FR2480773A1 - Upgrading of asphaltenic oils - by deasphalting, hydro:visbreaking and catalytic hydrotreating - Google Patents

Abstract

Conversion of asphaltenic oils to lighter fractions is carried out by (a) deasphalting the asphaltenic oil with a 5-7C aliphatic hydrocarbon solvent; (b) contacting the deasphalted oil with H2 at 440-530 deg.C and 40-140 bar for 1 sec to 10 hrs. in a non-catalytic reactor; and (c) contacting the product and H2 at 320-430 deg.C and 40-140 bar with at least one catalyst comprising at least one Mo and/or W cpd. and at least one Ni and/or Co cpd. The process gives higher distillate yields than similar processes using non-deasphalted or propane-deasphalted feeds.

Description

 The present invention relates to a process for the hydroconversion of deasphalted oils into lighter fractions1 comprising a thermal hydroviscoreduction step and a catalytic hydrostabilization step of the cracked products obtained. More specifically, this process is designed to be coupled with a deasphalting process where the solvent used is a hydrocarbon or a mixture of hydrocarbons containing at least predominantly five to seven carbon atoms.

 The deasphalted oils, the treatment of which is the subject of the invention, can be obtained by deasphalting the residues under vacuum or atmospheric residues of conventional crudes whose density is less than 0.950. These deasphalted oils can also be obtained from heavy oils with a density greater than 0.950, such as Boscan crude or heavy oils from the Orinoco belt in Venezuela or the Athabasca in Canada; in the latter case, the feedstock subjected to the prior deasphalting may be a vacuum residue or an atmospheric distillation residue but also a deessential crude or simply desalinated. In general, the hydrocarbon feeds whose treatment is the subject of the invention are deasphalted oils from the deasphalting of any hydrocarbon feed containing asphaltenes or resins, such as oil from coal liquefaction or pyrolysis of oil shales. Such feedstocks usually contain at least 80% by weight of constituents boiling normally above 360DC. Their asphaltenes content, which can be dosed with heptane, is usually greater than 0.5% by weight. it should nevertheless be noted that the deasphalting operation from which are derived the fillers whose treatment is the subject of the invention is a deasphalting or the solvent used is a hydrocarbon or a mixture of hydrocarbons containing from five to seven carbon atoms, so as to leave in the load most of the resins while achieving a good precipitation of asphaltenes.

 As part of the present technique, two main refining schemes have been recommended for the conversion of deasphalted oils into distillates; the first scheme uses a catalytic cracking and the second catalytic hydrocracking and in both cases the oil-deasphalted is previously hydrorefined to remove a number of impurities, including sulfur, nitrogen, and especially metals ( nickel and vanadium), and to lower the content of carbonizable compounds by partial hydrogenation of the pericondensed aromatic compounds. Catalytic cracking leads to gasoline of good octane number but to gas oils of poor cetane number which are generally used as domestic fuel oil components; hydrocracking leads to middle distillates, jet fuels and diesel fuel, of high quality but the naphtha obtained requires to be treated in a catalytic reforming to acquire the octane qualities required by the current gasolines.Face to these two refining schemes most commonly used, the treatment which is the object of the present invention constitutes a third way allowing the conversion of a deasphalted oil into naphtha, kerosene, gas oils, and vacuum gas oils which can in particular serve as a basis for the production of domestic fuels with low sulfur content or which can constitute an excellent load for a catalytic cracking if one seeks to increase the production of gasoline.

OBJECT OF THE INVENTION
The invention relates to a process for the hydroconversion of oils previously deasphalted with at least one hydrocarbon having 5 to 7 carbon atoms, in lighter fractions, with a weight yield of fractions distilling below 520 ° C which easily exceeds 50 70.

 The process comprises four steps: a first step of deasphalting with at least one hydrocarbon having 5 to 7 carbon atoms, a second visbreaking or thermal hydrocracking stage under hydrogen pressure, carried out at high temperature for times of 1 second at 10 hours, a third catalytic hydrostabilization step and a fourth distillation step for recovering a distillate and a distillation residue at least a portion of which is returned to the second step.

 In the third step, the cracking products, diolefins, olefins, aromatics, resins as well as the asphaltenes which have formed during the thermal step are totally or partially hydrolized. It is then possible to separate the gases and to distil the liquids. As indicated above, at least a portion of the residue of this distillation is recycled to the hydroviscoreduction stage. It is also possible to carry out other recycling of liquid or gaseous fractions in accordance with the indications given below, in particular those of the diagram presented in the figure.

A particular characteristic of the invention lies in
that the filler is an oil deasphalted by a hydrocarbon or a m
hydrocarbon mixture containing from five to seven carbon atoms.

Under these conditions, the conversion is carried out, for the essen
in the dhrydrovi-sbreaking zone at temperatures ranging from
440 ° C to 530 ° C.

According to a preferred procedure of the invention, the mixture,
d the exit of the cracking furnace, is cooled through
of a simple hydrogen gas quench to be sent directly into
the catalytic hydrorefining reactor. By quenching with hydrogen,
means the simple addition of hydrogen at a lower temperature than
that of the effluent from the visbreaking stage, so as to bring
quickly or almost instantaneously the temperature of this effluent
up to a value between 320 and 430 ° C, preferably between
350 and 410 ° C.

Sclon another preferred embodiment of the invention,
the catalytic hydrorefining operation uses two types of
different catalysts, arranged in two (or more) beds or
separate players. This arrangement of catalysts avoids poly
merisatioh and polycondensation of unstable compounds inevitable
produced during the high-temperature thermal cracking operation
temperature.

 According to a preferred embodiment, at least 10% and preferably at least 50% of the distillation residue of the fourth stage is recycled to the input of the thermal conversion zone from the bottom of the vacuum distillation column placed after hydrostabilization or in another variant from the bottom of the atmospheric distillation placed at the same point, when a maximum production of naphtha, jet fuel and engine gas oil is aimed at. This recycled fraction contains at least 80% of constituents boiling normally above 36O0C.

 Another embodiment of the invention consists in carrying out thermal hydrocracking and hydrorefining in the presence of steam, which makes it possible to reduce the fouling speed of the cracking furnace on the one hand, and catalysts hydrorefining, on the other hand.

DESCRIPTION OF THE PRIOR ART
Some patents show the state of integration of a heat treatment under pressure and a subsequent catalytic hydrotreatment.

U.S. Patent Nos. 2,717,285, 3,132,088; 3,148,135; 3,271,302, 3,691,058, 3,806,444; 4,005,006; 4.017.379, propose indeed, the integration of a heat treatment and a catalytic treatment either of the hydrorefining type or of the hydrocracking type. Nevertheless, none of these patents provides for treating a deasphalted residue, let alone a deasphalted residue under particular conditions.

 US Pat. Nos. 3,089,843 and 3,148,135 propose associating a thermal hydroconversion with a catalytic hydroconversion. The feedstock is normally a distillation residue, although the use of deasphalted residue is theoretically possible according to the first of these two patents; no details are given on the nature of the deasphalting solvent.

 No. 3,288,703 proposes associating a thermal hydro-cracking and a catalytic hydrocracking carried out on a previously deasphalted feedstock. In the exemplary embodiment, the contact time in the thermal hydrocracking zone is about 4 hours and only propane is used as a deasphalting solvent.

 No. 3,293,169 also proposes the combination of a thermal hydrocracking and a catalytic hydrocracking carried out on a deasphalted charge. In the exemplary embodiment, the deasphalting solvent is a propane-butane mixture and the reaction time in the thermal hydrocracking zone is from 30 minutes to 5 hours.

 None of the aforementioned patents foresaw the advantage of deasphalting with a hydrocarbon having 5 to 7 carbon atoms; by using such a hydrocarbon, it becomes possible to operate with much shorter contact times in the thermal zone, for example 5 to 300 seconds. None of the aforementioned patents has seen the benefit of recycling to the thermal stage of the residue obtained at the end of the catalytic hydroconversion stage. Nor is there any mention of quenching by the hydrogen gas of the effluent of the thermal reaction zone.

DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 gives, by way of example, a brief description of the process arrangement as recommended in the invention.

The feed is introduced into the unit through line 1 as deasphalted in a conventional manner by one or more C5 to C7 hydrocarbons in the deasphalter schematized in 1 a; the oil fraction, freed of asphalts and extraction solvent, is removed via line 1b to be mixed at point 2 with the untransformed heavy fraction and with a part of the hydrogen gas recycled via line 6. The resulting mixture passes through the exchanger 3 before being introduced, via line 4, into the thermal hydroviscoreduction furnace 7. The feedstock of this furnace is essentially a deasphalted oil (asphaltene content precipitated at a temperature preferably less than 0.1% by weight) by a hydrocarbon or a mixture of hydrocarbons containing from five to seven carbon atoms and resulting from the deasphalting of residues under vacuum, atmospheric residues of phenols, crude oils heavy of essences or any heavy oil containing compounds of réesic and asphaltenic type as for example some shale oils or some hydrogenates from the liquefaction of coal.The choice of the solvent used in the deasphalting is important because it has been found that, unexpectedly, the charges still containing their resin compounds were subjected under conditions of a given severity, a conversion into
more products are much lighter / larger than the loads from where these same. Resinic compounds were extracted by deasphalting using a light solvent such as propane / butanes or a mixture of these paraffinic hydrocarbons and their olefinic derivatives. This observation led to the choice; As deasphalting solvent, a hydrocarbon or a mixture of hydrocarbons having five seven carbon atoms. It should also be noted that the conversions obtained are far too high to be attributed to the only resin compounds still present in the charge but it would appear that these compounds behave as initiators of the thermal reactions involving all the molecules of the treated feed. In the absence of these compounds, in the case of the treatment of a vacuum gas oil, for example, thermal hydrocracking requires temperatures 30 to 60 ° C higher than those applied in the treatment of deasphalted atmospheric residues by C5 to C7 hydrocarbons and / or longer contact times
As the C5 to C7 hydrocarbon, there can be used, for example, n-pentane, isopentane, saturated C7, saturated C5-C7 or an olefinic C5 or C6.

 the deasphalting operation is usually carried out at about 150-2600 ° C. After this operation, the heptane precipitated asphaltenes content is advantageously less than 0.1% by weight.

The thermal hydroconversion operation is advantageously carried out in one or more tubes placed in the oven; the temperature of the reaction mixture (hydrocarbons + hydrogen) is maintained, at least in the second half of the tubes in which the cracking takes place, at a value of between 4400.degree. C. and 530.degree. C. and preferably between 4600.degree.C and 5100.degree. between 40 and 140 bar, and preferably between 70 and 110 bar, the residence time of the liquid charge is between 1 second and 10 hours and preferably between 1 and 500 seconds.The hydrogen gas used may contain hydrocarbons carbon dioxide, as well as small amounts of hydrogen sulphide and ammonia from recycled hydrogen gas.It is nevertheless recommended that the hydrogen content of the recycle gas, at the inlet of the cracking is greater than 50% by volume and preferably 70% by volume The quantity of hydrogen gas injected at the inlet of the oven 33 is advantageously between 100 and 5,000 m per m of load
3 3 and preferably between 300 and 1000 m per m of load.

 The products from the thermal cracking furnace are cooled at point 9 by hydrogen injection, for example, an on-line injection of a portion of the recycle gas premixed in point 8 with the makeup hydrogen required for offset the hydrogen consumption in the unit. It is advantageous that the additional hydrogen be introduced between the thermal hydrocracking step (hydroviscoreduction) and the catalytic hydrogenation step so as to ensure a hydrogen partial pressure at the level of the hydrogenation catalyst. to prevent the polymerization of olefins from thermal cracking and to move as much as possible to the production of naphthenes and naphtheno-aromatics, the thermodynamic equilibrium that governs the hydrogenation of aromatic molecules and, in particular, peri-condensed aromatic molecules.

 The mixture is introduced via line 10 into the hydrogenation reactor 11. It could be operated with a conventional hydrodesulfurization catalyst containing molybdenum and / or tungsten with a Group VIII metal such as nickel and / or cobalt. Substantially improved results with respect to product stability are, however, obtained when using two different types of catalysts.

 Whatever the type of catalyst initially introduced, it is found that during operation it operates mainly in sulphurous form. This sulphurization may be obtained, in known manner, by presulphurization of the catalyst or result from the presence of sulfur compounds in the feedstock.

 In the case of a preferred operation with several catalyst beds, in the first catalyst bed or in the first beds, a catalyst (A) based on Group VI A metal compounds promoted with cobalt compounds is preferably used. and / or nickel.

To avoid as much as possible the polymerization and polycondensation reactions of the unstable compounds, the atomic ratio = = Ni and / or Co
R = - and / or Mo is usefully set between 0.8 and 3 and preferably between 1 and 2. It is preferably carried out with a substantially neutral support characterized by a neutralization heat by adsorption of ammonia to 320qu less than 10 calories per gram under a ammonia pressure of 300 mm Hg. The technique for incorporating active metals is conventional. Among the supports corresponding to this characteristic, surface aluminas of between 40 and 120 m 2 / g which have been autoclaved under pressure of steam and aluminates of this type are particularly suitable. cobalt, nickel, magnesium, calcium and / or barium. In general, the catalysts described in US Pat. 4,019,976 can be used to form the first catalytic bed; nevertheless, in the precise context of the process which is the subject of the invention, the contents of active agents expressed in the weight contents of MoO 3, WO 3 NiO,
CoO will advantageously be between 6 and 30/0 and preferably between 14 and 24%
The preferred catalysts will be those containing the following pairs, Ni W, Ni No or Co Mo; the Ni Mo couple will preferably be used in the process forming the subject of the present invention.

In the last catalyst bed (s), a catalyst (B) is preferably used. The ratio R defined above is advantageously between 0.2 and 0.5, preferably between 0.25 and 0.35; the preferred catalysts are those containing the NiW couples,
Neither Mo, Co Mo but the Ni Mo pair is preferentially used in the process forming the subject of the present invention. Advantageously, a high surface area carrier, for example of alumina type Y ex boehmite or ex bayerite, or of silica-alumina type containing from 1 to 10% by weight of silica, or of alumina-magnesia or silica-magnesia type containing 5, is used. 10% by weight of magnesium and 95 to 90% by weight of alumina or silica respectively.

The acidity of the supports, determined as above> is usefully greater than 30 calories per gram. The surface of the support is preferably between 150 and 350 m 2 / g. Its pore volume is advantageously between 0.7 and 1 cm / g so that the pore diameter is greater than 90% of the pore volume greater than 100 Å.
In a manner known per se, the support is impregnated with or agglomerated with precursor salts of the active agents which, during operation, are molybdenum or tungsten sulphides promoted by nickel or cobalt sulphides. the weight contents of active agents, expressed in terms of oxides, are advantageously between 6 and 30% and preferably between 14 and 24%.

 The pressure used in the catalytic hydrogenation unit is preferably chosen between 40 and 140 bar. Elie is advantageously chosen equal to the pressure used in the thermal hydrocracking furnace. The space velocity is between 0.2 and 3 and preferably between 0.4 and 1.5. The temperature is between 320 and 430 ° C and preferably between 350 and 4000 ° C. The amount of hydrogen gas is 100 to 5,000, preferably 300 to 1000 m3 / m 3 of hydrocarbon feedstock. A and B charged in the reactor (s)) is advantageously between 0.1: 1 and 1: 1 and preferably between 0.3: 1 and 0.7: 1. Given the exothermicity of the transformation, advantageously performs between the various catalyst beds quenching with hydrogen gas introduced into the reactor through the pipe 14.

 the hydrogenation-stabilized products leave the reactor 11 through the pipe 12, pass through the exchanger 3 to arrive at the hot separator 13 where a mixture of hydrogen gas and gasoline is separated in gaseous form and in liquid form heavier liquid effluents that are fed via line 15 to the stripping column 16. As for the gaseous fraction, it is extracted from the separator 13, via the pipe 17, to be cooled in an exchanger 18 before being introduced into the cold separator 19; the liquid fraction leaving the separator 19 is decompressed and then injected at the top of the stripping column 16 via the pipe 20. The hydrogen gas coming from the separator 19 is fed via the pipe 21, to a washing, for example to the amines 22, where the All or part of the hydrogen sulphide is extracted before being recycled into the unit via line 23 after having been recompressed at 24. At the bottom of the column 16, steam is introduced (25 ) to separate at the top a light fraction containing hydrogen sulphide (line 26) while the heavy fraction, freed from its hydrogen sulphide, is introduced via line 27 into an atmospheric distillation column 28 where it is possible to separate, for example the petrol cuts (29), jet fuel (30) and atmospheric gas oil 31. The heavy product withdrawn at the bottom of this column via line 32 is introduced into the vacuum distillation column (33) from which it is extracted. head of e column a vacuum gas oil 34 which constitutes an excellent charge of catalytic cracking or catalytic hydrocracking; the heavy fraction extracted from the bottom of the vacuum distillation column via the pipe 35 is preferably recycled, totally or partially (for example 10 to 100%), via the pump 36, at the inlet of the Thermal cracking step, after mixing in 2 with the fresh feed and a portion of 11 recycle hydrogen. In certain operations using deasphalted oils heavily loaded with resins, a purge of heavy products may be carried out via line 37.

 In a variant of the process for a maximum production of middle distillates it is possible to bypass the vacuum distillation column and to recycle totally or partially (for example 10 to 100%) the unprocessed fraction withdrawn at the bottom of the atmospheric distillation. (line 38) and having an initial boiling point of about 350 ° C.

 The recycling of the heavy fraction extracted from the bottom of the atmospheric distillation column or from the bottom of the vacuum distillation column is one of the particular embodiments of the invention. It has indeed been observed that by operating in accordance with the recommendations of the invention that is to say by coupling. thermal hydroconversion with catalytic hydrorefining at a low conversion rate, while maintaining an acceptable cycle time.

for the catalyst, to recycle all or part of the heavy fraction; the small fraction of asphaltenes (0.2 to 6%) produced during the thermal step by polycondensation from the resins of the charge, is converted at least in large part during the hydrogenation step as it is. recommended in the invention.

 When the resin content of the filler is very high, for example 30% or more, it is advantageous to provide at the inlet of the thermal hydrocracking furnace, the injection of a small amount of water representing a fraction weight, between 0.2 and 10%, and preferably between 1 and 5%, of the total liquid hydrocarbon feed entering this oven; this water is injected in vapor form at 5, passes through the two thermal and catalytic stages and is collected at the top of the stripping column -26. The addition of this extra water vapor retards the coking of the furnace as well as the fouling of the catalysts. This water injection is particularly useful when the resin content of the filler is high (for example at least 30% by weight). The resins can be determined by propane precipitation carried out on a residue which has been deasphalted beforehand with heptane.

EXAMPLES
The various tests were carried out in a pilot unit that was substantially in accordance with the process scheme described in the invention up to the included stripping column. Only the atmospheric distillation operations and the vacuum distillation columns were carried out separately and the effect of the recycling of the heavy fractions was studied by mixing with the fresh feedstock in the feed tank all or part of the unprocessed heavy fraction. . The catalytic reactor operated with two isothermal beds of catalysts not requiring de-quenching by hydrogen gas between the two beds. In addition, the amine wash preferred in the invention was replaced by a washing with ammonia water.

 in these tests the asphaltenes were dosed by heptane precipitation (British Standard BS 4696: 1971 - IP 143/78).

EXAMPLE 1
The treated feedstock is a vacuum residue of light oil from Arabia, the characteristics of which are shown in Table I.

 It is first subjected to pentane deasphalting using a pentane / volume ratio ratio of 5/1. The deasphalted oil yield is 85% by weight.

After this deasphalting, the oil has the following characteristics
specific weight: 0.977 g / cm
Conradson carbon: 9.0
(% weight)
asphaltenes (insoluble with heptane) C 0.05% by weight
viscosity at 100 C: 120 cst
Ni: 2.5 ppm by weight
V: 14 ppm by weight by weight boiling below 520 ° C: 5%
The above deasphalted oil was used as a filler for three separate tests
Test No. 1: Hydroviscoreduction Only: a mixture of deasphalted oil and hydrogen was passed through an oven at 49 ° C. under a pressure of 100 bars, with a residence time of 10 seconds and a hydrogen / oil volume ratio of 500. liters / liter. The effluent was quenched at about 400 ° C. at its outlet by injection of cold hydrogen, the products were distilled and analyzed.

TEST # 2: Hydroviscoreduction followed by hydrostabilisation. For this, the deasphalted oil was first subjected to the same hydrovisoreduction treatment as in Test No. 1, up to and including hydrogen quenching. The product then passed with hydrogen directly into a catalytic reactor at 4000 ° C, at 100 bar, at a flow rate (WH) of 0.5 vol / vol. of catalyst / hour and with an H2 / hydrocarbons ratio of 700 liters / liter.

The catalyst was arranged in 2 successive steps
1st bed 2nd bed
% weight 30 70
Support surface m / g 102 210
% NiO + MoO3 (weight) 17 14
Or
R = Mo (and) 1 0.3
At the end of the operation, we distilled and analyzed the products.

TEST NO. 3: hydroviscoreduction followed by hydrostabilization with partial recycling, at the entry of the visbreaking, of the 520+ ° C. fraction obtained after hydrostabilisation (the fraction ratio recycled / fraction 520 C + was 0.5).

 The operating conditions of the hydroviscoréduction and the bydrostabilisation are the same as in test n ° 2.

 The results are given in Table II.

 It is found that most of the conversion takes place during the thermal stage, despite its short duration, that the second stage improves the yield and quality of the products obtained and finally that the yield is further increased by recycling.

EXAMPLE 2
A Boscan atmospheric residue is treated (Table I).

The deasphalting is carried out with pentane as in Example 1 with a yield of 70%. The deasphalted residue is treated as in Tests 2 (without recycling) and 3 (with recycling) of Example 1, with the same catalysts. However, the operating conditions had been modified as follows
hydroviscoreduction: P = 120 bar; T = 500 "C;
sidence = 5 sec; H2 flow rate = 500 liters / liter,
hydrostabilization: P = 120 bar; T = 400 ° C; VVH = 0.5;
H2 / hydrocarbons = 700 liters / liter.

 The results are given in Table III.

TABLE I
CHARACTERISTICS OF CHARGES
Light oil vacuum residue Atmospheric residue
- from Saudi Boscan 3
Specific weight (g / cm) 1,003 - 1,037
Pour point C: + 20 + 66
Viscosity at 1000C (cst): 345 5.250
SI weight: 4,05 5,90
N ppm weight: 2875 7880
Ni ppm Weight: 19,133
V ppm weight: 61 1264
Conradson Carbon (Z weight): 16.4 18.0
Asphaltenes Z weight (insoluble
with heptane): 4.2 15.3
Softening point C t - 46.6
TABLE II
TEST 1 2 3
Yields% by weight based on deasphalted residue 150 C- 9 13.5 14.5 150-3750C 24.3 36.7 42.1 375-520 C 200 28.6 33.9 5200C + 46.7 22.2 10 5
Fraction 150-3750C 15 d415 0.850 0.852 0.854
ZS by weight 1.70 0.05 0.03
Diesel index 46.5 47 46
Pour point C - 21 - 15 - 15
Fraction 375-5200C d415 0.930 0.929 0.940
SZ weight 3.13 O, hO 0.3
C.Conradson 0.30 0.06 0.06
Born ppm rate 0.1 0.1 0.1
Residue 5200C + d415 1,06 1,017 1,020
Viscosity at 1000C (cst) 480 350 450
SZ by weight 4.28 0.80 0.60
C. Conradson 23.8 16.0 20.0
Precipitable asphaltenes
to heptane (% wt) 5.0 2.0 2.5
Stability (ASTM D-1661-1) 1 1 1
TABLE III
YIELDS (% weight vs. residue Without
deasphalted) recycling recycling
1500C 12.0 13.5
150-3750C 38.0 43.2
375-520 C 29.0 32.3
520 C + 22.5 12.0
Fraction 150-3750C d415 0.855 0.857% S Weight 0.1 0.08
Diesel index 45 45
Pour point C - 15 - 15
Fraction 375-520 C d415 0.935 - 0.940 SZ Weight 0.5 0.4
C. Conra dson 0.1 - 0.1
Metals ppm - 0.1 0.1
Fraction 5200C +
15 1.03 1.04 d4
S% weight 1.0 0.8
C. Conradson 20.0 24
Asphaltenes precipitable with heptane (% wt) 2.5 5

Claims (12)

 1.- Process for converting an asphaltenic oil into fractions more  light, which includes the following steps  a) the asphaltenic oil is deasphalted by means of a. solvent  chosen from aliphatic hydrocarbons having from 5 to 7 atoms  carbon, and a deasphalted oil is collected,  b) the deasphalted oil is mixed with a recycle stream  from step (d) and the resulting mixture is heated with  hydrogen at 440-5300C, under a pressure of 40 to 140 bar, in  a non-catalytic conversion zone, for 1 second to 10 hours  res  c) the product of step (b) is sent with hydrogen in  a catalytic conversion zone at 320-4300C under pressure  from 40 to 140 bar, in contact with at least one catalyst containing at least  minus a molybdenum and / or tungsten compound and at least one compound  nickel and / or cobalt, and  d) fractionating the product of step (c) to collect at  minus a distillate fraction and at least a fraction of a residue  distillation, and at least a portion of the fraction of  residue in step (b). 2. The process according to claim 1, wherein from 10 to 100% of the residue  is returned to step (b). 3. A process according to claim 1 or 2, wherein  step (c) by passing the product of step (b) first  on a first catalyst and then on a second catalyst, the first  catalyst being characterized in that it has a  Ni and / or Co  R, defined as the atomic ratio W and / or Mo, of 0.8  at 3: 1, and the second catalyst being characterized in that  has an R ratio of 0.2: 1 to 0.5: 1. 4. - The method of claim 3, wherein the support of the pre  The catalyst has an acidity, measured by adsorption  ammonia at 320 ° C under ammonia pressure of 300 mm  mercury, less than 10 cal / g, and the support of the second  acidity, measured under the same conditions, of at least  30 cal / g. 5. A process according to claim 3 or 4 wherein the surface  specific for the support of the first catalyst is 40 to 120 m / g  and that of the support of the second catalyst from 150 to 350 m 2 / g. 6. A process according to one of claims 3 to 5, wherein for  1 part by weight of second catalyst is used of 0> 1 o  part by weight of first catalyst. 7.- Method according to one of claims 3 to 6, wherein the sup  port of the first catalyst is alumina or a co aluminate  balt, nickel, magnesium, calcium and / or barium. 8.- Method according to one of claims 3 to 7, wherein the sup  port of the second catalyst is an alumina, a silica-alumina,  an alumina-magnesia or a silica-magnesia. 9.- Method according to one of claims 1 to 8, wherein the  The product of step (b) is sent to step (c).  1b.- Method according to one of claims 1 to 9, wherein the gas  relatively cold hydrogen is added between steps (b) and  (c) to lower the temperature of the effluent of step (b)  up to a value between 320 and 4300C.  11. A process according to one of claims 1 to 10, wherein  adds 0.2 to 10% by weight of water to the deasphalted oil before  its passage in the conversion zones of steps (b) and (c).  12. A process according to one of claims 1 to 11, wherein the  residence time of step (b) is 1 - 500 seconds. 13. The process according to claim 12, wherein the flow of hydro  gene of steps (b) and (c) is from 300 to 1000 m / m hy  drocarbures.  14.- Method according to one of claims 1 to 13, wherein the oil  asphaltenic is a residue of atmospheric distillation and  in which the residue is subjected to prior distillation under  reduced pressure, the residue of this distillation under pressure  reduced being alone subjected to the deasphalting of step (a), and the  distillate being remixed to the deasphalted residue between the steps  (a) and (b) to be submitted, in combination with the latter, to  steps (b) and (c). 15.- Method according to one of claims 1 to 13, wherein the oil  asphaltenic is a residue of atmospheric distillation, in  which the fractionation of step (d) comprises a distillation  under vacuum and in which the recycled fraction is constituted by  at least a portion of the residue of this vacuum distillation. 16.- Method according to one of claims 1 to 13, wherein the oil  asphaltenic acid is a vacuum distillation residue and in which  the recycled fraction consists of a mixture of 20-80% of  atmospheric gas oil and 80-20% vacuum residue, said gas  atmospheric oil and said vacuum residue being obtained in  pe (d).