EP0621334B1 - Process for producing a fuel by extraction and hydrotreatment of a hydrocarboneous feed and produced gasoil - Google Patents

Abstract

Process for obtaining an internal combustion engine fuel from a hydrocarbon feedstock, including a stage a) of distillation (D1) in which a tail product (Q1) is obtained via a line 3 and a head product (T1) via a line 2, a stage b) of liquid/liquid extraction (LE) with the aid of a solvent (S1) in which an extract (E1) (line 6) and a raffinate (R1), (line 5) are obtained from the product (Q1), a stage c) of separation (D2) of the raffinate (R1) making it possible to obtain via a line 7 a product (Q2) impoverished in solvent (S1) and a stage d) of hydrotreatment (HDS) in which the mixture of the products (T1) and (Q2) is treated in hydrotreatment conditions under a partial hydrogen pressure lower than 10 megapascals and a product (P), is obtained (line 9) which has improved qualities and contains less than 500 ppm by weight of sulphur. According to a particular embodiment the extract (E1) (line 6) is distilled so as to obtain via a line 11 a tail product (Q3) which is subsequently sent to a hydrotreatment zone so as to obtain via a line 12 a product (P') containing less than 0.3% by weight of sulphur. The solvent (S1) recovered at the head of the distillations is recycled to the extraction stage b). <IMAGE>

Description

The invention relates to a petroleum product and a process for obtaining said product. tanker which can possibly be used for the formulation of a motor fuel internal combustion and the product obtained by the process. The diesel that we find currently on the market, either in the form of fuels for combustion engines internal compression ignition (diesel type), either as fuel, are most often refinery products that contain sulfur in one amount (expressed by weight of sulfur) of about 0.3%. They are usually obtained following a hydrodesulfurization treatment from a feed which can come from the direct distillation of crude oil or from a special treatment of a crude oil (e.g. pyrolysis or distillation followed by pyrolysis of the fraction recovered during distillation, or thermal or catalytic cracking) generally containing at least 0.8% by weight of sulfur.

In a number of industrial countries, sulfur content standards are in place. or will be implemented in the very near future. These standards are further more severe especially for diesel intended to be used as fuel for engines. Thus in France, in particular from 1995, the sulfur content of these gas oils must be at most 0.05% by weight (500 ppm) while diesel oils conforming to the standards in force have a sulfur content up to 0.3%.

Likewise, the diesel oils used in France as fuel for engines with internal combustion must currently have a cetane number at least equal to 48 and gas oils used as fuel, a cetane number at least equal to 40. We can expect more stringent standards in the near future and in particular that concerning diesel fuel used as fuel in engines.

Furthermore, given the diversity of the charges to be treated (gross of different origins, visbreaking, coking, hydroconversion, distillation or catalytic cracking) to produce diesel, it is desirable to be able to offer to the refiner a flexible process capable of adapting the products formed to the demand and meet future specifications both in terms of sulfur, nitrogen, cetane number, color and aromatic content.

Finally all existing processes such as hydrodesaromatization or hydrocracking which make it possible to obtain petroleum products with a low sulfur content and an index of relatively high cetane consumes significant amounts of hydrogen. By example, the hydrodearomatization process of a direct distillation charge of which the distillation intervals (ASTM D86) are 180 ° C <T 5% <300 ° C, 260 ° C <T 50% <350, 350 ° C <T 95% <460 ° C, consumes 0.6 to 1.1% hydrogen per compared to the load while the hydrocracking process requires more than 2% hydrogen relative to its charge. However, the hydrogen charge of the refinery which generally comes from the catalytic reforming unit will tend to become insufficient in the current context of stricter diesel standards which have for consequently an increase in hydrotreatments.

In addition, these existing processes lead to the production of a petroleum product of which the cetane number does not exceed 63, the latter being reached only at the cost of one hydrogenation of the aromatic hydrocarbons in the charge, a reaction which is consuming hydrogen. (See table).

It is therefore desirable to offer the refiner a process which allows him to produce a petroleum product that meets the various standards that will application in the very near future and from 1995 onwards as regards the content of sulfur.

The technological background is illustrated by the following patents: US-A-4,985,139, EP-A-0 215 496, GB-A-1 006 949 and GB-A-943 239.

The present invention therefore relates to a simple implementation method, consuming little hydrogen and being able to use installations already present in the refinery, in particular the existing industrial hydrodesulfurization units, which limits the investment necessary for its implementation. It improves the qualities of diesel produced and comply with future standards and in particular that concerning the sulfur content. The method of the invention further allows, as will be shown in the embodiment described below, to improve the cetane number diesel engine, to reduce its content of aromatic compounds not containing of sulfur heteroatom in their molecule, to reduce its content of nitrogenous compounds to improve its color and its odor and finally to reduce the formation of particles solids when used in an internal combustion engine.

• une étape a) de distillation, de préférence à la pression atmosphérique, dans laquelle on sépare en queue un produit (Q1) contenant la majorité des composés polyaromatiques et un produit de tête (T1),
• une étape b) d'extraction liquide/liquide dans laquelle on met en contact, à une température d'au plus 140°C, de préférence de 0 à 80°C, dans des conditions d'extraction des composés polyaromatiques, le produit de queue (Q1) obtenu à l'étape a) avec un solvant ou un mélange de solvants (S1) permettant d'extraire au moins en partie les composés polyaromatiques qu'il contient, ledit solvant ayant un point initial d'ébullition inférieur d'au moins 20 °C et de préférence inférieur d'au moins 50 °C au point initial d'ébullition du produit de queue (Q1) obtenu à l'étape a), et au cours de laquelle on récupère un extrait (E1) enrichi en composés polyaromatiques et un raffinat (R1),
• une étape c) de séparation, par exemple de distillation, de préférence à la pression atmosphérique, du raffinat (R1) obtenu à l'étape b) dans laquelle on sépare un produit enrichi en solvant (S1) d'un produit (Q2) appauvri en solvant (S1),
• une étape d) d'hydrotraitement dans laquelle on introduit dans un réacteur d'hydrotraitement une partie au moins du produit de tête (T1) obtenu à l'étape a) et une partie au moins du produit (Q2) obtenu à l'étape c), puis on effectue l'hydrodésulfuration du mélange obtenu, sous une pression partielle d'hydrogène généralement inférieure à 10 mégapascals (MPa), avantageusement inférieure à 5 MPa et de préférence de 1,5 à 3,5 MPa, et on récupère un produit (P) ayant des qualités améliorées et contenant moins de 500 ppm en poids de soufre, par exemple 100 à 480 ppm.

More particularly, the invention relates to a process for obtaining a petroleum product which can serve as a base in the composition of a fuel for an internal combustion engine with compression ignition, having an improved cetane number and a sulfur content, from a hydrocarbon feedstock having an initial boiling point of at least 150 ° C and a final boiling point of at most 500 ° C, containing 0.05% to 5% by weight of sulfur, 10 % to 60% by weight of n- and iso-alkanes, 10% to 90% by weight of aromatic hydrocarbons at least partly in the form of polyaromatic compounds (sulfur or not), having a cetane number of 20 to 60 and a nitrogen content of 50 to 5,000 ppm (parts per million) by weight, said method being characterized in that it comprises the following steps:

• a distillation step a), preferably at atmospheric pressure, in which a product (Q1) containing the majority of the polyaromatic compounds and a top product (T1) are separated at the tail,
• a step b) of liquid / liquid extraction in which is brought into contact, at a temperature of at most 140 ° C., preferably from 0 to 80 ° C., under conditions of extraction of the polyaromatic compounds, the product of tail (Q1) obtained in step a) with a solvent or a mixture of solvents (S1) making it possible to extract at least in part the polyaromatic compounds which it contains, said solvent having a lower initial boiling point of at least 20 ° C and preferably at least 50 ° C lower than the initial boiling point of the bottoms product (Q1) obtained in step a), and during which an enriched extract (E1) is recovered polyaromatic compounds and a raffinate (R1),
• a step c) of separation, for example of distillation, preferably at atmospheric pressure, of the raffinate (R1) obtained in step b) in which a product enriched in solvent (S1) is separated from a product (Q2) depleted in solvent (S1),
• a hydrotreatment stage d) in which at least part of the top product (T1) obtained in stage a) and at least part of the product (Q2) obtained in stage are introduced into a hydrotreatment reactor c), then the hydrodesulfurization of the mixture obtained is carried out, under a partial pressure of hydrogen generally less than 10 megapascals (MPa), advantageously less than 5 MPa and preferably from 1.5 to 3.5 MPa, and recovering a product (P) having improved qualities and containing less than 500 ppm by weight of sulfur, for example 100 to 480 ppm.

For the sake of simplicity, we will use in the following description, the term hydrodesulfurization (HDS) instead of hydrotreatment.

By polyaromatic compounds is meant compounds having at least two aromatic cycles, sulfur or not.

The initial and final boiling point temperatures are TBP cut points.

Most often in this embodiment, at least 50% is introduced. volume of the product (Q2) and preferably at least 90%, or even all of this product preferably in the hydrodesulfurization reactor, all of the overhead product T1 from the distillation. This achievement allows to obtain a quantity of petroleum product with a very low sulfur content. In other terms we thus obtain a greater quantity of a recoverable product entering the composition of a fuel for internal combustion engines.

The hydrocarbon feedstock which is treated according to the process of the invention is the most often referred to as diesel fuel cut and preferably has an initial boiling point of 150 ° C and a final boiling point of 400 ° C, its sulfur content is usually more than 0.1% and most often more than 0.5% by weight, its aromatic content at least partly in the form of compounds polyaromatics is usually 15% to 70% by weight and its content of n- and iso-alkanes is 30 to 45% by weight. This charge is most often a diesel fuel direct distillation or pyrolysis diesel. The color of this charge measured according to the ASTM D 1500 method is usually greater than or equal to 2. The index of cetane according to ISO 5165, this charge is most often less than about 60 and it is for example from 50 to 55. The nitrogen content of this charge is usually 20 to 3000 ppm expressed by weight of nitrogen relative to the weight of load.

The product (P) obtained by the process of the present invention usually has a nitrogen content expressed by weight of nitrogen usually 2 times less than that of the initial charge and often 4 to 5 times less. This product (P) most often has a color measured according to the Saybolt standard from 10 to 30, most often 15 to 25 and the cetane number of this product is generally at least 2 points higher and often at least 5 points at the cetane number of the initial charge (e.g. 2 to 10 points). The content of aromatic compounds containing no atom sulfur in their molecule in this product (P) is usually reduced by at least 10% by weight relative to that of the initial charge and often at least 30% in weight. The sulfur content compared to that of the initial charge is lower or equal to 5% by weight. The content of n-and iso-alkanes generally increases from 4 to 15 points and most often from 6 to 11 points compared to that of the initial charge.

The invention advantageously relates to a petroleum product, which can be used in particular as a base for the composition of a fuel, characterized in that the distillation cut corresponds to 95% by weight distilled between 320 ° C and 460 ° C, its cetane number is greater than 60, its content of n- and iso-alkanes is at least equal to 48% by weight, its sulfur content less than or equal to 500 ppm (weight) and its nitrogen content less than 600 ppm, preferably 50 to 125 ppm.

It also has a solvent content generally less than 10 ppm in weight, advantageously less than 5 ppm and most often less than 1 ppm.

The distillation is carried out under conditions allowing a product of head (T1) containing only a small proportion of compounds with at least one atom of sulfur in their molecule very easily hydrotreated. When the distillation is performed at atmospheric pressure, the top product is usually a fraction whose final boiling point is less than 360 ° C, preferably less than 330 ° C and for example 310 ° C. The tail product (Q1) is usually a fraction with an initial boiling point above 300 ° C, often above 330 ° C and sometimes higher than 360 ° C, which eliminates sulfur compounds raffinate refractories that would require further pressure hydrotreatment high and therefore at a much higher cost.

In addition, by distilling at these preferred conditions, it is sent to the extraction unit a quantity of residue representing, for example, at most 30% of the initial charge, which allows the use of existing extraction units which are generally low capacity and optimize the capacity of these units.

The liquid / liquid extraction step is a step carried out under conditions classics. This extraction could for example be carried out against the current in a conventional device, for example a filling column, trays or mechanical agitation (R.D.C.: rotating disc contactor) generally having from 1 to 20 theoretical stages and preferably 5 to 10 stages at a temperature generally between 0 ° C and 140 ° C, advantageously between 30 ° C and 80 ° C and under a pressure allowing to operate in the liquid phase and therefore between 0.1 and 1 MPa, preferably between 0.1 and 0.3 MPa. The volume ratio of the solvent (S1) the volume of the tail product (Q1) is generally 0.2: 1 to 5: 1, preferably from 0.5: 1 to 2: 1 and most often from 1: 1. The solvent is preferably chosen from the group of solvents making it possible to extract at least part of the compounds aromatic, not containing sulfur atom in their molecule, present in the product (Q1) obtained in step a). The extraction conditions are preferably chosen so as to obtain a raffinate (R1) containing by weight not more than 90% and preferably at most 70% by weight of the total weight of the aromatic compounds, do not containing no sulfur atom in their molecule, present in the product (Q1) obtained in step a). The extract (E1) under these conditions will contain at least 10% and often at least 30% by weight of the total weight of the aromatic compounds, containing no sulfur atom in their molecule, present in the product (Q1) obtained in step a).

The extraction solvent is most often a single solvent, but it is also possible use solvent mixtures. This solvent generally contains less than 20% and often less than 10% by weight of water. This solvent can be an anhydrous solvent. he is most often chosen from the group formed by methanol, acetonitrile, monomethylformamide, dimethylformamide, dimethylacetamide, furfural, N-methylpyrolidone and dimethyl sulfoxide. We very often use the dimethylformamide, N-methylpyrolidone or furfural.

It is also possible to add to the extraction solvent at least one cosolvent which can be an alcohol of 1 to 6 carbon atoms, for example a linear or branched alcohol, or furfuryl alcohol.

If the feed to be treated has a high final boiling point and is particularly rich in nitrogen compounds, especially basic, it may be advantageous to introduce with the extraction solvent alone or as a mixture, a minor amount of acids, in particular carboxylic (less than 1% by weight relative to the solvent for example). Among these, it is advantageous to cite carboxylic acids of 1 to 6 atoms of carbon and more particularly, acids having a boiling point below 250 ° C, in particular formic acid, acetic acid, propionic acid, butanoic acid, pentanoic acid, maleic acid, crotonic acid, acid isobutyric, valeric acid, trimethylacetic acid, benzoic acid, and acid 2-furoic.

The raffinate (R1) obtained in step b) is then sent to a distillation zone for example, in which it is distilled under conditions to recover an overhead fraction enriched, and preferably highly enriched, in solvent (S1) and a product (Q2) preferably highly depleted in solvent (S1). Most often conditions of this distillation are chosen so as to obtain a fraction of the top containing almost all of the solvent, for example more than 95% by weight the quantity of solvent contained in the raffinate (R1) and introduced into this zone distillation. At least 99% by weight of the amount is thus preferably recovered. of solvent contained in the raffinate (R1).

The raffinate, according to another mode of implementation, can be sent in at least a separation flask where a liquid-vapor balance (flash) is achieved and obtains a product (S1) enriched in solvent and a product (Q2) depleted in solvent. This or these balloons can be followed by stripping, for example with steam or nitrogen to recover the last traces of solvent.

The parameters of the hydrodesulfurization step generally chosen most often correspond to those of a hydrodesulfurization carried out under mild conditions. In other words, the spatial speed can be high, for example greater than 2 h ^-1 .
The catalyst is one of those, for example, sold by the company PROCATALYSE.

Likewise, in a particular embodiment, the extract (E1) obtained in step b) is then sent to a separation zone, for example a distillation in which it is distilled under conditions allowing to recover a fraction enriched, and preferably highly enriched, in solvent (S1) and a product (Q3) depleted in solvent (S1). Most often, the conditions for this separation are chosen so as to obtain a product containing almost all of the solvent, that is to say for example more than 95% by weight of the amount of solvent contained in the extract (E1) and introduced into this separation zone. We thus recover from preferably at least 99% by weight of the amount of solvent contained in the extract (E1).

In an advantageous embodiment of the invention, the product (Q3) is sent in a hydrodesulfurization zone in which it is subjected to a hydrodesulfurization, for example in the presence of a catalyst marketed by the PROCATALYSE under generally more severe conditions allowing to obtain a product (P ') having a sulfur content less than or equal to 0.3% by weight and preferably less than or equal to 0.2% by weight, or even less or equal 0.1% by weight. This product (P ') will of course not be usable as fuel for engines, since most often containing a quantity of sulfur higher than the future standard, however we can probably use it as combustible.

According to another embodiment, at least part of the product (Q2) can be recovered at the end of step c) by lines (7) and (13) and be used as is combustible or be mixed with the product (P ') resulting from the hydrodesulfurization of product (Q3) or even be sent mixed with at least part of the product (Q3) in a hydrodesulfurization zone. We then obtain, according to this embodiment, an amount of product at least partially desulphurized, usable as fuel more important.

In a particularly advantageous embodiment of the invention, the one or more products, obtained by separation of the raffinate (R1) and possibly of the extract (E1), enriched with solvent, are recycled in step b) of liquid / liquid extraction.

The method of the present invention has increased flexibility over the methods described in the prior art.
It also has the following main advantages: a higher content of n- and iso-alkanes is obtained in the raffinate (table) than according to the hydrocracking or hydrodesaromatization processes, a higher cetane number, in despite an aromatic hydrocarbon content greater than 10%. Furthermore, the consumption of hydrogen in hydrotreatment is lower. It can be reduced for example to 0.15% by weight with respect to the charge, when the hydrogenation is limited to the maximum. COMPARATIVE TABLE hydrocracking hydrodesaromatization Method according to the invention density 0.815-0.825 0.820-0.850 0.815-0.840 cetane 53-63 45-60 62-71 n- and iso-alkanes 42-47 35-45 49-56 Naphthenes 49-55 25-55 30-41 Aromatic 3-7 10-20 10-20 Consumption in hydrogen% > 2 0.6-1.1 <0.5

The following example illustrates the invention without limiting its scope.

EXAMPLE

The feed used in this example is straight-run diesel having a cetane number of 55, a total content of aromatic, sulfur and non-sulfur, 34% by weight, an n- and iso-alkane content of 18% by weight and 22% by weight, a sulfur content of 1.22% by weight, a nitrogen content expressed by weight of nitrogen of 255 ppm and a color measured according to standard ASTM D 1500 equal to 2. This diesel has an initial distillation point of 150 ° C and an end point of 400 ° C distillation.

This charge is introduced via line 1 into a distillation zone from which is recovered by line 2 a fraction of head (T1) of end point boiling below 320 ° C which contains 0.88% by weight of sulfur, and by the line 3 a tail fraction (Q1) with a final boiling point above 320 ° C containing 1.7% by weight of sulfur. The top product (T1) is sent through the pipe 2 and line 8 in a hydrodesulfurization zone (HDS).

The bottoms product (Q1) leaving the distillation zone D1 is sent by the line 3 in the extraction zone (LE) into which line 4 is introduced an amount of dimethylformamide equal in volume to the amount of bottoms product (Q1) introduced in this area. This zone is an extraction column comprising a packing formed by Pall rings corresponding to three theoretical stages. Extraction is carried out against the current, at atmospheric pressure and at temperature 70 ° C. We obtain a raffinate (R1) which we send via line 5 to the zone of distillation D2 in which the dimethylformamide which is recovered is separated at the top via line 10 a for possible recycling to the extraction zone and at the tail a raffinate (Q2) containing practically no more dimethylformamide, having a sulfur content of 0.51% which is sent via line 7 and line 8 to the zone (HDS) hydrodesulfurization.

The products (T1) and (Q2) introduced into the hydrodesulfurization zone are subjected to a hydrodesulfurization treatment under a partial hydrogen pressure of 2.5 MPa in the presence of an industrial catalyst containing cobalt and molybdenum on an alumina support sold by the company PROCATALYSE under the reference HR 306C, the temperature is maintained at 330 ° C, the hydrogen recycling is equal to 200 liters per liter of charge and the hourly space speed is 2.5 h ^-1 . By way of comparison, such a high-performance hydrodesulfurization carried out directly on the same diesel fuel must be carried out at an hourly space speed of 1.5 h ^-1 , all the other conditions remaining substantially equal elsewhere.

A product (P) containing 450 ppm of sulfur, 20% in weight of aromatic compounds. This product has a color measured according to the method Saybolt equal to 20 and a nitrogen content of 50 ppm by weight. The cetane number of product (P) is 62. This product is incorporated into the Diesel pool. The content of n- and iso-alkanes is 21% by weight and 31% by weight.

An extract (E1) is also recovered via line 6 which is sent to a distillation zone D3 in which the dimethylformamide is separated at the head which is recovered by line 10 b for possible recycling to the zone of extraction and at the tail an extract (Q3) containing practically no more dimethylformamide, having a sulfur content of 5.1% which is sent via line 11 to a hydrodesulfurization zone (HDS) distinct from that into which one has introduced the raffinate (Q2) and the top product (T1). This hydrodesulfurization is carried out in the presence of the HR 306C catalyst, under a partial hydrogen pressure of 4 MPa, at a temperature of 350 ° C. with a hydrogen recycling of 300 liters per liter of charge and an hourly space velocity of 1, 2 hrs ^-1 .

A product (P ') containing 0.2% by weight of sulfur is recovered via line 12, 75% by weight of aromatic compounds. This product has a color measured according to the ASTM D-1500 method equal to 1 and a nitrogen content of 200 ppm by weight. he can be sent to the domestic fuel pool.

Claims (13)

1. A process for obtaining a pretroleum product which can be used as a base in the composition of a fuel for an internal combustion engine with compressiion ignition, having an improved cetane index and an improved sulphur content, from a hydrocarbon charge which has an initial boiling point of at least 150°C and a final boiling point of a maximum of 500°C, containing 0.05 % to 5 % by weight of sulphur, 10 to 60 % weight of n- and iso-alkanes, 10 % to 90 % by weight of aromatic hydrocarbons at least partly in the form of sulphured or unsulphured polyaromatic compounds, having a cetane index of 20 to 60 and having a nitrogen content of 50 to 5 000 ppm by weight, said process being characterized in that it comprises the following steps :

   a step (a) for distillation in which at the bottom a product (Q1) is separated which contains the majority of the polyaromatic compounds and a product (T1), at the top,

   a step (b) for liquid/liquid extraction in which the bottom product (Q1) obtained in step a) is contacted at a maximum temperature of 140° C, under conditions for the extraction of polyaromatic compounds, with a solvent or a mixture of solvents (S1) which enable at least part of the polyaromatic compounds which it contains to be extracted, said solvent having an initial boiling point which is at least 20° C less than the initial boiling poiint of the bottom product (Q1) obtained in step (a), and during which an extract (E1) which has a high content of polyaromatic compounds and a raffinate (R1) are recovered.

   a step c) for separating the raffinate (R1) obtained in step (b) in which at the top a product is separated which has a high content of a solvent (S1) of a product (Q2) which has a low content of solvent (S1).

   A hydrotreatment step (d) in which at least part of the top product (T1) obtained in step a) and at least part of the product (Q2) obtained in step c) are introduced into a hydrotreatment reactor, and the mixture obtained is then subjected to hydrotreatment at partial hydrogen pressure of less than about 10 megapascals, and a product (P) is recovered which has a cetane index greater by at least 2 points than that of the charge and containing less than 500 ppm by weight of sulphur.
2. A process according to Claim 1 in which a top product having a final boiling point less than 360° C and preferably less than 330° C, is separated in step (a).
3. A process according to Claim 1 or Claim 2 in which step (b) is carried out with a solvant (S1) volume to a bottom product Q1 volume ratio of 0.2 : 1 to 5 : 1 which enable a raffinate (R1) to be obtained which contains by weight a maximum of 90 %, and preferably a maximum of 70 % by weight, of the total weight of aromatic compounds, not containing any sulphur atoms in their molecule, present in the product (Q1) obtained in step a).
4. A process according to one of Claims 1 to 3 in which said extract (E1) obtained in step b) is conveyed to a separation zone in order to recover a product which has a high content of solvent (S1) and a product (Q3) which has a low content of solvent (S1).
5. A process according to Claim 4 in which the product (Q3) is conveyed to a hydrotreatment zone in which it is subjected to a hydrotreatment under conditions enabling a product (P') to be obtained which has a sulphur content which is less than or equal to 0.3 % by weight, and preferably less than or equal to 0.2 % by weight.
6. A process according to one of Claims 1 to 5 in which the top product(s) obtained by separating the raffinate (R1) and possibly the extract (E1) which has/have a high content of solvent (S1) are recycled to step (b) for extraction.
7. A process according to one of Claims 1 to 6 in which the solvent is selected from the group formed by methanol, acetonitrile, monomethylformamide, dimethylformamide, dimethylacetamide, furfural, N-methyl pyrolidone and dimethylsulphoxide.
8. A process according to Claim 7 in which the solvent is selected from the group formed by dimethylformamide, N-methylpyrolidone and furfural.
9. A process according to one of Claims 1 to 8 in which at least part of the product (Q3) resulting from separation of the extract and at least part of the product (Q2) obtained in step (c) are introduced into another hydrotreatment zone, and the mixture thus obtained is subjected to hydrotreatment under suitable conditions, and a mixture is recovered which is at least partly desulphured and which can be used as a fuel.
10. A process according to one of Claims 5 to 8, in which at least part of the product (Q2) obtained in step (c) is mixed with the product (P') resulting from hydrotreatment of the product (Q3), and a mixture which is at least desulphured is recovered which can be used as fuel.
11. A petroleum product which can be used, in particular as a base entering into the composition of a fuel for an internal combustion engine with compression ignition, having the following properties : Cetane index 62 - 71 Normal and iso-alkanes 48 - 56 % by weight Naphthenes 30 - 41 % by weight Aromatics 10 - 20 % by weight Sulphur less than 500 ppm Nitrogen less than 600 ppm Colour (according to Saybolt method) 10 - 30.
12. A petroleum product according to claim 11 wherein the sulphur content is 100 - 480 ppm.
13. A petroleum product according to any one of claims 11 and 12 wherein the nitrogen content is at least 50 ppm.

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