EP0201364B1 - Process for de-asphalting a hydrocarbon charge containing asphaltene - Google Patents

Description

The process which is the subject of the present invention applies to the treatment of residues of conventional crude oils, whether atmospheric residues or residues under vacuum, as well as to the treatment of heavy or extra heavy oils topped such as they can be obtained, for example, from the deposits of FAJA PETROLIFERA in VENEZUELA or from the deposits of ATHABASCA in CANADA. By extension, the method as claimed can also be advantageously used for the treatment of atmospheric or vacuum residues which result from another thermal or catalytic preliminary treatment such as visbreaking, hydroviscoreduction, heat treatment in the presence of a hydrogen donor solvent, various catalytic hydrotreatments with more or less extensive conversion of the charge treated.

These various charges are characterized by the fact that they contain resins and asphaltenes, organic products of high molecular weight, rich in heteroatoms S, N and O which are complexed with metals and in particular nickel and vanadium.

The drawbacks that these asphaltenes and resins provide in refining are well known, whether in the field of catalytic processes or that of thermal processes.

These drawbacks are linked to their high content of heteroatoms but above all to their low H / C ratio and to the presence of complexed metals, nickel and vanadium.

In catalytic cracking, in the presence of zeolitic catalysts, for example, the presence in the charge of compounds of this type simultaneously causes the increase in the deposition of coke on the catalyst at the risk of upsetting the thermal equilibrium of the unit and of raising the regeneration temperature to values such that the zeolites quickly lose their crystallinity, the presence of nickel causes the deposition of this same metal on the catalyst with as a consequence the increase in the production of incondensable gases and hydrogen and increased coke deposition. As for vanadium, when it is deposited on the catalyst, it can also form with the rare earth exchanged zeolites, which constitute the active catalytic phase of catalysts usual for this type of reaction, a mixed compound which causes the loss of crystallinity and hence the loss of activity.

In hydrotreating, such notorious catalyst poisonings are well known. The progressive deposition of nickel and vanadyl sulphides on the active agents which are the sulphides of group VIA (molybdenum and tungsten) promoted by the sulphides of group VIII (nickel and cobalt) leads to a progressive reduction in the desulphurizing, nitrogenous and hydrogenating activities of these catalysts.

In hydrocracking the asphaltenes content, determined by heptane precipitation according to the French standard AFNOR NFT 60115, must be almost undetectable if one wishes to avoid rapid poisoning of the acid sites of the catalyst with subsequent production of coke.

In visbreaking, the severity of the operating conditions is also linked to the content of these asphaltenic products and to their intrinsic stability. For a given load, too high a severity expressed in terms of temperature and / or too high maturation time, causes the partially cracked asphaltenic molecules to coagulate with the appearance of colloidal micelles which tend to decant during storage and to clog the filters of the devices of use.

All these drawbacks have prompted refineries to seek to selectively separate the asphaltene and resin compounds from the oily fraction which contained them. This separation, called deasphalting by a solvent, consists in breaking the balance existing between the asphaltenes and the surrounding maltenic medium by adding a solvent which decreases the viscosity and especially the surface tension of the oily medium. The recommended solvents are generally paraffins or (and) light olefins with 3, 4, 5, 6, and (or) 7 carbon atoms. In fact, light paraffin plays an anti-solvent role with respect to asphaltenes and possibly with respect to resins. Asphaltenes and resins are rejected out of the oily medium in the form of a distinct phase and this all the better when the density and the surface tension of the solvent medium plus oil are lower. Consequently, the yield in "asphalt phase" and the quality of the deasphalted oil are linked for a given charge to the following parameters and variables: nature of the solvent, solvent content, temperature and pressure, but also very strongly depend on the characteristics of the technology. used.

The process which the subject of the present invention therefore relates to deasphalting with hydrocarbon solvents comprising paraffinic or olefinic hydrocarbons having from 3 to 7 carbon atoms. However, the use of the hydrocarbon solvent is carried out in such a way that it makes it possible to obtain excellent yields of a very good quality oil with a minimum solvent content and that it makes it possible to design industrial extrapolation to units capable of processing annual capacities of around 2 to 4 million tonnes in a single line.

Object of the invention

A first object of the present invention is to carry out the deasphalting of a hydrocarbon charge containing asphaltenes in particular of a residue or of a heavy oil, with a solvent having from 3 to 7 carbon atoms, used in a ratio solvent / charge volume from 2.5 / 1 to 6/1, so as to obtain an oil containing less than 0.05% of asphaltenes precipitated by heptane according to AFNOR NFT 60115 standard.

A second object of the invention is to selectively carry out the operation, that is to say to obtain, concurrently with the quality of the deasphalted oil, a very good yield in this same oil and this by implementing the minimum solvent, i.e. metric solvent / oil volumetric ratios which may be as low as 3/1 to 4/1. A third object of the invention consists in carrying out the operation by separating the elementary physicochemical operations which make up the overall deasphalting operation: mixing-precipitation, decantation of the asphalt phase, washing-peptization of the asphalt phase.

The process which is the subject of the invention allows the treatment of very large annual residues or heavy oils in a single decanter with respect for the quality and yield criteria which constitute the first and second subject of the invention.

Prior art

The prior art covers a very wide spectrum of deasphalting techniques basing their originality on the nature of the solvent used, on the range of operating conditions recommended, on the use of special additives, on certain technical characteristics of the process or on the realization of the operation in several successive stages.

US Pat. No. 1,948,296, for example, claims propane, n-butane, isobutane, light petroleum fractions, naphtha, alcohols or mixtures of these various products as a solvent.

The patent US-A 2,081,473 presents the general concept of the deasphalting operation, consequently recommends the whole range of solvents generally cited, from methane to naphtha via propane, butane and light gasoline, but it does not specifies neither the range of solvent / oil ratios recommended, nor a fortiori, the "de facto" dissociation of the operation into its elementary physico-chemical stages with application for each stage of a range of optimal operating conditions.

The patents US-A 2 587 643 and 2 882 219 claim the addition of modifiers or additives either with solvent, namely organic carbonates for the patent US-A 2 587 643, or with the load, namely aromatics for the US-A patent 2,882,219.

US-A patents 3,278,415 and 3,331,394 also recommend the addition of solvent additives, namely phenol and glycol respectively.

As for the patents US-A 2,002,004, 2,101,308 and 3,074,882, they recommend carrying out the deasphalting operation in two or more successive stages but the sequences of stages envisaged are conceptually different from the staggering of stages of the present invention. Thus, US Pat. No. 2,002,004 relates to a two-stage deasphalting process with intermediate distillation of the hydrocarbon phase rich in solvent originating from the first extraction zone. The effluent from the bottom of the distillation column is subjected to a second deasphalting step which in fact makes it possible to isolate resins.

The patent US-A 2 101 308 proposes a first step of deasphalting with light gasoline as solvent; the light oil-essence mixture from this first is treated with SO ₂ , for a subsequent elimination of resins and aromatics.

US-A 3,074,882 operates a first butane precipitation. The butane is separated from the oil-butane mixture and the residual oil is treated with propane in two successive stages making it possible, on the one hand, to obtain resins and, on the other hand, a deasphalted and de-resinated oil.

The use of separate solvents in two stages of the process is also described in GB 735 333.

As for US-A 3,830,732, it also recommends a deasphalting in two stages consisting first of all in precipitating asphaltenes and resins with a first solvent in a volumetric solvent / oil ratio of less than 4/1; in a second step, the asphaltic phase resulting from the first step is in turn repeptified by a solvent having at least one carbon atom more than the solvent recommended in the first step. This peptization of the asphalt phase makes it possible to redissolve the resins in the second solvent. After recovery of both of the solvents which are recycled to their respective stages, there is therefore a deasphalted and de-resinated oil, a resin phase and an asphalt phase. A particular claim of this patent recommends that the operation in the first step is carried out at a temperature higher than that of the second step.

• - La repeptisation de la phase asphaltique est réalisée par substantiellement le même solvant que la précipitation de cette même phase asphaltique.
• - Le mélange du solvant avec l'huile, de même que la précipitation, sont réalisés avant le décanteur et non dans le décanteur lui-même.
• - Le fait de n'utiliser qu'un seul solvant permet la mise en oeuvre d'une technique originale pour réaliser de façon optimum l'enchaînement des étapes que sont le mélange-précipitation, la décantation de la phase asphaltique et son lavage. Selon la capacité à traiter, la technique revendiquée dans la présente invention pourra se présenter sous diverses variantes relevant toutes du même principe de base.
• - Les recyclages préconisés dans les diverses variantes du procédé permettent d'accéder à un rendement maximum en une huile désasphaltée contenant moins de 0,05% d'asphalténés (Norme AFNOR NFT 60115).

If, conceptually, the present invention has some analogy with US-A 3,830,732, it clearly differs from it by three essential points.

• - The repeptisation of the asphalt phase is carried out by substantially the same solvent as the precipitation of this same asphalt phase.
• - The mixing of the solvent with the oil, as well as the precipitation, are carried out before the decanter and not in the decanter itself.
• - The fact of using only one solvent allows the implementation of an original technique for optimally carrying out the sequence of steps that are the mixing-precipitation, the settling of the asphalt phase and its washing. Depending on the capacity to be treated, the technique claimed in the present invention may be presented in various variants, all relating to the same basic principle.
• - The recycling recommended in the various variants of the process gives access to a maximum yield of a deasphalted oil containing less than 0.05% of asphaltenes (AFNOR standard NFT 60115).

Summary of the invention

The process of the invention can implement the following preferred characteristics:

The asphaltic phase washing solvent is the same as that used for the precipitation.

The mixture between the charge to be deasphalted and the deasphalting solvent is produced upstream of the exchanger which raises the mixing temperature to the value required to achieve good precipitation and good decantation.

The charge-solvent mixture passes through the tubes of the exchanger and not on the shell side.

The residence time of the charge-solvent mixture in the precipitation mixing zone is between 5 sec and 5 min, preferably between 20 seconds and 120 seconds.

The residence time of the mixture in the settling zone is between 4 and 20 minutes.

The residence time of the oil-solvent mixture in the washing zone also remains between 4 and 20 minutes.

The upward speeds of the oil-solvent mixtures both in the settling zone and in the washing zone will usefully remain less than 1 cm / s and preferably less than 0.5 cm / s.

The temperature applied in the washing zone will be 5 to 50 _° C lower than the temperature applied in the decanting zone.

The oil-solvent mixture from the washing zone will be recycled in the decanter and even more advantageously upstream from the exchanger located at the entrance to the decantation zone.

The solvent / asphalt phase ratio recommended in the washing zone will be between 0.5 and 8 and preferably between 1 and 5.

According to one of its variants, the process can comprise two stages, each stage including the three basic stages of precipitation, decantation and washing. In this specific case, the temperature recommended in each stage of the first stage is preferably on average 10 to 40 _° C lower than the temperature of each corresponding stage of the second stage. The process which is the subject of the invention can use hydrocarbon solvents having from 3 to 7 carbon atoms, paraffinic, olefinic or cyclanic, alone, mixed together in various proportions or added with additives, for example, of the type phenol, glycol, alcohols from C1 to C6. The process of the present invention lends itself more advantageously to the use of paraffinic and / or olefinic solvents having from 4 to 6 carbon atoms.

Detailed description of the process

FIG. 1 presents the essential characteristics of the method corresponding to the invention. The load to be treated is introduced via line (1) to the mixing valve (2), where the solvent S1 and S "1 is introduced, originating from the recovery of the solvent (23) contained respectively in the solvent mixture. - oil or in the solvent-asphalt phase mixture (lines 3 and 4). The charge-solvent mixture passes through an exchanger (5) where it is brought to the temperature required for the deasphalting operation considered; this temperature will vary between 100 and 220 _° C according to the solvent considered (for example isobutane, butane, isopentane, pentane, light gasoline) according to the type of feed to be treated (headless crude, atmospheric residue, vacuum residue), according to the origin of the crude oil considered and according to the solvent / oil ratio used. For example in the case of a vacuum residue of the SAFANYA type, for a solvent / oil ratio ranging from 3/1 to 5/1, the temperature at outlet of the exchanger will be between 190 and 170 ° C and the pressure between 4 and 5 M Pascals da ns to the extent that one aims to obtain a deasphalted oil containing less than 0.05% of asphalts according to the AFNOR NFT 60115 STANDARD. It is important to specify that according to one of the preferred characteristics of the process, the charge-solvent mixture passes in the exchanger tubes and not on the shell side, in addition, it is recommended to carry out a gravity flow in this exchanger, that is to say that the charge-solvent mixture travels up and down the exchanger tubes .

At the outlet of the exchanger, the mixture brought to the required temperature is introduced via line (6) into the extractor flask (7) where the decantation takes place. The precipitation of the asphalt phase begins almost instantaneously at the level of the mixing valve and is followed in the exchanger (5) as the temperature rises. To ensure good precipitation and good coagulation of the asphaltic miscelles before the entry of the settling tank, it is preferred that the residence time of the mixture between the mixing valve and the entry of the settling tank is between 5 seconds and 5 minutes and preferably between 20 seconds and 120 seconds. Similarly, the turbulence in line 6 is usefully controlled to avoid the bursting into too small particles of the micelles of asphaltic phase in suspension in the oil-solvent medium; in practice, it is recommended that at the outlet of the exchanger the number of REYNOLDS in the mixture be between 2.104 and 106 and preferably between 5.104 and 5.105. In this range of values, it can also be seen that the agglomeration of the micelles is initiated, making subsequent settling in the settling tank easier and faster.

In the settling tank (7), the asphaltic phase micelles are agglomerated and decanted. The volume and the geometry of the decanter are calculated so that the residence time of the solvent-oil mixture is between 4 and 20 minutes and preferably between 8 and 15 minutes and so that the rate of rise of the solvent-oil mixture is always less than 1 cm per second. The ball decanter preferably operates in an isothermal manner, that is to say at a temperature substantially equal to the inlet temperature of the mixture, apart from the heat losses. The asphalt phase is collected in an underlying boot (8) where a level control causes it to be drawn off by the pump (10) via the pipes (9 and 11) up to the column (12) where the washing of the asphaltic phase and the selective repeptisation of part of the resins by the solvent S'1 recycled from the fractionation unit (23) via the pipe (14). The exchanger (15) makes it possible to adjust the temperature of the washing solvent to the optimum temperature for the envisaged operation.

The pressure applied in the washing tower is preferably very close to the upstream decanter pressure; the temperature of the solvent S'1 at the entrance to the tower will preferably be 5 to 50 _° C lower than the temperature of the asphalt phase introduced by line (11) at the top of the washing zone. The temperature gradient established between the inlets of the pipes (11) and (14) makes it possible to adjust for a given solvent flow rate S'1 and an asphaltic phase of a given nature the rate of repeptation of the resins, that is to say -dith allows to regulate the asphalt yield and the softening point of the asphalt. The solvent flow rate also affects the asphalt yield and its softening point. According to the process which is the subject of the invention, this flow rate is adjusted so that the volume ratio of solvent / asphalt phase is between 0.5 and 8 and preferably between 1 and 5.

The column is advantageously operated so that the level of settling of the asphalt phase (17) is adjusted below the injection pipe (14) of the solvent S'1 and more precisely below the distribution device ( 16) of this same solvent in the continuous solvent-oil medium although a setting at a higher level still gives good performance. The column is preferably equipped with baffle plates (13) which allow better contact between the micelles of the asphalt phase and the upward flow of solvent. These baffles are preferably calculated in such a way that the rate of rise of the solvent or more precisely of the solvent phase added with the washed oil and the peptized resins remains less than 36 m / hour. In any case, the column head is preferably devoid of baffles to reduce this rate of rise and can be designed with a slightly larger diameter to avoid any entrainment of the colloidal particles of asphalt phase of diameter less than one micron. In one embodiment of the process, the product from the top of the column is recycled in the liquid phase via the line (18) in the solvent S1 slightly upstream of the mixing valve (2).

The asphalt phase swollen with almost pure solvent is withdrawn from the bottom of the washing column by means of the pump (20) via the line (19) up to the vaporization tower (21) where the asphalt, which has been withdrawn, is separated. via the line (22), solvent which is recycled via the line (4), either at the top of the decanter, or upstream of this decanter and preferably at the level of the mixing valve. As for the recovery of the solvent associated with the deasphalted oil, it is shown diagrammatically by the rectangle (23) and can for example be carried out in the process relating to the invention by vaporization of the solvent in a cascade of evaporators or of the exchanger type. conventional, either preferably of the falling film exchanger type or by separation of the solvent phase from the oil phase in a decanter operating under supercritical conditions or by ultrafiltration of the solvent on appropriate mineral membranes. The deasphalted oil leaves through the line (27).

In the embodiment described above, the decanter was in elongated form, was provided with a boot and was preferably inclined by 5 to 10 _° relative to the horizontal plane to allow the asphalt phase to flow freely towards the boot underlying. The invention does not however stipulate that this decanter is necessarily elongated; it can also be vertical as shown in FIG. 2, insofar as this geometry makes it possible to comply with the constraints of rising speed and of settling time recommended above. This geometry which requires less floor space will therefore be recommended for the treatment of annual capacities of less than 2 million tonnes: Although the decanter is, for process conditions, arranged vertically, the arrangement of the stages and the operating conditions recommended are strictly those which are the subject of the present invention.

The method in a last variant can also be applied to the case where the operation is carried out in two stages with precipitation of a hard asphalt phase in a first stage and precipitation of a resin phase in a second stage. The simple idea of separate production of an asphalt phase and a resin phase has been known and practiced industrially for a very long time and is not part of the body of the invention. The object of the invention relates to the fact that each stage, as shown in FIG. 3, comprises a staggering of the 3 elementary stages: mixing-precipitation, decantation, washing-repeping, completely similar to that described in the previous variants where the asphalts and resins were precipitated in a single phase. In accordance with this variant, the precipitation and decantation are carried out in the first stage at a temperature of 20 to 60 _° C lower than that which is applied when the precipitation is carried out in one go, that is to say say at the minimum temperature so that the asphalt phase remains liquid and sufficiently fluid at the outlet of the decanter to be able to be handled without problem. The step of washing the asphalt phase in this variant is carried out at a temperature equal to or slightly higher than that of the decanter. The solvent-oil-resin mixture from washing through line 18 is mixed with the solvent-oil-resin mixture from the first decanter (24).

In the second stage, the oil-resin solvent mixture is heated (35) to a temperature 30 to 70 _° C higher than that applied in the first decanter. As in the first stage, the solvent-oil-resins mixture preferably passes through the tubes of the exchanger and not on the shell side; moreover the flow of the solvent-oil-resins mixture will be a gravity flow; the extract is separated by the line (38) for fractionation in the separator (23). The raffinate is sent by line (39) to the washer (40). The ascending speeds and the residence times in the settling tank (37) and the column (40) are included in the ranges recommended above for the tank (7) and the column (12). The solvent / resin phase ratio at (40) is between 2 and 4. The solvent-oil mixture is recycled via line (43) upstream of the exchanger (35). The solvent for washing the resin phase is injected through line (41) at the bottom of the column (40) for washing the resin phase after passing through the exchanger (42) so as to adjust the temperature of said solvent to a value lower than that of the decanter (37) by 5 to 30 _° C.

The resin phase (44) is released from the solvent entrained in (45) by "flash" and / or steam entrainment. The resin phase (46) is recovered. The recovered solvent is sent via line (47) to the pipe (4). The process therefore makes it possible, in two stages of similar designs, to very flexibly ensure the production of an oil phase (27) devoid of asphaltenes and very poor in resins as well as the simultaneous production of an asphaltic phase and a resin phase, the proportions of these last two phases can be adjusted at will, for a given charge, a solvent and given solvent levels, by the choice of the temperatures applied in (7) and (37) on the one hand, in (15) and (42) on the other hand.

Free 1

A SAFANIYA residue is deasphalted by addition of a solvent essentially consisting of a mixture of pentane and isopentane. The characteristics of the residue are presented in Table 1 and the composition of section C5 in Table 2.

The operation is carried out in a unit capable of treating from 1 t / h to 3 t / h of residue and whose process characteristics are similar to those which are the subject of the invention described above. The tubular exchanger is arranged vertically. The washing-repeptation column is equipped with crossed horizontal baffles so as to achieve the equivalent of 2 theoretical stages for both mass and heat transfer. A series of 10 tests were carried out in accordance with the diagram in FIG. 1. The operating conditions applied are presented in Table 3. In this series of tests the solvent of the oil-solvent mixture was recovered for 90% in a cascade of falling film evaporators and for the last 10 percent by stripping of the oily phase under pressure conditions lower than those applied in the decanting operation. After removal of the solvent both in the oil phase and in the asphalt phase respectively in (23) and (21) as indicated in FIG. 1, the oily and asphalt phases are stored and analyzed. Table 4 gives the yields and some characteristics of the products obtained.

This series of tests confirms the correctness of the process diagram and the recommended operating conditions. It can be seen that the quality of the oil increases when the precipitation and _/ or decantation temperature increases and, for a given temperature, when the solvent / charge ratio increases. The last four tests show more particularly the importance of the washing step and the operating conditions applied in this step on the oil yields on the one hand and on the characteristics of the asphalt on the other hand: the oil yield deasphalted increases when the flow of washing solvent increases and when the temperature of the bottom of the washing column decreases.

Free 2

The deasphalting of a BOSCAN atmospheric residue is carried out by adding the same solvent of the C5 cut type as that used in Example 1. The operation is carried out in the same unit as that described in connection with Example 1. The conditions The procedures applied in the tests selected to illustrate the advantage of the process of the invention are presented in Table 6. Table 5 gives the essential characteristics of the charge treated and Table 7 the yields and characteristics of the products obtained. This example was more particularly chosen to illustrate the importance of the washing step on the yields of desasperated oil. This series of tests further highlights the importance of the conditions applied in the washing step. The oil yields are higher the lower the washing temperature and the higher the solvent / asphalt phase ratio. In all the tests carried out, the volume of asphalt phase which, at the outlet of the decanter, is composed of the asphalt swollen with solvent and oil, is between 1.6 and 2 times the volume of the final asphalt which leaves the washing tower. This implies that the ratio of the solvent to the asphalt phase entering the washing tower in the previous tests remains well between 0.5 and 8.

Free 3

The deasphalting of the SAFANIYA vacuum residue is carried out, the characteristics of which are presented in Table 1 but using for the precipitation a C4 cut containing by weight 3% of propane, 35% of isobutane, 61% of butane and 1% of isopentane. The tests are carried out in the same unit as that described in the previous examples. The operating conditions of the series of tests are summarized in Table 8, the yields and characteristics of the products obtained are presented in Table 9.

Claims (11)

1. A process for deasphalting an asphaltene-containing hydrocarbons charge, wherein the charge is treated with a solvent and the resultant phases are separated, comprising the following steps of:

a) introducing, at 100-220_°C, in a settling zone, a preformed mixture of hydrocarbon charge with a first fraction of solvent charge comprising at least one paraffinic, olefinic or cyclanic hydrocarbon having 3 to 7 carbon atoms, the volume ratio of the solvent charge to the hydrocarbons charge being from 2,5/1 to 6/1,

b) allowing the mixture to settle, in a settling zone, at a temperature from 100 to 220_°C, with an upflow velocity of the light phase lower than 1 cm/second, and separating a light phase, containing deasphalted oil, from a heavy asphalt phase,

c) subjecting the heavy asphalt phase to washing, in a substantially vertical washing zone, by allowing its downward flow, counter-currently with an upward flow of a second fraction of said solvent charge, said second fraction having the same composition as the first fraction and being introduced at a temperature from 5 to 50_°C lower than the temperature of introduction of the heavy asphalt phase in the washing zone, the solvent/asphalt phase volume ratio ranging from 0.5/1 to 8/1, and recovering an oil- solvent upper phase of low asphaltenes content and a lower phase of high asphaltenes content,

d) feeding back the upper phase of step (c) to the settling zone of step (a),

e) separating the solvent from the lower phase of step (c) and recovering an asphalt phase, and

f) separating the solvent from the light phase of step (b) and recovering the deasphalted oil phase.

2. A process according to claim 1, wherein the mixture of hydrocarbons charge with the first fraction of solvent charge, introduced at 100-220_°C in the settling zone, is obtained by admixtion of the two charges, subsequent heating up to 100-220_°C, then feeding of the heated mixture to the settling zone, the REYNOLDS number of the heated mixture thus fed to the settling zone being from 2.10⁴ to 10⁶ and the time interval between the beginning of the heating to the time of introduction in the settling zone being from 5 seconds to 120 seconds.

3. A process according to claim 2, wherein step (d) is performed by admixing the upper phase of step (c) with the hydrocarbons charge and the first fraction of solvent charge of step (a) before heating the mixture of the two last charges, the resultant mixture being then heated to 100-220_°C and fed to the settling zone with said REYNOLDS number and said time interval.

4. A process according to any one of claims 1 to 3, wherein the upper portion of the washing zone, located above the point of introduction the heavy asphalt phase, is at a temperature higher than that of the lower portion, thereby providing for a reduction of the asphaltenes content of the upper phase recovered in step (c).

5. A process according to any one of claims 1 to 4, wherein the heating of the mixture in step (a) is performed in a tubular, vertical exchanger and said mixture flows downwarly in said exchanger.

6. A process according to any one of claims 1 to 5, wherein step (a) lasts from 20 to 120 seconds and the REYNOLDS number is from 5.10⁴ to to 5.105.

7. A process according to any one of claims 1 to 6, wherein the settling zone is of elongate shape, inclined by 5 to 10_° to the horizontal, in the direction of flow of the mixture.

8. A process according to any one of claims 1 to 7, wherein the solvent to asphalt phase volume ratio in the washing zone is from 2/1 to 4/1 and the sectional area of said washing zone is larger, as an average, above the point of introduction of the asphalt heavy phase than below that point.

9. A process according to any one of claims 1 to 8, wherein the solvent to hydrocarbons charge volume ratio in step (a) is from 3/1 to 4/1.

10. A process according to any one of claims 1 to 9, wherein the residence time in each of steps (b) and (c) is from 4 to 20 minutes.

11. A process according to any one of claims 1 to 10, performed in two stages, wherein each stage comprises the three elementary steps of precipitation, settling and washing, with an average temperature in the first stage from 10 to 40_°C lower than the average temperature in the second stage.

Images