CA1050917A - Hydrocarbon reforming process - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A process wherein the inherent hydrocracking activity of a platinum group metal-rhenium catalyst is reduced without permanently substantially damaging the desired hydrocarbon reforming activity and stability of the catalyst which comprises;
(1) contacting a hydrocarbon feed containing from about 15 ppm. to 100 ppm. by weight of sulfur with the catalyst in the presence of hydrogen at hydrocarbon reforming conditions, provided that the total amount of sulfur entering the reaction zone during this contacting equals from about 0.5 moles to about 50 moles of sulfur per mole of rhenium in the catalyst; and (2) introducing a hydrocarbon chargestock containing less than about 10 ppm. by weight of sulfur into the reaction zone and contacting the hydrocarbon chargestock with the catalyst in the presence of hydrogen at hydrocarbon reforming conditions.

Description

-' ~1[3S~9~L7 This invention relates to a new and improved hydrocarbon reforming process. More particularly, the invention relates to an improved process which involves utilizing a catalyst comprising at least one platinum group metal and rheni~m to promote reforming of a hydrocarbon feedstock.
The use of catalysts comprising minor amounts of at least one platinum group met~l and rhenium on a major amount of porous support, e.g., alumina, to promote hydrocarbon reforming has previously been disclosed. One disadvantage to using such a catalyst in hydrocarbon reforming is the high inherent hydro-cracking activity of the catalyst. Thus, the yield of desired reformate product may be decreased, particularly in the initial portion of the hydrocarbon re~orming cycle, if measures are not taken to reduce the inherent hydrocracking activity of the I catalyst.
Zl Various schemes have been proposed to reduce the , inherent hydrocracking activity of these platinum group metal-rhenium reforming catalysts. For example, U.S. Patent 3,617,520 discloses sulfiding a low platinum, i.e., less than 0.3~ by weight of platinum, catalyst wi-th H2S in flowing hydroge~ followed by a hydrogen treatment,all prior to hydrocarbon reforming. In addition, U.S. Patent 3,438,888 suggests initially conta~ting the catalyst with hydrocarbon containing a high concentration, i.e., greater than 50 volume percent, of aromatics. However, each of these proposals involves additional processing steps, either in the catalyst preparation procedure (catalyst -presulfiding) or in the reforming process itself ~high aromatic ~ feedstock processing). Therefore, it would be advantageous to ,~ provide an improvea method for reducing the inherent hydro~
`! 30 cracking activity of a platinum group metal-rhenium hydro-' carbon reforming catalyst.

~ , , ~ . , , . . . , .. . :

~S~ '7 An additional disadvantage of hydrocarbon reforming utilizing a platinum group metal-rhenium catalyst is the sulfur-sensitivity of -the catalyst. Thus, U.S. Patent 3,415,737 teaches that contacting the catalyst with a sulfur-~containing hydro-: carbon reduces not only the inherent hydrocracking activity of the catalyst but also permanently adversely affects the desired .
hydrocarbon reforming activity and stability of the catalyst.
Therefore, one of the objects of the present invention is to provide an improved method for reduc:ing the inherent hydro-crac~ing activity of a platinum group-metal-rhenium hydrocarbon : reforming catalyst.
Another object of the present invention is to provide a method for reducing the inherent hydrocracking activity of a platinum group metal-rhenium hydrocarbon reforminy catalyst ~ithout permanently substantially damaging, i.e., adversely affecting,the desired hydrocarbon reforming activity and stability of the catalyst. Other objects and advantages of the ~i present invention will become apparent hereinafter.
An improved process has been found wherein hydrocarbon is contacted with a catalyst comprising a major amount of a porous solid support, e.g., alumina, about 0.01~ to about 3.0~
by weight of at least one platinum group metal. and about 0.01%
to about 5.0~ by weight of rhenium in the presence of hydrogen at reforming conditions. The improved process comprises: -1) contacting a hydrocarbon feed with a cata~yst, as described hereinabove, in the presence of - hydrogen in at least one reaction zone at hydrocarbon reforming conditions; the hydro-carbon feed containing from about 15 ppm. to about 100 ppm., pre erably from about 15 ppm.

5~7 to about 50 ppm., by weight of sulfur, this contacting occurring for a time sufficient to reduce the inherent hydrocracking activi-ty of the catalystl ... . ..
provided that the total amount of sulfur entering the reaction zone during such contacting equals from about 0.5 moles to about 50 moles, preferably from about 3 moles to about 20 moles, per mole of rheni~ in the catalyst; and

2) introducing a hydroca~bon chargestock into the reaction zone and contacting the hydro-carbon chargestock with the catalyst in the presence of hydrogen at hydrocarbon reforming conditions, provided that the hydrocarbon chargestock contains less than about 10 ppm., preferably less than about 5 ppm., and more ` preferably less than about 1 ppm., by weight of sulfur, based on the weight of hydrocarbon chargestock.
According to step (1) of the present invention, a hydrocarbon feed containing from about 15 ppm. to about 100 ppm., preferably from about 15 ppm. to about 50 ppm., by weight '~ of sulfur, is contacted with a catalyst of the type described above in the presence of hydrogen in at least one reaction zone for a time sufficient to reduce the inherent hydro-crackin~ activity of the catalyst without permanently substan- -tially damaging the desired hydrocarbon reforming activity and sta~ility of the catalyst. By practicing the present invention, it has been found that by allowing step (1) of the present ~3~
'' I

~ SV~'7 invention to proceed so that up to a total of about 50 moles of sulfur enter the reaction zone per mole of rhenium in the catalyst, -the inherent hydrocracking activlty of a platinum group metal-rhenium-containing hydrocarbon reforming catalyst can be effectively and efficiently reduced without permanently substantially damaging the desired reforming activity and sta-bility of the catalyst. Although the amount of sulfur entering the reaction zone during step (1) may be as low as 0.5 moles per mole of rhenium on the catalyst, in order to optimally achieve the substantial benefits of the present invention while mini-mizing detrimental effects, e.g., metal corrosion causecl by presence of sulfur, it is more preferred that the total amount of sulfur entering the reaction zone during step (1) be in the range from about 3 moles to about 20 moles per mole of rhenium on this catalyst.
Step (2) of the present invention may occur before or after, preferably after, step (1) and involves contacting a hydrocarbon chargestock containing less than about 10 ppm., preferably less than about 5 ppm., and more preferably less than about 1 ppm., by weight of sulfur with the catalyst such as described above in the presence of hydrogen in at least one reaction zone at hydrocarbon reforming conditions. It is preferred that step (2) follow step (1) since, for example, improved product yields may be obtained in step (2) if the inherent hydrocracking activity of the catalyst is reduced in step (1).
The two steps of the above process may be accomplished by using the catalyst in a fixed bed system, a moving bed system, a fluidized bed system, or in a batch type operation~ ~owever, in view of the danger of attrition losses of the valuable :, catalyst and of well-known operational advantages, it is preferred to use a fixed bed system. In this system, hydrogen-rich gas and the hydrocarbon are preheated by any suitable heating means to the desired reaction temperature and then are passed into at least one reaction zone containing a fixed bed of the catalyst as hereinabove characterized. It is understood that the reaction system may include one or more separate reaction zones with suitable means there ~etween to compensate for the net endothermic nature of the reactions that take place in each catalyst bed and thus insure that the desired reaction temperature is maintained at the entrance to each reactor. The reactants, e.g., hydrocarbon feed or chargestock and hydrogen, may be contacted with the catalyst bed in either upward, downward, or radial flow fashi.on. In addition, the reactants may be in the liquid phase, a mixed liquia-vapor phase, or a vapor phase when they contact the catalyst, with best results obtained in the ~apor phase.
The hydrocarbon feed and chargestock used in the ;
present process comprise hydrocarbon fractions containing naphthenes and paraffins that boil within the gasoline rangeO
These hydrocarbon materials used in steps ~1) and (2) may be the same (other than sulfur content) or different. Typically, these hydrocarbon materials may comprise from about 20% to about 1 7~% by weight of naphthenes and from about 25% to about 75%
i by weight of paraffins. The preferred hydrocarbons for use :~
as feed and chargestock consist essent~ally of naphthenes and ~ paraffins, although in some cases aromatics and/or olefins may ', aiso be presentO When aromatics are included, these compounds comprise from about 5% to about 25% by weight of the total hydrocarbon material. A preferred class of hydrocarbon feed and ` ~5-, . ~, ~s~

chargestock includes straight run gasolines, natural gasolines, synthetic gasolines and the like. On the other hand, it is frequently advantageous to use as hydrocarbon feed and chargestock thermally or catalytically cracked gasolines or higher boiling ; fractions thereof, called heavy naphthas. Mixtures of straight run and cracked gasolines can also be used. The gasoline used as hydrocarbon feed and chargestock may be full boiling range gasoline having an initial boiling point of from about 5QF
to about 150F. and an end boiling point within the range of from about 325F. to about 425~F. r 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 about C7 ko about ~00F. In some cases, it is also advantageous to use pure hydrocarbons or mixtures of hydrocarbons that have been extracted from hydrocarbon distillates -- for example, a straight-chain paraffin -- which are to be converted to aromatics. It is preferred that at least a portion of these hydrocarbon materials used in steps (1) and (2) be treated by conventional pretreatment methods, if necessary, to remove substantially all sulfurous and nitrogenous contaminants therefrom. Thus, for example, the ~ hydrocarbon feed to be used in step (1) of the present invention ; may be substantially completely desulfurized and then sulfur-containing compounds or material added back to produce a hydro-carbon feed having the required sulfur content. Alternately, a portion of the raw sulfur containing hydrocarbon material can be made to bypass certain conventional reforming feed pretreat-ment processing, e~g., hydrodesulfurization, and then be added to the pr~treated, eOg., hydrodesulfurized, remainder of the hydrocarbon material to provide a hydrocarbon feed for step (1) ~'~

,', : :

~ ~SV9~'7 having the proper sulfur content. In any event, step (l) of the present invention involves the use of a hydrocarbon feed having a sulfur content in the range from about 15 ppm. to about 100 ppm., preferably from about 15 ppm. to about 50 ppm. by weight based on the total hydrocarbon feed.
If the hydrocarbon feed used in step (1) is made by adding sulfur-containing compounds or materials to a substan-tially desulfurized hydrocarbon material, the hydrocarbon chargestock used in step ~2) may possibly be obtained simply by ; 10 refraining from such addition. For example, if the hydrocarbon feed of step (1) results from by-passing a conventional hydro- ~
desulfurization step with a portion of the raw hydrocarbon ~ -material, the hydrocarbon chargestock of step (2) can be obtained by omitting the by passed portion from the reaction i zone or, alternatively, by eliminating the by-pass. In any event, the hydrocarbon chargestock used in step (2) of the present invention contains less than about 10 ppm., preferably I less than about 5 ppm. and more preferably less than about l l ppm., by weight of sulfur.
As indicated above, the catalyst utilized in the , present invention comprises a solid porous support, e.gO, alumina, a platinum group metal and rhenium. It is preferred that the solid porous support be a material comprising a major amount of alumina having a surface area of from about 25 m2/gm.to about 600 m./gm.or more. The solid porous support comprises a major pro-l portion, preferably at least about 80%, and more preferably at least 90%, by weight o~ the catalyst. The preferred catalyst support, or base, is an alumina derived from hydrous alumina ~ predominating in alumina trihydrate, alumina monohydrate, amor-`~ 30 phous hydrous alumina and mixtures thereof, more preferably, ~, alumina monohydxate, amorphous hydrous alumina and mixtures thereof, which alumina when formed as pellets and calcined, has an apparent bulk density of from about 0.60 gm./ccO to .', about 0.85 gm./cc., pore volume from about 0.45 ml/gm. to about 0.70 ml./gm., and surface area from about 100 m?/gm to about 500 m.2/gm. The solid porous support may contain, in addition, minor proportions of other well known refractory inorganic oxides such as silica, zirconia, magnesia and the like. However, the most preferred support is substantially pure alumina derived from hydrous alumina predominating in alumina monohydrate.
The alumina support may be synthetically prepared in any suitable manner and may be activated prior to use by one or more treatments including drying, calcination, steaming and the like. Thus, for instance, hydrated alumina in the form of a hydrogel can be precipitated from an a~ueous solution of a soluble aluminum salt such as aluminum chloride. Ammonium hydroxide is a useful agent for effecting the precipitation.
Control of the pH to maintain it within the values of about 7 to about 10 during the precipitation is desira~le for obtaining a good rate of conversion. Extraneous ions, such as halide ions, which are introduced in pr0paring the hydrogel, can, if desired, be removed by filtering the alumina hydrogen from its mother liquor and washing the filter cake with water. Also, if desired, the hydrogel can be aged, say for a period of several days. The effect of such aging is to build up the concentration of alumina trihydrate in the hydrogel. Such trihydrate forma-tion can also be enhanced by seeding an aqueous slurry of the hydrogel with alumina trihydrate crystallites, for example, gibbsite.
The alumina may be formed into macrosize particles of any desired shape such as pills, cakes, extrudates, powders, granules, spheres, and the like using conventional methods.
The size selected for the macrosize particles can be dependent ' ' . . , .. . .. . . .. . . ..

`' ~IL~35~7 upon the intended environment in which the final catalyst is to be used -- as, for example, whether in a fixed or moving bed reaction system. Thus, for example, where as in the preferred embodiment of the present invention, the final catalyst is designed for use in hydrocarbon reforming operations employing a fixed bed of catalyst, the alumina will prefer-ably be formed into particles having a minimum dimension of at least about 0.01 inch and a maximum dimension up to about one-half inch or one i~ch or more. Spherical particles having a diameter of about 0.03 inch to about 0.25 inch, preferably about 0.03 inch to about 0.15 inch, are often useful, expecially in a fixed bed reforming operation.
As indicated above, the catalyst utilized in the present invention also contains a platinum group metal. The platinum group metals include platinum, palladium, rhodium, ruthenium and the like with platinum being preferred Eor use in the present invention. The platinum group metal, such as platinum, may exist within the final catalyst at least in part , as a compound such as an oxide,sulfide, halide and the like, or in the elemental state. Generally, the amount of the platinum group metal component present in the final catalyst is small compared to the ~uantities of the other components combined therewith. In fact, the platinum yroup metal component generally comprises from about 0.01% to abouk 3.0%, preferably from about 0.05% to abou-t 1.0~, by weight of the catalyst, calculated on an elemental basis. Excellent results are obtained when the catalyst contains from 0.2% to about 0.9% by weight of

3 the platinum group metal.
The platinum group component may be incorporated in the catalyst in any suitable manner, such as by coprecipitation _g_ , .

., , , . , , ~, . .. ... . .
. - . . . . . . .

3~5~9~7 or cogellation with the alumina support, ion-exchange with the alumina support and/or alumina hydrogel, or by the impregnation of the alumina support and/or alumina hydrogel at any stage in its preparation and either after or before calcination of the alumina hydrogel. One preferred method for adding the platinum group metal to the alumina support involves the utilization of a water soluble compound of the platinum group metal to impregnate the alumina support prior to calcination. For example, platinum may be added to the support by comingling the uncalcined alumina with an aqueous solution of chloroplatinic acid. Other water-soluble compounds of platinum may be employed as impregnation solutions, including, for example, ammonium chloroplatinate and platinum chloride. The utilization of a platinum-chlorine compound, such a~ chloroplatinic acid, is preferred since it facilitates the incorporation of both the platinum and at least a minor ~uantity of the optional halogen component of the catalyst, described hereinafter. It is preferred to impregnate the support with the platinum group metal and rhenium when it is in a hydrous state. Following this impregnation, the resulting impregnated support is shaped (e.g., extruded), dried and subjected to a high temperature calcination or oxidation procedure at a temperature in the range from about 700F. to about 1500F., preferably from about 850F. to about 1300F., for a period of time from about one hour to about 20 hours, preferably from about one hour to about five hours. ~he major , portion of the optional halogen component may be added to this j otherwise fully composited calcined catalyst by contacting this catalyst with a substantially anhydrous stream of halogen~
containing gas.
Another essential co~stituent of the catalyst utilized ~ ' '' . I ~ .

.~

~51~)9~7 in the present invention is an additional component exemplified by rhenium. This component may be present as an elemental metal, as a chemical compound, such as the oxide, sulfide, or halide, or in a physical or chemical association with the alumina support and/or the other components of the catalyst. Generally, the ; rhenium is utilized in an amount which results in a catalyst containing from about 0.01% to about 5%, preferably from about 0.05% to about 1.0%, by weight of rhenium, calculated as the elemental metal. The rhenium component may be incorporated in the catalyst in any suitable manner and at any stage in the preparation of the catalyst. The procedure for incorporating the rhenium component may in~olve the impregnation of the alumina support or its precursor either before, duriny or after the time the other components referred to above are added. The impregnation solution can in some cases be an aqueous solution of a suitable rhenium salt such as ammonium perrhenate, and the like salts or it may be an aqueous solution of perrhenic acid. In addition, aqueous solutions of rhenium halides such as the chloride may be used if desired. It is preferred to use perrhenic acid as the source of rhenium for the catalysts utilized in the present invention. In general, the rhenium component can be impregnated either prior to, simultaneously with, or after the platinum group metal component is added to the support. ~Iowever, it has been found that best results are achieved when the rhenium omponent is impregnated simultaneously with the platinum group component. In fact, a preferred impregnation solution contains chloroplatinic acid and perrhenic acid. In the instance where the catal~st support, e.g.~ alumina derived from hydrous alumina pr~dominating in alumina monohydrate, is formed ! 30 into spheres using the conventional oil drop method, it is preferred to add the platinum group metal and rhenium after calcination of the spheroidal particles~ ~

;

~IOtSal g~L~7 An optional constituent of the catalyst used in the present invention is a halogen component. Although the precise chemistry of the association of the halogen component with the alumina support is not entirely known, it is customary in the art to refer to the halogen compone:nt as being combined with the alumina support, or with the other ingredients of the catalyst. This combined halogen may be fluorine, chlorine, bro-mine, and mixtures thereof. Of these, fluorine and, particu-larly, chlorine are preferred for the purposes of the present invention. The halogen may be added to the alumina support in any suitable manner, either during preparation of the support, or before or after the addition of the catalytically active metallic components. For example, at least a portion of the halogen may be added at any stage of the preparation of the support, or to the calcined catalyst support, as an a~ueous solution of an acid such as hydrogen fluoride, hydrogen chloride, -: :
hydrogen bromide and the like or as a substantially anhydrous gaseous stream of these halogen-containing components.
The halogen component, or a portion thereof, may be composited with alumina during the impregnation of the latter with the platinum group component and/or rhenium component; for example, through the utilization of a mixture of chloroplatinic acid and/or perrhenic acid and hydrogen chloride. In another situation, the alumina hydrogel which is typically utilized to form the alumina component may contain halogen and thus contribute at least a portion of the halogen component to the final composite. For purposes of the present invention, .
when the catalyst support is used in the form of an extrudate, ., and platinum and rhenium are added before extrusion, it is preferred to add the major portion of the halogen component , .
., , , . .
- . : : :

~ 0~
to the otherwise fully composited calcined catalyst by contacting this catalyst with a substantially anhydrous stream of halogen-containing gas. When the catalyst is prepared by impregnating calcined, formed alumina, for example, spheres produced by the conventional oil drop method, it is preferxed to impregnate the support simultaneously with the platinum group metal, rhenium component and halogen. In any event, the halogen may be added in such a manner as to result in a fully composited catalyst that contains from about 0.1% to about 1.5~ and preferably from about 0.6~ to about 1.3% by weight of halogen calculated on an elemental basis. During both steps (1) and (2) of the present invention, the halogen content of the catalyst can be main-tained at or restored to the desired level by the addition of halogen-containiny compounds, such as carbon tetrachloride, ethyl trichloride, t-butyl chloride and the like, to the hydrocarbon before entering the reaction zone.
The final fully composited catalyst prepared, for example, by a method set forth above, is generally dried at a temperature of from about 200F. to about 600F. for a period of from about 2 to 24 hours or more and finally calcined at a temperature of about 700F. to about 1500F., preferably from about 850F. to about 1300F. for a period of from about 1 hour to abowt 20 hours and preferably from about 1 hour to about ; 5 hours.
The resultant calcined catalyst may be subjected to reduction prior to use in reforming hydrocarbons. This step is designed to insure chemical reduction of at least a portion of the metallic components.
The reducing media may be contacted with the calcined catalyst at a temperature of about 800F. to about 1200F. and ' :~)5~
at a pressure in the range from about 0 psig. to about 500 psig. and for a period of time of about 0.5 to 10 hours or more and in any event, for a time which is effec-tive to chemically reduce at least a portion, preferably a major portion, of each of the metallic components, iOe., platinum group metal and rhenium component, of the catalyst. By chemical reduction is meant the lowering of oxidation states of the metallic components below the oxida-tion state of the metallic component in the unreduced catalyst. For example, the unreduced catalyst may contain platinum salts in which the platinum has an oxidation state which can be lowered or even reduced to elemental platinum by contacting the unreduced catalyst with hydrogen. This reduction treatment is preferably performed in situ,(i.e., in the reaction zone in which it is to be used), as part oE a start-up operation using fresh unreduced catalyst or regenerated (e.~., regenerated by treatment with an oxygen-containing gas stream) catalyst. Thus, the process of the present invention may be practiced using virgin catalyst and/or catalyst that has previously been used to reform hydrocarbon and has been subsequently subjected to conventional treatments to restore, e.g., regenerate and/or reactivate, the hydrocarbon reforming activity and stability of the catalyst.
The following examples illustrate more clearly the processes of the present invention. However, these illustrations , are not to be interpreted as specific limitations on this invention.
EXAMPLE I
This example il]ustrates certain of the benefits of the present inventionO
A commercially available catalyst prepared by co-5(~ .t~J
impregnating a gamma~ alumina s~pport with chloroplatinic acid and perrhenic acid utilizing conventional procedures was selected for testing. This catalyst, comprising 0.35~ by weight of platinum (calculated on an elemental basis), 0.43~ by weight of rhenium (calculated on an elemental basis) and 1.13~ by weight chlorine ~calculated on an elemental basis) was placed into a fixed bed reactor. The catalyst was xeduced by flowing hydrogen through the reactor at the rate of 2 SCF/hr. for 16 hours at 900F.
The reduced catalyst was used, in a "once-thxough", i.e., no hydrogen or hydrocarbon recycle, reforming test to reform a naphtha having the following specifications.
API Gravity 55.6 Research Octane _ Number (clear) 46.4 Distillation (ASTM IBP 200F.
D-86) 10% 228F.
30% 240F.
50% 262F.
90~ 336F.
95% 351~F.
E.P. 392F.
' ' ~' Component Type Analysis: Wt.%
Paraffin 47.8 Naphthene 42.8 Aromatic 9 . 4 *Sulfur Concentration 32 ppm. (by weight) *Naphtha as is,contained essentially no sulfur, iOe., less than 1 ppm. Sulfur concentration achieved by adding thiophene to the naphtha. Also, the naphkha conta:ined about 8 ppm. of chloride as chlorobenæene to maintain the chlorine concentration of the catalyst~

The reforming conditions were as follows:

Temperature - 950F

Pressure - 300 psig.
H2/Hydrocarbon Mole Ratio - 3 The reforming of the above sulfur-containing feedstock was continued for 78 hours. During this period of time the rate of catalyst activity loss (as measured by research octane number (clear) decline) was about 4 times as great as would be expected during processing an essentially sulfur-free chargestock with the catalyst. A total of about 13.5 moles of sulfur per mole of rhenium on the catalyst entered the reaction zone during this period o time. Af-ter the initial 78 hours, the above-noted feedstock without sulfur addition r was contacted with the catalyst at the above-noted conditions.
It was found that the catalyst recovered essentially all the desired reforming activity and stability. That is, the catalyst had essentially the same activity and stability after, for example r 170 hours of contact with the sulfur-containing hydrocarbon feed and essentially sulfur-free chargestock des-cribed above as the catalyst would be expected to have after 170 hours of reforming service with an essentially sulfur-free chargestock.
EXAMPLE II
This example further illustrates certain of the advantages of the present invention.
The catalys~, reforming conditions and naphtha used in this example are the same as used in Example I except that the temperature was 955F., the hydrogen to hydrocarbon S~ L7 mole ratio was 6 and the naphtha used during the first part of the processing contained 47 ppm. by weight of sulfur through the addition of thiophene.
The reforming of this thiophene-containing feed was :
continued for 174 hours. Duxing this period the research octane number (clear) of the li~uid product, i.e., reformate, decreased approximately 3 numbers. This activity decline is the equivalent of an increase of about 20F. to maintain a constant octane number product. A total of 44.3 moles of sulfur per mole of rhenium on the catalyst entered the reactor during this 17~ hour period. After the system was switched to a second reforming operation, i.e., reforming the substantially sulfur-free naphtha, essentially all of the desired reorming activity of the catalyst was recovered within 24 hours. Thus, the catalyst had essentially the same activity ; after 195 hours of the mixed reforming service described above as the catalyst would be expected to have after 1~5 hours of reforming service with an essentially sulfur-free feedstock.
EXAMPLE III
., This example illustrates certain other of the benefits of the present invention.
catalyst asdescribed in Example I is used to reform a thiophene-containing naphtha as in Examples I and II After such reforming, it is determined that the inherent hydrocracking activity of the catalyst has been reduced.
, Thus, it can be seen by carefully choosing the .I proper reforming conditions, e.g., the amount of sulfur entering the reaction zone during the first reforming, significant benefits can be achieved. The inherent hydro-, ' .

,~

~, :
. '~

s~
cracking activity of the platinum yroup metal-rhenium catalyst :
is reduced without permanently substantially damaging the desired hydrocarbon reforming activity and stability of -the catalyst. This is clearly unexpected from the prior art which teaches that the addition of sulfur during hydrocarbon processing permanently adversely affects the hydrocarbon reforming capabilities of the catalyst.

~0 ~, :

.
;s , -18-i . . ' . .

. . . ., . . ,, , ,, . , , ; .. , : . . ,

Claims (11)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a reforming process wherein hydrocarbon is contacted with a catalyst comprising a major amount of a porous solid support, about 0.01% to about 3.0% by weight of at least one platinum group metal and about 0.01% to about 5% by weight of rhenium in the presence of hydrogen at reforming conditions, the improvement which comprises:
l) contacting a hydrocarbon feed with said catalyst in the presence of hydrogen in at least one reaction zone at hydrocarbon reforming conditions; said hydrocarbon feed containing from about 15 ppm. to about 100 ppm. by weight of sulfur, said contacting occurring for a time sufficient to reduce the inherent hydrocracking activity of said catalyst, provided that the total amount of sulfur entering said reaction zone during said contacting equals from about 0.5 moles to about 50 moles per mole of rhenium on said catalyst; and 2) introducing a hydrocarbon chargestock into said reaction zone and contacting said chargestock with said catalyst in the presence of hydrogen at reforming conditions, provided that said chargestock contains less than about 10 ppm. by weight of sulfur, based on the weight of said chargestock.

2. The process of claim 1 wherein said porous solid support comprises a major amount of alumina and said platinum group metal comprises platinum.

3. The process of claim 2 wherein the total amount of sulfur entering said reaction zone during said contacting is in the range from about 3 moles to about 20 moles of sulfur per mole of rhenium in said catalyst.

4. The process of claim 2 wherein said hydrocarbon feed contains from about 15 ppm. to about 50 ppm. by weight of sulfur and said hydrocarbon chargestock contains less than about 5 ppm. sulfur.

5. The process of claim 3 wherein said hydrocarbon feed contains from about 15 ppm. to about 50 ppm. by weight of sulfur and said hydrocarbon chargestock contains less than about 5 ppm. sulfur.

6. The process of claim 4 wherein said alumina is derived from hydrous alumina predominating in alumina trihydrates, alumina monohydrate, amorphous hydrous alumina and mixtures thereof, and said catalyst further comprises from about 0.1%
to about 1.5% by weight of halide.

7. The process of claim 5 wherein said alumina is derived from hydrous alumina predominating in alumina trihydrates, alumina monohydrate, amorphous hydrous alumina and mixtures thereof, and said catalyst further comprises from about 0.1%
to about 1.5% by weight of halide.

8. The process of claim 6 wherein said catalyst comprises from about 0.05% to about 1.0% by weight of platinum, from about 0.05% to about 1.0% by weight of rhenium and from about 0.6% to about 1.3% by weight of chloride, and step (1) occurs prior to step (2).

9. The process of claim 7 wherein said catalyst comprises from about 0.05% to about 1.0% by weight of platinum, from about 0.05% to about 1.0% by weight of rhenium and from about 0.6% to about 1.3% by weight of chloride, and step (1) occurs prior to step (2).

10. The process of claim 8 wherein said alumina is derived from an alumina predominating in alumina monohydrate.

11. The process of claim 9 wherein said alumina is derived from an alumina predominating in alumina monohydrate.