EP0661371A1 - Process for the production of an internal combustion engine fuel by hydro treatment and extraction and final product - Google Patents

Abstract

Petroleum product and process for obtaining the said petroleum product which can optionally be used for the formulation of an internal combustion engine fuel, including a stage a) of hydrotreatment in which a hydrocarbon feedstock is treated in hydrocarbon conditions under a partial pressure of hydrogen leaving the reactor of approximately 0.5 MPa to approximately 6 MPa, a stage b) of separation of the product (P) originating from stage a) into a product (P1) of initial boiling point lower than approximately 300 DEG C and a product (P2) of final boiling point higher than the final boiling point of product (P1), a stage c) of liquid/liquid extraction with the aid of a solvent (S1), in which an extract (E1) and a raffinate (R1) are obtained from the product (P2), a stage d) of recovery of the solvent (S1) from the raffinate (R1) making it possible to obtain a product (Q1) depleted in solvent (S1), having improved properties and containing less than 500 ppm by weight of sulphur. According to a particular embodiment the extract (E1) is distilled so as to obtain a tail product (Q2) which is subsequently conveyed into a hydrotreatment zone so as to obtain a product (P3) preferably containing less than 0.3 % by weight of sulphur. The solvent (S1) recovered at the head of the distillation is recycled to the extraction stage c). This solvent is chosen from the group consisting of dimethylformamide, dimethylacetamide, furfural, N-methylpyrrolidone and dimethyl sulphoxide.

Description

The invention relates to a petroleum product and a process for obtaining said petroleum product which can optionally be used for the formulation of a fuel for an internal combustion engine and the product obtained by the process. The gas oils that are currently on the market, either in the form of fuels for internal combustion engines, or in the form of fuel, are most often products resulting from refining which contain sulfur in a quantity (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 a crude oil or from a specific treatment of a crude oil (for example a pyrolysis or a 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.

The prior art is illustrated by US Pat. No. 5,059,303 which describes a process for stabilizing hydrocarbon fractions (syncrude oils) very sensitive to the effects of light, heat and oxygen for example. These hydrocarbons are generally shale oils, the main characteristic of which, which makes them unacceptable as fillers for conventional treatment processes, is their high content of particularly basic nitrogen compounds (nitrogen content of between 1 and 3% at least). . These particular hydrocarbon fractions must therefore be pretreated before their use, under severe hydrotreatment conditions.

In a number of industrial countries, sulfur and cetane content standards are in place or will be implemented in the very near future. These standards are becoming more and more stringent, particularly for diesel oils 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 equal to 0.05% by weight (500 ppm) while gas oils which comply with the standards in force have a content of sulfur up to 0.3%.

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

In addition, given the diversity of the charges to be treated (crudes of different origins, visbreaking, coking, hydroconversion, distillation or catalytic cracking) to produce diesel, it is desirable to be able to offer the refiner a flexible process , capable of adapting the products formed to demand and of meeting future specifications 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 a relatively high cetane number consume significant quantities of hydrogen. For example, the hydrodearomatization process of a direct distillation charge whose 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% of hydrogen with respect to the feed while the hydrocracking process requires more than 2% of hydrogen with respect to its feed. However, the hydrogen charge of the refinery, which is generally the catalytic reforming unit, will tend to become insufficient in the current context of harsher diesel standards which result in an increase in hydrotreatments.

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

It is therefore desirable to propose to the refiner a process which allows him to produce a petroleum product meeting the various standards which will come into application in the very near future and from 1995, as far as is sulfur content. It is likewise desirable to be able to produce a petroleum product having the least pronounced odor possible.

The present invention therefore relates to a simple implementation process, consuming little hydrogen. This process uses industrial hydrotreatment units (hydrodesulfurization in particular). It makes it possible to improve the qualities of the diesel fuel produced and to comply with future standards and in particular that concerning the sulfur content. The method of the invention also makes it possible to improve the cetane engine index of diesel, to reduce its content of aromatic compounds not containing sulfur heteroatom in their molecule, to reduce its content of nitrogenous compounds, d '' improve its color and odor and finally reduce the formation of solid particles when used in an internal combustion engine. The present invention provides a solution to the specific problem of obtaining, in as large a quantity as possible relative to the starting product, a petroleum product entering into the composition of an engine quality diesel or diesel engine from a particular hydrocarbon cut having characteristics which makes it difficult to recover in the form of engine diesel.

The invention also relates to the process for obtaining a petroleum product used in the composition of a domestic fuel oil.

• une étape a) d'hydrotraitement dans laquelle on effectue l'hydrotraitement de ladite charge dans des conditions permettant d'obtenir un produit (P) contenant une quantité de soufre de 2 à 50 fois moindre, et le plus souvent de 3 à 30 fois moindre que celle de la charge initiale, ledit hydrotraitement étant généralement effectué sous une pression partielle d'hydrogène en sortie de réacteur d'environ 0,5 MPa (mégapascal) à environ 6MPa, telle que le taux de désaromatisation de la charge est au plus égale à 30%.
• une étape b) de séparation, par exemple par strippage ou par distillation, du produit (P) en un produit (P2) ayant un point d'ébullition initial supérieur à la température d'ébullition du solvant d'extraction de l'étape suivante c) et de préférence au moins supérieur de 20°C, et en un produit (P1) ayant un point d'ébullition final inférieur au point d'ébullition initial du produit P2,
• une étape c) d'extraction liquide/liquide dans laquelle on met en contact, à une température d'extraction d'au plus 140°C, par exemple 0 - 80°C, dans des conditions d'extraction des composés polyaromatiques, le produit (P2) obtenu à l'étape b) avec un solvant ou un mélange de solvants (S1) permettant d'extraire au moins en partie les composés polyaromatiques qu'il contient, ledit solvant ou mélange de solvants ayant un point initial d'ébullition inférieur, et de préférence inférieur d'au moins 20 °C, au point initial d'ébullition du produit (P2) obtenu à l'étape b), et au cours de laquelle on récupère un extrait (E1) enrichi en composés polyaromatiques et un raffinat (R1) et,
• une étape d) de récupération du solvant (S1) employé à l'étape c), par exemple par distillation ou par strippage, à partir du raffinat (R1) obtenu à l'étape c) dans laquelle on récupère un produit enrichi en solvant (S1) et un produit (Q1) appauvri en solvant (S1) ayant des qualités améliorées et contenant moins de 500 ppm en poids de soufre.

More particularly, the invention relates to a process for obtaining a base used in the composition of a fuel for an internal combustion engine with compression ignition having in particular an improved cetane number and a sulfur content, starting from a hydrocarbon feedstock having an initial boiling point of at least 150 ° C and an end boiling point of at most 500 ° C, containing from about 0.05% to about 5% by weight of sulfur, from about 10 to approximately 60% by weight of n- and isoalkanes, approximately 10% to approximately 85% by weight of aromatic hydrocarbons at least in part in the form of polyaromatic compounds (sulfur or not), having a cetane number of approximately 20 to approximately 60 and having a nitrogen content of about 50 to about 5,000 ppm (parts per million) by weight, said method being characterized in that it comprises the following steps:

• a hydrotreatment stage a) in which the hydrotreatment of said feed is carried out under conditions making it possible to obtain a product (P) containing a quantity of sulfur from 2 to 50 times less, and most often from 3 to 30 times less than that of the initial charge, said hydrotreatment generally being carried out under a partial pressure of hydrogen at the outlet of the reactor of approximately 0.5 MPa (megapascal) to approximately 6MPa, such that the rate of dearomatization of the charge is at most equal to 30%.
• a step b) of separation, for example by stripping or by distillation, of the product (P) into a product (P2) having an initial boiling point higher than the boiling point of the extraction solvent of the following step c) and preferably at least 20 ° C. higher, and in a product (P1) having a final boiling point lower than the initial boiling point of the product P2,
• a step c) of liquid / liquid extraction in which is brought into contact, at an extraction temperature of at most 140 ° C., for example 0 - 80 ° C., under conditions of extraction of the polyaromatic compounds, the product (P2) obtained in step b) with a solvent or a mixture of solvents (S1) making it possible to extract at least partially the polyaromatic compounds which it contains, said solvent or mixture of solvents having an initial point of lower boiling, and preferably at least 20 ° C lower, than the initial boiling point of the product (P2) obtained in step b), and during which an extract (E1) enriched in polyaromatic compounds is recovered and a raffinate (R1) and,
• a step d) of recovery of the solvent (S1) used in step c), for example by distillation or by stripping, from the raffinate (R1) obtained in step c) in which a product enriched in solvent is recovered (S1) and a product (Q1) depleted in solvent (S1) having improved qualities and containing less than 500 ppm by weight of sulfur.

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

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

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

The hydrocarbon feed which is treated according to the process of the invention is most often called a diesel cut and it preferably has an initial boiling point of approximately 150 ° C. and a final boiling point of approximately 400 ° C., its sulfur content is usually greater than 0.1% and most often greater than 0.5% by weight, its content of n- and iso-alkanes is approximately 30 to 45% by weight, its aromatic content is usually from about 15% to about 65% by weight. This feedstock is most often a direct distillation gas oil, a pyrolysis gas oil or a mixture of the two. This charge can advantageously be mixed with an L.C.O. (light cycle oil) from a catalytic cracking unit and preferably in an LCO / diesel ratio of 1: 4 to 1: 1. The color of this filler measured according to the ASTM D 1500 method is usually greater than or equal to 2. The cetane number according to ISO 5165 of this filler is most often less than around 60 and it is for example around 50 to about 55. The nitrogen content of this feed is very often about 100 to about 1000 ppm expressed by weight of nitrogen relative to the weight of the feed.

The product Q1 obtained is a new product taking into account all of its characteristics (cutting point, cetane, paraffin content and sulfur content) which is particularly advantageous for obtaining, by formulation with other diesel cuts, quality fuels.

The product (Q1) obtained by the process of the present invention usually has a nitrogen content expressed by weight of nitrogen 2 times less than that of the initial charge and often 4 to 5 times less. This product (Q1) most often has a color measured according to ASTM 1500 standard less than 1 and the cetane number of this product is generally at least 3 points higher and often at least 5 points higher than the cetane number of the initial charge (for example from 3 to 14 points). Its sulfur content compared to that of load is usually less than or equal to 5% by weight. Its net iso-alkane content generally increases by at least 4 points, advantageously by 5 to 20 points and most often by 6 to 11 points, compared to that of the filler. The content of aromatic compounds containing no sulfur atom in their molecule in this product (Q1) is usually reduced by at least 10% by weight relative to that of the initial charge and often by at least 30% by weight. weight. The odor of this product is less strong than that of the initial charge.

The invention advantageously relates to a petroleum product 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, and its sulfur content less than or equal to 500 ppm (weight).

According to the present invention, the hydrodesulfurization is advantageously carried out in a hydrodesulfurization unit under mild conditions making it possible to desulfurize the sulfur molecules by hydrogenating as little as possible. This approach is not obvious to a person skilled in the art of the 1990s, who is rather led to the solution of severifying the conditions of a hydrotreatment in order to simultaneously decrease the sulfur content and increase the cetane of the charges. Under these conditions, the temperature is 320 to 370 ° C, the hourly space velocity is from 1 to 5, the pressure from 1 to 5 MPa and the volume ratio H₂ on load from 50 to 350 Nm³ / m³. The charge dearomatization rate is then at most equal to around 15%. We can thus distinguish two particularly advantageous cases of implementation of this hydrodesulfurization making it possible to obtain an excellent charge for the following extraction step.

According to the first possibility which is preferred, the operation is carried out in the presence of a selective catalyst for the hydrodesulfurization of the sulfur molecules with respect to the hydrogenation of aromatics, adapted to limit the hydrogenation, for example one of those marketed by the PROCATALYSE, under a partial pressure of hydrogen at the outlet of the hydrodesulfurization reactor advantageously between approximately 1.0 MPa and approximately 3.0 MPa and a product (P) containing an amount of sulfur from 2 to 30 times less, ie between 0.1 and 0.3% by weight depending on the charge, for example, and most often from 3 to 10 times less than that of the initial charge. The charge dearomatization rate is then significantly less than 10%. The other conditions for carrying out this hydrodesulfurization step are conventional conditions for hydrodesulfurization qualified by those skilled in the art of simple and gentle hydrodesulfurization.

According to the second possibility, the operation is carried out in the presence of a conventional catalyst adapted to limit the hydrogenation, for example one of those sold by the company PROCATALYSE, under a partial pressure of hydrogen at the outlet of the hydrodesulfurization reactor, advantageously included. between approximately 2 MPa and approximately 5 MPa and a product (P) containing a quantity of sulfur of 5 to 60 times less, ie less than 0.1% by weight, for example between 0.02 and 0.05%, is recovered, and most often 10 to 40 times less than that of the initial charge. Furthermore, the rate of dearomatization of the charge is at most equal to approximately 15%. The other conditions for carrying out this hydrodesulfurization step are conventional conditions for more severe hydrodesulfurization. This hydrodesulfurization is carried out using a larger volume of catalyst than in the case of simple hydrodesulfurization, for example a volume of catalyst 2 times greater, as well as a higher hydrogen pressure, calculated to carry out a more hydrodesulfurization. thrust.

A description of several commercial hydrodesulfurization catalysts and of the industrial conditions for implementing hydrodesulfurization can for example be found in volume 1 of the book by P. WUITHIER, edited by TECHNIP editions under the title PETROLEUM, REFINING AND CHEMICAL ENGINEERING , pages 816 to 831. One can advantageously choose, for example, a catalyst containing molybdenum and cobalt, known to limit hydrogenation.

The separation step, well known to those skilled in the art generally comprises a steam stripping of the total liquid hydrotreatment effluent, followed or not by an additional distillation step. This last step is generally required when you want to send to extracting a fraction P2 whose initial boiling point is higher than that of the hydrotreatment effluent once stripped. The operating conditions are generally: reduced pressure less than 1 bar, advantageously 10 to 100 mbar, preferably 20 to 50 mbar (1 bar = 10⁵Pa) and temperature between 80 and 250 ° C.

The liquid / liquid extraction step is a step carried out under conventional conditions. This extraction can for example be carried out against the current in a conventional device, for example a filling column, with trays or with mechanical agitation (RDC: rotating disc contactor) generally having an efficiency of 3 to 20 theoretical stages and preferably of 5 to 10 theoretical 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 0.6 MPa. The volume ratio of the solvent (S1) to the volume of the product (P2), obtained in step b), is preferably from approximately 0.2: 1 to approximately 5: 1, advantageously 0.5: 1 to 2 : 1 and most often about 1: 1. The solvent is preferably chosen from the group of solvents making it possible also to extract at least part of the aromatic compounds, not containing a sulfur atom in their molecule, present in the product (P2) obtained in step b). The extraction conditions are preferably chosen so as to obtain a raffinate (R1) containing by weight at most 90% and preferably at most 70% of the total weight of the aromatic compounds, not containing a sulfur atom in their molecule , present in the product (P2) obtained in step b). 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, not containing a sulfur atom in their molecule, present in the product (P2) obtained at step b), as well as preferably at least 30% and often at least 50% and frequently at least 80% by weight of the total weight of the sulfur-containing compounds, most often dibenzothiophenic and naphthobenzothiophenic initially contained in the product (P2). The product (Q1) thus obtained usually contains from 2 to 10 times less sulfur than the product (P2) from step b) and most often from 4 to 10 times less.

The extraction solvent is most often a single solvent, but mixtures of solvent can also be used. This solvent generally contains less than 20% and often less than 10% by weight of water. This solvent can be an anhydrous solvent. It is often chosen from the group formed by methanol, acetonitrile, monomethylformamide, dimethylformamide, dimethylacetamide, furfural, N-methylpyrolidone and dimethylsulfoxide. Very often a solvent containing no nitrogen is used and most often an oxygenated non-nitrogenous solvent. The preferred solvent is furfural.

It is also possible to add to the extraction solvent at least one cosolvent which may 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 in mixture, a minor amount of acids, in particular carboxylic (less than 1% by weight relative to the solvent for example). Among these, mention may advantageously be made of carboxylic acids of 1 to 6 carbon atoms 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, isobutyric acid, valeric acid, trimethylacetic acid, benzoic acid, and 2-furoic acid .

The solvent can be recovered from the raffinate by stripping or distillation, preferably by steam stripping, the conditions of which have been described above.

The raffinate (R1) obtained in step c) is then sent to step d) for example in a steam stripping zone in which it is separated under conditions making it possible to recover an enriched head fraction, and preferably highly enriched in solvent (S1) and a bottoms product (Q1) preferably highly depleted in solvent (S1). Most often, the conditions of this separation are chosen so as to obtain a overhead fraction 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 raffinate (R1) and introduced into this stripping zone. There is thus preferably recovered at least about 99% by weight of the amount of solvent contained in the raffinate (R1).

Similarly, in a particular embodiment, the extract (E1) obtained in step c) is then sent to a solvent recovery zone (S1) used in step c) in which a product enriched in is recovered. solvent (S1) and a product (Q2) depleted in solvent (S1). The separation of the solvent from the extract is generally carried out by distillation and / or steam stripping and preferably by distillation followed by steam stripping under the conditions set out above. This extract is therefore separated under conditions making it possible to recover a fraction of the head enriched, and preferably highly enriched, in solvent (S1) and a bottom product (Q2) depleted in solvent (S1). Most often the conditions of this separation are chosen so as to obtain a top fraction 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. At least about 99% by weight of the amount of solvent contained in the extract (E1) is thus preferably recovered.

When operating in step a) under substantially more severe hydrodesulfurization conditions, that is to say in particular in the presence of a very large quantity of catalyst, the product (Q2) which is obtained by distillation of the extract (E1) will most often have a sulfur content of less than or equal to about 0.3% by weight. This product (Q2) will of course not be usable as fuel for the engines, since it most often contains a quantity of sulfur greater than the future standard; on the other hand, it can probably be used as fuel.

In a particularly advantageous embodiment of the invention, the top product (s), obtained by separation of the raffinate (R1) and optionally of the extract (E1), enriched in solvent, are recycled in step c) d liquid / liquid extraction.

According to a particular form of implementation of the method according to the invention, at least part of the product (Q2) obtained from the extract (E1) after separation of the solvent (S1) can be sent to a hydrodesulfurization zone separate from the hydrodesulfurization zone of the initial charge or even be returned to the hydrodesulfurization zone of step a). In this zone, distinct from the hydrodesulfurization zone of step a), the part of the product (Q2) is subjected to hydrodesulfurization under conditions making it possible to obtain a product (P3) having a sulfur content less than or equal at 0.3% by weight and preferably less than or equal to 0.2% by weight.

According to a variant of the process according to the present invention, the hydrocarbon feedstock, having an initial boiling point of at least 150 ° C and a final boiling point of at most 500 ° C, is sent to a distillation zone in which a fraction (F1) having a final boiling point of at least 250 ° C is separated at the head and a fraction (F2) having an initial boiling point of at least 250 ° C at the bottom. According to the present variant, the fraction (F2) is treated according to the process described above for the hydrocarbon feed 150-500 ° C. steps a) to d). The fraction (F1) is sent to a hydrodesulfurization zone separate from that of step a) in which it is hydrodesulfurization under conventional conditions and for example under the simple conditions described above, then the product (P ') hydrodesulfurized obtained is sent to a separation zone, for example by stripping or by distillation, of the product (P ') in a fraction (P10) having a final boiling point below 150 ° C, and in a fraction (P20) having an initial boiling point higher than the final boiling point of the fraction (P10). This product (P20) can, at least in part, be mixed with the product (Q1) obtained from the fraction (F2) to form a product (Q10) having the qualities required as engine fuel. The fraction (P10) is essentially formed of compounds resulting from side reactions during hydrodesulfurization. This fraction (P10) generally represents less than 2% by volume relative to the total volume of the fraction (F1).

The main advantages of the invention are as follows: in the raffinate (table) a higher content of n- and iso-alkanes is obtained than according to the hydrocracking or hydrodesaromatization processes, a cetane number higher, despite an aromatic hydrocarbon content greater than 10%. In addition, 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.

The comparison of the chromatogram profiles of the sulfur compounds (specific gas chromatography detector: Sievers) shows that for the HDS and extraction scheme (raffinate) the sulfur compounds collected in the raffinate are in essentially benzothiophenic form, the dibenzothiophenic and naphthobenzothiophenic compounds are essentially found in the extract whereas for the conventional schemes, whether by deep hydrodesulfurization or hydrodesaromatization, the sulfur compounds remaining in the petroleum product are essentially in the dibenzothiophenic and naphthobenzothiophenic form.

Figures 1 and 2 schematically represent the main variants for the implementation of the method according to the present invention. In these figures, similar bodies are designated by the same numbers and reference letters.

According to FIG. 1, the hydrocarbon feedstock to be treated is sent by line (1) to the hydrodesulfurization zone (HDS1) at the outlet of which recover by line 2 a product (P) which is sent to a separation zone (SEP. 1) from which we recover by line 3 a product (P1) and by line 4 a product (P2) whose initial boiling point is higher than the final boiling point of the product (P1). This product (P2) is sent via line 4 to an extraction zone (EXT.) Into which an extraction solvent (S1) is also introduced via line 5 and from which an extract (E1) is recovered. by line 7 and a raffinate (R1) by line 6. This raffinate (R1) is sent by line 6 to a zone (D1) for recovering the solvent (S1) by line 8 and a petroleum product ( Q1) possibly being used as a base in the composition of an engine diesel of improved qualities, by line 9. The extract (E1) is sent by line 7 to a zone (D2) for recovering the solvent (S1) by line 10 and a product (Q2) through line 11. This product (Q2) can be, at least in part, recovered by line 11a when the valve V4 is open, or be, at least in part, sent by line 11b when the valve V1 is open either in a hydrodesulfurization zone (HDS3) not shown diagrammatically or in the hydrodesulfurization zone (HDS1). When this product (Q2) is recovered by line 11a it can be valued as fuel but does not meet future standards on engine diesel fuel and cannot be used as such as fuel.

According to FIG. 2, the hydrocarbon feedstock to be treated is sent by the line (100) to a zone (TOP) from which a heavy fraction (F2) of initial boiling point greater than about 250 ° C. is recovered which is treated as the hydrocarbon feedstock according to the description above made in connection with FIG. 1. From zone (D1) the product (Q1) can be, at least partly recovered by line 9 and line 9a when the valve V2 is open, or be, at least in part sent by line 9b in line 140 when the valve V3 is open. When it is recovered by line 9a, this petroleum product partially forms a base used in the composition of an engine diesel of improved qualities. From zone (TOP), a light fraction (F1) of final boiling point greater than about 250 ° C. is recovered via line 110. This fraction (F1) is sent by line 110 to a hydrodesulfurization zone (HDS2) at the outlet of which a hydrodesulfurized product (P ') is recovered by line 120 which is sent to a separation zone (SEP 2) from which we recover by line 130 a product (P10) and by line 140 a product (P20) whose initial boiling point is higher than the final boiling point of the product (P10). This product (P20) is optionally mixed with the product (Q1) arriving via line 9b. This mixture or the product (P20) forms a base used in the composition of a diesel engine of improved qualities which is recovered by line 149.

The following examples illustrate the invention without limiting its scope.

EXAMPLE 1

The feed used in this example is a straight-run diesel cut having a cetane number of 55, a total content of aromatic compounds, sulfur and non-sulfur, of 30% by weight, a content of n and iso -alkanes of 39% by weight, a naphthenes content of 31%, 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 the ASTM D standard 1500 equal to 2. This diesel cut has an initial distillation point of 150 ° C and a final distillation point of 400 ° C.

This charge is introduced via line 1 into a hydrodesulfurization zone in which it is subjected to a hydrodesulfurization treatment under a partial hydrogen pressure of 2.0 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 quantity of hydrogen introduced is equal to 200 liters per liter of charge and the hourly space speed is 2, 5 h⁻¹. The amount of hydrogen consumed is 0.25% by weight relative to the charge.

A product (P) containing 0.2% by weight of sulfur, 28% by weight of sulfur and non-sulfur aromatic compounds and a content of n- and iso-alkanes of 40% is recovered via line 2. This product has a color measured according to the ASTM D-1500 method less than 1 and a nitrogen content of 175 ppm by weight. The cetane number of the product (P) is 56. This product has a final distillation point of 400 ° C. It is sent to a steam stripping zone of water (SEP1) from which a product (P1) having a final distillation point of 220 ° C is recovered via line 3 and a product (P2) having an initial distillation point of 220 ° via line 4 C and a final distillation point of 400 ° C. This product (P2) after cooling to 70 ° C, that is to say at the temperature of the extraction zone, is sent to an extraction zone (EXT.) By line 4 into which we introduce also by line 5 an amount of furfural equal in volume to the amount of product (P2) introduced into this zone. This zone is an extraction column comprising a packing formed by Pall rings with an overall efficiency substantially equal to three theoretical stages. The extraction is carried out against the current, at atmospheric pressure and at a temperature of 70 ° C. A raffinate is obtained (R1) which is sent via line 6 to the steam stripping zone (D1) in which the furfural which is recovered at the head is separated by line 8 for possible recycling at extraction zone and at the bottom a raffinate (Q1) containing less than 5 ppm of furfural for example, having a sulfur content of 0.04% by weight, a cetane number of 67, a content by weight of sulfur-containing aromatic compounds and non-sulfur of 12%, an n- and iso-alkane content of 49%, a nitrogen content of 40 ppm and a Saybolt color of 30 and which can be introduced into the diesel tank (pool). From this extraction zone, an extract (E1) is also recovered which is sent to a distillation zone (D2) followed by a steam stripping zone in which the furfural which is recovered is separated at the head. via line 10 for possible recycling to the extraction zone and at the tail an extract (Q2) containing practically no more furfural, having a sulfur content of 0.6% by weight, a cetane number of 25 , a content by weight of sulfur and non-sulfur aromatic compounds of 77% and a nitrogen content of 500 ppm.

This product Q2 can be sent via lines 11 and 11b to a hydrodesulfurization zone (HDS3) distinct from that into which the initial charge has been introduced. This hydrodesulfurization is carried out in the presence of the HR 306C catalyst, under a partial hydrogen pressure of 2.5 MPa, at a temperature of 330 ° C. with a hydrogen recycling of 200 liters per liter of charge and an hourly space velocity of 2.5 h⁻¹. At the outlet of this hydrodesulfurization, a product is obtained having a sulfur content of 0.2% by weight. Its other characteristics are practically unchanged. This product can be mixed with domestic fuel, that is to say introduced into what those skilled in the art call the domestic fuel pool.

EXAMPLE 2

The charge used in this example is the same as that used in Example 1.

This charge is introduced via line 1 into a hydrodesulfurization zone in which it is 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 quantity of hydrogen is equal to 200 liters per liter of charge and the hourly space speed is 1 h⁻ ¹. The amount of hydrogen consumed is 0.4% by weight relative to the charge.

A product (P) containing 0.05% by weight of sulfur, 27% by weight of sulfur and non-sulfur aromatic compounds and a content of n- and iso-alkanes of 40% by weight is recovered via line 2. This product has a color measured according to the ASTM D-1500 method less than 1 and a nitrogen content of 130 ppm by weight. The cetane number of the product (P) is 57. This product has a final distillation point of 400 ° C. It is sent to a stripping zone with water vapor (SEP1) from which a product (P1) is recovered by line 3 having an end point of distillation of 220 ° C. and by line 4 a product ( P2) having an initial distillation point of 220 ° C and a final distillation point of 400 ° C. This product (P2) after having been cooled to 70 ° C., is sent to an extraction zone (EXT.) By line 4 into which is also introduced by line 5 an amount of furfural equal in volume to the amount of product (P2), introduced in this area. This zone is an extraction column comprising a packing formed by Pall rings of an efficiency substantially equivalent to three theoretical stages. The extraction is carried out against the current, at atmospheric pressure and at a temperature of 70 ° C. A raffinate is obtained (R1) which is sent via line 6 to the steam stripping zone (D1) in which the furfural which is recovered at the head is separated by line 8 for recycling possible at the extraction zone and at the bottom a raffinate (Q1) containing practically no more furfural, having a sulfur content of 0.01% by weight, a cetane number of 69, a content by weight of aromatic sulfur compounds and non-sulfur of 10%, an n- and iso-alkane content of 50% by weight, a nitrogen content of 20 ppm and a Saybolt color of 30. This raffinate is sent by line 9 to the diesel pool. From this extraction zone, an extract (E1) is also recovered which is sent to a distillation zone followed by a steam stripping zone D2 in which the furfural which is recovered by the head is separated. line 10 for possible recycling to the extraction zone and at the tail an extract (Q2) containing practically no more furfural, having a sulfur content of 0.15% by weight, a cetane number of 26, a content by weight of sulfur and non-sulfur aromatic compounds of 77% and a nitrogen content of 500 ppm.

This product Q2 can be sent via lines 11 and 11a to the domestic fuel pool.

EXAMPLE 3

The charge used in this example is the same as that used in Example 1.

This charge is introduced via line 1 into a hydrodesulfurization zone in which it is 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 quantity of hydrogen introduced is equal to 200 liters per liter of charge and the hourly space speed is 1 h ⁻¹. The amount of hydrogen consumed is 0.4% by weight relative to the charge.

A product (P) containing 0.05% by weight of sulfur, 27% by weight of sulfur and non-sulfur aromatic compounds is recovered via line 2. This product has a color measured by the ASTM D-1500 method less than 1 and a nitrogen content of 130 ppm by weight. The cetane number of the product (P) is 57. This product has a final distillation point of 400 ° C. Product P is stripped with steam to remove the light fractions (<150 ° C) and the hydrogen sulfide formed in the hydrodesulfurization reactor (less than 2% of the initial charge). It is then sent to a distillation zone from which a product (P1) having a final distillation point of 300 ° C is recovered via line 3 and a product (P2) having an initial distillation point through line 4 300 ° C. The product (P2) after having been cooled to 70 ° C., is sent to an extraction zone (EXT.) By line 4 into which is also introduced by line 5 an amount of furfural equal in volume to the amount of product (P2) introduced into this area. This zone is an extraction column comprising a packing formed by Pall rings of an efficiency substantially equivalent to three theoretical stages. The extraction is carried out against the current, at atmospheric pressure and at a temperature of 70 ° C. A raffinate (R1) is obtained which is sent via line 6 to the distillation zone D1 in which the furfural which is recovered at the head is separated by line 8 for possible recycling to the extraction zone and at the tail, by line 9, a raffinate (Q1) containing practically no more furfural. At least part of this product (Q1) is mixed with at least part of the product (P1) stripped of its light fraction and one then obtains a fraction (F) having a sulfur content of 0.01% by weight, a cetane number of 62, a content by weight of sulfur and non-sulfur aromatic compounds of 15%, its content of n- and isoalkanes is 49% by weight, a nitrogen content of 30 ppm and a Saybolt color of 20. This fraction 7 is mixed with the diesel pool. From this extraction zone, an extract (E1) is also recovered which is sent to a distillation zone D2 in which the furfural which is recovered at the top is separated by line 10 for possible recycling at the extraction zone and at the tail an extract (Q2) containing practically no more furfural, having a sulfur content of 0.25% by weight, a cetane number of 25, a content by weight of aromatic sulfur compounds and not 82% sulfur and a nitrogen content of 700 ppm.

This product Q2 can be treated as described above in Example 1.

EXAMPLE 4

The charge used in this example is the same as that used in Example 1. It is introduced via line 100 into a distillation zone from which a fraction (F1) having a point of recovery is recovered via line 110. initial boiling point of 150 ° C and a final boiling point of 300 ° C. This fraction is introduced via line 110 into a hydrodesulfurization zone in which it is subjected to a hydrodesulfurization treatment under a partial hydrogen pressure of 2.0 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 quantity of hydrogen introduced is equal to 150 liters per liter of charge and the hourly space speed is 4 h ⁻¹. The amount of hydrogen consumed is 0.05% by weight relative to the charge. A product (P ′) containing 0.005% by weight of sulfur, 20% by weight of sulfur and non-sulfur aromatic compounds is recovered via line 120. This product has a color measured according to the ASTM D-1500 method less than 1 and a nitrogen content of 20 ppm by weight. The cetane number of the product (P ') is 57. This product has a final distillation point of 300 ° C. It is sent to a stripping zone with water vapor (SEP2) from which a product (P10) is recovered by line 130 having an end point of distillation of 150 ° C. and by line 140 a product ( P20) having an initial distillation point of 150 ° C and a final distillation point of 300 ° C. This product (P20) is sent by line 140 and line 149 to the engine fuel pool.

From the distillation zone (TOP), a fraction (F2) is recovered via line 1 having an initial boiling point of 300 ° C and a final boiling point of 400 ° C. Its aromatic hydrocarbon content is 37% by weight and its content of n- and iso-alkanes is 34% by weight. This charge is introduced via line 1 into a hydrodesulfurization zone in which it is subjected to a hydrodesulfurization treatment under a partial hydrogen pressure of 3.0 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 316C, the temperature is maintained at 350 ° C., the quantity of hydrogen introduced is equal to 200 liters per liter of charge and the hourly space speed is 1h⁻¹. The amount of hydrogen consumed is 0.45% relative to the feed.

A product (P) containing 0.15% by weight of sulfur, 34% by weight of sulfur and non-sulfur aromatic compounds and a content of n and iso-alkanes of 35% is recovered via line 2. This product has a color measured according to the ASTM D-1500 method less than 2 and a nitrogen content of 300 ppm by weight. The cetane number of the product (P) is 56. This product has a final distillation point of 400 ° C. It is sent to a stripping zone with water vapor (SEP1) from which a product (P1) is recovered by line 3 having an end point of distillation of 300 ° C. and by line 4 a product ( P2) having an initial distillation point of 300 ° C and a final distillation point of 400 ° C. This product, after having been cooled to 70 ° C., (P2) is sent to an extraction zone (EXT.) By line 4 into which is also introduced by line 5 an amount of furfural equal in volume to the amount of product (P2) introduced into this zone. This zone is an extraction column comprising a packing formed by Pall rings of an efficiency substantially equivalent to three theoretical stages. The extraction is carried out against the current, at atmospheric pressure and at a temperature of 70 ° C. A raffinate is obtained (R1) which is sent via line 6 to the steam stripping zone D1 in which the furfural which is recovered at the head is separated by line 8 with a view to its possible recycling to zone d extraction and tail a raffinate (Q1) containing practically no more furfural, having a sulfur content of 0.04% by weight, a cetane number of 67, a content by weight of aromatic sulfur and non-sulfur compounds of 20 %, an n- and iso-alkane content of 48% by weight, a nitrogen content of 30 ppm and a Saybolt color of 20. From this extraction zone an extract (E1) is also recovered that the we send to a distillation zone D2 in which the furfural which is recovered at the head is separated at the head 10 for possible recycling to the extraction zone and at the tail an extract (Q2) containing practically no more furfural, having a sulfur content of 0.5% by weight, a cetane number of 25, a e content by weight of aromatic sulfur and non-sulfur compounds of 80% and a nitrogen content of 1000 ppm.

The product (Q1) is sent via lines 9, 9b, and 149 to the engine fuel pool. The mixture of P20 and Q1 is a product having a cetane number of 61, a content by weight of sulfur and non-sulfur aromatic compounds of 23%, a sulfur content of 0.02% by weight, a nitrogen content of 30 ppm and a Saybolt color of 25.
This mixture can also be mixed, at least in part, with at least part of the product P1, once stripped.

EXAMPLE 5

A charge of direct distillation diesel fuel with an initial distillation point of 150 ° C. and a final distillation point of 400 ° C. containing 35% by weight of aromatics and sulfur compounds and 10% of di- and polyaromatics is treated according to the Example 1 under hydrotreatment conditions defined below. Hydrogen partial pressure (MPa) Product P Aromatics + sulfur compounds% by weight Product P Di- and polyaromatics% by weight Cetane gain after extraction between Q₁ and P products (isorefficient) 3.0 34 7 + 12 5.0 32 4 + 10 7.0 (comparison) 23 1 + 6

Knowing that a gain in cetane index of 14 points was observed by direct liquid-liquid extraction, it is shown by this example that the performance of the downstream extraction unit depends on the severity of the hydrotreatment step .

In particular, they are all the more important as the content of aromatic hydrocarbons in the hydrotreatment effluent is substantially identical to that of the initial charge and the step of hydrogenation of di- and polyaromatic hydrocarbons is limited.

It is thus shown that a selection of the conditions of the hydrotreatment step of the process according to the invention conditions the performance of the extraction step.

EXAMPLE 6

The feed used in this example is a mixture of direct distillation diesel cut and diesel cut resulting from catalytic cracking, LCO type.

The direct distillation diesel cut has a density at 15 ° C of 857, a refractive index at 60 ° C of 1.4617, a cetane index of 55, a total content of aromatic compounds, sulfur and non-sulfur, of 35 , 4% by weight, a content of n- and iso-alkanes and naphthenes of 64.6% by weight, a sulfur content of 1.33% by weight and a nitrogen content expressed by weight of nitrogen of 124 ppm.

The LCO diesel cut has a density at 15 ° C of 944.1, a refractive index at 60 ° C of 1.5245, a cetane index of 23, a total content of aromatic, sulfur and non-sulfur compounds of 67.4 % by weight, a content of n- and iso-alkanes and naphthenes of 32.6% by weight, a sulfur content of 3.13% by weight and a nitrogen content expressed by weight of nitrogen of 930 ppm.

Note load C₁, the load containing 80% of direct distillation diesel cut and 20% of LCO cut, and load C₂, the load containing 50% of direct distillation diesel cut and 50% of LCO cut. The sections C₁ and C₂ have an initial distillation point of 200 ° C and a final distillation point of 400 ° C. The charge C₁ is introduced via line 1 into a hydrodesulfurization zone in which it is subjected to a hydrodesulfurization treatment under a partial hydrogen pressure of 2.0 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 quantity of hydrogen introduced is equal to 200 liters of charge and the hourly space speed is 2.5 h⁻¹. The amount of hydrogen consumed is 0.25% by weight relative to the charge.

A product (P ′) with a density at 15 ° C. of 862.2 and containing 0.051% of sulfur, 31% by weight of sulfur and non-sulfur aromatic compounds, 61% by weight of n- is recovered via line 2 and iso-alkanes and 285 ppm nitrogen.

The cetane number of the product (P ') is 53 and its final point of distillation is 400 ° C. It is sent to a stripping zone with water vapor (SEP1) from which a product (P'1) having a final distillation point of 230 ° C. is recovered via line 3, and through line 4 a product (P'2) having an initial distillation point of 230 ° C and a final distillation point of 400 ° C. This product (P'2) after cooling to 70 ° C, that is to say at the temperature of the extraction zone, is sent to an extraction zone (EXT.) By line 4 in which line 5 is also introduced with an amount of furfural equal in volume to the amount of product (P'2) introduced into this zone. This zone is an extraction column comprising a packing formed of Pall rings with an overall efficiency substantially equal to three theoretical stages. The extraction is carried out against the current, at atmospheric pressure and at a temperature of 70 ° C. A raffinate is obtained (R'1) which is sent via line 6 to the steam stripping zone (D1) in which the furfural which is recovered at the head is separated by line 8 for possible recycling. at the extraction zone and at the tail a raffinate (Q'1) containing less than 5 ppm of furfural for example, having a sulfur content of 0.02% by weight, a cetane number of 67.3, a content by weight of sulfur and non-sulfur aromatic compounds of 19.1, a content of n- and iso-alkanes and naphthenes of 80.9% by weight, a nitrogen content of 54 ppm and a density at 15 ° C. of 826, 5 and which can be introduced into the diesel tank. From this extraction zone, an extract (E'1) is also recovered which is sent to a distillation zone (D2) followed by a steam stripping zone in which the furfural which is separated at the head is separated. is recovered via line 10 for possible recycling to the extraction zone and at the tail an extract (Q'2) containing practically no more furfural, having a sulfur content of 0.14% by weight, a content by weight of sulfur and non-sulfur aromatic compound of 87.2%, a nitrogen content of 800 ppm, a content of n- and iso-alkanes and naphthenes of 12.8% by weight and a density at 15 ° C. of 1002, 8.

The load C₂ undergoes the same treatment as the load C1.

Line 2 is used to recover a product (P '') with a density at 15 ° C of 888.1 and containing 0.067% by weight of sulfur, 44.6% by weight of aromatic sulfur and non-sulfur compounds, 47, 4% by weight of n- and iso-alkanes and naphthenes and 527 ppm of nitrogen.
The cetane number of the product (P '') is 43 and its final point of distillation is 400 ° C.

The product (P''1) recovered by line 3 has a final distillation point of 230 ° C, and the product (P''2) recovered by line 4 has an initial distillation point of 230 ° C and a 400 ° C final distillation point.

The raffinate (R''1) obtained after extraction is sent via line 6 to the steam stripping zone (D1) in the same way as the raffinate (R'1). The raffinate (Q''1) obtained at the tail contains less than 5 ppm of furfural, for example, 0.02% by weight of sulfur, a cetane number of 66.1, 17% by weight of aromatic sulfur and non-sulfur compounds , 83% by weight of n- and isoalkanes and naphthenes, 150 ppm of nitrogen and a density at 15 ° C of 883.9.

The extract (E''1) obtained after extraction is sent to the distillation zone (D2) followed by steam stripping. The extract (Q''2) obtained at the tail contains practically no more furfural, 0.12% by weight of sulfur, 87.9% by weight of sulfur and non-sulfur aromatic compounds, 900 ppm of nitrogen, 12, 1% by weight of n- and iso-alkanes and naphthenes, and a density at 15 ° C of 985.3.

The products Q'2 and Q''2 can be sent via lines 11 and 11b to a hydrodesulfurization zone (HDS3) distinct from that into which the initial charge has been introduced. This hydrodesulfurization is carried out in the presence of the HR 306C catalyst, under partial hydrogen pressure of 2.5 MPa, at a temperature of 330 ° C. with a hydrogen recycling of 200 liters per liter of charge and an hourly space speed of 2 , 5 h⁻¹. At the outlet of this hydrodesulfurization, a product is obtained having a sulfur content of 0.2% by weight. Its other characteristics are practically unchanged. This product can be mixed with domestic fuel, that is to say introduced into what those skilled in the art call the domestic fuel pool.

Claims (15)

1 - 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 an end boiling point of at most 500 ° C, containing from about 0.05% to about 5% by weight of sulfur, from about 10 to about 60% by weight of n- and iso-alkanes, about 10% to about 85% by weight of aromatic hydrocarbons at least partly in the form of polyaromatic compounds, sulfur or not, having a cetane number of about 20 to about 60 and having a nitrogen content of about 50 to about 5,000 ppm by weight, said process being characterized in that it comprises the following steps: a hydrotreatment stage a) in which the hydrotreatment of said charge is carried out under conditions allowing a product (P) containing a quantity of sulfur from 2 to 50 times less than that of the initial charge to be obtained, said hydrotreatment being carried out under a partial pressure of hydrogen at the outlet of the reactor from approximately 0.5 MPa (megapascal) to approximately 6 MPa, such that the charge dearomatization rate is at most equal to 30%, a step b) of separation of the product (P) into a product (P2) having an initial boiling point higher than the boiling point of the extraction solvent of the following step c) and preferably at least higher 20 ° C, and a product (P1) having a final boiling point lower than the initial boiling point of product P2, a step c) of liquid / liquid extraction in which the product (P2) obtained at 1 is at contact, at an extraction temperature at most equal to 140 ° C., under conditions of extraction of the polyaromatic compounds step b) with a solvent or a mixture of solvent (S1) making it possible to extract at least partially the polyaromatic compounds which it contains, said solvent having an initial boiling point lower than the initial boiling point of the product ( P2) obtained in step b), and during which a extract (E1) enriched in polyaromatic compounds, sulfur or not and a raffinate (R1) and, a step d) of recovery of the solvent (S1) used in step c) from the raffinate (R1) obtained in step c) in which a product enriched in solvent (S1) and a product (Q1) is recovered ) depleted in solvent (S1) having improved qualities and containing less than 500 ppm by weight of sulfur. 2 - Process according to claim 1, wherein the hydrogen pressure at the outlet of the reactor is from 1 to 5 MPa, so that the rate of dearomatization of the charge is at most equal to approximately 15%. 3 - Method according to one of claims 1 to 2 wherein step c) is carried out under conditions allowing to obtain a raffinate (R1) containing by weight at most 90% and preferably at most 70% by weight of the total weight of aromatic hydrocarbons, not containing a sulfur atom in their molecule, present in the product (P2) obtained in step b). 4 - Method according to one of claims 1 to 3 wherein the extract (El) obtained in step c) is sent to a solvent recovery zone (S1) used in step c) in which one recovers a product enriched in solvent (S1) and a product (Q2) depleted in solvent (S1). 5 - Process according to claim 4 in which the bottoms product (Q2) is sent to a hydrotreatment zone distinct from the hydrotreatment zone of step a), in which it is subjected to hydrotreatment under conditions allowing to obtain a product (P3) having a sulfur content less than or equal to 0.3% by weight and preferably less than or equal to 0.2% by weight. 6 - Method according to one of claims 1 to 5 wherein the top product or products, obtained by separation of the raffinate (R1) and optionally the extract (E1), enriched (s) in solvent (S1), are recycled in step c) of liquid / liquid extraction. 7 - Method according to one of claims 1 to 6 wherein the solvent is selected from the group formed by methanol, acetonitrile, monomethylformamide, dimethylformamide, dimethylacetamide, furfural, N-methylpyrolidone and dimethylsulfoxide. 8- Method according to one of claims 1 to 7 wherein the solvent used is a non-nitrogenous oxygenated solvent, preferably furfural. 9 - Method according to one of claims 1 to 8 wherein in step a) of hydrotreatment is introduced into the hydrotreatment reactor, in addition to the hydrocarbon feed to be treated, at least part of the bottom product (Q2) obtained from the extract (E1) of step c) after separation of the solvent (S1). 10 - Method according to one of claims 1 to 9 wherein at least part of the product (P1) resulting from step b) is freed of its light fraction and is mixed with at least part of the product (Q1) resulting from step d). 11 - Process in which the hydrocarbon feedstock having an initial boiling point of at least 150 ° C and a final boiling point of at most 500 ° C is sent to a distillation zone in which a head is separated fraction (F1) having a final boiling point of at least 250 ° C and at the tail a fraction (F2) having an initial boiling point of at least 250 ° C, said process being characterized in that the fraction (F2) is treated according to the method of one of claims 1 to 11 and in that the fraction (F1) is sent to a hydrotreating zone separate from that of step a) from which a hydrotreated product (P ') which is sent to a separation zone from which a fraction (P10) having a final boiling point below 150 ° C is recovered, and a fraction (P20) having a d point 'initial boiling above the final boiling point of the fraction (P10). 12 - Process according to claims 10 and 11 wherein the fraction (P20) is at least partly mixed with the product (Q1) obtained in step d) or with the mixture of products (P1) and (Q1). 13 - Petroleum product characterized in that it is obtained by the process according to one of claims 1 to 12. 14 - Petroleum product according to claim 13 usable in particular as a base used in the composition of a fuel for an internal combustion engine with compression ignition having a cetane number higher by at least 3 points than that of the charge from which it comes, a content of n- and iso-alkanes greater by at least 4 points than that of the filler and a sulfur content relative to the filler less than or equal to 5% by weight. 15 - Petroleum product according to one of claims 13 to 14 characterized in that the distillation cut corresponds to 95% 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, and its sulfur content less than or equal to 500 ppm (weight).

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