin compound is a tin salt. Examples of suitable tin salts or water-soluble compounds of tin include without limitation stannous bromide, stannous chloride, stannous fluoride, stannous iodide, stannous sulfate, stannous tartrate, stannous oxalate, stannous acetate and the like compounds. The utilization of a tin salt in the form of a chloride compound, such as stannous or stannic chloride is particularly preferred since it facilitates the incorporation of both the tin component and at least a minor amount of a halogen component in a single step. Highly preferred is a salt with stannous tin having a plus two oxidation state. [0024] The chelating ligands which can be used in the process of this invention include amino acids which upon decomposing do not leave overly detrimental components on the support, e.g., sulfur. Specific examples of these amino acids include ethylenediaminetetraacetic acid ("EDTA"), nitrilotriacetic acid, N-methylaminodiacetic acid, iminodiacetic acid, glycine, alanine, sarcosine, α-aminoisobutyric acid, N,N-dimethylglycine, α,β-diaminopropionate, aspartate, glutamate, histidine, and methionine.

[0025] The chelate-metal complex solution, which is preferably a chelate-tin complex solution, is heated for a time of 5 minutes to 5 hours at a temperature of 40° to 100°C or its boiling point. The ratio of chelating ligand to the metal salt will vary from 1 to 8 and preferably from 1.5 to 4. [0026] The chelate-metal solution described above may also contain a basic compound selected from the group consisting of ammonium hydroxide and quaternary ammonium compounds having the formula NRjR2R3R4⁺X^" where Rj, R2, R3, R4 are each separately methyl, ethyl, propyl, butyl or t-butyl and X is hydroxide. The purpose of adding one or more of these basic compounds is to adjust the pH of the solution in order to vary the distribution of the metals. Further, the distribution of the IVA(IUPAC 14) metal may be different from the distribution of the platinum-group or other promoter metal. For the present invention, it is preferred that the tin component and platinum-group components are uniformly distributed throughout the catalyst.

[0027] The chelate-metal complex solution is now used to deposit the metal onto the support by means well known in the art. Examples of said means include spray impregnation and evaporative impregnation. Spray impregnation involves taking a small volume of the mixed solution and spraying it over the support while the support is moving. When the spraying is over, the wetted support can be transferred to other apparatus for drying or finishing steps. One particular method of evaporative impregnation involves the use of a steam-jacketed rotary dryer. In this method the support is immersed in the impregnating solution which has been placed in the dryer and the support is tumbled by the rotating motion of the dryer. Evaporation of the solution in contact with the tumbling support is expedited by applying steam to the dryer jacket. The impregnated support is then dried at a temperature of 60° to 300°C and then calcined at a temperature of 300° to 850°C for a time of 30 minutes to 18 hours to give the calcined catalyst. Finally, the calcined catalyst is reduced by heating the catalyst under a reducing atmosphere, preferably dry hydrogen, at a temperature of 300° to 850°C for a time of 30 minutes to 18 hours.

[0028] In one aspect of the invention, the refractory oxide support is first impregnated with the tin chelate complex, and then impregnated with a platinum-group component. In another aspect of the invention, the tin chelate complex is impregnated after the platinum- group component. Note that the impregnation steps may overlap as well, thus functioning effectively as a co-impregnation. Preferably, once at least 80 mass-% of the platinum-group component has been impregnated onto the support then immediately thereafter impregnation with a tin chelate complex can begin. Alternatively, when two distinct impregnation procedures are performed then the support may be dried and/or calcined in between procedures as needed under the drying and calcination conditions listed hereinafter.

Preferably, the calcination after the first distinct impregnation is sufficient to convert the tin to a tin-oxide compound.

[0029] An essential ingredient of the catalyst is a dispersed platinum-group component. This platinum-group component may exist within the final catalytic composite as a compound such as an oxide, sulfide, halide, oxyhalide, etc., in chemical combination with one or more of the other ingredients of the composite or as an elemental metal. It is preferred that substantially all of this component is present in the elemental state and is uniformly dispersed within the support material. This component may be present in the final catalyst composite in any amount which is catalytically effective, but relatively small amounts are preferred. Of the platinum-group metals which can be dispersed on the desired support, preferred metals are rhodium, palladium, platinum, and platinum being most preferred. Platinum generally comprises 0.01 to 2 mass-% of the final catalytic composite, calculated on an elemental basis. Excellent results are obtained when the catalyst contains 0.05 to 1 mass-% of platinum. [0030] This platinum component may be incorporated into the catalytic composite in any suitable manner, such as coprecipitation or cogelation, ion-exchange, or impregnation, in order to effect a uniform dispersion of the platinum component within the carrier material. The preferred method of preparing the catalyst involves the utilization of a soluble, decomposable compound of platinum to impregnate the carrier material. For example, this component may be added to the support by commingling the latter with an aqueous solution of chloroplatinic acid. Other water-soluble compounds of platinum may be employed in impregnation solutions and include ammonium chloroplatinate, bromoplatinic acid, platinum dichloride, platinum tetrachloride hydrate, platinum dichlorocarbonyl dichloride, dinitrodiaminoplatinum, etc. The utilization of a platinum chloride compound, such as chloroplatinic acid, is preferred since it facilitates the incorporation of both the platinum component and at least a minor quantity of the halogen component in a single step. Best results are obtained in the preferred impregnation step if the platinum compound yields complex anions containing platinum in acidic aqueous solutions. 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 distribution of the metallic component. 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 compounds; however, in some cases, it may be advantageous to impregnate the carrier material when it is in a gelled state.

[0031] Rhenium is a metal promoter of the catalyst. The platinum and rhenium components of the terminal catalytic composite may be composited with the refractory inorganic oxide in any manner which results in a preferably uniform distribution of these components such as coprecipitation, cogelation, coextrusion, ion exchange or impregnation. Alternatively, non-uniform distributions such as surface impregnation are within the scope of the present invention. The preferred method of preparing the catalytic composite involves the utilization of soluble decomposable compounds of platinum and rhenium for impregnation of the refractory inorganic oxide in a relatively uniform manner. For example, the platinum and rhenium components may be added to the refractory inorganic oxide by commingling the latter with an aqueous solution of chloroplatinic acid and thereafter an aqueous solution of perrhenic acid. Other water-soluble compounds or complexes of platinum and rhenium may be employed in the impregnation solutions. Typical decomposable rhenium compounds which may be employed include ammonium perrhenate, sodium perrhenate, potassium perrhenate, potassium rhenium oxychloride, potassium hexachlororhenate (IV), rhenium chloride, rhenium heptoxide, and the like compounds. The utilization of an aqueous solution of perrhenic acid is preferred in the impregnation of the rhenium component.

[0032] As heretofore indicated, any procedure may be utilized in compositing the platinum component and rhenium component with the refractory inorganic oxide as long as such method is sufficient to result in relatively uniform distributions of these components. Accordingly, when an impregnation step is employed, the platinum component and rhenium component may be impregnated by use of separate impregnation solutions or, as is preferred, a single impregnation solution comprising decomposable compounds of platinum component and rhenium component. Irrespective of whether single or separate impregnation solutions are utilized, hydrogen chloride, nitric acid, or the like acid may be also added to the impregnation solution or solutions in order to further facilitate uniform distribution of the platinum and rhenium components throughout the refractory inorganic oxide. Additionally, it is generally preferred to impregnate the refractory inorganic oxide after it has been calcined in order to minimize the risk of washing away valuable platinum and rhenium compounds; however, in some cases, it may be advantageous to impregnate refractory inorganic oxide when it is in a gelled, plastic dough or dried state. If two separate impregnation solutions are utilized in order to composite the platinum component and rhenium component with the refractory inorganic oxide, separate oxidation and reduction steps may be employed between application of the separate impregnation solutions. Additionally, halogen adjustment steps may be employed between application of the separate impregnation solutions. Such halogenation steps will facilitate incorporation of the catalytic components and halogen component into the refractory inorganic oxide.

[0033] It may be desirable to use the methods of US 5,482,910 to use chelating agents to incorporate the platinum-group and/or rhenium components in a dual component, or co- impregnation type manner of the platinum-group and/or rhenium compounds along with a chelate tin complex, or independent of the complex.

[0034] Irrespective of its exact formation, the dispersion of platinum component and rhenium component must be sufficient so that the platinum component comprises, on an elemental basis, from 0.01 to 2 mass-% of the finished catalytic composite. Additionally, there must be sufficient rhenium component present to comprise, on an elemental basis, from 0.01 to 5 mass-% of the finished composite.

[0035] In addition to the catalytic components described above, other components may be added to the catalyst. For example, a modifier metal selected from the group consisting of germanium, lead, indium, gallium, iridium, lanthanum, cerium, phosphorous, cobalt, nickel, iron and mixtures thereof may be added to the catalyst.

[0036] An optional step in the process of this invention involves halogenation, which is preferably oxychlorination, of the reduced catalyst described above. If such a step is desired, the catalyst is placed in a reactor and a gaseous stream containing a halogen, which is preferably chloride or chlorine, is flowed over the catalyst at a flow rate of 0.9 kg/hr to 18.1 kg/hr, at a temperature of 300° to 85O⁰C for atime of 10 minutes to 12 hours. The gaseous stream can be a hydrogen chloride/chlorine stream, a water/HCl stream, a water/Cl2 stream or a chlorine stream. The purpose of this step is to provide optimum dispersion of the Group VIII and provide a certain amount of halide, preferably chloride, on the final catalyst. The halogen content of the final catalyst should be such that there is sufficient halogen to comprise, on an elemental basis, from 0.1 to 10 mass-% of the finished composite. Optionally, the catalytic composite may be subjected to a presulfiding step. The optional sulfur component may be incorporated into the catalyst by any known technique.

EXAMPLE 1

[0037] Comparatively many catalyst formulations require the addition of tin to modify catalyst metal and acid functions. For example, in the case of spherical alumina support preparation, tin is added in alumina-sol which, due to very high acidity, provided the excellent conditions for uniform tin distribution. When extrudate was used as a support, tin could be incorporated by addition of corresponding tin salts (typically SnCl^ water solution) to dough before extrusion or by impregnation of extrudate. The addition of tin in dough results usually in tin precipitation due to the buffering of solution pH to 4-5 by alumina and formation of tin clumps containing agglomerated tin. Highly dispersed and nearly uniform tin may be produced by the impregnation of support with SnCLj. solution but to avoid tin precipitation, a high concentration of acid is generally required (10-12 wt-% HCl, for example) which makes this impregnation procedure undesirable from a commercial point of view that includes alumina losses and practical corrosion concerns. Initially, it was established that only stannous Sn+2 produces stable complex solution with EDTA at a temperature of 40° to 9O⁰C while, in contrast, stannic Sn+4 precipitated at any conditions. For comparison, +4 tin distribution on support prepared by impregnation of tin in the presence of 12% HCl was not quite uniform and had an increased concentration on the surface when analyzed using Scanning Electron Microscopy (SEM). In other words, +4 tin could not be dissolved with EDTA and could not properly be distributed through a catalyst support when a precipitate formed. In order to determine how +4 tin would go into a catalyst, it was impregnated without EDTA but with a high concentration of HCl. Applicants observed how uniformly the +4 tin would go in an acidic environment. Yet the +4 tin was still skewed towards the surface and was unable to be uniformly distributed throughout the support. In fact, a rough calculation showed that almost 66% of the +4 tin was present in the surface half a first 400 μm of the catalyst particle.

EXAMPLE 2

[0038] A comparative study was performed using the method of US 3,994,832 to characterize the resulting catalyst and determine tin profiles throughout the catalyst particles using this method of treating an alumina support with EDTA prior to any metals impregnation.

[0039] A catalyst support material was treated with a chelating agent according to the method of the US 3,994,832 patent by dissolving 6.17 grams of EDTA in 5 cubic centimeters of concentrated ammonium hydroxide and diluting the solution to 500 cubic centimeters with water. Approximately 500 cubic centimeters of 1/16 inch gamma-alumina spheres were then immersed in the solution contained in a steam jacketed rotary dryer. The spheres were tumbled in the solution for a ¹A hour at room temperature, after which steam was applied to the dryer jacket and the solution evaporated to dryness in contact with the tumbling spheres. [0040] About 100 cubic centimeters of the chelate impregnated alumina spheres were impregnated with a common solution of stannic chloride and chloroplatinic acid. The impregnating solution was prepared by dissolving 0.37 grams of stannic chloride pentahydrate in 2.5 cubic centimeters of concentrated hydrochloric acid and 20 cubic centimeters of water. Then 18.8 cubic centimeters of chloroplatinic acid (10 milligrams of platinum per cubic centimeter) was added and the resulting solution diluted to 100 cubic centimeters with water. The chelate-impregnated spheres were tumbled in the impregnating solution for a ¹A hour at room temperature utilizing a steam jacketed rotary dryer. Steam was thereafter applied to the dryer jacket and the solution evaporated to dryness in contact with the chelate impregnated alumina spheres. The dried spheres were subsequently heated to 392⁰F in air and, after a ¹A hour at said temperature, heated to 1000⁰F in air and held at 1000⁰F for 2 ¹A hours. The spheres were then treated in a substantially pure hydrogen stream for anl hour at 1050⁰F to yield the reduced form of the catalyst. The final catalyst product contained 0.375 wt. % platinum and 0.25 wt. % tin, calculated as the elemental metal. [0041] Tin profiles throughout catalyst particles were measured using Scanning Electron Microscopy (SEM). SEM data showed that in all cases, tin impregnated by the method of the '832 patent was not uniformly distributed throughout the support pills. SEM data showed that stannic tin was not uniform and had an increased concentration on the surface half, or first 400 μm of the catalyst particle.

EXAMPLE 3

[0042] Tin was added to the support when as part of the forming process called extrusion, or preferably co-extrusion. 2500 g of alumina powder (commercially available under the trade names Catapal B and/or Versal 250) was added to a mixer. A solution was prepared using 60.8 g nitric acid (67.5% HNO3) with 220 g deionized water, followed by the addition of 5.91 g of tin tartrate, and the solution was stirred. The solution was added to the alumina powder in the mixer, and mulled to make a dough suitable for extrusion. The dough was extruded through a die plate to form extrudate particles. The extrudate particles were dried at on a belt calciner operating with a first zone at 37O⁰C for 15 minutes and a second zone at 62O⁰C for 30 minutes. [0043] The extrudate particles were placed in a rotary evaporator and heated to 6O⁰C. A solution comprising deionized water, hydrochloric acid, chloroplatinic acid, and perrhenic acid was added to the rotary evaporator and temperature was raised to 100°C and the support rolled for 5 hours. Next the impregnated support was heated to a temperature of 525°C in dry air. When the temperature was reached, an air stream containing HCl and CI2 was flowed through the catalyst for 6 hours. Finally, the catalyst was reduced by flowing pure hydrogen over the catalyst at a temperature of 510°C for 2.5 hours.

[0044] Analysis of the catalyst showed it to contain 0.25 mass-% Pt and 0.25 mass-% Re and 0.1 mass-% Sn. The platinum, rhenium and tin were evenly distributed throughout the support. This catalyst was identified as Catalyst A.

EXAMPLE 4

[0045] A spherical alumina support was prepared by the well-known oil dropping method, per US 3,929,683. A tin component was incorporated in the support by commingling a tin component precursor with the alumina hydrosol and thereafter gelling the hydrosol. The catalyst particles were then dried at 600⁰C for 2 hours.

[0046] This support was placed in a rotary evaporator and heated to 6O⁰C. A solution comprising deionized water, hydrochloric acid, chloroplatinic acid, and perrhenic acid was added to the rotary evaporator and temperature was raised to 100⁰C and the support rolled for 5 hours. Next the impregnated support was heated to a temperature of 525°C in dry air. When the temperature was reached, an air stream containing HCl and CI2 was flowed through the catalyst for 6 hours. Finally, the catalyst was reduced by flowing pure hydrogen over the catalyst at a temperature of 510⁰C for 2.5 hours.

[0047] Analysis of the catalyst showed it to contain 0.25 mass-% Pt and 0.25 mass-% Re and 0.3 mass-% Sn. The platinum, rhenium and tin were evenly distributed throughout the support. This catalyst was identified as Catalyst B.

EXAMPLE 5

[0048] A tin-EDTA solution was prepared by combining in a flask 300 g of deionized water, 1.42 g of ammonium hydroxide (concentration 29.6% NH4OH), and 0.88 g of EDTA and stirred to dissolve EDTA. Then 0.3392 g of tin chloride (Sn Cl2*2H2θ) was added while stirring the solution and heated to 60°C to dissolve.

[0049] A second solution was prepared by the addition to 300 g of deionized water of 14.21 g of hydrochloric acid (37.6% HCl) and 17.48 ml of chloroplatinic acid (HyPtC^ solution with a Pt concentration 27.6 mg/ml). Next was added 14.65 ml of perrhenic acid (HReθ4 solution with a Re concentration 32.8 mg/ml).

[0050] 178.92 Grams of gamma alumina extrudates was placed in a rotary evaporator and heated to 60°C. The tin-EDTA solution was added to the gamma alumina in the rotary evaporator and the temperature was raised to 100°C and the support rolled for 5 hours. [0051] Then, the second solution was added to the rotary evaporator. The second solution was evaporated during 5 hours. Next the impregnated support was heated to a temperature of 525⁰C in dry air. When the temperature was reached, an air stream containing HCl and CI2 was flowed through the catalyst for 6 hours. Finally, the catalyst was reduced by flowing pure hydrogen over the catalyst at a temperature of 510⁰C for 2.5 hours. [0052] Analysis of the catalyst showed it to contain 0.25 mass-% Pt and 0.25 mass-% Re and 0.1 mass-% Sn. The platinum, rhenium and tin were evenly distributed throughout the support. This catalyst was identified as Catalyst C.

EXAMPLE 6

[0053] Catalysts A, B, C with even and uniform metals distributions were tested for catalytic reforming ability in a pilot plant using a typical naphtha feedstock available from the western United States as follows. Process conditions were selected to achieve a research octane number (RONC) of 100. Pressure was 1379 kPa (200 psig), hydrogen to hydrocarbon mole ratio was 1.5, and liquid hourly space velocity was 2.5 hr"l. Catalyst life was measured by the prevailing industry standard using Barrels of feed Per Cubic Foot of catalyst, or BPCF, as shown in FIG. 1 and FIG. 2. First, FIG. 1 presents plots of C5⁺ liquid yields as a function of catalyst life. Second, FIG. 2 presents plots of average reactor block temperatures corresponding to catalyst activity as a function of catalyst life. The results from this test are summarized in the table below indicating equivalent start of run activity and yield at 12.5 BPCF. TABLE

indicate that Catalyst C had the best yield and best activity.

Claims

CLAIMS:

1. A catalyst effective for naphtha reforming comprising a particulate refractory inorganic oxide support having distributed throughout a stannous tin component, a platinum- group metal component, and a rhenium component; the catalyst characterized in that the tin is uniformly distributed throughout the support and the platinum-group metal is uniformly distributed throughout the support; the tin being distributed throughout the support with an impregnation using a tin chelate complex.

2. The catalyst as claimed in claim 1 wherein the chelate is a chelating agent selected from the group consisting of ethylenediaminetetraacetic acid, nitrilotriacetic acid, N-methylaminodiacetic acid, iminodiacetic acid, glycine, alanine, sarcosine, α-aminoisoburyric acid, N,N-dimethylglycine, α,β-diaminopropionate, aspartate, glutamate, histidine, and methionine

3. The catalyst as claimed in claims 1 or 2 wherein the chelating agent is ethylenediaminetetraacetic acid.

4. The catalyst as claimed in claims 1, 2, or 3 wherein the catalyst further comprises

0.1 to 10 mass-% on an elemental basis of a halogen component.

5. The catalyst as claimed in claims 1 to 3, or 4 wherein the support is alumina.

6. The catalyst as claimed in claims 1 to 4, or 5 wherein the stannous tin component is present in an amount of 0.01 to 5 mass-% on an elemental basis.

7. The catalyst as claimed in claims 1 to 5, or 6 wherein the platinum-group metal component is platinum, which is present in an amount of 0.01 to 2 mass-% on an elemental basis.

8. The catalyst as claimed in claims 1 to 6, or 7 wherein the rhenium component is present in an amount of 0.05 to 5 mass-% on an elemental basis.

9. The catalyst as claimed in claims 2 to 7, or 8 wherein the chelating agent and stannous tin compound are present in a ratio of 1 to 8.

10. A process for the catalytic reforming of a naphtha feedstock which comprises contacting the feedstock at reforming conditions with the catalyst as claimed in claims 1 to 8, or 9, wherein the reforming conditions comprise a temperature of 315°C to 600⁰C, a pressure of 100 kPa to 7 MPa (abs), a liquid hourly space velocity of 0.1 to 20 hr-1, and a mole ratio of hydrogen to naphtha feedstock of 1 to 20.