EP1699905A1

EP1699905A1 - Method for treating a hydrocarbon feedstock including resin removal

Info

Publication number: EP1699905A1
Application number: EP04805695A
Authority: EP
Inventors: Christophe Gueret; Raphaël HUYGHE; Hugues Dulot; Patrick Euzen
Original assignee: IFP Energies Nouvelles IFPEN
Current assignee: IFP Energies Nouvelles IFPEN
Priority date: 2003-12-23
Filing date: 2004-12-13
Publication date: 2006-09-13
Also published as: FR2864103A1; BRPI0418119A; US20070108102A1; RU2006126676A; KR101186726B1; CA2548455C; BRPI0418119B1; FR2864103B1; RU2358005C2; WO2005071047A1; CA2548455A1; KR20060130133A; US7582204B2

Abstract

The invention relates to a method for treating a hydrocarbon feedstock whose at least 80 % of compounds have a boiling point equal or higher than 340 °C. Said method also involves resin removal and consists in transferring said feedstock for a fractionating stage for recovering at least one heavy fraction and at least one light fraction, in transferring at least one part of the heavy fraction for extracting stage for extracting resins contained in said heavy fraction and recovering a purified fraction, in producing a mixture containing at least one part of the purified fraction obtainable at the extracting stage and at least one light fraction obtainable at the fractionating stage and in transferring the thus obtained mixture for to a cracking stage.

Description

The present invention relates to the technical field of the cracking of hydrocarbon charges. In particular, the invention relates to a process in which the resins are removed from a charge comprising hydrocarbons before the cracking of this charge.

International patent application WO 99/67345 describes a method for producing cleaner fuels in which natural polar compounds are previously eliminated from a petroleum fraction of hydrocarbons having a boiling point of between 110 and 560 ° C. which improves the efficiency of catalytic treatments intended to produce said fuels. This patent application describes, more particularly, that this elimination of the natural polar compounds is carried out by adsorption / desorption or by solvent extraction.

In this type of method, the elimination of pollutants is generally carried out on the entire load of hydrocarbons which must undergo a catalytic treatment. This implies a suitable dimensioning of the means for extracting these pollutants as a function of the flow rate of the charge. In addition, the extraction means used must be sized according to the concentration and the nature of these pollutants.

US patent US 4,454,023 describes a process for improving the fluidity of a heavy and viscous hydrocarbon including visbreaking, distillation and solvent extraction. This patent does not refer to any cracking step. In addition, the fraction sent to the solvent extraction step corresponds to the heaviest fraction of the distillation.

It has been found that the implementation of an extraction step in which the resins are selectively extracted, and this on a specific fraction of a feed comprising a vacuum distillate, leads to a significant reduction in the amount of investment and operating costs of the resin removal process and cracking said load while maintaining a good level of cracking performance of said load. This level of cracking performance can be assessed in terms of lengthening the cycle time of the catalyst used or more economical operating conditions, for example a reduction in pressure.

The subject of the present invention is therefore a process for the treatment of a hydrocarbon feedstock of which at least 80% of the compounds have a boiling point greater than or equal to 340 ° C., process in which: a) the feedstock is sent to a fractionation step during which we recover:

- at least one heavy fraction comprising at least 90% by weight of compounds boiling above 450 ° C and below 700 ° C,

- and at least one light fraction boiling below the heavy fraction (s),

- a boiling residue above the yeast fraction (s), b) at least part of the heavy fraction is sent in an extraction step during which at least part of the resins are extracted contained in said heavy fraction and a purified fraction is recovered, c) a mixture is produced comprising at least part of the purified fraction obtained in the extraction stage and at least a light fraction obtained in the fractionation stage, and d) the mixture thus obtained is sent in a cracking step.

The hydrocarbon charge of the invention is such that at least 80% of the compounds have a boiling point greater than or equal to 340 ° C, preferably greater than 350 ° C.

The hydrocarbon charge generally contains more than 30% by weight, preferably more than 50% by weight, of boiling compounds 340 ° C and 700 ° C. The hydrocarbon feedstock can be a residue from direct (atmospheric) distillation, a conversion process such as coking, a fixed bed hydroconversion process such as the HYVAHL process or a process in a bubbling bed such as the H-Oil process. The hydrocarbon charge can be formed by mixing the charges mentioned above, and this in any proportion.

The invention proves to be particularly advantageous for fillers of hydrocarbons rich in impurities such as nitrogen, polyaromatics or having a Conradson Carbon or a high asphaltene content. This is for example the case of heavy crude residue, or West African residue.

According to one aspect of the invention, an extraction step is carried out on at least part of a heavy fraction of the hydrocarbon feedstock. All the heavy fractions are generally obtained with a yield of at least 15% by weight relative to the 340-700 ° C fraction of the hydrocarbon feed. Preferably, the heavy fraction is obtained with a yield of at least 20% by weight, or even at least 30% by weight relative to the distillate under vacuum.

The heavy fraction may contain at least 90% by weight of compounds boiling below 700 ° C and above 480 ° C, or even above 500 ° C.

At the same time as this heavy fraction, at least one light fraction is obtained during the fractionation step which, unlike said heavy fraction, is not extracted. At least one light fraction is obtained with a yield of at least 5% by weight relative to the 340-700 ° C fraction of the filler, preferably at least 20% or at least 50%.

Preferably, this light fraction comprises at least 90% by weight of compounds boiling below 450 ° C, preferably below 480 ° C, more preferably below 500 ° C. Preferably, a single heavy fraction is obtained, and preferably all of this fraction is treated in the extraction step.

According to another aspect of the invention, the extraction step is implemented to selectively extract resins.

These resins are generally present in the 340 ° C-700 ° C fraction of the hydrocarbon feedstock used in the process of the invention.

The resin content in the 340 ° C-700 ° C fraction of the filler can range from 3 to 15% by weight.

The heavy fraction resulting from the first fractionation stage may, for its part, have a resin content of more than 5% by weight, or even more than 10% by weight, or even even more than 15% by weight.

In the petroleum field, the term resin generally designates constituents which have been eluted on solid adsorbents by polar solvents. Thus, resins are generally characterized by their polarity rather than their chemical nature; hence the implementation of separation methods to isolate them.

These separation methods (such as ASTM-D-4124) making it possible to isolate the resins can be methods of liquid chromatography on petroleum fractions of the distillate type under vacuum or residue, in which: - firstly, these sections with a solvent such as n-heptane to precipitate asphaltenes and recover a soluble portion comprising the maltenes, and - in a second step, the resins are isolated by elution of said soluble portion in a chromatographic column containing, for example, activated alumina and silica gel using a very polar solvent, such as a mixture of methylene chloride, toluene and methanol. The resins isolated by these characterization methods mainly consist of a mixture comprising condensed naphtheno-aromatic compounds, compounds containing sulfur, nitrogen, oxygen, and possibly metals such as nickel and vanadium. .

It has been found that an extraction step, in which the aim is to selectively extract the resins, makes it possible to improve the activity and / or the selectivity of the catalysts used in the subsequent steps of the process of the invention. Thus, the selective extraction of the resins defined above makes it possible to significantly improve the performance of the subsequent cracking step of the process of the invention.

During the extraction step, at least 10% by weight of the resins contained in said heavy fraction are extracted from the heavy fraction (quantitative determination by a separation method of the ASTM-D-4124 type).

Preferably, at least 20% by weight, preferably at least 40% by weight, or even at least 50% by weight, are extracted from the resins contained in the heavy fraction.

The resins extracted from the heavy fraction are generally polar compounds. The polarity of these resins can be determined from the relationship that exists between, on the one hand said polarity and, on the other hand, the naphtheno-aromatic structure and the nitrogen content of these resins. In fact, at least 90% by weight, or even at least 95% by weight of the nitrogen of a vacuum distillate is generally contained in the resins of said vacuum distillate.

The naphtheno-aromatic structure can be determined by nuclear magnetic resonance (NMR ¹³ C and ¹ H, cf. ASTM D5292). The nitrogen content can, for its part, be measured by chemiluminescence (cf. ASTM D4629).

Analysis by nuclear magnetic resonance (C ¹³ NMR) shows that the average structure of the resins in the heavy fraction can be characterized by: an aromatic carbon content (CA) greater than 50% by weight, or even greater than 60% by weight, - a quaternary aromatic carbon content greater than 30% by weight, or even greater than 35% by weight, an aromatic carbon content quaternary condensed greater than 10% by weight, or even greater than 15% by weight, and a condensation index greater than 2.3, or even greater than 2.6.

Analysis by C ¹³ NMR of the resins of the 340 ° C-700 ° C fraction of the filler shows that the average structure of these resins can be characterized by: an aromatic carbon (CA) level of less than 50% by weight , a quaternary aromatic carbon content of less than 30% by weight, a condensed quaternary aromatic carbon content of less than 10% by weight, and a condensation index of less than 2.3.

An analysis by chemiluminescence of the nitrogen content shows that the nitrogen content of the resins of the heavy fraction can be 1, 5 times greater, or even 2 times greater, or even 2.5 times greater than that of the resins of the filler.

The polarity of the resins of this heavy fraction of the vacuum distillate is therefore generally greater than that of the resins of the filler.

Extraction of the resins from the heavy fraction generally makes it possible to obtain a purified fraction having a content of polyaromatic compounds comprising up to 5 cycles of less than 2% by weight, preferably less than 1% by weight. This polyaromatic content comprising up to 5 cycles of the purified fraction can be measured by Fischer mass spectrometry (cf. Fischer IP, Fischer P., Talanta, 21, 867-875 (1974) and Bouquet M., Brument J. , Fuel Science and Technology INTL, 8 (9), 961-986 (1990)).

Extraction of the resins from the heavy fraction can also make it possible to obtain a purified fraction having a nitrogen content which is reduced by at least 20% by weight, preferably 30% by weight, more preferably 40% by weight relative to the heavy fraction introduced in the extraction step. This nitrogen content of the purified fraction can be measured by chemiluminescence (cf. ASTM D4629).

The extraction step can be carried out by any means known to those skilled in the art. In particular, this extraction step can be carried out by adsorption / desorption or, preferably by solvent extraction.

In the preferred case where the extraction step is carried out by solvent extraction, this extraction step generally comprises bringing the heavy fraction into contact with a solvent based on light hydrocarbons. This contacting can be carried out in an extraction zone or by simple mixing. The quantity of solvent, the temperature, the pressure are chosen so as to allow the formation of two distinct phases constituted on the one hand by a liquid mixture essentially comprising solvent and de-resinated oil and, on the other hand, a mixture fluid essentially comprising solvent and resin oil. The phases thus formed can then be separated from one another, for example by decantation. The solvent of each phase can finally be removed by vaporization so that it can be recycled.

This extraction step thus makes it possible to extract a large part of the resin compounds from the treated filler, these compounds generally having naphtheno-aromatic structures.

The solvent used during the extraction step is preferably a paraffinic solvent. This solvent can essentially comprise (or consist of) compounds having from 3 to 7 carbon atoms, preferably from 3 to 5 carbon atoms.

The yield of oil extracted and the quality of the oil depend on the nature of the solvent used. The yield of the de-resinated oil generally increases with the carbon number of the solvent to the detriment of the quality of the oil extracted. The extraction step is generally carried out in a settling mixer or, preferably in an extraction column.

The operating conditions of the extraction step can be comparable to those of a deasphalting process. The volume ratio between the solvent based on light hydrocarbons on the heavy fraction to be extracted is usually between 2 and 12, preferably between 3 and 5.

For example, during the extraction step, a preformed mixture comprising the heavy fraction and a first fraction of solvent is introduced into an extraction column in order to carry out the precipitation of a resin phase by decantation at the bottom. of the column. A second fraction of solvent is introduced into the decantation zone. The settling of the resin part is then obtained by washing with pure solvent against the current of the emulsion of the resin fraction in a mixture essentially comprising solvent and oil. It is favored by an increase in the solvent content, that is to say by replacing the environment comprising the solvent and the oil with a pure solvent environment, and this at a low temperature.

Furthermore, the existence of a temperature gradient between the head and the bottom of the extraction column generally makes it possible to create an internal reflux, which has the effect of improving the separation between the oily medium and the resins. Indeed, the mixture essentially comprising solvent and oil which is heated at the top of the extraction column makes it possible to precipitate a resin fraction which descends into the extraction column. The rising counter-current of this mixture therefore tends to dissolve, at a lower temperature, the lighter resin fractions. The temperature depends on the nature of the solvent used and is generally between 70 and 220 ° C.

In the case of a solvent extraction in an extraction column using a solvent which is propane, advantageous operating conditions for the extraction are: - a solvent content between 2/1 and 12/1, preferably between 4/1 and 10/1, - a temperature of the extractor head between 55 and 95 ° C, - a temperature of the extractor bottom between 30 and 80 ° C, - an extractor pressure between 300 and 400 MPa, to be adjusted so that all the products remain in the liquid state, and - a number of theoretical stages between 2 and 5.

According to yet another aspect of the process of the invention, the cracking step is carried out on a mixture comprising the purified fraction obtained during the extraction step with at least one light fraction obtained during the splitting.

Preferably, during the mixing step of the process of the invention, a mixture is produced which comprises, in addition, other fractions which can be obtained during the fractionation step, or even from all of these others. fractions.

It has been observed that the implementation of the step of cracking hydrocarbons on a mixture for which, on the one hand only a well-defined fraction of said mixture has been previously subjected to an extraction step, and on the other hand part for which the extraction of said fraction aims to extract very precise compounds, in this case resins, does not penalize in any way the performance of this cracking, and on the contrary makes it possible to work at lower temperatures in cracking.

In fact, it has been found that the extraction of the resins on the entire load, except for the residue (that is to say all the heavy and light fractions) produces an effluent which is more refractory to cracking than l effluent according to the invention, for an equivalent resin content in the 340 ° C-700 ° C fraction of the feed.

In addition to this technical advantage, the fact that the equipment required for the resin extraction stage has a reduced size. The cracking step of the process of the invention can comprise a catalytic cracking and / or a hydrocracking.

The specific conditions of the extraction step of the process of the invention are such that the mixture at the inlet of the cracking step has a high level of purity allowing efficient catalytic cracking.

In the case where the cracking step comprises a catalytic cracking, at least part of the mixture is cracked by a catalytic cracking to obtain an effluent comprising gasoline, diesel and a residue. This catalytic cracking can be a cracking in a fluidized bed, known under the Anglo-Saxon name of "fluid catalytic cracking" or abbreviated as FCC.

In the case of an FCC type cracking, the process of the invention makes it possible to obtain, at the entry to the cracking step, an effluent having a reduced content of Conradson Carbon and of nitrogen suitable for obtaining a high conversion of the mixture associated with obtaining high gasoline and diesel yields.

In the case of a catalytic cracking, at least part of the mixture can be catalytically cracked under conditions well known to those skilled in the art to produce a fuel fraction, which can itself comprise a petrol fraction and a diesel fraction, as well as a fraction of type "slurry". This fuel fraction is usually sent, at least in part, to fuel pools. The fraction of the "slurry" type can be sent, at least in part, to the heavy fuel pool or recycled, at least in part at the inlet of the catalytic cracking.

In the context of the present invention, the expression conventional catalytic cracking includes cracking processes comprising at least one regeneration step by partial combustion and those comprising at least one regeneration step by total combustion and / or those comprising both at least a partial combustion step and at least one total combustion step. Catalytic cracking is generally described in Ullmans Encyclopedia Of Industrial Chemistry Volume A 18, 1991, pages 61 to 64.

The catalytic cracking step can advantageously be preceded by a hydrotreatment. To purify the mixture of impurities, such as sulfur and nitrogen which were not completely removed during the extraction step, a pretreatment of the mixture by a catalytic process in the presence of hydrogen may be necessary in order, by for example, to protect the cracking catalysts or to improve the quality of the cracking products. This step can be done, for example, with a catalyst of NiMo type on alumina under conditions well known to those skilled in the art.

Preferably, the cracking step is a hydrocracking.

In this hydrocracking step at least part of the mixture is cracked on the catalyst in the presence of hydrogen, under conditions well known to those skilled in the art, in order to produce, after distillation, at least one fuel fraction (petrol fraction , a kerosene fraction, a diesel fraction). This fuel fraction (s) is generally sent, at least in part, to the fuel pools.

In the case of hydrocracking, the residue fraction obtained can be treated in different ways. In one embodiment, this residue fraction can be sent, at least in part, to a dewaxing and hydrofinishing section to produce oil bases. In another embodiment with a fuel objective, this residue fraction can be recycled, at least in part, at the entrance to the hydrocracking step. In yet another embodiment, this residue fraction can be sent, at least in part, to an FCC unit.

The operating conditions used according to this mode make it possible to achieve conversion by pass into products having boiling points below 340 ° C, or even below 370 ° C, which is greater than 10% by weight, preferably between 15 and 95% by weight. Hydrocracking can be carried out at a temperature ranging from 340 to 450 ° C., preferably ranging from 340 to 420 ° C. The pressure can be significantly reduced compared to the hydrocracking stages of vacuum distillates of the prior art which generally require a high hydrogen partial pressure.

The hydrocracking pressure can advantageously range from 4 to 20 MPa, preferably from 4 to 16 MPa. We can distinguish low or moderate pressures (4 to 10 MPa) from higher pressures (more than 10 MPa to 16MPa).

The term hydrocracking includes mild hydrocracking, the objective of which is a pretreatment converting a charge originating from an FCC, hydrorefining, the objective of which is the production of a residue for making lubricating oils and middle distillates, and conventional hydrocracking whose flexibility allows either to produce middle distillates, or jointly middle distillates and a residue to make lubricating oils.

An advantage of the process of the invention is to reduce the loss of activity of the catalyst (s) used during the cracking step and / or the catalytic pretreatment step by reducing the impurities which tend to strongly adsorb on the catalyst, which reduce its cracking acid function and / or which are coke precursors. This results, in the case of a catalytic cracking step, by a reduced consumption of fresh catalyst for a given conversion level and, in the case of a hydrocracking step, by a longer cycle time.

Another advantage of the process of the invention is, in the case where the cracking step comprises (or is) hydrocracking, to allow a significant reduction in the pressure at which the hydrocracking step is carried out. Selective extraction of the resins makes it possible, in fact, to eliminate the unsaturated compounds which usually consume a large amount of hydrogen from hydrocracking. The implementation of the process of the invention thus makes it possible to reduce the operating cost of the hydrocracker. Another advantage of the invention is to limit the negative effects of resins and nitrogen, in particular on the cracking catalyst.

Another advantage of the invention is to limit the negative effects of polyaromatics on the stability of the catalysts and the quality of the products.

Another advantage of the process of the invention is, in the case where the cracking step comprises (or is) hydrocracking, of reducing the size of the equipment used during this hydrocracking.

Another advantage of the method of the invention is to allow a reduction in the size of the equipment used during the extraction step, the extraction being carried out only on a heavy fraction of the distillate under vacuum.

For a better understanding, a preferred embodiment of the method of the invention is illustrated in Figure 1. This embodiment is given by way of example and has no limiting character. This illustration of the process of the invention does not include all of the components necessary for its implementation. Only the elements necessary for understanding the invention are represented, the skilled person being able to complete this representation to implement the invention.

The hydrocarbon feedstock is sent via line 1 to a vacuum distillation column 2. From this distillation column, a light fraction is drawn off through line 3, a heavy fraction through line 4 and a vacuum residue through line 5.

The heavy fraction withdrawn from column 2 is sent via line 4 to liquid extraction means 10 with a solvent. The solvent is sent to the extraction means via a pipe 11. Solvent can optionally be added via a pipe 12. To the heavy fraction of the vacuum distillate an external charge can be added through the pipe 13. This charge is for example a vacuum distillate, such as a straight-run vacuum distillate (crude), a vacuum distillate from a heavy load conversion process (coking, H-oil or T-Star bubbling bed, Hyvahl fixed bed). It can also be an aromatic extract from an aromatic extraction unit.

The purified fraction and of the solvent coming from the extraction means 10 are drawn off through line 15 and sent to a device for recovering and regenerating the solvent 16. The solvent thus regenerated is sent to the extraction zone through line 11.

The residue comprising the resins extracted and the solvent are drawn off through a line 19 and sent to a recovery and regeneration system for the solvent 20. The solvent thus regenerated is sent to the extraction zone via a line 21 and the line 11. The residue comprising the extracted resins which has been freed from the solvent is withdrawn through line 22.

The purified fraction freed from the solvent is withdrawn, via a conduit 30. This purified fraction is mixed with the light fraction of the vacuum distillate supplied by the conduit 3. The purified fraction and the light fraction of the vacuum distillate are sent as a mixture, with hydrogen supplied by a line 31, in hydrocracking means 32. The effluent from the hydrocracking means is discharged through line 33 and sent to means 34 for separating the gas and the liquid. The gas is evacuated through a pipe 35.

The liquid from the separation means 34 is discharged through a pipe 40 to an atmospheric distillation column 41. From this column are drawn off a gaseous fraction by a pipe 42, a gasoline cut by a pipe 43, a kerosene cut by a pipe 44 , a diesel cut through a pipe 45 and a residue cut through a pipe 46.

As mentioned earlier, the residue can be

1) at least partly recycled in hydrocracking (except for the purge),

2) at least partly sent to a catalytic cracking unit in a fluid bed, or 3) at least partly sent to a dewaxing unit (preferably catalytic dewaxing) and then to a hydrofinishing unit; partial recycling of the residue to the hydrocracking stage also being possible with options 2) or 3).

Example 1 A vacuum distillate was distilled from an atmospheric residue with a yield of 40% by weight. This vacuum distillate has the following properties:

This vacuum distillate is introduced into a pilot comprising two reactors in series. The first reactor R1 is filled with catalyst known under the reference HR448 from the company AXENS, a pre-treatment catalyst for vacuum distillate of the NiMo type on alumina, the objective of which is to de-nitrogen the vacuum distillate at very low contents. The second reactor R2 is filled with the catalyst known under the reference HYC642 from the company AXENS, a zeolitic hydrocracking catalyst (zeolite Y on alumina) allowing a conversion of the order of 70% by weight of the 370 ° C + fraction of the vacuum distillate. The operating conditions and yields are given in the following table:

Example 2 (according to the invention)

The vacuum distillate of Example 1 is distilled under vacuum to obtain a light fraction and a heavy fraction corresponding to a cutting point of 500 ° C. The yields and properties of the vacuum distillate and of the two fractions are as follows:

The heavy fraction is de-resinated by liquid-liquid extraction with a non-polar paraffinic solvent, propane. The technology used is that commonly used to perform deasphalting of residues under vacuum. 40 kilograms of the heavy fraction were mixed with propane in a stirred reactor with a solvent / heavy fraction volume ratio of 8/1. The mixture is brought to 90 ° C. and stirred for 60 minutes. After this period, the stirring is stopped and the mixture settles for 90 minutes to cause the separation of two phases. The purified phase of the resins at the top of the capacity and the phase rich in resins at the bottom of the capacity are drawn off separately and treated to evaporate the propane. The purified phase of the resins and the phase rich in resins after evaporation of the propane have the following properties, compared to that of the heavy fraction:

40% by weight of the heavy fraction of the distillate was removed under vacuum from the resins contained in this fraction. The purified fraction of the resins is then mixed with the light fraction of the vacuum distillate in order to reconstitute a wide vacuum distillate which will be hydrocracked.

The mixture thus reconstituted has the following properties compared to the vacuum distillate of Example 1:

The mixture has resin and nitrogen contents reduced by about 30% compared to the vacuum distill t of Example 1. This partial purification of the feed may seem low, nevertheless it has the advantage of requiring equipment for 'reduced extraction and have a significant impact on the hydrocracking operating conditions. The mixture thus reconstituted is introduced into the same pilot as in Example 1 with the same catalytic system. To carry out the same overall conversion of the order of 70% by weight of the 370 ° C. + fraction of the mixture as in Example 1, the following operating conditions must be established:

The operating conditions of Example 2 are characterized with respect to Example 1 by a lower partial pressure of hydrogen of 30 bars, all other things being equal. The yield structure is identical to Example 1 as well as the quality of the products but associated with a hydrogen consumption reduced by 13%.

Claims

1. Process for treating a hydrocarbon feedstock of which at least 80% of the compounds have a boiling point greater than or equal to 340 ° C., process in which: a) the feedstock is sent in a fractionation step during which recovers:

- and at least one light fraction boiling below the heavy fraction (s),

- a boiling residue above the heavy fraction (s), b) at least part of the heavy fraction is sent in an extraction stage during which at least part of the resins are extracted contained in said heavy fraction and a purified fraction is recovered, c) a mixture is produced comprising at least part of the purified fraction obtained in the extraction stage and at least a light fraction obtained in the fractionation stage, and d) the mixture thus obtained is sent in a cracking step.

2. Method according to claim 1, in which the content of resins in the 340 ° C-700 ° C fraction of the filler is between 3 and 15% by weight.

3. Method according to one of claims 1 to 2, wherein the heavy fraction from the first fractionation step has a resin content greater than 5% by weight.

4. Method according to one of claims 1 to 3, wherein at least 20% by weight of the resins contained in the heavy fraction are extracted.

5. Method according to one of claims 1 to 4, in which the extraction of the resins from the heavy fraction makes it possible to obtain a purified fraction having a content of polyaromatic compounds comprising up to 5 cycles of less than 2% by weight.

6. Method according to one of claims 1 to 5, in which the extraction of the resins from the heavy fraction makes it possible to obtain a purified fraction having a nitrogen content which is reduced by at least 20% by weight relative to the heavy fraction introduced into the extraction step.

7. Method according to one of claims 1 to 6, in which the extraction step is carried out in an extraction column, using propane, under the following operating conditions: - a solvent content of between 2/1 and 12/1, - a temperature of the extractor head between 55 and 95 ° C, - a temperature of the extractor bottom between 30 and 80 ° C, - a pressure of the extractor between 300 and 400 MPa, and - a number of theoretical stages between 2 and 5.

8. Method according to one of claims 1 to 7, wherein the cracking step is a hydrocracking.

9. The method of claim 8 wherein a residue fraction is obtained from the hydrocracking step and is sent, at least in part, to a dewaxing and hydrofinishing section to make oil bases.

10. The method of claims 1 to 8, wherein a residue fraction is obtained from the hydrocracking step and is sent, at least in part, to an FCC unit.

11. Method according to one of claims 8 to 10, in which a residue fraction is obtained from the hydrocracking step and is recycled, at least in part, to the hydrocracking step.

12. Method according to one of claims 1 to 7, in which the cracking step is a catalytic cracking in a fluidized bed (FCC).

13. The method of claim 12, wherein the FCC step is preceded by a hydrotreatment step.

14. Method according to one of the preceding claims, in which the feedstock is chosen from a direct distillation residue, a residue from a conversion process, a coking residue, a residue from a fixed bed hydroconversion process. , a residue from a bubbling bed conversion process, or any mixture thereof.

15. Method according to one of the preceding claims, in which an external charge is added to the heavy fraction entering the extraction step, said charge being a vacuum distillate or an aromatic extract.