CA2013423C - Hydrocarbon dehydrogenation catalyst - Google Patents

Abstract

A novel catalytic composition comprises a combination of a Group VIII
nobel metal component, a Group IA or IIA metal component, and a component selected from the group consisting of tin, germanium, lead, indium, gallium, thallium, or mixtures thereof, with a theta-alumina support having a surface area of 80-120 m2/g, and an ABD of 0.5g/cm3 or more. The novel catalytic composite has particular utility as a hydrocarbon dehydrogenation catalyst.

Description

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HYDROCARBON DEHYDROGENATION CATALYST~

FIELD OF THE INVENTION

This invention relates to the conversion of hydrocarbons, especially the dehydrogenation of dehydrogenatable hydrocarbons, in the presence of a catalyst 5 composite. This invention also pertains to a new catalyst co" ,posile.

BACKGROUND OF THE INVENTION

The dehydrGger ,alion of hydl ocarbons is an important commercial 10 process because of the great demand for dehydrogenated hydrocarbons for the manufacture of various chemical products such as delergents, high octane gasolines, pharmaceutical products, plastics, synthetic rubbers, and other products well known to those skilled in the art. One example of this ~rocess is dehydrogenating isobutane to produce isobutylene which can be 15 polymerized to provide tackifying agents for adhesives, viscosity-index additives for motor oils and impact-resistant and anti-oxidant additives for plastics.
The prior art is cogr,kanl of various catalytic composites which contain a Group Vlll metal component, an alkali or alkaline component, and a component selected from the group consisting of tin, germanium, lead, indium, gallium, 20 thallium, or mixtures thereof. However, the prior art has not yet known of a catalyst composite comprising the above components composited on a theta-alumina support having a surface area of 20 m2/g or less and having an apparent bulk density (ABD) of 0.5 g/cm3 or greater.
U.S. Patent 4,070,413 describes a dehydrogenation process utilizing a 25 catalyst comprising a Group Vlll metal and lithium, both impregnated on an alumina support. The alumina support is further characteri~ed in that it has been hydrothermally treated in steam at a terl,perature from about 800~ to 1200~C. The catalyst of this invention is distinguished from that of the '413 patent in that the instant catalyst comprises, in adrlition to a Group Vlll metal component and an alkali 3 0 or alkaline earth metal component, a component selected from the group consisting of tin, germanium, lead, indium, gallium, thallium, or mixtures thereof. Additionally, the catalyst support of this invention has a higher ABD than that disclosed in the '413 patent. The '413 patent discloses a catalyst having a pre-hydrothermally treatedABD of from about 0.25 to about 0.45 g/cm3. From Example lll, it is seen that the final catalyst composites of the catalyst of U.S. Patent '413 have an ABD of about 0.3. The catalyst of this invention must have a final ABD of at least 0.5 g/cm3.U.S. Patent 4,608,360 describes a cata Iytic composite comprising a Group Vlll noble metal component, a co-formed IVA metal component, and an alkalior alkaline earth metal on an alumina support having a surface area of from 5 to 150 m2/g. Additionally, the alumina support of the '360 patent is characterized in that the mean pore diameter is about 300 angstroms or less and more than about 55% of thetotal pore volume of the support is associated with pores having a mean diameter of 600 angstroms or more. In distinction, the catalyst of this invention is characterized lO in that it has a surface area of 120 m2/g or less and an ABD of 0.5 g/cm3 or more.
The catalyst of the '360 patent from Example ll has an ABD of about 0.3.
Additionally, the catalyst of the present invention contains very little of its total pore volume in pores having a diameter of 600 angstroms or more while the '360 catalyst has over 50% of its total pore volume associated with pores having mean diameters of about 600 angstroms or more.
U.S. Patent 4,717,779 discloses a process for dehydrogenating dehydrogenatable hydrocarbons using a selective oxidation catalyst comprising a Group Vlll noble metal component, a Group IVA component, and if desired a Group IA or IIA component. The components are composited on an alumina support wherein an alumina precursor possesses an ABD less than about 0.6 g/cm3 which, after calcination at a temperature of from about 900~ to 1500~C, will result in an alumina possessing an ABD of from 0.3 to 1.1 g/cm3 and where more than 40% of the pore volume is present in pores greater than 1500 angstroms. In contrast, the catalyst of the present invention comprises an ABD of 0.5 g/cm3 or greater and 25 preferably from 0.6 g/cm3 or greater. Additionally, very little of the total catalyst pore volume, that is, much less than 40% of the total catalyst pore volume, is comprised of pores of 1500 angstroms or greater.
The present invention is a catalytic component and process for its use with the catalyst having a surface area of 80-120 m2/g in conjunction with an 30 ABD of 0.5g/cm3 or greater. Nowhere in the prior art is such an alumina catalyst base known to have been utilized in conjunction with a platinum group metal component, a Group IVA metal component, and an alkali or alkaline metal component for the dehydrogenation of dehydrogenatable hydrocarbons.
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OBJECTIONS AND EMBODIMENTS

It is an object of the present invention to provide an improved catalytic composite and a process for the conversion of hydrocarbons and especially for the dehydrogenation of dehydrogenatable hydrocarbons utilizing the improved catalytic composite.
Accordingly, in a broad embodiment, the present invention is a catalytic composite comprising a combination of a first Group Vlll noble metal component, a second component selected from the group consisting of alkali or alkaline metal components or mixtures thereof, and a third component selected from the group consisting of tin, germanium, lead, indium, gallium, thallium, or mixtures thereof with alumina crystallites having a surface area of 80-120 m2/g and an ABD of 0.5g/cm3 or more wherein the alumina crystallites are at least 75% theta-alumina crystallites.
In a more preferred embodiment, the catalytic composite comprises a combination of catalytically effective amounts of platinum, cesium, and a third component selected from the group consisting of tin, germanium, lead, indium, gallium, thallium, or mixtures thereof, with a theta-alumina support having a surface area of from 80 to 120 m2/g and an ABD of 0.6g/cm3 or more.
In yet another embodiment, the invention is a process for the conversion of hydrocarbons utilizing one of the catalysts described immediately above. In a most preferred embodiment, the hydrocarbon conversion process is dehydrogenation wherein the dehydrogenation occurs at dehydrogenation conditions including a temperature of from 400~ to 900~C, a pressure of from 0.1 to 10 atmospheres and a liquid hourly space velocity of from 0.1 to 100 hr.~1.

JJ:vs n i ~v., DESCRIPTION OF THE DRAWINGS

Figures 1 and 2 are graphical representations of the performance in a dehydrogenation process of Catalysts D, E, and F. Figure 1 is a graph of the conversions in weight percent as a function of hours on-stream of the test.
Figure 2 is a plot of the selectivities of the catalysts in mole percent for producing propylene as a function of hours on-stream.

DETAILED DESCRIPTION OF THE INVENTION

An essential feature of the present invention lies in the characteristics of the support for the instant catalyst. Specifically, it is important that the alumina catalyst support have a surface area of 80-120 m2/g and a corresponding apparent bulk density (ABD) of 0.5 g/cm3 or greater. The support comprises a number of catalytic components including a Group Vlll noble component, an alkali or alkaline component, and a component selected from the group consisting of tin, germanium, lead, indium, gallium, thallium, or mixtures thereof. Such a catalyst exhibits improved catalyst conversion and selectivity in a hydrocarbon dehydrogenation process in comparison to similar dehy-JJ:vs f' 9~
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5~ 2013423 ~hoge,)ation catalysts of the prior art. It is believed the improvement is due in particular to the in~ased sizes of the pores of the catalyst. The catalyst poresare brger in co",parison to similar catalysts of the prior art so they do not L.econ,e easily plugged with coke and the stability of the catalyst as well as 5 ~ccess to the pores is improved.
As indicated above, one essential feature of the catalytic c~",posit~ of the invention is a first component selected *om Group Vlll noble meWs or mixtures ll ,ereof. The Group Vlll noble meW may be selecte~ I *om the group consisting of platinum, palladium, iridium, rhodium, osmium, ruthenium, or lO mixtures thereof. Platinum, however, is the prefer,ed Group Vlll noble metal co",,l~onent. It is believed that subs~ ially all of the Group Vlll noble metal coi "ponent exists within the catalyst in the elemenlal metallic state.
r,e~erd~ly the Group Vlll noble metal coi"ponenl is well dis"~er~d throughout the catalyst. It generally will co" ,,urise about 0.01 to 5 wt.%, calcu-15 lated on an elemental basis, of the final catalytic co"~po~i~e. r,eferably, thecatalyst co",prises about 0.1 to 2.0 wt.% Group Vlll noble metal coi"pGnent, especially about 0.1 to about 2.0 wt.% platinum.
The Group Vlll noble metal coi"pone,lt may be incor~.orsted in the catalytic coi"posile in any suitable manner such as, for example, by copreapi-20 tation or cogelation, ion exchange or i,npregnation, or deposition from a vaporphase or from an atomic source or by like procedures either before, while, or after other catalytic components are inco")or~te.l. The preferred method of incorl,orating the Group Vlll noble metal co,nponenl is to impregnate the alumina support with a solution or suspension of a decomposable compound of 25 a Group Vlll noble metal. For example, platinum may be added to the support by commingling the latter with an aqueous solution of chlorG~Jldtinic acid.
Another acid, for example, nitric acid or other oplional components, may be added to the impregndting solution to further assist in evenly dispersing or fixing the Group Vlll noble metal co",,,~onei~t in the final catalyst com ~ e.
Another essential feature of the catalyst of this invention is a second catalytic component coi"prised of an alkali or alkaline earth componenl. The alkali or alkaline earth con ,ponent of the present invention may be selected from the group consisli,,y of cesium, rubidium, potassium, sodium, and lithium or from the group consisting of barium, strontium, calcium, and magnesium or 3 5 mixtures of metals from either or both of these groups. Cesium, however, is the preferred secor"~ catalytic compGi,ent when only a single co",,,~onenl is ~le~ ~d for the co",pos~te of the invention. It is believed that the alkali and alkaline earth co",~nenl exists in the final catalytic o~",posite in an oxid~on state above that of the ele",ental metal. The alkali and alkaline earth corr~
~nent may be present as a compound such as the oxide, for exampb, ar 5 combined with the carrier ,oaterial or with the other catalytic con".~,"e-~.
rle~r~, the alkali and alkaline earth c~,nponent is well d;s~r:jed throughout the catalytic co"~>o~7te The alkali or alkaline earth com~ one.lt generally will comprise about 0.01 to 10 wt.%, cala~'c~ed on an elei "enlal basis of the final catalytic CGm~ ~s'te. When the alkali and alkaline earth corr,~,onenl 10 coi"~,rises first and secor,~l alkali metal, it generally will coi"prise from about 0.05 to about 2.0 wt.% of the first alkali metal, and from about 0.05 to about 10.0 wt.% of the second alkali metal, calculated on an elemental basis of the final catalytic co".po~rte.
The alkali or alkaline earth component may be incorpor~te.l in the 15 catalytic composite in any suitable manner such as, for example, by co,cre~
tation or cogela1io", by ion exchanye or impregnation, or by like proceJures either before, while, or after other catalytic components are incorporateJ. A
prefer,ecl Illetll~ of incorpGralin~ the first and second alkali colll,~o~ ls is to impregnate the carrier material with a solution of cesium nitrate.

2 o A third essential component of the catalyst of the present invention is a modifier metal COm~GI ~el)t selected from the group consislin~ of tin, germa-nium, lead, indium, gallium, thallium, and mixtures thereof. The effective amount of the third modifier metal cGmponenl is preferably u~ w~ly i"l,~,reg-nated. Gei ,erzlly, the catalyst will comprise from about 0.01 to about 10 wt.% of 25 the third modifier metal component calculated on an elemental basis on the weight of the final composite r, eferably, the catalyst will comprise from about0.1 to about 5 wt.% of the third ",oclifier metal co",pone, n.
The Gp~ional third modifier metal co"~poneu~ of the present invention pier~ra~ly is tin. ~l of the tin com,uo"e,ll may be ~reselll in ths catalyst in an 30 oxidation state above that of the elemental metal. This co",~onenl may exist within the composite as a co" ,pound such as the oxide, suHide, halide, oxychlo-ride, aluminate, etc., or in combination with the carrier material or other ingredi-ents of the comrosite. r,eferably, the tin component is used in an amount sufficient to result in the final catalytic composite containing, on an elemental 35 basis, about 0.01 to about 10 wt.% tin, with best results typically obtained with about 0.1 to about 5 wt.% tin.

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Suitable tin salts or water-soluble c~i"pounds of ffn which may be used include stannous bromide, stannous chloride, stannic chloride, stannic chloride pental ,~drate, stannic chloride tetrahydrate, stannic chloride trihydrate, stannic chloride diamine, stannic trichloride bromide, stannic cl)ro",dt~, 8tan 5 nous fluoride, stannic fluoride, stannic iodide, stannic sulfate, stannic t~
and the like com~.ounds. The utilization of a tin chloride cGmpound, such as stannous or stannic chloride is particularly pr~f~,. ,t,~l The third component of the catalyst may be c~"),,~os~ed with the support in any sequence. Thus, the first or secor,d co,-,pon~nt may be 10 impregnated on the support followed by sequential surface or uniform impregnation of one or more optiGual third components. Allen ,ati-/ely, the third component or col"pon~nts may be surface or uniformly impregnated on the support followed by i" ,pregnation of the other catalytic compon~n~.
The catalytic con,posi~e of this invention may also contain a halogen 15 component. The halogen c~",ponent may be fluorine, chlorine, bromine, or iodine, or mixtures II ,ereof. Chlorine is the prefel ,ed halogen con,ponenls. The halogen component is generally present in a combined state with the porous carrier material and alkali wl"pon~,lt. ~,eferal~ly, the halogen component is well dispersed throughout the catalytic corr~ros~e. The halogen COI"~O~ t 20 may comprise from more than 0.01 wt.% to about 15 wt.%, calculated on an elemental basis, of the final catalytic composrte.
The halogen c~mponent may be incorporated in the catalytic com-posite in any suitable " ,anner, either during the preparation of the carrier mate-rial or before, while, or after other catalytic c~",ponenls are incGr~.orat~.l. For 25 example, the alumina sol utilized to form the prefel,ed aluminum carrier ",aterial may contain halogen and thus conlribute at least some pOI lion of the halogen content in the final catalyst corr~posite. Also, the halogen component or a portion thereof may be added to the catalyst co",posite during the inc~r~ora-tion of the carrier material with other catalyst components, for example, by 30 using chloroplalinic acid to impregnate the platinum component. Also, the halogen component or a portion ll ,ereof may be added to the catalyst con ,pos-ite by contacting the catalyst with the halogen or a compound or solution containing the halogen before or after other catalyst components are incor-porated with the carrier male,ial. Suitab' compounds containing the halogen 35 include acids containing the halogen, for example, hydrochloric acid. Or, thehalogen component or a portion thereof may be inc~rporaled by contacting the ~01 3423 catalyst with a compound or solution containing the halogen in 8 subsequent catalyst regeneration step. In the regeneration step, carbon deposited on ~e catalyst as coke during use of the catalyst in a hydrocarbon conversion process ~s burned ofl and the catalyst and the platinum group component on the cata-5 Iyst is redistributed to provide a regenerated catalyst with performance charsc-teristics much like the fresh catalyst. The halogen component may be added during the carbon burn step or during the platinum group component redistri-bution step, for example, by contacting the catalyst with a hydrogen chloride gas. Also, the halogen component may be added to the catalyst composite by 10 adding the halogen or a compound or solution containing the halogen, such as propylene dichloride, for example, to the hydrocarbon feed stream or to the recycle gas during operation of the hydrocarbon conversion process. The halogen may also be added as chlorine gas (Cl2) .
The carrier material of the present invention is alumina having a surface 15 area of 80-120 m2/g. In addition, the catalyst carrier alumina should have an ABD of 0.5 9/cm3 or more. The alumina carrier material may be prepared in any suitable manner from synthetic or naturally occurring raw materials. The carrier may be formed in any desired shape such as spheres, pills, cakes, extrudates, powders, granules, etc., and it may be utilized in any20 particle size. A preferred shape of alumina is the sphere. A preferred particle size is about 1/t6-inch in diameter, though particles as small as about 1/32-inch and smaller may also be utilized.
To make alumina spheres, aluminum metal is converted into an alumina sol by reacting it with a suitable peptizing agent and water, and then 25 dropping a mixture of the sol into an oil bath to form spherical particles of the alumina gel. It is also an aspect of this invention that the third modifier metal component may be added to the alumina sol before it is reacted with a peptiz-ing agent and dropped into the hot oil bath. Other shapes of the alumina carriermaterial may also be prepared by conventional methods. After the alumina 3 o particles optionally containing the co-formed third component are shaped, they are dried and calcined.
It is the drying and calcination of the alumina base component that is most important in imparting the catalyst base with the desired characteristics of this invention. It is important that the catalyst alumina base of this invention35 have a surface area of 80-120 m2/g and a corresponding ABD of 0.50 g/cm3 or more. These characteristics are imparted in the alumina by a final calcination of the alumina at a te",per~l~re ~"9;. ,9 from 950~ to 1200~C. i~t is ~re~erable that the final calcination step bs at conditions sufficient to convert ~e alumina into theta-alumina which conror",s to the desired characteristics of thealumina base of the instant catalyst. Such c~,).,lilions would include a caldna-tion temperature closely controlled between 950~ and 1100~C and prerer~iy from 975~ to 1020~C.
It is to be understood that the surface area of the catalyst as set forth in the desc,ipliol, of the invention and the appended claims are derived by the well-known mercury intrusion technique. This method may be used for deter-o mining the pore size distribution and pore surface area of porous subsla"ces by mercury intrusion using a Microl"6rilics Auto Pore 9200 Analyzer. In this method, high pressurs mercury is forced into the pores of the catalyst particlesat incrementally increasing pressures to a maximum of 413,700 kPa (60,000 psia). Pore volume readings are taken at predetermined pressures. A maxi-mum of 85 pressure points can be chosen. Accordingly by this method, a thorough distribution of pore volumes may be determined.
The effect of ca'c;nation of an alumina base especially at the elevated temperatures disclosed in this inYention is to densify the alumina base. The densification, i.e. increase in ABD, is caused by a decrease in the overall cata-Iyst pore volume. In addition, the high calcination temperatures cause the existing pores to expand. To accomplish this apparently contradictory mech-anism, the catalyst necessarily contracts in size while the existing pores expand.
By expanding, the mouths of the existing pores increase so that they become less likely to be plugged or restricted by coke build-up.
It is preferred that the alumina component is essentially theta-alumina. By "essentially theta-alumina~, it is meant that at least 75% of the alumina crystallites are theta-alumina crystallites. The remaining crystallites of alumina will likely be in the form of alpha-alumina or gamma-alumina. However, ot~er ~orms of alumina crystallites known in the art may also be present. It is most preferred if the essentially theta-alumina component comprises at least 90% crystallites of theta-alumina.
As explained, the theta-alumina form of crystalline alumina is produced from the amorphous alumina precursor by closely controlling the maximum calcination temperature experienced by the catalyst support.
Calcination temperatures ranging from 800~ to 950~C are known to produce alumina comprising essentially crystallites of gamma-alumina. Calcination *Trade-m~rk -10 201342:~
temperatures of 1100~C and above are known to pro",ote the f~r",~tio" of alpha-alumina crystallites while t~",p~r~tures of from 950~ to 1100~C and espe~ally from 975~ to 1020~C ~,ron,~e the for",~tion of theta-alumina aystallites.
After the catalyst com~onei ~ have been combined with the de~;f~l alumina support, the resulting catalyst cor"posite will generally be dried at a te" "~eratl~re of from about 100~ to about 320~C for a period of typically about 1 to 24 hours or more and U ,ereafler calcined at a te, nper~ture of about 320~ toabout 600~C for a period of about 0.5 to about 10 or more hours. This final lO calcination typically does not affect the alumina crystallites or ABD. However, the high temperature calc;nalion of the support may be accomplished at this point N desired. Finally, the calcined catalyst coinposite is typically subjected to a reduction step before use in the hydrocarbon conversion process. This reduction step is ef~c~ecl at a temperature of about 230~ to about 650~C for a period of about 0.5 to about 10 or more hours in a reducing env;.or""enl, ~.referaL,ly dry hydrogen, the te",per~re and time being selecte~ to be suffi-cient to reduce sul,sl~ntially all of the platinum group component to the ele.r)ental metallic state.
As indicated above, the catalyst of the present invention has particu-lar utility as a hydl ocarbon conversion catalyst. The hydrocar6O" which is to be converted is contacted with the catalyst at hydroca,6On conversion conditions.
These conditions include a teloper~t.lre of from about 200~ to 1000~C, a pres-sure of from 0.25 atmospheres absolute (ATMA) to about 25 atmospl,eres gauge, and liquid hourly space veloc;ties of from about 0.1 to about 200 hr~1.
According to one embodiment, the hydrocar60n conversion ,urocess of the invention is dehy.llogenation. In the prefer,ed process, dehydrogel)at-able hydrocarbons are contac~ed with the catalytic composite of the instant invention in a dehydrogenation zone maintained at dehydrogenation conditions.
~his contacl;ng may be accomplished in a fixed catalyst bed system, a moving catalyst bed system, a fluidized bed system, etc., or in a batch-type operation.A fixed bed system is preferred. In this fixed bed system, the hydrocarbon feed stream is preheated to the desired reaction tel,lperalure and then passed into the dehydl ogenalion zone containing a fixed bed of the catalyst. The dehydro-genation zone may itself comprise one or more separate reaction zones with heating means therebetween to ensure that the desired reaction temperature can be maintained at the en~rance to each reaction zone. The hydrocarbon may be col~-;teJ with the catalyst bed in either upward, ~k".n~;a.-~, or radial flow fashion. Radial fbw of the hy~J~ocar6Gn throu~h the catalyst bed is ,~r~fer,eJ for co"""erc,al scale r~a~,tor~. The hyd~oc~60n may be in the liquid phase, a mixed vapor-liquid phase, or the vapor phase when it oGIlt~ 7e s catalyst. rl arer~bly, it is in the vapor phase.
Hydrocar60ns which may be dehydr~enatt,d include dehydro-,Jenatal,le hydrocar6Gns having from 2 to 30 or more carbon atoms including pal~ffills, alkylaro",~tics, naph~l,enes, and olefins. One group of hyd~oc rl,ons which can be dehy~J~ ogen~ecJ with the catalyst is the group of normal paraffinso having from 2 to 30 or more carl~n atoms. The catalyst is particularly useful for dehydrogenating par~ffins having from 2 to 15 or more carbon atoms to the corresponding monoolefins or for dehydrogenating monoolefins having from 3 to 15 or more carl,o" atoms to the cor,espo"ding diolefins. The catalyst is especially useful in the dehyd~ogenation of C2-C6 par~Fins, pri",arily propane 15 and butanes, to monoolefins.
Dehydro~Jenalion conditions indude a temperature of from about 400~ to about 900~C, a pressure of from about 0.01 to 10 atmos~l,e~s absolute, and a liquid hourly space velocity (LHS\I~ of from about 0.1 to 100 hr~1. Generally for normal ,uardfFins, the lower the molecular weight, the higher 20 the temperature required for co",parable conversion. The pressure in the dehydrogenation zone is maintained as low as practicable, consistent with equipment limitations, to " ,axi"~i~e the chemical equilibrium advantages.
The emuent stream from the dehy-Jrogenation zone generally will contain unconverted dehydrogenatable hyd~ocarbGi~s, hyd~ogen, and the 25 products of dehydlogenation reac~iGns. This effluent stream is typically cooled and passed to a hydrogen separation zone to separale a hydrogen-rich vapor phase from a hydrocarbon-rich liquid phase. Generally, the hydrocarLon-rich liquid phase is further separated by means of either a suitable selective adsor-~ent, a selectlve solvent, a selective reactiGn or reactions, or by means of a 30 suitable fractionation scheme. Unconverted dehydrogenatable hydrocarbons are recovered and may be recycled to the dehydrogenation zone. Products of the dehydrogenation reactions are recovered as final products or as inler",edi-ate products in the preparalion of other compounds.
The dehydrogenatable hydrocarbons may be admixed with a diluent 3 5 material before, while, or after being passe~l to the dehydrogenation zone. The diluent material may be hydrogen, steam, methane, ethane, carbon dioxide, nitrogen, argon, and the like or a mixture U ,ereof. Hy~JI ogen and steam are the pref~r,~d diluents. Ordinarily, when hyd~ n or steam is utilized as the diluent,Jt is utilized in amounts sufficient to ensure 8 diluent-to-hy~hoc~on mole ratioof about 0.1:1 to about 40:1, with best results being obtained when the mob - 5 ratio range is about 1:1 to about 10:1. The diluent stream l~sse-~ to the dehy-.lroyer,a~iol) zone will typically be recyded diluent separ~t~ from the emuent from the dehy-lrogenalion zone in a sepaf~tion zone.
A combination of diluents, such as steam with hydrogen, may be employed. When hydroge., is the primary diluent water or a ",alerial which 10 deco",poses at dehydlogenatiol- conditions to form water such as an alcohol, aldehyde, ether, or ketone, for example, may be added to the dehydl oge"dtion zone, either continuously or intermittently, in an amount to provide, calculatedon the basis of equivalent water, about 1 to about 20,000 weight ppm of the hydrocarbon feed stream. About 1 to about 10,000 weight ppm of water 5 addition gives best results when dehy.Jrogenating par~ffins have from 6 to 30 or more carbon atoms.
To be commercially successful, a dehy-llogenatiGn catalyst should exhibit three charac~erislics, namely, high activity, high selectivity, and goodstability. Activity is a measure of the catalyst's abilny to convert reactants into 20 products at a spedf,c set of reaction cor,d,tions, that is, at a specified tel~" era-ture, pressure, conta~ time, and concenlralion of diluent such as hydlogen, if any. For dehydrogenation catalyst activity, the conversion or disappearanoe of paraf~ins in percent relative to the amount of par~ns in the feedslocl< is measured. Selectivity is a measure of the catalyst's ability to convert rea..~ants 25 into the desired product or products relative to the amount of reactants converted. For catalyst selectivity, the amount of olefins in the product, in mole percent, relative to the total moles of the par~f~ins converted is measured.
Stability is a measure of the rate of change with time on stream of the activityand selectivity parameters -- the smaller rates implying the more stable cata-3 o Iysts.
~ he dehydrogenation of hydrocarbons is an endothermic process. Ina system employing a dehydrogenation catalyst only, it is typically necessa, y to add superheated steam at various points in the process or to intermi~ler~ly remove and reheat the reaction stream between catalyst beds. In an improve-3s ment, processes have been developed which utilize a two-catalyst system with distinct beds or reactors of dehyd~ogenation or selective oxidalion catalysts.

The purpose of the selective o~ oo catalysts is to selectively o~Ji~ the hyJrc~en produced as a result of the dehyd~oyer,a~iG" r~actiun with oxy~en that had been added to the ~Yid~ion zone to ~enerale heat intemally in the p ocess. The heat generated typically is suffident to cause the rea.,tion mik~re5 to reach desi~eJ dehy.JrogenatiGn t~n,~er~tures for the next dehy-Jr~enation step. The instant process may be accom?lished in this previously ",~lltion~d system. If such a process is employed, the instant catalyst would co""~rise at least the dehydl Ggena~iGn catalyst with anutl ,er speeif;c catalyst being used to accomplish the oldd~1;on lea~;tiu". Before explaining the pr~n~d reactor lO configurations, more details of the o~id~l;on aspect of the invention are d;~closed~
The selective oxid~lion step, if utilized, uses the hy~llogel, which has been produced in the dehydroyenation step of the process to supply heat to the next dehydrogenation rea tion section. To accomplish this, an oxygen-lS containing gas is first introduced into the reactor, preferably at a point adjacent to the selective oxidative catalyst section. The oxygen in the oxygen-containinggas is necess~ to oxidize the hydlogen contained in the reaction stream.
Examples of oxygen-containing gases which may be utilized to effect the selec-tive oxidalion of the hyd~ogen which is presen~ will include air, oxygen, or air or 2 0 oxygen diluted with other gases such as steam, c~r~on dioxide and inert gases such as nitrogen, argon, helium, etc. The amount of oxygen which is intro-duced to conlact the process stream may range from about 0.01:1 to about 2:1 moles of oxygen per mole of hydroyen contained in the ~,rocess stream at the point where oxygen is added to the process stream. In the selective oxidalion 25 reaction, the process stream which c~i",~,rises unreacted dehydrogenalal)le hydrocarbon, dehydrûgenated hydrocarbon, and hyd~ogen is leacted with oxygen in the presence of the selective steam oxWa~ion/dehydloger,a~ion catalyst whereby hyd,oyen is selectively oxidized to produce water and heat ener~y with very little of the oxygen reacti,-g with the hydrGc~, ~ons.
The selective steam oxid~tion/dehydrogenation catalyst may be one that is useful for the selective oxid~tion of hydroegn in the presence of hydrocarlJons. An example of such a catalyst is cJisclosed in U.S. Patent 4,418,237. Aller"dLi~/ely, the catalyst used for the selective oxidation step may be identical to the catalyst utilized for the dehydl ogenation step. Such catalysts or processes for their use are d;;CIQSed in U.S. Patenls 4,613,715 and 3,670,044. The instant catalyst exhibits both dehydrogenation and selective .
A~;on f~nctio"s. Tl,er~ore it is possible that the catalyst of this invention could be used in a single catalyst containing a process for the dehydl c~6n~tionand selective o~i. 1;3tjo" of hyd~ o~ LG"S.
nhe oxygen-containing reactar)t may be added to the instant proc~ss s in various ways such as by a~ liXJ"y oxygen with a relatively cool hyd,~c~l~, feed stream or with the steam diluent, or it may be added direc~y to the reactorindependently of the feed hydr~,L,ons or the steam diluent. In addition, the oxygen-containing rea.~nl can be added at one or more points in the rea~r in such a fashion as to minimize local co"ce,ltla~ions of oxygen relative to o hydrogen in order to distribute the beneficial tei"pera~ure rise produced by the selective hyd~ ogen oxWal;on over the entire length of the reaction zone. In fact, using a plurality of injection points for introducing the oxygen-containing ~as into the steam oJd.41;on/dehydlo~eh~tion reaction zone is a prefer-~d mode of operation. This procedure minimizes the opportunity for local build-up of the 15 concentration of oxygen relative to the amount of hydrogen, U ,ereL,~ minimizin~
the opportunity for undesired reaction of the oxygen-conlaining gas with either feed or product hyd~ oca, bons.
The following examples are introdlJced to further describe the catalyst and process of the invention. The examples are inler,ded as illustrative 20 embodiments and should not be consWer~d to restrict the othenNise broad in~e, prelalion of the invention as set forth in the claims appended hereto.

EXAMPLE 1:

In order to de",onslr~te the advantages to be achieved by the present invention, a number of catalysts of this invention and dif~erenl from the 25 invention were prepared. First for all catalysts, a spherical alumina supportwas prepared by the well-known oil-drop me~l,Gd. A tin co",ponent was incor-porated in the support by commingling a tin componenl precursor with the alumina hydrosol and ll ,ere~ler gelling the hydrosol. The tin co" "~onen~ in this case was unifor",ly distributed throughout the catalyst particle. The catalyst 30 pallicles were then dried at 600~C for about 2 hours and calcined at various temperatures as i~ei "iLed in Table 1 below. Note that the calc;natio"
te",perat.Jre repo,led is the maximum calcination temperature used for each catalyst.

The calcined tin-containing particles were then contacted with a chloroplatinic acid solution, snd a cesium nitrate solution to uniformly illl,ul~sJ-nate the alumina base with platinum and cesium. After impregnation, the cata-~yst was oven-dried at about 150~C for 2 hours in the presence of 10% steam 5 followed by heating at 540~C for 1 /2 hour in the absence of steam.
Table 1 below details the metal content and physical properties such as surface area and ABD of each catalyst produced.

Catalyst A B C D E F
CalcinationTemp. (~C) 600 1160 1088 1088 963 1200 Surface Area (m2/g) 180 85 83 80 107 45 ABD (g/cm3) 0.57 0.63 0.65 0.67 0.58 0.84 Pt (wt.%) 0.73 0.70 0.74 0.75 0.75 0.72 Sn (wt.%) 0.50 0.50 0.50 0.50 0.50 0.50 Cs (wt.%) 4.41 3.86 3.5 4.0 3.5 3.5 Catalysts A and F are not catalysts according to this invention.
Catalysts B, C, D, and E are all catalysts prepared in accordance with this invention .
EXAMPLE ll:

Catalysts A and B were evaluated in a pilot plant for their ability to 20 dehydrogenate a propane feedstock. The pilot plant operated at an inlet tem-perature of 600~C, a pressure of 1 atmosphere, and a liquid hourly space velocity of 3 hr~1. Water and propans were co-fed into the pilot plant reactor at an H2O/C3 molar ratio of 2. C3 conversion and selectivity data for both catalysts can be found in Table 2.

I~B

., onversion (mole %) C3 Selectivity (mole %) Hours s On-Stream Catalyst A Catalyst B Catalyst A Catalyst B
23 33 91.0 95.4 22 32 92.1 95.4 21 34 92.0 95.7 90.2 96.1 88.2 95.6 From Table 2, it is clear that Catalyst B, the catalyst of this invention, is far superior in its ability to deh~drogenate C3 hydrGcar6ons at high selectivity and conversion than Catalyst A of the prior art. Additonally, Catalyst B was analyzed by x-ray dfflraction techniques and was found to co,11prise theta-15 alumina.

E)~AMPLE lll:

The effect of cesium level on a catalyst of this invention is examined inthis example. In Example ll, the catalysts, bss;des having very dif~ere, lt surface areas, also had dif~erent cesium levels. This example is intended to demon-2 0 strate that cesium level has only a very minor impact on catalyst performance.
In this example, Catalysts C and D, both of this invention, were evalu-ated in a pilot plant for their ability to dehydl oge"ate parafFins in a mixed paraf-fin/olefin feedstock. Catalysts C and D both contained 0.75 wt.% platinum and 0.5 wt.% tin on ess~ntially the same support. However, Catalyst C contained 25 3.5 wt.% cesium while Catalyst D contained 4.0 wt.% cesium.
Both catalysts were evaluated identically in the same two-reactor pilot plant. The feed to the pilot plant consisted of 0.3 moles propylene, 0.7 moles propane, 2.07 moles of water, 0.3 moles of hydrogen, and 0.13 moles of nitro-gen. Both reactors were operated at an inlet temperature of 600~C. The pilot 3 o plant pressure was controlled such that the second reactor outlet pressure was maintained at 1.34 at",os~ heres. The first reactor liquid hourly space velocitybased upon the hydrocarbon feed rate was 80 hr~1. The space velocity of the second reactor was 8 hf1. The results of the evaluations are found in Table 3 b~low.

C3 Conversion (mole %) C3 Selectivity (mole %) 5HoursCatalyst C Catalyst D Catalyst C Catalyst D
On-Sl,ea,nRx #1 -Rx #2~x #1 Rx #2Rx #1 Rx #2Rx #1 Rx #2 2.5 13.0 3.2 11.0 100+ 97.2 100+ 97.0 2.0 11.8 3.0 10.0 100+ 97.5 100+ 97.2 1.5 10.5 2.4 9.0 100+ 97.5 100+ 97.0 1.0 9.0 1.4 8.0 100+ 97.5 100+ 97.0 0.5 7.0 1.0 6.0 100+ 97.2 ~00+

From Table 3, it can be seen that the two catalysts exhibit similar conversion and selectivity pc,~r",ance. Obviousqr, the performance is not equivalent and the cesium level does have some effect. It should be recogniLecJ
15 that the deactivation rates of these two catalysts are very similar. That is in contfas~ to the two catalysts of Example ll where the catalyst of the prior art deactivated at a much faster rate than the catalyst of this invention. That is due to the propensity of the high surface support catalysts to have its small pore enl,ances plugged by coke while the instant, lower surface area catalyst does 2 o not exhibit such a speedy deactivation.

EXAMPLE IV:

In this example Catalysts D, E, and F as prepared in Example I were evaluated in the same pilot plant test desc, il~e.l in Example lll. The purpose of the testing was to evaluate di~erences in dehydrogena~ion catalyst performance 25 due to varying surface areas of the three catalysts. By way of review Catalyst D
has a surface area of 80 m2/g, Catalyst E has a surface area of 108 m2/9, and Catalyst F has a surface area of 45 m2/g. All three catalysts had an ABD of above 0.5 g/cm3. The secon.J reactor activity and selectivity results of the tests have been detailed in Figures 1 and 2.

Figure 1 represents the C3 mole conversion of each catalyst in the second of two reactors as a function of time. Figure 2 represents propylene selectivity in mole % of each catalyst in the second reactor, also as a function of time.
The Figures indicate that Catalyst D, having a surface area of 80 m2/g, exhibited conversion and selectivity performances superior to those of Catalysts E and F. Catalyst F, having a surface area of 45 m2/g, exhibited a conversion and selectivity performance far below those of Catalysts D and E. Catalysts D and E exhibited similar C3 conversion performances with Catalyst D's conversion stability being slightly superior to that of Catalyst E.Catalyst D clearly exhibited superior propylene selectivity in comparison to Catalyst E.
These results indicate that there may be a catalyst surface area of around 80 m2/g which exhibits the maximum propane conversion and propylene selectivity and that such conversion and selectivity drops off as the catalyst surface area approaches about 45 m2/g and 100 m2/g.

JJ:vs '7, ' 3t5~

Claims (13)

1. A catalytic composite comprising a combination of a Group VIII
noble metal component, an alkali or alkaline earth metal component, and a third component selected from the group consisting of tin, germanium, lead, indium, gallium, thallium, or mixtures thereof, all dispersed on an alumina support consisting of alumina crystallites having a surface area of 80 to 120 m2/g and an ABD of 0.5g/cm3 or more wherein said alumina crystallites are at least 75% theta-alumina crystallites.

2. The catalytic composite of Claim 1 further characterized in that the alumina crystallites have an ABD of 0.6 g/cm3 or more.

3. The catalytic composite of Claim 1 or 2 further characterized in that the Group VIII noble metal component is platinum, the alkali or alkaline earth component is cesium and the third component is tin.

4. The catalytic composite of Claim 3 further characterized in that the catalyst comprises from 0.01 to 5.0 wt.% platinum, from 0.01 to 10.0 wt.% cesium, and from 0.01 to 5.0 wt.% tin.

5. The catalytic composite of Claim 4 further characterized in that the catalyst contains 0.1 to 4 wt.% cesium.

6. A process for the dehydrogenation of dehydrogenatable hydrocarbons comprising contacting a dehydrogenatable hydrocarbon at hydrocarbon dehydrogenation conditions with a catalyst characterized in Claim 1, 2, 4, or 5.

7. A process for the dehydrogenation of dehydrogenatable hydrocarbons comprising contacting a dehydrogenatable hydrocarbon at hydrocarbon dehydrogenation conditions with a catalyst characterized in Claim 3.

8. The process of Claim 6 further characterized in that the dehydrogenatable hydrocarbons comprise C2-C30 dehydrogenatable hydrocarbons.

9. The process of Claim 6 further characterized in that the hydrocarbon dehydrogenation conditions include a temperature of from 400° to 900°C, a pressure of from 0.1 to 10 atmospheres, and a liquid hourly space velocity (LHSV) of from 0.1 to 100 hr-1.

10. The process of Claim 6 further characterized in that the dehydrogenatable hydrocarbons comprise C2-C6 paraffins.

11. The process of Claim 7 further characterized in that the dehydrogenatable hydrocarbons comprise C2-C30 dehydrogenatable hydrocarbons.

12. The process of Claim 7 further characterized in that the hydrocarbon dehydrogenation conditions include a temperature of from 400° to 900°C, a pressure of from 0.1 to 10 atmospheres, and a liquid hourly space velocity (LHSV) of from 0.1 to 100 hr-1.

13. The process of Claim 7 further characterized in that the dehydrogenatable hydrocarbons comprise C2-C6 paraffins.