EP0849350A1 - Process for the transformation of gas-oils in order to produce dearomised and desulphurised high cetane carburants - Google Patents

Abstract

The transformation of gasoline feed to produce a dearomatised and a desulfurated fuel with high cetane index is claimed. It consists of: (a) desulfuration and denitrogenation step where the gasoline charge and hydrogen are passed onto a catalyst containing a mineral support, a metal or a metallic compound from group VIB at 0.5-40 wt.% w.r.t. the catalyst a metal or a metallic compound from group VIII at 0.1-30 wt.% w.r.t. the catalyst phosphorous or a phosphorous compound at 0.01-20% expressed in weight of P2O5 w.r.t. the support (b) dearomatisation step, where part of the product resulting from step (a) is passed onto a mineral support containing a precious or a compound of a precious metal from group VIII at 0.01-20% expressed in weight of metal w.r.t. weight of catalyst.

Description

The present invention relates to the field of fuels for combustion engines internal. It relates more particularly to the manufacture of a motor fuel compression ignition. In this field, the invention relates to a method of transformation of a diesel cut to produce a fuel with a high cetane number, flavored and desulfurized.

Currently the diesel cuts that they come from the direct distillation of an oil crude or whether they come from the catalytic cracking process still contain significant amounts of aromatics, nitrogen compounds and sulfur compounds. In the current legislative framework of the majority of industrialized countries the fuel usable in engines must contain less than about 500 parts per million by weight (ppm). In some countries, there is no the moment of standards imposing a maximum content of aromatics and nitrogen. We notes, however, that several countries or states, like Sweden and the California plan to limit aromatics to less than 20% in volume, or even less than 10% in volume and some experts even think that this content could be limited to 5% by volume. In Sweden in particular, some diesel fuel classes must already meet very strict specifications. In this country, Class II diesel fuel must not contain more than 50 ppm of sulfur and more than 10% by volume of aromatic compounds and that of class I more than 10 ppm of sulfur and 5% by volume of aromatic compounds. Currently in Sweden Class III diesel fuel must contain less than 500 ppm sulfur and less than 25% by volume of aromatic compounds. Similar limits are also to be observed for the sale of this type of fuel in California.

Meanwhile, engine manufacturers in several countries are pushing for legislation obliges oil tankers to produce and sell a fuel whose index of cetane has a minimum value. French law currently requires an index of cetane minimum of 49, but it is foreseeable that in the near future this index minimum or at least 50 (as is already the case for Class I fuel in Sweden) and probably even at least 55 and more likely understood between 55 and 70.

Many specialists are seriously considering the possibility of having in the future a standard imposing a nitrogen content of less than about 200 ppm for example and even certainly less than 100 ppm. Indeed a low nitrogen content allows obtain better product stability and will generally be sought as well by the seller of the product than by the manufacturer.

It is therefore necessary to develop a reliable and efficient process allowing to obtain from conventional diesel distillation cuts direct or from catalytic cracking (LCO cut) or another conversion process (coking, visbreaking, hydroconversion of residue etc.) a product with improved characteristics with regard to both the cetane number and the aromatic, sulfur and nitrogen contents. It is particularly important, and it is one of the advantages of the process of the present invention, of producing the minimum of gaseous hydrocarbon compounds and being able to have an effluent directly and fully recoverable as a very high quality fuel cutter. Otherwise, the process of the present invention allows production over a period of time important without the need to regenerate the catalysts employed, which have the advantage of being very stable over time.

In its broadest formulation, the present invention therefore relates to a method of transformation of a diesel cut to produce a fuel with a high cetane number, flavored and desulphurized in at least two successive stages. It also concerns the fuel obtained by said process.

a) au moins une première étape dite de désulfuration et de déazotation profonde dans laquelle on fait passer ladite coupe gazole et de l'hydrogène sur un catalyseur comprenant un support minéral, au moins un métal ou composé de métal du groupe VIB de la classification périodique des éléments en une quantité exprimée en poids de métal par rapport au poids du catalyseur fini d'environ 0,5 à 40%, au moins un métal ou composé de métal du groupe VIII de ladite classification périodique en une quantité exprimée en poids de métal par rapport au poids du catalyseur fini d'environ 0,1 à 30% et du phosphore ou au moins un composé de phosphore en quantité exprimée en poids de pentoxyde de phosphore par rapport au poids du support d'environ 0,001 à 20 % et

b) au moins une deuxième étape subséquente dite de désaromatisation dans laquelle on fait passer au moins une partie, et de préférence la totalité, du produit qui est issu de la première étape, au moins en partie, et de préférence en totalité désulfuré et déazoté et de l'hydrogène sur un catalyseur comprenant, sur un support minéral au moins un métal noble ou composé de métal noble du groupe VIII en une quantité exprimée en poids de métal par rapport au poids du catalyseur fini d'environ 0,01 à 20%, et de préférence au moins un halogène.

More specifically, the present invention relates to a process for converting a diesel cut into a fuel with a high cetane number, which is flavored and desulphurized, comprising the following steps:

a) at least a first step known as desulphurization and deep denitrogenation in which said diesel cut and hydrogen are passed over a catalyst comprising an inorganic support, at least one metal or metal compound of group VIB of the periodic table elements in an amount expressed by weight of metal relative to the weight of the finished catalyst of approximately 0.5 to 40%, at least one metal or metal compound of group VIII of said periodic classification in an amount expressed by weight of metal relative to the weight of the finished catalyst of approximately 0.1 to 30% and of phosphorus or at least one phosphorus compound in an amount expressed by weight of phosphorus pentoxide relative to the weight of the support of approximately 0.001 to 20% and

b) at least a second second step called the dealomatization in which at least part, and preferably all, of the product which is obtained from the first step, at least in part, and preferably completely desulfurized and denitrogenated, is passed through and hydrogen on a catalyst comprising, on an inorganic support at least one noble metal or compound of noble metal from group VIII in an amount expressed by weight of metal relative to the weight of the finished catalyst of about 0.01 to 20 %, and preferably at least one halogen.

Advantageously, according to the method, the hydrogen is introduced at each of the first and second stages, and is optionally recycled at the level of the first and second stages, independently of each other, which means that there is no management common gas from said stages.
Preferably, according to the process, the effluent from the first stage is subjected to a stripping with water vapor so as to separate at least partially the gaseous phase, which can be treated and optionally recycled at least in part to level of said step. At least part of the product from stripping is subjected to the second step of the process according to the invention.
The effluent preferably leaving the last stage is stripped with steam, advantageously passes through a coalescer and is optionally dried.

In a preferred embodiment of the invention, the operating conditions of the steps a) and b) are chosen according to the characteristics of the load which can be a direct distillation diesel cut, a diesel cut from cracking catalytic or diesel cut from coking or visbreaking (visbreaking) of residues or a mixture of two or more of these cuts so as to obtain a product containing less than 100 ppm of sulfur and less than 200 ppm, or better than 50 ppm of nitrogen and the conditions of step b) are chosen so as to obtain a product containing less than 10% by volume of aromatic compounds. These conditions can be tightened so as to obtain after the second stage a fuel containing less than 5% by volume of aromatic compounds, less than 50 ppm or even less than 10 ppm sulfur, less than 20 ppm or even less than 10 ppm nitrogen and having a cetane number of at least 50 and even at least 55 and most often between 55 and 60.

To obtain such results, the conditions of step a) include a temperature from about 300 ° C to about 450 ° C, a total pressure from about 2 MPa to about 20 MPa and an overall hourly space velocity of liquid charge of about 0.1 to about 10 and preferably 0.1 to 4 and that of step b) a temperature of about 200 ° C to about 400 ° C, a total pressure from about 2 MPa to about 20 MPa and a speed overall hourly liquid charge space from about 0.5 to about 10.

When one wishes to remain in a relatively low pressure range while wishing to obtain excellent results it is possible to carry out a first step a1) under conditions allowing the sulfur content of the product to be reduced to a value about 500 to 800 ppm and then send this product in a subsequent step a2) under which conditions will be chosen to reduce the sulfur content to a less than about 100 ppm, preferably less than about 50 ppm and the product from this step a2) is then sent to step b). In this form of realization the conditions of step a2) are identical or preferably milder that when, for a given charge, we operate in a single step a), since the product sent in this step a2) already has a greatly reduced sulfur content. In this embodiment the catalyst of step a1) can be a conventional catalyst prior art such as that described in the text of patent applications in the name of the applicant FR-A-2197966 and FR-A-2538813 and that of step a2) is the one described above for step a). We would not go beyond the scope of this invention using in steps a1) and a2) the same catalyst.

In these steps a), a1), a2) the catalyst support can be chosen from the group formed by alumina, silica, silica-aluminas, zeolites, titanium oxide, magnesia, zirconia, clays and mixtures of at least two of these compounds minerals. Alumina is very commonly used.

In a preferred embodiment of the invention, the catalyst for these steps a), a1), a2) will comprise, deposited on the support, at least one metal or a compound of metal, advantageously chosen from the group formed by molybdenum and tungsten and at least one metal or a metal compound advantageously chosen in the group formed by nickel, cobalt and iron. Most often this catalyst includes molybdenum or a molybdenum compound and at least one metal or metal compound chosen from the group formed by nickel and cobalt.

In a particular and preferred form of the invention, the catalyst for these steps a), a1), a2) will comprise boron or at least one boron compound preferably in one quantity expressed by weight of boron trioxide relative to the weight of the support less than or equal to 10%, and preferably deposited on the support.

The amount of metal or group VIB metal compound (preferred Mo) expressed by weight of metal relative to the weight of the finished catalyst will preferably be approximately 2 to 30% and more often about 5 to 25% and that of the metal or the compound of group VIII metal (Ni or Co preferred) will preferably be approximately 0.5 to 15% and the more often around 1 to 10%.

Preferably, a catalyst containing Ni, Mo, P is used, the proportions of these elements having been previously described, or better yet Ni, Mo, P, B.

A particularly advantageous catalyst is that described in patent EP-297,949 whose teaching is included in this description.

This catalyst comprises: a) a support comprising a porous mineral matrix, boron or a boron compound and phosphorus or a phosphorus compound, and b) at least one metal or metal compound from group VIB of the periodic table and at least one metal or metal compound from group VIII of said classification, in which the sum of the quantities of boron and phosphorus, expressed respectively by weight of boron trioxide (B ₂ O ₃ ) and phosphorus pentoxide (P ₂ O ₅ ) relative to the weight of the support is approximately 5 to 15%, preferably approximately 6 to 12% and advantageously approximately 8 to 11.5%, the atomic ratio boron on phosphorus (B / P) is d '' about 1.05: 1, to 2: 1 and preferably about 1.1: 1 to 1.8: 1. Advantageously at least 40% and preferably at least 50% of the total pore volume of the finished catalyst is contained in pores with an average diameter greater than 13 nanometers.

The catalyst preferably has a total pore volume of between 0.38 and 0.51 cm ³ xg ^-1 .

The quantity of group VIB metal or metals contained in the catalyst is usually such as the phosphorus-to-metal atomic ratio or metals of the VIB group (P / VIB) is about 0.5: 1 to 1.5: 1 and preferably about 0.7: 1 to 0.9: 1.

The respective quantities of group VIB metal or metals and of metal or metals of group VIII contained in the catalyst are usually such that the ratio atomic metal or metals of group VIII on metal or metals of group VIB (VIII / VIB) or from about 0.3: 1 to 0.7: 1 and preferably from about 0.3: 1 to about 0.45: 1.

The quantity by weight of the metals contained in the finished catalyst expressed by weight of metal relative to the weight of the finished catalyst is usually, for metal or the metals of group VIB of approximately 2 to 30% and preferably of approximately 5 to 25%, and for the metal or metals of group VIII of about 0.1 to 15% and more particularly about 0.1 to 5% and preferably about 0.15 to 3% in the case of metals nobles of group VIII (Pt, Pd, Ru, Rh, Os, Ir) and about 0.5 to 15% and preferably about 1 to 10% in the case of non-noble metals from group VIII (Fe, Co, Ni).

In step b) the mineral support can be chosen from the group formed by alumina, silica, silica-aluminas, zeolites, titanium oxide, magnesia, oxide of boron, zirconia, clays and mixtures of at least two of these compounds minerals. This support will preferably comprise at least one halogen chosen from the group formed by chlorine, fluorine, iodine and bromine and preferably chlorine and fluorine. In an advantageous embodiment, this support will include chlorine and fluorine. The amount of halogen will most often be from about 0.5 to about 15% by weight relative to the weight of the support. The most commonly used medium is alumina. The halogen is usually introduced onto the support from corresponding acid halides and the noble metal, preferably platinum or palladium, for example from aqueous solutions of their salts or compounds such as for example hexachloroplatinic acid in the case of platinum.

The quantity of noble metal (Pt or Pd preferred) of this catalyst of step b) will be preferably about 0.01 to 10%, often about 0.01 to 5% and most often about 0.03 to 3% expressed by weight of metal relative to the weight of the catalyst finished.

A particularly advantageous catalyst is described in patent FR-2,240,905, the teaching of which is included. It comprises a noble metal, alumina, a halogen, and it was prepared by mixing the aluminous support with a compound of the noble metal and a reducing agent of formula AlX _y R _3-y where y is equal to 1.3 / 2 or 2, X is a halogen and R is a monovalent hydrocarbon radical.

Another catalyst which is very suitable is that described in US Pat. No. 4,225,461. he includes a noble metal and a halogen and has been specially prepared.

The following examples illustrate the invention without limiting its scope.

Example 1

• une première étape sur un catalyseur contenant sous forme d'oxyde environ 3 % de nickel, 16,5 % de molybdène et 6 % de P₂O₅sur alumine. Cette première étape vise à la désulfuration et à la déazotation profonde de la coupe gazole
• une deuxième étape sur un catalyseur contenant environ 0,6 % de platine sur alumine. Cette deuxième étape vise essentiellement à la désaromatisation profonde de l'effluent de la première étape, mais permet également de diminuer encore la teneur en soufre.

There is a direct distillation diesel cut. Its characteristics are shown in Table No. 1. Its sulfur content is 1.44%.
We treat this diesel cut according to a 2-step diagram:

• a first step on a catalyst containing in the form of oxide about 3% of nickel, 16.5% of molybdenum and 6% of P ₂ O ₅ on alumina. This first stage aims at desulfurization and deep denitrogenation of the diesel cut
• a second step on a catalyst containing approximately 0.6% of platinum on alumina. This second stage essentially aims at the deep aromatization of the effluent from the first stage, but also makes it possible to further reduce the sulfur content.

The first step is carried out in a pilot hydrotreating unit. This includes two reactors in series which can contain up to 20 l. of catalyst in a fixed bed. Unity includes a hydrogen recycling compressor. The flow of fluids is descending in each of the reactors. The unit has a row column of steam stripping which allows stripping the reaction effluent which is thus completely free of the H2S and NH3 formed during the reaction.

This pilot unit is loaded with 5 l. of the same catalyst in each of the reactors.

• VVH=1,5 h^-1
• pression totale=50 bar (10 bar = 1 MPa)
• Recyclage H2 = 400 Normaux litre H2/litre de charge (NI/I)
• Température=340 °C

In this unit, a deep desulphurization and denitrogenation of the said diesel cut is carried out by applying the following operating conditions to it:

• VVH = 1.5 h ^-1
• total pressure = 50 bar (10 bar = 1 MPa)
• Recycling H2 = 400 Normal liter H2 / liter of charge (NI / I)
• Temperature = 340 ° C

A deeply desulphurized product is thus obtained (sulfur content less than 50 ppm) and very deeply denitrogenized (nitrogen content less than 6 ppm).

Its characteristics are shown in table N ° 1. The material balance is shown in table 2.

The effluent is kept for second stage pilot tests.

The second step is carried out in a smaller pilot unit comprising a 1 l reactor with upward flow of fluids. The unit has no recycling compressor.

1 l is loaded into this unit. catalyst in a fixed bed.

• VVH=6 h^-1
• Pression totale=50 bar
• Débit H2 = 400 NI. H2 /l. de charge
• Température =300 °C

The operating conditions are as follows:

• VVH = 6 h ^-1
• Total pressure = 50 bar
• H2 flow = 400 NI. H2 / l. dump
• Temperature = 300 ° C

This produces a very deeply flavored product (aromatic content less than 5%) and having a very high cetane motor index (65).

Its detailed characteristics are given in table N ° 1.

The material balance is reported in Table 2. No gas formation was detected during the operation. The entire effluent can therefore be used as a very high quality fuel cutter. Load and effluent analysis 1st and 2nd stage properties Diesel Fuel SR 1st step 2nd stage Density 15/4 0.852 0.830 0.824 Refraction index 1.4748 1.4600 1.454 Flow point ° C -3 -3 -6 Pt. Aniline ° C 71.7 79.1 86.7 Sulfur ppm 14400 30 4 Nitrogen ppm 110 6 6 Aromatics% p 30 22 2 Cetane engine index 56 61 65 D86: PI ° C 223 205 205 D86: 95% v ° C 375 365 359 (D86 means according to the ASTM-D86 method) Material balance 1st and 2nd stage % wt / charge 1st step 2nd stage H2S 1.53 0.01 NH3 0.01 0.00 C1 0.01 0.00 C2 0.01 0.00 C3 0.02 0.00 C4 0.02 0.00 C5 + 99.14 100.49 Total 100.74 100.50

Example 2

• une première étape sur un catalyseur contenant sous forme d'oxyde environ 3 % de nickel, 16,5 % de molybdène et 6 % de P₂O₅ sur alumine . Cette première étape vis à la désulfuration et à la déazotation profonde de la coupe gazole
• une deuxième étape sur un catalyseur contenant environ 0,6 % de platine sur alumine. Cette deuxième étape vise essentiellement à la désaromatisation profonde de l'effluent de la première étape, mais permet également de diminuer encore la teneur en soufre et en azote.

We have a catalytic cracking (LCO) diesel cut. Its characteristics are shown in Table No. 3. Its sulfur content is 1.56%.
We treat this diesel cut according to a 2-step diagram:

• a first step on a catalyst containing in the form of oxide about 3% of nickel, 16.5% of molybdenum and 6% of P ₂ O ₅ on alumina. This first step involves desulfurization and deep denitrogenation of the diesel cut
• a second step on a catalyst containing approximately 0.6% of platinum on alumina. This second stage essentially aims at the deep aromatization of the effluent from the first stage, but also allows the sulfur and nitrogen content to be further reduced.

The first step is carried out in a pilot hydrotreating unit. This includes two reactors in series which can contain up to 20 l. of catalyst. The unit has a hydrogen recycling compressor. The flow of fluids is descending in each of the reactors. The unit has an in-line stripping column vapor which strikes the reaction effluent which is thus completely freed from H2S and NH3 formed during the reaction.

This pilot unit is loaded with 5 l. of the same catalyst in each of the reactors.

• VVH=1 h^-1
• pression totale=80 bar (10 bar = 1 MPa)
• Recyclage H2 = 400 NI H2/l de charge
• Température=375 °C

In this unit, a deep desulphurization and denitrogenation of the said diesel cut is carried out by applying the following operating conditions to it:

• VVH = 1 hr ^-1
• total pressure = 80 bar (10 bar = 1 MPa)
• H2 recycling = 400 NI H2 / l of charge
• Temperature = 375 ° C

This gives a deeply desulphurized product (sulfur content less than 50 ppm) and very deeply denitrogenized (nitrogen content less than 6 ppm).
Its characteristics are shown in Table No. 3. The material balance is shown in Table 4.

The effluent is kept for second stage pilot tests.

The second step is carried out in a smaller pilot unit comprising a 1 l reactor with upward flow of fluids. The unit has no recycling compressor.

1 unit of catalyst is loaded into this unit.

• VVH=4 h^-1
• Pression totale=50 bar
• Débit H2 = 400 l. H2 /l. de charge
• Température =300 °C

The operating conditions are as follows:

• VVH = 4 h ^-1
• Total pressure = 50 bar
• H2 flow = 400 l. H2 / l. dump
• Temperature = 300 ° C

This produces a very deeply flavored product (aromatic content less than 5%) and having a motor cetane number of 54.

Its detailed characteristics are given in table N ° 3.

The material balance is reported in Table 4. No gas formation is detected during the operation. The entire effluent can therefore be used as a very high quality fuel cutter. Load and effluent analysis 1st and 2nd stage properties LCO load 1st step 2nd stage Density 15/4 0.942 0.873 0.857 Refraction index 1.5417 1.4818 1.4676 Flow point ° C 3 3 3 Pt. Aniline ° C 37 62 76 Sulfur ppm 15600 30 5 Nitrogen ppm 1089 16 8 Aromatics% p 72 32 4 Cetane engine index 27 45 54 D86: PI ° C 184 147 174 D86: 95% v ° C 394 382 380 Material balance 1st and 2nd stage % wt / charge 1st step 2nd stage H2S 1.66 0.00 NH3 0.13 0.00 C1 0.08 0.00 C2 0.08 0.00 C3 0.06 0.00 C4 0.05 0.00 C5 + 100.36 100.92 Total 102.42 100.93

Example 3

The same charge is treated as that mentioned in Example 2, under the same VVH conditions, total pressure, recycling H ₂ and temperature in each of the stages, the only difference being that in the 1st stage, a catalyst is used containing, under oxide form, approximately 3% nickel, 15% molybdenum, 6% P ₂ O ₅ and 3.5% B ₂ O ₃ on alumina and in the 2nd stage a catalyst containing approximately 0.6% of platinum , 1% chlorine and 1% fluorine on alumina. The material balance for each of these stages is the same as that given in Example 2, Table 4. The analysis of the effluent from 1st stage and from 2nd is reported in the table below. Properties LCO load 1st step 2nd stage Density 15/4 0.942 0.873 0.856 Refractive index 1.5417 1.4816 1.4666 Flow point ° C 3 3 3 Pt aniline ° C 37 62 77 Sulfur ppm 15,600 21 4 Nitrogen ppm 1,089 8 4 Aromatics% by weight 72 32 3 Cetane engine index 27 45 45 D86 PI ° C 184 147 174 D86 95% ° C 394 382 380

This example clearly shows the effect of using a boron-containing catalyst in the 1st stage and it also shows the influence of the use of a catalyst containing both chlorine and fluorine in 2nd stage.

Claims (14)

Process for converting a diesel cut into a fuel with a high cetane number, de-aromatized and desulphurized, characterized in that it comprises the following steps with the introduction of hydrogen and possible recycling of hydrogen in each of the first and second steps independently of each other: a) at least a first step known as desulphurization and deep denitrogenation in which said diesel cut and hydrogen are passed over a catalyst comprising an inorganic support, at least one metal or metal compound of group VIB of the periodic table elements in an amount expressed by weight of metal relative to the weight of the finished catalyst of approximately 0.5 to 40%, at least one metal or metal compound of group VIII of said periodic classification in an amount expressed by weight of metal relative to the weight of the finished catalyst of approximately 0.1 to 30% and of phosphorus or at least one phosphorus compound in an amount expressed by weight of phosphorus pentoxide relative to the weight of the support of approximately 0.001 to 20% and b) at least one second subsequent step, referred to as de-aromatization, in which at least a portion of the product resulting from steam stripping of the effluent obtained at the end of the first step is passed, product which is at least partially desulfurized and denitrogenated, and hydrogen on a catalyst comprising, on an inorganic support at least one noble metal or compound of noble metal of group VIII in an amount expressed by weight of metal relative to the weight of the finished catalyst of approximately 0, 01 to 20%. The method of claim 1 wherein the operating conditions of step a) are chosen so as to obtain a product containing less than 100 ppm of sulfur and less than 200 ppm nitrogen and the conditions of step b) are chosen to so as to obtain a product containing less than 10% by volume of compounds aromatic. Method according to claim 1 or 2, in which the operating conditions of step a) include a temperature of 300 ° C to 450 ° C, a total pressure of 2 MPa to 20 MPa and an overall hourly space velocity of liquid charge of 0 , 1 to 10 h ^-1 and that of step b) a temperature of 200 C to 400 ° C, a total pressure of 2 MPa to 20 MPa and an overall hourly space velocity of liquid charge of 0.5 to 10 h ^-1 . Method according to one of claims 1 to 3 wherein the catalyst of step a) comprises at least one metal or a metal compound chosen from the group formed with molybdenum and tungsten and at least one metal or a metal compound chosen from the group formed by nickel, cobalt and iron. Process according to one of Claims 1 to 4, in which the catalyst of step a) includes molybdenum or a molybdenum compound in an amount expressed by weight of metal relative to the weight of the finished catalyst of approximately 2 to 30% and a metal or a metal compound chosen from the group formed by nickel and cobalt in an amount expressed by weight of metal relative to the weight of the finished catalyst from about 0.5 to 15%. Method according to one of Claims 1 to 5, in which the metal of GVIII is nickel and the metal of GVIB molybdenum. Process according to one of Claims 1 to 6, in which the catalyst of step a) further comprises boron or at least one boron compound in an amount expressed by weight of boron trioxide relative to the weight of the lower support or equal to 10%. Method according to one of claims 1 to 7 wherein the support of catalysts used in step a) and in step b) are chosen independently each other in the group formed by alumina, silica, silica-aluminas, zeolites, titanium oxide, magnesia, boron oxide, zirconia, clays and mixtures of at least two of these mineral compounds. Process according to one of Claims 1 to 8, in which the support for the catalyst of step b) comprises at least one halogen. Method according to one of claims 1 to 9 wherein the support of the catalyst of step b) comprises an amount of halogen from approximately 0.5 to approximately 15 % by weight relative to the weight of the support. The method of claim 9 or 10 wherein the support of the catalyst step b) comprises at least one halogen chosen from the group formed by chlorine and fluorine. Method according to one of claims 9 to 11 wherein the support of the catalyst of step b) comprises chlorine and fluorine. Process according to one of Claims 1 to 12, in which the catalyst for step b) comprises at least one metal or a metal compound chosen from the group formed by palladium and platinum in an amount expressed by weight of metal relative to the weight of the finished catalyst of about 0.01 to 10%. Fuel obtained according to the process of any one of Claims 1 to 13.