FR2597496A1 - Catalytic reforming process - Google Patents

Abstract

Process for catalytic reforming with the aid of catalysts containing a support, platinum and rhenium, performed in a number of successive catalyst beds in which the catalyst employed in the first catalyst bed has an Re/Pt ratio higher than the Re/Pt ratio of the catalyst employed in the last catalyst bed, the said catalyst in the said last catalyst bed containing at least 0.005 % of rhenium in relation to the support. The catalysts preferably contain at least one halogen in a weight proportion in relation to the support of 0.1 to 15 % and the support is preferably alumina-based. In a preferred form 3 successive catalyst beds are employed, the Re/Pt ratios being overall decreasing from the first bed to the last bed.

Description

 Catalytic reforming or hydroreforming is a well-known process of the refining industry, the objective of which is generally the improvement of the octane number of heavy species or species of direct distillation of oil and / or the production of aromatic hydrocarbons. This operation must be carried out industrially with the highest possible yield in research products: base for fuels or aromatic compounds for petrochemistry. Usually the yield is measured by the quantity produced of gasoline containing hydrocarbons containing five carbon atoms and more by compared to the injected charge, commonly known as the C5 gasoline cutter. Currently, another factor directly related to the previous one, takes a growing importance: the production of hydrogen. The goal to be strived for is to achieve the highest C5 gasoline and hydrogen yields possible.

 In the near future, the application of antipollution standards will lead to a decrease in the concentration of lead in gasolines, eventually leading to the elimination of organo-plonbic additives in automotive fuels for spark ignition engines. This regulation imposes on refiners an increase in the severity of the operational operating conditions of the reforming units in order to meet the quality criteria required for satisfactory operation of automobile engines. In addition, the restructuring of the refinery in favor of a growing share of conversion and hydrotreating units will significantly increase the need for hydrogen in refineries.

Satisfaction of these additional hydrogen requirements is largely a function of catalytic reforming or hydroreforming, the operating conditions of which must be adjusted to meet this demand.

 Increasing the severity of the operating conditions of the industrial installations, for example decreasing the operating pressure and, if necessary, increasing the temperature, is thermodynamically favorable to the reactions leading to the desired products (aromatics and hydrogen) but strongly penalizes the reaction. stability of the catalysts. Indeed, under conditions of increased severity, the carbon deposition rate, in the form of coke, on the catalyst increases, which results in a faster decrease in the activity of the catalyst.

 This development leads to an increase in the regeneration frequency of the catalysts and consequently a reduction in the operating time and therefore in the total processing capacity of the industrial installations. It is clear that any improvement in the stability of the catalysts, which will result in a decrease in the regeneration frequency or, in other words, an increase in the operating time between two successive regenerations, represents a significant progress towards tending towards the most rational use possible of industrial installations.

 Catalysts used in catalytic reforming are generally based on alumina containing a noble metal of group VIII of the periodic table of elements, generally platinum for catalysts of the first generation such as for example those described by V. HAENSEL in OIL AND GAS JOURNAL, vol. 48, No. 47, pages 82 et seq., 1950. A second generation of catalysts has appeared in which a promoter element is added to the Group VIII metal. Among the most frequently used promoters are exemplified US rhenium. -A-3415737, tin US-A-3700588, indium and thallium US-A-2814599. The addition of these various promoters has resulted in significant gains in stability and / or selectivity compared to catalysts said The addition of two promoter elements has also been described as providing significant progress in terms of stability and / or selectivity.A catalyst comprising on a support of alumina, platinum, rhenium and tin is for example described in US-A-3702294.

These various catalysts have been tested and / or used over long periods, sometimes equal to or even longer than a year, for example. Each catalytic formula has both advantages and disadvantages: - platinum-rhenium catalyst has excellent stability but
does not allow to observe a maximum selectivity in the production
of good quality species, - platinum-tin, platinum-indium or platinum-thallium catalysts
allow to obtain an excellent selectivity but have a stabi
significantly lower than the platinum-rhenium catalyst, - the use of catalysts containing three metals (eg
platinum, rhenium and tin) does not provide stability
equal to that of platinum-rhenium, nor a selectivity equivalent to
that of platinum-tin, platinum-indium or platinum-thallium.

 In order to improve the stability of the catalysts containing platinum and rhenium deposited on alumina, the increase in the ratio, atomic or by weight, of the amount of rhenium on the amount of platinum contained in the catalyst has been proposed and described in the Belgian patent. BE-A-875386.

Thus, in patent BE-A-875386, the catalytic composition described makes mention of a rhenium / platinum weight ratio of between 2 and 5 and preferably of between 2.25 and 4. The use of catalysts enriched with rhenium results in a relative increase of the cycle time up to 65% compared to the use of catalysts containing substantially the same amount of platinum metals plus rhenium. Nevertheless, the use of catalysts enriched with rhenium generally leads to a loss of gasoline yield
C5 + greater than 1% weight. In addition, the positive effect of rhenium enrichment on stability is observed only if the sulfur content of the naphtha used is less than 0.5 ppm by weight.

 In order to overcome this decrease in selectivity due to the use of rhenium-enriched catalysts in all reactors, it has been recommended to use a platinum-rheniuc catalyst whose weight ratio of rhenium to platinum is less than or equal to about 1 in the first reactor or reactors and a platinum-rhenium catalyst, whose weight ratio rhenium on platinum is greater than or equal to about 2, in the last reactors or reactors. Such arrangements are, for example, described in the following documents: FR-A-2467236, US-A-4427533 and US-A-4436612. In this case, an equivalent or greater stability is observed and a selectivity in petrol cut slightly improved compared with to the catalyst containing platinum and rhenium, in a weight ratio of less than or equal to about 1 used in all the reactors.

 Furthermore, in the European patent application EP-A-153891, the use in the first reactor of a catalyst having a better stability than that of the catalysts employed in the other reactors makes it possible to appreciably improve the stability and selectivity of all the catalytic beds contained in the different reactors of the unit.

 The object of the present invention is to obtain gasoline of required quality for long periods, with a very satisfactory selectivity. Another object of the invention is to obtain relatively large quantities of hydrogen.

 Surprisingly, it has been found that increased yields of C5 petrol cuts and hydrogen can be obtained when circulating a hydrocarbon feed under reforming conditions, in the presence of hydrogen, successively through at least two fixed beds of catalyst, each bed containing a catalyst containing a support, platinum, rhenium and optionally at least one halogen, the catalyst of the first or first beds crossed by the feedstock being a so-called type A catalyst whose Rhenium on platinum (Re / Pt) weight ratio expressed in metallic element is greater than the weight ratio Re / Pt of the so-called type B catalyst contained in the last bed (s) passed through by the feedstock, said type B catalyst containing at least minus 0.005% by weight of rhenium relative to the support. The catalysts of type A and type B may be identical or different in their constituents. These catalysts are preferably constituted essentially by a support, platinum, rhenium and at least one halogen. In an advantageous embodiment of the invention, the two types of catalyst contain the same support and generally the same halogen, the only difference being the weight ratio Re / Pt.

The essential point of the invention is that the catalyst contained in the first bed or beds crossed by the load at a weight ratio Re / Pt greater than the weight ratio Re / Pt of the catalyst contained in the last bed or beds crossed by the load.

In an advantageous embodiment of the invention, the catalyst of type A is a catalyst having a weight ratio
Re / Pt of 1: 1 to 5: 1 and the catalyst of type B is a catalyst having a weight ratio Re / Pt of 0.1: 1 to 3: 1 and preferably the catalyst of type A has a weight ratio of R. / Pt of 1.6: 1 to 4: 1 and the type B catalyst has a weight ratio Re / Pt of 0.5: 1 to 1.5: 1 and most preferably the weight ratio Re / Pt of the type A catalyst is from 2: 1 to 3: 1 and the weight ratio Re / Pt of the type B catalyst is from 0.8: 1 to 1.1: 1.

 The supports of the catalysts (identical or different) used in the present invention are generally chosen from the oxides of the metals of groups II, III and / or IV of the periodic table of the elements, such as, for example, magnesium oxides, aluminum, titanium, zirconium, thorium or silicon, taken alone or mixed with one another or with oxides of other elements of the periodic table, such as, for example, boron. You can also use coal. It is also possible to use zeolites or molecular sieves of the X or Y type, or of the mordenite or faujasite type, or of the ZSM-5, ZSM-4, ZSM-8 and the like type, as well as mixtures of metal oxides of the groups. II, III and / or IV with zeolite material.

 In a preferred manner, a support formed mainly of alumina, that is to say of which alumina represents at least 50% by weight relative to the total weight of the support and preferably at least 80% by weight, is employed. and most preferably, alumina alone is employed.

 Advantageously, the catalysts employed in the present invention contain, by weight relative to the support, 0.05 to 3% platinum and 0.005 to 3% rhenium. In a preferred manner, the type A catalyst contains from 0.05 to 0.6% of platinum and from 0.08 to 3% of rhenium by weight relative to the support, and the type B catalyst contains from 0.05 to 0.6% platinum and 0.025 to 1% rhenium. Most preferably, the type A catalyst contains, by weight with respect to the support, from 0.1 to 0.5% of platinum and from 0.1 to 2% and more particularly 0.2 to 1.5% of rhenium and the type B catalyst contains 0.1 to 0.5% platinum and 0.05 to 0.9% and more particularly 0.08 to 0.75% rhenium.

 The proportions of rhenium and platinum must be chosen in such a way that the weight ratio Re / Pt of the catalyst contained in the first catalytic bed or beds crossed by the feedstock is greater than the weight ratio Re / Pt of the catalyst contained in the last catalytic beds crossed by the load.

 To increase the catalyst yield in reforming operations, it is generally advantageous to add at least one halogen to the catalysts.

 In a preferred manner, chlorine and / or fluorine are used.

The introduction of halogen into the catalyst can be carried out by any process at any time during its preparation or its regeneration or during the reaction. The halogen may also be introduced using a halogenated compound such as a halogenated acid for example or a halogenated organic compound such as carbon tetrachloride. The use of halogen is particularly advantageous in the case where the support is alumina.

 The amount of halogen or halogenated compound employed will preferably be such that the catalysts contain from 0.1 to 15% by weight of at least one halogen relative to the carrier and preferably from 0.2 to 5% by weight.

 The weight ratio of the type E catalyst used in the last catalytic bed or beds through which the feedstock is advantageously is from 60 to 92% by weight of the total catalytic mass used in the process and preferably from 80 to 90%.

 In a preferred manner, the process of the invention consists in circulating a hydrocarbon feedstock successively through at least three fixed beds of catalyst.

 The following are described by way of non-limiting examples some possible arrangements, the skilled person is able to imagine all kinds of arrangements of catalytic beds at least in part in series, the essential according to the invention being that the feedstock first passes through at least one catalytic bed containing a catalyst whose weight ratio Re / Pt is higher than the weight ratio Re / Pt of the last catalytic bed or beds crossed by the feedstock. The use of two or more catalytic beds in parallel is within the scope of the invention.

A first exemplary arrangement consists in circulating the feed successively through at least three separate catalytic fixed beds, the first catalyst bed traversed by the feed containing a type A catalyst whose weight ratio Re / Pt is greater than the weight ratios. Re / Pt respective catalysts of type A and / or B and B for the last bed, contained in the other catalytic beds. For example, in the case of three beds, the catalyst contained in the first bed will have a weight ratio
Re / Pt greater than the weight ratio Re / Pt of the catalysts contained in the two following beds.

 A second exemplary arrangement consists in circulating the charge successively through at least three distinct catalytic fixed beds, the first and second catalytic beds traversed by the feed each containing a type A catalyst whose respective weight ratios Re / Pt are higher than the weight ratio Re / Pt of the type B catalysts contained in the last catalytic bed or beds crossed by the load. Thus, for example, in the case of three catalyst beds, the catalysts contained in the first two beds will have a weight ratio Re / Pt greater than the weight ratio Re / Pt of the catalyst contained in the last bed.

 A third exemplary arrangement consists in circulating the feed successively through at least three separate catalytic fixed beds, each containing a catalyst whose weight ratios Re / Pt are generally decreasing from the first bed containing a catalyst of type A to last bed containing a type B catalyst.

 More precisely in the case where three catalytic beds are used arranged in series in the same reactor or in several reactors, and if ra is denoted by the weight ratio Re / Pt of the catalyst contained in the first catalytic bed. passed through the feedstock, by rb the weight ratio Re / Pt of the catalyst contained in the second catalyst bed traversed by the feedstock and by rc the weight ratio Re / Pt of the catalyst contained in the third and last catalyst bed traversed by the feed, according to the invention, in all cases the magnitude relation ra> rc or ra / rc> 1.

The following various magnitude relations are possible ra # rb, ra <rb, rb # rc and rb <rc. Among these various cases the following relationships of quantities are those which are preferred to employ - preferably with a range of from 1.6: 1 to 4: 1 and from
most preferred way from 2: 1 to 3: 1 and rb and rc preferably varying
from 0.5: 1 to 1.5: 1 and most preferably from 0.8: 1 to 1.1: 1.

the preferred values being those given above.

- ra #rb and rb #rc with always ra> rc, ra preferably varying
from 1.6: 1 to 4: 1, and most preferably from 2: 1 to 3: 1 rb
preferably ranging from 1: 1 to 2: 1 and preferably varying from
0.8: 1 to 1.1: 1.

 The various catalyst beds may be contained in a single reactor, preferably having at least three separate superposed beds of catalyst, in the case of a downstream stream the upper bed containing a catalyst of type A and in the case of an updraft the lower bed containing a type A catalyst.

 The various catalytic beds may also be contained in at least two reactors preferably placed in series, for example side by side or superimposed, the first reactor through which the charge contains a type A catalyst and the other reactors containing one or more catalyst beds of type A and / or B and at least the last bed crossed by the charge contained in the last reactor containing a type B catalyst.

 The reforming operations are started by regulating, under operating conditions, hydrogen and feed rates as well as temperature and pressure. The general conditions of the reforming are well known to those skilled in the art, generally the catalytic reforming is carried out at a temperature of 400 to 600 C, under an absolute pressure of 0.1 to 3.5 MPa, with a speed of time (VVH ) from 0.1 to 10 volumes of filler per volume of catalyst per hour, and a hydrosene / hydrocarbon (H2 / HC) molar ratio of 1: 1 to 20: 1. Preferred conditions are: temperature 500 to 580 C, pressure 0.5 to 1.8 MPa, VVH 1 to 10 and H2 / C 3: 1 to 10: 1.

 In the reforming reactions, the lack of selectivity generally results in a poor yield in the dehydrogenation of naphthenes to aromatic hydrocarbons, by parasitic cracking of paraffins with secondary formation of olefinic hydrocarbons which will be at the origin of the formation. coke. The present process makes it possible to dehydrogenate the naphthenic hydrocarbons as much as possible to aromatic hydrocarbons, to minimize the cracking of paraffins and thus not to obtain light hydrocarbons but, on the contrary, also to convert them as far as possible into aromatic hydrocarbons. Thus, according to the invention, the first reaction zone, where an excellent stability catalyst is used, essentially dehydrogenates hydrocarbons, especially naphthenes in aromatic hydrocarbons and in the other reaction zones, because of the selectivity allowed by the appropriate choice of a catalyst, paraffins are cycled in particular without cracking the latter.

 The following nonlimiting examples illustrate the invention.

EXAMPLE 1

It is proposed to treat a load having the following characteristics
ASTM distillation: 90-160 ° C
density at 15 "C: 0.741
composition
paraffinic hydrocarbons: 60% by volume
naphthenic hydrocarbons: 29% by volume
aromatic hydrocarbons: 11% by volume.

The feed is treated with hydrogen under operating conditions equivalent, for the catalysts used, to accelerated aging tests, these conditions being as follows:
Pressure: 0.8 MPa (8 bar)
Temperature: 510 C 2 / HC (molar) 3
Hourly flow of liquid charge: 3 times the total volume of
catalyst
The charge flows successively through three reactors in series with fixed catalyst beds. Catalyst A contains, by weight, 0.25% of platinum and 0.5% of rhenium relative to the support of the catalyst, which is an alumina having a specific surface area of 220 m 2 / give a pore volume of 0.58 cm 3 / g. Catalyst A additionally contains 1.15% chlorine (the specific surface area and the pore volume of catalyst A are equal to 215 m 2/9 and 0.56 cm 3 / g, respectively).

The weight ratio Re / Pt of catalyst A is 2.

Catalyst B contains the same support as catalyst A and contains by weight with respect to this support
0.25 X platinum,
0.25% rhenium
- 1.15 X of chlorine.

 The weight ratio Re / Rt of catalyst B is 1.

The following Table 1 gives the results obtained after 100 hours of operation under the abovementioned conditions for various types of arrangement of the catalytic beds.
- arrangement 1: catalyst A in all the reactors,
- arrangement 2: catalyst B in all the reactors,
- arrangement 3: catalyst A in the first reactor (15% by weight of the total amount of catalysts used),
catalyst B in the second and third reactors (85% by weight of the total amount of catalysts used),
- arrangement 4: catalyst A in the first and second reactors (40% by weight of the total amount of catalysts used),
catalyst B in the third reactor (60% by weight of the total amount of catalysts used),
- arrangement 5: catalyst B in the first reactor (15% by weight of the total amount of catalysts),
catalyst A in the second and third reactors (85% by weight of the total catalyst quality),
-Option 6: catalyst B in the first and second reactors (60% by weight of the total amount of catalysts),
catalyst A in the third reactor (40% by weight of the total amount of catalysts).

 Examination of the results in Table 1 shows that the arrangements 3 and 4 according to the invention lead to the best yields in C5 petrol cut and hydrogen while maintaining a high level of activity.

TABLE 1
BALANCE SHEET AFTER 100 H OF OPERATION (% WEIGHT)

<tb> 4 <SEP> l <SEP> m <SEP>&verbar;<SEP> - <SEP> l <SEP> F
<tb> ARRANGEMENT <SEP> ARRANGEMENT <SEP> ARRANGEMENT <SEP> ARRANGEMENT <SEP> ARRANGEMENT <SEP> ARRANGEMENT <SEP> AGENCY
<tb><SEP> 1 <SEP> 2 <SEP> 3 <SEP> 4 <SEP> 5 <SEP> 6
<tb><SEP> H2 <SEP> 2.70 <SEP> 2.78 <SEP> 2.98 <SEP> 2.80 <SEP> 2.74 <SEP> 2.76
<tb><SEP>.<SEP> CH4 + C2H6 <SEP> 3.06 <SEP> 2.43 <SEP> 2.09 <SEP> 2.61 <SEP> 2.86 <SEP> 2.89
<tb><SEP> C3H8 + C4H1o <SEP> 6.24 <SEP> 5.79 <SEP> 4.93 <SEP> 5.29 <SEP> 5.85 <SEP> 5.90
<tb><SEP> C5 + <SEP> 1 <SEP> 88.00 <SEP> 89.00 <SEP> 90.00 <SEP> 89.30 <SEP> 88.55 <SEP> 88.45
<tb><SEP> Caracteris
<tb><SEP> ticks <SEP> of
<tb><SEP> the + fraction
<tb><SEP> C5
<tb><SEP> d15 <SEP> 0.799 <SEP> 0.790 <SEP> 0.800 <SEP> 0.793 <SEP> 0.798 <SEP> 0.797
<tb><SEP> 4
<tb><SEP> NOR <SEP> 97.4 <SEP> 96.1 <SEP> 97.5 <SEP> 96.8 <SE> 97.3 <SEP> 97
<tb><SEP> C <SEP> weight
<tb><SEP> olefins () <SEP>0;; 4 <SEP> 0.8 <SEP> 0.3 <SEP> 0.4 <SEP> 0.4 <SEP> 0.6
<tb><SEP> X <SEP> weight
<tb><SEP> naphthenesb) <SEP> 3.9 <SEP> 5.5 <SEP> 4.0 <SEP> 4.0 <SEP> 4.8 <SEP> 5.0
<tb><SEP>%<SEP> weight
<tb><SEP> aromatic <SEP> 67.6 <SEP> 65.5 <SEP> 67.8 <SEP> 60r, 6 <SEP> 67.5 <SEP> 67.2
<Tb>
(ê): precursor of coke
(* n): in relation to the dehydrogenating activity.

EXAMPLE 2
The procedure is carried out under the same conditions as in Example 1 (arrangement 3) but replacing catalyst A with catalyst C which contains the same support as catalyst A and contains by weight with respect to the support
- 0.25% platinum,
- 1.00 X rhenium,
- 1.15% chlorine.

 The weight ratio Re / Pt of the catalyst C is 4. After 100 hours of operation the performances are given in Table 2, which also shows the results of the arrangements 1, 3 and 6 of Example 1. The arrangement 7 catalyst C in the first reactor (15% by weight of the total amount of catalysts used) catalyst B in the second and third reactors (85% by weight of the total amount of catalysts used).

TABLE 2

<tb><SEP> ARRANGEMENT <SEP> ARRANGEMENT <SEP> 1 <SEP> ARRANGEMENT <SEP> 3 <SEP> ARRANGEMENT <SEP> 6 <SEP> ARRANGEMENT <SEP> 7
<tb><SEP> H2 <SEP> 2.70 <SEP> 2.98 <SEP> 2.76 <SEP> 2.80
<tb> CH4 <SEP> + <SEP> C2H6 <SEP><SEP> 3.06 <SEP> 2.09 <SEP> 2.89 <SEP> 2.60
<tb> CH8 <SEP> + <SEP> C4H1o <SEP> 6.24 <SEP> 4.93 <SEP> 5.90 <SEP> 5.35
<tb><SEP> C5 + <SEP> 88.00 <SEP> 90.00 <SEP> 88.45 <SEP> 89.25 <SEP>
<tb> Features
<tb> of <SEP> the <SEP> fraction
<tb><SEP> C5 + <SEP>
<tb><SEP> d15 <SEP> 0.799 <SEP> 0.800 <SEP> 0.797 <SEP> 0.795 <SEP>
<tb><SEP> 4 <SEP>
<tb><SEP> NOR <SEP> 97.4 <SEP> 97.5 <SEP> 97.0 <SEP> 97.0
<tb> weight <SEP> olefins <SEP> 0.4 <SEP> 0.3 <SEP> 0.6 <SEP> 0.5
<tb> X <SEP> weight <SEP> naphthenes <SEP> 3.9 <SEP> 4.0 <SEP> 5.0 <SEP> 4.1
<tb> X <SEP> aromatic <SEP> weight <SEP> 67.5 <SEP> 67.8 <SEP> ~ <SEP><SEP> 67.2 <SEP> 67.0
<Tb>
The use in the first reactor of a fixed bed of platinum-rhenium catalyst whose weight ratio rhenium on platinum is equal to 4 leads to yields of hydrogen and gasoline C5 cut slightly lower than those obtained with an arrangement of catalysts, in the various reactors including the first catalyst at a weight ratio Re / Pt in the preferred range according to the invention.

 It is also noted that the arrangement 7 according to the invention makes it possible to obtain a better efficiency in C5 + petrol cut and hydrogen than the arrangements 1 and 6 not in accordance with the invention, while maintaining a high level of activity.

EXAMPLE 3
The procedure is carried out under the same conditions as in Example 1 (arrangement 3) but replacing catalyst A with catalyst D which contains the same support as catalyst A and contains by weight relative to the support
- 0.25% platinum,
0.8% rhenium,
- 1.15% chlorine.

 The rhenium / platinum weight ratio of catalyst D is 3.2.

 After 100 hours of operation, the performances are given in Table 3, in which the performance of the arrangement 3 of Example 1 is also taken. The arrangement 8: catalyst D in the first reactor (15% by weight of the total amount of catalysts used) catalyst e in the second and third reactor (85% by weight of the total amount of catalysts used).

TABLE 3

<tb><SEP> ARRANGEMENT <SEP> 3 <SEP> ARRANGEMENT <SEP> 8
<tb><SEP> H2 <SEP> 2.98 <SEP> 2.85
<tb><SEP> CH4 <SEP> + <SEP> C2H6 <SEP><SEP> 2.09 <SEP> 2.15 <SEP>
<tb><SEP> C3H8 <SEP> + <SEP> C4X10 <SEP> 4.93 <SEP> 5.30
<tb><SEP> C5 + <SEP> 90.00 <SEP> 89.70
<tb><SEP> Features
<tb> of <SEP> the <SEP> fraction <SEP> C5 +
<tb><SEP> d15 <SEP> 0.800 <SEP> 0.798
<tb><SEP> 4
<tb><SEP> NOR <SEP> 97.5 <SEP> 97.3
<tb>% <SEP> weight <SEP> olefins <SEP> 0.3 <SEP> 0.4
<tb> X <SEP> weight <SEP> naphthenes <SEP> 4.0 <SEP> 4.1
<tb> X <SEP> aromatic <SEP> weight <SEP> 67.8 <SEP> L <SEP><SEP> 67.5
<Tb>
The use in the first reactor of a fixed platinum-rhenium catalyst bed, whose rhenium to platinum weight ratio is 3.2, therefore close to the upper value of the range of values preferred for this ratio, makes it possible to obtain a good performance in C5 petrol cut and in hydrogen. The yield obtained, however, is slightly lower than that obtained with the arrangement 3 in which the first catalyst bed contains a catalyst A whose weight ratio Re / Pt is in the most preferred range.

EXAMPLE 4
The procedure is carried out under the same conditions as in Example 1, using in the first reactor a catalyst F containing the same support as catalyst A and containing by weight with respect to this support.
0.25% platinum,
0.52% rhenium,
1.15 X chlorine.

 The weight ratio Re / Pt of catalyst F is 2.08.

In the second reactor, a catalyst G is used having the same support as catalyst A and containing in weight relative to this support
0.25% platinum,
0.37% rhenium,
1.15 X chlorine.

 The weight ratio Re / Pt of catalyst G is 1.48.

 In the third reactor is used catalyst B described in Example 1.

 The arrangement 9 is used. The amount of catalysts F, G and B is respectively 15%, 40% and 45% by weight relative to the total amount of the catalysts used and the feedstock passes successively through the catalyst F, then the catalyst G and finally the catalyst B. The results are given in Table 4 below.

EXAMPLE 5 (Comparative)

The procedure is carried out under the same conditions as in example 1 arrangement 6 by replacing catalyst A with catalyst H which contains the same support as catalyst A and which contains relative to the support
0.25% platinum
1.15% chlorine.

 The catalyst H does not contain rhenium, the weight ratio Re / Pt of this catalyst is zero. The arrangement 10 comprises 60% by weight based on the total amount of Catalyst B catalyst distributed in the first two reactors and 40% by weight of the catalyst H relative to the total amount of catalyst in the third reactor. The results are given in Table 4 below.

TABLE 4

<tb><SEP> ARRANGEMENT <SEP> 3 <SEP> ARRANGEMENT <SEP> 9 <SEP> ARRANGEMENT <SEP> 10
<tb><SEP> H2 <SEP> 2.98 <SEP> 2.96 <SEP> 2.60
<tb><SEP> CH4 <SEP> + <SEP> C2H6 <SEP> 2.09 <SEP> 2.11 <SEP> 3.00
<tb><SEP> C3H8 <SEP> + <SEP> C4H10 <SEP> 4.93 <SEP> 5.03 <SEP> 7.40
<tb><SEP> + <SEP>
<tb><SEP> C5 <SEP> 90.00 <SEP> 89.90 <SEP> 87.00
<tb><SEP> Features
<tb><SEP> of <SEP> the <SEP> fraction
<tb><SEP> C5 <SEP>
<tb><SEP> d15 <SEP> 0.800 <SEP> 0.799 <SEP> 0.782
<tb><SEP> 4
<tb><SEP> NOR <SEP> 97.5 <SEP> 97.4 <SEP> 95.0
<tb> X <SEP> Olefin Weights <SEP> 0.3 <SEP> 0.4 <SEP> 2.2
<tb> X <SEP> Weight Lungs <SEP> 4.0 <SEP> 4.0 <SEP> 8.5
<tb> X <SEP> aromatic <SEP> weight <SEP> 67.8 <SEP> 67.7 <SEP> 62.5
<Tb>

Claims (13)

 rhenium / platinum metal weight (expressed as metal element) of the type B catalyst contained in the last or last beds traversed by the feed, said type B catalyst containing at least 0.005% by weight of rhenium relative to the support.  the catalyst of the first or first beds crossed by the feed being a type A catalyst whose weight ratio (expressed as metal element) rhenium / platinum is greater than the ratio  CLAIMS 1) Catalytic reforming process in which a hydrocarbon feed is circulated under conditions of reforming in the presence of hydrogen, successively through at least two fixed beds of catalyst containing a support, platinum, rhenium and optionally at least one halogen, 2) Process according to claim 1 wherein the rhenium / platinum ratio of the type A catalysts is from 1: 1 to 5: 1 and the rhenium / platinum weight ratio of the type B catalysts is from 0.1: 1 to 3: 1. 3) Process according to claim 2 wherein the rhenium / platinum ratio of the type A catalysts is from 1.6: 1 to 4: 1 and the rhenium / platinum ratio of the type B catalysts is from 0.5: 1 to 1 , 5: 1. 4) Method according to one of claims 1 to 3 wherein the catalyst of each bed through which the load contains by weight relative to the support of 0.05 to 3% platinum and 0.005 to 3% rhenium. 5) Method according to one of claims 1 to 4 wherein the catalyst of type A contains by weight relative to the support of 0.05 to 0.6% platinum and 0.08 to 3% of rhenium and the catalyst Type B contains 0.05 to 0.6% platinum and 0.025 to 1% rhenium, based on the support. 6) Method according to one of claims 1 to 5 wherein the catalyst of each bed through which the load contains 0.1 to 15%  by weight relative to the support of at least one halogen.  7) Method according to one of claims 1 to 6 wherein the support  of the catalyst of each bed traversed by the charge comprises principally  alumina.  8) Method according to one of claims 1 to 7 wherein the pro  weight portion of the catalyst of type B is from 60 to 92% by  relative to the total catalytic mass.  9) Method according to claim 8 wherein the proportion by weight  type B catalyst is 80 to 90% with respect to the mass cata  total lytic.  10) Method according to one of claims 1 to 9 wherein the load  of hydrocarbons passes successively through at least three cat beds  lyseur, the first catalytic bed traversed by the load containing  a type A catalyst whose weight ratio rhenium / platinum is  greater than the respective weight ratios rhenium / platinum cata  Type A and / or B and B lysers contained in other catalytic beds  ticks.  11) Method according to one of claims 1 to 9 wherein the hydrocarbon feed passes successively through at least three cat beds  lyseur, the first two catalytic beds traversed by the charoe  each containing a catalyst of type A whose weight ratios  respective rhenium / platinum are greater than the weight ratio  rhenium / platinum catalyst type B contained in the last  catalytic beds crossed by the load.  12) Method according to one of claims 1 to 11 wherein the  rhenium / platinum weight ratios of the catalysts contained in the  successive catalytic beds crossed by the load are globally  decreasing from the first bed containing a type A catalyst to the last bed containing a type B catalyst. 13) Method according to one of claims 10 to 12 wherein the rhenium / platinum weight ratio of the catalyst of type A in the first catalytic bed traversed by the load is 2: 1 to 3: 1, the weight ratio rhenium / platinum Type B catalyst in the last catalytic bed traversed by the feed is 0.8: 1 to 1.1: 1 and the rhenium / platinum weight ratio of type A catalysts and / or B catalysts contained in the intermediate beds are 1: 1 2: 1.