EP0064447A1 - Process for producing synthetic crude oil - Google Patents

Abstract

1. A process for producing synthetic crude oil from a hydrocarbon charge having a high voluminal mass, this process being characterised in that it comprises the following steps : a) optional fractionation (at 12) of the hydrocarbonic charge into at least two fractions : - at least one light fraction containing a majority of the compounds having the lowest boiling points, - a heavy fraction containing a majority of the compounds having the highest boiling points ; b) heat treatment (at 10, 10-) - either of the hydrocarbonic charge, when the fractionation of step 'a' has not been carried out, - or of the heavy fraction, when the fractionation of the charge has been carried out, said heat treatment results in an effluent being produced which is fractionated in a single step (at 100) so as to give : (1) a-first mixture containing hydrogen, hydrogen sulphide and hydrocarbons, (2) a second mixture consisting of hydrocarbons of higher molecular weights than those contained in the first mixture, (3) a third mixture of hydrocarbons having boiling points between the hydrocarbons of the first mixture and those of the second mixture, said third mixture constituting at least partly the synthetic crude oil ; c) treating with a solvent (at 27, 106) the second mixture obtained in step 'b', said treatment resulting in the production : - on the one hand, of a bituminous portion ; - on the other hand, of an oily portion which constitutes, at least partly, the synthetic crude oil.

Description

The present invention relates to a process for obtaining a liquid product hereinafter called "synthetic crude oil" from a hydrocarbon product having a higher density.

By hydrocarbon product is meant a product composed essentially of hydrocarbons _o but which may also contain other chemical compounds which, in addition to carbon and hydrogen atoms, may have heteroatoms, such as oxygen, nitrogen, sulfur or metals like vanadium and nickel.

The term "synthetic crude oil" used above is a commonly used term, but does not mean that synthetic crude oil comes from crude oil proper. This product can also come, for example, from heavy oils having a density at 15 ° C. greater than about 0.93 g / ml, bituminous shales, oil sands or even coal.

The current trend on the international petroleum market is an increasing demand for light crude oils of relatively low density. On the one hand, light crudes often contain less troublesome products for their refining, such as sulfur or metals. such as vanadium and nickel, on the other hand, in the coming years, the sale of light products such as fuels will increase relatively faster than that of heavy products such as fuel oils.

The demand for light crudes is therefore increasing and their prices are growing faster than that of heavy crudes.

It is therefore more interesting to transform heavy crude on the production fields into light crude before transporting it.

The heaviest part of crude oil, which is the residue from petroleum distillation, is made up of a mixture of oil and bituminous compounds.

• - les hydrocarbures aliphatiques, saturés op non saturés, ayant de 2 à 8 atomes de carbone, seuls ou en mélange,
• - les mélanges d'hydrocarbures, appelés distillats, obtenus par distillation du pétrole brut et ayant des poids moléculaires voisins de ceux des hydrocarbures ayant de 2 à 8 atomes de carbone,
• - les mélanges de tous les hydrocarbures précédemment cités.

The oily part and the bituminous part are separated by the so-called deasphalting process, which consists in extracting the oily part from the residue using a solvent. This solvent can be chosen from the group consisting of:

• - aliphatic hydrocarbons, saturated op unsaturated, having 2 to 8 carbon atoms, alone or as a mixture,
• - mixtures of hydrocarbons, called distillates, obtained by distillation of crude oil and having molecular weights close to those of hydrocarbons having from 2 to 8 carbon atoms,
• - mixtures of all the previously mentioned hydrocarbons.

The Applicant has devised a means of obtaining synthetic crude oil by a process integrating a heat treatment step and a deasphalting step.

The object of the present invention is therefore to obtain synthetic crude oil with a lower density from heavier products.

• a/ le fractionnement éventuel de la charge hydrocarbonée en au moins deux fractions :
  • - au moins une fraction légère, contenant la plus grande partie des composés ayant les points d'ébullition les plus faibles,
  • - une fraction lourde, contenant la plus grande partie des composés ayant les points d'ébullition les plus élevés,
• b/ le traitement thermique
  • - soit de la charge hydrocarbonée, quand le fractionnement de l'étape "a" n'est pas effectué,
  • - soit de la fraction lourde, quand le fractionnement de la charge a lieu,
  
  ledit traitement thermique conduisant à l'obtention d'un effluent qui est fractionné pour donner t
  • (1) un premier mélange contenant de l'hydrogène, de l'hydrogène sulfuré et des hydrocarbures de poids moléculaires peu élevés,
  • (2) au moins un second mélange constitué d'hydrocarbures de poids moléculaires plus élevés que ceux contenue dans le premier mélange,
• c/ le traitement par un solvant du second mélange obtenu dans l'étape "b", ledit traitement conduisant à l'obtention :
  • - d'une part, d'une partie bitumineuse,
  • - d'autre part, d'une partie huileuse,qui constitue, au moins en partie, le pétrole brut synthétique.

To this end, the subject of the invention is a process for obtaining synthetic crude oil from a hydrocarbon feedstock having a higher density, this process being characterized in that it comprises the following steps

• a / the possible fractionation of the hydrocarbon feedstock into at least two fractions:
  • - at least one light fraction, containing the greater part of the compounds having the lowest boiling points,
  • - a heavy fraction, containing the major part of the compounds having the highest boiling points,
• b / heat treatment
  • - either of the hydrocarbon charge, when the splitting of step "a" is not carried out,
  • - either of the heavy fraction, when the fractionation of the charge takes place,
  
  said heat treatment leading to the production of an effluent which is fractionated to give t
  • (1) a first mixture containing hydrogen, hydrogen sulphide and low molecular weight hydrocarbons,
  • (2) at least one second mixture consisting of hydrocarbons of higher molecular weight than those contained in the first mixture,
• c / the treatment with a solvent of the second mixture obtained in step "b", said treatment leading to obtaining:
  • - on the one hand, a bituminous part,
  • - on the other hand, an oily part, which constitutes, at least in part, synthetic crude oil.

The invention will be better understood from the description below, in which reference will be made to the accompanying drawings. In these drawings:

Figures 1 and 2 are diagrams of two types of units implementing the method according to the invention

Figures 3 and 4 are diagrams illustrating the results of an exemplary implementation of the invention.

With reference to FIG. 1, a hydrocarbon charge arrives in the unit via line 1.

Prior to any treatment, the charge may - and even must, in the case where this charge is notably crude oil - have been treated in a desaaleur 2, into which it is introduced, via line 1, in order to remove the salts it contains.

To this end, water is added to the charge in line l, through line 3, in order to dissolve the salts contained in the charge. In the desalter, the mixture separates into two phases, an aqueous phase 4 and a hydrocarbon phase 5.

In the case of fillers with a high density, greater than 0.96 g / ml at 15 ° C, it is preferable to dilute the load by introducing through line 6 a lighter hydrocarbon diluent, so as to lower the density of the filler and to improve the contact between the water and the filler, by promoting the dissolution of the salts in the water and, therefore, their separation. The nature of the diluent as well as the diluent ratio in relation to the load must be chosen so as to avoid precipitation of the asphaltenes.

The aqueous phase is eliminated by line 7 and the hydrocarbon feed to be treated by line 8 is recovered by the process according to the invention.

• 1. la charge peut être envoyée directement par la ligne 9 dans une enceinte 10, où elle subit un traitement thermique à une température comprise entre 400 et 600°C et à une pression comprise entre 1 et 100 bars ;
• 2. la charge peut être fractionnée dans une tour de fractionnement 12, où elle est conduite par la ligne 13. C'est notamment le cas lorsque la charge de la ligne 8 contient des produits légers,auxquels il est inutile de faire subir l'étape de traitement thermique ultérieur.

The load of line 8 can then be treated in two different ways, depending on its nature s

• 1. the load can be sent directly by line 9 to an enclosure 10, where it undergoes heat treatment at a temperature between 400 and 600 ° C and at a pressure between 1 and 100 bars;
• 2. the load can be fractionated in a fractionation tower 12, where it is led by line 13. This is particularly the case when the load of line 8 contains light products, which it is useless to subject to subsequent heat treatment step.

• - pour les pétroles bruts lourds nécessitant d'être dilués avant dessalage,
• - pour les pétroles bruts non "stabilisés" sur le champ de production, c'est-à-dire contenant encore une proportion non négligeable d'hydrocarbures à moins de 4 atomes de carbone,
• - pour les pétroles bruts dont une fraction importante distille avant 350°C.

This latter case is encountered in particular:

• - for heavy crude oils which need to be diluted before desalting,
• - for crude oils not "stabilized" on the production field, that is to say still containing a non-negligible proportion of hydrocarbons with less than 4 carbon atoms,
• - for crude oils, a large fraction of which distills before 350 ° C.

We can consider a split into two fractions or in addition to two fractions.

It is possible, for example, as shown in FIG. 1, to collect at the bottom of column 12, by line 14, a heavy fraction, the initial boiling point of which is equal to or greater than 350 ° C.

It is also possible, as shown in the figure, to collect by a lateral draw-off (line 16) the fraction called "diesel". This fraction can be used to constitute part of the synthetic crude and will be taken by line 16 to a tank 17, from which the synthetic crude will be collected by line 36.

Finally collected at the top of column 12, via line 15 the gaseous hydrocarbon at room temperature, and the liquid fraction called "gasoline ^*.

This fraction is conducted by line 15 in a reflux flask 18.

In this balloon, most of the hydrocarbons having from 1 to 4 or 5 carbon atoms, depending on the fractionation carried out, are collected in the gas phase by line 19.

The petrol fraction is collected in liquid form, via line 47. This fraction is recycled at least in part to tower 12 by line 20. It can also be used, at least in part, to constitute the diluent introduced by line 6 into the feed, in the case of heavy products. It is led in this case to line 6 by line 21. It can finally also be led, by line 48, to tank 17 and constitute a part of the synthetic crude.

The fraction collected by line 19 is conducted in a fractionation tower 22, the function of which will be explained below.

The flow of lines 9 or 14 undergoes in the enclosure 10 a heat treatment and the effluent is collected by line 23,

The effluent from line 23 is led into a first separator tank 24.

The operating conditions of operation of this balloon are chosen so as to collect via line 25 an overhead fraction containing at least hydrogen sulfide and most of the hydrocarbons containing from 1 to 4 or 5 carbon atoms, as the case may be, so that the bottom fraction, collected by line 26 and which will be conducted in a liquid extractor - deasphalting liquid 27, contains as little as possible of these gases.

In some cases, it may be advantageous to regulate the operating conditions of flask 24, so as to collect in the top fraction, via line 25, not only the hydrogen sulfide and the hydrocarbons with 1 to 4 or 5 carbon atoms. , depending on the case, but also heavier hydrocarbons, so as to have, as will be explained below, a deasphalting solvent consisting of a mixture of hydrocarbons having at least 5 carbon atoms.

The separation by expansion being however, by definition, summary, there may be in the top fraction heavier hydrocarbons than certain hydrocarbons contained in the bottom fraction.

The head fraction is led by line 25 in a second separator flask 30.

Is collected at the top of the balloon 30, by the line 31, hydrogen sulfide and most of the hydrocarbons having from 1 to 5 carbon atoms. The flow of line 31 is conducted in column 22.

• - soit totalement ou en partie dans le bac 17 par la ligne 37
• - soit totalement ou en partie dans l'extracteur de désasphaltage 27 par les lignes 35, 34 et 33 ; cette possibilité peut être avantageuse, lorsque l'on désire avoir un solvant de désasphaltage constitué par un mélange d'hydrocarbures ayant au moins 5 atomes de carboneo

Hydrocarbons heavier than those of the overhead fraction collected by line 31 are recovered at the bottom of the balloon 30, via line 32. The flow from line 32 can be conducted:

• - either totally or partially in the tray 17 by line 37
• - either completely or partially in the deasphalting extractor 27 by lines 35, 34 and 33; this possibility can be advantageous, when it is desired to have a deasphalting solvent consisting of a mixture of hydrocarbons having at least 5 carbon atoms

In the extractor 27, the oily part is extracted from the feed brought by line 26 by a solvent which is introduced into the extractor by line 33. This solvent can be chosen from the group consisting of aliphatic hydrocarbons, saturated or unsaturated, having from 2 to 8 carbon atoms, preferably from 3 to 5 carbon atoms, mixtures of hydrocarbons, called distillates, obtained by distillation of crude oil and having molecular weights close to those of hydrocarbons having 2 with 8 carbon atoms and mixtures of all the previously mentioned hydrocarbons.

The solvent for starting the unit comes from a source outside the unit, via line 34. The solvent losses can be compensated either by products coming from the unit, as will be explained more away, either by an external backup brought by line 34.

étant compris entre O,1 et 10.The pressure inside the extractor 27 can be between 1 and 100 bar absolute, the temperature between 15 and 300 ° C, the mass rate

being between O, 1 and 10.

The oily part in solution in the solvent is collected at the head of the extractor 27, via line 38. This mixture is conducted by line 38 in a fractionation assembly 39. For the purpose of simplification, this assembly has not been shown in detail, but it generally comprises a regulator controlling a pressure drop, evaporators and a drive column with steam.

At the outlet of the assembly 39, solvent is collected, on the one hand, by the line 40, which is recycled to the extractor 27, via the line 33, on the other hand, by the line 41, the oily part, which is led into the tank 17.

The precipitated bituminous part and the solvent are recovered at the bottom of the extractor 27 and this mixture is conducted, via line 42, in a fractionation assembly 43, which generally comprises an oven and an evaporator.

Is collected at the outlet of the assembly 43, on the one hand, by the line 49, of the solvent, which is recycled to the extractor 27, via the line 33 and, on the other hand, by line 44, the bituminous part.

The flows of lines 31 and possibly 19 are led, as it was said previously, in a fractionation column 22.

Is collected at the top of column 22, by line 45, hydrogen sulfide and hydrocarbons with 1 and 2 carbon atoms. After removal of the hydrogen sulfide by an appropriate treatment, the hydrocarbons can be burnt in an oven.

The heaviest fraction, collected at the bottom of column 22 by line 46 and consisting of hydrocarbons having at least 3 carbon atoms, can be taken to tank 17, as shown in FIG. 1.

It can also serve, at least in part, as a supplement for deasphalting solvent.

The addition of deasphalting solvent can also come from the fraction collected by line 48, or, as it was said previously, from line 35.

These different variants have not been shown, for the purpose of simplification.

The bituminous part of line 44 can be conducted in a coking unit.

This coking unit can be of various natures, but, in the case of an installation implementing the method according to the invention and located on the field of production of the charge, it is more advantageous that this unit provides little coke and that it can be easily used as fuel. This is the case for coking units in a fluidized bed, where the coke produced can be easily handled or even gasified.

This coking unit makes it possible to produce coke and an effluent, which, after separation of the hydrogen sulphide and the hydrocarbons with 1 and 4 carbon atoms which it contains, can give a product containing hydrocarbons with 5 and more than 5 carbon atoms, which may constitute part of the synthetic crude.

The synthetic crude oil obtained in tank 17, which therefore comes from line 41 and, optionally, lines 37, 16, 48 and 46, has a lower density than the starting product and contains fewer annoying products such as sulfur, and especially much less metals like nickel and vanadium, which is very interesting for the subsequent treatment of crude oil.

Reference will now be made to FIG. 2, in which the elements identical to those represented in FIG. 1 have been identified by the same numbers assigned to the index '. The start of the treatment is the same, but it changes in the treatment of the effluent collected by the line 23 ', at the outlet of the heat treatment enclosure 10'.

The flow of line 23 ′ is conducted in a fractionation tower 100.

• - une fraction de tête, évacuée par la ligne 101 et contenant notamment l'hydrogène sulfuré et les hydrocarbures à 1 et 2 atomes de carbone, qui ne doivent pas être conduits dans l'extracteur de désasphaltage ; cette fraction peut,par exemple,avoir un point d'ébullition final compris entre 80 et 160°C ;
• - une fraction intermédiaire, ayant par exemple un point d'ébullition initial compris entre 80 et 160°C et un point d'ébullition final de l'ordre de 370°C ₁ cette fraction, qui n'a pas besoin d'être soumise au désasphaltage, peut constituer au moins en partie le brut synthétique et est donc conduite par la ligne 102 au bac 104, d'où le brut synthétique est recueilli par la ligne 105 ;
• - une fraction de fond, dont le point initial d'ébullition est par exemple supérieur à 370°C et qui est conduite dans un extracteur liquide-liquide de désasphaltage 106.

The operating conditions of this tower are chosen so as to collect, respectively s

• - a fraction of the head, evacuated by line 101 and containing in particular hydrogen sulphide and hydrocarbons with 1 and 2 carbon atoms, which must not be led into the deasphalting extractor; this fraction can, for example, have a final boiling point of between 80 and 160 ° C;
• - an intermediate fraction, for example having an initial boiling point between 80 and 160 ° C and a final boiling point of the order of 370 ° C ₁ this fraction, which does not need to be subjected at deasphalting, can constitute at least partially the synthetic crude and is therefore conducted by line 102 to tank 104, from where the synthetic crude is collected by line 105;
• a bottom fraction, the initial boiling point of which is for example greater than 370 ° C. and which is carried out in a liquid-liquid deasphalting extractor 106.

The head fraction of line 101 is conducted in a reflux flask 107. At the top of the flask 107, hydrogen sulfide and most of the hydrocarbons having from 1 to 4 or 5 carbon atoms are collected .

The flow from line 108 is conducted in a fractionation column 22 ', the function of which is identical to that of column 22 in FIG. 1.

A gasoline fraction is collected at the bottom of the tank 107, via the line 109, which is recycled, at least in part, to the tower 100 by the line 110. It can also be conducted, at least in part, by a non-line. shown, for the sake of simplification, in line 6 ', to serve as a diluent for the load, in the case of heavy products. Finally, it can also be taken, by line 111, to tank 104, to constitute part of the synthetic crude.

The flow collected at the bottom of tower 100 by line 103 is led into the liquid-liquid extractor of deasphalting 106, into which, as described above, a solvent is introduced via line 112.

The oily part in solution in the solvent, collected at the top of the extractor 106, is led by the line 113 in a fractionation assembly 114.

At the outlet of the assembly 114, the solvent is collected, on the one hand, by line 115, which is recycled to column 106, via line 112, on the other hand, by line 116 , the oily part, which is led into the tank 104.

The precipitated bituminous part and the solvent are recovered at the bottom of the extractor 106 and this mixture is led, via line 117, directly into a fractionation assembly 118.

At the outlet of this assembly 118, solvent is collected, on the one hand, by line 119, which is recycled to extractor 106, via line 112, on the other hand, by line 120, the bituminous part.

A make-up of solvent can be introduced via line 121 into extractor 106, via line 121. This make-up can come, as the case may be, from the streams of lines 46 ', 48' and 111.

As in the case of FIG. 1, a coking unit can be provided to treat the bituminous part collected by line 120.

The example which follows, which is not limiting, illustrates the invention.

E X E M P L E

This example relates to the treatment, by the method according to the invention, of a crude oil, obtained from a deposit by extraction with steam.

The product thus obtained contains approximately 25% by weight of water, which is eliminated. A hydrocarbon product is thus obtained, the characteristics of which are shown in Table 1 below.

Ce produit est ensuite traité dans une installation de laboratoire,suivant le procédé selon l'invention.

This product is then treated in a laboratory installation, according to the method according to the invention.

The charge is first fractionated in a column at atmospheric pressure.

A fraction 1 is collected, the boiling point range of which is between 150 and 350 ° C., and a fraction 2, boiling above 350 ° C.

• - Fraction 1 : 16 % en poids,
• - Fraction 2 : 84 % en poids.

The yields obtained are as follows:

• - Fraction 1: 16% by weight,
• - Fraction 2: 84% by weight.

The characteristics of fractions 1 and 2 are given in Table II below

Fraction 2 was then treated thermally, at a temperature of 420 ° C.

• - le traitement A a été effectué pendant un temps de 1000 secondes,
• - le traitement B pendant un temps de 2500 secondes.

Two treatments A and B were carried out:

• - treatment A was carried out for a time of 1000 seconds,
• - treatment B for a time of 2500 seconds.

The characteristics of the products A and B obtained, after elimination of the gases with a boiling point below 15 ° C, are given in Table III below:

Then on these products A and B, as well as on fraction 2, before thermal treatment, deasphalting tests by varying the solvent, the temperature, the pressure and the mass content of solvent charge.

• 1. les courbes représentant la masse volumique de l'huile désasphaltée, en fonction du rendement en huile en % en poids ; ces courbes sont représentées sur la figure 3 des dessins annexés,
• 2. les courbes de rendement pondéral en huile en %, en fonction du taux massique solvant charge ; ces courbas sont représentées sur la figure 4.

We were able to trace, from the results of these tests

• 1. the curves representing the density of the deasphalted oil, as a function of the oil yield in% by weight; these curves are shown in FIG. 3 of the accompanying drawings,
• 2. the oil weight yield curves in%, as a function of the mass ratio of solvent filler; these curves are shown in Figure 4.

These Figures 3 and 4 will be commented successively below.

It can be seen from FIG. 3 that, for the same oil yield, the density of the deasphalted oil after heat treatment of the charge is reduced and that the combination of heat treatment and deasphalting makes it possible to lower the density of the product at values which it is difficult to obtain by a simple deasphalting of the load.

For example, Table IV below gives the operating conditions for deasphalting used to obtain an oil yield close to 70% by weight and the main characteristics of the oils obtained for fraction 2 which is not heat treated, as well as for products A and B obtained after heat treatment of fraction 2.

It is found that the density of the product not heat treated is greater.

If fraction 1 of Table II is mixed with the products obtained from A and B of Table IV, synthetic crude oils are obtained, the yields and characteristics of which are given in Table V below.

The synthetic crude oils obtained by the process according to the invention have a lower density and nickel, vanadium and sulfur contents than the starting crude oil. Their Conradson residue is also much lower.

For the same yield of synthetic crude oil, the nickel and vanadium contents and the Conradson residue decrease markedly with an increase in the duration of the heat treatment at 420 ° C.

• - solvant : propane (voir composition donnée précédemment,en relation avec le Tableau IV),
• - pression : 45 bars,
• - température : 90°C.

Reference will now be made to the curves in FIG. 4. The curves represented in this figure were drawn from tests carried out by varying the mass ratio of solvent charge, under the following conditions:

• - solvent: propane (see composition given above, in relation to Table IV),
• - pressure: 45 bars,
• - temperature: 90 ° C.

It is found that the oil yield is higher for the heat treated products than for a product that is simply deasphalted.

Table VI below gives the results for a mass ratio of solvent charge close to 2.

The process according to the invention therefore makes it possible to obtain, under the same operating conditions, a better yield of oil and of lower density.

If fraction 1 of Table II and the products obtained from A and B of Table VI are mixed, synthetic crude oils are obtained, the yields and characteristics of which are given in Table VII below.

The synthetic crude oils obtained by the process according to the invention have a lower density and nickel and vanadium contents than the starting crude oil.

Claims (8)

1.- Process for obtaining synthetic crude oil from a hydrocarbon feed having a higher density, this process being characterized in that it comprises the following stages: a / the possible fractionation of the hydrocarbon feedstock into at least two fractions: - at least one light fraction, containing most of the compounds with the lowest boiling points, - a heavy fraction, containing the major part of the compounds having the highest boiling points, b / heat treatment: - either of the hydrocarbon feedstock, when the fractionation of step "a" is not carried out, - either of the heavy fraction, when the fractionation of the charge takes place,
said heat treatment leading to the production of an effluent which is fractionated to give: (1) a first mixture containing hydrogen, hydrogen sulphide and low molecular weight hydrocarbons, (2) at least one second mixture consisting of hydrocarbons of higher molecular weight than those contained in the first mixture, c / the treatment with a solvent of the second mixture obtained in step "b", said treatment leading to obtaining: - on the one hand, a bituminous part, - on the other hand, an oily part, which constitutes, at least in part, synthetic crude oil. 2.- Method according to claim 1, characterized in that the fractionation of the effluent from the heat treatment consists of two separations which give, in addition to the first mixture and the second mixture, a third mixture consisting of hydrocarbons. 3.- Method according to claim 2, characterized in that at least part of the third mixture of hydrocarbons is used as solvent in step "c". 4.- Method according to claim 2, characterized in that at least part of the third mixture of hydrocarbons constitutes, at least in part, synthetic crude oil. 5.- Method according to claim 1, characterized in that the fractionation of the effluent from the heat treatment is carried out in a single step, so as to give a third mixture of hydrocarbons with boiling points between the hydrocarbons of first mixture and those of the second mixture, said third mixture constituting at least in part the synthetic crude oil. 6.- Method according to one of claims 1 to 5, characterized in that the hydrocarbon feedstock is subjected to a desalting operation and in that, prior to this desalting, the feedstock is added with at least part of the hydrocarbons contained in the light fraction obtained in the possible fractionation of step a 7.- Method according to one of claims 1 to 6, characterized in that at least part of the hydrocarbons contained in the light fraction obtained in the possible fractionation of step "a" constitutes, at least in part, the synthetic crude oil. 8.- Method according to one of claims 1 to 7, characterized in that the oily part is subjected to a coking and in that at least part of the coking effluent constitutes a part of synthetic crude oil.

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