EP0849350B1 - Process for the transformation of gas-oils in order to produce dearomised and desulphurised high cetane carburants - Google Patents

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 for compression ignition. In this field, the invention relates to a method of transforming a diesel fuel cut to produce a fuel with a high cetane number, deflavored and desulfurized.

Currently the diesel cuts that come from the direct distillation of an oil crude or from the catalytic cracking process still contain significant amounts of aromatic compounds, nitrogen compounds and sulfur compounds. In the current legislative framework of the majority of the industrialized countries The fuel used in the engines must contain a quantity of sulfur less than about 500 parts per million by weight (ppm). In some countries, there is no need for the moment of standards imposing a maximum content of aromatics and nitrogen. We notes, however, that several countries or states, like Sweden and California, to limit the aromatics content to less than 20% in volume, or even less than 10% in volume and some experts even think that content could be limited to 5% by volume. In Sweden in particular, some diesel fuel classes must already meet very stringent specifications. For example, Class II diesel fuel in this country 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 sulfur and 5% by volume of aromatic compounds. Currently in Sweden Class III diesel fuel must contain less than 500 ppm of sulfur and less than 25% by volume of aromatic compounds. Similar limits are also to be respected for the sale of this type of fuel in California.

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

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

US Patent 5,110,444 discloses a process for the hydrotreatment of middle distillates for produce a product with low sulfur and aromatic content. The process implements three reaction zones in series, two for desulfurization and one for hydrogenation, crossed by a single flow of hydrogen. The first zone includes a fixed bed of catalyst based on non-noble metal (cobalt, molybdenum, nickel and tungsten), the second and third zones use a fixed bed of catalyst to platinum group metal base. However, although the product obtained has a basis Sulfur content and aromatics, C2-C4 by-products hinder the efficiency of the process by decreasing its yield.

It is therefore necessary to develop a reliable and efficient process to obtain from conventional diesel fuel cuts of direct distillation or from the catalytic cracking (LCO cut) or other conversion process (coking, visbreaking (visbreaking), residue hydroconversion, etc.) a product having improved characteristics both with regard to the cetane number and the aromatics, sulfur and nitrogen contents. It's particularly important, and it's this is one of the advantages of the method of the present invention, to produce the minimum of gaseous hydrocarbon compounds and to be able to have an effluent directly and fully recoverable as a fuel cut of very high quality. Otherwise, the method 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 transforming a diesel fuel cut to produce a fuel with a high cetane number, deflavored and desulphurized in at least two successive steps. 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 au moins un halogène.

More specifically, the present invention relates to a process for converting a gasoil fraction into a fuel with a high cetane number, deflavored and desulphurized comprising the following steps:

a) at least a first so-called deep desulphurization and denitrogenation step in which said gas oil fraction and hydrogen are passed over a catalyst comprising a mineral support, at least one metal or group VIB metal compound of the periodic table; elements in an amount expressed by weight of metal relative to the weight of the finished catalyst of about 0.5 to 40%, at least one metal or metal compound of group VIII of said periodic table in an amount expressed by weight of metal relative to the weight of the finished catalyst of approximately 0.1 to 30% and phosphorus or at least one phosphorus compound in an amount expressed by weight of phosphorus pentoxide with respect to the weight of the support of approximately 0.001 to 20% and

b) at least a second subsequent so-called dearomatization step in which at least a portion, and preferably all, of the product which is derived from the first step is passed at least in part, and preferably completely desulphurized and denitrogenated; and hydrogen on a catalyst comprising, on a mineral support, at least one noble metal or group VIII noble metal compound in an amount expressed by weight of metal relative to the weight of the finished catalyst of about 0.01 to 20 %, and at least one halogen.

Advantageously, according to the process, hydrogen is introduced at each of the first and second stages, and is optionally recycled at the first and second stages, independently of each other, which means that there is no management. common gas from said steps.
Preferably, according to the method, the effluent from the first stage is stripped with steam so as to separate at least part of the gas phase, which can be treated and optionally recycled at least in part to level of said step. At least a portion of the product from the stripping is subjected to the second step of the process according to the invention.
The effluent leaving the last stage preferably is stripped with steam, advantageously passes into 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 straight-run diesel fuel cut, a diesel fuel cut from cracking Catalytic or diesel fuel from coking or visbreaking (visbreaking) 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 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 may 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 less than 10 ppm of sulfur, less than 20 ppm, or even less than 10 ppm of nitrogen and 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) comprise a temperature from about 300 ° C to about 450 ° C, a total pressure of about 2 MPa to about 20 MPa and an overall hourly space velocity of liquid charge of about 0.1 to about 10 and of preferably 0.1 to 4 and that of step b) a temperature of about 200 ° C to about 400 ° C, a total pressure of about 2 MPa to about 20 MPa and an hourly space velocity overall liquid charge of about 0.5 to about 10.

When you want to stay in a relatively low pressure range while wishing to obtain excellent results it is possible to perform a first step a1) under conditions that reduce the sulfur content of the product to a value from 500 to 800 ppm and then send this product to a subsequent step a2) in 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 preferably softer when, for a given load, one operates in a single step a), since the product sent in this step a2) already has a greatly reduced sulfur content. In this embodiment of the catalyst of step a1) may be a conventional catalyst of the art prior art such as for example that described in the text of patent applications in the name of of the applicant FR-A-2197966 and FR-A-2538813 and that of step a2) is that described above for step a). It would not be outside the scope of the present invention in using in steps a1) and a2) the same catalyst.

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

In a preferred embodiment of the invention the catalyst of these steps a), a1), a2) 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 selected 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 compound of metal selected from the group consisting of nickel and cobalt.

In a particular and preferred form of the invention, the catalyst of these steps a), a1), a2) will comprise boron or at least one boron compound, preferably 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 metal compound of Group VIB (preferred MB) expressed in weight of metal relative to the weight of the finished catalyst will preferably be about 2 to 30% and most often about 5 to 25% and that of the metal or the compound of Group VIII metal (preferred Ni or Co) will preferably be from about 0.5 to 15% and more often about 1 to 10%.

A catalyst containing Ni, Mo, P is preferably used, the proportions of these elements previously described, or better 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 group VIB metal compound of the periodic table of elements and at least one metal or group VIII metal compound of said classification, wherein the sum of the amounts 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 about 5 to 15%, preferably about 6 to 12% and preferably about 8 to 11.5%, the atomic ratio boron on phosphorus (B / P) is about 1.05: 1, 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 × g ^-1 .

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

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

The amount by weight of the metals contained in the finished catalyst expressed by weight of metal over the weight of the finished catalyst is usually, for the metal or the Group VIB metals of about 2 to 30% and preferably about 5 to 25%, and for the metal or Group VIII metals from about 0.1 to 15% and more particularly from about 0.1 to 5% and preferably from about 0.15 to 3% in the case of metals group VIII (Pt, Pd, Ru, Rh, Os, Ir) and about 0.5 to 15% and preferably from 1 to 10% in the case of non noble metals of 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, boron, zirconia, clays and mixtures of two or more of these compounds minerals. This support will comprise at least one halogen selected in the group formed by chlorine, fluorine, iodine and bromine and preferably chlorine and fluorine. In an advantageous embodiment, this support will comprise chlorine and fluorine. The amount of halogen will most often be from about 0.5 to about 15% by weight. weight relative to the weight of the support. The most commonly used support is alumina. Halogen is usually introduced onto the support from the acid halides corresponding and the noble metal, preferably platinum or palladium, from example of aqueous solutions of their salts or compounds such as for example the acid hexachloroplatinic in the case of platinum.

The amount of noble metal (preferred Pt or Pd) of this catalyst of step b) will be preferably about 0.01 to 10%, often about 0.01 to 5% and most often from 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 has been prepared by mixing the aluminous support with a noble metal compound and a reducing agent of the formula AlX _y R _3-y where y is equal to 1.3 / 2 or 2, X is halogen and R is a monovalent hydrocarbon radical.

Another suitable catalyst is that described in US Pat. No. 4,225,461. he comprises a noble metal and a halogen and has been prepared in a particular way.

The examples which follow 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.

A straight-run diesel fuel cup is available. Its characteristics are shown in Table 1. Its sulfur content is 1.44%.
This diesel fuel cut is treated according to a 2-step scheme:

• a first step on a catalyst containing as oxide about 3% of nickel, 16.5% of molybdenum and 6% of P ₂ O ₅ on alumina. This first step is aimed at the desulfurization and deep denitrogenation of the diesel fuel
• a second step on a catalyst containing about 0.6% platinum on alumina. This second step is essentially aimed at the deep dearomatization of the effluent of the first stage, but also makes it possible to further reduce the sulfur content.

The first step is carried out in a pilot hydrotreatment unit. This includes two reactors in series that can hold up to 20 l. fixed bed catalyst. The unit includes a hydrogen recycling compressor. Fluid flow is down in each of the reactors. The unit has an online column of steam stripping which allows to stripper the effluent of the reaction which is thus completely free of H2S and NH3 formed during the reaction.

This pilot unit is charged 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/l)
• Température=340 °C

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

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

This produces a deeply desulfurized product (sulfur content less than 50 ppm) and very deeply denitrogenated (nitrogen content of less than 6 ppm).
Its characteristics are shown in Table 1. The material balance is shown in Table 2.

The effluent is stored for second-stage pilot tests.

The second step is carried out in a smaller pilot unit with a reactor of 1 l. with upward flow of fluids. The unit does not have any recycling compressor.

This unit is charged with 1 l. fixed bed catalyst.

• 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
• Flow H2 = 400 NI. H2 / l. charge
• Temperature = 300 ° C

This produces a very deeply dearomatized product (aromatic content less than 5%) and having a very strong cetane number (65).

Its detailed characteristics are shown in Table 1.

The material balance is reported in Table 2. No formation of gas is detected during the operation. The entire effluent can therefore be upgraded as a fuel cut of very high quality. Load and effluent analysis 1st and 2nd stage properties SR Gasoline Charge 1st step 2nd step Density 15/4 0.852 0,830 0.824 Refraction Index 1.4748 1.4600 1,454 Pt.Flow ° C -3 -3 -6 Pt. Aniline ° C 71.7 79.1 86.7 Sulfur ppm 14400 30 4 Nitrogen ppm 110 6 6 Aromatic% 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 % w / charge 1st step 2nd step 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.

A catalytic cracked gasoil (LCO) cut is available. Its characteristics are shown in Table 3. Its sulfur content is 1.56%.
This diesel fuel cut is treated according to a 2-step scheme:

• a first step on a catalyst containing as oxide about 3% of nickel, 16.5% of molybdenum and 6% of P ₂ O ₅ on alumina. This first step is aimed at the desulfurization and deep denitration of the diesel cut
• a second step on a catalyst containing about 0.6% platinum on alumina. This second step is essentially aimed at the deep dearomatization of the effluent of the first stage, but also makes it possible to further reduce the sulfur and nitrogen content.

The first step is carried out in a pilot hydrotreatment unit. This includes two reactors in series that can hold up to 20 l. of catalyst. The unit has a hydrogen recycling compressor. Fluid flow is descending in each of the reactors. The unit has an inline steam stripping column which allows to stripper the effluent of the reaction which is thus completely freed from H2S and NH3 formed during the reaction.

This pilot unit is charged with 5 l. 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 is carried out desulphurization and deep denitrogenation of said gasoil cut by applying to it the following operating conditions:

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

This produces a deeply desulfurized product (sulfur content less than 50 ppm) and very deeply denitrogenated (nitrogen content of less than 6 ppm).
Its characteristics are shown in Table 3. The material balance is shown in Table 4.

The effluent is stored for second-stage pilot tests.

The second step is carried out in a smaller pilot unit with a reactor of 1 l. with upward flow of fluids. The unit does not have any recycling compressor.

This unit is charged with 1 l. catalyst.

• 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
• Flow H2 = 400 l. H2 / l. charge
• Temperature = 300 ° C

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

Its detailed characteristics are shown in Table 3.

The material balance is reported in Table 4. No formation of gas is detected during the operation. The entire effluent can therefore be upgraded as a fuel cut of very high quality. Load and effluent analysis 1st and 2nd stage properties LCO load 1st step 2nd step Density 15/4 0.942 0,873 0.857 Refraction Index 1.5417 1.4818 1.4676 Pt.Flow ° C 3 3 3 Pt. Aniline ° C 37 62 76 Sulfur ppm 15600 30 5 Nitrogen ppm 1089 16 8 Aromatic% 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 % W / load 1st step 2nd step 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 as that mentioned in Example 2 is treated under the same conditions of VVH, total pressure, H ₂ recirculation and temperature in each of the steps, the only difference being that in the first step a catalyst containing, under oxide form, about 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 about 0.6% platinum , 1% chlorine and 1% fluorine on alumina. The material balance of each of these steps is the same as that given in Example 2, Table 4. The analysis of the first stage effluent and 2nd is reported in the table below. properties LCO load 1st step 2nd step Density 15/4 0.942 0,873 0.856 Refractive index 1.5417 1.4816 1.4666 Flow rate ° C 3 3 3 Pt of aniline ° C 37 62 77 Sulfur ppm 15,600 21 4 Nitrogen ppm 1,089 8 4 Aromatic% weight 72 32 3 Motor cetane index 27 45 45 D86 PI ° C 184 147 174 D86 95% ° C 394 382 380

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

Claims (12)

1. A process for transforming a gas oil cut into a dearomatised and desulphurised fuel with a high cetane number, characterized in that it comprises the following steps with introduction of hydrogen and optional recycling of hydrogen to each of the first and second steps independently of each other:

   a) at least one first step for deep denitrogenation and desulphurisation in which the gas oil cut and hydrogen are passed over a catalyst comprising a mineral support, at least one metal or metal compound from group VIB of the periodic table in a quantity, expressed as the weight of metal with respect to the weight of finished catalyst, of about 0.5% to 40%, at least one metal or metal compound from group VIII of the periodic table in a quantity, expressed as the weight of metal with respect to the weight of finished catalyst, of about 0.1% to 30%, and phosphorous or at least one phosphorous compound in a quantity, expressed as the weight of phosphorous pentoxide with respect to the weight of the support, of about 0.001 % to 20%; and

   b) at least one subsequent second step for dearomatisation in which at least a portion of the product from steam stripping the effluent from the first step, which has been at least partially desulphurised and denitrogenated is passed with hydrogen over a catalyst comprising, on a mineral support, at least one noble metal or noble metal compound from group VIII in a quantity, expressed as the weight of metal with respect to the weight of finished catalyst, of about 0.01% to 20%, and the support for the catalyst comprising at least one halogen.
2. A process according to claim 1, in which the operating conditions of step a) are selected so as to obtain a product containing less than 100 ppm of sulphur and less than 200 ppm of nitrogen and the conditions of step b) are selected so as to obtain a product containing less than 10% by volume of aromatic compounds.
3. A process according to claim 1 or claim 2, in which the operating conditions of step a) include a temperature of about 300°C to about 450°C, a total pressure of about 2 MPa to about 20 MPa and an overall hourly space velocity of the liquid feed of about 0.1 to about 10 h^-1, and those in step b) include a temperature of about 200°C to about 400°C, a total pressure of about 2 MPa to about 20 MPa and an overall hourly space velocity of about 0.5 to about 10 h^-1.
4. A process according to any one of claims 1 to 3, in which the catalyst in step a) comprises at least one metal or metal compound selected from the group formed by molybdenum and tungsten and at least one metal or metal compound selected from the group formed by nickel, cobalt and iron.
5. A process according to any one of claims 1 to 4, in which the catalyst in step a) comprises molybdenum or a molybdenum compound in a quantity, expressed as the weight of metal with respect to the weight of finished catalyst, of about 2% to 30% and a metal or metal compound selected from the group formed by nickel and cobalt in a quantity, expressed as the weight of metal with respect to the weight of finished catalyst, of about 0.5% to 15%.
6. A process according to any one of claims 1 to 5, in which the GVIII metal is nickel and the GVIB metal is molybdenum.
7. A process according to any one of claims 1 to 6, in which the catalyst of step a) further comprises boron or at least one boron compound in a quantity of 10% or less, expressed as the weight of boron trioxide with respect to the weight of the support.
8. A process according to any one of claims 1 to 7, in which the support for the catalysts used in step a) and in step b) is selected independently of each other from 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.
9. A process according to any one of claims 1 to 8, in which the support for the catalyst of step b) comprises about 0.5% to about 15% by weight of halogen, with respect to the weight of the support.
10. A process according to claim 8 or claim 9, in which the support for the catalyst of step b) comprises at least one halogen selected from the group formed by chlorine and fluorine.
11. A process according to any one of claims 9 to 10, in which the support for the catalyst of step b) comprises chlorine and fluorine.
12. A process according to any one of claims 1 to 11, in which the catalyst of step b) comprises at least one metal or metal compound selected from the group formed by palladium and platinum in a quantity, expressed as the weight of metal with respect to the weight of finished catalyst, of about 0.01% to 10%.