GB1590124A - Low density alumina particles having high micropore volume - Google Patents

Description

(54) LOW DENSITY ALUMINA PARTICLES HAVING HIGH MICROPORE VOLUME (71) We, UOP INC., a Corporation organized under the laws of the State of Delaware, United States of America, of Ten UOP Plaza, Algonquin & Mt. Prospect Roads, Des Plaines, Illinois, United States of America, do hereby declare the invention, for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following Statement: The present invention relates to porous alumina particles such as are used as catalyst supports or carrier materials.

This invention provides porous alumina particles featuring low bulk density in combination with high micropore volume. The low density-high micropore volume alumina particles, when utilized as a catalyst support or carrier material, impart improved activity to the catalytic composite. The porous, low density-high micropore volume alumina particles are especially useful as a support or carrier material for a platinum group metal, alone or in combination with a promoter metal, to yield an improved reforming catalyst or a dehydrogenation catalyst.

The porous alumina particles according to this invention are characterized by an average bulk density of from 0.25 to 0.4 grams per cubic centimeter, with from 0.6 to 0.8 cubic centimetres per gram of the total pore volume being associated with pores having an average diameter of up to 600 Angstroms.

The total pore volume of porous alumina particles utilized as a catalyst support or carrier material is typically expressed in terms of pore size distribution, i.e. in terms of the pore volume attributable to macropores and pore volume attributable to micropores. As herein contemplated, micropores are those pores having an average diameter of up to 600 Angstroms as determined from the adsorption isotherm for nitrogen at liquid nitrogen temperatures and at a relative pressure (P/P(,) of 0.97. The micropore volume will then consist of that portion of the total pore volume attributable to ores up to 600 Angstroms in diameter, and the macropore volume will be the difference between the total pore volume and the micropore volume. The total surface area of the alumina particles is a function of the micropore volume, substantially all of the surface area being associated with pores of up to 600 Angstroms in diameter.

The alumina may be any of the various hydrated aluminum oxides or alumina gels including boehmite, gibbsite, bayerite, and the like. Activated aluminas, such as have been calcined or thermally treated at temperatures in excess of 400"C. with the elimination of at least a portion of the water and/or hydroxyl groups commonly associated therewith, are particularly useful, especially gamma- and eta-alumina prepared by the thermal treatment of boehmite and bayerite respectively at temperatures generally in the range of from 400" to 850"C. The alumina can be prepared by the addition of an alkaline reagent, such as ammonium hydroxide, to an aqueous aluminum salt solution, for example an aqueous aluminum chloride solution, to precipitate a colloidal hydrous alumina or alumina gel. The gel can be dried as hereinafter directed and calcined at a temperature generally in excess of 400"C. The alumina may be subsequently prepared in tableted or granular form of graded mesh size adaptable for use in a fixed catalyst bed.

Alumina particles of substantially spherical shape offer numerous advantages when employed as a support or carrier material for catalytically active metallic components.

When disposed in a fixed bed in a reaction or contact zone, the spherical particles permit more uniform packing and reduce the tendency of the reactant stream to channel through the catalyst bed. When employed in a moving bed type of operation, i.e. where the particles are transported from one zone to another by the reactants or an extraneous carrying medium, the spheroidal particles have a further advantage in that there are no sharp edges to break or wear off during processing thus creating a tendency to plug process equipment.

One preferred method of preparing the alumina as spheroidal particles involves the gelation of a hydrosol precursor of alumina in accordance with the oil drop method. The hydrosol may be prepared by hydrolyzing an acid salt of an appropriate metal in aqueous solution and treating the resulting solution at conditions to reduce the acid anion concentration thereof, e.g. by neutralization. The resulting olation reaction yields inorganic polymers of colloidal dimension dispersed and suspended in the remaining liquid. For example, an alumina hydrosol can be prepared by the hydrolysis of an acid salt of aluminum, such as aluminum chloride, in aqueous solution, and treating said solution at conditions to reduce the resulting chloride anion concentration thereof, as by neutralization, to achieve an aluminum/chloride anion weight ratio from 1:1 to 1.5:1. Reduction in the acid anion concentration may be accomplished in any conventional or otherwise convenient manner. Thus, the acid anion concentration can be reduced by utilizing aluminum metal as a neutralizing agent. In this case, the salt of neutralization is an aluminum salt subject to hydrolysis and ultimate sol formation. In some cases, as in the case of aluminum acetate, where the acid anion is sufficiently volatile, the desired acid anion deficiency is created simply by heating. Another method of producing a suitable alumina hydrosol is in the electrolysis of an aluminum salt solution, for example an aqueous chloride solution, in an electrolytic cell having a porous partition between the anode and the cathode whereby an acid anion deficiency is effected in cathode compartment with the formation of an alumina hydrosol therein.

Preferably, the alumina hydrosol is an aluminum chloride hydrosol, which may otherwise be referred to as an aluminum oxychloride hydrosol or aluminum hydroxychloride hydrosol, such as is formed utilizing aluminum metal as a neutralizing agent in conjunction with an aqueous aluminum chloride solution. The aluminum chloride hydrosol is typically prepared by digesting aluminum in aqueous hydrochloric acid and/or aluminum chloride solution at about reflux temperature, usually from 80" to 1050C., and reducing the chloride anion concentration of the resulting aluminum chloride solution by the device of maintaining an excess of the aluminum reactant in the reaction mixture as neutralizing agent. The aluminum chloride hydrosol is usually prepared to contain aluminum in from a 1:1 to 1.5:1 weight ratio with chloride anion.

In accordance with the oil drop method, the hydrosol is dispersed as droplets in a hot oil bath whereby gelatin occurs with the formation of spherical gel particles. In this type of operation, the hydrosol is set chemically utilizing ammonia as a neutralizing or setting agent. Usually, the ammonia is furnished by an ammonia precursor which is included in the hydrosol. The precursor is suitably hexamethylenetetramine, or urrea or mixtures thereof, although other weakly basic materials which are substantially stable at normal temperature but hydrolyzable to form ammonia with increasing temperature, are suitably employed.

Only a fraction of the ammonia precursor is hydrolyzed or decomposed in the relatively short period during which initial gelation occurs. During the subsequent aging process, the residual ammonia precursor retained in the spheriodal particles continues to hydrolyze and effect further polymerization of the alumina hydrogel whereby desirable pore characteristics are established. Aging of the hydrogel is suitably accomplished over a period of from 10 to 24 hours, preferably in the oil suspending medium, at a temperature of from 60 to 105"C. or more, and at a pressure to maintain the water content of the hydrogel spheres in a substantially liquid phase.

The foregoing oil drop method affords a convenient means of developing physical characteristics of the alumina which are desirable in a support or carrier material for catalytically active metallic components. The method involves a number of process variables which affect both the density and the micropore volume of the spheroidal gel product. Generally, the metals/acid anion ratio of the sol will influence the crystallization process and the average bulk density of the spheroidal gel particles -- higher ratios tending to give particles of lower average bulk density. Other process variables, including the time, temperature and pH at which the particles are aged, are effective to establish crystallite size and the micropore volume attendant therewith. Usually, temperatures in the higher range and longer aging periods result in lower average bulk densities.

In the usual course of drying and calcining the aged hydrogel particles, the drying step is invariably accompanied by large volume shrinkage of the particles and a corresponding increase in particle density. It has been observed that as the particle density increases there is a corresponding loss in the total pore volume of the paticles, and this is both logical and obvious. However, it has been further observed that as the particle density increases, the micropore volume of the particles tends to increase. It is postulated that substantially all of The tin, rhenium and/or germanium components, and particularly the tin and germanium components, are advantageously composited with the support or carrier material by coprecipitation or cogelation of said component with the alumina support or carrier material and, if so desired, subsequent impregnation and/or ion-exchange of the resulting composite with one or more of the remaining components herein set forth. For example, a soluble tin compound such as stannous or stannic chloride may be admixed with the described alumina hydrosol prior to dispersing the same as droplets in the hot oil bath, for cogelling. Following the aging process and subsequent calcination, an alumina support or carrier material is obtained comprising the tin component in intimate combination therewith and suitable for treatment by impregnation and/or ion-exchange techniques to incorporate, for example, the platinum group component. Porous particles which are a cogelled composite of alumina and tin containing from 0.1 to 5 wt. % tin, and characterised by an average bulk density of from 0.25 to 0.4 grams per cubic centimeter with from 0.6 to 0;8 cubic centimeters per gram of the total pore volume being associated with pores having an average diameter of up to 600 Angstroms, represent a preferred embodiment of this invention, said particles being optionally impregnated with from 0.1 to 2 wt % platinum group metal (particularly platinum) with or without similar amounts of rhenium and/or. germanium.

An alkali or alkaline earth component may be added to the alumina particles to enchance the dehydration activity of the catalyst, in the amount of from 0.01 to 5 wt. % of the catalyst calculated as the elemental metal. The preferred alkali or alkaline earth metal is lithium or potassium.

The alkali or alkaline earth component may be combined with the porous carrier material by any of the known procedures, and preferably by impregnating the carrier material either before or after it is calcined and either before, during or after the other components are added to the carrier material. It is preferred to add the platinum group (alone or together with the tin or germanium or rhenium component), dry and oxidise the resulting composite, then treat the oxidised composite with steam to reduce the halogen content thereof to less than 0.2 wt. %, and then add the alkali or alkaline earth component.

The final catalyst composite generally will be dried at a temperature of from 95" to 3150C. over a period of from 2 to 24 hours or more, and finally calcined at a temperature of from 375" to 595"C. in an ar atmosphere for a period of from 0.5 to 10 hours in order to convert the catalytic components substantially to the oxide form. Although not essential, it is preferred that the resultant calcined catalytic composite be subjected to a substantially water-free reduction step prior to its use in the conversion of hydrocarbons. This step is designed to insure a uniform and finely divided dispersion of the catalytic components throughout the carrier material. Preferably, substantially dry hydrogen is used as the reducing agent in this step. The reducing agent is suitably contacted with the calcined catalyst at a temperature of from 425" to 6500C. for a period of from 0.5 to 10 hours. This reduction treatment may be-performed in situ as part of a start-up sequence if precuations are taken to predry the plant to a substantially water-free state and if substantially water-free hydrogen is used.

The novel catalysts of this invention may be used for the reforming of petrol and the dehydrogenation of a dehydrogenatable hydrocarbon.

Example I An alumina hydrosol was prepared by digesting aluminum metal in dilute hydrochloric acid at a temperature of about 102"C. to yield a hydrosol containing aluminum in about 1.15:1 weight ratio with the chloride anion content thereof. Thereafter, an amount of stannic chloride calculated to provide alumina particles containing 0.5 wt: % tin was dissolved in the hydrosol. The hydrosol was then cooled and admixed with a 28% aqueous hexamethylenetetramine solution to provide a hydrosol containing about 12 wt. % hexamethylenetetramine and 8 wt. % alumina, the mixture being maintained at 50-70C. The hydrosol was formed into spheroidal hydrogel particles by emitting the same as droplets into a gas oil suspending medium contained in a dropping tower at about 90"C. The spherical gel particles were aged in a portion of the gas oil for about 11/2 hours at 1500C. and 300 psig pressure.

One portion of the aged spheres, hereinafter referred to as support A, was washed for about 1 hour in a flow of water. A second portion of the aged spheres, hereinafter referred to as support B, was washed substantially as described except that the washwater contained 1.0 wt. % surfactant (Antarox BL240). In each case, the spheres were dried for 1 hour at about 1900C., and calcined in air for 1 hour at 3450C., and then at 6750C. for 2 hours.

Ninety-four grams of each of the calcined supports, A and B, were impregnated with 275 milliliters of an aqueous chloroplatinic acid solution containing 1.636 milligrams of platinum per milliliter and 6 milliliters of concentrated hydrochloric acid. The supports the micropore volume is stablished during the aging processor presumably by the forinatoin aggregation or crystallites. This the aggregates are drawn close together during the drying operation with a resultant loss in total pore volume the micropore volum associated with said aggregates tends to increase In any case, when the aged hydrogel particles are dried at conditions to substantially obviate the aforesaid high volume shrinkage and resulting increase density the spheroidal gel product @@ characterized not only by low average bulk density bot als by the high micropore volume more tipical of the higher density products.

Drying conditions effective to substantially obviate the high volume shrinkage of the raged hydrogel particles particularly include a final water-washprior to drying with the adition of a surfactant to the wash water whereby the drying process effected in the presence of the surfactant. Preferably the surfactant is a nonionic surfactant although other surfactants may be employed. Suitable nonionic surfactants include the various and welle known polyoxyethylene alkylphenols, polyoxyethyleter alcohols, polyoxyethylene esters of fatty acids, polyoxyethylene mercaptans, polyoxyethylene Alkylamines, polyoxyethylene alkamides, and the like A polyoxyethylene alcohol with an average molecular weight of from 200 to 500 is particularly suitable. Preferably the nonionic surfactant is utilized in the wash water in a concentration of from 0.05 to 1.0 wt. %.

Drying of the particles is suitably effected at a temperature of from 38 to 250 . and the dried particles are suitably subsequently calcined, preferably in an oxidizing atmosphere suen as air, at a temperature of from 425 to 760 C. The calcined particles may be used per se or impregnates with one or more catalityc components.

In particular, the particles usefid a support or carier material for a platinum group component alone or in combination ith a tin component, a rhenium component and/or a germanium component to yield an improved reforming catalyst. The platinum group component is suitably composited with support on carries material by impregnation and/or ion exchange familiar in the art For example, ar soluble platinum group compound, i.e. a soluble compound of platinum, palladium, rhenium, ruthenium, osmium and/or iridium, is prepared in aqueous solution and the aluminium particles are soaked dipped, or otherwise immersed therein. Suitable platinium group compounds include platinum chlorid, chlorplatinic acid ammonium chloroplatinate, dinitrodilamino plati num and palladium chloride. It si common practice to impregnates the support or carrier material with an aqueous chloroplatinic acid solution acidified with hydrochlorid acid to facilitate an even distribution or platinum the support or carried material. The support or carrier material is preferably maintained in contact with the impregnating solution at ambient temperature conditionsm suitably for at least 30 minutes, and the impregnating solution there after evaporated to dryness. For example, a volume of the particulate support of carrier material is immersed in a substantially equal volume of impregnating solution a jacketed fotary dried and tumbled therein for a brief period at about room temperature.

Steam is there after applied to the dryer jacket to expedite evaporation of the impregnating solution and recovery of substantially dry impregnated particles.

The particles preferably contain from 0.01 or 0.1 to 2 wt. % of platinum group metal, especially platinum.

As heretofore stated, the porous alumina particles of this invention are also useful at a support or carrier material for a platinum group component in combination with a tin component, a rhenium component, and/or a germanium component. The tin, rhenium and/or germanium components be composite with the support or carrier material in any conventional otherwise convention manner. Suitable methods include impregnation and/or ion exchange of the support of carrier material with a suitable compound of one or more of the tin, rhenium and germanium components in any desired sequent, with or without intermediate calcination. In the impregnation of the support on carrier material it is a preferred practice to impregnate one or more of said components on said support or carrier simultaneously with the platinum group component from a common impregnating solution. For example, when the added component is in, stannic chlorides is conventiently and advantageous prepared in common solution with chloroplatinic acid, the concentra tion of each component therein being sufficient to yeild a catalyst product containing from 0.01 to 2 wt. % platinum and from 0.1 to 5 wt. % tin calculated as the elemental metals.

Similarly, when the desired added component is rhenium, perrhenic acid and chloroplatinic acid can be prepared a common aqueous solution to impregnate the support or carrier material, suitably with from 0.01 to 2 wt. % platinium and from 0.01 to 2 wt. % rhenium.

In still another embodiment of this invention, the added components germanium, and the germanium component can be impregnated on the support or carrier material from a common aqeuous solution of germanium tetrachloride and chloroplatinic acid to yield a catalyst product suitably containing from 0.01 to 2 wt. % platinium from 0.01 to 2 wt. % germanium. were each soaked in the impregnating solution for about 1/2 hour and the solution thereafter evaporated to dryness utilizing a rotary steam evaporator. In each case, the dried spheres were calcined for 1 hour in air at 1500C., and then for 1 hour at 525"C., and subsequently reduced in a hydrogen atmosphere for 1 hour at 565"C. The resulting Catalyst A and Catalyst B are described below: Catalyst A Catalyst B Average Bulk Density, gms/cc 0.50 0.315 Micropore Volume, cc/gm 0.66 0.66 Pt., wt. % 0.53 0.53 Sn, wt. % 0.50. 0.50 Cl, wt. % 1.19 1.31 Example II The catalysts were evaluated under substantially the same conditions utilizing a laboratory scale reforming apparatus comprising a reactor, a high pressure-high temperature hydrogen separator and a debutanizer column. A hydrogen-rich recycle gas was admixed with a naphtha charge stock to provide a hydrogen/hydrocarbon mole ratio of about 10:1. The hydrocarbon charge stock has an F-l clear octane rating of 40. The mixture was preheated and charged downflow in contact with a fixed bed of the catalyst contained in the reactor. The mixture was charged in contact with the catalyst at a liquid hourly space velocity of 1.5 with a reactor outlet pressure being maintained at 100 psig. The reactor effluent was passed through the hydrogen separator wherein the hydrogen-rich gaseous phase was separated at about 13"C., a portion of which was recycled to the reactor through a high surface area sodium scrubber. The liquid phase from the hydrogen separator was passed to the debutanizer column with a C5+ reformate product being recovered as bottoms from the column. The catalysts were in each case evaluated over six test periods, each test period comprising a 12-hour line-out period followed by a 24-hour test period, and the reactor inlet temperature was periodically adjusted to maintain the C5+ reformate octane rating at 102 F-l clear. The test results are tabulated below in terms of temperature required to make a 102 F-l clear octane product.

Temperature, "C.

Test Period Catalyst A Catalyst B 1 519 513 2 528 519 3 535 523 4 546 527 5 561 531 6 --- 536 The above-described comparative catalyst evaluation serves to illustrate one of the advantages to be derived from the practice of this invention, that is, improved activity and activity stability with respect to the reforming of gasoline boiling range feed stocks.

Claims (21)

WHAT WE CLAIM IS:

1. Porous alumina particles characterised by an average bulk density of from 0.25 to 0.4 grams per cubic centimeter, with from 0.6 to 0.8 cubic centimeters per gram of the total pore volume being associated with pores having an average diameter of up to 600 Angstroms.

2. Particles as claimed in claim 1 containing from 0.01 to 2 wt. % platinum group metal.

3. Particles as claimed in claim 2 wherein the platinum group metal is platinum.

4. Particles as claimed in claim 3 additionally containing from 0.01 to 2 wt. % rhenium.

5. Particles as claimed in claim 3 additionally containing from 0.01 to 2 wt. % germanium.

6. Particles as claimed in any of claims 1 to 5 additionally containing from 0.1 to 5 wt. % tin.

7. Particles as claimed in any of claims 1 to 6 containing from 0.01 to 5 wt. % alkali or alkaline earth component.

8. Particles as claimed in clam 7 wherein said alkaline or alkaline earth component is a lithium component.

9. Particles as claimed in claim 1 and substantially as hereinbefore described or exemplified.

10. A method of preparing alumina particles as claimed in claim 1 wherein an alumina hydrosol is gelled by the oil drop method, the resulting hydrogel particles are aged, the aged hydrogel particles are dried in the presence of a surfactant and the dried particles are calcined, the conditions in the gelling and aging steps being selected to provide a bulk density of from 0.25 to 0.4 grams per cubic centimeter for the particles and the drying conditions giving rise to a micropore volume of from 0.6 to 0.8 cubic centimeters per gram and retaining a bulk density of from 0.25 to 0.4 grams per cubic centimeter.

11. A method as claimed in claim 10 wherein the hydrogel particles are aged for 10 to 24 hours at 60 to 1050C under a pressure sufficient to maintain the water contained in the hydrogel particles in liquid phase and the particles are then washed with water containing a surfactant prior to drying at from 38 to 205"C and calcining in an oxidizing atmosphere at from 425 to 760"C.

12. A method as claimed in claim 10 or 11 wherein a non-ionic surfactant is used.

13. A method as claimed in any of claims 10 to 12 wherein the formed particles are impregnated with a platinum group component.

14. A method as claimed in claim 13 wherein the formed particles are additionally impregnated with a germanium component and/or a rhenium component and/or with a tin component.

15. A method as claimed in claim 13 wherein the alumina hydrosol is cogelled with a tin component and/or a germanium component.

16. A method as claimed in any of claims 13 to 15 wherein the impregnated particles are dried at from 95 to 3150C for at least 2 hours and calcined in air at from 375 to 5950C for 0.5 to 10 hours to convert the additional component(s) to oxide forms.

17. A method as claimed in claim 16 wherein the calcined material is subjected to water-free reduction with hydrogen at 425 to 6500C of from 0.5 to 10 hours.

18. A method of preparing alumina particles as claimed in claim 1 carried out substantially as described in the foregoing Example 1.

19. Alumina particles as claimed in claim 1 when prepared by a method as claimed in any. of claims 10 to 18.

20. A process for the reforming of petrol wherein the feedstock is contacted with particles as claimed in any of claims 1 to 9 or 19 at reforming conditions.

21. A process for the dehydrogenation of a dehydrogenatable hydrocarbon wherein the feedstock is contacted at dehydrogenation conditions with the particles as claimed in any of claims 1 to 9 to 19 which contain an alkali or alkaline earth component.