FR2735491A1 - Process for catalytically reforming n-paraffins and naphthenes to aromatics - Google Patents

Abstract

A process for transforming hydrocarbons into aromatics by contacting a charge contg. the hydrocarbons with a catalyst in conditions of temp. and pressure appropriate to the transformation. The catalyst comprises a matrix of 0-100 % epsilon -alumina and remainder psi -alumina; 0.001-2 % Si; 0.1-15 % F, Cl, Br, or I; 0.01-2 % a Pt-gp. metal; and 0.005-10 % promoter chosen from Sn, Ge, In, Ga, Tl, Sb, Pb, Re, Mn, Cr, Mo, or W. It is subjected to hydrothermal treatment at 300-1000 deg C in an atmos. contg. steam.

Description

PROCESS FOR CATALYTIC TRANSFORMATION OF HYDROCARBONS
IN AROMATIC COMPOUNDS WITH A CATALYST COMPRISING
SILICON
DESCRIPTION
The invention relates to a process for the catalytic conversion of hydrocarbons into aromatic compounds, usable in particular for the reforming of gasolines and the production of aromatics.

 More specifically, it relates to a process of this type using as catalyst a multifunctional alumina matrix catalyst.

 Catalytic reforming is a process for improving the octane number of petroleum fractions and in particular heavy distillation gasoline by converting n-paraffins and naphthenes to aromatic hydrocarbons.

The catalytic reforming operation therefore consists of converting n-paraffins on the one hand
C7-C10 in aromatics and light paraffins and on the other hand C7-C10 naphthenes in aromatics and light paraffins. These reactions are illustrated in particular by the conversion by dehydrogenation of cyclohexanes and the dehydroisomerisation of alkylcyclopentanes to give aromatics, methylcyclohexane giving, for example, toluene, as well as by the cyclization conversion of n-paraffins to aromatics, n-heptane giving by example of toluene.

 During catalytic reforming also occurs cracking reactions of n-paraffins heavy light paraffins leading in particular to C1-C4 products mainly propane, isobutane: these reactions are detrimental to the reformate yield.

 Finally, there is also the formation of coke by condensation of aromatic rings forming a solid product, rich in carbon which is deposited on the catalyst.

 In addition to coke, reforming catalysts are extremely sensitive to various poisons that can degrade their activity, particularly sulfur, nitrogen, metals and water.

 Coke, settling on the catalyst surface results in a loss of activity over time which leads to higher operating temperatures, lower reformate yield, and higher gas yield.

 Therefore, and with regard to the regeneration of the catalyst, the catalytic reforming process can be carried out in two different ways: semi-regeneratively or cyclically and continuously. In the first case, the process is carried out in a fixed bed, in the second in a moving bed.

 In the semi-regenerative process to compensate for the loss of catalyst activity, the temperature is gradually increased and the plant is shut down to regenerate the catalyst by removing the coke. In cyclic reforming, which is in fact a variant of the semi-regenerative process, the plant has several reactors in series and each is taken out of service in turn, the coke deposits are removed from the deactivated catalyst and the regenerated catalyst while the other reactors remain in operation.

 In continuous reforming, the reactors used are moving-bed reactors operating at low pressure (less than 15 bar), which makes it possible to significantly improve reformate and hydrogen yields by favoring aromatization reactions. to the detriment of that of cracking, against the formation of coke is strongly accelerated. The catalyst passes through the reactors and then a regenerative action.

 The processes for producing aromatics involve reactions of paraffinic and naphthenic hydrocarbons into aromatic compounds.

In these hydrocarbon conversion processes, bifunctional catalysts containing, for example, platinum and a chlorinated alumina support, which combine the acid function of the chlorinated alumina necessary for the isomerization reactions of cyclopentanic naphthenes and cyclization of paraffins to the dehydrogenating function of platinum necessary for dehydrogenation reactions. Catalysts of this type comprising in addition another metal such as rhenium, tin or lead have been described in
US-A-3,700,588 and US-A-3,415,737.

 As seen above, the catalytic reforming processes can be carried out using either a fixed bed or a moving catalyst bed.

 In each case, the catalyst undergoes a regeneration treatment taking place at high temperature and in the presence of steam, which consists, among other things, in burning the coke deposited on the catalyst. Unfortunately the conditions of this treatment are favorable to the degradation of the catalyst. It is therefore important to seek to increase the resistance of the catalyst under these conditions.

 The catalyst is generally in the form of extrudates or beads of a sufficient size so as to allow a relatively easy passage to the reagents and gaseous products. Catalyst wear occurs, particularly by friction in moving bed processes, resulting in the formation of finer dust and grain. These finer grains disturb the gas flow and force to increase the input pressure reagents or in some cases to stop the unit. In mobile bed units, this progressive wear also has the effect of disrupting the circulation of the catalyst and requiring the frequent addition of new catalyst.

 A catalyst such as a reforming catalyst must therefore meet a large number of requirements, some of which may appear to be contradictory. This catalyst must first have the greatest possible activity to obtain high yields, but this activity must be combined with the greatest possible selectivity, that is to say that the cracking reactions leading to products containing 1 to 4 carbon atoms should be limited.

 On the other hand, the catalyst must have a high stability vis-à-vis its deactivation by coke deposition; the catalyst must also have excellent resistance to degradation when it has to undergo the extreme conditions prevailing in the repeated regeneration operations that it must undergo.

 In the case of the continuous reforming process employing moving-bed reactors and as mentioned above, the catalysts are also subjected to intense and progressive wear by friction which leads to a significant decrease in their specific surface area and the formation of "fines" detrimental to the operation of the installation. Catalysts currently available, if they can meet one or more of these conditions, do not meet all the requirements mentioned above.

 Thus, despite the numerous improvements already made on the bifunctional catalysts used, new catalysts with improved performances are still sought, not only as regards the yield of the conversion reactions, but also the life of the catalyst.

 The present invention specifically relates to a hydrocarbon conversion process using a multi-functional catalyst which has improved catalytic performance and longer life in the reforming and aromatics reactions.

According to the invention, the process for converting hydrocarbons into aromatic compounds comprises contacting a feedstock of said hydrocarbons with a catalyst under conditions of temperature and pressure suitable for said transformation, and characterized in that the catalyst comprises
a matrix consisting of 0 to 100% by weight of transition alumina, the complement at 100% by weight of the matrix being of transition alumina 7, and
relative to the total weight of the catalyst,
from 0.001 to 2% by weight of silicon,
from 0.1 to 15% by weight of at least one halogen selected from the group consisting of fluorine, chlorine, bromine and iodine,
from 0.01 to 2% by weight of at least one noble metal of the platinum family,
from 0.005 to 10% by weight of at least one promoter metal selected from the group consisting of tin, germanium, indium, gallium, thallium, antimony, lead, rhenium, manganese, chromium, mobybdenum and tungsten.

 It is specified that in the remainder of this text all levels of silicon, halogen, noble metal and promoter metal are expressed in% by weight relative to the total weight of the catalyst, unless otherwise indicated.

Moreover, these contents correspond to the total content of component (halogen, noble metal or promoter metal) when the component comprises several elements (halogens or metals).

A preferred catalyst of the invention comprises
a support consisting of a matrix of alumina, alumina P or a mixture of alumina and alumina, and silicon,
at least one halogen,
a catalytic metal providing the dehydrogenation function of the catalyst, consisting of one or more noble metals of the platinum family, and
at least one promoter metal chosen from the metals mentioned above.

 According to the invention the matrix is based on a hydrated aluminum oxide. It is known that supports in aluminum oxide of general formula Al 2 O 3, nH 2 O, with n ranging from 0 to 0.6, which have a specific surface area of 150 to 400 m 2 / g, can be obtained by controlled dehydration of hydroxides of amorphous aluminum in which n has a value ranging from 1 to 3.

The starting amorphous hydroxides can exist in several forms of which the most common are boehmite (n = 1), gibbsite and bayerite (n = 3), and they can lead during the dehydration treatment with several oxides or transition aluminas such as the forms P, Y, p, X, 0, 6, K and a which differ essentially in the organization of their crystalline structure. During heat treatments, these different forms are susceptible to change between them, according to a complex parentage that depends on the operating conditions of the treatment. Form a, which has a surface area and almost zero acidity, is the most stable at high temperature. For reforming catalysts, shape transition alumina is most often used because of the compromise it presents. between its properties of acidity and thermal stability.

 According to the invention, transition alumina γ, transition alumina, or preferably a mixture of transition alumina γ and transition alumina are used.

 The transition alumina P can be obtained by calcining bayerite in dry air, at atmospheric pressure, between 250 and 5000C, preferably between 300 and 4500C. The specific surface area which depends on the final calcination temperature is between 300 and 500 m 2 / g. The alumina comes from boehmite by calcination under air at a temperature between 450 and 6000C. The specific surface area of the alumina obtained there is between 100 and 300 m 2 / g.

 These two transition aluminas have close but distinct crystalline structures. The X-ray diffraction technique makes it possible to differentiate them. Their structures are of the spinel type with defects, their networks deviating slightly from the cubic symmetry. This quadratic deformation is minimal for the n-form and clearly marked for the y-alumina whose mesh parameters are as follows: a = b = 7.95 A and c = 7.79 A.

 According to the invention, when a mixture of transition alumina and transition alumina is used, this can comprise from 0.1 to 99% or rather up to 84% by weight of alumina. Preferably, this mixture comprises 3 to 70% by weight, and more preferably 5 to 50% by weight of transition alumina, the balance to 100% by weight of the mixture being transition alumina y.

 According to the invention, the alumina matrix is modified with silicon.

 The silicon content of the catalyst is from 0.001 to 2% by weight, preferably from 0.01 to 1% by weight.

 The halogen (s) used to acidify the support may represent in total 0.1 to 15% by weight, preferably 0.2 to 10% by weight. Preferably, a single halogen is used, in particular chlorine.

 The catalyst also comprises one or more promoter metals which have the effect of promoting the dehydrogenating activity of the platinum group noble metal and of limiting the dispersion loss of the noble metal atoms on the surface of the support, which is partly responsible for deactivation of the catalyst.

 The total content of promoter metals is from 0.005 to 10% by weight, preferably from 0.01 to 1% by weight.

 The promoter metals are selected according to the mode of use of the catalyst.

 Thus, when the catalyst is to be used in a fixed bed process, the promoter metal is preferably selected from the group consisting of rhenium, manganese, chromium, molybdenum, tungsten, indium and thallium. .

 When the catalyst is to be used in a moving bed process, the promoter metal is preferably selected from the group consisting of tin, germanium, indium, antimony, lead, thallium and gallium.

 Of these, rhenium is more preferred for fixed bed processes and tin for moving bed processes because these provide the best effects of promoting catalyst activity.

 In particular, rhenium makes it possible to increase the stability of the catalyst with respect to its deactivation by coke deposition. Thus, rhenium is preferably used in catalysts intended for fixed-bed units because this gain in stability makes it possible to extend the duration of the reaction cycles between two regenerations of the catalyst.

 Tin, meanwhile, improves the performance of catalysts when used at low pressure. This joint improvement with the lower cracking activity of tin catalysts results in improved reformate yields, especially in continuous low-pressure bed regeneration processes operating at low operating pressure.

 The total content of metal (metals) promoter (s) is from 0.005 to 10% by weight, preferably from 0.01 to 1% by weight.

 When the catalyst contains only one promoter metal, for example rhenium or tin, it is preferably present in an amount of from 0.005 to 0.9% by weight and more preferably from 0.01 to 0.8% by weight. in weight.

 The catalyst of the invention further comprises at least one noble metal of the platinum family at a content of 0.01 to 2% by weight, preferably 0.1 to 0.8% by weight.

 The noble metals that can be used are platinum, palladium and iridium; platinum is preferred.

 The catalyst of the invention may be prepared by depositing its various constituents on the alumina matrix. The deposition of each component may be carried out, in whole or in part, on one or both aluminas of the matrix before or after shaping thereof. The constituents can be deposited separately or simultaneously in any order.

 Thus, when a mixture of aluminas is used as the matrix, the constituents of the catalyst can be deposited on the two aluminas or on one of them, preferably on the alumina n before mixing the two. aluminas and their shaping.

 It is also possible to partially or completely deposit one or more constituents on the two aluminas or one of them before mixing them, then to make the other deposits after mixing the two aluminas, either before or after the in the form of the mixture. When depositing one or more constituents before mixing the two aluminas, the deposition of silicon on the transition alumina is preferably carried out.

 However, according to the invention, it is generally preferred to mix the two aluminas before depositing the metal components and the halogen or halogen.

Also, according to the invention, the catalyst can be prepared by a process comprising the following steps
a) preparation optionally by mixing and then shaping a transition alumina matrix y, transition alumina R1, or a mixture of transition alumina n and transition alumina y,
b) deposition on at least one of the transition aluminas 7 and n of the following components, in the percentages by weight given below, which relate to the total weight of the catalyst,
from 0.001 to 2% by weight, preferably from 0.01 to 1% by weight, of silicon,
from 0.1 to 15%, preferably from 0.2 to 10%, by weight of at least one halogen chosen from the group consisting of fluorine, chlorine, bromine and iodine,
from 0.1 to 2% of at least one noble metal of the platinum family, and
from 0.005 to 10% by weight of at least one promoter metal selected from the group consisting of tin, germanium, indium, gallium, thallium, antimony, lead, rhenium, manganese, chromium, molybdenum and tungsten; the steps a) and b) can be performed in any order, but preferably step a) being performed before step b), and the deposits of step b) can be made in part only before step a) and can be performed in any order.

 According to a preferred embodiment of this process, a support formed from the matrix of alumina and Si is first prepared, then the promoter metal or metals, or the halogens, are deposited thereon, and the noble metal or metals of the platinum family.

 In this case, Si may be deposited on the alumina or the alumina mixture, before or after shaping.

 Preferably, the silicon is deposited after shaping of the alumina matrix.

 The deposition of the various constituents of the catalyst can be carried out by conventional techniques, in the liquid phase or in the gas phase, from appropriate precursor compounds. When the deposition is carried out on the formed alumina matrix, the techniques employed may be, for example, dry impregnation, impregnation with excess solution or ion exchange. This operation is followed if necessary by drying and calcination at a temperature of 300 to 9000 ° C, preferably in the presence of oxygen.

Thus, the silicon can be deposited from compounds such as alkyl tetraorthosilicates, silicon alkoxides, quaternary ammonium silicates, silanes, disilanes, silicones, siloxanes, silicon halides, halosilicates and silicon in the form of microspheres of colloidal silica. In the case where the silicon precursor is a fluorosilicate, it may correspond to the formula M2 / xSiF6, in which M is a metallic or non-metallic cation having the valence x, chosen from the following cations: NH 4 +, alkylammonium , K +, Na +, Li +, Ba2 +, Mg2 +, Cd2 +, Cu +, Cu2 +,
Ca2 +, Cs +, Fe2 +, Co2 +, Pb2 +, Mn2 +, Rb +, Ag +, Sr2 +,
Zn2 +, Tl + and H +.

 When the silicon is deposited after shaping of the alumina matrix, this deposition is preferably carried out by impregnation in an aqueous medium using an excess of aqueous precursor solution. The impregnating solvent is then removed, for example by drying, and calcination is carried out under air at a temperature of, for example, between 300 and 9000 ° C.

 The deposition of the noble metal (s) of the platinum family can also be carried out by conventional techniques, in particular the impregnation from an aqueous or non-aqueous solution containing a salt or a noble metal compound. By way of example of salts or compounds that may be used, mention may be made of chloroplatinic acid, ammonia compounds, ammonium chloroplatinate, platinum dicarbonyl dichloride, hexahydroxyplatinic acid, palladium chloride and palladium nitrate. .

In the case of platinum, the ammonia compounds may be, for example, the hexamines IV platinum salts of formula Pt (NH 3) 6X 4, the platinum IV halopentamine salts of formula (PtX (NH 3) 5) X 3, the platinum tetrahalogenodiamine salts of formula
PtX4 (NH3) 2X, platinum complexes with halogen-polyketones and halogenated compounds of formula H (Pt (aca) 2X) in which element X is a halogen selected from the group consisting of chlorine, fluorine, bromine and iodine, and preferably chlorine, and the aca group represents the residue of formula CsH702 derived from acetylacetone. The introduction of the noble metal of the platinum family is preferably carried out by impregnation with an aqueous or organic solution of one of the organometallic compounds mentioned above. Among the organic solvents that can be used, mention may be made of paraffinic, naphthenic or aromatic hydrocarbons, and halogenated organic compounds having, for example, 1 to 12 carbon atoms per molecule. For example, n-heptane, methylcyclohexane, toluene and chloroform may be mentioned. Solvent mixtures can also be used.

 After introduction of the noble metal, drying and calcination are preferably carried out, for example at a temperature of 400 to 7000 ° C.

 The noble metal (s) of the platinum family can be deposited at any time during the preparation of the catalyst. It may be carried out separately or simultaneously with the deposition of other constituents, for example promoter metal (s).

In the latter case, a solution containing all the constituents to be introduced simultaneously can be used for the impregnation.

 The deposition of the promoter metal or metals may also be carried out by conventional techniques from precursor compounds such as the halides, nitrates, acetates, tartrates, citrates, carbonates and oxalates of these metals. Any other salt or oxide of these metals soluble in water, acids, or other suitable solvent is also suitable as a precursor. By way of examples of such precursors, mention may be made of rhenates, chromates, molybdates and tungstates. The promoter metal (s) may also be introduced by mixing an aqueous solution of their precursor compound (s) with the alumina or aluminas before shaping, followed by calcination in air at room temperature. a temperature between 400 and 9000C.

 The introduction of the promoter metal or metals can also be carried out using a solution of an organometallic compound of said metals in an organic solvent. In this case, this deposition is preferably carried out after that of the noble metal (s) of the platinum family and calcination of the solid, optionally followed by a reduction with hydrogen at high temperature, for example between 300 and 5000 ° C. The organometallic compounds are selected from the group consisting of complexes of said promoter metal, in particular polyketone complexes and hydrocarbylmetals such as alkyl, cycloalkyl, aryl, alkylaryl and arylalkyl metals. It is also possible to use organohalogen compounds. In particular, tetrabutyltin may be mentioned in the case where the promoter metal is tin, tetraethylplomb in the case where the promoter metal is lead and triphenylindium in the case where the promoter metal is indium. The impregnating solvent may be selected from the group consisting of paraffinic, naphthenic or aromatic hydrocarbons containing from 6 to 12 carbon atoms per molecule and halogenated organic compounds containing from 1 to 12 carbon atoms per molecule. For example, n-heptane, methylcyclohexane and chloroform may be mentioned. It is also possible to use mixtures of the solvents defined above.

 The halogen, for example chlorine, may be introduced into the catalyst together with another metallic constituent, for example in the case where a halide is used as a precursor compound for the platinum family metal, the promoter metal or alkali or alkaline earth metal. This introduction can also be carried out by impregnating the support with an aqueous solution containing an acid or a halogenated salt. For example, chlorine can be deposited using a hydrochloric acid solution. The introduction of chlorine can also be carried out by calcination of the catalyst at a temperature ranging for example from 400 to 900 ° C, in the presence of a halogen-containing organic compound such as, for example, CCl 4, CH 2 Cl 2 and CH 3 Cl.

 Of course, at least two components of the catalyst can be introduced simultaneously, for example from a solution comprising precursor compounds thereof. The constituents can also be introduced successively in any order, from separate solutions. In the latter case, dryings and / or intermediate calcinations may be carried out.

 The shaping of the alumina matrix can be carried out using the catalyst shaping techniques known to those skilled in the art, such as, for example: extrusion, drop coagulation, coating, spray drying or pelletizing.

Preferably, the preparation process comprises the following successive steps
a) shaping the matrix of alumina or alumina n or a mixture of alumina and alumina,
b) deposition of silicon on this matrix,
c) depositing at least one promoter metal selected from tin, germanium, indium, gallium, thallium, antimony, lead, rhenium, manganese, chromium, molybdenum and tungsten ,
d) introducing at least one element selected from the group consisting of fluorine, chlorine, bromine and iodine, and
e) depositing at least one noble metal of the platinum family.

 After forming the matrix and depositing all the constituents, it is possible to carry out a final heat treatment between 300 and 10,000 ° C., which may comprise only one step at a temperature of 400 ° C. to 9 ° C. preferably, and under an atmosphere containing oxygen, and preferably in the presence of free oxygen or air. This treatment generally corresponds to drying-calcination following the deposition of the last component.

 After shaping the matrix and depositing all the constituents, a heat treatment is preferably carried out which may be complementary to the preceding treatment and which may be carried out at a temperature of 300 to 1000 ° C., preferably 400 to 7000 ° C. in a gaseous atmosphere containing water vapor and optionally a halogen such as chlorine.

 This treatment can be carried out in bed traversed by a stream of gas or in a static atmosphere. Preferably, the gaseous atmosphere contains water and optionally at least one halogen. The molar content of water is between 0.05 and 100%, preferably between 1 and 50%. The molar content of halogen is between 0 and 20 i, preferably between 0 and 10%, and more preferably between 0 and 2%. The duration of this treatment is variable depending on the conditions of temperature, partial pressure of water and amount of catalyst. This value is advantageously between one minute and 30 hours, preferably from 1 to 10 hours. The gaseous atmosphere used is for example based on air, oxygen, or an inert gas such as argon or nitrogen.

 The role of this high temperature treatment in the presence of water is important in some cases. As shown in the examples described hereinafter, in the presence of silicon which preserves the matrix of alumina (s) with a loss of specific surface area during the different regenerative treatments, unexpectedly, a severe heat treatment in the presence of Water applied to this type of catalyst has the effect of preserving a loss of specific surface, while improving the catalytic performance.

 After the final heat treatment, the catalyst can be subjected to an activation treatment under hydrogen at high temperature, for example at a temperature of 300 to 550 ° C.

 The hydrogen treatment procedure consists, for example, in a slow rise in the temperature under a stream of hydrogen up to the maximum reduction temperature, generally between 300 and 550 ° C. and preferably between 350 and 4500 ° C., followed by keeping at this temperature for a period generally ranging from 1 to 6 hours.

 According to the invention, the catalyst described above is used for the conversion of hydrocarbons, and more particularly in the processes for reforming gasolines and producing aromatics.

 The reforming processes make it possible to increase the octane number of the gasoline fractions originating from the distillation of crude oil and / or other refining processes.

 The aromatics production processes provide the bases (benzene, toluene and xylene) that can be used in petrochemicals. These processes are of additional interest in contributing to the production of large quantities of hydrogen essential for the hydrotreatment processes of the refinery.

 These two methods are distinguished by the choice of operating conditions and the composition of the charge.

 The typical feedstock treated by these processes contains paraffinic, naphthenic and aromatic hydrocarbons containing 5 to 12 carbon atoms per molecule. This load is defined, among other things, by its density and its weight composition.

 To carry out these processes, the hydrocarbon feedstock is contacted with the catalyst of the present invention under suitable conditions, for example at a temperature of 400 to 700 ° C, under pressure ranging from atmospheric pressure to 4 MPa. , using the technique of moving bed or fixed bed.

When operating in a fixed bed, the pressure is 1 to 2 MPa, when operating in a moving bed, the pressure is preferably 0.1 to 0.9 MPa.

 Generally the contacting is carried out with a mass flow rate of treated feedstock per unit mass of catalyst and per hour ranging from 0.1 to 10 kg / kg.h.

 Part of the hydrogen produced is recycled according to a molar recycling ratio ranging from 0.1 to 8.

This rate is the molar ratio of recycled hydrogen flow rate to the feed rate.

 Other features and advantages of the invention will appear better on reading the examples which follow, given of course by way of illustration and not limitation.

EXAMPLE 1
This example illustrates the manufacture of a catalyst comprising a matrix formed of a mixture of alumina 7 and alumina R1, on which silicon, chlorine, rhenium and platinum are deposited.

a) Shaping of the alumina matrix
The alumina matrix is firstly prepared by mechanical mixing of an alumina powder with a specific surface area of 220 m 2 / g and an alumina powder n with a specific surface area of 320 m 2 / g which was prepared by calcination of bayerite. The proportion of alumina n is 10% by weight. This mixture is then shaped by extrusion and then calcined under a stream of dry air at 520 ° C for 3 h.

b) Deposition of silicon
After cooling, silicon is deposited on the calcined matrix by contact with an ethanolic solution of tetraethyl orthosilicate Si (OC 2 H 5) 4. The concentration of this solution is 18.5 g of silicon per liter. This contacting is carried out at room temperature for 2 hours with stirring. The solvent is then evaporated under reduced pressure. The impregnated extrudates are then dried at 1200 ° C. for 15 hours and calcined at 530 ° C. under a stream of dry air for 2 hours.

(c) Deposition of platinum, tin and chlorine
Platinum, tin and chlorine are then simultaneously deposited on this support by impregnation with a chlorinated aqueous solution containing per liter
0.96 g of tin in the form of SnCl2, and
0.81 g platinum as H2PtCl6.

The solution is left in contact with the support for 2 hours. After drying and drying for 4 hours at 1200 ° C., the impregnated support is calcined at 53 ° C. for 3 hours under a stream of dry air.

d) Heat treatment
A heat treatment is then carried out in the presence of water and chlorine. In order to do this, the catalyst is treated at 510 ° C. for 2 hours under a current of 2000 dm 3 / h of air per 1 kg of solid product. This air contains water and chlorine injected into a preheating zone located upstream of the solid bed. The molar concentrations of water and chlorine are respectively 1% and 0.05%
The characteristics of the catalyst obtained are given in Table 1.

EXAMPLE 2
The same procedure as in Example 1 is followed to prepare a catalyst comprising the same constituents, except that the heat treatment of step d) is not carried out.

 The characteristics of the catalyst obtained are also given in Table 1.

COMPARATIVE EXAMPLE
In this example, the same operating procedure as in Example 1 is followed, but in step a) only γ-alumina is used, and step b) of silicon deposition is not carried out. step d) heat treatment.

 The characteristics of the catalyst obtained are also given in Table 1.

Table 1

<tb><SEP> Proportion <SEP> Surface <SEP> Content <SEP> Content <SEP> Content <SEP> Content
<tb> Catalyst <SEP> alumina <SEP> 1 <SEP> specific <SEP> in <SEP> in <SEP> in <SEP> in
<tb><SEP> (% <SEP> weight <SEP> of <SEP> (m2 / g) <SEP> platinum <SEP> tin <SEP> chlorine <SEP> silicon
<tb><SEP> the <SEP> matrix <SEP> (% <SEP> (% <SEP> (% <SEP> (% <SEP>
<tb><SEP> in <SEP> in <SEP> in <SEP> in
<tb><SEP> ids <SEP> weight) <SEP> weight) <SEP> weight)
<tb><SEP> Ex <SEP> 1 <SEP> 10 <SEP> 227 <SEP> 0.25 <SEP> 0.17 <SEP> 1.08 <SEP> 1.04
<tb><SEP> Ex2 <SEP> 2 <SEP> 10 <SEP> 228 <SEP> 0.24 <SEP> 0.18 <SEP> 1.13 <SEP> 1.02 <SEP>
<tb><SEP> Ex
<tb> comparative <SEP> 0 <SEP> 219 <SEP> ~ <SEP><SEP> 0.23 <SEP> 0.18 <SEP> 1.15 <SEP><SEP> 0
<Tb>
EXAMPLE 3
In this example, the catalysts of Examples 1 and 2 and of the comparative example are tested for the conversion of a hydrocarbon feedstock having the following characteristics:
density at 20 C 0.736 kg / dm3
desired octane number ~ 38
paraffin content 54.8% by weight
Naphthenes content 33.1% by weight
aromatic content 12.1% by weight
The following operating conditions are used
5000C temperature
total pressure 1.0 Mpa
charge rate 1.8 kg / kg of
catalyst and by h
duration 100 h
At the end of the operating time, the deactivated catalyst is regenerated by controlled combustion of the coke and adjustment of its chlorine content to about 1.10% by weight. The specific surface of the support is measured after this regeneration. Then after high temperature activation of the catalyst with hydrogen, the charge is injected for a new period of operation. Thus, each catalyst was subjected to 5 cycles of operation and regeneration. The specific surfaces corresponding to the beginning of the first and last cycles and the performances obtained after 15 hours of operation in each of these two cycles are reported in Table 2 below.

Table 2

<tb> Catalyst <SEP> cycle <SEP> Surface <SEP> yield <SEP> Index <SEP><SEP> Yield <SEP> Yield
<tb><SEP> specific <SEP> in <SEP> octane <SEP> in <SEP> in <SEP> C4
<tb><SEP> (m2 / g) <SEP> refonnat <SEP> searched <SEP> aromatic <SEP> (% <SEP> in <SEP> weight)
<tb><SEP>%<SEP> in <SEP> weight) <SEP> (% <SEP> in <SEP> ids <SEP>
<tb><SEP> Ex <SEP> 1 <SEP> 227 <SEP> 91.2 <SEP> 97.4 <SEP> 67.7 <SEP> 5.2
<tb><SEP> 5 <SEP> 226 <SEP> 91.6 <SEP> 96.9 <SEP> 66.8 <SEP> 5.1
<tb><SEP> Ex <SEP> 2 <SEP> 1 <SEP> 228 <SEP> 91.4 <SEP> 98.0 <SEP> 68.3 <SEP> 5.2
<tb><SEP> 5 <SEP> 225 <SEP> 91.9 <SEP> 97.2 <SEP> 67.2 <SEP> 4.3
<tb><SEP> Ex <SEP> 1 <SEP> 219 <SEP> 90.3 <SEP> 97.2 <SEP> 67.0 <SEP> 5.9
<tb> comparative
<tb><SEP> 5 <SEP> ~ <SEP><SEP> 197 <SEP> 91.7 <SEP> 94.8 <SEP> 64.8 <SEP> 5.1
<Tb>
If one compares the performance of the catalysts of the invention (Examples 1 and 2) with those of the catalyst of the prior art (comparative example), it is found that the catalysts of the invention have the best yields of aromatics and the best octane numbers of the reformate. We also note that these gains are made without reformat yields being affected.

 If we now consider the evolution during 5 cycles, it appears that the drop of the specific surfaces of the catalysts of the invention is much lower than that of the catalyst of the prior art.

This lower drop is accompanied by a better maintenance of aromatics yields and octane numbers.

 The process of the invention thus makes it possible to substantially improve the results obtained by the conversion of hydrocarbons into aromatic compounds, in terms of selectivity and stability during the reaction cycles.

Claims (23)

 A process for converting hydrocarbons into aromatic compounds comprising contacting a charge of said hydrocarbons with a catalyst under conditions of temperature and pressure suitable for said transformation, characterized in that the catalyst comprises  a matrix consisting of 0 to 100% by weight of transition alumina r 1, the complement at 100% by weight of the matrix being transition alumina y, and  relative to the total weight of the catalyst,  from 0.001 to 2% by weight of silicon,  from 0.001 to 8% by weight of at least one doping metal selected from the group of alkali and alkaline earth metals,  from 0.1 to 15% by weight of at least one halogen selected from the group consisting of fluorine, chlorine, bromine and iodine,  from 0.01 to 2% by weight of at least one noble metal of the platinum family, and  from 0.005 to 10% by weight of at least one promoter metal selected from the group consisting of tin, germanium, indium, gallium, thallium, antimony, lead, rhenium, manganese, chromium, mobybdenum and tungsten.  The process according to claim 1, wherein the catalyst matrix comprises from 0.1 to 84% by weight of transition alumina q.  The process of claim 1 wherein the catalyst matrix comprises from 3 to 70 weight percent transition alumina.  The process according to claim 1, wherein the catalyst matrix comprises from 5 to 50% by weight of transition alumina q.  5. Process according to any one of claims 1 to 4, wherein the silicon content of the catalyst is from 0.01 to 1% by weight.  6. Process according to any one of claims 1 to 5, wherein the halogen content of the catalyst is from 0.2 to 10% by weight,  7. A process according to any one of claims 1 to 6, wherein the total noble metal content of the catalyst is 0.1 to 0.8% by weight.  The process of any one of claims 1 to 7, wherein the catalyst promoter metal is selected from the group consisting of rhenium, manganese, chromium, molybdenum, tungsten, indium and thallium.  The process of claim 8 wherein the catalyst promoter metal is rhenium.  10. Process according to any one of claims 1 to 7 wherein the promoter metal is selected from the group consisting of tin, germanium, indium, antimony, lead, thallium and gallium.  The process of claim 10 wherein the catalyst promoter metal is tin.  The process according to any one of claims 1 to 11, wherein the total promoter metal content of the catalyst is 0.01 to 1% by weight.  The process according to any one of claims 1 to 11, wherein the catalyst comprises a single promoter metal in an amount of 0.005 to 0.9% by weight of the catalyst.  The process according to claim 13, wherein the promoter metal content of the catalyst is from 0.01 to 0.8% by weight.  The process of any of claims 1 to 14, wherein the halogen of the catalyst is chlorine.  16. Process according to any one of claims 1 to 15, characterized in that the noble metal of the catalyst is platinum.  17. Method according to any one of claims 1 to 16, characterized in that, before contacting the catalyst with the hydrocarbon feedstock, it is subjected to a heat treatment, carried out for a period of 1 minute at 30 hours, under a gaseous atmosphere comprising water whose molar content is from 0.05 to 100%.  18. The method of claim 17, characterized in that the gaseous atmosphere further comprises at least one halogen whose molar content is at most 20%.  19. Process according to any one of claims 1 to 18, in which the hydrocarbon feedstock contains paraffinic, naphthenic and aromatic hydrocarbons having 5 to 12 carbon atoms, and this feed is brought into contact with the catalyst. at a temperature of 400 to 7000C, under a pressure ranging from atmospheric pressure to 4 MPa.  20. The method of claim 8 or 19, wherein the pressure is 1 to 2 MPa.  21. The method of claims 10 or 19, wherein the pressure is 0.1 to 0.9 MPa.  22. Process according to any one of Claims 19 to 21, characterized in that the hydrocarbon feedstock is brought into contact with the catalyst at a mass flow rate of between 0.1 and 10 kg of feed per kg of feedstock. catalyst and per hour.  23. The process according to any one of claims 1 to 22, wherein the hydrocarbon conversion is catalytic reforming.